Publications by authors named "Thomas G H Diekwisch"

59 Publications

Evolution: Herbivore-Type Teeth in a Cretaceous Tuatara Relative.

Curr Biol 2020 May;30(9):R395-R397

Texas A&M University, Center for Craniofacial Research and Diagnosis, Dallas, TX 75246, USA. Electronic address:

In a new study, LeBlanc and co-workers have discovered an unusually complex dentition in a fossil relative of the modern-day tuatara that features compound occlusal surfaces, thick and prismatic enamel, and a novel enamel-to-bone tooth attachment. This finding suggests that complex dentitions arose independently in several reptilian lineages.
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http://dx.doi.org/10.1016/j.cub.2020.02.041DOI Listing
May 2020

Microporous Bio-orthogonally Annealed Particle Hydrogels for Tissue Engineering and Regenerative Medicine.

ACS Biomater Sci Eng 2019 Dec 11;5(12):6395-6404. Epub 2019 Nov 11.

Department of Periodontics, Texas A&M University, Dallas, Texas 75246, United States.

Microporous annealed particle (MAP) hydrogels are an emerging class of biomaterials with the potential to improve outcomes in tissue repair and regeneration. Here, a new MAP hydrogel platform comprising poly(ethylene) glycol (PEG) hydrogel microparticles that are annealed in situ using bio-orthogonal tetrazine click chemistry is reported (i.e., TzMAP hydrogels). Briefly, clickable PEG-peptide hydrogel microparticles with extracellular matrix mimetic peptides to permit cell adhesion and enzymatic degradation were fabricated via submerged electrospraying and stoichiometrically controlled thiol-norbornene click chemistry. Subsequently, unreacted norbornene groups in the microparticles were leveraged for functionalization with bioactive proteins as well as annealing into TzMAP hydrogels via the tetrazine-norbornene click reaction, which is highly selective and proceeds spontaneously without requiring an initiator or catalyst. The results demonstrate that the clickable particles can be easily applied to a tissue-like defect and then annealed into an inherently microporous structure in situ. In addition, the ability to produce TzMAP hydrogels with heterogeneous properties by incorporating multiple types of hydrogel microspheres is demonstrated, first with fluorophore-functionalized hydrogel microparticles and then with protein-functionalized hydrogel microparticles. For the latter, tetrazine-modified alkaline phosphatase was conjugated to PEG hydrogel microparticles, which were mixed with nonfunctionalized microparticles and used to produce TzMAP hydrogels. A biomimetic mineralized/nonmineralized interface was then produced upon incubation in calcium glycerophosphate. Finally, platelet-derived growth factor-BB (PDGF-BB) and human periodontal ligament stem cells (PDLSC) were incorporated into the TzMAP hydrogels during the annealing step to demonstrate their potential for delivering regenerative therapeutics, specifically for periodontal tissue regeneration. In vitro characterization revealed excellent PDGF-BB retention as well as PDLSC growth and spreading. Moreover, PDGF-BB loading increased PDLSC proliferation within hydrogels by 90% and more than doubled the average volume per cell. Overall, these results demonstrate that TzMAP hydrogels are a versatile new platform for the delivery of stem cells and regenerative factors.
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http://dx.doi.org/10.1021/acsbiomaterials.9b01205DOI Listing
December 2019

Triple PLGA/PCL Scaffold Modification Including Silver Impregnation, Collagen Coating, and Electrospinning Significantly Improve Biocompatibility, Antimicrobial, and Osteogenic Properties for Orofacial Tissue Regeneration.

ACS Appl Mater Interfaces 2019 Oct 7;11(41):37381-37396. Epub 2019 Oct 7.

Center of Stomatology , The Second Affiliated Hospital of Soochow University , Suzhou 215004 , People's Republic of China.

Biodegradable synthetic scaffolds hold great promise for oral and craniofacial guided tissue regeneration and bone regeneration. To overcome the limitations of current scaffold materials in terms of osteogenic and antimicrobial properties, we have developed a novel silver-modified/collagen-coated electrospun poly-lactic-co-glycolic acid/polycaprolactone (PLGA/PCL) scaffold (PP-pDA-Ag-COL) with improved antimicrobial and osteogenic properties. Our novel scaffold was generated by electrospinning a basic PLGA/PCL matrix, followed by silver nanoparticles (AgNPs) impregnation via in situ reduction, polydopamine coating, and then coating by collagen I. The three intermediate materials involved in the fabrication of our scaffolds, namely, PLGA/PCL (PP), PLGA/PCL-polydopamine (PP-pDA), and PLGA/PCL-polydopamine-Ag (PP-pDA-Ag), were used as control scaffolds. Scanning electron micrographs and mechanical testing indicated that the unique three-dimensional structures with randomly oriented nanofibrous electrospun scaffold architectures, the elasticity modulus, and the tensile strength were maintained after modifications. CCK-8 cell proliferation analysis demonstrated that the PP-pDA-Ag-COL scaffold was associated with higher MC3T3 proliferation rates than the three control scaffolds employed. Scanning electron and fluorescence light microscopy illustrated that PP-pDA-Ag-COL scaffolds significantly enhanced MC3T3 cell adhesion compared to the control scaffolds after 12 and 24 h culture, in tandem with the highest β1 integrin expression levels, both at the mRNA level and the protein level. Alkaline phosphatase activity, BMP2, and RUNX2 expression levels of MC3T3 cells cultured on PP-pDA-Ag-COL scaffolds for 7 and 14 days were also significantly higher when compared to controls ( < 0.001). There was a wider antibacterial zone associated in PP-pDA-Ag-COL and PP-pDA-Ag scaffolds versus control scaffolds ( < 0.05), and bacterial fluorescence was reduced on the Ag-modified scaffolds after 24 h inoculation against and . In a mouse periodontal disease model, the PP-pDA-Ag-COL scaffold enhanced alveolar bone regeneration (31.8%) and was effective for periodontitis treatment. These results demonstrate that our novel PP-pDA-Ag-COL scaffold enhanced biocompatibility and osteogenic and antibacterial properties and has therapeutic potential for alveolar/craniofacial bone regeneration.
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http://dx.doi.org/10.1021/acsami.9b07053DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7220812PMC
October 2019

Periodontal Homeostasis: From Vienna to Texas-A Century of Periodontal Research in the Spirit of Bernhard Gottlieb.

Stem Cells Dev 2019 08 22;28(15):961-962. Epub 2019 Jul 22.

Department of Periodontics, Bernhard Gottlieb Endowed Chair in Craniofacial Research, Center for Craniofacial Research and Diagnosis, Texas A&M University College of Dentistry, Dallas, Texas.

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http://dx.doi.org/10.1089/scd.2019.0126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6661909PMC
August 2019

The Wnt Antagonist SFRP1: A Key Regulator of Periodontal Mineral Homeostasis.

Stem Cells Dev 2019 08 22;28(15):1004-1014. Epub 2019 Jul 22.

Department of Periodontics, Center for Craniofacial Research and Diagnosis, Texas A&M College of Dentistry, Dallas, Texas.

The function of mammalian periodontal tissues depends on the presence of a nonmineralized periodontal ligament (PDL) juxtaposed in between mineralized tooth anchorage tissues alveolar bone (AB) and root cementum. In the present study we have hypothesized that the Wnt antagonist secreted frizzled related protein 1 (SFRP1) is an essential regulator of periodontal tissue mineral homeostasis. Our immunoreactions and western blot data demonstrated that SFRP1 was substantially expressed higher in PDL fibroblasts than in surrounding AB progenitors and cementoblasts. SFRP1 was also detected at higher levels in PDL fibroblasts than in dental follicle (DF) cells, but the difference was less pronounced. Preferential H3K4me3 active histone mark enrichment on the promoter and a lack of H3K27me3 repression were most dramatic in PDL progenitors, to a lesser degree in DF cells, and not detected in AB progenitors and cementoblasts. Selective inhibition of SFRP1 using a small molecule inhibitor WAY-316606 demonstrated that SFRP1 block increased PDL cell mineralization and mineralization gene expression such as β-catenin, alkaline phosphatase, osteocalcin, collagen I, and RUNX2. The effect of SFRP1 inhibition on PDL cell mineral homeostasis was confirmed by RNA silencing. These studies also demonstrated that SFRP1 knockdown promotes PDL differentiation through histone H3K4me3-mediated activation of and . Finally, when SFRP1 inhibition and silencing studies were performed using AB progenitors instead of PDL progenitors, there was little effect on mineralized state control and gene expression, with the exception of osteocalcin, which was dramatically upregulated upon SFRP1 silencing. Together, the results of our study document the highly specific role of the Wnt inhibitor SFRP1 in maintaining the nonmineralized state of PDL progenitors.
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http://dx.doi.org/10.1089/scd.2019.0124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6661921PMC
August 2019

Particle-Attachment-Mediated and Matrix/Lattice-Guided Enamel Apatite Crystal Growth.

ACS Nano 2019 03 25;13(3):3151-3161. Epub 2019 Feb 25.

TAMU Center for Craniofacial Research and Diagnosis , Dallas , Texas 75246 , United States.

Tooth enamel is a hard yet resilient biomaterial that derives its unique mechanical properties from decussating bundles of apatite crystals. To understand enamel crystal nucleation and growth at a nanoscale level and to minimize preparation artifacts, the developing mouse enamel matrix was imaged in situ using graphene liquid cells and atomic resolution scanning transmission electron and cryo-fracture electron microscopy. We report that 1-2 nm diameter mineral precipitates aggregated to form larger 5 nm particle assemblies within ameloblast secretory vesicles or annular organic matrix subunits. Further evidence for the fusion of 1-2 nm mineral precipitates into 5 nm mineral aggregates via particle attachment was provided by matrix-mediated calcium phosphate crystal growth studies. As a next step, aggregated particles organized into rows of 3-10 subunits and developed lattice suprastructures with 0.34 nm gridline spacings corresponding to the (002) planes of apatite crystals. Mineral lattice suprastructures superseded closely matched organic matrix patterns, suggestive of a combination of organic/inorganic templates guiding apatite crystal growth. Upon assembly of 2-5 nm subunits into crystal ribbons, lattice fringes indicative of the presence of larger ordered crystallites were observed surrounding elongating crystal ribbons, presumably guiding the c-axis growth of composite apatite crystals. Cryo-fracture micrographs revealed reticular networks of an organic matrix on the surface of elongating enamel crystal ribbons, suggesting that protein coats facilitate c-axis apatite crystal growth. Together, these data demonstrate (i) the involvement of particle attachment in enamel crystal nucleation, (ii) a combination of matrix- and lattice-guided crystal growth, and (iii) fusion of individual crystals via a mechanism similar to Ostwald ripening.
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http://dx.doi.org/10.1021/acsnano.8b08668DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7067265PMC
March 2019

Enamel biomimetics-fiction or future of dentistry.

Int J Oral Sci 2019 01 5;11(1). Epub 2019 Jan 5.

Center for Craniofacial Research and Diagnosis, Texas A&M College of Dentistry, Dallas, TX, USA.

Tooth enamel is a complex mineralized tissue consisting of long and parallel apatite crystals configured into decussating enamel rods. In recent years, multiple approaches have been introduced to generate or regenerate this highly attractive biomaterial characterized by great mechanical strength paired with relative resilience and tissue compatibility. In the present review, we discuss five pathways toward enamel tissue engineering, (i) enamel synthesis using physico-chemical means, (ii) protein matrix-guided enamel crystal growth, (iii) enamel surface remineralization, (iv) cell-based enamel engineering, and (v) biological enamel regeneration based on de novo induction of tooth morphogenesis. So far, physical synthesis approaches using extreme environmental conditions such as pH, heat and pressure have resulted in the formation of enamel-like crystal assemblies. Biochemical methods relying on enamel proteins as templating matrices have aided the growth of elongated calcium phosphate crystals. To illustrate the validity of this biochemical approach we have successfully grown enamel-like apatite crystals organized into decussating enamel rods using an organic enamel protein matrix. Other studies reviewed here have employed amelogenin-derived peptides or self-assembling dendrimers to re-mineralize mineral-depleted white lesions on tooth surfaces. So far, cell-based enamel tissue engineering has been hampered by the limitations of presently existing ameloblast cell lines. Going forward, these limitations may be overcome by new cell culture technologies. Finally, whole-tooth regeneration through reactivation of the signaling pathways triggered during natural enamel development represents a biological avenue toward faithful enamel regeneration. In the present review we have summarized the state of the art in enamel tissue engineering and provided novel insights into future opportunities to regenerate this arguably most fascinating of all dental tissues.
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http://dx.doi.org/10.1038/s41368-018-0038-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6320371PMC
January 2019

Titanium particles generated during ultrasonic scaling of implants.

J Periodontol 2019 03 14;90(3):241-246. Epub 2018 Nov 14.

Periodontal Department, Texas A&M College of Dentistry, Dallas, TX.

Background: There is growing concern that titanium particles may play a role in peri-implant breakdown. Ultrasonic scalers are routinely used in the debridement of peri-implant lesions. This in vitro study is designed to evaluate if titanium particles are produced when an ultrasonic scaler is used on an implant.

Methods: New sandblasted, large grit, acid etched (SLA) coated implants were subjected to ultrasonic scaling with stainless steel, titanium, and PEEK plastic tips. The implants were placed in a holding device and the ultrasonic scaler was positioned on the SLA surface under 25 grams of pressure. The implants were subjected to 30 scaling motions. The ultrasonic coolant water was collected and the number of metallic particles were counted under a light microscope. The particles were confirmed to be titanium via elemental analysis. The implants were visually evaluated for damage to the SLA coating.

Results: No metallic particles were detected in the water supplied to the ultrasonic scalers (passive control). Metallic particles were detected when implants were subjected to the ultrasonic coolant water only without the scaler tip touching the implant (active control). All implants that were scaled produced metallic particles and showed easily detectable damage to the SLA layer.

Conclusions: All ultrasonic scaling caused the production of titanium particles and caused damage to the SLA coating of the implant. Ultrasonic scalers should be used with great caution in the treatment of peri-implant conditions and care should be taken to not touch the SLA surface of the implant.
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http://dx.doi.org/10.1002/JPER.18-0230DOI Listing
March 2019

MicroRNAs and immunity in periodontal health and disease.

Int J Oral Sci 2018 08 6;10(3):24. Epub 2018 Aug 6.

Department of Periodontics, Texas A&M College of Dentistry, Chicago, IL, USA.

MicroRNAs (miRNAs) are critical regulators of the host immune and inflammatory response against bacterial pathogens. In the present review, we discuss target genes, target gene functions, the potential regulatory role of miRNAs in periodontal tissues, and the potential role of miRNAs as biomarkers and therapeutics. In periodontal disease, miRNAs exert control over all aspects of innate and adaptive immunity, including the functions of neutrophils, macrophages, dendritic cells and T and B cells. Previous human studies have highlighted some key miRNAs that are dysregulated in periodontitis patients. In the present study, we mapped the major miRNAs that were altered in our reproducible periodontitis mouse model relative to control animals. The miRNAs that were upregulated as a result of periodontal disease in both human and mouse studies included miR-15a, miR-29b, miR-125a, miR-146a, miR-148/148a and miR-223, whereas miR-92 was downregulated. The association of individual miRNAs with unique aspects of periodontal disease and their stability in gingival crevicular fluid underscores their potential as markers for periodontal disease progression or healthy restitution. Moreover, miRNA therapeutics hold great promise for the future of periodontal therapy because of their ability to modulate the immune response to infection when applied in conjunction with synthetic antagomirs and/or relatively straightforward delivery strategies.
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http://dx.doi.org/10.1038/s41368-018-0025-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6080405PMC
August 2018

Integrative Temporo-Spatial, Mineralogic, Spectroscopic, and Proteomic Analysis of Postnatal Enamel Development in Teeth with Limited Growth.

Front Physiol 2017 24;8:793. Epub 2017 Oct 24.

Texas A&M Center for Craniofacial Research and Diagnosis, Dallas, TX, United States.

Tooth amelogenesis is a complex process beginning with enamel organ cell differentiation and enamel matrix secretion, transitioning through changes in ameloblast polarity, cytoskeletal, and matrix organization, that affects crucial biomineralization events such as mineral nucleation, enamel crystal growth, and enamel prism organization. Here we have harvested the enamel organ including the pliable enamel matrix of postnatal first mandibular mouse molars during the first 8 days of tooth enamel development to conduct a step-wise cross-sectional analysis of the changes in the mineral and protein phase. Mineral phase diffraction pattern analysis using single-crystal, powder sample X-ray diffraction analysis indicated conversion of calcium phosphate precursors to partially fluoride substituted hydroxyapatite from postnatal day 4 (4 dpn) onwards. Attenuated total reflectance spectra (ATR) revealed a substantial elevation in phosphate and carbonate incorporation as well as structural reconfiguration between postnatal days 6 and 8. Nanoscale liquid chromatography coupled with tandem mass spectrometry (nanoLC-MS/MS) demonstrated highest protein counts for ECM/cell surface proteins, stress/heat shock proteins, and alkaline phosphatase on postnatal day 2, high counts for ameloblast cytoskeletal proteins such as tubulin β5, tropomyosin, β-actin, and vimentin on postnatal day 4, and elevated levels of cofilin-1, calmodulin, and peptidyl-prolyl cis-trans isomerase on day 6. Western blot analysis of hydrophobic enamel proteins illustrated continuously increasing amelogenin levels from 1 dpn until 8 dpn, while enamelin peaked on days 1 and 2 dpn, and ameloblastin on days 1-5 dpn. In summary, these data document the substantial changes in the enamel matrix protein and mineral phase that take place during postnatal mouse molar amelogenesis from a systems biological perspective, including (i) relatively high levels of matrix protein expression during the early secretory stage on postnatal day 2, (ii) conversion of calcium phosphates to apatite, peak protein folding and stress protein counts, and increased cytoskeletal protein levels such as actin and tubulin on day 4, as well as (iii) secondary structure changes, isomerase activity, highest amelogenin levels, and peak phosphate/carbonate incorporation between postnatal days 6 and 8. Together, this study provides a baseline for a comprehensive understanding of the mineralogic and proteomic events that contribute to the complexity of mammalian tooth enamel development.
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http://dx.doi.org/10.3389/fphys.2017.00793DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5660681PMC
October 2017

Intravesicular Phosphatase PHOSPHO1 Function in Enamel Mineralization and Prism Formation.

Front Physiol 2017 17;8:805. Epub 2017 Oct 17.

Department of Periodontics, Texas A&M College of Dentistry, Dallas, TX, United States.

The transport of mineral ions from the enamel organ-associated blood vessels to the developing enamel crystals involves complex cargo packaging and carriage mechanisms across several cell layers, including the ameloblast layer and the stratum intermedium. Previous studies have established PHOSPHO1 as a matrix vesicle membrane-associated phosphatase that interacts with matrix vesicles molecules phosphoethanolamine and phosphocholine to initiate apatite crystal formation inside of matrix vesicles in bone. In the present study, we sought to determine the function of during amelogenesis. PHOSPHO1 protein localization during amelogenesis was verified using immunohistochemistry, with positive signals in the enamel layer, ameloblast Tomes' processes, and in the walls of ameloblast secretory vesicles. These ameloblast secretory vesicle walls were also labeled for amelogenin and the exosomal protein marker HSP70 using immunohistochemistry. Furthermore, PHOSPHO1 presence in the enamel organ was confirmed by Western blot. mice lacked sharp incisal tips, featured a significant 25% increase in total enamel volume, and demonstrated a significant 2-fold reduction in silver grain density of von Kossa stained ground sections indicative of reduced mineralization in the enamel layer when compared to wild-type mice ( < 0.001). Scanning electron micrographs of mouse enamel revealed a loss of the prominent enamel prism "picket fence" structure, a loss of parallel crystal organization within prisms, and a 1.56-fold increase in enamel prism width ( < 0.0001). Finally, EDS elemental analysis demonstrated a significant decrease in phosphate incorporation in the enamel layer when compared to controls ( < 0.05). Together, these data establish that the matrix vesicle membrane-associated phosphatase PHOSPHO1 is essential for physiological enamel mineralization. Our findings also suggest that intracellular ameloblast secretory vesicles have unexpected compositional similarities with the extracellular matrix vesicles of bone, dentin, and cementum in terms of vesicle membrane composition and intravesicular ion assembly.
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http://dx.doi.org/10.3389/fphys.2017.00805DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5651051PMC
October 2017

Posttranslational Amelogenin Processing and Changes in Matrix Assembly during Enamel Development.

Front Physiol 2017 17;8:790. Epub 2017 Oct 17.

Texas A&M Center for Craniofacial Research and Diagnosis, Dallas, TX, United States.

The extracellular tooth enamel matrix is a unique, protein-rich environment that provides the structural basis for the growth of long and parallel oriented enamel crystals. Here we have conducted a series of and studies to characterize the changes in matrix shape and organization that take place during the transition from ameloblast intravesicular matrices to extracellular subunit compartments and pericrystalline sheath proteins, and correlated these changes with stages of amelogenin matrix protein posttranslational processing. Our transmission electron microscopic studies revealed a 2.5-fold difference in matrix subunit compartment dimensions between secretory vesicle and extracellular enamel protein matrix as well as conformational changes in matrix structure between vesicles, stippled materials, and pericrystalline matrix. Enamel crystal growth in organ culture demonstrated granular mineral deposits associated with the enamel matrix framework, dot-like mineral deposits along elongating initial enamel crystallites, and dramatic changes in enamel matrix configuration following the onset of enamel crystal formation. Atomic force micrographs provided evidence for the presence of both linear and hexagonal/ring-shaped full-length recombinant amelogenin protein assemblies on mica surfaces, while nickel-staining of the N-terminal amelogenin N92 His-tag revealed 20 nm diameter oval and globular amelogenin assemblies in N92 amelogenin matrices. Western blot analysis comparing loosely bound and mineral-associated protein fractions of developing porcine enamel organs, superficial and deep enamel layers demonstrated (i) a single, full-length amelogenin band in the enamel organ followed by 3 kDa cleavage upon entry into the enamel layer, (ii) a close association of 8-16 kDa C-terminal amelogenin cleavage products with the growing enamel apatite crystal surface, and (iii) a remaining pool of N-terminal amelogenin fragments loosely retained between the crystalline phases of the deep enamel layer. Together, our data establish a temporo-spatial correlation between amelogenin protein processing and the changes in enamel matrix configuration that take place during the transition from intracellular vesicle compartments to extracellular matrix assemblies and the formation of protein coats along elongating apatite crystal surfaces. In conclusion, our study suggests that enzymatic cleavage of the amelogenin enamel matrix protein plays a key role in the patterning of the organic matrix framework as it affects enamel apatite crystal growth and habit.
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http://dx.doi.org/10.3389/fphys.2017.00790DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5651044PMC
October 2017

Enamel Research: Priorities and Future Directions.

Front Physiol 2017 20;8:513. Epub 2017 Jul 20.

Department of Paediatrics, University of MelbourneMelbourne, VIC, Australia.

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http://dx.doi.org/10.3389/fphys.2017.00513DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5517532PMC
July 2017

Daughters of the Enamel Organ: Development, Fate, and Function of the Stratum Intermedium, Stellate Reticulum, and Outer Enamel Epithelium.

Stem Cells Dev 2016 10 9;25(20):1580-1590. Epub 2016 Sep 9.

4 Texas A&M Center for Craniofacial Research and Diagnosis , Texas A&M College of Dentistry, Dallas, Texas.

The tooth enamel organ (EO) is a complex epithelial cell assembly involved in multiple aspects of tooth development, including amelogenesis. The present study focuses on the role of the nonameloblast layers of the EO, the stratum intermedium, the stellate reticulum, and the outer enamel epithelium (OEE). The secretory stage stratum intermedium was distinguished by p63-positive epithelial stem cell marks, highly specific alkaline phosphatase labeling, as well as multiple desmosomes and gap junctions. At the location of the presecretory stage stellate reticulum, the pre-eruption EO prominently featured the papillary layer (PL) as a keratin immunopositive network of epithelial strands between tooth crowns and oral epithelium. PL cell strands contained numerous p63-positive epithelial stem cells, while BrdU proliferative cells were detected at the outer boundaries of the PL, suggesting that the stellate reticulum/PL epithelial cell sheath proliferated to facilitate an epithelial seal during tooth eruption. Comparative histology studies demonstrated continuity between the OEE and the general lamina of continuous tooth replacement in reptiles, and the outer layer of Hertwig's epithelial root sheath in humans, implicating the OEE as the formative layer for continuous tooth replacement and tooth root extension. Cell fate studies in organ culture verified that the cervical portion of the mouse molar EO gave rise to Malassez rest-like cell islands. Together, these studies indicate that the nonameloblast layers of the EO play multiple roles during odontogenesis, including the maintenance of several p63-positive stem cell reservoirs, a role during tooth root morphogenesis and tooth succession, a stabilizing function for the ameloblast layer, the facilitation of ion transport from the EO capillaries to the enamel layer, as well as safe and seamless tooth eruption.
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http://dx.doi.org/10.1089/scd.2016.0267DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5084366PMC
October 2016

Varanoid Tooth Eruption and Implantation Modes in a Late Cretaceous Mosasaur.

Front Physiol 2016 17;7:145. Epub 2016 May 17.

Department of Oral Biology, University of Illinois, Chicago, IL, USA; Center for Craniofacial Research and Diagnosis and Department of Periodontics, Texas A&M University Baylor College of DentistryDallas, TX, USA.

Erupting teeth are some of the oldest witnesses of developmental processes in the vertebrate fossil record and provide an important resource for vertebrate cladistics. Here, we have examined a mosasaur jaw fragment from central Texas using ultrathin ground section histology and 3D tomographic imaging to assess features critical for the cladistic placement of mosasaurs among varanoids vs. snakes: (i) the orientation of replacement teeth compared to the major tooth axis, (ii) the occurrence of resorption pits, and (iii) the mode of tooth implantation/attachment to the tooth bearing element (TBE). The replacement tooth studied here developed in an inclined position slightly distal of the deciduous parent tooth, similar to another varanoid squamate, the Gila monster Heloderma suspectum. Ground sections and tomographs also demonstrated that the replacement tooth attachment apparatus was entirely intact and that there was no evidence of mechanical deformation. Sections and tomographs further illustrated that the replacement tooth was located within a bony crypt and the inclination of the crypt matched the inclination of the replacement tooth. These preparations also revealed the presence of a resorption pit within the boundaries of the deciduous tooth that surrounded the developing replacement tooth. This finding suggests that developing mosasaur teeth developed within the walls of resorption pits similar to varanoid tooth germs and unlike developing snake teeth which are surrounded by fibrous connective tissue integuments. Finally, mosasaurs featured pseudo-thecodont tooth implantation with teeth anchored within a socket of mineralized tissue by means of a mineralized periodontal ligament. Together, these data indicate that the moderate inclination of the erupting mosasaur tooth studied here is neither a result of postmortem displacement nor a character representative of snakes, but rather a shared character between Mosasaurs and other varanoids such as Heloderma. In conjunction with the presence of resorption pits and the evidence for pseudothecodont tooth implantation, the tooth eruption and implantation characters described in the present study either place mosasaurs among the varanoids or suggest convergent evolution mechanisms between both clades, with mosasaurs evolving somewhat independently from a common varanoid ancestor.
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http://dx.doi.org/10.3389/fphys.2016.00145DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4869606PMC
May 2016

Our periodontal tissue: a masterpiece of evolution.

J Clin Periodontol 2016 Apr 29;43(4):320-2. Epub 2016 Mar 29.

Department of Periodontics, Center for Craniofacial Research and Diagnosis, Texas A&M University Baylor College of Dentistry, Dallas, TX, USA.

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http://dx.doi.org/10.1111/jcpe.12532DOI Listing
April 2016

Oral Biology and Chicago.

Evol Dev 2016 Jan-Feb;18(1):3-6

Departments of Oral Biology and Orthodontics, University of Illinois at Chicago College of Dentistry, Chicago, Illinois.

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http://dx.doi.org/10.1111/ede.12177DOI Listing
October 2016

SM50 repeat-polypeptides self-assemble into discrete matrix subunits and promote appositional calcium carbonate crystal growth during sea urchin tooth biomineralization.

Ann Anat 2016 Jan 6;203:38-46. Epub 2015 Jul 6.

UIC College of Dentistry, Department of Oral Biology, USA; Baylor College of Dentistry, Department of Periodontics, USA. Electronic address:

The two major proteins involved in vertebrate enamel formation and echinoderm sea urchin tooth biomineralization, amelogenin and SM50, are both characterized by elongated polyproline repeat domains in the center of the macromolecule. To determine the role of polyproline repeat polypeptides in basal deuterostome biomineralization, we have mapped the localization of SM50 as it relates to crystal growth, conducted self-assembly studies of SM50 repeat polypeptides, and examined their effect on calcium carbonate and apatite crystal growth. Electron micrographs of the growth zone of Strongylocentrotus purpuratus sea urchin teeth documented a series of successive events from intravesicular mineral nucleation to mineral deposition at the interface between tooth surface and odontoblast syncytium. Using immunohistochemistry, SM50 was detected within the cytoplasm of cells associated with the developing tooth mineral, at the mineral secreting front, and adjacent to initial mineral deposits, but not in muscles and ligaments. Polypeptides derived from the SM50 polyproline alternating hexa- and hepta-peptide repeat region (SM50P6P7) formed highly discrete, donut-shaped self-assembly patterns. In calcium carbonate crystal growth studies, SM50P6P7 repeat peptides triggered the growth of expansive networks of fused calcium carbonate crystals while in apatite growth studies, SM50P6P7 peptides facilitated the growth of needle-shaped and parallel arranged crystals resembling those found in developing vertebrate enamel. In comparison, SM50P6P7 surpassed the PXX24 polypeptide repeat region derived from the vertebrate enamel protein amelogenin in its ability to promote crystal nucleation and appositional crystal growth. Together, these studies establish the SM50P6P7 polyproline repeat region as a potent regulator in the protein-guided appositional crystal growth that occurs during continuous tooth mineralization and eruption. In addition, our studies highlight the role of species-specific polyproline repeat motifs in the formation of discrete self-assembled matrices and the resulting control of mineral growth.
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http://dx.doi.org/10.1016/j.aanat.2015.06.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4975641PMC
January 2016

Cyclic stretch and compression forces alter microRNA-29 expression of human periodontal ligament cells.

Gene 2015 Jul 28;566(1):13-7. Epub 2015 Mar 28.

University of Illinois at Chicago, College of Dentistry, Department of Orthodontics, United States. Electronic address:

MicroRNAs (miRs) play an important role in the development and remodeling of tissues through the regulation of large cohorts of extracellular matrix (ECM) genes. The purpose of the present study was to determine the response of miR-29 family expression to loading forces and their effects on ECM gene expression in periodontal ligament cells, the key effector cell population during orthodontic tooth movement. In a comparison between miRs from human periodontal ligament cells (PDLCs) and alveolar bone cells (ABCs) from healthy human subjects, the ABC cohort of miRs was substantially greater than the corresponding PDLC cohort. Cyclic mechanical stretch forces at 12% deformation at 0.1Hz for 24h decreased expression of miR-29 family member miRs about 0.5 fold while 2g/cm(2) compression force for 24h increased miR-29 family member expression in PDLCs 1.8-4 folds. Cyclic stretch up-regulated major ECM genes in PDLCs, such as COL1A1, COL3A1 and COL5A1, while the compression force resulted in a down-regulation of these ECM genes. Direct interactions of miR-29 and Col1a1, Col3a1 and Col5a1 were confirmed using a dual luciferase reporter gene assay. In addition, transient transfection of a miR-29b mimic in mouse PDLCs down-regulated Col1a1, Col3a1 and Col5a1 while the transfection of miR-29b inhibitor up-regulated these genes compared to control transfection indicating that these target ECM genes directly responded to the altered level of miR-29b. These results provided a possible explanation for the effects of the miR-29 family on loaded PDLCS and their roles in extracellular matrix gene expression.
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http://dx.doi.org/10.1016/j.gene.2015.03.055DOI Listing
July 2015

The expanded amelogenin polyproline region preferentially binds to apatite versus carbonate and promotes apatite crystal elongation.

Front Physiol 2014 11;5:430. Epub 2014 Nov 11.

Oral Biology, University of Illinois at Chicago Brodie Laboratory for Craniofacial Genetics, University of Illinois at Chicago College of Dentistry Chicago, IL, USA.

The transition from invertebrate calcium carbonate-based calcite and aragonite exo- and endoskeletons to the calcium phosphate-based vertebrate backbones and jaws composed of microscopic hydroxyapatite crystals is one of the great revolutions in the evolution of terrestrial organisms. To identify potential factors that might have played a role in such a transition, three key domains of the vertebrate tooth enamel protein amelogenin were probed for calcium mineral/protein interactions and their ability to promote calcium phosphate and calcium carbonate crystal growth. Under calcium phosphate crystal growth conditions, only the carboxy-terminus augmented polyproline repeat peptide, but not the N-terminal peptide nor the polyproline repeat peptide alone, promoted the formation of thin and parallel crystallites resembling those of bone and initial enamel. In contrast, under calcium carbonate crystal growth conditions, all three amelogenin-derived polypeptides caused calcium carbonate to form fused crystalline conglomerates. When examined for long-term crystal growth, polyproline repeat peptides of increasing length promoted the growth of shorter calcium carbonate crystals with broader basis, contrary to the positive correlation between polyproline repeat element length and apatite mineralization published earlier. To determine whether the positive correlation between polyproline repeat element length and apatite crystal growth versus the inverse correlation between polyproline repeat length and calcium carbonate crystal growth were related to the binding affinity of the polyproline domain to either apatite or carbonate, a parallel series of calcium carbonate and calcium phosphate/apatite protein binding studies was conducted. These studies demonstrated a remarkable binding affinity between the augmented amelogenin polyproline repeat region and calcium phosphates, and almost no binding to calcium carbonates. In contrast, the amelogenin N-terminus bound to both carbonate and apatite, but preferentially to calcium carbonate. Together, these studies highlight the specific binding affinity of the augmented amelogenin polyproline repeat region to calcium phosphates versus calcium carbonate, and its unique role in the growth of thin apatite crystals as they occur in vertebrate biominerals. Our data suggest that the rise of apatite-based biominerals in vertebrates might have been facilitated by a rapid evolution of specialized polyproline repeat proteins flanked by a charged domain, resulting in apatite crystals with reduced width, increased length, and tailored biomechanical properties.
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http://dx.doi.org/10.3389/fphys.2014.00430DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4227485PMC
November 2014

Lyophilized platelet-rich fibrin (PRF) promotes craniofacial bone regeneration through Runx2.

Int J Mol Sci 2014 May 14;15(5):8509-25. Epub 2014 May 14.

Department of Implantology, Stomatological Hospital, Jilin University, Changchun 130021, Jilin, China.

Freeze-drying is an effective means to control scaffold pore size and preserve its composition. The purpose of the present study was to determine the applicability of lyophilized Platelet-rich fibrin (LPRF) as a scaffold for craniofacial tissue regeneration and to compare its biological effects with commonly used fresh Platelet-rich fibrin (PRF). LPRF caused a 4.8-fold±0.4-fold elevation in Runt-related transcription factor 2 (Runx2) expression in alveolar bone cells, compared to a 3.6-fold±0.2-fold increase when using fresh PRF, and a more than 10-fold rise of alkaline phosphatase levels and mineralization markers. LPRF-induced Runx2 expression only occurred in alveolar bone and not in periodontal or dental follicle cells. LPRF also caused a 1.6-fold increase in osteoblast proliferation (p<0.001) when compared to fresh PRF. When applied in a rat craniofacial defect model for six weeks, LPRF resulted in 97% bony coverage of the defect, compared to 84% for fresh PRF, 64% for fibrin, and 16% without scaffold. Moreover, LPRF thickened the trabecular diameter by 25% when compared to fresh PRF and fibrin, and only LPRF and fresh PRF resulted in the formation of interconnected trabeculae across the defect. Together, these studies support the application of lyophilized PRF as a biomimetic scaffold for craniofacial bone regeneration and mineralized tissue engineering.
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http://dx.doi.org/10.3390/ijms15058509DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4057745PMC
May 2014

The use of light/chemically hardened polymethylmethacrylate, polyhydroxylethylmethacrylate, and calcium hydroxide graft material in combination with polyanhydride around implants and extraction sockets in minipigs: Part II: histologic and micro-CT evaluations.

J Periodontol 2014 Sep 6;85(9):1230-9. Epub 2014 Feb 6.

Department of Applied Oral Sciences, Center for Periodontology, The Forsyth Institute, Cambridge, MA.

Background: This report is the second part of the previously published study on the impact of light/chemical hardening technology and a newly formulated composite graft material for crestal augmentation during immediate implant placement.

Methods: A total of 48 implants were placed into the sockets of the mesial roots of freshly extracted mandibular premolar teeth in three minipigs. Crestal areas and intrabony spaces were randomly augmented with light-hardened graft materials including a composite graft consisting of polymethylmethacrylate, polyhydroxylethylmethacrylate, and calcium hydroxide (PPCH) plus polyanhydride (PA); PPCH graft; and PA graft, or left untreated. Distal sockets not receiving implants and the sockets of first molars (n = 60) were randomly treated with one of the graft materials or left empty. In addition, two molar sockets were treated with the original PPCH graft material. Quantitative microcomputed tomography (micro-CT) was used to assess alveolar bone structure and tissue compositions. Histologic evaluations included descriptive histology to assess the peri-implant wound healing, as well as histomorphometric measurements to determine bone-to-implant contact (BIC).

Results: Both trabecular and cortical bone measurements by micro-CT did not reveal any significant differences among the groups. Sites augmented with PPCH+PA resulted in significantly greater BIC surface than PPCH alone and no-graft-treated implants (P <0.05) histologically. Stained ground sections showed complete bone formation between bone and implant surface in the PPCH+PA group, whereas sites without augmentation showed large gaps between bone and implant surfaces, indicating a slower bone apposition and less BIC surface compared to all other groups. Similar to implant sections, all materials showed positive outcome on trabecular and cortical bone formation in extraction sockets with an intact crestal cortical bone.

Conclusion: Histologic evaluations supported the previous findings on implant stability and function and confirmed that PPCH+PA provides a greater BIC with a well-organized implant-bone interface and is useful in crestal augmentation during immediate implant placement.
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http://dx.doi.org/10.1902/jop.2014.120424DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4642446PMC
September 2014

Abnormal Ras signaling in Costello syndrome (CS) negatively regulates enamel formation.

Hum Mol Genet 2014 Feb 20;23(3):682-92. Epub 2013 Sep 20.

Department of Orofacial Sciences and Program in Craniofacial and Mesenchymal Biology.

RASopathies are syndromes caused by gain-of-function mutations in the Ras signaling pathway. One of these conditions, Costello syndrome (CS), is typically caused by an activating de novo germline mutation in HRAS and is characterized by a wide range of cardiac, musculoskeletal, dermatological and developmental abnormalities. We report that a majority of individuals with CS have hypo-mineralization of enamel, the outer covering of teeth, and that similar defects are present in a CS mouse model. Comprehensive analysis of the mouse model revealed that ameloblasts, the cells that generate enamel, lacked polarity, and the ameloblast progenitor cells were hyperproliferative. Ras signals through two main effector cascades, the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K) pathways. To determine through which pathway Ras affects enamel formation, inhibitors targeting either PI3K or MEK 1 and 2 (MEK 1/2), kinases in the MAPK pathway, were utilized. MEK1/2 inhibition rescued the hypo-mineralized enamel, normalized the ameloblast polarity defect and restored normal progenitor cell proliferation. In contrast, PI3K inhibition only corrected the progenitor cell proliferation phenotype. We demonstrate for the first time the central role of Ras signaling in enamel formation in CS individuals and present the mouse incisor as a model system to dissect the roles of the Ras effector pathways in vivo.
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http://dx.doi.org/10.1093/hmg/ddt455DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3888259PMC
February 2014

Alternative Splicing of the Amelogenin Gene in a Caudate Amphibian, Plethodon cinereus.

PLoS One 2013 26;8(6):e68965. Epub 2013 Jun 26.

College of Veterinary Medicine, Jilin University, Changchun, Jilin, China.

As the major enamel matrix protein contributing to tooth development, amelogenin has been demonstrated to play a crucial role in tooth enamel formation. Previous studies have revealed amelogenin alternative splicing as a mechanism for amelogenin heterogeneous expression in mammals. While amelogenin and its splicing forms in mammalian vertebrates have been characterized, splicing variants of amelogenin gene still remains largely unknown in non-mammalian species. Here, using PCR and sequence analysis we discovered two novel amelogenin transcript variants in tooth organ extracts from a caudate amphibian, the salamander Plethodoncinereus. The one was shorter -S- (416 nucleotides including untranslated regions, 5 exons) and the other larger -L- (851 nt, 7 exons) than the previously published "normal" gene in this species -M- (812 nucleotides, 6 exons). This is the first report demonstrating the amelogenin alternative splicing in amphibian, revealing a unique exon 2b and two novel amelogenin gene transcripts in Plethodoncinereus.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0068965PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3694012PMC
October 2017

Combinatorial Design of Hydrolytically Degradable, Bone-like Biocomposites Based on PHEMA and Hydroxyapatite.

Polymer (Guildf) 2013 Jan 13;54(2):909-919. Epub 2012 Dec 13.

Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States ; College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.

With advantages such as design flexibility in modifying degradation, surface chemistry, and topography, synthetic bone-graft substitutes are increasingly demanded in orthopedic tissue engineering to meet various requirements in the growing numbers of cases of skeletal impairment worldwide. Using a combinatorial approach, we developed a series of biocompatible, hydrolytically degradable, elastomeric, bone-like biocomposites, comprising 60 wt% poly(2-hydroxyethyl methacrylate--methacrylic acid), poly(HEMA--MA), and 40 wt% bioceramic hydroxyapatite (HA). Hydrolytic degradation of the biocomposites is rendered by a degradable macromer/crosslinker, dimethacrylated poly(lactide--ethylene glycol--lactide), which first degrades to break up 3-D hydrogel networks, followed by dissolution of linear pHEMA macromolecules and bioceramic particles. Swelling and degradation were examined at Hank's balanced salt solution at 37 °C in a 12-week period of time. The degradation is strongly modulated by altering the concentration of the co-monomer of methacrylic acid and of the macromer, and chain length/molecular weight of the macromer. 95% weight loss in mass is achieved after degradation for 12 weeks in a composition consisting of HEMA/MA/Macromer = 0/60/40, while 90% weight loss is seen after degradation only for 4 weeks in a composition composed of HEMA/MA/Macromer = 27/13/60 using a longer chain macromer. For compositions without a co-monomer, only about 14% is achieved in weight loss after 12-week degradation. These novel biomaterials offer numerous possibilities as drug delivery carriers and bone grafts particularly for low and medium load-bearing applications.
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http://dx.doi.org/10.1016/j.polymer.2012.12.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601847PMC
January 2013

Epigenetic marks define the lineage and differentiation potential of two distinct neural crest-derived intermediate odontogenic progenitor populations.

Stem Cells Dev 2013 Jun 15;22(12):1763-78. Epub 2013 Mar 15.

UIC Brodie Laboratory for Craniofacial Genetics, UIC College of Dentistry, Chicago, Illinois 60612, USA.

Epigenetic mechanisms, such as histone modifications, play an active role in the differentiation and lineage commitment of mesenchymal stem cells. In the present study, epigenetic states and differentiation profiles of two odontogenic neural crest-derived intermediate progenitor populations were compared: dental pulp (DP) and dental follicle (DF). ChIP on chip assays revealed substantial H3K27me3-mediated repression of odontoblast lineage genes DSPP and dentin matrix protein 1 (DMP1) in DF cells, but not in DP cells. Mineralization inductive conditions caused steep increases of mineralization and patterning gene expression levels in DP cells when compared to DF cells. In contrast, mineralization induction resulted in a highly dynamic histone modification response in DF cells, while there was only a subdued effect in DP cells. Both DF and DP progenitors featured H3K4me3-active marks on the promoters of early mineralization genes RUNX2, MSX2, and DLX5, while OSX, IBSP, and BGLAP promoters were enriched for H3K9me3 or H3K27me3. Compared to DF cells, DP cells expressed higher levels of three pluripotency-associated genes, OCT4, NANOG, and SOX2. Finally, gene ontology comparison of bivalent marks unique for DP and DF cells highlighted cell-cell attachment genes in DP cells and neurogenesis genes in DF cells. In conclusion, the present study indicates that the DF intermediate odontogenic neural crest lineage is distinguished from its DP counterpart by epigenetic repression of DSPP and DMP1 genes and through dynamic histone enrichment responses to mineralization induction. Findings presented here highlight the crucial role of epigenetic regulatory mechanisms in the terminal differentiation of odontogenic neural crest lineages.
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http://dx.doi.org/10.1089/scd.2012.0711DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3668503PMC
June 2013

Structure and function of ameloblastin as an extracellular matrix protein: adhesion, calcium binding, and CD63 interaction in human and mouse.

Eur J Oral Sci 2011 Dec;119 Suppl 1:270-9

Brodie Laboratory for Craniofacial Genetics, University of Illinois - Chicago, Chicago, IL 60612, USA.

The functional significance of extracellular matrix proteins in the life of vertebrates is underscored by a high level of sequence variability in tandem with a substantial degree of conservation in terms of cell-cell and cell-matrix adhesion interactions. Many extracellular matrix proteins feature multiple adhesion domains for successful attachment to substrates, such as integrin, CD63, and heparin. Here we have used homology and ab initio modeling algorithms to compare mouse ameloblastin (mAMBN) and human ameloblastin (hABMN) isoforms and to analyze their potential for cell adhesion and interaction with other matrix molecules as well as calcium binding. Sequence comparison between mAMBN and hAMBN revealed a 26-amino-acid deletion in mAMBN, corresponding to a helix-loop-helix frameshift. The human AMBN domain (174Q-201G), homologous to the mAMBN 157E-178I helix-loop-helix region, formed a helix-loop motif with an extended loop, suggesting a higher degree of flexibility of hAMBN compared with mAMBN, as confirmed by molecular dynamics simulation. Heparin-binding domains, CD63-interaction domains, and calcium-binding sites in both hAMBN and mAMBN support the concept of AMBN as an extracellular matrix protein. The high level of conservation between AMBN functional domains related to adhesion and differentiation was remarkable when compared with only 61% amino acid sequence homology.
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http://dx.doi.org/10.1111/j.1600-0722.2011.00889.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3402545PMC
December 2011

Ameloblastin-rich enamel matrix favors short and randomly oriented apatite crystals.

Eur J Oral Sci 2011 Dec;119 Suppl 1:254-60

Brodie Laboratory for Craniofacial Genetics, University of Illinois at Chicago, Chicago, IL, USA.

Molecular evolution studies suggest that amelogenin (AMELX), the principal component of the mammalian enamel matrix, emerged considerably later than ameloblastin (AMBN), and enamelin. Here, we created a transgenic mouse model to ask the question how a conceivable basal enamel lacking AMELX and enriched in the more basal AMBN might compare with recent mouse enamel. To answer this question we overexpressed AMBN using a keratin 14 (K14) promoter and removed AMELX from the genetic background by crossbreeding with amelx(-/-) mice. Enamel coverings of amelx(-/-) mice and of the squamate Iguana iguana were used for comparison. Scanning electron microscopic analysis documented that AMBN transgenic (TG) × amelx(-/-) mouse molars were covered by a 5 μm thin 'enameloid' layer resembling the thin enamel of the Iguana squamate. Transmission electron microscopy revealed that the enamel of developing AMBN TG × amelx(-/-) mouse molars contained short (approximately 70 nm) and randomly oriented crystals, while WT controls, AMBN overexpressors, and AMELX(-/-) mice all featured elongated and parallel oriented crystals measuring between 300 and 600 nm in average length. Together, these studies illustrate that AMBN promotes the growth of a crystalline enamel layer with short and randomly oriented crystals, but lacks the ability to facilitate the formation of long and parallel oriented apatite crystals.
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http://dx.doi.org/10.1111/j.1600-0722.2011.00905.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3402546PMC
December 2011

Amelogenin supramolecular assembly in nanospheres defined by a complex helix-coil-PPII helix 3D-structure.

PLoS One 2011 3;6(10):e24952. Epub 2011 Oct 3.

Brodie Laboratory for Craniofacial Genetics, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois, United States of America.

Tooth enamel, the hardest material in the human body, is formed within a self-assembled matrix consisting mostly of amelogenin proteins. Here we have determined the complete mouse amelogenin structure under physiological conditions and defined interactions between individual domains. NMR spectroscopy revealed four major amelogenin structural motifs, including an N-terminal assembly of four α-helical segments (S9-V19, T21-P33, Y39-W45, V53-Q56), an elongated random coil region interrupted by two 3(10) helices (∼P60-Q117), an extended proline-rich PPII-helical region (P118-L165), and a charged hydrophilic C-terminus (L165-D180). HSQC experiments demonstrated ipsilateral interactions between terminal domains of individual amelogenin molecules, i.e. N-terminal interactions with corresponding N-termini and C-terminal interactions with corresponding C-termini, while the central random coil domain did not engage in interactions. Our HSQC spectra of the full-length amelogenin central domain region completely overlapped with spectra of the monomeric Amel-M fragment, suggesting that the central amelogenin coil region did not involve in assembly, even in assembled nanospheres. This finding was confirmed by analytical ultracentrifugation experiments. We conclude that under conditions resembling those found in the developing enamel protein matrix, amelogenin molecules form complex 3D-structures with N-terminal α-helix-like segments and C-terminal PPII-helices, which self-assemble through ipsilateral interactions at the N-terminus of the molecule.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024952PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3184955PMC
January 2012

Successful periodontal ligament regeneration by periodontal progenitor preseeding on natural tooth root surfaces.

Stem Cells Dev 2011 Oct 9;20(10):1659-68. Epub 2011 Mar 9.

Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, Chicago, Illinois 60612, USA.

The regeneration of lost periodontal ligament (PDL) and alveolar bone is the purpose of periodontal tissue engineering. The goal of the present study was to assess the suitability of 3 odontogenic progenitor populations from dental pulp, PDL, and dental follicle for periodontal regeneration when exposed to natural and synthetic apatite surface topographies. We demonstrated that PDL progenitors featured higher levels of periostin and scleraxis expression, increased adipogenic and osteogenic differentiation potential, and pronounced elongated cell shapes on barren root chips when compared with dental pulp and dental follicle cells. When evaluating the effect of surface characteristics on PDL progenitors, natural root surfaces resulted in elongated PDL cell shapes, whereas PDL progenitors on synthetic apatite surfaces were rounded or polygonal. In addition, surface coatings affected PDL progenitor gene expression profiles: collagen I coatings enhanced alkaline phosphatase and osteocalcin expression levels and laminin-1 coatings increased epidermal growth factor (EGF), nestin, cadherin 1, and keratin 8 expression. PDL progenitors seeded on natural tooth root surfaces in organ culture formed new periodontal fibers after 3 weeks of culture. Finally, replantation of PDL progenitor-seeded tooth roots into rat alveolar bone sockets resulted in the complete formation of a new PDL and stable reattachment of teeth over a 6-month period. Together, these findings indicate that periodontal progenitor cell type as well as mineral surface topography and molecular environment play crucial roles in the regeneration of true periodontal anchorage.
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http://dx.doi.org/10.1089/scd.2010.0431DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3210028PMC
October 2011