Publications by authors named "Elisabeth R Barton"

72 Publications

Actions and interactions of IGF-I and MMPs during muscle regeneration.

Semin Cell Dev Biol 2021 May 4. Epub 2021 May 4.

Applied Physiology & Kinesiology, College of Health and Human Performance, University of Florida, 1864 Stadium Road, Gainesville, FL 32611, USA. Electronic address:

Muscle regeneration requires the coordination of several factors to mobilize satellite cells and macrophages, remodel the extracellular matrix surrounding muscle fibers, and repair existing and/or form new muscle fibers. In this review, we focus on insulin-like growth factor I and the matrix metalloproteinases, which are secreted proteins that act on cells and the matrix to resolve damage. While their actions appear independent, their interactions occur at the transcriptional and post-translational levels to promote feed-forward activation of each other. Together, these proteins assist at virtually every step of the repair process, and contribute significantly to muscle regenerative capacity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.semcdb.2021.04.018DOI Listing
May 2021

Hesperidin Promotes Osteogenesis and Modulates Collagen Matrix Organization and Mineralization In Vitro and In Vivo.

Int J Mol Sci 2021 Mar 22;22(6). Epub 2021 Mar 22.

Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL 32611, USA.

This study evaluated the direct effect of a phytochemical, hesperidin, on pre-osteoblast cell function as well as osteogenesis and collagen matrix quality, as there is little known about hesperidin's influence in mineralized tissue formation and regeneration. Hesperidin was added to a culture of MC3T3-E1 cells at various concentrations. Cell proliferation, viability, osteogenic gene expression and deposited collagen matrix analyses were performed. Treatment with hesperidin showed significant upregulation of osteogenic markers, particularly with lower doses. Mature and compact collagen fibrils in hesperidin-treated cultures were observed by picrosirius red staining (PSR), although a thinner matrix layer was present for the higher dose of hesperidin compared to osteogenic media alone. Fourier-transform infrared spectroscopy indicated a better mineral-to-matrix ratio and matrix distribution in cultures exposed to hesperidin and confirmed less collagen deposited with the 100-µM dose of hesperidin. In vivo, hesperidin combined with a suboptimal dose of bone morphogenetic protein 2 (BMP2) (dose unable to promote healing of a rat mandible critical-sized bone defect) in a collagenous scaffold promoted a well-controlled (not ectopic) pattern of bone formation as compared to a large dose of BMP2 (previously defined as optimal in healing the critical-sized defect, although of ectopic nature). PSR staining of newly formed bone demonstrated that hesperidin can promote maturation of bone organic matrix. Our findings show, for the first time, that hesperidin has a modulatory role in mineralized tissue formation via not only osteoblast cell differentiation but also matrix organization and matrix-to-mineral ratio and could be a potential adjunct in regenerative bone therapies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/ijms22063223DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8004833PMC
March 2021

Antagonistic control of myofiber size and muscle protein quality control by the ubiquitin ligase UBR4 during aging.

Nat Commun 2021 03 3;12(1):1418. Epub 2021 Mar 3.

Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN, USA.

Sarcopenia is a degenerative condition that consists in age-induced atrophy and functional decline of skeletal muscle cells (myofibers). A common hypothesis is that inducing myofiber hypertrophy should also reinstate myofiber contractile function but such model has not been extensively tested. Here, we find that the levels of the ubiquitin ligase UBR4 increase in skeletal muscle with aging, and that UBR4 increases the proteolytic activity of the proteasome. Importantly, muscle-specific UBR4 loss rescues age-associated myofiber atrophy in mice. However, UBR4 loss reduces the muscle specific force and accelerates the decline in muscle protein quality that occurs with aging in mice. Similarly, hypertrophic signaling induced via muscle-specific loss of UBR4/poe and of ESCRT members (HGS/Hrs, STAM, USP8) that degrade ubiquitinated membrane proteins compromises muscle function and shortens lifespan in Drosophila by reducing protein quality control. Altogether, these findings indicate that these ubiquitin ligases antithetically regulate myofiber size and muscle protein quality control.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-021-21738-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7930053PMC
March 2021

The D2.mdx mouse as a preclinical model of the skeletal muscle pathology associated with Duchenne muscular dystrophy.

Sci Rep 2020 08 21;10(1):14070. Epub 2020 Aug 21.

Department of Pharmacology and Therapeutics, University of Florida College of Medicine, 1200 Newell Dr., ARB R5-216, Gainesville, FL, 32610-0267, USA.

Duchenne muscular dystrophy (DMD) is an X-linked, lethal muscle degenerative disease caused by loss of dystrophin protein. DMD has no cure and few treatment options. Preclinical efforts to identify potential DMD therapeutics have been hampered by lack of a small animal model that recapitulates key features of the human disease. While the dystrophin-deficient mdx mouse on the C57BL/10 genetic background (B10.mdx) is mildly affected, a more severe muscle disease is observed when the mdx mutation is crossed onto the DBA/2J genetic background (D2.mdx). In this study, the functional and histological progression of the D2.mdx skeletal muscle pathology was evaluated to determine the distinguishing features of disease. Data herein details the muscular weakness and wasting exhibited by D2.mdx skeletal muscle, as well as severe histopathological features, which include the rapid progression of fibrosis and calcifications in the diaphragm and progressive fibrosis accumulation in limb muscles. Furthermore, a timeline of D2.mdx progression is provided that details distinct stages of disease progression. These data support the D2.mdx as a superior small animal model for DMD, as compared to the B10.mdx model. The insights provided in this report should facilitate the design of preclinical evaluations for potential DMD therapeutics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-020-70987-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7442653PMC
August 2020

The ties that bind: functional clusters in limb-girdle muscular dystrophy.

Skelet Muscle 2020 07 29;10(1):22. Epub 2020 Jul 29.

Myology Institute, University of Florida, Gainesville, FL, USA.

The limb-girdle muscular dystrophies (LGMDs) are a genetically pleiomorphic class of inherited muscle diseases that are known to share phenotypic features. Selected LGMD genetic subtypes have been studied extensively in affected humans and various animal models. In some cases, these investigations have led to human clinical trials of potential disease-modifying therapies, including gene replacement strategies for individual subtypes using adeno-associated virus (AAV) vectors. The cellular localizations of most proteins associated with LGMD have been determined. However, the functions of these proteins are less uniformly characterized, thus limiting our knowledge of potential common disease mechanisms across subtype boundaries. Correspondingly, broad therapeutic strategies that could each target multiple LGMD subtypes remain less developed. We believe that three major "functional clusters" of subcellular activities relevant to LGMD merit further investigation. The best known of these is the glycosylation modifications associated with the dystroglycan complex. The other two, mechanical signaling and mitochondrial dysfunction, have been studied less systematically but are just as promising with respect to the identification of significant mechanistic subgroups of LGMD. A deeper understanding of these disease pathways could yield a new generation of precision therapies that would each be expected to treat a broader range of LGMD patients than a single subtype, thus expanding the scope of the molecular medicines that may be developed for this complex array of muscular dystrophies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s13395-020-00240-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7389686PMC
July 2020

Matrix Metalloproteinase 13 from Satellite Cells is Required for Efficient Muscle Growth and Regeneration.

Cell Physiol Biochem 2020 Apr;54(3):333-353

Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA,

Background/aims: Cell migration and extracellular matrix remodeling underlie normal mammalian development and growth as well as pathologic tumor invasion. Skeletal muscle is no exception, where satellite cell migration replenishes nuclear content in damaged tissue and extracellular matrix reforms during regeneration. A key set of enzymes that regulate these processes are matrix metalloproteinases (MMP)s. The collagenase MMP-13 is transiently upregulated during muscle regeneration, but its contribution to damage resolution is unknown. The purpose of this work was to examine the importance of MMP-13 in muscle regeneration and growth in vivo and to delineate a satellite cell specific role for this collagenase.

Methods: Mice with total and satellite cell specific Mmp13 deletion were utilized to determine the importance of MMP-13 for postnatal growth, regeneration after acute injury, and in chronic injury from a genetic cross with dystrophic (mdx) mice. We also evaluated insulin-like growth factor 1 (IGF-1) mediated hypertrophy in the presence and absence of MMP-13. We employed live-cell imaging and 3D migration measurements on primary myoblasts obtained from these animals. Outcome measures included muscle morphology and function.

Results: Under basal conditions, Mmp13 mice did not exhibit histological or functional deficits in muscle. However, following acute injury, regeneration was impaired at 11 and 14 days post injury. Muscle hypertrophy caused by increased IGF-1 was blunted with minimal satellite cell incorporation in the absence of MMP-13. Mmp13 primary myoblasts displayed reduced migratory capacity in 2D and 3D, while maintaining normal proliferation and differentiation. Satellite cell specific deletion of MMP-13 recapitulated the effects of global MMP-13 ablation on muscle regeneration, growth and myoblast movement.

Conclusion: These results show that satellite cells provide an essential autocrine source of MMP-13, which not only regulates their migration, but also supports postnatal growth and resolution of acute damage.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.33594/000000223DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7293591PMC
April 2020

A Key Role for the Ubiquitin Ligase UBR4 in Myofiber Hypertrophy in Drosophila and Mice.

Cell Rep 2019 07;28(5):1268-1281.e6

Division of Developmental Biology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA; Department of Developmental Neurobiology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA. Electronic address:

Skeletal muscle cell (myofiber) atrophy is a detrimental component of aging and cancer that primarily results from muscle protein degradation via the proteasome and ubiquitin ligases. Transcriptional upregulation of some ubiquitin ligases contributes to myofiber atrophy, but little is known about the role that most other ubiquitin ligases play in this process. To address this question, we have used RNAi screening in Drosophila to identify the function of > 320 evolutionarily conserved ubiquitin ligases in myofiber size regulation in vivo. We find that whereas RNAi for some ubiquitin ligases induces myofiber atrophy, loss of others (including the N-end rule ubiquitin ligase UBR4) promotes hypertrophy. In Drosophila and mouse myofibers, loss of UBR4 induces hypertrophy via decreased ubiquitination and degradation of a core set of target proteins, including the HAT1/RBBP4/RBBP7 histone-binding complex. Together, this study defines the repertoire of ubiquitin ligases that regulate myofiber size and the role of UBR4 in myofiber hypertrophy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.06.094DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6697171PMC
July 2019

Functional muscle hypertrophy by increased insulin-like growth factor 1 does not require dysferlin.

Muscle Nerve 2019 10 30;60(4):464-473. Epub 2019 Jul 30.

Department of Physiology, Perleman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

Introduction: Dysferlin loss-of-function mutations cause muscular dystrophy, accompanied by impaired membrane repair and muscle weakness. Growth promoting strategies including insulin-like growth factor 1 (IGF-1) could provide benefit but may cause strength loss or be ineffective. The objective of this study was to determine whether locally increased IGF-1 promotes functional muscle hypertrophy in dysferlin-null (Dysf ) mice.

Methods: Muscle-specific transgenic expression and postnatal viral delivery of Igf1 were used in Dysf and control mice. Increased IGF-1 levels were confirmed by enzyme-linked immunosorbent assay. Testing for skeletal muscle mass and function was performed in male and female mice.

Results: Muscle hypertrophy occurred in response to increased IGF-1 in mice with and without dysferlin. Male mice showed a more robust response compared with females. Increased IGF-1 did not cause loss of force per cross-sectional area in Dysf muscles.

Discussion: We conclude that increased local IGF-1 promotes functional hypertrophy when dysferlin is absent and reestablishes IGF-1 as a potential therapeutic for dysferlinopathies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mus.26641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6771521PMC
October 2019

Smooth muscle atrophy and colon pathology in SMN deficient mice.

Am J Transl Res 2019 15;11(3):1789-1799. Epub 2019 Mar 15.

Department of Physiology, University of Pennsylvania Perelman School of Medicine Philadelphia, PA.

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder characterized by loss of motor neurons in the ventral horn of the spinal cord. Clinical features such as progressively lethal respiratory weakness and associated muscle wasting have been extensively studied but less attention has been given to gastrointestinal (GI) dysfunction, which is common symptomatology in SMA patients with 43% constipation, 15% abdominal pain, and 14% meteorism. In the current study, the PrP92-SMN mouse model of SMA was utilized, to complement previous studies in which cells of the Enteric Nervous system (ENS) were susceptible to Smn (survival motor neuron) deficiency and could possibly be the basis of the observed GI symptoms. Necropsy of our mouse model showed impairment in feces excretion and smaller bladder mass, compared to Wild-Type (WT) animals. Along with the reduction in bladder mass, we also observed a decrease in the size of smooth muscles, due to reduction in Cross-Sectional Area (CSA). Interstitial cells of Cajal (ICC) provide important regulatory functions in the GI tract. To investigate if ICC are implicated in Smn deficient-induced colonic dysmotility, we assessed ICC distribution and abundance, by c-Kit, a well-established marker. SMA mice exhibited fewer c-Kit positive cells with altered localization, compared to WT. In conclusion, the observed histopathological abnormalities of our mouse model, can be secondary to SMN deficiency and could possibly underlie the GI symptoms observed in SMA patients. Future therapeutic approaches for SMA, must address not only CNS symptoms, but also non-motor-neuron-related symptoms. The PrP92-SMN mouse model could be a useful model for assessing therapeutic rescue of GI dysfunction in SMA.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6456546PMC
March 2019

Deleting nebulin's C-terminus reveals its importance to sarcomeric structure and function and is sufficient to invoke nemaline myopathy.

Hum Mol Genet 2019 05;28(10):1709-1725

Department of Cellular and Molecular Medicine, University of Arizona, Tucson, Arizona, USA.

Nebulin is a large skeletal muscle protein wound around the thin filaments, with its C-terminus embedded within the Z-disk and its N-terminus extending out toward the thin filament pointed end. While nebulin's C-terminus has been implicated in both sarcomeric structure and function as well as the development of nemaline myopathy, the contributions of this region remain largely unknown. Additionally, the C-terminus is reported to contribute to muscle hypertrophy via the IGF-1 growth pathway. To study the functions of nebulin's C-terminus, we generated a mouse model deleting the final two unique C-terminal domains, the serine-rich region (SRR) and the SH3 domain (NebΔ163-165). Homozygous NebΔ163-165 mice that survive past the neonatal stage exhibit a mild weight deficit. Characterization of these mice revealed that the truncation caused a moderate myopathy phenotype reminiscent of nemaline myopathy despite the majority of nebulin being localized properly in the thin filaments. This phenotype included muscle weight loss, changes in sarcomere structure, as well as a decrease in force production. Glutathione S-transferase (GST) pull-down experiments found novel binding partners with the SRR, several of which are associated with myopathies. While the C-terminus does not appear to be a limiting step in muscle growth, the IGF-1 growth pathway remained functional despite the deleted domains being proposed to be essential for IGF-1 mediated hypertrophy. The NebΔ163-165 mouse model emphasizes that nebulin's C-terminus is necessary for proper sarcomeric development and shows that its loss is sufficient to induce myopathy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/hmg/ddz016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6494792PMC
May 2019

Insulin-Like Growth Factor I Regulation and Its Actions in Skeletal Muscle.

Compr Physiol 2018 12 13;9(1):413-438. Epub 2018 Dec 13.

Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida, USA.

The insulin-like growth factor (IGF) pathway is essential for promoting growth and survival of virtually all tissues. It bears high homology to its related protein insulin, and as such, there is an interplay between these molecules with regard to their anabolic and metabolic functions. Skeletal muscle produces a significant proportion of IGF-1, and is highly responsive to its actions, including increased muscle mass and improved regenerative capacity. In this overview, the regulation of IGF-1 production, stability, and activity in skeletal muscle will be described. Second, the physiological significance of the forms of IGF-1 produced will be discussed. Last, the interaction of IGF-1 with other pathways will be addressed. © 2019 American Physiological Society. Compr Physiol 9:413-438, 2019.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/cphy.c180010DOI Listing
December 2018

Generation and characterization of monoclonal antibodies that recognize human and murine supervillin protein isoforms.

PLoS One 2018 17;13(10):e0205910. Epub 2018 Oct 17.

Department of Radiology, Division of Cell Biology & Imaging, University of Massachusetts Medical School, Worcester, MA, United States of America.

Supervillin isoforms have been implicated in cell proliferation, actin filament-based motile processes, vesicle trafficking, and signal transduction. However, an understanding of the roles of these proteins in cancer metastasis and physiological processes has been limited by the difficulty of obtaining specific antibodies against these highly conserved membrane-associated proteins. To facilitate research into the biological functions of supervillin, monoclonal antibodies were generated against the bacterially expressed human supervillin N-terminus. Two chimeric monoclonal antibodies with rabbit Fc domains (clones 1E2/CPTC-SVIL-1; 4A8/CPTC-SVIL-2) and two mouse monoclonal antibodies (clones 5A8/CPTC-SVIL-3; 5G3/CPTC-SVIL-4) were characterized with respect to their binding sites, affinities, and for efficacy in immunoblotting, immunoprecipitation, immunofluorescence microscopy and immunohistochemical staining. Two antibodies (1E2, 5G3) recognize a sequence found only in primate supervillins, whereas the other two antibodies (4A8, 5A8) are specific for a more broadly conserved conformational epitope(s). All antibodies function in immunoblotting, immunoprecipitation and in immunofluorescence microscopy under the fixation conditions identified here. We also show that the 5A8 antibody works on immunohistological sections. These antibodies should provide useful tools for the study of mammalian supervillins.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0205910PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6192639PMC
April 2019

Deletion of muscle IGF-I transiently impairs growth and progressively disrupts glucose homeostasis in male mice.

FASEB J 2019 01 22;33(1):181-194. Epub 2018 Jun 22.

Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, Florida, USA.

Insulin-like growth factors (IGFs) are essential for local skeletal muscle growth and organismal physiology, but these actions are entwined with glucose homeostasis through convergence with insulin signaling. The objective of this work was to determine whether the effects of IGF-I on growth and metabolism could be separated. We generated muscle-specific IGF-I-deficient (MID) mice that afford inducible deletion of Igf1 at any age. After Igf1 deletion at birth or in young adult mice, evaluations of muscle physiology and glucose homeostasis were performed up to 16 wk of age. MID mice generated at birth had lower muscle and circulating IGF-I, decreased muscle and body mass, and impaired muscle force production. Eight-wk-old male MID had heightened insulin levels with trends of elevated fasting glucose. This phenotype progressed to impaired glucose handling and increased fat deposition without significant muscle mass loss at 16 wk of age. The same phenotype emerged in 16-wk-old MID mice induced at 12 wk of age, compounded with heightened muscle fatigability and exercise intolerance. We assert that muscle IGF-I independently modulates anabolism and metabolism in an age-dependent manner, thus positioning muscle IGF-I maintenance to be critical for both muscle growth and metabolic homeostasis.-Vassilakos, G., Lei, H., Yang, Y., Puglise, J., Matheny, M., Durzynska, J., Ozery, M., Bennett, K., Spradlin, R., Bonanno, H., Park, S., Ahima, R. S., Barton, E. R. Deletion of muscle IGF-I transiently impairs growth and progressively disrupts glucose homeostasis in male mice.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1096/fj.201800459RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6355069PMC
January 2019

Regulation of fibrosis in muscular dystrophy.

Matrix Biol 2018 08 2;68-69:602-615. Epub 2018 Feb 2.

Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, United States. Electronic address:

The production of force and power are inherent properties of skeletal muscle, and regulated by contractile proteins within muscle fibers. However, skeletal muscle integrity and function also require strong connections between muscle fibers and their extracellular matrix (ECM). A well-organized and pliant ECM is integral to muscle function and the ability for many different cell populations to efficiently migrate through ECM is critical during growth and regeneration. For many neuromuscular diseases, genetic mutations cause disruption of these cytoskeletal-ECM connections, resulting in muscle fragility and chronic injury. Ultimately, these changes shift the balance from myogenic pathways toward fibrogenic pathways, culminating in the loss of muscle fibers and their replacement with fatty-fibrotic matrix. Hence a common pathological hallmark of muscular dystrophy is prominent fibrosis. This review will cover the salient features of muscular dystrophy pathogenesis, highlight the signals and cells that are important for myogenic and fibrogenic actions, and discuss how fibrosis alters the ECM of skeletal muscle, and the consequences of fibrosis in developing therapies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.matbio.2018.01.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6519730PMC
August 2018

Contrast-Enhanced Near-Infrared Optical Imaging Detects Exacerbation and Amelioration of Murine Muscular Dystrophy.

Mol Imaging 2017 Jan-Dec;16:1536012117732439

1 Department of Physiology and Functional Genomics, University of Florida, Gainesville, FL, USA.

Assessment of muscle pathology is a key outcome measure to measure the success of clinical trials studying muscular dystrophies; however, few robust minimally invasive measures exist. Indocyanine green (ICG)-enhanced near-infrared (NIR) optical imaging offers an objective, minimally invasive, and longitudinal modality that can quantify pathology within muscle by imaging uptake of ICG into the damaged muscles. Dystrophic mice lacking dystrophin (mdx) or gamma-sarcoglycan (Sgcg) were compared to control mice by NIR optical imaging and magnetic resonance imaging (MRI). We determined that optical imaging could be used to differentiate control and dystrophic mice, visualize eccentric muscle induced by downhill treadmill running, and restore the membrane integrity in Sgcg mice following adeno-associated virus (AAV) delivery of recombinant human SGCG (desAAV8hSGCG). We conclude that NIR optical imaging is comparable to MRI and can be used to detect muscle damage in dystrophic muscle as compared to unaffected controls, monitor worsening of muscle pathology in muscular dystrophy, and assess regression of pathology following therapeutic intervention in muscular dystrophies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1177/1536012117732439DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5985549PMC
October 2018

The IGF axis in HPV associated cancers.

Mutat Res Rev Mutat Res 2017 Apr - Jun;772:67-77. Epub 2017 Feb 4.

Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, FL, USA.

Human papillomaviruses (HPV) infect and replicate in stratified epithelium at cutaneous and mucosal surfaces. The proliferation and maintenance of keratinocytes, the cells which make up this epithelium, are controlled by a number of growth factor receptors such as the keratinocyte growth factor receptor (KGFR, also called fibroblast growth factor receptor 2b (FGFR2b)), the epithelial growth factor receptor (EGFR) and the insulin-like growth factor receptors 1 and 2 (IGF1R and IGF2R). In this review, we will delineate the mutation, gene transcription, translation and processing of the IGF axis within HPV associated cancers. The IGFs are key for developmental and postnatal growth of almost all tissues; we explore whether this crucial axis has been hijacked by HPV.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.mrrev.2017.01.002DOI Listing
August 2017

Activin Receptor Type IIB Inhibition Improves Muscle Phenotype and Function in a Mouse Model of Spinal Muscular Atrophy.

PLoS One 2016 21;11(11):e0166803. Epub 2016 Nov 21.

Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.

Spinal muscular atrophy (SMA) is a devastating neurodegenerative disorder that causes progressive muscle atrophy and weakness. Using adeno-associated virus-mediated gene transfer, we evaluated the potential to improve skeletal muscle weakness via systemic, postnatal inhibition of either myostatin or all signaling via the activin receptor type IIB (ActRIIB). After demonstrating elevated p-SMAD3 content and differential content of ActRIIB ligands, 4-week-old male C/C SMA model mice were treated intraperitoneally with 1x1012 genome copies of pseudotype 2/8 virus encoding a soluble form of the ActRIIB extracellular domain (sActRIIB) or protease-resistant myostatin propeptide (dnMstn) driven by a liver specific promoter. At 12 weeks of age, muscle mass and function were improved in treated C/C mice by both treatments, compared to controls. The fast fiber type muscles had a greater response to treatment than did slow muscles, and the greatest therapeutic effects were found with sActRIIB treatment. Myostatin/activin inhibition, however, did not rescue C/C mice from the reduction in motor unit numbers of the tibialis anterior muscle. Collectively, this study indicates that myostatin/activin inhibition represents a potential therapeutic strategy to increase muscle mass and strength, but not neuromuscular junction defects, in less severe forms of SMA.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166803PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5117715PMC
June 2017

Osteopontin ablation ameliorates muscular dystrophy by shifting macrophages to a pro-regenerative phenotype.

J Cell Biol 2016 04 18;213(2):275-88. Epub 2016 Apr 18.

Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Center for Duchenne Muscular Dystrophy at UCLA, Los Angeles, CA 90095 Wellstone Muscular Dystrophy Center, University of Florida, Gainesville, FL 32610

In the degenerative disease Duchenne muscular dystrophy, inflammatory cells enter muscles in response to repetitive muscle damage. Immune factors are required for muscle regeneration, but chronic inflammation creates a profibrotic milieu that exacerbates disease progression. Osteopontin (OPN) is an immunomodulator highly expressed in dystrophic muscles. Ablation of OPN correlates with reduced fibrosis and improved muscle strength as well as reduced natural killer T (NKT) cell counts. Here, we demonstrate that the improved dystrophic phenotype observed with OPN ablation does not result from reductions in NKT cells. OPN ablation skews macrophage polarization toward a pro-regenerative phenotype by reducing M1 and M2a and increasing M2c subsets. These changes are associated with increased expression of pro-regenerative factors insulin-like growth factor 1, leukemia inhibitory factor, and urokinase-type plasminogen activator. Furthermore, altered macrophage polarization correlated with increases in muscle weight and muscle fiber diameter, resulting in long-term improvements in muscle strength and function in mdx mice. These findings suggest that OPN ablation promotes muscle repair via macrophage secretion of pro-myogenic growth factors.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1083/jcb.201510086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5084275PMC
April 2016

Increased collagen cross-linking is a signature of dystrophin-deficient muscle.

Muscle Nerve 2016 06 22;54(1):71-8. Epub 2016 Feb 22.

Pennsylvania Muscle Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.

Introduction: Collagen cross-linking is a key parameter in extracellular matrix (ECM) maturation, turnover, and stiffness. We examined aspects of collagen cross-linking in dystrophin-deficient murine, canine, and human skeletal muscle.

Methods: DMD patient biopsies and samples from mdx mice and golden retriever muscular dystrophy dog samples (with appropriate controls) were analyzed. Collagen cross-linking was evaluated using solubility and hydroxyproline assays. Expression of the cross-linking enzyme lysyl oxidase (LOX) was determined by real-time polymerase chain reaction, immunoblotting, and immunofluorescence.

Results: LOX protein levels are increased in dystrophic muscle from all species evaluated. Dystrophic mice and dogs had significantly higher cross-linked collagen than controls, especially in the diaphragm. Distribution of intramuscular LOX was heterogeneous in all samples, but it increased in frequency and intensity in dystrophic muscle.

Conclusion: These findings implicate elevated collagen cross-linking as an important component of the disrupted ECM in dystrophic muscles, and heightened cross-linking is evident in mouse, dog, and man. Muscle Nerve 54: 71-78, 2016.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mus.24998DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5067682PMC
June 2016

Role of IGF-I signaling in muscle bone interactions.

Bone 2015 Nov;80:79-88

Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, FL, USA. Electronic address:

Skeletal muscle and bone rely on a number of growth factors to undergo development, modulate growth, and maintain physiological strength. A major player in these actions is insulin-like growth factor I (IGF-I). However, because this growth factor can directly enhance muscle mass and bone density, it alters the state of the musculoskeletal system indirectly through mechanical crosstalk between these two organ systems. Thus, there are clearly synergistic actions of IGF-I that extend beyond the direct activity through its receptor. This review will cover the production and signaling of IGF-I as it pertains to muscle and bone, the chemical and mechanical influences that arise from IGF-I activity, and the potential for therapeutic strategies based on IGF-I. This article is part of a Special Issue entitled "Muscle Bone Interactions".
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.bone.2015.04.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4600536PMC
November 2015

Muscle hypertrophy induced by myostatin inhibition accelerates degeneration in dysferlinopathy.

Hum Mol Genet 2015 Oct 23;24(20):5711-9. Epub 2015 Jul 23.

Department of Molecular Biology and Genetics and

Myostatin is a secreted signaling molecule that normally acts to limit muscle growth. As a result, there is extensive effort directed at developing drugs capable of targeting myostatin to treat patients with muscle loss. One potential concern with this therapeutic approach in patients with muscle degenerative diseases like muscular dystrophy is that inducing hypertrophy may increase stress on dystrophic fibers, thereby accelerating disease progression. To investigate this possibility, we examined the effect of blocking the myostatin pathway in dysferlin-deficient (Dysf(-/-)) mice, in which membrane repair is compromised, either by transgenic expression of follistatin in skeletal muscle or by systemic administration of the soluble form of the activin type IIB receptor (ACVR2B/Fc). Here, we show that myostatin inhibition by follistatin transgene expression in Dysf(-/-) mice results in early improvement in histopathology but ultimately exacerbates muscle degeneration; this effect was not observed in dystrophin-deficient (mdx) mice, suggesting that accelerated degeneration induced by follistatin transgene expression is specific to mice lacking dysferlin. Dysf(-/-) mice injected with ACVR2B/Fc showed significant increases in muscle mass and amelioration of fibrotic changes normally seen in 8-month-old Dysf(-/-) mice. Despite these potentially beneficial effects, ACVR2B/Fc treatment caused increases in serum CK levels in some Dysf(-/-) mice, indicating possible muscle damage induced by hypertrophy. These findings suggest that depending on the disease context, inducing muscle hypertrophy by myostatin blockade may have detrimental effects, which need to be weighed against the potential gains in muscle growth and decreased fibrosis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/hmg/ddv288DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4581601PMC
October 2015

Selective Retinoic Acid Receptor γ Agonists Promote Repair of Injured Skeletal Muscle in Mouse.

Am J Pathol 2015 Sep 21;185(9):2495-504. Epub 2015 Jul 21.

Translational Research Program in Pediatric Orthopaedics, The Children's Hospital of Philadelphia Research Institute, Philadelphia. Electronic address:

Retinoic acid signaling regulates several biological events, including myogenesis. We previously found that retinoic acid receptor γ (RARγ) agonist blocks heterotopic ossification, a pathological bone formation that mostly occurs in the skeletal muscle. Interestingly, RARγ agonist also weakened deterioration of muscle architecture adjacent to the heterotopic ossification lesion, suggesting that RARγ agonist may oppose skeletal muscle damage. To test this hypothesis, we generated a critical defect in the tibialis anterior muscle of 7-week-old mice with a cautery, treated them with RARγ agonist or vehicle corn oil, and examined the effects of RARγ agonist on muscle repair. The muscle defects were partially repaired with newly regenerating muscle cells, but also filled with adipose and fibrous scar tissue in both RARγ-treated and control groups. The fibrous or adipose area was smaller in RARγ agonist-treated mice than in the control. In addition, muscle repair was remarkably delayed in RARγ-null mice in both critical defect and cardiotoxin injury models. Furthermore, we found a rapid increase in retinoid signaling in lacerated muscle, as monitored by retinoid signaling reporter mice. Together, our results indicate that endogenous RARγ signaling is involved in muscle repair and that selective RARγ agonists may be beneficial to promote repair in various types of muscle injuries.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ajpath.2015.05.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4597269PMC
September 2015

Masticatory muscles of mouse do not undergo atrophy in space.

FASEB J 2015 Jul 20;29(7):2769-79. Epub 2015 Mar 20.

*Department of Physiology, Medical School, National and Kapodistrian University of Athens, Goudi-Athens, Greece; Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA; Department of Kinesiology, McGill University, Montreal, Quebec, Canada; Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, Pennsylvania, USA; and Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA

Muscle loading is important for maintaining muscle mass; when load is removed, atrophy is inevitable. However, in clinical situations such as critical care myopathy, masticatory muscles do not lose mass. Thus, their properties may be harnessed to preserve mass. We compared masticatory and appendicular muscles responses to microgravity, using mice aboard the space shuttle Space Transportation System-135. Age- and sex-matched controls remained on the ground. After 13 days of space flight, 1 masseter (MA) and tibialis anterior (TA) were frozen rapidly for biochemical and functional measurements, and the contralateral MA was processed for morphologic measurements. Flight TA muscles exhibited 20 ± 3% decreased muscle mass, 2-fold decreased phosphorylated (P)-Akt, and 4- to 12-fold increased atrogene expression. In contrast, MAs had no significant change in mass but a 3-fold increase in P-focal adhesion kinase, 1.5-fold increase in P-Akt, and 50-90% lower atrogene expression compared with limb muscles, which were unaltered in microgravity. Myofibril force measurements revealed that microgravity caused a 3-fold decrease in specific force and maximal shortening velocity in TA muscles. It is surprising that myofibril-specific force from both control and flight MAs were similar to flight TA muscles, yet power was compromised by 40% following flight. Continued loading in microgravity prevents atrophy, but masticatory muscles have a different set point that mimics disuse atrophy in the appendicular muscle.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1096/fj.14-267336DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4478801PMC
July 2015

Gamma-sarcoglycan is required for the response of archvillin to mechanical stimulation in skeletal muscle.

Hum Mol Genet 2015 May 20;24(9):2470-81. Epub 2015 Jan 20.

Department of Anatomy and Cell Biology, School of Dental Medicine, Pennsylvania Muscle Institute, and

Loss of gamma-sarcoglycan (γ-SG) induces muscle degeneration and signaling defects in response to mechanical load, and its absence is common to both Duchenne and limb girdle muscular dystrophies. Growing evidence suggests that aberrant signaling contributes to the disease pathology; however, the mechanisms of γ-SG-mediated mechanical signaling are poorly understood. To uncover γ-SG signaling pathway components, we performed yeast two-hybrid screens and identified the muscle-specific protein archvillin as a γ-SG and dystrophin interacting protein. Archvillin protein and message levels were significantly upregulated at the sarcolemma of murine γ-SG-null (gsg(-/-)) muscle but delocalized in dystrophin-deficient mdx muscle. Similar elevation of archvillin protein was observed in human quadriceps muscle lacking γ-SG. Reintroduction of γ-SG in gsg(-/-) muscle by rAAV injection restored archvillin levels to that of control C57 muscle. In situ eccentric contraction of tibialis anterior (TA) muscles from C57 mice caused ERK1/2 phosphorylation, nuclear activation of P-ERK1/2 and stimulus-dependent archvillin association with P-ERK1/2. In contrast, TA muscles from gsg(-/-) and mdx mice exhibited heightened P-ERK1/2 and increased nuclear P-ERK1/2 localization following eccentric contractions, but the archvillin-P-ERK1/2 association was completely ablated. These results position archvillin as a mechanically sensitive component of the dystrophin complex and demonstrate that signaling defects caused by loss of γ-SG occur both at the sarcolemma and in the nucleus.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/hmg/ddv008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4383861PMC
May 2015

Targeting latent TGFβ release in muscular dystrophy.

Sci Transl Med 2014 Oct;6(259):259ra144

Department of Medicine, The University of Chicago, Chicago, IL 60637, USA. Department of Human Genetics, The University of Chicago, Chicago, IL 60637, USA.

Latent transforming growth factor-β (TGFβ) binding proteins (LTBPs) bind to inactive TGFβ in the extracellular matrix. In mice, muscular dystrophy symptoms are intensified by a genetic polymorphism that changes the hinge region of LTBP, leading to increased proteolytic susceptibility and TGFβ release. We have found that the hinge region of human LTBP4 was also readily proteolysed and that proteolysis could be blocked by an antibody to the hinge region. Transgenic mice were generated to carry a bacterial artificial chromosome encoding the human LTBP4 gene. These transgenic mice displayed larger myofibers, increased damage after muscle injury, and enhanced TGFβ signaling. In the mdx mouse model of Duchenne muscular dystrophy, the human LTBP4 transgene exacerbated muscular dystrophy symptoms and resulted in weaker muscles with an increased inflammatory infiltrate and greater LTBP4 cleavage in vivo. Blocking LTBP4 cleavage may be a therapeutic strategy to reduce TGFβ release and activity and decrease inflammation and muscle damage in muscular dystrophy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/scitranslmed.3010018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4337885PMC
October 2014

Whole body periodic acceleration is an effective therapy to ameliorate muscular dystrophy in mdx mice.

PLoS One 2014 2;9(9):e106590. Epub 2014 Sep 2.

Department of Molecular Biosciences, School of Veterinary Medicine, University of California Davis, Davis, California, United States of America; Department of Anesthesiology Perioperative and Pain Medicine, Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.

Duchenne muscular dystrophy (DMD) is a genetic disorder caused by the absence of dystrophin in both skeletal and cardiac muscles. This leads to severe muscle degeneration, and dilated cardiomyopathy that produces patient death, which in most cases occurs before the end of the second decade. Several lines of evidence have shown that modulators of nitric oxide (NO) pathway can improve skeletal muscle and cardiac function in the mdx mouse, a mouse model for DMD. Whole body periodic acceleration (pGz) is produced by applying sinusoidal motion to supine humans and in standing conscious rodents in a headward-footward direction using a motion platform. It adds small pulses as a function of movement frequency to the circulation thereby increasing pulsatile shear stress to the vascular endothelium, which in turn increases production of NO. In this study, we examined the potential therapeutic properties of pGz for the treatment of skeletal muscle pathology observed in the mdx mouse. We found that pGz (480 cpm, 8 days, 1 hr per day) decreased intracellular Ca(2+) and Na(+) overload, diminished serum levels of creatine kinase (CK) and reduced intracellular accumulation of Evans Blue. Furthermore, pGz increased muscle force generation and expression of both utrophin and the carboxy-terminal PDZ ligand of nNOS (CAPON). Likewise, pGz (120 cpm, 12 h) applied in vitro to skeletal muscle myotubes reduced Ca(2+) and Na(+) overload, diminished abnormal sarcolemmal Ca(2+) entry and increased phosphorylation of endothelial NOS. Overall, this study provides new insights into the potential therapeutic efficacy of pGz as a non-invasive and non-pharmacological approach for the treatment of DMD patients through activation of the NO pathway.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0106590PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4152333PMC
April 2015

Absence of γ-sarcoglycan alters the response of p70S6 kinase to mechanical perturbation in murine skeletal muscle.

Skelet Muscle 2014 1;4:13. Epub 2014 Jul 1.

Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA ; Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, PA, USA.

Background: The dystrophin glycoprotein complex (DGC) is located at the sarcolemma of muscle fibers, providing structural integrity. Mutations in and loss of DGC proteins cause a spectrum of muscular dystrophies. When only the sarcoglycan subcomplex is absent, muscles display severe myofiber degeneration, but little susceptibility to contractile damage, suggesting that disease occurs not by structural deficits but through aberrant signaling, namely, loss of normal mechanotransduction signaling through the sarcoglycan complex. We extended our previous studies on mechanosensitive, γ-sarcoglycan-dependent ERK1/2 phosphorylation, to determine whether additional pathways are altered with the loss of γ-sarcoglycan.

Methods: We examined mechanotransduction in the presence and absence of γ-sarcoglycan, using C2C12 myotubes, and primary cultures and isolated muscles from C57Bl/6 (C57) and γ-sarcoglycan-null (γ-SG(-/-)) mice. All were subjected to cyclic passive stretch. Signaling protein phosphorylation was determined by immunoblotting of lysates from stretched and non-stretched samples. Calcium dependence was assessed by maintaining muscles in calcium-free or tetracaine-supplemented Ringer's solution. Dependence on mTOR was determined by stretching isolated muscles in the presence or absence of rapamycin.

Results: C2C12 myotube stretch caused a robust increase in P-p70S6K, but decreased P-FAK and P-ERK2. Neither Akt nor ERK1 were responsive to passive stretch. Similar but non-significant trends were observed in C57 primary cultures in response to stretch, and γ-SG(-/-) cultures displayed no p70S6K response. In contrast, in isolated muscles, p70S6K was mechanically responsive. Basal p70S6K activation was elevated in muscles of γ-SG(-/-) mice, in a calcium-independent manner. p70S6K activation increased with stretch in both C57 and γ-SG(-/-) isolated muscles, and was sustained in γ-SG(-/-) muscles, unlike the transient response in C57 muscles. Rapamycin treatment blocked all of p70S6K activation in stretched C57 muscles, and reduced downstream S6RP phosphorylation. However, even though rapamycin treatment decreased p70S6K activation in stretched γ-SG(-/-) muscles, S6RP phosphorylation remained elevated.

Conclusions: p70S6K is an important component of γ-sarcoglycan-dependent mechanotransduction in skeletal muscle. Our results suggest that loss of γ-sarcoglycan uncouples the response of p70S6K to stretch and implies that γ-sarcoglycan is important for inactivation of this pathway. Overall, we assert that altered load-sensing mechanisms exist in muscular dystrophies where the sarcoglycans are absent.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/2044-5040-4-13DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4095884PMC
July 2014

Optimizing IGF-I for skeletal muscle therapeutics.

Growth Horm IGF Res 2014 Oct 19;24(5):157-63. Epub 2014 Jun 19.

Department of Anatomy and Cell Biology, School of Dental Medicine, and Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, PA, USA. Electronic address:

It is virtually undisputed that IGF-I promotes cell growth and survival. However, the presence of several IGF-I isoforms, vast numbers of intracellular signaling components, and multiple receptors results in a complex and highly regulated system by which IGF-I actions are mediated. IGF-I has long been recognized as one of the critical factors for coordinating muscle growth, enhancing muscle repair, and increasing muscle mass and strength. How to optimize this panoply of pathways to drive anabolic processes in muscle as opposed to aberrant growth in other tissues is an area that deserves focus. This review will address how advances in the bioavailability, potency, and tissue response of IGF-I can provide new potential directions for skeletal muscle therapeutics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ghir.2014.06.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4665094PMC
October 2014

Caspase-12 ablation preserves muscle function in the mdx mouse.

Hum Mol Genet 2014 Oct 30;23(20):5325-41. Epub 2014 May 30.

Department of Anatomy and Cell Biology, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA and Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, PA, USA

Duchenne muscular dystrophy (DMD) is a devastating muscle wasting disease caused by mutations in dystrophin. Several downstream consequences of dystrophin deficiency are triggers of endoplasmic reticulum (ER) stress, including loss of calcium homeostasis, hypoxia and oxidative stress. During ER stress, misfolded proteins accumulate in the ER lumen and the unfolded protein response (UPR) is triggered, leading to adaptation or apoptosis. We hypothesized that ER stress is heightened in dystrophic muscles and contributes to the pathology of DMD. We observed increases in the ER stress markers BiP and cleaved caspase-4 in DMD patient biopsies, compared with controls, and an increase in multiple UPR pathways in muscles of the dystrophin-deficient mdx mouse. We then crossed mdx mice with mice null for caspase-12, the murine equivalent of human caspase-4, which are resistant to ER stress. We found that deleting caspase-12 preserved mdx muscle function, resulting in a 75% recovery of both specific force generation and resistance to eccentric contractions. The compensatory hypertrophy normally found in mdx muscles was normalized in the absence of caspase-12; this was found to be due to decreased fibre sizes, and not to a fibre type shift or a decrease in fibrosis. Fibre central nucleation was not significantly altered in the absence of caspase-12, but muscle fibre degeneration found in the mdx mouse was reduced almost to wild-type levels. In conclusion, we have identified heightened ER stress and abnormal UPR signalling as novel contributors to the dystrophic phenotype. Caspase-4 is therefore a potential therapeutic target for DMD.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/hmg/ddu249DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4168821PMC
October 2014

Collagen content does not alter the passive mechanical properties of fibrotic skeletal muscle in mdx mice.

Am J Physiol Cell Physiol 2014 May 5;306(10):C889-98. Epub 2014 Mar 5.

Department of Anatomy and Cell Biology, School of Dental Medicine, Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, Pennsylvania

Many skeletal muscle diseases are associated with progressive fibrosis leading to impaired muscle function. Collagen within the extracellular matrix is the primary structural protein providing a mechanical scaffold for cells within tissues. During fibrosis collagen not only increases in amount but also undergoes posttranslational changes that alter its organization that is thought to contribute to tissue stiffness. Little, however, is known about collagen organization in fibrotic muscle and its consequences for function. To investigate the relationship between collagen content and organization with muscle mechanical properties, we studied mdx mice, a model for Duchenne muscular dystrophy (DMD) that undergoes skeletal muscle fibrosis, and age-matched control mice. We determined collagen content both histologically, with picosirius red staining, and biochemically, with hydroxyproline quantification. Collagen content increased in the mdx soleus and diaphragm muscles, which was exacerbated by age in the diaphragm. Collagen packing density, a parameter of collagen organization, was determined using circularly polarized light microscopy of picosirius red-stained sections. Extensor digitorum longus (EDL) and soleus muscle had proportionally less dense collagen in mdx muscle, while the diaphragm did not change packing density. The mdx muscles had compromised strength as expected, yet only the EDL had a significantly increased elastic stiffness. The EDL and diaphragm had increased dynamic stiffness and a change in relative viscosity. Unexpectedly, passive stiffness did not correlate with collagen content and only weakly correlated with collagen organization. We conclude that muscle fibrosis does not lead to increased passive stiffness and that collagen content is not predictive of muscle stiffness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajpcell.00383.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4024713PMC
May 2014