Publications by authors named "William D Hill"

70 Publications

Characterization of Differentially Expressed miRNAs by CXCL12/SDF-1 in Human Bone Marrow Stromal Cells.

Biomol Concepts 2021 Oct 13;12(1):132-143. Epub 2021 Oct 13.

Department of Orthopedics, Augusta University, Augusta, GA.

Stromal cell-derived factor 1 (SDF-1) is known to influence bone marrow stromal cell (BMSC) migration, osteogenic differentiation, and fracture healing. We hypothesize that SDF-1 mediates some of its effects on BMSCs through epigenetic regulation, specifically via microRNAs (miRNAs). MiRNAs are small non-coding RNAs that target specific mRNA and prevent their translation. We performed global miRNA analysis and determined several miRNAs were differentially expressed in response to SDF-1 treatment. Gene Expression Omnibus (GEO) dataset analysis showed that these miRNAs play an important role in osteogenic differentiation and fracture healing. KEGG and GO analysis indicated that SDF-1 dependent miRNAs changes affect multiple cellular pathways, including fatty acid biosynthesis, thyroid hormone signaling, and mucin-type O-glycan biosynthesis pathways. Furthermore, bioinformatics analysis showed several miRNAs target genes related to stem cell migration and differentiation. This study's findings indicated that SDF-1 induces some of its effects on BMSCs function through miRNA regulation.
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http://dx.doi.org/10.1515/bmc-2021-0015DOI Listing
October 2021

Tryptophan-Kynurenine Pathway in COVID-19-Dependent Musculoskeletal Pathology: A Minireview.

Mediators Inflamm 2021 5;2021:2911578. Epub 2021 Oct 5.

Department of Cell Biology and Anatomy, Augusta University, Augusta, GA, USA.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), affecting multiple organ systems, including the respiratory tract and lungs. Several studies have reported that the tryptophan-kynurenine pathway is altered in COVID-19 patients. The tryptophan-kynurenine pathway plays a vital role in regulating inflammation, metabolism, immune responses, and musculoskeletal system biology. In this minireview, we surmise the effects of the kynurenine pathway in COVID-19 patients and how this pathway might impact muscle and bone biology.
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http://dx.doi.org/10.1155/2021/2911578DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8492288PMC
October 2021

Age-associated changes in microRNAs affect the differentiation potential of human mesenchymal stem cells: Novel role of miR-29b-1-5p expression.

Bone 2021 12 14;153:116154. Epub 2021 Aug 14.

Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29403, United States of America; Ralph H. Johnson Veterans Affairs Medical Center, Charleston, SC 29403, United States of America; Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA 30912, United States of America; Center for Healthy Aging, Medical College of Georgia, Augusta University, Augusta, GA 30912, United States of America. Electronic address:

Age-associated osteoporosis is widely accepted as involving the disruption of osteogenic stem cell populations and their functioning. Maintenance of the local bone marrow (BM) microenvironment is critical for regulating proliferation and differentiation of the multipotent BM mesenchymal stromal/stem cell (BMSC) population with age. The potential role of microRNAs (miRNAs) in modulating BMSCs and the BM microenvironment has recently gained attention. However, miRNAs expressed in rapidly isolated BMSCs that are naïve to the non-physiologic standard tissue culture conditions and reflect a more accurate in vivo profile have not yet been reported. Here we directly isolated CD271 positive (+) BMSCs within hours from human surgical BM aspirates without culturing and performed microarray analysis to identify the age-associated changes in BMSC miRNA expression. One hundred and two miRNAs showed differential expression with aging. Target prediction and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the up-regulated miRNAs targeting genes in bone development pathways were considerably enriched. Among the differentially up-regulated miRNAs the novel passenger strand miR-29b-1-5p was abundantly expressed as a mature functional miRNA with aging. This suggests a critical arm-switching mechanism regulates the expression of the miR-29b-1-5p/3p pair shifting the normally degraded arm, miR-29b-1-5p, to be the dominantly expressed miRNA of the pair in aging. The normal guide strand miR-29b-1-3p is known to act as a pro-osteogenic miRNA. On the other hand, overexpression of the passenger strand miR-29b-1-5p in culture-expanded CD271+ BMSCs significantly down-regulated the expression of stromal cell-derived factor 1 (CXCL12)/ C-X-C chemokine receptor type 4 (SDF-1(CXCL12)/CXCR4) axis and other osteogenic genes including bone morphogenetic protein-2 (BMP-2) and runt-related transcription factor 2 (RUNX2). In contrast, blocking of miR-29b-1-5p function using an antagomir inhibitor up-regulated expression of BMP-2 and RUNX2 genes. Functional assays confirmed that miR-29b-1-5p negatively regulates BMSC osteogenesis in vitro. These novel findings provide evidence of a pathogenic anti-osteogenic role for miR-29b-1-5p and other miRNAs in age-related defects in osteogenesis and bone regeneration.
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http://dx.doi.org/10.1016/j.bone.2021.116154DOI Listing
December 2021

A Tryptophan-Deficient Diet Induces Gut Microbiota Dysbiosis and Increases Systemic Inflammation in Aged Mice.

Int J Mol Sci 2021 May 8;22(9). Epub 2021 May 8.

Department of Medicine, Augusta University, Augusta, GA 30912, USA.

The gut microflora is a vital component of the gastrointestinal (GI) system that regulates local and systemic immunity, inflammatory response, the digestive system, and overall health. Older people commonly suffer from inadequate nutrition or poor diets, which could potentially alter the gut microbiota. The essential amino acid (AA) tryptophan (TRP) is a vital diet component that plays a critical role in physiological stress responses, neuropsychiatric health, oxidative systems, inflammatory responses, and GI health. The present study investigates the relationship between varied TRP diets, the gut microbiome, and inflammatory responses in an aged mouse model. We fed aged mice either a TRP-deficient (0.1%), TRP-recommended (0.2%), or high-TRP (1.25%) diet for eight weeks and observed changes in the gut bacterial environment and the inflammatory responses via cytokine analysis (IL-1a, IL-6, IL-17A, and IL-27). The mice on the TRP-deficient diets showed changes in their bacterial abundance of Coriobacteriia class, genus, Lachnospiraceae family, species, sp genus, and genus. Further, these mice showed significant increases in IL-6, IL-17A, and IL-1a and decreased IL-27 levels. These data suggest a direct association between dietary TRP content, the gut microbiota microenvironment, and inflammatory responses in aged mice models.
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http://dx.doi.org/10.3390/ijms22095005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8125914PMC
May 2021

Kynurenine induces an age-related phenotype in bone marrow stromal cells.

Mech Ageing Dev 2021 04 22;195:111464. Epub 2021 Feb 22.

Department of Medicine, Augusta University, Augusta, GA, United States; Department of Cell Biology and Anatomy, Augusta University, Augusta, GA, United States; Center for Healthy Aging, Augusta University, Augusta, GA, United States. Electronic address:

Advanced age is one of the important contributing factors for musculoskeletal deterioration. Although the exact mechanism behind this degeneration is unknown, it has been previously established that nutritional signaling plays a vital role in musculoskeletal pathophysiology. Our group established the vital role of the essential amino acid, tryptophan, in aging musculoskeletal health. With advanced age, inflammatory factors activate indoleamine 2,3-dioxygenase (IDO1) and accumulate excessive intermediate tryptophan metabolites such as Kynurenine (KYN). With age, Kynurenine accumulates and suppresses osteogenic differentiation, impairs autophagy, promotes early senescence, and alters cellular bioenergetics of bone marrow stem cells. Recent studies have shown that Kynurenine negatively impacts bone marrow stromal cells (BMSCs) and, consequently, promotes bone loss. Overall, understanding the mechanism behind BMSCs losing their ability for osteogenic differentiation can provide insight into the prevention of osteoporosis and the development of targeted therapies. Therefore, in this article, we review Kynurenine and how it plays a vital role in BMSC dysfunction and bone loss with age.
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http://dx.doi.org/10.1016/j.mad.2021.111464DOI Listing
April 2021

Modulation of p75 on Mesenchymal Stem Cells Increases Their Vascular Protection in Retinal Ischemia-Reperfusion Mouse Model.

Int J Mol Sci 2021 Jan 15;22(2). Epub 2021 Jan 15.

Augusta Biomedical Research Corporation, Charlie Norwood VA Medical Center, Augusta, GA 30901, USA.

Mesenchymal stem cells (MSCs) are a promising therapy to improve vascular repair, yet their role in ischemic retinopathy is not fully understood. The aim of this study is to investigate the impact of modulating the neurotrophin receptor; p75 on the vascular protection of MSCs in an acute model of retinal ischemia/reperfusion (I/R). Wild type (WT) and p75 mice were subjected to I/R injury by increasing intra-ocular pressure to 120 mmHg for 45 min, followed by perfusion. Murine GFP-labeled MSCs (100,000 cells/eye) were injected intravitreally 2 days post-I/R and vascular homing was assessed 1 week later. Acellular capillaries were counted using trypsin digest 10-days post-I/R. In vitro, MSC-p75 was modulated either genetically using siRNA or pharmacologically using the p75 modulator; LM11A-31, and conditioned media were co-cultured with human retinal endothelial cells (HREs) to examine the angiogenic response. Finally, visual function in mice undergoing retinal I/R and receiving LM11A-31 was assessed by visual-clue water-maze test. I/R significantly increased the number of acellular capillaries (3.2-Fold) in WT retinas, which was partially ameliorated in p75 retinas. GFP-MSCs were successfully incorporated and engrafted into retinal vasculature 1 week post injection and normalized the number of acellular capillaries in p75 retinas, yet ischemic WT retinas maintained a 2-Fold increase. Silencing p75 on GFP-MSCs coincided with a higher number of cells homing to the ischemic WT retinal vasculature and normalized the number of acellular capillaries when compared to ischemic WT retinas receiving scrambled-GFP-MSCs. In vitro, silencing p75-MSCs enhanced their secretome, as evidenced by significant increases in SDF-1, VEGF and NGF release in MSCs conditioned medium; improved paracrine angiogenic response in HREs, where HREs showed enhanced migration (1.4-Fold) and tube formation (2-Fold) compared to controls. In parallel, modulating MSCs-p75 using LM11A-31 resulted in a similar improvement in MSCs secretome and the enhanced paracrine angiogenic potential of HREs. Further, intervention with LM11A-31 significantly mitigated the decline in visual acuity post retinal I/R injury. In conclusion, p75 modulation can potentiate the therapeutic potential of MSCs to harness vascular repair in ischemic retinopathy diseases.
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http://dx.doi.org/10.3390/ijms22020829DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7830385PMC
January 2021

Kynurenine Promotes RANKL-Induced Osteoclastogenesis In Vitro by Activating the Aryl Hydrocarbon Receptor Pathway.

Int J Mol Sci 2020 Oct 26;21(21). Epub 2020 Oct 26.

Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29403, USA.

There is increasing evidence of the involvement of the tryptophan metabolite kynurenine (KYN) in disrupting osteogenesis and contributing to aging-related bone loss. Here, we show that KYN has an effect on bone resorption by increasing osteoclastogenesis. We have previously reported that in vivo treatment with KYN significantly increased osteoclast number lining bone surfaces. Here, we report the direct effect of KYN on receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis in Raw 264.7 macrophage cells, and we propose a potential mechanism for these KYN-mediated effects. We show that KYN/RANKL treatment results in enhancement of RANKL-induced osteoclast differentiation. KYN drives upregulation and activation of the key osteoclast transcription factors, c-fos and NFATc1 resulting in an increase in the number of multinucleated TRAP+ osteoclasts, and in hydroxyapatite bone resorptive activity. Mechanistically, the KYN receptor, aryl hydrocarbon receptor (AhR), plays an important role in the induction of osteoclastogenesis. We show that blocking AhR signaling using an AhR antagonist, or AhR siRNA, downregulates the KYN/RANKL-mediated increase in c-fos and NFATc1 and inhibits the formation of multinucleated TRAP + osteoclasts. Altogether, this work highlights that the novelty of the KYN and AhR pathways might have a potential role in helping to regulate osteoclast function with age and supports pursuing additional research to determine if they are potential therapeutic targets for the prevention or treatment of osteoporosis.
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http://dx.doi.org/10.3390/ijms21217931DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7662708PMC
October 2020

MicroRNAs are critical regulators of senescence and aging in mesenchymal stem cells.

Bone 2021 01 3;142:115679. Epub 2020 Oct 3.

Department of Orthopedics, Augusta University, Augusta, GA, United States of America; Department of Medicine, Augusta University, Augusta, GA, United States of America; Institute of Healthy Aging, Augusta University, Augusta, GA, United States of America; Department of Cell Biology and Anatomy, Augusta University, Augusta, GA, United States of America. Electronic address:

MicroRNAs (miRNAs) have recently come under scrutiny for their role in various age-related diseases. Similarly, cellular senescence has been linked to disease and aging. MicroRNAs and senescence likely play an intertwined role in driving these pathologic states. In this review, we present the connection between these two drivers of age-related disease concerning mesenchymal stem cells (MSCs). First, we summarize key miRNAs that are differentially expressed in MSCs and other musculoskeletal lineage cells during senescence and aging. Additionally, we also reviewed miRNAs that are regulated via traditional senescence-associated secretory phenotype (SASP) cytokines in MSC. Lastly, we summarize miRNAs that have been found to target components of the cell cycle arrest pathways inherently activated in senescence. This review attempts to highlight potential miRNA targets for regenerative medicine applications in age-related musculoskeletal disease.
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http://dx.doi.org/10.1016/j.bone.2020.115679DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7901145PMC
January 2021

Age-related increase of kynurenine enhances miR29b-1-5p to decrease both CXCL12 signaling and the epigenetic enzyme Hdac3 in bone marrow stromal cells.

Bone Rep 2020 Jun 23;12:100270. Epub 2020 Apr 23.

Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29403, United States of America.

Mechanisms leading to age-related reductions in bone formation and subsequent osteoporosis are still incompletely understood. We recently demonstrated that kynurenine (KYN), a tryptophan metabolite, accumulates in serum of aged mice and induces bone loss. Here, we report on novel mechanisms underlying KYN's detrimental effect on bone aging. We show that KYN is increased with aging in murine bone marrow mesenchymal stem cells (BMSCs). KYN reduces bone formation via modulating levels of CXCL12 and its receptors as well as histone deacetylase 3 (Hdac3). BMSCs responded to KYN by significantly decreasing mRNA expression levels of CXCL12 and its cognate receptors, CXCR4 and ACKR3, as well as downregulating osteogenic gene RUNX2 expression, resulting in a significant inhibition in BMSCs osteogenic differentiation. KYN's effects on these targets occur by increasing regulatory miRNAs that target osteogenesis, specifically miR29b-1-5p. Thus, KYN significantly upregulated the anti-osteogenic miRNA miR29b-1-5p in BMSCs, mimicking the up-regulation of miR-29b-1-5p in human and murine BMSCs with age. Direct inhibition of miR29b-1-5p by antagomirs rescued CXCL12 protein levels downregulated by KYN, while a miR29b-1-5p mimic further decreased CXCL12 levels. KYN also significantly downregulated mRNA levels of Hdac3, a target of miR-29b-1-5p, as well as its cofactor NCoR1. KYN is a ligand for the aryl hydrocarbon receptor (AhR). We hypothesized that AhR mediates KYN's effects in BMSCs. Indeed, AhR inhibitors (CH-223191 and 3',4'-dimethoxyflavone [DMF]) partially rescued secreted CXCL12 protein levels in BMSCs treated with KYN. Importantly, we found that treatment with CXCL12, or transfection with an miR29b-1-5p antagomir, downregulated the AhR mRNA level, while transfection with miR29b-1-5p mimic significantly upregulated its level. Further, CXCL12 treatment downregulated IDO, an enzyme responsible for generating KYN. Our findings reveal novel molecular pathways involved in KYN's age-associated effects in the bone microenvironment that may be useful translational targets for treating osteoporosis.
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http://dx.doi.org/10.1016/j.bonr.2020.100270DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7210406PMC
June 2020

Kynurenine suppresses osteoblastic cell energetics in vitro and osteoblast numbers in vivo.

Exp Gerontol 2020 02 17;130:110818. Epub 2019 Dec 17.

Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; Department of Orthopaedic Surgery, Augusta University, Augusta, GA, USA. Electronic address:

Aging is a progressive process associated with declining tissue function over time. Kynurenine, an oxidized metabolite of the essential amino acid tryptophan that increases in abundance with age, drives cellular processes of aging and dysfunction in many tissues, and recent work has focused on understanding the pathways involved in the harmful effects of kynurenine on bone. In this study, we sought to investigate the effects of controlled kynurenine administration on osteoblast bioenergetics, in vivo osteoblast abundance, and marrow fat accumulation. Additionally, as an extension of earlier studies with dietary administration of kynurenine, we investigated the effects of kynurenine on Hdac3 and NCoR1 expression and enzymatic deacetylase activity as potential mechanistic contributors to the effects of kynurenine on osteoblasts. Kynurenine administration suppressed cellular metabolism in osteoblasts at least in part through impaired mitochondrial respiration, and suppressed osteoblastic numbers in vivo with no concurrent effects on marrow adiposity. Deleterious effects of kynurenine treatment on osteoblasts were more pronounced in female models as compared to males. However, kynurenine treatment did not inhibit Hdac3's enzymatic deacetylase activity nor its repression of downstream glucocorticoid signaling. As such, future work will be necessary to determine the mechanisms by which increased kynurenine contributes to aging bone bioenergetics. The current study provides novel further support for the idea that kynurenine contributes to impaired osteoblastic function, and suggests that impaired matrix production by kynurenine-affected osteoblasts is attributed in part to impaired osteoblastic bioenergetics. As circulating kynurenine levels in increase with age, and human bone density inversely correlates with the serum kynurenine to tryptophan ratio, these mechanisms may have important relevance in the etiology and pathogenesis of osteoporosis in humans.
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http://dx.doi.org/10.1016/j.exger.2019.110818DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7003726PMC
February 2020

Accumulation of kynurenine elevates oxidative stress and alters microRNA profile in human bone marrow stromal cells.

Exp Gerontol 2020 02 30;130:110800. Epub 2019 Nov 30.

Department of Orthopedics, Augusta University, Augusta, GA, United States of America; Department of Cell biology and Anatomy, Augusta University, Augusta, GA, United States of America; Institute of Healthy Aging, Augusta University, Augusta, GA, United States of America. Electronic address:

Kynurenine, a metabolite of tryptophan breakdown, has been shown to increase with age, and plays a vital role in a number of age-related pathophysiological changes, including bone loss. Accumulation of kynurenine in bone marrow stromal cells (BMSCs) has been associated with a decrease in cell proliferation and differentiation, though the exact mechanism by which kynurenine mediates these changes is poorly understood. MiRNAs have been shown to regulate BMSC function, and accumulation of kynurenine may alter the miRNA expression profile of BMSCs. The aim of this study was to identify differentially expressed miRNAs in human BMSCs in response to treatment with kynurenine, and correlate miRNAs function in BMSCs biology through bioinformatics analysis. Human BMSCs were cultured and treated with and without kynurenine, and subsequent miRNA isolation was performed. MiRNA array was performed to identify differentially expressed miRNA. Microarray analysis identified 50 up-regulated, and 36 down-regulated miRNAs in kynurenine-treated BMSC cultures. Differentially expressed miRNA included miR-1281, miR-330-3p, let-7f-5p, and miR-493-5p, which are important for BMSC proliferation and differentiation. KEGG analysis found up-regulated miRNA targeting glutathione metabolism, a pathway critical for removing oxidative species. Our data support that the kynurenine dependent degenerative effect is partially due to changes in the miRNA profile of BMSCs.
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http://dx.doi.org/10.1016/j.exger.2019.110800DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6998036PMC
February 2020

Stromal cell-derived factor-1 as a potential therapeutic target for osteoarthritis and rheumatoid arthritis.

Ther Adv Chronic Dis 2019 24;10:2040622319882531. Epub 2019 Oct 24.

Department of Orthopedic Surgery, Augusta University, 1459 Laney Walker, Augusta, GA, 30904, USA.

With age, joints become subject to chronic inflammatory processes that lead to degeneration of articular cartilage. Although multifactorial, cytokines have been shown to play a role in the pathogenesis of these chronic disease states. Stromal cell-derived factor 1 (SDF-1) is a chemokine that has been shown to be active in homeostatic mechanisms and developmental processes throughout the body, such as endochondral bone formation. SDF-1 plays a role in the transition from cartilage to bone. Although it has been shown to be a factor in normal development, it has also been shown to involve in the pathogenesis of rheumatoid arthritis (RA) and osteoarthritis (OA). In RA, SDF-1 has been shown to stimulate the recruitment of proinflammatory cells, as well as osteoclasts to the synovium, aiding in the facilitation of synovial degradation. Similarly, in OA, SDF-1 has been shown to regulate key proteins involved in the degradation of the cartilage of the joint. Because of its role in degenerative joint disease, SDF-1 has been investigated as a potential therapeutic target. Animal studies have been employing SDF-1 inhibitors, such as AMD3100 and T140, to study their effects on attenuating degenerative joint disease. These studies have shown promising results in slowing the progression of cartilage degradation and could potentially be used as therapeutic target for humans OA and RA.
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http://dx.doi.org/10.1177/2040622319882531DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6820172PMC
October 2019

MicroRNA-141-3p Negatively Modulates SDF-1 Expression in Age-Dependent Pathophysiology of Human and Murine Bone Marrow Stromal Cells.

J Gerontol A Biol Sci Med Sci 2019 08;74(9):1368-1374

Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Georgia.

Stromal cell-derived factor-1 (SDF-1 or CXCL12) is a cytokine secreted by cells including bone marrow stromal cells (BMSCs). SDF-1 plays a vital role in BMSC migration, survival, and differentiation. Our group previously reported the role of SDF-1 in osteogenic differentiation in vitro and bone formation in vivo; however, our understanding of the post-transcriptional regulatory mechanism of SDF-1 remains poor. MicroRNAs are small noncoding RNAs that post-transcriptionally regulate the messenger RNAs (mRNAs) of protein-coding genes. In this study, we aimed to investigate the impact of miR-141-3p on SDF-1 expression in BMSCs and its importance in the aging bone marrow (BM) microenvironment. Our data demonstrated that murine and human BMSCs expressed miR-141-3p that repressed SDF-1 gene expression at the functional level (luciferase reporter assay) by targeting the 3'-untranslated region of mRNA. We also found that transfection of miR-141-3p decreased osteogenic markers in human BMSCs. Our results demonstrate that miR-141-3p expression increases with age, while SDF-1 decreases in both the human and mouse BM niche. Taken together, these results support that miR-141-3p is a novel regulator of SDF-1 in bone cells and plays an important role in the age-dependent pathophysiology of murine and human BM niche.
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http://dx.doi.org/10.1093/gerona/gly186DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6696713PMC
August 2019

Stromal cell-derived factor-1 (CXCL12) and its role in bone and muscle biology.

Cytokine 2019 11 20;123:154783. Epub 2019 Jul 20.

Department of Orthopaedic Surgery, Augusta University, Augusta, GA 30912, United States; Cell Biology and Anatomy, Augusta University, Augusta, GA 30912, United States. Electronic address:

Musculoskeletal disorders are the leading cause of disability worldwide; two of the most prevalent of which are osteoporosis and sarcopenia. Each affect millions in the aging population across the world and the associated morbidity and mortality contributes to billions of dollars in annual healthcare cost. Thus, it is important to better understand the underlying pathologic mechanisms of the disease process. Regulatory chemokine, CXCL12, and its receptor, CXCR4, are recognized to be essential in the recruitment, localization, maintenance, development and differentiation of progenitor stem cells of the musculoskeletal system. CXCL12 signaling results in the development and functional ability of osteoblasts, osteoclasts, satellite cells and myoblasts critical to maintaining musculoskeletal homeostasis. Interestingly, one suggested pathologic mechanism of osteoporosis and sarcopenia is a decline in the regenerative capacity of musculoskeletal progenitor stem cells. Thus, because CXCL12 is critical to progenitor function, a disruption in the CXCL12 signaling axis might play a distinct role in these pathological processes. Therefore, in this article, we perform a review of CXCL12, its physiologic and pathologic function in bone and muscle, and potential targets for therapeutic development.
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http://dx.doi.org/10.1016/j.cyto.2019.154783DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6948927PMC
November 2019

Meta-Analysis and Evidence Base for the Efficacy of Autologous Bone Marrow Mesenchymal Stem Cells in Knee Cartilage Repair: Methodological Guidelines and Quality Assessment.

Stem Cells Int 2019 7;2019:3826054. Epub 2019 Apr 7.

Department of Orthopaedic Surgery, Augusta University, Augusta, GA, USA.

The aim of this study is to review all the published clinical trials on autologous bone marrow mesenchymal stem cells (BM-MSCs) in the repair of cartilage lesions of the knee. We performed a comprehensive search in three electronic databases: PubMed, Medline via Ovid, and Web of Science. A systematic review was conducted according to the guidelines of PRISMA protocol and the Cochrane Handbook for Systematic Reviews of Interventions. The modified Coleman methodology score was used to assess the quality of the included studies. Meta-analysis was conducted to estimate the effect size for Pain and function change after receiving BM-MSCs. Thirty-three studies-including 724 patients of mean age 44.2 years-were eligible. 50.7% of the included patients received cultured BM-MSCs for knee cartilage repair. There was improvement in the MINORS quality score over time with a positive correlation with the publication year. Meta-analysis indicated better improvement and statistical significance in the Visual Analog Scale for Pain, IKDC Function, Tegner Activity Scale, and Lysholm Knee Score after administration of noncultured BM-MSCs when compared to evaluation before the treatment. Meanwhile, there was a clear methodological defect in most studies with an average modified Coleman methodology score (MCMS) of 55. BM-MSCs revealed a clinically relevant improvement in pain, function, and histological regeneration.
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http://dx.doi.org/10.1155/2019/3826054DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6476108PMC
April 2019

What doesn't kill you makes you stranger: Dipeptidyl peptidase-4 (CD26) proteolysis differentially modulates the activity of many peptide hormones and cytokines generating novel cryptic bioactive ligands.

Pharmacol Ther 2019 06 10;198:90-108. Epub 2019 Feb 10.

Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29403, United States; Ralph H. Johnson Veterans Affairs Medical Center, Charleston, SC 29403, United States; Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA 30912, United States; Department of Orthopaedic Surgery, Medical College of Georgia, Augusta University, Augusta, GA 30912, United States; Center for Healthy Aging, Medical College of Georgia, Augusta University, Augusta, GA, 30912, United States. Electronic address:

Dipeptidyl peptidase 4 (DPP4) is an exopeptidase found either on cell surfaces where it is highly regulated in terms of its expression and surface availability (CD26) or in a free/circulating soluble constitutively available and intrinsically active form. It is responsible for proteolytic cleavage of many peptide substrates. In this review we discuss the idea that DPP4-cleaved peptides are not necessarily inactivated, but rather can possess either a modified receptor selectivity, modified bioactivity, new antagonistic activity, or even a novel activity relative to the intact parent ligand. We examine in detail five different major DPP4 substrates: glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), peptide tyrosine-tyrosine (PYY), and neuropeptide Y (NPY), and stromal derived factor 1 (SDF-1 aka CXCL12). We note that discussion of the cleaved forms of these five peptides are underrepresented in the research literature, and are both poorly investigated and poorly understood, representing a serious research literature gap. We believe they are understudied and misinterpreted as inactive due to several factors. This includes lack of accurate and specific quantification methods, sample collection techniques that are inherently inaccurate and inappropriate, and a general perception that DPP4 cleavage inactivates its ligand substrates. Increasing evidence points towards many DPP4-cleaved ligands having their own bioactivity. For example, GLP-1 can work through a different receptor than GLP-1R, DPP4-cleaved GIP can function as a GIP receptor antagonist at high doses, and DPP4-cleaved PYY, NPY, and CXCL12 can have different receptor selectivity, or can bind novel, previously unrecognized receptors to their intact ligands, resulting in altered signaling and functionality. We believe that more rigorous research in this area could lead to a better understanding of DPP4's role and the biological importance of the generation of novel cryptic ligands. This will also significantly impact our understanding of the clinical effects and side effects of DPP4-inhibitors as a class of anti-diabetic drugs that potentially have an expanding clinical relevance. This will be specifically relevant in targeting DPP4 substrate ligands involved in a variety of other major clinical acute and chronic injury/disease areas including inflammation, immunology, cardiology, stroke, musculoskeletal disease and injury, as well as cancer biology and tissue maintenance in aging.
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http://dx.doi.org/10.1016/j.pharmthera.2019.02.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7883480PMC
June 2019

Role of MicroRNA-141 in the Aging Musculoskeletal System: A Current Overview.

Mech Ageing Dev 2019 03 7;178:9-15. Epub 2018 Dec 7.

Department of Orthopedics, Augusta University, Augusta, GA, United States; Institute of Regenerative and Reparative medicine, Augusta University, Augusta, GA, United States. Electronic address:

MicroRNA's are small non-coding RNAs that regulate the expression of genes by targeting the 3' UTR's of mRNA. Studies reveal that miRNAs play a pivotal role in normal musculoskeletal function such as mesenchymal stem cell differentiation, survivability and apoptosis, osteogenesis, and chondrogenesis. Changes in normal miRNA expression have been linked to a number of pathological disease processes. Additionally, with aging, it is noted that there is dysregulation in the normal function of stem cell differentiation, bone formation/degradation, chondrocyte function, and muscle degeneration. Due to the change in expression of miRNA in degenerative musculoskeletal pathology, it is believed that these molecules may be at least partially responsible for cellular dysfunction. A number of miRNAs have already been identified to play a role in osteoarthritis, osteoporosis and sarcopenia. One miRNA that has become of interest recently is miRNA 141. The purpose of this article is to review the current literature available on miRNA 141 and how it could play a role in osteoporosis, osteoarthritis and musculoskeletal pathology overall.
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http://dx.doi.org/10.1016/j.mad.2018.12.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6998035PMC
March 2019

Selective serotonin re-uptake inhibitor sertraline inhibits bone healing in a calvarial defect model.

Int J Oral Sci 2018 09 3;10(3):25. Epub 2018 Sep 3.

Oral Health Sciences, Medical University of South Carolina, Charleston, SC, USA.

Bone wound healing is a highly dynamic and precisely controlled process through which damaged bone undergoes repair and complete regeneration. External factors can alter this process, leading to delayed or failed bone wound healing. The findings of recent studies suggest that the use of selective serotonin reuptake inhibitors (SSRIs) can reduce bone mass, precipitate osteoporotic fractures and increase the rate of dental implant failure. With 10% of Americans prescribed antidepressants, the potential of SSRIs to impair bone healing may adversely affect millions of patients' ability to heal after sustaining trauma. Here, we investigate the effect of the SSRI sertraline on bone healing through pre-treatment with (10 mg·kg sertraline in drinking water, n = 26) or without (control, n = 30) SSRI followed by the creation of a 5-mm calvarial defect. Animals were randomized into three surgical groups: (a) empty/sham, (b) implanted with a DermaMatrix scaffold soak-loaded with sterile PBS or (c) DermaMatrix soak-loaded with 542.5 ng BMP2. SSRI exposure continued until sacrifice in the exposed groups at 4 weeks after surgery. Sertraline exposure resulted in decreased bone healing with significant decreases in trabecular thickness, trabecular number and osteoclast dysfunction while significantly increasing mature collagen fiber formation. These findings indicate that sertraline exposure can impair bone wound healing through disruption of bone repair and regeneration while promoting or defaulting to scar formation within the defect site.
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http://dx.doi.org/10.1038/s41368-018-0026-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119683PMC
September 2018

Modulation of miRNAs by Vitamin C in Human Bone Marrow Stromal Cells.

Nutrients 2018 Feb 8;10(2). Epub 2018 Feb 8.

Department of Orthopaedic Surgery, Augusta University, Augusta, GA 30912, USA.

MicroRNAs (miRNAs) are small (18-25 nucleotides), noncoding RNAs that have been identified as potential regulators of bone marrow stromal cell (BMSC) proliferation, differentiation, and musculoskeletal development. Vitamin C is known to play a vital role in such types of biological processes through various different mechanisms by altering mRNA expression. We hypothesized that vitamin C mediates these biological processes partially through miRNA regulation. We performed global miRNA expression analysis on human BMSCs following vitamin C treatment using microarrays containing human precursor and mature miRNA probes. Bioinformatics analyses were performed on differentially expressed miRNAs to identify novel target genes and signaling pathways. Our bioinformatics analysis suggested that the miRNAs may regulate multiple stem cell-specific signaling pathways such as cell adhesion molecules (CAMs), fatty acid biosynthesis and hormone signaling pathways. Furthermore, our analysis predicted novel stem cell proliferation and differentiation gene targets. The findings of the present study demonstrate that vitamin C can have positive effects on BMSCs in part by regulating miRNA expression.
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http://dx.doi.org/10.3390/nu10020186DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5852762PMC
February 2018

Kynurenine, a Tryptophan Metabolite That Accumulates With Age, Induces Bone Loss.

J Bone Miner Res 2017 Nov 14;32(11):2182-2193. Epub 2017 Aug 14.

Institute for Regenerative and Reparative Medicine, Augusta University, Augusta, GA, USA.

Age-dependent bone loss occurs in humans and in several animal species, including rodents. The underlying causal mechanisms are probably multifactorial, although an age-associated increase in the generation of reactive oxygen species has been frequently implicated. We previously reported that aromatic amino acids function as antioxidants, are anabolic for bone, and that they may potentially play a protective role in an aging environment. We hypothesized that upon oxidation the aromatic amino acids would not only lose their anabolic effects but also potentially become a catabolic byproduct. When measured in vivo in C57BL/6 mice, the tryptophan oxidation product and kynurenine precursor, N-formylkynurenine (NFK), was found to increase with age. We tested the direct effects of feeding kynurenine (kyn) on bone mass and also tested the short-term effects of intraperitoneal kyn injection on bone turnover in CD-1 mice. μCT analyses showed kyn-induced bone loss. Levels of serum markers of osteoclastic activity (pyridinoline [PYD] and RANKL) increased significantly with kyn treatment. In addition, histological and histomorphometric studies showed an increase in osteoclastic activity in the kyn-treated groups in both dietary and injection-based studies. Further, kyn treatment significantly increased bone marrow adiposity, and BMSCs isolated from the kyn-injected mice exhibited decreased mRNA expression of Hdac3 and its cofactor NCoR1 and increased expression of lipid storage genes Cidec and Plin1. A similar pattern of gene expression is observed with aging. In summary, our data show that increasing kyn levels results in accelerated skeletal aging by impairing osteoblastic differentiation and increasing osteoclastic resorption. These data would suggest that kyn could play a role in age-induced bone loss. © 2017 American Society for Bone and Mineral Research.
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http://dx.doi.org/10.1002/jbmr.3224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5685888PMC
November 2017

Human Mesenchymal Stem Cells Partially Reverse Infertility in Chemotherapy-Induced Ovarian Failure.

Reprod Sci 2018 01 1;25(1):51-63. Epub 2017 May 1.

1 Division of Translation Research, Department of Obstetrics and Gynecology, Medical College of Georgia Augusta University, Augusta, GA, USA.

Introduction: Chemotherapy is the most commonly used modality to treat human cancers; however, in many cases it causes irreversible ovarian failure. In this work, we plan to evaluate the restorative function of human bone marrow mesenchymal stem cells (BMSCs) in a chemotherapy-induced ovarian failure mouse model.

Methods: Acclimatized 4 to 6 week-old female mice (C57BL/6) were assigned randomly to a vehicle-treated control group (group 1), chemotherapy-treated group followed by vehicle alone (group 2), or chemotherapy-treated group followed by stem cell intraovarian injection (group 3). Outcomes were evaluated using immunohistochemistry (IHC), serum hormonal assays, and estrous cycle monitoring and breeding potential.

Results: Post BMSCs administration, group 3 promptly showed detectable vaginal smears with estrogenic changes. Increase in total body weight, ovarian weight, and weight of estrogen-responsive organs (uterus and liver) was observed at 2 weeks and continued to end of the experiment. Hematoxylin and Eosin histological evaluation of the ovaries demonstrated a higher mean follicle count in group 3 than in group 2. Group 3 had lower follicle-stimulating hormone (FSH) levels ( P = .03) and higher anti-Müllerian hormone serum (AMH) levels ( P = .0005) than group 2. The IHC analysis demonstrated higher expression of AMH, FSH receptor, inhibin A, and inhibin B in growing follicles of group 3 versus group 2. Tracking studies demonstrated that human BMSCs evenly repopulated the growing follicles in treated ovaries. Importantly, breeding data showed significant increases in the pregnancies numbers, 2 pregnancies in group 1 and 12 in group 3 ( P = .02).

Conclusions: Intraovarian administered BMSCs are able to restore ovarian hormone production and reactivate folliculogenesis in chemotherapy-induced ovarian failure mouse model.
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http://dx.doi.org/10.1177/1933719117699705DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6344979PMC
January 2018

MicroRNA-183-5p Increases with Age in Bone-Derived Extracellular Vesicles, Suppresses Bone Marrow Stromal (Stem) Cell Proliferation, and Induces Stem Cell Senescence.

Tissue Eng Part A 2017 11 28;23(21-22):1231-1240. Epub 2017 Apr 28.

Department of Cellular Biology & Anatomy, Medical College of Georgia, Augusta University , Augusta, Georgia .

Microvesicle- and exosome-mediated transport of microRNAs (miRNAs) represents a novel cellular and molecular pathway for cell-cell communication. In this study, we tested the hypothesis that these extracellular vesicles (EVs) and their miRNAs might change with age, contributing to age-related stem cell dysfunction. EVs were isolated from the bone marrow interstitial fluid (supernatant) of young (3-4 months) and aged (24-28 months) mice to determine whether the size, concentration, and miRNA profile of EVs were altered with age in vivo. Results show that EVs isolated from bone marrow are CD63 and CD9 positive, and the concentration and size distribution of bone marrow EVs are similar between the young and aged mice. Bioanalyzer data indicate that EVs from both young and aged mice are highly enriched in miRNAs, and the miRNA profile of bone marrow EVs differs significantly between the young and aged mice. Specifically, the miR-183 cluster (miR-96/-182/-183) is highly expressed in aged EVs. In vitro assays demonstrate that aged EVs are endocytosed by primary bone marrow stromal cells (BMSCs), and these aged EVs inhibit the osteogenic differentiation of young BMSCs. Transfection of BMSCs with miR-183-5p mimic reduces cell proliferation and osteogenic differentiation, increases senescence, and decreases protein levels of the miR-183-5p target heme oxygenase-1 (Hmox1). In vitro assays utilizing HO-induced oxidative stress show that HO treatment of BMSCs increases the abundance of miR-183-5p in BMSC-derived EVs, and Amplex Red assays demonstrate that HO is elevated in the bone marrow microenvironment with age. Together, these data indicate that aging and oxidative stress can significantly alter the miRNA cargo of EVs in the bone marrow microenvironment, which may in turn play a role in stem cell senescence and osteogenic differentiation by reducing Hmox1 activity.
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http://dx.doi.org/10.1089/ten.TEA.2016.0525DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689127PMC
November 2017

Association of Plasma SDF-1 with Bone Mineral Density, Body Composition, and Hip Fractures in Older Adults: The Cardiovascular Health Study.

Calcif Tissue Int 2017 06 28;100(6):599-608. Epub 2017 Feb 28.

Charlie Norwood Veterans Affairs Medical Center, Augusta, GA, USA.

Aging is associated with an increase in circulating inflammatory factors. One, the cytokine stromal cell-derived factor 1 (SDF-1 or CXCL12), is critical to stem cell mobilization, migration, and homing as well as to bone marrow stem cell (BMSC), osteoblast, and osteoclast function. SDF-1 has pleiotropic roles in bone formation and BMSC differentiation into osteoblasts/osteocytes, and in osteoprogenitor cell survival. The objective of this study was to examine the association of plasma SDF-1 in participants in the cardiovascular health study (CHS) with bone mineral density (BMD), body composition, and incident hip fractures. In 1536 CHS participants, SDF-1 plasma levels were significantly associated with increasing age (p < 0.01) and male gender (p = 0.04), but not with race (p = 0.63). In multivariable-adjusted models, higher SDF-1 levels were associated with lower total hip BMD (p = 0.02). However, there was no significant association of SDF-1 with hip fractures (p = 0.53). In summary, circulating plasma levels of SDF-1 are associated with increasing age and independently associated with lower total hip BMD in both men and women. These findings suggest that SDF-1 levels are linked to bone homeostasis.
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http://dx.doi.org/10.1007/s00223-017-0245-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5649737PMC
June 2017

Skeletal stem cells for bone development, homeostasis and repair: one or many?

Bonekey Rep 2015 23;4:769. Epub 2015 Dec 23.

Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; Department of Orthopaedic Surgery, Medical College of Georgia, Augusta University, Augusta, GA, USA; The Institute for Regenerative and Reparative Medicine, Medical College of Georgia, Augusta University, Augusta, GA, USA; Charlie Norwood VA Medical Center, Augusta, GA, USA.

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http://dx.doi.org/10.1038/bonekey.2015.139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4704464PMC
January 2016

Mesenchymal stem cell expression of SDF-1β synergizes with BMP-2 to augment cell-mediated healing of critical-sized mouse calvarial defects.

J Tissue Eng Regen Med 2017 06 31;11(6):1806-1819. Epub 2015 Jul 31.

Department of Oral Health Sciences, Medical University of South Carolina, Charleston, SC, USA.

Bone has the potential for spontaneous healing. This process, however, often fails in patients with comorbidities. Tissue engineering combining functional cells, biomaterials and osteoinductive cues may provide alternative treatment strategies. We have recently demonstrated that stromal cell-derived factor-1β (SDF-1β) works in concert with bone morphogenetic protein-2 (BMP-2) to potentiate osteogenic differentiation of bone marrow-derived mesenchymal stem/stromal cells (BMSCs). Here, we test the hypothesis that SDF-1β overexpressed in Tet-Off-SDF-1β BMSCs, delivered on acellular dermal matrix (ADM), synergistically augments BMP-2-induced healing of critical-sized mouse calvarial defects. BMSC therapies alone showed limited bone healing, which was increased with co-delivery of BMP-2. This was further enhanced in Tet-Off-SDF-1β BMSCs + BMP-2. Only limited BMSC retention on ADM constructs was observed after 4 weeks in vivo, which was increased with BMP-2 co-delivery. In vitro cell proliferation studies showed that supplementing BMP-2 to Tet-Off BMSCs significantly increased the cell number during the first 24 h. Consequently, the increased cell numbers decreased the detectable BMP-2 levels in the medium, but increased cell-associated BMP-2. The data suggest that SDF-1β provides synergistic effects supporting BMP-2-induced, BMSC-mediated bone formation and appears suitable for optimization of bone augmentation in combination therapy protocols. Copyright © 2015 John Wiley & Sons, Ltd.
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http://dx.doi.org/10.1002/term.2078DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4733586PMC
June 2017

The crucial role of vitamin C and its transporter (SVCT2) in bone marrow stromal cell autophagy and apoptosis.

Stem Cell Res 2015 Sep 10;15(2):312-21. Epub 2015 Jun 10.

Department of Orthopaedic Surgery, Georgia Regents University, Augusta, GA 30912, USA; Institute of Regenerative and Reparative Medicine, Georgia Regents University, Augusta, GA 30912, USA. Electronic address:

Vitamin C is an antioxidant that plays a vital role in various biological processes including bone formation. Previously, we reported that vitamin C is transported into bone marrow stromal cells (BMSCs) through the sodium dependent Vitamin C Transporter 2 (SVCT2) and this transporter plays an important role in osteogenic differentiation. Furthermore, this transporter is regulated by oxidative stress. To date, however, the exact role of vitamin C and its transporter (SVCT2) in ROS regulated autophagy and apoptosis in BMSCs is poorly understood. In the present study, we observed that oxidative stress decreased survival of BMSCs in a dose-dependent manner and induced growth arrest in the G1 phase of the cell cycle. These effects were accompanied by the induction of autophagy, confirmed by P62 and LC3B protein level and punctate GFP-LC3B distribution. The supplementation of vitamin C significantly rescued the BMSCs from oxidative stress by regulating autophagy. Knockdown of the SVCT2 transporter in BMSCs synergistically decreased cell survival even under low oxidative stress conditions. Also, supplementing vitamin C failed to rescue cells from stress. Our results reveal that the SVCT2 transporter plays a vital role in the mechanism of BMSC survival under stress conditions. Altogether, this study has given new insight into the role of the SVCT2 transporter in oxidative stress related autophagy and apoptosis in BMSCs.
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http://dx.doi.org/10.1016/j.scr.2015.06.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4824057PMC
September 2015

The aromatic amino acid tryptophan stimulates skeletal muscle IGF1/p70s6k/mTor signaling in vivo and the expression of myogenic genes in vitro.

Nutrition 2015 Jul-Aug;31(7-8):1018-24. Epub 2015 Mar 17.

Georgia Regents University (Formerly Georgia Health Sciences University), Augusta, GA, USA. Electronic address:

Objectives: Nutrition plays a key role in the maintenance of muscle and bone mass, and dietary protein deficiency has in particular been associated with catabolism of both muscle and bone tissue. One mechanism thought to link protein deficiency with loss of muscle mass is deficiency in specific amino acids that play a role in muscle metabolism. The aim of this study was to test the hypothesis that the essential amino acid tryptophan, and its metabolite kynurenine, might directly affect muscle metabolism in the setting of protein deficiency.

Methods: Adult mice (12 mo) were fed a normal diet (18% protein), as well as diets with low protein (8%) supplemented with increasing concentrations (50, 100, and 200 uM) of kynurenine (Kyn) or with tryptophan (Trp; 1.5 mM) for 8 weeks. Myoprogenitor cells were also treated with Trp and Kyn in vitro to determine their effects on cell proliferation and expression of myogenic differentiation markers.

Results: All mice on the low-protein diets weighed less than the group fed normal protein (18%). Lean mass measured by dual-energy X-ray absorptiometry was lowest in mice on the high Kyn diet, whereas percent lean mass was highest in mice receiving Trp supplementation and percent body fat was lowest in mice receiving Trp. Enzyme-linked immunosorbent assays showed significant increases in skeletal muscle insulin-like growth factor-1, leptin, and the myostatin antagonist follistatin with Trp supplementation. mRNA microarray and gene pathway analysis performed on muscle samples demonstrate that mTor/eif4/p70s6k pathway molecules are significantly up-regulated in muscles from mice on Kyn and Trp supplementation. In vitro, neither amino acid affected proliferation of myoprogenitors, but Trp increased the expression of the myogenic markers MyoD, myogenin, and myosin heavy chain.

Conclusion: These findings suggest that dietary amino acids can directly affect molecular signaling in skeletal muscle, further indicating that dietary manipulation with specific amino acids could potentially attenuate muscle loss with dietary protein deficiency.
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http://dx.doi.org/10.1016/j.nut.2015.02.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465076PMC
May 2016

Caloric restriction and the adipokine leptin alter the SDF-1 signaling axis in bone marrow and in bone marrow derived mesenchymal stem cells.

Mol Cell Endocrinol 2015 Jul 14;410:64-72. Epub 2015 Mar 14.

Department of Cellular Biology & Anatomy, Georgia Regents University, Augusta, GA, USA; Institute for Regenerative and Reparative Medicine, Georgia Regents University, Augusta, GA, USA; Department of Orthopaedic Surgery, Georgia Regents University, Augusta, GA, USA; Charlie Norwood VA Medical Center, Augusta, GA, USA. Electronic address:

Growing evidence suggests that the chemokine stromal cell-derived factor-1 (SDF-1) is essential in regulating bone marrow (BM) derived mesenchymal stromal/stem cell (BMSC) survival, and differentiation to either a pro-osteogenic or pro-adipogenic fate. This study investigates the effects of caloric restriction (CR) and leptin on the SDF-1/CXCR4 axis in bone and BM tissues in the context of age-associated bone loss. For in vivo studies, we collected bone, BM cells and BM interstitial fluid from 12 and 20 month-old C57Bl6 mice fed ad-libitum (AL), and 20-month-old mice on long-term CR with, or without, intraperitoneal injection of leptin for 10 days (10 mg/kg). To mimic conditions of CR in vitro, 18 month murine BMSCs were treated with (1) control (Ctrl): normal proliferation medium, (2) nutrient restriction (NR): low glucose, low serum medium, or (3) NR + leptin: NR medium + 100 ng/ml leptin for 6-48 h. In BMSCs both protein and mRNA expression of SDF-1 and CXCR4 were increased by CR and CR + leptin. In contrast, the alternate SDF-1 receptor CXCR7 was decreased, suggesting a nutrient signaling mediated change in SDF-1 axis signaling in BMSCs. However, in bone SDF-1, CXCR4 and 7 gene expression increase with age and this is reversed with CR, while addition of leptin returns this to the "aged" level. Histologically bone formation was lower in the calorically restricted mice and BM adipogenesis increased, both effects were reversed with the 10 day leptin treatment. This suggests that in bone CR and leptin alter the nutrient signaling pathways in different ways to affect the local action of the osteogenic cytokine SDF-1. Studies focusing on the molecular interaction between nutrient signaling by CR, leptin and SDF-1 axis may help to address age-related musculoskeletal changes.
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http://dx.doi.org/10.1016/j.mce.2015.03.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4706462PMC
July 2015

Oxidation of the aromatic amino acids tryptophan and tyrosine disrupts their anabolic effects on bone marrow mesenchymal stem cells.

Mol Cell Endocrinol 2015 Jul 28;410:87-96. Epub 2015 Jan 28.

Institute for Regenerative and Reparative Medicine, Georgia Regents University, Augusta, GA, United States; Department of Neuroscience and Regenerative Medicine, Georgia Regents University, Augusta, GA, United States; Department of Orthopaedic Surgery, Georgia Regents University, Augusta, GA, United States; Department of Medicine, Georgia Regents University, Augusta, GA, United States; Department of Cellular Biology and Anatomy, Georgia Regents University, Augusta, GA, United States. Electronic address:

Age-induced bone loss is associated with greater bone resorption and decreased bone formation resulting in osteoporosis and osteoporosis-related fractures. The etiology of this age-induced bone loss is not clear but has been associated with increased generation of reactive oxygen species (ROS) from leaky mitochondria. ROS are known to oxidize/damage the surrounding proteins/amino acids/enzymes and thus impair their normal function. Among the amino acids, the aromatic amino acids are particularly prone to modification by oxidation. Since impaired osteoblastic differentiation from bone marrow mesenchymal stem cells (BMMSCs) plays a role in age-related bone loss, we wished to examine whether oxidized amino acids (in particular the aromatic amino acids) modulated BMMSC function. Using mouse BMMSCs, we examined the effects of the oxidized amino acids di-tyrosine and kynurenine on proliferation, differentiation and Mitogen-Activated Protein Kinase (MAPK) pathway. Our data demonstrate that amino acid oxides (in particular kynurenine) inhibited BMMSC proliferation, alkaline phosphatase expression and activity and the expression of osteogenic markers (Osteocalcin and Runx2). Taken together, our data are consistent with a potential pathogenic role for oxidized amino acids in age-induced bone loss.
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http://dx.doi.org/10.1016/j.mce.2015.01.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4444384PMC
July 2015
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