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Baldwin C, Kim J, Sivaraman S, Rao RR. Stem cell-based strategies for skeletal muscle tissue engineering. J Tissue Eng Regen Med 2022; 16:1061-1068. [PMID: 36223074 DOI: 10.1002/term.3355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 09/06/2022] [Accepted: 09/27/2022] [Indexed: 01/05/2023]
Abstract
Skeletal muscle tissue engineering has been a key area of focus over the years and has been of interest for developing regenerative strategies for injured or degenerative skeletal muscle tissue. Stem cells have gained increased attention as sources for developing skeletal muscle tissue for subsequent studies or potential treatments. Focus has been placed on understanding the molecular pathways that govern skeletal muscle formation in development to advance differentiation of stem cells towards skeletal muscle fates in vitro. Use of growth factors and transcription factors have long been the method for guiding skeletal muscle differentiation in vitro. However, further research in small molecule induced differentiation offers a xeno-free option that could result from use of animal derived factors.
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Affiliation(s)
- Christofer Baldwin
- Department of Biomedical Engineering, University of Arkansas, Fayetteville, Arkansas, USA
| | - Johntaehwan Kim
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah, USA
| | - Srikanth Sivaraman
- Department of Biomedical Engineering, University of Arkansas, Fayetteville, Arkansas, USA
| | - Raj R Rao
- Department of Biomedical Engineering, University of Arkansas, Fayetteville, Arkansas, USA
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2
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Li J, Wang Q, An Y, Chen X, Xing Y, Deng Q, Li Z, Wang S, Dai X, Liang N, Hou Y, Yang H, Shang Z. Integrative Single-Cell RNA-Seq and ATAC-Seq Analysis of Mesenchymal Stem/Stromal Cells Derived from Human Placenta. Front Cell Dev Biol 2022; 10:836887. [PMID: 35450295 PMCID: PMC9017713 DOI: 10.3389/fcell.2022.836887] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Accepted: 02/09/2022] [Indexed: 12/20/2022] Open
Abstract
Mesenchymal stem/stromal cells derived from placenta (PMSCs) are an attractive source for regenerative medicine because of their multidifferentiation potential and immunomodulatory capabilities. However, the cellular and molecular heterogeneity of PMSCs has not been fully characterized. Here, we applied single-cell RNA sequencing (scRNA-seq) and assay for transposase-accessible chromatin sequencing (scATAC-seq) techniques to cultured PMSCs from human full-term placenta. Based on the inferred characteristics of cell clusters, we identify several distinct subsets of PMSCs with specific characteristics, including immunomodulatory-potential and highly proliferative cell states. Furthermore, integrative analysis of gene expression and chromatin accessibility showed a clearer chromatin accessibility signature than those at the transcriptional level on immunomodulatory-related genes. Cell cycle gene-related heterogeneity can be more easily distinguished at the transcriptional than the chromatin accessibility level in PMSCs. We further reveal putative subset-specific cis-regulatory elements regulating the expression of immunomodulatory- and proliferation-related genes in the immunomodulatory-potential and proliferative subpopulations, respectively. Moreover, we infer a novel transcription factor PRDM1, which might play a crucial role in maintaining immunomodulatory capability by activating PRDM1-regulon loop. Collectively, our study first provides a comprehensive and integrative view of the transcriptomic and epigenomic features of PMSCs, which paves the way for a deeper understanding of cellular heterogeneity and offers fundamental biological insight of PMSC subset-based cell therapy.
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Affiliation(s)
- Jinlu Li
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | - Quanlei Wang
- BGI-Shenzhen, Shenzhen, China
- Key Laboratory of Regenerative Medicine of Ministry of Education, Biology Postdoctoral Research Station, Jinan University, Guangzhou, China
| | | | | | - Yanan Xing
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | - Qiuting Deng
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | - Zelong Li
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | - Shengpeng Wang
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | - Xi Dai
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
| | | | | | - Huanming Yang
- BGI-Shenzhen, Shenzhen, China
- James D. Watson Institute of Genome Sciences, Hangzhou, China
| | - Zhouchun Shang
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
- BGI-Shenzhen, Shenzhen, China
- BGI College, Northwest University, Xi’an, China
- *Correspondence: Zhouchun Shang,
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Barisic D, Erb M, Follo M, Al-Mudaris D, Rolauffs B, Hart ML. Lack of a skeletal muscle phenotype in adult human bone marrow stromal cells following xenogeneic-free expansion. Stem Cell Res Ther 2020; 11:79. [PMID: 32087752 PMCID: PMC7036219 DOI: 10.1186/s13287-020-1587-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2019] [Revised: 01/22/2020] [Accepted: 02/05/2020] [Indexed: 02/07/2023] Open
Abstract
Background Many studies have elegantly shown that murine and rat bone marrow-derived mesenchymal stromal cells (bmMSCs) contribute to muscle regeneration and improve muscle function. Yet, the ability of transplanted human bmMSCs to manifest myogenic potential shows conflicting results. While human adipose- and umbilical cord-derived MSCs can be differentiated into a skeletal muscle phenotype using horse serum (HS), bmMSCs have only been shown to differentiate towards the skeletal muscle lineage using a complex mixture of cytokines followed by transfection with notch intracellular domain. Methods Since xenogeneic-free growth supplements are increasingly being used in the expansion of bmMSCs in clinical trials, we investigated the effects of human plasma and platelet lysate (P/PL) on the expression of neuromuscular markers and whether P/PL-expanded human bmMSCs could be differentiated towards a skeletal myogenic phenotype. Neuromuscular markers were measured using the highly sensitive droplet digital polymerase chain reaction for measuring the expression of Myf5, MyoD, MyoG, ACTA1, Desmin, GAP-43, and Coronin 1b transcripts, by performing immunofluorescence for the expression of Desmin, GAP-43, and MEF2, and flow cytometry for the expression of CD56/neural cell adhesion molecule (NCAM). Results Despite that bmMSCs expressed the myogenic regulatory factor (MRF) MEF2 after expansion in P/PL, bmMSCs cultured under such conditions did not express other essential MRFs including Myf5, MyoD, MyoG, or ACTA1 needed for myogenesis. Moreover, HS did not induce myogenesis of bmMSCs and hence did not induce the expression of any of these myogenic markers. P/PL, however, did lead to a significant increase in neurogenic GAP-43, as well as Desmin expression, and resulted in a high baseline expression of the neurogenic gene Coronin 1b which was sustained under further P/PL or HS culture conditions. Fetal bovine serum resulted in equally high levels of GAP-43 and Coronin 1b. Moreover, the proportion of CD56/NCAM-positive bmMSCs cultured in P/PL was 5.9 ± 2.1. Conclusions These data suggest that P/PL may prime a small portion of bmMSCs towards an early neural precursor cell type. Collectively, this shows that P/PL partially primes the cells towards a neurogenic phenotype, but does not prime adult human bmMSCs towards the skeletal muscle lineage.
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Affiliation(s)
- Dominik Barisic
- G.E.R.N. Center for Tissue Replacement, Regeneration and Neogenesis, Department of Orthopaedics and Trauma Surgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Marita Erb
- G.E.R.N. Center for Tissue Replacement, Regeneration and Neogenesis, Department of Orthopaedics and Trauma Surgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Marie Follo
- Department of Medicine I, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Dahlia Al-Mudaris
- G.E.R.N. Center for Tissue Replacement, Regeneration and Neogenesis, Department of Orthopaedics and Trauma Surgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Bernd Rolauffs
- G.E.R.N. Center for Tissue Replacement, Regeneration and Neogenesis, Department of Orthopaedics and Trauma Surgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Melanie L Hart
- G.E.R.N. Center for Tissue Replacement, Regeneration and Neogenesis, Department of Orthopaedics and Trauma Surgery, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
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Huang G, Rocha GV, Pencina KM, Cox K, Krishnan V, Henriksen K, Mitchell P, Sissons SE, Li Z, Nedergaard AF, Karsdal MA, Sun S, Storer TW, Basaria S, Bhasin S. Circulating Biomarkers of Testosterone's Anabolic Effects on Fat-Free Mass. J Clin Endocrinol Metab 2019; 104:3768-3778. [PMID: 31120518 PMCID: PMC6656422 DOI: 10.1210/jc.2019-00505] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 05/17/2019] [Indexed: 01/08/2023]
Abstract
BACKGROUND Biomarkers that predict response to anabolic therapies could expedite the development of function promoting anabolic drugs. This study aimed to identify serum biomarkers that are responsive to testosterone administration and associated with increases in fat-free mass (FFM). METHODS Serum samples were obtained from the 5α-Reductase Trial, a randomized trial that compared the effects of graded doses of testosterone enanthate for 20-weeks in healthy men randomized to placebo or dutasteride (dual SRD5A inhibitor). Testosterone's effects on FFM or strength measures did not differ between placebo vs dutasteride groups. Accordingly, 54 subjects treated with testosterone plus placebo were included in the Discovery Cohort, and 48 randomized to dutasteride were included in the Validation Cohort. 1162 biomarkers were evaluated using pre-specified criteria. RESULTS In the Discovery Cohort, testosterone administration increased PRO-C3 and PRO-C6 levels in a dose- and concentration-dependent manner; increases in these biomarkers from baseline to week-12 were associated with changes in FFM from baseline to week-20 (PRO-C3: r2=0.437, p<0.001; PRO-C6: r2=0.434, p<0.001). Changes in PRO-C3 and PRO-C6 levels were significantly associated with changes in chest press strength (PRO-C3: r2=0.394, p<0.001; PRO-C6: r2=0.530, p<0.001). In the SOMAscan, changes in insulin-like growth factor binding protein-6 (IGFBP6) and Glypican 3 (GPC3) were associated with changes in total and free testosterone levels and FFM. These findings were replicated in the Validation Cohort. CONCLUSION PRO-C3, PRO-C6, IGFBP6 and GPC3 fulfilled the pre-specified criteria for biomarkers of testosterone-induced muscle anabolism: changes in these biomarkers were associated with changes in total and free testosterone concentrations and with testosterone-induced gains in FFM.
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Affiliation(s)
- Grace Huang
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
- Correspondence and Reprint Requests: Grace Huang, MD, Section on Men’s Health, Aging and Metabolism, Brigham and Women’s Hospital, Harvard Medical School, 221 Longwood Avenue, BLI-541, Boston, Massachussetts 02115. E-mail:
| | | | - Karol M Pencina
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
| | - Karen Cox
- Eli Lilly and Co., Indianapolis, Indiana
| | | | - Kim Henriksen
- Department of Endocrinology, Nordic Bioscience Biomarkers & Research, Herlev Hovedgade, Herlev, Denmark
| | | | | | - Zhuoying Li
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
| | - Anders F Nedergaard
- Department of Endocrinology, Nordic Bioscience Biomarkers & Research, Herlev Hovedgade, Herlev, Denmark
| | - Morten A Karsdal
- Department of Endocrinology, Nordic Bioscience Biomarkers & Research, Herlev Hovedgade, Herlev, Denmark
| | - Shu Sun
- Department of Endocrinology, Nordic Bioscience Biomarkers & Research, Herlev Hovedgade, Herlev, Denmark
| | - Thomas W Storer
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
| | - Shehzad Basaria
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
| | - Shalender Bhasin
- Section of Men’s Health: Aging and Metabolism, Boston Claude D. Pepper Older Americans Independence Center for Function Promoting Therapies, Brigham and Women’s Hospital-Harvard Medical School, Boston, Massachusetts
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Insulin-Like Growth Factor Binding Protein-6 Promotes the Differentiation of Placental Mesenchymal Stem Cells into Skeletal Muscle Independent of Insulin-Like Growth Factor Receptor-1 and Insulin Receptor. Stem Cells Int 2019; 2019:9245938. [PMID: 30911300 PMCID: PMC6397983 DOI: 10.1155/2019/9245938] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 12/16/2018] [Accepted: 01/06/2019] [Indexed: 12/15/2022] Open
Abstract
As mesenchymal stem cells (MSCs) are being investigated for regenerative therapies to be used in the clinic, delineating the roles of the IGF system in MSC growth and differentiation, in vitro, is vital in developing these cellular therapies to treat degenerative diseases. Muscle differentiation is a multistep process, starting with commitment to the muscle lineage and ending with the formation of multinucleated fibers. Insulin-like growth factor binding protein-6 (IGFBP-6), relative to other IGFBPs, has high affinity for IGF-2. However, the role of IGFBP-6 in muscle development has not been clearly defined. Our previous studies showed that in vitro extracellular IGFBP-6 increased myogenesis in early stages and could enhance the muscle differentiation process in the absence of IGF-2. In this study, we identified the signal transduction mechanisms of IGFBP-6 on muscle differentiation by placental mesenchymal stem cells (PMSCs). We showed that muscle differentiation required activation of both AKT and MAPK pathways. Interestingly, we demonstrated that IGFBP-6 could compensate for IGF-2 loss and help enhance the muscle differentiation process by triggering predominantly the MAPK pathway independent of activating either IGF-1R or the insulin receptor (IR). These findings indicate the complex interactions between IGFBP-6 and IGFs in PMSC differentiation into the skeletal muscle and that the IGF signaling axis, specifically involving IGFBP-6, is important in muscle differentiation. Moreover, although the major role of IGFBP-6 is IGF-2 inhibition, it is not necessarily the case that IGFBP-6 is the main modulator of IGF-2.
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He M, Li Y, Tang Q, Li D, Jin L, Tian S, Che T, He S, Deng L, Gao G, Gu Y, Jiang Z, Li X, Li M. Genome-Wide Chromatin Structure Changes During Adipogenesis and Myogenesis. Int J Biol Sci 2018; 14:1571-1585. [PMID: 30263009 PMCID: PMC6158721 DOI: 10.7150/ijbs.25328] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Accepted: 07/29/2018] [Indexed: 12/14/2022] Open
Abstract
The recently developed high-throughput chromatin conformation capture (Hi-C) technology enables us to explore the spatial architecture of genomes, which is increasingly considered an important regulator of gene expression. To investigate the changes in three-dimensional (3D) chromatin structure and its mediated gene expression during adipogenesis and myogenesis, we comprehensively mapped 3D chromatin organization for four cell types (3T3-L1 pre-adipocytes, 3T3-L1-D adipocytes, C2C12 myoblasts, and C2C12-D myotubes). We demonstrate that the dynamic spatial genome architecture affected gene expression during cell differentiation. A considerable proportion (~22%) of the mouse genome underwent compartment A/B rearrangement during adipogenic and myogenic differentiation, and most (~80%) upregulated marker genes exhibited an active chromatin state with B to A switch or stable A compartment. More than half (65.4%-73.2%) of the topologically associating domains (TADs) are dynamic. The newly formed TAD and intensified local interactions in the Fabp gene cluster indicated more precise structural regulation of the expression of pro-differentiation genes during adipogenesis. About half (32.39%-59.04%) of the differential chromatin interactions (DCIs) during differentiation are promoter interactions, although these DCIs only account for a small proportion of genome-wide interactions (~9.67% in adipogenesis and ~4.24% in myogenesis). These differential promoter interactions were enriched with promoter-enhancer interactions (PEIs), which were mediated by typical adipogenic and myogenic transcription factors. Differential promoter interactions also included more differentially expressed genes than nonpromoter interactions. Our results provide a global view of dynamic chromatin interactions during adipogenesis and myogenesis and are a resource for studying long-range chromatin interactions mediating the expression of pro-differentiation genes.
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Affiliation(s)
- Mengnan He
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Yan Li
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Qianzi Tang
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Diyan Li
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Long Jin
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Shilin Tian
- Novogene Bioinformatics Institute, Beijing 100089, China
| | - Tiandong Che
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Shen He
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Lamei Deng
- Novogene Bioinformatics Institute, Beijing 100089, China
| | - Guangliang Gao
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China.,Chongqing Academy of Animal Sciences, Chongqing 402460, China
| | - Yiren Gu
- Animal Breeding and Genetics Key Laboratory of Sichuan Province, Pig Science Institute, Sichuan Animal Science Academy, Chengdu 610066, China
| | - Zhi Jiang
- Novogene Bioinformatics Institute, Beijing 100089, China
| | - Xuewei Li
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
| | - Mingzhou Li
- Institute of Animal Genetics and Breeding, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China.,Farm Animal Genetic Resources Exploration and Innovation Key Laboratory of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, China
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Different Effects of Insulin-Like Growth Factor-1 and Insulin-Like Growth Factor-2 on Myogenic Differentiation of Human Mesenchymal Stem Cells. Stem Cells Int 2017; 2017:8286248. [PMID: 29387091 PMCID: PMC5745708 DOI: 10.1155/2017/8286248] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 09/28/2017] [Accepted: 10/10/2017] [Indexed: 11/18/2022] Open
Abstract
Insulin-like growth factors (IGFs) are critical components of the stem cell niche, as they regulate proliferation and differentiation of stem cells into different lineages, including skeletal muscle. We have previously reported that insulin-like growth factor binding protein-6 (IGFBP-6), which has high affinity for IGF-2, alters the differentiation process of placental mesenchymal stem cells (PMSCs) into skeletal muscle. In this study, we determined the roles of IGF-1 and IGF-2 and their interactions with IGFBP-6. We showed that IGF-1 increased IGFBP-6 levels within 24 hours but decreased after 3 days, while IGF-2 maintained higher levels of IGFBP-6 throughout myogenesis. IGF-1 increased IGFBP-6 in the early phase as a requirement for muscle commitment. In contrast, IGF-2 enhanced muscle differentiation as shown by the expression of muscle differentiation markers MyoD, MyoG, and MHC. IGF-1 and IGF-2 had different effects on muscle differentiation with IGF-1 promoting early commitment to muscle and IGF-2 promoting complete muscle differentiation. We also showed that PMSCs acquired increasing capacity to synthesize IGF-2 during muscle differentiation, and the capacity increased as the differentiation progressed suggesting an autocrine and/or paracrine effect. Additionally, we demonstrated that IGFBP-6 could enhance the muscle differentiation process in the absence of IGF-2.
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