Human myoblasts differentiate in various mesenchymal lineages and inhibit allogeneic T cell proliferation through an indolamine 2,3 dioxygenase dependent pathway

Critical roles of IL-6 signaling in myoblast differentiation of human adipose-derived mesenchymal stem cells

BACKGROUND

Ectopic fat is also formed in muscles as well as the liver, where adipose-derived mesenchymal stem cells (ADSCs) promote adipogenesis. On the other hand, after muscle injury, muscle satellite cells (SCs) contribute to muscle repair through myodifferentiation. Human ADSCs are multipotent stem cells, but it remains unclear whether they are involved in myoblast differentiation. The aim is to find a novel myogenic cytokine and its signaling pathway that promotes the differentiation of human ADSCs-a potential source of new muscle precursor cells-into myoblasts.

METHODS

An array kit was used to detect cytokines produced by ADSCs. After treating ADSCs with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-aza-C) and different JAK inhibitors, MyHC1, a myodifferentiation marker, was detected by immunofluorescence staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The expression status of signaling molecules was determined by Western blotting and the recruitment of transcription factors to the MYOG promoter by chromatin immunoprecipitation (ChIP).

RESULTS

IL-6 was detected at high concentrations in the culture supernatant of ADSCs. ADSCs stimulated with 5-aza-C became strongly positive for MyHC1 on day 21 post-stimulation. When co-stimulated with 5-aza-C and IL-6/sIL-6R, ADSCs became positive for MyHC1 protein and upregulated MYOG mRNA as early as day 14 post-stimulation. Co-stimulation with 5-aza-C and IL-6/sIL-6R resulted in phosphorylation of STAT1 and STAT3. The addition of a JAK2 inhibitor, but not JAK1/3 inhibitors, abolished the MyHC1 positivity and phosphorylation of STAT1 and STAT3. Co-stimulation with 5-aza-C and IL-6/sIL-6R during the myogenesis process resulted in the recruitment of STAT1, but not STAT3, to the MYOG promoter. Myoblast differentiation induced by stimulation with 5-aza-C was enhanced by activation of the IL-6/JAK2/STAT1/MYOG pathway.

CONCLUSIONS

Therefore, sustained IL-6/JAK2/STAT1 activation may serve as an important driver of human ADSC differentiation into myoblast, suggesting an important candidate signaling pathway for ameliorating muscle atrophy.

Platelet-Rich Plasma Promotes the Expansion of Human Myoblasts and Favors the In Vitro Generation of Human Muscle Reserve Cells in a Deeper State of Quiescence

Stem cell therapy holds significant potential for skeletal muscle repair, with in vitro-generated human muscle reserve cells (MuRCs) emerging as a source of quiescent myogenic stem cells that can be injected to enhance muscle regeneration. However, the clinical translation of such therapies is hampered by the need for fetal bovine serum (FBS) during the in vitro generation of human MuRCs. This study aimed to determine whether fresh allogeneic human platelet-rich plasma (PRP) combined or not with hyaluronic acid (PRP-HA) could effectively replace xenogeneic FBS for the ex vivo expansion and differentiation of human primary myoblasts. Cells were cultured in media supplemented with either PRP or PRP-HA and their proliferation rate, cytotoxicity and myogenic differentiation potential were compared with those cultured in media supplemented with FBS. The results showed similar proliferation rates among human myoblasts cultured in PRP, PRP-HA or FBS supplemented media, with no cytotoxic effects. Human myoblasts cultured in PRP or PRP-HA showed reduced fusion ability upon differentiation. Nevertheless, we also observed that human MuRCs generated from PRP or PRP-HA myogenic cultures, exhibited increased Pax7 expression and delayed re-entry into the cell cycle upon reactivation, indicating a deeper quiescent state of human MuRCs. These results suggest that allogeneic human PRP effectively replaces FBS for the ex vivo expansion and differentiation of human myoblasts and favors the in vitro generation of Pax7High human MuRCs, with important implications for the advancement of stem cell-based muscle repair strategies.

In vitro-generated human muscle reserve cells are heterogeneous for Pax7 with distinct molecular states and metabolic profiles

BACKGROUND

The capacity of skeletal muscles to regenerate relies on Pax7+ muscle stem cells (MuSC). While in vitro-amplified MuSC are activated and lose part of their regenerative capacity, in vitro-generated human muscle reserve cells (MuRC) are very similar to quiescent MuSC with properties required for their use in cell-based therapies.

METHODS

In the present study, we investigated the heterogeneity of human MuRC and characterized their molecular signature and metabolic profile.

RESULTS

We observed that Notch signaling is active and essential for the generation of quiescent human Pax7+ MuRC in vitro. We also revealed, by immunofluorescence and flow cytometry, two distinct subpopulations of MuRC distinguished by their relative Pax7 expression. After 48 h in differentiation medium (DM), the Pax7High subpopulation represented 35% of the total MuRC pool and this percentage increased to 61% after 96 h in DM. Transcriptomic analysis revealed that Pax7High MuRC were less primed for myogenic differentiation as compared to Pax7Low MuRC and displayed a metabolic shift from glycolysis toward fatty acid oxidation. The bioenergetic profile of human MuRC displayed a 1.5-fold decrease in glycolysis, basal respiration and ATP-linked respiration as compared to myoblasts. We also observed that AMPKα1 expression was significantly upregulated in human MuRC that correlated with an increased phosphorylation of acetyl-CoA carboxylase (ACC). Finally, we showed that fatty acid uptake was increased in MuRC as compared to myoblasts, whereas no changes were observed for glucose uptake.

CONCLUSIONS

Overall, these data reveal that the quiescent MuRC pool is heterogeneous for Pax7 with a Pax7High subpopulation being in a deeper quiescent state, less committed to differentiation and displaying a reduced metabolic activity. Altogether, our data suggest that human Pax7High MuRC may constitute an appropriate stem cell source for potential therapeutic applications in skeletal muscle diseases.

Immortalized human myoblast cell lines for the delivery of therapeutic proteins using encapsulated cell technology

Despite many promising results obtained in previous preclinical studies, the clinical development of encapsulated cell technology (ECT) for the delivery of therapeutic proteins from macrocapsules is still limited, mainly due to the lack of an allogeneic cell line compatible with therapeutic application in humans. In our work, we generated an immortalized human myoblast cell line specifically tailored for macroencapsulation. In the present report, we characterized the immortalized myoblasts and described the engineering process required for the delivery of functional therapeutic proteins including a cytokine, monoclonal antibodies and a viral antigen. We observed that, when encapsulated, the novel myoblast cell line can be efficiently frozen, stored, and thawed, which limits the challenge imposed by the manufacture and supply of encapsulated cell-based therapeutic products. Our results suggest that this versatile allogeneic cell line represents the next step toward a broader development and therapeutic use of ECT.