Myogenic potential of mouse embryonic stem cells lacking functional Pax7 tested in vitro by 5-azacitidine treatment and in vivo in regenerating skeletal muscle

Investigation of single nucleotide polymorphisms in differentially expressed genes and proteins reveals the genetic basis of skeletal muscle growth differences between Tibetan and Large White pigs

OBJECTIVE

Skeletal muscle growth is an important economic trait for meat production, with notable differences between Tibetan pigs (TIBPs, a slow-growing breed) and Large White pigs (LWPs, a fast-growing breed). However, the genetic underpinnings of this disparity remain unclear.

METHODS

In the current study, we integrated differentially expressed genes (DEGs) and proteins (DEPs) from 60-day-old embryonic muscle tissue, along with whole-genome single nucleotide polymorphisms (SNPs) displaying absolute allele frequency differences (ΔAF) of 0.5 or more between the TIBP and LWP breeds, to unravel the genetic factors influencing skeletal muscle growth.

RESULTS

Our analysis revealed 3,499 DEGs and 628 DEPs with SNPs having a ΔAF equal to or greater than 0.5. Further functional analysis identified 145 DEGs and 23 DEPs involved in biological processes related to skeletal muscle development, and 22 DEGs and 3 DEPs implicated in the mechanistic target of rapamycin kinase signaling pathway, which is known for positively regulating protein synthesis. Among these genes, several DEGs and DEPs, enriched with TIPB-specific SNPs in regulatory or/and coding regions, showed marked ΔAF between the TIBP and LWP breeds, including MYF5, MYOF, ASB2, PDE9A, SDC1, PDGFRA, MYOM2, ACVR1, ZIC3, COL11A1, TGFBR1, EDNRA, TGFB2, PDE4D, PGAM2, GRK2, SCN4B, CACNA1S, MYL4, IGF1, and FOXO1. Additionally, genes such as CAPN3, MYOM2, and PGAM2, identified as both DEPs and DEGs related to skeletal muscle development, contained multiple TIBP-specific and LWP-predominant SNPs in regulatory and/or coding regions, underscoring significant ΔAF differences between the two breeds.

CONCLUSION

This comprehensive investigation of SNPs in DEGs and DEPs identified a significant number of SNPs and genes related to skeletal muscle development during the prenatal stage. These findings not only shed light on potential causal genes for muscle divergence between the TIBP and LWP breeds but also offer valuable insights for pig breeding strategies aimed at enhancing meat production.

CD155 is essential for skeletal muscle regeneration by regulating satellite cell proliferation and differentiation

CD155, a member of the immunoglobulin superfamily, is closely related to cell proliferation, adhesion, and migration. CD155 is overexpressed on the surface of cancer cells to promote cell proliferation and is upregulated in damaged tissues as a stress-induced molecule. The process of skeletal muscle regeneration after injury is complex and involves injurious stimulation and subsequent satellite cell proliferation. However, the role of CD155 in this process remains unelucidated. This study aimed to explore the role of CD155 in injured skeletal muscle regeneration and to clarify its effect on satellite cell proliferation and differentiation. Here, quantitative real-time polymerase chain reaction (RT-qPCR) and immunofluorescence results indicated that CD155 expression in satellite cells increased after skeletal muscle injury. CD155 knockout in mice impaired the regeneration of skeletal muscle. A bone marrow transplantation mouse model was constructed and revealed that CD155 on skeletal muscle tissues, not immune cells, affected muscle regeneration. In vitro, CD155 knockdown in myoblasts inhibited their proliferation and differentiation. The transcriptomic analysis also indicated that CD155 absence can impair the biological proliferation and differentiation process of myoblasts. Our research demonstrates that CD155 directly promotes injured muscle regeneration by regulating satellite cell proliferation and differentiation, which may be a potential therapeutic molecule for skeletal muscle injury.

Stem cell-based strategies for skeletal muscle tissue engineering

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.

PAX7 Balances the Cell Cycle Progression via Regulating Expression of Dnmt3b and Apobec2 in Differentiating PSCs

PAX7 transcription factor plays a crucial role in embryonic myogenesis and in adult muscles in which it secures proper function of satellite cells, including regulation of their self renewal. PAX7 downregulation is necessary for the myogenic differentiation of satellite cells induced after muscle damage, what is prerequisite step for regeneration. Using differentiating pluripotent stem cells we documented that the absence of functional PAX7 facilitates proliferation. Such action is executed by the modulation of the expression of two proteins involved in the DNA methylation, i.e., Dnmt3b and Apobec2. Increase in Dnmt3b expression led to the downregulation of the CDK inhibitors and facilitated cell cycle progression. Changes in Apobec2 expression, on the other hand, differently impacted proliferation/differentiation balance, depending on the experimental model used.

Pax7 as molecular switch regulating early and advanced stages of myogenic mouse ESC differentiation in teratomas

Background

Pluripotent stem cells present the ability to self-renew and undergo differentiation into any cell type building an organism. Importantly, a lot of evidence on embryonic stem cell (ESC) differentiation comes from in vitro studies. However, ESCs cultured in vitro do not necessarily behave as cells differentiating in vivo. For this reason, we used teratomas to study early and advanced stages of in vivo ESC myogenic differentiation and the role of Pax7 in this process. Pax7 transcription factor plays a crucial role in the formation and differentiation of skeletal muscle precursor cells during embryonic development. It controls the expression of other myogenic regulators and also acts as an anti-apoptotic factor. It is also involved in the formation and maintenance of satellite cell population.

Methods

In vivo approach we used involved generation and analysis of pluripotent stem cell-derived teratomas. Such model allows to analyze early and also terminal stages of tissue differentiation, for example, terminal stages of myogenesis, including the formation of innervated and vascularized mature myofibers.

Results

We determined how the lack of Pax7 function affects the generation of different myofiber types. In Pax7−/− teratomas, the skeletal muscle tissue occupied significantly smaller area, as compared to Pax7+/+ ones. The proportion of myofibers expressing Myh3 and Myh2b did not differ between Pax7+/+ and Pax7−/− teratomas. However, the area of Myh7 and Myh2a myofibers was significantly lower in Pax7−/− ones. Molecular characteristic of skeletal muscles revealed that the levels of mRNAs coding Myh isoforms were significantly lower in Pax7−/− teratomas. The level of mRNAs encoding Pax3 was significantly higher, while the expression of Nfix, Eno3, Mck, Mef2a, and Itga7 was significantly lower in Pax7−/− teratomas, as compared to Pax7+/+ ones. We proved that the number of satellite cells in Pax7−/− teratomas was significantly reduced. Finally, analysis of neuromuscular junction localization in samples prepared with the iDISCO method confirmed that the organization of neuromuscular junctions in Pax7−/− teratomas was impaired.

Conclusions

Pax7−/− ESCs differentiate in vivo to embryonic myoblasts more readily than Pax7+/+ cells. In the absence of functional Pax7, initiation of myogenic differentiation is facilitated, and as a result, the expression of mesoderm embryonic myoblast markers is upregulated. However, in the absence of functional Pax7 neuromuscular junctions, formation is abnormal, what results in lower differentiation potential of Pax7−/− ESCs during advanced stages of myogenesis.

Myogenic differentiation of human amniotic mesenchymal cells and its tissue repair capacity on volumetric muscle loss

Stem cell-based tissue engineering therapy is the most promising method for treating volumetric muscle loss. Human amniotic mesenchymal cells possess characteristics similar to those of embryonic stem cells. In this study, we verified the stem cell characteristics of human amniotic mesenchymal cells by the flow cytometry analysis, and osteogenic and adipogenic differentiation. Through induction with the DNA demethylating agent 5-azacytidine, human amniotic mesenchymal cells can undergo myogenic differentiation and express skeletal muscle cell-specific markers such as desmin and MyoD. The Wnt/β-catenin signaling pathway also plays an important role. After 5-azacytidine-induced human amniotic mesenchymal cells were implanted into rat tibialis anterior muscle with volumetric muscle loss, we observed increased angiogenesis and improved local tissue repair. We believe that human amniotic mesenchymal cells can serve as a potential source of cells for skeletal muscle tissue engineering.

Transient MicroRNA Expression Enhances Myogenic Potential of Mouse Embryonic Stem Cells

MicroRNAs (miRNAs) are known regulators of various cellular processes, including pluripotency and differentiation of embryonic stem cells (ESCs). We analyzed differentiation of two ESC lines-D3 and B8, and observed significant differences in the expression of miRNAs and genes involved in pluripotency and differentiation. We also examined if transient miRNA overexpression could serve as a sufficient impulse modulating differentiation of mouse ESCs. ESCs were transfected with miRNA Mimics and differentiated in embryoid bodies and embryoid body outgrowths. miRNAs involved in differentiation of mesodermal lineages, such as miR145 and miR181, as well as miRNAs regulating myogenesis (MyomiRs)-miR1, miR133a, miR133b, and miR206 were tested. Using such approach, we proved that transient overexpression of molecules selected by us modulated differentiation of mouse ESCs. Increase in miR145 levels upregulated Pax3, Pax7, Myod1, Myog, and MyHC2, while miR181 triggered the expression of such crucial myogenic factors as Myf5 and MyHC2. As a result, the ability of ESCs to initiate myogenic differentiation and form myotubes was enhanced. Premature expression of MyomiRs had, however, an adverse effect on myogenic differentiation of ESCs. Stem Cells 2018;36:655-670.