miRNA-126a plays important role in myoblast and endothelial cell interaction

Muscle satellite cells (SCs) are stem cells and the main players in skeletal muscle reconstruction. Since satellite cells are located near or in direct contact with blood vessels their niche is formed, inter alia, by endothelial cells. The cross-talk between satellite cells and endothelial cells determines quiescence or proliferation of these cells. However, little is known about the role of miRNA in these interactions. In the present study we identified miRNA that were up-regulated in SC-derived myoblasts treated with stromal derived factor-1 (SDF-1) and/or down-regulated in cells in which the expression of CXCR4 or CXCR7, that is, SDF-1 receptors, was silenced. SDF-1 is one of the important regulators of cell migration, mobilization, skeletal muscle regeneration, and angiogenesis. We hypothesized that selected miRNAs affect SC-derived myoblast fate and interactions with endothelial cells. We showed that miR-126a-3p inhibited both, myoblast migration and fusion. Moreover, the levels of Cxcl12, encoding SDF-1 and Ackr3, encoding CXCR7, were reduced by miR-126a-3p mimic. Interestingly, the miR-126a-3p mimic significantly decreased the level of numerous factors involved in myogenesis and the miR-126a-5p mimic increased the level of Vefga. Importantly, the treatment of endothelial cells with medium conditioned by miR-126-5p mimic transfected SC-derived myoblasts promoted tubulogenesis.

SDF-1 and NOTCH signaling in myogenic cell differentiation: the role of miRNA10a, 425, and 5100

BACKGROUND

Skeletal muscle regeneration is a complex process regulated by many cytokines and growth factors. Among the important signaling pathways regulating the myogenic cell identity are these involving SDF-1 and NOTCH. SDF-1 participates in cell mobilization and acts as an important chemoattractant. NOTCH, on the other hand, controls cell activation and myogenic determination of satellite cells. Knowledge about the interaction between SDF-1 and NOTCH signaling is limited.

METHODS

We analyzed two populations of myogenic cells isolated from mouse skeletal muscle, that is, myoblasts derived from satellite cells (SCs) and muscle interstitial progenitor cells (MIPCs). First, microRNA level changes in response to SDF-1 treatment were analyzed with next-generation sequencing (NGS). Second, myogenic cells, i.e., SC-derived myoblasts and MIPCs were transfected with miRNA mimics, selected on the basis of NGS results, or their inhibitors. Transcriptional changes, as well as proliferation, migration, and differentiation abilities of SC-derived myoblasts and MIPCs, were analyzed in vitro. Naive myogenic potential was assessed in vivo, using subcutaneous engrafts and analysis of cell contribution to regeneration of the skeletal muscles.

RESULTS

SDF-1 treatment led to down-regulation of miR10a, miR151, miR425, and miR5100 in myoblasts. Interestingly, miR10a, miR425, and miR5100 regulated the expression of factors involved in the NOTCH signaling pathway, including Dll1, Jag2, and NICD. Furthermore, miR10a, miR425, and miR5100 down-regulated the expression of factors involved in cell migration: Acta1, MMP12, and FAK, myogenic differentiation: Pax7, Myf5, Myod, Mef2c, Myog, Musk, and Myh3. However, these changes did not significantly affect myogenic cell migration or fusion either in vitro or in vivo, except when miR425 was overexpressed, or miR5100 inhibitor was used. These two molecules increased the fusion of MIPCs and myoblasts, respectively. Furthermore, miR425-transfected MIPC transplantation into injured skeletal muscle resulted in more efficient regeneration, compared to control cell transplantation. However, skeletal muscles that were injected with miR10a transfected myoblasts regenerated less efficiently.

CONCLUSIONS

SDF-1 down-regulates miR10a, miR425, and miR5100, what could affect NOTCH signaling, differentiation of myogenic cells, and their participation in skeletal muscle regeneration.

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

Regeneration of skeletal muscle relies on the presence of satellite cells. Satellite cells deficiency accompanying some degenerative diseases is the reason for the search for the "replacement cells" that can be used in the muscle therapies. Due to their unique properties embryonic stem cells (ESCs), as well as myogenic cells derived from them, are considered as a promising source of therapeutic cells. Among the factors crucial for the specification of myogenic precursor cells is Pax7 that sustains proper function of satellite cells. In our previous studies we showed that ESCs lacking functional Pax7 are able to form myoblasts in vitro when differentiated within embryoid bodies and their outgrowths. In the current study we showed that ESCs lacking functional Pax7, cultured in vitro in monolayer in the medium supplemented with horse serum and 5azaC, expressed higher levels of factors associated with myogenesis, such as Pdgfra, Pax3, Myf5, and MyoD. Importantly, skeletal myosin immunolocalization confirmed that myogenic differentiation of ESCs was more effective in case of cells lacking Pax7. Our in vivo studies showed that ESCs transplanted into regenerating skeletal muscles were detectable at day 7 of regeneration and the number of Pax7-/- ESCs detected was significantly higher than of control cells. Our results support the concept that lack of functional Pax7 promotes proliferation of differentiating ESCs and for this reason more of them can turn into myogenic lineage.

Liquid perfluorochemical-supported hybrid cell culture system for proliferation of chondrocytes on fibrous polylactide scaffolds

CP5 bovine chondrocytes were cultured on biodegradable electrospun fibrous polylactide (PLA) scaffolds placed on a flexible interface formed between two immiscible liquid phases: (1) hydrophobic perfluorochemical (PFC) and (2) aqueous culture medium, as a new way of cartilage implant development. Robust and intensive growth of CP5 cells was achieved in our hybrid liquid-solid-liquid culture system consisting of the fibrous PLA scaffolds in contrast to limited growth of the CP5 cells in traditional culture system with PLA scaffold placed on solid surface. The multicellular aggregates of CP5 cells covered the surface of PLA scaffolds and the chondrocytes migrated through and overgrew internal fibers of the scaffolds. Our hybrid culture system simultaneously allows the adhesion of adherent CP5 cells to fibers of PLA scaffolds as well as, due to use of phase of PFC, enhances the mass transfer in the case of supplying/removing of respiratory gases, i.e., O2 and CO2. Our flexible (independent of vessel shape) system is simple, ready-to-use and may utilize a variety of polymer-based scaffolds traditionally proposed for implant development.

Myogenic potential of mesenchymal stem cells - the case of adhesive fraction of human umbilical cord blood cells

Different sources of stem cells are considered as a potential source of precursor cells that could improve skeletal muscle regeneration. Under physiological conditions muscle regeneration is based on the satellite cells, i.e. adult muscle precursor cells that are localized between muscle fiber and surrounding basal lamina. These cells remain quiescent but after skeletal muscle injury activate, proliferate, differentiate, and fuse either to form new muscle fibers or reconstruct the damaged ones. As it was shown in many studies few populations of stem cells other than satellite cells are able to support skeletal muscle regeneration. Among them are mesenchymal stem cells (MSCs) that are present in many niches within adult organism and also in fetal tissues, such as human umbilical cord blood (HUCB) or umbilical cord connective tissue, i.e. Wharton's jelly. Thus, MSCs are intensively tested to prove that they are able to differentiate into various cell types, including skeletal myoblasts, and therefore could be useful in regenerative medicine. In our previous study we showed that MSCs isolated from Wharton's jelly expressed pluripotency as well as myogenic markers and were able to undergo myogenic differentiation both in vitro and in vivo. We also analyzed the potential of HUCB cells population which contains not only MSCs but also hematopoietic precursors. Our analyses of whole population of HUCB cells showed that these cells express myogenic regulatory factors, i.e. MyoD, and are able to contribute to skeletal muscle regeneration. In the present study we document that adherent fraction of HUCB cells, i.e. the cells that constitute the subpopulation enriched in MSCs, expresses pluripotency and myogenic markers, and have a positive impact at the regeneration of injured mouse skeletal muscle.

From planarians to mammals - the many faces of regeneration

This report presents the history of the involvement of the Department of Cytology in studies of different aspects of regeneration. It can be divided into two major phases; the first focused on the regeneration of Turbellarians and the second on the regeneration of rat skeletal muscles including the differentiation of satellite cells in vitro. Regeneration of Turbellarians was investigated both at the cellular and molecular levels including the role of the protein kinase C (PKC) in this process. Studies on skeletal muscle regeneration initially focused on factors involved in regulation of signal transduction pathways. Next, we explored the influence of growth factors on the modulation of the regeneration process. Another important aspect of our studies was investigating of the distribution and function of different proteins involved in adhesion and fusion of myoblasts. Finally, we are also conducting research on the role of stem cells from other tissues in the regeneration of skeletal muscle.