Skeletal muscles exhibit great plasticity and an ability to reconstruct in response to injury. However, the repair process is often inefficient and hindered by the development of fibrosis. We explored the possibility that during muscle repair, the different regeneration ability of the fast (extensor digitorum longus; EDL) and slow twitch (Soleus) muscles depends on the differential expression of metalloproteinases (MMP-9 and MMP-2) involved in the remodeling of the extracellular matrix. Our results show that MMP-9 and MMP-2 are present in the intact muscle and are up-regulated after crush-induced muscle injury. The expression and the activity of these two enzymes depend on the type of muscle and the phase of muscle regeneration. In the regenerating Soleus muscle, elevated levels of MMP-9 occurred during the myolysis and reconstruction phase. In contrast, regenerating EDL muscles exhibited decreased MMP-9 levels during myolysis and increased MMP-2 activity at the reconstruction phase. Moreover, satellite cells (mononuclear myoblasts) derived from Soleus and EDL muscles showed no differences in localization or activity of MMP-9 and MMP-2 during proliferation and differentiation in vitro. MMP-9 activity was present during all stages of myoblast differentiation, whereas MMP-2 activity reached its highest level during myoblast fusion. We conclude that MMPs are involved in muscle repair, and that fast and slow twitch muscles exhibit different patterns of MMP-9 and MMP-2 activity.

No abstract

Changes in the expression of adhesion proteins involved in myoblast differentiation were investigated in monolayer (two-dimensional) and 3D (three-dimensional) cell cultures. The expression of integrin alpha3 subunit, integrin beta1 subunit, ADAM12 (a disintegrin and metalloproteinase 12), tetraspanins CD9 and CD81 and M-cadherin were examined in the murine myoblast cell line C2C12 and in a primary culture of rat satellite cells. Myoblasts in monolayer and 3D cultures showed significant differences in their morphology and cytoskeletal organization. All of the studied proteins participated in myoblast fusion in each culture examined, but differences in their levels of expression were observed. Satellite cell-derived myoblasts exhibited higher expression of adhesion protein mRNAs than C2C12 cells. Also, C2C12 cells from a 3D culture showed slightly higher expression of adhesion protein transcripts than the same cells cultured as a monolayer. Significantly, the levels of adhesion protein mRNAs were found to change in parallel in all cell culture types. Despite this finding, it is important that differences between satellite cell-derived myoblasts and cell line C2C12 grown in monolayer and 3D cultures are taken into account when studying processes of myoblast differentiation in vitro.

Nonhematopoietic cord blood cells and mesenchymal cells of umbilical cord Wharton's jelly have been shown to be able to differentiate into various cell types. Thus, as they are readily available and do not raise any ethical issues, these cells are considered to be a potential source of material that can be used in regenerative medicine. In our previous study, we tested the potential of whole mononucleated fraction of human umbilical cord blood cells and showed that they are able to participate in the regeneration of injured mouse skeletal muscle. In the current study, we focused at the umbilical cord mesenchymal stromal cells isolated from Wharton's jelly. We documented that limited fraction of these cells express markers of pluripotent and myogenic cells. Moreover, they are able to undergo myogenic differentiation in vitro, as proved by coculture with C2C12 myoblasts. They also colonize injured skeletal muscle and, with low frequency, participate in the formation of new muscle fibers. Pretreatment of Wharton's jelly mesenchymal stromal cells with SDF-1 has no impact on their incorporation into regenerating muscle fibers but significantly increased muscle mass. As a result, transplantation of mesenchymal stromal cells enhances the skeletal muscle regeneration.

When injured by crushing, the repair of the slow-twitch soleus rat muscle, unlike the fast-twitch EDL, is associated with fibrosis. As TGFβ1, whose activity can be controlled by glycosaminoglycans (GAG), plays a major role in fibrosis, we hypothesized that levels of TGFβ1 and GAG contents could account for this differential quality of regeneration. Here we show that the regeneration of the soleus was accompanied by elevated and more sustained TGFβ1 level than in the EDL. Neutralization of TGFβ1 effects by antibodies to TGFβ1 or its receptor TGFβ-R1 improved muscle repair, especially of the soleus muscle, increased in vitro growth of myoblasts, and accelerated their differentiation. These processes were accompanied by alterations of GAG contents. These results indicate that the control of TGFβ1 activity is important to improve regeneration of injured muscle and accelerate myoblast differentiation, in part through changes in GAG composition of muscle cell environment.

No abstract

No abstract

Formation of mammalian skeletal muscle myofibers, that takes place during embryogenesis, muscle growth or regeneration, requires precise regulation of myoblast adhesion and fusion. There are few evidences showing that adhesion proteins play important role in both processes. To follow the function of these molecules in myoblast differentiation we analysed integrin alpha3, integrin beta1, ADAM12, CD9, CD81, M-cadherin, and VCAM-1 during muscle regeneration. We showed that increase in the expression of these proteins accompanies myoblast fusion and myotube formation in vivo. We also showed that during myoblast fusion in vitro integrin alpha3 associates with integrin beta1 and ADAM12, and also CD9 and CD81, but not with M-cadherin or VCAM-1. Moreover, we documented that experimental modification in the expression of integrin alpha3 lead to the modification of myoblast fusion in vitro. Underexpression of integrin alpha3 decreased myoblasts' ability to fuse. This phenomenon was not related to the modifications in the expression of other adhesion proteins, i.e. integrin beta1, CD9, CD81, ADAM12, M-cadherin, or VCAM-1. Apparently, aberrant expression only of one partner of multiprotein adhesion complexes necessary for myoblast fusion, in this case integrin alpha3, prevents its proper function. Summarizing, we demonstrated the importance of analysed adhesion proteins in myoblast fusion both in vivo and in vitro.