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The commitment of myogenic cells in skeletal muscle differentiation requires earlier irreversible interruption of the cell cycle. At the molecular level, several key regulators of the cell cycle have been identified: cyclin-dependent kinases and their cyclins stimulate the cell cycle progress and its arrest is determined by the activity of cdk inhibitors (Cip/Kip and INK protein families) and pocket protein family: Rb, p107 and p130. The biological activity of cyclin/cdk complexes allows the successive phases of the cell cycle to occur. Myoblast specialization, differentiation and fusion require the activity of myogenic regulatory factors, which include MyoD, myogenin, Myf5 and MRF4. MyoD and Myf5 play a role in muscle cell specialization, myogenin controls the differentiation process, whereas MRF4 is involved in myotube maturation. The deregulation of the cell cycle leads to uncontrolled proliferation, which antagonizes the functions of myogenic factors and it explains the lack of differentiation-specific gene expression in dividing cells. Conversely, the myogenic factor MyoD seems to cooperate with cell cycle inhibitors leading to inhibition of cell cycle progress and commitment to the differentiation process. The hypophosphorylated form of Rb and cdk inhibitors play an important role in permanent arrest of the cell cycle in differentiated myotubes. Furthermore, cyclin/cdk complexes not only regulate cell division by phosphorylation of several substrates, but may also control other cellular processes such as signal transduction, differentiation and apoptosis. Beyond regulating the cell cycle, Cip/Kip proteins play an important role in cell death, transcription regulation, cell fate determination, cell migration and cytoskeletal dynamics. The article summarizes current knowledge concerning the interactions of intracellular signaling pathways controlling crucial stages of fetal and regenerative myogenesis.

The process of skeletal muscle regeneration comprises four phases: degeneration, inflammatory and immune response, regeneration and remodelling, which are regulated by a number of molecules secreted, by muscle cells and immune, epithelial, interstitial and other cells present in skeletal tissue. The molecules include cytokines, growth factors, erythropoietin, enzymes, and reactive oxygen and nitrogen species (RONS). Some of them are potent stimulators of the proliferation and growth of muscle cells while others may inhibit these processes. For several years, cytokines and growth factors have been used in regenerative medicine in the form of platelet concentrate or recombinant preparations. There have also been attempts to use muscle cells and muscle-derived stem cell (MDSC) cultures, which contain satellite glial cells, mesoanglioblasts and pericytes, as well as cultures of isolated satellite glial cells or myoblasts. The aim of the paper is to present current knowledge concerning the molecular and cellular mechanisms of regeneration and remodelling of skeletal muscles, the role of cytokines and growth factors in the proliferation of satellite glial cells and the possibilities of therapeutic use of stem cells of different origin for stimulating regeneration of damaged muscle fibres.

Urinary incontinence is currently considered to be not only medical, but also socio-economical problem. Periurethral injections are one of the treatment method, although substances used so far have been not effective enough. For last several years surveys are conducted for using myogenic cells as a new material for periurethral injections. It has been proven that undifferentiated muscle cells can be isolated in the amount sufficient for transplantation from small piece of skeletal muscle tissue. Myogenic cells survive and differentiate into muscle fibers when transplanted in the urethral sphincter. Indirect evidences suggest that injected cells can become innervated. Functional studies revealed that cellular transfer improve sphincter contractility and increase leak point pressure. In first clinical study in human medicine, where the effect was evaluated one year after surgery, 79% of patients was judged as cured. Apart from cells derived from muscle, also bone marrow-derived mesenchymal stem cells and cells seeded on biological scaffolds are considered for using in treatment of urinary incontinence.