SVILUPPO DI UN MODELLO SPERIMENTALE PER LO STUDIO DEI FATTORI DEGENERATIVI CHE INDUCONO IL DIFFERENZIAMENTO ADIPOCITARIO DI CELLULE STAMINALI MESENCHIMALI

In adult tissues, somatic stem cells represent a cell reservoir involved in physiological or pathological cell replacement within healthy or damaged tissue. Thanks to specific molecular or physical signals of the microenvironment, homeostasis process is guaranteed inside stem cell niches. Factors deriving from pathological events induce a shift in stem cell behaviour to cell differentiation, in order to reconstitute cell populations lost in the damaged tissue. In several myopathies, chronic inflammation is a part of pathological process that causes fibrotic infiltrations and adipose deposition within degenerating tissue, leading even to muscle substitution. Mechanisms underlying these events are not clear yet and represents a focus in etiopathogenetic studies on muscular research. The aim of this work was to develop an experimental model for mimicking in vitro the effects of a damaged muscle on a specific stem cell population; the methodological improvement is represented by the simultaneous culture of both the component in a microenvironment divided by a porous membrane. Parameters setting and standardization make the method reproducible and applicable to different culture conditions. First experimental session, performed on a population of human circulating myogenic progenitors expressing CD133 antigen, has shown how the presence of a murine muscle tissue section in culture can induce an higher cell proliferation and expression of an early marker of muscle differentiation, as Myf5. Nevertheless, because of their hematopoietic origin, these cells cannot complete their myogenic differentiation, that is usually achieved in a direct coculture with myotubes or myofibers. The same experimental design, applied for the culture of mesenchymal stem cells with myogenic potential, has shown how the biological factors, released by the murine muscle section, can induce an adipose differentiation in that stem cell population. Lipid drops in cell cytoplasm and expression of specific markers of adipose differentiation, such as perilipin A and FABP4, confirmed that the experimental model proposed can reproduce in vitro a culture condition similar to the one observed in degenerating muscle in several myopathies. This methodological approach represents a new model for in vitro study of adipose deposition in muscle, whose molecular mechanisms are not well characterized yet; using a whole tissue section in culture allows to reproduce in vitro a microenvironment similar to the once observed in vivo. For this reason the experimental model developed for this work can be seen as new perspective in the study of molecular process underlying adipose tissue formation in degenerating muscle.