Trophic factors can regulate cell cycle progression, differentiation and pax6 expression in Müller cells

POLITI L., INSUA F., GARELLI A. AND ROTSTEIN N.

Fort Lauderdale, Florida, EEUU

Congreso; ARVO Annual Meeting; 2005

ARVO

Trophic Factors Can Regulate Cell Cycle Progression, Differentiation and pax-6 Expression in Müller Cells L.E. Politi, F.Insua, A.Garelli, N.Rotstein. Neurobiology, Inst de Invest Bioquimicas, UNS CONICET, Bahía Blanca, Argentina.  Purpose: Müller cells have been proposed as stem cells and hence as a potential source for neuron replacement in retina degenerative losses. However, to take advantage of their therapeutic potential still requires answers to critical questions such as which factors regulate their cell cycle and how can they be induced to differentiate into specific neuronal phenotypes. Methods: To address these questions we used pure glial cells or cocultures of glial cells with retinal neurons and evaluated the effects of glial derived neurotrophic factor (GDNF), fibroblast growth factor (FGF) and docosahexaenoic acid (DHA), the major polyunsaturated fatty acid in the retina and a trophic factor for rod photoreceptors, on glia proliferation and differentiation. At different culture times BrDU incorporation and the expression of nestin, a stem cell marker, pax6, the essential master gene for eye morphogenesis, p27, a cell cycle inhibitor, and CRALBP, a marker of differentiated glial cells, were determined. Results: After 2 days in vitro, about 80% of glial cells incorporated BrDU and nearly 100% expressed nestin. In addition, at the initial steps of development about 85% of these cells expressed pax-6. At more advanced stages of development glial cells started losing their proliferative potential and pax-6 expression, and began expressing p27 and CRALBP. Exogenous addition of GDNF or FGF to pure glial cultures restored the mitotic potential of glial cells, which markedly regained BrDU uptake. GDNF significantly reduced CRALBP expression, simultaneously increasing that of pax-6 and nestin, suggesting that it induced the dedifferentiation of glial cells. These cells expressed GDNF and released it to the culture medium, both in pure cultures and in co-culture with neurons, suggesting an autocrine regulation of proliferation and postponement of glial differentiation. In contrast, DHA increased p27 and CRALBP expression, and decreased nestin expression, thus suggesting it promoted glial cell differentiation. Conclusions: These results suggest that glial cells might provide the retina with a reservoir of undifferentiated cells with high proliferative potential, which can be induced under appropriate trophic factor stimulation to proliferate or to differentiate as new neuronal or glial cells.