Lipid rafts and Prion Protein are involved in neuronal differentiation process of mesenchymal stem cells

INTRODUCTION. To date, the activation mechanisms of molecular and cellular pathways that lead stem cells to differentiate have not been completely clarified, as well as the involvement in the process of differentiation of particular membrane structures, the lipid rafts, seems to be poorly studied. Based on our previous work, we believe that a constitutive component of lipid rafts, the cellular Prion Protein (PrPC), whose expression is modulated according to the degree of stem cell differentiation, could be involved in the molecular signaling that underlies the neuronal differentiation process. METHODS. As experimental model, we used mesenchymal stem cells derived from the human Dental Pulp (hDPSCs). Through the administration of appropriate media for neuronal induction, in the presence or in the absence of substances which compromise the integrity of membrane lipid rafts such as [D]-PDMP (a competitive inhibitor of glucosylceramide synthetase) and MβCD (a compound which is known to induce cholesterol efflux from the membrane), we analyse the role of lipid rafts and related molecules in neural differentiation. RESULTS. We observed both a clear decrease in the expression of typical neuronal markers (B3 tubulin, NFH) in neuroinduced hDPSCs and a decrease in the phosphorylation of key protein kinases, such as Erk 1/2 and Akt, during the hDPSCs neuroinduction process. In addition, through co-immunoprecipitation experiments, we demonstrate the association between PrPC and EGF receptor (EGF-R) within rafts, this association becomes more evident after neuroinduction. Furthermore, the silencing of the PrPC gene (PRNP), allowed us to demonstrate that PrPC is necessary for both, the expression of B3 tubulin and NFH and the phosphorylation of Erk 1/2 and Akt, in a word for neuroinduction in hDPSCs. CONCLUSIONS. Taken together, these data suggest that lipid rafts represent specific chambers in which multimolecular signaling pathways, including lipids (gangliosides and cholesterol) and proteins (e.g. PrPC), play a key role in the hDPSCs differentiation process. Furthermore, we hypothesize that, after neuronal induction, the EGF-R is recruited within lipid rafts where its interaction with PrPC triggers signal transduction.