Proteomic identification of novel targets regulated by the mammalian target of rapamycin pathway during oligodendrocyte differentiation.

Previous work from our laboratory demonstrated that the mammalian target of rapamycin (mTOR) is active during and required for oligodendrocyte progenitor cell (OPC) differentiation. Here, we applied an iTRAQ mass spectrometry-based proteomic approach to identify novel targets of the mTOR pathway during OPC differentiation. Among the 978 proteins identified in this study, 328 (34%) exhibited a greater than 20% change (P < 0.05) in control versus rapamycin-treated cultures following 4 days of differentiation in vitro. Interestingly, 197 (20%) proteins were elevated in rapamycin-treated cultures, while 131 (13%) proteins were downregulated by rapamycin. In support of our previous data, inhibiting mTOR caused a dramatic reduction in the expression of myelin proteins. mTOR also was required for the induction of proteins involved in cholesterol and fatty acid synthesis, as well as the expression of many cytoskeletal proteins, cell signaling components, and nuclear/transcriptional regulators. Of particular interest was the identification of several critical mediators of oligodendrocyte differentiation. Specifically, mTOR activity controls the developmentally programmed upregulation of the prodifferentiation factors Fyn and Quaking, whereas the expression of the differentiation repressor Gpr17 was elevated by mTOR inhibition. These data reveal a distinct signature of mTOR-regulated protein expression during OPC differentiation.