Thymosin beta 4 up-regulates miR-200a expression and induces differentiation and survival of rat brain progenitor cells.

Thymosin beta 4 (T4), a secreted 43 amino acid peptide, promotes oligodendrogenesis, and improves neurological outcome in rat models of neurologic injury. We demonstrated that exogenous T4 treatment up-regulated the expression of the miR-200a invitro in rat brain progenitor cells and invivo in the peri-infarct area of rats subjected to middle cerebral artery occlusion (MCAO). The up-regulation of miR-200a down-regulated the expression of the following targets invitro and invivo models: (i) growth factor receptor-bound protein 2 (Grb2), an adaptor protein involved in epidermal growth factor receptor (EGFR)/Grb2/Ras/MEK/ERK1/c-Jun signaling pathway, which negatively regulates the expression of myelin basic protein (MBP), a marker of mature oligodendrocyte; (ii) ERRFI-1/Mig-6, an endogenous potent kinase inhibitor of EGFR, which resulted in activation/phosphorylation of EGFR; (iii) friend of GATA 2, and phosphatase and tensin homolog deleted in chromosome 10 (PTEN), which are potent inhibitors of the phosphatidylinositol-3-kinase (PI3K)/AKT signaling pathway, and resulted in marked activation of AKT; and (iv) transcription factor, p53, which induces pro-apoptotic genes, and possibly reduced apoptosis of the progenitor cells subjected to oxygen glucose deprivation (OGD). Anti-miR-200a transfection reversed all the effects of T4 treatment invitro. Thus, T4 up-regulated MBP synthesis, and inhibited OGD-induced apoptosis in a novel miR-200a dependent EGFR signaling pathway. Our findings of miR-200a-mediated protection of progenitor cells may provide a new therapeutic importance for the treatment of neurologic injury.