AP2α transcriptional activity is essential for retinoid-induced neuronal differentiation of mesenchymal stem cells

Abstract

Pre-activation of the retinoid signaling pathway by all-trans retinoic acid facilitates neuronal differentiation of mesenchymal stem cells. Using protein/DNA based screening assays, we identified activator protein 2α as an important downstream target of all-trans retinoic acid. Although all-trans retinoic acid treatment significantly increased activator protein 2α transcriptional activity, it did not affect its expression. Inhibition of activator protein 2α with dominant-negative mutants reduced ATRA-induced differentiation of mesenchymal stem cells into neurons and reversed its associated functional recovery of memory impairment in the cell-based treatment of a hypoxic-ischemic brain damage rat model. Dominant-negative mutants of activator protein 2α inhibited the expression of neuronal markers which were induced by retinoic acid receptor β activation. All-trans retinoic acid treatment increased phosphorylation of activator protein 2α and resulted in its nuclear translocation. This was blocked by siRNA-mediated knockdown of retinoic acid receptor β. Furthermore, we found that retinoic acid receptor β directly interacted with activator protein 2α. In summary, the regulation of all-trans retinoic acid on activator protein 2α transcriptional activity was mediated by activation of retinoic acid receptor β and subsequent phosphorylation and nuclear translocation of activator protein 2α. Our results strongly suggest that activator protein 2α transcriptional activity is essential for all-trans retinoic acid-induced neuronal differentiation of mesenchymal stem cells.

Keywords: AP2α; ATRA; Activator protein 2α; All-trans retinoic acid; GFAP; GLuc; Gaussia luciferase; MAP-2; MNM; MSC; Mesenchymal stem cells; NSE; Neurodifferentiation; RAR; Retinoic acid receptor β; Tuj1; activator protein 2α; all-trans retinoic acid; deleted TAD domain; deleted bHLH domain; dnAP2α; dominant negative deletion mutants of AP2α; glial fibrillary acidic protein; mesenchymal stem cells; microtubule-associated protein-2; modified neuronal induction medium; neuron specific enolase; neuron-specific class III beta-tubulin; retinoic acid receptor; ΔTAD; ΔbHLH.