Hypoxic preconditioning combined with curcumin promotes cell survival and mitochondrial quality of bone marrow mesenchymal stem cells, and accelerates cutaneous wound healing via PGC-1α/SIRT3/HIF-1α signaling

Restrained survival and function of relocated bone marrow mesenchymal stem cells (BMSCs) is a major impediment to BMSCs-mediated tissue repair. Accumulating evidences have indicated that hypoxic preconditioning of BMSCs could enhance BMSCs' adaptability after transplantation and thus improve their therapeutic properties. Curcumin, a natural dietary product, is known to exert profound protective effects on various cellular processes. Here we showed that mild hypoxic preconditioning combined with curcumin significantly increased cell survival, enriched more cells in G2/M and S phase, and improved mitochondrial function in BMSCs. Meanwhile, hypoxic preconditioning combined with curcumin altered mitochondrial cristae shape and strongly inhibited mitochondrial cytochrome c release, which consequently suppressed an apoptosis signal as revealed by reduced caspase-3 cleavage in BMSCs. Moreover, hypoxic preconditioning remarkably promoted mitochondrial quality via increasing mitochondrial fusion and elevating the activity of oxidative phosphorylation (OXPHOS) and mitochondrial complex I enzyme in BMSCs, which were in accordance with the up-regulated expression of OPA1, PINK1 and Parkin. At the mechanistic level, the destabilization of HIF-1 alpha and the up-regulated expression of PGC-1 a and SIRT3 synergistically contributed to the protective effects of hypoxic preconditioning combined with curcumin in BMSCs. The proteasome inhibitor MG132 stabilized HIF-1 alpha expression, but not PGC-1 alpha or SIRT3, and dramatically restrained BMSCs survival under hypoxia combined with curcumin condition. MG132 also increased mitochondrial superoxide and intracellular hydrogen peroxide (H2O2) production and caspase-3 activation in hypoxia combined with curcumin-treated BMSCs. Furthermore, knockdown of SIRT3 and PGC-1 alpha by RNAi both led to caspase-3 activation in BMSCs after hypoxia and curcumin treatment. Notably, SIRT3 RNAi suppressed OXPHOS activity, while PGC-1 alpha RNAi triggered mitochondrial superoxide and intracellular H2O2 production in hypoxia combined with curcumin-treated BMSCs. Finally, we showed that hypoxia combined with curcumin-treated BMSCs accelerated the cutaneous wound healing process in a mice wound model. Overall, this study suggests that hypoxic preconditioning combined with curcumin could serve as an attractive strategy for facilitating BMSCs-mediated tissue repair, and further sheds new light on the rich repertoire of PGC-1 alpha/SIRT3/HIF-1 alpha signaling involved in the regulation of mitochondrial quality and function for cellular adaption to hypoxia.