Downregulation of Nrf2 promotes autophagy-dependent osteoblastic differentiation of adipose-derived mesenchymal stem cells.

Adipose derived stem cells (ADSCs) are an important source of stem cells for tissue repair and regeneration; therefore, understanding the mechanisms that regulate stem cell differentiation into a specific lineage is critical. The NF-E2-related factor 2 (Nrf2) pathway and autophagy promote cell survival in response to oxidative stress. However, the roles of Nrf2 and autophagy in bone metabolism under oxidative stress are controversial. Here, we explored the involvement of Nrf2 signaling and autophagy on the differentiation of ADSCs under conditions of oxidative stress. Exposure of ADSCs to H2 O2 promoted reactive oxygen species (ROS) accumulation concomitant with the reduction of cell viability, upregulation of Nrf2, the induction of apoptosis and autophagy, and the promotion of osteogenesis. Suppression of autophagic activity at particular stages resulted in the activation of the Nrf2 pathway, whereas osteoblastic differentiation of ADSCs was inhibited upon ROS stimulation. Silencing of Nrf2 promoted autophagy and osteoblastic differentiation upon ROS stimulation in vitro, and this effect was confirmed in vivo in a mouse model, in which bone formation was enhanced in mice receiving Nrf2-knockdown ADSCs. Taken together, these findings indicate that a negative interaction between the Nrf2 pathway and autophagy may modulate oxidative stress-induced ADSC osteogenesis, and suggest that Nrf2 is a potential target to regulate the differentiation of ADSCs into a specific lineage.