p62 is linked to mitophagy in oleic acid-induced adipogenesis in human adipose-derived stromal cells

Background Obesity is closely related to the abnormal differentiation of adipocytes, which are subjected to high plasma levels of free fatty acids (FFAs). As the most abundant FFA in the bloodstream, oleic acid (OA) has the ability to induce adipogenic differentiation in human adipose-derived stromal cells (hADSCs). Recently, p62, an autophagy mediator, has been shown to play a role in obesity and adipose tissue metabolism. Therefore, the aim of this study was to investigate the roles of autophagy and mitochondrial function at different stages of OA (in combination with insulin and dexamethasone)-induced adipogenesis in hADSCs. Methods The hADSCs were incubated with OA, insulin, and dexamethasone after pretreatment with autophagy inhibitors or knockdown of p62 with shRNA. The adiposeness level was then analyzed by oil red O staining in the cells. The related proteins or mRNA levels were detected by western blot analysis or quantitative real-time polymerase chain reaction (PCR). Results Treatment with 80 μM OA (substituted for isobutylmethylxantine; IBMX) for 10 days successfully induced hADSCs to adipocytes. During OA-induced adipogenesis, autophagy was induced, with an increased LC3II/I ratio on day 3 and a decreased protein level of p62 on and after day 3. Inhibition of autophagy with 3-methyladenine (3MA) at the early stage (day 0 to day 3) of differentiation, but not at the middle or late stage, significantly decreased OA-induced adipogenesis; while knockdown of p62 with shRNA significantly promoted adipogenesis in hADSCs. Moreover, the copy number of mtDNA (the ND1 gene) and the protein level of TOM20, a mitochondrial membrane protein, were increased following OA treatment, which was related to the stability of mitochondria. Interestingly, knockdown of p62 increased the mito-LC3II/I and cyto-LC3II/I ratios by 110.1% and 73.3%, respectively. The increase in the ratio of mito-LC3II/I was higher than that of cyto-LC3II/I. Furthermore, p62 knockdown-enhanced adipogenesis in hADSCs was abolished by inhibiting mitophagy with cyclosporine A. Conclusions These results suggested that p62 plays a protective role in adipogenesis of hADSCs through regulating mitophagy.