FISETIN ENHANCES PPAR GAMMA EXPRESSION TO PREVENT VASCULAR SMOOTH MUSCLE CELL SENESCENCE VIA MTORC2-AKT-FOXO3A SIGNALING PATHWAY

Abstract

Objective: Cellular senescence is caused by diverse stimuli and is contributed to cardiovascular diseases such as atherosclerosis, coronary heart disease, and hypertension. Several studies have indicated that PPAR gamma is mainly a key mediator in lipid metabolism and adipocyte differentiation. In addition, PPAR gamma has a protective effect in vascular biology and regulates the inflammation and reactive oxygen species (ROS). Nevertheless, the anti-aging mechanism of PPAR gamma has not been elucidated in vascular smooth muscle cell (VSMC). Although mTORC2 is involved in the cellular senescence and autophagy, there are significantly fewer studies than mTORC1. Therefore, we focused on mTORC2 function and then aimed to investigate the correlation between PPAR gamma and mTORC2, and to identify the anti-aging mechanism in VSMC. Design and method: To generate the oxidative stress-induced VSMC senescence, we treated with hydrogen peroxide (H2O2). The anti-aging effect and underlying mechanism of fisetin were evaluated by Western blot analysis, senescence-associated beta-galactosidase (SA-beta-gal) staining, flow cytometry, immunofluorescence analysis, and immunoprecipitation analysis. Results: We found hydrogen peroxide (H2O2) induced not only PPAR gamma translocation from nuclear to cytosol but also mTORC2 activation with VSMC senescence. We determined mTORC2 activation contributed to the senescence by suppressing FoxO3a-autophagy signaling pathway. Furthermore, the double knockdown of mTORC1 and mTORC2 decreased the cellular senescence and increased the autophagy activation more than single knockdown. However, fisetin acted as a PPAR gamma activator, leading to the inhibition of VSMC senescence through mTORC2-Akt (Ser473)-FoxO3a signaling pathway which is related to autophagy. Conclusions: These results demonstrate PPAR gamma is associated with cellular senescence and fisetin has anti-aging effect via PPAR gamma activation and mTORC2 inhibition. Moreover, mTORC2 signaling pathway could regulate autophagy, which suggests mTORC2 is considered a significant target for preventing cellular senescence and aging-related disease.