MEHP induces pyroptosis and autophagy alternation by cathepsin B activation in INS-1 cells

Mono-(2-ethylhexyl) phthalate (MEHP) is a primary metabolite of di-(2-ethyl hexyl) phthalate (DEHP) in the organism, which is a major component of plasticizers used worldwide. Exposure to DEHP causes pancreatic beta-cell (INS-1 cells) dysfunction, which is associated with insulin resistance and type 2 diabetes. The present study shows that MEHP decreases the cell viability of INS-1 cells in a concentration-dependent manner and induces pyroptosis at 400 μM. Furthermore, the 400 μM MEHP causes increased lysosomal membrane permeability and cathepsin B (CTSB) release, resulting in NLRP3 activation and pyroptosis. Additionally, low concentration of MEHP (50–200 μM) induces upregulation of autophagy, while 400 μM MEHP reduces autophagy level in INS-1 cells via altering mTORC1 phosphorylation. Surprisingly, CTSB contributes to mTORC1 activation in INS-1 cells treated with 400 μM MEHP. Furthermore, autophagy can alleviate inflammatory response by reducing CTSB activation in MEHP-treated INS-1 cells. These results indicate that exposure to MEHP induces pyroptosis and upregulates autophagy levels in a CTSB-dependent manner, and autophagy plays an essential role in pyroptosis onset in INS-1 cells. Our findings provide a new perspective of the connection between CTSB and autophagy. Graphical abstract