PGC-1 alpha inhibits the NLRP3 inflammasome via preserving mitochondrial viability to protect kidney fibrosis

Abstract

The NLRP3 inflammasome is activated by mitochondrial damage and contributes to kidney fibrosis. However, it is unknown whether PGC-1 alpha, a key mitochondrial biogenesis regulator, modulates NLRP3 inflammasome in kidney injury. Primary renal tubular epithelial cells (RTECs) were isolated from C57BL/6 mice. The NLRP3 inflammasome, mitochondrial dynamics and morphology, oxidative stress, and cell injury markers were examined in RTECs treated by TGF-beta 1 with or without Ppargc1a plasmid, PGC-1 alpha activator (metformin), and siPGC-1 alpha. In vivo, adenine-fed and unilateral ureteral obstruction (UUO) mice were treated with metformin. In vitro, TGF-beta 1 treatment to RTECs suppressed the expressions of PGC-1 alpha and mitochondrial dynamic-related genes. The NLRP3 inflammasome was also activated and the expression of fibrotic and cell injury markers was increased. PGC-1 alpha induction with the plasmid and metformin improved mitochondrial dynamics and morphology and attenuated the NLRP3 inflammasome and cell injury. The opposite changes were observed by siPGC-1 alpha. The oxidative stress levels, which are inducers of the NLRP3 inflammasome, were increased and the expression of TNFAIP3, a negative regulator of NLRP3 inflammasome regulated by PGC-1 alpha, was decreased by TGF-beta 1 and siPGC-1 alpha. However, PGC-1 alpha restoration reversed these alterations. In vivo, adenine-fed and UUO mice models showed suppression of PGC-1 alpha and TNFAIP3 and dysregulated mitochondrial dynamics. Moreover, the activation of oxidative stress and NLRP3 inflammasome, and kidney fibrosis were increased in these mice. However, these changes were significantly reversed by metformin. This study demonstrated that kidney injury was ameliorated by PGC-1 alpha-induced inactivation of the NLRP3 inflammasome via modulation of mitochondrial viability and dynamics.