TRIM6 Promotes ROS-Mediated Inflammasome Activation and Pyroptosis in Renal Tubular Epithelial Cells via Ubiquitination and Degradation of GPX3 Protein

Abstract

Background: Pyroptosis is a critical form of cell death during the development of chronic kidney disease (CKD). Tripartite motif 6 (TRIM6) is an E3-ubiquitin ligase that participates in the progression renal fibrosis (RF). The aim of this study was to investigate the roles of TRIM6 and Glutathione peroxidase 3 (GPX3) in oxidative stress-induced inflammasome activation and pyroptosis in Ang-II treated renal tubular epithelial cells. Methods: To study its role in RF, TRIM6 expression was either reduced or increased in human kidney-2 (HK2) cells using lentivirus, and Ang-II, NAC and BMS-986299 were served as reactive oxygen species (ROS) inducer, ROS scavenger and NLRP3 agonist respectively. Pyroptosis and mitochondrial ROS were measured by flow cytometry. The levels of malondialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD) were determined using commercial kits, while the levels of IL-1β, IL-18, IL-6, and tumor necrosis factor-α (TNF-α) were determined by Enzyme-Linked Immunosorbent Assay (ELISA). Co-immunoprecipitation (Co-IP) assay was used to evaluate the interaction between TRIM6 and GPX3. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot were used to measure mRNA and protein expression, respectively. Results: Treatment with Angiotensin II (Ang II) increased the protein and mRNA levels of TRIM6 in HK2 cells. Ang II also increased mitochondrial ROS production and the malondialdehyde (MDA) level, but decreased the levels of GSH and SOD. In addition, Ang II enhanced HK2 cell pyroptosis, increased the levels of IL-1β, IL-18, IL-6, and TNF-α, and promoted the expression of active IL-1β, NLRP3, caspase-1, and GSDMD-N proteins. These effects were reversed by knockdown of TRIM6 and by treatment with N-acetyl-L-cysteine (NAC), a ROS scavenger. BMS-986299, an NLRP3 agonist treatment, did not affect ROS production in HK2 cells exposed to Ang II combined with NAC, but cell pyroptosis and inflammation were aggravated. Moreover, the overexpression of TRIM6 in HK2 cells resulted in similar effects to Ang II. NAC and GPX3 overexpression in HK2 cells could reverse ROS production, inflammation, and pyroptosis induced by TRIM6 overexpression. TRIM6 overexpression decreased the GPX3 protein level by promoting its ubiquitination, without affecting the GPX3 mRNA level. Thus, TRIM6 facilitates GPX3 ubiquitination, contributing to increased ROS levels and pyroptosis in HK2 cells. Conclusions: TRIM6 increases oxidative stress and promotes the pyroptosis of HK2 cells by regulating GPX3 ubiquitination. These findings could contribute to the development of novel drugs for the treatment of RF.

Keywords

• renal fibrosis
• oxidative stress
• pyroptosis
• ubiquitination
• tripartite motif containing proteins