344-OR: Post-translational Modification of SHDA Regulating Macrophage Polarization and Inflammation in Obesity

Abstract

The succinate dehydrogenase enzyme (SDH) catalyzes the oxidation of succinate into fumarate in the tricarboxylic acid cycle. Among the four subunits, SDHA and SDHB carry the catalytic activity. Mounting evidence implicates the link between the catalytic subunit SDHA expression and mitochondrial energy metabolism. However, the molecular mechanisms regulating SDH subunits stabilization in macrophages remain largely unknown. Here, we showed that AMPK, an energy sensor, could be a key regulator of SDHA ubiquitination through directly binding to sentrin-specific protease in adipose tissue macrophages, thus contributing to obesity-induced inflammation. Our study identified that SDHA expression was significantly downregulated in AMPKα siRNA RAW264.7 cells. Moreover, MG132 could significantly rescue AMPKα knockdown-induced SDHA degradation in cells, indicating that AMPK regulates SDHA stabilization via proteasomal degradation. However, AMPK protein interaction analyses by yeast two-hybrid showed that SDHA is not AMPK downstream target. Instead sentrin-specific protease was identified as a novel, putative AMPK substrate. To further clarify the potential interaction between AMPK, SDHA, and sentrin-specific protease, Co-IP experiment was included, and results indicated that AMPK directly binds with sentrin-specific protease instead of SDHA. As a desumoylating enzyme, SENP catalyzes hydrolysis peptide bond of SUMO. How the SUMOylation of SDHA impacts its ubiquitination still needs more investigations. In our scenario, we identified a new regulatory mechanism of SDHA stabilization, AMPKα-induced SUMOylation, that partially impacts the ubiquitination level of SDHA in activated macrophages. AMPKα-induced SUMOylation level change of SDHA is directly involved in the regulation of macrophage polarization, which may contribute to adipose inflammation. Disclosure R.Wu: None. H.Jiang: None.