Loss of Splicing Factor SRSF3 Impairs Lipophagy through Ubiquitination and Degradation of Syntaxin17 in Hepatocytes

Lipid accumulation in hepatocytes is the distinctive characteristic of non-alcoholic fatty liver disease (NAFLD). Serine/arginine-rich splicing factor 3 (SRSF3) is highly expressed in the liver, and expression decreases in high-fat conditions. However, the role of SRSF3 in hepatic lipid metabolism needs to be clarified. Here, we showed that loss of SRSF3 was associated with lipid accumulation. We determined that SRSF3 regulated lipophagy, the process of selective degradation of lipid droplets by Autophagy. Mechanistically, loss of SRSF3 impaired the fusion of the autophagosome and lysosome by promoting the proteasomal degradation of syntaxin 17 (STX17), a key autophagosomal SNARE protein. We found that ubiquitination of STX17 was increased and up-regulation of seven in absentia homolog 1 (SIAH1) was responsible for the increased post-translational modification of STX17. Taken together, our data primarily demonstrate that loss of SRSF3 weakens the clearance of fatty acids by impairing lipophagy in the progression of NAFLD, indicating a novel potential therapeutic target for fatty liver disease treatment.

E3 ligase; NAFLD; SNARE protein; autophagic flux; lipid droplets; lipid/oxidation; liver; obesity; proteasome; triglyceride.