Work

6478 Loss of TSPO Inhibits Autophagy and Exacerbates Steatosis via Fatty Acid Uptake

Year: 2024

Type: article

Abstract: Disclosure: Y. Li: None. L. Chen: None. C. Sottas: None. N.D. Patel: None. M.C. Raul: None. S. Garza: None. V. Papadopoulos: None. Nonalcoholic fatty liver disease (NAFLD) is a chronic clinicopathological condition characterized by substantial lipid accumulation in hepatocytes, posing an increased risk of liver injury. Previous research suggested that the depletion of translocator protein (TSPO, 18kDa), a ubiquitously distributed high-affinity cholesterol- and drug-binding protein located in the outer mitochondrial membrane, triggers simple steatosis (SS) in hepatocytes. However, the precise role of TSPO in SS remains elusive. In this study, we investigated the impact of Tspo deletion in rats fed with an 8-week high-fat-fructose-cholesterol (GAN) diet. Feeding TSPO knockout (KO) rats with the GAN diet led to the development of insulin and glucose resistance, accompanied by elevated plasma cholesterol and hepatic triacylglycerol levels. Fatty acid synthase, responsible for de novo lipogenesis, was upregulated in the livers of these rats. Furthermore, livers from GAN diet-fed TSPO KO rats showed increased CD36 expression, a fatty acid translocase facilitating the transport of long-chain free fatty acids into cells. In vitro experiments on Huh7 cells with stably overexpressed CD36 (CD36_OE) demonstrated impaired mitochondrial membrane potential and mitochondrial function, manifested by reduced oxygen consumption rate and ATP production. Acetyl-CoA (AcCoA), a precursor for fatty acid synthesis, exhibited significant upregulation in CD36_OE compared to control in Huh7, regardless of fatty acid treatment. This pattern of elevated AcCoA was consistent with observations in the livers of TSPO KO rats fed with GAN diet. The elevated AcCoA stimulated the acetylation of the regulatory-associated protein of mTOR (Raptor), activating mTORC1 and hindering autophagy. These results were corroborated by immunoprecipitation studies conducted on liver samples from both wild-type (WT) and TSPO KO rats fed with GAN diet. Additionally, the inhibition of autophagy in response to TSPO loss in livers from rats fed with GAN diet was mediated by unc-51-like autophagy-activating kinase 1 (ULK1) phosphorylation. In summary, our study underscores that TSPO deficiency intensifies the progression of NAFLD by amplifying CD36-mediated free fatty acid uptake, compromising mitochondrial function, increasing AcCoA levels, and impairing autophagy during the initial stages of steatosis (SS). Presentation: 6/2/2024

Source: Journal of the Endocrine Society

DOI: 10.1210/jendso/bvae163.591