Hepatocyte-specific activity of TSC22D4 triggers progressive NAFLD by impairing mitochondrial function.

OBJECTIVE: Fibrotic organ responses have recently been identified as long-term complications in diabetes. Indeed, insulin resistance and aberrant hepatic lipid accumulation represent driving features of progressive non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis and non-alcoholic steatohepatitis (NASH) to fibrosis. Effective pharmacological regimens to stop progressive liver disease are still lacking to-date.

METHODS: Based on our previous discovery of transforming growth factor beta-like stimulated clone (TSC)22D4 as a key driver of insulin resistance and glucose intolerance in obesity and type 2 diabetes, we generated a TSC22D4-hepatocyte specific knockout line (TSC22D4-HepaKO) and exposed mice to control or NASH diet models. Mechanistic insights were generated by metabolic phenotyping and single-nuclei RNA sequencing.

RESULTS: Hepatic TSC22D4 expression was significantly correlated with markers of liver disease progression and fibrosis in both murine and human livers. Indeed, hepatic TSC22D4 levels were elevated in human NASH patients as well as in several murine NASH models. Specific genetic deletion of TSC22D4 in hepatocytes led to reduced liver lipid accumulation, improvements in steatosis and inflammation scores and decreased apoptosis in mice fed a lipogenic MCD diet. Single-nuclei RNA sequencing revealed a distinct TSC22D4-dependent gene signature identifying an upregulation of mitochondrial-related processes in hepatocytes upon loss of TSC22D4. An enrichment of genes involved in the TCA cycle, mitochondrial organization, and triglyceride metabolism underscored the hepatocyte-protective phenotype and overall decreased liver damage as seen in mouse models of hepatocyte-selective TSC22D4 loss-of-function.

CONCLUSIONS: Together, our data uncover a new connection between targeted depletion of TSC22D4 and intrinsic metabolic processes in progressive liver disease. Hepatocyte-specific reduction of TSC22D4 improves hepatic steatosis and promotes hepatocyte survival via mitochondrial-related mechanisms thus paving the way for targeted therapies.