Epigenetic regulation of thyroid hormone action in human metabolic dysfunction-associated steatohepatitis

Objective: Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by inflammation, fibrosis, and accumulation of fatty acids in the liver. MASH disease progression has been associated with reduced thyroid hormone (TH) signaling in the liver, including reduced expression of deiodinase type I (DIO1) and TH receptor beta (THRB). However, the underlying mechanisms mediating these effects remain elusive. Here, we hypothesized that epigenetic mechanisms may be involved in modulating hepatic TH action. Methods: Liver samples from patients with and without MASH were analyzed by qRT-PCR and correlated with clinical parameters. Luciferase reporter assays and overexpression of miRNA in HepG2 cells were used to validate the functional binding of miRNA to predicted targets. DNA methylation was analyzed by bisulfite pyrosequencing. Results: miR-34a-5p was upregulated in MASH patients and correlated positively with the clinical parameters of MASH. Using in silico and in vitro analysis, we demonstrate that miR-34a-5p is capable of targeting several modulators of local hepatic TH action, as evidenced by the functional binding of miR-34a-5p to the seed sequence in the THRB and DIO1 genes. Consequently, overexpression of miR-34a-5p in HepG2 cells reduced the expression of THRA, THRB, DIO1, and SLC10A1, thus potentially mediating an acquired hepatic resistance to TH in MASH. As an additional regulatory mechanism, DNA methylation of THRB intron 1 was increased in MASH and negatively correlated with THRB expression. Conclusion: miR-34a-5p constitutes a possible epigenetic master regulator of hepatic TH action, which together with THRB-specific DNA methylation could explain a possible developing TH resistance in the liver during MASH progression on the molecular level.