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) signalling 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 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 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 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 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.