Mir214-3p and Hnf4a/Hnf4α reciprocally regulate Ulk1 expression and autophagy in nonalcoholic hepatic steatosis

Abstract

Macroautophagy/autophagy, a self-degradative process, regulates metabolic homeostasis in response to various stress conditions and is a therapeutic target for nonalcoholic fatty liver disease. We found that autophagic activity was inhibited as a result of a significant reduction in the expression of autophagyrelated genes such as Ulk1 in a mouse model and patients with fatty liver. This downregulation was caused by increased Mir214-3p levels and decreased Hnf4a/Hnf4α mRNA levels in hepatocytes. Mir214-3p suppressed Ulk1 expression through direct binding at a 3′ untranslated region sequence. Hnf4a directly activated transcription of Ulk1. We investigated lipid accumulation and the expression of autophagyrelated genes in the livers of mice treated with anti-Mir214-3p. Hepatic steatosis was alleviated, and Ulk1 mRNA levels were significantly increased by locked nucleic acid-mediated Mir214-3p silencing. Additionally, autophagosome formation and MAP1LC3/LC3-II protein levels were increased, indicating an increase in autophagic activity. Interestingly, suppression of Mir214-3p did not ameliorate fatty liver under Ulk1 suppression, suggesting that reduced Mir214-3p levels mitigate hepatic steatosis through upregulation of Ulk1. These results demonstrate that inhibition of Mir214-3p expression ameliorated fatty liver disease through increased autophagic activity by increasing the expression of Ulk1. Thus, Mir214-3p is a potential therapeutic target for nonalcoholic fatty disease.

Concerted regulation of non-alcoholic fatty liver disease progression by microRNAs in apolipoprotein E-deficient mice

“…However, after 18 weeks of feeding, ULK1 expression and LC3 lipidation were decreased in the livers from ApoE -/-HFD mice, suggesting autophagy inhibition, a feature previously described in advanced stages of NAFLD (Ding et al, 2020;Lee et al, 2020;Lu et al, 2020). In this sense, Lee et al attributed this phenomenon to long-term HFD feeding (Lee et al, 2020). Likewise, similar outcomes were displayed in SIRT1 expression, another regulator of autophagy through autophagy-related (ATG) protein modulation.…”

“…In consonance to what we mentioned above, our results displayed an increased LC3 lipidation in 8-week-fed ApoE -/-HFD mice and, therefore, autophagic flux activation as observed in early stages of NAFLD. However, after 18 weeks of feeding, ULK1 expression and LC3 lipidation were decreased in the livers from ApoE -/-HFD mice, suggesting autophagy inhibition, a feature previously described in advanced stages of NAFLD (Ding et al, 2020;Lee et al, 2020;Lu et al, 2020). In this sense, Lee et al attributed this phenomenon to long-term HFD feeding (Lee et al, 2020).…”

The roles of autophagy and thyroid hormone in the pathogenesis and treatment of NAFLD

“…Furthermore, NAFLD patients had elevated let-7a and miR-34a levels with simultaneous decreases in ATG4B and Rab-8B levels [57] . Nguyen et al [58] showed that SREBP-1C-induced miR-216a expression resulted in reduced cystathionine gamma-lyase and hepatic H2S levels, sulfhydration-dependent activation of ULK1, and autophagy flux and lipid degradation. In addition, the expression of ULK1 was downregulated in a mouse model of NAFLD and patients with NAFLD [59] .…”

“…[ 58 ] showed that SREBP-1C-induced miR-216a expression resulted in reduced cystathionine gamma-lyase and hepatic H2S levels, sulfhydration-dependent activation of ULK1, and autophagy flux and lipid degradation. In addition, the expression of ULK1 was downregulated in a mouse model of NAFLD and patients with NAFLD [ 59 ] . Increased Mir214-3p and decreased Hnf4a expression led to reduced Ulk1 levels in a mouse model of NAFLD [ 59 ] .…”

“…In addition, the expression of ULK1 was downregulated in a mouse model of NAFLD and patients with NAFLD [ 59 ] . Increased Mir214-3p and decreased Hnf4a expression led to reduced Ulk1 levels in a mouse model of NAFLD [ 59 ] . Hepatic expression of Acyl-CoA oxidase 1, the enzyme that catalyzes the first step in peroxisomal β-oxidation, was upregulated by HFD feeding; increased hepatic peroxisomal β-oxidation derived acetyl-CoA, raptor acetylation, and activation of mTORC1; and led to decreased autophagy and increased hepatic triglycerides [ 60 ] .…”