In Steatotic Cells, ATP-Citrate Lyase mRNA Is Efficiently Translated through a Cap-Independent Mechanism, Contributing to the Stimulation of De Novo Lipogenesis

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease in which excessive amount of lipids is accumulated as droplets in hepatocytes. Recently, cumulative evidences suggested that a sustained de novo lipogenesis can play an important role in NAFLD. Dysregulated expression of lipogenic genes, including ATP-citrate lyase (ACLY), has been found in liver diseases associated with lipid accumulation. ACLY is a ubiquitous cytosolic enzyme positioned at the intersection of nutrients catabolism and cholesterol and fatty acid biosyntheses. In the present study, the molecular mechanism of ACLY expression in a cell model of steatosis has been reported. We identified an internal ribosome entry site (IRES) in the 5 untranslated region of the ACLY mRNA, that can support an efficient mRNA translation through a Cap-independent mechanism. In steatotic HepG2 cells, ACLY expression was up-regulated through IRES-mediated translation. Since it has been demonstrated that lipid accumulation in cells induces endoplasmic reticulum (ER) stress, the involvement of this cellular pathway in the translational regulation of ACLY has been also evaluated. Our results showed that ACLY expression was increased in ER-stressed cells, through IRES-mediated translation of ACLY mRNA. A potential role of the Cap-independent translation of ACLY in NAFLD has been discussed. Int. J. Mol. Sci. 2020, 21, 1206 48 h of treatment ( Figure 1B). In agreement with previous results [9], treatment with FFAs caused an increment of SREBP-1 mRNA abundance ( Figure 1A). The content of precursor (pSREBP-1) and active nuclear (nSREBP-1) of SREBP-1 protein increased in FFAs-treated cells with respect to control ( Figure 1B). Int. J. Mol. Sci. 2020, 21, 1206 Then ACLY levels showed a constant increase, becoming about 3.5-fold greater than the control after 48 h of treatment ( Figure 1B). In agreement with previous results [9], treatment with FFAs caused an increment of SREBP-1 mRNA abundance ( Figure 1A). The content of precursor (pSREBP-1) and active nuclear (nSREBP-1) of SREBP-1 protein increased in FFAs-treated cells with respect to control ( Figure 1B).

Hepatocyte Injury and Hepatic Stem Cell Niche in the Progression of Non-Alcoholic Steatohepatitis

“…NAFLD patients are characterized by an increased load of free fatty acids (FFAs) in the liver, which can be due both to increased lipolysis from adipose tissue but also to de novo lipogenesis in hepatocytes [24][25][26][27][28][29][30]. Insulin resistance has a prominent role in these processes by favoring an increased lipolytic response to the meal, and by inducing the expression of lipogenic pathways in the liver [24,25,27,31,32]. In the liver, FFAs are metabolized by beta-oxidation in mitochondria, or esterified as triglycerides (TGs), and either secreted within very-low-density lipoproteins (VLDL) or stored in lipid droplets leading to hepatic steatosis [25].…”

ATP citrate lyase inhibitor Bempedoic Acid alleviate long term HFD induced NASH through improvement in glycemic control, reduction of hepatic triglycerides & total cholesterol, modulation of inflammatory & fibrotic genes and improvement in NAS score

“…Insulin resistance is known to lead to an abnormal response in liver wherein elevated blood insulin levels don't efficiently reduce gluconeogenesis but instead activates hepatic De Novo Lipogenesis. In insulin resistant liver, activated De Novo Lipogenesis together with increased influx of fatty acids from adipose tissue lipolysis leads to triglycerides and lipotoxic metabolites accumulation ( Siculella et al., 2020 ). Long term dietary cholesterol is known to cause profound liver damage, evident by significant accumulation of both hepatic TG and cholesterol, marked decrease in liver density, accompanied by increased plasma levels of ALT and AST, indicating impaired liver function ( Jensen et al., 2018 ).…”

Evidence for a Negative Correlation between Human Reactive Enamine-Imine Intermediate Deaminase A (RIDA) Activity and Cell Proliferation Rate: Role of Lysine Succinylation of RIDA

“…RNA extraction and reverse transcription were carried out as previously reported [ 36 ]. Quantitative gene expression analysis was carried out on CFX Connect™ Real-Time PCR Detection System (Bio-Rad Laboratories, Segrate, Italy), using SYBR ® Select Master Mix for CFX (Life Technologies) and 18S rRNA for normalization [ 37 ]. The primers used for real-time PCR analysis were as follows hRIDAfor (5′-GGAGGGGTAGCAGAAGAAG-3′); hRIDArev (5′-TGAAGTCATTTATGTCAGCCAG-3′); hSIRT5for (5′-GTCCACACGAAACCAGATTTGCC-3′); hSIRT5rev (5′-TCCTCTGAAGGTCGGAACACCA-3′).…”