Increased Hepatic ATG7 mRNA and ATG7 Protein Expression in Nonalcoholic Steatohepatitis Associated with Obesity

Abstract

The autophagy gene ATG7 has been shown to be essential for the induction of autophagy, a process that used to be suppressed in nonalcoholic fatty liver disease (NAFLD). However, the specific role of ATG7 in NAFLD remains unclear. The aim of this study was to analyze hepatic ATG7 mRNA and ATG7 protein expression regarding obesity-associated NAFLD. Patients included women classified into normal weight (NW, n = 6) and morbid obesity (MO, n = 72). The second group was subclassified into normal liver (NL, n = 11), simple steatosis (SS, n= 29), and nonalcoholic steatohepatitis (NASH, n = 32). mRNA expression was analyzed by RT-qPCR and protein expression was evaluated by Western blotting. Our results showed that NASH patients presented higher ATG7 mRNA and ATG7 protein levels. ATG7 mRNA expression was increased in NASH compared with SS, while ATG7 protein abundance was enhanced in NASH compared with NL. ATG7 mRNA correlated negatively with the expression of some hepatic lipid metabolism-related genes and positively with endocannabinoid receptors, adiponectin hepatic expression, and omentin levels. These results suggest that ATG7-mediated autophagy may play an important role in the pathogenesis of NAFLD, especially in NASH, perhaps playing a possible protective role. However, this is a preliminary study that needs to be further studied.

Keywords: ATG7; NAFLD; autophagy; lipid metabolism; nonalcoholic steatohepatitis.

Figure 1

Role of ATG7 in autophagy process and in the context of metabolic-associated fatty liver (NAFLD) progression. ATG, autophagy-related gene protein.

Figure 2

Differential relative ATG7 mRNA (A) and ATG7 protein (B) abundance in liver samples between women with NW and MO. mRNA expression analysis: NW (n = 6) and MO (n = 72); and protein expression analysis: NW (n = 5) and MO (n = 16). NW, normal weight; MO, morbid obesity; ATG7/ATG7, autophagy-related 7 gene/protein; A.U, arbitrary units; D.U, densitometry units. Differences between groups were calculated using the Mann–Whitney test and p < 0.05 was considered statistically significant.

Figure 3

Differential relative ATG7 mRNA (A) and ATG7 protein (B) abundance in hepatic tissue between women classified according to the presence or the absence of NAFLD. Differential relative ATG7 mRNA (C) and ATG7 protein (D) abundance between women classified according to the presence or the absence of NASH. mRNA expression analysis: non-NAFLD (n = 17), NAFLD (n = 61), non-NASH (n = 46), and NASH (n = 32); and protein expression analysis: non-NAFLD (n = 10), NAFLD (n = 11), non-NASH (n = 15), and NASH (n = 6). ATG7/ATG7, autophagy-related 7 gene/protein; NAFLD, metabolic associated fatty liver disease; NASH, nonalcoholic steatohepatitis; A.U arbitrary units; D.U, densitometry units. Differences between groups were calculated using the Mann–Whitney test and p < 0.05 was considered statistically significant.

Figure 4

Differential relative ATG7 mRNA (A) and ATG7 protein (B) abundance in hepatic tissue between women with NW and MO subclassified as NL, SS, and NASH. mRNA expression analysis: NW (n = 6), NL (n = 11), SS (n = 29), and NASH (n = 32); and protein expression analysis: NW (n = 5), NL (n = 5), SS (n = 5), and NASH (n = 6). NW, normal weight; MO, morbid obesity; ATG7/ATG7, autophagy-related 7 gene/protein; SS, simple steatosis; NASH, nonalcoholic steatohepatitis; A.U, arbitrary units; D.U, densitometry units. Differences between groups were calculated using the Mann–Whitney test and p < 0.05 was considered statistically significant.

Figure 5

Significant correlations between ATG7 mRNA hepatic expression and (A) CPT1a, (B) LXRα, (C) RBP4, (D) CB1, (E) CB2, and (F) adiponectin hepatic expression using Spearman’s (rho) correlation test. CPT1a, carnitine palmitoyl transferase deficiency-type 1; LXRα, liver X receptor alpha; RBP4, retinol transporter protein type 4; CB, cannabinoids receptors; A.U, arbitrary units. p < 0.05 was considered statistically significant.