AGER1 downregulation associates with fibrosis in nonalcoholic steatohepatitis and type 2 diabetes
Ali Dehnad, … , Mohammed Ali, Natalie J. Török
Ali Dehnad, … , Mohammed Ali, Natalie J. Török
Published July 13, 2020
Citation Information: J Clin Invest. 2020;130(8):4320-4330. https://doi.org/10.1172/JCI133051.
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AGER1 downregulation associates with fibrosis in nonalcoholic steatohepatitis and type 2 diabetes

Abstract

Type 2 diabetes is clinically associated with progressive necroinflammation and fibrosis in nonalcoholic steatohepatitis (NASH). Advanced glycation end-products (AGEs) accumulate during prolonged hyperglycemia, but the mechanistic pathways that lead to accelerated liver fibrosis have not been well defined. In this study, we show that the AGEs clearance receptor AGER1 was downregulated in patients with NASH and diabetes and in our NASH models, whereas the proinflammatory receptor RAGE was induced. These findings were associated with necroinflammatory, fibrogenic, and pro-oxidant activity via the NADPH oxidase 4. Inhibition of AGEs or RAGE deletion in hepatocytes in vivo reversed these effects. We demonstrate that dysregulation of NRF2 by neddylation of cullin 3 was linked to AGER1 downregulation and that induction of NRF2 using an adeno-associated virus–mediated approach in hepatocytes in vivo reversed AGER1 downregulation, lowered the level of AGEs, and improved proinflammatory and fibrogenic responses in mice on a high AGEs diet. In patients with NASH and diabetes or insulin resistance, low AGER1 levels were associated with hepatocyte ballooning degeneration and ductular reaction. Collectively, prolonged exposure to AGEs in the liver promotes an AGER1/RAGE imbalance and consequent redox, inflammatory, and fibrogenic activity in NASH.

Authors

Ali Dehnad, Weiguo Fan, Joy X. Jiang, Sarah R. Fish, Yuan Li, Suvarthi Das, Gergely Mozes, Kimberly A. Wong, Kristin A. Olson, Gregory W. Charville, Mohammed Ali, Natalie J. Török

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Figure 4

NRF2 activity is decreased by AGEs as a result of CUL3 neddylation.

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NRF2 activity is decreased by AGEs as a result of CUL3 neddylation. (A) ...
(A) Expression of Nae1 was increased in WT mice on a HiAD and significantly reduced in RageHepKO mice, whereas the deneddylase Den1 was reduced by a HiAD and reversed in RageHepKO mice. (B) Liver homogenates from WT or RageHepKO mice on a chow or HiAD were tested for CUL3, and immunoblotting revealed increased neddylation (Nedd) in WT mice on a HiAD, whereas RageHepKO mice were protected. (C) Time course of CUL3 neddylation by AGEs in HepG2 cells. (D) To determine whether NOX4 is involved in regulating NAE1 expression, primary hepatocytes were transduced with Ad-Nox4 or a control vector and after 48 hours were treated with 100 mg/mL AGEs or control BSA for 30 minutes. Expression of Nae1 was increased by NOX4 and exposure to AGEs. (E) The NAE1 inhibitor MLN4924 (3 μM) in hepatocytes reversed the effects of AGEs on Ager1, Gstp1, Hmox1, and Nqo1 expression. Data in A indicate the mean ± SEM; date in D were combined from 3 replicates; data in E were combined from 4–5 replicates. In D and E, bars indicate the 25th–75th percentiles, lines indicate the median, and whiskers indicate minimum and maximum values. *P < 0.05, **P < 0.01, and ***P < 0.001, by 1-way ANOVA with Tukey’s post hoc test (A, D, and E).