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 3

Ager1 is downregulated in HiAD-fed WT but not HiAD-fed RageHepKO mice.

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Ager1 is downregulated in HiAD-fed WT but not HiAD-fed RageHepKO mice. ...
(A) Expression of Ager1, the clearance receptor for AGEs, was downregulated in WT mice on a HiAD, and this was reversed by the AGEs inhibitor PM and in RageHepKO mice on a HiAD. (B) The AGER1 promoter region (–3302 bp) was analyzed using ALGGEN–PROMO. Of the predicted transcriptional activators, NRF2 had 6 binding sites with less than 10% dissimilarity (shown as position and sequence dissimilarity). To study the role of NRF2 in AGER1 regulation, the NRF2 targets Gstp1 and Hmox1 were evaluated. Gstp1 and Hmox1 expression was reduced in mice on a HiAD, and this was reversed by PM treatment and in RageHepKO mice on HiAD. (C) To address NRF2 stability, primary WT hepatocytes were treated with AGEs (or control BSA) for 24 hours. Cells were incubated with cycloheximide (0.5 μg/mL), and although initially there was an increase in NRF2, this was lost by prolonged exposure to AGEs (a representative Western blot from 3 independent experiments is shown). (D) RT-qPCR analysis revealed no significant change in Nrf2 mRNA expression in primary WT hepatocytes exposed to BSA or AGEs. Data in A and B represent the mean ± SEM. *P < 0.05 and **P < 0.01, by 1-way ANOVA with Tukey’s post hoc test. Data in D were combined from 5 replicates; bars indicate the 25th–75th percentiles, lines indicate the median, and whiskers indicate minimum and maximum values.