Akt Isoforms in the Pathogenesis of Alcoholic Liver Disease
Authors: Reyes‐Gordillo Karina , Shah Ruchi , Lakshman Raj 
Published: June 2021

Alcoholic liver disease (ALD) represents a major public health problem with substantial morbidity and mortality. Chronic Ethanol/Binge/LPS (EBL) liver mouse model resembles a relevant “2‐hit” model of alcoholic liver disease. In this model, LPS is selected as the second hit agent because in the initial step EtOH increases gut permeability leading to generation of endotoxins that activate NFκB in Kupffer cells (KC), resulting in the production of proinflammatory cytokines; TNFα and IL1β. Moreover, in the hepatocytes, EtOH is oxidized to its toxic metabolite, acetaldehyde (ACE) that leads to the generation of reactive oxygen species and increased oxidative stress, resulting in the activation of hepatic stellate cells (HSC), which causes HSC proliferation, migration, and up regulation of the fibrogenic genes; PDGF β‐receptor, α‐SMA, extracellular matrix proteins and epigenetic repressor gene, methyl‐CpG binding protein. In contrast, adipogenic gene, PPARγ is suppressed resulting in the loss of vitamin A, and their trans‐differentiation from quiescent lipid storing cells to active myofibroblastic phenotype. Akt isoforms, the key phosphorylating kinases, seem to play vital roles in all aspects of this pathogenic process. Although Akt has been the subject of extensive investigations, very few studies have addressed the specific role/s of each isoform and it is generally assumed that the Akt isoforms play redundant and overlapping roles. This study proposes to identify what specific roles each of these isoforms of Akt plays in alcoholic liver injury utilizing both in in vitro human HSC and in vivo mouse models. Our results were as follows:

In vitro: In the EtOH/LPS and/or ACE/LPS model of the independent cultures of human HSC, KC and VL17A hepatocytes, siRNA‐directed silencing of (A) Akt2, but not Akt1, significantly suppressed cell inflammatory markers in HSC and KC; (B) Akt1 and Akt2 inhibited cell proliferation in HSC; (C) Akt2 alone inhibited cell migration in HSC; (D) Akt1 and Akt2, but not Akt3 inhibited the fibrogenic markers in hepatocytes and HSC. Moreover, although Akt isoforms show extensive sequence similarity, they are localized in different subcellular compartments in normal HSC with their distinct functions.

In vivo: EBL treatment in wild‐type C57BL/6 mice (a) stimulated all three isoforms of Akt (b) with concomitant increases in phosphorylated species of phosphoinositide‐dependent kinase‐1 and mammalian target of rapamycin complex 2, and phosphatidylinositol 3‐kinase, resulting in increases in inflammatory, proliferative, and fibrogenic genes. In addition, pharmacological blocking (c) of Akt2, but not Akt1, inhibited EBL‐induced inflammation; and (d) of Akt1 and Akt2 inhibited the fibrogenic markers.

In conclusion, each isoform of Akt has a specific regulatory function in EBL‐mediated liver injury. Akt1 and Akt2 play crucial roles in EBL‐induced HSC fibrogenesis and proliferation; (ii) only Akt2 appears to be involved in inflammation and migration; and (iii) Akt3 may not play a significant role in EBL‐induced liver injury.

Support or Funding Information

Thanks to NIH/NIAAA‐funded research

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.