GSK-3β as a potential coordinator of anabolic and catabolic pathways in hepatitis C virus insulin resistance.

INTRODUCTION: Chronic HCV infection results in insulin resistance (IR) through interaction of pathways for glucose homeostasis, insulin signaling, and autophagy. Not known is how soon the pathways are activated, and how IR is related to the signals generated by catabolic and anabolic conditions occurring in infected cells. We have extended our studies to a cell culture system mimicking acute infection and to downstream pathways involving energy-sensor AMPK and nutrient-sensor mTOR that are active in catabolic and anabolic processes within the infected cells.

METHODS: Huh7 liver cells were infected with HCV. We performed proteomics analysis of key proteins in infected cells by western blotting and IP experiments, with or without interferon-α exposure.

RESULTS: We show that IRS-1 Ser312, Beclin-1, protein conjugate Atg12-Atg5 or GS Ser641 are upregulated early in infection by activating the same pathways utilized for persistent infection; Bcl-XL, an inhibitor of both autophagy and apoptosis, is present in a core-complex with IRS-1 Ser312 and Beclin-1 during progression of IR; AMPK level remains the same in infected cells where it is activated by phosphorylation at Thr172 concomitant with increased autophagy, a hallmark of catabolic conditions; an mTOR level that promotes anabolism is increased rather than decreased under an expanded autophagy; hypophosphorylation of translational repressor 4E-BP1 downstream of mTOR is suggestive of reduced protein synthesis; and β-catenin is upregulated but not phosphorylated suggesting indirectly our previous contention that its kinase, GSK-3β, is mostly in an inactive state.

DISCUSSION/CONCLUSION: We report that in the development of IR following chronic infection, anabolic and catabolic pathways are activated early, and the metabolic interaction occurs possibly in a core-complex with IRS-1 Ser312, Beclin-1 and autophagy inhibitor BcL-XL. Induction of autophagy is usually controlled by a two-edged mechanism acting in opposition under anabolic and catabolic conditions by AMPK/mTOR/4E-BP1 pathways with GSK-3β mediated feed-back loops. However, we observed that an up-regulation of mTOR along with an up-regulation of AMPK caused by HCV infection is a deviation from the normal scenario described above which might be of therapeutic interest.