Dual proteotoxic stress accelerates liver injury via activation of p62-Nrf2

Abstract

Protein accumulation is the hallmark of various neuronal, muscular, and other human disorders. It is also often seen in the liver as a major protein-secretory organ. For example, aggregation of mutated alpha1-antitrypsin (AAT), referred to as PiZ, is a characteristic feature of AAT deficiency, whereas retention of hepatitis B surface protein (HBs) is found in chronic hepatitis B (CHB) infection. We investigated the interaction of both proteotoxic stresses in humans and mice. Animals overexpressing both PiZ and HBs (HBs-PiZ mice) had greater liver injury, steatosis, and fibrosis. Later they exhibited higher hepatocellular carcinoma load and a more aggressive tumor subtype. Although PiZ and HBs displayed differing solubility properties and distinct distribution patterns, HBs-PiZ animals manifested retention of AAT/HBs in the degradatory pathway and a marked accumulation of the autophagy adaptor p62. Isolation of p62-containing particles revealed retained HBs/AAT and the lipophagy adapter perilipin-2. p62 build-up led to activation of the p62–Nrf2 axis and emergence of reactive oxygen species. Our results demonstrate that the simultaneous presence of two prevalent proteotoxic stresses promotes the development of liver injury due to protein retention and activation of the p62–Nrf2 axis. In humans, the PiZ variant was over-represented in CHB patients with advanced liver fibrosis (unadjusted odds ratio = 9.92 [1.15–85.39]). Current siRNA approaches targeting HBs/AAT should be considered for these individuals. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.