Lipid-induced NOX2 activation inhibits autophagic flux by impairing lysosomal enzyme activity

Bharat Jaishy,Quanjiang Zhang,Heaseung S Chung,Christian Riehle,Jamie Soto,Stephen Jenkins,Patrick Abel,L.Ashley Cowart,Jennifer E Van Eyk,E.Dale Abel

doi:10.1194/jlr.m055152

Abstract

Autophagy is a catabolic process involved in maintaining energy and organelle homeostasis. The relationship between obesity and the regulation of autophagy is cell type specific. Despite adverse consequences of obesity on cardiac structure and function, the contribution of altered cardiac autophagy in response to fatty acid overload is incompletely understood. Here, we report the suppression of autophagosome clearance and the activation of NADPH oxidase (Nox)2 in both high fat-fed murine hearts and palmitate-treated H9C2 cardiomyocytes (CMs). Defective autophagosome clearance is secondary to superoxide-dependent impairment of lysosomal acidification and enzyme activity in palmitate-treated CMs. Inhibition of Nox2 prevented superoxide overproduction, restored lysosome acidification and enzyme activity, and reduced autophagosome accumulation in palmitate-treated CMs. Palmitate-induced Nox2 activation was dependent on the activation of classical protein kinase Cs (PKCs), specifically PKCβII. These findings reveal a novel mechanism linking lipotoxicity with a PKCβ-Nox2-mediated impairment in pH-dependent lysosomal enzyme activity that diminishes autophagic turnover in CMs.

Highlights

Autophagy is a catabolic process involved in maintaining energy and organelle homeostasis
high fat diet (HFD) significantly increased (‫ف‬40%) microtubule-associated protein 1 light chain 3 ␤ II (LC3-II) levels compared with control chow (NCD) controls (Fig. 1A)
This study demonstrates that HFD increases cardiac autophagosome abundance independently of canonical autophagy initiation signaling via insulin or mechanistic target of rapamycin (mTOR)

Summary

Introduction

Autophagy is a catabolic process involved in maintaining energy and organelle homeostasis. The relationship between obesity and the regulation of autophagy is cell type specific. Palmitate-induced Nox activation was dependent on the activation of classical protein kinase Cs (PKCs), PKC␤II These findings reveal a novel mechanism linking lipotoxicity with a PKC␤-Nox2-mediated impairment in pH-dependent lysosomal enzyme activity that diminishes autophagic turnover in CMs.—Jaishy, B., Q. Lipid-induced NOX2 activation inhibits autophagic flux by impairing lysosomal enzyme activity. Studies using mouse models of increased myocardial lipid availability showed that increasing lipid accumulation directly in cardiomyocytes (CMs) was sufficient to induce lipotoxic cardiomyopathy and premature cell death independently of systemic or neurohumoral effects of obesity [3,4,5].

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