Regulation of cardiac autophagy in response to lipid overload

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Publication Type dissertation
School or College School of Medicine
Department Biochemistry
Author Jaishy, Bharat Prasad
Title Regulation of cardiac autophagy in response to lipid overload
Date 2013-08
Description Obesity is an independent risk factor for several cardiac pathologies. Sustained exposure to nutrient overload in obesity overwhelms cellular homeostatic apparatus, leading to metabolic disorders and organelle dysfunction. The integrity of homeostatic machinery is crucial for the heart to meet its energy need and for cardiomyocytes to survive. Recently, autophagy has emerged as a major catabolic process in maintaining energy and organelle homeostasis. Growing evidence suggest a role for autophagy in obesity related cardiac pathologies. Yet, the regulation of cardiac autophagy in obesity is unclear. In this study, we explored mechanisms regulating cardiac autophagy in an invivo mouse model of diet-induced obesity and an invitro cell culture model of lipid overload. 12 weeks of high-fat diet (HFD) (45% kcal fat) significantly increased the autophagy marker protein LC3-II and autophagosome number in the murine heart independently of canonical upstream signaling through mTORC1 and AMPK. Interestingly, high-fat fed mice displayed a defective autophagosome turnover that may have led to autophagosome accumulation. Alteration in Beclin1 expression had no effect on HFD-induced autophagy, ruling out a major contribution of autophagy initiation pathways in this process. In vitro, cultured H9C2 cardiomyocytes displayed a biphasic autophagic response to palmitate. To explore the mechanism of early autophagic response to lipid overload, we performed most experiments after 4 h of treatment when features of ER stress and cell death were absent. Similar to HFD, palmitate increased autophagosome accumulation primarily via an impairment in autophagosome turnover. Oleate alone had no effect on autophagy but cotreatment normalized the palmitate-induced autophagosome accumulation. Moreover, palmitate treatment led to a massive accumulation of superoxide which correlated with impaired lysosomal acidification and pH-dependent lysosomal enzyme activity. Using specific inhibitors and siRNA mediated gene silencing, we identified Nox2 as the major source of superoxide production. The activation of Nox2 was dependent on the palmitate-induced activation of classical PKCs. Together, our study has identified a novel mechanism wherein palmitate-induced activation of PKC-Nox2 pathway led to impaired lysosomal enzyme activity and diminished autophagic turnover in cardiomyocytes. The Nox2-mediated inhibition of autophagic flux might contribute to other known pathological roles of Nox2-mediated oxidative stress in obesity.
Type Text
Publisher University of Utah
Subject Autophagy; Heart; High-fat feeding; NADPH oxidase; Obesity; Oxidative stress
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Bharat Prasad Jaishy 2013
Format Medium application/pdf
Format Extent 3,324,091 bytes
Identifier etd3/id/2540
ARK ark:/87278/s6g47zgr
Setname ir_etd
Date Created 2013-11-22
Date Modified 2021-05-06
ID 196116
Reference URL https://collections.lib.utah.edu/ark:/87278/s6g47zgr