Pak2 Regulation of Nrf2 Serves as a Novel Signaling Nexus Linking ER Stress Response and Oxidative Stress in the Heart.

Norbert Frey,Pablo Binder,Min Zi,Elizabeth J Cartwright,Jonathan Chernoff,Oliver J Müller,Susanne S Hille,Lucy Collins,Foteini Christou,Kaomei Guan,Xiaojing Luo,Binh Nguyen,Wei Liu,Xin Wang

doi:10.3389/fcvm.2022.851419

Abstract

Endoplasmic Reticulum (ER) stress and oxidative stress have been highly implicated in the pathogenesis of cardiac hypertrophy and heart failure (HF). However, the mechanisms involved in the interplay between these processes in the heart are not fully understood. The present study sought to determine a causative link between Pak2-dependent UPR activation and oxidative stress via Nrf2 regulation under pathological ER stress. We report that sustained ER stress and Pak2 deletion in cardiomyocytes enhance Nrf2 expression. Conversely, AAV9 mediated Pak2 delivery in the heart leads to a significant decrease in Nrf2 levels. Pak2 overexpression enhances the XBP1-Hrd1 UPR axis and ameliorates tunicamycin induced cardiac apoptosis and dysfunction in mice. We found that Pak2 deletion and altered proteostasis render Nrf2 detrimental by switching from its antioxidant role to renin-angiotensin aldosterone system (RAAS) gene regulator. Mechanistically, Pak2 mediated Hrd1 expression targets Nrf2 for ubiquitination and degradation thus preventing its aberrant activation. Moreover, we find a significant increase in Nrf2 with a decrease in Pak2 in human myocardium of dilated heart disease. Using human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we find that Pak2 is able to ameliorate Nrf2 induced RAAS activation under ER stress. These findings demonstrate that Pak2 is a novel Nrf2 regulator in the stressed heart. Activation of XBP1-Hrd1 is attributed to prevent ER stress-induced Nrf2 RAAS component upregulation. This mechanism explains the functional dichotomy of Nrf2 in the stressed heart. Thus, Pak2 regulation of Nrf2 homeostasis may present as a potential therapeutic route to alleviate detrimental ER stress and heart failure.

Highlights

Heart failure (HF) is a chronic condition where the heart is unable to pump sufficient blood and is commonly the final stage of cardiovascular disease [1]
Similar to what we observed with transverse aortic constriction (TAC), p21 activated kinase 2 (Pak2) cardiac depletion in mice subjected to endoplasmic reticulum (ER) stress show increased reactive oxygen species (ROS) (Figure 1C), imbalance of GSH/GSSG ratio (Figure 1D; Supplementary Figures 2C,D) and increased cell death (Figure 1E)
We show that Pak2 mediated cardiac protection in response to ER stress and oxidative stress can be attributed to enhancing unfolded protein response (UPR) and alleviation of aberrant Nuclear factor erythroid 2–related factor 2 (Nrf2) activity

Summary

Introduction

Heart failure (HF) is a chronic condition where the heart is unable to pump sufficient blood and is commonly the final stage of cardiovascular disease [1]. Excessive protein synthesis leading to accumulation of misfolded or damaged proteins results in proteotoxic stress and reactive oxygen species (ROS) generation altering cardiomyocyte function [4]. Accumulation of misfolded proteins in the ER, triggers GRP78 dissociation from these sensors resulting in their activation, termed the unfolded protein response (UPR) [6]. UPR activation increases protein folding efficiency and enhances the clearance of defective proteins by induction of the Endoplasmic-reticulum-associated protein degradation (ERAD) via the cytosolic ubiquitin-proteasome system (UPS) [7]. Under basal conditions Nrf localizes in the cytosol and its activity is regulated via ubiquitination by the Cul3/Rbx1-based E3-ubiquitin ligase complex for its proteasomal degradation, facilitated by Kelch-like ECH-associated protein 1 (Keap1) [15]. Nrf dissociates from Keap, and translocates into the nucleus, activating antioxidant response element (ARE)driven gene transcription [16].

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