Inhibition of Mitofusin-2 Promotes Cardiac Fibroblast Activation via the PERK/ATF4 Pathway and Reactive Oxygen Species

Yanguo Xin,Song Lei,Jing Qu,Xiaojiao Wang,Wenchao Wu,Lixing Yuan,Xiaojing Liu

doi:10.1155/2019/3649808

Abstract

Mitofusin-2 (Mfn2) is a key outer mitochondrial membrane protein, which maintains normal mitochondrial dynamics and function. However, its role in cardiac fibroblast activation remains poorly understood. In the present study, a rat model of transverse aortic constriction (TAC) was established to observe the cardiac fibroblast activation in vivo. TGF-β1 treatment for 24 hours was used to induce cardiac fibroblast activation in vitro. As a result, the expression of Mfn2 decreased in the hypertrophic heart tissues and cardiac fibroblasts treated with TGF-β1. siMfn2 and adenovirus were applied to mediate Mfn2 gene silencing and overexpression in cardiac fibroblasts to elucidate the relationship between Mfn2 and cardiac fibroblast activation, as well as the possible underlying mechanisms. Knockdown of Mfn2 further promoted TGF-β1-induced cardiac fibroblast activation, while forced expression of Mfn2 attenuated this pathological reaction. The PERK/ATF4 pathway, one of the branches of endoplasmic reticulum (ER) stress, was identified to be involved in this process. Knockdown and overexpression of Mfn2 lead to aggravation or alleviation of the PERK/ATF4 pathway. Blocking this pathway by silencing ATF4 with siATF4 attenuated the pathological process. During the activation of cardiac fibroblasts, knockdown of Mfn2 also increased the production of reactive oxygen species (ROS), while ROS scavenger N-acetyl-l-cysteine (NAC) could attenuate the effect caused by knockdown of Mfn2. Our data suggested that inhibition of Mfn2 could promote cardiac fibroblast activation by activating the PERK/ATF4 signaling pathway and increasing the generation of ROS.

Highlights

Cardiac hypertrophy occurring in pathological conditions is an independent risk factor of cardiac morbidity and mortality
Echocardiography indicators and HE staining suggested that cardiac hypertrophy is induced by the transverse aortic constriction (TAC) model successfully in our previous papers [11, 18]
We found that followed by blockade of the protein kinase RNA-like ER kinase (PERK)/activating transcriptional factor 4 (ATF4) pathway, the activation of cardiac fibroblasts was attenuated with the evidence that protein expressions of connective tissue growth factor (CTGF), transforming growth factor β (TGF-β), and α-smooth muscle actin (α-SMA) decreased by about 20%, 30%, and 30%, respectively, comparing with those of the siRNAs for Mfn2 (siMfn2) group (Figure 4(e))

Summary

Introduction

Cardiac hypertrophy occurring in pathological conditions (such as hypertension, valvular heart diseases, myocardial infarction, and cardiomyopathy) is an independent risk factor of cardiac morbidity and mortality It is a complex cellular reprogramming process involving cardiomyocyte hypertrophy and cardiac fibroblast activation [1]. The fusion and fission events are regulated by specific GTPdependent proteins that allow a tubule reticular networking morphology via fusion of the outer mitochondrial membrane (OMM) and inner mitochondrial membrane (IMM) fusion with redistribution of matrix components [6]. All of these mitochondrial dynamic-related proteins are present in the heart and vascular system but their roles there have only begun to be elucidated

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