Ubiquitin C-terminal hydrolase L1 (UCHL1) regulates post-myocardial infarction cardiac fibrosis through glucose-regulated protein of 78\xa0kDa (GRP78)

Qian Lei,Zhan Lv,Yanggan Wang,Hang Li,Zhijie Yan,Tao Yi,Gerui Li

doi:10.1038/s41598-020-67746-4

Abstract

Abnormal cardiac fibrosis indicates cardiac dysfunction and poor prognosis in myocardial infarction (MI) patients. Many studies have demonstrated that the ubiquitin proteasome system (UPS) plays a significant role in the pathogenesis of fibrosis. Ubiquitin C-terminal hydrolase L1 (UCHL1), a member of the UPS, is related to fibrosis in several heart diseases. However, whether UCHL1 regulates cardiac fibrosis following MI has yet to be determined. In the present study, we found that UCHL1 was dramatically increased in infarct hearts and TGF-β1-stimulated cardiac fibroblasts (CFs). Inhibition of UCHL1 with LDN57444 (LDN) reversed the myocardial fibrosis in post-MI heart and improved cardiac function. Treatment of LDN or UCHL1 siRNA abolished the TGF-β1-induced fibrotic response of CFs. We further identified GRP78 as an interactor of UCHL1 through screening using immunoprecipitation-mass spectrometer. We determined that UCHL1 interacted with glucose-regulated protein of 78 kDa (GRP78) and prompted GRP78 degradation via ubiquitination. Furthermore, we found that GRP78 was upregulated after UCHL1 knockdown and that the GRP78 inhibitor HA15 diminished the antifibrotic function exerted by UCHL1 knockdown in CFs stimulated with TGF-β1. This suggests that UCHL1 regulates cardiac fibrosis post MI through interactions with GRP78. This work identifies that the UCHL1-GRP78 axis is involved in cardiac fibrosis after MI.

Highlights

Myocardial infarction (MI) has been the main cause of cardiovascular diseases for centuries and remains a major issue
Our data show that ubiquitin C-terminal hydrolase L1 (UCHL1) protein levels increased in both fibrotic post-myocardial infarction (MI) hearts and TGF-β1-induced cardiac fibroblasts (CFs), suggesting that UCHL1 may be involved in the process of cardiac fibrosis following MI
Since the role of ubiquitin proteasome system (UPS) in mediating cardiac fibrosis is unknown, we sought to determine the role of UCHL1 in cardiac fibrosis following MI

Summary

Introduction

Myocardial infarction (MI) has been the main cause of cardiovascular diseases for centuries and remains a major issue. CFs are mainly stimulated by TGFβ-1 following MI and differentiate into activated myofibroblasts which express α-smooth muscle actin (α-SMA) This results in the secretion of a large amount of extracellular matrix, including fibronectin and collagen I (Col1), which is, in part, regulated by the activation of Smad2/34,7,8. We investigated the role of UCHL1 in mouse MI models and primary CFs. Of note, we found that inhibition of UCHL1 improved cardiac function and attenuated cardiac fibrosis post MI. We found that inhibition and knockdown of UCHL1 hindered the cardiac fibrotic response via upregulation of glucose-regulated protein of 78 kDa (GRP78) in CFs. The underlying mechanism of this is largely attributed to the interaction between UCHL1 and GRP78, and the subsequent degradation of GRP78 by ubiquitination. We developed a novel mechanism for maladaptive cardiac fibrosis post MI, providing insight into potential pathways to target for novel antifibrotic therapies

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