The Lysosomal Membrane Protein Lamp2 Alleviates Lysosomal Cell Death by Promoting Autophagic Flux in Ischemic Cardiomyocytes.

Lin Cui,Lei Yang,Qiong Zhang,Yao Huang,Dong-Xia Zhang,Jie-Zhi Jia,Xu-Pin Jiang,Yuesheng Huang,Jing-Ying Ye,Li-Ping Zhao

doi:10.3389/fcell.2020.00031

Abstract

Lysosomal membrane permeabilization (LMP) has recently been recognized as an important cell death pathway in various cell types. However, studies regarding the correlation between LMP and cardiomyocyte death are scarce. Lysosomal membrane-associated protein 2 (Lamp2) is an important component of lysosomal membranes and is involved in both autophagy and LMP. In the present study, we found that the protein content of Lamp2 gradually decreased in response to oxygen, glucose and serum deprivation (OGD) treatment in vitro. To further elucidate its role in ischemic cardiomyocytes, particularly with respect to autophagy and LMP, we infected cardiomyocytes with adenovirus carrying full-length Lamp2 to restore its protein level in cells. We found that OGD treatment resulted in the occurrence of LMP and a decline in the viability of cardiomyocytes, which were remarkably reversed by Lamp2 restoration. Exogenous expression of Lamp2 also significantly alleviated the autophagic flux blockade induced by OGD treatment by promoting the trafficking of cathepsin B (Cat B) and cathepsin D (Cat D). Through drug intervention and gene regulation to alleviate and exacerbate autophagic flux blockade respectively, we found that impaired autophagic flux in response to ischemic injury contributed to the occurrence of LMP in cardiomyocytes. In conclusion, our present data suggest that Lamp2 overexpression can improve autophagic flux blockade probably by promoting the trafficking of cathepsins and consequently conferring cardiomyocyte resistance against lysosomal cell death (LCD) that is induced by ischemic injury. These results may indicate a new therapeutic target for ischemic heart damage.

Highlights

Cardiac ischemia, characterized by inadequate supply of oxygen and nutrients, often leads to irreversible damage to the myocardium, which is manifested as contractile tissue loss and compensatory cardiac hypertrophy
We found that ischemia/hypoxia robustly reduces the protein content of lysosomal membrane-associated protein 2 (Lamp2) and that restoration of this protein significantly enhances the trafficking of lysosomal cathepsins and reverses the autophagic flux blockade induced by ischemia/hypoxia treatment, promoting the resistance to lysosomal cell death (LCD) and protecting cardiomyocytes against ischemic injury
Since cation-dependent mannose 6-phosphate receptor (CD-M6PR) and cation-independent mannose 6-phosphate receptor (Cl-M6PR) are two proteins known to be crucial for the trafficking of lysosomal hydrolases, we examined the levels of these proteins

Summary

Introduction

Cardiac ischemia, characterized by inadequate supply of oxygen and nutrients, often leads to irreversible damage to the myocardium, which is manifested as contractile tissue loss and compensatory cardiac hypertrophy. Many pathological conditions, such as coronary heart disease, and heart diseases caused by other factors, including long residence in plateau regions, severe burns, traumatic hemorrhage and organ transplantation, lead to ischemic injury (Edtinger et al, 2014; Duke et al, 2016). LCD is characterized by lysosomal membrane permeabilization (LMP) and mediated by the release of lysosomal cathepsins into the cytoplasm, which causes caspase-dependent and caspase-independent cell death (Windelborn and Lipton, 2008; Jiang et al, 2016; Clerc et al, 2018). The correlation between LMP and myocardial ischemic injury is not as well established (Tiwari et al, 2008)

Objectives

Methods

Results

Conclusion