Oxidized low-density lipoprotein inhibits the degradation of cyclophilin A via the lysosome in vascular smooth muscle cells

Zizhuo Su; Maohuan Lin; Yinqing Su; Jiajie Li; Rongjie Lin; Maoxiong Wu; Xiaoyu Wang; Lili Huang; Yuyang Chen; Xiaorong Shu; Shumin Liang; Haifeng Zhang; Tucheng Huang; Ruqiong Nie; Jingfeng Wang; Shuanglun Xie

Oxidized low-density lipoprotein inhibits the degradation of cyclophilin A via the lysosome in vascular smooth muscle cells

Am J Transl Res. 2020 Jul 15;12(7):3964-3973. eCollection 2020.

Authors

Zizhuo Su^{1

2}, Maohuan Lin^{1

2}, Yinqing Su^{1

2}, Jiajie Li^{1

2}, Rongjie Lin^{1

2}, Maoxiong Wu^{1

2}, Xiaoyu Wang^{1

2}, Lili Huang^{1

2}, Yuyang Chen^{1

2}, Xiaorong Shu^{1

2}, Shumin Liang^{1

2}, Haifeng Zhang^{1

2}, Tucheng Huang^{1

2}, Ruqiong Nie^{1

2}, Jingfeng Wang^{1

2}, Shuanglun Xie^{1

2}

Affiliations

¹ Department of Cardiology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University Guangzhou 510120, Guangdong, China.
² Guangdong Province Key Laboratory of Arrhythmia and Electrophysiology Guangzhou 510120, Guangdong, China.

PMID: 32774749
PMCID: PMC7407676

Abstract

Background: Cyclophilin A (CyPA) plays an important role in the progression of atherosclerosis. Additionally, it has been reported that lysosomal function is markedly impaired in atherosclerosis induced by oxidized low-density lipoprotein (ox-LDL). As the CyPA degradation pathway remains to be elucidated, we aimed to uncover the role of lysosomes and ox-LDL in the degradation of CyPA.

Methods: We exploited RNA interference (RNAi) in combination with either the lysosomal inhibitor chloroquine (CQ) or the proteasomal inhibitor MG-132 to examine CyPA turnover. We also investigated the role of ox-LDL in lysosomal function and the CyPA degradation pathway and determined whether CyPA interacts with the selective autophagy adaptor p62.

Results: CQ markedly reversed the CyPA downregulation induced by RNAi and increased intracellular levels of LC3 and p62. MG-132 significantly suppressed polyubiquitinated protein degradation but did not inhibit RNAi-induced CyPA downregulation. Additionally, neither CQ nor MG-132 influenced the gene-silencing efficiency of CyPA siRNA. Moreover, ox-LDL induced cytosolic accumulation of p62 was inconsistent with increased expression of LC3-II. Meanwhile, ox-LDL inhibited RNAi-induced downregulation of CyPA. Immunofluorescence indicated colocalization of endogenous CyPA with ubiquitin and with p62 in response to CQ treatment, and co-immunoprecipitation analysis confirmed interaction between CyPA and p62.

Conclusion: CyPA is degraded by a lysosome-dependent pathway that may involve p62-mediated selective autophagy. Furthermore, ox-LDL modulates the degradation of CyPA via its inhibitory role in lysosomes, contributing to increased expression of CyPA in atherosclerotic plaques.

Keywords: Oxidized low-density lipoprotein; RNA interference; atherosclerotic plaques; cycloheximide; cyclophilin A; lysosome.