Abstract
Saturated free fatty acids (FFAs) elevate in metabolic symptom leading to endothelial dysfunction. Cystic fibrosis transmembrane regulator (CFTR) functionally expresses in endothelial cells. The role of CFTR in FFA-induced endothelial dysfunction remains unclear. This study is aimed at exploring the effects of CFTR on palmitate- (PA-) induced endothelial dysfunction and its underlying mechanisms. We found that PA-induced endothelial dysfunction is characterized by a decrease of cell viability, reduction of NO generation and mitochondrial membrane potential, impairment of the tube formation, but an increase of ROS generation and cell apoptosis. Simultaneously, PA decreased CFTR protein expression. CFTR agonist Forskolin upregulated CFTR protein expression and protected against PA-induced endothelial dysfunction, while CFTR knockdown exacerbated endothelial dysfunction induced by PA and blunted the protective effects of Forskolin. In addition, PA impaired autophagic flux, and autophagic flux inhibitors aggravated PA-induced endothelial apoptosis. CFTR upregulation significantly restored autophagic flux in PA-insulted endothelial cells, which was involved in increasing the protein expression of Atg16L, Atg12-Atg5 complex, cathepsin B, and cathepsin D. In contrast, CFTR knockdown significantly inhibited the effects of Forskolin on autophagic flux and the expression of the autophagy-regulated proteins. Our findings illustrate that CFTR upregulation protects against PA-induced endothelial dysfunction by improving autophagic flux and underlying mechanisms are involved in enhancing autophagic signaling mediated by the Atg16L-Atg12-Atg5 complex, cathepsin B, and cathepsin D. CFTR might serve as a novel drug target for endothelial protection in cardiovascular diseases with a characteristic of elevation of FFAs.
Highlights
Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide
We found that (1) Palmitic acid (PA) significantly caused a significant decrease of Cystic fibrosis transmembrane regulator (CFTR) expression in endothelial cells; (2) Forskolin significantly restored CFTR protein expression and inhibited PA-induced decrease of cellular viability and apoptosis in endothelial cells by inhibiting the mitochondriamediated apoptotic pathway; (3) CFTR upregulation by Forskolin restored the balance between reactive oxygen species (ROS) and nitric oxide (NO) generation and increased tube formation in PA-insulted endothelial cells; (4) CFTR upregulation significantly improved autophagic flux in endothelial cells impaired by PA, which was involved in the restoration of the Atg12-Atg5 complex, Atg16L protein, Cathepsin B (CTSB), and cathepsin D (CTSD) protein expression; and (5) CFTR knockdown aggravated endothelial cell injury induced by PA and suppressed the protective effects of Forskolin against endothelial injury
We found that PA did not affect the beclin-1 expression but significantly increased the ratio of LC3-II/LC3-I and SQSTM1/p62 protein expression, indicating that PAinduced abnormal autophagy does not depend on beclin-1 signaling and PA stimulation causes a blockage of autophagic flux in endothelial cells
Summary
Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide. Saturated free fatty acids (FFAs) significantly increase in metabolic syndrome and obesity, especially in type 2 diabetes, attributing to the development of CVDs [1]. The elevation of FFAs causes endothelial dysfunction, which is an early event in the progression of CVDs [2]. Endothelium as the first barrier of vessels accounts for the regulation of vasodilation, contraction, and inflammatory response and thereby maintains normal circulatory function [3]. Elevated FFAs impair endothelium function, characterized by increased apoptosis, excessive reactive oxygen species (ROS) generation, and decreased nitric oxide (NO) production. The mechanisms underlying FFA-induced endothelial dysfunction were shown to be involved in inhibition of vascular insulin signaling and eNOS activity, excessive generation of ROS derived from NADPH oxidase and mitochondria, and activation of the NF-κB signaling pathway which promotes inflammatory responses [4], whereas it remains largely unknown, and the interventive drug targets still need further research
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