Palmitic acid‑induced autophagy increases reactive oxygen species via the Ca2+/PKCα/NOX4 pathway and impairs endothelial function in human umbilical vein endothelial cells

Abstract

It is well known that the lipotoxic mechanism of palmitic acid (PA), a main constituent of triglyceride, is dependent on reactive oxygen species (ROS). Recently, it has also been reported that PA is an autophagy inducer. However, the causal association and underlying mechanism of induced autophagy and ROS in PA toxicity remain unclear. The present study demonstrates for the first time that PA-induced autophagy enhances ROS generation via activating the calcium ion/protein kinase Cα/nicotinamide adenine dinucleotide phosphate oxidase 4 (Ca2+/PKCα/NOX4) pathway in human umbilical vein endothelial cells (HUVECs). It was revealed that PA treatment resulted in a significant increase in ROS generation and autophagic activity, leading to endothelial dysfunction as indicated by downregulated nitric oxide synthesis, decreased capillary-like structure formation and damaged cell repair capability. Furthermore, PA effectively activated the Ca2+/PKCα/NOX4 pathway, which is indicative of upregulated cytosolic Ca2+ levels, activated PKCα and increased NOX4 protein expression. 3-Methyladenine was then used to inhibit autophagy, which significantly reduced PA-induced ROS generation and blocked the Ca2+/PKCα/NOX4 pathway. The endothelial dysfunction caused by PA was ameliorated by downregulating ROS generation using a NOX4 inhibitor. In conclusion, PA-induced autophagy contributes to endothelial dysfunction by increasing oxidative stress via the Ca2+/PKCα/NOX4 pathway in HUVECs.

AICAR Protects Vascular Endothelial Cells from Oxidative Injury Induced by the Long-Term Palmitate Excess

“…Here, we show that high concentrations of free fatty acid palmitate dramatically reduce the viability of cultured human endothelial cells, confirming the previous observations [ 12 , 15 , 43 , 44 ]. PA does not, per se, affect the barrier capacity and insulin signaling in viable cells until they were gradually injured by oxidative stress originating from mitochondria.…”

“…Molecular mechanisms of vascular endothelial dysfunction in obesity and dyslipidemia are not fully explored, largely because of restricted access to this tissue in vivo, and the absence of appropriate cell models in vitro. Experimental models of hyperlipidemia commonly use palmitic acid as a typical FFA and HUVEC [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ], producing results compatible with other endothelial cell models [ 19 , 20 , 21 ]. They linked FFA-induced oxidative stress to increased ROS in the primary form of O 2 -superoxide anion radical, suggesting their mitochondrial origin.…”

“…The plasma concentrations of albumin-bound FFA range from 0.1 mM to 0.7 mM, subject to their diurnal fluctuations and variable composition with respect to molecular mass [ 1 ]. Vast evidence is now available that non-esterified FFA, usually typified by PA, abruptly triggers endothelial cell apoptosis in vitro [ 11 , 12 , 13 , 14 , 17 , 18 , 19 , 20 , 21 , 25 ]. HUVEC could not be maintained longer than 2 days even at low PA (or other FFA) concentrations that are compatible with their normal levels in human blood.…”

Long noncoding RNA HULC accelerates the growth of human liver cancer stem cells by upregulating CyclinD1 through miR675-PKM2 pathway via autophagy

“…(f) HULC enhances CyclinD1 to increase pRB and inhibit P21 WAF1/CIP1 via autophagy-PKM2 pathway in human liver cancer stem cells. A study shows that autophagy impairs endothelial function [44] and ubiquitination of MAP 1LC3B is associated with autophagy [45]. Interestingly, TLR2 enhances autophagy [46].…”

Dickkopf‑1/cysteine‑rich angiogenic inducer 61 axis mediates palmitic acid‑induced inflammation and apoptosis of vascular endothelial cells

“…However, little is currently known about the role of CCN1 in PA-induced endothelial cell injury. Human umbilical vein endothelial cells (HUVECs) are widely used to study the functions of endothelial cells (15)(16)(17). The present study aimed to explore the mechanism by which CCN1 exerts its effects on the inflammation and apoptosis of PA-induced HUVECs.…”