Homocysteine Induces Programmed Cell Death in Human Vascular Endothelial Cells through Activation of the Unfolded Protein Response

Abstract

Severe hyperhomocysteinemia is associated with endothelial cell injury that may contribute to an increased incidence of thromboembolic disease. In this study, homocysteine induced programmed cell death in human umbilical vein endothelial cells as measured by TdTmediated dUTP nick end labeling assay, DNA ladder formation, induction of caspase 3-like activity, and cleavage of procaspase 3. Homocysteine-induced cell death was specific to homocysteine, was not mediated by oxidative stress, and was mimicked by inducers of the unfolded protein response (UPR), a signal transduction pathway activated by the accumulation of unfolded proteins in the lumen of the endoplasmic reticulum. Dominant negative forms of the endoplasmic reticulum-resident protein kinases IRE1␣ and -␤, which function as signal transducers of the UPR, prevented the activation of glucose-regulated protein 78/immunoglobulin chain-binding protein and C/EBP homologous protein/growth arrest and DNA damage-inducible protein 153 in response to homocysteine. Furthermore, overexpression of the point mutants of IRE1 with defective RNase more effectively suppressed the cell death than the kinase-defective mutant. These results indicate that homocysteine induces apoptosis in human umbilical vein endothelial cells by activation of the UPR and is signaled through IRE1. The studies implicate that the UPR may cause endothelial cell injury associated with severe hyperhomocysteinemia.

Role of hyperhomocysteinemia in endothelial dysfunction and atherothrombotic disease

“…These effects in gene expression directly involve the UPR because homocysteine treatment has been shown to induce the activation of both PERK 80,81 and IRE-1. 23 Severe or prolonged ER stress elicited by homocysteine has been shown to activate several cellular functions involved in the development and progression of atherosclerosis, including dysregulation of lipid metabolism, apoptotic cell death, and inflammation. We as well as others have demonstrated recently that homocysteine-induced ER stress causes dysregulation of lipid biosynthesis in hepatocytes by activating the SREBPs, 56,82 which are ER-resident transcription factors responsible for the induction of genes in the cholesterol/triglyceride biosynthesis and uptake pathways.…”

“…23 Apoptotic cell death was dependent on IRE-1 signaling and was also induced by other ER stress agents, including tunicamycin and thapsigargin. Homocysteine-induced IRE-1 activation causes a rapid and sustained activation of JNK protein kinases, 84 a result consistent with the finding that activation of JNK by ER stress involves binding of IRE-1 to TRAF2.…”

“…Up to 40% of patients diagnosed with premature coronary artery disease, peripheral vascular disease, or recurrent venous thrombosis present with HHcy. [14][15][16][17][18][19] Recent studies have now demonstrated that homocysteine causes endothelial cell dysfunction and induces apoptotic cell death in cell types relevant to atherothrombotic disease, including endothelial cells 22,23 and smooth muscle cells. 24 Furthermore, a direct causal relationship between induction of HHcy and accelerated atherosclerosis has been reported in apolipoprotein E (apoE)-deficient mice with diet-and/or genetic-induced HHcy.…”

Hydrogen sulfide inhibits homocysteine-induced endoplasmic reticulum stress and neuronal apoptosis in rat hippocampus via upregulation of the BDNF-TrkB pathway

“…Disturbance of protein folding under various physiological or pathological conditions, such as alteration of cellular redox, deprivation of glucose, aberration of Ca 2+ regulation, and viral infections, creates the ER stress [20] . Wei et al reported that exposure to Hcy of the rat embryonic heart-derived cell line H9c2 can increase the expression of ER stress response genes, such as glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and cleaved caspase-12 [21] , suggesting that ER stress is involved in the mechanisms of Hcy-induced cellular dysfunction [8,[22][23][24][25] . Therefore, it is logical to speculate that inhibiting Hcy-induced ER stress may be a novel therapeutic strategy to prevent and ameliorate AD progression.…”

A Monoclonal Antibody against Human Homocysteine-Induced Endoplasmic Reticulum Protein (Herp): A Useful Tool for Evaluating Endoplasmic Reticulum Stress

“…The bacterial pellet was suspended in phosphate-buffered saline (PBS), centrifuged at 2,300 g for 15 min and frozen at −80°C overnight. Extraction of proteins from the pellet was done using the B-PER Bacterial Protein Extraction Reagent (Pierce, Rockford, endoplasmic reticulum (ER) stress (Zhang et al 2001). Homocysteine-induced ER stress contributes to the development of atherosclerosis in apolipoprotein E-deficient mice (Zhou et al 2004) and a high level of plasma homocysteine is one of the risk factors for atherosclerosis (Lawrence et al 2003), ischemic cardiovascular diseases, cerebrovascular diseases, and thrombosis ).…”