Clin Res Cardiol (2021). 10.1007/s00392-021-01933-9

Circulating Chaperone glucose-regulated protein 78kD (GRP78) is elevated in Patients with Coronary Artery Disease and reduces endothelial dysfunction
E. Repges1, M. Al Zaidi1, S. Sommer-Weisel1, M. U. Becher1, F. Jansen1, S. Zimmer1, V. Tiyerili2, G. Nickenig1, A. Aksoy1
1Medizinische Klinik und Poliklinik II, Universitätsklinikum Bonn, Bonn; 2Klinik für Innere Medizin I, St.-Johannes-Hospital Dortmund, Dortmund;

Introduction

Circulating chaperones have emerged as both effectors and prognostic markers for various cardiovascular diseases, including Coronary Artery Disease (CAD) and Acute Coronary Syndrome (ACS).  Glucose-Regulated Protein 78kD (GRP78) is a chaperone and main regulator of the endoplasmic-reticulum (ER) stress response which is triggered by a variety of conditions that disturb folding of proteins in the ER. In case of ER Stress, GRP78 activates the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasisA prolonged activation of the UPR triggers inflammation, thus contributing to the progression of CAD.

The aim of this study was to investigate the role of circulating chaperone GRP78 in CAD.

 

Methods and Results

 

Serum concentration of GRP78 was measured by ELISA in an all-comers cohort of 794 patients undergoing coronary angiography. Mean age was 70.9 ± 11.8 years and 65% of patients were male. CAD defined as >50% stenosis in any major epicardial coronary artery was confirmed in 575 patients (72.4%). Serum levels of GRP78 were higher in patients with CAD as compared to patients with excluded CAD (2640 ng/ml [95% CI: 2415-2864] vs. 2178 ng/ml [95% CI: 1893-2463], p=0.024, n=794). Additionally, patients presenting with chronic coronary syndrome (CCS) showed higher GRP78 serum concentrations compared to patients presenting with ACS (2822 ng/ml [95% CI: 2531-3113] vs. 2284 ng/ml [95% CI: 1944-2624], p=0.027, n=575). Patients are currently followed-up for the combined primary endpoint of 12-month death, myocardial infarction, stroke, unplanned rehospitalization and major bleeding.

 

To study the effect of GRP78 on vascular biology we performed in vitro experiments.

First, we sought to investigate, if vascular cells contribute to the secretion of GRP78. Herefore, human coronary artery endothelial cells (HCAEC) were incubated with the ER stress inductor tunicamycin and both intracellular and extracellular GRP78 protein levels were determined by Western Blot and ELISA. After ER Stress induction we observed an increased intracellular GRP78 expression. Intriguingly, prolonged ER Stress also promoted extracellular secretion of GRP78. Co-incubation with Brefeldin A, an inhibitor of ER-Golgi protein transport, abolished extracellular secretion. Hence, ER-Stress-induced GRP78 secretion appears to be an actively regulated process.

Next, the effect of GRP78 containing conditioned medium on HCAEC was analyzed.

Treatment with GRP78 containing conditioned medium decreased GRP78 mRNA expression in target cells (0.35-fold vs. control [+BFA], p<0.0001). Furthermore, it increased viability (93.0 % vs. 79.6%, p=0.0168) and decreased expression of markers of vascular inflammation and ER Stress (e.g., NF-κB and CHOP). In addition, we observed a decrease in formation ofreactive oxygen species (0.78-fold, p=0.07).

Mechanistically, PCR profiling assays of GRP78-treated HCAEC showed a robust increase of chemokine C-X-C motif chemokine ligand 10 (CXCL10), which has been attributed both proatherogenic and protective properties in vascular inflammation (6.51-fold). 

Conclusion

GRP78 enhances viability and alleviates oxidative stress in HCEAC, suggesting protective properties of circulating chaperones in endothelial inflammation. GRP78 might be a feasible therapeutic option in order to decelerate progression of cardiovascular diseases andcould serve as a biomarker with diagnostic and prognostic significance.

 
 
 
 
 
 
 
 

 


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