1Universitätsklinikum Bonn Medizinische Klinik und Poliklinik II Bonn, Deutschland; 2Kreiskrankenhaus Waldbröl GmbH Klinik für Innere Medizin, Kardiologie Waldbröl, Deutschland; 3Institute for Genomic Statistics and Bioinformatics Bonn, Deutschland; 4Institute for Biochemistry and Molecular Biology Bonn, Deutschland; 5Gemeinschaftspraxis Kardiologie Köln am Neumarkt Köln, Deutschland
Aims:
Endoplasmic-reticulum-stress (ER-Stress) chaperones such as the main ER-Stress moderator GRP78 (glucose-regulated-protein, 78kDa) are implicated in coronary artery disease (CAD) pathogenesis. Besides their established intracellular role, these chaperones are also secreted extracellularly. However, the significance of extracellular ER chaperones in CAD remains unclear.
Methods and Results:
Serum GRP78 levels were measured by ELISA in 622 patients undergoing coronary angiography. ER-Stressor treated human coronary artery endothelial cells (HCAEC) were used to assess the effects of ER-Stress conditioned medium (CM) on recipient cell viability, apoptosis, reactive oxygen species (ROS) formation, and gene expression.
GRP78 levels were higher in CAD patients' blood samples than in non-CAD patients (2584 ng/ml vs. 2061 ng/ml, p = 0.009). Elevated GRP78 levels were independently associated with lower one-year mortality, even after adjustment (4.5% vs. 9.0%, log-rank p = 0.022). Increased GRP78 levels were associated with higher BMI with no difference regarding age, sex, or cardiovascular risk factors. Mass spectrometry analyses of the HCAEC secretome and ELISA revealed increased extracellular GRP78 secretion after ER-Stress activation. Brefeldin A, an ER-Golgi-trafficking inhibitor, confirmed actively regulated GRP78 secretion. GRP78-containing CM improved viability and reduced apoptosis, ROS formation, ER-Stress-signaling, and inflammation in recipient HCAEC compared to CM lacking GRP78 due to BFA treatment or GRP78-knockdown. Likewise, recombinant GRP78 improved HCAEC viability. Mechanistically, the epidermal growth factor related Cripto mediated protective extracellular GRP78 signaling.
Conclusion:
GRP78 is significantly increased in patients with CAD. Intriguingly, elevated levels are associated with reduced one-year mortality. ER-Stress-induced GRP78 secretion may represent a feedback mechanism to ameliorate ER-Stress and inflammation in recipient endothelial cells.