Increased Endoplasmic Reticulum Amino Peptidase‐1 in Sickle Cell Disease: Role of Hypoxia

Abstract

Sickle cell disease (SCD) is a genetic disorder caused by a single amino acid substitution in the β‐globin gene that results in hemoglobin polymerization, deformed erythrocytes and endothelial cell activation leading to chronic inflammation, anemia, hypoxemia and vaso‐occlusive crisis (VOC). These events contribute to the development of acute and often severe and debilitating, painful episodes in patients with SCD through unclear mechanisms. In SCD, chronic hypoxia and subacute inflammation contribute to endothelial cell activation that is associated with increased inflammatory cytokine markers such as endothelin‐1 (ET‐1), tumor necrosis factor‐α (TNFα), and TNFα receptor‐1 (TNFR1). Endoplasmic Reticulum Aminopeptidase‐1 (ERAP1) is a ubiquitously expressed zinc‐metallopeptidase involved in regulating immune function and inflammation that cleaves cytokine cell surface receptors such as TNFR1 and plays an important role in the pathophysiology of ankylosing spondylitis. However, the relationship between ERAP1 and SCD is, to the best of our knowledge, unexplored. We first studied the effects of deoxygenation (5% O2) on ERAP1 mRNA expression levels by qRT‐PCR in the human endothelial cell line, EA.hy926. We observed a 3‐fold increase in the expression of ERAP1 after 4 hrs of hypoxia (p<0.05, n=4) and 4‐fold increase after 8 hrs of hypoxia (p<0.05, n=4); events that were associated with a 3.5‐fold increase in the hypoxia‐inducible factor 1‐α mRNA levels at these time points. Consistent with these results, activation of EA.hy926 cells with agonist such as angiotensin II was likewise associated with increased ERAP1 mRNA (p<0.05, n=4). We then studied two sickle transgenic knockout mouse models expressing human sickle hemoglobin, the βSAntilles and Berkeley (BERK) mice. We observed significant increases in ERAP1 mRNA levels (n=7 each; p<0.01) in kidneys from sickle transgenic mice when compared to control transgenic knockout mice expressing human hemoglobin A (HbA). In addition, and as previously documented in other sickle mouse models, our sickle mice had increased circulating TNFα by ELISA as compared to HbA mice (p<0.05, n=6–10 of each mouse type). In conclusion, increases in ERAP1 levels represent a novel target in SCD that is likely secondary to hypoxia and activated endothelial cells.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.