GENETIC VARIANTS OF ERYTHROPOIETIN AND THEIR BIOLOGICAL SIGNIFICANCE

Abstract

Erythropoietin (EPO) is a hematopoietic cytokine with a multitude of functions, that are erythropoietic, metabolic or cytoprotective. The erythropoietic functions of EPO have led to the development of many erythropoietic stimulating agents (ESAs) that are recombinant human EPOs (rhEPO) biologic therapies. ESAs have primarily been used to treat anemia, but have also been investigated to treat ischemic injuries, such as acute myocardial infarction and stroke. ESAs can vary in their glycosylation pattern that can affect their pharmacodynamics. Genetic variants in EPO have also been associated with microvascular complications and anemia in diabetes. In our study we investigated the regulation of EPO by single nucleotide polymorphisms (SNPs) and post transcriptionally by intron retention. We explore the potential differences in EPO’s function in different ESAs formulations in vitro. We sequenced the rs1617640, rs507392 and rs551238 SNPs in EPO in a cardiovascular surgery population. We found the C allele in rs1617640 correlated with anemia and the GG genotype in rs507392 correlated with dyslipidemia. In an in vitro cell model, intron retention was found to be increased in response to ischemia in brain cells, but not kidney and liver. The variation in intron retention also shows temporal and circadian changes. Epoetin α, Peprotech are rhEPOs with three N-glycosylation sites compared to five in darbepoetin α (which also has five amino acid substitutions). Epoietin α has similar erythropoietic functions compared to a recombinant mouse Epo (rmEpo). In H9c2 these showed a higher degree of proliferation compared to darbepoetin α, with Peprotech being in between. H9c2 cells treated with epoetin α for 24 hours resulted in an increase in mitochondrial oxygen consumption. Pre-treatment with epoetin α or Peprotech, but not darbeopoetin α, provide cytoprotection against hydrogen peroxide, but not against staurosporine or hemin. Taken together, our study shows variations in EPO at the various molecular levels have physiological implications, which require further study.