EV-3, an endogenous human erythropoietin isoform with distinct functional relevance

Generation of multiple mRNAs by alternative splicing is well known in the group of cytokines and has recently been reported for the human erythropoietin (EPO) gene. Here, we focus on the alternatively spliced EPO transcript characterized by deletion of exon 3 (hEPO Delta 3). We show co-regulation of EPO and hEPO Delta 3 in human diseased tissue. The expression of hEPO Delta 3 in various human samples was low under normal conditions, and distinctly increased in pathological states. Concomitant up-regulation of hEPO Delta 3 and EPO in response to hypoxic conditions was also observed in HepG2 cell cultures. Using LC-ESI-MS/MS, we provide first evidence for the existence of hEPO Delta 3 derived protein EV-3 in human serum from healthy donors. Contrary to EPO, recombinant EV-3 did not promote early erythroid progenitors in cultures of human CD34+ haematopoietic stem cells. Repeated intraperitoneal administration of EV-3 in mice did not affect the haematocrit. Similar to EPO, EV-3 acted anti-apoptotic in rat hippocampal neurons exposed to oxygen-glucose deprivation. Employing the touch-screen paradigm of long-term visual discrimination learning, we obtained first in vivo evidence of beneficial effects of EV-3 on cognition. This is the first report on the presence of a naturally occurring EPO protein isoform in human serum sharing non-erythropoietic functions with EPO.