Tubular Erythropoietin Receptor Expression Mediates Erythropoietin-Induced Renoprotection

Erythropoietin (EPO) has been shown to have tissue protective properties by binding to its receptor (EPOR) which is also expressed on non-haematopoietic cells. The mechanisms underlying this protection have not yet been eluci- dated and the renal cell types mediating these effects remain ill-defined. This study aimed to identify the EPOR expression in human tubular epithelial cells (hTECs) and in rat kidney and to investigate the role of EPOR in EPO-mediated renopro- tection. Male Wistar rats were treated with saline or EPO (3000 U/kg, i.p.) 24h prior to sham-operation or 30 min bilateral renal ischemia. Renal morphology and function, tubular regeneration, apoptosis and expression of EPOR, heme- oxygenase-1 (HO-1) and hepatocyte growth factor (HGF) were analyzed. Primary cultures of human proximal (PTC) and distal/collecting duct (DTC) tubular cells were incubated with EPO (5-50-500 ng/mL) either or not in the presence of so- luble EPOR. Total RNA was extracted and mRNA expression of HO-1 was investigated by quantitative RT-PCR. EPOR mRNA could be demonstrated in hTECs and in cortical tubules of the rat kidney. Furthermore, EPOR protein was expressed at the membrane and as intracellular vesicles in hTECs. In vivo, EPO treatment attenuated histological and func- tional renal damage, decreased both cell necrosis and apoptotic cell death, enhanced tubular regeneration and resulted in an upregulation of HO-1 and HGF mRNA. In vitro, EPO administration resulted in an early upregulation of HO-1 mRNA which was restricted to PTC and inhibited by simultaneous addition of supra-equivalent amounts of soluble EPOR. These data strongly suggest that the EPO-mediated renoprotection results from direct interaction of EPO with EPOR on tubular cells.