Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA250

Poster Communications

Different subsets of renal interstitial PDGFR-β+ cells are able to produce Erythropoietin (EPO)

K. Gerl1, C. Wagner1, B. Kurt1, A. Kurtz1

1. Physiology, University of Regensburg, Regensburg, Bavaria, Germany.

Anemia due to insufficient renal EPO production is a typical complication of chronic kidney disease. Therefore a better understanding of the identity of renal EPO producing cells (REPs) is of great clinical relevance. Originally REPs were described as tubulointerstitial CD73+ fibroblasts located along the border area of inner cortex and outer medulla with recruitment of additional cortical fibroblasts for EPO expression during hypoxic periods. More recent findings suggest that PDGFR-β+ fibroblasts/pericytes are the exclusive renal production sites for EPO and that interstitial PDGFR-β+ cells which are in principle able to produce EPO are widely distributed throughout all kidney zones. Therefore we were interested to know if different subsets of PDGFR-β+ EPO expressing cells exist in the kidney. For this purpose we investigated the inducibility of EPO expression in three subsets of renal PDGFR-β+ interstitial cells, namely those coexpressing either CD73, Gli-1 or SMMHC together with PDGFR-β. Inducibility of EPO expression was tested by cell type specific deletion of the von Hippel-Lindau protein (Vhl) using tamoxifen inducible Cre-loxP systems. Hematocrit (hct) values, plasma EPO concentrations and renal EPO mRNA expression levels were determined as readout of EPO gene expression. Localization and number of EPO expressing cells were determined by EPO mRNA in situ hybridization (ISH) using RNAscope®. Values are means ± S.E.M. In Pdgfr-β-CreERT2 Vhlflfl mice (n=15) 3589±224 REPs per kidney section (pks) could be detected throughout all kidney zones using EPO mRNA-ISH (controls: 13±7 REPs pks). Co-ISH for EPO and CD73 revealed that 97% of cortical REPs coexpressed CD73 whereas there was no coexpression in REPs of the outer and inner medulla. Gli1-CreERT2 Vhlflfl mice (n=12) showed 20-fold increased renal EPO mRNA abundance that led to elevated plasma EPO concentrations (1335.0±95.6pg/ml) and hct values (70.8±0.8%). Control mice (n=20) had hct values of 49.8±0.6% and plasma EPO concentrations of 137.9±18.8 pg/ml. Via RNAscope® 188±38 REPs pks could be detected that were mostly located in the outer stripe of the outer medulla. Only single REPs were localized in the cortex. EPO mRNA abundance in SMMHC-CreERT2 Vhlflfl mice (n=15) was 10-fold elevated (plasma EPO: 1278.0±93.0pg/ml; hct: 69.2±1.6%) and 107±16 REPs pks could be detected on average. These REPs were mostly located in the interstitium of the outer medulla and the proximal part of the inner medulla. Taken together our results show that different subpopulations of interstitial PDGFR-β+ cells exist, which are in principle able to produce EPO. These cells are CD73+ cells that are mainly localized in the cortical interstitium, Gli-1 expressing interstitial cells mainly localized in the outer medulla and SMMHC-positive pericytes mainly localized in the outer medulla and the proximal part of the inner medulla.

Where applicable, experiments conform with Society ethical requirements