MOLECULAR AND CELLULAR MECHANISMS OF DISEASE Bidirectional signalling between EphA2 and ephrinA1 increases tubular cell attachment, laminin secretion and modulates erythropoietin expression after renal hypoxic injury Stéphane Rodriguez 1,3 & Stefan Rudloff 1 & Katrin Franziska Koenig 1,4 & Swapna Karthik 1 & David Hoogewijs 2,5 & Uyen Huynh-Do 1 Received: 29 January 2016 /Revised: 1 May 2016 /Accepted: 10 May 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Acute kidney injury (AKI) is common in hospital- ized patients and has a poor prognosis, the severity of AKI being linked to progression to chronic kidney disease. This stresses the need to search for protective mechanisms during the acute phase. We investigated kidney repair after hypoxic injury using a rat model of renal artery branch ligation, which led to an oxygen gradient vertical to the corticomedullary axis. Three distinct zones were observed: tubular necrosis, infarc- tion border zone and preserved normal tissue. EphA2 is a receptor tyrosine kinase with pivotal roles in cell architecture, migration and survival, upon juxtacrine contact with its membrane-bound ligand EphrinA1. Following hypoxia, EphA2 was up-regulated in cortical and medullary tubular cells, while EphrinA1 was up-regulated in interstitial cells adjacent to peritubular capillaries. Moreover, erythropoietin (EPO) messenger RNA (mRNA) was strongly expressed in the border zone of infarcted kidney within the first 6 h. To gain more insight into the biological impact of EphA2 and EphrinA1 up-regulation, we activated the signalling pathways in vitro using recombinant EphrinA1/Fc or EphA2/Fc pro- teins. Stimulation of EphA2 forward signalling in the proxi- mal tubular cell line HK2 increased cell attachment and lam- inin secretion at the baso-lateral side. Conversely, activation of reverse signalling through EphrinA1 expressed by Hep3B cells promoted EPO production at both the transcriptional and protein level. Strikingly, in co-culture experiments, juxtacrine contact between EphA2 expressing MDCK and EphrinA1 expressing Hep3B was sufficient to induce a signif- icant up-regulation of EPO mRNA production in the latter cells, even in the absence of hypoxic conditions. The syner- gistic effects of EphA2 and hypoxia led to a 15–20-fold in- crease of EPO expression. Collectively, our results suggest an important role of EphA2/EphrinA1 signalling in kidney repair after hypoxic injury through stimulation of (i) tubular cell attachment, (ii) secretion of basal membrane proteins and (iii) EPO production. These findings could thus pave the way to new therapeutic approaches. Keywords EphA2 . EphrinA1 . EPO . Bidirectional . Kidney repair Introduction The incidence of acute kidney injury (AKI) in hospitalized patients has dramatically increased from 5 % in 1982 to 20 % in 2012 [1]. AKI not only results in a high morbidity and mortality but also often progresses to chronic kidney dis- ease (CKD) with its high economic burden. Although hypoxia is a major factor contributing to the pathogenesis of this renal disease [2], the precise mechanism is still poorly understood. Stéphane Rodriguez and Stefan Rudloff contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00424-016-1838-1) contains supplementary material, which is available to authorized users. * Uyen Huynh-Do Uyen.Huynh-Do@insel.ch 1 Division of Nephrology, Hypertension and Clinical Pharmacology, Inselspital, University of Bern Medical School, CH-3010 Bern, Switzerland 2 Institute of Physiology, University of Zurich, Zurich, Switzerland 3 Present address: U917 Inserm unit, University of Rennes, Rennes, France 4 Present address: Division of Nephrology, University Hospital of Basel, Basel, Switzerland 5 Present address: Institute of Physiology, University of Duisburg-Essen, Essen, Germany Pflugers Arch - Eur J Physiol DOI 10.1007/s00424-016-1838-1