REGULAR ARTICLE Expression and localization of GPR91 and GPR99 in murine organs Julia Diehl 1 & Barbara Gries 1 & Uwe Pfeil 1 & Anna Goldenberg 1 & Petra Mermer 1 & Wolfgang Kummer 1 & Renate Paddenberg 1 Received: 9 March 2015 /Accepted: 21 October 2015 # Springer-Verlag Berlin Heidelberg 2015 Abstract Energy substrates and metabolic intermediates are proven ligands of a growing number of G-protein coupled recep- tors. In 2004, GPR91 and GPR99 were identified as receptors for the citric acid cycle intermediates, succinate and α-ketoglutarate, respectively. GPR91 seems to act as a first responder to local stress and GPR99 participates in the regulation of the acid–base balance through an intrarenal paracrine mechanism. However, a systematic analysis of the distribution of both receptors in mouse organs is still missing. The aim of this study was to examine the expression of GPR91 and GPR99 in a large number of different murine organs both at mRNA and protein level. Whereas GPR91 mRNA was detectable in almost all organs, GPR99 mRNA was mainly expressed in neuronal tissues. Widespread expression of GPR91 was also detected at the protein level by western blotting and immunohistochemistry. In addition to neuronal cells, GPR99 protein was found in renal intercalated cells and epididymal nar- row cells. Double-labeling immunohistochemistry demonstrated the colocalization of GPR99 with the B1 subunit isoform of vacuolar H + -ATPases which is expressed only by a very limited number of cell types. In summary, our detailed expression anal- ysis of GPR91 and GPR99 in murine tissues will allow a more directed search for additional functions of both receptors. Keywords GPR91 . GPR99 . Tissue distribution . Immunohistochemistry . Quantitative real time RT-PCR Introduction G-protein coupled receptors (GPCRs) are responsible for about 80 % of the signal transduction across cell membranes (Millar and Newton 2010) and, with about 800 members, they consti- tute the single largest family of cell surface receptors (Civelli 2005). Signaling through GPCRs participates in the regulation of virtually all cellular and physiological functions of the body including cellular metabolism and growth, secretion, cell differ- entiation, neurotransmission, and inflammatory and immune re- sponses. Yet, there are many orphan GPCRs for which no li- gands are known. In 2004, the citric acid cycle intermediates, succinate and α-ketoglutarate (αKG), were identified as “unex- pected” ligands for the plasma membrane-bound receptors GPR91 (SUCNR1) and GPR99 (GPR80, OXGR1), respective- ly (He et al. 2004). Since then, it has become clear that both intermediates are not restricted to mitochondria but are also physiologically present in body fluids. Blood concentrations of succinate have been reported to be in the range of 6–20 μM for rodents and 2–20 μM for humans (Sadagopan et al. 2007; Kushnir et al. 2001), and 20–30 μM succinate has been mea- sured in urine of mice (Toma et al. 2008). Mean plasma levels of αKG are about 25 μM (He et al. 2004). Importantly, a number of diseases such as metabolic acidosis, heart failure and kidney cancer are accompanied by changes in the concentrations of succinate and αKG, implicating a participation in pathological conditions. For instance, urine samples of patients suffering from renal cell carcinoma exhibit increased concentrations of αKG as compared to healthy controls (Kim et al. 2011). We observed decreased concentrations of αKG in right and left ventricles of mice which were exposed to hypoxia for 4 days Electronic supplementary material The online version of this article (doi:10.1007/s00441-015-2318-1) contains supplementary material, which is available to authorized users. * Renate Paddenberg Renate.Paddenberg@anatomie.med.uni-giessen.de 1 Institute of Anatomy and Cell Biology, Excellence Cluster Cardiopulmonary System, Justus-Liebig-University, Aulweg 123, 35385 Giessen, Germany Cell Tissue Res DOI 10.1007/s00441-015-2318-1