Delineating the role of CTF and NTF of Gpr126 in physiology and pathophysiology
Felix B. Engel, University of Erlangen-Nürnberg
The major activation mechanism of adhesion G protein-coupled receptor (aGPCRs) signaling is the interaction of a cryptic tethered agonist with the seven transmembrane domain. This agonist can be liberated by autocatalytical cleavage at the GPS motif within the GAIN domain, yielding an N-terminal fragment (NTF) and a C-terminal fragment (CTF) or through isomerization upon changes occurring at the NTF such as ligand binding or mechanical force. The aGPCR Gpr126 (Adgrg6) is essential for heart, ear, and Schwann cell development. However, while Gpr126 knockout (KO) mice exhibit a heart and peripheral nerve phenotype, zebrafish mutants lacking the CTF exhibit only the peripheral nerve phenotype, suggesting that the NTF has a specific role in heart. Moreover, rescue experiments in zebrafish suggest that GPR126 has domain-specific functions. Yet, such a phenomenon has not been described for any other aGPCR, no data in mouse are available, and it remains unclear whether receptor cleavage is important as well as which functions the individual domains have. To demonstrate that the NTF has an independent function from the CTF, we have obtained or generated during the first funding period several animal models including Gpr126 reporter mice, conditional Gpr126 KO mice and several transgenic zebrafish lines. Analysis of these models identified several gross morphological as well as cellular and molecular phenotypes upon alteration of Gpr126 expression. During the second funding period we will continue the structure-function analysis of Gpr126. An important focus of our work is to determine if the embryonic lethal phenotype in Gpr126 KO mice is indeed due to defective heart development and whether NTF expression in endocardial cells is sufficient for proper heart development. Further, we will elucidate the role of Gpr126 in heart valve development as our data suggest a role for Gpr126 in endothelial mesenchymal transformation. Finally, we will characterize the role of Gpr126 during kidney physiology and pathophysiology. Our data indicate that Gpr126 is expressed in several renal cell types. Moreover, its expression is highly upregulated upon injury. Finally, our data suggest that the NTF might act in the heart as well as in the kidney in a paracrine manner. Collectively, we have generated a wide variety of tools that will allow us to delineate the role of CTF and NTF of Gpr126 in physiology and pathophysiology contributing to a better understanding of aGPCR signaling and function.