A novel role for the non-catalytic intracellular domain of Neprilysins in muscle physiology. Mareike Panz¹, Arne Jendretzki², Jürgen Heinisch², Achim Paululat¹, Heiko Harten¹. 1) Zoology, University of Osnabruck, Osnabruck, Germany; 2) Genetics, University of Osnabruck, Osnabruck, Germany.

   Neprilysins are membrane bound M13-endopeptidases responsible for the activation and/or inactivation of peptide signaling events on cell surfaces. By hydrolyzing their respective substrates, mammalian neprilysins are involved in the metabolism of numerous bioactive peptides especially in the nervous, immune, cardiovascular and inflammatory systems. Based on their involvement in essential physiological processes, proteins of the neprilysin family constitute putative therapeutic agents as well as targets in different diseases, including Alzheimers disease. We here demonstrate that overexpression of Neprilysin 4 (Nep4) in Drosophila melanogaster leads to a severe muscle degeneration phenotype. This phenotype is observed for overexpression of full length Nep4 in somatic muscles and is accompanied by severely impaired movement of larvae and lethality in late larval development. On the other hand, downregulation of expression causes only the latter two effects. By expressing several mutated and truncated forms of Nep4 in transgenic animals, we show that the intracellular domain is responsible for the observed phenotypes while catalytic activity of the enzyme is apparently dispensable. A Yeast two-hybrid screen identified a yet uncharacterized carbohydrate kinase as a first interaction partner of the intracellular domain of Nep4. These data represent the first report of an intracellular neprilysin domain being involved in muscle integrity.