Clinical and molecular characterization of a novel congenital disease; the role of PREPL in regulated secretion and neuromuscular transmission

PREPL (PRolyl EndoPeptidase-Like) is deleted in a recessive metabolic disorder characterized by muscle weakness and growth hormone deficiency. Based on the homology with PREP (PRolyl EndoPeptidase) PREPL was predicted to encode an oligopeptidase. Although activity of the catalytic machinery has been demonstrated, no peptide substrates have been identified so far. Recently, we have achieved a breakthrough in determining the physiological function of PREPL; we have found that administration of an acetylcholine-esterase inhibitor greatly improves weakness in some PREPL-deficient patients, pointing at impaired exocytosis at the neuromuscular junction. Furthermore, PREPL knockdown in a neuroendocrine cell line reduced regulated secretion. Finally, an interaction with the adaptor protein AP-1 was found, which also requires phosphatidylinositol 4-phosphate (PI-4-P) for high-affinity binding. Since PREPL increases membrane dissociation of AP-1, we hypothesize that PREPL hydrolyzes PI-4-P.

The aim of this research is to characterize the role of PREPL in regulated secretion and neuromuscular transmission. The three objectives of the project are: 

1. To test an alternative for the acetylcholine-esterase inhibitor, which may not only have a broader effect on weakness but might also improve growth.
2. To study the role of PREPL in regulated secretion in cell lines, in hippocampal neurons and in somatotrophs of a mouse model.
3. To determine if PREPL has PI-4-P hydrolase activity.