1893-P: The Integrative Role of ER Protein Quality Control Pathways (ERQC) in Prohormone Maturation

Background: Peptide hormones are crucial regulators of metabolism. However, maturation of hormone precursors (prohormones) in the endoplasmic reticulum (ER) in vivo remains largely unexplored. Aims: This project aims to study the integrative role of the two major protein quality control pathways in the ER, ER-Associated Degradation (ERAD) and autophagy, in regulating prohormone maturation under physiological conditions. Taking vasopressin precursor (proAVP) as a model, this project will provide novel insights on hormone maturation and the physiological function of ERQC pathways. Methods: We generated AVP neuron specific ERAD and Autophagy deficient mouse models by deleting Sel1L and Atg7, respectively. We also generated Sel1L and Atg7 deficient cell models. We used immunostaining, sucrose sedimentation, and Western blots to dissect the roles of ERAD and autophagy in proAVP folding and maturation. Results: Mice with Atg7 deficiency in AVP neurons maintain normal water homeostasis, while Sel1L deficient mice develop central diabetes insipidus. Further, Atg7 deficient neurons show reduced proAVP protein and altered subcellular distribution, but its ER export remains functional. Mechanically, unlike Sel1L deficiency, Atg7 deficiency alone shows amber accumulation of misfolded proAVP in vitro; however, further blocking autophagy with ERAD deficiency shows increased portion of misfolded proAVP comparing with ERAD deficiency along. Further, combined deletion of Atg7 and Sel1L in AVP neurons leads to earlier development of Diabetes Insipidus comparing with Sel1L deficiency alone, suggesting a critical role of autophagy in maintaining AVP maturation with compromised ERAD. Conclusions: Here we demonstrate that autophagy alone is dispensable for the maturation of proAVP in the ER, but is indispensable in the event of compromised ERAD function both in vivo and in vitro. This study points to the differential roles and crosstalk between ERAD and autophagy in neuroendocrine cells. Disclosure G. Shi: None. X. Pan: None. H. Wang: None. P. Arvan: None. L. Qi: None. Funding National Institutes of Health (R01DK120047); University of Michigan (U064133)