Blunted first-phase insulin secretion and insulin deficiency are indicators of β cell dysfunction and diabetes manifestation. Therefore, insights into molecular mechanisms that regulate insulin homeostasis might provide entry sites to replenish insulin content and restore β cell function. Here, we identify the insulin inhibitory receptor (inceptor; encoded by the gene IIR/ELAPOR1) as an insulin-binding receptor that regulates insulin stores by lysosomal degradation. Using human induced pluripotent stem cell (SC)-derived islets, we show that IIR knockout (KO) results in enhanced SC β cell differentiation and survival. Strikingly, extended in vitro culture of IIR KO SC β cells leads to greatly increased insulin content and glucose-stimulated insulin secretion (GSIS). We find that inceptor localizes to clathrin-coated vesicles close to the plasma membrane and in the trans-Golgi network as well as in secretory granules, where it acts as a sorting receptor to direct proinsulin and insulin towards lysosomal degradation. Targeting inceptor using a monoclonal antibody increases proinsulin and insulin content and improves SC β cell GSIS. Altogether, our findings reveal the basic mechanisms of β cell insulin turnover and identify inceptor as an insulin degradation receptor.
GrantsMarie Curie Actions (MSCA) Helmholtz Future Topic 'Aging and Metabolic programming' (AMPro) Helmholtz Society Helmholtz Portfolio Theme 'Metabolic Dysfunction and Common Disease' German Research Foundation German Center for Diabetes Research (DZD) European Research Council NWO TA grant European Union Horizon 2020 programme INFRAIA project Epic-XS Helmholtz Zentrum Munchen Deutsches Forschungszentrum fur Gesundheit und Umwelt (GmbH) European Union