Objective: Risk alleles for type 2 diabetes at the STARD10 locus are associated with lowered STARD10 expression in the beta-cell, impaired glucose-induced insulin secretion, and decreased circulating proinsulin:insulin ratios. Although likely to serve as a mediator of intracellular lipid transfer, the identity of the transported lipids and thus the pathways through which STARD10 regulates beta-cell function are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the beta-cell and the role of the protein in controlling proinsulin processing and insulin granule biogenesis and maturation.Metkods: We used isolated islets from mice deleted selectively in the beta-cell for Stard10 (beta Stard10KO) and performed electron microscopy, pulse-chase, RNA sequencing, and lipidomic analyses. Proteomic analysis of STARD10 binding partners was executed in the INS1 (832/13) cell line. X-ray crystallography followed by molecular docking and lipid overlay assay was performed on purified STARD10 protein.Results: beta Stard10KO islets had a sharply altered dense core granule appearance, with a dramatic increase in the number of "rod-like" dense cores. Correspondingly, basal secretion of proinsulin was increased versus wild-type islets. The solution of the crystal structure of STARD10 to 2.3 angstrom resolution revealed a binding pocket capable of accommodating polyphosphoinositides, and STARD10 was shown to bind to inositides phosphorylated at the 3' position. Lipidomic analysis of beta Stard10KO islets demonstrated changes in phosphatidylinositol levels, and the inositol lipid kinase PIP4K2C was identified as a STARD10 binding partner. Also consistent with roles for STARD10 in phosphoinositide signalling, the phosphoinositide-binding proteins Pirt and Synaptotagmin 1 were amongst the differentially expressed genes in beta Stard10KO islets.Conclusion: Our data indicate that STARD10 binds to, and may transport, phosphatidylinositides, influencing membrane lipid composition, insulin granule biosynthesis, and insulin processing.
Institut(e)Institute for Pancreatic Beta Cell Research (IPI)
FörderungenInstitute of Molecular and Cell Biology (IMCB), A*STAR MRC MRC Experimental Challenge Grant (DIVA) MRC Programme Diabetes UK Imperial Confidence in Concept (ICiC) Royal Society Wolfson Research Merit Award NUS Research Scholarship German Ministry for Education and Research (BMBF) Wellcome Trust Multi-User Equipment Grant BBSRC Cancer Research UK Medical Research Council EFPIA European Union's Horizon 2020 research and innovation programme Innovative Medicines Initiative 2 Joint Undertaking European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme Wellcome Trust Institutional Support Award Diabetes UK R.D. Lawrence Fellowship NIH Wellcome Trust