Theodoros Stylianides, Fabien Alpy, Peter I. Benke, Alexandra Piunti, Victoria Salem, Michele Solimena, Alejandra Tomas, David J. Hodson, Andrew Cakebread, Andreas Müller, Kate J. Heesom, Nur Shabrina Amirruddin, Federico Torta, Isabelle Leclerc, Leena Haataja, Peter Arvan, Timothy J. Pullen, Annie C. H. Fung, Linford J.B. Briant, Kaiying Cheng, Gaelle Carrat, Alice P.S. Kong, Dale B. Wigley, Philip A. Lewis, Richard B. Sessions, Elizabeth Haythorne, Mutian Huang, Adrian Kee Keong Teo, Guy A. Rutter, Eleni Georgiadou, Walter Distaso, Imperial College London, University of Michigan Medical School [Ann Arbor], University of Michigan [Ann Arbor], University of Michigan System-University of Michigan System, Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG), Max-Planck-Gesellschaft, Université de Lille, King‘s College London, Loughborough University, National University of Singapore (NUS), University of Bristol [Bristol], University of Birmingham [Birmingham], University of Nottingham, UK (UON), University of Oxford [Oxford], The Chinese University of Hong Kong [Hong Kong], Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), University of Oxford, Université de Strasbourg (UNISTRA)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), and ALPY, Fabien
Objective Risk alleles for type 2 diabetes at the STARD10 locus are associated with lowered STARD10 expression in the β-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 β-cell function are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the β-cell and the role of the protein in controlling proinsulin processing and insulin granule biogenesis and maturation. Methods We used isolated islets from mice deleted selectively in the β-cell for Stard10 (βStard10KO) 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 βStard10KO 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 Å 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 βStard10KO 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 βStard10KO islets. Conclusion Our data indicate that STARD10 binds to, and may transport, phosphatidylinositides, influencing membrane lipid composition, insulin granule biosynthesis, and insulin processing., Highlights • βStard10KO β-cells show altered granule morphology. • Deletion of Stard10 increased basal secretion of newly synthesised proinsulin. • βStard10KO islets had an altered lipidomics profile, including phosphatidylinositols. • STARD10 bound to phosphoinositides in a lipid overlay assay. • STARD10 structure reveals that its cavity readily accommodates phosphatidylinositols.