1771-P: STIM1 Maintains Beta-Cell Identity and Function

Impairments in endoplasmic reticulum (ER) Ca2+ homeostasis have been linked to β cell dysfunction and diabetes development; however, the pathways mediating these effects are not fully understood. Store-operated Ca2+ entry (SOCE) replenishes ER Ca2+ levels through reversible gating of plasma membrane Ca2+ channels by the ER Ca2+ sensor, stromal interaction molecule 1 (STIM1). We found that female, but not male, mice with β cell-specific STIM1 deletion (STIM1Δβ) had reduced β cell mass, increased α cell mass, and reduced expression of markers of β cell identity. To determine the mechanisms underlying this sexually dimorphic phenotype, RNA sequencing, immunofluorescent staining, and Ca2+ imaging experiments were performed using islets from control and STIM1Δβ mice and WT and STIM1 KO INS-1 cells. RNA sequencing of islets from STIM1Δβ mice identified 55 pathways that were significantly modulated (P<0.05), including “estrogen receptor signaling”, “mitochondrial dysfunction”, and “endocytosis”, and “estrogen receptor signaling”. Consistent with a role for SOCE in mitochondrial function, STIM1 KO cells decreased mitochondrial Ca2+ levels. Furthermore, we used the novel fluorescent time construct, syncollin-dsRedE5TIMER, to demonstrate an abnormal accumulation of aged insulin granules in STIM1 KO cells. Lastly, to test the relationship between STIM1 expression and glucose regulation in humans, we queried a publicly available NCBI GEO dataset derived from organ donors with and without type 2 diabetes (T2D). In this dataset, islet STIM1 expression was negatively correlated with HbA1c levels in female organ donors (n=35, r=-0.38, p=0.035), while there was no correlation in male donors. Together, these data highlight a novel role for STIM1 in the maintenance of mitochondrial function and insulin granule turnover. These findings confirm the importance of Ca2+ regulation within the β cell and highlight the significant role of sex as a biological variable in diabetes pathogenesis. Disclosure T.Kono: None. M.Slak rupnik: None. P.Krishnan: None. P.Sohn: None. M.Mclaughlin: None. W.Wu: None. S.Postic: None. P.Krishnan: None. C.Lee: None. M.Slak rupnik: None. C.Evans-molina: Advisory Panel; Provention Bio, Inc., DiogenX, Avotres Inc., Neurodon, MaiCell Therapeutics, Other Relationship; Isla Technology, Bristol-Myers Squibb Company, Nimbus Therapeutics, Research Support; Lilly, Astellas Pharma Inc. Funding National Institutes of Health (R01DK093954, R01DK127236, U01DK127786, R01DK127308, UC4DK104166); U.S. Department of Veterans Affairs (I01BX001733)