Indiana University-Purdue University Indianapolis (IUPUI) / Type 2 diabetes mellitus is a chronic disorder characterized by hyperglycemia,
insulin resistance, and insufficient insulin secretion from the pancreatic β cells. To
maintain adequate levels of insulin secretion, β cells rely on highly coordinated
control of luminal ER Ca2+. Stromal Interaction Molecule 1 (STIM1) is an ER Ca2+
sensor that serves to replenish ER Ca2+ stores in response to depletion by gating
plasmalemmal Orai1 channels in a process known as store-operated calcium entry
(SOCE). We developed a method for the direct measurement of SOCE in
pancreatic β cells and found that deletion of STIM1 in INS-1 cells (STIM1KO) is
sufficient to block Ca2+ influx in response to store-depletion. To determine the
physiological importance of β cell STIM1, we created mice with pancreatic β cell
specific deletion of STIM1 (STIM1Δβ) and placed them on a high fat diet (HFD)
with 60% of kilocalories derived from fat. After 8 weeks of HFD, female, but not
male, STIM1Δβ mice exhibited increased body weight and fat mass as well as
significant glucose intolerance and impaired insulin secretion without observable
differences in insulin tolerance. Immunohistochemical analysis revealed a
reduction of β cell mass and an increase of α cell mass; ELISA of islet lysates
revealed a similar significant reduction in insulin content and increased glucagon
content. RNA-sequencing performed on STIM1Δβ islets revealed differentially
expressed genes for functions related to apoptosis, lipid metabolism, and epithelial cell differentiation, as well as loss of β cell identity. Proteomics analysis of
STIM1KO cells phenocopied the metabolic findings, revealing significantly
increased glucagon expression. Analysis of islet RNA-sequencing results showed
modulation of pathways related to 17-β estradiol (E2) signaling, with notable
downregulation of G-protein coupled estrogen receptor 1 (GPER1) expression.
Consistently, treatment of female wild-type islets with pharmacological SOCE
inhibitors led to reduced expression GPER1, while STIM1KO cells showed lower
mobilization of intracellular cAMP levels in response to GPER agonist treatment.
Taken together, these findings identify a novel interaction between SOCE and E2
signaling in the female islet and suggest that loss of STIM1 and impairments in
SOCE may contribute to diabetes pathophysiology through loss of β cell identity. / 2022-12-28
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/27276 |
| Date | 12 1900 |
| Creators | Sohn, Paul |
| Contributors | Evans-Molina, Carmella, Elmendorf, Jeffrey, Linnemann, Amelia, Sankar, Uma |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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