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Store operated Ca2+ entry (SOCE) controls ameloblast cell function and enamel development

ABSTRACT: Abstarct:Mutations in the endoplasmic reticulum (ER) Ca2+ sensor stromal interaction molecule 1 (STIM1) result is a number of disease states including abnormal enamel formation. However, these defects in enamel have remained unclear given a lack of animal models available. We generated Stim1/2K14Cre mice to ablate the activity of STIM1 and its homologue STIM2 in enamel cells. These mice showed impaired Ca2+ entry in enamel cells and although enamel formed, it was severely hypomineralized and mechanically weak. RNA-sequencing of enamel cells provided a global overview of loss of Ca2+ sensor activity. ER stress markers associated with unfolded protein response (UPR) were increased. Cell morphology was altered showing loss of the typical ruffled-border and mislocalized mitochondria. We also identified decreased glutathione system and potentially associated with this, increased ROS and abnormal mitochondria. The Ca2+ extrusion system and enamel gene expression were also altered. These data might represent the first in vivo study linking Stim1/2 ablation with increased UPR function, decreased glutathione metabolism, increased ROS and abnormal mitochondria. Loss of ER Ca2+ sensors Stim1/2 in enamel cells has substantial detrimental effects at the cell and mineral phase level.

ORGANISM(S): Mus musculus

PROVIDER: GSE93655 | GEO | 2017/01/17

SECONDARY ACCESSION(S): PRJNA361476

REPOSITORIES: GEO

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Project description:STIM1 is an endoplasmic reticulum (ER) calcium (Ca2+) sensor that serves to replenish ER Ca2+ stores in response to ER Ca2+ depletion through gating of plasmalemmal Orai1 channels in a process known as store operated calcium entry (SOCE). Previously, we have shown that SOCE is impaired in the diabetic pancreatic β cell; however, the consequences of reduced β cell SOCE have not been well studied. To test this, we generated mice with pancreatic β cell specific deletion of STIM1 (STIM1Δβ). Our results revealed a striking sexual dimorphism in metabolic phenotypes when STIM1Δβ mice were challenged with high fat diet for 8 weeks. Male STIM1Δβ mice showed no differences in total weight, lean or fat mass, or glucose tolerance compared to WT littermate controls. In contrast, female STIM1Δβ mice displayed significantly increased total body weight, fat mass, and reduced glucose tolerance, in vivo glucose-stimulated insulin secretion and β cell mass compared to WT littermate controls, while insulin sensitivity, food intake, and energy expenditure were unchanged. To investigate mechanisms underlying these findings, RNA sequencing was performed in isolated islets and revealed altered 17-beta estradiol (E2) signaling, lipid metabolism, epithelial cell differentiation and decreased noncanonical estradiol receptor GPER. Consistent with this, alpha cell mass was increased in female STIM1Δβ, while proteomics and immunoblot analysis of STIM1 knockout (STIM1KO) INS-1 beta cells revealed reduce insulin expression and increased glucagon expression, suggesting STIM1 may be required for the maintenance of β cell identity. To this end, we show that a reduction of a noncanonical estradiol receptor GPER in STIM1 deficient islets contributes to the marked sexual dimorphism observed during beta cell dysfunction in female STIM1Δβ mice. This present study delineates a sexually dimorphic regulation of STIM1 in the maintenance of pancreatic beta cell identity through GPER and may expand the field of therapeutic approaches to diabetes. Our findings demonstrate the importance of STIM1 and GPER expression stability in the anti-diabetogenic response from estradiol.

Project description:SEPN1 is a type II protein of the endoplasmic reticulum (ER) whose loss of function gives rise to a collection of debilitating autosomal recessive myopathies gathered under the umbrella term of SEPN1-related myopathy (RM). At the moment, SEPN1-RM lacks an effective pharmacological treatment; thus, the medical management of the disease is only supportive. The potentially fatal diaphragmatic weakness leading to respiratory insufficiency in patients still ambulant is the main reason for medical concerns. Thus, studies on SEPN1-RM pathogenesis are necessary to implement a targeted pharmacological therapy aimed at relieving the general muscle weakness and the more worrisome diaphragmatic dysfunction. Here, we show a physical and functional interaction between SEPN1 and the ER stress mediator ERO1 alpha (henceforth, ERO1). Both SEPN1 and ERO1 are involved in the redox regulation of proteins into the ER, although in an opposite way SEPN1 imposes a less oxidant ER poise while ERO1 a more oxidant one, conceivable with a reductase function of SEPN1 and an oxidase one of ERO1. Furthermore, both are mainly localized in a region of the ER in close contact with mitochondria termed mitochondria-associated membranes (MAMs) and their loss impacts oppositely on the short-range MAMs, thereby impinging ER-mitochondria Ca2+ dynamics, OXPHOS, and bioenergetics. We find that ERO1 depletion restores the impaired short-range MAMs due to SEPN1 loss together with mitochondrial ATP. ERO1 knockout in a mouse background of SEPN1 loss blunts ER stress and the consequent Unfolded Protein Response (UPR) while it rescues the diaphragmatic weakness by improving ER/mitochondria contacts, calcium dynamics, and OXPHOS. Importantly, treatments of SEPN1 knock out mice with the chemical chaperone tauroursodeoxycholic acid (TUDCA) mimic the results of ERO1 loss improving calcium dynamics, OXPHOS, ER/mitochondria contacts, thereby rescuing diaphragmatic weakness as well. In addition, TUDCA-treated SEPN1-RM patients-derived myoblasts show a dynamic dose-dependent increase in ATP levels under ER stress conditions suggesting improved mitochondrial function. Thus, our findings point to the ERO1 axis in the pathogenesis of SEPN1-RM thereby impinging on MAMs and mitochondria bioenergetics and recall for the efficacy of a pharmacology therapy with ad hoc ER stress/ERO1 inhibitors for SEPN1-RM.

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Store operated Ca2+ entry (SOCE) controls ameloblast cell function and enamel development

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