Functional Characterization of Wolfram Syndrome 1 Protein in ß-Cell Function and Viability

Abstract

Endoplasmic reticulum (ER) homeostasis is crucial for proper β-cell function as evidenced by rare monogenic diabetic disorders, such as Wolfram syndrome, arising from genetic defects in key ER molecules. Wolfram syndrome stems from mutation of the ER transmembrane protein, Wolfram Syndrome 1 (WFS1), resulting in a recessive, progressive neurodegenerative disorder that first manifests as juvenile-onset diabetes mellitus (DM). While many WFS1 variants are associated with DM, the role of WFS1 in β-cell viability and function remains unclear. Our central hypothesis is that WFS1 regulates β-cell viability through downregulation of ER stress-responsive pro-apoptotic factors and β-cell function through modulation of key ER Ca2+ transporters. To test this hypothesis, we generated inducible β-cell models of WFS1 knockdown and overexpression using rat insulinoma cell lines to monitor β-cell function and β-cell death. We employed chemical and physiologic stimuli to model ER stress and monitored its downstream effects by real-time PCR, immunoblot and intracellular calcium mobilization. Our data indicate that β-cells depleted of WFS1 exhibit impaired insulin secretion and reduced insulin content. Additionally, knockdown of WFS1 is associated with decreased ER Ca2+, increased cytosolic Ca2+ and increased β-cell death. Conversely, increasing WFS1 expression in vitro increases insulin production and confers protection against ER stress-mediated β-cell death. Our data suggest that WFS1 may preserve β-cell viability by reducing the expression of pro-apoptotic factors CHOP and TRIB3. Future studies seek to clarify the mechanisms by which WFS1 protects β-cells against metabolic stressors and promotes insulin production. These studies will expand our understanding of the broader mechanisms by which ER dysfunction triggers β-cell pathology in more common forms of diabetes, and provide potential novel targets for intervention that center on preserving ER homeostasis. Disclosure D. Abreu: None. Z. Lavagnino: None. C.M. Brown: None. D.W. Piston: None. F. Urano: Research Support; Self; Eli Lilly and Company. Stock/Shareholder; Self; CytRx.