Functional and therapeutic insights into Wolfram syndrome pathophysiology

Wolfram syndrome is a rare, progressive neurodegenerative disorder characterized by juvenile-onset diabetes mellitus, optic nerve atrophy, diabetes insipidus and deafness. Although the monogenic origins of this multisystemic disorder were discovered to be recessive mutations in the WFS1 gene nearly two decades ago, little is known about the molecular functions of the associated endoplasmic reticulum (ER) protein. Increasingly, evidence from animal and cell models support a role for WFS1 in maintaining ER homeostasis. Wolfram syndrome is therefore considered a prototype of ER stress disease. To date, no therapies exist to stop or delay disease progression in patients with Wolfram syndrome. In this dissertation, we leverage Wolfram syndrome as a model of ER stress-mediated -cell dysfunction to identify PSP/reg as a potential circulating biomarker of -cell ER dyshomeostasis. We demonstrate that PSP/reg is not only induced by WFS1 loss-of-function, but also upregulated by wide-ranging causes of ER stress. We further explore the role of WFS1 in -cell viability and -cell function by carefully characterizing WFS1 knockout mouse models and investigating the associated molecular pathways regulated by WFS1 in the context of ER stress. Using cell models of WFS1-depletion and -overexpression, we identify a role for WFS1 in -cell survival through the negative regulation of the Chop–Trib3 axis, leading to the activation of Akt survival pathways. We also propose a role for WFS1 in maintaining -cell function by promoting -cell maturity and insulin biosynthesis, particularly under ER dyshomeostasis. To capitalize on our insights into the role of calcium dysfunction in Wolfram syndrome pathophysiology for therapeutic development, we evaluate dantrolene sodium as a potential treatment for this disease. Prompted by evidence of dantrolene efficacy in pancreatic -cell WFS1 knockout models and neural progenitor cells derived from induced pluripotent stem cells generated from Wolfram patients, we conducted the first clinical trial in patients with Wolfram syndrome through a 6-month phase 1b/2 study of dantrolene sodium with an optional extension phase up to 24-months (NCT02829268). The endpoints of this study were to assess: (1) dantrolene safety and tolerability in pediatric and adult Wolfram syndrome patients and (2) its effects on remaining -cell, visual and neurologic functions and quality of life measures. Among pediatric subjects, we found dantrolene well-tolerated at a daily dose of 0.5-mg/kg in those \u3c 50-kg and 2-mg/kg in those \u3e 50-kg. Adults tolerated dantrolene well between 50-mg – 100-mg daily. While common adverse events included mild fatigue, diarrhea, headache and hypoglycemia, no patient discontinued the trial regimen due to adverse effects. Notably, a mild increase in 30-minute mixed-meal-stimulated C-peptide was observed in subjects after 6- and 12-months of dantrolene treatment, with pediatric subjects exhibiting a sustained ~40% increase in stimulated C-peptide levels over 1.5-years of dantrolene treatment. Taken together, the findings presented in this dissertation propose a new clinical biomarker for monitoring -cell ER stress, expand our current understanding of WFS1 pathophysiology in -cell viability and function, and advance a novel therapeutic strategy for treatment of Wolfram syndrome. This work collectively demonstrates the power of studying rare disease in order to address the unmet medical and research needs of an orphan disorder while simultaneously expanding pathophysiological insights into the biology of more common diseases, such as type 2 diabetes