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    Contribution of WFS1 to Pancreatic Beta Cell Survival and Adaptive Alterations in WFS1 Deficiency: A Dissertation

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    Authors
    O'Sullivan-Murphy, Bryan M.
    Faculty Advisor
    Dr. Fumihiko Urano
    Academic Program
    MD/PhD
    UMass Chan Affiliations
    Molecular Medicine
    Document Type
    Doctoral Dissertation
    Publication Date
    2012-04-20
    Keywords
    Diabetes Mellitus
    Membrane Proteins
    Insulin-Secreting Cells
    Endoplasmic Reticulum
    Amino Acids, Peptides, and Proteins
    Biochemistry, Biophysics, and Structural Biology
    Cell and Developmental Biology
    Cells
    Cellular and Molecular Physiology
    Endocrine System Diseases
    Hormones, Hormone Substitutes, and Hormone Antagonists
    Immune System Diseases
    Nutritional and Metabolic Diseases
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    Abstract
    Diabetes mellitus comprises a cohort of genetic and metabolic diseases which are characterized by the hallmark symptom of hyperglycemia. Diabetic subtypes are based on their pathogenetic origins: the most prevalent subtypes are the autoimmune-mediated type 1 diabetes mellitus (T1DM) and the metabolic disease of type 2 diabetes mellitus (T2DM). Genetic factors are major contributory aspects to diabetes development, particularly in T2DM where there is close to 80% concordance rates between monozygotic twins. However, the functional state of the pancreatic β cell is of paramount importance to the development of diabetes. Perturbations that lead to β cell dysfunction impair insulin production and secretion and precede diabetes onset. The endoplasmic reticulum (ER) is a subcellular organelle network of tubes and cisternae with multifaceted roles in cellular metabolism. Alterations to ER function such as those begotten by the accumulation of misfolded and unfolded ER client proteins upset the ER homeostatic balance, leading to a condition termed ER stress. Subsequent sensing of ER stress by three ER transmembrane proteins, initiates an adaptive reaction to alleviate ER stress: this is known as the unfolded protein response (UPR). Divergent cascades of the UPR attempt to mitigate ER stress and restore ER homeostasis: Failing that, the UPR initiates pro-apoptotic pathways. The demand of insulin production on the β cell necessitates the presence of a highly functional ER. However, the consequence of dependence on the ER for insulin synthesis and secretion portends disaster for the functional state of the β cell. Disturbances to the ER that elicit ER stress and UPR activation causes β cell dysfunction and may lead to apoptosis. There are numerous well-characterized models of ER stress-mediated diabetes, including genetic mutations in UPR transducers and insulin. Recently, polymorphisms in Wolfram syndrome 1 (WFS1), an ER transmembrane protein involved in the UPR, were suggested to contribute to T2DM risk. In this thesis, one of the highlighted WFS1 polymorphism, H611R, was examined to identify its contribution to β cell function and viability, and hence, diabetes risk. It was revealed that augmentation of WFS1 expression increased insulin secretion and cellular content. In addition, WFS1 protected β cells against ER stress-mediated dysfunction, with a more pronounced effect in the WFS1-R611 protective allele. Subsequent gene expression analysis identified netrin-1 as a WFS1-induced survival factor. As a contributory factor to diabetes progression, ER stress and UPR are potential drug and biomarker targets. In this dissertation, a novel UPR-regulating microRNA (miRNA) family was uncovered in ER stressed, WFS1-deficient islets. These miRNAs, the miR-29 family, are induced in WFS1 -/- islets as a possible adaptive alteration to chronic ER stress conditions, and indirectly decreases the expression of UPR transducers, while directly targeting downstream ER stress-related pro-apoptotic factors. Collectively, this work extends the function of WFS1 as a protective factor in the pancreatic β cell through the induction of netrin-1 signaling. Additionally, it further strengthens the role of miRNA as regulatory members of the UPR which contribute to cell survival.
    DOI
    10.13028/c6e3-gx67
    Permanent Link to this Item
    http://hdl.handle.net/20.500.14038/31935
    Rights
    Copyright is held by the author, with all rights reserved.
    ae974a485f413a2113503eed53cd6c53
    10.13028/c6e3-gx67
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