Non-insulin dependent diabetes (NIDDM) is an aging-related disease associated with arnyloid formation in the pancreas and loss of beta cell mass. The mechanism(s) of pancreatic beta cell death in NIDDM are unknown. NIDDM is a major disease that currently affects approximately 7.2 million Americans with annual costs exceeding $100 billion. A mutation (IAPPS20G) in he human wild-type islet amyloid precursor protein (hIAPPWT, amylin) has been associated with premature onset NIDDM in Japanese populations, providing a direct linkage of the IAPP gene with the genesis of NIDDM. IAPP is the major component of islet cell amyloid deposits which are a hallmark of NIDDM, suggesting that islet amyloid may be involved in the pathogenesis of this disease. We demonstrated that hIAPPWT expression in COS-1 and betaTC-3 cells results in the accumulation of intracellular amyloid within the endoplasmic reticulum (ER)/Golgi and induction of apoptosis. The expression of IAPPS2OG in these cells results in increased cytotoxicty and this is correlated with its increased in vitro amyloidogenic character as compared to IAPPWT. Accordingly, we have hypothesized that: (i) intracellular amyloidogenesis is a primary cause of beta cell death, and (ii) protective mechanisms that prevent intracellular amyloidogenesis are compromised by factors predisposing to NIDDM. Our preliminary data indicate that the accumulation of amyloid within he ER/Golgi is associated with an early induction of the molecular chaperone Bip/GRP78, a protein that appears to be signalling intermediate for two ER stress response pathways, unfolded protein response (UPR) and ER overload response (EOR), that are involved in ER quality control. Our data suggest that intracellular amyloid accumulation and subsequent induction of apoptosis may be mediated by one or both of these pathways. In the current studies we will: (1) assess the physiologic relevance of IAPPWT and IAPPS20G expression and amyloid formation and their relative ability to lead to diabetes in mouse knock-in models, (2) establish whether the UPR or EOR stress response is activated by intracellular amyloid accumulation and their role(s) in inducing apoptosis, (3) determine whether changes in ER Ca2+ activate apoptosis. (4) Determine the relative role of mitochondrial proteins in amyloid-induced apoptosis, and (5) define the distal caspase mediated pathways leading to apoptosis. These studies will increase our understanding of the contribution of intracellular amyloid accumulation, induction of apoptosis, and/or interference with ER trafficking to the pathogenesis of NIDDM.
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