Non-insulin dependent diabetes (NIDDM) is an aging-related disease associated with amyloid 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 dollars. A mutation (S20G) in the human islet amyloid precursor protein (hIAPP, amylin) has been associated with premature onset NIDDM in Japanese populations, providing a direct linkage of the IAPP gene with 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 hIAPP expression in COS-1 cells results in the accumulation of intracellular amyloid within the endoplasmic reticulum (ER)/Golgi and induction of apoptosis. 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. In preliminary studies we have found that the accumulation of amyloid within the ER/Golgi is associated with an early induction of the molecular chaperone Bip/GRP78, a protein that is involved in sealing ER translocon pores and protein folding. The induction of Bip/GRP78 is a characteristic of two ER stress response pathways: unfolded protein response (UPR) and ER overload response (EOR). Both of these pathways are involved in ER quality control. To date our data suggest that intracellular amyloid accumulation and subsequent induction of apoptosis may be mediated by one or both of these pathways. The current studies will: (i) assess the relative apoptogenic activity of the wild-type and mutant IAPPS20G expression on COS-1 and pancreatic betaTC-3 cells, (ii) establish whether the UPR or EOR stress response is activated by intracellular amyloid accumulation and their role(s) in inducing apoptosis, (iii) determine whether changes in ER Ca2+ activate apoptosis, (iv) determine the relative role of mitochondrial proteins in amyloid-induced apoptosis, and (v) define the distal caspase-mediated pathways leading to apoptosis. These studies will increase our understanding of the contribution of intracellular amyloid accumulation to the pathogenesis of NIDDM.
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