OBJECTIVE-Endoplasmic reticulum (ER) stress-induced apoptosis may be a common cause of cell attrition in diseases characterized by misfolding and oligomerisation of amyloidogenic proteins. The islet in type 2 diabetes is characterized by islet amyloid derived from islet amyloid polypeptide (IAPP) and increased -cell apoptosis. We questioned the following: 1) whether IAPP-induced -cell apoptosis is mediated by ER stress and 2) whether -cells in type 2 diabetes are characterized by ER stress.
RESEARCH DESIGN AND METHODS-The mechanism of IAPP-induced apoptosis was investigated in INS-1 cells and human IAPP (HIP) transgenic rats. ER stress in humans was investigated by -cell C/EBP homologous protein (CHOP) expression in 7 lean nondiabetic, 12 obese nondiabetic, and 14 obese type 2 diabetic human pancreata obtained at autopsy. To assure specificity for type 2 diabetes, we also examined pancreata from eight cases of type 1 diabetes.RESULTS-IAPP induces -cell apoptosis by ER stress in INS-1 cells and HIP rats. Perinuclear CHOP was rare in lean nondiabetic (2.6 Ϯ 2.0%) and more frequent in obese nondiabetic (14.6 Ϯ 3.0%) and obese diabetic (18.5 Ϯ 3.6%) pancreata. Nuclear CHOP was not detected in lean nondiabetic and rare in obese nondiabetic (0.08 Ϯ 0.04%) but six times higher (P Ͻ 0.01) in obese diabetic (0.49 Ϯ 0.17%) pancreata. In type 1 diabetic pancreata, perinuclear CHOP was rare (2.5 Ϯ 2.3%) and nuclear CHOP not detected. B oth type 1 and type 2 diabetes are characterized by deficits in -cell mass and increased -cell apoptosis (1-6). The mechanism that initiates -cell apoptosis in type 1 diabetes is believed to be autoimmune-mediated cytokine production (5). Several mechanisms have been proposed for increased -cell apoptosis in type 2 diabetes, including oxygen free radicals (7), free fatty acid toxicity (8), interleukin-1 (9), and formation of islet amyloid polypeptide (IAPP) toxic oligomers (10 -12).
CONCLUSIONS-ERProgrammed cell death, or apoptosis, is important in multicellular organisms to permit organ development and remodeling (13). In disease states, apoptosis permits selective removal of cells that are damaged, particularly in relation to cell cycle, so that damage is not propagated (3,14). Apoptosis may be initiated by a wide variety of cellular insults, which are currently thought to act through at least three pathways that converge to accomplish irreversible destruction of the cell's chromosomes. These three major pathways have been designated as the extrinsic and intrinsic pathways and endoplasmic reticulum (ER) stress pathway (15,16). The extrinsic pathway is classically exemplified by cytokine-induced cell death, mediated through cell surface death receptors (17). The intrinsic pathway is most often described as a response to mitochondrial disruption, for example, secondary to oxygen free radicals (18). ER stress-induced apoptosis is classically ascribed to aggregates of misfolded protein that are believed to compromise the ER membrane (15).The human pancreatic -cell is vulnerable to al...