Intracellular amyloidogenesis by human islet amyloid polypeptide induces apoptosis in COS-1 cells

Human islet amyloid polypeptide (hIAPP) is co-secreted with insulin from pa ncreatic islet beta cells. This peptide spontaneously aggregates in the for m of fibrils, and amyloid deposits are associated with dead or degenerating beta cells, a hallmark of noninsulin-dependent diabetes mellitus. We demon strated that COS-1 cells transfected with vectors expressing hIAPP exhibite d intracellular amyloid deposits that were associated with cell death (O'Br ien, Butler, Kreutter, Kane, Eberhardt, Am J Pathol 1995, 147:609-616). To establish the mechanism of cell death, we transfected COS-1 cells with vect ors expressing amyloidogenic hIAPP or nonamyloidogenic rat IAPP and mutant hIAPP constructs and assayed them for markers characteristic of apoptosis a nd necrosis by fluorescence-activated cell sorting analysis, Amyloidogenic hIAPP-transfected COS cells contained up to threefold more apoptotic cells present at 96 hours after transfection compared with the nonamyloidogenic v ector controls. The hIAPP-induced apoptosis was negligible at 24 and 48 hou rs after transfection and was maximal at 96 hours which parallels the time course of amyloidogenesis. Immunohistochemical staining and confocal micros copy showed that hIAPP is localized with distinct clustering in the endopla smic reticulum and Golgi apparatus with no discernable extracellular staini ng. These experiments provide direct evidence that intracellular hIAPP amyl oid causes cell death by triggering apoptotic pathways.