Induction of endoplasmic reticulum stress-induced β-cell apoptosis and accumulation of polyubiquitinated proteins by human islet amyloid polypeptide

Huang C-j, Haataja L, Gurlo T, Butler AE, Wu X, Soeller WC, Butler PC. Induction of endoplasmic reticulum stress-induced beta-cell apoptosis and accumulation of polyubiquitinated proteins by human islet amyloid polypeptide. Am J Physiol Endocrinol Metab 293: E1656-E1662, 2007. First published October 2, 2007; doi: 10.1152/ajpendo.00318.2007. - The islet in type 2 diabetes is characterized by an similar to 60% beta-cell deficit, increased beta-cell apoptosis, and islet amyloid derived from islet amyloid polypeptide ( IAPP). Human IAPP (hIAPP) but not rodent IAPP ( rIAPP) forms toxic oligomers and amyloid fibrils in an aqueous environment. We previously reported that overexpression of hIAPP in transgenic rats triggered endoplasmic reticulum ( ER) stress-induced apoptosis in beta-cells. In the present study, we sought to establish whether the cytotoxic effects of hIAPP depend on its propensity to oligomerize, rather than as a consequence of protein overexpression. To accomplish this, we established a novel homozygous mouse model overexpressing rIAPP at a comparable expression rate and, on the same background, as a homozygous transgenic hIAPP mouse model previously reported to develop diabetes associated with beta-cell loss. We report that by 10 wk of age hIAPP mice develop diabetes with a deficit in beta-cell mass due to increased beta-cell apoptosis. The rIAPP transgenic mice counterparts do not develop diabetes or have decreased beta-cell mass. Both rIAPP and hIAPP transgenic mice have increased expression of BiP, but only hIAPP transgenic mice have elevated ER stress markers (X-box-binding protein-1, nuclear localized CCAAT/enhancer binding-protein homologous protein, active caspase-12, and accumulation of ubiquitinated proteins). These findings indicate that the beta-cell toxic effects of hIAPP depend on the propensity of IAPP to aggregate, but not on the consequence of protein overexpression.