The S20G substitution in hIAPP is more amyloidogenic and cytotoxic than wild-type hIAPP in mouse islets.

AIMS/HYPOTHESIS: The S20G human islet amyloid polypeptide (hIAPP) substitution is associated with an earlier onset of type 2 diabetes in humans. Studies of synthetic S20G hIAPP in cell-free systems and immortalised beta cells have suggested that this may be due to increased hIAPP amyloidogenicity and cytotoxicity. Thus, using primary islets from mice with endogenous S20G hIAPP expression, we sought to determine whether the S20G gene mutation leads to increased amyloid-induced toxicity, beta cell loss and reduced beta cell function. METHODS: Islets from mice in which mouse Iapp was replaced with human wild-type or S20G hIAPP were isolated and cultured in vitro under amyloid-forming conditions. Levels of insulin and hIAPP mRNA and protein, amyloid deposition and beta cell apoptosis and area, as well as glucose-stimulated insulin and hIAPP secretion, were quantified. RESULTS: Islets expressing S20G hIAPP cultured in 16.7 mmol/l glucose demonstrated increased amyloid deposition and beta cell apoptosis, reduced beta cell area, decreased insulin content and diminished glucose-stimulated insulin secretion, compared with islets expressing wild-type hIAPP. Amyloid deposition and beta cell apoptosis were also increased when S20G islets were cultured in 11.1 mmol/l glucose (the concentration that is thought to be physiological for mouse islets). CONCLUSIONS/INTERPRETATION: S20G hIAPP reduces beta cell number and function, thereby possibly explaining the earlier onset of type 2 diabetes in individuals carrying this gene mutation.

Determination of Optimal Sample Size for Quantification of ß-Cell Area, Amyloid Area and ß-Cell Apoptosis in Isolated Islets.

Culture of isolated rodent islets is widely used in diabetes research to assess different endpoints, including outcomes requiring histochemical staining. As islet yields during isolation are limited, we determined the number of islets required to obtain reliable data by histology. We found that mean values for insulin-positive ß-cell area/islet area, thioflavin S-positive amyloid area/islet area and ß-cell apoptosis do not vary markedly when more than 30 islets are examined. Measurement variability declines as more islets are quantified, so that the variability of the coefficient of variation (CV) in human islet amyloid polypeptide (hIAPP) transgenic islets for ß-cell area/islet area, amyloid area/islet area and ß-cell apoptosis are 13.20% ± 1.52%, 10.03% ± 1.76% and 6.78% ± 1.53%, respectively (non-transgenic: 7.65% ± 1.17% ß-cell area/islet area and 8.93% ± 1.56% ß-cell apoptosis). Increasing the number of islets beyond 30 had marginal effects on the CV. Using 30 islets, 6 hIAPP-transgenic preparations are required to detect treatment effects of 14% for ß-cell area/islet area, 30% for amyloid area/islet area and 23% for ß-cell apoptosis (non-transgenic: 9% for ß-cell area/islet area and 45% for ß-cell apoptosis). This information will be of value in the design of studies using isolated islets to examine ß cells and islet amyloid.