ULTRASTRUCTURAL EVIDENCE THAT APOPTOSIS IS THE MECHANISM BY WHICH HUMAN AMYLIN EVOKES DEATH IN RINm5F PANCREATIC ISLET β-CELLS

Abstract

A view is emerging that human amylin (HA) kills pancreatic islet β-cells by apoptosis. This study strengthens this view by documenting time-dependent morphological and ultrastructural changes in 10μm HA-treated cultured RINm5F islet β-cells. Membrane blebbing and microvilli loss were the earliest detectable apoptosis-related phenomena, already evident 1h after HA exposure. Following 6–12h of HA-treatment, chromatin margination became evident, consistent with detecting DNA laddering about the same time. Nuclear shrinkage, nuclear membrane convolution and prominent cytoplasmic vacuolization were clearly recognized at 22h post-treatment. Together, these cellular changes constitute a strong case for HA-induced apoptosis, and further demonstrates that electron microscopy is a more sensitive tool for early apoptosis detection in cultured cells than classical biochemical assays like visualizing DNA laddering. The ultrastructural changes reported here contribute further evidence to be included in the ongoing dissection of molecular mechanisms underlying HA-induced apoptosis, as may occur in type-2 diabetes mellitus.