beta-Cell granules contain proteins involved in fuel regulation, which when altered, contribute to metabolic disorders including diabetes mellitus. We analyzed proteins present in purified granules from the INS-1E beta-cell model. Fifty-one component proteins were identified by LC-MS/MS including hormones, granins, protein processing components, cellular trafficking components, enzymes implicated in cellular metabolism and chaperone proteins. These findings may increase understanding of granule secretion and the processes leading to protein aggregation and beta-cell death in type-2 diabetes.

During insulin-dependent diabetes mellitus, immune cells infiltrate pancreatic islets progressively and mediate beta cell destruction over a prolonged asymptomatic prediabetic period. Apoptosis may be a major mechanism of beta cell loss during the disease. This process involves a proteolytic cascade in which upstream procaspases are activated which themselves activate downstream caspases, including caspase-3, a key enzyme involved in the terminal apoptotic cascade. Here dual-label immunohistochemistry was employed to examine the intra-islet expression, distribution and cellular sources of active caspase-3 in the non-obese diabetic (NOD) mouse given cyclophosphamide to accelerate diabetes. NOD mice were treated at day 95 and caspase-3 expression was studied at days 0, 4, 7, 11 and 14. Its expression was also correlated with advancing disease and compared with age-matched NOD mice treated with diluent alone. At day 0 (=day 95), caspase-3 immunolabelling was observed in several peri-islet and intra-islet macrophages, but not in CD4 and CD8 cells and only extremely rarely in beta cells. At day 4, only a few beta cells weakly expressed the enzyme, in the absence of significant insulitis. At day 7, caspase-3 expression was observed in a small proportion of intra-islet macrophages. At day 11, there was a marked increase in the number of intra-islet macrophages positive for caspase-3 while only a few CD4 cells expressed the enzyme. At day 14, caspase-3 labelling became prominent in a significant proportion of macrophages. Only a few CD4 and CD8 cells expressed the enzyme. Capase-3 labelling was also present in a proportion of macrophages in perivascular and exocrine regions. Surprisingly, beta cell labelling of caspase-3 at days 11 and 14 was rare. At this stage of heightened beta cell loss, a proportion of intra-islet interleukin-1beta-positive cells coexpressed the enzyme. Caspase-3 was also observed in numerous Fas-positive cells in heavily infiltrated islets. During this late stage, only a proportion of caspase-3-positive cells contained apoptotic nuclei, as judged by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL). We conclude that during cyclophosphamide-accelerated diabetes in the NOD mouse, the predominant immunolabelling of caspase-3 in intra-islet macrophages suggests that apoptosis of macrophages may be an important mechanism for its elimination. The virtual absence of caspase-3 immunolabelling in most beta cells even during heightened beta cell loss supports their rapid clearance following their death during insulin-dependent diabetes mellitus.