Requirements of calcium fluxes and ERK kinase activation for glucose- and interleukin-1β-induced β-cell apoptosis

Increasing evidence indicates that β-cell apoptosis and impaired secretory function were partly mediated by interleukin (IL)-1β and/ or high-glucose-induced β-cell production of IL-1β. However, the specific signal transduction pathways and molecular events involved in β-cell dysfunction remain largely unresolved. In this study, we investigated whether Ca²⁺ and extracellular signal-regulated kinase (ERK) activation plays a role for IL-1β action in rat islets. Exposure of rat islets for 4 days to 33.3 mM glucose and 140ng/ml IL-1β-induced β-cell apoptosis and impaired glucose-stimulated insulin secretion. By Western blotting with phosphospecific antibodies, glucose and IL-1β were shown to activate ERK. Ca²⁺ channel blocker nimodipine or ERK inhibitor PD98059 prevented glucose- and IL-1β-induced ERK activation, β-cell apoptosis, and impaired function. Furthermore, treatment with Ca²⁺ ionophore ionomycin, or exposure to thapsigargin, an inhibitor of sarco(endo)plasmic reticulum Ca²⁺ ATPase, all caused an amplification of IL-1β-induced ERK activation in rat islet. On the other hand, a chelator of intracellular free Ca²⁺ [bis-(o-aminophenoxy)-N,N,N,N-tetraacetic acid-acetoxymethyl] (BAPTA/ AM) and an inhibitor of calmodulin (W7) diminished IL-1β-induced phosphorylation of ERK. Finally, islet release of IL-1β in response to high glucose could be abrogated by nimodipine, mibefradil, or PD98059. Together, these data suggest that glucose- and IL-1β-induced β-cell secretory dysfunction and apoptosis are Ca²⁺ influx and ERK dependent in rat islets.