Effects of endothelin B receptor agonists on amyloid β protein (25–35)-induced neuronal cell death

Abstract

Endothelin (ET), a vasoconstrictive peptide, acts as an anti-apoptotic factor, and endothelin receptor B (ET B receptor) is associated with neuronal survival in the brain. In the Alzheimer’s disease (AD) brain, accumulation of amyloid β protein (Aβ) is thought to cause neuronal cell death via apoptosis. In the present study, we investigated effects of ET B receptor agonists on Aβ-induced neuronal cell death. In primary cultures of rat cortical neurons, Aβ(25–35) caused neuronal cell death in a concentration- and time-dependent manner. Aβ(25–35)-induced neuronal cell death was accompanied by chromatin condensation and DNA fragmentation, exhibiting apoptotic features. ET-3 and IRL-1620, ET B receptor agonists, significantly prevented neurons from undergoing Aβ(25–35)-induced cell death. Prior to cell death, Aβ increased concentration of intracellular Ca 2+ ([Ca 2+] i). Nimodipine, an L-type voltage-sensitive Ca 2+ channel (L-VSCC) blocker, suppressed the Aβ-induced Ca 2 influx, and attenuated Aβ-induced neuronal apoptosis. On the other hand, ω-conotoxin GIVA, an N-type VSCC blocker and ω-conotoxin MVIIC and ω-agatoxin IVA, P/Q-type VSCC blockers, had no effect. ET-3 and IRL-1620 significantly blocked Aβ(25–35)-induced Ca 2 influx. Furthermore, BQ788, an ET B receptor antagonist, inhibited both an anti-apoptotic effect and an L-VSCC-inactivating effect of ET B receptor agonists. In conclusion, ET B receptor agonists exhibit a protective effect against neurotoxicity of Aβ. Furthermore, these agonists appear to act as anti-apoptotic factors by blocking of L-VSCCs.