Protection of MES23.5 dopaminergic cells by obestatin is mediated by proliferative rather than anti-apoptotic action

Obestatin is an endogenous peptide sharing a precursor with ghrelin. This study aims to investigate whether and how obestatin protects MES23.5 dopaminergic cells against 1-methyl-4-phenylpyridinium (MPP⁺)-induced neurotoxicity. MES23.5 cells were pretreated with obestatin (10 ^-13-10^-6 mol/L) for 20 min prior to incubation with 200 μmol/L MPP⁺ for 12 or 24 h, or treated with obestatin alone (10^-13 to 10^-6 mol/L) for 0, 6, 12, and 24 h. The methyl thiazolyl tetrazolium (MTT) assay was used to measure cell viability. Flow cytometry was used to measure the caspase-3 activity and the mitochondrial transmembrane potential. Proliferating cell nuclear antigen (PCNA) protein levels were determined by Western blotting. Obestatin (10^-13 to 10^-7 mol/L) pretreatment blocked or even reversed the MPP ⁺-induced reduction of viability in MES23.5 cells, but had no effect on MPP⁺-induced mitochondrial transmembrane potential collapse and caspase-3 activation. When applied alone, obestatin increased viability. Elevated PCNA levels occurred with 10^-7, 10^-9, 10 ^-11 and 10^-13 mol/L obestatin treatment for 12 h. The results suggest that the protective effects of obestatin against MPP⁺ in MES23.5 cells are due to its proliferation-promoting rather than anti-apoptotic effects.