Vanadium induces dopaminergic neurotoxicity via protein kinase Cdelta dependent oxidative signaling mechanisms: Relevance to etiopathogenesis of Parkinson's disease

Environmental exposure to neurotoxic metals through various sources including exposure to welding fumes has been linked to an increased incidence of Parkinson's disease (PD). Welding fumes contain many different metals including vanadium typically present as particulates containing vanadium pentoxide (V2O5). However, possible neurotoxic effects of this metal oxide on dopaminergic neuronal cells are not well studied. In the present Study, we characterized vanadium-induced oxidative stress-dependent cellular events in cell culture models of PD. V2O5 was neurotoxic to dopaminergic neuronal cells including primary nigral dopaminergic neurons and the EC50 was determined to be 37 mu M in N27 dopaminergic neuronal cell model. The neurotoxic effect was accompanied by a time-dependent uptake of vanadium and Upregulation of metal transporter proteins Tf and DMT1 in N27 cells. Additionally, vanadium resulted in a threefold increase in reactive oxygen species generation, followed by release of mitochondrial cytochrome c into cytoplasm and Subsequent activation of caspase-9 (>fourfold) and caspase-3 (>ninefold). Interestingly, vanadium exposure induced proteolytic cleavage of native protein kinase Cdelta (PKC delta, 72-74 kDa) to yield a 41 kDa catalytically active fragment resulting in a persistent increase in PKC delta kinase activity. Co-treatment with pan-caspase inhibitor Z-VAD-FMK significantly blocked vanadium-induced PKC delta proteolytic activation, indicating that caspases mediate PKC delta cleavage. Also, co-treatment with Z-VAD-FMK almost completely inhibited V2O5-induced DNA fragmentation. Furthermore, PKC delta knockdown using siRNA protected N27 cells from V2O5-induced apoptotic cell death. Collectively, these results demonstrate that vanadium can exert neurotoxic effects in dopaminergic neuronal cells via caspase-3-dependent PKC delta cleavage, suggesting that metal exposure may promote nigral dopaminergic degeneration. (C) 2009 Elsevier Inc. All rights reserved.