Cytotoxicity of paraquat in microglial cells: Involvement of PKCδ- and ERK1/2-dependent NADPH oxidase

Abstract

Excess production of reactive oxygen species (ROS) is an important mechanism underlying the pathogenesis of a number of neurodegenerative diseases including Parkinson's disease (PD) which is characterized by a progressive loss of dopaminergic neurons in the substantia nigra. Exposure to paraquat, an herbicide with structure similar to the dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium (MPP + ), has been shown to produce PD-like symptoms. Despite previous focus on the dopaminergic neurons and signaling pathways involved in their cell death, recent studies have implicated microglial cells as a major producer of ROS for damaging neighboring neurons. In this study, we examined the source of ROS and the underlying signaling pathway for paraquat-induced cytotoxicity to BV-2 microglial cells. Paraquat-induced ROS production (including superoxide anions) in BV-2 cells was accompanied by translocation of the p67phox cytosolic subunit of NADPH oxidase to the membrane. Paraquat-induced ROS production was inhibited by NADPH oxidase inhibitors, apocynin and diphenylene iodonium (DPI), but not the xanthine/xanthine oxidase inhibitor, allopurinol. Apocynin and DPI also rescued cells from paraquat-induced toxicity. The inhibitors for protein kinase C delta (PKCδ) or extracellular signal-regulated kinases (ERK1/2) could partially attenuate paraquat-induced ROS production and cell death. Rottlerin, a selective PKCδ inhibitor, also inhibited paraquat-induced translocation of p67phox. Taken together, this study demonstrates the involvement of ROS from NADPH oxidase in mediating paraquat cytotoxicity in BV-2 microglial cells and this process is mediated through PKCδ-and ERK-dependent pathways.

Suppression of ROS generation by 4,4'-diaminodiphenylsulfone in non-phagocytic human diploid fibroblasts

“…PKC is involved in the ligand-initiated assembly of NADPH oxidase (NOX) for the generation of superoxide anions (Martins et al, 2002). Recently, paraquat has been shown to induce ROS through activation of PKC-delta dependent NOX (Miller et al, 2007). In addition, mitochondria are involved in paraquat-induced oxidative stress and toxicity.…”

Resveratrol: A miraculous natural compound for diseases treatment

“…Although environmental and genetic factors contribute to PD development, the exact etiology remains unclear yet (Gasser, 2005; Sun et al., 2010). Recent studies showed that neurotoxic agents are possible inducers of PD such as manganese (Sun, Yang, & Kim, 1993), dimethoxy phenyl‐ethylamine (Koshimura et al., 1997), paraquat (Miller, Sun, & Sun, 2007), and 1‐methyl‐4‐phenyl‐1, 2, 3,6‐tetrahydropyridine (MPTP) causing oxidative stress, and also mitochondrial dysfunction (Alvira et al., 2007) and inflammation are important factors in dopaminergic neurons degeneration in PD (Giasson, Ischiropoulos, Lee, & Trojanowski, 2002; Sun et al., 2010). Mitochondrial dysfunction plays an important role in the pathogenesis of PD.…”

Protective effect of 4,4'-diaminodiphenylsulfone against paraquat-induced mouse lung injury

“…PKC isoforms have been implicated in the generation of superoxide anions via NOX activation (Miller et al, 2007). Western blot analysis with antiphospho-PKC antibodies was carried out to examine the phosphorylation status of specific PKC isoforms in mouse lung after PQ treatment.…”

“…Notably, NADPH oxidases, NOX2 and NOX4, are predominantly expressed in lung tissues (van der Vliet, 2008;Hecker et al, 2009). Moreover, protein kinase C (PKC) participates in the ligand-initiated assembly of NOX, which proceeds the generation of superoxide anions (Miller et al, 2007). Among more than 20 different PKC isoforms present in mammalian cells, several PKC isoforms are already reported to be linked with expression or activation of NOX; such as PKC μ in lung (Rennecke et al, 1996), PKC δ in mouse adipocytes (Talior et al, 2005) and microglial cells (Miller et al, 2007), and PKC α in human endothelial cells (Xu et al, 2008).…”

“…Moreover, protein kinase C (PKC) participates in the ligand-initiated assembly of NOX, which proceeds the generation of superoxide anions (Miller et al, 2007). Among more than 20 different PKC isoforms present in mammalian cells, several PKC isoforms are already reported to be linked with expression or activation of NOX; such as PKC μ in lung (Rennecke et al, 1996), PKC δ in mouse adipocytes (Talior et al, 2005) and microglial cells (Miller et al, 2007), and PKC α in human endothelial cells (Xu et al, 2008). Since several PKC isoforms, including PKC α, β, δ, and μ, are expressed in lung, it is necessary to confirm the possible involvement of a specific PKC isoform that is associated with PQ-induced ROS generation in the mouse lung.…”