title: Methamphetamine-induced neurotoxicity linked to ubiquitin-proteasome system dysfunction and autophagy-related changes that can be modulated by protein kinase C delta in dopaminergic neuronal cells.
abstract: A compromised protein degradation machinery has been implicated in methamphetamine (MA)-induced neurodegeneration. However, the signaling mechanisms that induce autophagy and ubiquitin-proteasome system (UPS) dysfunction are not well understood. The present study investigates the contributions of protein kinase C delta (PKCδ)-mediated signaling events in MA-induced autophagy, UPS dysfunction, and cell death. Using an in vitro mesencephalic dopaminergic cell culture model, we demonstrate that MA-induced early induction of autophagy is associated with reduction in proteasomal function and concomitant dissipation of mitochondrial membrane potential (MMP), followed by significantly increased PKCδ activation, caspase-3 activation, accumulation of ubiquitin-positive aggregates and microtubule-associated light chain-3 (LC3-II) levels. Interestingly, siRNA-mediated knockdown of PKCδ or overexpression of cleavage-resistant mutant of PKCδ dramatically reduced MA-induced autophagy, proteasomal function, and associated accumulation of ubiquitinated protein aggregates, which closely paralleled cell survival. Importantly, when autophagy was inhibited either pharmacologically (3-MA) or genetically (siRNA-mediated silencing of LC3), the dopaminergic cells became sensitized to MA-induced apoptosis through caspase-3 activation. Conversely, overexpression of LC3 partially protected against MA-induced apoptotic cell death, suggesting a neuroprotective role for autophagy in MA-induced neurotoxicity. Notably, rat striatal tissue isolated from MA-treated rats also exhibited elevated LC3-II, ubiquitinated protein levels, and PKCδ cleavage. Taken together, our data demonstrate that MA-induced autophagy serves as an adaptive strategy for inhibiting mitochondria-mediated apoptotic cell death and degradation of aggregated proteins. Our results also suggest that the sustained activation of PKCδ leads to UPS dysfunction, resulting in the activation of caspase-3-mediated apoptotic cell death in the nigrostriatal dopaminergic system.
authors.affiliation: Parkinson's Disorder Research Laboratory, Iowa Center for Advanced Neurotoxicology, Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA.
authors.forename: M
authors.initials: M
authors.lastname: Lin
authors.forename: P
authors.initials: P
authors.lastname: Chandramani-Shivalingappa
authors.forename: H
authors.initials: H
authors.lastname: Jin
authors.forename: A
authors.initials: A
authors.lastname: Ghosh
authors.forename: V
authors.initials: V
authors.lastname: Anantharam
authors.forename: S
authors.initials: S
authors.lastname: Ali
authors.forename: A G
authors.initials: AG
authors.lastname: Kanthasamy
authors.forename: A
authors.initials: A
authors.lastname: Kanthasamy
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D000697:Central Nervous System Stimulants / Q000633:toxicity*; D053938:DNA Fragmentation; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008694:Methamphetamine / Q000633:toxicity*; D046529:Microscopy, Electron, Transmission; D009410:Nerve Degeneration / Q000139:chemically induced / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D051745:Protein Kinase C-delta / Q000378:metabolism*; D034741:RNA, Small Interfering; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D043743:Ubiquitin-Protein Ligase Complexes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000697:Central Nervous System Stimulants; D034741:RNA, Small Interfering; D008694:Methamphetamine; D043743:Ubiquitin-Protein Ligase Complexes; D051745:Protein Kinase C-delta; D046988:Proteasome Endopeptidase Complex