title: Manganese nanoparticle activates mitochondrial dependent apoptotic signaling and autophagy in dopaminergic neuronal cells.
abstract: The production of man-made nanoparticles for various modern applications has increased exponentially in recent years, but the potential health effects of most nanoparticles are not well characterized. Unfortunately, in vitro nanoparticle toxicity studies are extremely limited by yet unresolved problems relating to dosimetry. In the present study, we systematically characterized manganese (Mn) nanoparticle sizes and examined the nanoparticle-induced oxidative signaling in dopaminergic neuronal cells. Differential interference contrast (DIC) microscopy and transmission electron microscopy (TEM) studies revealed that Mn nanoparticles range in size from single nanoparticles (~25 nM) to larger agglomerates when in treatment media. Manganese nanoparticles were effectively internalized in N27 dopaminergic neuronal cells, and they induced a time-dependent upregulation of the transporter protein transferrin. Exposure to 25-400 μg/mL Mn nanoparticles induced cell death in a time- and dose-dependent manner. Mn nanoparticles also significantly increased ROS, accompanied by a caspase-mediated proteolytic cleavage of proapoptotic protein kinase Cδ (PKCδ), as well as activation loop phosphorylation. Blocking Mn nanoparticle-induced ROS failed to protect against the neurotoxic effects, suggesting the involvement of other pathways. Further mechanistic studies revealed changes in Beclin 1 and LC3, indicating that Mn nanoparticles induce autophagy. Primary mesencephalic neuron exposure to Mn nanoparticles induced loss of TH positive dopaminergic neurons and neuronal processes. Collectively, our results suggest that Mn nanoparticles effectively enter dopaminergic neuronal cells and exert neurotoxic effects by activating an apoptotic signaling pathway and autophagy, emphasizing the need for assessing possible health risks associated with an increased use of Mn nanoparticles in modern applications.
authors.affiliation: Department of Biomedical Sciences, Iowa Center for Advanced Neurotoxicology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Hilary
authors.initials: H
authors.lastname: Afeseh Ngwa
authors.forename: Arthi
authors.initials: A
authors.lastname: Kanthasamy
authors.forename: Yan
authors.initials: Y
authors.lastname: Gu
authors.forename: Ning
authors.initials: N
authors.lastname: Fang
authors.forename: Vellareddy
authors.initials: V
authors.lastname: Anantharam
authors.forename: Anumantha G
authors.initials: AG
authors.lastname: Kanthasamy
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001343:Autophagy / Q000187:drug effects* / Q000502:physiology; D015153:Blotting, Western; D002460:Cell Line; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D006861:Hydrogen Peroxide / Q000378:metabolism; D017895:Manganese Compounds / Q000494:pharmacology*; D053768:Metal Nanoparticles / Q000648:ultrastructure; D051379:Mice; D046529:Microscopy, Electron, Transmission; D008857:Microscopy, Interference; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013481:Superoxides / Q000378:metabolism
chemical_list: D017895:Manganese Compounds; D013481:Superoxides; D006861:Hydrogen Peroxide