Melatonin attenuates kainic acid-induced neurotoxicity in mouse hippocampus via inhibition of autophagy and α-synuclein aggregation.
In this study, the protective effect of melatonin on kainic acid (KA)-induced neurotoxicity involving autophagy and α-synuclein aggregation was investigated in the hippocampus of C57/BL6 mice. Our data showed that intraperitoneal injection of KA (20 mg/kg) increased LC3-II levels (a hallmark protein of autophagy) and reduced mitochondrial DNA content and cytochrome c oxidase levels (a protein marker of mitochondria). Atg7 siRNA transfection prevented KA-induced LC3-II elevations and mitochondria loss. Furthermore, Atg7 siRNA attenuated KA-induced activation of caspases 3/12 (biomarkers of apoptosis) and hippocampal neuronal loss, suggesting a pro-apoptotic role of autophagy in the KA-induced neurotoxicity. Nevertheless, KA-induced α-synuclein aggregation was not affected in the Atg7 siRNA-transfected hippocampus. The neuroprotective effect of melatonin (50 mg/kg) orally administered 1 hr prior to KA injection was studied. Melatonin was found to inhibit KA-induced autophagy-lysosomal activation by reducing KA-induced increases in LC3-II, lysosomal-associated membrane protein 2 (a biomarker of lysosomes) and cathepsin B (a lysosomal cysteine protease). Subsequently, KA-induced mitochondria loss was prevented in the melatonin-treated mice. At the same time, melatonin reduced KA-increased HO-1 levels and α-synuclein aggregation. Our immunoprecipitation study showed that melatonin enhanced ubiquitination of α-synuclein monomers and aggregates. The anti-apoptotic effect of melatonin was demonstrated by attenuating KA-induced DNA fragmentation, activation of caspases 3/12, and neuronal loss. Taken together, our study suggests that KA-induced neurotoxicity may be mediated by autophagy and α-synuclein aggregation. Moreover, melatonin may exert its neuroprotection via inhibiting KA-induced autophagy and a subsequent mitochondrial loss as well as reducing α-synuclein aggregation by enhancing α-synuclein ubiquitination in the CNS.
Institute of Pharmacology, National Yang-Ming University, Taipei, Taiwan.
Chia-Fu
CF
Chang
Hui-Ju
HJ
Huang
Hsin-Chen
HC
Lee
Kai-Chih
KC
Hung
Rong-Tsun
RT
Wu
Anya Maan-Yuh
AM
Lin
D000818:Animals; D001343:Autophagy / Q000187:drug effects; D001483:Base Sequence; D006624:Hippocampus / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D047468:Immunoprecipitation; D007608:Kainic Acid / Q000494:pharmacology*; D008550:Melatonin / Q000494:pharmacology*; D051379:Mice; D034741:RNA, Small Interfering; D051844:alpha-Synuclein / Q000378:metabolism*
D034741:RNA, Small Interfering; D051844:alpha-Synuclein; D008550:Melatonin; D007608:Kainic Acid