title: Axonal protection by Nmnat3 overexpression with involvement of autophagy in optic nerve degeneration.
abstract: Axonal degeneration often leads to the death of neuronal cell bodies. Previous studies demonstrated the crucial role of nicotinamide mononucleotide adenylyltransferase (Nmnat) 1, 2, and 3 in axonal protection. In this study, Nmnat3 immunoreactivity was observed inside axons in the optic nerve. Overexpression of Nmnat3 exerts axonal protection against tumor necrosis factor-induced and intraocular pressure (IOP) elevation-induced optic nerve degeneration. Immunoblot analysis showed that both p62 and microtubule-associated protein light chain 3 (LC3)-II were upregulated in the optic nerve after IOP elevation. Nmnat3 transfection decreased p62 and increased LC3-II in the optic nerve both with and without experimental glaucoma. Electron microscopy showed the existence of autophagic vacuoles in optic nerve axons in the glaucoma, glaucoma+Nmnat3 transfection, and glaucoma+rapamycin groups, although preserved myelin and microtubule structures were noted in the glaucoma+Nmnat3 transfection and glaucoma+rapamycin groups. The axonal-protective effect of Nmnat3 was inhibited by 3-methyladenine, whereas rapamycin exerted axonal protection after IOP elevation. We found that p62 was present in the mitochondria and confirmed substantial colocalization of mitochondrial Nmnat3 and p62 in starved retinal ganglion cell (RGC)-5 cells. Nmnat3 transfection decreased p62 and increased autophagic flux in RGC-5 cells. These results suggest that the axonal-protective effect of Nmnat3 may be involved in autophagy machinery, and that modulation of Nmnat3 and autophagy may lead to potential strategies against degenerative optic nerve disease.
authors.affiliation: Department of Ophthalmology, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kitaoka
authors.forename: Y
authors.initials: Y
authors.lastname: Munemasa
authors.forename: K
authors.initials: K
authors.lastname: Kojima
authors.forename: A
authors.initials: A
authors.lastname: Hirano
authors.forename: S
authors.initials: S
authors.lastname: Ueno
authors.forename: H
authors.initials: H
authors.lastname: Takagi
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001343:Autophagy / Q000187:drug effects; D001369:Axons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002460:Cell Line; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D007429:Intraocular Pressure / Q000187:drug effects; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009410:Nerve Degeneration / Q000201:enzymology* / Q000473:pathology* / Q000503:physiopathology; D018696:Neuroprotective Agents / Q000378:metabolism; D009612:Nicotinamide-Nucleotide Adenylyltransferase / Q000378:metabolism*; D009900:Optic Nerve / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology / Q000648:ultrastructure; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D000071456:Sequestosome-1 Protein; D020123:Sirolimus / Q000494:pharmacology; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000225:Adenine; D049452:Green Fluorescent Proteins; D006360:Heat-Shock Proteins; D008869:Microtubule-Associated Proteins; D018696:Neuroprotective Agents; D009612:Nicotinamide-Nucleotide Adenylyltransferase; D000071456:Sequestosome-1 Protein; D020123:Sirolimus; D014409:Tumor Necrosis Factor-alpha; C526109:Anxa3 protein, rat; C491079:Sqstm1 protein, rat; C485184:enhanced green fluorescent protein; C025946:3-methyladenine; C529445:NMNAT3 protein, rat