title: Calpain-mediated degradation of G-substrate plays a critical role in retinal excitotoxicity for amacrine cells.
abstract: The role of neuronal N-methyl-D-aspartate (NMDA) receptor-mediated intracellular signaling has been elucidated in both physiological and pathological conditions. However, the details of relative vulnerability for excitotoxicity remain unknown. Retinal excitotoxicity is involved in various diseases leading to irreversible blindness. Here, we used the visual system and explored the mechanistic details of the NMDA-elicited intracellular events, especially in the amacrine cells, which are the most vulnerable type of neuron in the retina. G-substrate, a specific substrate of cyclic guanosine 3',5'-monophosphate (cGMP)-dependent protein kinase, is colocalized with amacrine cells and acts as an endogenous inhibitor of protein phosphatase. To elucidate how G-substrate was involved in NMDA-induced amacrine cell death, the immunohistochemical analysis with G-substrate antibody was performed following NMDA injury. In vivo, NMDA immediately decreased G-substrate immunoreactivity, and the suppression of calpain activation using ALLN or calpain III, an inhibitor of calpain, blocked this decrease. In vitro, degraded fragments of G-substrate were detected within 10 min after coincubation of G-substrate and calpain. Moreover, G-substrate knockout (G-substrate(-/-)) mice were more susceptible to NMDA injury than wild-type mice. ALLN did not have a neuroprotective effect in G-substrate(-/-) mice. These data strongly suggest that calpain-mediated loss of G-substrate represents an important mechanism contributing to NMDA-induced amacrine cell death.
authors.affiliation: Department of Ophthalmology, Tohoku Graduate School of Medicine, Sendai, Japan. ntoru@fa2.so-net.ne.jp
authors.forename: Toru
authors.initials: T
authors.lastname: Nakazawa
authors.forename: Masahiko
authors.initials: M
authors.lastname: Shimura
authors.forename: Ryu
authors.initials: R
authors.lastname: Mourin
authors.forename: Mineo
authors.initials: M
authors.lastname: Kondo
authors.forename: Shunji
authors.initials: S
authors.lastname: Yokokura
authors.forename: Takaomi C
authors.initials: TC
authors.lastname: Saido
authors.forename: Kohji
authors.initials: K
authors.lastname: Nishida
authors.forename: Shogo
authors.initials: S
authors.lastname: Endo
mesh_terms: D025042:Amacrine Cells / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002154:Calpain / Q000378:metabolism*; D016923:Cell Death; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007976:Leupeptins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016202:N-Methylaspartate / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000473:pathology / Q000502:physiology*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; C029152:G-substrate; D007976:Leupeptins; D009419:Nerve Tissue Proteins; C063261:acetylleucyl-leucyl-norleucinal; D016202:N-Methylaspartate; D051057:Proto-Oncogene Proteins c-akt; D002154:Calpain; C058076:calpain inhibitor III