Contribution of calpains to photoreceptor cell death in N-methyl-N-nitrosourea-treated rats

Takayuki Oka, Takeshi Nakajima, Yoshiyuki Tamada, Thomas (Tom) Shearer, Mitsuyoshi Azuma

Research output: Contribution to journalArticle

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Abstract

The purpose of the present study was to determine if proteolysis by the calcium-dependent enzyme calpains (EC 3.4.22.17) contributed to retinal cell death in a rat model of photoreceptor degeneration induced by intraperitoneal injection of N-methyl-N-nitrosourea (MNU). Retinal degeneration was evaluated by H&E staining, and cell death was determined by TUNEL assay. Total calcium in retina was measured by atomic absorption spectrophotometry. Activation of calpains was determined by casein zymography and immunoblotting. Proteolysis of α-spectrin and p35 (regulator of Cdk5) were evaluated by immunoblotting. Calpain inhibitor SNJ-1945 was orally administrated to MNU-treated rats to test drug efficacy. MNU decreased the thickness of photoreceptor cell layer, composed of the outer nuclear layer (ONL) and outer segment (OS). Numerous cells in the ONL showed positive TUNEL staining. Total calcium was increased in retina after MNU. Activation of calpains and calpain-specific proteolysis of α-spectrin were observed after MNU injection. Oral administration of SNJ-1945 to MNU-treated rats showed a significant protective effect against photoreceptor cell loss, confirming involvement of calpains in photoreceptor degeneration. Conversion of p35 to p25 was well correlated with calpain activation, suggesting prolonged activation of Cdk5/p25 as a possible downstream mechanism for MNU-induced photoreceptor cell death. SNJ-1945 reduced photoreceptor cells death, even though MNU is one of the most severe models of photoreceptor cell degeneration. Oral calpain inhibitor SNJ-1945 may be a candidate for testing as a medication against retinal degeneration in retinitis pigmentosa.

Original languageEnglish (US)
Pages (from-to)39-48
Number of pages10
JournalExperimental Neurology
Volume204
Issue number1
DOIs
StatePublished - Mar 2007

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Methylnitrosourea
Photoreceptor Cells
Calpain
Cell Death
Proteolysis
Spectrin
Retinal Degeneration
In Situ Nick-End Labeling
Calcium
Immunoblotting
Retina
Staining and Labeling
Atomic Spectrophotometry
Retinitis Pigmentosa
Caseins
Intraperitoneal Injections
Oral Administration
Injections
((1S)-1-((((1S)-1-benzyl-3-cyclopropylamino-2,3-di-oxopropyl)amino)carbonyl)-3-methylbutyl)carbamic acid 5-methoxy-3-oxapentyl ester
Enzymes

Keywords

  • α-Spectrin
  • Calcium
  • Calpain
  • Cdk5/p25
  • MNU
  • Retinitis pigmentosa
  • SNJ-1945

ASJC Scopus subject areas

  • Neurology
  • Neuroscience(all)

Cite this

Contribution of calpains to photoreceptor cell death in N-methyl-N-nitrosourea-treated rats. / Oka, Takayuki; Nakajima, Takeshi; Tamada, Yoshiyuki; Shearer, Thomas (Tom); Azuma, Mitsuyoshi.

In: Experimental Neurology, Vol. 204, No. 1, 03.2007, p. 39-48.

Research output: Contribution to journalArticle

Oka, Takayuki ; Nakajima, Takeshi ; Tamada, Yoshiyuki ; Shearer, Thomas (Tom) ; Azuma, Mitsuyoshi. / Contribution of calpains to photoreceptor cell death in N-methyl-N-nitrosourea-treated rats. In: Experimental Neurology. 2007 ; Vol. 204, No. 1. pp. 39-48.
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