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A. Takamiya, S. Masli, A. Yoshida, D. F. Chen; N-Methyl-D-Aspartate (Umda)-Induced Excitotoxicity in Thrombospondin-1 Deficient Mice. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4365.
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Thrombspondin-1 (TSP-1) is a glycoprotein which binds to the latent form of transforming growth factor (TGF) beta and converts it into an active form. Growing evidence suggests that TGF-beta serves as a key neurotrophic factor in the central nervous system and that reduced signaling of TGF-beta is associated with neurodegeneration in the adult. To understand the functional significance of TGF-beta signaling in adult retinal neurons, mice deficient in TSP-1 were examined in an experimental model of excitotoxic neural damage.
Retinal neural damage was induced in adult wild type (WT) and TSP-1-/- mice by intravitreal injection of a glutamate analog, N-methyl-D-aspartate (NMDA) (20 nmol). Induction of TGF-beta signaling was detected by immunodetection for phosphorylated Smad2 (pSmad2). Retinal neuronal death was determined by TDT-mediated-dUTP nick end labeling (TUNEL) at day 1 after NMDA treatment. At day 7 after the treatment, survival retinal ganglion cells were immunostained with a primary antibody against a ganglion cell specific marker, beta-III tubulin and the number of cells was counted.
Under the normal condition, pSmad2 signaling was not detected in the retinas of adult mice. NMDA-treatment induced pSmad2 expression in the ganglion cell layer (GCL) of WT mice within 24 hours. Consistent with the notion that TGF-beta is activated by TSP-1, much less pSmad2 positive cells were detected in the GCL of TSP-1-/- mice, while more TUNEL+ cells were counted from retinal sections of TSP-1-/- mice than that of WT mice. Moreover, most of these TUNEL positive cells did not co-localize with pSmad2 immunostaining, strongly suggesting a neuroprotective role of the TGF-beta/Smad2 pathway in excitotoxicity-induced neuronal death. More ganglion cells survived in the retinas of WT mice than that in TSP-1-/- mice at day 7 after NMDA treatment.
Our results revealed decreased Smad2 phosphorylation and increased retinal ganglion cell death following NMDA-treatment in TSP-1-/- mice than that in WT mouse retinas. The data suggest a role for TSP-1 in protecting retinal neurons against neuroexcitotoxicity-induced cell death, likely, via activation of TGF-beta/Smad2 pathways.
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