Involvement of RhoA and neuroprotective effect of fasudil, a Rho kinase inhibitor, in NMDA–induced neurotoxicity in the rat retina

Abstract

Abstract: : Purpose: RhoA, a key protein involved in cytoskeleton regulation modulating neurogenesis, neural plasticity, has been implicated in a variety of cellular functions. We examined its involvement in N–methyl–d–aspartate (NMDA) induced–excitotoxicity in the retina, and evaluated the possible neuroprotective effect of fasudil, a Rho kinase inhibitor, in NMDA–induced retinal neurotoxicity. Methods: Eight–week–old male Wistar rats were used as subjects. RhoA protein levels in NMDA–treated retina were assessed by Western blot analysis and were localized by immunohistochemistry. Fasudil (10^–6 – 10^–4 M together with 4 × 10^–2 M NMDA) was given intravitreally. The number of cells in the ganglion cell layer (GCL) and the thickness of the inner plexiform layer (IPL), and retinal Thy–1 mRNA levels were evaluated at 5 days after injection. Results: Western blot analysis showed a transient increase of retinal RhoA protein 1 day after intravitreal NMDA injection, and that this increment was significantly prevented by simultaneous injection of fasudil. Immunohistochemistry showed that NMDA induced substantial increases in RhoA immunoreactivity in the GCL and the IPL. Fasudil injection reduced cell loss in the GCL and reduction in IPL thickness after NMDA injection. The reductions in Thy–1 mRNA levels by NMDA were also significantly attenuated by concomitant injection of fasudil. Conclusions: These results suggest that RhoA might be activated and involved in NMDA–induced retinal neurotoxicity, and that fasudil is neuroprotective against glutamate–related excitotoxicity.

Keywords: excitatory amino acid receptors • ganglion cells • neuroprotection