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Y. Shinohara, M. Nakatani, M. Hosoi, C. Taki, K. Ohtsuki, S. Nishimura; Protective Effect of Hydrophobic Dipeptide Leu-Ile Against Retinal Ganglion Cell Death in vivo and in vitro. : Involvement of GDNF Induction in Müller Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):646.
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© ARVO (1962-2015); The Authors (2016-present)
We investigated whether Leu-Ile, a hydrophobic dipeptide, promotes retinal ganglion cell (RGC) survival in kainic-acid (KA)-induced retinal damage in vivo and in culture. We also examined the involvement of Müller cells in the neuroprotective effect of Leu-Ile.
Leu-Ile or saline was injected into the vitreous body of adult rats 2 days before KA injection. Neuronal damage was evaluated 7 days after KA (5 nmol) injection by counting the retrograde fluorogold-labeled RGC densities in the retina and measuring phosphorylated neurofilament (pNF-H) contents in optic nerve extracts by ELISA. Survival-enhancing effect of Leu-Ile in purified RGC culture was evaluated by counting calcein-AM-stained RGCs after being exposed to Leu-Ile for two days. In the retina of Leu-Ile-treated eyes, immunohistochemistry and western blot analysis were conducted to elucidate localization and expression of glial cell line-derived neurotrophic factor (GDNF). After the Müller cell culture was exposed to Leu-Ile for 24 hours, the levels of GDNF expression in Müller cells were estimated by western blotting.
In KA-injected eyes, treatment with Leu-Ile (37 nmol) significantly inhibited the death of RGCs in the retina compared with the saline-treated control. Furthermore, the loss of pNF-H contents in the optic nerve was reduced by Leu-Ile treatment compared with the control. In cultured RGCs, treatment with 10 µM of Leu-Ile significantly increased the number of surviving RGCs compared with the control culture. Immunohistochemistry of Leu-Ile-injected eyes showed upregulated expression of GDNF in radial staining throughout the retina (presumably Müller cells). Western blot analysis showed increase in protein expression of GDNF in Leu-Ile-exposed Müller cell culture as well as in the retina of Leu-Ile-injected eye.
Leu-Ile protected RGCs from death after retinal damage. Additionally, our results suggest that Leu-Ile also have indirect protective effects on RGCs via the induction of GDNF in Müller cells.
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