Cellular and vascular changes in the retina of neonatal rats following an acute exposure to hypoxia
Charanjit Kaur 1*,
Viswanathan Sivakumar 2,
Wallace S Foulds 3,
Chi D Luu 4,
and
Eng-Ang Ling 2
1 Anatomy, National University of Singapore, MD BLK 10, 4 Medical drive, Faculty of Medicine, National University of Singapore, Singapore, 117597, Singapore
2 Anatomy, National University of Singapore, Singapore, Singapore
3 University of Glasgow, Glasgow, United Kingdom
4 The University of Melbourne, Melbourne, Victoria, Australia
* To whom correspondence should be addressed. E-mail: antkaurc{at}nus.edu.sg.
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Abstract |
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PURPOSE. This study was undertaken to examine the effects of an acute hypoxic exposure on the retinal cells and production of vascular factors such as vascular endothelial growth factor (VEGF) and nitric oxide (NO) which may affect vascular permeability in the developing retina.
METHODS. Retinas of 1-day old rats were examined at 3 hours to 14 days after hypoxic exposure. The mRNA and protein expression of hypoxia inducible factor-1alpha(HIF-1alpha), VEGF, endothelial, neuronal, and inducible nitric oxide synthase (eNOS, nNOS, and iNOS) was determined by real-time RT-PCR, Western blot analysis and immunohistochemistry. Electron microscopy was used to examine the structural alterations in retinal cells and rhodamine isothiocyanate (RhIC)/ horseradish peroxidase (HRP) were administered intraperitoneally/ intravenously to determine the vascular permeability.
RESULTS. The mRNA and protein expression of HIF-1alpha, VEGF, eNOS, nNOS, and iNOS along with VEGF concentration and NO production were increased in response to hypoxia. Swollen Muller cell processes, apoptotic and necrotic cells in the inner nuclear layer coupled with changes in ganglion cells such as swollen and disrupted mitochondria were observed in hypoxic animals. Increased leakage from retinal and hyaloid vessels of RhIC and HRP was seen following hypoxia.
CONCLUSIONS. We suggest that increased VEGF and NO production in hypoxia resulted in increased vascular permeability leading to changes in Muller cells and degeneration of neural cells. Melatonin administration reduced VEGF and NO levels as well as leakage of RhIC and HRP and promoted cell proliferation suggesting this as a potential therapeutic agent in reducing hypoxia associated damage in the developing retina.
Key Words:
hypoxia, retinal development, nitric oxide, hyalocytes, melatonin, vascular endothelial growth factor
