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Shanu Markand, Amany Tawfik, Srinivas Sonne, Pamela Martin, Sylvia Smith; Retinal disruption in MTHFR deficient mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2467.
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Hyperhomocysteinemia (Hhcy) is due to multiple causes including a deficiency in methylelenetetrahydrofolate reductase (MTHFR), an enzyme in the remethylation pathway. Hhcy is an independent risk factor for cardiovascular diseases and implicated in central retinal vein occlusion, diabetic retinopathy, and AMD. There is discrepancy in the literature regarding MTHFR mutations and associated ocular problems, which is crucial because 44% of Americans are heterozygous for MTHFR mutations and 12% are homozygous.Given the importance of Hhcy, coupled with high prevalence of MTHFR mutations, we investigated mthfr expression and began studies of the retinal phenotype in mthfr deficient mice.
RNA was isolated from normal mouse retina, primary ganglion, Müller and RPE cells and analyze mthfr expression. In situ hybridization was conducted on normal mouse retinal cryosections using fluorescent mthfr-specific RNA antisense or sense probes. The level and localization MTHFR protein in mouse retina was determined by immunoblotting and immunohistochemical (IHC) analysis, respectively. Retinal cryosections were prepared from mthfr +/+, +/- mice (3,6 and 9 mo) or -/-(3 wk) mice to assess retinal architecture.
mthfr was expressed at a robust level in normal mouse retina and in isolated retinal cell types. The anti-sense probes used in in situ hybridization studies showed mthfr expression in the ganglion cell layer, the inner/outer nuclear layers and RPE. Immunoblotting detected MTHFR in neural retina. IHC analysis detected MTHFR in the same retinal layers as in situ hybridization. Morphologic evaluation of the retinal phenotype in mthfr-/- mice showed considerable disruption including rosette formation in the retina. mthfr+/- mutant mice (3 mo) showed a milder phenotype characterized by migration of cells from the ONL to the INL and to RPE. This migration accelerated at 6 and 9 months mthfr+/- mice.
The mthfr gene and the protein it encodes are expressed in mouse retina and isolated neuron, glial and epithelial cells. Marked deficiency of MTHFR leads to retinal disruption, while moderate deficiency of MTHFR shows a later-onset retinal disruption. The study provided first evidence of retinal abnormality associated with MTHFR deficiency and sets the stage for comprehensive analysis of retinal phenotype in MTHFR deficiency.
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