Retinal Ganglion Cell Loss and Mild Vasculopathy in Methylene Tetrahydrofolate Reductase (Mthfr)-Deficient Mice: A Model of Mild Hyperhomocysteinemia.
Markand Shanu, Saul Alan, Roon Penny, Prasad Puttur, Martin Pamela, Rozen Rima, Ganapathy Vadivel, Smith Sylvia B
AI Summary
Mthfr-deficient mice with mild hyperhomocysteinemia showed retinal ganglion cell loss, nerve fiber layer thinning, and mild vasculopathy. This suggests hyperhomocysteinemia may contribute to human neurovasculopathies like glaucoma.
Abstract
Purpose
Methylenetetrahydrofolate reductase (Mthfr) is a key enzyme in homocysteine-methionine metabolism. We investigated Mthfr expression in retina and asked whether mild hyperhomocysteinemia, due to Mthfr deficiency, alters retinal neurovascular structure and function.
Methods
Expression of Mthfr was investigated at the gene and protein level using quantitative (q) RT-PCR, in situ hybridization, immunoblotting, and immunohistochemistry (IHC). The Mthfr+/+ and Mthfr+/- mice were subjected to comprehensive evaluation using ERG, funduscopy, fluorescein angiography (FA), spectral-domain optical coherence tomography (SD-OCT), HPLC, and morphometric and IHC analysis of glial fibrillary acidic protein (GFAP) at 8 to 24 weeks.
Results
Gene and protein analyses disclosed widespread retinal expression of Mthfr. Electroretinography (ERG) revealed a significant decrease in positive scotopic threshold response in retinas of Mthfr+/- mice at 24 weeks. Fundus examination in mice from both groups was normal; FA revealed areas of focal vascular leakage in 20% of Mthfr+/- mice at 12 to 16 weeks and 60% by 24 weeks. The SD-OCT revealed a significant decrease in nerve fiber layer (NFL) thickness at 24 weeks in Mthfr+/- compared to Mthfr+/+ mice. There was a 2-fold elevation in retinal hcy at 24 weeks in Mthfr+/- mice by HPLC and IHC. Morphometric analysis revealed an approximately 20% reduction in cells in the ganglion cell layer of Mthfr+/- mice at 24 weeks. The IHC indicated significantly increased GFAP labeling suggestive of Müller cell activation.
Conclusions
Mildly hyperhomocysteinemic Mthfr+/- mice demonstrate reduced ganglion cell function, thinner NFL, and mild vasculopathy by 24 weeks. The retinal phenotype is similar to that of hyperhomocysteinemic mice with deficiency of cystathionine-β-synthase (Cbs) reported earlier. The data support the hypothesis that hyperhomocysteinemia may be causative in certain retinal neurovasculopathies.
MeSH Terms
Shields Classification
Key Concepts6
Electroretinography (ERG) revealed a significant decrease in positive scotopic threshold response in retinas of Mthfr+/- mice at 24 weeks compared to Mthfr+/+ mice.
Fluorescein angiography (FA) revealed areas of focal vascular leakage in 20% of Mthfr+/- mice at 12 to 16 weeks and 60% by 24 weeks, while fundus examination in both Mthfr+/+ and Mthfr+/- mice was normal.
Spectral-domain optical coherence tomography (SD-OCT) revealed a significant decrease in nerve fiber layer (NFL) thickness at 24 weeks in Mthfr+/- mice compared to Mthfr+/+ mice.
Morphometric analysis revealed an approximately 20% reduction in cells in the ganglion cell layer of Mthfr+/- mice at 24 weeks, accompanied by a 2-fold elevation in retinal homocysteine (hcy) levels.
Immunohistochemistry (IHC) indicated significantly increased glial fibrillary acidic protein (GFAP) labeling, suggestive of Müller cell activation, in Mthfr+/- mice.
Methylenetetrahydrofolate reductase (Mthfr) expression was investigated at the gene and protein level in the retina of Mthfr+/+ and Mthfr+/- mice using quantitative (q) RT-PCR, in situ hybridization, immunoblotting, and immunohistochemistry (IHC).
Related Articles5
Leber Hereditary Optic Neuropathy Gene Therapy: Longitudinal Relationships Among Visual Function and Anatomical Measures.
Clinical TrialIn Vivo Fluorescence Retinal Imaging Following AAV2-Mediated Gene Delivery in the Rat Retina.
Basic ScienceMitochondrial pathophysiology beyond the retinal ganglion cell: occipital GABA is decreased in autosomal dominant optic neuropathy.
Basic ScienceFive-Year Outcomes of Lenadogene Nolparvovec Gene Therapy in Leber Hereditary Optic Neuropathy.
Clinical TrialTranscriptomic neuron types vary topographically in function and morphology.
Basic ScienceIs this article assigned to the wrong chapter(s)? Let us know.