title: Retinal Ganglion Cell Loss and Mild Vasculopathy in Methylene Tetrahydrofolate Reductase (Mthfr)-Deficient Mice: A Model of Mild Hyperhomocysteinemia.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Cellular Biology and Anatomy Georgia Regents University, Augusta, Georgia, United States 2The James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Shanu
authors.initials: S
authors.lastname: Markand
authors.affiliation: The James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, Georgia, United States 3Department of Ophthalmology, Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Alan
authors.initials: A
authors.lastname: Saul
authors.affiliation: Department of Cellular Biology and Anatomy Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Penny
authors.initials: P
authors.lastname: Roon
authors.affiliation: Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Puttur
authors.initials: P
authors.lastname: Prasad
authors.affiliation: The James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, Georgia, United States 4Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Pamela
authors.initials: P
authors.lastname: Martin
authors.affiliation: Departments of Pediatrics and Human Genetics, McGill University, Montreal, Canada.
authors.forename: Rima
authors.initials: R
authors.lastname: Rozen
authors.affiliation: The James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, Georgia, United States 4Department of Biochemistry and Molecular Biology, Georgia Regents University, Augusta, Georgia, United States.
authors.forename: Vadivel
authors.initials: V
authors.lastname: Ganapathy
authors.affiliation: Department of Cellular Biology and Anatomy Georgia Regents University, Augusta, Georgia, United States 2The James and Jean Culver Vision Discovery Institute, Georgia Regents University, Augusta, Georgia, United States 3Department of Ophthalmology, Georgia.
authors.forename: Sylvia B
authors.initials: SB
authors.lastname: Smith
mesh_terms: D000818:Animals; D004247:DNA / Q000235:genetics*; D004195:Disease Models, Animal; D004596:Electroretinography; D005451:Fluorescein Angiography; D005654:Fundus Oculi; D005786:Gene Expression Regulation; D006712:Homocystinuria / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D020138:Hyperhomocysteinemia / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D015151:Immunoblotting; D007150:Immunohistochemistry; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009128:Muscle Spasticity / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D011618:Psychotic Disorders / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D060888:Real-Time Polymerase Chain Reaction; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence
chemical_list: D004247:DNA; D042965:Methylenetetrahydrofolate Reductase (NADPH2)