ELOVL4
Elongation of very long chain fatty acids protein 4 (EC 2.3.1.199) (3-keto acyl-CoA synthase ELOVL4) (ELOVL fatty acid elongase 4) (ELOVL FA elongase 4) (Very long chain 3-ketoacyl-CoA synthase 4) (Very long chain 3-oxoacyl-CoA synthase 4)
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To investigate differentially expressed genes in eyecup and retina of the ELOVL4 transgenic mouse, a model of Stargardt-like macular dystrophy (STGD3). We examined gene and protein expression in known pathways relevant to retinal degeneration using PCR arrays, Western blotting, and immunohistochemistry. Investigations were performed on ELOVL4 transgenic mice at 9 months, when 50% of rod (but no cone) photoreceptors had degenerated. Age-matched wild-type littermates served as controls. Significant expression level changes were found in only 17 of the 252 genes examined. Nine were upregulated (Fgf2, Fgfr1, Ntf5, Cbln1, Ngfr, Ntrk1, Trp53, Tlr6, and Herpud1), and eight were downregulated (Ccl22, Ccr3, Il18rap, Nf1, Ccl11, Atf6β, Rpn1, and Serp1). Overexpression of FGF2 was detected at 1 month, before rod loss onset, and was maintained at high levels until cone loss (18 months). By 9 months, FGF2 overexpression was seen in photoreceptor cell bodies. Increased glial fibrillary acidic protein (GFAP) expression due to glial cell reactivity followed the same time course. Levels of NGFR/p75NTR remained invariant. Although present in rod outer segments at 1 month, the macrophage chemoattracting chemokine CCL22 became undetectable by 9 months, a likely consequence of progressive rod outer segment truncation. At a mid-degeneration stage, major changes in gene expression in the ELOVL4 transgenic mouse retina included upregulation of Fgf2 and Fgfr1 and downregulation of Ccl22. Modulation of FGF2 occurred very early, concomitant with an increase in GFAP expression. Future studies will address which factors upstream of Fgf2 could provide potential therapeutic targets to slow photoreceptor degeneration in STGD3.
MeSH Terms
- Aging
- Animals
- Blotting, Western
- Chemokine CCL22
- Chromosome Disorders
- Chromosomes, Human, Pair 6
- Disease Models, Animal
- Fibroblast Growth Factor 2
- Gene Expression Regulation
- Glial Fibrillary Acidic Protein
- Macular Degeneration
- Mice
- Mice, Transgenic
- Polymerase Chain Reaction
- Receptor, Fibroblast Growth Factor, Type 1
- Receptor, Nerve Growth Factor
- Receptors, Nerve Growth Factor
Age-related macular degeneration (AMD) is the most prevalent form of irreversible blindness worldwide in the elderly population. The pathology of dry AMD consists of macular degeneration of photoreceptors and the RPE, lipofuscin (A2E) accumulation, and drusen formation. Mice have been widely used for generating models that simulate human AMD features for investigating the pathogenesis, treatment and prevention of the disease. Although the mouse has no macula, focal atrophy of photoreceptors and RPE, lipofuscin accumulation, and increased A2E can develop in aged mouse eyes. However, drusen are rarely seen in mice because of their simpler Bruch's membrane and different process of lipofuscin extrusion compared with humans. Thus, analyzing basal deposits at the ultrastructural level and understanding the ultrastructural pathologic differences between various mouse AMD models are critical to comprehending the significance of research findings and response to possible therapeutic options for dry AMD. Based on the multifactorial pathogenesis of AMD, murine dry AMD models can be classified into three groups. First, genetically engineered mice that target genes related to juvenile macular dystrophies are the most common models, and they include abcr(-/-) (Stargardt disease), transgenic ELOVL4 (Stargardt-3 dominant inheritary disease), Efemp1(R345W/R345W) (Doyne honeycomb retinal dystrophy), and Timp3(S156C/S156C) (Sorsby fundus dystrophy) mice. Other murine models target genes relevant to AMD, including inflammatory genes such as Cfh(-/-), Ccl2(-/-), Ccr2(-/-), Cx3cr1(-/-), and Ccl2(-/-)/cx3cr1(-/-), oxidative stress associated genes such as Sod1(-/-) and Sod2 knockdown, metabolic pathway genes such as neprilysin(-/-) (amyloid beta), transgenic mcd/mcd (cathepsin D), Cp(-/-)/Heph(-/Y) (ferroxidase ceruloplasmin/hepaestin, iron metabolism), and transgenic ApoE4 on high fat and high cholesterol diet (lipid metabolism). Second, mice have also been immunologically manipulated by immunization with carboxyethylpyrrole (CEP), an oxidative fragment of DHA found in drusen, and found to present with dry AMD features. Third, natural mouse strains such as arrd2/arrd2 (Mdm gene mutation) and the senescence accelerated mice (SAM) spontaneously develop features of dry AMD like photoreceptor atrophy and thickening of Bruch's membrane. All the aforementioned models develop retinal lesions with various features that simulate dry AMD lesions: focal photoreceptor degeneration, abnormal RPE with increased lipofuscin, basal infolding, decreased melanosomes and degeneration. However, Bruch's membrane changes are less common. Most mice develop retinal lesions at an older age (6-24 months, depending on the models), while the Ccl2(-/-)/cx3cr1(-/-) mice develop lesions by 4-6 weeks. Although murine models present various degrees of retinal and/or RPE degeneration, classical drusen is extremely rare. Using electron microscopy, small drusenoid deposits are found between RPE and Bruch's membrane in a few models including Efemp1(R345W/R345W), Ccl2(-/-)/cx3cr1(-/-), neprilysin(-/-), transgenic mcd/mcd, and ApoE4 transgenic mice on a high fat diet. High A2E levels are measured in the retinas of abcr(-/-), transgenic ELOVL4, and Ccl2(-/-)/cx3cr1(-/-) mice. In summary, murine models provide useful tools for studying AMD pathogenesis and evaluating novel therapies for this disease. This review compares the major dry AMD murine models and discusses retinal pathology at the ultrastructural level.
MeSH Terms
- Aging
- Animals
- Disease Models, Animal
- Geographic Atrophy
- Humans
- Mice
- Mice, Transgenic
- Mutation
- Retina
Purpose. To investigate the impact of progressive age-related photoreceptor degeneration on retinal integrity in Stargardt-like macular dystrophy (STGD3). Methods. The structural design of the inner retina of the ELOVL4 transgenic mouse model of STGD3 was compared with that of age-matched littermate wild-type (WT) mice from 1 to 24 months of age by using immunohistofluorescence and confocal microscopy and by relying on antibodies against cell-type-specific markers, synapse-associated proteins, and neurotransmitters. Results. Müller cell reactivity occurred at the earliest age studied, before photoreceptor loss. This finding is perhaps not surprising, considering the cell's ubiquitous roles in retina homeostasis. Second-order neurons displayed salient morphologic changes as a function of photoreceptoral input loss. Age-related sprouting of dendritic fibers from rod bipolar and horizontal cells into the ONL did not occur. In contrast, with the loss of photoreceptor sensory input, these second-order neurons progressively bore fewer synapses. After rod loss, the few remaining cones showed abnormal opsin expression, revealing tortuous branched axons. After complete ONL loss (beyond 18 months of age), localized areas of extreme retinal disruptions were observed in the central retina. RPE cell invasion, dense networks of strongly reactive Müller cell processes, and invagination of axons and blood vessels were distinctive features of these regions. In addition, otherwise unaffected cholinergic amacrine cells displayed severe perturbation of their cell bodies and synaptic plexi in these areas. Conclusions. Remodeling in ELOVL4 transgenic mice follows a pattern similar to that reported after other types of hereditary retinopathies in animals and humans, pointing to a potentially common pathophysiologic mechanism.
MeSH Terms
- Aging
- Animals
- Biomarkers
- Carrier Proteins
- Disease Models, Animal
- Electroretinography
- Eye Proteins
- Female
- Fluorescent Antibody Technique, Indirect
- Genotype
- Macular Degeneration
- Male
- Membrane Proteins
- Mice
- Mice, Inbred C57BL
- Mice, Transgenic
- Microscopy, Confocal
- Photoreceptor Cells, Vertebrate
- Pyridinium Compounds
- Retinal Neurons
- Retinoids
- Reverse Transcriptase Polymerase Chain Reaction
- cis-trans-Isomerases
Age-related maculopathy (ARM) is a leading cause of visual impairment in elderly Americans and is a complex genetic disorder. Hypothesized pathways for the etiology of ARM include cholesterol and lipoprotein metabolism and transport, extracellular matrix integrity, oxidative stress and inflammatory/immunologic processes. This study investigates 21 polymorphisms within 15 candidate genes whose products function within these pathways by performing family and case-control genetic association studies using clearly affected familial cases (n=338 families, 796 individuals), clearly affected, unrelated sporadic cases (n=196) and clearly unaffected, unrelated controls (n=120). Two genes demonstrated significant association with ARM status. A Met299Val variant in the elongation of very long chain fatty acids-like 4 (ELOVL4) gene was significantly associated with ARM in the case-control allele (P=0.001), case-control genotype (P=0.001) and case-control family (P<0.0001) tests. A Tyr402His variant in exon 9 in the complement factor H (CFH) gene was also significantly associated with ARM in the case-control allele (P<0.0001), case-control genotype (P<0.0001) and case-control family (P<0.0001) tests. All of these results remain significant after adjusting for false discovery rates to control for the impact of multiple testing. In addition, the CFH variant appears to play a role in exudative and atrophic disease, whereas the ELOVL4 variant may play a greater role in exudative disease in our population. These results support a potential role for multiple pathways in the etiology of ARM, including pathways involved with fatty acid biosynthesis and the complement system.
MeSH Terms
- Aging
- Alleles
- Base Sequence
- Case-Control Studies
- Complement System Proteins
- DNA Primers
- Fatty Acids
- Gene Frequency
- Humans
- Macular Degeneration
- Phenotype
- Polymorphism, Genetic