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Mice Homozygous for a Deletion in the Glaucoma Susceptibility Locus INK4 Show Increased Vulnerability of Retinal Ganglion Cells to Elevated Intraocular Pressure.

ABSTRACT: A genomic region located on chromosome 9p21 is associated with primary open-angle glaucoma and normal tension glaucoma in genome-wide association studies. The genomic region contains the gene for a long noncoding RNA called CDKN2B-AS, two genes that code for cyclin-dependent kinase inhibitors 2A and 2B (CDKN2A/p16(INK4A) and CDKN2B/p15(INK4B)) and an additional protein (p14(ARF)). We used a transgenic mouse model in which 70 kb of murine chromosome 4, syntenic to human chromosome 9p21, are deleted to study whether this deletion leads to a discernible phenotype in ocular structures implicated in glaucoma. Homozygous mice of this strain were previously reported to show persistent hyperplastic primary vitreous. Fundus photography and optical coherence tomography confirmed that finding but showed no abnormalities for heterozygous mice. Optokinetic response, eletroretinogram, and histology indicated that the heterozygous and mutant retinas were normal functionally and morphologically, whereas glial cells were activated in the retina and optic nerve head of mutant eyes. In quantitative PCR, CDKN2B expression was reduced by approximately 50% in the heterozygous mice and by 90% in the homozygous mice, which suggested that the CDKN2B knock down had no deleterious consequences for the retina under normal conditions. However, compared with wild-type and heterozygous animals, the homozygous mice are more vulnerable to retinal ganglion cell loss in response to elevated intraocular pressure.

SUBMITTER: Gao S

PROVIDER: S-EPMC5848263 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Project description:BackgroundThere is theoretical and empirical evidence for strong sexual selection in males having positive effects on population viability by serving to purify the genome of its mutation load at a low demographic cost. However, there is also theoretical and empirical evidence for negative effects of sexual selection on female fitness, and therefore population viability, known as the gender load. This can take the form of sexually antagonistic (SA) genetic variation where alleles with a selective advantage in males pose a detriment to female fitness, and vice versa. Here, using seed beetles, we shed light on a previously unexplored manifestation of the gender load: the effect of SA genetic variation on tolerance to inbreeding.ResultsWe found that genotypes encoding high male, but low female fitness exhibited significantly greater rates of extinction upon enforced inbreeding relative to genotypes encoding high female but low male fitness. Also, genotypes encoding low fitness in both sexes exhibited greater rates of extinction relative to generally high-fitness genotypes (though marginally non-significant), an expected finding attributable to variation in mutation load across genotypes. Despite follow-up investigations aiming to identify the mechanism(s) underlying these findings, it remains unclear whether the gender load and the mutation load have independent consequences for tolerance to inbreeding, or whether these two types of genetic architecture interact epistatically to render male-benefit genetic variation relatively intolerant to inbreeding.ConclusionsRegardless of the underlying mechanism(s), our results show that male-benefit/female-detriment SA genetic variation poses a previously unseen detriment to population viability due to its elevated vulnerability to inbreeding/homozygosity. This suggests that sexual selection in the context of SA genetic variance for fitness may enhance the gender load on population viability more than previously appreciated, due to selecting for male-benefit SA genetic variation that engenders lineages to extinction upon inbreeding. We note that our results imply that SA alleles that are sexually selected for in males may be underrepresented or even lacking in panels of inbred lines.

Project description:Glaucoma can result in retinal ganglion cell (RGC) death and permanently damaged vision. Pathologically high intraocular pressure (ph-IOP) is the leading cause of damaged vision during glaucoma; however, controlling ph-IOP alone does not entirely prevent the loss of glaucomatous RGCs, and the underlying mechanism remains elusive. In this study, we reported an increase in ferric iron in patients with acute primary angle-closure glaucoma (the most typical glaucoma with ph-IOP damage) compared with the average population by analyzing free iron levels in peripheral serum. Thus, iron metabolism might be involved in regulating the injury of RGCs under ph-IOP. In vitro and in vivo studies confirmed that ph-IOP led to abnormal accumulation of ferrous iron in cells and retinas at 1-8 h post-injury and elevation of ferric iron in serum at 8 h post-injury. Nuclear receptor coactivator 4 (NCOA4)-mediated degradation of ferritin heavy polypeptide 1(FTH1) is essential to disrupt iron metabolism in the retina after ph-IOP injury. Furthermore, knockdown of Ncoa4 in vivo inhibited FTH1 degradation and reduced the retinal ferrous iron level. Elevated ferrous iron induced by ph-IOP led to a marked accumulation of pro-ferroptotic factors (lipid peroxidation and acyl CoA synthetase long-chain family member 4) and a depletion of anti-ferroptotic factors (glutathione, glutathione peroxidase 4, and nicotinamide adenine dinucleotide phosphate). These biochemical changes resulted in RGC ferroptosis. Deferiprone can pass through the blood-retinal barrier after oral administration and chelated abnormally elevated ferrous iron in the retina after ph-IOP injury, thus inhibiting RGC ferroptosis and protecting visual function. In conclusion, this study revealed the role of NCOA4-FTH1-mediated disturbance of iron metabolism and ferroptosis in RGCs during glaucoma. We demonstrate the protective effect of Deferiprone on RGCs via inhibition of ferroptosis, providing a research direction to understand and treat glaucoma via the iron homeostasis and ferroptosis pathways.

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Mice Homozygous for a Deletion in the Glaucoma Susceptibility Locus INK4 Show Increased Vulnerability of Retinal Ganglion Cells to Elevated Intraocular Pressure.

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