A G-Protein Coupled Receptor and Macular Degeneration

RPE melanin and its influence on the progression of AMD

OBJECTIVE

The aim of this review article is to summarize the latest findings and current understanding of the origin of melanin in the retinal pigment epithelium (RPE), its function within the RPE, its role in the pathogenesis of age-related macular degeneration (AMD), its effect on retinal development, and its potential therapeutic benefit in the treatment of AMD.

METHODS

A comprehensive search of peer-reviewed journals was conducted using various combinations of key terms such as "melanin," "retinal pigment epithelium" or "RPE," "age-related macular degeneration" or AMD," "lipofuscin," "oxidative stress," and "albinism." Databases searched include PubMed, Scopus, Science Direct, and Google Scholar. 147 papers published between the years of 1957 and 2023 were considered with an emphasis on recent findings.

SUMMARY OF FINDINGS

AMD is thought to result from chronic oxidative stress within the RPE that results in cellular dysfunction, metabolic dysregulation, inflammation, and lipofuscin accumulation. Melanin functions as a photoscreener, free radical scavenger, and metal cation binding reservoir within the RPE. RPE melanin does not regenerate, and it undergoes degradation over time in response to chronic light exposure and oxidative stress. RPE melanin is important for retinal development and RPE function, and in the aging eye, melanin loss is associated with increased lipid peroxidation, inflammation, and the accumulation of toxic oxidized cellular products. Therefore, melanin-based treatments may serve to preserve RPE and retinal function in AMD.

CONCLUSIONS

The pathogenesis of AMD is not fully understood, but RPE dysfunction and melanin loss in response to chronic oxidative stress and inflammation are thought to be primary drivers of the disease. Due to melanin's antioxidative effects, melanin-based nanotechnology represents a promising avenue for the treatment of AMD.

Olfaction evaluation in dogs with sudden acquired retinal degeneration syndrome

PURPOSE

To evaluate olfaction in dogs with sudden acquired retinal degeneration syndrome (SARDS) compared with sighted dogs and blind dogs without SARDS as control groups.

ANIMALS STUDIED

Forty client-owned dogs.

PROCEDURE

Olfactory threshold testing was performed on three groups: SARDS, sighted, and blind/non-SARDS using eugenol as the test odorant. The olfactory threshold was determined when subjects indicated the detection of a specific eugenol concentration with behavioral responses. Olfactory threshold, age, body weight, and environmental room factors were evaluated.

RESULTS

Sixteen dogs with SARDS, 12 sighted dogs, and 12 blind/non-SARDS dogs demonstrated mean olfactory threshold pen numbers of 2.8 (SD = 1.4), 13.8 (SD = 1.4), and 13.4 (SD = 1.1), respectively, which correspond to actual mean concentrations of 0.017 g/mL, 1.7 × 10-13  g/mL and 4.26 × 10-13  g/mL, respectively. Dogs with SARDS had significantly poorer olfactory threshold scores compared with the two control groups (p < .001), with no difference between the control groups (p = .5). Age, weight, and room environment did not differ between the three groups.

CONCLUSIONS

Dogs with SARDS have severely decreased olfaction capabilities compared with sighted dogs and blind/non-SARDS dogs. This finding supports the suspicion that SARDS is a systemic disease causing blindness, endocrinopathy, and hyposmia. Since the molecular pathways are similar in photoreceptors, olfactory receptors, and steroidogenesis with all using G-protein coupled receptors in the cell membrane, the cause of SARDS may exist at the G-protein associated interactions with intracellular cyclic nucleotides. Further investigations into G-protein coupled receptors pathway and canine olfactory receptor genes in SARDS patients may be valuable in revealing the cause of SARDS.

Association of TAS2R16 gene (rs860170, rs978739, rs1357949) polymorphisms and TAS2R16 serum levels in patients with age-related macular degeneration

BACKGROUND

The aim of this study is to determine the association of TAS2R16 (rs860170, rs978739, rs1357949) gene polymorphisms and TAS2R16 serum levels in patients with the occurrence of age-related macular degeneration (AMD).

METHODS

Subjects with early AMD, subjects with exudative AMD, and healthy controls participated in the study. DNA was isolated by salting out leukocytes from peripheral venous blood. Single nucleotide polymorphisms (SNPs) were analysed by RT-PCR. TAS2R16 levels were determined by enzyme-linked immunosorbent assay (ELISA) using the Abbexa Human Taste Receptor Type 2 Member 16 (TAS2R16) ELISA kit. Statistical data analysis was performed using "IBM SPSS Statistics 27.0" and SNPstats statistical data analysis programmes.

RESULTS

The TAS2R16 rs860170 TT genotype is statistically significantly less frequent in the exudative AMD group than in the control group, whereas the TAS2R16 rs860170 C allele gene is statistically significantly more frequent in the exudative AMD group. Each C allele of TAS2R16 rs860170 is associated with a 2.8-fold increased probability of occurrence of exudative AMD. The C allele of TAS2R16 rs860170 is statistically significantly more frequent in men and women with exudative AMD than in the control group. The C allele of TAS2R16 rs860170 is associated with a 2.8-fold increased odds of occurrence of exudative AMD in women and a 2.9-fold increased odds of occurrence of exudative AMD in men. In TAS2R16 (rs860170, rs978739, and rs1357949), the T-T-A haplotype is associated with a 2.6-fold decreased likelihood of developing early AMD and the T-T-A haplotype is associated with a 3.2-fold decreased likelihood of developing early AMD in women. For TAS2R16 (rs860170, rs978739, and rs1357949), carriers of the T-T-G and T-T-A haplotypes are associated with a 2.2- and 3.2-fold decreased probability of exudative AMD, respectively. Individuals with the C-C-A haplotype are 9.2-fold more likely to develop exudative AMD. Specifically, the C-C-A haplotype is associated with a 9.3-fold increased likelihood of exudative AMD in men. In contrast, women with the T-T-A haplotype are 5.6-fold less likely to develop exudative AMD.

CONCLUSION

TAS2R16 plays an important role in the development of AMD.

Levodopa Is Associated with Reduced Development of Neovascular Age-Related Macular Degeneration

OBJECTIVE

To determine whether levodopa (L-DOPA) is associated with a reduced likelihood of developing neovascular age-related macular degeneration (AMD).

DESIGN

Three studies were performed: retrospective analyses in the Vestrum Health Retina Database (#1-2) and case-control analysis in the Merative MarketScan Research Databases (#3).

PARTICIPANTS

Eyes with neovascular AMD and 2 years of follow-up (#1). Eyes with non-neovascular AMD and 1 to 5 years of follow-up (#2). Patients aged ≥ 55 years with newly diagnosed neovascular AMD matched to controls without neovascular AMD (#3).

METHODS

Eyes were divided into 2 groups (#1-2): exposed to L-DOPA before or on the date of neovascular (#1) or nonneovascular (#2) AMD diagnosis, and eyes not exposed to L-DOPA. We extracted AMD risk factors, number of intravitreal injections (#1), and conversion rate to neovascular AMD (#2). We calculated the percentage of newly diagnosed neovascular AMD cases and matched controls exposed to any L-DOPA and determined the cumulative 2-year dose in grams by tertiles (< 100 mg, approximately 100-300 mg, and approximately > 300 mg per day, #3).

MAIN OUTCOME MEASURES

Number of intravitreal injections (#1) and detection of new-onset neovascular AMD (#2-3) after adjusting for AMD risk factors.

RESULTS

In the Vestrum database, eyes with neovascular AMD that were exposed to L-DOPA underwent 1 fewer intravitreal injection over 2 years (N = 84 088 control vs. 530 L-DOPA eyes, P = 0.006). In eyes with nonneovascular AMD (N = 42 081-203 155 control vs. 314-1525 L-DOPA eyes), L-DOPA exposure was associated with a reduced risk of conversion to neovascular AMD by 21% at year 2 (P = 0.029), 35% at years 3 to 4 (P < 0.001), and 28% at year 5 (P = 0.024). In the MarketScan databases (N = 86 900 per group), cumulative 2-year doses of L-DOPA between approximately 100 to 300 mg per day and approximately > 300 mg were associated with decreased odds of developing neovascular AMD by 15% (odds ratio [OR], 0.85; 95% confidence interval [CI], 0.75-0.97) and 23% (OR, 0.77; 95% CI, 0.67-0.87), respectively.

CONCLUSIONS

Levodopa use was associated with reduced detection of new-onset neovascular AMD. A prospective, randomized clinical trial should be considered to investigate whether low-dose L-DOPA reduces neovascular AMD conversion.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Galanin receptor 3 - A new pharmacological target in retina degeneration

The neuropeptide galanin receptor 3 (GALR3) is a class A G protein-coupled receptor (GPCR) broadly expressed in the nervous system, including the retina. GALR3 is involved in the modulation of immune and inflammatory responses. Tight control of these processes is critical for maintaining homeostasis in the retina and is required to sustain vision. Here, we investigated the role of GALR3 in retina pathologies triggered by bright light and P23H mutation in the rhodopsin (RHO) gene, associated with the activation of oxidative stress and inflammatory responses. We used a multiphase approach involving pharmacological inhibition of GALR3 with its antagonist SNAP-37889 and genetic depletion of GALR3 to modulate the GALR3 signaling. Our in vitro experiments in the retinal pigment epithelium-derived cells (ARPE19) susceptible to all-trans-retinal toxicity indicated that GALR3 could be involved in the cellular stress response to this phototoxic product. Indeed, blocking the GALR3 signaling in Abca4-/-/Rdh8-/- and wild-type Balb/cJ mice, sensitive to bright light-induced retina damage, protected retina health in these mice exposed to light. The retina morphology and function were substantially improved, and stress response processes were reduced in these mouse models compared to the controls. Furthermore, in P23H Rho knock-in mice, a model of retinitis pigmentosa (RP), both pharmacological inhibition and genetic ablation of GALR3 prolonged the survival of photoreceptors. These results indicate that GALR3 signaling contributes to acute light-induced and chronic RP-linked retinopathies. Together, this work provides the pharmacological knowledge base to evaluate GALR3 as a potential target for developing novel therapies to combat retinal degeneration.

Causes and Five-Year Proportion of New Irreversible Visual Impairment in Jinshan District, Shanghai, from 2009-2018

Purpose

To describe the age distribution and main causes of new registered irreversible visual impairment (VI) and to compare the five-year proportion of VI in Jinshan district, Shanghai, from 2009 to 2018.

Methods

The new irreversible VI data were collected in the registry system from the Disabled Persons' Federation in Jinshan district from January 1, 2009, to December 31, 2018. Age, gender, and causes of VI were included, and the 5-year proportion of VI was calculated.

Results

The peak occurrence of blindness occurred in the 50–59 yrs group in 2009–2013 and in the ≥70 yrs group in 2014–2018. The peak occurrence of low vision occurred in the 40–49 yrs group in 2009–2013 and in the 50–59 yrs group in 2014–2018. Myopic macular degeneration (MMD, 15.5%), diabetic retinopathy (DR, 14.3%), and other optic nerve atrophy (ONA, 14.3%) were the three leading causes of blindness in 2009-2013, whereas MMD (21.3%), age-related macular degeneration (AMD, 19.6%), ONA (14.9%) were the three leading causes of blindness in 2014–2018. MMD (39.2%), DR (9.6%), ONA (8.8%) were the three leading causes of low vision in 2009–2013, whereas MMD (38.7%), AMD (23.3%), ONA (7.4%) were the three leading causes of low vision in 2014–2018. The proportions of blindness and low vision caused by AMD were higher in 2014–2018 than those in 2009–2013 (P=0.034 and P < 0.001, respectively).

Conclusion

The present study demonstrated an increasing trend in the number of irreversibly visually impaired individuals from 2009 to 2018. More attention should be paid to people with high myopia and old age.

Identification of a novel GPR143 mutation in a large Chinese family with isolated foveal hypoplasia

Background

Pathogenic variants of G-protein coupled receptor 143 (GPR143) gene often leads to ocular albinism type I (OA1) characterized by nystagmus, iris and fundus hypopigmentation, and foveal hypoplasia. In this study, we identified a novel hemizygous nonsense mutation in GPR143 that caused an atypical manifestation of OA1.

Case presentation

We reported a large Chinese family in which all affected individuals are afflicted with poor visual acuity and foveal hypoplasia without signs of nystagmus. Fundus examination of patients showed an absent foveal reflex and mild hypopigmentation. The fourth grade of foveal hypoplasia and the reduced area of blocked fluorescence at foveal region was detected in OCT. OCTA imaging showed the absence of foveal avascular zone. In addition, the amplitude of multifocal ERG was reduced in the central ring. Gene sequencing results revealed a novel hemizygous mutation (c.939G > A) in GPR143 gene, which triggered p.W313X. However, no iris depigmentation and nystagmus were observed among both patients and carriers.

Conclusions

In this study, we reported a novel nonsense mutation of GPR143 in a large family with poor visual acuity and isolated foveal hypoplasia without nystagmus, which further expanded the genetic mutation spectrum of GPR143.

Genotype-Phenotype Analysis and Mutation Spectrum in a Cohort of Chinese Patients With Congenital Nystagmus

Purpose: Congenital nystagmus (CN) is a genetically and clinically heterogeneous ocular disorder that manifests as involuntary, periodic oscillations of the eyes. To date, only FRMD7 and GPR143 have been reported to be responsible for causing CN. Here, we aimed to identify the disease-causing mutations and describe the clinical features in the affected members in our study.

Methods: All the subjects underwent a detailed ophthalmic examination. Direct sequencing of all coding exons and splice site regions in FRMD7 and GPR143 and a mutation assessment were performed in each patient.

Results: We found 14 mutations in 14/37 (37.8%) probands, including nine mutations in the FRMD7 gene and five mutations in the GPR143 gene, seven of which are novel, including c.284G>A(R95K), c.964C>T(P322S), c.284+10T>G, c.901T>C (Y301H), and c.2014_2023delTCACCCATGG(S672Pfs^*12) in FRMD7, and c.250+1G>C, and c.485G>A (W162^*) in GPR143. The mutation detection rate was 87.5% (7/8) of familial vs. 24.1% (7/29) of sporadic cases. Ten mutations in 24 (41.7%) non-syndromic subjects and 4 mutations in 13(30.8%) syndromic subjects were detected. A total of 77.8% (7/9) of mutations in FRMD7 were concentrated within the FERM and FA domains, while all mutations in GPR143 were located in exons 1, 2, 4 and 6. We observed that visual acuity tended to be worse in the GPR143 group than in the FRMD7 group, and no obvious difference in other clinical manifestations was found through comparisons in different groups of patients.

Conclusions: This study identified 14 mutations (seven novel and seven known) in eight familial and 29 sporadic patients with congenital nystagmus, expanding the mutational spectrum and validating FRMD7 and GPR143 as mutation hotspots. These findings also revealed a significant difference in the screening rate between different groups of participants, providing new insights for the strategy of genetic screening and early clinical diagnosis of CN.