Visualizing the Heterogeneity of Retinal Microglia.

In this issue of Immunity, O'Koren et al. (2019) report that murine retinal microglia are long lived and are divided into two spatially and functionally distinct niches in the retina. In models of retinal neurodegeneration, retinal microglia migrate to the subretinal space, an inducible disease-associated niche, where they are neuroprotective.

Disrupted cholesterol metabolism promotes age-related photoreceptor neurodegeneration.

Photoreceptors have high intrinsic metabolic demand and are exquisitely sensitive to metabolic perturbation. In addition, they shed a large portion of their outer segment lipid membranes in a circadian manner, increasing the metabolic burden on the outer retina associated with the resynthesis of cell membranes and disposal of the cellular cargo. Here, we demonstrate that deletion of both ABCA1 and ABCG1 in rod photoreceptors leads to age-related accumulation of cholesterol metabolites in the outer retina, photoreceptor dysfunction, degeneration of rod outer segments, and ultimately blindness. A high-fat diet significantly accelerates rod neurodegeneration and vision loss, further highlighting the role of lipid homeostasis in regulating photoreceptor neurodegeneration and vision.

NAD+-dependent deacetylase SIRT3 in adipocytes is dispensable for maintaining normal adipose tissue mitochondrial function and whole body metabolism.

Mitochondrial dysfunction in adipose tissue is involved in the pathophysiology of obesity-induced systemic metabolic complications, such as type 2 diabetes, insulin resistance, and dyslipidemia. However, the mechanisms responsible for obesity-induced adipose tissue mitochondrial dysfunction are not clear. The aim of present study was to test the hypothesis that nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase sirtuin-3 (SIRT3) in adipocytes plays a critical role in adipose tissue mitochondrial biology and obesity. We first measured adipose tissue SIRT3 expression in obese and lean mice. Next, adipocyte-specific mitochondrial Sirt3 knockout (AMiSKO) mice were generated and metabolically characterized. We evaluated glucose and lipid metabolism in adult mice fed either a regular-chow diet or high-fat diet (HFD) and in aged mice. We also determined the effects of Sirt3 deletion on adipose tissue metabolism and mitochondrial biology. Supporting our hypothesis, obese mice had decreased SIRT3 gene and protein expression in adipose tissue. However, despite successful knockout of SIRT3, AMiSKO mice had normal glucose and lipid metabolism and did not change metabolic responses to HFD-feeding and aging. In addition, loss of SIRT3 had no major impact on putative SIRT3 targets, key metabolic pathways, and mitochondrial function in white and brown adipose tissue. Collectively, these findings suggest that adipocyte SIRT3 is dispensable for maintaining normal adipose tissue mitochondrial function and whole body metabolism. Contrary to our hypothesis, loss of SIRT3 function in adipocytes is unlikely to contribute to the pathophysiology of obesity-induced metabolic complications.

WNT7A/B promote choroidal neovascularization.

Perturbations in WNT signaling are associated with congenital eye disorders, including familial exudative vitreoretinopathy and Norrie disease. More recently, activation of the WNT pathway has also been shown to be associated with age-related macular degeneration (AMD). In this study, we identified that in choroidal neovascular membranes from AMD patients, ß-catenin is activated specifically in the vascular endothelium, suggesting that WNT promotes pathologic angiogenesis by directly affecting vascular endothelial cells. WNT7B has been shown to be important during eye development for regression of the fetal hyaloid vasculature. However, it has not yet been established whether WNT7A and/or WNT7B are involved in neovascular AMD pathogenesis. Here, we show that WNT7A and WNT7B increase the proliferation of human dermal microvascular endothelial cells in a dose-dependent manner. Both WNT7A and WNT7B also stimulated vascular sprouting from mouse choroidal explants in vitro. To evaluate in vivo relevance, we generated mice systemically deficient in Wnt7a and/or Wnt7b. Genetic deletion of both Wnt7a and Wnt7b decreased the severity of laser injury-induced choroidal neovascularization (CNV), while individual deletion of either Wnt7a or Wnt7b did not have a significant effect on CNV, suggesting that WNT7A and WNT7B have redundant pro-angiogenic roles in vivo. Cumulatively, these findings identify specific WNT isoforms that may play a pathologic role in CNV as observed in patients with neovascular AMD. Although the source of increased WNT7A and/or WNT7B in CNV requires further investigation, WNT signaling may be a potential target for therapeutic intervention if these results are demonstrated to be relevant in human disease.

Role of Sirtuins in Retinal Function Under Basal Conditions.

Sirtuins are NAD+-dependent enzymes that govern cellular homeostasis by regulating the acylation status of their diverse target proteins. We recently demonstrated that both rod and cone photoreceptors rely on NAMPT-mediated NAD+ biosynthesis to meet their energetic requirements. Moreover, we found that this NAD+-dependent retinal homeostasis relies, in part, on maintenance of optimal activity of the mitochondrial sirtuins and of SIRT3 in particular. Nonetheless, it is unknown whether other sirtuin family members also play important roles in retinal homeostasis. Our results suggest that SIRT1, SIRT2, SIRT4, and SIRT6 are dispensable for retinal survival at baseline, as individual deletion of each of these sirtuins does not cause retinal degeneration by fundus biomicroscopy or retinal dysfunction by ERG. These findings have significant implications and inform future studies investigating the mechanisms underlying the central role of NAD+ biosynthesis in retinal survival and function.

Retinal detachment.

Retinal detachment (RD) occurs when the neurosensory retina, the neurovascular tissue responsible for phototransduction, is separated from the underlying retinal pigment epithelium (RPE). Given the importance of the RPE for optimal retinal function, RD invariably leads to decreased vision. There are three main types of RD: rhegmatogenous, tractional and exudative (also termed serous) RD. In rhegmatogenous RD, one or more retinal breaks enable vitreous fluid to enter the subretinal space and separate the neurosensory retina from the RPE. In tractional RD, preretinal, intraretinal or subretinal membranes contract and exert tangential forces and elevate the retina from the underlying RPE. Finally, in exudative RD, an underlying inflammatory condition, vascular abnormality or the presence of a tumour causes exudative fluid to accumulate in the subretinal space, exceeding the osmotic pump function of the RPE. The surgical management of RD usually involves pars plana vitrectomy, scleral buckling or pneumatic retinopexy. The approach taken often depends on patient characteristics as well as on practitioner experience and clinical judgement. Advances in surgical technology and continued innovation have improved outcomes for many patients. However, even if retinal re-attachment is achieved, some patients still experience decreased vision or other visual symptoms, such as metamorphopsia, that diminish their quality of life. Continued research in the areas of neuroprotection and retinal biology as well as continued surgical innovation are necessary to enhance therapeutic options and outcomes for these patients.

Ocular effects of Rho kinase (ROCK) inhibition: a systematic review.

Topical therapies targeting Rho-associated protein kinase (ROCK) signalling, including netarsudil (Rhopressa®) and ripasudil (Glanatec®), have become widely adopted as part of standard clinical practice to lower intraocular pressure (IOP) in patients with ocular hypertension or glaucoma. Given the pleiotropic roles of ROCK signalling, ROCK inhibition has the potential to cause unintended ocular side effects beyond IOP lowering in other substructures of the eye, both beneficial and deleterious. Additional experience and observation of patients treated with this class of medications have uncovered both new side effects not reported in the initial clinical trials, as well as potential benefits that have inspired off-label uses and that have been the topic of numerous clinical studies, case series, case reports, and translational studies. Here, we performed a comprehensive systematic review and identified 170 studies describing ocular effects of ROCK inhibition. In addition to describing well-established ocular effects associated with inhibition of ROCK signalling, such as conjunctival hyperaemia, corneal verticillata, and reticular corneal epithelial oedema, we also highlight other effects, such as corneal haemorrhages, changes in corneal contour, anterior subcapsular opacities, contact dermatitis, punctal stenosis, and eyelid wound dehiscence, which have been described in case series and case reports. Finally, we evaluated studies describing potential novel applications of ROCK inhibition for treating disorders affecting the cornea, the retina, and the optic nerve, finding strong evidence in support of a beneficial effect of ROCK inhibitors on corneal oedema due to corneal endothelial cell dysfunction. The other potential applications require further research.

Comparing Outcomes of 45 Xen Implantation Ab Interno With Closed Conjunctiva to Ab Externo With Open Conjunctiva Approaches.

PRCIS: Ab externo with open conjunctiva placement may lead to improved gelatin stent (XEN Gel Stent; Allergan) success rate compared with ab interno with closed conjunctiva because it conferred more favorable intraocular pressure (IOP) and medication burden reduction based on our complete and qualified success criteria. PURPOSE: To compare outcomes of a gelatin stent (XEN 45 Gel Stent; Allergan) placed either ab interno with closed conjunctiva (AIC) or ab externo with open conjunctiva (AEO) with or without cataract surgery in patients with glaucoma. DESIGN: Retrospective, nonrandomized comparative study of 85 eyes from 85 glaucoma patients who received XEN 45 Gel Stent placed either AIC (N=32) or AEO (N=53) with or without cataract surgery between July 2018 and January 2022 at Massachusetts Eye and Ear. Patients were included if they were 18 years of age or above and had at least 30 days of follow-up without any disqualifying event. RESULTS: Baseline demographics were similar between both groups, except for the glaucoma type. Both AIC and AEO procedures resulted in significant patterns of IOP and medication reduction from baseline up to 1 year. At postoperative year (POY)1, mean IOP was reduced to 11.34±4 mmHg on 1.29±1.34 medications after AEO and 13.70±3.32 mmHg on 2±1.81 medications after AIC. The average IOP reduction was significantly greater in the AEO group at all postoperative time points beyond postoperative week 2. There were significant differences in the survival curves of AEO and AIC groups under both the complete success criteria and the qualified success criteria. Under the complete success criteria, the cumulative probability of survival at POY1 was 28.5% in the AEO group and 3.8% in the AIC group. Under the qualified success criteria, the cumulative probability of survival at POY1 was 60.3% in the AEO group and 21.9% in the AIC group. CONCLUSIONS: In our study, we demonstrate that both placements reduce IOP and medication from baseline, with AEO placement having more favorable success rates compared with AIC placement.

ENDOGENOUS ENDOPHTHALMITIS DUE TO STREPTOCOCCUS ANGINOSUS IN A HEALTHY, YOUNG WOMAN.

PURPOSE: The purpose of this study was to present a case of indolent endogenous endophthalmitis in a young, seemingly healthy woman. METHODS: This study is a retrospective case report. RESULTS: A 25-year-old woman with no significant medical history presented with vision loss in the left eye over the course of 1 month. Examination showed vitritis and a white-yellow lesion overlying the macula and optic nerve in the left eye. Initial laboratory testing for infectious and inflammatory causes was unrevealing. A diagnostic vitrectomy was performed, and the patient was found to have presumed endogenous endophthalmitis due to Streptococcus anginosus, an extremely uncommon bacterium. Subsequent workup did not reveal evidence of bacteremia, endocarditis, or orbital infection. This case is unique because, unlike the three previously reported cases of S. anginosus endophthalmitis, this patient was seemingly healthy, never had an elevated white blood cell count, never had documented bacteremia, had a normal echocardiogram, and had normal orbital findings on magnetic resonance imaging and computed tomography scans. Further questioning revealed a remote history of facial cellulitis and possible sinusitis treated with oral antibiotics, which are the presumed etiology. CONCLUSION: Streptococcus anginosus endophthalmitis can occur in young, seemingly healthy patients. Endogenous endophthalmitis should be considered in the differential diagnosis even without systemic comorbidities or other risk factors. Detailed questioning about medical history and thorough review of systems, including nonocular symptoms, are essential.

Neurofilament Light Chain in Aqueous Humor as a Marker of Neurodegeneration in Glaucoma.

Purpose: Neurofilament light chain (NfL) is a neuronal cytoskeletal protein that has been identified as a marker of neurodegeneration in diseases of the central nervous system. In this study, we investigated whether NfL in the aqueous humor (AH) can serve as a marker of neurodegeneration in glaucoma in a racially diverse North American population. Design: Single-center, case-control study. Participants: We enrolled patients with various types and stages of glaucoma undergoing planned ophthalmic surgery as part of their routine care and compared them with patients without glaucoma undergoing phacoemulsification for age-related cataract. Methods: We collected AH from 39 glaucoma patients and 10 patients without glaucoma. AH NfL was quantified using the Single-Molecule Array (Simoa)® NF-light assay (Quanterix). Demographic information, such as age, body mass index, sex, and self-reported race, as well as clinical information, such as pre-operative intraocular pressure (IOP), maximum IOP, and number of pre-operative glaucoma medications, was obtained by reviewing the medical record. Main Outcome Measures: Levels of AH NfL. Results: In a model controlling for age and body mass index (BMI), NfL was significantly elevated in AH from glaucoma patients (mean: 429 pg/mL; standard deviation [SD]: 1136 pg/mL) compared to AH from patients without glaucoma (mean: 3.1 pg/mL; SD: 1.9 pg/mg): P = 0.002. Higher AH NfL was associated with higher maximum IOP (R = 0.44, P = 0.005), higher pre-operative IOP (R = 0.46, P = 0.003), and more pre-operative glaucoma medications (Rs = 0.61, P < 0.001). There was no association between AH NfL and Humphrey visual field mean deviation (R = -0.20, P = 0.220), retinal nerve fiber layer thickness as measured with optical coherence tomography (R = 0.07, P = 0.694), or glaucoma stage (Rs = 0.015, P = 0.935). Conclusion: Our findings suggest that AH NfL may have clinical utility as a marker of glaucomatous neurodegeneration.

Neuroprotection for Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Early to intermediate AMD is characterized by the accumulation of lipid- and protein-rich drusen. Late stages of the disease are characterized by the development of choroidal neovascularization, termed "exudative" or "neovascular AMD," or retinal pigment epithelium (RPE) cell and photoreceptor death, termed "geographic atrophy" (GA) in advanced nonexudative AMD. Although we have effective treatments for exudative AMD in the form of anti-VEGF agents, they have no role for patients with GA. Neuroprotection strategies have emerged as a possible way to slow photoreceptor degeneration and vision loss in patients with GA. These approaches include reduction of oxidative stress, modulation of the visual cycle, reduction of toxic molecules, inhibition of pathologic protein activity, prevention of cellular apoptosis or programmed necrosis (necroptosis), inhibition of inflammation, direct activation of neurotrophic factors, delivery of umbilical tissue-derived cells, and RPE replacement. Despite active investigation in this area and significant promise based on preclinical studies, many clinical studies have not yielded successful results. We discuss selected past and current neuroprotection trials for AMD, highlight the lessons learned from these past studies, and discuss our perspective regarding remaining questions that must be answered before neuroprotection can be successfully applied in the field of AMD research.

Systemic Complement Activation Profiles in Nonexudative Age-Related Macular Degeneration: A Systematic Review.

Topic: To evaluate whether differences exist in systemic complement activation profiles in patients with early to intermediate nonexudative age-related macular degeneration (AMD) or geographic atrophy (GA) compared with control participants without AMD. Clinical Relevance: Complement inhibition has emerged as a therapeutic strategy for GA, although clinical trials to date have yielded mixed results. Despite these efforts, no clear consensus exists regarding what portions of the complement pathway are dysregulated in AMD or when this dysregulation occurs relative to AMD stage. Although past studies have compared systemic complement activation profiles in patients with AMD versus in control participants without AMD, differences in AMD case definition and differing analytical approaches complicate their interpretation. Methods: We performed a systematic review by identifying articles from database inception through October 11, 2020, that reported systemic complement activation profiles in patients with early or intermediate nonexudative AMD or GA versus control participants without AMD by searching PubMed, Google Scholar, and Embase. Risk of bias was assessed using a modified Newcastle-Ottawa score. Results: The 8 reviewed studies included 2131 independent participants. Most studies report significantly higher systemic levels of products associated with complement activation and significantly lower systemic levels of products associated with complement inhibition in patients with early and advanced nonexudative AMD compared with control participants without AMD. Discussion: Evidence suggests that systemic complement overactivation is a feature of early or intermediate and advanced nonexudative AMD. However, given significant heterogeneity, these findings are not conclusive and warrant further investigation.

Systemic Complement Activation Profiles in Nonexudative Age-Related Macular Degeneration: A Meta-Analysis.

Although complement inhibition has emerged as a possible therapeutic strategy for age-related macular degeneration (AMD), there is not a clear consensus regarding what aspects of the complement pathway are dysregulated in AMD and when this occurs relative to disease stage. We recently published a systematic review describing systemic complement activation profiles in patients with early/intermediate AMD or geographic atrophy (GA) compared to non-AMD controls. Here, we sought to meta-analyze these results to estimate the magnitude of complement dysregulation in AMD using restricted maximum likelihood estimation. The seven meta-analyzed studies included 710 independent participants with 23 effect sizes. Compared with non-AMD controls, patients with early/intermediate nonexudative AMD (N = 246) had significantly higher systemic complement activation, as quantified by the levels of complement proteins generated by common final pathway activation, and significantly lower systemic complement inhibition. In contrast, there were no statistically significant differences in the systemic levels of complement common final pathway activation products or complement inhibition in patients with GA (N = 178) versus non-AMD controls. We provide evidence that systemic complement over-activation is a feature of early/intermediate nonexudative AMD; no such evidence was identified for patients with GA. These findings provide mechanistic insights and inform future clinical trials.

Dyslipidemia in age-related macular degeneration.

Lipid-rich drusen are the sine qua non of age-related macular degeneration (AMD), the leading cause of blindness in older adults in the developed world. Efforts directed at uncovering effective therapeutic strategies have led to the hypothesis that altered lipid metabolism may play a pathogenic role in AMD. This hypothesis is supported by the fact that: (1) drusen, the hallmark histopathologic feature of AMD, are composed of lipids, (2) polymorphisms of genes involved in lipid homeostasis are associated with increased odds of AMD, (3) metabolomics studies show that patients with AMD have alterations in metabolites from lipid pathways, and (4) alterations in serum lipid profiles as a reflection of systemic dyslipidemia are associated with AMD. There is strong evidence that statins, which are well described for treating dyslipidemia and reducing risk associated with cardiovascular disease, may have a role for treating certain cohorts of AMD patients, but this has yet to be conclusively proven. Of interest, the specific changes in serum lipoprotein profiles associated with decreased cardiovascular risk (i.e., high HDL levels) have been shown in some studies to be associated with increased risk of AMD. In this review, we highlight the evidence that supports a role for altered lipid metabolism in AMD and provide our perspective regarding the remaining questions that need to be addressed before lipid-based therapies can emerge for specific cohorts of AMD patients.

Neurodegeneration Markers Galectin-3 and Apolipoprotein E Are Elevated in the Aqueous Humor of Eyes With Glaucoma.

Purpose: Galectin-3 (Gal-3) and apolipoprotein E (APOE) are markers of activated microglia in neurodegenerative diseases of the central nervous system, whose targeting is protective in mouse models of glaucoma. In this study, we examined levels of Gal-3 and APOE in human aqueous humor (AH) and defined their clinical associations with glaucoma. Methods: We collected AH from 59 glaucoma patients and 15 controls at the start of planned ophthalmic surgery. Gal-3 and APOE levels were quantified by enzyme-linked immunosorbent assay. Total protein in AH was quantified by bicinchoninic acid assay. Significant associations between Gal-3, APOE, and clinical covariates were defined using univariate and multivariate linear regression models. Results: Gal-3 and APOE levels were significantly elevated in the AH of glaucoma patients compared to controls (P = 0.004 and P < 0.001, respectively). Gal-3 and APOE were positively correlated across the entire cohort (r = 0.65, P = 6.2E-9). No association was observed between Gal-3 and total protein or APOE and total protein (P = 0.35 and P = 0.50, respectively), indicating that their levels were not increased in glaucomatous AH due to nonspecific protein accumulation. Multivariate linear regression modeling revealed significant associations between Gal-3 and maximum recorded intraocular pressure (P = 0.009) and between APOE and number of past ophthalmic surgeries (P = 0.031). Conclusions: We demonstrate that Gal-3 and APOE are significantly elevated in the AH of eyes with glaucoma and are associated with a history of poorly controlled disease. Translational Relevance: Gal-3 and APOE in AH may inform clinical decision-making as quantifiable readouts of microglial activation in eyes with glaucoma.

Object and spatial imagery dimensions in visuo-haptic representations.

Visual imagery comprises object and spatial dimensions. Both types of imagery encode shape but a key difference is that object imagers are more likely to encode surface properties than spatial imagers. Since visual and haptic object representations share many characteristics, we investigated whether haptic and multisensory representations also share an object-spatial continuum. Experiment 1 involved two tasks in both visual and haptic within-modal conditions, one requiring discrimination of shape across changes in texture, the other discrimination of texture across changes in shape. In both modalities, spatial imagers could ignore changes in texture but not shape, whereas object imagers could ignore changes in shape but not texture. Experiment 2 re-analyzed a cross-modal version of the shape discrimination task from an earlier study. We found that spatial imagers could discriminate shape across changes in texture but object imagers could not and that the more one preferred object imagery, the more texture changes impaired discrimination. These findings are the first evidence that object and spatial dimensions of imagery can be observed in haptic and multisensory representations.

Longitudinal Growth Differentiation Factor 15 (GDF15) and Long-term Intraocular Pressure Fluctuation in Glaucoma: A Pilot Study.

PURPOSE: Growth Differentiation Factor 15 (GDF15) was previously identified as a molecular marker of retinal ganglion cell stress in rodent models of glaucoma and was elevated in the aqueous humor (AH) of patients with primary open-angle glaucoma as a possible risk factor for glaucoma progression. The purpose of this study was to determine whether changes in the AH GDF15 levels were associated with intraocular pressure (IOP) changes in eyes undergoing glaucoma surgery. METHODS: Here, we performed a prospective, longitudinal pilot study in nine patients to determine whether changes in AH GDF15 levels from surgery to post-surgery follow-up were associated with IOP fluctuation. An initial AH sample was taken from the peripheral corneal paracentesis during planned glaucoma surgery, and a second sample was taken during an outpatient follow-up visit, approximately six months later. RESULTS: There was a statistically significant correlation between GDF15 fold change and IOP standard deviation (r = 0.87, P = 0.003), IOP range (r = 0.87, P = 0.003), and maximum IOP (r = 0.86, P = 0.003). There was no correlation between the GDF15 fold change and baseline IOP (r = 0.50, P = 0.17), final IOP (r = 0.038, P = 0.92), or mean IOP (r = 0.40, P = 0.28). CONCLUSION: Our findings in this pilot study suggest that longitudinal changes in AH GDF15 may be associated with IOP fluctuation during the postoperative period. Further studies are necessary to corroborate these findings in a larger patient population and to explore the possibility that AH GDF15 may be used not only to improve treatment algorithms but also as a surrogate endpoint in clinical trials.

A Review of Completed and Ongoing Complement Inhibitor Trials for Geographic Atrophy Secondary to Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is a leading cause of irreversible blindness among older adults in the Western world. While therapies exist for patients with exudative AMD, there are currently no approved therapies for non-exudative AMD and its advanced form of geographic atrophy (GA). The discovery of genetic variants in complement protein loci with increased susceptibility to AMD has led to the investigation of the role of complement inhibition in AMD with a focus on GA. Here, we review completed and ongoing clinical trials evaluating the safety and efficacy of these studies. Overall, complement inhibition in GA has yielded mixed results. The inhibition of complement factor D has failed pivotal phase 3 trials. Studies of C3 and C5 inhibition meeting their primary endpoint are limited by high rates of discontinuation and withdrawal in the treatment arm and higher risks of conversion to exudative AMD. Studies evaluating other complement members (CFB, CFH, CFI and inhibitors of membrane attack complex-CD59) are ongoing and could offer other viable strategies.

Complement Inhibition for Geographic Atrophy: A Tempting Target with Mixed Results.

Age-related macular degeneration (AMD) is a leading cause of blindness in older adults. One of the strongest genetic risk factors for AMD is a complement factor H (CFH) gene polymorphism characterized by a tyrosine-histidine change at amino acid position 402 (Y402H). The magnitude of this association between the Y402H variant and AMD is among the strongest that has been identified for any complex, multifactorial human disease. This strong association has motivated researchers to investigate a potential link between various elements of the complement pathway and AMD pathogenesis. Given the possible contribution of complement dysregulation to AMD, complement inhibition has emerged as a therapeutic strategy for slowing geographic atrophy (GA). Randomized clinical trials thus far have yielded mixed results. In this article, we provide the historical context for complement inhibition as a strategy for treating GA, discuss potential advantages and disadvantages of complement inhibition, and highlight the questions that must be addressed before complement inhibition can take center stage as a therapy for AMD.