A Review of the Role of the Intestinal Microbiota in Age-Related Macular Degeneration

Blindness from age-related macular degeneration (AMD) is an escalating problem, yet AMD pathogenesis is incompletely understood and treatments are limited. The intestinal microbiota is highly influential in ocular and extraocular diseases with inflammatory components, such as AMD. This article reviews data supporting the role of the intestinal microbiota in AMD pathogenesis. Multiple groups have found an intestinal dysbiosis in advanced AMD. There is growing evidence that environmental factors associated with AMD progression potentially work through the intestinal microbiota. A high-fat diet in apo-E-/- mice exacerbated wet and dry AMD features, presumably through changes in the intestinal microbiome, though other independent mechanisms related to lipid metabolism are also likely at play. AREDS supplementation reversed some adverse intestinal microbial changes in AMD patients. Part of the mechanism of intestinal microbial effects on retinal disease progression is via microbiota-induced microglial activation. The microbiota are at the intersection of genetics and AMD. Higher genetic risk was associated with lower intestinal bacterial diversity in AMD. Microbiota-induced metabolite production and gene expression occur in pathways important in AMD pathogenesis. These studies suggest a crucial link between the intestinal microbiota and AMD pathogenesis, thus providing a novel potential therapeutic target. Thus, the need for large longitudinal studies in patients and germ-free or gnotobiotic animal models has never been more pressing.

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Role of intestinal microbiome in the pathogenesis of age-related macular degeneration

Medical Hypothesis, Discovery & Innovation in Optometry ◽

10.51329/mehdioptometry105 ◽

2020 ◽

Vol 1 (1) ◽

pp. 29-36

Author(s):

Dimitrios Kalogeropoulos ◽

Konstantinos Katsikatsos ◽

Konstantinos Dallas ◽

Soon Wai Ch’ng ◽

Ioannis Asproudis ◽

...

Keyword(s):

Macular Degeneration ◽

Intestinal Microbiota ◽

English Language ◽

Inflammatory Diseases ◽

Active Role ◽

Age Related Macular Degeneration ◽

Intestinal Microbiome ◽

Therapeutic Modalities ◽

Age Related

Background: The microbiome is strongly linked to many extra-intestinal disorders. Gut commensal microbiota, in particular, plays an active role in human immune and intestinal homeostasis. Complex interactions of the microbiota with host genetics and other underlying factors lead to intestinal dysbiosis, which is thought to be linked to ocular inflammatory diseases. Thus, the aim of this review is to analyze the role of intestinal microbiome in age-related macular degeneration (AMD). Methods: A thorough literature search was performed using PubMed/MEDLINE, limited to English language publications, from January 2004 to March 2020. An additional search was made employing Google Scholar to complete the collected data as per the above-mentioned time-line and language limitations. The main keywords used included age-related macular degeneration, microbiome, dysbiosis, autoimmunity, gut microbiota, epigenetics, immune-mediated inflammatory diseases, and gut-retina axis. Results: Recent studies have proposed the role of intestinal microbiota in the pathogenesis of AMD. Changes in the microbiome have been shown to trigger several ocular inflammatory processes. There is increasing evidence demonstrating that intestinal microbial imbalance may play an important role in the pathogenesis of AMD. Conclusions: This review summarizes how alterations in the intestinal microbiota can be associated with the pathogenesis of AMD and how new therapeutic modalities can be designed to target this microbiome to limit the severe nature of this disease. Future advances in microbiome research may unveil a new era in understanding and managing AMD.

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Differential Expression of Kinin Receptors in Human Wet and Dry Age-Related Macular Degeneration Retinae

Pharmaceuticals ◽

10.3390/ph13060130 ◽

2020 ◽

Vol 13 (6) ◽

pp. 130

Author(s):

Rahmeh Othman ◽

Simon Berbari ◽

Elvire Vaucher ◽

Réjean Couture

Keyword(s):

Macular Degeneration ◽

Retinal Disease ◽

Clinical Findings ◽

Age Related Macular Degeneration ◽

Primary Role ◽

Kinin Receptors ◽

Age Related ◽

Mediators Of Inflammation ◽

Dry Amd ◽

Wet Amd

Kinins are vasoactive peptides and mediators of inflammation, which signal through two G protein-coupled receptors, B1 and B2 receptors (B1R, B2R). Recent pre-clinical findings suggest a primary role for B1R in a rat model of wet age-related macular degeneration (AMD). The aim of the present study was to investigate whether kinin receptors are differentially expressed in human wet and dry AMD retinae. The cellular distribution of B1R and B2R was examined by immunofluorescence and in situ hybridization in post-mortem human AMD retinae. The association of B1R with inflammatory proteins (inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor A (VEGFA)), fibrosis markers and glial cells was also studied. While B2R mRNA and protein expression was not affected by AMD, a significant increase of B1R mRNA and immunoreactivity was measured in wet AMD retinae when compared to control and dry AMD retinae. B1R was expressed by Müller cells, astrocytes, microglia and endothelial/vascular smooth muscle cells, and colocalized with iNOS and fibrosis markers, but not with VEGFA. In conclusion, the induction and upregulation of the pro-inflammatory and pro-fibrotic kinin B1R in human wet AMD retinae support previous pre-clinical studies and provide a clinical proof-of-concept that B1R represents an attractive therapeutic target worth exploring in this retinal disease.

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Complement C5 is not critical for the formation of sub-RPE deposits in Efemp1 mutant mice

Scientific Reports ◽

10.1038/s41598-021-89978-8 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Donita L. Garland ◽

Eric A. Pierce ◽

Rosario Fernandez-Godino

Keyword(s):

Macular Degeneration ◽

Retinal Pigment ◽

Age Related Macular Degeneration ◽

Deposit Formation ◽

Genetic Ablation ◽

Age Related ◽

Complement Dysregulation

AbstractThe complement system plays a role in the formation of sub-retinal pigment epithelial (RPE) deposits in early stages of age-related macular degeneration (AMD). But the specific mechanisms that connect complement activation and deposit formation in AMD patients are unknown, which limits the development of efficient therapies to reduce or stop disease progression. We have previously demonstrated that C3 blockage prevents the formation of sub-RPE deposits in a mouse model of EFEMP1-associated macular degeneration. In this study, we have used double mutant Efemp1R345W/R345W:C5-/- mice to investigate the role of C5 in the formation of sub-RPE deposits in vivo and in vitro. The data revealed that the genetic ablation of C5 does not eliminate the formation of sub-RPE deposits. Contrarily, the absence of C5 in RPE cultures promotes complement dysregulation that results in increased activation of C3, which likely contributes to deposit formation even in the absence of EFEMP1-R345W mutant protein. The results also suggest that genetic ablation of C5 alters the extracellular matrix turnover through an effect on matrix metalloproteinases in RPE cell cultures. These results confirm that C3 rather than C5 could be an effective therapeutic target to treat early AMD.

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Outer retinal tubulation formation and clinical course of advanced age-related macular degeneration

Scientific Reports ◽

10.1038/s41598-021-94310-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Alessandro Arrigo ◽

Emanuela Aragona ◽

Ottavia Battaglia ◽

Andrea Saladino ◽

Alessia Amato ◽

...

Keyword(s):

Macular Degeneration ◽

Müller Cells ◽

Geographic Atrophy ◽

Age Related Macular Degeneration ◽

Advanced Age ◽

Age Related ◽

Dry Amd ◽

Foveal Sparing ◽

Wet Amd

AbstractOuter retinal tubulations (ORT) are a relatively new finding characterizing outer retinal atrophy. The main aim of the present study was to describe ORT development in advanced age-related macular degeneration (AMD) and to assess its relationship with disease’s severity. Patients with advanced AMD characterized either by macular neovascularization or geographic atrophy, showing signs of outer retinal disruption or retinal pigment epithelium atrophy on structural optical coherence tomography (OCT) at the inclusion examination were prospectively recruited. All the patients underwent complete ophthalmologic evaluation, structural OCT scans and fundus autofluorescence imaging. The planned follow-up was of 3-years. Main outcome measures were ORT prevalence, mechanism of ORT formation, mean time needed for complete ORT formation, best-corrected visual acuity (BCVA), definitely decreased autofluorescence (DDAF) area, questionably decreased autofluorescence (QDAF) area, retinal layer thickness, foveal sparing, number of intravitreal injections. We also assessed the possible role of external limiting membrane (ELM) and Müller cells in ORT pathogenesis. Seventy eyes (70 patients) were included; 43 showed dry AMD evolving to geographic atrophy, while 27 displayed the features of wet AMD. Baseline BCVA was 0.5 ± 0.5 LogMAR, decreasing to 0.9 ± 0.5 LogMAR at the 3-year follow-up (p < 0.01). We detected completely formed ORT in 26/70 eyes (37%), subdivided as follows: 20 eyes (77%) wet AMD and 6 eyes (23%) dry AMD (p < 0.01). ORT took 18 ± 8 months (range 3–35 months) to develop fully. We described the steps leading to ORT development, characterized by progressive involvement of, and damage to the photoreceptors, the ELM and the RPE. Eyes displaying ORT were associated with a smaller QDAF area, less retinal layers damage and lower rate of foveal sparing than eyes free of ORT (p < 0.01). We also described pigment accumulations simulating ORT, which were detected in 16/70 eyes (23%), associated with a greater loss of foveal sparing, increased DDAF area and smaller QDAF area at the 3-year follow-up (p < 0.01). In conclusion, this study provided a description of the steps leading to ORT development in AMD. ELM and Müller cells showed a role in ORT pathogenesis. Furthermore, we described a subtype of pigment hypertrophy mimicking ORT, evaluating its clinical utility.

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Age-Related Macular Degeneration: Role of Oxidative Stress and Blood Vessels

International Journal of Molecular Sciences ◽

10.3390/ijms22031296 ◽

2021 ◽

Vol 22 (3) ◽

pp. 1296

Author(s):

Yue Ruan ◽

Subao Jiang ◽

Adrian Gericke

Keyword(s):

Oxidative Stress ◽

Macular Degeneration ◽

Vascular Function ◽

Vascular Dysfunction ◽

Therapeutic Strategies ◽

Vision Impairment ◽

Age Related Macular Degeneration ◽

Oxygen Species ◽

Age Related

Age-related macular degeneration (AMD) is a common irreversible ocular disease characterized by vision impairment among older people. Many risk factors are related to AMD and interact with each other in its pathogenesis. Notably, oxidative stress and choroidal vascular dysfunction were suggested to be critically involved in AMD pathogenesis. In this review, we give an overview on the factors contributing to the pathophysiology of this multifactorial disease and discuss the role of reactive oxygen species and vascular function in more detail. Moreover, we give an overview on therapeutic strategies for patients suffering from AMD.

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Oxidative Stress and Mitochondrial Damage in Dry Age-Related Macular Degeneration Like NFE2L2/PGC-1α -/- Mouse Model Evoke Complement Component C5a Independent of C3

Biology ◽

10.3390/biology10070622 ◽

2021 ◽

Vol 10 (7) ◽

pp. 622

Author(s):

Iswariyaraja Sridevi Gurubaran ◽

Hanna Heloterä ◽

Stephen Marry ◽

Ali Koskela ◽

Juha M. T. Hyttinen ◽

...

Keyword(s):

Oxidative Stress ◽

Mouse Model ◽

Macular Degeneration ◽

Complement Component ◽

Factor H ◽

Age Related Macular Degeneration ◽

Related Factor ◽

Complement Factor ◽

Age Related ◽

Dry Amd

Aging-associated chronic oxidative stress and inflammation are known to be involved in various diseases, e.g., age-related macular degeneration (AMD). Previously, we reported the presence of dry AMD-like signs, such as elevated oxidative stress, dysfunctional mitophagy and the accumulation of detrimental oxidized materials in the retinal pigment epithelial (RPE) cells of nuclear factor erythroid 2-related factor 2, and a peroxisome proliferator-activated receptor gamma coactivator 1-alpha (NFE2L2/PGC1α) double knockout (dKO) mouse model. Here, we investigated the dynamics of inflammatory markers in one-year-old NFE2L2/PGC1α dKO mice. Immunohistochemical analysis revealed an increase in levels of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in NFE2L2/PGC1α dKO retinal specimens as compared to wild type animals. Further analysis showed a trend towards an increase in complement component C5a independent of component C3, observed to be tightly regulated by complement factor H. Interestingly, we found that thrombin, a serine protease enzyme, was involved in enhancing the terminal pathway producing C5a, independent of C3. We also detected an increase in primary acute phase C-reactive protein and receptor for advanced glycation end products in NFE2L2/PGC1α dKO retina. Our main data show C5 and thrombin upregulation together with decreased C3 levels in this dry AMD-like model. In general, the retina strives to mount an orchestrated inflammatory response while attempting to maintain tissue homeostasis and resolve inflammation.

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