The association of matrix metalloproteinases polymorphisms and interleukins in advanced age-related macular degeneration

Targeting inflammasomes and pyroptosis in retinal diseases-molecular mechanisms and future perspectives

Retinal diseases encompass various conditions associated with sight-threatening immune responses and are leading causes of blindness worldwide. These diseases include age-related macular degeneration, diabetic retinopathy, glaucoma and uveitis. Emerging evidence underscores the vital role of the innate immune response in retinal diseases, beyond the previously emphasized T-cell-driven processes of the adaptive immune system. In particular, pyroptosis, a newly discovered programmed cell death process involving inflammasome formation, has been implicated in the loss of membrane integrity and the release of inflammatory cytokines. Several disease-relevant animal models have provided evidence that the formation of inflammasomes and the induction of pyroptosis in innate immune cells contribute to inflammation in various retinal diseases. In this review article, we summarize current knowledge about the innate immune system and pyroptosis in retinal diseases. We also provide insights into translational targeting approaches, including novel drugs countering pyroptosis, to improve the diagnosis and treatment of retinal diseases.

Metabolic activity of visceral adipose tissue is associated with age-related macular degeneration: a pilot 18F-FDG PET/CT study

Background

Obesity is known to increase the risk and severity of age-related macular degeneration (AMD). Increased inflamed metabolic activity of visceral adipose tissue (VAT) is considered as a crucial underlying mechanism for the harmful effects of obesity. In this study, we aimed to investigate the inflamed metabolic activity of VAT with 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and their association with AMD.

Materials and methods

A total of 57 elderly participants (aged ≥ 50 years) who underwent 18F-FDG PET/CT for health screening and subsequent fundoscopic exam for complaint of recently impaired vision were enrolled. The metabolic activity of VAT was measured from the maximum standardized uptake value (SUVmax) of VAT. The early AMD participant was defined as the participant with either eye satisfying AMD and without any sign of advanced AMD (neovascular AMD or geographic atrophy). The late AMD participant was defined as the participant with either eye satisfying advanced AMD.

Results

VAT SUVmax was highest in participants with late AMD, intermediate in early AMD, and lowest in non-AMD participants. The levels of systemic inflammation surrogate markers were also highest in late AMD group. Furthermore, VAT SUVmax was positively correlated with systemic inflammation surrogate markers and independently associated with the late AMD.

Conclusions

The metabolic activity of VAT evaluated by 18F-FDG PET/CT was associated with the severity of AMD and synchronized with the level of systemic inflammation. Thus, VAT SUVmax could be potentially employed as a surrogate marker of obesity-driven VAT inflammation associated with AMD.

Disturbed Matrix Metalloproteinases Activity in Age-Related Macular Degeneration

Matrix metalloproteinases (MMPs) are a tightly regulated family of proteolytic enzymes that break down extracellular matrix (ECM) and basement membrane components. Because it is associated with development, morphogenesis, tissue remodeling, and repair, ECM remodeling is an important mechanism. MMPs are thought to act as a double-edged sword, as they contribute to maintaining photoreceptors/retinal pigment epithelium (RPE)/Bruch's membrane (BM)/choroid complex homeostasis and also contribute to the onset and progression of age-related macular degeneration (AMD). Polymorphisms and/or altered expression in MMPs and their tissue inhibitors (TIMPs) are associated with age-related macular degeneration (AMD). Here, we review the evidence for MMPs' role in the onset and progression of AMD via addressing their regulation and TIMPs' significant regulatory functions.

Molecular Genetic Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is among the leading causes of irreversible blindness worldwide. In addition to environmental risk factors, such as tobacco use and diet, genetic background has long been established as a major risk factor for the development of AMD. However, our ability to predict disease risk and personalize treatment remains limited by our nascent understanding of the molecular mechanisms underlying AMD pathogenesis. Research into the molecular genetics of AMD over the past two decades has uncovered 52 independent gene variants and 34 independent loci that are implicated in the development of AMD, accounting for over half of the genetic risk. This research has helped delineate at least five major pathways that may be disrupted in the pathogenesis of AMD: the complement system, extracellular matrix remodeling, lipid metabolism, angiogenesis, and oxidative stress response. This review surveys our current understanding of each of these disease mechanisms, in turn, along with their associated pathogenic gene variants. Continued research into the molecular genetics of AMD holds great promise for the development of precision-targeted, personalized therapies that bring us closer to a cure for this debilitating disease.

Inflammatory adipose activates a nutritional immunity pathway leading to retinal dysfunction

Age-related macular degeneration (AMD), the leading cause of irreversible blindness among Americans over 50, is characterized by dysfunction and death of retinal pigment epithelial (RPE) cells. The RPE accumulates iron in AMD, and iron overload triggers RPE cell death in vitro and in vivo. However, the mechanism of RPE iron accumulation in AMD is unknown. We show that high-fat-diet-induced obesity, a risk factor for AMD, drives systemic and local inflammatory circuits upregulating interleukin-1β (IL-1β). IL-1β upregulates RPE iron importers and downregulates iron exporters, causing iron accumulation, oxidative stress, and dysfunction. We term this maladaptive, chronic activation of a nutritional immunity pathway the cellular iron sequestration response (CISR). RNA sequencing (RNA-seq) analysis of choroid and retina from human donors revealed that hallmarks of this pathway are present in AMD microglia and macrophages. Together, these data suggest that inflamed adipose tissue, through the CISR, can lead to RPE pathology in AMD.

The Role of Inflammation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a blinding eye disease which incidence gradually increases with age. Inflammation participates in AMD pathogenesis, including choroidal neovascularization and geographic atrophy. It is also a kind of self-protective regulation from injury for the eyes. In this review, we described inflammation in AMD pathogenesis, summarized the roles played by inflammation-related cytokines, including pro-inflammatory and anti-inflammatory cytokines, as well as leukocytes (macrophages, dendritic cells, neutrophils, T lymphocytes and B lymphocytes) in the innate or adaptive immunity in AMD. Possible clinical applications such as potential diagnostic biomarkers and anti-inflammatory therapies were also discussed. This review overviews the inflammation as a target of novel effective therapies in treating AMD.

Matrix Metalloproteinases in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a complex, multifactorial and progressive retinal disease affecting millions of people worldwide. In developed countries, it is the leading cause of vision loss and legal blindness among the elderly. Although the pathogenesis of AMD is still barely understood, recent studies have reported that disorders in the regulation of the extracellular matrix (ECM) play an important role in its etiopathogenesis. The dynamic metabolism of the ECM is closely regulated by matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs). The present review focuses on the crucial processes that occur at the level of the Bruch’s membrane, with special emphasis on MMPs, TIMPs, and the polymorphisms associated with increased susceptibility to AMD development. A systematic literature search was performed, covering the years 1990–2020, using the following keywords: AMD, extracellular matrix, Bruch’s membrane, MMPs, TIMPs, and MMPs polymorphisms in AMD. In both early and advanced AMD, the pathological dynamic changes of ECM structural components are caused by the dysfunction of specific regulators and by the influence of other regulatory systems connected with both genetic and environmental factors. Better insight into the pathological role of MMP/TIMP complexes may lead to the development of new strategies for AMD treatment and prevention.

Systemic levels of interleukin-6 in patients with age-related macular degeneration: a systematic review and meta-analysis

Age-related macular degeneration (AMD) is the most prevalent cause of irreversible vision loss in industrialized countries. Several studies have investigated systemic interleukin-6 (IL-6) levels of patients with AMD. In this study, we systemically reviewed the literature to provide an overview of the field and used meta-analyses to provide a summary estimate of the standardized mean difference (SMD) of systemic IL-6 between patients with AMD and control individuals. We searched the literature databases PubMed/MEDLINE, Embase, Web of Science and the Cochrane Central on 1 June 2019 for relevant studies on humans. Two authors independently extracted data and evaluated risk of bias. We identified 19 studies for the qualitative review with a total of more than 3586 individuals (1865 controls and 1721 with AMD). We found an overall random-effects SMD in systemic IL-6 levels 0.63 (95% CI: 0.28 to 0.99, p = 0.0005) corresponding to a medium effect size. In a subgroup analysis, we found that early AMD was not strongly associated with elevated IL-6 levels (0.12, 95% CI: -0.01 to 0.24, p = 0.06), which was in contrast to the significantly elevated IL-6 levels in patients with geographic atrophy (1.21, 95% CI: 0.41 to 2.01, p = 0.003) and patients with neovascular AMD (0.99, 95% CI: 0.34 to 1.63, p = 0.003). Our results show that the evidence today suggests an increased systemic IL-6 in patients with AMD, but that this may be a phenomenon more closely related to the late subtypes of AMD.

IL-6: An endogenous activator of MMP-9 in preterm birth

Preterm birth or PTB (<37 weeks) is a heterogeneous phenotype with numerous biological pathways. The lack of explanation due to complex pathways, inconsistent observations indicates the need for employing the role of genetic determinants to anticipate the danger of PTB. In this present study, we investigated the possible gene-gene interaction of five SNPs with PTB and its association with total MMP-9 levels. A total of 510 recruitments (250 terms and preterm each) were made and were genotyped by Restriction Fragment length polymorphism (RFLP). Generalized Multifactor Dimensionality Reduction (GMDR) method was carried out for determining gene-gene interaction. ANOVA and t-test were used to identify the association of IL-6 polymorphism with PTB alone and correspondingly with PTB and low birth weight infants (i.e. < 2500 kg). The combination of IL-6 and MMP-9 and MMP-1, MMP-8 and MMP-9 polymorphism was selected through GMDR analysis concerning mothers with preterm and term birth (accuracy 0.5921 and 0.8030 with Cross-Validation Consistency (CVC) 10/10 respectively). Increased expression of MMP-9 was reported in cases in those mothers carrying IL-6 G allele, which was profoundly associated with PTB independently. IL-6 polymorphisms showed synergistic effects in terms of increased total MMP-9 levels in the present study.

Elovanoids counteract oligomeric β-amyloid-induced gene expression and protect photoreceptors

This study uncovers biosynthetic pathway insufficiencies of prohomeostatic/neuroprotective mediators neuroprotectin D1 and elovanoids in the retina during early pathogenesis in transgenic Alzheimer’s disease 5xFAD mouse. These changes correlate with photoreceptor cell functional impairments preceding their loss. Amyloid beta (Aβ) peptide accumulates in drusen in AMD. Thus, injecting oligomeric Aβ in wild-type mice behind the retina leads to photoreceptor cell degeneration and transcriptional disruptions including upregulation of a senescence program and of senescence-associated secretory phenotype (SASP). Similar changes take place in human retinal pigment epithelium cells in culture. Novel lipid mediators, the elovanoids, restore Aβ-peptide-induced gene expression changes and SASP secretome and, in turn, protect these cells. This study opens avenues of potential therapeutic exploration of elovanoids for AMD.

The onset of neurodegenerative diseases activates inflammation that leads to progressive neuronal cell death and impairments in cognition (Alzheimer’s disease) and sight (age-related macular degeneration [AMD]). How neuroinflammation can be counteracted is not known. In AMD, amyloid β-peptide (Aβ) accumulates in subretinal drusen. In the 5xFAD retina, we found early functional deficiencies (ERG) without photoreceptor cell (PRC) death and identified early insufficiency in biosynthetic pathways of prohomeostatic/neuroprotective mediators neuroprotectin D1 (NPD1) and elovanoids (ELVs). To mimic an inflammatory milieu in wild-type mouse, we triggered retinal pigment epithelium (RPE) damage/PRC death by subretinally injected oligomeric β-amyloid (OAβ) and observed that ELVs administration counteracted their effects, protecting these cells. In addition, ELVs prevented OAβ-induced changes in gene expression engaged in senescence, inflammation, autophagy, extracellular matrix remodeling, and AMD. Moreover, as OAβ targets the RPE, we used primary human RPE cell cultures and demonstrated that OAβ caused cell damage, while ELVs protected and restored gene expression as in mouse. Our data show OAβ activates senescence as reflected by enhanced expression of p16^INK4a, MMP1, p53, p21, p27, and Il-6, and of senescence-associated phenotype secretome, followed by RPE and PRC demise, and that ELVs 32 and 34 blunt these events and elicit protection. In addition, ELVs counteracted OAβ-induced expression of genes engaged in AMD, autophagy, and extracellular matrix remodeling. Overall, our data uncovered that ELVs downplay OAβ-senescence program induction and inflammatory transcriptional events and protect RPE cells and PRC, and therefore have potential as a possible therapeutic avenue for AMD.

IL-1 Family Members Mediate Cell Death, Inflammation and Angiogenesis in Retinal Degenerative Diseases

Inflammation underpins and contributes to the pathogenesis of many retinal degenerative diseases. The recruitment and activation of both resident microglia and recruited macrophages, as well as the production of cytokines, are key contributing factors for progressive cell death in these diseases. In particular, the interleukin 1 (IL-1) family consisting of both pro- and anti-inflammatory cytokines has been shown to be pivotal in the mediation of innate immunity and contribute directly to a number of retinal degenerations, including Age-Related Macular Degeneration (AMD), diabetic retinopathy, retinitis pigmentosa, glaucoma, and retinopathy of prematurity (ROP). In this review, we will discuss the role of IL-1 family members and inflammasome signaling in retinal degenerative diseases, piecing together their contribution to retinal disease pathology, and identifying areas of research expansion required to further elucidate their function in the retina.