TUMOR NECROSIS FACTOR-α GENE POLYMORPHISMS IN AGE-RELATED MACULAR DEGENERATION

Cholesterol Accumulation Promotes Photoreceptor Senescence and Retinal Degeneration

Purpose

Dysregulated cholesterol metabolism is critical in the pathogenesis of AMD. Cellular senescence contributes to the development of numerous age-associated diseases. In this study, we investigated the link between cholesterol burden and the cellular senescence of photoreceptors.

Methods

Retinas from rod-specific ATP binding cassette subfamily A member 1 (Abca1) and G member 1 (Abcg1) (Abca1/g1-rod/-rod) knockout mice fed with a high-fat diet were analyzed for the signs of cellular senescence. Real-time quantitative PCR and immunofluorescence were used to characterize the senescence profile of the retina and cholesterol-treated photoreceptor cell line (661W). Inducible elimination of p16(Ink4a)-positive senescent cells (INK-ATTAC) mice or the administration of senolytic drugs (dasatinib and quercetin: D&Q) were used to examine the impact of senolytics on AMD-like phenotypes in Abca1/g1-rod/-rod retina.

Results

Increased accumulation of senescent cells as measured by markers of cellular senescence was found in Abca1/g1-rod/-rod retina. Exogenous cholesterol also induced cellular senescence in 661W cells. Selective elimination of senescent cells in Abca1/g1-rod/-rod;INK-ATTAC mice or by administration of D&Q improved visual function, lipid accumulation in retinal pigment epithelium, and Bruch's membrane thickening.

Conclusions

Cholesterol accumulation promotes cellular senescence in photoreceptors. Eliminating senescent photoreceptors improves visual function in a model of retinal neurodegeneration, and senotherapy offers a novel therapeutic avenue for further investigation.

The role of the cytokine TNF-α in choroidal neovascularization: a systematic review

TNF-α is a multifunctional cytokine produced by macrophages and T cells. This proinflammatory substance is considered to play a crucial role in the inflammatory process associated with age-related macular degeneration (AMD). The current review aimed to describe evidence for an association between TNF-α and AMD reported in various studies. The MEDLINE, Embase, PubMed and Global Health databases were systematically searched to identify studies that investigated the role of TNF-α in AMD. A total of 24 studies were deemed eligible for the review. To better understand and integrate the evidence, the studies were categorised into four major groups in relation to the role of TNF-α in AMD: (1) those examining biological signalling pathways through which TNF-α exerts its effect; (2) investigating levels of TNF-α; (3) exploring the genetics underlying the role of TNF-α; and (4) assessing anti-TNF-α agents as potential treatments for AMD. TNF-α is thought to directly contribute to choroidal neovascularization (CNV) enhancement and has been shown to exert its effect by augmenting the inflammatory response through other signalling pathways. Additionally, different genes have been found to be associated with activities linked to TNF-α in AMD. Overall, measurement of systemic and local levels of TNF-α has not yielded consistent findings, with variable conclusions for the role of anti-TNF-α agents in remission of AMD symptoms. The role of TNF-α in neovascular AMD is not clear, and not all anti-TNF-α agents are safe. The potential of this cytokine in atrophic AMD has not been examined. Future studies should address these unresolved questions.

Divergent Metabolomic Signatures of TGFβ2 and TNFα in the Induction of Retinal Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is a dedifferentiation program in which polarized, differentiated epithelial cells lose their cell-cell adhesions and transform into matrix-producing mesenchymal cells. EMT of retinal pigment epithelial (RPE) cells plays a crucial role in many retinal diseases, including age-related macular degeneration, proliferative vitreoretinopathy, and diabetic retinopathy. This dynamic process requires complex metabolic reprogramming to accommodate the demands of this dramatic cellular transformation. Both transforming growth factor-beta 2 (TGFβ2) and tumor necrosis factor-alpha (TNFα) have the capacity to induce EMT in RPE cells; however, little is known about their impact on the RPE metabolome. Untargeted metabolomics using high-resolution mass spectrometry was performed to reveal the metabolomic signatures of cellular and secreted metabolites of primary human fetal RPE cells treated with either TGFβ2 or TNFα for 5 days. A total of 638 metabolites were detected in both samples; 188 were annotated as primary metabolites. Metabolomics profiling showed distinct metabolomic signatures associated with TGFβ2 and TNFα treatment. Enrichment pathway network analysis revealed alterations in the pentose phosphate pathway, galactose metabolism, nucleotide and pyrimidine metabolism, purine metabolism, and arginine and proline metabolism in TNFα-treated cells compared to untreated control cells, whereas TGFβ2 treatment induced perturbations in fatty acid biosynthesis metabolism, the linoleic acid pathway, and the Notch signaling pathway. These results provide a broad metabolic understanding of the bioenergetic rewiring processes governing TGFβ2- and TNFα-dependent induction of EMT. Elucidating the contributions of TGFβ2 and TNFα and their mechanistic differences in promoting EMT of RPE will enable the identification of novel biomarkers for diagnosis, management, and tailored drug development for retinal fibrotic diseases.

Dimethyl Fumarate Blocks Tumor Necrosis Factor-Alpha-Driven Inflammation and Metabolic Rewiring in the Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) acts as a metabolic gatekeeper between photoreceptors and the choroidal vasculature to maintain retinal function. RPE dysfunction is a key feature of age-related macular degeneration (AMD), the leading cause of blindness in developed countries. Inflammation is a key pathogenic mechanism in AMD and tumor necrosis factor-alpha (TNFα) has been implicated as a pro-inflammatory cytokine involved in AMD. While mitochondrial dysfunction has been implicated in AMD pathogenesis, the interplay between inflammation and cellular metabolism remains elusive. The present study explores how the pro-inflammatory cytokine, TNFα, impacts mitochondrial morphology and metabolic function in RPE. Matured human primary RPE (H-RPE) were treated with TNFα (10 ng/ml) for up to 5 days. TNFα-induced upregulation of IL-6 secretion and inflammatory genes (IL-6, IL-8, MCP-1) was accompanied by increased oxidative phosphorylation (OXPHOS) and reduced glycolysis, leading to an increase in cellular adenosine triphosphate (ATP) content. Transmission electron microscopy (TEM) revealed defects in mitochondrial morphology with engorged mitochondria and loss of cristae integrity following TNFα treatment. Pre-treatment with the anti-inflammatory drug, 80 μM dimethyl fumarate (DMFu), blocked TNFα-induced inflammatory activation of RPE (IL-6, IL-8, MCP-1, CFH, CFB, C3) and normalized their bioenergetic profile to control levels by regulating PFKFB3 and PKM2 gene expression. Furthermore, DMFu prevented TNFα-induced mitochondrial dysfunction and morphological anomalies. Thus, our results indicate that DMFu serves as a novel therapeutic avenue for combating inflammatory activation and metabolic dysfunction of RPE in AMD.

Effect of Humanin G (HNG) on inflammation in age-related macular degeneration (AMD)

Inflammation plays a crucial role in the etiology and pathogenesis of AMD (Age-related Macular Degeneration). Humanin G (HNG) is a Mitochondrial Derived Peptide (MDP) that is cytoprotective in AMD and can protect against mitochondrial and cellular stress induced by damaged AMD mitochondria. The goal of this study was to test our hypothesis that inflammation-associated marker protein levels are increased in AMD and treatment with HNG leads to reduction in their protein levels. Humanin protein levels were measured in the plasma of AMD patients and normal subjects using ELISA assay. Humanin G was added to AMD and normal (control) cybrids which had identical nuclei from mitochondria-deficient ARPE-19 cells but differed in mitochondrial DNA (mtDNA) content derived from clinically characterized AMD patients and normal (control) subjects. Cell lysates were extracted from untreated and HNG-treated AMD and normal cybrids, and the Luminex XMAP multiplex assay was used to measure the levels of inflammatory proteins. AMD plasma showed reduced Humanin protein levels, but higher protein levels of inflammation markers compared to control plasma samples. In AMD RPE cybrid cells, Humanin G reduced the CD62E/ E-Selectin, CD62P/ P-Selectin, ICAM-1, TNF-α, MIP-1α, IFN–γ, IL-1β, IL-13, and IL-17A protein levels, thereby suggesting that Humanin G may rescue from mtDNA-mediated inflammation in AMD cybrids. In conclusion, we present novel findings that: A) show reduced Humanin protein levels in AMD plasma vs. normal plasma; B) suggest the role of inflammatory markers in AMD pathogenesis, and C) highlight the positive effects of Humanin G in reducing inflammation in AMD.

TNF-α gene polymorphisms: association with age-related macular degeneration in Russian population

AIM

To study polymorphisms in promotor regions of tumor necrosis factor (TNF)-α TNF-863A/C (rs1800630), TNF-308A/G (rs1800629), and TNF-238A/G (rs361525) in patients with age-related macular degeneration (AMD) and associations of complex TNF-α genotypes with AMD.

METHODS

One hundred and two patients (82 women, 20 men; mean age 64.2±1.2y) with AMD and 100 healthy age- and sex-matched controls (82 women, 18 men; 60±1.4y) were included in the study. All subjects were Caucasian, all subjects and their parents were inhabitants of Russia. Genomic DNA was obtained from EDTA-preserved blood using the standard phenol-chloroform method. Polymorphisms were detected by polymerase chain reaction followed by the restriction fragment length polymorphism method. The following TNF-α genotypes were studied: TNF-α-238 AA, GA, GG, TNF-α-308 AA, GA, GG, TNF-α-863 AA, CA, CC.

RESULTS

Differences in TNF-α-863 and TNF-α-238 genotypes frequencies in patients with AMD and healthy controls were not found. The distribution of TNF-α-308 AA and TNF-α-308 GA genotypes was significantly different between the studied group and the controls [odds ratios (OR) =0.22, P=0.0287 and OR=2.91, P=0.0063, respectively]. TNF-863CC/TNF-308GA and TNF-308GA/TNF-238GG genotypes were associated with the increased risk of AMD (OR=2.48, P=0.0332 and OR=2.51, P=0.0187, respectively). Five genotypes combinations appeared to be protective.

CONCLUSION

In the present study, single nucleotide polymorphisms and complex polymorphisms of one of the key inflammatory cytokines TNF-α, and a number of significant associations of these polymorphisms with AMD in Russian population have been shown. Complex analysis of genotypes could be important in AMD risk factors detection and studying pathogenesis.

Rap1 GTPase Inhibits Tumor Necrosis Factor-α-Induced Choroidal Endothelial Migration via NADPH Oxidase- and NF-κB-Dependent Activation of Rac1

Macrophage-derived tumor necrosis factor (TNF)-α has been found in choroidal neovascularization (CNV) surgically removed from patients with age-related macular degeneration. However, the role of TNF-α in CNV development remains unclear. In a murine laser-induced CNV model, compared with un-lasered controls, TNF-α mRNA was increased in retinal pigment epithelial and choroidal tissue, and TNF-α colocalized with lectin-stained migrating choroidal endothelial cells (CECs). Inhibition of TNF-α with a neutralizing antibody reduced CNV volume and reactive oxygen species (ROS) level around CNV. In CECs, pretreatment with the antioxidant apocynin or knockdown of p22phox, a subunit of NADPH oxidase, inhibited TNF-α-induced ROS generation. Apocynin reduced TNF-α-induced NF-κB and Rac1 activation, and inhibited TNF-α-induced CEC migration. TNF-α-induced Rac1 activation and CEC migration were inhibited by NF-κB inhibitor Bay11-7082. Overexpression of Rap1a prevented TNF-α-induced ROS generation and reduced NF-κB and Rac1 activation. Activation of Rap1 by 8-(4-chlorophenylthio)adenosine-2'-O-Me-cAMP prevented TNF-α-induced CEC migration and reduced laser-induced CNV volume, ROS generation, and activation of NF-κB and Rac1. These findings provide evidence that active Rap1a inhibits TNF-α-induced CEC migration by inhibiting NADPH oxidase-dependent NF-κB and Rac1 activation and suggests that Rap1a de-escalates CNV development by interfering with ROS-dependent signaling in several steps of the pathogenic process.

Tumor Necrosis Factor Gene Polymorphisms in Advanced Non-exudative Age-related Macular Degeneration

Purpose:

To investigate tumor necrosis factor (TNF)-α gene polymorphisms in advanced dry-type age-related macular degeneration (AMD) in a population from Northeastern Iran.

Methods:

In this case-control study, 50 patients with geographic macular atrophy and 73 gender-matched controls were enrolled. Genomic deoxyribonucleic acid (DNA) was extracted from the peripheral blood. Polymerase chain reaction was performed to analyze 2 candidate single nucleotide polymorphisms in the TNF-α gene, namely −1031 thymine (T)/cytosine (C) and −308 guanine (G)/adenine (A).

Results:

The distribution of the - 1031 T/C genotype was TT, 62%; TC, 36%; CC, 2% in the patients and TT, 60%; TC, 36%; CC, 4% in the controls (P = 0.94). Genotype analysis of TNF-α −308 also revealed no significant difference in distribution between patients (G, 78%; GA, 22%; AA, 0%) and controls (GG, 74%; GA, 23%; AA, 3%) (P = 0.51). None of the haplotypes nor alleles of studied TNF-α polymorphisms were significantly associated with advanced dry-type AMD.

Conclusion:

The findings of this study show that polymorphisms in the TNF-α gene, do not play an important role in dry-type AMD in the studied population.

Impact of visceral fat and pro-inflammatory factors on the pathogenesis of age-related macular degeneration

PURPOSE

Previous studies have indicated that the immune system is involved in the pathogenesis of the AMD. Increased visceral fat, in addition, has a pro-inflammatory effect on the organism by producing or influencing different kinds of inflammatory factors. The aim of this study is to determine the relationship of body fat distribution in patients with age-related macula degeneration in comparison to a control group in the Austrian population.

METHODS

In this case-control study, body weight and height, and body mass index (BMI) were measured for each subject in 54 patients with exudative AMD and compared to 46 gender- and age-matched healthy control subjects. Body composition and abdominal fat areas were measured using dual-energy X-ray absorptiometry (DEXA). Data on age, gender distribution, smoking history and systemic diseases, respectively, were compared. The inflammatory markers CRP, tumour necrosis factor-alpha (TNF-alpha), leptin, amyloid A, amyloid beta and interleukin-6 (IL-6) were assayed by ELISA (R&D).

RESULTS

DEXA revealed central-abdominal-to-total body fat ratio of 0.073 +/- 0.011 in AMD patients compared to 0.061 +/- 0.013 in the controls (p <0.001; d = 0.98). The calculation of BMI has provided a significant result (p =0.045). U-test results for Aß1-42, IL-6, SAA and CRP each were significant (p < 0.05), with higher values in AMD patients. Leptin, TNF-alpha and Aß1-40 showed no significant differences between the groups.

CONCLUSION

Our results suggest that abdominal fat distribution is significantly associated with age-related macular degeneration. Analysis of patients with exudative AMD revealed higher levels of CRP, amyloid ß1-42, IL-6 and amyloid alpha.

Intravitreal tumor necrosis factor-alpha inhibitors for neovascular age-related macular degeneration suboptimally responsive to antivascular endothelial growth factor agents: a pilot study from the Pan American Collaborative Retina Study Group

PURPOSE

To compare the short-term visual and anatomic outcomes after intravitreal injections of 2 different tumor necrosis factor-α inhibitors to continued antivascular endothelial growth factor (VEGF) therapy in eyes with choroidal neovascularization (CNV) secondary to age-related macular degeneration that responded suboptimally to anti-VEGF agents.

METHODS

Retrospective comparative case series of 26 eyes. Eyes were injected intravitreally with 1 mg infliximab, 2 mg infliximab, 2 mg adalimumab, or 1.25 mg bevacizumab. The main outcomes measured were the best-corrected visual acuity (BCVA) and the central macular thickness (CMT) at 3 months of follow-up.

RESULTS

The mean log minimal angle of resolution BCVA changed from 1.04±0.23 at baseline to 1.06±0.51 at 3 months (P=0.9455) in the 1-mg infliximab group; 0.94±0.48 at baseline to 0.85±0.43 in the 2-mg infliximab group (P=0.2802); 1.58±0.50 at baseline to 1.38±0.43 in the adalimumab group (P=0.1116); and 1.08±0.1 at baseline to 1.03±0.16 in the bevacizumab group (P=0.9928). The mean CMT changed from 387±54 μm at baseline to 342±108 μm (P=0.1053) in the 1-mg infliximab group; 301±42 μm at baseline to 284±73 μm (P=0.4854) in the 2-mg infliximab group; remained unchanged at 348±106 μm (P=0.308) in the adalimumab group; and 362±66 μm to 340±27 μm in the bevacizumab group (P=0.4622). Adverse events included uveitis in 37.5% (6/16) of eyes injected with infliximab.

CONCLUSION

Intravitreal infliximab and adalimumab do not appear to benefit eyes with CNV that responded suboptimally to anti-VEGF agents. Intravitreal injections of infliximab may elicit a severe intraocular inflammatory reaction.