High-Fat Diet Alters the Retinal Transcriptome in the Absence of Gut Microbiota

Nutritional Genomics: Implications for Age-Related Macular Degeneration

Background: Age-related macular degeneration (AMD) is a leading cause of vision loss in older individuals, driven by a multifactorial etiology involving genetic, environmental, and dietary factors. Nutritional genomics, which studies gene-nutrient interactions, has emerged as a promising field for AMD prevention and management. Genetic predispositions, such as variants in CFH, C3, C2/CFB, APOE, and oxidative stress pathways, significantly affect the risk and progression of AMD. Methods: This narrative review synthesizes findings from randomized controlled trials and recent advances in nutritional genomics research. It examines the interplay between genetic predispositions and dietary interventions, exploring how personalized nutritional strategies can optimize AMD management. Results and Discussion: The AREDS and AREDS2 trials demonstrated that supplements, including vitamins C, E, zinc, copper, lutein, and zeaxanthin, can reduce the progression to advanced AMD. Nutritional interventions tailored to genetic profiles show promise: CFH risk alleles may enhance zinc supplementation's anti-inflammatory effects, while APOE variants influence the response to omega-3 fatty acids. Adjusting carotenoid intake, such as lutein and zeaxanthin, based on genetic susceptibility exemplifies emerging precision nutritional approaches. Ongoing research seeks to integrate nutrigenomic testing into clinical settings, enabling clinicians to tailor interventions to individual genetic profiles. Conclusions: Further studies are needed to assess the long-term effects of personalized interventions, investigate additional genetic variants, and develop tools for clinical implementation of nutrigenomics. Advancing these strategies holds the potential to improve patient outcomes, optimize AMD management, and pave the way for precision nutrition in ophthalmology.

Are Hyperglycemia-Induced Changes in the Retina Associated with Diabetes-Correlated Changes in the Brain? A Review from Zebrafish and Rodent Type 2 Diabetes Models

Diabetes is prevalent worldwide, with >90% of the cases identified as Type 2 diabetes. High blood sugar (hyperglycemia) is the hallmark symptom of diabetes, with prolonged and uncontrolled levels contributing to subsequent complications. Animal models have been used to study these complications, which include retinopathy, nephropathy, and peripheral neuropathy. More recent studies have focused on cognitive behaviors due to the increased risk of dementia/cognitive deficits that are reported to occur in older Type 2 diabetic patients. In this review, we collate the data reported from specific animal models (i.e., mouse, rat, zebrafish) that have been examined for changes in both retina/vision (retinopathy) and brain/cognition, including db/db mice, Goto-Kakizaki rats, Zucker Diabetic Fatty rats, high-fat diet-fed rodents and zebrafish, and hyperglycemic zebrafish induced by glucose immersion. These models were selected because rodents are widely recognized as established models for studying diabetic complications, while zebrafish represent a newer model in this field. Our goal is to (1) summarize the published findings relevant to these models, (2) identify similarities in cellular mechanisms underlying the disease progression that occur in both tissues, and (3) address the hypothesis that hyperglycemic-induced changes in retina precede or predict later complications in brain.

Composition of the gut microbiome, role of diet, lifestyle, and antioxidant therapies in diabetes mellitus and diabetic retinopathy

The gut microbiome is a complex ecosystem in the gastrointestinal tract composed of trillions of bacteria, viruses, fungi, and protozoa. Disruption of this delicate ecosystem, formally called "dysbiosis", has been linked to a variety of metabolic and inflammatory pathologies. Several studies have focused on abnormal microbiome composition and correlated these findings with the development of type 2 diabetes mellitus (T2DM) and diabetic retinopathy (DR). However, given the complexity of this ecosystem, the current studies are narrow in design and present variable findings. Composition of the gut microbiome in patients with DR significantly differs from patients with diabetes without retinopathy as well as from healthy controls. Additionally, the gut microbiome has been shown to modify effects of medication, diet, exercise, and antioxidant use on the development and progression of DR. In this paper, we present a comprehensive review of literature on the effect of oxidative stress, antioxidant therapies, and dysbiosis on DR.

The Emerging Role of Gut Microbiota in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a progressive, degenerative retinal disease that is a leading cause of blindness globally. Although multiple risk factors have been identified regarding disease incidence and progression, including smoking, genetics, and diet, the understanding of AMD pathogenesis remains unclear. As such, primary prevention is lacking, and current treatments have limited efficacy. More recently, the gut microbiome has emerged as an influential player in various ocular pathologies. As mediators of metabolism and immune regulation, perturbations in gut microbiota may impart significant effects distally on the neuroretina and its adjacent tissues, termed the gut-retina axis. In this review, key studies over the past several decades are summarized, both in humans and in animal models, which shed insight on the relationships between the gut microbiome and retinal biology and their implications for AMD. The literature linking gut dysbiosis with AMD is examined, along with preclinical animal models and techniques apt for studying the role of gut microbiota in AMD pathogenesis, which include interactions with systemic inflammation, immune regulation, chorioretinal gene expression, and diet. As understanding of the gut-retina axis continues to advance, so too will the possibility for more accessible and effective prevention and therapy of this vision-threatening condition.

The Link Between Gastrointestinal Microbiome and Ocular Disorders

The gut-eye axis has been hypothesized to be a factor in many eye pathologies. This review examines papers from PubMed about this topic. Bacterial commensals could either be protective by regulating the immune system or prove to be damaging to the gut mucosal wall and incite an inflammatory process. The balance between the two appears to be crucial in maintaining eye health. Imbalances have been implicated in ophthalmologic conditions. The use of probiotics, dietary modifications, antibiotics, and faecal microbiota transplant in mice with pathologies such as those encountered in our practice appears to reverse disease course or at least prevent its progression. Clinical trials are currently underway to investigate their clinical significance in diseased patients.

The role of the gut microbiome in eye diseases

The gut microbiome is a complex ecosystem of microorganisms and their genetic entities colonizing the gastrointestinal tract. When in balanced composition, the gut microbiome is in symbiotic interaction with its host and maintains intestinal homeostasis. It is involved in essential functions such as nutrient metabolism, inhibition of pathogens and regulation of immune function. Through translocation of microbes and their metabolites along the epithelial barrier, microbial dysbiosis induces systemic inflammation that may lead to tissue destruction and promote the onset of various diseases. Using whole-metagenome shotgun sequencing, several studies have shown that the composition and associated functional capacities of the gut microbiome are associated with age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis. In this review, we provide an overview of the current knowledge about the gut microbiome in eye diseases, with a focus on interactions between the microbiome, specific microbial-derived metabolites and the immune system. We explain how these interactions may be involved in the pathogenesis of age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis and guide the development of new therapeutic approaches by microbiome-altering interventions for these diseases.

Analysis of differentially expressed genes in individuals with noninfectious uveitis based on data in the gene expression omnibus database

Noninfectious uveitis (NIU), an intraocular inflammation caused by immune-mediated reactions to eye antigens, is associated with systemic rheumatism and several autoimmune diseases. However, the mechanisms underlying the pathogenesis of uveitis are poorly understood. Therefore, we aimed to identify differentially expressed genes (DEGs) in individuals with NIU and to explore its etiologies using bioinformatics tools. GSE66936 and GSE18781 datasets from the gene expression omnibus (GEO) database were merged and analyzed. Functional enrichment analysis was performed, and protein-protein interaction (PPI) networks were constructed. A total of 89 DEGs were identified. Gene ontology (GO) enrichment analysis identified 21 enriched gene sets. Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis identified four core enriched pathways: antigen processing and expression signaling, natural killer (NK) cell-mediated cytotoxicity signaling, glutathione metabolic signal transduction, and arachidonic acid metabolism pathways. PPI network analysis revealed an active component-target network with 40 nodes and 132 edges, as well as several hub genes, including CD27, LTF, NCR3, SLC4A1, CD69, KLRB1, KIR2DL3, KIR3DL1, and GZMK. The eight potential hub genes may be associated with the risk of developing NIU. NK cell-mediated cytotoxicity signaling might be the key molecular mechanism in the occurrence and development of NIU. Our study provided new insights on NIU, its genetics, molecular pathogenesis and new therapeutic targets.

The role and mechanisms of gut microbiota in diabetic nephropathy, diabetic retinopathy and cardiovascular diseases

Type 2 diabetes mellitus (T2DM) and T2DM-related complications [such as retinopathy, nephropathy, and cardiovascular diseases (CVDs)] are the most prevalent metabolic diseases. Intriguingly, overwhelming findings have shown a strong association of the gut microbiome with the etiology of these diseases, including the role of aberrant gut bacterial metabolites, increased intestinal permeability, and pathogenic immune function affecting host metabolism. Thus, deciphering the specific microbiota, metabolites, and the related mechanisms to T2DM-related complications by combined analyses of metagenomics and metabolomics data can lead to an innovative strategy for the treatment of these diseases. Accordingly, this review highlights the advanced knowledge about the characteristics of the gut microbiota in T2DM-related complications and how it can be associated with the pathogenesis of these diseases. Also, recent studies providing a new perspective on microbiota-targeted therapies are included.

High-Fat Diet Alters the Retinal Pigment Epithelium and Choroidal Transcriptome in the Absence of Gut Microbiota

Relationships between retinal disease, diet, and the gut microbiome have started to emerge. In particular, high-fat diets (HFDs) are associated with the prevalence and progression of several retinal diseases, including age-related macular degeneration (AMD) and diabetic retinopathy (DR). These effects are thought to be partly mediated by the gut microbiome, which modulates interactions between diet and host homeostasis. Nevertheless, the effects of HFDs on the retina and adjacent retinal pigment epithelium (RPE) and choroid at the transcriptional level, independent of gut microbiota, are not well-understood. In this study, we performed the high-throughput RNA-sequencing of germ-free (GF) mice to explore the transcriptional changes induced by HFD in the RPE/choroid. After filtering and cleaning the data, 649 differentially expressed genes (DEGs) were identified, with 616 genes transcriptionally upregulated and 33 genes downregulated by HFD compared to a normal diet (ND). Enrichment analysis for gene ontology (GO) using the DEGs was performed to analyze over-represented biological processes in the RPE/choroid of GF-HFD mice relative to GF-ND mice. GO analysis revealed the upregulation of processes related to angiogenesis, immune response, and the inflammatory response. Additionally, molecular functions that were altered involved extracellular matrix (ECM) binding, ECM structural constituents, and heparin binding. This study demonstrates novel data showing that HFDs can alter RPE/choroid tissue transcription in the absence of the gut microbiome.

Multi-Omics Reveals Inhibitory Effect of Baicalein on Non-Alcoholic Fatty Liver Disease in Mice

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, whose etiology is poorly understood. Accumulating evidence indicates that gut microbiota plays an important role in the occurrence and progression of various human diseases, including NAFLD. In this study, NAFLD mouse models were established by feeding a high-fat diet (HFD). Baicalein, a natural flavonoid with multiple biological activities, was administered by gavage, and its protective effect on NAFLD was analyzed by histopathological and blood factor analysis. Gut microbiota analysis demonstrated that baicalein could remodel the overall structure of the gut microbiota from NAFLD model mice, especially Anaerotruncus, Lachnoclostridium, and Mucispirillum. Transcriptomic analysis showed baicalein restored the expressions of numerous genes that were upregulated in hepatocytes of NAFLD mice, such as Apoa4, Pla2g12a, Elovl7, Slc27a4, Hilpda, Fabp4, Vldlr, Gpld1, and Apom. Metabolomics analysis proved that baicalein mainly regulated the processes associated with lipid metabolism, such as alpha-Linolenic acid, 2-Oxocarboxylic acid, Pantothenate and CoA biosynthesis, and bile secretion. Multi-omics analysis revealed that numerous genes regulated by baicalein were significantly correlated with pathways related to lipid metabolism and biosynthesis and secrection of bile acid, and baicalein might affect lipid metabolism in liver via regulating the ecological structure of gut microbiota in NAFLD mice. Our results elucidated the correlated network among diet, gut microbiota, metabolomic, and transcriptional profiling in the liver. This knowledge may help explore novel therapeutic approaches against NAFLD.

Gut microbiome and retinal diseases: an updated review

PURPOSE OF REVIEW

The gut microbiome, trillions of microorganisms residing in our digestive tract, is now believed to play a significant role in retinal diseases. Breakthroughs in computational biology and specialized animal models have allowed researchers not only to characterize microbes associated with retinal diseases, but also to provide early insights into the function of the microbiome in relation to biological processes in the retinal microenvironment. This review aims to provide an update on recent advances in the current knowledge on the relationship between the gut microbiome and retinal disorders.

RECENT FINDINGS

Recent work demonstrates distinct gut microbial compositions associated with retinal diseases such as agerelated macular degeneration and retinopathy of prematurity. Currently, it is believed that gut dysbiosis leads to increased gut permeability, elevated circulation of bacterial products, microbial metabolites and inflammatory mediators that result in immune dysregulation at distant anatomic sites including the retina.

SUMMARY

Emerging evidence for the gut-retina axis can elucidate previously unknown pathways involved in retinal diseases and also presents an exciting potential therapeutic avenue. Further preclinical and clinical studies are necessary to establish causation and delineate the precise relationship of the gut microbiome with retinal disorders.