Hyperlipidemia Affects Tight Junctions and Pump Function in the Corneal Endothelium

Proliferator-Activated Receptor Alpha Inhibits Abnormal Extracellular Matrix Accumulation and Maintains Energy Metabolism in Late-Onset Fuchs Endothelial Corneal Dystrophy

Purpose

Fuchs endothelial corneal dystrophy (FECD) is the most common corneal endothelial dystrophy and guttae are crucial in causing progressive loss of corneal endothelium. This study aimed to find a way to inhibit the formation of guttae in FECD.

Methods and Results

Mitochondria fatty acid β-oxidation (FAO) and tricarboxylic acid (TCA) cycle processes were negatively enriched in the FECD group according to gene set enrichment analysis in GSE171830. In vivo UV-A-induced late-onset FECD mouse model were established. After irradiation, aged proliferator-activated receptor alpha (PPARα-/-) mice manifested greater corneal opacity, cornea edema, and varied corneal endothelial cell morphology compared with wild-type mice. The total metabolites in cornea of aged PPARα-/- mice and wild-type mice were detected by mass spectrometry. Metabolites of the FAO pathway were decreased in corneas of PPARα-/- mice, coincident with enzymes of FAO decreased in GSE171830. The score for FAO energy metabolism was negatively related to that of the TGF-β pathway according to gene set variation analysis. The express of alpha smooth muscle actin (αSMA) and Col1a were increased in aged PPARα-/- mice and small interfering PPARα B4G12 cell lines. After irradiation, activation or overexpression of PPARα demonstrated reduced corneal endothelial damage and reversal of Descemet membrane thickening, along with downregulation of fibrosis-related genes such as αSMA and collagen type I alpha 1 (Col1a). In vitro experiments revealed that fenofibrate could reverse fibrosis and damage of cell-to-cell connections induced by TGF-β. Additionally, fenofibrate was found to alleviate mitochondrial damage in B4G12 and increase oxygen consumption rates after TGF-β treatment.

Conclusions

Overall, we suggested that the overexpression or activation of PPARα can inhibit FAO energy dysfunction of corneal endothelium and the abnormal extracellular matrix formation in Descemet's membrane, which is the primary pathology of FECD. Thus, PPARα may be a potential target for attenuating the progression of FECD.

Diurnal rhythm-modulated transcriptome analysis of meibomian gland in hyperlipidemic mice using RNA sequencing

AIM

To explore the regulatory mechanism of meibomian gland (MG) in hyperlipidemic mice under a diurnal rhythm by transcriptomic analysis based on high-throughput sequencing.

METHODS

The mouse model of hyperlipidemia induced by four months of high-fat diet (HFD) feeding to a regular light-dark (LD) cycle for 2 weeks was used in this study. Phenotypic observation and RNA sequencing (RNA-seq) of MGs of the experimental mice were then performed to investigate transcriptional changes due to hyperlipidemia and the diurnal rhythm and their effects on meibomian gland dysfunction (MGD).

RESULTS

The expression levels of the identified dysregulated genes were then validated by qRT-PCR. Several significantly regulated genes and enriched pathways were identified as associated with MGD in hyperlipidemic mice under a diurnal rhythm; these genes included some core diurnal clock genes, e.g., Clock, Per2 and Per3. Phenotypic and histological analysis reveals abnormal morphology concomitantly with a modification of the transcriptional landscape of MG caused by HFD.

CONCLUSION

Our findings provide us with a deeper understanding of the diurnal rhythm regulation of MG in hyperlipidemic mice altered by daily nutritional challenge.

Evolution of therapeutic strategy based on oxidant-antioxidant balance for fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) stands as the most prevalent primary corneal endothelial dystrophy worldwide, posing a significant risk to corneal homeostasis and clarity. Corneal endothelial cells exhibit susceptibility to oxidative stress, suggesting a nuanced relationship between oxidant-antioxidant imbalance and FECD pathogenesis, irrespective of FECD genotype. Given the constrained availability of corneal transplants, exploration into non-surgical interventions becomes crucial. This encompasses traditional antioxidants, small molecule compounds, biologics, and diverse non-drug therapies, such as gene-related therapy, hydrogen therapy and near infrared light therapy. This review concentrates on elucidating the mechanisms behind oxidant-antioxidant imbalance and the evolution of strategies to restore oxidant-antioxidant balance in FECD. It provides a comprehensive overview of both conventional and emerging therapeutic approaches, offering valuable insights for the advancement of non-surgical treatment modalities. The findings herein might establish a robust foundation for future research and the therapeutic strategy of FECD.

RTP4 Enhances Corneal HSV-1 Infection in Mice With Type 2 Diabetes Mellitus

Purpose

The purpose of this study was to investigate whether corneal lesions in mice with type 2 diabetes mellitus (T2D) infected with herpes simplex virus (HSV)-1 are more severe, and to elucidate the specific underlying mechanism.

Methods

The corneas of control mice and T2D mice induced by a high-fat diet combined with streptozotocin were infected with the HSV-1 Mckrae strain to assess corneal infection, opacity, and HSV-1 replication. RNA sequencing of the corneal epithelium from wild-type and db/db mice (a genetic T2D mouse model) was conducted to identify the key gene affecting T2D infection. Immunofluorescence staining was performed on corneal sections from T2D mice and patients with T2D. The effect of small interfering RNA (siRNA) knockdown on corneal HSV-1 infection was evaluated in both in vitro and in vivo models.

Results

T2D mice exhibited a more severe infection phenotype following HSV-1 infection, characterized by augmented corneal opacity scores, elevated viral titers, and transcripts compared to control mice. Transcriptome analysis of corneal epithelium revealed a hyperactive viral response in T2D mice, highlighting the differentially expressed gene Rtp4 (encoding receptor transporter protein 4). Receptor transporter protein 4 (RTP4) expression was enhanced in the corneal epithelium of T2D mice and patients with T2D. Virus binding assays demonstrated that RTP4 facilitated HSV-1 binding to human corneal epithelial cells. Silencing RTP4 alleviated HSV-1 infection in both in vitro and in vivo T2D models.

Conclusions

The findings indicate that elevated RTP4 exacerbates HSV-1 infection by enhancing its binding to corneal epithelial cells, whereas Rtp4 knockdown mitigated corneal lesions in T2D mice. This implies RTP4 as a potential target for intervention in diabetic HSV-1 infection.

Metabolic and proteomic indications of diabetes progression in human aqueous humor

Diabetes mellitus is a multiorgan systemic disease impacting numerous ocular structures that results in significant ocular morbidity and often results in more frequent corneal and glaucoma surgeries for affected individuals. We hypothesize that the systemic metabolic and proteomic derangement observed in the progression of diabetes influences the composition of the aqueous humor (AH), which ultimately impacts the anterior segment health of the eye. To identify changes associated with diabetes progression, we mapped the metabolite profile and proteome of AH samples from patients with varying severities of type II diabetes (T2DM). Patients were classified as nondiabetic (ND or control), non-insulin-dependent diabetic without advanced features of disease (NAD-ni), insulin-dependent diabetic without advanced features (NAD-i), or diabetic with advanced features (AD). AH samples collected from the anterior chamber during elective ophthalmic surgery were evaluated for metabolite and protein expression changes associated with diabetic severity via gas chromatography/mass spectrometry and ultra-high performance liquid chromatography tandem mass spectrometry, respectively. Metabolic and proteomic pathway analyses were conducted utilizing MetaboAnalyst 4.0 and Ingenuity Pathway Analysis. A total of 14 control, 12 NAD-ni, 4 NAD-I, and 14 AD samples were included for analysis. Elevated levels of several branched amino acids (e.g., valine, leucine, isoleucine), and lipid metabolites (e.g., palmitate) were found only with increasing diabetic severity (i.e., the AD group). Similar proteomic trends were noted in amino acid and fatty acid metabolism and the unfolded protein/stress response. These results represent the first report of both metabolomic and proteomic evaluation of aqueous humor. Diabetes results in metabolic and proteomic perturbations detectable in the AH, and unique changes become manifest as T2DM severity worsens. Changes in AH composition may serve as an indicator of disease severity, risk assessment of anterior segment cells and structures, and potential future therapies.

Fenofibrate suppresses corneal neovascularization by regulating lipid metabolism through PPARα signaling pathway

Purpose: The purpose of this study was to explore the potential underlying mechanism of anti-vascular effects of peroxisome proliferator-activated receptor α (PPARα) agonist fenofibrate against corneal neovascularization (CNV) through the changes of lipid metabolism during CNV. Methods: A suture-induced CNV model was established and the clinical indications were evaluated from day 1 to day 7. Treatments of vehicle and fenofibrate were performed for 5 days after suture and the CNV areas were compared among the groups. The eyeballs were collected for histological analysis, malondialdehyde (MDA) measurement, terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL) staining, western blot, quantitative real-time PCR (qRT-PCR) assays and immunohistochemical (IHC) staining to elucidate pathological changes and the underlying mechanism. Results: Lipi-Green staining and MDA measurement showed that lipid deposition and peroxidation were increased in the CNV cornea while the expression of long-chain acyl-coenzyme A synthetase 1 (ACSL1), carnitine palmitoyltransterase 1A(CPT1A) and medium-chain acyl-coenzyme A dehydrogenase (ACADM), which are key enzymes of fatty acid β-oxidation (FAO) and targeted genes of peroxisome proliferator-activated receptor alpha (PPARα) pathway, were decreased in CNV cornea. Fenofibrate suppressed lipid accumulation and peroxidation damage in the CNV cornea. Fenofibrate upregulated the expression levels of PPARα, ACSL1, CPT1A, and ACADM compared with vehicle group. IHC staining indicated that fenofibrate also decreased the expression of VEGFa, VEGFc, TNFα, IL1β and CD68. Conclusion: Disorder of lipid metabolism may be involved in the formation of suture-induced CNV and fenofibrate played anti-neovascularization and anti-inflammatory roles on cornea by regulating the key enzymes of lipid metabolism and ameliorating lipid peroxidation damage of cornea through PPARα signaling pathway.

Downregulation of p38 MAPK signaling pathway ameliorates tissue engineered corneal epithelium

Tissue engineered corneal epithelium transplantation is effective treatment for severe limbal stem cell deficiency (LSCD), while epithelial terminal differentiation, tans-differentiation and insufficient stem cell during construction affects the quality of tissue engineered corneal epithelium. In this study, we applied SB203580 in the culture medium to downregulate the P38 MAPK signaling pathway during construction of tissue engineered corneal epithelium. With application of SB203580, tissue engineered corneal epithelium showed enhanced strength and condensed structure. The expression of progenitor cell markers ABCG2, P63, K14, Wnt7a was increased, differentiation markers K12, Pax6, K10, K13, and trans-differentiation markers α-SMA and Snail1 was decreased, while cell junction markers Claudin-1 and E-cadherin was increased in the tissue engineered corneal epithelium. The wnt/β-catenin signaling pathway was upregulated in the epithelium after p38 MAPK inhibition. Transplantation of tissue engineered corneal epithelium treated with SB203580 to rabbit LSCD model showed faster wound healing and improved epithelial quality. We conclude that downregulation of p38 MAPK signaling pathway helps maintain the stemness, prevent terminal differentiation and abnormal differentiation of corneal epithelial cells during epithelium construction process, thus can improve the quality of tissue engineered corneal epithelium.

Voxel-Mirrored Homotopic Connectivity Is Altered in Meibomian Gland Dysfunction Patients That Are Morbidly Obese

Purpose: To investigate the altered functional connectivity (FC) of the cerebral hemispheres in patients with morbid obesity (MO) with meibomian gland dysfunction (MGD) by voxel-mirrored homotopic connectivity (VMHC). Methods: Patients and matched healthy controls (HCs) were recruited, and all subjects underwent functional resonance magnetic imaging (fMRI), and VMHC results were processed statistically to assess the differences in FC in different brain regions between the two groups. We further used ROC curves to evaluate the diagnostic value of these differences. We also used Pearson’s correlation analysis to explore the relationship between changes in VMHC values in specific brain regions, visual acuity, and Mini-Mental State Examination (MMSE) score. Conclusions: Patients with morbid obesity and MGD had abnormal FC in the cerebral hemispheres in several specific brain areas, which were mainly concentrated in pathways related to vision and perception and may correlate to some extent with the clinical presentations of the patients.

Phaseolus vulgaris extract ameliorates high-fat diet-induced colonic barrier dysfunction and inflammation in mice by regulating peroxisome proliferator-activated receptor expression and butyrate levels

Obesity is a health concern worldwide, and its onset is multifactorial. In addition to metabolic syndrome, a high-fat diet induces many deleterious downstream effects, such as chronic systemic inflammation, a loss of gut barrier integrity, and gut microbial dysbiosis, with a reduction of many butyrate-producing bacteria. These conditions can be ameliorated by increasing legumes in the daily diet. White and kidney beans (Phaseolus vulgaris L.) and their non-nutritive bioactive component phaseolamin were demonstrated to mitigate several pathological features related to a metabolic syndrome-like condition. The aim of the present study was to investigate the molecular pathways involved in the protective effects on the intestinal and liver environment of a chronic oral treatment with P. vulgaris extract (PHAS) on a murine model of the high-fat diet. Results show that PHAS treatment has an anti-inflammatory effect on the liver, colon, and cecum. This protective effect was mediated by peroxisome proliferator-activated receptor (PPAR)-α and γ. Moreover, we also observed that repeated PHAS treatment was able to restore tight junctions’ expression and protective factors of colon and cecum integrity disrupted in HFD mice. This improvement was correlated with a significant increase of butyrate levels in serum and fecal samples compared to the HFD group. These data underline that prolonged treatment with PHAS significantly reduces some pathological features related to the metabolic syndrome-like condition, such as inflammation and intestinal barrier disruption; therefore, PHAS could be a valid tool to be associated with the therapeutic strategy.

Risk factors for fluctuations in corneal endothelial cell density (Review)

The cornea is a transparent, avascular and abundantly innervated tissue through which light rays are transmitted to the retina. The innermost layer of the cornea, also known as the endothelium, consists of a single layer of polygonal endothelial cells that serve an important role in preserving corneal transparency and hydration. The average corneal endothelial cell density (ECD) is the highest at birth (~3,000 cells/mm²), which then decrease to ~2,500 cells/mm² at adulthood. These endothelial cells have limited regenerative potential and the minimum (critical) ECD required to maintain the pumping function of the endothelium is 400-500 cells/mm². ECD < the critical value can result in decreased corneal transparency, development of corneal edema and reduced visual acuity. The condition of the corneal endothelium can be influenced by a number of factors, including systemic diseases, such as diabetes or atherosclerosis, eye diseases, such as uveitis or dry eye disease (DED) and therapeutic ophthalmological interventions. The aim of the present article is to review the impact of the most common systemic disorders (pseudoexfoliation syndrome, diabetes mellitus, cardiovascular disease), eye diseases (DED, uveitis, glaucoma, intraocular lens dislocation) and widely performed ophthalmic interventions (cataract surgery, intraocular pressure-lowering surgeries) on corneal ECD.

Effects of Xylooligosaccharides on Lipid Metabolism, Inflammation, and Gut Microbiota in C57BL/6J Mice Fed a High-Fat Diet

Xylooligosaccharide (XOS) is a source of prebiotics with multiple biological activities. The present study aimed to investigate the effects of XOS on mice fed a high-fat diet. Mice were fed either a normal diet or a high-fat diet supplemented without or with XOS (250 and 500 mg/kg), respectively, for 12 weeks. The results showed that the XOS inhibited mouse weight gain, decreased the epididymal adipose index, and improved the blood lipid levels, including triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels. Moreover, XOS reduced the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and alleviated the damage to the liver caused by the high-fat diet. XOS also reduced hyperlipidemia-associated inflammatory responses. Additionally, quantitative real-time polymerase chain reaction results showed that XOS intervention activated the AMP-activated protein kinase (AMPK) pathway to regulate the fat synthesis, decomposition, and β oxidation; upregulated the mRNA expression levels of carnitine palmitoyl transferase 1 (CPT-1), peroxisome proliferator-activated receptors α (PPAR-α), and cholesterol 7-alpha hydroxylase (CYP7A1); and downregulated the mRNA expression levels of acetyl-CoA carboxylase (ACC), CCAAT/enhancer-binding protein alpha (C/EBPα), and lipoprotein lipase (LPL). On the other hand, XOS enhanced the mRNA expression levels of zonula occludens-1 (ZO-1), occludin, and claudin-1 in the small intestine; increased the strength of the intestinal barrier; and optimized the composition of the intestinal microbiota. Therefore, it was concluded that XOS regulated the intestinal barrier, changed the intestinal microecology, and played an important role in preventing hyperlipidemia through the unique anatomical advantages of the gut-liver axis.

Impacts of high fat diet on ocular outcomes in rodent models of visual disease

High fat diets (HFD) have been utilized in rodent models of visual disease for over 50 years to model the effects of lipids, metabolic dysfunction, and diet-induced obesity on vision and ocular health. HFD treatment can recapitulate the pathologies of some of the leading causes of blindness, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) in rodent models of visual disease. However, there are many important factors to consider when using and interpreting these models. To synthesize our current understanding of the importance of lipid signaling, metabolism, and inflammation in HFD-driven visual disease processes, we systematically review the use of HFD in mouse and rat models of visual disease. The resulting literature is grouped into three clusters: models that solely focus on HFD treatment, models of diabetes that utilize both HFD and streptozotocin (STZ), and models of AMD that utilize both HFD and genetic models and/or other exposures. Our findings show that HFD profoundly affects vision, retinal function, many different ocular tissues, and multiple cell types through a variety of mechanisms. We delineate how HFD affects the cornea, lens, uvea, vitreous humor, retina, retinal pigmented epithelium (RPE), and Bruch's membrane (BM). Furthermore, we highlight how HFD impairs several retinal cell types, including glia (microglia), retinal ganglion cells, bipolar cells, photoreceptors, and vascular support cells (endothelial cells and pericytes). However, there are a number of gaps, limitations, and biases in the current literature. We highlight these gaps and discuss experimental design to help guide future studies. Very little is known about how HFD impacts the lens, ciliary bodies, and specific neuronal populations, such as rods, cones, bipolar cells, amacrine cells, and retinal ganglion cells. Additionally, sex bias is an important limitation in the current literature, with few HFD studies utilizing female rodents. Future studies should use ingredient-matched control diets (IMCD), include both sexes in experiments to evaluate sex-specific outcomes, conduct longitudinal metabolic and visual measurements, and capture acute outcomes. In conclusion, HFD is a systemic exposure with profound systemic effects, and rodent models are invaluable in understanding the impacts on visual and ocular disease.

The effect of high-fat diet-induced metabolic disturbance on corneal neuroimmune features

PURPOSE

The highly innervated cornea is susceptible to nerve loss secondary to systemic diseases such as diabetes and metabolic disturbances caused by high-fat diet. In this study, we characterize the effect of high-fat diet on the mouse corneal neuroimmune phenotype, including changes to corneal nerve density and resident immune cells, alongside the clinical assessment of corneal thickness and endothelial cell density.

METHODS

Male C57Bl6/J mice, aged 10 weeks, were fed a high-fat diet (60 kcal% fat, 5.2 kcal/g) or control diet (10 kcal%, 3.8 kcal/g) for 16 weeks. At the study endpoint, metabolic parameters (HbA1c, weight, fasting glucose, body fat) were measured to confirm metabolic disturbance. Clinical imaging of the anterior segment was performed using optical coherence tomography to measure the corneal epithelial and stromal thickness. Corneal sensory nerves were visualized using flatmount immunostaining and confocal microscopy. The topographical distribution and density of sensory nerves (BIII-tubulin⁺), intraepithelial CD45⁺ and MHC- II⁺ cells, stromal macrophages (IBA1⁺CD206⁺) and endothelial cells (ZO-1⁺) were analysed using FIJI.

RESULTS

High-fat diet mice had significantly higher blood HbA1c, higher body weight, a higher percentage of body fat and elevated fasting glucose compared to the control diet mice. Corneal epithelial and stromal thickness was similar in both groups. The sum length of the basal nerve plexus was lower in the central and peripheral cornea of mice fed a high-fat diet. In contrast, the sum length of superficial nerve terminals was similar between groups. Epithelial immune cell density was two-fold higher in the central corneas of high-fat diet mice compared to control diet mice. IBA1⁺CD206⁺ macrophage density was similar in the anterior stroma of both groups but was significantly higher in the posterior stroma of the peripheral cornea in the high-fat diet mice compared to controls. The percentage of nerve-associated MHC-II⁺ cells in the epithelium and stroma was higher in HFD mice compared to controls. Endothelial cell density was similar in the corneas of high-fat diet mice compared to controls.

CONCLUSION

Together with corneal neuropathy, corneal immune cells in mice fed a high-fat diet were differentially affected depending on their topographical distribution and location within cornea, and appeared in closer proximity to epithelial and stromal nerves, suggesting a local neuroimmune disruption induced by systemic metabolic disturbance.

Disruption of tight junctions contributes to hyposalivation of salivary glands in a mouse model of type 2 diabetes

Tight junction (TJ) plays an important role in regulating paracellular fluid transport in salivary glands; however, little is known about the involvement of TJs in diabetes salivary glands. This study aimed to investigate the alterations of TJs and their possible contribution in diabetes-induced hyposalivation. Here, we observed that the morphologies of submandibular glands (SMGs) were impaired, characterized by enlarged acini accumulation with giant secretory granules, which were significantly reduced in atrophic ducts in SMGs of db/db mice, a spontaneous model of type-2 diabetes. However, the secretory granules were increased and scattered in the acini of diabetes parotid glands (PGs). Other ultrastructural damages including swollen mitochondria, expansive endoplasmic reticulum, and autophagosomes were observed in the diabetes group. The levels of TJ proteins including claudin-1 (Cldn1) and claudin-3 (Cldn3) were increased, whereas those of claudin-4 (Cldn4), occludin (Ocln), and zonula occludens-1 (ZO-1) were decreased in SMGs of db/db mice. Higher Cldn1 and Cldn3 and lower claudin-10 (Cldn10) and Ocln levels were observed in PGs of diabetes mice. Taken together, the structures of SMGs and PGs were impaired in diabetes mice, and the disruption of TJ integrity in both SMGs and PGs may contribute to diabetes-induced hyposalivation.