Multi-ancestry GWAS analysis identifies two novel loci associated with diabetic eye disease and highlights APOL1 as a high risk locus in patients with diabetic macular edema.

Diabetic retinopathy (DR) is a common complication of diabetes. Approximately 20% of DR patients have diabetic macular edema (DME) characterized by fluid leakage into the retina. There is a genetic component to DR and DME risk, but few replicable loci. Because not all DR cases have DME, we focused on DME to increase power, and conducted a multi-ancestry GWAS to assess DME risk in a total of 1,502 DME patients and 5,603 non-DME controls in discovery and replication datasets. Two loci reached GWAS significance (p<5x10-8). The strongest association was rs2239785, (K150E) in APOL1. The second finding was rs10402468, which co-localized to PLVAP and ANKLE1 in vascular / endothelium tissues. We conducted multiple sensitivity analyses to establish that the associations were specific to DME status and did not reflect diabetes status or other diabetic complications. Here we report two novel loci for risk of DME which replicated in multiple clinical trial and biobank derived datasets. One of these loci, containing the gene APOL1, is a risk factor in African American DME and DKD patients, indicating that this locus plays a broader role in diabetic complications for multiple ancestries. Trial Registration: NCT00473330, NCT00473382, NCT03622580, NCT03622593, NCT04108156.

Dysregulated CD200-CD200R signaling in early diabetes modulates microglia-mediated retinopathy.

Diabetic retinopathy (DR) is a neurovascular complication of diabetes. Recent investigations have suggested that early degeneration of the neuroretina may occur prior to the appearance of microvascular changes; however, the mechanisms underlying this neurodegeneration have been elusive. Microglia are the predominant resident immune cell in the retina and adopt dynamic roles in disease. Here, we show that ablation of retinal microglia ameliorates visual dysfunction and neurodegeneration in a type I diabetes mouse model. We also provide evidence of enhanced microglial contact and engulfment of amacrine cells, ultrastructural modifications, and transcriptome changes that drive inflammation and phagocytosis. We show that CD200-CD200R signaling between amacrine cells and microglia is dysregulated during early DR and that targeting CD200R can attenuate high glucose-induced inflammation and phagocytosis in cultured microglia. Last, we demonstrate that targeting CD200R in vivo can prevent visual dysfunction, microglia activation, and retinal inflammation in the diabetic mouse. These studies provide a molecular framework for the pivotal role that microglia play in early DR pathogenesis and identify a potential immunotherapeutic target for treating DR in patients.

Stress resilience-enhancing drugs preserve tissue structure and function in degenerating retina via phosphodiesterase inhibition.

Chronic, progressive retinal diseases, such as age-related macular degeneration (AMD), diabetic retinopathy, and retinitis pigmentosa, arise from genetic and environmental perturbations of cellular and tissue homeostasis. These disruptions accumulate with repeated exposures to stress over time, leading to progressive visual impairment and, in many cases, legal blindness. Despite decades of research, therapeutic options for the millions of patients suffering from these disorders remain severely limited, especially for treating earlier stages of pathogenesis when the opportunity to preserve the retinal structure and visual function is greatest. To address this urgent, unmet medical need, we employed a systems pharmacology platform for therapeutic development. Through integrative single-cell transcriptomics, proteomics, and phosphoproteomics, we identified universal molecular mechanisms across distinct models of age-related and inherited retinal degenerations, characterized by impaired physiological resilience to stress. Here, we report that selective, targeted pharmacological inhibition of cyclic nucleotide phosphodiesterases (PDEs), which serve as critical regulatory nodes that modulate intracellular second messenger signaling pathways, stabilized the transcriptome, proteome, and phosphoproteome through downstream activation of protective mechanisms coupled with synergistic inhibition of degenerative processes. This therapeutic intervention enhanced resilience to acute and chronic forms of stress in the degenerating retina, thus preserving tissue structure and function across various models of age-related and inherited retinal disease. Taken together, these findings exemplify a systems pharmacology approach to drug discovery and development, revealing a new class of therapeutics with potential clinical utility in the treatment or prevention of the most common causes of blindness.

LncRNA VEAL2 regulates PRKCB2 to modulate endothelial permeability in diabetic retinopathy.

Long non-coding RNAs (lncRNAs) are emerging as key regulators of endothelial cell function. Here, we investigated the role of a novel vascular endothelial-associated lncRNA (VEAL2) in regulating endothelial permeability. Precise editing of veal2 loci in zebrafish (veal2gib005Δ8/+ ) induced cranial hemorrhage. In vitro and in vivo studies revealed that veal2 competes with diacylglycerol for interaction with protein kinase C beta-b (Prkcbb) and regulates its kinase activity. Using PRKCB2 as bait, we identified functional ortholog of veal2 in humans from HUVECs and named it as VEAL2. Overexpression and knockdown of VEAL2 affected tubulogenesis and permeability in HUVECs. VEAL2 was differentially expressed in choroid tissue in eye and blood from patients with diabetic retinopathy, a disease where PRKCB2 is known to be hyperactivated. Further, VEAL2 could rescue the effects of PRKCB2-mediated turnover of endothelial junctional proteins thus reducing hyperpermeability in hyperglycemic HUVEC model of diabetic retinopathy. Based on evidence from zebrafish and hyperglycemic HUVEC models and diabetic retinopathy patients, we report a hitherto unknown VEAL2 lncRNA-mediated regulation of PRKCB2, for modulating junctional dynamics and maintenance of endothelial permeability.

Intravitreal aflibercept 8 mg in diabetic macular oedema (PHOTON): 48-week results from a randomised, double-masked, non-inferiority, phase 2/3 trial.

BACKGROUND: A high-dose formulation of intravitreal aflibercept (8 mg) could improve treatment outcomes in diabetic macular oedema (DMO) by requiring fewer injections than the standard comparator, aflibercept 2 mg. We report efficacy and safety results of aflibercept 8 mg versus 2 mg in patients with DMO. METHODS: PHOTON was a randomised, double-masked, non-inferiority, phase 2/3 trial performed at 138 hospitals and specialty retina clinics in seven countries. Eligible patients were adults aged 18 years or older with type 1 or 2 diabetes and centre-involved DMO. Patients were randomly assigned (1:2:1) to intravitreal aflibercept 2 mg every 8 weeks (2q8), aflibercept 8 mg every 12 weeks (8q12), or aflibercept 8 mg every 16 weeks (8q16), following initial monthly dosing. From week 16, dosing intervals for the aflibercept 8 mg groups were shortened if patients met prespecified dose regimen modification criteria denoting disease activity. The primary endpoint was change from baseline in best-corrected visual acuity (BCVA) at week 48 (non-inferiority margin of 4 letters). Efficacy and safety analyses included all randomly assigned patients who received at least one dose of study treatment. This trial is registered with ClinicalTrials.gov (NCT04429503). FINDINGS: Between June 29, 2020, and June 28, 2021, 970 patients were screened for eligibility. After exclusions, 660 patients were enrolled and randomly assigned to receive aflibercept 8q12 (n=329), 8q16 (n=164), or 2q8 (n=167); two patients were randomly assigned in error and did not receive treatment. 658 (99·7%) patients were treated and included in the full analysis set and safety analysis set (8q12 n=328, 8q16 n=163, and 2q8 n=167). Mean patient age was 62·3 years (SD 10·4). 401 (61%) patients were male. 471 (72%) patients were White. Aflibercept 8q12 and 8q16 demonstrated non-inferior BCVA gains to aflibercept 2q8 (BCVA mean change from baseline 8·8 letters [SD 9·0] in the 8q12 group, 7·9 letters [8·4] in the 8q16 group, and 9·2 letters [9·0] in the 2q8 group). The difference in least squares means was -0·57 letters (95% CI -2·26 to 1·13, p value for non-inferiority <0·0001) between 8q12 and 2q8 and -1·44 letters (-3·27 to 0·39, p value for non-inferiority 0·0031) between aflibercept 8q16 and 2q8. Proportions of patients with ocular adverse events in the study eye were similar across groups (8q12 n=104 [32%], 8q16 n=48 [29%], and 2q8 n=46 [28%]). INTERPRETATION: Aflibercept 8 mg demonstrated efficacy and safety with extended dosing intervals and could decrease treatment burden in patients with DMO. FUNDING: Regeneron Pharmaceuticals and Bayer.

Aflibercept Monotherapy or Bevacizumab First for Diabetic Macular Edema.

BACKGROUND: In eyes with diabetic macular edema, the relative efficacy of administering aflibercept monotherapy as compared with bevacizumab first with a switch to aflibercept if the eye condition does not improve sufficiently (a form of step therapy) is unclear. METHODS: At 54 clinical sites, we randomly assigned eyes in adults who had diabetic macular edema involving the macular center and a visual-acuity letter score of 24 to 69 (on a scale from 0 to 100, with higher scores indicating better visual acuity; Snellen equivalent, 20/320 to 20/50) to receive either 2.0 mg of intravitreous aflibercept or 1.25 mg of intravitreous bevacizumab. The drug was administered at randomization and thereafter according to the prespecified retreatment protocol. Beginning at 12 weeks, eyes in the bevacizumab-first group were switched to aflibercept therapy if protocol-specified criteria were met. The primary outcome was the mean change in visual acuity over the 2-year trial period. Retinal central subfield thickness and visual acuity at 2 years and safety were also assessed. RESULTS: A total of 312 eyes (in 270 adults) underwent randomization; 158 eyes were assigned to receive aflibercept monotherapy and 154 to receive bevacizumab first. Over the 2-year period, 70% of the eyes in the bevacizumab-first group were switched to aflibercept therapy. The mean improvement in visual acuity was 15.0 letters in the aflibercept-monotherapy group and 14.0 letters in the bevacizumab-first group (adjusted difference, 0.8 letters; 95% confidence interval, -0.9 to 2.5; P = 0.37). At 2 years, the mean changes in visual acuity and retinal central subfield thickness were similar in the two groups. Serious adverse events (in 52% of the patients in the aflibercept-monotherapy group and in 36% of those in the bevacizumab-first group) and hospitalizations for adverse events (in 48% and 32%, respectively) were more common in the aflibercept-monotherapy group. CONCLUSIONS: In this trial of treatment of moderate vision loss due to diabetic macular edema involving the center of the macula, we found no evidence of a significant difference in visual outcomes over a 2-year period between aflibercept monotherapy and treatment with bevacizumab first with a switch to aflibercept in the case of suboptimal response. (Funded by the National Institutes of Health; Protocol AC ClinicalTrials.gov number, NCT03321513.).

Ferroptosis Contributes to Microvascular Dysfunction in Diabetic Retinopathy.

Ferroptosis is a new form of cell death characterized by iron-dependent lipid peroxidation. Whether ferroptosis is involved in retinal microvascular dysfunction under diabetic condition is not known. Herein, the expression of ferroptosis-related genes in patients with proliferative diabetic retinopathy and in diabetic mice was determined with quantitative RT-PCR. Reactive oxygen species, iron content, lipid peroxidation products, and ferroptosis-associated proteins in the cultured human retinal microvascular endothelial cells (HRMECs) and in the retina of diabetic mice were examined. The association of ferroptosis with the functions of endothelial cells in vitro was evaluated. After administration of ferroptosis-specific inhibitor, Fer-1, the retinal microvasculature in diabetic mice was assessed. Characteristic changes of ferroptosis-associated markers, including glutathione peroxidase 4, ferritin heavy chain 1, long-chain acyl-CoA synthetase 4, transferrin receptor protein 1, and cyclooxygenase-2, were detected in the retinal fibrovascular membrane of patients with proliferative diabetic retinopathy, cultured HRMECs, and the retina of diabetic mice. Elevated levels of reactive oxygen species, lipid peroxidation, and iron content were found in the retina of diabetic mice and in cultured HRMECs. Ferroptosis was found to be associated with HRMEC dysfunction under high-glucose condition. Inhibition of ferroptosis with specific inhibitor Fer-1 in diabetic mice significantly reduced the severity of retinal microvasculopathy. Ferroptosis contributes to microvascular dysfunction in diabetic retinopathy, and inhibition of ferroptosis might be a promising strategy for the therapy of early-stage diabetic retinopathy.

MSC-Derived Small Extracellular Vesicles Alleviate Diabetic Retinopathy by Delivering miR-22-3p to Inhibit NLRP3 Inflammasome Activation.

PURPOSE: This study aimed to investigate the effect of mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEVs) on diabetic retinopathy (DR) and its underlying mechanism. METHODS: In vivo, MSC-sEVs were injected intravitreally into diabetic rats to determine the therapeutic efficacy. In vitro, MSC-sEVs with/without miR-22-3p inhibition were cocultured with advanced glycation end-products (AGEs)-induced microglia with/without NLRP3 overexpression to explore the molecular mechanism. RESULTS: In vivo, MSC-sEVs inhibited NLRP3 inflammasome activation, suppressed microglial activation, decreased inflammatory cytokines levels in the retina, and alleviated DR as evidenced by improved histological morphology and blood-retinal barrier function. Based on miRNA sequencing of MSC-sEVs, bioinformatic software, and dual-luciferase reporter assay, miR-22-3p stood out as the critical molecule for the role of MSC-sEVs in regulating NLRP3 inflammasome activation. Diabetic rats had lower level of miR-22-3p in their retina than those of control and sEV-treated rats. Confocal microscopy revealed that sEV could be internalized by microglia both in vivo and in vitro. In vitro, compared with sEV, the anti-inflammation effect of sEVmiR-22-3p(-) on AGEs-induced microglia was compromised, as they gave a lower suppression of NLRP3 inflammasome activation and inflammatory cytokines. In addition, NLRP3 overexpression in microglia damped the anti-inflammatory effect of sEV. CONCLUSION: These results indicated that MSC-sEVs alleviated DR via delivering miR-22-3p to inhibit NLRP3 inflammasome activation. Our findings indicate that MSC-sEVs might be a potential therapeutic method for DR.

Pericyte in retinal vascular diseases: A multifunctional regulator and potential therapeutic target.

Retinal vascular diseases (RVDs), in particular diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity, are leading contributors to blindness. The pathogenesis of RVD involves vessel dilatation, leakage, and occlusion; however, the specific underlying mechanisms remain unclear. Recent findings have indicated that pericytes (PCs), as critical members of the vascular mural cells, significantly contribute to the progression of RVDs, including detachment from microvessels, alteration of contractile and secretory properties, and excessive production of the extracellular matrix. Moreover, PCs are believed to have mesenchymal stem properties and, therefore, might contribute to regenerative therapy. Here, we review novel ideas concerning PC characteristics and functions in RVDs and discuss potential therapeutic strategies based on PCs, including the targeting of pathological signals and cell-based regenerative treatments.

LL37/FPR2 regulates neutrophil mPTP promoting the development of neutrophil extracellular traps in diabetic retinopathy.

Diabetic retinopathy (DR) is characterized by chronic, low-grade inflammation. This state may be related to the heightened production of neutrophil extracellular traps (NETs) induced by high glucose (HG). Human cathelicidin antimicrobial peptide (LL37) is an endogenous ligand of G protein-coupled chemoattractant receptor formyl peptide receptor 2 (FPR2), expressed on neutrophils and facilitating the formation and stabilization of the structure of NETs. In this study, we detected neutrophils cultured under different conditions, the retinal tissue of diabetic mice, and fibrovascular epiretinal membranes (FVM) samples of patients with proliferative diabetic retinopathy (PDR) to explore the regulating effect of LL37/FPR2 on neutrophil in the development of NETs during the process of DR. Specifically, HG or NG with LL37 upregulates the expression of FPR2 in neutrophils, induces the opening of mitochondrial permeability transition pore (mPTP), promotes the increase of reactive oxygen species and mitochondrial ROS, and then leads to the rise of NET production, which is mainly manifested by the release of DNA reticular structure and the increased expression of NETs-related markers. The PI3K/AKT signaling pathway was activated in neutrophils, and the phosphorylation level was enhanced by FPR2 agonists in vitro. In vivo, increased expression of NETs markers was detected in the retina of diabetic mice and in FVM, vitreous fluid, and serum of PDR patients. Transgenic FPR2 deletion led to decreased NETs in the retina of diabetic mice. Furthermore, in vitro, inhibition of the LL37/FPR2/mPTP axis and PI3K/AKT signaling pathway decreased NET production induced by high glucose. These results suggested that FPR2 plays an essential role in regulating the production of NETs induced by HG, thus may be considered as one of the potential therapeutic targets.

ITF2357 regulates NF-κB signaling pathway to protect barrier integrity in retinal pigment epithelial cells.

The robust integrity of the retinal pigment epithelium (RPE), which contributes to the outer brain retina barrier (oBRB), is compromised in several retinal degenerative and vascular disorders, including diabetic macular edema (DME). This study evaluates the role of a new generation of histone deacetylase inhibitor (HDACi), ITF2357, in regulating outer blood-retinal barrier function and investigates the underlying mechanism of action in inhibiting TNFα-induced damage to RPE integrity. Using the immortalized RPE cell line (ARPE-19), ITF2357 was found to be non-toxic between 50 nM and 5 µM concentrations. When applied as a pre-treatment in conjunction with an inflammatory cytokine, TNFα, the HDACi was safe and effective in preventing epithelial permeability by fortifying tight junction (ZO-1, -2, -3, occludin, claudin-1, -2, -3, -5, -19) and adherens junction (E-cadherin, Nectin-1) protein expression post-TNFα stress. Mechanistically, ITF2357 depicted a late action at 24 h via attenuating IKK, IκBα, and p65 phosphorylation and ameliorated the expression of IL-1ß, IL-6, and MCP-1. Also, ITF2357 delayed IκBα synthesis and turnover. The use of Bay 11-7082 and MG132 further uncovered a possible role for ITF2357 in non-canonical NF-κB activation. Overall, this study revealed the protection effects of ITF2357 by regulating the turnover of tight and adherens junction proteins and modulating NF-κB signaling pathway in the presence of an inflammatory stressor, making it a potential therapeutic application for retinal vascular diseases such as DME with compromised outer blood-retinal barrier.

IL-10-induced modulation of macrophage polarization suppresses outer-blood-retinal barrier disruption in the streptozotocin-induced early diabetic retinopathy mouse model.

Diabetic retinopathy (DR) is associated with ocular inflammation leading to retinal barrier breakdown, vascular leakage, macular edema, and vision loss. DR is not only a microvascular disease but also involves retinal neurodegeneration, demonstrating that pathological changes associated with neuroinflammation precede microvascular injury in early DR. Macrophage activation plays a central role in neuroinflammation. During DR, the inflammatory response depends on the polarization of retinal macrophages, triggering pro-inflammatory (M1) or anti-inflammatory (M2) activity. This study aimed to determine the role of macrophages in vascular leakage through the tight junction complexes of retinal pigment epithelium, which is the outer blood-retinal barrier (BRB). Furthermore, we aimed to assess whether interleukin-10 (IL-10), a representative M2-inducer, can decrease inflammatory macrophages and alleviate outer-BRB disruption. We found that modulation of macrophage polarization affects the structural and functional integrity of ARPE-19 cells in a co-culture system under high-glucose conditions. Furthermore, we demonstrated that intravitreal IL-10 injection induces an increase in the ratio of anti-inflammatory macrophages and effectively suppresses outer-BRB disruption and vascular leakage in a mouse model of early-stage streptozotocin-induced diabetes. Our results suggest that modulation of macrophage polarization by IL-10 administration during early-stage DR has a promising protective effect against outer-BRB disruption and vascular leakage. This finding provides valuable insights for early intervention in DR.

Maintenance of Enteral ACE2 Prevents Diabetic Retinopathy in Type 1 Diabetes.

BACKGROUND: We examined components of systemic and intestinal renin-angiotensin system on gut barrier permeability, glucose homeostasis, systemic inflammation, and progression of diabetic retinopathy (DR) in human subjects and mice with type 1 diabetes (T1D). METHODS: T1D individual with (n=18) and without (n=20) DR and controls (n=34) were examined for changes in gut-regulated components of the immune system, gut leakage markers (FABP2 [fatty acid binding protein 2] and peptidoglycan), and Ang II (angiotensin II); Akita mice were orally administered a Lactobacillus paracasei (LP) probiotic expressing humanized ACE2 (angiotensin-converting enzyme 2) protein (LP-ACE2) as either a prevention or an intervention. Akita mice with genetic overexpression of humanAce2 by small intestine epithelial cells (Vil-Cre.hAce2KI-Akita) were similarly examined. After 9 months of T1D, circulatory, enteral, and ocular end points were assessed. RESULTS: T1D subjects exhibit elevations in gut-derived circulating immune cells (ILC1 cells) and higher gut leakage markers, which were positively correlated with plasma Ang II and DR severity. The LP-ACE2 prevention cohort and genetic overexpression of intestinal ACE2 preserved barrier integrity, reduced inflammatory response, improved hyperglycemia, and delayed development of DR. Improvements in glucose homeostasis were due to intestinal MasR activation, resulting in a GSK-3ß (glycogen synthase kinase-3 beta)/c-Myc (cellular myelocytomatosis oncogene)-mediated decrease in intestinal glucose transporter expression. In the LP-ACE2 intervention cohort, gut barrier integrity was improved and DR reversed, but no improvement in hyperglycemia was observed. These data support that the beneficial effects of LP-ACE2 on DR are due to the action of ACE2, not improved glucose homeostasis. CONCLUSIONS: Dysregulated systemic and intestinal renin-angiotensin system was associated with worsening gut barrier permeability, gut-derived immune cell activation, systemic inflammation, and progression of DR in human subjects. In Akita mice, maintaining intestinal ACE2 expression prevented and reversed DR, emphasizing the multifaceted role of the intestinal renin-angiotensin system in diabetes and DR.

Imaging the Retinal Vascular Mural Cells In Vivo: Elucidating the Timeline of Their Loss in Diabetic Retinopathy.

BACKGROUND: Vascular mural cells (VMCs) are integral components of the retinal vasculature with critical homeostatic functions such as maintaining the inner blood-retinal barrier and vascular tone, as well as supporting the endothelial cells. Histopathologic donor eye studies have shown widespread loss of pericytes and smooth muscle cells, the 2 main VMC types, suggesting these cells are critical to the pathogenesis of diabetic retinopathy (DR). There remain, however, critical gaps in our knowledge regarding the timeline of VMC demise in human DR. METHODS: In this study, we address this gap using adaptive optics scanning laser ophthalmoscopy to quantify retinal VMC density in eyes with no retinal disease (healthy), subjects with diabetes without diabetic retinopathy, and those with clinical DR and diabetic macular edema. We also used optical coherence tomography angiography to quantify capillary density of the superficial and deep capillary plexuses in these eyes. RESULTS: Our results indicate significant VMC loss in retinal arterioles before the appearance of classic clinical signs of DR (diabetes without diabetic retinopathy versus healthy, 5.0±2.0 versus 6.5±2.0 smooth muscle cells per 100 µm; P<0.05), while a significant reduction in capillary VMC density (5.1±2.3 in diabetic macular edema versus 14.9±6.0 pericytes per 100 µm in diabetes without diabetic retinopathy; P=0.01) and capillary density (superficial capillary plexus vessel density, 37.6±3.8 in diabetic macular edema versus 45.5±2.4 in diabetes without diabetic retinopathy; P<0.0001) is associated with more advanced stages of clinical DR, particularly diabetic macular edema. CONCLUSIONS: Our results offer a new framework for understanding the pathophysiologic course of VMC compromise in DR, which may facilitate the development and monitoring of therapeutic strategies aimed at VMC preservation and potentially the prevention of clinical DR and its associated morbidity. Imaging retinal VMCs provides an unparalleled opportunity to visualize these cells in vivo and may have wider implications in a range of diseases where these cells are disrupted.

AQP4 regulates ferroptosis and oxidative stress of Muller cells in diabetic retinopathy by regulating TRPV4.

Diabetic retinopathy (DR) is a common microvascular complication that causes visual impairment or loss. Aquaporin 4 (AQP4) is a regulatory protein involved in water transport and metabolism. In previous studies, we found that AQP4 is related to hypoxia injury in Muller cells. Transient receptor potential cation channel subfamily V member 4 (TRPV4) is a non-selective cation channel protein involved in the regulation of a variety of ophthalmic diseases. However, the effects of AQP4 and TRPV4 on ferroptosis and oxidative stress in high glucose (HG)-treated Muller cells are unclear. In this study, we investigated the functions of AQP4 and TRPV4 in DR. HG was used to treat mouse Muller cells. Reverse transcription quantitative polymerase chain reaction was used to measure AQP4 mRNA expression. Western blotting was used to detect the protein levels of AQP4, PTGS2, GPX4, and TRPV4. Cell count kit-8, flow cytometry, 5,5',6,6'-tetrachloro-1,1,3,3'-tetraethylbenzimidazolyl carbocyanine iodide staining, and glutathione (GSH), superoxide dismutase (SOD), and malondialdehyde (MDA) kits were used to evaluate the function of the Muller cells. Streptozotocin was used to induce DR in rats. Haematoxylin and eosin staining was performed to stain the retina of rats. GSH, SOD, and MDA detection kits, immunofluorescence, and flow cytometry assays were performed to study the function of AQP4 and TRPV4 in DR rats. Results found that AQP4 and TRPV4 were overexpressed in HG-induced Muller cells and streptozotocin-induced DR rats. AQP4 inhibition promoted proliferation and cell cycle progression, repressed cell apoptosis, ferroptosis, and oxidative stress, and alleviated retinal injury in DR rats. Mechanistically, AQP4 positively regulated TRPV4 expression. Overexpression of TRPV4 enhanced ferroptosis and oxidative stress in HG-treated Muller cells, and inhibition of TRPV4 had a protective effect on DR-induced retinal injury in rats. In conclusion, inhibition of AQP4 inhibits the ferroptosis and oxidative stress in Muller cells by downregulating TRPV4, which may be a potential target for DR therapy.

Mesenchymal stem cells-derived exosomes alleviate senescence of retinal pigment epithelial cells by activating PI3K/AKT-Nrf2 signaling pathway in early diabetic retinopathy.

Diabetic retinopathy (DR) is a major cause of vision loss and blindness in adults. Cellular senescence was involved in the pathogenesis of early-stage DR and is positively correlated with progression. Thus, our study aimed at exploring the effect and potential mechanism of Mesenchymal stem cells-derived exosomes (MSCs-EXOs) on Retinal Pigment Epithelial (RPE) cells senescence at an early stage of DR in vivo and in vitro. ARPE-19 cells were incubated in high glucose (HG) medium mixed with MSCs-EXOs to observe the changes in cell viability. Senescence-associated ß-galactosidase (SA-ß-gal) staining, Western blot and qRT-PCR were used to assess the expression of senescence-related genes and antioxidant mediators. Quantitative Real-Time polymerase chain reaction (qRT-PCR), Optical coherence tomography (OCT) Hematoxylin and eosin (HE) staining and Electroretinogram (ERG) were respectively used to verify cellular senescence, the structure and function of the retina. Our findings demonstrated that MSCs-EXOs inhibited HG-induced senescence in ARPE-19 cells. Furthermore, MSCs-EXOs reduced HG-induced cell apoptosis and oxidative stress levels while promoting cell proliferation. Mechanistically, HG suppressed PI3K/AKT phosphorylation as well as nuclear factor erythroid 2-related factor 2 (Nrf2) expression along with its downstream target gene expression in ARPE-19 cells. However, MSCs-EXOs reversed these changes by alleviating cellular senescence while enhancing antioxidant activity. In line with our results in vitro, MSCs-EXOs significantly ameliorated hyperglycemia-induced senescence in DR mice by downregulating mRNA expression of P53, P21, P16, and SASP. Additionally, MSCs-EXOs improved the functional and structural integrity of the retina in DR mice. Our study revealed the protective effect of MSCs-EXOs on cellular senescence, offering new insights for the treatment of DR.

Glial cell alterations in diabetes-induced neurodegeneration.

Type 2 diabetes mellitus is a global epidemic that due to its increasing prevalence worldwide will likely become the most common debilitating health condition. Even if diabetes is primarily a metabolic disorder, it is now well established that key aspects of the pathogenesis of diabetes are associated with nervous system alterations, including deleterious chronic inflammation of neural tissues, referred here as neuroinflammation, along with different detrimental glial cell responses to stress conditions and neurodegenerative features. Moreover, diabetes resembles accelerated aging, further increasing the risk of developing age-linked neurodegenerative disorders. As such, the most common and disabling diabetic comorbidities, namely diabetic retinopathy, peripheral neuropathy, and cognitive decline, are intimately associated with neurodegeneration. As described in aging and other neurological disorders, glial cell alterations such as microglial, astrocyte, and Müller cell increased reactivity and dysfunctionality, myelin loss and Schwann cell alterations have been broadly described in diabetes in both human and animal models, where they are key contributors to chronic noxious inflammation of neural tissues within the PNS and CNS. In this review, we aim to describe in-depth the common and unique aspects underlying glial cell changes observed across the three main diabetic complications, with the goal of uncovering shared glial cells alterations and common pathological mechanisms that will enable the discovery of potential targets to limit neuroinflammation and prevent neurodegeneration in all three diabetic complications. Diabetes and its complications are already a public health concern due to its rapidly increasing incidence, and thus its health and economic impact. Hence, understanding the key role that glial cells play in the pathogenesis underlying peripheral neuropathy, retinopathy, and cognitive decline in diabetes will provide us with novel therapeutic approaches to tackle diabetic-associated neurodegeneration.

Glucose tolerance and insulin resistance/sensitivity associate with retinal layer characteristics: the LIFE-Adult-Study.

AIMS/HYPOTHESIS: As the prevalence of insulin resistance and glucose intolerance is increasing throughout the world, diabetes-induced eye diseases are a global health burden. We aim to identify distinct optical bands which are closely related to insulin and glucose metabolism, using non-invasive, high-resolution spectral domain optical coherence tomography (SD-OCT) in a large, population-based dataset. METHODS: The LIFE-Adult-Study randomly selected 10,000 participants from the population registry of Leipzig, Germany. Cross-sectional, standardised phenotyping included the assessment of various metabolic risk markers and ocular imaging, such as SD-OCT-derived thicknesses of ten optical bands of the retina. Global and Early Treatment Diabetic Retinopathy Study (ETDRS) subfield-specific optical retinal layer thicknesses were investigated in 7384 healthy eyes of 7384 participants from the LIFE-Adult-Study stratified by normal glucose tolerance, prediabetes (impaired fasting glucose and/or impaired glucose tolerance and/or HbA1c 5.7-6.4% [39-47 mmol/mol]) and diabetes. The association of optical retinal band characteristics with different indices of glucose tolerance (e.g. fasting glucose, area under the glucose curve), insulin resistance (e.g. HOMA2-IR, triglyceride glucose index), or insulin sensitivity (e.g. estimated glucose disposal rate [eGDR], Stumvoll metabolic clearance rate) was determined using multivariable linear regression analyses for the individual markers adjusted for age, sex and refraction. Various sensitivity analyses were performed to validate the observed findings. RESULTS: In the study cohort, nine out of ten optical bands of the retina showed significant sex- and glucose tolerance-dependent differences in band thicknesses. Multivariable linear regression analyses revealed a significant, independent, and inverse association between markers of glucose intolerance and insulin resistance (e.g. HOMA2-IR) with the thickness of the optical bands representing the anatomical retinal outer nuclear layer (ONL, standardised ß=-0.096; p<0.001 for HOMA2-IR) and myoid zone (MZ; ß=-0.096; p<0.001 for HOMA2-IR) of the photoreceptors. Conversely, markers of insulin sensitivity (e.g. eGDR) positively and independently associated with ONL (ß=0.090; p<0.001 for eGDR) and MZ (ß=0.133; p<0.001 for eGDR) band thicknesses. These global associations were confirmed in ETDRS subfield-specific analyses. Sensitivity analyses further validated our findings when physical activity, neuroanatomical cell/tissue types and ETDRS subfield categories were investigated after stratifying the cohort by glucose homeostasis. CONCLUSIONS/INTERPRETATION: An impaired glucose homeostasis associates with a thinning of the optical bands of retinal ONL and photoreceptor MZ. Changes in ONL and MZ thicknesses might predict early metabolic retinal alterations in diabetes.

Dysregulated 24 h melatonin secretion associated with intrinsically photosensitive retinal ganglion cell function in diabetic retinopathy: a cross-sectional study.

AIMS/HYPOTHESIS: The aim of this study was to explore whether diabetic retinopathy is associated with alterations of the circadian system, and to examine the role of reduced intrinsically photosensitive retinal ganglion cell (ipRGC) function. METHODS: Participants with type 2 diabetes, with diabetic retinopathy (n=14) and without diabetic retinopathy (n=9) underwent 24 h blood sampling for melatonin and cortisol under controlled laboratory conditions. ipRGC function was inferred from the post-illumination pupil response (PIPR). Habitual sleep duration, efficiency and variability were assessed by actigraphy. RESULTS: Participants with diabetic retinopathy compared to participants without diabetic retinopathy had smaller PIPR (p=0.007), lower 24 h serum melatonin output (p=0.042) and greater day-to-day sleep variability (p=0.012). By contrast, 24 h cortisol profiles, sleep duration and efficiency were similar in both groups. Six individuals with diabetic retinopathy had no detectable dim-light melatonin onset. PIPR correlated with 24 h mean melatonin levels (r=0.555, p=0.007). CONCLUSIONS/INTERPRETATION: ipRCG dysfunction in diabetic retinopathy is associated with disruptions of the 24 h melatonin rhythm, suggesting circadian dysregulation in diabetic retinopathy.

Risk of diabetic retinopathy and diabetic macular oedema with sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide 1 receptor agonists in type 2 diabetes: a real-world data study from a global federated database.

AIMS/HYPOTHESIS: A protective role of sodium-glucose cotransporter 2 inhibitors (SGLT2is) and glucagon-like peptide 1 receptor agonists (GLP1-ra) in the development of diabetic retinopathy and diabetic macular oedema has been described in some recent studies, which may extend beyond glycaemic control. We aimed to review the clinical impact of SGLT2i and GLP1-ra therapy on the risk of diabetic retinopathy and diabetic macular oedema in individuals with type 2 diabetes taking insulin. METHODS: This is a retrospective cohort analysis of approximately two million people with type 2 diabetes receiving insulin across 97 healthcare organisations using a global federated health research network (TriNetX, Cambridge, USA). Two intervention cohorts (SGLT2i + insulin, n=176,409; GLP1-ra + insulin, n=207,034) were compared against a control cohort (insulin with no SGLT2i/GLP1-ra, n=1,922,312). Kaplan-Meier survival analysis was performed and estimated HRs were reported for each outcome. Propensity score was used to 1:1 match for age, sex, ischaemic heart disease, hypertension, microvascular complications, chronic kidney disease, HbA1c, BMI and use of pioglitazone, lipid modifying agents, antilipemic agents, ACE inhibitors, angiotensin II inhibitors and metformin. A sub-analysis comparing the two intervention cohorts was also performed. RESULTS: SGLT2i with insulin was associated with a reduced HR (95% CI) for diabetic macular oedema compared with the control cohort (0.835; 0.780, 0.893), while GLP1-ra with insulin demonstrated a lack of signal with no statistical significance to the HR (1.013; 0.960, 1.069). SGLT2i with insulin was not associated with a clinically significant increase in the risk of developing diabetic retinopathy (1.076; 1.027, 1.127), while GLP1-ra with insulin increased diabetic retinopathy risk (1.308; 1.261, 1.357). Compared with SGLT2i with insulin, GLP1-ra with insulin was associated with higher risk of diabetic retinopathy (1.205; 1.153, 1.259) and diabetic macular oedema (1.130; 1.056, 1.208). CONCLUSIONS/INTERPRETATION: Our study suggests that the combination of SGLT2i and insulin is associated with lower risk of developing diabetic macular oedema. However, the use of GLP1-ra was associated with an increased risk of diabetic retinopathy in individuals with type 2 diabetes also taking insulin. A comparative analysis showed favourable outcomes with SGLT2i and insulin in the development of diabetic macular oedema and diabetic retinopathy. RCTs using dedicated  retinal imaging are required to determine the causal relationship with these therapies.