Exendin-4 promotes retinal ganglion cell survival and function by inhibiting calcium channels in experimental diabetes

Topical administration of GLP-1 eyedrops improves retinal ganglion cell function by facilitating presynaptic GABA release in early experimental diabetes

JOURNAL/nrgr/04.03/01300535-202602000-00048/figure1/v/2025-05-05T160104Z/r/image-tiff Diabetic retinopathy is a prominent cause of blindness in adults, with early retinal ganglion cell loss contributing to visual dysfunction or blindness. In the brain, defects in γ-aminobutyric acid synaptic transmission are associated with pathophysiological and neurodegenerative disorders, whereas glucagon-like peptide-1 has demonstrated neuroprotective effects. However, it is not yet clear whether diabetes causes alterations in inhibitory input to retinal ganglion cells and whether and how glucagon-like peptide-1 protects against neurodegeneration in the diabetic retina through regulating inhibitory synaptic transmission to retinal ganglion cells. In the present study, we used the patch-clamp technique to record γ-aminobutyric acid subtype A receptor-mediated miniature inhibitory postsynaptic currents in retinal ganglion cells from streptozotocin-induced diabetes model rats. We found that early diabetes (4 weeks of hyperglycemia) decreased the frequency of GABAergic miniature inhibitory postsynaptic currents in retinal ganglion cells without altering their amplitude, suggesting a reduction in the spontaneous release of γ-aminobutyric acid to retinal ganglion cells. Topical administration of glucagon-like peptide-1 eyedrops over a period of 2 weeks effectively countered the hyperglycemia-induced downregulation of GABAergic mIPSC frequency, subsequently enhancing the survival of retinal ganglion cells. Concurrently, the protective effects of glucagon-like peptide-1 on retinal ganglion cells in diabetic rats were eliminated by topical administration of exendin-9-39, a specific glucagon-like peptide-1 receptor antagonist, or SR95531, a specific antagonist of the γ-aminobutyric acid subtype A receptor. Furthermore, extracellular perfusion of glucagon-like peptide-1 was found to elevate the frequencies of GABAergic miniature inhibitory postsynaptic currents in both ON- and OFF-type retinal ganglion cells. This elevation was shown to be mediated by activation of the phosphatidylinositol-phospholipase C/inositol 1,4,5-trisphosphate receptor/Ca 2+ /protein kinase C signaling pathway downstream of glucagon-like peptide-1 receptor activation. Moreover, multielectrode array recordings revealed that glucagon-like peptide-1 functionally augmented the photoresponses of ON-type retinal ganglion cells. Optomotor response tests demonstrated that diabetic rats exhibited reductions in visual acuity and contrast sensitivity that were significantly ameliorated by topical administration of glucagon-like peptide-1. These results suggest that glucagon-like peptide-1 facilitates the release of γ-aminobutyric acid onto retinal ganglion cells through the activation of glucagon-like peptide-1 receptor, leading to the de-excitation of retinal ganglion cell circuits and the inhibition of excitotoxic processes associated with diabetic retinopathy. Collectively, our findings indicate that the γ-aminobutyric acid system has potential as a therapeutic target for mitigating early-stage diabetic retinopathy. Furthermore, the topical administration of glucagon-like peptide-1 eyedrops represents a non-invasive and effective treatment approach for managing early-stage diabetic retinopathy.

Potential mechanisms of epigenetic regulation in diabetic retinopathy from the perspectives of multi-omics

PURPOSE

Diabetic retinopathy (DR) is a significant complication of diabetes, with complex pathogenesis involving epigenetic modifications. This study aimed to explore the epigenetic regulatory mechanisms contributing to DR.

METHODS

DR-related data, including DNA methylation, mRNA, and miRNA expression datasets, were obtained from the Gene Expression Omnibus database. Differential gene expression analysis was performed to identify differentially methylated genes and expressed mRNAs and miRNAs. Cross-analysis established the methylation-expression and miRNA-mRNA regulatory networks. A comprehensive DR-related epigenetic regulatory network was constructed, identifying hub genes. The expression characteristics of these hub genes in various immune cells were examined using single-cell RNA sequencing.

RESULTS

We identified 10,716 differentially methylated genes, 1,181 differentially expressed mRNAs, and 615 differentially expressed miRNAs in DR. The methylation-expression regulatory network was associated with pathways such as TGF-beta and ErbB signaling. The miRNA regulatory network was linked to pathways related to cellular senescence, adherents junctions, and endocytosis. Five hub genes were identified: TFRC, AP2M1, AP2A1, DAB2, and PPP1CB. Single-cell RNA sequencing revealed specific expression of these genes in particular immune cells, highlighting their potential roles in DR pathogenesis.

CONCLUSION

This study constructed a comprehensive epigenetic regulatory network for DR and identified key regulatory genes, offering new insights into the molecular mechanisms underlying DR and potential therapeutic targets for diagnosis and treatment.

Glaucomatous retinal ganglion cells: death and protection

Glaucoma is a group of diseases characterized by progressive optic nerve degeneration, with the characteristic pathological change being death of retinal ganglion cells (RGCs), which ultimately causes visual field loss and irreversible blindness. Elevated intraocular pressure (IOP) remains the most important risk factor for glaucoma, but the exact mechanism responsible for the death of RGCs is currently unknown. Neurotrophic factor deficiency, impaired mitochondrial structure and function, disrupted axonal transport, disturbed Ca2+ homeostasis, and activation of apoptotic and autophagic pathways play important roles in RGC death in glaucoma. This review was conducted using Web of Science, PubMed, Project, and other databases to summarize the relevant mechanisms of death of RGCs in glaucoma, in addition to outlining protective treatments to improve the degradation of RGCs.

Cell and molecular targeted therapies for diabetic retinopathy

Diabetic retinopathy (DR) stands as a prevalent complication in the eye resulting from diabetes mellitus, predominantly associated with high blood sugar levels and hypertension as individuals age. DR is a severe microvascular complication of both type I and type II diabetes mellitus and the leading cause of vision impairment. The critical approach to combatting and halting the advancement of DR lies in effectively managing blood glucose and blood pressure levels in diabetic patients; however, this is seldom achieved. Both human and animal studies have revealed the intricate nature of this condition involving various cell types and molecules. Aside from photocoagulation, the sole therapy targeting VEGF molecules in the retina to prevent abnormal blood vessel growth is intravitreal anti-VEGF therapy. However, a substantial portion of cases, approximately 30-40%, do not respond to this treatment. This review explores distinctive pathophysiological phenomena of DR and identifiable cell types and molecules that could be targeted to mitigate the chronic changes occurring in the retina due to diabetes mellitus. Addressing the significant research gap in this domain is imperative to broaden the treatment options available for managing DR effectively.

The role of neurovascular coupling dysfunction in cognitive decline of diabetes patients

Neurovascular coupling (NVC) is an important mechanism to ensure adequate blood supply to active neurons in the brain. NVC damage can lead to chronic impairment of neuronal function. Diabetes is characterized by high blood sugar and is considered an important risk factor for cognitive impairment. In this review, we provide fMRI evidence of NVC damage in diabetic patients with cognitive decline. Combined with the exploration of the major mechanisms and signaling pathways of NVC, we discuss the effects of chronic hyperglycemia on the cellular structure of NVC signaling, including key receptors, ion channels, and intercellular connections. Studying these diabetes-related changes in cell structure will help us understand the underlying causes behind diabetes-induced NVC damage and early cognitive decline, ultimately helping to identify the most effective drug targets for treatment.