Connexin43 hemichannel block protects against the development of diabetic retinopathy signs in a mouse model of the disease

Targeting inflammasomes and pyroptosis in retinal diseases-molecular mechanisms and future perspectives

Retinal diseases encompass various conditions associated with sight-threatening immune responses and are leading causes of blindness worldwide. These diseases include age-related macular degeneration, diabetic retinopathy, glaucoma and uveitis. Emerging evidence underscores the vital role of the innate immune response in retinal diseases, beyond the previously emphasized T-cell-driven processes of the adaptive immune system. In particular, pyroptosis, a newly discovered programmed cell death process involving inflammasome formation, has been implicated in the loss of membrane integrity and the release of inflammatory cytokines. Several disease-relevant animal models have provided evidence that the formation of inflammasomes and the induction of pyroptosis in innate immune cells contribute to inflammation in various retinal diseases. In this review article, we summarize current knowledge about the innate immune system and pyroptosis in retinal diseases. We also provide insights into translational targeting approaches, including novel drugs countering pyroptosis, to improve the diagnosis and treatment of retinal diseases.

Correlative light and X-ray tomography jointly unveil the critical role of connexin43 channels on inflammation-induced cellular ultrastructural alterations

Non-junctional connexin43 (Cx43) plasma membrane hemichannels have been implicated in several inflammatory diseases, particularly playing a role in ATP release that triggers activation of the inflammasome. Therapies targeting the blocking of the hemichannels to prevent the pathological release or uptake of ions and signalling molecules through its pores are of therapeutic interest. To date, there is no close-to-native, high-definition documentation of the impact of Cx43 hemichannel-mediated inflammation on cellular ultrastructure, neither is there a robust account of the ultrastructural changes that occur following treatment with selective Cx43 hemichannel blockers such as Xentry-Gap19 (XG19). A combination of same-sample correlative high-resolution three-dimensional fluorescence microscopy and soft X-ray tomography at cryogenic temperatures, enabled in the identification of novel 3D molecular interactions within the cellular milieu when comparing behaviour in healthy states and during the early onset or late stages under inflammatory conditions. Notably, our findings suggest that XG19 blockage of connexin hemichannels under pro-inflammatory conditions may be crucial in preventing the direct degradation of connexosomes by lysosomes, without affecting connexin protein translation and trafficking. We also delineated fine and gross cellular phenotypes, characteristic of inflammatory insult or road-to-recovery from inflammation, where XG19 could indirectly prevent and reverse inflammatory cytokine-induced mitochondrial swelling and cellular hypertrophy through its action on Cx43 hemichannels. Our findings suggest that XG19 might have prophylactic and therapeutic effects on the inflammatory response, in line with functional studies.

O-GlcNAcylation Inhibition Upregulates Connexin43 Expression in the Endothelium to Protect the Tight Junction Barrier in Diabetic Retinopathy

Purpose

This study aimed to investigate the effects of O-linked N-acetylglucosamine modification (O-GlcNAcylation) on connexin43 (Cx43) expression and its subsequent effects on tight junction properties in diabetic retinopathy (DR).

Methods

O-GlcNAcylation levels in primary human retinal vascular endothelial cells (HRVECs) and retinas from rats with diabetes were regulated by treatment with Thiamet G or alloxan. Immunoprecipitation was used to examine the relationship between O-GlcNAcylation and Cx43 expression. Stable overexpression and knockdown of Cx43 in HRVECs were achieved using lentivirus constructs; further, their effects on occludin and zonula occluden-1 (ZO-1) expression and tight junction barrier function were determined.

Results

O-GlcNAcylation level increased significantly, whereas Cx43 expression decreased in retinas from rats with diabetes and HRVECs cultured under high-glucose conditions. Immunoprecipitation revealed that Cx43 was modified by O-GlcNAcylation and phosphorylation simultaneously. O-GlcNAcylation inhibition negatively regulated both total Cx43 and phosphorylated Cx43 expression, subsequently disrupting tight junction properties. Conversely, Cx43 overexpression reversed the disruption of tight junction properties and downregulated vascular endothelial growth factor expression. Consistently, Cx43 overexpression increased transendothelial electrical resistance values in HRVEC layers.

Conclusions

O-GlcNAcylation negatively regulated Cx43 expression, contributing to the disruption of the blood retinal barrier. However, O-GlcNAcylation inhibition and Cx43 overexpression could reverse the tight junction disruption. Therefore, O-GlcNAcylation inhibition is a potential target for avoiding tight junction disruption through the Cx43 pathway in DR.

Comprehensive Grading System for Experimental Autoimmune Uveitis in Mice

Experimental autoimmune uveitis (EAU) is the most commonly used animal model to study the progression of chronic uveitis and to test various therapies to treat the disease. However, to accurately evaluate the effectiveness of such treatments, a grading system that combines the latest imaging techniques with definitive quantitative grading thresholds is required. This study aimed to develop a comprehensive grading system that objectively evaluates EAU progression in C57BL/6J mice. EAU was induced following immunisation with interphotoreceptor retinoid-binding protein (IRBP) and pertussis toxin. Weekly fundus and optical coherence tomography (OCT) images were acquired over 12 weeks using a Micron IV imaging system. Each mouse was graded (between 0 to 4) based on changes seen on both the fundus (optic disc, retinal blood vessels and retinal tissue) and OCT (vitreous and retinal layers) images. A total EAU response (with a maximum score of 48) was calculated for each mouse based on the sum of the individual scores each week. Analysis of the clinical scores depicted a gradual increase in inflammatory signs including optic disc and vascular swelling, leukocyte infiltration in the vitreous, lesions in the retina and formation of granulomas and hyper-reflective foci in the retinal layers in EAU mice, with most signs reaching a plateau towards the end of the study period. Development of these signs into sight-threatening complications such as optic disc atrophy, structural damage to the retina and subretinal oedema were noted in 80-90% of mice suggesting consistent disease induction. Overall, a comprehensive and objective grading system encompassing all pathologies occurring in EAU mice was developed to enhance the preclinical evaluation of novel uveitis treatments.

The central role of the NLRP3 inflammasome pathway in the pathogenesis of age-related diseases in the eye and the brain

With increasing age, structural changes occur in the eye and brain. Neuronal death, inflammation, vascular disruption, and microglial activation are among many of the pathological changes that can occur during ageing. Furthermore, ageing individuals are at increased risk of developing neurodegenerative diseases in these organs, including Alzheimer's disease (AD), Parkinson's disease (PD), glaucoma and age-related macular degeneration (AMD). Although these diseases pose a significant global public health burden, current treatment options focus on slowing disease progression and symptomatic control rather than targeting underlying causes. Interestingly, recent investigations have proposed an analogous aetiology between age-related diseases in the eye and brain, where a process of chronic low-grade inflammation is implicated. Studies have suggested that patients with AD or PD are also associated with an increased risk of AMD, glaucoma, and cataracts. Moreover, pathognomonic amyloid-β and α-synuclein aggregates, which accumulate in AD and PD, respectively, can be found in ocular parenchyma. In terms of a common molecular pathway that underpins these diseases, the nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) inflammasome is thought to play a vital role in the manifestation of all these diseases. This review summarises the current evidence regarding cellular and molecular changes in the brain and eye with age, similarities between ocular and cerebral age-related diseases, and the role of the NLRP3 inflammasome as a critical mediator of disease propagation in the eye and the brain during ageing.

NLRP3 Inflammasome as a Potential Therapeutic Target in Dry Eye Disease

Dry eye disease (DED) is a multifactorial ocular surface disorder arising from numerous interrelated underlying pathologies that trigger a self-perpetuating cycle of instability, hyperosmolarity, and ocular surface damage. Associated ocular discomfort and visual disturbance contribute negatively to quality of life. Ocular surface inflammation has been increasingly recognised as playing a key role in the pathophysiology of chronic DED. Current readily available anti-inflammatory agents successfully relieve symptoms, but often without addressing the underlying pathophysiological mechanism. The NOD-like receptor protein-3 (NLRP3) inflammasome pathway has recently been implicated as a key driver of ocular surface inflammation, as reported in pre-clinical and clinical studies of DED. This review discusses the intimate relationship between DED and inflammation, highlights the involvement of the inflammasome in the development of DED, describes existing anti-inflammatory therapies and their limitations, and evaluates the potential of the inflammasome in the context of the existing anti-inflammatory therapeutic landscape as a therapeutic target for effective treatment of the disease.

The mechanisms of NLRP3 inflammasome/pyroptosis activation and their role in diabetic retinopathy

In the working-age population worldwide, diabetic retinopathy (DR), a prevalent complication of diabetes, is the main cause of vision impairment. Chronic low-grade inflammation plays an essential role in DR development. Recently, concerning the pathogenesis of DR, the Nod-Like Receptor Family Pyrin Domain Containing 3 (NLRP3) inflammasome in retinal cells has been determined as a causal factor. In the diabetic eye, the NLRP3 inflammasome is activated by several pathways (such as ROS and ATP). The activation of NPRP3 leads to the secretion of inflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18), and leads to pyroptosis, a rapid inflammatory form of lytic programmed cell death (PCD). Cells that undergo pyroptosis swell and rapture, releasing more inflammatory factors and accelerating DR progression. This review focuses on the mechanisms that activate NLRP3 inflammasome and pyroptosis leading to DR. The present research highlighted some inhibitors of NLRP3/pyroptosis pathways and novel therapeutic measures concerning DR treatment.

Targeting the NLRP3 inflammasome in diabetic retinopathy: From Pathogenesis to Therapeutic Strategies

Diabetic retinopathy (DR) is a common diabetic microvascular complication and the main cause of vision loss in working-aged people. The NLRP3 inflammasome is a cytosolic multimeric complex that plays a significant role in innate immunity. After sensing injury, the NLRP3 inflammasome induces inflammatory mediator secretion and triggers a form of inflammatory cell death known as pyroptosis. Studies over the past five years have shown increased expression of NLRP3 and related inflammatory mediators in vitreous samples from DR patients at different clinical stages. Many NLRP3-targeted inhibitors have shown great antiangiogenic and anti-inflammatory effects in diabetes mellitus models, suggesting that the NLRP3 inflammasome is involved in the progression of DR. This review covers the molecular mechanisms of NLRP3 inflammasome activation. Furthermore, we discuss the implications of the NLRP3 inflammasome in DR, including the induction of pyroptosis and inflammation and the promotion of microangiopathy and retinal neurodegeneration. We also summarize the research progress on targeting the NLRP3 inflammasome in DR therapeutics with the expectation of providing new insights into DR progression and treatment.

Orally Delivered Connexin43 Hemichannel Blocker, Tonabersat, Inhibits Vascular Breakdown and Inflammasome Activation in a Mouse Model of Diabetic Retinopathy

Diabetic retinopathy (DR), a microvascular complication of diabetes, is associated with pronounced inflammation arising from the activation of a nucleotide-binding and oligomerization domain-like receptor (NLR) protein 3 (NLRP3) inflammasome. Cell culture models have shown that a connexin43 hemichannel blocker can prevent inflammasome activation in DR. The aim of this study was to evaluate the ocular safety and efficacy of tonabersat, an orally bioavailable connexin43 hemichannel blocker, to protect against DR signs in an inflammatory non-obese diabetic (NOD) DR mouse model. For retina safety studies, tonabersat was applied to retinal pigment epithelial (ARPE-19) cells or given orally to control NOD mice in the absence of any other stimuli. For efficacy studies, either tonabersat or a vehicle was given orally to the inflammatory NOD mouse model two hours before an intravitreal injection of pro-inflammatory cytokines, interleukin-1 beta, and tumour necrosis factor-alpha. Fundus and optical coherence tomography images were acquired at the baseline as well as at 2- and 7-day timepoints to assess microvascular abnormalities and sub-retinal fluid accumulation. Retinal inflammation and inflammasome activation were also assessed using immunohistochemistry. Tonabersat did not have any effect on ARPE-19 cells or control NOD mouse retinas in the absence of other stimuli. However, the tonabersat treatment in the inflammatory NOD mice significantly reduced macrovascular abnormalities, hyperreflective foci, sub-retinal fluid accumulation, vascular leak, inflammation, and inflammasome activation. These findings suggest that tonabersat may be a safe and effective treatment for DR.

Rodent Models of Diabetic Retinopathy as a Useful Research Tool to Study Neurovascular Cross-Talk

Diabetes is a group of metabolic diseases leading to dysfunction of various organs, including ocular complications such as diabetic retinopathy (DR). Nowadays, DR treatments involve invasive options and are applied at the sight-threatening stages of DR. It is important to investigate noninvasive or pharmacological methods enabling the disease to be controlled at the early stage or to prevent ocular complications. Animal models are useful in DR laboratory practice, and this review is dedicated to them. The first part describes the characteristics of the most commonly used genetic rodent models in DR research. The second part focuses on the main chemically induced models. The authors pay particular attention to the streptozotocin model. Moreover, this section is enriched with practical aspects and contains the current protocols used in research in the last three years. Both parts include suggestions on which aspect of DR can be tested using a given model and the disadvantages of each model. Although animal models show huge variability, they are still an important and irreplaceable research tool. Note that the choice of a research model should be thoroughly considered and dependent on the aspect of the disease to be analyzed.

Upregulation of retinal VEGF and connexin 43 in murine nonarteritic anterior ischemic optic neuropathy induced with 577 nm laser

Nonarteritic anterior ischemic optic neuropathy (NAION) is a common acute optic neuropathy and cause of irreversible vision loss in those older than 50 years of age. There is currently no effective treatment for NAION and the biological mechanisms leading to neuronal loss are not fully understood. Promising novel targets include glial cells activation and intercellular communication mediated by molecules such as gap junction protein Connexin 43 (Cx43), which modulate neuronal fate in central nervous system disorders. In this study, we investigated retinal glial changes and neuronal loss following a novel NAION animal model using a 577 nm yellow laser. We induced unilateral photochemical thrombosis using rose bengal at the optic nerve head vasculature in adult C57BL/6 mice using a 577 nm laser and performed morphometric analysis of the retinal structure using serial in vivo optical coherence tomography (OCT) and histology for glial and neuronal markers. One day after experimental NAION, in acute phase, OCT imaging revealed peripapillary thickening of the retinal ganglion cell complex (GCC, baseline: 79.5 ± 1.0 μm, n = 8; NAION: 93.0 ± 2.5 μm, n = 8, P < 0.01) and total retina (baseline: 202.9 ± 2.4 μm, n = 8; NAION: 228.1 ± 6.8 μm, n = 8, P < 0.01). Twenty-one days after ischemia, at a chronic phase, there was significant GCC thinning (baseline 78.3 ± 2.1 μm, n = 6; NAION: 72.2 ± 1.9 μm, n = 5, P < 0.05), mimicking human disease. Examination of molecular changes in the retina one day after ischemia revealed that NAION induced a significant increase in retinal VEGF levels (control: 2319 ± 195, n = 5; NAION: 4549 ± 683 gray mean value, n = 5, P < 0.05), which highly correlated with retinal thickness (r = 0.89, P < 0.05). NAION also led to significant increase in mRNA level for Cx43 (Gj1a) at day 1 (control: 1.291 ± 0.38; NAION: 3.360 ± 0.58 puncta/mm2, n = 5, P < 0.05), but not of glial fibrillary acidic protein (Gfap) at the same time (control: 2,800 ± 0.59; NAION: 4,690 ± 0.90 puncta/mm2 n = 5, P = 0.19). Retinal ganglion cell loss at day 21 was confirmed by a 30% decrease in Brn3a+ cells (control: 2,844 ± 235; NAION: 2,001 ± 264 cells/mm2, n = 4, P < 0.05). We described a novel protocol of NAION induction by photochemical thrombosis using a 577 nm laser, leading to retinal edema and VEGF increase at day 1 and RGCs loss at day 21 after injury, consistent with the pathophysiology of human NAION. Early changes in glial cells intercommunication revealed by increased Cx43+ gap junctions are consistent with a retinal glial role in mediating cell-to-cell signaling after an ischemic insult. Our study demonstrates an early glial response in a novel NAION animal model and reveals glial intercommunication molecules such as Cx43 as a promising therapeutic target in acute NAION.

Characterization of NLRP3 Inflammasome Activation in the Onset of Diabetic Retinopathy

The aim of this study was to characterize the role of nucleotide-binding oligomerization domain- (NOD-) like receptor (NLR) protein 3 (NLRP3) inflammasome activation in the onset of diabetic retinopathy (DR) using retina and vitreous from donors without diabetes mellitus (CTL), with diabetes mellitus alone (DM), and with DR. Retinal expression of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1), the key markers of retinal inflammation, connexin43 (Cx43) which is involved in upstream inflammasome regulation, as well as NLRP3 and cleaved caspase-1, the main markers of inflammasome activation, were evaluated using immunohistochemistry and Western blotting. Vitreous interleukin (IL)-1β and IL-18, biomarkers of the activated inflammasome, were measured using a Luminex multiplex assay. Results showed a significant increase in the number and size of Iba-1⁺ cells and NLRP3 expression in DM, while a significant increase in GFAP, Cx43, cleaved caspase-1 and vitreous IL-18, as well as a further increase in Iba-1 and NLRP3 was found in DR. This suggests that the inflammasome is already primed in DM before its activation in DR. Furthermore, IL-18 may act as the major effector of inflammasome activation in DR while nuclear translocation of cleaved caspase-1 may play a role in gene transcription contributing to DR onset.

Optic nerve head: A gatekeeper for vitreous infectious insults?

The axons of retinal ganglion cells (RGCs) pass through the optic nerve head (ONH) and form the optic nerve (ON). The ONH serves as an anatomical interface between the vitreous cavity and subarachnoid space. After inducing acute neuroinflammation by intravitreal injection of lipopolysaccharides (LPS), we observed inflammatory activation in the retina, but detect no signs of inflammation in the posterior ON or infiltration of inflammatory cells in the ONH. Therefore, we hypothesized that the ONH functions as a barrier to vitreous inflammation. Using transmission electron microscopy, we identified significant increase in G-ratio in the posterior ON on day 7 post intravitreal injection (PII) of LPS compared with the phosphate buffered saline (PBS) group. Moreover, using confocal imaging of ex vivo tissue extracted from Aldh1L1-eGFP reporter mice, we observed that the ONH astrocytes altered their spatial orientation by elongating their morphology along the axonal axis of RGCs in LPS- versus PBS-treated eyes; this was quantified by the ratio of longitudinal (D_L) and transverse (D_T) diameter of astrocytes and the proportion of longitudinally locating astrocytes. Supportive evidences were further provided by transmission electron microscopic imaging in rat ONH. We further conducted RNA sequencing of ONH on day 1 PII and found LPS induced clear upregulation of immune and inflammatory pathways. Furthermore, gene set enrichment analysis revealed that astrocyte and microglia contributed prominently to the transcriptomic alterations in ONH. Here, we report that the vitreous infectious insults induce morphological changes of ONH astrocytes and transcriptomic alterations in the ONH. Glial responses in the ONH may defend against vitreous infectious insults and serve as a barrier to inflammation for the central nervous system.

Synthesis and Biological Evaluation of Termini-Modified and Cyclic Variants of the Connexin43 Inhibitor Peptide5

Peptide5 is a 12–amino acid mimetic peptide that corresponds to a region of the extracellular loop 2 (EL2) of connexin43. Peptide5 regulates both cellular communication with the cytoplasm (hemichannels) and cell-to-cell communication (gap junctions), and both processes are implicated in neurological pathologies. To address the poor in vivo stability of native peptide5 and to improve its activity, twenty-five novel peptide5 mimetics were designed and synthesized. All the analogues underwent biological evaluation as a hemichannel blocker and as a gap junction disruptor, and several were assessed for stability in human serum. From this study, it was established that several acylations on the N-terminus were tolerated in the hemichannel assay. However, the replacement of the L-Lys with an N-methylated L-Lys to give H-VDCFLSRPTE-N-MeKT-OH showed good hemichannel and gap junction activity and was more stable in human serum. The cyclic peptide variants generally were not tolerated in either the hemichannel and gap junction assay although several possessed outstanding stability in human serum.

Correlation between the progression of diabetic retinopathy and inflammasome biomarkers in vitreous and serum – a systematic review

Activation of the NOD-like receptor protein 3 (NLRP3) inflammasome pathway has been implicated in Diabetic retinopathy (DR) pathogenesis, but its impact on DR development and progression remains unclear. Therefore, the primary aim of this systematic literature review was to determine the role of the inflammasome in DR development. Furthermore, the secondary aim was to determine whether systemic inflammasome activity can be used to predict DR progression. Studies measuring vitreous and/or serum inflammasome biomarkers in DR patients with Type 2 Diabetes Mellitus (T2DM) were searched systematically using online databases EMBASE, PubMed and Web of Science with the last search conducted on 29^th of September 2021. The risk of bias was assessed using the Newcastle Ottawa Scale and 20 studies were eligible for narrative analysis. Limitations included the heterogeneity in detection assays used, the small and uneven sample size, a lack of vitreous data in earlier disease stages, and not accounting for patients with other systemic co-morbidities. Analysis showed that inflammasome biomarkers IL-1β and IL-18 increased significantly from non-proliferative DR to proliferative DR in both vitreous and serum, suggesting the inflammasome pathway is activated as DR progresses and that serum inflammasome levels could be explored as potential biomarkers for DR progression.

The Role of Connexin Hemichannels in Inflammatory Diseases

The connexin protein family consists of approximately 20 members, and is well recognized as the structural unit of the gap junction channels that perforate the plasma membranes of coupled cells and, thereby, mediate intercellular communication. Gap junctions are assembled by two preexisting hemichannels on the membranes of apposing cells. Non-junctional connexin hemichannels (CxHC) provide a conduit between the cell interior and the extracellular milieu, and are believed to be in a protectively closed state under physiological conditions. The development and characterization of the peptide mimetics of the amino acid sequences of connexins have resulted in the development of a panel of blockers with a higher selectivity for CxHC, which have become important tools for defining the role of CxHC in various biological processes. It is increasingly clear that CxHC can be induced to open by pathogen-associated molecular patterns. The opening of CxHC facilitates the release of damage-associated molecular patterns, a class of endogenous molecules that are critical for the pathogenesis of inflammatory diseases. The blockade of CxHC leads to attenuated inflammation, reduced tissue injury and improved organ function in human and animal models of about thirty inflammatory diseases and disorders. These findings demonstrate that CxHC may contribute to the intensification of inflammation, and serve as a common target in the treatments of various inflammatory diseases. In this review, we provide an update on the progress in the understanding of CxHC, with a focus on the role of these channels in inflammatory diseases.

Connexin 43: A Target for the Treatment of Inflammation in Secondary Complications of the Kidney and Eye in Diabetes

Of increasing prevalence, diabetes is characterised by elevated blood glucose and chronic inflammation that precedes the onset of multiple secondary complications, including those of the kidney and the eye. As the leading cause of end stage renal disease and blindness in the working population, more than ever is there a demand to develop clinical interventions which can both delay and prevent disease progression. Connexins are membrane bound proteins that can form pores (hemichannels) in the cell membrane. Gated by cellular stress and injury, they open under pathophysiological conditions and in doing so release 'danger signals' including adenosine triphosphate into the extracellular environment. Linked to sterile inflammation via activation of the nod-like receptor protein 3 inflammasome, targeting aberrant hemichannel activity and the release of these danger signals has met with favourable outcomes in multiple models of disease, including secondary complications of diabetes. In this review, we provide a comprehensive update on those studies which document a role for aberrant connexin hemichannel activity in the pathogenesis of both diabetic eye and kidney disease, ahead of evaluating the efficacy of blocking connexin-43 specific hemichannels in these target tissues on tissue health and function.

The NLRP3 inflammasome in age-related eye disease: Evidence-based connexin hemichannel therapeutics

The inflammasome pathway is a fundamental component of the innate immune system, playing a key role especially in chronic age-related eye diseases (AREDs). The inflammasome is of particular interest because it is a common disease pathway that once instigated, can amplify and perpetuate itself leading to chronic inflammation. With aging, it becomes more difficult to shut down inflammation after an insult but the common pathway means that a shared solution may be feasible that could be effective across multiple disease indications. This review focusses on the NLRP3 inflammasome, the most studied and characterized inflammasome in the eye. It describes the two-step signalling required for NLRP3 inflammasome complex activation, and provides evidence for its role in AREDs. In the final section, the article gives an overview of potential NLRP3 inflammasome targeting therapies, before presenting evidence for connexin hemichannel regulators as upstream blockers of inflammasome activation. These have shown therapeutic efficacy in multiple ocular disease models.

Connexin channels modulation in pathophysiology and treatment of immune and inflammatory disorders

Connexin-mediated intercellular communication mechanisms include bidirectional cell-to-cell coupling by gap junctions and release/influx of molecules by hemichannels. These intercellular communications have relevant roles in numerous immune system activities. Here, we review the current knowledge about the function of connexin channels, mainly those formed by connexin-43, on immunity and inflammation. Focusing on those evidence that support the design and development of therapeutic tools to modulate connexin expression and/or channel activities with treatment potential for infections, wounds, cancer, and other inflammatory conditions.

Animal models of diabetic retinopathy

The retina is the posterior neuro-integrated layer of the eye that conducts impulses induced by light to the optic nerve for human vision. Diseases of the retina often leads to diminished vision and in some cases blindness. Diabetes mellitus (DM) is a worldwide public health issue and globally, there is an estimated 463 million people that are affected by DM and its consequences. Diabetic retinopathy (DR) is a blinding complication of chronic uncontrolled DM and is the most common cause of blindness in the United States between the ages 24-75. It is estimated that the global prevalence of DR will increase to 191.0 million by 2030, of those 56.3 million possessing vision-threatening diabetic retinopathy (VTDR). For the most part, current treatment modalities control the complications of DR without addressing the underlying pathophysiology of the disease. Therefore, there is an unmet need for new therapeutics that not only repair the damaged retinal tissue, but also reverse the course of DR. The key element in developing these treatments is expanding our basic knowledge by studying DR pathogenesis in animal models of proliferative and non-proliferative DR (PDR and NPDR). There are numerous models available for the research of both PDR and NPDR with substantial overlap. Animal models available include those with genetic backgrounds prone to hyperglycemic states, immunologic etiologies, or environmentally induced disease. In this review we aimed to comprehensively summarize the available animal models for DR while also providing insight to each model's ocular therapeutic potential for drug discovery.

Blocking the inflammasome: A novel approach to treat uveitis

Uveitis is a complex ocular inflammatory disease often accompanied by bacterial or viral infections (infectious uveitis) or underlying autoimmune diseases (non-infectious uveitis). Treatment of the underlying infection along with corticosteroid-mediated suppression of acute inflammation usually resolves infectious uveitis. However, to develop more effective therapies for non-infectious uveitis and to better address acute inflammation in infectious disease, an improved understanding of the underlying inflammatory pathways is needed. In this review, we discuss the disease aetiology, preclinical in vitro and in vivo uveitis models, the role of inflammatory pathways, as well as current and future therapies. In particular, we highlight the involvement of the inflammasome in the development of non-infectious uveitis and how it could be a future target for effective treatment of the disease.

Identification of connexin43 in diabetic retinopathy and its downregulation by O-GlcNAcylation to inhibit the activation of glial cells

BACKGROUND

Despite advances in the treatments of diabetic complications, proliferative diabetic retinopathy (PDR) still remains a major cause leading to visual loss, mainly because of the lack of pathological mechanisms and complicated protein expressions in vivo. Current study aimed to investigate the patterns of connexin43 (Cx43) changes and the possible interactions with O-GlcNAcylation in DR.

METHODS

Clinical samples of vitreous and fibrovascular membranes were acquired from PDR patients during pars plana vitrectomy. Brown Norway rats were used to build diabetic animal models; to investigate the effects of O-GlcNAcylation on Cx43 expressions, total retinal O-GlcNAcylation was changed by intravitreal injections. Levels of protein expressions were examined by immunofluorescence staining and western blot.

RESULTS

Our results revealed increased Cx43 expressions in a vessel-shape pattern followed by the distribution of glial fibrillary acidic protein (GFAP) in diabetic fibrovascular membranes. Similarly, Cx43 and GFAP expressions were elevated in PDR vitreous and diabetic animal retinas. Retinal O-GlcNAcylation was effectively regulated by intravitreal injections, and the increase of Cx43 and GFAP was significantly suppressed by O-GlcNAcylation inhibition under hyperglycemia conditions.

CONCLUSIONS

We systemically proved the changes of Cx43 with different retinal cells, and reported the effective methods to regulate retinal O-GlcNAcylation by intravitreal injections, and clearly illustrated the downregulated effects of O-GlcNAcylation inhibition on Cx43 and GFAP expressions.

GENERAL SIGNIFICANCE

Targeting connexin43 in glial cells reveals a novel mechanism to understand the formation of diabetic fibrovascular membranes and offers a potential therapeutic strategy to interfere the development of PDR.

Xentry-Gap19 inhibits Connexin43 hemichannel opening especially during hypoxic injury

Hypoxic injury results in cell death, tissue damage and activation of inflammatory pathways. This is mediated by pathological Connexin43 (Cx43) hemichannel (HC) opening resulting in osmotic and ionic imbalances as well as cytokine production perpetuating the inflammatory environment. Gap19 is an intracellularly acting Cx43 mimetic peptide that blocks HC opening and thus promotes cell survival. However, native Gap19, which must enter the cell in order to function, exhibits low cell permeability. In this study, Gap19 was conjugated to the cell-penetrating peptide, Xentry, to investigate if cellular uptake could be improved while maintaining peptide function. Cellular uptake of Xentry-Gap19 (XG19) was much greater than that of native Gap19 even under normal cell culture conditions. Peptide function was maintained post uptake as shown by reduced ethidium homodimer influx and ATP release due to Cx43 HC block. While XG19 blocked pathologic HC opening though, normal gap junction communication required for cell repair and survival mechanisms was not affected as shown in a dye scrape-load assay. Under hypoxic conditions, increased expression of Syndecan-4, a plasma membrane proteoglycan targeted by Xentry, enabled even greater XG19 uptake leading to higher inhibition of ATP release and greater cell survival. This suggests that XG19, which is targeted specifically to hypoxic cells, can efficiently and safely block Cx43 HC and could therefore be a novel treatment for hypoxic and inflammatory diseases.

Animal models of diabetes-associated vascular diseases: an update on available models and experimental analysis

Diabetes is a chronic metabolic disorder associated with the accelerated development of macrovascular (atherosclerosis and coronary artery disease) and microvascular complications (nephropathy, retinopathy and neuropathy), which remain the principal cause of mortality and morbidity in this population. Current understanding of cellular and molecular pathways of diabetes-driven vascular complications, as well as therapeutic interventions has arisen from studying disease pathogenesis in animal models. Diabetes-associated vascular complications are multi-faceted, involving the interaction between various cellular and molecular pathways. Thus, the choice of an appropriate animal model to study vascular pathogenesis is important in our quest to identify innovative and mechanism-based targeted therapies to reduce the burden of diabetic complications. Herein, we provide up-to-date information on available mouse models of both Type 1 and Type 2 diabetic vascular complications as well as experimental analysis and research outputs.

Astrocyte Networks as Therapeutic Targets in Glaucomatous Neurodegeneration

Astrocytes are intimately involved in the response to neurodegenerative stress and have become an attractive target for the development of neuroprotective therapies. However, studies often focus on astrocytes as single-cell units. Astrocytes are densely interconnected by gap junctions that are composed primarily of the protein connexin-43 (Cx43) and can function as a broader network of cells. Such networks contribute to a number of important processes, including metabolite distribution and extracellular ionic buffering, and are likely to play an important role in the progression of neurodegenerative disease. This review will focus on the pro-degenerative and pro-survival influence of astrocyte Cx43 in disease progression, with a focus on the roles of gap junctions and hemichannels in the spread of degenerative stress. Finally, we will highlight the specific evidence for targeting these networks in the treatment of glaucomatous neurodegeneration and other optic neuropathies.

Primary Osteocyte Supernatants Metabolomic Profiling of Two Transgenic Mice With Connexin43 Dominant Negative Mutants

Osteocytes could release some small molecules (≤ 1 kDa) through gap junctions and hemichannels to extracellular environment, such as prostaglandin E2 (PGE2), nitric oxide (NO) and adenosine triphosphate (ATP), which play key roles in transferring signals between bone cells and other tissue cells. Connexin (Cx) 43 is the most abundant connexin in osteocytes. To further discover molecules released by osteocytes through Cx43 channels and better understand the regulatory function of Cx43 channels in osteocytes, we performed non-targeted global metabolomics analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) on conditioned medium collected from osteocytes isolated from two transgenic mouse models with Cx43 dominant negative mutants driven by a 10 kb-DMP1 promoter: R76W (gap junctions are blocked, whereas hemichannels are promoted) and Δ130-136 (both gap junctions and hemichannels are blocked). The results revealed that several new categories of molecules, such as "fatty acyls" and "carboxylic acids and derivatives", could be released through osteocytic Cx43 channels. In addition, alteration of Cx43 channel function affected the release of metabolites related to inflammatory reaction and oxidative stress. Pathway analysis further showed that citric acid cycle was the most differential metabolic pathway regulated by Cx43 channels. In sum, these results isolated new potential metabolites released by osteocytes through Cx43 channels, and offered a novel perspective to understand the regulatory mechanisms of osteocytes on themselves and other cells as well.

Role of pyroptosis in diabetic retinopathy and its therapeutic implications

Pyroptosis has recently been established as a term of programmed-inflammatory cell death. Pyroptosis is mainly divided into two molecular signaling pathways, including caspase-1-dependent canonical and caspase-4/5/11-dependent non-canonical inflammasome pathways. Extensive investigations have reported inflammasome activation facilitates the maturation and secretion of the inflammatory factors interleukin-1β/18 (IL-1β/18), cleavage of gasdermin D (GSDMD), and leading to the stimulation of pyroptosis-mediated cell death. Furthermore, accumulating studies report NLRP3 inflammasome activation plays a significant role in triggering the pyroptosis-mediated cell death and promotes the pathogenesis of diabetic retinopathy (DR). Our current review elaborates on the molecular mechanisms of pyroptosis-signaling pathways and their potential roles in the pathogenesis and impact of DR development. We also emphasize several investigational molecules regulating key steps in pyroptotic-cell death to create new comprehensions and findings to explore the pathogenesis of DR advancement. Our narrative review concisely suggests these potential pharmacological agents could be promising therapies to treat and manage DR in the future.

Peptidic Connexin43 Therapeutics in Cardiac Reparative Medicine

Connexin (Cx43)-formed channels have been linked to cardiac arrhythmias and diseases of the heart associated with myocardial tissue loss and fibrosis. These pathologies include ischemic heart disease, ischemia-reperfusion injury, heart failure, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and Duchenne muscular dystrophy. A number of Cx43 mimetic peptides have been reported as therapeutic candidates for targeting disease processes linked to Cx43, including some that have advanced to clinical testing in humans. These peptides include Cx43 sequences based on the extracellular loop domains (e.g., Gap26, Gap 27, and Peptide5), cytoplasmic-loop domain (Gap19 and L2), and cytoplasmic carboxyl-terminal domain (e.g., JM2, Cx43tat, CycliCX, and the alphaCT family of peptides) of this transmembrane protein. Additionally, RYYN peptides binding to the Cx43 carboxyl-terminus have been described. In this review, we survey preclinical and clinical data available on short mimetic peptides based on, or directly targeting, Cx43, with focus on their potential for treating heart disease. We also discuss problems that have caused reluctance within the pharmaceutical industry to translate peptidic therapeutics to the clinic, even when supporting preclinical data is strong. These issues include those associated with the administration, stability in vivo, and tissue penetration of peptide-based therapeutics. Finally, we discuss novel drug delivery technologies including nanoparticles, exosomes, and other nanovesicular carriers that could transform the clinical and commercial viability of Cx43-targeting peptides in treatment of heart disease, stroke, cancer, and other indications requiring oral or parenteral administration. Some of these newly emerging approaches to drug delivery may provide a path to overcoming pitfalls associated with the drugging of peptide therapeutics.

RNA sequencing reveals BMP4 as a basis for the dual-target treatment of diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR), currently considered as a neurovascular disease, has become the major cause of blindness. More and more scholars believe that DR is no longer just a kind of microvascular disease, but accompanied by retinal neurodegenerative changes. Intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs is a classic treatment for DR; however, anti-VEGF drugs can exacerbate fibrosis and eventually lead to retinal detachment. The aim of this study was to explore the pathogenesis of DR and identified new treatments that can provide dual-target intervention for angiogenesis and fibrosis.

METHODS

We explored changes in gene expression in high glucose-induced vascular endothelial cells using RNA sequencing (RNA-seq) technology. We identified bone morphogenetic protein 4 (BMP4) and SMAD family member 9 (SMAD9) among 449 differentially expressed genes from RNA-seq data and confirmed the expression of these two genes in the blood of diabetes patients by RT-PCR and in streptozotocin-induced rat retinas by RT-PCR, immunofluorescence, and western blot. Moreover, considering that DR is a multifactorial and multicellular disease, we used hydrogen peroxide (H2O2), advanced glycation end products (AGEs), CoCl2, 4-hydroxynonenal (4-HNE), and hypoxia to induce three human retinal cell types (Müller, retinal pigment epithelium, and human retinal capillary endothelial cells) to simulate the pathogenesis of DR, and MTT experiment, scratch experiment, Transwell experiment, and lumen formation experiment were used to test whether the model was successfully established. Then, we verified the overexpression of these two genes in the cell models by RT-PCR, immunofluorescence, and western blot. We further tested the effects of BMP4 on retinal cells. We use BMP4 to stimulate retinal cells and observe the effect of BMP4 on retinal cells by MTT experiment, scratch experiment, and RT-PCR.

RESULTS

The results demonstrated that BMP4 and SMAD9 were highly expressed in both in vivo and in vitro models, while BMP4 could significantly upregulate the expression of SMAD9 and promote the expression of VEGF and fibrosis factors.

CONCLUSIONS

This study is the first to analyze the mechanism by which high glucose levels affect retinal vascular endothelial cells through RNA transcriptome sequencing and indicates that BMP4 may be a potential target for the dual-target treatment (anti-VEGF and anti-fibrosis) of DR.

KEY MESSAGES

• High-glucose effect on vascular endothelial cell was analyzed by RNA-seq. • KEGG analysis revealed enrichment of TGF-beta signaling pathway. • SMAD9 and BMP4 expression was upregulated in all samples. • Dual-target therapy of PDR by antagonizing BMP4.

Tonabersat Inhibits Connexin43 Hemichannel Opening and Inflammasome Activation in an In Vitro Retinal Epithelial Cell Model of Diabetic Retinopathy

This study was undertaken to evaluate the connexin hemichannel blocker tonabersat for the inhibition of inflammasome activation and use as a potential treatment for diabetic retinopathy. Human retinal pigment epithelial cells (ARPE-19) were stimulated with hyperglycemia and the inflammatory cytokines IL-1β and TNFα in order to mimic diabetic retinopathy molecular signs in vitro. Immunohistochemistry was used to evaluate the effect of tonabersat treatment on NLRP3, NLRP1, and cleaved caspase-1 expression and distribution. A Luminex cytokine release assay was performed to determine whether tonabersat affected proinflammatory cytokine release. NLRP1 was not activated in ARPE-19 cells, and IL-18 was not produced under disease conditions. However, NLRP3 and cleaved caspase-1 complex formation increased with hyperglycemia and cytokine challenge but was inhibited by tonabersat treatment. It also prevented the release of proinflammatory cytokines IL-1β, VEGF, and IL-6. Tonabersat therefore has the potential to reduce inflammasome-mediated inflammation in diabetic retinopathy.

Connexin43 hemichannel block inhibits NLRP3 inflammasome activation in a human retinal explant model of diabetic retinopathy

Diabetic retinopathy (DR), the most common ocular complication associated with diabetes, is a chronic vascular and inflammatory disease that leads to vision loss. The inflammasome pathway, a key part of the innate immune system, is required to activate chronic inflammation in DR. Unfortunately, current therapies for DR target pathological signs that are downstream of the inflammasome pathway, making them only partly effective in treating the disease. Using in vitro and in vivo DR models, it was discovered that connexin43 hemichannel blockers can inhibit activation of the inflammasome pathway. However, those studies were conducted using in vitro cell culture and in vivo animal disease models that are predictive but do not, of course, like any model, completely replicate the human condition. Here, we have developed an addition to our armamentarium of useful models, an ex vivo human organotypic retinal culture model of DR by exposing human donor retinal explants to a combination of high glucose (HG) and pro-inflammatory cytokines, interleukin-1 beta (IL-1β) and tumour necrosis factor alpha (TNF-α). We hypothesized that in this model, connexin43 hemichannel block would protect against NLRP3 inflammasome complex assembly which would in turn decrease signs of inflammation characteristic of DR. To test our hypothesis, molecular changes in the inflammatory and inflammasome pathway were assessed using immunohistochemistry and a Luminex cytokine release assay. Our results showed that the human retinal explant DR model was associated with increased inflammation and activation of the inflammasome pathway, characteristic of the human condition. Furthermore, we showed that by blocking connexin43 hemichannels with the hemichannel modulator, tonabersat, we were able to prevent NLRP3 inflammasome complex assembly, Müller cell activation, as well as release of pro-inflammatory cytokines and VEGF. This further supports the possible use of connexin43 hemichannel blockers as potential new therapies for DR.

Connexins: Key Players in the Control of Vascular Plasticity and Function

Of the 21 members of the connexin family, 4 (Cx37, Cx40, Cx43, and Cx45) are expressed in the endothelium and/or smooth muscle of intact blood vessels to a variable and dynamically regulated degree. Full-length connexins oligomerize and form channel structures connecting the cytosol of adjacent cells (gap junctions) or the cytosol with the extracellular space (hemichannels). The different connexins vary mainly with regard to length and sequence of their cytosolic COOH-terminal tails. These COOH-terminal parts, which in the case of Cx43 are also translated as independent short isoforms, are involved in various cellular signaling cascades and regulate cell functions. This review focuses on channel-dependent and -independent effects of connexins in vascular cells. Channels play an essential role in coordinating and synchronizing endothelial and smooth muscle activity and in their interplay, in the control of vasomotor actions of blood vessels including endothelial cell reactivity to agonist stimulation, nitric oxide-dependent dilation, and endothelial-derived hyperpolarizing factor-type responses. Further channel-dependent and -independent roles of connexins in blood vessel function range from basic processes of vascular remodeling and angiogenesis to vascular permeability and interactions with leukocytes with the vessel wall. Together, these connexin functions constitute an often underestimated basis for the enormous plasticity of vascular morphology and function enabling the required dynamic adaptation of the vascular system to varying tissue demands.

Fast and Automated Hyperreflective Foci Segmentation Based on Image Enhancement and Improved 3D U-Net in SD-OCT Volumes with Diabetic Retinopathy

Purpose

To design a robust and automated hyperreflective foci (HRF) segmentation framework for spectral-domain optical coherence tomography (SD-OCT) volumes, especially volumes with low HRF-background contrast.

Methods

HRF in retinal SD-OCT volumes appear with low-contrast characteristics that results in the difficulty of HRF segmentation. Therefore to effectively segment the HRF we proposed a fully automated method for HRF segmentation in SD-OCT volumes with diabetic retinopathy (DR). First, we generated the enhanced SD-OCT images from the denoised SD-OCT images with an enhancement method. Then the enhanced images were cascaded with the denoised images as the two-channel input to the network against the low-contrast HRF. Finally, we replaced the standard convolution with slice-wise dilated convolution in the last layer of the encoder path of 3D U-Net to obtain long-range information.

Results

We evaluated our method using two-fold cross-validation on 33 SD-OCT volumes from 27 patients. The average dice similarity coefficient was 70.73%, which was higher than that of the existing methods with significant difference (P < 0.01).

Conclusions

Experimental results demonstrated that the proposed method is faster and achieves more reliable segmentation results than the current HRF segmentation algorithms. We expect that this method will contribute to clinical diagnosis and disease surveillance.

Translational Relevance

Our framework for the automated HRF segmentation of SD-OCT volumes may improve the clinical diagnosis of DR.

Connexin43 Hemichannel Targeting With TAT-Gap19 Alleviates Radiation-Induced Endothelial Cell Damage

BACKGROUND

Emerging evidence indicates an excess risk of late occurring cardiovascular diseases, especially atherosclerosis, after thoracic cancer radiotherapy. Ionizing radiation (IR) induces cellular effects which may induce endothelial cell dysfunction, an early marker for atherosclerosis. In addition, intercellular communication through channels composed of transmembrane connexin proteins (Cxs), i.e. Gap junctions (direct cell-cell coupling) and hemichannels (paracrine release/uptake pathway) can modulate radiation-induced responses and therefore the atherosclerotic process. However, the role of endothelial hemichannel in IR-induced atherosclerosis has never been described before.

MATERIALS AND METHODS

Telomerase-immortalized human Coronary Artery/Microvascular Endothelial cells (TICAE/TIME) were exposed to X-rays (0.1 and 5 Gy). Production of reactive oxygen species (ROS), DNA damage, cell death, inflammatory responses, and senescence were assessed with or without applying a Cx43 hemichannel blocker (TAT-Gap19).

RESULTS

We report here that IR induces an increase in oxidative stress, cell death, inflammatory responses (IL-8, IL-1β, VCAM-1, MCP-1, and Endothelin-1) and premature cellular senescence in TICAE and TIME cells. These effects are significantly reduced in the presence of the Cx43 hemichannel-targeting peptide TAT-Gap19.

CONCLUSION

Our findings suggest that endothelial Cx43 hemichannels contribute to various IR-induced processes, such as ROS, cell death, inflammation, and senescence, resulting in an increase in endothelial cell damage, which could be protected by blocking these hemichannels. Thus, targeting Cx43 hemichannels may potentially exert radioprotective effects.

Connexin Hemichannel Block Using Orally Delivered Tonabersat Improves Outcomes in Animal Models of Retinal Disease

Increased Connexin43 hemichannel opening is associated with inflammasome pathway activation and inflammation in a range of pathologies including ocular disorders, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR). In this study, the effect on retinal function and morphology of clinically safe doses of orally delivered tonabersat, a small molecule connexin hemichannel blocker, was investigated in the light-damaged retina animal model of dry AMD and in a spontaneous rat model of DR. Clinical parameters (fundus imaging, optical coherence tomography (OCT), and electroretinography) and inflammatory markers (immunohistochemistry for Iba-1 microglial marker, astrocyte marker glial fibrillary acidic protein, and Connexin43 protein expression) were assessed. Tonabersat treatment reduced inflammation in the retina in parallel with preservation of retinal photoreceptor function when assessed up to 3 months post light damage in the dry AMD model. In the DR model, clinical signs, including the presence of aneurysms confirmed using Evans blue dye perfusion, were reduced after daily tonabersat treatment for 2 weeks. Inflammation was also reduced and retinal electrical function restored. Tonabersat regulates assembly of the inflammasome (NLRP3) through Connexin43 hemichannel block, with the potential to reduce inflammation, restore vascular integrity and improve anatomical along with some functional outcomes in retinal disease.

Targeting connexin hemichannels to control the inflammasome: the correlation between connexin43 and NLRP3 expression in chronic eye disease

Introduction: Chronic inflammatory diseases, including retinal diseases that are a major cause of vision loss, are associated with activation of the nucleotide-binding domain and leucine-rich repeat containing (NLR) protein-3 (NLRP3) inflammasome pathway. In chronic disease, the inflammasome becomes self-perpetuating, indicating a common pathway in such diseases irrespective of underlying etiology, and implying a shared solution is feasible. Connexin43 hemichannels correlate directly with NLRP3 inflammasome complex assembly (shown here in models of retinal disease). Connexin43 hemichannel-mediated ATP release is proposed to be the principal activator signal for inflammasome complex assembly in primary signal-sensitized cells. Connexin hemichannel block on its own is sufficient to inhibit the inflammasome pathway. Areas covered: We introduce chronic retinal disease, discuss available preclinical models and examine findings from these models regarding the targeting of connexin43 hemichannels and its effects on the inflammasome. Expert opinion: In over 25 animal disease models, connexin hemichannel regulation has shown therapeutic benefit, and one oral connexin hemichannel blocker, tonabersat (Xiflam), is Phase II ready with safety evidence in over 1000 patients. Regulating the connexin hemichannel provides a means to move quickly into clinical trials designed to ameliorate the progression of devastating chronic diseases of the eye, but also elsewhere in the body.

Connexin43 hemichannels: A potential drug target for the treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a chronic vascular disease of the retina that causes vision loss in patients with type 1 and type 2 diabetes, and is associated with vascular dysfunction and occlusion, retinal oedema, haemorrhage and inadequate growth of new blood vessels. Current DR therapies primarily target downstream, later-stage vascular defects with a significant proportion of diabetic macular oedema patients being non-responders. Moreover, other evidence suggests that prolonged use of therapies targeting vascular endothelial growth factor (VEGF) might be associated with increased onset of geographic atrophy and retinal ganglion cell death. It is therefore highly desirable to prevent the onset of DR or arrest its progression at a stage preceding the appearance of more-advanced pathology by targeting upstream disease mechanisms. Connexin43 hemichannels play a part in the pathogenesis of chronic inflammatory diseases, including inflammasome pathway activation; and hemichannel block has been shown to alleviate vascular leak and inflammation. This review discusses the inflammatory changes occurring in DR as well as current therapies and their limitations. It then focuses on the role of connexin43 in DR, providing evidence for the utility of connexin43 hemichannel blockers as novel therapeutics for DR treatment.