Down-expression of the NLRP3 inflammasome delays the progression of diabetic retinopathy

Therapeutic potential of flavopiridol in diabetic retinopathy: Targeting DDX58

Diabetic retinopathy (DR), a common complication of diabetes, is characterized by inflammation and neovascularization, and is intricately regulated by the ubiquitin-proteasome system (UPS). Despite advancements, identifying ubiquitin-related genes and drugs specifically targeting DR remains a significant challenge. In this study, bioinformatics analyses and the Connectivity Map (CMAP) database were utilized to explore the therapeutic potential of genes and drugs for DR. Through these methodologies, flavopiridol was identified as a promising therapeutic candidate. To evaluate flavopiridol's therapeutic potential in DR, an in vitro model using Human Umbilical Vein Endothelial Cells (HUVECs) induced by high glucose (HG) conditions was established. Additionally, in vivo models using mice with streptozotocin (STZ)-induced DR and oxygen-induced retinopathy (OIR) were employed. The current study reveals that flavopiridol possesses robust anti-inflammatory and anti-neovascularization properties. To further elucidate the molecular mechanisms of flavopiridol, experimental validation and molecular docking techniques were employed. These efforts identified DDX58 as a predictive target for flavopiridol. Notably, our research demonstrated that flavopiridol modulates the DDX58/NLRP3 signaling pathway, thereby exerting its therapeutic effects in suppressing inflammation and neovascularization in DR. This study unveils groundbreaking therapeutic agents and innovative targets for DR, and establishes a progressive theoretical framework for the application of ubiquitin-related therapies in DR.

Tonabersat suppresses priming/activation of the NOD-like receptor protein-3 (NLRP3) inflammasome and decreases renal tubular epithelial-to-macrophage crosstalk in a model of diabetic kidney disease

BACKGROUND

Accompanied by activation of the NOD-like receptor protein 3 (NLRP3) inflammasome, aberrant connexin 43 (Cx43) hemichannel-mediated ATP release is situated upstream of inflammasome assembly and inflammation and contributes to multiple secondary complications of diabetes and associated cardiometabolic comorbidities. Evidence suggests there may be a link between Cx43 hemichannel activity and inflammation in the diabetic kidney. The consequences of blocking tubular Cx43 hemichannel-mediated ATP release in priming/activation of the NLRP3 inflammasome in a model of diabetic kidney disease (DKD) was investigated. We examined downstream markers of inflammation and the proinflammatory and chemoattractant role of the tubular secretome on macrophage recruitment and activation.

METHODS

Analysis of human transcriptomic data from the Nephroseq repository correlated gene expression to renal function in DKD. Primary human renal proximal tubule epithelial cells (RPTECs) and monocyte-derived macrophages (MDMs) were cultured in high glucose and inflammatory cytokines as a model of DKD to assess Cx43 hemichannel activity, NLRP3 inflammasome activation and epithelial-to-macrophage paracrine-mediated crosstalk. Tonabersat assessed a role for Cx43 hemichannels.

RESULTS

Transcriptomic analysis from renal biopsies of patients with DKD showed that increased Cx43 and NLRP3 expression correlated with declining glomerular filtration rate (GFR) and increased proteinuria. In vitro, Tonabersat blocked glucose/cytokine-dependant increases in Cx43 hemichannel-mediated ATP release and reduced expression of inflammatory markers and NLRP3 inflammasome activation in RPTECs. We observed a reciprocal relationship in which NLRP3 activity exacerbated increased Cx43 expression and hemichannel-mediated ATP release, events driven by nuclear factor kappa-B (NFκB)-mediated priming and Cx43 hemichannel opening, changes blocked by Tonabersat. Conditioned media (CM) from RPTECs treated with high glucose/cytokines increased expression of inflammatory markers in MDMs, an effect reduced when macrophages were pre-treated with Tonabersat. Co-culture using conditioned media from Tonabersat-treated RPTECs dampened macrophage inflammatory marker expression and reduced macrophage migration.

CONCLUSION

Using a model of DKD, we report for the first time that high glucose and inflammatory cytokines trigger aberrant Cx43 hemichannel activity, events that instigate NLRP3-induced inflammation in RPTECs and epithelial-to-macrophage crosstalk. Recapitulating observations previously reported in diabetic retinopathy, these data suggest that Cx43 hemichannel blockers (i.e., Tonabersat) may dampen multi-system damage observed in secondary complications of diabetes.

Role of NLRP3 Inflammasomes in Monocyte and Microglial Recruitments in Choroidal Neovascularization

Although the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice and immunostaining techniques to confirm localization of NLRP3 inflammasomes in the laser-induced CNV (LCNV) lesions. Confocal microscopy was used to image and quantify LCNV volumes. MCC950 was used as NLRP3 inhibitor. ELISA and quantitative RT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that red fluorescent protein (RFP)-positive monocyte-derived macrophages and GFP-positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP-positive macrophages, Cx3cr1GFP-positive microglia, and other cells, resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice showed significantly increased lesion size compared with age-matched controls. Inhibition of NLRP3 resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

NLRP3 Inflammasome Priming in the Retina of Diabetic Mice Requires REDD1-Dependent Activation of GSK3β

Purpose

Inflammasome activation has been implicated in the development of retinal complications caused by diabetes. This study was designed to identify signaling events that promote retinal NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation in response to diabetes.

Methods

Diabetes was induced in mice by streptozotocin administration. Retinas were examined after 16 weeks of diabetes. Human MIO-M1 Müller cells were exposed to hyperglycemic culture conditions. Genetic and pharmacological interventions were used to interrogate signaling pathways. Visual function was assessed in mice using a virtual optomotor system.

Results

In the retina of diabetic mice and in Müller cell cultures, NLRP3 and interleukin-1β (IL-1β) were increased in response to hyperglycemic conditions and the stress response protein Regulated in Development and DNA damage 1 (REDD1) was required for the effect. REDD1 deletion prevented caspase-1 activation in Müller cells exposed to hyperglycemic conditions and reduced IL-1β release. REDD1 promoted nuclear factor κB signaling in cells exposed to hyperglycemic conditions, which was necessary for an increase in NLRP3. Expression of a constitutively active GSK3β variant restored NLRP3 expression in REDD1-deficient cells exposed to hyperglycemic conditions. GSK3 activity was necessary for increased NLRP3 expression in the retina of diabetic mice and in cells exposed to hyperglycemic conditions. Müller glia-specific REDD1 deletion prevented increased retinal NLRP3 levels and deficits in contrast sensitivity in diabetic mice.

Conclusions

The data support a role for REDD1-dependent activation of GSK3β in NLRP3 inflammasome transcriptional priming and in the production of IL-1β by Müller glia in response to diabetes.

MCC950 Ameliorates Diabetic Muscle Atrophy in Mice by Inhibition of Pyroptosis and Its Synergistic Effect with Aerobic Exercise

Diabetic muscle atrophy is an inflammation-related complication of type-2 diabetes mellitus (T2DM). Even though regular exercise prevents further deterioration of atrophic status, there is no effective mediator available for treatment and the underlying cellular mechanisms are less explored. In this study, we investigated the therapeutic potential of MCC950, a specific, small-molecule inhibitor of NLRP3, to treat pyroptosis and diabetic muscle atrophy in mice. Furthermore, we used MCC950 to intervene in the protective effects of aerobic exercise against muscle atrophy in diabetic mice. Blood and gastrocnemius muscle (GAS) samples were collected after 12 weeks of intervention and the atrophic state was assessed. We initially corroborated a diabetic muscle atrophy phenotype in db/db mice (D) by comparison with control m/m mice (W) by examining parameters such as fasting blood glucose (D vs. W: 24.47 ± 0.45 mmol L-1 vs. 4.26 ± 0.6 mmol L-1, p < 0.05), grip strength (D vs. W: 166.87 ± 15.19 g vs. 191.76 ± 14.13 g, p < 0.05), exercise time (D vs. W: 1082.38 ± 104.67 s vs. 1716 ± 168.55 s, p < 0.05) and exercise speed to exhaustion (D vs. W: 24.25 ± 2.12 m min-1 vs. 34.75 ± 2.66 m min-1, p < 0.05), GAS wet weight (D vs. W: 0.07 ± 0.01 g vs. 0.13 ± 0.01 g, p < 0.05), the ratio of GAS wet weight to body weight (D vs. W: 0.18 ± 0.01% vs. 0.54 ± 0.02%, p < 0.05), and muscle fiber cross-sectional area (FCSA) (D vs. W: 1875 ± 368.19 µm2 vs. 2747.83 ± 406.44 µm2, p < 0.05). We found that both MCC950 (10 mg kg-1) treatment and exercise improved the atrophic parameters that had deteriorated in the db/db mice, inhibited serum inflammatory markers and significantly attenuated pyroptosis in atrophic GAS. In addition, a combined MCC950 treatment with exercise (DEI) exhibited a further improvement in glucose uptake capacity and muscle performance. This combined treatment also improved the FCSA of GAS muscle indicated by Laminin immunofluorescence compared to the group with the inhibitor treatment alone (DI) (DEI vs. DI: 2597 ± 310.97 vs. 1974.67 ± 326.15 µm2, p < 0.05) or exercise only (DE) (DEI vs. DE: 2597 ± 310.97 vs. 2006.33 ± 263.468 µm2, p < 0.05). Intriguingly, the combination of MCC950 treatment and exercise significantly reduced NLRP3-mediated inflammatory factors such as cleaved-Caspase-1, GSDMD-N and prevented apoptosis and pyroptosis in atrophic GAS. These findings for the first time demonstrate that targeting NLRP3-mediated pyroptosis with MCC950 improves diabetic muscle homeostasis and muscle function. We also report that inhibiting pyroptosis by MCC950 can enhance the beneficial effects of aerobic exercise on diabetic muscle atrophy. Since T2DM and muscle atrophy are age-related diseases, the young mice used in the current study do not seem to fully reflect the characteristics of diabetic muscle atrophy. Considering the fragile nature of db/db mice and for the complete implementation of the exercise intervention, we used relatively young db/db mice and the atrophic state in the mice was thoroughly confirmed. Taken together, the current study comprehensively investigated the therapeutic effect of NLRP3-mediated pyroptosis inhibited by MCC950 on diabetic muscle mass, strength and exercise performance, as well as the synergistic effects of MCC950 and exercise intervention, therefore providing a novel strategy for the treatment of the disease.

Role of pyroptosis in diabetic cardiomyopathy: an updated review

Diabetic cardiomyopathy (DCM), one of the common complications of diabetes, presents as a specific cardiomyopathy with anomalies in the structure and function of the heart. With the increasing prevalence of diabetes, DCM has a high morbidity and mortality worldwide. Recent studies have found that pyroptosis, as a programmed cell death accompanied by an inflammatory response, exacerbates the growth and genesis of DCM. These studies provide a theoretical basis for exploring the potential treatment of DCM. Therefore, this review aims to summarise the possible mechanisms by which pyroptosis promotes the development of DCM as well as the relevant studies targeting pyroptosis for the possible treatment of DCM, focusing on the molecular mechanisms of NLRP3 inflammasome-mediated pyroptosis, different cellular pyroptosis pathways associated with DCM, the effects of pyroptosis occurring in different cells on DCM, and the relevant drugs targeting NLRP3 inflammasome/pyroptosis for the treatment of DCM. This review might provide a fresh perspective and foundation for the development of therapeutic agents for DCM.

Intraperitoneal Injection of MCC950 Inhibits the Progression of Myopia in Form-Deprivation Myopic Mice

Myopia, one of the most prevalent ocular diseases worldwide, is projected to affect nearly half of the global population by 2050. The main cause of myopia in most patients is axial myopia, which primarily occurs due to the elongation of the eyeball, driven by changes in the extracellular matrix (ECM) of scleral cells. Previous studies have shown that NLRP3, an important inflammatory mediator, plays a critical role in regulating the expression of MMP-2 in the sclera. This, in turn, leads to a decrease in the expression of Collagen-1, a major component of the scleral ECM, triggering the remodeling of the scleral ECM. This study aimed to investigate the effect of MCC950, an inhibitor of NLRP3, on the progression of myopia using a mouse form-deprivation myopia (FDM) model. The FDM mouse model was constructed by subjecting three-week-old C57BL/6J mice to form-deprivation. The mice were divided into experimental (n = 10/group; FDM2M, FDM4M, FDM2W, and FDM4W) and control groups (n = 5/group). The experimental groups were further categorized based on the duration of form deprivation (2 and 4 weeks, labeled as 2 and 4, respectively) and the type of injection received (MCC950 or saline, labeled as M and W, respectively). MCC950 was injected at a concentration of 50 mg/mL, with a dose of 10 mg per kilogram of body weight. Meanwhile, the saline group received the same volume of saline. Refraction and axial length measurements were performed for each eye. The expression levels of NLRP3, caspase-1, IL-1β, IL-18, MMP-2, and Collagen-1 in the sclera were assessed using immunohistochemistry and Western blotting. The intraperitoneal injection of MCC950 did not significantly affect refraction or axial length in normal mice (p > 0.05). However, in FDM mice, MCC950 attenuated the elongation of the axial length and resulted in a smaller shift towards myopia compared to the saline group (FDM4M vs. FDM4W, p = 0.03 and p < 0.05, respectively). MCC950 decreased MMP-2 expression (p < 0.05) but increased Collagen-1 expression (p < 0.05) in the experimental eyes when compared to the saline group. Within the MCC950 group, the expression of MMP-2 was increased in the experimental eyes at 4 weeks (p < 0.05), while that of Collagen-1 was decreased (p < 0.05), which is consistent with changes in refractive error. Immunohistochemical analysis yielded similar results (p < 0.05). MCC950 also reduced the expression levels of NLRP3 (p = 0.03), caspase-1 (p < 0.05), IL-1β (p < 0.05), and IL-18 (p < 0.05) in the experimental eyes compared to the saline group. Within the MCC950 group, the expression levels of NLRP3 and caspase-1 were comparable between the experimental and control eyes (p > 0.05), whereas IL-18 expression was higher in experimental eyes (p < 0.05). IL-1β expression was higher in the experimental eyes only at week 4 (p < 0.05). The intraperitoneal injection of MCC950 can inhibit the progression of myopia in FDM mice, possibly by regulating collagen remodeling in the sclera through the NLRP3-MMP-2 signaling pathway. Therefore, MCC950 holds promise as a potential therapeutic agent for controlling the progression of myopia.

Genipin relieves diabetic retinopathy by down-regulation of advanced glycation end products via the mitochondrial metabolism related signaling pathway

BACKGROUND

Glycation is an important step in aging and oxidative stress, which can lead to endothelial dysfunction and cause severe damage to the eyes or kidneys of diabetics. Inhibition of the formation of advanced glycation end products (AGEs) and their cell toxicity can be a useful therapeutic strategy in the prevention of diabetic retinopathy (DR). Gardenia jasminoides Ellis (GJE) fruit is a selective inhibitor of AGEs. Genipin is an active compound of GJE fruit, which can be employed to treat diabetes.

AIM

To confirm the effect of genipin, a vital component of GJE fruit, in preventing human retinal microvascular endothelial cells (hRMECs) from AGEs damage in DR, to investigate the effect of genipin in the down-regulation of AGEs expression, and to explore the role of the CHGA/UCP2/glucose transporter 1 (GLUT1) signal pathway in this process.

METHODS

In vitro, cell viability was tested to determine the effects of different doses of glucose and genipin in hRMECs. Cell Counting Kit-8 (CCK-8), colony formation assay, flow cytometry, immunofluorescence, wound healing assay, transwell assay, and tube-forming assay were used to detect the effect of genipin on hRMECs cultured in high glucose conditions. In vivo, streptozotocin (STZ) induced mice were used, and genipin was administered by intraocular injection (IOI). To explore the effect and mechanism of genipin in diabetic-induced retinal dysfunction, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino]-2-deoxy-d-glucose (2-NBDG) assays were performed to explore energy metabolism and oxidative stress damage in high glucose-induced hRMECs and STZ mouse retinas. Immunofluorescence and Western blot were used to investigate the expression of inflammatory cytokines [vascular endothelial growth factor (VEGF), SCG3, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-18, and nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing 3 (NLRP3)]. The protein expression of the receptor of AGEs (RAGE) and the mitochondria-related signal molecules CHGA, GLUT1, and UCP2 in high glucose-induced hRMECs and STZ mouse retinas were measured and compared with the genipin-treated group.

RESULTS

The results of CCK-8 and colony formation assay showed that genipin promoted cell viability in high glucose (30 mmol/L D-Glucose)-induced hRMECs, especially at a 0.4 μmol/L dose for 7 d. Flow cytometry results showed that high glucose can increase apoptosis rate by 30%, and genipin alleviated cell apoptosis in AGEs-induced hRMECs. A high glucose environment promoted ATP, ROS, MMP, and 2-NBDG levels, while genipin inhibited these phenotypic abnormalities in AGEs-induced hRMECs. Furthermore, genipin remarkably reduced the levels of the pro-inflammatory cytokines TNF-α, IL-1β, IL-18, and NLRP3 and impeded the expression of VEGF and SCG3 in AGEs-damaged hRMECs. These results showed that genipin can reverse high glucose induced damage with regard to cell proliferation and apoptosis in vitro, while reducing energy metabolism, oxidative stress, and inflammatory injury caused by high glucose. In addition, ROS levels and glucose uptake levels were higher in the retina from the untreated eye than in the genipin-treated eye of STZ mice. The expression of inflammatory cytokines and pathway protein in the untreated eye compared with the genipin-treated eye was significantly increased, as measured by Western blot. These results showed that IOI of genipin reduced the expression of CHGA, UCP2, and GLUT1, maintained the retinal structure, and decreased ROS, glucose uptake, and inflammation levels in vivo. In addition, we found that SCG3 expression might have a higher sensitivity in DR than VEGF as a diagnostic marker at the protein level.

CONCLUSION

Our study suggested that genipin ameliorates AGEs-induced hRMECs proliferation, apoptosis, energy metabolism, oxidative stress, and inflammatory injury, partially via the CHGA/UCP2/GLUT1 pathway. Control of advanced glycation by IOI of genipin may represent a strategy to prevent severe retinopathy and vision loss.

Role of NLRP3 inflammasomes in monocyte and microglial recruitments in choroidal neovascularization

Though the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice to characterize migration of Ccr2RFP positive monocytes and Cx3cr1GFP positive microglial cells into CNV lesions after laser-induced rupture of Bruch's membrane. MCC950 was used as NLRP3 inhibitor. Immunostaining was used to confirm localization of NLRP3 inflammasomes in the LCNV lesions. Confocal microscopy was used to image and quantify LCNV volumes. ELISA and qRT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that RFP positive monocyte-derived macrophages and GFP positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP positive macrophages, Cx3cr1GFP positive microglia, and other cells resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice, showed significantly increased lesion size compared to age-matched controls. Inhibition of NLRP3, resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

Pathological role of inflammation in ocular disease progress and its targeting by mesenchymal stem cells (MSCs) and their exosome; current status and prospect

Because of their unique capacity for differentiation to a diversity of cell lineages and immunosuppressive properties, mesenchymal stem cells (MSC) are being looked at as a potential new treatment option in ophthalmology. The MSCs derived from all tissue sources possess immunomodulatory attributes through cell-to-cell contact and releasing a myriad of immunomodulatory factors (IL-10, TGF-β, growth-related oncogene (GRO), indoleamine 2,3 dioxygenase (IDO), nitric oxide (NO), interleukin 1 receptor antagonist (IL-1Ra), prostaglandin E2 (PGE2)). Such mediators, in turn, alter both the phenotype and action of all immune cells that serve a pathogenic role in the progression of inflammation in eye diseases. Exosomes from MSCs, as natural nano-particles, contain the majority of the bioactive components of parental MSCs and can easily by-pass all biological barriers to reach the target epithelial and immune cells in the eye without interfering with nearby parenchymal cells, thus having no serious side effects. We outlined the most recent research on the molecular mechanisms underlying the therapeutic benefits of MSC and MSC-exosome in the treatment of inflammatory eye diseases in the current article.

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.

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.

Spotlight on pyroptosis: role in pathogenesis and therapeutic potential of ocular diseases

Pyroptosis is a programmed cell death characterized by swift plasma membrane disruption and subsequent release of cellular contents and pro-inflammatory mediators (cytokines), including IL‐1β and IL‐18. It differs from other types of programmed cell death such as apoptosis, autophagy, necroptosis, ferroptosis, and NETosis in terms of its morphology and mechanism. As a recently discovered form of cell death, pyroptosis has been demonstrated to be involved in the progression of multiple diseases. Recent studies have also suggested that pyroptosis is linked to various ocular diseases. In this review, we systematically summarized and discussed recent scientific discoveries of the involvement of pyroptosis in common ocular diseases, including diabetic retinopathy, age-related macular degeneration, AIDS-related human cytomegalovirus retinitis, glaucoma, dry eye disease, keratitis, uveitis, and cataract. We also organized new and emerging evidence suggesting that pyroptosis signaling pathways may be potential therapeutic targets in ocular diseases, hoping to provide a summary of overall intervention strategies and relevant multi-dimensional evaluations for various ocular diseases, as well as offer valuable ideas for further research and development from the perspective of pyroptosis.

The Role of the NLRP3 Inflammasome in Mediating Glomerular and Tubular Injury in Diabetic Nephropathy

The NOD-like receptor protein 3 (NLRP3) inflammasome is a multi-protein signalling complex integral to the chronic inflammatory response, activated in response to sterile and non-sterile cellular damage. The assembly and activation of the NLRP3 inflammasome comprise a two-step process involving nuclear factor kappa B (NFkB)-mediated priming, followed by canonical, non-canonical or alternative signalling pathways. These result in the maturation and release of inflammatory cytokines interleukin 1 beta (IL1ß) and interleukin-18 (IL18), which are associated with chronic inflammatory conditions including diabetic kidney disease. Diabetic nephropathy is a condition affecting ∼40% of people with diabetes, the key underlying pathology of which is tubulointerstitial inflammation and fibrosis. There is growing evidence to suggest the involvement of the NLRP3 inflammasome in this chronic inflammation. Early deterioration of kidney function begins in the glomerulus, with tubular inflammation dictating the progression of late-stage disease. Priming and activation of the NLRP3 inflammasome have been linked to several clinical markers of nephropathy including proteinuria and albuminuria, in addition to morphological changes including mesangial expansion. Treatment options for diabetic nephropathy are limited, and research that examines the impact of directly targeting the NLRP3 inflammasome, or associated downstream components are beginning to gain favour, with several agents currently in clinical trials. This review will explore a role for NLRP3 inflammasome activation and signalling in mediating inflammation in diabetic nephropathy, specifically in the glomerulus and proximal tubule, before briefly describing the current position of therapeutic research in this field.

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.

PKA and Epac1 Reduce Nek7 to Block the NLRP3 Inflammasome Proteins in the Retinal Vasculature

Purpose

To determine whether protein kinase a (PKA) and exchange protein for cAMP 1 (Epac1) inhibit NIMA-related kinase 7 (Nek7) to block the NOD-like receptor family pyrin domain-containing family member 3 (NLRP3) signaling pathway.

Methods

Retinal endothelial cells (RECs) were grown in normal (5 mM) or high (25 mM) glucose. Some cells were treated with a Nek7 cDNA plasmid, Nek7 siRNA; an Epac1 agonist, forskolin; a PKA agonist; or an empty vector. Epac1 floxed and Cdh5-cre Epac1 mice and Nek7 floxed and Cdh5-cre Nek7 mice were also used. Western blot analyses were done on cell culture or whole retinal lysates for NLRP3, cleaved caspase 1, interleukin-1-beta (IL-1β). A PKA activity assay was also done.

Results

Nek7 cDNA increased NLRP3 signaling proteins, but Nek7 siRNA inhibited high-glucose induction of these proteins in retinal endothelial cells. Epac1 and forskolin both reduced Nek7 and NLRP3 pathway proteins, even when given in combination with Nek7 cDNA. Elimination of Nek7 in endothelial cells reduced NLRP3 signaling proteins in whole retinal lysates from mice.

Conclusions

Nek7 regulated NLRP3 inflammasome protein levels both in vitro and in vivo. Both Epac1 and PKA lie upstream of Nek7 and NLRP3 and can overcome excessive Nek7 levels. These studies establish that cAMP proteins can inhibit Nek7 and block activation of the NLRP3 inflammasome proteins.