Inflammatory resolution and vascular barrier restoration after retinal ischemia reperfusion injury

Preserving blood-retinal barrier integrity: a path to retinal ganglion cell protection in glaucoma and traumatic optic neuropathy

Retinal ganglion cells (RGCs) are the visual gateway of the brain, with their axons converging to form the optic nerve, making them the most vulnerable target in diseases such as glaucoma and traumatic optic neuropathy (TON). In both diseases, the disruption of the blood-retinal barrier(BRB) is considered an important mechanism that accelerates RGC degeneration and hinders axon regeneration. The BRB consists of the inner blood-retinal barrier (iBRB) and the outer blood-retinal barrier (oBRB), which are maintained by endothelial cells(ECs), pericytes(PCs), and retinal pigment epithelial (RPE), respectively. Their functions include regulating nutrient exchange, oxidative stress, and the immune microenvironment. However, in glaucoma and TON, the structural and functional integrity of the BRB is severely damaged due to mechanical stress, inflammatory reactions, and metabolic disorders. Emerging evidence highlights that BRB disruption leads to heightened vascular permeability, immune cell infiltration, and sustained chronic inflammation, creating a hostile microenvironment for RGC survival. Furthermore, the dynamic interplay and imbalance among ECs, PCs, and glial cells within the neurovascular unit (NVU) are pivotal drivers of BRB destruction, exacerbating RGC apoptosis and limiting optic nerve regeneration. The intricate molecular and cellular mechanisms underlying these processes underscore the BRB's critical role in glaucoma and TON pathophysiology while offering a compelling foundation for therapeutic strategies targeting BRB repair and stabilization. This review provides crucial insights and lays a robust groundwork for advancing research on neural regeneration and innovative optic nerve protective strategies.

Genome-wide KAS-Seq mapping of leukocytes in ischemia-reperfusion model reveals IL7R as a potential therapeutic target for ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is one of the leading causes of mortality and disability worldwide. Owing to its complex pathogenesis, there is still a lack of effective therapeutic targets in clinical practice, and exploring the mechanism and targets of IRI is still a major clinical challenge. This study aimed to explore the genetic alterations in leukocytes in peripheral blood after ischemia-reperfusion, aiming to discover new biomarkers and potential therapeutic targets. KAS-Seq (Kethoxal-assisted single-strand DNA sequencing) was used to obtain gene expression profiles of circulating leukocytes in a porcine ischemia-reperfusion model at 24, 48, and 72 h post-ischemia‒reperfusion. This method integrated genes that exhibited regular changes over time. In this study, we thoroughly analyzed the dynamic changes in gene expression post-IRI, revealing significant enrichment in key signaling pathways that regulate immune responses and T-cell activation over time. Our identification of the interleukin-7 receptor (IL7R) was particularly striking, as it plays a crucial molecular role in IRI. Additionally, using database mining technology, we confirmed the close relationship between IL7R and IRI, explored the interaction between interferon-γ (IFNG) and IL7R in T-cell activation, and clarified their joint influence on ischemia-reperfusion injury. Using KAS-Seq analysis of leukocytes from peripheral blood, we successfully delineated the temporal patterns of gene expression and changes in signal transduction pathways in porcine models of ischemia-reperfusion. Subsequent in-depth analysis identified IL7R as a potential novel therapeutic target for IRI. The pivotal role of this gene in modulating immune responses provides innovative avenues for the development of IRI treatments.

LCN2 deficiency mitigates the neuroinflammatory damage following acute glaucoma

Rationale: Acute high intraocular pressure (IOP) induces retinal ischemia/reperfusion (RI/R) that further initiates neuroinflammatory responses. This event can cause retinal tissue damage and neuronal death, ultimately resulting in irreversible blindness worldwide that lacks effective therapies, validated treatment targets and underlying mechanisms. We sought to explore the potential mechanisms on the causal link between the neuroinflammatory response and neurodegeneration following acute high IOP. Methods: A rat model of RI/R induced by acute high IOP was used to investigate the spatiotemporal profiles of blood-retinal barrier (BRB) disruption, peripheral immune cell infiltration, and innate immune cell response following acute glaucomatous injury. RNA sequencing and in vivo transfection with adeno-associated virus (AAV) were used to explore the pathogenic mechanisms of acute high IOP-induced neuroinflammation. Results: Disruption of the inner BRB and infiltration of macrophages and lymphocytes occurred during the early stage after acute high IOP. These events were accompanied by an innate immune response. RNA sequencing revealed that Lipocalin-2 (Lcn2) was one of the most significantly up-regulated inflammation-related genes. Lcn2 knockdown ameliorated inner BRB disruption, peripheral immune cell infiltration, and innate immune cell response, resulting in neuroprotective effects. Furthermore, we found that acute glaucomatous injury triggers high expression of LCN2 in the peripheral serum, which is strongly associated with the severity of the neuroinflammatory response in the retina. Conclusions: A "neuroinflammatory cascade" characterized by breakdown of inner BRB, peripheral immune cell infiltration, and innate immune cell response occurs during the initial stage following glaucomatous injury. We also identified a novel mechanism for LCN2 in acute high IOP-induced neuroinflammation. LCN2 has the potential to serve as a candidate biomarker for predicting the severity of the neuroinflammatory response following acute glaucoma, which may provide new evidence to retinal repair strategies for better visual function recovery at intervention time points and new targets.

Astragalus polysaccharide attenuates retinal ischemia reperfusion-induced microglial activation through sortilin-related vacuolar protein sorting 10 domain containing receptor 2/laminin subunit alpha 1 upregulation

Objective

Microglial activation is a hallmark of pathogenic retinal conditions such as retinal ischemia-reperfusion (RIR). While sortilin-related vacuolar protein sorting 10 domain containing receptor 2 (Sorcs2) and laminin subunit alpha 1 (Lama1) have been implicated in neuroinflammatory processes, their roles in regulating microglial activation in RIR are not reported. The current work studied the potential of Sorcs2 and Lama1 as negative regulators of microglial activation in RIR and assessed the therapeutic potential of Astragalus polysaccharide (AP).

Material and Methods

Transcriptome profiling was conducted in retinal specimens of RIR group 72 h after RIR induction. Oxygen-glucose deprivation/reperfusion (OGD/R) in rat microglial cells was employed as the cellular induction model of RIR. The functional role of Sorcs2 and Lama1 in dictating microglial activation was investigated in vitro and in vivo using lentivirus-based gene expression. Further, the potential effect of AP on RIR-mediated microglial activation was investigated.

Results

Sorcs2 and Lama1 were identified as two downregulated genes in retinal samples following RIR. OGD/R induction triggered pro-inflammatory microglial activation and induced the downregulation of Sorcs2 and Lama1. Sorcs2 or Lama1 overexpression hindered OGD/R-induced microglial activation in vitro and attenuated inflammatory expansion of microglia cells in RIR-induced rat retinal samples. AP treatment was able to neutralize the oxidative stress, promote the expression of Sorcs2 and Lama1, and suppress microglial activation.

Conclusion

Our findings pinpoint Sorcs2 and Lama1 as negative regulators of microglial activation in RIR. AP could be employed as an antioxidant to attenuate microglial activation and ameliorate the inflammatory damages in RIR.

TGF-β1-induced apoptosis in retinal endothelial cells is implicated in retinal vein occlusion

Retinal vein occlusion (RVO) is a serious vascular condition that impairs vision due to retinal endothelial cell injury and apoptosis. This study aimed to identify key molecular pathways and therapeutic targets involved in RVO pathogenesis. Transcriptomic analysis of the retinal tissues from a mouse RVO model was performed to identify differentially expressed genes and co-expression modules associated with RVO. Protein-protein interaction network analysis pinpointed putative hub genes. In vitro experiments using human retinal microvascular endothelial cells (HRMECs) validated the involvement of identified genes/pathways in apoptosis induced by oxygen-glucose deprivation/reperfusion (OGD/R) and UV exposure. Gene expression was assessed by RT-qPCR, while protein levels and phosphorylation were measured by ELISA and Western blotting. Apoptosis was evaluated using flow cytometry, and reactive oxygen species (ROS) were quantified using a fluorescence-based assay. A total of 392 genes were identified as putatively involved in RVO-associated apoptosis, enriched in MAPK, TGF-β and other signaling pathways. Among top hub genes, TGF-β1 emerged as a central regulator whose expression and signaling (pSmad2/3) increased after OGD/R induction or UV exposure in HRMECs. TGF-β1-induced HRMEC apoptosis was mediated by p38/JNK activation. Similar effects were observed for OGD/R and UV triggering TGF-β1-dependent p38/JNK signaling and apoptosis. Pharmacological inhibition of TGF-β signaling attenuated the apoptotic and oxidative stress responses induced by OGD/R and UV exposure. This study elucidates TGF-β1 as a crucial mediator of retinal endothelial injury through p38/JNK-induced apoptosis, suggesting TGF-β1 pathway inhibition as a potential therapeutic strategy for RVO.

Diabetes Renders Photoreceptors Susceptible to Retinal Ischemia-Reperfusion Injury

Purpose

Studies have suggested that photoreceptors (PR) are altered by diabetes, contributing to diabetic retinopathy (DR) pathology. Here, we explored the effect of diabetes on retinal ischemic injury.

Methods

Retinal ischemia-reperfusion (IR) injury was caused by elevation of intraocular pressure in 10-week-old BKS db/db type 2 diabetes mellitus (T2DM) mice or C57BL/6J mice at 4 or 12 weeks after streptozotocin (STZ)-induced type 1 diabetes mellitus (T1DM), and respective nondiabetic controls. Retinal neurodegeneration was evaluated by retinal layer thinning, TUNEL staining, and neuron loss. Vascular permeability was evaluated as retinal accumulation of circulating fluorescent albumin. The effects of pretreatment with a sodium-glucose co-transporter (SGLT1/2) inhibitor, phlorizin, were examined.

Results

Nondiabetic control mice exhibited no significant outer retinal layer thinning or PR loss after IR injury. In contrast, db/db mice exhibited significant outer retina thinning (49%, P < 0.0001), loss of PR nuclei (45%, P < 0.05) and inner segment (IS) length decline (45%, P < 0.0001). STZ-induced diabetic mice at 4 weeks showed progressive thinning of the outer retina (55%, by 14 days, P < 0.0001) and 4.3-fold greater number of TUNEL+ cells in the outer nuclear layer (ONL) than injured retinas of control mice (P < 0.0001). After 12 weeks of diabetes, the retinas exhibited similar outer layer thinning and PR loss after IR. Diabetes also delayed restoration of the blood-retinal barrier after IR injury. Phlorizin reduced outer retinal layer thinning from 49% to 3% (P < 0.0001).

Conclusions

Diabetes caused PR to become highly susceptible to IR injury. The ability of phlorizin pretreatment to block outer retinal thinning after IR suggests that the effects of diabetes on PR are readily reversible.

Neuroprotective effect of ciclopirox olamine in retinal ischemia/reperfusion injury

Retinal ischemia-reperfusion (IR) injury is a basic pathological procedure in clinic and associated with various ischemic retinal diseases, including glaucoma, diabetic retinopathy, retinal vascular occlusion, etc. The purpose of this work is to investigate the effect of ciclopirox olamine (CPX) on retinal IR injury and further explore the underlying mechanism. In vitro assay exhibited that CPX exhibited significant neuroprotection against oxygen glucose deprivation (OGD) and oxidative stress-induced injuries in 661W photoreceptor cells. OGD injury showed a proinflammatory phenotype characterized by significantly increased production of cytokines (IL-6, IL-23 and TNF-α), while CPX significantly inhibited their secretion. In addition, the in vivo experiment demonstrated that CPX significantly preserved the normal thickness of the retina. Therefore, we suggest that CPX is identified in our research as a prospective therapeutic agent for retinal IR injury.

Transcriptional responses in a mouse model of silicone wire embolization induced acute retinal artery ischemia and reperfusion

Acute retinal ischemia and ischemia-reperfusion injury are the primary causes of retinal neural cell death and vision loss in retinal artery occlusion (RAO). The absence of an accurate mouse model for simulating the retinal ischemic process has hindered progress in developing neuroprotective agents for RAO. We developed a unilateral pterygopalatine ophthalmic artery occlusion (UPOAO) mouse model using silicone wire embolization combined with carotid artery ligation. The survival of retinal ganglion cells and visual function were evaluated to determine the duration of ischemia. Immunofluorescence staining, optical coherence tomography, and haematoxylin and eosin staining were utilized to assess changes in major neural cell classes and retinal structure degeneration at two reperfusion durations. Transcriptomics was employed to investigate alterations in the pathological process of UPOAO following ischemia and reperfusion, highlighting transcriptomic differences between UPOAO and other retinal ischemia-reperfusion models. The UPOAO model successfully replicated the acute interruption of retinal blood supply observed in RAO. 60 min of Ischemia led to significant loss of major retinal neural cells and visual function impairment. Notable thinning of the inner retinal layer, especially the ganglion cell layer, was evident post-UPOAO. Temporal transcriptome analysis revealed various pathophysiological processes related to immune cell migration, oxidative stress, and immune inflammation during the non-reperfusion and reperfusion periods. A pronounced increase in microglia within the retina and peripheral leukocytes accessing the retina was observed during reperfusion periods. Comparison of differentially expressed genes (DEGs) between the UPOAO and high intraocular pressure models revealed specific enrichments in lipid and steroid metabolism-related genes in the UPOAO model. The UPOAO model emerges as a novel tool for screening pathogenic genes and promoting further therapeutic research in RAO.

Heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation

AIMS/HYPOTHESIS

Diabetic retinopathy is characterised by neuroinflammation that drives neuronal and vascular degenerative pathology, which in many individuals can lead to retinal ischaemia and neovascularisation. Infiltrating macrophages and activated retina-resident microglia have been implicated in the progression of diabetic retinopathy, although the distinct roles of these immune cells remain ill-defined. Our aim was to clarify the distinct roles of macrophages/microglia in the pathogenesis of proliferative ischaemic retinopathies.

METHODS

Murine oxygen-induced retinopathy is commonly used as a model of ischaemia-induced proliferative diabetic retinopathy (PDR). We evaluated the phenotype macrophages/microglia by immunostaining, quantitative real-time RT-PCR (qRT-PCR), flow cytometry and scRNA-seq analysis. In clinical imaging studies of diabetic retinopathy, we used optical coherence tomography (OCT) and OCT angiography.

RESULTS

Immunostaining, qRT-PCR and flow cytometry showed expression levels of M1-like macrophages/microglia markers (CD80, CD68 and nitric oxide synthase 2) and M2-like macrophages/microglia markers (CD206, CD163 and macrophage scavenger receptor 1) were upregulated in areas of retinal ischaemia and around neo-vessels, respectively. scRNA-seq analysis of the ischaemic retina revealed distinct ischaemia-related clusters of macrophages/microglia that express M1 markers as well as C-C chemokine receptor 2. Inhibition of Rho-kinase (ROCK) suppressed CCL2 expression and reduced CCR2-positive M1-like macrophages/microglia in areas of ischaemia. Furthermore, the area of retinal ischaemia was reduced by suppressing blood macrophage infiltration not only by ROCK inhibitor and monocyte chemoattractant protein-1 antibody but also by GdCl3. Clinical imaging studies of diabetic retinopathy using OCT indicated potential involvement of macrophages/microglia represented by hyperreflective foci in areas of reduced perfusion.

CONCLUSIONS/INTERPRETATION

These results collectively indicated that heterotypic macrophages/microglia differentially contribute to retinal ischaemia and neovascularisation in retinal vascular diseases including diabetic retinopathy. This adds important new information that could provide a basis for a more targeted, cell-specific therapeutic approach to prevent progression to sight-threatening PDR.

Roflumilast Attenuates Microglial Senescence and Retinal Inflammatory Neurodegeneration Post Retinal Ischemia Reperfusion Injury Through Inhibiting NLRP3 Inflammasome

Purpose

Retinal ischemia-reperfusion (RIR) injury is implicated in various retinal diseases, leading to retinal ganglion cells (RGCs) degeneration. Microglial senescence exacerbates inflammation, contributing to neurodegeneration. This study aimed to investigate the potential therapeutic role of Roflumilast (Roflu) in ameliorating microglial senescence and neuroinflammation following RIR injury.

Methods

C57BL/6J mice underwent RIR surgery, and Roflu treatment was administered intraperitoneally. BV2 microglial cells were subjected to oxygen-glucose deprivation and reoxygenation (OGD/R) to simulate ischemic conditions in vitro. SA-β-gal staining was used to detect cellular senescence. Quantitative PCR and ELISA were used to examine the levels of senescence-associated secretory phenotype (SASP) factors. Hematoxylin and eosin (H&E) staining was performed on retinal sections to assess retinal morphology and thickness. Surviving RGCs were labeled and quantified in retinal whole-mounts using immunofluorescence (IF). Furthermore, Western blot and IF staining were used to quantify the proteins associated with the cell cycle and NLRP3 inflammasomes.

Results

Roflu treatment reduced microglial senescence, ROS production, and secretion of pro-inflammatory cytokines in OGD/R-exposed BV2 cells. It also restored cell proliferation capacity and reversed OGD/R-induced cell cycle arrest. In vivo, Roflu alleviated retinal senescence, preserved retinal thickness, and protected against RGCs death in the RIR mouse model. Mechanistically, Roflu inhibited the NLRP3 inflammasome activation and suppressed DNA damage signaling pathway in microglia.

Conclusions

Roflu exerts neuroprotective effects by mitigating microglial senescence and inflammation via inhibition of the NLRP3 inflammasome in RIR injury. These findings suggest that Roflu may serve as a promising therapeutic strategy for retinal diseases associated with ischemic injury by targeting microglial senescence.

Role of caspase-11 non-canonical inflammasomes in retinal ischemia/reperfusion injury

BACKGROUND

Retinal ischemia/reperfusion (IR) injury is a common pathological process in many ophthalmic diseases. Interleukin-1β (IL-1β) is an important inflammatory factor involved in the pathology of retinal IR injury, but the mechanism by which IL-1β is regulated in such injury remains unclear. Caspase-11 non-canonical inflammasomes can regulate the synthesis and secretion of IL-1β, but its role in retinal IR injury has not been elucidated. This study aimed to evaluate the role of caspase-11 non-canonical inflammasomes in retinal IR injury.

METHODS

Retinal IR injury was induced in C57BL/6J mice by increasing the intraocular pressure to 110 mmHg for 60 min. The post-injury changes in retinal morphology and function and in IL-1β expression were compared between caspase-11 gene knockout (caspase-11-/-) mice and wild-type (WT) mice. Morphological and functional changes were evaluated using hematoxylin-eosin staining and retinal whole mount staining and using electroretinography (ERG), respectively. IL-1β expression in the retina was measured using enzyme-linked immunosorbent assay (ELISA). The levels of caspase-11-related protein were measured using western blot analysis. The location of caspase-11 in the retina was determined via immunofluorescence staining. Mouse type I astrocytes C8-D1A cells were used to validate the effects of caspase-11 simulation via hypoxia in vitro. Small-interfering RNA targeting caspase-11 was constructed. Cell viability was evaluated using the MTT assay. IL-1β expression in supernatant and cell lysate was measured using ELISA. The levels of caspase-11-related protein were measured using western blot analysis.

RESULTS

Retinal ganglion cell death and retinal edema were more ameliorated, and the ERG b-wave amplitude was better after retinal IR injury in caspase-11-/- mice than in WT mice. Further, caspase-11-/- mice showed lower protein expressions of IL-1β, cleaved caspase-1, and gasdermin D (GSDMD) in the retina after retinal IR injury. Caspase-11 protein was expressed in retinal glial cells, and caspase-11 knockdown played a protective role against hypoxia in C8-D1A cells. The expression levels of IL-1β, cleaved caspase-1, and GSDMD were inhibited after hypoxia in the si-caspase-11 constructed cells.

CONCLUSIONS

Retinal IR injury activates caspase-11 non-canonical inflammasomes in glial cells of the retina. This results in increased protein levels of GSDMD and IL-1β and leads to damage in the inner layer of the retina.

Vascular changes in the retinal capillary network in fellow eye of the patients with central retinal artery occlusion

BACKGROUND

We aimed to evaluate the retinal vascular changes in the superficial and deep retinal vascular networks in the fellow eye of patients with central retinal artery occlusion (CRAO) and compare them with controls using optical coherence tomography angiography (OCT-A).

METHODS

In a cross-sectional study, 27 patients with CRAO and 189 normal controls were included. Ophthalmic examination and OCT-A images were performed on all participants.

RESULTS

The total vascular density of the superficial capillary network in the 6-mm scan was significantly lower in the fellow eye of patients with CRAO than in the control group (p = 0.02). No significant difference was observed in the FAZ area of the affected eyes and their fellow eyes compared with the controls. Total vascular density at 300 microns around the fovea was lower in the fellow eye compared with the control group (p = 0.034).

CONCLUSIONS

The retinal vascular network changes in the fellow eyes of patients with CRAO suggest that persistent microvascular changes may be present before the onset of CRAO. This finding indicates that such changes could serve as an early diagnostic window for systemic vascular changes before catastrophic vascular events occur.

Hypoxia Postconditioning Attenuates Hypoxia-Induced Inflammation and Endothelial Barrier Dysfunction

INTRODUCTION

In recent years, a number of studies have demonstrated that hypoxia reoxygenation (HR) induced by ischemia postconditioning (IPC) reduces endothelial barrier dysfunction and inflammation in various models. When HR occurs, the P38 mitogen-activated protein kinase (P38 MAPK) breaks down the endothelial barrier. But no study has clearly clarified the effect of hypoxia postconditioning (HPC) on P38 MAPK in human dermal microvascular endothelial cells. Therefore, we investigated the function of HPC on P38 MAPK during HR in vitro.

METHODS

Human dermal microvascular endothelial cells were cultured in a hypoxic incubator for 8 h. Then cells were reperfused for 12 h (reoxygenation) or postconditioned by 5 min of reoxygenation and 5 min of re-hypoxia 3 times followed by 11.5 h reoxygenation. SB203580 was used as an inhibitor of P38 MAPK. Cell counting kit-8 assay kits were employed to detect cell activity. The corresponding levels of IL-6, IL-8 and IL-1β were examined via Enzyme-Linked ImmunoSorbent Assay. The endothelial barrier was evaluated using fluorescein isothiocyanate-dextran leakage assay. Western blot was used to detect claudin-5, phosphorylation of P38 MAPK (P-P38 MAPK) and P38 MAPK expression. Claudin-5 localization was studied by immunofluorescence.

RESULTS

HR induced endothelial barrier hyperpermeability, elevated inflammation levels, and increased the P-P38 MAPK. But HPC reduced cell injury and maintained the integrity of the endothelial barrier while inhibiting P-P38 MAPK and increasing expression of claudin-5. HPC redistributed claudin-5 in a continuous and linear pattern on the cell membrane.

CONCLUSIONS

HPC protects against HR induced downregulation and redistribution of claudin-5 by inhibiting P-P38 MAPK.

Suppression of inner blood-retinal barrier breakdown and pathogenic Müller glia activation in ischemia retinopathy by myeloid cell depletion

Ischemic retinopathies including diabetic retinopathy are major causes of vision loss. Inner blood-retinal barrier (BRB) breakdown with retinal vascular hyperpermeability results in macular edema. Although dysfunction of the neurovascular unit including neurons, glia, and vascular cells is now understood to underlie this process, there is a need for fuller elucidation of the underlying events in BRB dysfunction in ischemic disease, including a systematic analysis of myeloid cells and exploration of cellular cross-talk. We used an approach for microglia depletion with the CSF-1R inhibitor PLX5622 (PLX) in the retinal ischemia-reperfusion (IR) model. Under non-IR conditions, PLX treatment successfully depleted microglia in the retina. PLX suppressed the microglial activation response following IR as well as infiltration of monocyte-derived macrophages. This occurred in association with reduction of retinal expression of chemokines including CCL2 and the inflammatory adhesion molecule ICAM-1. In addition, there was a marked suppression of retinal neuroinflammation with reduction in expression of IL-1b, IL-6, Ptgs2, TNF-a, and Angpt2, a protein that regulates BRB permeability. PLX treatment significantly suppressed inner BRB breakdown following IR, without an appreciable effect on neuronal dysfunction. A translatomic analysis of Müller glial-specific gene expression in vivo using the Ribotag approach demonstrated a strong suppression of Müller cell expression of multiple pro-inflammatory genes following PLX treatment. Co-culture studies of Müller cells and microglia demonstrated that activated microglia directly upregulates Müller cell-expression of these inflammatory genes, indicating Müller cells as a downstream effector of myeloid cells in retinal IR. Co-culture studies of these two cell types with endothelial cells demonstrated the ability of both activated microglia and Müller cells to compromise EC barrier function. Interestingly, quiescent Müller cells enhanced EC barrier function in this co-culture system. Together this demonstrates a pivotal role for myeloid cells in inner BRB breakdown in the setting of ischemia-associated disease and indicates that myeloid cells play a major role in iBRB dysregulation, through direct and indirect effects, while Müller glia participate in amplifying the neuroinflammatory effect of myeloid cells.

Endothelial and macrophage interactions in the angiogenic niche

The interactions between vascular cells, especially endothelial cells, and macrophages play a pivotal role in maintaining the subtle balance of vascular biology, which is crucial for angiogenesis in both healthy and diseased states. These cells are central to ensuring a harmonious balance between tissue repair and preventing excessive angiogenic activity, which could lead to pathological conditions. Recent advances in sophisticated genetic engineering vivo models and novel sequencing approaches, such as single-cell RNA-sequencing, in immunobiology have significantly enhanced our understanding of the gene expression and behavior of macrophages. These insights offer new perspectives on the role macrophages play not only in development but also across various health conditions. In this review, we explore the complex interactions between multiple types of macrophages and endothelium, focusing on their impact on new blood vessel formation. By understanding these intricate interactions, we aim to provide insights into new methods for managing angiogenesis in various diseases, thereby offering hope for the development of novel therapeutic approaches.

Deletion of myeloid HDAC3 promotes efferocytosis to ameliorate retinal ischemic injury

Ischemia-induced retinopathy is a hallmark finding of common visual disorders including diabetic retinopathy (DR) and central retinal artery and vein occlusions. Treatments for ischemic retinopathies fail to improve clinical outcomes and the design of new therapies will depend on understanding the underlying disease mechanisms. Histone deacetylases (HDACs) are an enzyme class that removes acetyl groups from histone and non-histone proteins, thereby regulating gene expression and protein function. HDACs have been implicated in retinal neurovascular injury in preclinical studies in which nonspecific HDAC inhibitors mitigated retinal injury. Histone deacetylase 3 (HDAC3) is a class I histone deacetylase isoform that plays a central role in the macrophage inflammatory response. We recently reported that myeloid cells upregulate HDAC3 in a mouse model of retinal ischemia-reperfusion (IR) injury. However, whether this cellular event is an essential contributor to retinal IR injury is unknown. In this study, we explored the role of myeloid HDAC3 in ischemia-induced retinal neurovascular injury by subjecting myeloid-specific HDAC3 knockout (M-HDAC3 KO) and floxed control mice to retinal IR. The M-HDAC3 KO mice were protected from retinal IR injury as shown by the preservation of inner retinal neurons, vascular integrity, and retinal thickness. Electroretinography confirmed that this neurovascular protection translated to improved retinal function. The retinas of M-HDAC3 KO mice also showed less proliferation and infiltration of myeloid cells after injury. Interestingly, myeloid cells lacking HDAC3 more avidly engulfed apoptotic cells in vitro and after retinal IR injury in vivo compared to wild-type myeloid cells, suggesting that HDAC3 hinders the reparative phagocytosis of dead cells, a process known as efferocytosis. Further mechanistic studies indicated that although HDAC3 KO macrophages upregulate the reparative enzyme arginase 1 (A1) that enhances efferocytosis, the inhibitory effect of HDAC3 on efferocytosis is not solely dependent on A1. Finally, treatment of wild-type mice with the HDAC3 inhibitor RGFP966 ameliorated the retinal neurodegeneration and thinning caused by IR injury. Collectively, our data show that HDAC3 deletion enhances macrophage-mediated efferocytosis and protects against retinal IR injury, suggesting that inhibiting myeloid HDAC3 holds promise as a novel therapeutic strategy for preserving retinal integrity after ischemic insult.

Homer1a reduces inflammatory response after retinal ischemia/reperfusion injury

JOURNAL/nrgr/04.03/01300535-202407000-00042/figure1/v/2023-11-20T171125Z/r/image-tiff

Elevated intraocular pressure (IOP) is one of the causes of retinal ischemia/reperfusion injury, which results in NLRP3 inflammasome activation and leads to visual damage. Homer1a is reported to play a protective role in neuroinflammation in the cerebrum. However, the effects of Homer1a on NLRP3 inflammasomes in retinal ischemia/reperfusion injury caused by elevated IOP remain unknown. In our study, animal models were constructed using C57BL/6J and Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice with elevated IOP-induced retinal ischemia/reperfusion injury. For in vitro experiments, the oxygen-glucose deprivation/reperfusion injury model was constructed with Müller cells. We found that Homer1a overexpression ameliorated the decreases in retinal thickness and Müller cell viability after ischemia/reperfusion injury. Furthermore, Homer1a knockdown promoted NF-κB P65Ser536 activation via caspase-8, NF-κB P65 nuclear translocation, NLRP3 inflammasome formation, and the production and processing of interleukin-1β and interleukin-18. The opposite results were observed with Homer1a overexpression. Finally, the combined administration of Homer1a protein and JSH-23 significantly inhibited the reduction in retinal thickness in Homer1flox/ –/Homer1a+/ –/Nestin-Cre+/ – mice and apoptosis in Müller cells after ischemia/reperfusion injury. Taken together, these studies demonstrate that Homer1a exerts protective effects on retinal tissue and Müller cells via the caspase-8/NF-κB P65/NLRP3 pathway after I/R injury.

Gallic acid pretreatment mitigates parathyroid ischemia-reperfusion injury through signaling pathway modulation

Thyroid surgery often results in ischemia-reperfusion injury (IRI) to the parathyroid glands, yet the mechanisms underlying this and how to ameliorate IRI remain incompletely explored. Our study identifies a polyphenolic herbal extract-gallic acid (GA)-with antioxidative properties against IRI. Through flow cytometry and CCK8 assays, we investigate the protective effects of GA pretreatment on a parathyroid IRI model and decode its potential mechanisms via RNA-seq and bioinformatics analysis. Results reveal increased apoptosis, pronounced G1 phase arrest, and significantly reduced cell proliferation in the hypoxia/reoxygenation group compared to the hypoxia group, which GA pretreatment mitigates. RNA-seq and bioinformatics analysis indicate GA's modulation of various signaling pathways, including IL-17, AMPK, MAPK, transient receptor potential channels, cAMP, and Rap1. In summary, GA pretreatment demonstrates potential in protecting parathyroid cells from IRI by influencing various genes and signaling pathways. These findings offer a promising therapeutic strategy for hypoparathyroidism treatment.

Microglia-neuron-vascular interactions in ischemia

Cerebral ischemia is a devastating condition that results in impaired blood flow in the brain leading to acute brain injury. As the most common form of stroke, occlusion of cerebral arteries leads to a characteristic sequence of pathophysiological changes in the brain tissue. The mechanisms involved, and comorbidities that determine outcome after an ischemic event appear to be highly heterogeneous. On their own, the processes leading to neuronal injury in the absence of sufficient blood supply to meet the metabolic demand of the cells are complex and manifest at different temporal and spatial scales. While the contribution of non-neuronal cells to stroke pathophysiology is increasingly recognized, recent data show that microglia, the main immune cells of the central nervous system parenchyma, play previously unrecognized roles in basic physiological processes beyond their inflammatory functions, which markedly change during ischemic conditions. In this review, we aim to discuss some of the known microglia-neuron-vascular interactions assumed to contribute to the acute and delayed pathologies after cerebral ischemia. Because the mechanisms of neuronal injury have been extensively discussed in several excellent previous reviews, here we focus on some recently explored pathways that may directly or indirectly shape neuronal injury through microglia-related actions. These discoveries suggest that modulating gliovascular processes in different forms of stroke and other neurological disorders might have presently unexplored therapeutic potential in combination with neuroprotective and flow restoration strategies.

Qi-Ju-Di-Huang-Pill delays the progression of diabetic retinopathy

ETHNOPHARMACOLOGICAL RELEVANCE

Qi-Ju-Di-Huang-Pill (QJDH pill) is a Chinese decoction. Although it is commonly used to treat eye conditions, such as diabetic retinopathy (DR), its exact mechanism of action is unknown.

AIM OF THE STUDY

To investigate the specific mechanism by which QJDH pill slows the progression of diabetic retinopathy (DR) based on animal and cellular experiments.

MATERIAL AND METHODS

The major components of QJDH pill were characterized by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLCMS/MS). C57BL/6J mice were randomly divided into five groups as follows: normal group (control group), model group (STZ group), low-dosage QJDH pill group (QJDH-L group), medium-dosage QJDH pill group (QJDH-M group) and high-dosage QJDH pill group (QJDH-H group). Changes in water intake, urination, food intake, and body mass were monitored weekly, while changes in blood glucose were monitored monthly. Fluorescein fundus angiography (FFA), optical coherence tomography angiography (OCTA), and optical coherence tomography (OCT) were utilized to analyze the changes in fundus imaging indications. Hematoxylin & eosin (H&E) and transmission electron microscopy (TEM) were employed to examine histopathologic and ultrastructural changes in retina. The levels of interleukin-6 (IL-6), interleukin-17 (IL-17), tumor necrosis factor-α (TNF-α), and vascular endothelial growth factor (VEGF) in peripheral blood were detected using Enzyme-linked immunosorbent assay (ELISA). The mouse retina apoptotic cells were labeled with green fluorescence via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (Tunel). The protein levels of Bcl-2-Associated X (Bax), B cell lymphoma 2 (Bcl-2), Caspase-3, PI3K, phosphorylated PI3K (p-PI3K), protein kinase B (AKT) and phosphorylated AKT (p-AKT) were quantified by Western blot (WB). The retinal pigment epithelium (RPE) cells were cultured and classified into five groups as follows: normal glucose group (NG group), high glucose group (HG group), high glucose + QJDH pill group (HG + QJDH group), high glucose + inhibitor group (HG + LY294002 group), and high glucose + inhibitor + QJDH pill group (HG + LY294002 + QJDH group). Cell viability and apoptosis were detected via Cell Counting Kit-8 (CCK8) and then analyzed by flow cytometry.

RESULTS

In vivo experiments revealed that the QJDH pill effectively reduced blood glucose, symptoms of increased water intake, elevated urination, increased food intake and decreased body mass in DR mice. QJDH pill also slowed the development of a series of fundus imaging signs, such as retinal microangiomas, tortuous dilatation of blood vessels, decreased vascular density, and thinning of retinal thickness, downregulated IL-6, IL-17, TNF-α, and VEGF levels in peripheral blood, and inhibited retinal cell apoptosis by activating the PI3K/AKT signaling pathway. Moreover, in vitro experiments showed that high glucose environment inhibited RPE cell viability and activated RPE cell apoptosis pathway. In contrast, lyophilized powder of QJDH pill increased RPE cell viability, protected RPE cells from high glucose-induced damage, and decreased apoptosis of RPE cells by activating the pi3k pathway.

CONCLUSION

QJDH pill induces hypoglycemic, anti-inflammatory effects, anti-VEGF and anti-retinal cell apoptosis by activating PI3K/AKT signaling pathway, and thus can protect the retina and slow the DR progression.

Peripheral blood transcriptomic analysis identifies potential inflammation and immune signatures for central retinal artery occlusion

Central retinal artery occlusion (CRAO) is an acute retinal ischaemic disease, but early diagnosis is challenging due to a lack of biomarkers. Blood samples were collected from CRAO patients and cataract patients. Gene expression profiles were distinct between arterial/venous CRAO blood (A-V group) and venous CRAO/control blood (V-C group) samples. Differentially expressed genes (DEGs) were subjected to GO and KEGG enrichment analyses. Hub genes were identified by Cytoscape and used to predict gene interactions via GeneMANIA. Immune cell infiltration was analysed by CIBERSORT. More than 1400 DEGs were identified in the A-V group and 112 DEGs in the V-C group compared to controls. The DEGs in both groups were enriched in the ribosome pathway, and those in the V-C group were also enriched in antigen processing/MHC pathways. Network analysis identified ribosomal proteins (RPS2 and RPS5) as the core genes of the A-V group and MHC genes (HLA-F) as the core genes of the V-C group. Coexpression networks showed ribosomal involvement in both groups, with additional immune responses in the V-C group. Immune cell analysis indicated increased numbers of neutrophils and T cells. Ribosomal and MHC-related genes were identified as potential CRAO biomarkers, providing research directions for prevention, diagnosis, treatment and prognosis.

BMX deletion mitigates neuroinflammation induced by retinal ischemia/reperfusion through modulation of the AKT/ERK/STAT3 signaling cascade

Aims

Retinal ischemia/reperfusion (I/R) injury is implicated in the etiology of various ocular disorders. Prior research has demonstrated that bone marrow tyrosine kinase on chromosome X (BMX) contributes to the advancement of ischemic disease and inflammatory reactions. Consequently, the current investigation aims to evaluate BMX's impact on retinal I/R injury and clarify its implied mechanism of action.

Main methods

This study utilized male and female systemic BMX knockout (BMX-/-) mice to conduct experiments. The utilization of Western blot assay and immunofluorescence labeling techniques was employed to investigate variations in the expression of protein and tissue localization. Histomorphological changes were observed through H&E staining and SD-OCT examination. Visual function changes were assessed through electrophysiological experiments. Furthermore, apoptosis in the retina was identified using the TUNEL assay, as well as the ELISA technique, which has been utilized to determine the inflammatory factors level.

Key findings

Our investigation results revealed that the knockdown of BMX did not yield a significant effect on mouse retina. In mice, BMX knockdown mitigated the negative impact of I/R injury on retinal tissue structure and visual function. BMX knockdown effectively reduced apoptosis, suppressed inflammatory responses, and decreased inflammatory factors subsequent to I/R injury. The outcomes of the current investigation revealed that BMX knockdown partially protected the retina through downregulating phosphorylation of AKT/ERK/STAT3 pathway.

Significance

Our investigation showed that BMX-/- reduces AKT, ERK, and STAT3 phosphorylation, reducing apoptosis and inflammation. Thus, this strategy protected the retina from structural and functional damage after I/R injury.

Steroid inhibited Serpina3n expression which was positively correlated with the degrees of spinal cord injury

Aims

The aim of our project was to identify proteins associated with the extent of spinal cord injury (SCI) and subsequent long-term neurological recovery.

Methods

Through proteomic analysis, we identified proteins that are differentially expressed specifically in the acute phase of injury. We analyzed the concentrations of differentially expressed proteins in serum and the injured spinal cord segment by ELISA.

Results

Serpina3n protein expression in the injured spinal cord segment was increased 101-fold at 12 h after severe SCI and 89-fold at 12 h after mild SCI, as determined by LC‒MS/MS. In the mild and severe SCI groups, serum Serpina3n levels began to increase at 12 h and peaked at 24 h. At 12 h, 24 h and 3 d after injury, serum Serpina3n protein levels were significantly correlated with the severity of injury (12 h: r = 0.6034, P = 0.008; 24 h: r = 0.7542, P = 0.0003; 3 d: r = 0.862, P < 0.001). Serum Serpina3n levels at 2 h, 24 h and 3 d post injury were significantly correlated with long-term neurological recovery at 28 d after SCI (2 h: r = -0.5781, P = 0.012; 24 h: r = -0.5912, P = 0.0098; 3 d: r = -0.7792, P < 0.0001). Methylprednisolone treatment would decrease the serum Serpina3n levels in mice with mild and severe SCI compared with those in placebo-group mice at 12 h and 24 h after SCI. The serum Serpina3n concentration in the severe SCI group was significantly reduced on the third day after steroid treatment.

Conclusion

Taken together, these data suggest that serpina3n may be a circulating biomarker of acute SCI and may be closely associated with injury severity and long-term motor function recovery.

Role of myeloid cells in ischemic retinopathies: recent advances and unanswered questions

Myeloid cells including microglia and macrophages play crucial roles in retinal homeostasis by clearing cellular debris and regulating inflammation. These cells are activated in several blinding ischemic retinal diseases including diabetic retinopathy, where they may exert both beneficial and detrimental effects on neurovascular function and angiogenesis. Myeloid cells impact the progression of retinal pathologies and recent studies suggest that targeting myeloid cells is a promising therapeutic strategy to mitigate diabetic retinopathy and other ischemic retinal diseases. This review summarizes the recent advances in our understanding of the role of microglia and macrophages in retinal diseases and focuses on the effects of myeloid cells on neurovascular injury and angiogenesis in ischemic retinopathies. We highlight gaps in knowledge and advocate for a more detailed understanding of the role of myeloid cells in retinal ischemic injury to fully unlock the potential of targeting myeloid cells as a therapeutic strategy for retinal ischemia.

Immunological Landscape of Retinal Ischemia-Reperfusion Injury: Insights into Resident and Peripheral Immune Cell Responses

Retinal ischemia-reperfusion injury (RIRI) is a complex condition characterized by immune cell-mediated inflammation and consequent neuronal damage. This review delves into the immune response mechanisms in RIRI, particularly emphasizing the roles played by resident and peripheral immune cells. It highlights the pivotal role of microglia, the primary resident immune cells, in exacerbating neuroinflammation and neuronal damage through their activation and subsequent release of pro-inflammatory mediators. Additionally, the review explores the contributions of other glial cell types, such as astrocytes and Müller cells, in modulating the immune response within the retinal environment. The dual role of the complement system in RIRI is also examined, revealing its complex functions in both safeguarding and impairing retinal health. Inflammasomes, triggered by various danger signals, are discussed as crucial contributors to the inflammatory pathways in RIRI, with an emphasis on the involvement of different NOD-like receptor family proteins. The review further analyzes the infiltration and impact of peripheral immune cells like neutrophils, macrophages, and T cells, which migrate to the retina following ischemic injury. Critical to this discussion is the interplay between resident and peripheral immune cells and its implications for RIRI pathophysiology. Finally, the review outlines future research directions, focusing on basic research and the potential for clinical translation to enhance understanding and treatment of RIRI.

Natural compounds efficacy in Ophthalmic Diseases: A new twist impacting ferroptosis

Ferroptosis, a distinct form of cell death, is characterized by the iron-mediated oxidation of lipids and is finely controlled by multiple cellular metabolic pathways. These pathways encompass redox balance, iron regulation, mitochondrial function, as well as amino acid, lipid, and sugar metabolism. Additionally, various disease-related signaling pathways also play a role in the regulation of ferroptosis. In recent years, with the introduction of the concept of ferroptosis and the deepening of research on its mechanism, ferroptosis is closely related to various biological conditions of eye diseases, including eye organ development, aging, immunity, and cancer. This article reviews the development of the concept of ferroptosis, the mechanism of ferroptosis, and its latest research progress in ophthalmic diseases and reviews the research on ferroptosis in ocular diseases within the framework of metabolism, active oxygen biology, and iron biology. Key regulators and mechanisms of ferroptosis in ocular diseases introduce important concepts and major open questions in the field of ferroptosis and related natural compounds. It is hoped that in future research, further breakthroughs will be made in the regulation mechanism of ferroptosis and the use of ferroptosis to promote the treatment of eye diseases. At the same time, natural compounds may be the direction of new drug development for the potential treatment of ferroptosis in the future. Open up a new way for clinical ophthalmologists to research and prevent diseases.

Gliosis-dependent expression of complement factor H truncated variants attenuates retinal neurodegeneration following ischemic injury

Inherited, age-related, and acute retinal diseases are often exacerbated by an aberrant or excessive activity of the complement system. Consequently, cells not directly affected by an acute event or genetic variants may degenerate, resulting in enhanced visual impairment. The therapeutic potential of supplementation of complement factor H (FH), a key regulator of the complement cascade, is therefore particularly promising in the context of retinal diseases caused by complement activation. In this study, we engineered adeno-associated viruses (AAVs) containing sequences of two truncated human FH variants. The expression of these variants was regulated by the glial fibrillary acidic protein (GFAP) promoter, which is selectively active in gliotic Müller cells. Both FH variants consisted of FH domains 19-20, which were connected to domains 1-4 and 1-7, respectively, by a polyglycine linker. These AAVs were intravitreally injected following ischemic injury of C57BL/6J mouse retinas. We observed transgene expression in gliotic Müller cells and to some extent in astrocytes. The expression correlated directly with damage severity. Interventions resulted in decreased complement activation, accelerated normalization of microglia activity and morphological improvements. Reduced levels of C3 transcripts and C3d protein in conjunction with higher transcript levels of inhibitory regulators like Cfi and Cfh, hinted at attenuated complement activity. This study demonstrates the great potential of complement regulatory gene addition therapy. With further in vivo testing it could be applied to treat a wide range of retinal diseases where no causative therapies are available.

Myopia, Sodium Chloride, and Vitreous Fluid Imbalance: A Nutritional Epidemiology Perspective

Theories of myopia etiology based on near work and lack of outdoor exposure have had inconsistent support and have not prevented the rising prevalence of global myopia. New scientific theories in the cause and prevention of myopia are needed. Myopia prevalence is low in native people consuming traditional diets lacking in sodium chloride, and nutritional epidemiological evidence supports the association of rising myopia prevalence with dietary sodium intake. East Asian populations have among the highest rates of myopia associated with high dietary sodium. Similar associations of sodium and rising myopia prevalence were observed in the United States in the late 20th century. The present perspective synthesizes nutritional epidemiology evidence with pathophysiological concepts and proposes that axial myopia occurs from increased fluid retention in the vitreous of the eye, induced by dietary sodium chloride intake. Salt disturbs ionic permeability of retinal membranes, increases the osmotic gradient flow of fluid into the vitreous, and stretches ocular tissue during axial elongation. Based on the present nutritional epidemiology evidence, experimental research should investigate the effect of sodium chloride as the cause of myopia, and clinical research should test a very low-salt diet in myopia correction and prevention.

Single-Cell Transcriptomic Sequencing Reveals Tissue Architecture and Deciphers Pathological Reprogramming During Retinal Ischemia in Macaca fascicularis

Purpose

Acute retinal arterial ischemia diseases (ARAIDs) are ocular emergencies that require immediate intervention within a restricted therapeutic window to prevent blindness. However, the underlying molecular mechanisms contributing to the pathogenesis of ARAIDs remain enigmatic. Herein, we present the single-cell RNA sequencing (scRNA-seq) alterations during ischemia in the primate retina as a preliminary endeavor in understanding the molecular complexities of ARAIDs.

Methods

An ophthalmic artery occlusion model was established through ophthalmic artery ligation in two Macaca fascicularis. scRNA-seq and bioinformatics analyses were used to detect retinal changes during ischemia, which are further validated by immunofluorescence analysis. Western blot and flow cytometry assays were performed to measure the microglia polarization status.

Results

The findings of this study reveal notable changes in the retina under acute ischemic conditions. Particularly, retinal ischemia compromised mitochondrial functions of rod photoreceptors, partly leading to the rapid loss of healthy rods. Furthermore, we observed a noteworthy transcriptional alteration in the activation of microglia induced by ischemia. The targeted correction of the proinflammatory cytokine CXCL8 effectively suppresses microglia M1 polarization in retinal ischemia, ultimately reducing the proinflammatory transformation in vitro. In addition, retina ischemia induced the apoptotic inclination of endothelial cells and the heightened interaction with microglia, which signifies the influence of microglia in disrupting the retinal-blood barrier.

Conclusions

Our research has successfully identified and described the pathologic alterations occurring in several cell types during a short period of ischemia. These observations provide valuable insights for ameliorating retinal damage and promoting the restoration of vision.

Discussing pathologic mechanisms of Diabetic retinopathy & therapeutic potentials of curcumin and β-glucogallin in the management of Diabetic retinopathy

Diabetic retinopathy (DR) is a form of retinal microangiopathy that occurs as a result of long-term Diabetes mellitus (DM). Patients with Diabetes mellitus typically suffer from DR as a progression of the disease that may be due to initiation and dysregulation of pathways like the polyol, hexosamine, the AGE/RAGE, and the PKC pathway, which all have negative impacts on eye health and vision. In this review, various databases, including PubMed, Google Scholar, Web of Science, and Science Direct, were scoured for data relevant to the aforementioned title. The three most common therapies for DR today are retinal photocoagulation, anti-vascular endothelial growth factor (VEGF) therapy, and vitrectomy, however, there are a number of drawbacks and limits to these methods. So, it is of critical importance and profound interest to discover treatments that may successfully address the pathogenesis of DR. Curcumin and β-glucogallin are the two potent compounds of natural origin that are already being used in various nutraceutical formulations for several ailments. They have been shown potent antiapoptotic, anti-inflammatory, antioxidant, anticancer, and pro-vascular function benefits in animal experiments. Their parent plant species have been used for generations by practitioners of traditional herbal medicine for the treatment and prevention of various eye ailments. In this review, we will discuss about pathophysiology of Diabetic retinopathy and the therapeutic potentials of curcumin and β-glucogallin one of the principal compounds from Curcuma longa and Emblica officinalis in Diabetic retinopathy.

Diabetes Modulates Iodothyronine Deiodinase 2 Expression in the Mouse Retina: A Role for Thyroid Hormone in the Pathogenesis of Diabetic Retinopathy

Purpose

Clinical investigations associate hypothyroidism with an increased risk for microvascular complications, yet the mechanism by which thyroid hormone regulates the development of diabetic retinopathy is not clearly understood. We investigated the role of iodothyronine deiodinase 2 (DIO2) in the pathogenesis of diabetic retinopathy.

Methods

Retinas from streptozotocin-induced diabetic and nondiabetic mice were evaluated by RNA sequencing, RT-PCR, and immunostaining. Media and cell lysates from mouse retinal microvascular endothelial cells and retinal astrocytes exposed to physiologic (5 mM) and high glucose (25 mM) containing media were assessed by liquid chromatography-tandem mass spectrometry to measure tetraiodothyronine (T4) and tri-iodothyronine (T3) concentrations and by Western blot analysis to determine the relationship of T4/T3 to oxidative stress and inflammatory mediators. Cell death was determined by Trypan Blue exclusion assay.

Results

At 12 weeks of diabetes duration, retinas from diabetic mice compared with nondiabetic mice demonstrated a significant decrease in Dio2 transcripts and Dio2 gene and protein (P < 0.05) expression. When cultured in the presence of high glucose, both mouse retinal astrocytes and microvascular endothelial cells demonstrated a significant reduction of DIO2 protein compared with cells cultured in physiologic glucose. High glucose inhibited generation of T3, leading to a significantly increased T4/T3 (P < 0.0079). Supplementation of cells with T3, but not T4, prevented the high glucose-induced rise in endothelial nitric oxide synthase, intercellular cell adhesion molecule 1, and endothelial cell death (P < 0.0079).

Conclusions

Decreased intraretinal T3 owing to diabetes-induced loss of DIO2 may lead to dysfunction and death of cells in the retina, thereby contributing to the pathogenesis of early diabetic retinopathy.

Therapeutic potential of iron chelators in retinal vascular diseases

Iron is one of the necessary metal elements in the human body. There are numerous factors that control the balance of iron metabolism, and its storage and transportation mechanisms are intricate. As one of the most energy-intensive tissues in the body, the retina is susceptible to iron imbalance. The occurrence of iron overload in the retina leads to the generation of a significant quantity of reactive oxygen species. This will aggravate local oxidative stress and inflammatory reactions and even lead to ferroptosis, eventually resulting in retinal dysfunction. The blood-retina-retinal barrier is eventually harmed by oxidative stress and elevated inflammation, which are characteristics of retinal vascular disorders. The pathophysiology of retinal vascular disorders may be significantly influenced by iron. Recently, iron-chelating agents have been found to have antioxidative and anti-inflammatory actions in addition to iron chelating. Therefore, iron neutralization is considered to be a new and potentially useful therapeutic strategy. This article reviews the iron overload in retinal vascular diseases and discusses the therapeutic potential of iron-chelating agents.

Pharmacological Modulation of β-Catenin Preserves Endothelial Barrier Integrity and Mitigates Retinal Vascular Permeability and Inflammation

Compromised blood-retinal barrier (BRB) integrity is a significant factor in ocular diseases like uveitis and retinopathies, leading to pathological vascular permeability and retinal edema. Adherens and tight junction (AJ and TJ) dysregulation due to retinal inflammation plays a pivotal role in BRB disruption. We investigated the potential of ICG001, which inhibits β-catenin-mediated transcription, in stabilizing cell junctions and preventing BRB leakage. In vitro studies using human retinal endothelial cells (HRECs) showed that ICG001 treatment improved β-Catenin distribution within AJs post lipopolysaccharide (LPS) treatment and enhanced monolayer barrier resistance. The in vivo experiments involved a mouse model of LPS-induced ocular inflammation. LPS treatment resulted in increased albumin leakage from retinal vessels, elevated vascular endothelial growth factor (VEGF) and Plasmalemmal Vesicle-Associated Protein (PLVAP) expression, as well as microglia and macroglia activation. ICG001 treatment (i.p.) effectively mitigated albumin leakage, reduced VEGF and PLVAP expression, and reduced the number of activated microglia/macrophages. Furthermore, ICG001 treatment suppressed the surge in inflammatory cytokine synthesis induced by LPS. These findings highlight the potential of interventions targeting β-Catenin to enhance cell junction stability and improve compromised barrier integrity in various ocular inflammatory diseases, offering hope for better management and treatment options.

Retinal Microenvironment-Protected Rhein-GFFYE Nanofibers Attenuate Retinal Ischemia-Reperfusion Injury via Inhibiting Oxidative Stress and Regulating Microglial/Macrophage M1/M2 Polarization

Retinal ischemia is involved in the occurrence and development of various eye diseases, including glaucoma, diabetic retinopathy, and central retinal artery occlusion. To the best of our knowledge, few studies have reported self-assembling peptide natural products for the suppression of ocular inflammation and oxidative stress. Herein, a self-assembling peptide GFFYE is designed and synthesized, which can transform the non-hydrophilicity of rhein into an amphiphilic sustained-release therapeutic agent, and rhein-based therapeutic nanofibers (abbreviated as Rh-GFFYE) are constructed for the treatment of retinal ischemia-reperfusion (RIR) injury. Rh-GFFYE significantly ameliorates oxidative stress and inflammation in an in vitro oxygen-glucose deprivation (OGD) model of retinal ischemia and a rat model of RIR injury. Rh-GFFYE also significantly enhances retinal electrophysiological recovery and exhibits good biocompatibility. Importantly, Rh-GFFYE also promotes the transition of M1-type macrophages to the M2 type, ultimately altering the pro-inflammatory microenvironment. Further investigation of the treatment mechanism indicates that Rh-GFFYE activates the PI3K/AKT/mTOR signaling pathway to reduce oxidative stress and inhibits the NF-κB and STAT3 signaling pathways to affect inflammation and macrophage polarization. In conclusion, the rhein-loaded nanoplatform alleviates RIR injury by modulating the retinal microenvironment. The findings are expected to promote the clinical application of hydrophobic natural products in RIR injury-associated eye diseases.

The arginase 1/ornithine decarboxylase pathway suppresses HDAC3 to ameliorate the myeloid cell inflammatory response: implications for retinal ischemic injury

The enzyme arginase 1 (A1) hydrolyzes the amino acid arginine to form L-ornithine and urea. Ornithine is further converted to polyamines by the ornithine decarboxylase (ODC) enzyme. We previously reported that deletion of myeloid A1 in mice exacerbates retinal damage after ischemia/reperfusion (IR) injury. Furthermore, treatment with A1 protects against retinal IR injury in wild-type mice. PEG-A1 also mitigates the exaggerated inflammatory response of A1 knockout (KO) macrophages in vitro. Here, we sought to identify the anti-inflammatory pathway that confers macrophage A1-mediated protection against retinal IR injury. Acute elevation of intraocular pressure was used to induce retinal IR injury in mice. A multiplex cytokine assay revealed a marked increase in the inflammatory cytokines interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the retina at day 5 after IR injury. In vitro, blocking the A1/ODC pathway augmented IL-1β and TNF-α production in stimulated macrophages. Furthermore, A1 treatment attenuated the stimulated macrophage metabolic switch to a pro-inflammatory glycolytic phenotype, whereas A1 deletion had the opposite effect. Screening for histone deacetylases (HDACs) which play a role in macrophage inflammatory response showed that A1 deletion or ODC inhibition increased the expression of HDAC3. We further showed the involvement of HDAC3 in the upregulation of TNF-α but not IL-1β in stimulated macrophages deficient in the A1/ODC pathway. Investigating HDAC3 KO macrophages showed a reduced inflammatory response and a less glycolytic phenotype upon stimulation. In vivo, HDAC3 co-localized with microglia/macrophages at day 2 after IR in WT retinas and was further increased in A1-deficient retinas. Collectively, our data provide initial evidence that A1 exerts its anti-inflammatory effect in macrophages via ODC-mediated suppression of HDAC3 and IL-1β. Collectively we propose that interventions that augment the A1/ODC pathway and inhibit HDAC3 may confer therapeutic benefits for the treatment of retinal ischemic diseases.

Inhibition of NOX4 with GLX351322 alleviates acute ocular hypertension-induced retinal inflammation and injury by suppressing ROS mediated redox-sensitive factors activation

Reactive oxygen species (ROS) overproduction plays an essential role in the etiology of ischemic/hypoxic retinopathy caused by acute glaucoma. NADPH oxidase (NOX) 4 was discovered as one of the main sources of ROS in glaucoma. However, the role and potential mechanisms of NOX4 in acute glaucoma have not been fully elucidated. Therefore, the current study aims to investigate the NOX4 inhibitor GLX351322 that targets NOX4 inhibition in acute ocular hypertension (AOH)-induced retinal ischemia/hypoxia injury in mice. Herein, NOX4 was highly expressed in AOH retinas, particularly the retinal ganglion cell layer (GCL). Importantly, the NOX4 inhibitor GLX351322 reduced ROS overproduction, inhibited inflammatory factor release, suppressed glial cell activation and hyperplasia, inhibited leukocyte infiltration, reduced retinal cell senescence and apoptosis in damaged areas, reduced retinal degeneration and improved retinal function. This neuroprotective effect is at least partially associated with mediated redox-sensitive factor (HIF-1α, NF-κB, and MAPKs) pathways by NOX4-derived ROS overproduction. These results suggest that inhibition of NOX4 with GLX351322 attenuated AOH-induced retinal inflammation, cellular senescence, and apoptosis by inhibiting the activation of the redox-sensitive factor pathway mediated by ROS overproduction, thereby protecting retinal structure and function. Targeted inhibition of NOX4 is expected to be a new idea in the treatment of acute glaucoma.

Multi-color Flow Cytometry Protocol to Characterize Myeloid Cells in Mouse Retina Research

Myeloid cells, specifically microglia and macrophages, are activated in retinal diseases and can improve or worsen retinopathy outcomes based on their inflammatory phenotype. However, assessing the myeloid cell response after retinal injury in mice remains challenging due to the small tissue size and the challenges of distinguishing microglia from infiltrating macrophages. In this protocol paper, we describe a flow cytometry-based protocol to assess retinal microglia/macrophage and their inflammatory phenotype after injury. The protocol is amenable to the incorporation of other markers of interest to other researchers. Key features This protocol describes a flow cytometry-based method to analyze the myeloid cell response in retinopathy mouse models. The protocol can distinguish between microglia- and monocyte-derived macrophages. It can be modified to incorporate markers of interest. We show representative results from three different retinopathy models, namely ischemia-reperfusion injury, endotoxin-induced uveitis, and oxygen-induced retinopathy.

Retinal stroke: research models, targets and experimental drugs

INTRODUCTION

Retinal artery occlusion (RAO), often caused by a microembolus and resulting in inner retinal ischemia, could be considered as the retinal analog to cerebral stroke. Although several therapeutic targets have been suggested in animal models of retinal ischemia and several potential treatments have been evaluated on small series of patients, central retinal artery occlusion (CRAO) is still rarely treatable in clinical practice.

AREAS COVERED

Here, we review several animal models of RAO, including increased intraocular pressure, laser, vasoconstriction, embolization and clamp. We also review the pathogenic mechanisms that contribute to cell death cascades during ischemia, and the therapeutic strategies targeting these events. These strategies aim to restore blood flow by fibrinolysis, increase the oxygen or glucose supply, decrease the energy demands, restrict ionic leak fluxes or reduce the detrimental effects of glutamate, calcium and free radicals. The current literature suggests that tPA treatment could be effective for CRAO.

EXPERT OPINION

Eye care professionals must make a rapid and accurate diagnosis and immediately refer patients with acute retinal stroke to specialized centers. CRAO management should also be facilitated by developing local networks to encourage collaboration among ophthalmologists, retina specialists and stroke neurologists.

Delineating effects of angiopoietin-2 inhibition on vascular permeability and inflammation in models of retinal neovascularization and ischemia/reperfusion

Introduction

Clinical trials demonstrated that co-targeting angiopoietin-2 (Ang-2) and vascular endothelial growth factor (VEGF-A) with faricimab controls anatomic outcomes and maintains vision improvements, with strong durability, through 2 years in patients with neovascular age-related macular degeneration and diabetic macular edema. The mechanism(s) underlying these findings is incompletely understood and the specific role that Ang-2 inhibition plays requires further investigation.

Methods

We examined the effects of single and dual Ang-2/VEGF-A inhibition in diseased vasculatures of JR5558 mice with spontaneous choroidal neovascularization (CNV) and in mice with retinal ischemia/reperfusion (I/R) injuries.

Results

In JR5558 mice, Ang-2, VEGF-A, and dual Ang-2/VEGF-A inhibition reduced CNV area after 1 week; only dual Ang-2/VEGF-A inhibition decreased neovascular leakage. Only Ang-2 and dual Ang-2/VEGF-A inhibition maintained reductions after 5 weeks. Dual Ang-2/VEGF-A inhibition reduced macrophage/microglia accumulation around lesions after 1 week. Both Ang-2 and dual Ang-2/VEGF-A inhibition reduced macrophage/microglia accumulation around lesions after 5 weeks. In the retinal I/R injury model, dual Ang-2/VEGF-A inhibition was statistically significantly more effective than Ang-2 or VEGF-A inhibition alone in preventing retinal vascular leakage and neurodegeneration.

Discussion

These data highlight the role of Ang-2 in dual Ang-2/VEGF-A inhibition and indicate that dual inhibition has complementary anti-inflammatory and neuroprotective effects, suggesting a mechanism for the durability and efficacy of faricimab in clinical trials.

Melatonin Alleviates Retinal Ischemia-Reperfusion Injury by Inhibiting p53-Mediated Ferroptosis

Retinal ischemia-reperfusion (RIR) injury caused by high intraocular pressure (IOP) is an important risk factor contributing to retinal ganglion cell (RGC) death, eventually causing blindness. A key progressive pathological process in the development of RIR is the death of RGCs. However, the detailed mechanisms underlying RGC death caused by RIR have not yet been clearly elucidated, and effective treatments are lacking. Ferroptosis is a recently defined form of programmed cell death that is closely related to organ injury. Melatonin (MT) is a promising neuroprotective agent, but its effects on RIR injury remain unclear. In this study, murine models of acute ocular hypertension and oxygen and glucose deprivation/reoxygenation (OGD/R) model were adopted to simulate retinal ischemia. MT alleviated retinal damage and RGC death in RIR mice, significantly attenuating RIR-induced ferroptosis. Furthermore, MT reduced the expression of p53, a master regulator of ferroptosis pathways, and the upregulation of p53 promoted ferroptosis and largely abolished the neuroprotective effects of MT. Mechanistically, the overexpression (OE) of p53 suppressed the expression of the solute carrier family 7 member 11 (Slc7a11), which was accompanied by increased 12-lipoxygenase (Alox12) expression, triggering retinal ferroptosis. Moreover, MT-ameliorated apoptosis, neuroinflammation and microglial activation were observed. In summary, MT conferred neuroprotection against RIR injury by inhibiting p53-mediated ferroptosis. These findings indicate that MT is a retina-specific ferroptosis inhibitor and a promising therapeutic agent for retinal neuroprotection.

PDGFRB upregulation contributes to retinal damages in the rat model of retinal ischemia-reperfusion

Retinal ischemic disease is a major type of retinal diseases causing vision loss. Identifying the molecular mechanisms mediating the retinal ischemia-reperfusion (RIR) is the key to targeted intervention. In this study, we performed RNA-seq analysis of the retinal tissues of a retinal ischemia-reperfusion model of Sprague-Dawley (SD) rats, followed by differential gene expression analysis, gene ontology (GO) enrichment analysis, and protein-protein interaction (PPI) analysis. After studying we found that: The major biological processes affected after RIR was the regulation of vascular development. PPI analysis unveiled a regulatory module in which Platelet Derived Growth Factor Receptor Beta (PDGFRB) was upregulated. In the RIR cell model of human retinal microvascular endothelial cells (HRCEC) induced by oxygen-glucose deprivation/reperfusion (OGD/R), silencing PDGFRB at least partially rescued the detrimental effect on cell proliferation and in vitro angiogenic ability. In the rat model of RIR, the administration of PDGFR inhibitor alleviated the damages in the retinal microvascular system. Besides, we further demonstrated the protective effect of procyanidin against RIR induced damages in both the cell and animal model by dampening the overexpression of PDGFRB. Together, our data indicate that the upregulation of PDGFRB contributes to RIR-induced damages in retinal microvascular system, which provides a targetable strategy for therapeutic intervention.

N,N-Dimethyl-3β-hydroxycholenamide attenuates neuronal death and retinal inflammation in retinal ischemia/reperfusion injury by inhibiting Ninjurin 1

BACKGROUND

Retinal ischemia-reperfusion (RIR) injury refers to an obstruction in the retinal blood supply followed by reperfusion. Although the molecular mechanism underlying the ischemic pathological cascade is not fully understood, neuroinflammation plays a crucial part in the mortality of retinal ganglion cells.

METHODS

Single-cell RNA sequencing (scRNA-seq), molecular docking, and transfection assay were used to explore the effectiveness and pathogenesis of N,N-dimethyl-3β-hydroxycholenamide (DMHCA)-treated mice with RIR injury and DMHCA-treated microglia after oxygen and glucose deprivation/reoxygenation (OGD/R).

RESULTS

DMHCA could suppress inflammatory gene expression and attenuate neuronal lesions, restoring the retinal structure in vivo. Using scRNA-seq on the retina of DMHCA-treated mice, we provided novel insights into RIR immunity and demonstrated nerve injury-induced protein 1 (Ninjurin1/Ninj 1) as a promising treatment target for RIR. Moreover, the expression of Ninj1, which was increased in RIR injury and OGD/R-treated microglia, was downregulated in the DMHCA-treated group. DMHCA suppressed the activation of the nuclear factor kappa B (NF-κB) pathways induced by OGD/R, which was undermined by the NF-κB pathway agonist betulinic acid. Overexpressed Ninj1 reversed the anti-inflammatory and anti-apoptotic function of DMHCA. Molecular docking indicated that for Ninj1, DMHCA had a low binding energy of - 6.6 kcal/mol, suggesting highly stable binding.

CONCLUSION

Ninj1 may play a pivotal role in microglia-mediated inflammation, while DMHCA could be a potential treatment strategy against RIR injury.

Mild Traumatic Brain Injury Induces Time- and Sex-Dependent Cerebrovascular Dysfunction and Stroke Vulnerability

Mild traumatic brain injury (mTBI) produces subtle cerebrovascular impairments that persist over time and promote increased ischemic stroke vulnerability. We recently established a role for vascular impairments in exacerbating stroke outcomes 1 week after TBI, but there is a lack of research regarding long-term impacts of mTBI-induced vascular dysfunction, as well as a significant need to understand how mTBI promotes stroke vulnerability in both males and females. Here, we present data using a mild closed head TBI model and an experimental stroke occurring either 7 or 28 days later in both male and female mice. We report that mTBI induces larger stroke volumes 7 days after injury, however, this increased vulnerability to stroke persists out to 28 days in female but not male mice. Importantly, mTBI-induced changes in blood-brain barrier permeability, intravascular coagulation, angiogenic factors, total vascular area, and glial expression were differentially altered across time and by sex. Taken together, these data suggest that mTBI can result in persistent cerebrovascular dysfunction and increased susceptibility to worsened ischemic outcomes, although these dysfunctions occur differently in male and female mice.

Activation of retinal glial cells contributes to the degeneration of ganglion cells in experimental glaucoma

Elevation of intraocular pressure (IOP) is a major risk factor for neurodegeneration in glaucoma. Glial cells, which play an important role in normal functioning of retinal neurons, are well involved into retinal ganglion cell (RGC) degeneration in experimental glaucoma animal models generated by elevated IOP. In response to elevated IOP, mGluR I is first activated and Kir4.1 channels are subsequently inhibited, which leads to the activation of Müller cells. Müller cell activation is followed by a complex process, including proliferation, release of inflammatory and growth factors (gliosis). Gliosis is further regulated by several factors. Activated Müller cells contribute to RGC degeneration through generating glutamate receptor-mediated excitotoxicity, releasing cytotoxic factors and inducing microglia activation. Elevated IOP activates microglia, and following morphological and functional changes, these cells, as resident immune cells in the retina, show adaptive immune responses, including an enhanced release of pro-inflammatory factors (tumor neurosis factor-α, interleukins, etc.). These ATP and Toll-like receptor-mediated responses are further regulated by heat shock proteins, CD200R, chemokine receptors, and metabotropic purinergic receptors, may aggravate RGC loss. In the optic nerve head, astrogliosis is initiated and regulated by a complex reaction process, including purines, transmitters, chemokines, growth factors and cytokines, which contributes to RGC axon injury through releasing pro-inflammatory factors and changing extracellular matrix in glaucoma. The effects of activated glial cells on RGCs are further modified by the interplay among different types of glial cells. This review is concluded by presenting an in-depth discussion of possible research directions in this field in the future.

Microglia: The breakthrough to treat neovascularization and repair blood-retinal barrier in retinopathy

Microglia are the primary resident retinal macrophages that monitor neuronal activity in real-time and facilitate angiogenesis during retinal development. In certain retinal diseases, the activated microglia promote retinal angiogenesis in hypoxia stress through neurovascular coupling and guide neovascularization to avascular areas (e.g., the outer nuclear layer and macula lutea). Furthermore, continuously activated microglia secrete inflammatory factors and expedite the loss of the blood-retinal barrier which causes irreversible damage to the secondary death of neurons. In this review, we support microglia can be a potential cellular therapeutic target in retinopathy. We briefly describe the relevance of microglia to the retinal vasculature and blood-retinal barrier. Then we discuss the signaling pathway related to how microglia move to their destinations and regulate vascular regeneration. We summarize the properties of microglia in different retinal disease models and propose that reducing the number of pro-inflammatory microglial death and conversing microglial phenotypes from pro-inflammatory to anti-inflammatory are feasible for treating retinal neovascularization and the damaged blood-retinal barrier (BRB). Finally, we suppose that the unique properties of microglia may aid in the vascularization of retinal organoids.

Pemafibrate prevents choroidal neovascularization in a mouse model of neovascular age-related macular degeneration

Background

Pathological choroidal neovascularization (CNV) is one of the major causes of visual impairment in neovascular age-related macular degeneration (AMD). CNV has been suppressed by using anti-vascular endothelial growth factor (VEGF) antibodies. However, some clinical cases have demonstrated the failure of anti-VEGF therapies. Furthermore, anti-VEGF agents might induce the development of ocular atrophy. Recently, peroxisome proliferator-activated receptor alpha (PPARα) activation using pemafibrate treatment was suggested as one of the promising therapeutic targets in the prevention of ocular ischemia. However, the preventive role of pemafibrate remains unclear in CNV. We aimed to examine the preventive role of pemafibrate on laser-induced pathological CNV.

Methods

Adult male C57BL/6 mice were orally supplied pemafibrate (0.5 mg/kg) for four days, followed by laser irradiation. Then, pemafibrate was consecutively given to mice with the same condition. CNV was visualized with isolectin-IB4. The eye (retina and/or retinal pigment epithelium [RPE]-choroid), liver, and serum were used for biomolecular analyses.

Results

We found that pemafibrate administration suppressed CNV volumes. Pemafibrate administration activated PPARα downstream genes in the liver and eye (especially, RPE-choroid). Furthermore, pemafibrate administration elevated serum fibroblast growth factor 21 levels and reduced serum levels of triglycerides.

Conclusions

Our data suggest a promising pemafibrate therapy for suppressing CNV in AMD.

Anti-PANoptosis is involved in neuroprotective effects of melatonin in acute ocular hypertension model

Acute ocular hypertension (AOH) is the most important characteristic of acute glaucoma, which can lead to retinal ganglion cell (RGC) death and permanent vision loss. So far, approved effective therapy is still lacking in acute glaucoma. PANoptosis (pyroptosis, apoptosis, and necroptosis), which consists of three key modes of programmed cell death-apoptosis, necroptosis, and pyroptosis-may contribute to AOH-induced RGC death. Previous studies have demonstrated that melatonin (N-acetyl-5-methoxytryptamine) exerts a neuroprotective effect in many retinal degenerative diseases. However, whether melatonin is anti-PANoptotic and neuroprotective in the progression of acute glaucoma remains unclear. Thus, this study aimed to explore the role of melatonin in AOH retinas and its underlying mechanisms. The results showed that melatonin treatment attenuated the loss of ganglion cell complex thickness, retinal nerve fiber layer thickness, and RGC after AOH injury, and improved the amplitudes of a-wave, b-wave, and oscillatory potentials in the electroretinogram. Additionally, the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells was decreased, and the upregulation of cleaved caspase-8, cleaved caspase-3, Bax, and Bad and downregulation of Bcl-2 and p-Bad were inhibited after melatonin administration. Meanwhile, both the expression and activation of MLKL, RIP1, and RIP3, along with the number of PI-positive cells, were reduced in melatonin-treated mice, and p-RIP3 was in both RGC and microglia/macrophage after AOH injury. Furthermore, melatonin reduced the expression of NLRP3, ASC, cleaved caspase-1, gasdermin D (GSDMD), and cleaved GSDMD, and decreased the number of Iba1/interleukin-1β-positive cells. In conclusion, melatonin ameliorated retinal structure, prevented retinal dysfunction after AOH, and exerted a neuroprotective effect via inhibition of PANoptosis in AOH retinas.

Single-cell RNA sequencing reveals a landscape and targeted treatment of ferroptosis in retinal ischemia/reperfusion injury

BACKGROUND

The aim of this study was to establish a complete retinal cell atlas of ischemia-reperfusion injury by single-cell RNA sequencing, and to explore the underlying mechanism of retinal ischemia-reperfusion injury in mice.

METHODS

Single-cell RNA sequencing was used to evaluate changes in the mouse retinal ischemia reperfusion model. In vivo and in vitro experiments were performed to verify the protective effect of inhibiting ferroptosis in retinal ischemia-reperfusion injury.

RESULTS

After ischemia-reperfusion injury, retinal cells were significantly reduced, accompanied by the activation of myeloid and a large amount of blood-derived immune cell infiltration. The IFNG, MAPK and NFKB signaling pathways in retinal neuronal cells, together with the TNF signaling pathway in myeloid give rise to a strong inflammatory response in the I/R state. Besides, the expression of genes implicating iron metabolism, oxidative stress and multiple programed cell death pathways have changed in cell subtypes described above. Especially the ferroptosis-related genes and blocking this process could apparently alleviate the inflammatory immune responses and enhance retinal ganglion cells survival.

CONCLUSIONS

We established a comprehensive landscape of mouse retinal ischemia-reperfusion injury at the single-cell level, revealing the important role of ferroptosis during this injury, and targeted inhibition of ferroptosis can effectively protect retinal structure and function.

Hematopoietic Cells Influence Vascular Development in the Retina

Hematopoietic cells play a crucial role in the adult retina in health and disease. Monocytes, macrophages, microglia and myeloid angiogenic cells (MACs) have all been implicated in retinal pathology. However, the role that hematopoietic cells play in retinal development is understudied. The temporal changes in recruitment of hematopoietic cells into the developing retina and the phenotype of the recruited cells are not well understood. In this study, we used the hematopoietic cell-specific protein Vav1 to track and investigate hematopoietic cells in the developing retina. By flow cytometry and immunohistochemistry, we show that hematopoietic cells are present in the retina as early as P0, and include microglia, monocytes and MACs. Even before the formation of retinal blood vessels, hematopoietic cells localize to the inner retina where they eventually form networks that intimately associate with the developing vasculature. Loss of Vav1 lead to a reduction in the density of medium-sized vessels and an increased inflammatory response in retinal astrocytes. When pups were subjected to oxygen-induced retinopathy, hematopoietic cells maintained a close association with the vasculature and occasionally formed 'frameworks' for the generation of new vessels. Our study provides further evidence for the underappreciated role of hematopoietic cells in retinal vasculogenesis and the formation of a healthy retina.

Nicotinamide Mononucleotide Prevents Retinal Dysfunction in a Mouse Model of Retinal Ischemia/Reperfusion Injury

Retinal ischemia/reperfusion (I/R) injury can cause severe vision impairment. Retinal I/R injury is associated with pathological increases in reactive oxygen species and inflammation, resulting in retinal neuronal cell death. To date, effective therapies have not been developed. Nicotinamide mononucleotide (NMN), a key nicotinamide adenine dinucleotide (NAD+) intermediate, has been shown to exert neuroprotection for retinal diseases. However, it remains unclear whether NMN can prevent retinal I/R injury. Thus, we aimed to determine whether NMN therapy is useful for retinal I/R injury-induced retinal degeneration. One day after NMN intraperitoneal (IP) injection, adult mice were subjected to retinal I/R injury. Then, the mice were injected with NMN once every day for three days. Electroretinography and immunohistochemistry were used to measure retinal functional alterations and retinal inflammation, respectively. The protective effect of NMN administration was further examined using a retinal cell line, 661W, under CoCl2-induced oxidative stress conditions. NMN IP injection significantly suppressed retinal functional damage, as well as inflammation. NMN treatment showed protective effects against oxidative stress-induced cell death. The antioxidant pathway (Nrf2 and Hmox-1) was activated by NMN treatment. In conclusion, NMN could be a promising preventive neuroprotective drug for ischemic retinopathy.