Enhancing fractalkine/CX3CR1 signalling pathway can reduce neuroinflammation by attenuating microglia activation in experimental diabetic retinopathy

Microglia in retinal diseases: From pathogenesis towards therapeutic strategies

Microglia, a widely dispersed cohort of immune cells in the retina, are intricately involved in a diverse range of pivotal biological processes, including inflammation, vascular development, complement activation, antigen presentation, and phagocytosis. Within the retinal milieu, microglia are crucial for the clearance of dead cells and cellular debris, release of anti-inflammatory agents, and orchestration of vascular network remodeling to maintain homeostasis. In addition, microglia are key mediators of neuroinflammation. Triggered by oxidative stress, elevated intraocular pressure, genetic anomalies, and immune dysregulation, microglia release numerous inflammatory cytokines, contributing to the pathogenesis of various retinal disorders. Recent studies on the ontogeny and broad functions of microglia in the retina have elucidated their characteristics during retinal development, homeostasis, and disease. Furthermore, therapeutic strategies that target microglia and their effector cytokines have been developed and shown positive results for some retinal diseases. Therefore, we systematically review the microglial ontogeny in the retina, elucidate their dual roles in retinal homeostasis and disease pathogenesis, and demonstrate microglia-based targeted therapeutic strategies for retinal diseases.

MDSCs promote pathological angiogenesis in ocular neovascular disease

BACKGROUND

Ocular neovascular diseases, which contribute significantly to vision loss, lack effective preventive treatments. Recent studies have highlighted the significant involvement of immune cells in neovascular retinopathy. Myeloid-derived suppressor cells (MDSCs) promote the development of neovascularization, but it is unknown whether they participate in pathological neovascularization and whether they are expected to be a therapeutic target.

METHOD

We investigated the role of MDSCs in promoting pathological angiogenesis using an oxygen-induced retinopathy (OIR) model, employing flow cytometry, immunofluorescence, and smart-seq analysis. Then, we evaluated the proportion of MDSCs in patient blood samples using flow cytometry. Additionally, we assessed the effect of MDSC depletion using an anti-Gr-1 monoclonal antibody on retinal vasculopathy and alterations in retinal microglia.

RESULTS

In the OIR model, an elevated ratio of MDSCs was observed in both blood and retinal tissue during phase II (Neovascularization). The depletion of MDSCs resulted in reduced retinal neovascularization and vaso-obliteration, along with a decrease in microglia within the neovascularization area. Furthermore, analysis of gene transcripts associated with MDSCs indicated activation of vascular endothelial growth factor (VEGF) regulation and inflammation. Importantly, infants with ROP exhibited a higher proportion of MDSCs in their blood samples.

CONCLUSION

Our results suggested that excessive MDSCs represent an unrecognized feature of ocular neovascular diseases and be responsible for the retinal vascular inflammation and angiogenesis, providing opportunities for new therapeutic approaches to ocular neovascular disease.

Multifunctional nanogel loaded with cerium oxide nanozyme and CX3CL1 protein: Targeted immunomodulation and retinal protection in uveitis rat model

Effectively addressing retinal issues represents a pivotal aspect of blindness-related diseases. Novel approaches involving reducing inflammation and rebalancing the immune response are paramount in the treatment of these conditions. This study delves into the potential of a nanogel system comprising polyethylenimine-benzene boric acid-hyaluronic acid (PEI-PBA-HA). We have evaluated the collaborative impact of cerium oxide nanozyme and chemokine CX3CL1 protein for targeted immunomodulation and retinal protection in uveitis models. Our nanogel system specifically targets the posterior segment of the eyes. The synergistic effect in this area reduces oxidative stress and hampers the activation of microglia, thereby alleviating the pathological immune microenvironment. This multifaceted drug delivery system disrupts the cycle of oxidative stress, inflammation, and immune response, suppressing initial immune cells and limiting local retinal structural damage induced by excessive immune reactions. Our research sheds light on interactions within retinal target cells, providing a promising avenue for the development of efficient and innovative drug delivery platforms.

Redefining our vision: an updated guide to the ocular immune system

Balanced immune responses in the eyes are crucial to preserve vision. The ocular immune system has long been considered distinct, owing to the so-called 'immune privilege' of its component tissues. More recently, intravital imaging and transcriptomic techniques have reshaped scientific understanding of the ocular immune landscape, such as revealing the specialization of immune cell populations in the various tissues of the eye. As knowledge of the phenotypes of corneal and retinal immune cells has evolved, links to both the systemic immune system, and the central and peripheral nervous systems, have been identified. Using intravital imaging, T cells have recently been found to reside in, and actively patrol, the healthy human cornea. Disease-associated retinal microglia with links to retinal degeneration have also been identified. This Review provides an updated guide to the ocular immune system, highlighting current knowledge of the immune cells that are present in steady-state and specific diseased ocular tissues, as well as evidence for their relationship to systemic disease. In addition, we discuss emerging intravital imaging techniques that can be used to visualize immune cell morphology and dynamics in living human eyes and how these could be applied to advance understanding of the human immune system.

Microvascular destabilization and intricated network of the cytokines in diabetic retinopathy: from the perspective of cellular and molecular components

Microvascular destabilization is the primary cause of the inner blood-retinal barrier (iBRB) breakdown and increased vascular leakage in diabetic retinopathy (DR). Microvascular destabilization results from the combinational effects of increased levels of growth factors and cytokines, involvement of inflammation, and the changed cell-to-cell interactions, especially the loss of endothelial cells and pericytes, due to hyperglycemia and hypoxia. As the manifestation of microvascular destabilization, the fluid transports via paracellular and transcellular routes increase due to the disruption of endothelial intercellular junctional complexes and/or the altered caveolar transcellular transport across the retinal vascular endothelium. With diabetes progression, the functional and the structural changes of the iBRB components, including the cellular and noncellular components, further facilitate and aggravate microvascular destabilization, resulting in macular edema, the neuroretinal damage and the dysfunction of retinal inner neurovascular unit (iNVU). Although there have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying the microvascular destabilization, some still remain to be fully elucidated. Recent data indicate that targeting the intricate signaling pathways may allow to against the microvascular destabilization. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in the microvascular destabilization in DR. In this review, we discuss: (1) the brief introduction of DR and microvascular destabilization; (2) the cellular and molecular components of iBRB and iNVU, and the breakdown of iBRB; (3) the matrix and cell-to-cell contacts to maintain microvascular stabilization, including the endothelial glycocalyx, basement membrane, and various cell-cell interactions; (4) the molecular mechanisms mediated cell-cell contacts and vascular cell death; (5) the altered cytokines and signaling pathways as well as the intricate network of the cytokines involved in microvascular destabilization. This comprehensive review aimed to provide the insights for microvascular destabilization by targeting the key molecules or specific iBRB cells, thus restoring the function and structure of iBRB and iNVU, to treat DR.

Macrophage activation contributes to diabetic retinopathy

Diabetic retinopathy (DR) is recognized as a neurovascular complication of diabetes, and emerging evidence underscores the pivotal role of inflammation in its pathophysiology. Macrophage activation is increasingly acknowledged as a key contributor to the onset and progression of DR. Different populations of macrophages originating from distinct sources contribute to DR-associated inflammation. Retinal macrophages can be broadly categorized into two main groups based on their origin: intrinsic macrophages situated within the retina and vitreoretinal interface and macrophages derived from infiltrating monocytes. The former comprises microglia (MG), perivascular macrophages, and macrophage-like hyalocytes. Retinal MG, as the principal population of tissue-resident population of mononuclear phagocytes, exhibits high heterogeneity and plasticity while serving as a crucial connector between retinal capillaries and synapses. This makes MG actively involved in the pathological processes across various stages of DR. Activated hyalocytes also contribute to the pathological progression of advanced DR. Additionally, recruited monocytes, displaying rapid turnover in circulation, augment the population of retinal macrophages during DR pathogenesis, exerting pathogenic or protective effect based on different subtypes. In this review, we examine novel perspectives on macrophage biology based on recent studies elucidating the diversity of macrophage identity and function, as well as the mechanisms influencing macrophage behavior. These insights may pave the way for innovative therapeutic strategies in the management of DR.

Translocator protein (18 kDa) (Tspo) in the retina and implications for ocular diseases

Translocator protein (18 kDa) (Tspo), formerly known as peripheral benzodiazepine receptor is a highly conserved transmembrane protein primarily located in the outer mitochondrial membrane. In the central nervous system (CNS), especially in glia cells, Tspo is upregulated upon inflammation. Consequently, Tspo was used as a tool for diagnostic in vivo imaging of neuroinflammation in the brain and as a potential therapeutic target. Several synthetic Tspo ligands have been explored as immunomodulatory and neuroprotective therapy approaches. Although the function of Tspo and how its ligands exert these beneficial effects is not fully clear, it became a research topic of interest, especially in ocular diseases in the past few years. This review summarizes state-of-the-art knowledge of Tspo expression and its proposed functions in different cells of the retina including microglia, retinal pigment epithelium and Müller cells. Tspo is involved in cytokine signaling, oxidative stress and reactive oxygen species production, calcium signaling, neurosteroid synthesis, energy metabolism, and cholesterol efflux. We also highlight recent developments in preclinical models targeting Tspo and summarize the relevance of Tspo biology for ocular and retinal diseases. We conclude that glial upregulation of Tspo in different ocular pathologies and the use of Tspo ligands as promising therapeutic approaches in preclinical studies underline the importance of Tspo as a potential disease-modifying protein.

CX3CR1 mediates motor dysfunction in mice through 5-HTR2a

CX3CR1 knockout could induce motor dysfunction in several neurological disease models mainly through regulating microglia's function. While CX3CR1 was expressed on neurons in a few reports, whether neuronal CX3CR1 could affect the function of neurons and mediate motor dysfunction under physiological conditions is unknown. To elucidate the roles of neuronal CX3CR1 on motor dysfunction, CX3CR1 knockout mice were created. Rotarod test and Open field test found that the CX3CR1-/- mice's motor capacity was reduced. Immunofluorescence staining detected the expression of CX3CR1 in neurons both in vivo and in vitro. Immunohistochemistry and West blot found that knockout of CX3CR1 did not affect the neurons' number in both spinal cord and brain of mice. While inhibiting the function of CX3CR1 by AZD8797 could decrease the expression of 5-Hydroxytryptamine receptor(5-HTR2a), which involved in the regulation of motor function. Further investigation revealed that CX3CR1 regulated the expression of HTR2a through the NF-κB pathway. For the first time, we reported that neuronal CXCR1 mediates motor dysfunction. Our results suggest that modulating CXCR1 activity offers a novel therapeutic strategy for motor dysfunction.

Inflammation and Neurodegeneration in Glaucoma: Isolated Eye Disease or a Part of a Systemic Disorder? - Serum Proteomic Analysis

Introduction

Glaucoma is the most common optic neuropathy and the leading cause of irreversible blindness worldwide, which affects 3.54% of the population aged 40-80 years. Despite numerous published studies, some aspects of glaucoma pathogenesis, serum biomarkers, and their potential link with other diseases remain unclear. Recent articles have proposed that autoimmune, oxidative stress and inflammation may be involved in the pathogenesis of glaucoma.

Methods

We investigated the serum expression of 92 inflammatory and neurotrophic factors in glaucoma patients. The study group consisted of 26 glaucoma patients and 192 healthy subjects based on digital fundography.

Results

Patients with glaucoma had significantly lower serum expression of IL-2Rβ, TWEAK, CX3CL1, CD6, CD5, LAP TGF-beta1, LIF-R, TRAIL, NT-3, and CCL23 and significantly higher expression of IL-22Rα1.

Conclusion

Our results indicate that patients with glaucoma tend to have lower levels of neuroprotective proteins and higher levels of neuroinflammatory proteins, similar to those observed in psychiatric, neurodegenerative and autoimmune diseases, indicating a potential link between these conditions and glaucoma pathogenesis.

Therapeutic Delivery of Soluble Fractalkine Ameliorates Vascular Dysfunction in the Diabetic Retina

Diabetic retinopathy (DR)-associated vision loss is a devastating disease affecting the working-age population. Retinal pathology is due to leakage of serum components into retinal tissues, activation of resident phagocytes (microglia), and vascular and neuronal damage. While short-term interventions are available, they do not revert visual function or halt disease progression. The impact of microglial inflammatory responses on the neurovascular unit remains unknown. In this study, we characterized microglia-vascular interactions in an experimental model of DR. Early diabetes presents activated retinal microglia, vascular permeability, and vascular abnormalities coupled with vascular tortuosity and diminished astrocyte and endothelial cell-associated tight-junction (TJ) and gap-junction (GJ) proteins. Microglia exclusively bind to the neuronal-derived chemokine fractalkine (FKN) via the CX3CR1 receptor to ameliorate microglial activation. Using neuron-specific recombinant adeno-associated viruses (rAAVs), we therapeutically overexpressed soluble (sFKN) or membrane-bound (mFKN) FKN using intra-vitreal delivery at the onset of diabetes. This study highlights the neuroprotective role of rAAV-sFKN, reducing microglial activation, vascular tortuosity, fibrin(ogen) deposition, and astrogliosis and supporting the maintenance of the GJ connexin-43 (Cx43) and TJ zonula occludens-1 (ZO-1) molecules. The results also show that microglia-vascular interactions influence the vascular width upon administration of rAAV-sFKN and rAAV-mFKN. Administration of rAAV-sFKN improved visual function without affecting peripheral immune responses. These findings suggest that overexpression of rAAV-sFKN can mitigate vascular abnormalities by promoting glia-neural signaling. sFKN gene therapy is a promising translational approach to reverse vision loss driven by vascular dysfunction.

The ideal treatment timing for diabetic retinopathy: the molecular pathological mechanisms underlying early-stage diabetic retinopathy are a matter of concern

Diabetic retinopathy (DR) is a prevalent complication of diabetes, significantly impacting patients' quality of life due to vision loss. No pharmacological therapies are currently approved for DR, excepted the drugs to treat diabetic macular edema such as the anti-VEGF agents or steroids administered by intraocular route. Advancements in research have highlighted the crucial role of early intervention in DR for halting or delaying disease progression. This holds immense significance in enhancing patients' quality of life and alleviating the societal burden associated with medical care costs. The non-proliferative stage represents the early phase of DR. In comparison to the proliferative stage, pathological changes primarily manifest as microangiomas and hemorrhages, while at the cellular level, there is a loss of pericytes, neuronal cell death, and disruption of components and functionality within the retinal neuronal vascular unit encompassing pericytes and neurons. Both neurodegenerative and microvascular abnormalities manifest in the early stages of DR. Therefore, our focus lies on the non-proliferative stage of DR and we have initially summarized the mechanisms involved in its development, including pathways such as polyols, that revolve around the pathological changes occurring during this early stage. We also integrate cutting-edge mechanisms, including leukocyte adhesion, neutrophil extracellular traps, multiple RNA regulation, microorganisms, cell death (ferroptosis and pyroptosis), and other related mechanisms. The current status of drug therapy for early-stage DR is also discussed to provide insights for the development of pharmaceutical interventions targeting the early treatment of DR.

Microglial inflammation modulates opioid analgesic tolerance

As we all know, opioids are the drugs of choice for treating severe pain. However, very often, opioid use leads to tolerance, dependence, and hyperalgesia. Therefore, understanding the mechanisms underlying opioid tolerance and designing strategies for increasing the efficacy of opioids in chronic pain are important areas of research. Microglia are brain macrophages that remove debris and dead cells from the brain and participate in immune defense of the central nervous system during an insult or injury. However, recent studies indicate that microglial activation and generation of proinflammatory molecules (e.g., cytokines, nitric oxide, eicosanoids, etc.) in the brain may contribute to opioid tolerance and other side effects of opioid use. In this review, we will summarize the evidence and possible mechanisms by which proinflammatory molecules produced by activated microglia may antagonize the analgesic effect induced by opioids, and thus, lead to opioid tolerance. We will also delineate specific examples of studies that suggest therapeutic targets to counteract the development of tolerance clinically using suppressors of microglial inflammation.

Down-regulation of histone deacetylase 7 reduces biological activities of retinal microvascular endothelial cells under high glucose condition and related mechanism

AIM

To investigate the expression and effect of histone deacetylase 7 (HDAC7) in human retinal microvascular endothelial cells (HRMECs) under high glucose condition and related mechanism, and the expression of HDAC7 in the retinal tissue in diabetic rats.

METHODS

The expression of HDAC7 in HRMECs under high glucose and the retinal tissue from normal or diabetic rats were detected with immunohistochemistry and Western blot. LV-shHDAC7 HRMECs were used to study the effect of HDAC7 on cell activities. Cell count kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, scratch test, Transwell test and tube formation assay were used to examine the ability of cell proliferation, migration, and angiogenesis. Finally, a preliminary exploration of its mechanism was performed by Western blot.

RESULTS

The expression of HDAC7 was both up-regulated in retinal tissues of diabetic rats and high glucose-treated HRMECs. Down-regulation of HDAC7 expression significantly reduced the ability of proliferation, migration, and tube formation, and reversed the high glucose-induced high expression of CDK1/Cyclin B1 and vascular endothelial growth factor in high glucose-treated HRMECs.

CONCLUSION

High glucose can up-regulate the expression of HDAC7 in HRMECs. Down-regulation of HDAC7 can inhibit HRMECs activities. HDAC7 is proposed to be involved in pathogenesis of diabetic retinopathy and a therapeutic target.

Immune Fingerprint in Diabetes: Ocular Surface and Retinal Inflammation

Diabetes is a prevalent global health issue associated with significant morbidity and mortality. Diabetic retinopathy (DR) is a well-known inflammatory, neurovascular complication of diabetes and a leading cause of preventable blindness in developed countries among working-age adults. However, the ocular surface components of diabetic eyes are also at risk of damage due to uncontrolled diabetes, which is often overlooked. Inflammatory changes in the corneas of diabetic patients indicate that inflammation plays a significant role in diabetic complications, much like in DR. The eye's immune privilege restricts immune and inflammatory responses, and the cornea and retina have a complex network of innate immune cells that maintain immune homeostasis. Nevertheless, low-grade inflammation in diabetes contributes to immune dysregulation. This article aims to provide an overview and discussion of how diabetes affects the ocular immune system's main components, immune-competent cells, and inflammatory mediators. By understanding these effects, potential interventions and treatments may be developed to improve the ocular health of diabetic patients.

Pharmacological depletion of microglia alleviates neuronal and vascular damage in the diabetic CX3CR1-WT retina but not in CX3CR1-KO or hCX3CR1I249/M280-expressing retina

Diabetic retinopathy, a microvascular disease characterized by irreparable vascular damage, neurodegeneration and neuroinflammation, is a leading complication of diabetes mellitus. There is no cure for DR, and medical interventions marginally slow the progression of disease. Microglia-mediated inflammation in the diabetic retina is regulated via CX3CR1-FKN signaling, where FKN serves as a calming signal for microglial activation in several neuroinflammatory models. Polymorphic variants of CX3CR1, hCX3CR1I249/M280 , found in 25% of the human population, result in a receptor with lower binding affinity for FKN. Furthermore, disrupted CX3CR1-FKN signaling in CX3CR1-KO and FKN-KO mice leads to exacerbated microglial activation, robust neuronal cell loss and substantial vascular damage in the diabetic retina. Thus, studies to characterize the effects of hCX3CR1I249/M280 -expression in microglia-mediated inflammation in the diseased retina are relevant to identify mechanisms by which microglia contribute to disease progression. Our results show that hCX3CR1I249/M280 mice are significantly more susceptible to microgliosis and production of Cxcl10 and TNFα under acute inflammatory conditions. Inflammation is exacerbated under diabetic conditions and coincides with robust neuronal loss in comparison to CX3CR1-WT mice. Therefore, to further investigate the role of hCX3CR1I249/M280 -expression in microglial responses, we pharmacologically depleted microglia using PLX-5622, a CSF-1R antagonist. PLX-5622 treatment led to a robust (~70%) reduction in Iba1+ microglia in all non-diabetic and diabetic mice. CSF-1R antagonism in diabetic CX3CR1-WT prevented TUJ1+ axonal loss, angiogenesis and fibrinogen deposition. In contrast, PLX-5622 microglia depletion in CX3CR1-KO and hCX3CR1I249/M280 mice did not alleviate TUJ1+ axonal loss or angiogenesis. Interestingly, PLX-5622 treatment reduced fibrinogen deposition in CX3CR1-KO mice but not in hCX3CR1I249/M280 mice, suggesting that hCX3CR1I249/M280 expressing microglia influences vascular pathology differently compared to CX3CR1-KO microglia. Currently CX3CR1-KO mice are the most commonly used strain to investigate CX3CR1-FKN signaling effects on microglia-mediated inflammation and the results in this study indicate that hCX3CR1I249/M280 receptor variants may serve as a complementary model to study dysregulated CX3CR1-FKN signaling. In summary, the protective effects of microglia depletion is CX3CR1-dependent as microglia depletion in CX3CR1-KO and hCX3CR1I249/M280 mice did not alleviate retinal degeneration nor microglial morphological activation as observed in CX3CR1-WT mice.

Effects of diabetes on microglial physiology: a systematic review of in vitro, preclinical and clinical studies

Diabetes mellitus is a heterogeneous chronic metabolic disorder characterized by the presence of hyperglycemia, commonly preceded by a prediabetic state. The excess of blood glucose can damage multiple organs, including the brain. In fact, cognitive decline and dementia are increasingly being recognized as important comorbidities of diabetes. Despite the largely consistent link between diabetes and dementia, the underlying causes of neurodegeneration in diabetic patients remain to be elucidated. A common factor for almost all neurological disorders is neuroinflammation, a complex inflammatory process in the central nervous system for the most part orchestrated by microglial cells, the main representatives of the immune system in the brain. In this context, our research question aimed to understand how diabetes affects brain and/or retinal microglia physiology. We conducted a systematic search in PubMed and Web of Science to identify research items addressing the effects of diabetes on microglial phenotypic modulation, including critical neuroinflammatory mediators and their pathways. The literature search yielded 1327 records, including 18 patents. Based on the title and abstracts, 830 papers were screened from which 250 primary research papers met the eligibility criteria (original research articles with patients or with a strict diabetes model without comorbidities, that included direct data about microglia in the brain or retina), and 17 additional research papers were included through forward and backward citations, resulting in a total of 267 primary research articles included in the scoping systematic review. We reviewed all primary publications investigating the effects of diabetes and/or its main pathophysiological traits on microglia, including in vitro studies, preclinical models of diabetes and clinical studies on diabetic patients. Although a strict classification of microglia remains elusive given their capacity to adapt to the environment and their morphological, ultrastructural and molecular dynamism, diabetes modulates microglial phenotypic states, triggering specific responses that include upregulation of activity markers (such as Iba1, CD11b, CD68, MHC-II and F4/80), morphological shift to amoeboid shape, secretion of a wide variety of cytokines and chemokines, metabolic reprogramming and generalized increase of oxidative stress. Pathways commonly activated by diabetes-related conditions include NF-κB, NLRP3 inflammasome, fractalkine/CX3CR1, MAPKs, AGEs/RAGE and Akt/mTOR. Altogether, the detailed portrait of complex interactions between diabetes and microglia physiology presented here can be regarded as an important starting point for future research focused on the microglia-metabolism interface.

miRNA-124 Prevents Rat Diabetic Retinopathy by Inhibiting the Microglial Inflammatory Response

Diabetic retinopathy (DR) is characterized by vasoregression and glial activation. miRNA-124 (miR-124) reduces retinal microglial activation and alleviates vasoregression in a neurodegenerative rat model. Our aim was to determine whether miR-124 affects vascular and neural damage in the early diabetic retina. Diabetes was induced in 8-week-old Wistar rats by streptozotocin (STZ) injection. At 16 and 20 weeks, the diabetic rats were intravitreally injected with miR-124 mimic, and retinae were analyzed at 24 weeks. Microvascular damage was identified by evaluating pericyte loss and acellular capillary (AC) formation. Müller glial activation was assessed by glial fibrillary acidic protein (GFAP) immunofluorescence staining. Microglial activation was determined by immunofluorescent staining of ionized calcium-binding adaptor molecule 1 (Iba1) in whole mount retinae. The neuroretinal function was assessed by electroretinography. The expression of inflammation-associated genes was evaluated by qRT-PCR. A wound healing assay was performed to quantitate the mobility of microglial cells. The results showed that miR-124 treatment alleviated diabetic vasoregression by reducing AC formation and pericyte loss. miR-124 blunted Müller glial- and microglial activation in diabetic retinae and ameliorated neuroretinal function. The retinal expression of inflammatory factors including Tnf-α, Il-1β, Cd74, Ccl2, Ccl3, Vcam1, Tgf-β1, Arg1, and Il-10 was reduced by miR-124 administration. The elevated mobility of microglia upon high glucose exposure was normalized by miR-124. The expression of the transcription factor PU.1 and lipid raft protein Flot1 was downregulated by miR-124. In rat DR, miR-124 prevents vasoregression and glial activation, improves neuroretinal function, and modulates microglial activation and inflammatory responses.

Microglial Activation and Priming in Alzheimer's Disease: State of the Art and Future Perspectives

Alzheimer's Disease (AD) is the most common cause of dementia, having a remarkable social and healthcare burden worldwide. Amyloid β (Aβ) and protein Tau aggregates are disease hallmarks and key players in AD pathogenesis. However, it has been hypothesized that microglia can contribute to AD pathophysiology, as well. Microglia are CNS-resident immune cells belonging to the myeloid lineage of the innate arm of immunity. Under physiological conditions, microglia are in constant motion in order to carry on their housekeeping function, and they maintain an anti-inflammatory, quiescent state, with low expression of cytokines and no phagocytic activity. Upon various stimuli (debris, ATP, misfolded proteins, aggregates and pathogens), microglia acquire a phagocytic function and overexpress cytokine gene modules. This process is generally regarded as microglia activation and implies that the production of pro-inflammatory cytokines is counterbalanced by the synthesis and the release of anti-inflammatory molecules. This mechanism avoids excessive inflammatory response and inappropriate microglial activation, which causes tissue damage and brain homeostasis impairment. Once the pathogenic stimulus has been cleared, activated microglia return to the naïve, anti-inflammatory state. Upon repeated stimuli (as in the case of Aβ deposition in the early stage of AD), activated microglia shift toward a less protective, neurotoxic phenotype, known as "primed" microglia. The main characteristic of primed microglia is their lower capability to turn back toward the naïve, anti-inflammatory state, which makes these cells prone to chronic activation and favours chronic inflammation in the brain. Primed microglia have impaired defence capacity against injury and detrimental effects on the brain microenvironment. Additionally, priming has been associated with AD onset and progression and can represent a promising target for AD treatment strategies. Many factors (genetics, environmental factors, baseline inflammatory status of microglia, ageing) generate an aberrantly activated phenotype that undergoes priming easier and earlier than normally activated microglia do. Novel, promising targets for therapeutic strategies for AD have been sought in the field of microglia activation and, importantly, among those factors influencing the baseline status of these cells. The CX3CL1 pathway could be a valuable target treatment approach in AD, although preliminary findings from the studies in this field are controversial. The current review aims to summarize state of the art on the role of microglia dysfunction in AD pathogenesis and proposes biochemical pathways with possible targets for AD treatment.

CX3CR1 deficiency exacerbates immune-mediated hepatitis by increasing NF-κB-mediated cytokine production in macrophage and T cell

Immune-mediated hepatitis is marked by liver inflammation characterized by immune cell infiltration, chemokine/cytokine production, and hepatocyte injury. C-X3C motif receptor 1 (CX3CR1), as the receptor of chemokine C-X3C motif ligand 1 (CX3CL1)/fractalkine, is mainly expressed on immune cells including monocytes and T cells. Previous studies have shown that CX3CR1 protects against liver fibrosis, but the exact role of CX3CL1/CX3CR1 in acute immune-mediated hepatitis remains unknown. Here, we investigate the role of the CX3CL1/CX3CR1 axis in immune-mediated hepatitis using concanavalin A (ConA)-induced liver injury model in CX3CR1-deficient (Cx3cr1^-/-) mice. We observed that Cx3cr1^-/- mice had severe liver injury and increased pro-inflammatory cytokines (tumor necrosis factor-alpha [TNF-α], interferon-gamma [IFN-γ], interleukin-1 beta [IL-1β], and IL-6) in serum and liver compared to wild-type (Cx3cr1^+/+) mice after ConA injection. The deficiency of CX3CR1 did not affect ConA-induced immune cell infiltration in liver but led to elevated production of TNF-α in macrophages as well as IFN-γ in T cells after ConA treatment. On the contrary, exogenous CX3CL1 attenuated ConA-induced cytokine production in wild type, but not CX3CR1-deficient macrophages and T cells. Furthermore, in vitro results showed that CX3CR1 deficiency promoted the pro-inflammatory cytokine expression by increasing the phosphorylation of nuclear factor kappa B (NF-κB) p65 (p-NF-κB p65). Finally, pre-treatment of p-NF-κB p65 inhibitor, resveratrol, attenuated ConA-induced liver injury and inflammatory responses, especially in Cx3cr1^-/- mice. In conclusion, our data show that the deficiency of CX3CR1 promotes pro-inflammatory cytokine production in macrophages and T cells by enhancing the phosphorylation of NF-κB p65, which exacerbates liver injury in ConA-induced hepatitis.

The role of inflammation in immune system of diabetic retinopathy: Molecular mechanisms, pathogenetic role and therapeutic implications

Diabetic retinopathy is one of the most common complications of diabetes mellitus and the leading cause of low vision and blindness worldwide. Mounting evidence demonstrates that inflammation is a key mechanism driving diabetes-associated retinal disturbance, yet the pathophysiological process and molecular mechanisms of inflammation underlying diabetic retinopathy are not fully understood. Cytokines, chemokines, and adhesion molecules interact with each other to form a complex molecular network that propagates the inflammatory and pathological cascade of diabetic retinopathy. Therefore, it is important to understand and elucidate inflammation-related mechanisms behind diabetic retinopathy progression. Here, we review the current understanding of the pathology and pathogenesis of inflammation in diabetic retinopathy. In addition, we also summarize the relevant clinical trials to further suggest inflammation-targeted therapeutics for prevention and management of diabetic retinopathy.

More than meets the eye: The role of microglia in healthy and diseased retina

Microglia are the main resident immune cells of the nervous system and as such they are involved in multiple roles ranging from tissue homeostasis to response to insults and circuit refinement. While most knowledge about microglia comes from brain studies, some mechanisms have been confirmed for microglia cells in the retina, the light-sensing compartment of the eye responsible for initial processing of visual information. However, several key pieces of this puzzle are still unaccounted for, as the characterization of retinal microglia has long been hindered by the reduced population size within the retina as well as the previous lack of technologies enabling single-cell analyses. Accumulating evidence indicates that the same cell type may harbor a high degree of transcriptional, morphological and functional differences depending on its location within the central nervous system. Thus, studying the roles and signatures adopted specifically by microglia in the retina has become increasingly important. Here, we review the current understanding of retinal microglia cells in physiology and in disease, with particular emphasis on newly discovered mechanisms and future research directions.

Neuroinflammation in retinitis pigmentosa: Therapies targeting the innate immune system

Retinitis pigmentosa (RP) is an important cause of irreversible blindness worldwide and lacks effective treatment strategies. Although mutations are the primary cause of RP, research over the past decades has shown that neuroinflammation is an important cause of RP progression. Due to the abnormal activation of immunity, continuous sterile inflammation results in neuron loss and structural destruction. Therapies targeting inflammation have shown their potential to attenuate photoreceptor degeneration in preclinical models. Regardless of variations in genetic background, inflammatory modulation is emerging as an important role in the treatment of RP. We summarize the evidence for the role of inflammation in RP and mention therapeutic strategies where available, focusing on the modulation of innate immune signals, including TNFα signaling, TLR signaling, NLRP3 inflammasome activation, chemokine signaling and JAK/STAT signaling. In addition, we describe epigenetic regulation, the gut microbiome and herbal agents as prospective treatment strategies for RP in recent advances.

Diabetic Macular Edema: Current Understanding, Molecular Mechanisms and Therapeutic Implications

Diabetic retinopathy (DR), with increasing incidence, is the major cause of vision loss and blindness worldwide in working-age adults. Diabetic macular edema (DME) remains the main cause of vision impairment in diabetic patients, with its pathogenesis still not completely elucidated. Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of DR and DME. Currently, intravitreal injection of anti-VEGF agents remains as the first-line therapy in DME treatment due to the superior anatomic and functional outcomes. However, some patients do not respond satisfactorily to anti-VEGF injections. More than 30% patients still exist with persistent DME even after regular intravitreal injection for at least 4 injections within 24 weeks, suggesting other pathogenic factors, beyond VEGF, might contribute to the pathogenesis of DME. Recent advances showed nearly all the retinal cells are involved in DR and DME, including breakdown of blood-retinal barrier (BRB), drainage dysfunction of Müller glia and retinal pigment epithelium (RPE), involvement of inflammation, oxidative stress, and neurodegeneration, all complicating the pathogenesis of DME. The profound understanding of the changes in proteomics and metabolomics helps improve the elucidation of the pathogenesis of DR and DME and leads to the identification of novel targets, biomarkers and potential therapeutic strategies for DME treatment. The present review aimed to summarize the current understanding of DME, the involved molecular mechanisms, and the changes in proteomics and metabolomics, thus to propose the potential therapeutic recommendations for personalized treatment of DME.

Diabetic retinopathy: Involved cells, biomarkers, and treatments

Diabetic retinopathy (DR), a leading cause of vision loss and blindness worldwide, is caused by retinal neurovascular unit dysfunction, and its cellular pathology involves at least nine kinds of retinal cells, including photoreceptors, horizontal and bipolar cells, amacrine cells, retinal ganglion cells, glial cells (Müller cells, astrocytes, and microglia), endothelial cells, pericytes, and retinal pigment epithelial cells. Its mechanism is complicated and involves loss of cells, inflammatory factor production, neovascularization, and BRB impairment. However, the mechanism has not been completely elucidated. Drug treatment for DR has been gradually advancing recently. Research on potential drug targets relies upon clear information on pathogenesis and effective biomarkers. Therefore, we reviewed the recent literature on the cellular pathology and the diagnostic and prognostic biomarkers of DR in terms of blood, protein, and clinical and preclinical drug therapy (including synthesized molecules and natural molecules). This review may provide a theoretical basis for further DR research.