New insights into mononuclear phagocyte biology from the visual system

Functional genomics in age-related macular degeneration: From genetic associations to understanding disease mechanisms

Genome-wide association studies have been remarkably successful in identifying genetic variants associated with age-related macular degeneration (AMD), demonstrating a strong genetic component largely driven by common variants. However, progress in translating these genetic findings into a deeper understanding of disease mechanisms and new therapies has been slow. Slow progress in this area can be attributed to limited knowledge of the functional impact of AMD-associated non-coding variants on gene function, the molecular mechanisms and cell types underlying disease. This review offers a comprehensive overview of functional genomics approaches to uncover the genetic, epigenetic, cellular and molecular mechanisms underlying AMD and outlines future directions for research.

The neuroimmune interface in retinal regeneration

Retinal neurodegeneration leads to irreversible blindness due to the mammalian nervous system's inability to regenerate lost neurons. Efforts to regenerate retina involve two main strategies: stimulating endogenous cells to reprogram into neurons or transplanting stem-cell derived neurons into the degenerated retina. However, both approaches must overcome a major barrier in getting new neurons to grow back down the optic nerve and connect to appropriate visual targets in environments that differ significantly from developmental conditions. While immune privilege has historically been associated with the central nervous system, an emerging literature highlights the active role of immune cells in shaping neurodegeneration and regeneration. This review explores the neuroimmune interface in retinal repair, dissecting how immune interactions influence glial reprogramming, transplantation outcomes, and axonal regeneration. By integrating insights from regenerative species with mammalian models, we highlight novel immunomodulatory strategies to optimize retinal regeneration.

Emerging nanomedicines for macrophage-mediated cancer therapy

Tumor-associated macrophages (TAMs) contribute to tumor progression by promoting angiogenesis, remodeling the tumor extracellular matrix, inducing tumor invasion and metastasis, as well as immune evasion. Due to the high plasticity of TAMs, they can polarize into different phenotypes with distinct functions, which are primarily categorized as the pro-inflammatory, anti-tumor M1 type, and the anti-inflammatory, pro-tumor M2 type. Notably, anti-tumor macrophages not only directly phagocytize tumor cells, but also present tumor-specific antigens and activate adaptive immunity. Therefore, targeted regulation of TAMs to unleash their potential anti-tumor capabilities is crucial for improving the efficacy of cancer immunotherapy. Nanomedicine serves as a promising vehicle and can inherently interact with TAMs, hence, emerging as a new paradigm in cancer immunotherapy. Due to their controllable structures and properties, nanomedicines offer a plethora of advantages over conventional drugs, thus enhancing the balance between efficacy and toxicity. In this review, we provide an overview of the hallmarks of TAMs and discuss nanomedicines for targeting TAMs with a focus on inhibiting recruitment, depleting and reprogramming TAMs, enhancing phagocytosis, engineering macrophages, as well as targeting TAMs for tumor imaging. We also discuss the challenges and clinical potentials of nanomedicines for targeting TAMs, aiming to advance the exploitation of nanomedicine for cancer immunotherapy.

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.

Redefining the ontogeny of hyalocytes as yolk sac-derived tissue-resident macrophages of the vitreous body

BACKGROUND

The eye is a highly specialized sensory organ which encompasses the retina as a part of the central nervous system, but also non-neural compartments such as the transparent vitreous body ensuring stability of the eye globe and a clear optical axis. Hyalocytes are the tissue-resident macrophages of the vitreous body and are considered to play pivotal roles in health and diseases of the vitreoretinal interface, such as proliferative vitreoretinopathy or diabetic retinopathy. However, in contrast to other ocular macrophages, their embryonic origin as well as the extent to which these myeloid cells might be replenished by circulating monocytes remains elusive.

RESULTS

In this study, we combine transgenic reporter mice, embryonic and adult fate mapping approaches as well as parabiosis experiments with multicolor immunofluorescence labeling and confocal laser-scanning microscopy to comprehensively characterize the murine hyalocyte population throughout development and in adulthood. We found that murine hyalocytes express numerous well-known myeloid cell markers, but concomitantly display a distinct immunophenotype that sets them apart from retinal microglia. Embryonic pulse labeling revealed a yolk sac-derived origin of murine hyalocytes, whose precursors seed the developing eye prenatally. Finally, postnatal labeling and parabiosis established the longevity of hyalocytes which rely on Colony Stimulating Factor 1 Receptor (CSF1R) signaling for their maintenance, independent of blood-derived monocytes.

CONCLUSION

Our study identifies hyalocytes as long-living progeny of the yolk sac hematopoiesis and highlights their role as integral members of the innate immune system of the eye. As a consequence of their longevity, immunosenescence processes may culminate in hyalocyte dysfunction, thereby contributing to the development of vitreoretinal diseases. Therefore, myeloid cell-targeted therapies that convey their effects through the modification of hyalocyte properties may represent an interesting approach to alleviate the burden imposed by diseases of the vitreoretinal interface.

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Divergent local and systemic antitumor response in primary uveal melanomas

Uveal melanoma (UM) is the most common cancer of the eye. The loss of chromosome 3 (M3) is associated with a high risk of metastases. M3 tumors are more infiltrated by T-lymphocytes than low-risk disomic-3 (D3) tumors, contrasting with other tumor types in which T cell infiltration correlates with better prognosis. Whether these T cells represent an antitumor response and how these T cells would be primed in the eye are both unknown. Herein, we characterized the T cells infiltrating primary UMs. CD8+ and Treg cells were more abundant in M3 than in D3 tumors. CD39+PD-1+CD8+ T cells were enriched in M3 tumors, suggesting specific responses to tumor antigen (Ag) as confirmed using HLA-A2:Melan-A tetramers. scRNAseq-VDJ analysis of T cells evidenced high numbers of proliferating CD39+PD1+CD8+ clonal expansions, suggesting in situ antitumor Ag responses. TCRseq and tumor-Ag tetramer staining characterized the recirculation pattern of the antitumor responses in M3 and D3 tumors. Thus, tumor-Ag responses occur in localized UMs, raising the question of the priming mechanisms in the absence of known lymphatic drainage.

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.

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.

Revolutionizing Cancer Treatment: Unleashing the Power of Viral Vaccines, Monoclonal Antibodies, and Proteolysis-Targeting Chimeras in the New Era of Immunotherapy

In the realm of cancer immunotherapy, a profound evolution has ushered in sophisticated strategies that encompass both traditional cancer vaccines and emerging viral vaccines. This comprehensive Review offers an in-depth exploration of the methodologies, clinical applications, success stories, and future prospects of these approaches. Traditional cancer vaccines have undergone significant advancements utilizing diverse modalities such as proteins, peptides, and dendritic cells. More recent innovations have focused on the physiological mechanisms enabling the human body to recognize and combat precancerous and malignant cells, introducing specific markers like peptide-based anticancer vaccines targeting tumor-associated antigens. Moreover, cancer viral vaccines, leveraging engineered viruses to stimulate immune responses against specific antigens, exhibit substantial promise in inducing robust and enduring immunity. Integration with complementary therapeutic methods, including monoclonal antibodies, adjuvants, and radiation therapy, has not only improved survival rates but also deepened our understanding of viral virulence. Recent strides in vaccine design, encompassing oncolytic viruses, virus-like particles, and viral vectors, mark the frontier of innovation. While these advances hold immense potential, critical challenges must be addressed, such as strategies for immune evasion, potential off-target effects, and the optimization of viral genomes. In the landscape of immunotherapy, noteworthy innovations take the spotlight from the use of immunomodulatory agents for the enhancement of innate and adaptive immune collaboration. The emergence of proteolysis-targeting chimeras (PROTACs) as precision tools for cancer therapy is particularly exciting. With a focus on various cancers, from melanoma to formidable solid tumors, this Review critically assesses types of cancer vaccines, mechanisms, barriers in vaccine therapy, vaccine efficacy, safety profiles, and immune-related adverse events, providing a nuanced perspective on the underlying mechanisms involving cytotoxic T cells, natural killer cells, and dendritic cells. The Review also underscores the transformative potential of cutting-edge technologies such as clinical studies, molecular sequencing, and artificial intelligence in advancing the field of cancer vaccines. These tools not only expedite progress but also emphasize the multidimensional and rapidly evolving nature of this research, affirming its profound significance in the broader context of cancer therapy.

Shedding light on macrophage immunotherapy in lung cancer

The search for therapeutic options for lung cancer continues to advance, with rapid advances in the search for therapies to improve patient prognosis. At present, systemic chemotherapy, immune checkpoint inhibitor therapy, antiangiogenic therapy, and targeted therapy for driver gene positivity are available in the clinic. Common clinical treatments fail to achieve desired outcomes due to immunosuppression of the tumor microenvironment (TME). Tumor immune evasion is mediated by cytokines, chemokines, immune cells, and other cells such as vascular endothelial cells within the tumor immune microenvironment. Tumor-associated macrophages (TAMs) are important immune cells in the TME, inducing tumor angiogenesis, encouraging tumor cell proliferation and migration, and suppressing antitumor immune responses. Thus, TAM targeting becomes the key to lung cancer immunotherapy. This review focuses on macrophage phenotype, polarization mechanism, role in lung cancer, and advances in macrophage centric immunotherapies.

Ocular Vascular Diseases: From Retinal Immune Privilege to Inflammation

The eye is an immune privileged tissue that insulates the visual system from local and systemic immune provocation to preserve homeostatic functions of highly specialized retinal neural cells. If immune privilege is breached, immune stimuli will invade the eye and subsequently trigger acute inflammatory responses. Local resident microglia become active and release numerous immunological factors to protect the integrity of retinal neural cells. Although acute inflammatory responses are necessary to control and eradicate insults to the eye, chronic inflammation can cause retinal tissue damage and cell dysfunction, leading to ocular disease and vision loss. In this review, we summarized features of immune privilege in the retina and the key inflammatory responses, factors, and intracellular pathways activated when retinal immune privilege fails, as well as a highlight of the recent clinical and research advances in ocular immunity and ocular vascular diseases including retinopathy of prematurity, age-related macular degeneration, and diabetic retinopathy.

HIF1α-dependent hypoxia response in myeloid cells requires IRE1α

Cellular adaptation to low oxygen tension triggers primitive pathways that ensure proper cell function. Conditions of hypoxia and low glucose are characteristic of injured tissues and hence successive waves of inflammatory cells must be suited to function under low oxygen tension and metabolic stress. While Hypoxia-Inducible Factor (HIF)-1α has been shown to be essential for the inflammatory response of myeloid cells by regulating the metabolic switch to glycolysis, less is known about how HIF1α is triggered in inflammation. Here, we demonstrate that cells of the innate immune system require activity of the inositol-requiring enzyme 1α (IRE1α/XBP1) axis in order to initiate HIF1α-dependent production of cytokines such as IL1β, IL6 and VEGF-A. Knockout of either HIF1α or IRE1α in myeloid cells ameliorates vascular phenotypes in a model of retinal pathological angiogenesis driven by sterile inflammation. Thus, pathways associated with ER stress, in partnership with HIF1α, may co-regulate immune adaptation to low oxygen.

Mapping Resident Immune Cells in the Murine Ocular Surface and Lacrimal Gland by Flow Cytometry

BACKGROUND

The ocular surface and lacrimal gland have a frontline position in mucosal immunology. However, there have been few updates to the immune cell atlas of these tissues in recent years.

PURPOSE

To map the immune cells in murine ocular surface tissues and lacrimal gland.

METHODS

Central and peripheral corneas, conjunctiva, and lacrimal gland were dissociated into single cell suspensions, followed by flow cytometry. Discrepancy of immune cells between the central and peripheral corneas was compared. In the conjunctiva and lacrimal gland, myeloid cells were clustered by tSNE and FlowSOM based on the expression of F4/80, Ly6C, Ly6G, and MHC II. ILCs, type 1 immune cells, and type 3 immune cells were analyzed.

RESULTS

The number of immune cells in peripheral corneas was about 16 folds of that in central corneas. B cells accounted for 8.74% of immune cells in murine peripheral corneas. In the conjunctiva and lacrimal gland, most myeloid cells tended out to be monocytes, macrophages, and classical dendritic cells (cDCs). ILC3 were 6.28% and 3.63% of ILCs in the conjunctiva and lacrimal gland, respectively. Th1, Tc1, and NK cells were predominant type 1 immune cells. γδ T17 cells and ILC3 outnumbered Th17 cells among type 3 T cells.

CONCLUSION

B cells resident in murine corneas were reported for the first time. Additionally, we proposed a strategy of clustering myeloid cells to better understand their heterogeneity in the conjunctiva and lacrimal gland based on tSNE and FlowSOM. Furthermore, we identified the ILC3 in the conjunctiva and lacrimal gland for the first time. Compositions of type 1 and type 3 immune cells were summarized. Our study provides a fundamental reference and novel insights for ocular surface immune homeostasis and diseases.

Myeloid masquerade: Microglial transcriptional signatures in retinal development and disease

Microglia are dynamic guardians of neural tissue and the resident immune cells of the central nervous system (CNS). The disease-associated microglial signature (DAM), also known as the microglial neurodegenerative phenotype (MGnD), has gained significant attention in recent years as a fundamental microglial response common to various neurodegenerative disease pathologies. Interestingly, this signature shares many features in common with developmental microglia, suggesting the existence of recycled gene programs which play a role both in early neural circuit formation as well as in response to aging and disease. In addition, recent advances in single cell RNA sequencing have revealed significant heterogeneity within the original DAM signature, with contributions from both yolk sac-derived microglia as well as bone marrow-derived macrophages. In this review, we examine the role of the DAM signature in retinal development and disease, highlighting crosstalk between resident microglia and infiltrating monocytes which may critically contribute to the underlying mechanisms of age-related neurodegeneration.

Microglia Preserve Visual Function in a Mouse Model of Retinitis Pigmentosa with Rhodopsin-P23H Mutant

Most forms of outer retinal degenerative diseases involve the ectopic accumulation of microglia/macrophages in the subretinal space, including retinitis pigmentosa. However, their role in the loss of photoreceptor function during retinal degeneration remains unknown. Here, we examined the effect of conditional microglial depletion on photoreceptor numbers and visual function in mice with the rhodopsin P23H mutation, a dominant form of retinitis pigmentosa in humans. We found that microglial depletion led to an elevated level of rhodopsin and increased photoreceptor layer thickness. However, overall electrophysiological functions of the retina were reduced with microglial depletion. Therefore, these results identify an essential role of microglia specially in preserving visual function in outer retinal degeneration.

CD68: Potential Contributor to Inflammation and RPE Cell Dystrophy

Age-related macular degeneration (AMD) is the leading cause of visual impairment in the elderly in developed countries. It is a complex, multifactorial, progressive disease with diverse molecular pathways, including inflammation, regulating its pathogenesis. The myeloid marker CD68 is a protein highly expressed in circulating and tissue macrophages. Recent observations of immune markers in human AMD tissues have varied with some finding ectopic RPE cells in advanced AMD and others noting negligible numbers of CD68-positive cells. Additionally, animal models of retinal degeneration have shown upregulation of CD68, in a protective population of retinal microglia. Herein, we review the potential role of CD68 in regulating RPE health and inflammation in the sub-retinal space and discuss observations on its localization in a mouse model that presents with AMD-like features.

Continuous Hypoxia Reduces Retinal Ganglion Cell Degeneration in a Mouse Model of Mitochondrial Optic Neuropathy

Purpose

To test whether continuous hypoxia is neuroprotective to retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy.

Methods

RGC degeneration was assessed in genetically modified mice in which the floxed gene for the complex I subunit NDUFS4 is deleted from RGCs using Vlgut2-driven Cre recombinase. Beginning at postnatal day 25 (P25), Vglut2-Cre;ndufs4loxP/loxP mice and control littermates were housed under hypoxia (11% oxygen) or kept under normoxia (21% oxygen). Survival of RGC somas and axons was assessed at P60 and P90 via histological analysis of retinal flatmounts and optic nerve cross-sections, respectively. Retinal tissue was also assessed for gliosis and neuroinflammation using western blot and immunofluorescence.

Results

Consistent with our previous characterization of this model, at least one-third of RGCs had degenerated by P60 in Vglut2-Cre;ndufs4loxP/loxP mice remaining under normoxia. However, continuous hypoxia resulted in complete rescue of RGC somas and axons at this time point, with normal axonal myelination observed on electron microscopy. Though only partial, hypoxia-mediated rescue of complex I-deficient RGC somas and axons remained significant at P90. Hypoxia prevented reactive gliosis at P60, but the retinal accumulation of Iba1+ mononuclear phagocytic cells was not substantially reduced.

Conclusions

Continuous hypoxia achieved dramatic rescue of early RGC degeneration in mice with severe mitochondrial dysfunction. Although complete rescue was not durable to P90, our observations suggest that investigating the mechanisms underlying hypoxia-mediated neuroprotection of RGCs may identify useful therapeutic strategies for optic neuropathies resulting from less profound mitochondrial impairment, such as Leber hereditary optic neuropathy.

Immune response in retinal degenerative diseases - Time to rethink?

Retinal degeneration comprises a group of diseases whereby either the retinal neurons or the neurovascular unit degenerates leading to the loss of visual function. Although the initial cause varies in different conditions, inflammation is known to play an important role in disease pathogenesis. Recent advances in molecular and cell biology and systems biology have yielded unexpected findings, including the heterogeneity of immune cells in the degenerative retina, bidirectional neuron-microglia cross talk, and links to the gut microbiome. Here we discuss the immune response in retinal degenerative conditions, taking into account both regional (retinal) and systemic factors. We propose to classify retinal degeneration into dry and wet forms based on whether the blood-retinal barrier (BRB) is breached and fluid is accumulated in retinal parenchyma. The dry form has a relatively intact BRB and is characterised by progressive retinal thinning. Immune response to degenerative insults is dominated by the retinal defence system, which remains to be regulated by neurons. In contrast, the wet form has retinal oedema due to BRB damaged. Inflammation is executed by infiltrating immune cells as well as the retinal defence system. The gut microbiome will have easy access to the retina in wet retinal degeneration and may affect significantly retinal immune response.

Macrophage-mediated tissue response evoked by subchronic inhalation of lead oxide nanoparticles is associated with the alteration of phospholipases C and cholesterol transporters

Background

Inhalation of lead oxide nanoparticles (PbO NPs), which are emitted to the environment by high-temperature technological processes, heavily impairs target organs. These nanoparticles pass through the lung barrier and are distributed via the blood into secondary target organs, where they cause numerous pathological alterations. Here, we studied in detail, macrophages as specialized cells involved in the innate and adaptive immune response in selected target organs to unravel their potential involvement in reaction to subchronic PbO NP inhalation. In this context, we also tackled possible alterations in lipid uptake in the lungs and liver, which is usually associated with foam macrophage formation.

Results

The histopathological analysis of PbO NP exposed lung revealed serious chronic inflammation of lung tissues. The number of total and foam macrophages was significantly increased in lung, and they contained numerous cholesterol crystals. PbO NP inhalation induced changes in expression of phospholipases C (PLC) as enzymes linked to macrophage-mediated inflammation in lungs. In the liver, the subchronic inhalation of PbO NPs caused predominantly hyperemia, microsteatosis or remodeling of the liver parenchyma, and the number of liver macrophages also significantly was increased. The gene and protein expression of a cholesterol transporter CD36, which is associated with lipid metabolism, was altered in the liver. The amount of selected cholesteryl esters (CE 16:0, CE 18:1, CE 20:4, CE 22:6) in liver tissue was decreased after subchronic PbO NP inhalation, while total and free cholesterol in liver tissue was slightly increased. Gene and protein expression of phospholipase PLCβ1 and receptor CD36 in human hepatocytes were affected also in in vitro experiments after acute PbO NP exposure. No microscopic or serious functional kidney alterations were detected after subchronic PbO NP exposure and CD68 positive cells were present in the physiological mode in its interstitial tissues.

Conclusion

Our study revealed the association of increased cholesterol and lipid storage in targeted tissues with the alteration of scavenger receptors and phospholipases C after subchronic inhalation of PbO NPs and yet uncovered processes, which can contribute to steatosis in liver after metal nanoparticles exposure.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00494-7.

The innate immune receptor Nlrp12 suppresses autoimmunity to the retina

Background

Nod-like receptors (NLRs) are critical to innate immune activation and induction of adaptive T cell responses. Yet, their role in autoinflammatory diseases of the central nervous system (CNS) remains incompletely defined. The NLR, Nlrp12, has been reported to both inhibit and promote neuroinflammation in an animal model of multiple sclerosis (experimental autoimmune encephalomyelitis, EAE), where its T cell-specific role has been investigated. Uveitis resulting from autoimmunity of the neuroretina, an extension of the CNS, involves a breach in immune privilege and entry of T cells into the eye. Here, we examined the contribution of Nlrp12 in a T cell-mediated model of uveitis, experimental autoimmune uveitis (EAU).

Methods

Mice were immunized with interphotoreceptor retinoid-binding protein peptide 1–20 (IRBP_1–20) emulsified in Complete Freund’s adjuvant, CFA. Uveitis was evaluated by clinical and histopathological scoring, and comparisons were made in WT vs. Nlrp12^−/− mice, lymphopenic Rag1^−/− mice reconstituted with WT vs. Nlrp12^−/− CD4⁺ T cells, or among bone marrow (BM) chimeric mice. Antigen-specific Th-effector responses were evaluated by ELISA and intracellular cytokine staining. Cellular composition of uveitic eyes from WT or Nlrp12^−/− mice was compared using flow cytometry. Expression of Nlrp12 and of cytokines/chemokines within the neuroretina was evaluated by immunoblotting and quantitative PCR.

Results

Nlrp12^−/− mice developed exacerbated uveitis characterized by extensive vasculitis, chorioretinal infiltrates and photoreceptor damage. Nlrp12 was dispensable for T cell priming and differentiation of peripheral Th1 or Th17 cells, and uveitis in immunodeficient mice reconstituted with either Nlrp12^−/− or WT T cells was similar. Collectively, this ruled out T cells as the source of Nlrp12-mediated protection to EAU. Uveitic Nlrp12^−/− eyes had more pronounced myeloid cell accumulation than uveitic WT eyes. Transplantation of Nlrp12^−/− BM resulted in increased susceptibility to EAU regardless of host genotype, but interestingly, a non-hematopoietic origin for Nlrp12 function was also observed. Indeed, Nlrp12 was found to be constitutively expressed in the neuroretina, where it suppressed chemokine/cytokine induction.

Conclusions

Our data identify a combinatorial role for Nlrp12 in dampening autoimmunity of the neuroretina. These findings could provide a pathway for development of therapies for uveitis and potentially other autoinflammatory/autoimmune diseases of the CNS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02425-x.

Myeloid cell modulation by a GLP-1 receptor agonist regulates retinal angiogenesis in ischemic retinopathy

Ischemic retinopathies including diabetic retinopathy are major causes of blindness. Although neurons and Müller glia are recognized as important regulators of reparative and pathologic angiogenesis, the role of mononuclear phagocytes (MPs) — particularly microglia, the resident retinal immune cells — is unclear. Here, we found MP activation in human diabetic retinopathy, especially in neovessels from human neovascular membranes in proliferative retinopathy, including TNF-α expression. There was similar activation in the mouse oxygen-induced retinopathy (OIR) model of ischemia-induced neovascularization. Glucagon-like peptide-1 receptor (GLP-1R) agonists are in clinical use for glycemic control in diabetes and are also known to modulate microglia. Herein, we investigated the effect of a long-acting GLP-1R agonist, NLY01. Following intravitreal administration, NLY01 selectively localized to MPs in retina with OIR. NLY01 modulated MPs but not retinal endothelial cell viability, apoptosis, and tube formation in vitro. In OIR, NLY01 treatment inhibited MP infiltration and activation, including MP expression of cytokines in vivo. NLY01 significantly suppressed global induction of retinal inflammatory cytokines, promoted reparative angiogenesis, and suppressed pathologic retinal neovascularization. Collectively, these findings indicate the important role of mononuclear phagocytes in regulation of retinal vascularization in ischemia and suggest modulation of MPs as a potentially new treatment strategy for ischemic retinopathies.

Cellular components of the idiopathic epiretinal membrane

Idiopathic epiretinal membrane (iERM) is a fibrocellular proliferation on the inner surface of the retina, which leads to decreased visual acuity and even central visual loss. As iERM is associated to advanced age and posterior vitreous detachment, a higher prevalence is expected with increasing life expectancy and aging of the global population. Although various cell types of retinal and extra-retinal origin have been described in iERMs (Müller glial cells, astrocytes, hyalocytes, retinal pigment epithelium cells, myofibroblasts, and fibroblasts), myofibroblasts have a central role in collagen production and contractile activity. Thus, myofibroblast differentiation is considered a key event for the iERM formation and progression, and fibroblasts, Müller glial cells, hyalocytes, and retinal pigment epithelium have been identified as myofibroblast precursors. On the other side, the different cell types synthesize growth factors, cytokines, and extracellular matrix, which have a crucial role in ERM pathogenesis. In the present review, the major cellular components and their functions are summarized, and their possible roles in the iERM formation are discussed. By exploring in detail the cellular and molecular aspects of iERM, we seek to contribute for better understanding of this fibrotic disease and the origin of myofibroblasts, which may eventually drive to more targeted therapeutic approaches.

Reduced nuclear NAD+ drives DNA damage and subsequent immune activation in the retina

Mutations in NMNAT1, a key enzyme involved in the synthesis of NAD+ in the nucleus, lead to an early onset severe inherited retinal degeneration (IRD). We aimed to understand the role of nuclear NAD+ in the retina and to identify the molecular mechanisms underlying NMNAT1-associated disease, using a mouse model that harbors the p.V9M mutation in Nmnat1 (Nmnat1V9M/V9M). We identified temporal transcriptional reprogramming in the retinas of Nmnat1V9M/V9M mice prior to retinal degeneration, which begins at 4 weeks of age, with no significant alterations in gene expression at 2 weeks of age and over 2600 differentially expressed genes by 3 weeks of age. Expression of the primary consumer of NAD+ in the nucleus, PARP1, an enzyme involved in DNA damage repair and transcriptional regulation, as well as 7 other PARP family enzymes, was elevated in the retinas of Nmnat1V9M/V9M. This was associated with elevated levels of DNA damage, PARP-mediated NAD+ consumption, and migration of Iba1+/CD45+ microglia/macrophages to the subretinal space in the retinas of Nmnat1V9M/V9M mice. These findings suggest that photoreceptor cells are especially sensitive to perturbation of genome homeostasis, and that PARP-mediated cell death may play a role in other genetic forms of IRDs, and potentially other forms of neurodegeneration.

Progesterone alters the activation and typing of the microglia in the optic nerve crush model

Microglia have a protective effect on the central nervous system (CNS), but their over-proliferation can cause secondary injury to the retina following optic nerve crush (ONC). Progesterone as a steroid gonadal hormone has been used in some experimental animal models for its neuroprotective effect. However, there is limited attention on the interactions between progesterone and microglia in retinal diseases. This study investigated the proliferation, morphology changes, and cell types of microglia at 3 days and 7 days after ONC. We found that progesterone treatment in unilateral optic nerve injury mice significantly reduced densities and morphological change of microglia at 7 days in the ganglion cell layer (GCL), especially in the retinal central. Inhibition of the microglia proliferation and transformation of ramified microglia into ameboid macrophages also appeared in the inner plexiform layer (IPL). Moreover, progesterone also regulated the TNF signal pathway, which was similar to the specific elimination of the M1 phenotype. M1 marks such as tumor necrosis factor alpha (TNF-α), inducible NOS(iNOS), interleukin-6 (IL-6), and Fc receptor (CD16 and CD32) significantly downregulated by progesterone treatment whether at 3 days or 7 days after ONC. On the other hand, progesterone continuously increased the expression of the M2 marks, including interleukin-4 (IL-4), arginase 1 (Arg1), and mannose receptor (CD206) since the third day, while the expression levels of transforming growth factor (TGF-β) only increased at 7 days. In general, this study elucidated the mechanism that progesterone prevented further damage on the retina by inhibiting proliferation, activation, and changing the type of microglia.

VEGFR1 signaling in retinal angiogenesis and microinflammation

Five vascular endothelial growth factor receptor (VEGFR) ligands (VEGF-A, -B, -C, -D, and placental growth factor [PlGF]) constitute the VEGF family. VEGF-A binds VEGF receptors 1 and 2 (VEGFR1/2), whereas VEGF-B and PlGF only bind VEGFR1. Although much research has been conducted on VEGFR2 to elucidate its key role in retinal diseases, recent efforts have shown the importance and involvement of VEGFR1 and its family of ligands in angiogenesis, vascular permeability, and microinflammatory cascades within the retina. Expression of VEGFR1 depends on the microenvironment, is differentially regulated under hypoxic and inflammatory conditions, and it has been detected in retinal and choroidal endothelial cells, pericytes, retinal and choroidal mononuclear phagocytes (including microglia), Müller cells, photoreceptor cells, and the retinal pigment epithelium. Whilst the VEGF-A decoy function of VEGFR1 is well established, consequences of its direct signaling are less clear. VEGFR1 activation can affect vascular permeability and induce macrophage and microglia production of proinflammatory and proangiogenic mediators. However the ability of the VEGFR1 ligands (VEGF-A, PlGF, and VEGF-B) to compete against each other for receptor binding and to heterodimerize complicates our understanding of the relative contribution of VEGFR1 signaling alone toward the pathologic processes seen in diabetic retinopathy, retinal vascular occlusions, retinopathy of prematurity, and age-related macular degeneration. Clinically, anti-VEGF drugs have proven transformational in these pathologies and their impact on modulation of VEGFR1 signaling is still an opportunity-rich field for further research.

Mitochondrial miRNA494-3p in extracellular vesicles participates in cellular interplay of iPS-Derived human retinal pigment epithelium with macrophages

To explore new molecular targets for therapy in human model systems by discerning the role of extracellular vesicle (EV) microRNAs (miRs) secreted by human retinal pigment epithelium (hRPE) cells and their cellular interplay with macrophages (Mps). Human Mps differentiated from THP-1 cells stimulated by phorbol myristate acetate were co-cultured with induced pluripotent stem cell-derived differentiated hRPE (iPS-hRPE) cells in Transwell® system separated by 0.40 μm or 0.03 μm filters. EV-associated CD63⁺ proteins (CD63⁺ EV) were detected by western blotting, and secreted EVs were analyzed by Nanosight tracking. The miR profiles of the secreted EVs were determined using 3D-gene human microRNA chips (Toray Industries, Inc.). Levels of CD63⁺ EV were increased in co-cultures concomitantly with the increased production of EV particles (50-150 nm). The increased production of EVs was associated with higher production of MCP-1, IL-6, IL-8 from hRPE cells, and VEGF and repressed production of TNF-α from Mps and pigment epithelium-derived factor (PEDF) from RPE cells. Ultracentrifugation of semi-purified EVs increased the secretion of these pro-inflammatory cytokines and EV particles from hRPE cells, but this effect was eliminated in transwells equipped with 0.03 μm filters, whereas no repression of PEDF and TNF-α secretion occurred. 3D-gene miR analysis revealed a selective increase in secretion of miR494-3p in EVs from iPS-hRPE cells during the interplay with Mps. The miRs in EVs secreted by hRPE cells may have a critical role in the vicious inflammatory cycle, whereas repression of TNF-α and PEDF require cell-to-cell contact that is independent of EVs or exosomes. MiR494-3p may be a candidate molecular target of diagnosis and therapy for age-related macular degeneration.

The cornea IV immunology, infection, neovascularization, and surgery chapter 1: Corneal immunology

PURPOSE

of Review: This review offers an informed and up-to-date insight on the immune profile of the cornea and the factors that govern the regulation of such a unique immune environment.

SUMMARY

The cornea is a unique tissue that performs the specialized task of allowing light to penetrate for visual interpretation. To accomplish this, the ocular surface requires a distinct immune environment that is achieved through unique structural, cellular and molecular factors. Not only must the cornea be able to fend off invasive infectious agents but also control the inflammatory response as to avoid collateral, and potentially blinding damage; particularly of post-mitotic cells such as the corneal endothelium. To combat infections, both innate and adaptive arms of the inflammatory immune response are at play in the cornea. Dendritic cells play a critical role in coordinating both these responses in order to fend off infections. On the other side of the spectrum, the ocular surface is also endowed with a variety of anatomic and physiologic components that aid in regulating the immune response to prevent excessive, potentially damaging, inflammation. This attenuation of the immune response is termed immune privilege. The balance between pro and anti-inflammatory reactions is key for preservation of the functional integrity of the cornea.

RECENT FINDINGS

The understanding of the molecular and cellular factors governing corneal immunology and its response to antigens is a growing field. Dendritic cells in the normal cornea play a crucial role in combating infections and coordinating the inflammatory arms of the immune response, particularly through coordination with T-helper cells. The role of neuropeptides is recently becoming more highlighted with different factors working on both sides of the inflammatory balance.

CD63+ extracellular vesicles from retinal pigment epithelial cells participate in crosstalk with macrophages in the innate inflammatory axis

The aim of the study is to clarify the participation of extracellular vesicles (EV) secreted by murine primary retinal pigment epithelial (mpRPE) cells in the cell to cell communication with macrophages (Mps), firstly described by the authors in 2016. In ocular inflammation, Mps act as sources of tumor necrosis factor-α (TNF-α), an activator of RPE cells. TNF-α stimulates the production of monocyte chemotactic protein (MCP-1) by RPE cells, thereby causing greater recruitment of Mps to the sub-RPE space. Murine RAW 264.7 Mps cells were co-cultured with C57BL/6 mouse mpRPE cells, either together or separated in transwells, vertically or horizontally connectable, with 0.40 or 0.03 μm membrane filters. The association of EV with mpRPE or RAW 264.7 was quantified by fluorescence cell sorting (FACS) using Qdot655 streptavidin-conjugated biotinylated EV. Increased levels of CD63⁺ EV were detected in co-cultures by western blotting or FACS analysis, in accordance with the increased production of nanoparticles (50-150 nm) detected by Nanosight tracking analysis. The gene expressions of cytokines, MCP-1, IL-6, IL-8, and VEGF in mpRPE cells and the corresponding proteins were increased in co-cultures even in transwells, vertically connected with 0.40 μm membrane filters, while the repressed TNF-α protein production was not affected. Most of the CD63⁺ EVs produced by mpRPE cells in co-cultures were associated with Raw264.7, but not with mpRPE cells. Semi-purified CD63⁺ EV secreted from mpRPE cells, increased the secretion of MCP-1, IL-6, and VEGF in co-cultures with RAW 264.7. Culture chamber separation horizontally connected with 0.03 μm membrane filters reduced this increased secretion. Collectively, mpRPE derived CD63⁺ EV partly participate in the sub-retinal innate inflammation. To evaluate the functional damage of RPE cells upon chronic exposure to here defined EVs will be the critical issue to uncover their roles in chronic retinal degenerative diseases.

Dendrimer-Triamcinolone Acetonide Reduces Neuroinflammation, Pathological Angiogenesis, and Neuroretinal Dysfunction in Ischemic Retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults. Severe visual loss in DR is primarily due to proliferative diabetic retinopathy, characterized by pathologic preretinal angiogenesis driven by retinal ischemia. Microglia, the resident immune cells of the retina, have emerged as a potentially important regulator of pathologic retinal angiogenesis. Corticosteroids including triamcinolone acetonide (TA), known for their antiangiogenic effects, are used in treating retinal diseases, but their use is significantly limited by side effects including cataracts and glaucoma. Generation-4 hydroxyl polyamidoamine dendrimer nanoparticles are utilized to deliver TA to activated microglia in the ischemic retina in a mouse model of oxygen-induced retinopathy (OIR). Following intravitreal injection, dendrimer-conjugated TA (D-TA) exhibits selective localization and sustained retention in activated microglia in disease-associated areas of the retina. D-TA, but not free TA, suppresses inflammatory cytokine production, microglial activation, and preretinal neovascularization in OIR. In addition, D-TA, but not free TA, ameliorates OIR-induced neuroretinal and visual dysfunction. These results indicate that activated microglia are a promising therapeutic target for retinal angiogenesis and neuroprotection in ischemic retinal diseases. Furthermore, dendrimer-based targeted therapy and specifically D-TA constitute a promising treatment approach for DR, offering increased and sustained drug efficacy with reduced side effects.

Secreted Phosphoprotein 1 Expression in Retinal Mononuclear Phagocytes Links Murine to Human Choroidal Neovascularization

Age-related macular degeneration (AMD) represents the most common cause of blindness in the elderly in the Western world. An impairment of the outer blood-retina barrier and a localized inflammatory microenvironment cause sprouting of choroidal neovascular membranes (CNV) in neovascular AMD that are in intimate contact with surrounding myeloid cells, such as retinal microglia, and ultimately lead to visual impairment. The discovery of novel target molecules to interfere with angiogenesis and inflammation is vital for future treatment approaches in AMD patients. To explore the transcriptional profile and the function of retinal microglia at sites of CNV, we performed a comprehensive RNA-seq analysis of retinal microglia in the mouse model of laser-induced choroidal neovascularization (mCNV). Here, we identified the angiogenic factor Osteopontin (Opn), also known as "secreted phosphoprotein 1" (Spp1), as one of the most highly expressed genes in retinal microglia in the course of CNV formation. We confirmed the presence of SPP1 at the lesion site in recruited retinal microglia in Cx3cr1 ^CreER:Rosa26-tdTomato reporter mice by confocal microscopy and in whole retinal tissue lysates by ELISA highlighting a massive local production of SPP1. Inhibition of SPP1 by intravitreal injection of an anti-SPP1 antibody significantly increased the lesion size compared to IgG-treated control eyes. In line with our results in rodents, we found an increased SPP1 mRNA expression in surgically extracted human choroidal neovascular (hCNV) membranes by the quantitative RNA-seq approach of massive analysis of cDNA ends (MACE). Numerous IBA1⁺SPP1⁺ myeloid cells were detected in human CNV membranes. Taken together, these results highlight the importance of SPP1 in the formation of CNV and potentially offer new opportunities for therapeutic intervention by modulating the SPP1 pathway.

Innate Immunity in Age-Related Macular Degeneration

Multiple lines of investigation have demonstrated that inflammation plays significant roles in etiology of age-related macular degeneration (AMD). Although interventional trials in AMD therapy targeting inflammatory pathways have been conducted, they have not yet been successful and a detailed understanding as to why some have failed is still elusive. One limitation is the relative dearth of information on how immune cells interact with retinal cells to generate AMD phenotypes at each disease stage. Here, we summarize current research evidence and hypotheses regarding potential pathogenic roles of innate immune cells in the eye, which include resident retinal microglia, macrophages derived from infiltrating systemic monocytes, and macrophages resident in the choroid. We relate recent findings regarding the physiology, function, and cellular interactions involving innate immune cells in the retina and choroid to AMD-related processes, including: (1) drusen formation and regression, (2) the onset and spread of degeneration in late atrophic AMD, and (3) the initiation, growth, and exudation of neovascular vessels in late "wet" AMD. Understanding how innate immune cells contribute to specific AMD phenotypes can assist in generating a comprehensive view on the inflammatory etiology of AMD and aid in identifying anti-inflammatory therapeutic strategies and selecting appropriate clinical outcomes for the planned interventions.

Strategic Outlook toward 2030: Japan's research for allergy and immunology - Secondary publication

Strategic Outlook toward 2030: Japan's Research for Allergy and Immunology (Strategy 2030) is the national research strategy based on Japan's Basic Law on Measures Against Allergic Diseases, a first of its kind worldwide. This strategy was established by a multi-disciplinary committee consisting of administrators of the Ministry of Health, Labour and Welfare of Japan, young and senior experts from various research societies and associations, and representatives of patient and public groups. Whereas the issues of transition, integration, and international collaboration have yet to be solved in this research realm in Japan, identification of unmet needs, digitization of information and transparent procedures, and strategic planning for complex problems (a process dubbed MIERUKA by the Toyota Way) are crucial to share and tackle the same vision and goals. The committee developed three specific actions focusing on preemptive treatment, interdisciplinarity and internationality, and life stage. The real success of Strategy 2030 is made by the spontaneous contributions of doctors, dentists, veterinarians, and other medical professionals; basic and clinical research scientists, research supporters, and pharmaceutical/medical device companies; manufacturers of food, healthcare, and home appliances; and patients, their families, and the public. The hope is to establish a stable society in which people can live long, healthy lives, as free as possible from allergic and immunological diseases, at each individual life stage. This article is based on a Japanese review first reported in Arerugi, introduces the developmental process and details of Strategy 2030.

Study of Usutu virus neuropathogenicity in mice and human cellular models

Usutu virus (USUV), an African mosquito-borne flavivirus closely related to West Nile virus, was first isolated in South Africa in 1959. USUV emerged in Europe two decades ago, causing notably massive mortality in Eurasian blackbirds. USUV is attracting increasing attention due to its potential for emergence and its rapid spread in Europe in recent years. Although mainly asymptomatic or responsible for mild clinical signs, USUV was recently described as being associated with neurological disorders in humans such as encephalitis and meningoencephalitis, highlighting the potential health threat posed by the virus. Despite this, USUV pathogenesis remains largely unexplored. The aim of this study was to evaluate USUV neuropathogenicity using in vivo and in vitro approaches. Our results indicate that USUV efficiently replicates in the murine central nervous system. Replication in the spinal cord and brain is associated with recruitment of inflammatory cells and the release of inflammatory molecules as well as induction of antiviral-responses without major modulation of blood-brain barrier integrity. Endothelial cells integrity is also maintained in a human model of the blood-brain barrier despite USUV replication and release of pro-inflammatory cytokines. Furthermore, USUV-inoculated mice developed major ocular defects associated with inflammation. Moreover, USUV efficiently replicates in human retinal pigment epithelium. Our results will help to better characterize the physiopathology related to USUV infection in order to anticipate the potential threat of USUV emergence.

Number of emerging arboviruses involved in human infections has increased considerably in the past years. Among them, Usutu virus (USUV) is an African mosquito-borne virus first isolated in South Africa that recently emerged. USUV infection in humans is considered to be most often asymptomatic or to cause mild clinical signs. Nonetheless, increased cases of neurological complications such as encephalitis or meningoencephalitis have been reported in Europe but the mechanisms behind this neuropathogenesis remain largely unclear. In this study we showed that USUV can infect efficiently several organs and cells of the central nervous system associated with a drastic inflammation and various deleterious effects. Our results contribute to the characterization of the neurotropism related to USUV infection.

Microglia versus Monocytes: Distinct Roles in Degenerative Diseases of the Retina

Unlike in the healthy mammalian retina, macrophages in retinal degenerative states are not solely comprised of microglia but may include monocyte-derived recruits. Recent studies have applied transgenics, lineage-tracing, and transcriptomics to help decipher the distinct roles of these two cell types in the diseasesettings of inherited retinal degenerations and age-related macular degeneration.Literature discussed here focuses on the ectopic presence of both macrophage types in the extracellular site surrounding the outer aspect ofphotoreceptor cells (i.e.,the subretinal space), which is crucially involved in the pathobiology. From these studies we propose a working model in which perturbed photoreceptor states cause microglial dominant migration to the subretinal space as a protective response, whereas the abundant presence ofmonocyte-derived cells there instead drives and accelerates pathology. The latter, we propose, is underpinned by specific genetic and nongenetic determinants that lead to a maladaptive macrophage state.

Retinal Degeneration in MPS-IIIA Mouse Model

Mucopolysaccharidosis type IIIA (MPS-IIIA, Sanfilippo A) is one of the most severe lysosomal storage disorder (LSD) caused by the inherited deficiency of sulfamidase, a lysosomal sulfatase enzyme involved in the stepwise degradation of heparan sulfates (HS). MPS-IIIA patients show multisystemic problems, including a strong impairment of central nervous system (CNS), mild somatic involvement, and ocular manifestations that result in significant visual impairment. Despite the CNS and somatic pathology have been well characterized, studies on visual system and function remain partially explored. Here, we characterized the retina morphology and functionality in MPS-IIIA mouse model and analyzed how the SGSH deficiency affects the autophagic flux. MPS-IIIA mice exhibited a progressive retinal dystrophy characterized by significant alterations in visual function. The photoreceptor degeneration was associated with HS accumulation and a block of autophagy pathway. These events caused a reactive microgliosis, and a development of apoptotic processes in MPS-IIIA mouse retina. Overall, this study provides the first phenotypic spectrum of retinal disorders in MPS-IIIA and significantly contributes for diagnosis, counseling, and potential therapies development.

Shihu Yeguang Pill protects against bright light-induced photoreceptor degeneration in part through suppressing photoreceptor apoptosis

Photoreceptor cells are first-order retinal neurons that directly contribute to the formation of vision. Photoreceptor degeneration is the primary cause of vision impairment during the course of retinopathies such as retinitis pigmentosa and age-related macular degeneration, for which photoreceptor-targeted therapies are currently unavailable. Shihu Yeguang Pill (SYP), a classic formula in traditional Chinese medicine, has a long histology of clinical application for the treatment of a wide range of retinopathies in China. However, whether SYP is pharmacological effective at protecting photoreceptor cells is unclear. The current study thus directly addressed the pharmacological implications of SYP in photoreceptor degeneration in a mouse model characterized by bright light-induced retinal degeneration. Non-invasive full-retinal assessment was carried out to evaluate the effect of SYP on the retinal structure and function through optical coherence tomography and electroretinography, respectively. In addition, photoreceptor apoptosis, second-order neuron impairment and reactive changes in retinal microglial and müller cells, hallmark pathologies associated with photoreceptor degeneration, were assessed using immunohistochemistry and real-time PCR analyses. The results showed that SYP treatment attenuated bright light-induced impairment of the retinal structure and function. Moreover, SYP treatment suppressed photoreceptor apoptosis, alleviated the impairment of bipolar and horizontal cells and mitigated the reactive changes of müller and microglial cells in the bright light-exposed retinas. Real-time PCR analyses showed that dysregulated expression of pro-apoptotic c-fos and c-jun and anti-apoptotic bcl-2 as well as proinflammatory TNF-α in the bright light-exposed retinas was partially normalized as a result of SYP treatment. In summary, the work here demonstrates for the first time that SYP treatment protects the retinas from developing bright light-induced photoreceptor degeneration and associated alterations in second-order neurons and glial cells. The findings here thus provide experimental evidence to better support the mechanism-guided clinical application of SYP in the treatment of related retinal degenerative diseases.

Antigen-presenting cells in ocular surface diseases

PURPOSE

To review the role of antigen-presenting cells (APC) in the pathogenesis of ocular surface diseases (OSD).

METHODS

A thorough literature search was performed in PubMed database. An additional search was made in Google Scholar to complete the collected items.

RESULTS

APCs have the ability to initiate and direct immune responses and are found in most lymphoid and non-lymphoid tissues. APCs continuously sample their environment, present antigens to T cells and co-ordinate immune tolerance and responses. Many different types of APCs have been described and there is growing evidence that these cells are involved in the pathogenesis of OSD. OSD is a complex term for a myriad of disorders that are often characterized by ocular surface inflammation, tear film instability and impairment of vision.

CONCLUSIONS

This review summarizes the current knowledge concerning the immunotopographical distribution of APCs in the normal ocular surface. APCs appear to play a critical role in the pathology of a number of conditions associated with OSD including infectious keratitis, ocular allergy, dry eye disease and pterygium.

Keep an eye on adenosine: Its role in retinal inflammation

Adenosine is an endogenous purine nucleoside ubiquitously distributed throughout the body that interacts with G protein-coupled receptors, classified in four subtypes: A₁R, A_2AR, A_2BR and A₃R. Among the plethora of functions of adenosine, it has been increasingly recognized as a key mediator of the immune response. Neuroinflammation is a feature of chronic neurodegenerative diseases and contributes to the pathophysiology of several retinal degenerative diseases. Animal models of retinal diseases are helping to elucidate the regulatory roles of adenosine receptors in the development and progression of those diseases. Mounting evidence demonstrates that the adenosinergic system is altered in the retina during pathological conditions, compromising retinal physiology. This review focuses on the roles played by adenosine and the elements of the adenosinergic system (receptors, enzymes, transporters) in the neuroinflammatory processes occurring in the retina. An improved understanding of the molecular and cellular mechanisms of the signalling pathways mediated by adenosine underlying the onset and progression of retinal diseases will pave the way towards the identification of new therapeutic approaches.

Identification of a Unique Subretinal Microglia Type in Retinal Degeneration Using Single Cell RNA-Seq

As the resident macrophages of central nervous system, microglia reside in the plexiform and nerve fiber layers of the retina. In degenerative diseases, monocyte-derived macrophages can be recruited to the retina, and histopathology shows abnormal accumulation of macrophages subretinally. However, due to lack of known markers, recruited cells and resident microglia are phenotypically indistinguishable, leaving a major knowledge gap about their potentially independent roles. Here, we used single cell RNA-seq and analyzed over 10,000 immune cells of mouse retinas from normal control and light damage-induced retinal degeneration. We observed ten major macrophage clusters. Moreover, combining trajectory analysis and in situ validation allowed us to pinpoint that subretinal phagocytes are microglia-derived and express high levels of Gal3, Cd68, and Lpl but not P2ry12. Hence, we have identified novel subretinal macrophage markers indicative of their origin and phenotype, which may be useful in other degeneration models and human specimens.

Modulation of three key innate immune pathways for the most common retinal degenerative diseases

This review highlights the role of three key immune pathways in the pathophysiology of major retinal degenerative diseases including diabetic retinopathy, age‐related macular degeneration, and rare retinal dystrophies. We first discuss the mechanisms how loss of retinal homeostasis evokes an unbalanced retinal immune reaction involving responses of local microglia and recruited macrophages, activity of the alternative complement system, and inflammasome assembly in the retinal pigment epithelium. Presenting these key mechanisms as complementary targets, we specifically emphasize the concept of immunomodulation as potential treatment strategy to prevent or delay vision loss. Promising molecules are ligands for phagocyte receptors, specific inhibitors of complement activation products, and inflammasome inhibitors. We comprehensively summarize the scientific evidence for this strategy from preclinical animal models, human ocular tissue analyses, and clinical trials evolving in the last few years.

Retinal microglia initiate neuroinflammation in ocular autoimmunity

Autoimmune uveitis is a sight-threatening ocular inflammatory condition in which the retina and uveal tissues become a target of autoreactive immune cells. While microglia have been studied extensively in autoimmune uveitis, their exact function remains uncertain. The objective of the current study was to determine whether resident microglia are necessary and sufficient to initiate and amplify retinal inflammation in autoimmune uveitis. In this study, we clearly demonstrate that microglia are essential for initiating infiltration of immune cells utilizing a murine model of experimental autoimmune uveoretinitis (EAU) and the recently identified microglia-specific marker P2ry12. Initiating disease is the primary function of microglia in EAU, since eliminating microglia during the later stages of EAU had little effect, indicating that the function of circulating leukocytes is to amplify and sustain destructive inflammation once microglia have triggered disease. In the absence of microglia, uveitis does not develop, since leukocytes cannot gain entry through the blood-retinal barrier, illustrating that microglia play a critical role in regulating infiltration of inflammatory cells into the retina.

Microglia are not required for prion-induced retinal photoreceptor degeneration

Degeneration of photoreceptors in the retina is a major cause of blindness in humans. Often retinal degeneration is due to inheritance of mutations in genes important in photoreceptor (PR) function, but can also be induced by other events including retinal trauma, microvascular disease, virus infection or prion infection. The onset of apoptosis and degeneration of PR neurons correlates with invasion of the PR cellular areas by microglia or monocytes, suggesting a causal role for these cells in pathogenesis of PR degenerative disease. To study the role of microglia in prion-induced retinal disease, we fed prion-infected mice a CSF-1 receptor blocking drug, PLX5622, to eliminate microglia in vivo, and the effects on retinal degeneration were analyzed over time. In mice not receiving drug, the main inflammatory cells invading the degenerating PR areas were microglia, not monocytes. Administration of PLX5622 was highly effective at ablating microglia in retina. However, lack of microglia during prion infection did not prevent degeneration of PR cells. Therefore, microglia were not required for the PR damage process during prion infection. Indeed, mice lacking microglia had slightly faster onset of PR damage. Similar results were seen in C57BL/10 mice and transgenic mice expressing GFP or RFP on microglia and monocytes, respectively. These results were supported by experiments using prion-infected Cx3cr1 knockout mice without PLX5622 treatment, where microglial expansion in retina was delayed, but PR degeneration was not. Contrary to predictions, microglia were not a causative factor in retinal damage by prion infection. Instead, newly generated PrPSc accumulated around the inner segment region of the PR cells and appeared to correlate with initiation of the pathogenic process in the absence of microglia.

Molecular profiling of resident and infiltrating mononuclear phagocytes during rapid adult retinal degeneration using single-cell RNA sequencing

Neuroinflammation commonly accompanies neurodegeneration, but the specific roles of resident and infiltrating immune cells during degeneration remains controversial. Much of the difficulty in assessing myeloid cell-specific functions during disease progression arises from the inability to clearly distinguish between activated microglia and bone marrow-derived monocytes and macrophages in various stages of differentiation and activation within the central nervous system. Using an inducible model of photoreceptor cell death, we investigated the prevalence of infiltrating monocytes and macrophage subpopulations after the initiation of degeneration in the mouse retina. In vivo retinal imaging revealed infiltration of CCR2⁺ leukocytes across retinal vessels and into the parenchyma within 48 hours of photoreceptor degeneration. Immunohistochemistry and flow cytometry confirmed and characterized these leukocytes as CD11b⁺CD45⁺ cells. Single-cell mRNA sequencing of the entire CD11b⁺CD45⁺ population revealed the presence of resting microglia, activated microglia, monocytes, and macrophages as well as 12 distinct subpopulations within these four major cell classes. Our results demonstrate a previously immeasurable degree of molecular heterogeneity in the innate immune response to cell-autonomous degeneration within the central nervous system and highlight the necessity of unbiased high-throughput and high-dimensional molecular techniques like scRNAseq to understand the complex and changing landscape of immune responders during disease progression.

Microglial Function Is Distinct in Different Anatomical Locations during Retinal Homeostasis and Degeneration

Microglia from different nervous system regions are molecularly and anatomically distinct, but whether they also have different functions is unknown. We combined lineage tracing, single-cell transcriptomics, and electrophysiology of the mouse retina and showed that adult retinal microglia shared a common developmental lineage and were long-lived but resided in two distinct niches. Microglia in these niches differed in their interleukin-34 dependency and functional contribution to visual-information processing. During certain retinal-degeneration models, microglia from both pools relocated to the subretinal space, an inducible disease-associated niche that was poorly accessible to monocyte-derived cells. This microglial transition involved transcriptional reprogramming of microglia, characterized by reduced expression of homeostatic checkpoint genes and upregulation of injury-responsive genes. This transition was associated with protection of the retinal pigmented epithelium from damage caused by disease. Together, our data demonstrate that microglial function varies by retinal niche, thereby shedding light on the significance of microglia heterogeneity.

Fate Mapping In Vivo to Distinguish Bona Fide Microglia Versus Recruited Monocyte-Derived Macrophages in Retinal Disease

With the new understanding that adult microglia in mice have embryonic origins and are maintained in situ throughout life, it has become pertinent to now understand how these unique cells differ from monocyte-derived macrophages. The latter are recruited into the neural retina (and elsewhere in CNS) in certain diseased states, such as in various forms of retinal degeneration. However, phenotypic markers expressed by microglia and monocyte-derived macrophages largely overlap, thereby making it technically challenging to distinguish the two cell types in disease. To address this problem in mice, we have established an in vivo fate mapping system that enables distinguishing these two cell types in retinal disease models. Our approach leverages the seminal work that originally developed Cx3cr1-CreER mice and is based on commercially available mouse strains. Here, we detail our protocol and how to apply this fate mapping method paired with flow cytometry (or immunohistochemistry) to faithfully distinguish and examine microglia vs. monocyte-derived macrophages in a mutually exclusive manner. This approach will henceforth empower new efforts to identify functional specializations of these two populations in the pathobiology of retinal degenerative diseases and possibly other conditions of the retina where monocyte recruitment is observed, such as in glaucoma, diabetic retinopathy, ischemia reperfusion, retinal detachment, and so on.

Immune cells in the retina and choroid: Two different tissue environments that require different defenses and surveillance

In the eye immune defenses must take place in a plethora of differing microenvironments ranging from the corneal and conjunctival epithelia facing the external environment to the pigmented connective tissue of the uveal tract containing smooth muscle, blood vessels and peripheral nerves to the innermost and highly protected neural retina. The extravascular environment of the neural retina, like the brain parenchyma, is stringently controlled to maintain conditions required for neural transmission. The unique physiological nature of the neural retina can be attributed to the blood retinal barriers (BRB) of the retinal vasculature and the retinal pigment epithelium, which both tightly regulate the transport of small molecules and restrict passage of cells and macromolecules from the circulation into the retina in a similar fashion to the blood brain barrier (BBB). The extracellular environment of the neural retina differs markedly from that of the highly vascular, loose connective tissue of the choroid, which lies outside the BRB. The choroid hosts a variety of immune cell types, including macrophages, dendritic cells (DCs) and mast cells. This is in marked contrast to the neural parenchyma of the retina, which is populated almost solely by microglia. This review will describe the current understanding of the distribution, phenotype and physiological role of ocular immune cells behind or inside the blood-retinal barriers and those in closely juxtaposed tissues outside the barrier. The nature and function of these immune cells can profoundly influence retinal homeostasis and lead to disordered immune function that can lead to vision loss.

Impaired monocyte cholesterol clearance initiates age-related retinal degeneration and vision loss

Advanced age-related macular degeneration (AMD), the leading cause of blindness among people over 50 years of age, is characterized by atrophic neurodegeneration or pathologic angiogenesis. Early AMD is characterized by extracellular cholesterol-rich deposits underneath the retinal pigment epithelium (RPE) called drusen or in the subretinal space called subretinal drusenoid deposits (SDD) that drive disease progression. However, mechanisms of drusen and SDD biogenesis remain poorly understood. Although human AMD is characterized by abnormalities in cholesterol homeostasis and shares phenotypic features with atherosclerosis, it is unclear whether systemic immunity or local tissue metabolism regulates this homeostasis. Here, we demonstrate that targeted deletion of macrophage cholesterol ABC transporters A1 (ABCA1) and -G1 (ABCG1) leads to age-associated extracellular cholesterol-rich deposits underneath the neurosensory retina similar to SDD seen in early human AMD. These mice also develop impaired dark adaptation, a cardinal feature of RPE cell dysfunction seen in human AMD patients even before central vision is affected. Subretinal deposits in these mice progressively worsen with age, with concomitant accumulation of cholesterol metabolites including several oxysterols and cholesterol esters causing lipotoxicity that manifests as photoreceptor dysfunction and neurodegeneration. These findings suggest that impaired macrophage cholesterol transport initiates several key elements of early human AMD, demonstrating the importance of systemic immunity and aging in promoting disease manifestation. Polymorphisms in genes involved with cholesterol transport and homeostasis are associated with a significantly higher risk of developing AMD, thus making these studies translationally relevant by identifying potential targets for therapy.