Targeting proliferative retinopathy: Arginase 1 limits vitreoretinal neovascularization and promotes angiogenic repair

Current therapies for treatment of proliferative retinopathy focus on retinal neovascularization (RNV) during advanced disease and can trigger adverse side-effects. Here, we have tested a new strategy for limiting neurovascular injury and promoting repair during early-stage disease. We have recently shown that treatment with a stable, pegylated drug form of the ureohydrolase enzyme arginase 1 (A1) provides neuroprotection in acute models of ischemia/reperfusion injury, optic nerve crush, and ischemic stroke. Now, we have determined the effects of this treatment on RNV, vascular repair, and retinal function in the mouse oxygen-induced retinopathy (OIR) model of retinopathy of prematurity (ROP). Our studies in the OIR model show that treatment with pegylated A1 (PEG-A1), inhibits pathological RNV, promotes angiogenic repair, and improves retinal function by a mechanism involving decreased expression of TNF, iNOS, and VEGF and increased expression of FGF2 and A1. We further show that A1 is expressed in myeloid cells and areas of RNV in retinal sections from mice with OIR and human diabetic retinopathy (DR) patients and in blood samples from ROP patients. Moreover, studies using knockout mice with hemizygous deletion of A1 show worsened RNV and retinal injury, supporting the protective role of A1 in limiting the OIR-induced pathology. Collectively, A1 is critically involved in reparative angiogenesis and neuroprotection in OIR. Pegylated A1 may offer a novel therapy for limiting retinal injury and promoting repair during proliferative retinopathy.

IL-27 Derived From Macrophages Facilitates IL-15 Production and T Cell Maintenance Following Allergic Hypersensitivity Responses

Crosstalk between T cells, dendritic cells, and macrophages in temporal leukocyte clusters within barrier tissues provides a new concept for T cell activation in the skin. Activated T cells from these leukocyte clusters play critical roles in the efferent phase of allergic contact hypersensitivity (CHS). However, the cytokines driving maintenance and survival of pathogenic T cells during and following CHS remain mostly unknown. Upon epicutaneous allergen challenge, we here report that macrophages produce IL-27 which then induces IL-15 production from epidermal keratinocytes and dermal myeloid cells within leukocyte clusters. In agreement with the known role of IL-15 as a T cell survival factor and growth cytokine, this signaling axis enhances BCL2 and survival of skin T cells. Genetic depletion or pharmacological blockade of IL-27 in CHS mice leads to abrogated epidermal IL-15 production resulting in a decrease in BCL2 expression in T cells and a decline in dermal CD8⁺ T cells and T cell cluster numbers. These findings suggest that the IL-27 pathway is an important cytokine for regulating cutaneous T cell immunity.

Single-Cell RNA Sequencing Reveals Cellular and Transcriptional Changes Associated With M1 Macrophage Polarization in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by recurrent abscesses, nodules, and sinus tracts in areas of high hair follicle and sweat gland density. These sinus tracts can present with purulent drainage and scar formation. Dysregulation of multiple immune pathways drives the complexity of HS pathogenesis and may account for the heterogeneity of treatment response in HS patients. Using transcriptomic approaches, including single-cell sequencing and protein analysis, we here characterize the innate inflammatory landscape of HS lesions. We identified a shared upregulation of genes involved in interferon (IFN) and antimicrobial defense signaling through transcriptomic overlap analysis of differentially expressed genes (DEGs) in datasets from HS skin, diabetic foot ulcers (DFUs), and the inflammatory stage of normal healing wounds. Overlap analysis between HS- and DFU-specific DEGs revealed an enrichment of gene signatures associated with monocyte/macrophage functions. Single-cell RNA sequencing further revealed monocytes/macrophages with polarization toward a pro-inflammatory M1-like phenotype and increased effector function, including antiviral immunity, phagocytosis, respiratory burst, and antibody-dependent cellular cytotoxicity. Specifically, we identified the STAT1/IFN-signaling axis and the associated IFN-stimulated genes as central players in monocyte/macrophage dysregulation. Our data indicate that monocytes/macrophages are a potential pivotal player in HS pathogenesis and their pathways may serve as therapeutic targets and biomarkers in HS treatment.

ENTPD1 (CD39) Expression Inhibits UVR-Induced DNA Damage Repair through Purinergic Signaling and Is Associated with Metastasis in Human Cutaneous Squamous Cell Carcinoma

UVR and immunosuppression are major risk factors for cutaneous squamous cell carcinoma (cSCC). Regulatory T cells promote cSCC carcinogenesis, and in other solid tumors, infiltrating regulatory T cells and CD8⁺ T cells express ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) (also known as CD39), an ectoenzyme that catalyzes the rate-limiting step in converting extracellular adenosine triphosphate (ATP) to extracellular adenosine (ADO). We previously showed that extracellular purine nucleotides influence DNA damage repair. In this study, we investigate whether DNA damage repair is modulated through purinergic signaling in cSCC. We found increased ENTPD1 expression on T cells within cSCCs when compared with the expression on T cells from blood or nonlesional skin, and accordingly, concentrations of derivative extracellular adenosine diphosphate (ADP), adenosine monophosphate (AMP), and ADO are increased in tumors compared with those in normal skin. Importantly, ENTPD1 expression is significantly higher in human cSCCs that metastasize than in those that are nonmetastatic. We also identify in a mouse model that ENTPD1 expression is induced by UVR in an IL-27-dependent manner. Finally, increased extracellular ADO is shown to downregulate the expression of NAP1L2, a nucleosome assembly protein we show to be important for DNA damage repair secondary to UVR. Together, these data suggest a role for ENTPD1 expression on skin-resident T cells to regulate DNA damage repair through purinergic signaling to promote skin carcinogenesis and metastasis.

Multifactorial Design of a Supramolecular Peptide Anti-IL-17 Vaccine Toward the Treatment of Psoriasis

Current treatments for chronic immune-mediated diseases such as psoriasis, rheumatoid arthritis, or Crohn's disease commonly rely on cytokine neutralization using monoclonal antibodies; however, such approaches have drawbacks. Frequent repeated dosing can lead to the formation of anti-drug antibodies and patient compliance issues, and it is difficult to identify a single antibody that is broadly efficacious across diverse patient populations. As an alternative to monoclonal antibody therapy, anti-cytokine immunization is a potential means for long-term therapeutic control of chronic inflammatory diseases. Here we report a supramolecular peptide-based approach for raising antibodies against IL-17 and demonstrate its efficacy in a murine model of psoriasis. B-cell epitopes from IL-17 were co-assembled with the universal T-cell epitope PADRE using the Q11 self-assembling peptide nanofiber system. These materials, with or without adjuvants, raised antibody responses against IL-17. Exploiting the modularity of the system, multifactorial experimental designs were used to select formulations maximizing titer and avidity. In a mouse model of psoriasis induced by imiquimod, unadjuvanted nanofibers had therapeutic efficacy, which could be enhanced with alum adjuvant but reversed with CpG adjuvant. Measurements of antibody subclass induced by adjuvanted and unadjuvanted formulations revealed strong correlations between therapeutic efficacy and titers of IgG1 (improved efficacy) or IgG2b (worsened efficacy). These findings have important implications for the development of anti-cytokine active immunotherapies and suggest that immune phenotype is an important metric for eliciting therapeutic anti-cytokine antibody responses.

IL-27 signaling activates skin cells to induce innate antiviral proteins and protects against Zika virus infection

In the skin, antiviral proteins and other immune molecules serve as the first line of innate antiviral defense. Here, we identify and characterize the induction of cutaneous innate antiviral proteins in response to IL-27 and its functional role during cutaneous defense against Zika virus infection. Transcriptional and phenotypic profiling of epidermal keratinocytes treated with IL-27 demonstrated activation of antiviral proteins OAS1, OAS2, OASL, and MX1 in the skin of both mice and humans. IL-27-mediated antiviral protein induction was found to occur in a STAT1- and IRF3-dependent but STAT2-independent manner. Moreover, using IL27ra mice, we demonstrate a significant role for IL-27 in inhibiting Zika virus morbidity and mortality following cutaneous, but not intravenous, inoculation. Together, our results demonstrate a critical and previously unrecognized role for IL-27 in cutaneous innate antiviral immunity against Zika virus.

Noncanonical autophagy in dermal dendritic cells mediates immunosuppressive effects of UV exposure

BACKGROUND

Control of the inflammatory response is critical to maintaining homeostasis, and failure to do so contributes to the burden of chronic inflammation associated with several disease states. The mechanisms that underlie immunosuppression, however, remain largely unknown. Although defects in autophagy machinery have been associated with inflammatory pathologic conditions, we now appreciate that autophagic components participate in noncanonical pathways distinct from classical autophagy. We have previously demonstrated that LC3-associated phagocytosis (LAP), a noncanonical autophagic process dependent on Rubicon (rubicon autophagy regulator [RUBCN]), contributes to immunosuppression.

OBJECTIVE

We used Rubcn^-/- mice to examine the role of the LAP pathway in mediating the UV-induced immunotolerant program in a model of contact hypersensitivity (CHS).

METHODS

Flow cytometry and transcriptional analysis were used to measure immune cell infiltration and activation in the skin of Rubcn^+/+ and Rubcn^-/- mice during the CHS response.

RESULTS

Here, we demonstrate that LAP is required for UV-induced immunosuppression and that UV exposure induces a broadly anti-inflammatory transcriptional program dependent on Rubicon. Rubcn^-/- mice are resistant to UV-induced immunosuppression and instead display exaggerated inflammation in a model of CHS. Specifically, RUBCN deficiency in CD301b⁺ dermal dendritic cells results in their increased antigen presentation capacity and subsequent hyperactivation of the CD8⁺ T-cell response.

CONCLUSIONS

LAP functions to limit the immune response and is critical in maintaining the balance between homeostasis and inflammation.

Shifting Paradigms in Allergic Contact Dermatitis: The Role of Innate Immunity

The role of the innate immune system in allergic contact dermatitis (ACD) has traditionally been confined to the initial antigen sensitization phase. However, more recent findings have shown the role of innate immunity in additional aspects of ACD, including the effector phase of the classic type IV hypersensitivity reaction. As a result, the precise immunologic mechanisms mediating ACD are more complex than previously believed. The aim of this review is to provide insight into recent advances in understanding the role of the innate immune system in the pathogenesis of ACD, including novel mechanistic roles for macrophages, innate lymphoid cells, natural killer cells, innate γδ T cells, and other signaling molecules. These insights provide new opportunities for therapeutic intervention in ACD.

Perivascular dendritic cells elicit anaphylaxis by relaying allergens to mast cells via microvesicles

Anaphylactic reactions are triggered when allergens enter the blood circulation and activate immunoglobulin E (IgE)-sensitized mast cells (MCs), causing systemic discharge of prestored proinflammatory mediators. As MCs are extravascular, how they perceive circulating allergens remains a conundrum. Here, we describe the existence of a CD301b⁺ perivascular dendritic cell (DC) subset that continuously samples blood and relays antigens to neighboring MCs, which vigorously degranulate and trigger anaphylaxis. DC antigen transfer involves the active discharge of surface-associated antigens on 0.5- to 1.0-micrometer microvesicles (MVs) generated by vacuolar protein sorting 4 (VPS4). Antigen sharing by DCs is not limited to MCs, as neighboring DCs also acquire antigen-bearing MVs. This capacity of DCs to distribute antigen-bearing MVs to various immune cells in the perivascular space potentiates inflammatory and immune responses to blood-borne antigens.

Biased agonists of the chemokine receptor CXCR3 differentially control chemotaxis and inflammation

The chemokine receptor CXCR3 plays a central role in inflammation by mediating effector/memory T cell migration in various diseases; however, drugs targeting CXCR3 and other chemokine receptors are largely ineffective in treating inflammation. Chemokines, the endogenous peptide ligands of chemokine receptors, can exhibit so-called biased agonism by selectively activating either G protein- or β-arrestin-mediated signaling after receptor binding. Biased agonists might be used as more targeted therapeutics to differentially regulate physiological responses, such as immune cell migration. To test whether CXCR3-mediated physiological responses could be segregated by G protein- and β-arrestin-mediated signaling, we identified and characterized small-molecule biased agonists of the receptor. In a mouse model of T cell-mediated allergic contact hypersensitivity (CHS), topical application of a β-arrestin-biased, but not a G protein-biased, agonist potentiated inflammation. T cell recruitment was increased by the β-arrestin-biased agonist, and biopsies of patients with allergic CHS demonstrated coexpression of CXCR3 and β-arrestin in T cells. In mouse and human T cells, the β-arrestin-biased agonist was the most efficient at stimulating chemotaxis. Analysis of phosphorylated proteins in human lymphocytes showed that β-arrestin-biased signaling activated the kinase Akt, which promoted T cell migration. This study demonstrates that biased agonists of CXCR3 produce distinct physiological effects, suggesting discrete roles for different endogenous CXCR3 ligands and providing evidence that biased signaling can affect the clinical utility of drugs targeting CXCR3 and other chemokine receptors.

Arginase1 Deficiency in Monocytes/Macrophages Upregulates Inducible Nitric Oxide Synthase To Promote Cutaneous Contact Hypersensitivity

The innate immune components that modulate allergic contact hypersensitivity (CHS) responses are poorly defined. Using human skin from contact dermatitis patients and a mouse model of CHS, we find that hapten allergens disrupt the Arginase1 (Arg1) and inducible NO synthase (iNOS) dynamic in monocytes/macrophages (mono/MΦ), which renders those cells ineffectual in suppressing skin inflammation. Mice lacking Arg1 in MΦ develop increased CHS characterized by elevated ear thickening, mono/MΦ-dominated dermal inflammation, and increased iNOS and IL-6 expression compared with control mice. Treatment of Arg1^flox/flox; LysMCre^+/- mice with a selective NOS inhibitor or knockout of Nos2, encoding iNOS, significantly ameliorates CHS. Our findings suggest a critical role for Arg1 in mono/MΦ in suppressing CHS through dampening Nos2 expression. These results support that increasing Arg1 may be a potential therapeutic avenue in treating allergic contact dermatitis.

IL-27 Facilitates Skin Wound Healing through Induction of Epidermal Proliferation and Host Defense

Skin wound repair requires a coordinated program of epithelial cell proliferation and differentiation as well as resistance to invading microbes. However, the factors that trigger epithelial cell proliferation in this inflammatory process are incompletely understood. In this study, we demonstrate that IL-27 is rapidly and transiently produced by CD301b⁺ cells in the skin after injury. The functional role of IL-27 and CD301b⁺ cells is demonstrated by the finding that CD301b-depleted mice exhibit delayed wound closure in vivo, which could be rescued by topical IL-27 treatment. Furthermore, genetic ablation of the IL-27 receptor (Il27Ra^−/−) attenuates wound healing, suggesting an essential role for IL-27 signaling in skin regeneration in vivo. Mechanistically, IL-27 feeds back on keratinocytes to stimulate cell proliferation and re-epithelialization in the skin, whereas IL-27 leads to suppression of keratinocyte terminal differentiation. Finally, we identify that IL-27 potently increases expression of the antiviral oligoadenylate synthetase 2, but does not affect expression of antibacterial human beta defensin 2 or regenerating islet-derived protein 3-alpha. Together, our data suggest a previously unrecognized role for IL-27 in regulating epithelial cell proliferation and antiviral host defense during the normal wound healing response.

Emerging Skin T-Cell Functions in Response to Environmental Insults

Skin is the primary barrier between the body and the outside world, functioning not only as a physical barrier, but also as an immunologic first line of defense. A large number of T cells populate the skin. This review highlights the ability of these cutaneous T cells to regulate skin-specific environmental threats, including microbes, injuries, solar UV radiation, and allergens. Since much of this knowledge has been advanced from murine studies, we focus our review on how the mouse state has informed the human state, emphasizing the key parallels and differences.

Arginase 2 deficiency prevents oxidative stress and limits hyperoxia-induced retinal vascular degeneration

Background

Hyperoxia exposure of premature infants causes obliteration of the immature retinal microvessels, leading to a condition of proliferative vitreoretinal neovascularization termed retinopathy of prematurity (ROP). Previous work has demonstrated that the hyperoxia-induced vascular injury is mediated by dysfunction of endothelial nitric oxide synthase resulting in peroxynitrite formation. This study was undertaken to determine the involvement of the ureahydrolase enzyme arginase in this pathology.

Methods and Findings

Studies were performed using hyperoxia-treated bovine retinal endothelial cells (BRE) and mice with oxygen-induced retinopathy (OIR) as experimental models of ROP. Treatment with the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) prevented hyperoxia-induced apoptosis of BRE cells and reduced vaso-obliteration in the OIR model. Furthermore, deletion of the arginase 2 gene protected against hyperoxia-induced vaso-obliteration, enhanced physiological vascular repair, and reduced retinal neovascularization in the OIR model. Additional deletion of one copy of arginase 1 did not improve the vascular pathology. Analyses of peroxynitrite by quantitation of its biomarker nitrotyrosine, superoxide by dihydroethidium imaging and NO formation by diaminofluoroscein imaging showed that the protective actions of arginase 2 deletion were associated with blockade of superoxide and peroxynitrite formation and normalization of NOS activity.

Conclusions

Our data demonstrate the involvement of arginase activity and arginase 2 expression in hyperoxia-induced vascular injury. Arginase 2 deletion prevents hyperoxia-induced retinal vascular injury by preventing NOS uncoupling resulting in decreased reactive oxygen species formation and increased nitric oxide bioavailability.

Anti-angiogenic actions of the mangosteen polyphenolic xanthone derivative α-mangostin

Retinal neovascularization is a major cause of vision loss in diseases characterized by retinal ischemia and is characterized by the pathological growth of abnormal vessels. Vascular endothelial growth factor (VEGF) is known to play an important role in this process. Oxidative stress has been strongly implicated in up-regulation of VEGF associated with neovascularization in various tissues. Hence, compounds with anti-oxidant actions can prevent neovascularization. α-Mangostin, a component of mangosteen (Garcinia mangostana Linn), has been shown to have an anti-oxidant property in pathological conditions involving angiogenesis such as cancer. However, the effect of α-mangostin on ROS formation and angiogenic function in microvascular endothelial cells has not been studied. Hence, this study demonstrated the anti-angiogenic effects of α-mangostin in relation to ROS formation in bovine retinal endothelial cells (REC). α-Mangostin significantly and dose-dependently reduced formation of ROS in hypoxia-treated REC. α-Mangostin also significantly and dose-dependently suppressed VEGF-induced increases in permeability, proliferation, migration and tube formation in REC and blocked angiogenic sprouting in the ex vivo aortic ring assay. In addition, α-mangostin inhibited VEGF-induced phosphorylation of VEGFR2 and ERK1/2-MAPK. According to our results, α-mangostin reduces oxidative stress and limits VEGF-induced angiogenesis through a process involving abrogation of VEGFR2 and ERK1/2-MAPK activation.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

Arginase 2 deletion reduces neuro-glial injury and improves retinal function in a model of retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity (ROP) is a major cause of vision impairment in low birth weight infants. While previous work has focused on defining the mechanisms of vascular injury leading to retinal neovascularization, recent studies show that neurons are also affected. This study was undertaken to determine the role of the mitochondrial arginine/ornithine regulating enzyme arginase 2 (A2) in retinal neuro-glial cell injury in the mouse model of ROP.

METHODS AND FINDINGS

Studies were performed using wild type (WT) and A2 knockout (A2-/-) mice exposed to Oxygen Induced Retinopathy (OIR). Neuronal injury and apoptosis were assessed using immunohistochemistry, TUNEL (terminal deoxynucleotidyl transferase dUTP nick end) labeling and Western blotting. Electroretinography (ERG) was used to assess retinal function. Neuro-glial injury in WT ROP mice was evident by TUNEL labeling, retinal thinning, decreases in number of rod bipolar cells and glial cell activation as compared with room air controls. Significant reduction in numbers of TUNEL positive cells, inhibition of retinal thinning, preservation of the rod bipolar cells and prevention of glial activation were observed in the A2-/- retinas. Retinal function was markedly impaired in the WT OIR mice as shown by decreases in amplitude of the b-wave of the ERG. This defect was significantly reduced in A2-/- mice. Levels of the pro-apoptotic proteins p53, cleaved caspase 9, cytochrome C and the mitochondrial protein Bim were markedly increased in WT OIR retinas compared to controls, whereas the pro-survival Mitochondrial protein BCL-xl was reduced. These alterations were largely blocked in the A2-/- OIR retina.

CONCLUSIONS

Our data implicate A2 in neurodegeneration during ROP. Deletion of A2 significantly improves neuronal survival and function, possibly through the regulation of mitochondrial membrane permeability mediated apoptosis during retinal ischemia. These molecular events are associated with decreased activation of glial cells, suggesting a rescue effect on macroglia as well.