The Functional Roles of IL-33/ST2 Axis in Ocular Diseases

Interleukin-33/serum stimulation-2 pathway: Regulatory mechanisms and emerging implications in immune and inflammatory diseases

Interleukin (IL)- 33, a nuclear factor and pleiotropic cytokine of the IL-1 family, is gaining attention owing to its important role in chronic inflammatory and autoimmune diseases. This review extends our knowledge of the effects exerted by IL-33 on target cells by binding to its specific receptor serum stimulation-2 (ST2). Depending on the tissue context, IL-33 performs multiple functions encompassing host defence, immune response, initiation and amplification of inflammation, tissue repair, and homeostasis. The levels and activity of IL-33 in the body are controlled by complex IL-33-targeting regulatory pathways. The unique temporal and spatial expression patterns of IL-33 are associated with host homeostasis and the development of immune and inflammatory disorders. Therefore, understanding the origin, function, and processes of IL-33 under various conditions is crucial. This review summarises the regulatory mechanisms underlying the IL-33/ST2 signalling axis and its potential role and clinical significance in immune and inflammatory diseases, and discusses the current complex and conflicting findings related to IL-33 in host responses.

Strategies targeting IL-33/ST2 axis in the treatment of allergic diseases

Interleukin-33 (IL-33) and its receptor Serum Stimulation-2 (ST2, also called Il1rl1) are members of the IL-1 superfamily that plays a crucial role in allergic diseases. The interaction of IL-33 and ST2 mainly activates NF-κB signaling and MAPK signaling via the MyD88/IRAK/TRAF6 module, resulting in the production and secretion of pro-inflammatory cytokines. The IL-33/ST2 axis participates in the pathogenesis of allergic diseases, and therefore serves as a promising strategy for allergy treatment. In recent years, strategies blocking IL-33/ST2 through targeting regulation of IL-33 and ST2 or targeting the molecules involved in the signal transduction have been extensively studied mostly in animal models. These studies provide various potential therapeutic agents other than antibodies, such as small molecules, nucleic acids and traditional Chinese medicines. Herein, we reviewed potential targets and agents targeting IL-33/ST2 axis in the treatment of allergic diseases, providing directions for further investigations on treatments for IL-33 induced allergic diseases.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Dual Immune Regulatory Roles of Interleukin-33 in Pathological Conditions

Interleukin-33 (IL-33), a member of the IL-1 cytokine family and a multifunctional cytokine, plays critical roles in maintaining host homeostasis and in pathological conditions, such as allergy, infectious diseases, and cancer, by acting on multiple types of immune cells and promoting type 1 and 2 immune responses. IL-33 is rapidly released by immune and non-immune cells upon stimulation by stress, acting as an “alarmin” by binding to its receptor, suppression of tumorigenicity 2 (ST2), to trigger downstream signaling pathways and activate inflammatory and immune responses. It has been recognized that IL-33 displays dual-functioning immune regulatory effects in many diseases and has both pro- and anti-tumorigenic effects, likely depending on its primary target cells, IL-33/sST2 expression levels, cellular context, and the cytokine microenvironment. Herein, we summarize our current understanding of the biological functions of IL-33 and its roles in the pathogenesis of various conditions, including inflammatory and autoimmune diseases, infections, cancers, and cases of organ transplantation. We emphasize the nature of context-dependent dual immune regulatory functions of IL-33 in many cells and diseases and review systemic studies to understand the distinct roles of IL-33 in different cells, which is essential to the development of more effective diagnoses and therapeutic approaches for IL-33-related diseases.

The Role of Inflammation in Retinal Neurodegeneration and Degenerative Diseases

Retinal neurodegeneration is predominantly reported as the apoptosis or impaired function of the photoreceptors. Retinal degeneration is a major causative factor of irreversible vision loss leading to blindness. In recent years, retinal degenerative diseases have been investigated and many genes and genetic defects have been elucidated by many of the causative factors. An enormous amount of research has been performed to determine the pathogenesis of retinal degenerative conditions and to formulate the treatment modalities that are the critical requirements in this current scenario. Encouraging results have been obtained using gene therapy. We provide a narrative review of the various studies performed to date on the role of inflammation in human retinal degenerative diseases such as age-related macular degeneration, inherited retinal dystrophies, retinitis pigmentosa, Stargardt macular dystrophy, and Leber congenital amaurosis. In addition, we have highlighted the pivotal role of various inflammatory mechanisms in the progress of retinal degeneration. This review also offers an assessment of various therapeutic approaches, including gene-therapies and stem-cell-based therapies, for degenerative retinal diseases.

Increased serum level of interleukin-33 in Vogt-Koyanagi-Harada correlates with disease activity

OBJECTIVES

To measure the serum level of IL-33 in patients with Vogt-Koyanagi-Harada disease (VKH) and Behçet's uveitis (BU) in the Chinese Han population and investigate its associations with disease activity and clinical parameters.

METHODS

Serum was collected from 41 VKH patients (16 active and 25 inactive patients), 60 BU patients (24 active and 36 inactive patients), and 36 healthy controls. The serum level of IL-33 was measured using the enzyme-linked immunosorbent assay (ELISA) method. Demographic features, clinical manifestations, and intraocular inflammation activity scores (anterior chamber cells score, anterior chamber flare score, and vitreal haze score) were recorded.

RESULTS

The serum level of IL-33 significantly increased in all VKH patients, active VKH patients, and inactive VKH patients, as compared to healthy controls (p < 0.001, p < 0.001, and p = 0.002, respectively), and was higher in the active VKH than in the inactive VKH patients (p = 0.049). The serum level of IL-33 positively correlated with the anterior chamber cells score, vitreal haze score, and the annualized number of relapses in VKH patients (Rho = 0.359, p = 0.021; Rho = 0.344, p = 0.028; Rho = 0.537, p < 0.001, respectively). Serum IL-33 level was significantly associated with the annualized number of relapses in patients with BU (Rho = 0.361, p = 0.005).

CONCLUSION

Serum IL-33 level is significantly increased in VKH patients in the Chinese Han population. IL-33 level is in positive correlation with the activity and relapses of VKH. Increased IL-33 might contribute to the pathogenesis of VKH and serve as a potential biomarker for VKH disease.

Pollen shells and soluble factors play non-redundant roles in the development of allergic conjunctivitis in mice

PURPOSE

We aimed to clarify the role of particulate allergen exposure to the conjunctiva in the development of allergic conjunctivitis.

METHODS

We administered ragweed pollen suspension, pollen extract, pollen shell, particulate air pollutants, and their combinations to the mouse conjunctiva five days a week without prior sensitization. Clinical signs were scored. Histological changes, cellular infiltrations, mRNA expressions, lymph node cell recall responses, and serum immunoglobulin levels were assessed. Immune cell-depleting antibodies and ST2 knockout mice were used to investigate the cellular and molecular requirements.

RESULTS

Pollen suspension, but not the extract or shell alone, induced robust eosinophilic conjunctivitis, accompanied by a proliferative response of epithelial cells. A combination of pollen extract and shell completely restored eosinophil accumulation. In addition, eosinophilic conjunctivitis was induced by a mixture of particulate air pollutants and pollen extract. Mechanistically, eosinophil accumulation was ameliorated by deficiency of the IL-33 receptor ST2 and abolished by depleting CD4⁺ T cells. Pollen shells, but not the extract, induced IL-33 release from conjunctival epithelial cells in vivo.

CONCLUSIONS

Our results indicate the non-redundant roles for the allergens' particulate properties and soluble factors in the development of allergic conjunctivitis.

Inflammation and tumor progression: signaling pathways and targeted intervention

Cancer development and its response to therapy are regulated by inflammation, which either promotes or suppresses tumor progression, potentially displaying opposing effects on therapeutic outcomes. Chronic inflammation facilitates tumor progression and treatment resistance, whereas induction of acute inflammatory reactions often stimulates the maturation of dendritic cells (DCs) and antigen presentation, leading to anti-tumor immune responses. In addition, multiple signaling pathways, such as nuclear factor kappa B (NF-kB), Janus kinase/signal transducers and activators of transcription (JAK-STAT), toll-like receptor (TLR) pathways, cGAS/STING, and mitogen-activated protein kinase (MAPK); inflammatory factors, including cytokines (e.g., interleukin (IL), interferon (IFN), and tumor necrosis factor (TNF)-α), chemokines (e.g., C-C motif chemokine ligands (CCLs) and C-X-C motif chemokine ligands (CXCLs)), growth factors (e.g., vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β), and inflammasome; as well as inflammatory metabolites including prostaglandins, leukotrienes, thromboxane, and specialized proresolving mediators (SPM), have been identified as pivotal regulators of the initiation and resolution of inflammation. Nowadays, local irradiation, recombinant cytokines, neutralizing antibodies, small-molecule inhibitors, DC vaccines, oncolytic viruses, TLR agonists, and SPM have been developed to specifically modulate inflammation in cancer therapy, with some of these factors already undergoing clinical trials. Herein, we discuss the initiation and resolution of inflammation, the crosstalk between tumor development and inflammatory processes. We also highlight potential targets for harnessing inflammation in the treatment of cancer.

Endothelin-1 Serum Concentration in Pediatric Chronic Idiopathic Uveitis

Purpose

The aim of our study was to determine endothelin-1 (ET-1) concentration in chronic idiopathic uveitis in children and adolescents depending on anatomical location and grade of inflammation.

Methods

The cross-sectional study was conducted among 17 patients with chronic idiopathic uveitis and 22 healthy controls. Concentration of ET-1 in serum was determined using a commercially available ELISA kit. The concentration of C reactive protein (CRP) in serum was determined by immunoturbidimetric method using CRP4 reagent kit (Roche Diagnostics GmbH, Mannheim, Germany).

Results

Statistically significant difference between ET-1 concentration in patients with chronic idiopathic uveitis and controls was found 1.33 (1.22; 1.48) vs 1.93 (1.1; 3.11), p = 0.008). No correlations were found between ET-1 concentration and age, either in chronic idiopathic uveitis patients or controls. Nine out of 17 patients presented with anterior uveitis, 5 with posterior and 3 with panuveitis. There were no differences in ET-1 concentration between anterior, posterior and panuveitis (p = 0.634), and in terms of grade of inflammation.

Conclusion

ET-1 expression is disturbed in pediatric chronic idiopathic uveitis irrespective of the anatomical location and grade of inflammation. Lower expression of ET-1 plays a crucial role in disturbed vascular tone control and can result in permanent visual impairment in chronic non-infectious uveitis.