Dynamic Interplay of Innate and Adaptive Immunity During Sterile Retinal Inflammation: Insights From the Transcriptome

Assessing the role of T cells in response to retinal injury to uncover new therapeutic targets for the treatment of retinal degeneration

BACKGROUND

Retinal degeneration is a disease affecting the eye, which is an immune-privileged site because of its anatomical and physiological properties. Alterations in retinal homeostasis-because of injury, disease, or aging-initiate inflammatory cascades, where peripheral leukocytes (PL) infiltrate the parenchyma, leading to retinal degeneration. So far, research on PL's role in retinal degeneration was limited to observing a few cell types at specific times or sectioning the tissue. This restricted our understanding of immune cell interactions and response duration.

METHODS

In vivo microscopy in preclinical mouse models can overcome these limitations enabling the spatio-temporal characterization of PL dynamics. Through in vivo imaging, we assessed structural and fluorescence changes in response to a focal injury at a defined location over time. We also utilized minimally invasive techniques, pharmacological interventions, and knockout (KO) mice to determine the role of PL in local inflammation. Furthermore, we investigated PL abundance and localization during retinal degeneration in human eyes by histological analysis to assess to which extent our preclinical study translates to human retinal degeneration.

RESULTS

We demonstrate that PL, especially T cells, play a detrimental role during retinal injury response. In mice, we observed the recruitment of helper and cytotoxic T cells in the parenchyma post-injury, and T cells also resided in the macula and peripheral retina in pathological conditions in humans. Additionally, we found that the pharmacological PL reduction and genetic depletion of T-cells reduced injured areas in murine retinas and rescued the blood-retina barrier (BRB) integrity. Both conditions promoted morphological changes of Cx3cr1+ cells, including microglial cells, toward an amoeboid phenotype during injury response. Interestingly, selective depletion of CD8+ T cells accelerated recovery of the BRB compared to broader depletions. After anti-CD8 treatment, the retinal function improved, concomitant to a beneficial immune response.

CONCLUSIONS

Our data provide novel insights into the adaptive immune response to retinal injury in mice and human retinal degeneration. Such information is fundamental to understanding retinal disorders and developing therapeutics to modulate immune responses to retinal degeneration safely.

Elastin turnover in ocular diseases: A special focus on age-related macular degeneration

The extracellular matrix (ECM) and its turnover play a crucial role in the pathogenesis of several inflammatory diseases, including age-related macular degeneration (AMD). Elastin, a critical protein component of the ECM, not only provides structural and mechanical support to tissues, but also mediates several intracellular and extracellular molecular signaling pathways. Abnormal turnover of elastin has pathological implications. In the eye elastin is a major structural component of Bruch's membrane (BrM), a critical ECM structure separating the retinal pigment epithelium (RPE) from the choriocapillaris. Reduced integrity of macular BrM elastin, increased serum levels of elastin-derived peptides (EDPs), and elevated elastin antibodies have been reported in AMD. Existing reports suggest that elastases, the elastin-degrading enzymes secreted by RPE, infiltrating macrophages or neutrophils could be involved in BrM elastin degradation, thus contributing to AMD pathogenesis. EDPs derived from elastin degradation can increase inflammatory and angiogenic responses in tissues, and the elastin antibodies are shown to play roles in immune cell activity and complement activation. This review summarizes our current understanding on the elastases/elastin fragments-mediated mechanisms of AMD pathogenesis.

IL-1/IL-1R signaling induced by all-trans-retinal contributes to complement alternative pathway activation in retinal pigment epithelium

The underlying mechanisms of complement activation in Stargardt disease type 1 (STGD1) and age-related macular degeneration (AMD) are not fully understood. Overaccumulation of all-trans-retinal (atRAL) has been proposed as the pathogenic factor in both diseases. By incubating retinal pigment epithelium (RPE) cells with atRAL, we showed that C5b-9 membrane attack complexes (MACs) were generated mainly through complement alternative pathway. An increase in complement factor B (CFB) expression as well as downregulation of complement regulatory proteins CD46, CD55, CD59, and CFH were observed in RPE cells after atRAL treatment. Furthermore, interleukin-1β production was provoked in both atRAL-treated RPE cells and microglia/macrophages. Coincubation of RPE cells with interleukin-1 receptor antagonist (IL1Ra) and atRAL ameliorated complement activation and downregulated CFB expression by attenuating both p38 and c-Jun N-terminal kinase (JNK) signaling pathways. Our findings demonstrate that atRAL induces an autocrine/paracrine IL-1/IL-1R signaling to promote complement alternative pathway activation in RPE cells and provide a novel perspective on the pathomechanism of macular degeneration.

The immune response after noise damage in the cochlea is characterized by a heterogeneous mix of adaptive and innate immune cells

Cells of the immune system are present in the adult cochlea and respond to damage caused by noise exposure. However, the types of immune cells involved and their locations within the cochlea are unclear. We used flow cytometry and immunostaining to reveal the heterogeneity of the immune cells in the cochlea and validated the presence of immune cell gene expression by analyzing existing single-cell RNA-sequencing (scRNAseq) data. We demonstrate that cell types of both the innate and adaptive immune system are present in the cochlea. In response to noise damage, immune cells increase in number. B, T, NK, and myeloid cells (macrophages and neutrophils) are the predominant immune cells present. Interestingly, immune cells appear to respond to noise damage by infiltrating the organ of Corti. Our studies highlight the need to further understand the role of these immune cells within the cochlea after noise exposure.

Immunization Against Oxidized Elastin Exacerbates Structural and Functional Damage in Mouse Model of Smoke-Induced Ocular Injury

Purpose

Age-related macular degeneration (AMD) is the leading cause of blindness in Western populations. While an overactive complement system has been linked to pathogenesis, mechanisms contributing to its activation are largely unknown. In aged and AMD eyes, loss of the elastin layer (EL) of Bruch's membrane (BrM) has been reported. Elastin antibodies are elevated in patients with AMD, the pathogenic significance of which is unclear. Here we assess the role of elastin antibodies using a mouse model of smoke-induced ocular pathology (SIOP), which similarly demonstrates EL loss.

Methods

C57BL/6J mice were immunized with elastin or elastin peptide oxidatively modified by cigarette smoke (ox-elastin). Mice were then exposed to cigarette smoke or air for 6 months. Visual function was assessed by optokinetic response, retinal morphology by spectral-domain optical coherence tomography and electron microscopy, and complement activation and antibody deposition by Western blot.

Results

Ox-elastin IgG and IgM antibodies were elevated in ox-elastin immunized mice following 6 months of smoke, whereas elastin immunization had a smaller effect. Ox-elastin immunization exacerbated smoke-induced vision loss, with thicker BrM and more damaged retinal pigment epithelium (RPE) mitochondria compared with mice immunized with elastin or nonimmunized controls. These changes were correlated with increased levels of IgM, IgG2, IgG3, and complement activation products in RPE/choroid.

Conclusions

These data demonstrate that SIOP mice generate elastin-specific antibodies and that immunization with ox-elastin exacerbates ocular pathology. Elastin antibodies represented complement fixing isotypes that, together with the increased presence of complement activation seen in immunized mice, suggest that elastin antibodies exert pathogenic effects through mediating complement activation.

Contribution of microglia and monocytes to the development and progression of age related macular degeneration

PURPOSE

Age related macular degeneration (AMD) is the leading cause of irreversible vision loss in industrialised nations. Based on genetics, as well as proteome analysis of drusen, the role the innate immune system in the development and/or progression of the disease is well established. Mononuclear phagocytes, such as microglia and monocytes, play critical roles in innate immunity. Here, the role of retinal microglia in mediating normal retinal function, and how these cells change with age is discussed, so as to understand their role in the development and progression of AMD.

RECENT FINDINGS

It is now known that microglia dynamically survey the neural environment, responding rapidly to even the most subtle neural injury. The dynamic and phagocytic roles of microglia can change with age contributing to alteration in the response of these cells to damage with age. Accumulation of innate immune cells in the subretinal space is a hallmark feature of the development of AMD, reflecting either an increase in migration of monocytes into the retina, or a failure of immune cell elimination from the retina. Furthermore, changes in phagocytic ability of immune cells could contribute to the accumulation of drusen deposits in the posterior eye.

SUMMARY

An overview of how retinal microglia maintain retinal homeostasis under normal conditions is provided, and then how they contribute to each stage of AMD. In addition, circulating monocytes are altered in those with AMD, contributing to the overall inflammatory state. Understanding the role of cells of the innate immune system in AMD may uncover novel therapeutic targets with which to reduce either the development or progression of disease.

The Interplay Between Systemic Inflammatory Factors and MicroRNAs in Age-Related Macular Degeneration

We aimed to explore the expression of systemic inflammatory factors and selected intracellular miRNAs that regulate inflammatory signaling pathways potentially involved in age-related macular degeneration (AMD) pathogenesis. A total of 179 patients with wet AMD, 175 with dry AMD and 121 controls were enrolled in the study. Soluble inflammatory factors were analyzed in plasma samples using Luminex technology. Expression of selected miRNAs was analyzed in isolated nucleated peripheral blood cells (PBNCs) using real-time qPCR. Wet AMD was an independent factor associated with higher concentrations of IL-6 (β = +0.24, p = 0.0004), GM-CSF (β = +0.31, p < 0.001), IFN-γ (β = +0.58, p < 0.001), higher expression of miRNA-23a-3p (β = +0.60, p < 0.0001), miRNA-30b (β = +0.32, p < 0.0001), miRNA-191-5p (β = +0.28, p < 0.0001) and lower concentration of IL-1β (β = −0.25, p = 0.0003), IL-5 (β = −0.45, p < 0.001), IL-10 (β = −0.45, p < 0.001), IL-12 (β = −0.35, p < 0.001), lower expression of miRNA-16-5p (β = −0.31, p < 0.0001), miRNA-17-3p (β = −0.18, p = 0.01), miRNA-150-5p (β = −0.18, p = 0.01) and miRNA-155-5p (β = −0.47, p < 0.0001). Multivariate analysis revealed that dry AMD was an independent factor associated with higher concentration of GM-CSF (β = +0.34, p < 0.001), IL-6 (β = +0.13, p = 0.05), higher expression of miRNA-23a-3p (β = +0.60, p < 0.0001), miRNA-126-3p (β = +0.23, p = 0.0005), miRNA-126-5p (β = +0.16, p = 0.01), miRNA 146a (β = +0.14, p = 0.03), and mRNA191-5p (β = +0.15, p = 0.03) and lower concentrations of TNF-α (β = +0.24, p = 0.0004), IL-1β (β = −0.39, p < 0.001), IL-2 (β = −0.20, p = 0.003), IL-5 (β = −0.54, p < 0.001), IL-10 (β = −0.56, p < 0.001), IL-12 (β = −0.51, p < 0.001), lower expression of miRNA-16-5p (β = −0.23, p = 0.0004), miRNA-17-3p (β = −0.20, p = 0.003) and miRNA-17-5p (β = −0.19, p = 0.004). Negative correlations between visual acuity and WBC, lymphocyte count, TNF-α, IL-1 β, IL-2, IL-4, IL-6, IL-10 concentrations and miRNA-191-5p, as well as positive correlations between visual acuity and miRNA-126-3p, -126-5p, and -155-5p PBNCs expression were found in AMD patients. No such correlations were found in the control group. Our results may suggest the role of both intra- and extracellular mechanisms implicated in inflammatory response regulation in multifactorial AMD pathogenesis.