Study on Macular Degeneration Reveals Inhibitory Effect of Natural Killer Cells on Disease Progression

Background

Age-related Macular Degeneration (AMD) is the leading cause of irreversible blindness among the elderly globally. With an aging population, the incidence of AMD is significantly increasing. Early features of AMD include the accumulation of insoluble lipids (drusen) under the retina, while late stages manifest as retinal pigment epithelium (RPE) and photoreceptor atrophy (dry AMD) and choroidal neovascularization (wet AMD). Wet AMD accounts for about 90% of vision loss cases.

Although anti-vascular endothelial growth factor (VEGF) therapy has been successful in treating wet AMD, many patients respond incompletely to this treatment, still experiencing persistent fluid leakage, bleeding, and fibrosis. This suggests that a deeper understanding of AMD’s pathological mechanisms could lead to new therapeutic strategies.

Inflammation plays a crucial role in AMD progression. In the early stages of AMD, drusen containing immunologically modified lipoproteins, complement proteins, and immunoglobulins accumulate in the subretinal space, triggering an imbalanced retinal immune response and attracting immune cells including retinal microglia and recruited macrophages. If phagocytes fail to adequately clear drusen, it will trigger an angiogenic response, promoting disease progression to late stages. In this process, immune cells regulate angiogenesis by synthesizing multiple pro-angiogenic factors and degrading enzymes.

While the contribution of myeloid cells (such as microglia, macrophages, and neutrophils) to AMD pathology has been studied, the role of lymphocytes remains unclear. Natural killer (NK) cells, as innate immune cells, control the initiation of inflammatory responses by producing interferon-γ (IFN-γ) and can eliminate target cells through cytotoxic activity. NK cells respond rapidly to inflammatory signals and are among the first cell types to arrive at target organs. However, the potential role and impact of NK cells in AMD have not been defined.

Research Overview

This article was published in Science Translational Medicine on August 14, 2024, by a research team including Xue Dong, Yinting Song, and others from multiple research institutions including Tianjin Medical University, Nankai University, Tulane University, and Queen’s University Belfast.

The study aimed to analyze the phenotype and function of natural killer cells in AMD lesions through samples and mouse models, and to investigate their contribution to AMD pathology. The research showed that NK cells inhibit choroidal angiogenesis and slow down AMD progression by inducing the formation of neutrophil extracellular traps (NETs).

Research Methods and Process

Research Subjects and Samples

This paper mainly analyzed sample data from patients and mouse models. Patient samples were used to determine the presence and role of NK cells in lesion tissues through single-cell RNA sequencing (scRNA-seq) and proteomics analysis. Mouse models employed classic AMD models such as laser-induced photocoagulation and vldlr−/− mice.

Analysis Methods

For mouse samples, the team conducted bulk RNA sequencing (RNA-seq), flow cytometry, and immunofluorescence staining, among other experiments. The study also employed innovative experimental methods, including NK cell knockout and specific receptor inhibition, to observe their effects on lesions.

Main Operational Procedures

1. Sample Collection: Collected eye tissues from AMD patients and control groups for RNA and protein level analysis.
2. NK Cell Analysis: Identified NK cell enrichment and molecular characteristics through flow cytometry and RNA-seq.
3. Functional Validation: Observed neutrophil activity and pathological changes in lesion tissues through NK cell knockout and specific receptor inhibition.
4. Cell Interaction Study: Used in vitro NK cell and neutrophil co-culture experiments to study the effect of NK cells on NETs formation.
5. Intrinsic Mechanism Analysis: Analyzed NK cell signaling and intercellular interactions in lesion tissues by combining multiple gene expression databases.

Research Results

1. Massive Enrichment of NK Cells in Lesion Tissues: The study found that NK cells were significantly enriched in the retina-choroid complex of CNV model mice and AMD patients.
2. Protective Role of NK Cells: Knocking out NK cells or inhibiting their activation receptors (such as NKG2D) led to decreased formation of neutrophil NETs, exacerbated vascular leakage, and worsened pathological angiogenesis.
3. Role of NETs: Neutrophils form NETs in AMD lesions, which help clear aging blood vessels, thereby preventing further development of lesions. When NETs formation is blocked, lesions worsen.
4. Inflammatory Signaling Pathway Analysis: NK cells mediate neutrophil NETosis through signals such as IFN-γ and IL-18. Additionally, CCR5 plays an important role in NK cell recruitment.
5. Age-related Changes: The cytotoxicity of NK cells decreases significantly with age. In older mice, less active NK cells failed to effectively inhibit lesions.

Conclusion

This study systematically demonstrates for the first time the protective role of NK cells in AMD, indicating that NK cells could serve as a potential therapeutic target for wet AMD patients. By inducing NETs formation, NK cells effectively prevent the excessive spread of pathological angiogenesis and inflammatory responses. The study also points out that the protective effect of NK cells significantly weakens with age, providing new insights into potential treatment strategies for the elderly population.

Research Highlights

1. Protective Role of NK Cells: Discovered that NK cells inhibit the progression of macular degeneration lesions through interaction with neutrophils.
2. Newly Discovered Intercellular Signaling Mechanism: Revealed the molecular mechanism of NK cells’ protective action dependent on IFN-γ and IL-18 signaling pathways.
3. Age Impact: Showed the effect of age on NK cell activity and protective effects, suggesting that elderly patients may need specific immune intervention strategies.

Research Significance

This study not only fills the gap in NK cell research in AMD pathology but also provides important references for future therapeutic strategies. Enhancing NK cell activity may become a new method for treating AMD, especially for patients who respond poorly to anti-VEGF therapy.

This research proves the key protective role of NK cells in wet AMD, offering new possibilities for immune therapy of the disease. This discovery helps develop new treatment strategies, improve the quality of life for the elderly population, and adds new perspectives and ideas to medical research.