Assessing the role of cellular complement and immune system dysregulation in the pathogenesis of age-related macular degeneration
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Philipps-Universität Marburg
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Abstract
Age-related macular degeneration (AMD) is a leading cause of vision loss in the elderly, characterised by progressive damage to the macula, retinal degeneration, and central vision impairment. The complex pathomechanisms underlying the late form of non-exudative AMD, characterised by geographic atrophy, have hindered the development of effective treatments, despite the urgent clinical need. In recent years, research has focused on identifying biomarkers in the aqueous humour (AH) of the eye’s anterior chamber to elucidate immune system dysregulation in disease pathogenesis. Additionally on a cellular level, hyperreflective foci (HRF) have been investigated as indicators of AMD progression, with studies identifying retinal pigment epithelial (RPE) cells that lose their specificity and contribute to disease pathology. Beyond cellular stress responses, dysregulation of the complement system is a hallmark of AMD. The recent approval of complement inhibitors by the U. S. Food and Drug Administration represents a significant therapeutic advance. However, these treatments slow disease progression without fully preventing geographic atrophy.
To investigate cellular complement profiles, C3 processing, and TGF-β1-mediated stress responses, a model of immature and mature RPE cells was established, representing HRF-associated and healthy RPE cells, respectively. Mature induced pluripotent stem cell (iPSC) derived RPE cells exhibited key characteristics of healthy RPE, including the absence of VIM staining and actin stress fibres, the presence of basal BEST1, apical actin and tight junctions, and enhanced barrier function. Complement production followed a maturation-dependent pattern, with mature RPE cells displaying increased apical and basal secretion of complement components (C3, FB, FH/FHL-1, FI) and a distinct apical localisation of complement proteins. Intracellular C3 processing revealed cleavage products distinct from known C3 fragments, with only mature iPSC-RPE cells secreting active C3 forms (C3(H2O), C3a) and exhibiting intact C3 α/β chains. In contrast, immature RPE cells exhibited a stressed phenotype, characterised by reduced secretion of inactive C3 and C3 fragments and their intracellular accumulation. While iPSC-RPE cells demonstrated greater resistance to TGF-β1-induced stress compared to ARPE-19 cells, complement secretion was altered in both cell types, whereas C3a release and intracellular C3 cleavage remained unaffected.
In addition to in vitro analyses, this thesis aimed to translate experimental findings into a clinical context by examining complement components and inflammatory mediators in AMD patients. A case-control study was conducted to collect AH samples from patients with non-exudative AMD and control subjects. A comprehensive multiplex analysis quantified 78 inflammatory mediators and complement components in AH, allowing for a comparative assessment between patient and control groups. Additionally, potential associations between biomarker levels and demographic factors such as age, smoking status, and sex were examined. All investigated immunological factors were detected in AH and categorised into high-, medium-, and low-concentration groups. AH contained high levels of complement proteins, including iC3b, FH/FHL-1, C4B, and FI. Reduced levels of C4, IL-10, and FI were observed in non-exudative AMD patients compared to controls, while drusen volume in AMD patients correlated positively with CCL4 and IL-16 levels. Demographic factors influenced biomarker levels, with age positively correlating with MMP-1 and negatively with CCL20. Smokers exhibited altered levels of inflammatory proteins (CCL7, IL-7, IL-6, IL-9, FGF-2, NGF-β), while sex differences were observed in FB, C4B, FI, FH/FHL-1, TNF-α, and MMP-1 levels.
This study demonstrates that both healthy and stressed RPE cells produce complement components, activate C3 intracellularly, and secrete active C3 forms at both apical and basal sides. The cellular presence of activated C3 forms suggests that their biological activity may persist despite complement inhibition therapies. Furthermore, basal secretion of C3 fragments may evade the effects of intravitreal treatments, which primarily target apical C3. The incomplete inhibition of C3 activation products may contribute to the limited efficacy of current therapies. Additionally, dysregulation of the complement and immune system was also evident in patient-derived AH samples, as analyses in this study identified associations between inflammatory mediators, complement imbalance, and non-exudative AMD, further underscoring the involvement of immune processes in disease pathogenesis and progression.
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Created: 2025Issued: 2025-08-11Updated: 2025-08-11
Faculty
Medizin
Publisher
Philipps-Universität Marburg
Language
eng
Data types
DoctoralThesis
Keywords
ophthalmologyImmunologyOphthalmologieImmunologie
DFG-subjects
altersabhängige MakuladegenerationImmunsystemRetinaKomplementsystem
DDC-Numbers
570
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Schikora, Juliane: Assessing the role of cellular complement and immune system dysregulation in the pathogenesis of age-related macular degeneration. : Philipps-Universität Marburg 2025-08-11. DOI: https://doi.org/10.17192/z2025.0413.
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This item has been published with the following license: In Copyright