Changes in extracellular matrix cause RPE cells to make basal deposits and activate the alternative complement...

Area of Science:

• Ophthalmology
• Molecular Biology
• Immunology

Background:

• Age-related macular degeneration (AMD) pathogenesis is poorly understood, particularly the role of basal deposits.
• Basal deposits form between retinal pigment epithelium (RPE) and Bruch's membrane (BrM) and involve complement system activation.
• Efficient AMD therapies are limited by the lack of understanding of these early disease mechanisms.

Purpose of the Study:

• To investigate the roles of Bruch's membrane (BrM), retinal pigment epithelium (RPE), and complement in AMD pathogenesis.
• To model early AMD by generating abnormal extracellular matrix (ECM) and studying its interaction with complement.
• To identify potential therapeutic targets for early-stage AMD.

Main Methods:

• Generated abnormal ECM using CRISPR-edited ARPE-19 cells with the EFEMP1 p.R345W mutation.
• Introduced the EFEMP1 p.R345W mutation, known to cause early-onset macular degeneration.
• Co-cultured normal human fetal RPE (hfRPE) cells with abnormal ECM or AMD donor BrM explants.

Main Results:

• Abnormal ECM binds active complement C3, inducing basal deposit formation by normal hfRPE cells.
• hfRPE cells on abnormal ECM or AMD BrM explants showed chronic alternative complement pathway activation with C3b deposition.
• Impaired ECM turnover, due to increased matrix metalloproteinase-2 activity, exacerbated complement activation.

Conclusions:

• Local cleavage of C3 via convertase-independent mechanisms represents a potential therapeutic target for early AMD.
• Abnormal ECM plays a critical role in initiating basal deposit formation and complement activation in AMD.
• Understanding ECM-RPE-complement interactions is crucial for developing novel AMD therapies.