Complement expression in retinal pigment epithelial cells is modulated by activated macrophages

Area of Science:

• Ophthalmology
• Immunology
• Cell Biology

Background:

• Complement activation is implicated in various retinal diseases.
• Retinal pigment epithelial (RPE) cells are key producers of complement components in the eye.
• Macrophages accumulate near RPE cells under inflammatory conditions.

Purpose of the Study:

• To investigate the impact of activated macrophages on complement gene expression in RPE cells.
• To determine how different macrophage activation states influence RPE complement production.
• To elucidate the role of macrophage-RPE interactions in retinal complement dysregulation.

Main Methods:

• Primary mouse RPE cells were treated with supernatants from various activated bone marrow-derived macrophages (BM-DMs): un-activated (M0), classically activated (M1), and alternatively activated (M2a, M2b, M2c).
• Gene expression of inflammatory cytokines and complement components/regulators in RPE cells was quantified using real-time RT-PCR.
• Protein levels of complement factors CFB, C3, C1INH, and C1r were assessed via Western blot.

Main Results:

• Unstimulated RPE cells express complement regulators more than components.
• Macrophage supernatants upregulated inflammatory cytokines, chemokines, and complement genes in RPE cells.
• M1 and M2b macrophage supernatants markedly increased RPE expression of CFB and C3 (10-30 fold), while M0, M2a, and M2c had milder effects (2-3.5 fold).
• M1 and M2b supernatants also enhanced CFB protein (Bb fragment) and C3 secretion by RPE cells, potentially via the STAT1 pathway.

Conclusions:

• Activated macrophages, particularly M1 and M2b, significantly induce complement component (CFB, C3) expression in RPE cells.
• This macrophage-induced RPE complement production may promote the alternative pathway of complement activation in the retina.
• These findings highlight a critical interaction between macrophages and RPE cells in driving retinal inflammation and disease.