Porcine iris pigment epithelial cells can take up retinal outer segments

Area of Science:

• Ophthalmology
• Cell Biology
• Biochemistry

Background:

• Retinal pigment epithelial (RPE) cells are crucial for photoreceptor health through phagocytosis.
• The phagocytic capabilities of iris epithelial cells (IPE) are less understood.
• Investigating IPE phagocytosis offers insights into ocular tissue maintenance and potential therapeutic strategies.

Purpose of the Study:

• To quantify and compare the phagocytic ability of iris epithelial cells (IPE) versus RPE cells.
• To determine if IPE cells can ingest rod outer segments (ROS).
• To characterize the cellular mechanisms involved in phagocytosis by IPE and RPE cells.

Main Methods:

• Utilized a pH-sensitive fluorescent dye (carboxy SNAFL) for light microscopy to measure ROS ingestion by IPE and RPE cells.
• Employed ferritin-labeled ROS and electron microscopy to count phagosomes in cultured cells.
• Performed immunocytochemical staining to identify cell types and ultrastructure, including phagosome analysis via EELS spectra.

Main Results:

• Both IPE and RPE cells demonstrated positive staining for NaK-ATPase and cytokeratin, confirming their epithelial nature.
• Ultrastructural analysis revealed numerous small phagosomes (<1 micron) in both cell types.
• Quantitative microscopy showed cultured IPE cells possess 64% of the phagocytic capacity of RPE cells for phagosomes >1 micron.

Conclusions:

• Iris epithelial cells (IPE) exhibit notable phagocytic capabilities, comparable to RPE cells.
• IPE cells actively ingest rod outer segments (ROS), contributing to ocular tissue homeostasis.
• This study highlights a previously underappreciated phagocytic role for IPE in the eye.