Macrophages engulf endothelial cell membrane particles preceding pupillary membrane capillary regression

Area of Science:

• Developmental Biology
• Vascular Biology
• Cellular Mechanisms

Background:

• Programmed capillary regression and remodeling are crucial developmental processes.
• The precise cellular and molecular mechanisms governing vessel regression remain incompletely understood.
• The transient mouse pupillary membrane (PM) vasculature provides a model to study these events.

Purpose of the Study:

• To investigate the cellular and molecular mechanisms regulating the regression of the embryonic mouse pupillary membrane (PM) vasculature.
• To elucidate the role of endothelial cells (ECs) and macrophages in PM vessel elimination.
• To determine the signaling pathways involved in PM regression.

Main Methods:

• In vivo dynamic confocal imaging of mouse transgenic reporters.
• Static confocal and electron microscopy.
• Genetic ablation of macrophages.
• Wnt/β-catenin signaling assessment using Tcf/Lef-H2B::GFP reporter mice.

Main Results:

• Macrophages actively interact with PM endothelial cells (ECs), engulfing released EC membrane particles.
• Engulfment of EC membrane particles by macrophages does not correlate with EC apoptosis.
• Wnt/β-catenin signaling is unlikely to be involved in PM EC regression, unlike in hyaloid vasculature.
• EC membrane particle shedding occurs independently of macrophage presence, suggesting macrophages are scavengers, not inducers.

Conclusions:

• Resident macrophages play a role in programmed capillary regression by scavenging EC microparticles from PM vessels.
• This scavenging occurs embryonically, preceding postnatal vessel regression, and suggests an early disruption in vessel homeostasis.
• The findings reveal a novel mechanism in programmed vascular regression, highlighting macrophage-EC interactions.