# Fas Ligand enhances vessel maturation and inhibits vascular leakage associated with age-related macular degeneration

## TL;DR

This study shows that Fas Ligand helps reduce vascular leakage in age-related macular degeneration by promoting vessel maturation and interacting with immune cells.

## Contribution

The study reveals that FasL's anti-angiogenic effects depend on cleavage and Fas+ myeloid cell engagement in AMD.

## Key findings

- Heterozygous FasLΔCS/WT mice showed reduced vascular leakage and faster neovessel maturation.
- FasL-mediated CNV inhibition requires FasL cleavage and Fas+ myeloid cell interaction.
- Accelerated vessel maturation prevents vascular leakage in AMD.

## Abstract

Neovascular age-related macular degeneration (AMD), results from choroidal neovascularization (CNV), retinal edema and loss of photoreceptors. Previous studies suggested that Fas Ligand (FasL) on retinal pigment epithelial cells inhibited CNV by inducing apoptosis of infiltrating Fas+ vascular endothelial cells. However, induction of apoptosis depends on membrane-bound (mFasL) while the FasL cleavage product (sFasL) is neuroprotective. To better understand how FasL regulates the development of CNV, we used a mouse model of laser CNV to evaluate the development of CNV in mice with a FasL cleavage site mutation (ΔCS) and can only express the membrane-bound form of FasL. There was no significant difference in CNV size and area of vascular leakage in homozygous FasLΔCS/ΔCS mice when compared to wild type mice. Unexpectedly, heterozygous FasLΔCS/WT mice developed significantly less vascular leakage and showed accelerated neovessel maturation. However, CNV was not prevented in heterozygous FasLΔCS/WT mice if the Fas receptor was deleted in myeloid cells (FasLΔCS/+ Fasflox/flox CreLysM). Thus, FasL-mediated CNV inhibition depends on the extent of FasL cleavage, and on FasL engagement of Fas+ myeloid cells. Moreover, accelerated neovessel maturation prevents vascular leakage in AMD.