FOXO1 stimulates tip cell-enriched gene expression in endothelial cells

Area of Science:

• Molecular Biology
• Cell Biology
• Developmental Biology

Background:

• Forkhead box O (FOXO) proteins are critical regulators of cellular functions, including metabolism, apoptosis, and aging.
• FOXO1 is essential for embryonic development, with FOXO1-null mice showing lethality due to defects in endothelial cell (EC) maturation and vascular remodeling.
• The precise genome-wide regulatory mechanisms of FOXO1 in ECs, particularly in vascular development, remain incompletely understood.

Purpose of the Study:

• To elucidate the genome-wide regulatory role of FOXO1 in endothelial cells (ECs) during vascular development.
• To investigate the dynamic regulation of FOXO1 by Vascular Endothelial Growth Factor (VEGF) and its downstream effects on EC function.
• To identify specific genes and regulatory regions controlled by FOXO1 in the context of VEGF-mediated tip cell specification.

Main Methods:

• Utilized RNA sequencing (RNA-seq) in conjunction with FOXO1 overexpression and knockdown in primary cultured ECs.
• Performed chromatin immunoprecipitation sequencing (ChIP-seq) to map endogenous FOXO1 binding sites genome-wide.
• Investigated FOXO1 translocation dynamics in response to VEGF stimulation and identified regulatory pathways involving PP2A phosphatase.

Main Results:

• Demonstrated that VEGF dynamically regulates the translocation of FOXO1 between the cytosol and nucleus in ECs, mediated by PP2A phosphatase.
• Identified FOXO1 as a key regulator of VEGF-responsive, tip cell-enriched genes and a negative regulator of DLL4-NOTCH signaling.
• FOXO1 ChIP-seq revealed direct binding to EC-unique tip-enriched genes, co-localizing with EC master regulators in condensed chromatin regions, acting as a pioneer factor. Identified ESM1 and ANGPT2 as novel FOXO1-regulated targets.

Conclusions:

• This study provides the first cell type-specific functional characterization of FOXO1 in primary ECs.
• FOXO1 plays a critical role in defining VEGF-mediated tip cell identity by regulating specific gene expression programs.
• FOXO1 acts as a pioneer factor, binding to accessible chromatin regions to govern the expression of key genes involved in vascular tip cell formation.