Endothelial Cell SMAD6 Balances ACVRL1/Alk1 Function to Regulate Adherens Junctions and Hepatic Vascular Development

Area of Science:

• Vascular Biology
• Cell Signaling
• Developmental Biology

Background:

• Bone morphogenetic protein (BMP) signaling is essential for blood vessel formation and function.
• The precise roles of pathway components in regulating vascular development are not fully understood.

Approach:

• Investigated the function of inhibitory SMAD6 in endothelial cells.
• Utilized genetic manipulation (gene dosage reduction) and cellular assays to examine endothelial cell behavior.
• Explored mechanistic aspects including actomyosin contractility and PI3K signaling.

Key Points:

• SMAD6 negatively regulates ALK1/ACVRL1-mediated responses in endothelial cells.
• SMAD6 is required to prevent dysmorphogenesis and hemorrhage in embryonic liver vasculature.
• Co-depletion of SMAD6 and ALK1 rescued endothelial junction defects and impaired barrier function.
• SMAD6 loss leads to increased ALK1 signaling, disrupting endothelial junctions via PI3K and contractility pathways.

Conclusions:

• SMAD6 modulates ALK1 function to control PI3K signaling and contractility in endothelial cells.
• Balanced ALK1 signaling, regulated by SMAD6, is critical for proper vascular development.
• ALK1 acts as a "Goldilocks" pathway in vascular biology.