Incongruence between transcriptional and vascular pathophysiological cell states

Area of Science:

• Endothelial biology
• Molecular signaling
• Vascular homeostasis

Background:

• The Notch pathway is crucial for endothelial transcriptional specification.
• Targeting Notch receptors or Delta-like ligand 4 (Dll4) disrupts angiogenesis.
• Understanding ligand-receptor dynamics is key to vascular health.

Purpose of the Study:

• To investigate the distinct roles of Notch ligands and receptors in liver vascular homeostasis.
• To elucidate the molecular mechanisms underlying Dll4-mediated endothelial proliferation and tip-cell states.
• To differentiate vascular phenotypes from neoplasms in relation to anti-Dll4 antibody toxicity.

Main Methods:

• Analysis of single and compound genetic mutants for all Notch signaling members.
• Gene expression profiling to identify transcriptional switches (e.g., Myc).
• Pharmacological inhibition of pro-angiogenic pathways (MAPK/ERK, mTOR, VEGFA).

Main Results:

• Notch receptor loss induced endothelial hypermitogenic cell-cycle arrest and senescence.
• Dll4 loss triggered a Myc-driven switch promoting endothelial proliferation and tip-cell state.
• Myc loss partially rescued Dll4 loss-induced angiogenesis but not vascular enlargement; anti-VEGFA treatment prevented vascular expansion but not all transcriptional programs.

Conclusions:

• Ligands and receptors differentially regulate liver vascular homeostasis, with distinct impacts on endothelial cell fate.
• Vascular structure abnormalities, not neoplasms, likely cause anti-Dll4 antibody toxicity.
• Incongruence exists between single-cell transcriptional states, vascular phenotypes, and pathophysiology.