Introduction Atherosclerosis is a chronic inflammatory disease marked by hardening and thickening of the arteries. The disease develops predominantly at arterial branches and bends. These atheroprone areas are subjected to disturbed blood flow, which generates low and oscillatory wall shear stress (LOSS), a frictional force exerted on endothelial cells (EC). LOSS increases EC inflammatory activation and drives endothelial-to-mesenchymal transition (EndoMT), which promotes atherosclerosis. The molecular basis of EC responses to shear stress is not fully elucidated.

Notch signaling is a major regulator of vascular development and homeostasis. It plays a critical role in communication between EC, initiated by the interaction of a receptor (i.e. Notch1 or 4) with a ligand (Dll4 or Jag1) present on a neighbouring cell. A recent study revealed that Notch1 is a mechanosensor protecting adult arteries from developing atherosclerosis (Mack et al., 2017, Nat Commun.;8(1):1620). However the role of other Notch actors in this disease is unknown. Here we investigated the role of the Notch ligand Jag1 in EC pathophysiology and atherosclerosis.

Methods To study the effect of shear stress on Notch actors, Human Coronary Aortic EC (HCAEC) were exposed to LOSS (4dynes/cm² ±1Hz) versus high shear stress (12dynes/cm²) using a parallel plate system (Ibidi). After 2 to 4 days of culture under flow, expression levels of transcripts and proteins were assessed by qRT-PCR and western blotting. The function of Jag1 in HCAEC exposed to LOSS was studied using neutralizing antibodies. The function of Jag1 in EC was studied in vivo by tamoxifen inducible conditional deletion in mice (CDH5Cre/Ert2; Jag1fl/fl). The EC phenotype was analysed by immunostaining, qRT-PCR and western blotting.

Results qRT-PCR and en face staining revealed that Jag1 is enriched at LOSS sites in both the pig (p<0.05) and mouse aorta (p<0.05). We concluded that LOSS is responsible for focal Jag1 expression at atheroprone areas because it induced Jag1 in HCAEC (p<0.05). We then investigated whether Jag1 influences EC dysfunction in response to LOSS. Blocking Jag1 activity reduced expression of inflammatory markers (e.g. VCAM-1, E-Selectin and MCP-1) as well as mesenchymal markers (e.g. Snail, N-Cadherin and SMA) in HCAEC exposed to LOSS. It also significantly increased proliferation. Thus LOSS activation of Jag1 drives EC activation and EndoMT and reduces proliferative potential. Co-staining of Jag1 with markers of inflammation and EndoMT revealed a strong colocalization in the mouse aorta. Jag1 was also detected in EC above atherosclerotic plaques. To investigate whether endothelial Jag1 plays a role in atherosclerosis, we carried out an inducible knockout of Jag1 in EC, which resulted in a decrease of plaque formation.

Conclusion Our data reveal a critical role for the Notch ligand Jag1 as a pro-atherogenic factor, controlling inflammation, EC fate and proliferation at atheroprone sites.

Conflict of interest none