Laminar flow downregulates Notch activity to promote lymphatic sprouting

Area of Science:

• Vascular Biology
• Mechanobiology
• Molecular Biology

Background:

• The lymphatic system drains interstitial fluid, and its expansion is triggered by increased fluid flow.
• Lymphatic sprouting, essential for fluid drainage, shares similarities with angiogenesis.
• Understanding the molecular mechanisms of lymphatic sprouting is crucial for related diseases.

Purpose of the Study:

• To identify the mechanotransduction pathway linking laminar flow-induced shear stress to lymphatic sprouting.
• To elucidate the molecular players involved in regulating lymphatic endothelial cell (LEC) responses to shear stress.

Main Methods:

• Investigated the role of ORAI1, KLF2, PROX1, DTX1, and DTX3L in lymphatic sprouting.
• Utilized endothelial-specific knockouts (KO) of Orai1 and Klf2.
• Examined the effects of Dtx3l loss and gain of function on lymphatic sprouting.
• Assessed Notch activity and calcium signaling in LECs under laminar flow.

Main Results:

• Laminar flow activates a pathway in LECs involving ORAI1-mediated calcium influx and calmodulin activation.
• This leads to a PROX1/KLF2 complex that upregulates DTX1 and DTX3L, downregulating NOTCH1 activity.
• Endothelial-specific Orai1 and Klf2 KOs impaired lymphatic sprouting.
• Dtx3l loss of function caused defective sprouting, while its gain of function rescued Orai1 KO phenotypes.

Conclusions:

• A novel mechanotransduction pathway translates laminar flow-induced shear stress into lymphatic sprouting.
• The pathway involves ORAI1, KLF2, PROX1, and the DTX1/DTX3L E3 ligase complex, which collectively downregulate Notch signaling.
• This molecular mechanism is critical for regulating lymphatic development and fluid homeostasis.