A bioengineered lymphatic vessel model for studying lymphatic barrier function

Lymphatic vessels play a role in maintaining fluid homeostasis by draining interstitial fluid. A failure in lymphatic drainage triggers interstitial fluid accumulation causing lymphedema, a major lymphatic disease. Since lymphatic drainage is influenced by lymphatic barrier function, bioengineered models that can assess lymphatic barrier function would be instrumental. We built a lymphatic vessel (LV) on‐chip by fabricating a microfluidic device that includes a hollow microchannel embedded in hydrogel. Employing luminal flow in the microchannel, lymphatic endothelial cells (LECs) seeded in the microchannel formed an engineered LV exhibiting conduit structure. In the device, LECs formed permeable junctions in collagen hydrogel. However, adding fibronectin to the collagen tightened LEC junctions. We tested lymphatic barrier function by introducing dextran into lymphatic lumens. LECs in collagen showed permeable barriers. LECs in fibronectin/collagen showed enhanced barrier, which was reversed by integrin a5 inhibition. We knocked out lymphatic endothelial markers (LYVE‐1 and podoplanin) and tested their roles in barrier function. We learned podoplanin deficiency tightened LEC junctions, whereas LYVE‐1 did not show any effect on LEC junctions. Mechanistically, LECs expressed integrin alpha 5 that is inactivated in collagen. However, integrin alpha 5 can be activated either in fibronectin or in podoplanin deficiency, enhancing lymphatic barrier function. In conclusion, our LV‐on‐chip provides a platform for studying lymphatic barrier function, and reveals integrin alpha 5 as a regulator of lymphatic barrier function.