Certain cells have an unusual shape that is similar to an oak leaf or puzzle piece, and researchers have found that the form of these cells helps them withstand dramatic changes in volume. These cells can be found in all of the lymphatic vessels of humans, and similar cell shapes are also found in plants, where they also contribute mechanical resilience. These findings have been reported in Nature.
The lymphatic system is a network of vessels in the body that move lymph, or excess fluid from the body. The vessels also move a variety of molecules and cells that perform immune functions. The smaller lymph vessels are known as lymph capillaries and their walls are composed of a single cell layer.
The lymph capillaries are also permeable, allowing fluids and other stuff including cells to move around freely from tissues to these capillaries. That means that the vessels must withstand significant volume changes without tearing.
In this study, the researchers assessed how the cells that make up these vessels can handle swelling. They determined that the shape of these cells is crucial to that adaptability.
While scientists have long known about the lobate, puzzle-like shape of capillary lymphatic endothelial cells, the reason for the shape was unknown, noted senior study author Taija Mäkinen, a professor at Uppsala University.
The investigators grew lymphatic endothelial cells in a thin layer and repeatedly stretched them out. Then the cells took on their lobate shape, said Mäkinen. "There was also a greater overlap between the cells, which meant that each cell's contact surface with their neighboring cells increased."
The cells the make up the surfaces of plant leaves have a similar shape. And they endure pressures from changing fluid volumes in that environment as well.
"The lobate shape of the plant cells is controlled by a specific signaling pathway and a corresponding pathway is also present in lymphatic endothelial cells. When we tested blocking this signaling pathway in cultured cells, the stretch-induced overlap between the cells was reduced," said Mäkinen.
When one pathway molecule was removed from a mouse model, the lymphatic endothelial cells' shape was changed, and their function and integrity was disrupted. The lymphatic capillaries seem to need redundancy provided by that pathway so that the vessels can expand but not rip as pressure increases, noted Mäkinen.
Sources: Uppsala University, Nature
