Lymphatic vessel cells and plant cells similarly shaped to enhance structural stability
The cells that make up the walls of lymphatic capillaries have a lobate, oak leaf shape that makes them resilient to mechanical stress. The same unique shape is also found in cells of the outmost layer of plants, serving a similar structural function. This is shown by researchers from IGP in a new article in the journal Nature.
Puzzle-like shape of mammalian lymphatic endothelial cells (Image: Hans Schoofs).
The lymphatic system consists of a network of lymph vessels that maintains the body’s fluid balance and supports immune defence. The smallest of these vessels, called lymphatic capillaries, have walls that are made up of a single layer of lymphatic endothelial cells that allow fluids, cells and large molecules enter from the surrounding tissues for transport to other parts of the body. The dilemma is that these vessels need to be highly permeable to take up fluid efficiently but also adaptable to sudden changes in tissue volume, such as swelling, without rupturing.
In the current study, the researchers have investigated how the thin layer of lymphatic endothelial cells can withstand changes in vessel calibre when it takes up fluid. This turned out to be due to the cells’ capacity to continuously change their peculiar shape.
“It has been known for a long time that capillary lymphatic endothelial cells have a lobate shape, like oak leaves or jigsaw puzzle pieces. However, the reason for this unique morphology is not known, and it has never been successfully replicated in cultured cells. In our study, we found that when we exposed a layer of cultured lymphatic endothelial cells to intermittent multidirectional stretching, they started to adopt features of this puzzle-like shape and increased overlaps between the cells,” says Taija Mäkinen, professor at IGP, who has led the study.
Similar to plant cells
Puzzle shapes can also be found in a completely different type of cells – on the surface of plants. There their role is to withstand fluid pressure, i.e. the turgor pressure required for plants to grow and increase the rigidity of the structure.
“The puzzle shape of the plant cells is controlled by a specific signalling pathway and a corresponding pathway is also present in lymphatic endothelial cells. When we tested to block this pathway in cultivated cells, the stretch-induced overlap between the cells was reduced. In mice that lacked one of the signalling molecules in the pathway, not only the shape of the lymphatic endothelial cells was altered but also the integrity and the function of the lymphatic capillaries was impaired. This indicates that in the lymphatic capillaries, this overlap is necessary for the vessel to be able to expand without rupturing when pressure increases,” says Taija Mäkinen.
The lobate shape shared between puzzle-shaped plant cells and mammalian lymphatic endothelial cells stands out as a distinctive feature among the diversity of cell shapes observed in nature. The researchers suggest that this is due to their specialised function to withstand changes in fluid volume, revealing a biological design principle across kingdoms that enhances structural stability in living systems.