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Researchers from Uppsala University have discovered that the cells forming the walls of the smallest lymphatic vessels, known for their unique lobate, oak leaf-like structure, offer remarkable resistance to variations in fluid volume. This finding, published in the journal Nature, highlights a fascinating similarity between these lymphatic cells and the mechanical stability found in plant structures.
The lymphatic system plays a crucial role in maintaining the body’s fluid equilibrium and supporting immune functions. The most delicate segments of this system are the lymph capillaries, characterized by walls composed of a single layer of lymphatic endothelial cells. These cells are selectively permeable, allowing fluids, cells, and large molecules from surrounding tissues to pass through for transport to various body parts. The design of these vessels must facilitate efficient fluid flow while simultaneously being resistant to fluctuations in surrounding tissue volume, especially during instances of swelling, without risking rupture.
Resilient cells adopt a unique form
The investigation focused on how the lymphatic endothelial cells can endure alterations in the vessel diameter as they absorb fluid. The study revealed that these cells possess the ability to continuously modify their distinctive shape to accommodate such changes.
“For years, it was acknowledged that capillary lymphatic endothelial cells exhibit a lobate morphology similar to oak leaves or jigsaw pieces. However, the underlying reason for this shape was largely unexplored, with prior attempts to replicate it in cultured cells unsuccessful. Our research involved exposing a thin film of cultured lymphatic endothelial cells to repeated multidirectional stretching, which resulted in the cells adopting a lobate appearance and increased overlapping with their adjacent cells,” remarked Taija Makinen, a professor leading the study at Uppsala University.
Connecting plants and lymphatic cells
This lobate shape is not exclusive to lymphatic cells; it is also observed in plants, specifically on the surfaces of their leaves, where it serves to manage turgor pressure—the fluid pressure necessary for plants to grow upright.
“The lobate formation in plant cells is regulated by a specific signaling pathway, and a similar pathway exists in lymphatic endothelial cells. When we blocked this signaling pathway in cultured cells, the overlap induced by stretching diminished,” Professor Mäkinen explained. She added, “In mice deficient in one of these signaling molecules, we noted not just alterations in the shape of lymphatic endothelial cells but also compromised integrity and functionality of their lymphatic capillaries. This suggests that such cell overlap is essential for vessels to expand without breaking under increased fluid pressure,” she stated.
The lobate shape of both plant and mammalian lymphatic endothelial cells emerges as a remarkable characteristic amid the vast array of cell shapes identified in nature. The researchers propose that this morphological trait is a result of the specialized functions these cells serve, particularly their ability to adapt to fluid volume changes. This underscores a fundamental biological design principle shared across diverse species, aimed at enhancing structural stability.
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