Lymphangiocrine signals are required for proper intestinal repair after cytotoxic injury.

The intestinal tract contains the second largest epithelium in the body and serves essential functions, including nutrient absorption, protection against environment insults from viruses, bacteria and parasites, as well as the secretion of various hormones. Consequently, intestinal epithelial dysfunction leads to diseases of enormous morbidity, such as inflammatory bowel disease and ulcerative colitis. Cancer patients receiving radiation and chemotherapy are also at risk of developing enteritis. Diseases of the small and large intestine affect millions of people across the world and are on the rise, with many therapies being supportive in nature. Thus, studying how epithelial cells in the intestine maintain their function and become dysregulated in disease is of major importance for human health. The intestinal mucosa is organized into millions of units consisting of invaginations known as crypts and finger-like protrusions called villi. The villi are comprised of differentiated epithelial cells that take up nutrients and serve as a barrier to the environment. Presumably, in order to function in the presence of environmental stress, the epithelial cells rapidly turn over every 3-5 days. This demand for continuous replacement of the intestinal epithelium is fulfilled through production of cells at the base of the crypts, where intestinal stem cells reside. Intestinal stem cells are highly proliferative and compete for niche position at the bottom of the crypt to retain their stemness, while differentiating into all the epithelial lineages as they move up the villus. Maintenance of intestinal stem cell self-renewal potential depends in part on the modulation of Wnt signaling through Wnt ligands and R-spondins. While ISCs have been extensively studied, much less is known about the niche that controls their self-renewal and differentiation. Blood and lymphatic vessels are primarily known for carrying blood and lymph. However, their role extends beyond “plumbing”, and in the last decade several groups have shown that factors secreted by endothelial cells, which line blood and lymphatic vessels, also function in tissue regeneration. The role of endothelial cells as part of the intestinal niche and their potential role in intestinal regeneration has not been studied yet. In our work, we determine that lymphatic endothelial cells are part of the intestinal niche and reside in proximity to intestinal stem cells in the crypt. Additionally, by utilizing single cell RNA-sequencing we show that lymphatic endothelial cells secrete molecules such as R-spondin3 that support intestinal stem cell renewal and repair. We establish that lymphatic endothelial cells are an essential source of Wnt signaling in the small intestine, as loss of lymphatic derived R-spondin3 leads to a lower number of intestinal stem and progenitor cells and hinders mucus secretion and recovery after injury from chemotherapy drugs. Together, our findings identify lymphatic endothelial cells as an essential niche component for optimal intestinal recovery after injury.