Unveiling heterogeneity of intestinal stromal cells and organotypic lymphatic endothelial cells

Abstract

Throughout the body, blood and lymphatic vessels are developed to facilitate delivery of oxygen and nutrients, as well as the removal of cellular waste products, crucial for producing specialized biological functions. Disruption in this system leads to onset of various diseases. Blood vessels and lymphatic vessels develop specialized morphologies and functions tailored to unique demands and environments of tissues or organs where they are located. These specializations of the vascular system are called as organotypic vasculatures. Recent advances in single-cell RNA sequencing led to more detailed classification of cell types based on the gene expression profiles. This enabled comparison not only of the differences within tissues but also across different tissues, advancing understanding of cells composing the body. This dissertation consists mainly of two parts, Part I describes identification of heterogeneity of small intestinal stromal cells. Mainly 7 distinct stromal cell types compose the intestinal stroma, and among them, 3 newly identified fibroblast subsets (FB1-3) localize adjacent to the lacteals. In response to mechanical stimulus, YAP/TAZ signaling pathway is activated in FB1-3, resulting in secretion of lymphatic endothelial cell (LEC) growth factor, VEGF-C to regulate proliferation of lacteals. This work proposes a new type of cellular interactions between fibroblasts and LECs called fibrocrine. Part II reveals organotypic features and heterogeneity of LECs in three primary drainage sites, skin, gut, and dura, and their corresponding draining lymph nodes. Comparative analysis showed conserved genetic characteristics of capillary lymphatics regardless of the drainage sites, which could be crucial for the initial draining functions in the lymphatic system. In addition, tissue-specific expression patterns were revealed, demonstrating organotypic characteristics of the lymphatic system. This work provides key insights into unique biological functions of organotypic LECs.