Mechanoreceptor plexin D1 regulates lymphatic valve morphogenesis and lymphedema pathogenesis.

Lymphatic valves are essential for maintaining tissue fluid homeostasis, and their dysfunction leads to lymphedema, a morbid and disfiguring disease without a cure. Mechanical forces due to lymph flow are required for proper lymphatic valve development, yet it remains unclear how lymphatic endothelial cells (LECs) sense and decode mechanical signals. In this study, we identify the cell guidance semaphorin receptor plexin D1 (PLXND1) as a lymphatic mechanosensor required for lymphatic valve morphogenesis. Conditional genetic ablation of Plxnd1 in LECs caused major defects in lymphatic valve development in 2 different lymphatic vascular beds. Mechanistically, PLXND1 acted as a mechanosensor within a lymphatic mechanocomplex, initiating distinct mechanical signals and activating the lymphatic valve transcriptional program through an unconventional pathway. Screening of patients with primary lymphedema identified PLXND1 missense variants, and functional analysis established 2 pathogenic variants that selectively disrupt the ligand versus mechanosensing functions of this receptor. Variants associated with lymphedema in members of the mechanocomplex disrupted its formation, underscoring the central role of this complex in lymphatic valve biology. Our work uncovers a mechanosensing mechanism guiding lymphatic valve development, and has profound implications for the understanding and treatment of primary lymphedema in humans.