A stem cell-driven lymphoangiogenic switch

Tissues rely on stem cells (SCs) for homeostasis and wound-repair. SCs reside in specialized microenvironments (niches) whose complexities and roles in orchestrating tissue growth are still unfolding. Here, we identify lymphatic capillaries as critical SC niche components. In skin, lymphatics form intimate networks around the SCs of each hair follicle (HF) during their non-regenerative phase, and remodel upon regeneration. Seeking understanding, we unravel a secretome switch within SCs that controls lymphatic behavior. Resting SCs express Angiopoietin-like 7 (Angptl7), promoting lymphatic drainage. Upon activation, SCs trigger an anti-lympho-angiogenic program, transiently sparking lymphatic dilation and dampened drainage. In mammals, this dynamic aria between SCs and lymphatics is essential for coordinating HFSC behavior and hair regeneration: Upon either depleting lymphatics, silencing Angptl7 or super-activating anti-lympho-angiogenesis, SCs precociously proliferate and HF regeneration becomes asynchronous. In unearthing lymphatic capillaries as a hitherto under-appreciated SC-niche element, we’ve learned how SCs coordinate their activity across a tissue.