Loss of Neuropilin 2 in Adult Lymphatic Endothelium Promotes Lymphedema

Abstract

The lymphatic system is essential in mediating tissue fluid balance. Lymphatic diseases including lymphedema occur as a result of dysfunctional lymphatic networks and are a significant public health issue with no known cure. Our long‐term goal is to understand the cellular and molecular processes that control lymphatic function in order to better treat lymphatic diseases. Some primary lymphedema patients have mutations in the neuropilin‐2 gene (NRP2). NRP2 is a transmembrane receptor found in lymphatic endothelial cells (LEC) that is unique in its ability to transmit both pro‐lymphangiogenic signals from VEGF‐C/D ligands as well as suppressive signals from Semaphorin‐3F (SEMA3F). Previously, we observed elevated tissue swelling in constitutive Nrp2‐deficient mice compared to wild‐type littermates following acute inflammatory reactions. However, it was unclear whether tissue swelling was due to increased vascular leakage (edema) or decreased lymphatic drainage (lymphedema) or both. We hypothesize that Nrp2 regulates lymphatic drainage function in adult tissues and that loss of Nrp2 in adult lymphatic vessels may aggravate lymphedema and swelling. In order to more carefully dissect the molecular signaling events in adult LEC that may contribute to lymphedema, we created inducible, LEC‐specific Nrp2 knockout mice (prox1‐creERT2;Nrp2f/f) and examined lymphangiogenesis and lymphedema models after tamoxifen treatment in adult mice. Compared to appropriate littermate controls, mice lacking Nrp2 in LEC are poorly lymphangiogenic in VEGFC‐induced corneal lymphangiogenesis models and display massive swelling due to increased interstitial fluid and reduced lymphatic drainage in acute and chronic delayed‐type hypersensitivity models and secondary lymphedema models in vivo. Further, culture of primary dermal mouse LEC (mLEC) isolated from Prox1‐iNrp2‐KO mice following tamoxifen treatment reveal suppressed VEGFR3 activation compared to mLEC isolated from control mice. Taken together, our new data indicate that Nrp2 is a critical mediator of homeostatic lymphatic function and overall fluid balance in adult tissues. Our data suggests that the Nrp2 axis may be a pivotal pathway to stimulate lymphangiogenesis and lymphatic drainage in lymphedema conditions resulting from a paucity of lymphatic vessels.Support or Funding InformationR01 HL141858, R01 HL133216, R01 HL137229