RASA1-driven cellular export of collagen IV is required for the development of lymphovenous and venous valves in mice

RASA1, a negative regulator of the Ras-mitogen-activated protein kinase (MAPK) signaling pathway, is essential for the development and maintenance of lymphatic vessel (LV) valves. However, whether RASA1 is required for the development and maintenance of lymphovenous valves (LVV) and venous valves (VV) is unknown. In this study we show that induced endothelial cell (EC)-specific disruption of Rasa1 in mid-gestation mouse embryos did not affect initial specification of LVV or central VV but did affect their continued development. Similarly, switch to expression of a catalytically inactive form of RASA1 resulted in impaired LVV and VV development. Blocked development of LVV in RASA1-deficient embryos was associated with accumulation of the basement membrane protein, collagen IV, in LVV-forming EC and could be partially or completely rescued by MAPK inhibitors and drugs that promote collagen IV folding. Disruption of Rasa1 in adult mice resulted in venous hypertension and impaired VV function that was associated with loss of EC from VV leaflets. In conclusion, RASA1 functions as a negative regulator of Ras signaling in EC that is necessary for EC export of collagen IV, thus permitting the development of LVV and the development and maintenance of VV.