Endothelial Rho kinase controls blood vessel integrity and angiogenesis.

The Rho kinases 1 and 2 (ROCK1/2) are serine-threonine specific protein kinases that control actin cytoskeleton dynamics. They are expressed in all cells throughout the body, including cardiomyocytes, smooth muscle cells and endothelial cells (ECs), and are intimately involved in cardiovascular health and disease. Pharmacological ROCK inhibition is beneficial in mouse models of hypertension, atherosclerosis, and neointimal thickening that display overactivated ROCK. However, the consequences of endothelial ROCK signalling deficiency in vivo remained unknown. To address this issue, we generated Cdh5CreERT2 driven, tamoxifen inducible loss of function alleles of ROCK1 and ROCK2 and analysed mouse survival and vascular defects through cellular, biochemical, and molecular biology approaches. We observed that postnatal or adult loss of endothelial ROCK1 and 2 was lethal within a week. Mice developed multi-organ haemorrhage along with loss of vascular integrity. ECs displayed deficient cytoskeletal actin polymerization that prevented focal adhesion formation and disrupted junctional integrity. Retinal sprouting angiogenesis was also perturbed, as sprouting vessels exhibited lack of polymerized actin and defective lumen formation. In a three-dimensional endothelial sprouting assay, combined knockdown of ROCK1/2 or individual knockdown of ROCK2 but not ROCK1 led to reduced sprouting, lumenization and cell polarization defects caused by defective actin and altered VE-cadherin dynamics. The isoform specific role of endothelial ROCK2 correlated with ROCK2 substrate specificity for FAK and LIMK. By analysing single and three allele mutants we show that one intact allele of ROCK2 is sufficient to maintain vascular integrity in vivo. Endothelial ROCK1 and 2 maintain junctional integrity and ensure proper angiogenesis and lumen formation. The presence of one allele of ROCK2 is sufficient to maintain vascular growth and integrity. These data indicate the need for careful consideration when using ROCK inhibitors in disease settings.