Changes in vascular permeability occur during inflammation and the actin cytoskeleton plays a crucial role in regulating endothelial cell contacts and permeability. We demonstrated recently that the actin-binding protein cortactin regulates vascular permeability via Rap1. However, it is unknown if the actin cytoskeleton contributes to increased vascular permeability without cortactin. As we consistently observed more actin fibres in cortactin-depleted endothelial cells, we hypothesised that cortactin depletion results in increased stress fibre contractility and endothelial barrier destabilisation. Analysing the contractile machinery, we found increased ROCK1 protein levels in cortactin-depleted endothelium. Concomitantly, myosin light chain phosphorylation was increased while cofilin, mDia and ERM were unaffected. Secretion of the barrier-stabilising hormone adrenomedullin, which activates Rap1 and counteracts actomyosin contractility, was reduced in plasma from cortactin-deficient mice and in supernatants of cortactin-depleted endothelium. Importantly, adrenomedullin administration and ROCK1 inhibition reduced actomyosin contractility and rescued the effect on permeability provoked by cortactin deficiency in vitro and in vivo. Our data suggest a new role for cortactin in controlling actomyosin contractility with consequences for endothelial barrier integrity.

Inflammatory bowel diseases (IBD) such as ulcerative colitis (UC) and Crohn's disease (CD) are multifactorial, relapsing disorders of the gastrointestinal tract. However, the etiology is still poorly understood but involves altered immune responses, epithelial dysfunction, environmental factors, and nutrition. Recently, we have shown that the diet supplement corabion has cardioprotective effects due to reduction of oxidative stress and inflammation. Since oxidative stress and inflammation are also prominent risk factors in IBD, we speculated that corabion also has beneficial effects on experimental colitis. Colitis was induced in male mice by administration of 3.5% (w/v) dextran sulfate sodium (DSS) in drinking water for a period of 3 or 7 days with or without daily gavage feeding of corabion consisting of vitamin C, vitamin E, L-arginine, and eicosapentaenoic and docosahexaenoic acid. We found that corabion administration attenuated DSS-induced colon shortening, tissue damage, and disease activity index during the onset of colitis. Mechanistically, these effects could be explained by reduced neutrophil recruitment, oxidative stress, production of proinflammatory cytokines, and internalization of the junctional proteins ZO-1 and E-cadherin leading to less edema formation. Thus, corabion may be a useful diet supplement for the management of chronic inflammatory intestinal disorders such as IBD.

Inflammatory processes lead to changes in vascular permeability via the opening and closure of cell‐cell contacts. The actin cytoskeleton plays a crucial role in the regulation of endothelial cell contacts and thus permeability. Several molecules regulate actin cytoskeleton dynamics, one of these being cortactin, an actin nucleator protein capable of directly bind to Arp2/3 complex, filamentous‐(F)‐actin and additionally, to molecules involved in the regulation of actin dynamics such as myosin light chain kinase (MLKC) and ezrin, but also, proteins from cell contacts such as ZO‐1. These capabilities render cortactin as a potential regulator of endothelial cell actin dynamics and thus cell‐cell contacts. We already showed that cortactin regulates vascular permeability in vivo via Rap1, part of this regulation depends on Rap1 ability to regulate the actin cytoskeleton by blocking RhoA activity, a very well‐studied enhancer of vascular permeability. However, the exact mechanism that contributes to increased permeability without cortactin is not known. In a mass spectrometric analysis, we found that ROCK1 is induced ~3‐fold in cortactin‐KO endothelium. This was confirmed by Western blot and immunofluorescence of tissues from cortactin‐KO mice and human HMEC‐1 cells stably depleted for cortactin. Concomitantly, we observed increased phosphorylation of myosin light chain (MLC) and more stress fibres without cortactin. Other molecules involved in stress fibres formation and stabilization such as mDia1, MLCK and ezrin, were not affected by cortactin absence. Secretion of the endogenous hormone adrenomedullin (ADM), that is known to activate Rap1 and counteract formation of stress fibres, is reduced in cortactin‐KO mouse serum and supernatant of cortactin‐depleted HMEC‐1 cells. Importantly, adrenomedullin administration or ROCK1 inhibition reduced actomyosin contractility and rescued the effect on permeability provoked by cortactin deficiency in vitro and in vivo. Our data suggest a new role for cortactin in controlling ctomyosin contractility with consequences for endothelial barrier integrity.Support or Funding InformationCONACyT grants 179895 and 233395 to MS and an international, bilateral grant of CONACyT and the German Ministry for Education and Research (BMBF); 207268/01DN14039 to MS and AZ)