SummaryThe endothelial barrier of the vasculature is of utmost importance for separating the blood stream from underlying tissues. This barrier is formed by tight and adherens junctions (TJ and AJ) that form intercellular endothelial contacts. TJ and AJ are integral membrane structures that are connected to the actin cytoskeleton via various adaptor molecules. Consequently, the actin cytoskeleton plays a crucial role in regulating the stability of endothelial cell contacts and vascular permeability. While a circumferential cortical actin ring stabilises junctions, the formation of contractile stress fibres, e. g. under inflammatory conditions, can contribute to junction destabilisation. However, the role of actin-binding proteins (ABP) in the control of vascular permeability has long been underestimated. Naturally, ABP regulate permeability via regulation of actin remodelling but some actin-binding molecules can also act independently of actin and control vascular permeability via various signalling mechanisms such as activation of small GTPases. Several studies have recently been published highlighting the importance of actin-binding molecules such as cortactin, ezrin/ radixin/moesin, Arp2/3, VASP or WASP for the control of vascular permeability by various mechanisms. These proteins have been described to regulate vascular permeability under various pathophysiological conditions and are thus of clinical relevance as targets for the development of treatment strategies for disorders that are characterised by vascular hyperpermeability such as sepsis. This review highlights recent advances in determining the role of ABP in the control of endothelial cell contacts and vascular permeability.

The intestinal epithelium forms a stable barrier protecting underlying tissues from pathogens in the gut lumen. This is achieved by specialized integral membrane structures such as tight and adherens junctions that connect neighboring cells and provide stabilizing links to the cytoskeleton. Junctions are constantly remodeled to respond to extracellular stimuli. Assembly and disassembly of junctions is regulated by interplay of actin remodeling, endocytotic recycling of junctional proteins, and various signaling pathways. Accumulating evidence implicate small G proteins of the Ras superfamily as important signaling molecules for the regulation of epithelial junctions. They function as molecular switches circling between an inactive GDP-bound and an active GTP-bound state. Once activated, they bind different effector molecules to control cellular processes required for correct junction assembly, maintenance and remodelling. Here, we review recent advances in understanding how GTPases of the Rho, Ras, Rab and Arf families contribute to intestinal epithelial homeostasis.

Autoantibodies against desmoglein (Dsg) 1 and Dsg3 primarily cause blister formation in the autoimmune disease pemphigus vulgaris (PV). Src was proposed to contribute to loss of keratinocyte cohesion. However, the role and underlying mechanisms are unclear. In keratinocytes, cell cohesion in response to autoantibodies was reduced in a Src‐dependent manner by two patient‐derived PV‐IgG fractions as well as by AK23, but not by a third PV‐IgG fraction, although Src was activated by all autoantibodies. Loss of cell cohesion was progredient and AK23 similar to PV‐IgG interfered with reconstitution of cell cohesion after Ca2+‐switch, indicating that the autoantibodies also interfered with desmosome assembly. Dsg3 co‐localized along cell contacts and interacted with the Src substrate cortactin. Concomitantly, cell adhesion was impaired in keratinocytes isolated from cortactin‐deficient mice in comparison to keratinocytes isolated from wildtype (wt). AK23‐induced loss of cell cohesion was Src‐dependent only when cortactin was expressed. Similarly, AK23 impaired reconstitution of desmosomal adhesion in Src‐dependent fashion only in the presence of cortactin and AK23‐induced skin blistering was abolished by Src inhibition in wt but not cortactin‐deficient mice. However, in human epidermis, PV‐IgG‐induced skin blistering and ultrastructural alterations of desmosomes were not affected by Src inhibition. Our data suggest that Src and cortactin are involved in pemphigus skin blistering but the contribution of Src is variable. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The intestinal epithelium constitutes a first line of defense of the innate immune system. Epithelial dysfunction is a hallmark of intestinal disorders such as inflammatory bowel diseases (IBDs). The actin cytoskeleton controls epithelial barrier integrity but the function of actin regulators such as cortactin is poorly understood. Given that cortactin controls endothelial permeability, we hypothesized that cortactin is also important for epithelial barrier regulation. We found increased permeability in the colon of cortactin-KO mice that was accompanied by reduced levels of ZO-1, claudin-1, and E-cadherin. By contrast, claudin-2 was upregulated. Cortactin deficiency increased RhoA/ROCK1-dependent actomyosin contractility, and inhibition of ROCK1 rescued the barrier defect. Interestingly, cortactin deficiency caused increased epithelial proliferation without affecting apoptosis. KO mice did not develop spontaneous colitis, but were more susceptible to dextran sulfate sodium colitis and showed severe colon tissue damage and edema formation. KO mice with colitis displayed strong mucus deposition and goblet cell depletion. In healthy human colon tissues, cortactin co-localized with ZO-1 at epithelial cell contacts. In IBDs patients, we observed decreased cortactin levels and loss of co-localization with ZO-1. Thus, cortactin is a master regulator of intestinal epithelial barrier integrity in vivo and could serve as a suitable target for pharmacological intervention in IBDs.

Background/Aims: Endothelial dysfunction, a common feature among hypertensive and type-2 diabetic patients, is associated with inflammation, increased levels of circulating soluble adhesion molecules (SAM), and urinary albumin excretion. The aim of this study was to evaluate the role of circulating SAM levels in the development of albuminuria in hypertensive type-2 diabetic patients. Methods: We studied 30 hypertensive type-2 diabetic patients and 30 non-diabetic normotensive subjects, and measured their VCAM-1, ICAM-1 and E-selectin levels by ELISA, and their 24-hour urinary albumin excretion by nephelometry; the levels of circulating adhesion molecules and albuminuria were correlated with the Spearman correlation coefficient. Results: We found that the diabetic patients had significantly (p < 0.001) higher levels of circulating SAM than control subjects. When levels of circulating SAM were correlated with albuminuria, we found a significant correlation between VCAM-1 levels and 24-hour urinary albumin excretion (r = 0.4, p < 0.02). Conclusion: Our results suggest that VCAM-1 may be a marker of nephropathy in hypertensive type-2 diabetic patients.