Endothelial progenitor cells are reduced in refractory hypertension.

Circulating endothelial progenitor cells (EPCs) play a key role in the maintenance of endothelial homoeostasis and promote vascular repair. They may also be of predictive value for cardiovascular events. Reduced EPC number and functional activity have been associated with several cardiovascular risk factors, but their relationship with hypertension remains unclear. The objective of this study was to investigate if number and function of circulating EPCs are reduced in patients with refractory hypertension (RHT). Circulating EPCs (CD34+ CD133+/CD45+) were isolated from peripheral blood by flow cytometry in 39 RHT and 30 normotensive controls. EPC number was also determined in vitro after 7 days in culture. After age adjustment, EPC concentration was significantly reduced in RHT as compared with controls (mean (95% CI), 33.8 (18.1-49.6) vs 69.1 (50.7-87.5) EPCs per 10(5) peripheral mononuclear cells (MNCs), respectively; P=0.014). After in vitro culture, EPCs were also reduced in patients as compared with controls (mean (95% CI), 142.3 (49.5-235.0) vs 611.0 (480.2-741.8) EPCs per field, respectively, P<0.001). In multiple linear regression analysis, circulating EPCs were significantly reduced by 56.3% in RHT as compared with control (P=0.006), independently of all other known risk factors. Moreover, RHT had a high independent predictive value for lower EPC proliferation. The number of EPCs per field was reduced by 76.7% in RHT with respect to controls (P<0.001). In summary, the number of circulating EPCs after culture is reduced in patients with RHT, which may be related to the increased rate of endothelial dysfunction, atherosclerotic disease and cardiovascular events observed in this population.

Association of junctional adhesion molecule with calcium/calmodulin-dependent serine protein kinase (CASK/LIN-2) in human epithelial caco-2 cells.

We report here that junctional adhesion molecule (JAM) interacts with calcium/calmodulin-dependent serine protein kinase (CASK), a protein related to membrane-associated guanylate kinases. In Caco-2 cells, JAM and CASK were coprecipitated and found to colocalize at intercellular contacts along the lateral surface of the plasma membrane. Association of JAM with CASK requires the PSD95/dlg/ZO-1 (PDZ) domain of CASK and the putative PDZ-binding motif Phe-Leu-Val(COOH) in the cytoplasmic tail of JAM. Temporal dissociation in the junctional localization of the two proteins suggests that the association with CASK is not required for recruiting JAM to intercellular junctions. Compared with mature intercellular contacts, junction assembly was characterized by both enhanced solubility of CASK in Triton X-100 and reduced amounts of Triton-insoluble JAM-CASK complexes. We propose that JAM association with CASK is modulated during junction assembly, when CASK is partially released from its cytoskeletal associations.

Homophilic interaction of junctional adhesion molecule.

Junctional adhesion molecule (JAM) is an integral membrane protein that belongs to the immunoglobulin superfamily, localizes at tight junctions, and regulates both paracellular permeability and leukocyte transmigration. To investigate molecular determinants of JAM function, the extracellular domain of murine JAM was produced as a recombinant soluble protein (rsJAM) in insect cells. rsJAM consisted in large part of noncovalent homodimers, as assessed by analytical ultracentrifugation. JAM dimers were also detected at the surface of Chinese hamster ovary cells transfected with murine JAM, as evaluated by cross-linking and immunoprecipitation. Furthermore, fluid-phase rsJAM bound dose-dependently solid-phase rsJAM, and such homophilic binding was inhibited by anti-JAM Fab BV11, but not by Fab BV12. Interestingly, Fab BV11 exclusively bound rsJAM dimers (but not monomers) in solution, whereas Fab BV12 bound both dimers and monomers. Finally, we mapped the BV11 and BV12 epitopes to a largely overlapping sequence in proximity of the extracellular amino terminus of JAM. We hypothesize that rsJAM dimerization induces a BV11-positive conformation which in turn is critical for rsJAM homophilic interactions. Dimerization and homophilic binding may contribute to both adhesive function and junctional organization of JAM.

Interaction of junctional adhesion molecule with the tight junction components ZO-1, cingulin, and occludin.

Junctional adhesion molecule (JAM) is an integral membrane protein that has been reported to colocalize with the tight junction molecules occludin, ZO-1, and cingulin. However, evidence for the association of JAM with these molecules is missing. Transfection of Chinese hamster ovary cells with JAM (either alone or in combination with occludin) resulted in enhanced junctional localization of both endogenous ZO-1 and cotransfected occludin. Additionally, JAM was coprecipitated with ZO-1 in the detergent-insoluble fraction of Caco-2 epithelial cells. A putative PDZ-binding motif at the cytoplasmic carboxyl terminus of JAM was required for mediating the interaction of JAM with ZO-1, as assessed by in vitro binding and coprecipitation experiments. JAM was also coprecipitated with cingulin, another cytoplasmic component of tight junctions, and this association required the amino-terminal globular head of cingulin. Taken together, these data indicate that JAM is a component of the multiprotein complex of tight junctions, which may facilitate junction assembly.