We present and discuss the role of endothelial and astroglial cells in managing the blood-brain barrier (BBB) and aspects of pathological alterations in the BBB. The impact of astrocytes, pericytes, and perivascular cells on the induction and maintenance of the gliovascular unit is largely unidentified so far. An understanding of the signaling pathways that lie between these cell types and the endothelium and that possibly are mediated by components of the basal lamina is just beginning to emerge. The metabolism for the maintenance of the endothelial barrier is intimately linked to and dependent on the microenvironment of the brain parenchyma. We report the structure and function of the endothelial cells of brain capillaries by describing structures involved in the regulation of permeability, including transporter systems, caveolae, and tight junctions. There is increasing evidence that caveolae are not only vehicles for endo- and transcytosis, but also important regulators of tight-junction-based permeability. Tight junctions separate the luminal from the abluminal membrane domains of the endothelial cell ("fence function") and control the paracellular pathway ("gate function") thus representing the most significant structure of the BBB. In addition, the extracellular matrix between astrocytes/pericytes and endothelial cells contains numerous molecules with inherent signaling properties that have to be considered if we are to improve our knowledge of the complex and closely regulated BBB.

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The results clearly show that the bevacizumab molecule can penetrate the retina and is also transported into the retinal pigment epithelium, the choroid and, in particular, into photoreceptor outer segments after intravitreal injection of Avastin. Active transport mechanisms seem to be involved.

Abstract-Stress-dependent regulation of cardiac action potential duration is mediated by the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis. It is accompanied by an increased magnitude of the slow outward potassium ion current, I Ks . KCNQ1 and KCNE1 subunits coassemble to form the I Ks channel. Mutations in either subunit cause long QT syndrome, an inherited cardiac arrhythmia associated with an increased risk of sudden cardiac death.Here we demonstrate that exocytosis of KCNQ1 proteins to the plasma membrane requires the small GTPase RAB11, whereas endocytosis is dependent on RAB5. We further demonstrate that RAB-dependent KCNQ1/KCNE1 exocytosis is enhanced by the serum-and glucocorticoid-inducible kinase 1, and requires phosphorylation and activation of phosphoinositide 3-phosphate 5-kinase and the generation of PI(3,5)P 2 . Identification of KCNQ1/KCNE1 recycling and its modulation by serum-and glucocorticoid-inducible kinase 1-phosphoinositide 3-phosphate 5-kinase -PI(3,5)P 2 provides a mechanistic insight into stress-induced acceleration of cardiac repolarization. (Circ Res. 2007;100:686-692.)Key Words: kinase Ⅲ PIP2 Ⅲ RAB Ⅲ trafficking Ⅲ PIKfyve E motional stress activates the sympathetic nervous system 1 and the release of stress hormones such as cortisol via the hypothalamic-pituitary-adrenal (HPA) axis 2 and is a common trigger of sudden cardiac death. 3,4 One of the many genes regulated by cortisol is the serum-and glucocorticoidinducible kinase 1 (SGK1). 5,6 In vitro experiments have shown that SGK1 stimulates I Ks 7 , a repolarizing potassium current conducted by channels composed of KCNQ1 ␣-subunits and KCNE1 ␤-subunits. 8,9 Moreover, a gain-offunction variant of SGK1 is associated with shortening of the QT interval. 10 SGK1-mediated regulation of I Ks might be particularly important in patients with KCNQ1 (Kv7.1, Kv-LQT1) or KCNE1 (minK) mutations that are prone to fatal cardiac arrhythmias triggered by physical and psychological stress. 4 The mechanism responsible for regulation of I Ks channels by SGK1 have remained elusive. SGK1 enhances the abundance of other types of channel protein in the plasma membrane by inhibiting the ubiquitin ligase Nedd4 -2 11 in addition to other mechanisms (summarized by Lang et al 2006 12 ).Other candidate signaling molecules that may affect channel trafficking include RAB family proteins, GTPases involved in vesicle cycling. [13][14][15][16][17][18] RAB5, a monomeric GTPase of the Ras superfamily, has been implicated in the regulation of early steps in the endocytic pathway, whereas the RAB11 GTPase is localized at the trans-Golgi network, post-Golgi vesicles and the recycling endosome. 19 Both RAB5 and RAB11 are expressed in cardiac tissue. 17 Mammalian cells and Xenopus laevis oocytes have been shown to possess and use highly conserved RAB-dependent trafficking pathways. 20,21 Endocytosis by RAB5 and exocytosis by RAB11 have been reported to participate in the regulation of CFTR chloride channels 22 and the glucose transporter GluT4. 15...

Rationale: Macrophage migration inhibitory factor (MIF) is released on platelet activation. Circulating MIF could potentially regulate platelets and thereby platelet-mediated inflammatory and regenerative mechanisms. However, the effect of MIF on platelets is unknown. Objective: The present study evaluated MIF in regulating platelet survival and thrombotic potential. Methods and Results: MIF interacted with CXCR4-CXCR7 on platelets, defining CXCR7 as a hitherto unrecognized receptor for MIF on platelets. MIF internalized CXCR4, but unlike CXCL12 (SDF-1α), it did not phosphorylate Erk1/2 after CXCR4 ligation because of the lack of CD74 and failed in subsequent CXCR7 externalization. MIF did not alter the activation status of platelets. However, MIF rescued platelets from activation and BH3 mimetic ABT-737–induced apoptosis in vitro via CXCR7 and enhanced circulating platelet survival when administered in vivo. The antiapoptotic effect of MIF was absent in Cxcr7 −/− murine embryonic cells but pronounced in CXCR7-transfected Madin–Darby canine kidney cells. This prosurvival effect was attributed to the MIF–CXCR7–initiated PI3K-Akt pathway. MIF induced CXCR7-Akt–dependent phosphorylation of BCL-2 antagonist of cell death (BAD) both in vitro and in vivo. Consequentially, MIF failed to rescue Akt −/− platelets from thrombin-induced apoptosis when challenged ex vivo, also in prolonging platelet survival and in inducing BAD phosphorylation among Akt −/− mice in vivo. MIF reduced thrombus formation under arterial flow conditions in vitro and retarded thrombotic occlusion after FeCl 3 -induced arterial injury in vivo, an effect mediated through CXCR7. Conclusion: MIF interaction with CXCR7 modulates platelet survival and thrombotic potential both in vitro and in vivo and thus could regulate thrombosis and inflammation.

Glucocorticoid excess predisposes to the development of diabetes, at least in part through impairment of insulin secretion. The underlying mechanism has remained elusive. We show here that dexamethasone upregulates transcription and expression of the serumand glucocorticoid-inducible kinase 1 (SGK1) in insulinsecreting cells, an effect reversed by mifepristone (RU486), an antagonist of the nuclear glucocorticoid receptor. G lucocorticoids are known to induce diabetes (1-3). In addition to peripheral insulin resistance and increased hepatic glucose production by stimulating gluconeogenesis (4), glucocorticoids interfere with insulin secretion of pancreatic ␤-cells (5-7). Despite extensive (8 -12) studies, the molecular mechanism is still a matter of debate. Increased expression of ␣ 2 -adrenoceptors has been proposed to account for dexamethasone-induced inhibition of insulin secretion (9). Thus, transgenic mice overexpressing glucocorticoid receptors in ␤-cells show 30% more UK14304 binding, a selective adrenoceptor agonist, than wild-type islets (2). These mice are glucose intolerant and have reduced plasma insulin levels. Since pertussis toxin and cAMP overcome dexamethasone inhibition of glucose-induced insulin release, decreased cAMP levels during dexamethasone treatment may be responsible for inhibition of secretion (6,13). Furthermore, dexamethasone was reported to decrease Glut2 protein abundance at the plasma membrane, a change that may contribute to impaired glucose-induced insulin secretion (8). Dexamethasone also downregulates glucokinase mRNA in an insulin-secreting cell line (14). Mifepristone (RU486), a nuclear glucocorticoid receptor antagonist, completely abolished dexamethasone-induced inhibition of insulin secretion (5,6), pointing to the involvement of glucocorticoid-dependent gene expression. Glucocorticoid-sensitive genes include the serum-and glucocorticoid-inducible kinase 1 (SGK1) (rev. in 15). The kinase is expressed in virtually all human tissues tested. Unlike its isoforms SGK2 and SGK3 and the related kinase protein kinase B, SGK1 is under strong transcriptional control of glucocorticoids (15) and mineralocorticoids (16). SGK1 has been shown to regulate a variety of ion channels including K ϩ channels such as voltage-gated K v channels (17).Ion channel activity is in turn decisive for insulin secretion from pancreatic ␤-cells. 4-AP, 4-aminopyridine; GAPDH, glyceraldehyde-3-phsophate dehydrogenase; SGK1, serum-and glucocorticoid-inducible kinase 1; TEA, tetraethylammonium.

CorrectionsBIOCHEMISTRY. For the article ''Differential effects of a centrally acting fatty acid synthase inhibitor in lean and obese mice,'' by Monica V. Kumar, Teruhiko Shimokawa, Tim R. Nagy, and M. Daniel Lane, which appeared in number 4, February 19, 2002, of Proc. Natl. Acad. Sci. USA (99, 1921-1925, the authors note the following. ''Under a licensing agreement between FASgen, Inc., and The Johns Hopkins University, Dr. Lane is entitled to a share of royalty received by the University on sales of products that embody the technology described in this article. (98, 10687-10691; First Published August 28, 2001; 10.1073͞pnas.181354398), the authors note the following. In the Introduction and Discussion of our paper, we failed to reference a recent article by Rousseau et al.(1), which demonstrated that single point mutations can significantly perturb the equilibrium between monomeric and domain-swapped dimeric p13suc1. Rational methods were used to redesign p13suc1 from a fully monomeric protein (dissociation constant of Ϸ900 mM) to a fully dimeric protein (dissociation constant of Ϸ100 nM). Fig. 3 appeared incorrectly. The correct version of the figure and its legend appear below.

Platelets store and release CXCL12 (SDF-1), which governs differentiation of hematopoietic progenitors into either endothelial or macrophage-foam cells. CXCL12 ligates CXCR4 and CXCR7 and regulates monocyte/macrophage functions. This study deciphers the relative contribution of CXCR4–CXCR7 in mediating the effects of platelet-derived CXCL12 on monocyte function, survival, and differentiation. CXCL12 and macrophage migration inhibitory factor (MIF) that ligate CXCR4–CXCR7 induced a dynamic bidirectional trafficking of the receptors, causing CXCR4 internalization and CXCR7 externalization during chemotaxis, thereby influencing relative receptor availability, unlike MCP-1. In vivo we found enhanced accumulation of platelets and platelet-macrophage co-aggregates in peritoneal fluid following induction of peritonitis in mice. The relative surface expression of CXCL12, CXCR4, and CXCR7 among infiltrated monocytes was also enhanced as compared with peripheral blood. Platelet-derived CXCL12 from collagen-adherent platelets and recombinant CXCL12 induced monocyte chemotaxis specifically through CXCR4 engagement. Adhesion of monocytes to immobilized CXCL12 and CXCL12-enriched activated platelet surface under static and dynamic arterial flow conditions were mediated primarily through CXCR7 and were counter-regulated by neutralizing platelet-derived CXCL12. Monocytes and culture-derived-M1–M2 macrophages phagocytosed platelets, with the phagocytic potential of culture-derived-M1 macrophages higher than M2 involving CXCR4–CXCR7 participation. CXCR7 was the primary receptor in promoting monocyte survival as exerted by platelet-derived CXCL12 against BH3-mimetic induced apoptosis (phosphatidylserine exposure, caspase-3 activation, loss of mitochondrial transmembrane potential). In co-culture experiments with platelets, monocytes predominantly differentiated into CD163+ macrophages, which was attenuated upon CXCL12 neutralization and CXCR4/CXCR7 blocking antibodies. Moreover, OxLDL uptake by platelets induced platelet apoptosis, like other platelet agonists TRAP and collagen-related peptide (CRP). CXCL12 facilitated phagocytosis of apoptotic platelets by monocytes and M1–M2 macrophages, also promoted their differentiation into foam cells via CXCR4 and CXCR7. Thus, platelet-derived CXCL12 could regulate monocyte-macrophage functions through differential engagement of CXCR4 and CXCR7, indicating an important role in inflammation at site of platelet accumulation.