Regulation of endothelial cell cytoskeletal reorganization by a secreted frizzled-related protein-1 and frizzled 4- and frizzled 7-dependent pathway: role in neovessel formation

Consistent with findings of Wnt pathway members involved in vascular cells, a role for Wnt/Frizzled signaling has recently emerged in vascular cell development. Among the few Wnt family members implicated in vessel formation in adult, Wnt7b and Frizzled 4 have been shown as involved in vessel formation in the lung and in the retina, respectively. Our previous work has shown a role for secreted Frizzled-related protein-1 (sFRP-1), a proposed Wnt signaling inhibitor, in neovascularization after an ischemic event and demonstrated its role as a potent angiogenic factor. However the mechanisms involved have not been investigated. Here, we show that sFRP-1 treatment increases endothelial cell spreading on extracellular matrix as revealed by actin stress fiber reorganization in an integrin-dependent manner. We demonstrate that sFRP-1 can interact with Wnt receptors Frizzled 4 and 7 on endothelial cells to transduce downstream to cellular machineries requiring Rac-1 activity in cooperation with GSK-3beta. sFRP-1 overexpression in endothelium specifically reversed the inactivation of GSK-3 beta and increased neovascularization in ischemia-induced angiogenesis in mouse hindlimb. This study illustrates a regulated pathway by sFRP-1 involving GSK-3beta and Rac-1 in endothelial cell cytoskeletal reorganization and in neovessel formation.

Phase diagram with an enhanced spin-glass region of the mixed Ising–XY magnet LiHo{x}Er{1-x}F{4}

We present the experimental phase diagram of LiHoxEr1-xF4, a dilution series of dipolar-coupled model magnets. The phase diagram was determined using a combination of ac susceptibility and neutron scattering. Three unique phases in addition to the Ising ferromagnet LiHoF4 and the XY antiferromagnet LiErF4 have been identified. Below x = 0.86, an embedded spin-glass phase is observed, where a spin glass exists within the ferromagnetic structure. Below x = 0.57, an Ising spin glass is observed consisting of frozen needlelike clusters. For x ∼ 0.3–0.1, an antiferromagnetically coupled spin glass occurs. A reduction of TC(x) for the ferromagnet is observed which disobeys the mean-field predictions that worked for LiHoxY1-xF4.

Cis-4-methylsphingosine is a sphingosine-1-phosphate receptor modulator

Sphingosine-1-phosphate (S1P) acts as high affinity agonist at specific G-protein-coupled receptors, S1P(1-5), that play important roles e.g. in the cardiovascular and immune systems. A S1P receptor modulating drug, FTY720 (fingolimod), has been effective in phase III clinical trials for multiple sclerosis. FTY720 is a sphingosine analogue and prodrug of FTY720-phosphate, which activates all S1P receptors except S1P(2) and disrupts lymphocyte trafficking by internalizing the S1P(1) receptor. Cis-4-methylsphingosine (cis-4M-Sph) is another synthetic sphingosine analogue that is readily taken up by cells and phosphorylated to cis-4-methylsphingosine-1-phosphate (cis-4M-S1P). Therefore, we analysed whether cis-4M-Sph interacted with S1P receptors through its metabolite cis-4M-S1P in a manner similar to FTY720. Indeed, cis-4M-Sph caused an internalization of S1P receptors, but differed from FTY720 as it acted on S1P(2) and S1P(3) and only weakly on S1P(1), while FTY720 internalized S1P(1) and S1P(3) but not S1P(2). Consequently, pre-incubation with cis-4M-Sph specifically desensitized S1P-induced [Ca(2+)](i) increases, which are mediated by S1P(2) and S1P(3), in a time- and concentration-dependent manner. This effect was not shared by sphingosine or FTY720, indicating that metabolic stability and targeting of S1P(2) receptors were important. The desensitization of S1P-induced [Ca(2+)](i) increases was dependent on the expression of SphKs, predominantly of SphK2, and thus mediated by cis-4M-S1P. In agreement, cis-4M-S1P was detected in the supernatants of cells exposed to cis-4M-Sph. It is concluded that cis-4M-Sph, through its metabolite cis-4M-S1P, acts as a S1P receptor modulator and causes S1P receptor internalization and desensitization. The data furthermore help to define requirements for sphingosine kinase substrates as S1P receptor modulating prodrugs.

Strategies for routine biopsies in heart transplantation based on 8-year results with more than 13,000 biopsies

The endomyocardial biopsy (EMB) in heart transplant recipients has been considered the "gold standard" for diagnosis of graft rejection (REJ). The purpose of this retrospective study is to develop long-term strategies (frequency and postoperative duration of EMB) for REJ monitoring. Between 1985 and 1992, 346 patients (mean age 44.5 years, female patients = 14%) received 382 heart grafts. For graft surveillance EMBs were performed according to a fixed schedule depending on postoperative day and the results of previous biopsies. In the first year the average number (no.) of EMBs/patient was 20 with 19% positive for REJ in the first quarter, dropping to 7% REJ/EMB by the end of the first year. The percentage of REJ/EMB declined annually from 4.7% to 4.5%, 2.2% and less than 1% after the fifth year. Individual biopsy results in the first 3 postoperative months had little predictive value. Patients with fewer than two REJ (group 1), vs patients with two or more REJ in the first 6 postoperative months (group 2), were significantly less likely to reject in the second half of the first year (group 1: 0.29 +/- 0.6 REJ/patient; group 2:0.83 +/- 1.3 REJ/patient; P < 0.001) and third postoperative year (group 1:0.12 +/- 0.33 REJ/patients; group 2:0.46 +/- 0.93 REJ/patient; P < 0.05). In conclusion, routine EMBs in the first 3 postoperative months have only limited predictive value, however the number of routine EMBs can be drastically reduced later depending on the intermediate postoperative REJ pattern.