Angiopoietin-1/Tek signaling is a critical regulator of blood vessel development, with conventional knockout of angiopoietin-1 or Tek in mice being embryonically lethal due to vascular defects. In addition, angiopoietin-1 is thought to be required for the stability of mature vessels. Using a Cre-Lox conditional gene targeting approach, we have studied the role of angiopoietin-1 in embryonic and adult vasculature. We report here that angiopoietin-1 is critical for regulating both the number and diameter of developing vessels but is not required for pericyte recruitment. Cardiac-specific knockout of angiopoietin-1 reproduced the phenotype of the conventional knockout, demonstrating that the early vascular abnormalities arise from flow-dependent defects. Strikingly, deletion in the entire embryo after day E13.5 produced no immediate vascular phenotype. However, when combined with injury or microvascular stress, angiopoietin-1 deficiency resulted in profound organ damage, accelerated angiogenesis, and fibrosis. These findings redefine our understanding of the biological roles of angiopoietin-1: it is dispensable in quiescent vessels but has a powerful ability to modulate the vascular response after injury.

Triple pelvic osteotomy was performed in 15 dogs with bilateral hip dysplasia. Ten dogs were treated bilaterally and five dogs were treated unilaterally. Ten untreated dogs with normal hips served as controls. Force plate analysis, lameness evaluation, and radiography were performed before surgery and at weeks 5, 10, 15, and 28. Three dogs treated unilaterally were euthanatized and the hips were examined grossly and microscopically. Force plate data indicated that young dysplastic dogs transmitted significantly less vertical force through the hip joints than normal dogs. The force transmitted through treated hips reached or approached control levels by week 28 and was significantly greater than the force transmitted through untreated hips. Clinical lameness resolved in 92% of limbs and progression of radiographically detectable degenerative joint disease was minimal. Gross and microscopic degenerative changes in the articular cartilage were similar in the treated and untreated hips. The synovial membrane was less reactive in treated hips.

Despite the clear importance of Hedgehog (Hh) signaling in blood vascular development as shown by genetic analysis, its mechanism of action is still uncertain. To better understand the role of Hh in vascular development, we further characterized its roles in vascular development in mouse embryos and examined its interaction with vascular endothelial growth factor (VEGF), a well-known signaling pathway essential to blood vascular development. We found that VEGF expression in the mouse embryo depended on Hh signaling, and by using genetic rescue approaches, we demonstrated that the role of Hh both in endothelial tube formation and Notch-dependent arterial identity was solely dependent on its regulation of VEGF. In contrast, overactivation of the Hh pathway through deletion of Patched1 (Ptch1), a negative regulator of Hh signaling, resulted in reduced vascular density and increased Delta-like ligand 4 expression. The Ptch1 phenotype was independent of VEGF pathway dysregulation and was not rescued when Delta-like ligand 4 levels were restored to normal. These findings establish that Hh uses both VEGF-and Notch-dependent and -independent mechanisms to pattern specific events in early blood vascular development. (Blood. 2010;116(4):653-660) IntroductionThe blood vascular system is the first organ to develop in the mammalian embryo, establishing a basic circulatory system between embryonic (E) day 7.5 and E8.5. The vessels that initially comprise the blood vascular system form by the process of vasculogenesis: the assembly of endothelial precursors (angioblasts) into simple endothelial tubes in the absence of preexisting vessels. Failure to establish these initial vessels results in growth arrest and embryonic lethality by E9.5. 1 Subsequent remodeling and expansion of these and other vessels requires the intricate and coordinated process of angiogenesis: the branching, splitting, pruning, and proliferation of preexisting vessels. The Hedgehog (Hh) signaling pathway is known to play an important role in blood vessel development, 2 but its mechanism of action remains incompletely defined. To better understand this role, we have used the mouse embryo as a model to examine the interplay between Hh and vascular endothelial growth factor (VEGF) signaling, another pathway essential for blood vascular development. 3 The interplay between Hh and VEGF in vascular development is exemplified in the establishment of artery/vein identity in zebrafish. In this pathway, notochordal Hh induces expression of VEGF in neighboring somites, which in turn induces Notchdependent arterial identity in endothelial cells. 4 In mice, Notch signaling is essential for artery specification, 5 and numerous receptors and ligands for this pathway become restricted to arteries, 6 key among them are Notch1, 7 Notch4, 8 and Delta-like ligand 4 (Dll4). 9 Although the role for Notch in assignment of arterial identity in mice is unequivocal, the requirement for either Hh or VEGF upstream of Notch in vivo during mouse development has not been determined.Hh i...

The fabrication of high quality, robust and photoactive ITO electrodes-in the form of well-defined two-and three-dimensional films-is reported following the Langmuir-Scha ¨fer (LS) and the layer-by-layer (LBL) methods. In the LS approach C 60 -NiP multilayers were transferred from the air-water interface, while the LBL approach utilizes electrostatic and van der Waals interactions for the step-by-step deposition of individual C 60 -NiP molecules out of solution. These complementary techniques allow control over the thickness and composition of the films at a molecular level and guarantee the specific alignment and the orientation of the incorporated donor-acceptor system. Modified ITO electrodes were probed in photocurrent experiments, in which the LBL-modified electrodes reveal smaller photon to current conversion efficiencies relative to the LS-modified electrodes.

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Periprosthetic osteolysis involves osteoclast activation by wear particulates and their exposure to mechanical perturbation through exposure to shear forces generated by periprosthetic fluid as well as interface micromotion. This study aimed to determine the interactions between wear particulates, mechanical stimulation, and osteoclasts. In static cultures, wear particulates increased osteoclast differentiation. Addition of neutralizing antibodies to RANKL (receptor activator of nuclear factor kappa ligand) inhibited the particle-induced increase in osteoclast numbers. Cyclic 5000 microstrains were applied with the use of a custom-built device to marrow-derived cultures to assess the effect on osteoclast differentiation. Mechanical strain application alone decreased osteoclast differentiation, which was further decreased by the addition of particles despite increases in the soluble RANKL to osteoprotegerin (OPG) ratio. Mechanical strain alone induced mature osteoclast apoptosis in a dose-dependent manner. In contrast, in the mature osteoclast model, the addition of nonmetal particulates protected the osteoclasts from becoming apoptopic. Titanium (Ti) and cobalt chromium (CoCr) particles, however, induced osteoclast apoptosis, whereas polyethylene (PE) and polymethylmethacrylate (PMMA) did not. Wear particulates and mechanical stimulation interact via an eicosanoid-dependent pathway to alter osteoclast function and survival. The addition of mechanical perturbation to a particle-laden system thus appears to enhance the potential for osteolytic activity by enhancing osteoclast survival.

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