Mesenchymal stem cells (MSC) are multipotent postnatal stem cells, involved in the treatment of ischemic vascular diseases. We investigate the ability of MSC, exposed to short-term hypoxic conditions, to participate in vascular and tissue regeneration in an in vivo model of hindlimb ischemia. Transplantation of hypoxic preconditioned murine MSC (HypMSC) enhanced skeletal muscle regeneration at day 7, improved blood flow and vascular formation compared to injected nonpreconditioned MSC (NormMSC). These observed effects were correlated with an increase in HypMSC engraftment and a putative role in necrotic skeletal muscle fiber clearance. Moreover, HypMSC transplantation resulted in a large increase in Wnt4 (wingless-related MMTV integration site 4) expression and we demonstrate its functional significance on MSC proliferation and migration, endothelial cell (EC) migration, as well as myoblast differentiation. Furthermore, suppression of Wnt4 expression in HypMSC, abrogated the hypoxia-induced vascular regenerative properties of these cells in the mouse hindlimb ischemia model. Our data suggest that hypoxic preconditioning plays a critical role in the functional capabilities of MSC, shifting MSC location in situ to enhance ischemic tissue recovery, facilitating vascular cell mobilization, and skeletal muscle fiber regeneration via a paracrine Wnt-dependent mechanism.

Vascular exploration of small animals requires imaging hardware with a very high spatial resolution, capable of differentiating large as well as small vessels, in both in vivo and ex vivo studies. Micro Computed Tomography (micro-CT) has emerged in recent years as the preferred modality for this purpose, providing high resolution 3D volumetric data suitable for analysis, quantification, validation, and visualization of results. The usefulness of micro-CT, however, can be adversely affected by a range of factors including physical animal preparation, numerical quantification, visualization of results, and quantification software with limited possibilities. Exacerbating these inherent difficulties is the lack of a unified standard for micro-CT imaging. Most micro-CT today is aimed at particular applications and the software tools needed for quantification, developed mainly by imaging hardware manufacturers, lack the level of detail needed to address more specific aims. This review highlights the capabilities of micro-CT for vascular exploration, describes the current state of imaging protocols, and offers guidelines and suggestions aimed at making micro-CT more accurate, replicable, and robust.

Mesenchymal stem cell (MSC) transplantation offers a great angiogenic opportunity in vascular regenerative medicine. The canonical Wnt/beta-catenin signaling pathway has been demonstrated to play an essential role in stem cell fate. Recently, genetic studies have implicated the Wnt/Frizzled (Fz) molecular pathway, namely Wnt7B and Fz4, in blood growth regulation. Here, we investigated whether MSC could be required in shaping a functional vasculature and whether secreted Frizzled-related protein-1 (sFRP1), a modulator of the Wnt/Fz pathway, could modify MSC capacities, endowing MSC to increase vessel maturation. In the engraftment model, we show that murine bone marrow-derived MSC induced a beneficial vascular effect through a direct cellular contribution to vascular cells. MSC quickly organized into primitive immature vessel tubes connected to host circulation; this organization preceded host endothelial cell (EC) and smooth muscle cell (SMC) recruitment to later form mature neovessel. MSC sustained neovessel organization and maturation. We report here that sFRP1 forced expression enhanced MSC surrounding neovessel, which was correlated with an increase in vessel maturation and functionality. In vitro, sFRP1 strongly increased platelet-derived growth factor-BB (PDGF-BB) expression in MSC and enhanced beta-catenin-dependent cell-cell contacts between MSC themselves and EC or SMC. In vivo, sFRP1 increased their functional integration around neovessels and vessel maturation through a glycogen synthase kinase 3 beta (GSK3beta)-dependent pathway. sFRP1-overexpressing MSC compared with control MSC were well elongated and in a closer contact with the vascular wall, conditions required to achieve an organized mature vessel wall. We propose that genetically modifying MSC to overexpress sFRP1 may be potentially effective in promoting therapeutic angiogenesis/arteriogenesis processes. Disclosure of potential conflicts of interest is found at the end of this article.

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A single combined procedure of surgical epicardial pacemaker implantation and pacemaker system extraction appears to be a safe and effective method for managing pacemaker-dependent patients with infected pacemakers.

Objectives-Studying the mechanisms of neovascularization and evaluating the effects of proangiogenic strategies require accurate analysis of the neovascular network. We sought to evaluate the contribution of the microcomputed tomography (mCT) providing high-resolution 3-dimensional (3D) structural data, to a better comprehension of the well-studied mouse hindlimb postischemic neovascularization. Methods and Results-We showed a predominant arteriogenesis process in the thigh and a predominant angiogenesisrelated process in the tibiofibular region, in response to ischemia during the first 15 days. After 15 days, mCT quantitative analysis reveals a remodeling of arterial neovessels and a regression depending on the restoration of the blood flow. We provided also new mCT data on the rapid and potent angiogenic effects of mesenchymal stem cell therapy on vessel formation and organization. We discussed the contribution of this technique compared with or in addition to data generated by the more conventional approaches. A s mouse models are largely used to study mechanisms of neovascularization, vascular repair, and growth of collateral vessels, 1 a throughout analysis of the vascular network has gained of interest. Understanding neovessel formation mechanisms requires a complete view of the vascular architecture over the whole of the tissue analyzed: size, orientation, branching, and organization of collaterality. However, the classical methods of assessment are not always quantitative, restricted to a limited area of view, evaluate capillary density in 2D sections, or report superficial blood flow data. 1 Hence, microcomputed tomography (mCT) can, after the injection of a radiopaque contrast agent, image the vascular network in 3D in an entire organ 2,3 and give quantitative data. Several studies have investigated the microvascularization of the kidney, heart, and liver in the rat. 4 -6 Only a few teams have used quantitative tools for studying postischemic angiogenesis in the mouse. 2,3 Here, we used a contrast agent and mCT acquisition procedure dedicated to analyze postischemic kinetics of vessel formation and remodeling restricted to arterial network in the mouse hindlimb. We discussed the contribution of these images compared with or in addition to data produced by the conventional laser Doppler and immunolabeling approaches. Our results revealed a predominant arteriogenesis process in the thigh and in contrast a predominant angiogenesis related process in the tibiofibular region. We showed that neovessel remodeling depends on the restoration of the blood flow. We then provided new data on the mesenchymal stem cell therapy on the feature of vessel formation and organization. Conclusion-This Materials and MethodsMaterials and methods related to MSC culture, animal care, model of ischemia, micro-CT data processing and analysis, and histological vascularization quantification appear in the supplemental Materials and Methods section (available online at http:// atvb.ahajournals.org). Briefly, we studied the format...

Freedom SOLO valve has very good early- and intermediate-term results. Short implantation times and its haemodynamic performances, particularly in small diameters, allow us to use it by first intention in older and often sicker patients. These results must be confirmed by long-term outcomes.