Hybrid fiber reinforcement and crack formation in cementitious composite materials

The use of different types of fibers simultaneously for reinforcing cementitious matrices is motivated by the concept of a multi-scale nature of the crack propagation process. Fibers with different geometrical and mechanical properties are used to bridge cracks of different sizes from the micro- to the macroscale. In this study, the performance of different fiber reinforced cementitious composites is assessed in terms of their tensile stress-crack opening behavior. The results obtained from this investigation allow a direct quantitative comparison of the behavior obtained from the different fiber reinforcement systems. The research described in this paper shows that the multi-scale conception of cracking and the use of hybrid fiber reinforcements do not necessarily result in an improved tensile behavior of the composite. Particular material design requirements may nevertheless justify the use of hybrid fiber reinforcements.Fundação para a Ciência e a Tecnologia (FCT) - SFRH / BD / 36515 / 200

GATA2 is required for lymphatic vessel valve development and maintenance.

Heterozygous germline mutations in the zinc finger transcription factor GATA2 have recently been shown to underlie a range of clinical phenotypes, including Emberger syndrome, a disorder characterized by lymphedema and predisposition to myelodysplastic syndrome/acute myeloid leukemia (MDS/AML). Despite well-defined roles in hematopoiesis, the functions of GATA2 in the lymphatic vasculature and the mechanisms by which GATA2 mutations result in lymphedema have not been characterized. Here, we have provided a molecular explanation for lymphedema predisposition in a subset of patients with germline GATA2 mutations. Specifically, we demonstrated that Emberger-associated GATA2 missense mutations result in complete loss of GATA2 function, with respect to the capacity to regulate the transcription of genes that are important for lymphatic vessel valve development. We identified a putative enhancer element upstream of the key lymphatic transcriptional regulator PROX1 that is bound by GATA2, and the transcription factors FOXC2 and NFATC1. Emberger GATA2 missense mutants had a profoundly reduced capacity to bind this element. Conditional Gata2 deletion in mice revealed that GATA2 is required for both development and maintenance of lymphovenous and lymphatic vessel valves. Together, our data unveil essential roles for GATA2 in the lymphatic vasculature and explain why a select catalogue of human GATA2 mutations results in lymphedema

A non-canonical role for desmoglein-2 in endothelial cells: implications for neoangiogenesis

Desmogleins (DSG) are a family of cadherin adhesion proteins that were first identified in desmosomes and provide cardiomyocytes and epithelial cells with the junctional stability to tolerate mechanical stress. However, one member of this family, DSG2, is emerging as a protein with additional biological functions on a broader range of cells. Here we reveal that DSG2 is expressed by nondesmosome- forming human endothelial progenitor cells as well as their mature counterparts [endothelial cells (ECs)] in human tissue from healthy individuals and cancer patients. Analysis of normal blood and bone marrow showed that DSG2 is also expressed by CD34?CD45dim hematopoietic progenitor cells. An inability to detect other desmosomal components, i.e., DSG1, DSG3 and desmocollin (DSC)2/3, on these cells supports a solitary role for DSG2 outside of desmosomes. Functionally, we show that CD34?CD45dimDSG2? progenitor cells are multi-potent and pro-angiogenic in vitro. Using a ‘knockout-first’ approach, we generated a Dsg2 loss-of-function strain of mice (Dsg2lo/lo) and observed that, in response to reduced levels of Dsg2: (i) CD31? ECs in the pancreas are hypertrophic and exhibit altered morphology, (ii) bone marrowderived endothelial colony formation is impaired, (iii) ex vivo vascular sprouting from aortic rings is reduced, and (iv) vessel formation in vitro and in vivo is attenuated. Finally, knockdown of DSG2 in a human bone marrow EC line reveals a reduction in an in vitro angiogenesis assay as well as relocalisation of actin and VE-cadherin away from the cell junctions, reduced cell–cell adhesion and increased invasive properties by these cells. In summary, we have identified DSG2 expression in distinct progenitor cell subpopulations and show that, independent from its classical function as a component of desmosomes, this cadherin also plays a critical role in the vasculature.Lisa M. Ebert, Lih Y. Tan, M. Zahied Johan, Kay Khine Myo Min, Michaelia P. Cockshell, Kate A. Parham, Kelly L. Betterman, Paceman Szeto, Samantha Boyle, Lokugan Silva, Angela Peng, YouFang Zhang, Andrew Ruszkiewicz, Andrew C. W. Zannettino, Stan Gronthos, Simon Koblar, Natasha L. Harvey, Angel F. Lopez, Mark Shackleton, Claudine S. Bonde

Central nervous system lymphatic unit, immunity, and epilepsy : Is there a link?

Summary The recent definition of a network of lymphatic vessels in the meninges surrounding the brain and the spinal cord has advanced our knowledge on the functional anatomy of fluid movement within the central nervous system (CNS). Meningeal lymphatic vessels along dural sinuses and main nerves contribute to cerebrospinal fluid (CSF) drainage, integrating the cerebrovascular and periventricular routes, and forming a circuit that we here define as the CNS-lymphatic unit. The latter unit is important for parenchymal waste clearance, brain homeostasis, and the regulation of immune or inflammatory processes within the brain. Disruption of fluid drain mechanisms may promote or sustain CNS disease, conceivably applicable to epilepsy where extracellular accumulation of macromolecules and metabolic by-products occur in the interstitial and perivascular spaces. Herein we address an emerging concept and propose a theoretical framework on: (a) how a defect of brain clearance of macromolecules could favor neuronal hyperexcitability and seizures, and (b) whether meningeal lymphatic vessel dysfunction contributes to the neuroimmune cross-talk in epileptic pathophysiology. We propose possible molecular interventions targeting meningeal lymphatic dysfunctions, a potential target for immune-mediated epilepsy.Peer reviewe

Investigating lymphatic vascular remodelling during postnatal mouse mammary gland morphogenesis.

The lymphatic vasculature, an essential component of the cardiovascular system, serves several functions critical to embryonic development and adult homeostasis. Lymphatic vessels return interstitial protein-rich fluid to the bloodstream, transport immune cells during immune surveillance and infection and absorb lipids from the digestive tract (Alitalo et al., 2005; Tammela and Alitalo, 2010). The aberrant growth and development of lymphatic vessels (lymphangiogenesis) is a common feature of human disorders including lymphoedema, inflammatory diseases and tumour metastasis (Alitalo et al., 2005; Tammela and Alitalo, 2010). Lymphatic vessels are of key importance to breast cancer patients. Lymphatic vessels are exploited as a key route of metastasis for tumour cells and the ability of a tumour to promote lymphangiogenesis has been linked with metastasis and poor patient prognosis (Gu et al., 2008; Nakamura et al., 2005; Nakamura et al., 2003; Ran et al., 2010; Skobe et al., 2001). Moreover, lymphatic vascular damage incurred during the surgical resection of lymph nodes commonly results in secondary lymphoedema, a debilitating complication for up to 40% of breast cancer patients (Armer et al., 2009). Despite the involvement of lymphatic vessels in breast cancer, the genes and molecular mechanisms that regulate lymphangiogenesis in the breast remain relatively uncharacterised. The mammary epithelium and blood vasculature undergo dynamic remodelling events in response to hormonal signals and functional demands during postnatal mouse mammary gland morphogenesis (Djonov et al., 2001; Matsumoto et al., 1992; Richert et al., 2000; Watson and Khaled, 2008). The aims of this project were: 1. To investigate the spatial organisation of lymphatic vessels in the mouse mammary gland. 2. To investigate whether lymphatic vessels, like blood vessels and the mammary epithelial tree, are temporally remodelled during mouse mammary gland morphogenesis. 3. To define signals that regulate lymphangiogenesis during postnatal mouse mammary gland morphogenesis. This study provides the first evidence demonstrating that the lymphatic vasculature is dynamically remodelled along with the mammary epithelial tree and blood vasculature during postnatal mouse mammary gland morphogenesis. In addition, this study reveals an intimate association of lymphatic vessels with epithelial ducts, a finding that has important implications for tumour metastasis, as well as the spatial organisation of lymphatic vessels in other branched epithelial tissues, including the lung, kidney, pancreas and prostate. Furthermore, we established that vascular endothelial growth factor (Vegf) C (Vegfc) and Vegfd mRNA levels are significantly increased early during pregnancy and that proteolytically-processed, active VEGF-D is expressed selectively in pregnant, but not virgin mouse mammary glands, corresponding with the stage of peak lymphatic vessel density. In accordance with these data, we demonstrated that a tyrosine kinase inhibitor specific for VEGF receptor 3 (Kirkin et al., 2001; Kirkin et al., 2004), the principal receptor for mouse VEGF-C and VEGF-D, can block the proliferation of primary dermal lymphatic endothelial cells that is stimulated by mammary epithelial and stromal cell conditioned media ex vivo. These data suggest that VEGF-C and VEGF-D, two of the best characterised lymphangiogenic stimuli to date, are likely to play key roles in the stimulation of lymphangiogenesis in the pregnant mouse mammary gland. Elucidation of the molecular mechanisms controlling lymphangiogenesis in the mammary gland has the potential to reveal important targets for the future generation of pro- and anti-lymphangiogenic therapeutics, with the ultimate goal to repair surgically damaged lymphatic vessels and prevent breast cancer metastasis, respectively.Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 201

The lymphatic vasculature: development and role in shaping immunity

The lymphatic vasculature is an integral component of the immune system. Lymphatic vessels are a key highway via which immune cells are trafficked, serving not simply as a passive route of transport, but to actively shape and coordinate immune responses. Reciprocally, immune cells provide signals that impact the growth, development, and activity of the lymphatic vasculature. In addition to immune cell trafficking, lymphatic vessels are crucial for fluid homeostasis and lipid absorption. The field of lymphatic vascular research is rapidly expanding, fuelled by rapidly advancing technology that has enabled the manipulation and imaging of lymphatic vessels, together with an increasing recognition of the involvement of lymphatic vessels in a myriad of human pathologies. In this review we provide an overview of the genetic pathways and cellular processes important for development and maturation of the lymphatic vasculature, discuss recent work revealing important roles for the lymphatic vasculature in directing immune cell traffic and coordinating immune responses and highlight the involvement of lymphatic vessels in a range of pathological settings.Kelly L. Betterman, Natasha L. Harve

Getting out and about: the emergence and morphogenesis of the vertebrate lymphatic vasculature

The lymphatic vascular system develops from the pre-existing blood vasculature of the vertebrate embryo. New insights into lymphatic vascular development have recently been achieved with the use of alternative model systems, new molecular tools, novel imaging technologies and growing interest in the role of lymphatic vessels in human disorders. The signals and cellular mechanisms that facilitate the emergence of lymphatic endothelial cells from veins, guide migration through the embryonic environment, mediate interactions with neighbouring tissues and control vessel maturation are beginning to emerge. Here, we review the most recent advances in lymphatic vascular development, with a major focus on mouse and zebrafish model systems.Katarzyna Koltowska, Kelly L. Betterman, Natasha L. Harvey and Benjamin M. Hoga