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Open Access Publications from the University of California

Scholarly Works (67 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2021)

Despite advances in our understanding of cardiovascular risk factors, cardiovascular disease (CVD) continues to be the leading cause of mortality worldwide. The underlying pathology involved in many forms of CVD is atherosclerosis, a condition characterized by lipid deposition and chronic inflammation within the arterial wall of large blood vessels. The aorta is the largest artery of the body and subjected to significant physical forces due to the pressure of blood emanating from the heat. In this manner, distinct areas of the aorta are subjected to oscillatory, laminar, disturbed, and pulsatile flow due to their shape and proximity to the heart. Regions that experience oscillatory or “disturbed” blood flow are prone to developing atherosclerotic plaques whereas regions that experience uniform laminar flow are athero-protected. Further understanding of how different flow dynamics impact the tunica intima during homeostasis will help clarify the differential impact of distinct types of physiological shear stresses and the unique region-specific susceptibilities to disease development. Here, we show that the closure of the ductus arteriosus immediately post-birth initiates drastic hemodynamic changes in the aorta. Using single-cell RNA-sequencing, we found that the closure of the ductus arteriosus requires vimentin, the most abundant intermediate filament in vascular cells. Deletion of vimentin in mice caused patent ductus arteriosus, a congenital heart defect where the ductus fails to close. Additionally, we identified a tissue-resident macrophage population that is not pathologically induced, instead it is developmentally programmed to cope with the natural hemodynamic changes at birth that result in localized disturbed flow dynamics. This aortic intima-resident macrophage (MacAIR) population shares the luminal surface with the endothelium becoming interwoven in the tunica intima. Moreover, we found that MacAIRs are essential to regulate thrombin activity and clear fibrin deposits in regions of turbulent blood flow. Infection with SARS-Cov-2 also promoted rapid loss of intimal macrophages and robust accumulation of intravascular fibrin on the surface of the endothelium in infected rhesus macaque. These findings advance our knowledge of how vascular endothelial cells profit from this unique interaction with macrophages to preserve a non-thrombogenic surface, prevent intravascular clotting, and ensure vascular health.

    Cover page: Aortic intimal resident macrophages are essential for maintenance of the non-thrombogenic intravascular state
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (1993)
    Transforming growth factor-beta 1 (TGF-beta 1) has been implicated in the positive regulation of angiogenesis in vivo, whereas it inhibits the proliferation of endothelial cells in vitro. To reconcile these apparently contradictory effects, we have investigated the effect of TGF-beta 1 on bovine aortic endothelial cells that exhibit spontaneous angiogenesis in vitro. We show that concentrations of TGF-beta 1 which stimulate proliferation of cells that form endothelial cords and/or tubes inhibit proliferation of the same cells grown at subconfluent densities. An increase in cell number of 35% over control cultures was achieved with 0.5 ng TGF-beta 1/ml. The proliferative effect was blocked by antibodies against TGF-beta. Immunological detection of BrdU-labeled nuclei revealed an increase greater than 220% in cells treated with TGF-beta 1. Moreover, a population of cells within the cords appeared to be a selective target for this cytokine. The stimulatory effect was not restricted to bovine aortic endothelial cells, as similar results were obtained with endothelial cells derived from rat microvessels. Significant levels of active TGF-beta 1 were detected in cultures containing cords/tubes, whereas only latent TGF-beta 1 was detected in subconfluent cultures. We show further that endothelial cells exhibiting angiogenesis in vitro secrete plasminogen activator, an enzyme that regulates activation of TGF-beta. The major increases in mRNA transcripts for extracellular matrix proteins that are typically associated with TGF-beta 1 were not seen in cells exhibiting angiogenesis in vitro. Since the formation of tubular networks requires both invasion and proliferation, we propose that TGF-beta 1 is a major morphoregulatory factor in angiogenesis that specifically controls endothelial cell proliferation and extracellular matrix turnover.
      Cover page: Endothelial cells exhibiting angiogenesis in vitro proliferate in response to TGF‐β1
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2014)
      The distribution and patterning of blood vessels is controlled by vascular endothelial growth factor (VEGF), which is precisely regulated throughout its life cycle. Okabe et al. show that VEGF is titrated away from the endothelium by adjacent neurons via endocytosis, regulating density and trajectory of blood vessels.
        • Thesis
        • Peer Reviewed
        UCLA Electronic Theses and Dissertations (2014)

        Vascular Endothelial Growth Factor (VEGF) is a potent endothelial cytokine and mitogen that directs the development of vasculature. Canonical VEGF signaling is a well described phenomenon whereby hypoxic tissues secrete VEGF, which then diffuses to surrounding VEGF- specific receptors. Interaction of VEGF and its receptors stimulates growth of the vascular system, through vasculogenic and angiogenic processes. Once formed, the circulatory system allows for the delivery of oxygen and nutrients to all tissues in the body. Blockade of VEGF signaling is used in the clinic to impede angiogenesis in some cancer settings, which suppresses tumor load by limiting the available blood supply required for survival and metastasis. However, patients treated with anti-VEGF therapy are beset by unexpected cardiovascular side-effects that suggest other non-canonical functions of VEGF protein. Here we identify several novel non-canonical roles for VEGF in the developing embryo heart and in the adult endothelium.

        In embryogenesis, VEGF receptors are expressed in diverse tissues apart from the inner layer of the vasculature, which indicates that these tissues respond to VEGF in a non-canonical manner. Using a chimera approach, we found evidence that VEGF takes part in cardiac chamber specification of the ventricles, which was further demonstrated with VEGF gain- and loss-of-function genetic models. Because VEGF is implicated in early cardiomyocyte differentiation, we investigated the expression patterns of VEGF's major receptor (VEGFR2) throughout cardiogenesis with a reporter mouse model. We identified subsets of cardiomyocytes that express VEGFR2 in the atrial septum and the primordial conduction system.

        VEGF is expressed by the adult endothelium, and is essential for a non-canonical pathway that promotes homeostasis via autocrine signaling. Using mouse models and primary human cell culture, we were able to demonstrate that endothelial VEGF maintains cell survival through constitutive suppression of the transcription factor Foxo1. In the absence of VEGF, cellular Foxo1 levels increase and causes deregulation of cell metabolism and autophagy, which ultimately induces cell death.

        Together, this work describes several novel non-canonical roles for VEGF in the heart, and further elucidates the molecular mechanisms behind autocrine VEGF signaling in the endothelium. These findings expand our understanding of the basic biology of VEGF and expose potential limitations for the use of anti-VEGF blockade in human patients.

          Cover page: Novel Vascular Endothelial Growth Factor Signaling in Heart Development and Endothelial Homeostasis
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2015)

          Summary

          The signaling specificity conveyed by distinct combination of NOTCH receptors/ligands has remained elusive. In this issue of Cancer Discovery, through the development of ligand-specific NOTCH inhibitors, Kangsamaksin and colleagues uncovered unique signaling outcomes downstream of DLL- and JAG-receptor activation and demonstrated their effects in the suppression of tumor angiogenesis.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2014)
            Expansion of a vascular network requires breaking through the basement membrane, a highly crosslinked barrier that tightly adheres to mature vessels. Angiogenic endothelial cells are now shown to form podosome rosettes that are able to focally degrade the extracellular matrix, prior to vascular sprouting in tumour angiogenesis.
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2015)
              Thrombosis and restenosis are the most prevalent late complications of coronary artery stenting. Current standards of clinical care focus on prevention of smooth muscle cell proliferation by the use of drug-eluting stents able to release anti-proliferative drugs. Unfortunately, these drugs also block endothelial cell proliferation and, in this manner, prevent recovery of endothelial cell coverage. Continued lack of endothelial repair leaves the root cause of thrombosis and restenosis unchanged, creating a vicious cycle where drug-mediated prevention of restenosis simultaneously implies promotion of thrombosis. In this issue of Vascular Pharmacology, Hussner and colleagues provide in vitro evidence and a mechanistic basis for the use of atorvastatin in stents as a way to bypass this roadblock. Here we review the pathological mechanisms and therapeutic approaches to restore flow in occluded arteries. We argue that rational design of drug eluting stents should focus on specific inhibition of smooth muscle cell proliferation with concurrent stimulation of endothelial regeneration. We comment on the current poor understanding of the cellular and molecular regulation of endothelial cell proliferation in the context of a functional artery, and on the pitfalls of extrapolating from the well-studied process of neovascularization by sprouting vessel formation.
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2016)
                The link between signaling and metabolism was first recognized with insulin signal transduction. Efficient glucose uptake by the endothelium requires insulin receptor activation to deliver GLUT receptors to the cell surface. More recently however, additional evidence has emerged for a broader crosstalk as signaling events have been shown to regulate a large number of metabolic enzymes. Changes in the metabolic status of endothelial and smooth muscle cells are observed at times of increased proliferative activity and these coincide with activation of cell surface receptors. Intriguingly, a rise in glycolysis appears to be associated with remodeling of the actin cytoskeleton during migration and angiogenesis. Overall, understanding how do signaling and metabolic pathways intersect and cross-regulate each other has become an important question and an emerging cornerstone in vascular biology.
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2018)

                  Purpose of review

                  The formation of a hierarchical vascular network is a complex process that requires precise temporal and spatial integration of several signaling pathways. Amongst those, Notch has emerged as a key regulator of multiple steps that expand from endothelial sprouting to arterial specification and remains relevant in the adult. This review aims to summarize major concepts and rising hypotheses on the role of Notch signaling in the endothelium.

                  Recent findings

                  A wealth of new information has helped to clarify how Notch signaling cooperates with other pathways to orchestrate vascular morphogenesis, branching, and function. Endothelial vascular endothelial growth factor, C-X-C chemokine receptor type 4, and nicotinamide adenine dinucleotide phosphate oxidase 2 have been highlighted as key regulators of the pathway. Furthermore, blood flow forces during vascular development induce Notch1 signaling to suppress endothelial cell proliferation, enhance barrier function, and promote arterial specification. Importantly, Notch1 has been recently recognized as an endothelial mechanosensor that is highly responsive to the level of shear stress to enable differential Notch activation in distinct regions of the vessel wall and suppress inflammation.

                  Summary

                  Although it is well accepted that the Notch signaling pathway is essential for vascular morphogenesis, its contributions to the homeostasis of adult endothelium were uncovered only recently. Furthermore, its exquisite regulation by flow and impressive interface with multiple signaling pathways indicates that Notch is at the center of a highly interactive web that integrates both physical and chemical signals to ensure vascular stability.
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (1992)
                    Type VIII collagen was initially characterized as a biosynthetic product of bovine aortic endothelial cells in vitro and thus named Endothelial Collagen(EC). The protein has now been identified in avian and mammalian species as a product secreted by cultured corneal endothelial cells, keratinocytes, fibroblasts, astrocytoma and other tumor cells, and endothelial cells derived from several classes of blood vessels. In vivo, the distribution of type VIII collagen is restricted to specialized extracellular matrices such as meninges, periosteum, perichondrium, and Descemet's membrane of the cornea. It is also present in the subendothelium of large and small blood vessels and has been localized in capillary-like structures formed by sprouting cultures of endothelial cells. Data from protein and nucleotide sequencing have identified two distinct chains, termed α1 (VIII) and α2 (VIII); however, the assembly of these chains in the extracellular space is still poorly understood. Protein extracts from Descemet's membrane indicate that, in this tissue, type VIII collagen is a heterotrimer. Our understanding of the biological role of type VIII collagen is rather limited. Although type VIII collagen seems to perform a structural role in the Descemet's membrane, its temporally and spatially restricted expression during development suggests an involvement in tissue remodeling and differentiation.
                      Cover page: Structure and Biology of Type VIII Collagen
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