The discovery of nitric oxide (NO) as the endothelial-derived relaxing factor has led to significant research on NO and the proteins involved in its function, generation, location and regulation. Synthesis of NO by blood vessel endothelial cells results from the enzymatic oxidation of arginine by endothelial nitric oxide synthase (eNOS) resulting in the formation of equimolar amounts of NO and citrulline. Citrulline is sequentially recycled to arginine by successive reactions involving the enzymes argininosuccinate synthase (AS) and argininosuccinate lyase (AL), respectively. eNOS activity has been shown to be regulated by post-translational modifications including dynamic phosphorylation on multiple serine/threonine and tyrosine residues and dynamic O-linked beta-N-acetylglucosamine (O-GlcNAc) modifications on serine/threonine residues.Previous studies showed that even though intracellular endothelial arginine levels range from 0.1 to 0.8 mM and the Km of eNOS for arginine is 3 uM, the addition of exogenous arginine caused an increase in NO production. To explain this "arginine paradox" we hypothesize that there is a separate and distinct cellular source of arginine substrate directed to NO production and that this source is maintained through the regeneration of arginine via a citrulline-NO cycle. The presented research has provided the following evidence in support of this hypothesis: Citrulline stimulates NO production in an arginine-rich medium, without an increase in intracellular arginine. The enzymes of the citrulline-NO cycle, eNOS, AS and AL, co-fractionate with caveolin-1 in an endothelial cell caveolar membrane fraction. In vitro interaction assays demonstrate protein-protein interactions between fusion tagged AS or AL with eNOS or caveolin-1. Simultaneous monitoring of apparent citrulline and NO production demonstrates an efficient and essential coupling of the reactions of the citrulline-NO cycle. Glucosamine treatment of endothelial cells results in increased NO production in the basal state and decreased NO production in the stimulated state.Our findings demonstrate the enzymes of the citrulline-NO cycle, eNOS, AS and AL, are functionally associated, the reactions are efficiently coupled and enzyme activities are changed by post-translational modifications based on nutrient levels. These alterations ensure a constant and distinct source of arginine which is available for NO production to ensure vascular health.

Collagens are abundant components of the extracellular matrix in the atherosclerotic plaque. In addition to contributing to lesion volume and mechanical stability, collagens can influence the behavior of macrophages and smooth muscle cells (SMCs) and have profound effects on both inflammation and fibrosis during lesion development. The aim of this thesis was to define a functional role for the discoidin domain receptor 1 (DDR1), a collagen receptor tyrosine kinase, in murine models of atherogenesis. In our first study, using Ddr1+/+;Ldlr-/- and Ddr1-/-;Ldlr-/- mice fed a high fat diet, we identified DDR1 as a novel positive regulator of atherogenesis. Targeted deletion of DDR1 attenuated atherosclerotic plaque development by limiting inflammation and accelerating matrix accumulation and resulted in the formation of macrophage poor, matrix rich lesions. In the second study, we used bone marrow transplantation to generate chimeric mice with a deficiency of DDR1 in bone marrow derived cells and reveal a central role for macrophage DDR1 in atherogenesis. Deficiency of DDR1 in bone marrow derived cells reduced lesion size by limiting macrophage accumulation in the developing plaque. Moreover using BrdU pulse labeling, we demonstrated reduced monocyte recruitment into the early fatty streak lesions of Ddr1-/-;Ldlr-/- mice. In our third study, we again utilized bone marrow transplantation to generate mice with deficiency of DDR1 in the host derived tissues such as the vessel wall and uncovered a distinct role for DDR1 expressed on resident vessel wall smooth muscle cells in the regulation of matrix accumulation and fibrous cap formation during atherogenesis. Deficiency of DDR1 in vessel wall cells resulted in robust accumulation of collagen and elastin and resulted in the formation of larger atherosclerotic plaques, with thick fibrous caps. Taken together, these studies support a critical role for DDR1 in the development of the atherosclerotic plaque. We demonstrate that DDR1 exerts distinct and opposing effects on lesion size by regulating both monocyte recruitment and matrix accumulation. These studies underscore the importance of collagen signaling during atherogenesis, and identify DDR1 as a key transducer; providing signals that regulate both inflammation and fibrosis during atherogenesis.

Introduction: Inferior vena cava (IVC) malformations are extremely rare. Their impact with additional risk factors has not been well studied. Here, we present a case of a young female with absent IVC. She presented with an extensive left lower extremity (LLE) deep venous thrombosis (DVT) after starting oral contraceptives. Case: A 21-year-old female with no past medical history presented with progressively worsening back pain and LLE edema. Her only medication was combined oral contraceptive (OCP) which was started 4 months ago. Physical exam was significant for blue discoloration of her LLE extending from foot to thigh. The ultrasound showed multiple thrombi within the left common and deep femoral veins, left popliteal vein and left peroneal vein. The abdominal computerized tomography revealed the absence of an infrarenal IVC with collateral azygous, hemiazygous and prominent left gonadal veins. Occlusion by the thrombi extended from the left femoral vein to the left iliac vein. Some extension was noted into the right common iliac vein. She was treated with a catheter directed tissue plasminogen activator (tPA) infusion into the left iliac vein followed by continuous heparin infusion. Hypercoagulable testing was negative. While on heparin, she developed asymptomatic gross hematuria. CT urogram showed a significant dilation of the left gonadal vein, a large vein along the left psoas muscle draining into the left renal vein, and a mild enlargement of right gonadal vein. The urine analysis was negative for bacterial infection; but it contained a numerous amount of red blood cells and protein. Once the hematuria had resolved, she was discharged on apixaban. Her OCP was discontinued. Discussion: There have been several case reports describing IVC abnormalities associated with DVT. In our case, DVT was likely provoked by usage of OCP. Current guidelines would require provoked DVTs to be treat for at least 3-12 months with anticoagulation therapy. Case reports of IVC malformations illustrated that these patients are at high risk for DVT at baseline. Hence the underlying abnormality still poses a lifetime risk. Also, with abnormal venous vasculature, gross hematuria, proteinuria and the lack of other causes, we suspect underlying Nutcracker syndrome (NS). Her pelvic abdominal pain can also be attributed to pelvic congestion syndrome, which is commonly associated with NS. Conclusion: There are several questions that arise from this case including: selecting a type of contraceptive method; safety of direct thrombin inhibitors in patients with NS; indefinite direct thrombin inhibitors in young patients. Unfortunately, due to the rarity of this condition, no set guidelines are available on how to manage these individuals.

Vascular smooth muscle cells (SMCs) regulate vessel contraction but during diseases including atherosclerosis, SMCs undergo functional changes that contribute to pathology. Chronic inflammation in the vasculature exacerbates disease progression. Acute phase serum amyloid A (SAA) is up-regulated during inflammation and expressed in atherosclerotic lesions. Previous work in our laboratory demonstrated that SAA activates secretory phospholipase A2 group IIA (sPLA2), whose products impact cellular cholesterol homeostasis. It was hypothesized that SAA promotes cholesterol trafficking from the plasma membrane to the endoplasmic reticulum (ER) in an sPLA2-dependent manner. SAA induced SMC cholesterol accumulation in the ER. Levels of plasma membrane cholesterol decreased, confirming that cholesterol moved from the plasma membrane to the ER. Another family member, (cytosolic phospholipase A2, group IV), was also required for SAA-induced sPLA2 activation and cholesterol mobilization. SAA activated neutral sphingomyelinase and blocking this activity inhibited cholesterol trafficking. These studies show that SAA activated sPLA2 which activated neutral sphingomyelinase. As a result, sphingomyelin was cleaved, which liberated cholesterol for movement to the ER. Additional studies demonstrated that SAA repressed expression of SMC contractile markers including Acta2 and Myh11. Toll-like receptor 2 (TLR2) is an SAA receptor implicated in atherogenesis and it was hypothesized that TLR2 plays a role in SAA-mediated phenotype/gene changes. The TLR2 ligands, FSL and Pam3CSK4, down-regulated SMC contractile marker expression. Knockdown of TLR2 demonstrated that SAA-mediated phenotype modulation was TLR2-dependent. SAA, FSL, and Pam3CSK4 also induced mRNA expression of pro-inflammatory and adhesion genes, changes inhibited by TLR2 knockdown. SAA repressed activity of the αSMA promoter, demonstrating transcriptional regulation. Myocardin, a transcription factor required to drive expression of SMC contractile genes, was down-regulated by SAA and FSL. Myocardin overexpression abrogated SAA- and FSL-mediated repression of the αSMA and SM22α promoters. These studies demonstrate that SAA promoted a phenotypic switch through activation of TLR2 and down-regulation of myocardin expression. Taken together, novel SAA- and TLR2-mediated mechanisms of cholesterol trafficking and phenotypic modulation in SMCs are shown. Importantly, this work uncovers previously unknown effects of TLR2 signaling on vascular SMCs and provides a context by which TLR2 activation and lesion-associated SAA may promote atherosclerosis. / 2017-12-01T00:00:00Z

No description available.

Yes / Insulin resistance is associated with impaired endothelial regeneration in response to mechanical injury. We recently demonstrated that insulinlike growth factor–binding protein-1 (IGFBP1) ameliorated insulin resistance and increased nitric oxide generation in the endothelium. In this study, we hypothesized that IGFBP1 would improve endothelial regeneration and restore endothelial reparative functions in the setting of insulin resistance. In male mice heterozygous for deletion of insulin receptors, endothelial regeneration after femoral artery wire injury was enhanced by transgenic expression of human IGFBP1 (hIGFBP1). This was not explained by altered abundance of circulating myeloid angiogenic cells. Incubation of human endothelial cells with hIGFBP1 increased integrin expression and enhanced their ability to adhere to and repopulate denuded human saphenous vein ex vivo. In vitro, induction of insulin resistance by tumor necrosis factor α (TNFα) significantly inhibited endothelial cell migration and proliferation. Coincubation with hIGFBP1 restored endothelial migratory and proliferative capacity. At the molecular level, hIGFBP1 induced phosphorylation of focal adhesion kinase, activated RhoA and modulated TNFα-induced actin fiber anisotropy. Collectively, the effects of hIGFBP1 on endothelial cell responses and acceleration of endothelial regeneration in mice indicate that manipulating IGFBP1 could be exploited as a putative strategy to improve endothelial repair in the setting of insulin resistance. / Funded by a British Heart Foundation Clinical Research Training Fellowship for A.A. R.M.C. holds a British Heart Foundation Intermediate Clinical Research Fellowship. M.T.K. holds a British Heart Foundation Chair in Cardiology. S.B.W. holds a European Research Council Starting Grant.

Despite the advent of stents, intimal hyperplasia subsequent to vascular interventional procedures remains a major obstacle. Vascular smooth muscle cells (VSMC) play a critical role in the pathogenesis of intimal hyperplasia; therefore, regulation of VSMC gene expression is a logical intervention point. FXR1 is a muscle-enhanced RNA binding protein and its expression is increased in injured arteries. We have shown that modulation of FXR1 levels affects stability and abundance of inflammatory transcripts in VSMC, suggesting that FXR1 is a negative regulator of inflammation. RNA-sequencing analysis in FXR1-depleted human VSMC (hVSMC) identified a number of transcripts with decreased abundance, the overwhelming majority of which were associated with proliferation and cell division. This drives our hypothesis that FXR1 is involved in mitigating vascular disease by regulating inflammatory and proliferative mRNA in VSMC. The mRNA abundance and stability of a number of these transcripts was decreased in FXR1 depleted hVSMC, and RIP-sequencing demonstrated that FXR1 interacts with transcripts involved in cell cycle control, and stability of these transcripts is decreased with FXR1 depletion. FXR1-depleted cells showed decreased proliferation (p<0.05), however, an increase in β-galactosidase (p<0.05) and γH2AX (p<0.01), indicative of senescence was noted. Senescent cells exhibit a senescence associated secretory phenotype (SASP) with characteristic gene expression leading to increased inflammation in the tissue microenvironment. HVSMC depleted of FXR1 had increased transcripts abundance of many SASP genes, as well as an increase of both mRNA and protein expression of canonical senescence markers p53 and p21. We developed a novel SMC-specific conditional knockout mouse (FXR1SMC/SMC) to further study these results in a more translational context. In a carotid artery ligation model of intimal hyperplasia, FXR1SMC/SMC mice have significantly reduced neointima formation (p<0.001) post-ligation compared to controls. qPCR analysis from FXR1 conditional knockout mouse VSMC (mVSMC) show increased transcripts associated with senescence (p21, p16, p53) as well as increased SASP-associated mRNA, a decrease in proliferation, and an increase in β-galactosidase staining. Our results are the first to suggest that in addition to destabilization of inflammatory transcripts, FXR1 may stabilize cell cycle related genes in VSMC, and absence of FXR1 leads to induction of a senescent phenotype, an increase in SASP genes, and reduction of intimal hyperplasia. / Organ Systems & Translational Medicine

No description available.

Humans have two plasminogen activators (PAs), tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), which generate plasmin to breakdown fibrin and other barriers to cell migration. Both PAs are used as pharmaceuticals but their efficacies are limited by their rapid clearance from the circulation, predominantly by parenchymal cells of the liver. At the commencement of the work presented here, the hepatic receptors responsible for mediating the catabolism of the PAs were little understood. tPA degradation by hepatic cell lines was known to depend on the formation of binary complexes with the major PA inhibitor, plasminogen activator inhibitor type-1 (PAI-1). Initial studies presented here established that uPA was catabolised in a fashion similar to tPA by the hepatoma cell line, HepG2. Other laboratories around this time found that the major receptor mediating the binding and endocytosis of the PAs is Low Density Lipoprotein Receptor-related Protein (LRP1). LRP1 is a giant 600 kDa protein that binds a range of structurally and functionally diverse ligands including, activated α2 macroglobulin, apolipoproteins, β amyloid precursor protein, and a number of serpin-enzymes complexes, including PA??PAI-1 complexes. Further studies for the work presented here centred on this receptor. By using radiolabelled binding assays, ligand blots, and Western blots on cultured cells, the major findings are that: (1) basal LRP1 expression on HepG2 is low compared to a clone termed, HepG2a16, but appears to increase in long term culture; (2) a soluble form of LRP1, which retains ligand-binding capacity, is present in human circulation; (3) soluble LRP1 is also present in cerebral spinal fluid where its role in neurological disorders such as Alzheimer??s disease is a developing area of interest; and (4) the release of LRP1 is a mechanism conserved in evolution, possibly as distantly as molluscs. The discovery, identification, and characterisation of soluble LRP1 introduces this protein in the human circulation, and presents a possible further level of regulation for its associated receptor system.