Mechanobiology of the Aortic Valve Interstitial Cell

The aortic valve (AV) is essentially a passive organ that permits unidirectional blood flow from the left ventricle to the systemic circulation and prohibits regurgitant flow during diastole. The extracellular matrix (ECM) of the AV leaflet is tri-layered with type I collagen making up the fibrosa layer (aortic side), glycosaminoglycans constituting the middle spongiosa layer, and elastin fibers largely in the ventricularis layer. Each component of the ECM is synthesized, enzymatically degraded, and maintained by the resident population of interstitial cells (AVICs) dispersed throughout the leaflet. The AVICs have been recognized as a heterogeneous mix of cells which include fibroblasts, smooth muscle cells, and myofibroblasts, which have characteristics of both fibroblasts and smooth muscle cells but are unique from each. The hypothesis of this dissertation is that the phenotype and function of the AVIC is predicated on the mechanical environment in which it resides, and during times of activated remodeling (increased myofibroblasts), the mechanobiological response of the AVIC may be contributor to changes in valvular tissue integrity. To test this hypothesis, we examine 1) the mechanical properties of the AVIC and the correlation to biosynthesis, 2) the strong connectivity of the AVIC to the ECM which is demonstrated by the AVICs ability to generate tissue-level forces due to contraction, 3) potential tissue remodeling capabilities of the AVIC via collagen gel contraction, 4) the micromechanics of the AVIC to increasing strain levels, and 5) synergistic response of the in situ AVIC to TGF-â1 and cyclic strain.Results from this work highlight the mechanobiological properties of the AVIC myofibroblast phenotype and its role in valvular tissue homeostasis, remodeling, and dysfunction. Moreover, these results demonstrate the unexamined mechanical properties of the AVIC and the strong correlate with ECM biosynthesis. As the AVIC is situated in a tissue with large strains and varying modes of deformation, the mechanical properties of the cell are likely prominent in their function. We believe that these results will add to the growing body of AVIC literature and further believe that our focus on the AVIC micro-mechanical environment will be very relevant to understanding the mechanobiologic function of the AVIC

Measuring the Duration of Judicial and Administrative Proceedings

A method of estimating the probable duration of litigation is useful for a variety of purposes. First, the probable duration of a case may, to some extent, determine strategy in litigation since prolonged litigation is often perceived as an appreciable cost to one party and as a benefit to the other. An estimate of the duration of a criminal case, for example, probably influences the respective postures of a defendant and a prosecutor in plea bargaining. Similarly, civil litigants may be able to use an estimate of the probable duration of litigation, together with other factors, in deciding whether to sue, defend, or settle. Second, a forecast of the probable duration of litigation may help improve the efficiency of our judicial system. On a general level,such an estimate provides information needed in the formation of policy for judicial administration. More specifically, it may help determine the relative efficiency of various courts and administrative tribunals in adjudicating different types of cases and thus provide a valuable aid in assigning cases and staffing courts and tribunals. Finally, the estimate may be useful in the study of law and social change. The duration of litigation is one quantitative measure of legal activity that, in combination with other legal, social, economic and political data, may permit the development of hypotheses about law and society that can be tested empirically. In this way, an index of the duration of litigation may prove to be a basic working tool for an empirical social science of the law

5-HT2B antagonism arrests non-canonical TGF-β1-induced valvular myofibroblast differentiation

Transforming growth factor-β1 (TGF-β1) induces myofibroblast activation of quiescent aortic valve interstitial cells (AVICs), a differentiation process implicated in calcific aortic valve disease (CAVD). The ubiquity of TGF-β1 signaling makes it difficult to target in a tissue specific manner; however, the serotonin 2B receptor (5-HT2B) is highly localized to cardiopulmonary tissues and agonism of this receptor displays pro-fibrotic effects in a TGF-β1-dependent manner. Therefore, we hypothesized that antagonism of 5-HT2B opposes TGF-β1-induced pathologic differentiation of AVICs and may offer a druggable target to prevent CAVD. To test this hypothesis, we assessed the interaction of 5-HT2B antagonism with canonical and non-canonical TGF-β1 pathways to inhibit TGF-β1-induced activation of isolated porcine AVICs in vitro. Here we show that AVIC activation and subsequent calcific nodule formation is completely mitigated by 5-HT2B antagonism. Interestingly, 5-HT2B antagonism does not inhibit canonical TGF-β1 signaling as identified by Smad3 phosphorylation and activation of a partial plasminogen activator inhibitor-1 promoter (PAI-1, a transcriptional target of Smad3), but prevents non-canonical p38 MAPK phosphorylation. It was initially suspected that 5-HT2B antagonism prevents Src tyrosine kinase phosphorylation; however, we found that this is not the case and time-lapse microscopy indicates that 5-HT2B antagonism prevents non-canonical TGF-β1 signaling by physically arresting Src tyrosine kinase. This study demonstrates the necessity of non-canonical TGF-β1 signaling in leading to pathologic AVIC differentiation. Moreover, we believe that the results of this study suggest 5-HT2B antagonism as a novel therapeutic approach for CAVD that merits further investigation

Serotonin receptors and heart valve disease—It was meant 2B

Carcinoid heart disease was one of the first valvular pathologies studied in molecular detail, and early research identified serotonin produced by oncogenic enterochromaffin cells as the likely culprit in causing changes in heart valve tissue. Researchers and physicians in the mid-1960s noted a connection between the use of several ergot-derived medications with structures similar to serotonin and the development of heart valve pathologies similar to those observed in carcinoid patients. The exact serotonergic target that mediated valvular pathogenesis remained a mystery for many years until similar cases were reported in patients using the popular diet drug Fen-Phen in the late 1990s. The Fen-Phen episode sparked renewed interest in serotonin-mediated valve disease, and studies led to the identification of the 5-HT2B receptor as the likely molecular target leading to heart valve tissue fibrosis. Subsequent studies have identified numerous other activators of the 5-HT2B receptor, and consequently, the use of many of these molecules has been linked to heart valve disease. Herein, we: review the molecular properties of the 5-HT2B receptor including factors that differentiate the 5-HT2B receptor from other 5-HT receptor subtypes, discuss the studies that led to the identification of the 5-HT2B receptor as the mediator of heart valve disease, present current efforts to identify potential valvulopathogens by screening for 5-HT2B receptor activity, and speculate on potential therapeutic benefits of 5-HT2B receptor targeting

The Global Dominance of European Competition Law Over American Antitrust Law

The world’s biggest consumer markets – the European Union and the United States – have adopted different approaches to regulating competition. This has not only put the EU and US at odds in high-profile investigations of anticompetitive conduct, but also made them race to spread their regulatory models. Using a novel dataset of competition statutes, we investigate this race to influence the world’s regulatory landscape and find that the EU’s competition laws have been more widely emulated than the US’s competition laws. We then argue that both “push” and “pull” factors explain the appeal of the EU’s competition regime: the EU actively promotes its model through preferential trade agreements and has an administrative template that is easy to emulate. As EU and US regulators offer competing regulatory models in domains as diverse as privacy, finance, and environmental protection, our study sheds light on how global regulatory races are fought and won

The Structure of a Rigorously Conserved RNA Element within the SARS Virus Genome

We have solved the three-dimensional crystal structure of the stem-loop II motif (s2m) RNA element of the SARS virus genome to 2.7-Å resolution. SARS and related coronaviruses and astroviruses all possess a motif at the 3′ end of their RNA genomes, called the s2m, whose pathogenic importance is inferred from its rigorous sequence conservation in an otherwise rapidly mutable RNA genome. We find that this extreme conservation is clearly explained by the requirement to form a highly structured RNA whose unique tertiary structure includes a sharp 90° kink of the helix axis and several novel longer-range tertiary interactions. The tertiary base interactions create a tunnel that runs perpendicular to the main helical axis whose interior is negatively charged and binds two magnesium ions. These unusual features likely form interaction surfaces with conserved host cell components or other reactive sites required for virus function. Based on its conservation in viral pathogen genomes and its absence in the human genome, we suggest that these unusual structural features in the s2m RNA element are attractive targets for the design of anti-viral therapeutic agents. Structural genomics has sought to deduce protein function based on three-dimensional homology. Here we have extended this approach to RNA by proposing potential functions for a rigorously conserved set of RNA tertiary structural interactions that occur within the SARS RNA genome itself. Based on tertiary structural comparisons, we propose the s2m RNA binds one or more proteins possessing an oligomer-binding-like fold, and we suggest a possible mechanism for SARS viral RNA hijacking of host protein synthesis, both based upon observed s2m RNA macromolecular mimicry of a relevant ribosomal RNA fold

Deficient Signaling via Alk2 (Acvr1) Leads to Bicuspid Aortic Valve Development

Bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly in humans. Despite recent advances, the molecular basis of BAV development is poorly understood. Previously it has been shown that mutations in the Notch1 gene lead to BAV and valve calcification both in human and mice, and mice deficient in Gata5 or its downstream target Nos3 have been shown to display BAVs. Here we show that tissue-specific deletion of the gene encoding Activin Receptor Type I (Alk2 or Acvr1) in the cushion mesenchyme results in formation of aortic valve defects including BAV. These defects are largely due to a failure of normal development of the embryonic aortic valve leaflet precursor cushions in the outflow tract resulting in either a fused right- and non-coronary leaflet, or the presence of only a very small, rudimentary non-coronary leaflet. The surviving adult mutant mice display aortic stenosis with high frequency and occasional aortic valve insufficiency. The thickened aortic valve leaflets in such animals do not show changes in Bmp signaling activity, while Map kinase pathways are activated. Although dysfunction correlated with some pro-osteogenic differences in gene expression, neither calcification nor inflammation were detected in aortic valves of Alk2 mutants with stenosis. We conclude that signaling via Alk2 is required for appropriate aortic valve development in utero, and that defects in this process lead to indirect secondary complications later in life

Transcriptomic analysis of the temporal host response to skin infestation with the ectoparasitic mite Psoroptes ovis

<p>Abstract</p> <p>Background</p> <p>Infestation of ovine skin with the ectoparasitic mite <it>Psoroptes ovis </it>results in a rapid cutaneous immune response, leading to the crusted skin lesions characteristic of sheep scab. Little is known regarding the mechanisms by which such a profound inflammatory response is instigated and to identify novel vaccine and drug targets a better understanding of the host-parasite relationship is essential. The main objective of this study was to perform a combined network and pathway analysis of the <it>in vivo </it>skin response to infestation with <it>P. ovis </it>to gain a clearer understanding of the mechanisms and signalling pathways involved.</p> <p>Results</p> <p>Infestation with <it>P. </it>ovis resulted in differential expression of 1,552 genes over a 24 hour time course. Clustering by peak gene expression enabled classification of genes into temporally related groupings. Network and pathway analysis of clusters identified key signalling pathways involved in the host response to infestation. The analysis implicated a number of genes with roles in allergy and inflammation, including pro-inflammatory cytokines (<it>IL1A, IL1B, IL6, IL8 </it>and <it>TNF</it>) and factors involved in immune cell activation and recruitment (<it>SELE, SELL, SELP, ICAM1, CSF2, CSF3, CCL2 </it>and <it>CXCL2</it>). The analysis also highlighted the influence of the transcription factors NF-kB and AP-1 in the early pro-inflammatory response, and demonstrated a bias towards a Th2 type immune response.</p> <p>Conclusions</p> <p>This study has provided novel insights into the signalling mechanisms leading to the development of a pro-inflammatory response in sheep scab, whilst providing crucial information regarding the nature of mite factors that may trigger this response. It has enabled the elucidation of the temporal patterns by which the immune system is regulated following exposure to <it>P. ovis</it>, providing novel insights into the mechanisms underlying lesion development. This study has improved our existing knowledge of the host response to <it>P. ovis</it>, including the identification of key parallels between sheep scab and other inflammatory skin disorders and the identification of potential targets for disease control.</p