Regulation of epithelial permeability by the actin cytoskeleton

The actin cytoskeleton is a dynamic structure necessary for cell and tissue organization, including the maintenance of epithelial barriers. The epithelial barrier regulates the movement of ions, macromolecules, immune cells and pathogens, and is thus essential for normal organ function. Disruption in the epithelial barrier has been shown to coincide with alterations of the actin cytoskeleton in several disease states. These disruptions primarily manifest as increased movement through the paracellular space, which is normally regulated by tight junctions. Despite extensive research demonstrating a direct link between the actin cytoskeleton and epithelial permeability, our understanding of the physiological mechanisms that link permeability and tight junction structure are still limited. In this review we explore the role of the actin cytoskeleton at tight junctions and present several areas for future study

Epithelial barrier assembly requires coordinated activity of multiple domains of the tight junction protein ZO-1

Tight junctions (TJs) regulate the paracellular movement of ions, macromolecules and immune cells across epithelia. Zonula occludens (ZO)-1 is a multi-domain polypeptide required for the assembly of TJs. MDCK II cells lacking ZO-1, and its homolog ZO-2, have three distinct phenotypes: reduced localization of occludin and some claudins to the TJs, increased epithelial permeability, and expansion of the apical actomyosin contractile array found at the apical junction complex (AJC). However, it is unclear exactly which ZO-1 binding domains are required to coordinate these activities. We addressed this question by examining the ability of ZO-1 domain-deletion transgenes to reverse the effects of ZO depletion. We found that the SH3 domain and the U5 motif are required to recruit ZO-1 to the AJC and that localization is a prerequisite for normal TJ and cytoskeletal organization. The PDZ2 domain is not required for localization of ZO-1 to the AJC, but is necessary to establish the characteristic continuous circumferential band of ZO-1, occludin and claudin-2. PDZ2 is also required to establish normal permeability, but is not required for normal cytoskeletal organization. Finally, our results demonstrate that PDZ1 is crucial for the normal organization of both the TJ and the AJC cytoskeleton. Our results establish that ZO-1 acts as a true scaffolding protein and that the coordinated activity of multiple domains is required for normal TJ structure and function

Wnt1/βcatenin injury response activates the epicardium and cardiac fibroblasts to promote cardiac repair: Wnt1/βcatenin injury response regulates cardiac repair

Wnts are required for cardiogenesis but the role of specific Wnts in cardiac repair remains unknown. In this report, we show that a dynamic Wnt1/βcatenin injury response activates the epicardium and cardiac fibroblasts to promote cardiac repair. Acute ischaemic cardiac injury upregulates Wnt1 that is initially expressed in the epicardium and subsequently by cardiac fibroblasts in the region of injury. Following cardiac injury, the epicardium is activated organ-wide in a Wnt-dependent manner, expands, undergoes epithelial–mesenchymal transition (EMT) to generate cardiac fibroblasts, which localize in the subepicardial space. The injured regions in the heart are Wnt responsive as well and Wnt1 induces cardiac fibroblasts to proliferate and express pro-fibrotic genes. Disruption of downstream Wnt signalling in epicardial cells decreases epicardial expansion, EMT and leads to impaired cardiac function and ventricular dilatation after cardiac injury. Furthermore, disruption of Wnt/βcatenin signalling in cardiac fibroblasts impairs wound healing and decreases cardiac performance as well. These findings reveal that a pro-fibrotic Wnt1/βcatenin injury response is critically required for preserving cardiac function after acute ischaemic cardiac injury

Mechanisms of Cardiovascular Development

Epithelial to mesenchymal transition (EMT) is an essential process during embryogenesis for the development of organ systems, including the heart and its vasculature. The development of both coronary vessels and heart valves depends on EMT. In this dissertation, we first present data demonstrating that increasedoligosaccharide hyaluronan (o-HA) levels after EMT induction within atrioventricular (AV) valves leads to a decrease in EMT due to the induction of VEGF expression. Regulated EMT inhibition prevents the formation of hyperplastic valves. Next, we show that the proepicardium, which provides the precursor cells required for epicardial and coronary vessel development, migrates to the developing heart via direct contact of multicellular proepicardial villi to the developing myocardium. This shifts the paradigm from a migration consisting of floating cysts to one of direct contact and differential adhesion forces to form the initial epicardium. A subset of epicardial cells undergoes EMT, migrates into the developing heart, and differentiates into cardiac fibroblast, vascular endothelial, and smooth muscle cells. In order to more effectively study epicardial EMT in vitro, we developed several new methods for the in vitro study of coronary vessel development. We developed an improved protocol for isolating embryonic myocyte cells, for use in co-cultures with epicardial cells. This co-culture system allows investigation into the effects of myocyte derived soluble factors uponepicardial EMT and mesenchymal cell differentiation. We also present a protocol for isolating epicardial clonal colonies from an epicardial cell line derived from the ImmortoMouse. These clones provided direct evidence that the epicardium is a heterogeneous population of cells. These unique clones allow for to study into specific epicardial cell lineages and phenotypes. Finally, we provide data defining the expression of Wnts within the developing heart and the role may play during epicardial EMT. We conclude that canonical Wnts are both necessary and sufficient to inhibit epicardial EMT. These results provide the first direct evidence for a role of Wnt proteins during coronary vessel development. Collectively our results provide significant advancements in our understanding of EMT regulation during cardiac development

Measuring Distress Risk: The Effect of R&D Intensity

Because of upward trends in research and development activity, accounting measures of financial distress have become less accurate. We document that (1) higher research and development spending increases the likelihood of misclassifying solvent firms, (2) adjusting for conservative accounting of research and development increases the number of correctly identified distressed firms, and (3) adjusted measures of distress alleviate previously documented anomalously low returns of large, high distress risk, low book-to-market firms. The results hold after updating stale parameters and under various tax assumptions. Our evidence raises concerns about interpretation of extant literature that relies on accounting measures of distress. Copyright 2007 by The American Finance Association.

Where Is Garlic Mustard? Understanding the Ecological Context for Invasions of \u3ci\u3eAlliaria petiolata\u3c/i\u3e

The invasive plant Alliaria petiolata (garlic mustard) has spread throughout forest understory and edge communities in much of North America, but its persistence, density, and impacts have varied across sites and time. Surveying the literature since 2008, we evaluated both previously proposed and new mechanisms for garlic mustard\u27s invasion success and note how they interact and vary across ecological contexts. We analyzed how and where garlic mustard has been studied and found a lack of multisite and longitudinal studies, as well as regions that may be under- or overstudied, leading to poor representation for understanding and predicting future invasion dynamics. Inconsistencies in how sampling units are scaled and defined can also hamper our understanding of invasive species. We present new conceptual models for garlic mustard invasion from a macrosystems perspective, emphasizing the importance of synergies and feedbacks among mechanisms across spatial and temporal scales to produce variable ecological contexts

Review of Organic Wastewater Compound Concentrations and Removal in Onsite Wastewater Treatment Systems

Onsite wastewater treatment systems, such as septic systems, serve 20% of U.S. households and are common in areas not served by wastewater treatment plants (WWTPs) globally. They can be sources of nutrients and pathogen pollution and have been linked to health effects in communities where they contaminate drinking water. However, few studies have evaluated their ability to remove organic wastewater compounds (OWCs) such as pharmaceuticals, hormones, and detergents. We synthesized results from 20 studies of 45 OWCs in conventional drainfield-based and alternative onsite wastewater treatment systems to characterize concentrations and removal. For comparison, we synthesized 31 studies of these same OWCs in activated sludge WWTPs. OWC concentrations and removal in drainfields varied widely and depended on wastewater sources and compound-specific removal processes, primarily sorption and biotransformation. Compared to drainfields, alternative systems had similar median and higher maximum concentrations, reflecting a wider range of system designs and redox conditions. OWC concentrations and removal in drainfields were generally similar to those in conventional WWTPs. Persistent OWCs in groundwater and surface water can indicate the overall extent of septic system impact, while the presence of well-removed OWCs, such as caffeine and acetaminophen, may indicate discharges of poorly treated wastewater from failing or outdated septic systems