Platelets: Implications in Aortic Valve Stenosis and Bioprosthetic Valve Dysfunction From Pathophysiology to Clinical Care

Aortic stenosis (AS) is the most common heart valve disease requiring surgery in developed countries, with a rising global burden associated with aging populations. The predominant cause of AS is believed to be driven by calcific degeneration of the aortic valve and a growing body of evidence suggests that platelets play a major role in this disease pathophysiology. Furthermore, platelets are a player in bioprosthetic valve dysfunction caused by their role in leaflet thrombosis and thickening. This review presents the molecular function of platelets in the context of recent and rapidly evolving understanding the role of platelets in AS, both of the native aortic valve and bioprosthetic valves, where there remain concerns about the effects of subclinical leaflet thrombosis on long-term prosthesis durability. This review also presents the role of antiplatelet and anticoagulation therapies on modulating the impact of platelets on native and bioprosthetic aortic valves, highlighting the need for further studies to determine whether these therapies are protective and may increase the life span of surgical and transcatheter aortic valve implants. By linking molecular mechanisms through which platelets drive disease of native and bioprosthetic aortic valves with studies evaluating the clinical impact of antiplatelet and antithrombotic therapies, we aim to bridge the gaps between our basic science understanding of platelet biology and their role in patients with AS and ensuing preventive and therapeutic implications.

Nanopore sequencing and its application to the study of microbial communities

Since its introduction, nanopore sequencing has enhanced our ability to study complex microbial samples through the possibility to sequence long reads in real time using inexpensive and portable technologies. The use of long reads has allowed to address several previously unsolved issues in the field, such as the resolution of complex genomic structures, and facilitated the access to metagenome assembled genomes (MAGs). Furthermore, the low cost and portability of platforms together with the development of rapid protocols and analysis pipelines have featured nanopore technology as an attractive and ever-growing tool for real-time in-field sequencing for environmental microbial analysis. This review provides an up-to-date summary of the experimental protocols and bioinformatic tools for the study of microbial communities using nanopore sequencing, highlighting the most important and recent research in the field with a major focus on infectious diseases. An overview of the main approaches including targeted and shotgun approaches, metatranscriptomics, epigenomics, and epitranscriptomics is provided, together with an outlook to the major challenges and perspectives over the use of this technology for microbial studies.

Spatial distribution of functional components in the starchy endosperm of wheat grains

The starchy endosperm of the mature wheat grain comprises three major cell types, namely sub-aleurone cells, prismatic cells and central cells, which differ in their contents of functional components: gluten proteins, starch, cell wall polysaccharides (dietary fibre) and lipids. Gradients are established during grain development but may be modified during grain maturation and are affected by plant nutrition, particularly nitrogen application, and environmental factors. Although the molecular controls of their formation are unknown, the high content of protein and low content of starch of sub-aleurone cells, compared to the other starchy endosperm cells types, may result from differences in developmental programming related to the cells having a separate origin (from anticlinal division of the aleurone cells). The gradients within the grain may be reflected in differences in the compositions of mill streams, particularly those streams enriched in the central and outer cells of the starchy endosperm, respectively, allowing the production of specialist flours for specific end uses.

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The mature starchy endosperm of wheat comprises three cell types.

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These differ in their contents of functional components.

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These differences are reflected in the compositions of mill streams.

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These differences may affect functionality.

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Hence innovative milling can be used to prepare flours for special uses.

Long walk to genomics: History and current approaches to genome sequencing and assembly

Genomes represent the starting point of genetic studies. Since the discovery of DNA structure, scientists have devoted great efforts to determine their sequence in an exact way. In this review we provide a comprehensive historical background of the improvements in DNA sequencing technologies that have accompanied the major milestones in genome sequencing and assembly, ranging from early sequencing methods to Next-Generation Sequencing platforms. We then focus on the advantages and challenges of the current technologies and approaches, collectively known as Third Generation Sequencing. As these technical advancements have been accompanied by progress in analytical methods, we also review the bioinformatic tools currently employed in de novo genome assembly, as well as some applications of Third Generation Sequencing technologies and high-quality reference genomes.

Trimellitic anhydride induces low-grade mast cell degranulation without specific IgE

Objectives

Low-molecular-weight (LMW) substances are known to be causative agents of occupational asthma (OA) and occupational rhinitis (OR). Although most LMW substances are irritants or allergens, some can cause immediate type immunoglobulin E (IgE)-mediated allergic reactions. Trimellitic anhydride (TMA) is one such LMW substance, which is known as an immunological sensitizer. However, the exact molecular biological details of the effects of TMA remain unclear.

Methods

We measured the β-hexosaminidase release from mast cells after directly exposing the cells to various LMW substances. The tyrosine phosphorylation of whole cellular molecules and the phosphorylation of extracellular signal-regulated kinase (ERK) were assessed by immunoblot assay.

Results

Among the LMW substances tested, only TMA induced β-hexosaminidase release. However, the mast cell degranulation induced by TMA was lower than that induced by an antigen or a calcium ionophore. Moreover, the pattern of tyrosine phosphorylation of whole cellular molecules was quite different between IgE-mediated antigen stimulation and TMA exposure. The TMA effect on mast cells was independent of not only IgE but also Ca²⁺ influx. ERK phosphorylation was not detected in mast cells exposed to TMA.

Conclusions

TMA induced mild degranulation of mast cells without IgE, even though the phosphorylation of ERK was not detected. This reaction suggests that TMA affects humans even upon first exposure. Therefore, it is imperative to avoid human exposure to high concentrations of TMA. In order to stop the development of severe asthma in individuals with OR, we need to be able to identify cases of OR caused by TMA as soon as possible.

Cathepsin-L and transglutaminase dependent processing of ps20: A novel mechanism for ps20 regulation via ECM cross-linking

Whey-acidic-protein (WAP) four-disulphide core (WFDC) proteins have important roles in the regulation of innate immunity, anti-microbial function, and the inhibition of inflammatory proteases at mucosal surfaces. It was recently demonstrated that the WFDC protein, prostate stromal 20 (ps20), encoded by the WFDC1 gene, is a potent growth inhibitory factor, and shares with other WFDC proteins the ability to modulate wound healing processes and immune responses to viral infections. However, ps20 remains relatively uncharacterised at the protein level. Using a panel of ps20 antibodies for western-blotting (WB), ELISA and immunoaffinity purification, we isolated, biochemically characterised and tested ps20 preparations for three biological properties: (i) interactions with glycosaminoglycans (GAG) (ii) inhibition of cell proliferation, and (iii) transglutaminase2 (TG2) mediated crosslinking of ps20 to fibronectin, a process implicated in wound healing. We show herein that ps20 preparations contain multiple molecular forms including full-length ps20 (resolving at ≈27 kDa), an exon 3 truncated form (≈22 kDa) that lacks aa113-140, and variable amounts of a putatively cleaved lower MW (≈15-17 kDa) species. Untagged purified ps20 preparations containing a mixture of these forms are biologically active in significantly suppressing prostate cell proliferation. We show that one mechanism by which lower LMW forms of ps20 arise is through cathepsin L (CL) cleavage, and confirm that CL cleaves ps20 at the C-terminus, but this does not inhibit its growth inhibitory function. However, CL cleavage abrogated the interaction between ps20 and solid-phase fibronectin. Therefore, we demonstrate for the first time that LMW forms of ps20 that lack a C-terminal immunogenic epitope can arise through CL cleavage and this cleavage impairs multimerisation and potential capacity to cross-link to ECM, but not the capacity of ps20 to inhibit cell proliferation. We propose that ps20 like other WFDC proteins can become associated with GAGs and the ECM. Furthermore, we suggest post-translational processing and cleavage of ps20 is required to generate functional protein species, and TG2 mediated crosslinking and CL cleavage form components of a ps20 regulatory apparatus.

Normal menstrual cycle steroid hormones variation does not affect the blood levels of total adiponectin and its multimer forms

Objective

Plasma total adiponectin reveals a sexual dimorphism indicating that gonadal steroids may be involved in its secretion and/or metabolism. However, results from previous reports are conflicting and data regarding the influence of ovarian steroids on adiponectin's multimer forms are scarce. The objective of the study was to assess if total adiponectin and its isoforms are affected by the changes of estradiol and progesterone during the normal menstrual cycle and the association of total adiponectin and its isoforms with the gonadal steroid levels.

Materials/methods

Quantitative determination of plasma adiponectin and its multimers was conducted in the three phases of an ovulatory cycle in 13 premenopausal women, in the follicular phase of 10 more premenopausal women, in 20 postmenopausal women and in 21 men. Moreover, serum levels of FSH, LH, prolactin, estradiol, progesterone, and testosterone, sex hormone binding globulin, glucose, and insulin were measured.

Results

The circulating levels of total adiponectin and its multimers were not affected by the normal variation of estradiol and progesterone across the ovulatory menstrual cycle. In the whole number of participants, the total adiponectin and high molecular weight adiponectin levels were significantly different between genders and associated positively with age and sex hormone binding globulin levels, and negatively with testosterone and progesterone levels and the waist/hip ratio. In the multiple logistic regression analysis, after adjustment for age, gender, and sex hormone binding globulin and progesterone levels, significant predictors of total adiponectin levels were the waist/hip ratio and testosterone levels, and of high molecular weight adiponectin the testosterone levels.

Conclusions

Normal menstrual cycle ovarian steroids are not involved directly in the regulation of secretion and/or metabolism of total adiponectin and its multimers. Testosterone seems to be responsible for the adiponectin's sexual dimorphism.

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Adiponectin and its multimers were assessed in the three-step hormonal model of normal menstrual cycle.

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Estrogens may not be involved directly in the regulation of adiponectin's secretion and/or metabolism.

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Androgens appear to be responsible for the sexual dimorphism of adiponectin.

Relationship of circulating adipokines to body composition in pregnant women

Circulating adipokines are associated with physiological and pathophysiological processes in both obesity and pregnancy. Obesity in pregnancy increases the risk of pregnancy complications and the majority of research uses body mass index (BMI) to assess fatness. Specific fat compartments are associated with obesity-induced health risks yet it is not known how abdominal fat mass in pregnancy is related to circulating adipokines. Plasma leptin, resistin, visfatin, and adiponectin were measured by immunoassay in healthy pregnant women of normal weight (BMI 18.5-24.9; n = 17) and overweight/obese pregnant women (BMI 25.0-40, n = 21) in the third trimester. Total body and abdominal subcutaneous and visceral fat mass were measured at 1-3 weeks postpartum. Overweight/obese women had greater total body fat (t = -6.210, P < 0.001) and abdominal subcutaneous fat (t = -5.072, P < 0.001) than normal-weight women while there was no difference in abdominal visceral fat. Overweight/obese women had higher leptin (66.3 ± 34.2 vs. 35.7 ± 19.3 ng/mL, P < 0.001) compared to normal-weight women. Leptin was associated with total body fat (r = 0.782, P < 0.001) and resistin was associated with abdominal visceral fat (r = 0.452, P = 0.045). No significant correlations were observed between adiponectin or visfatin and any measure of body composition. In pregnant women, resistin has the potential to be a circulating biomarker for visceral fat, an ectopic fat compartment. These observational data may provide insight for the pathophysiological roles of adipokines and the impact of visceral fat in pregnant women.

Clostridium difficile virulence factors: Insights into an anaerobic spore-forming pathogen

The worldwide emergence of epidemic strains of Clostridium difficile linked to increased disease severity and mortality has resulted in greater research efforts toward determining the virulence factors and pathogenesis mechanisms used by this organism to cause disease. C. difficile is an opportunist pathogen that employs many factors to infect and damage the host, often with devastating consequences. This review will focus on the role of the 2 major virulence factors, toxin A (TcdA) and toxin B (TcdB), as well as the role of other putative virulence factors, such as binary toxin, in C. difficile-mediated infection. Consideration is given to the importance of spores in both the initiation of disease and disease recurrence and also to the role that surface proteins play in host interactions.