Research on the technology of sealing disk-baffle integrated structure design

Sealing disk-baffle integrated structure has been widely applied in modern advanced aero-engines. In this paper, the features of typical sealing disk-baffle integrated structure were analyzed in order to explore the feasible direction of the structure design and optimization. The finite element models were analyzed for the CFM56 series aero-engines [1], and the stress was computed under the different temperature fields, operating speeds and non-linear contacting. The design technologies were summarized for the sealing disk-baffle integrated structure. The results provided bases and references for structure design and engineering applications of the sealing disk-baffle integrated structure

Rac1 signaling is critical to cardiomyocyte polarity and embryonic heart development

Background-Defects in cardiac septation are the most common form of congenital heart disease, but the mechanisms underlying these defects are still poorly understood. The small GTPase Rac1 is implicated in planar cell polarity of epithelial cells in Drosophila; however, its role in mammalian cardiomyocyte polarity is not clear. We tested the hypothesis that Rac1 signaling in the second heart field regulates cardiomyocyte polarity, chamber septation, and right ventricle development during embryonic heart development. Methods and Results-Mice with second heart field-specific deficiency of Rac1 (Rac1SHF) exhibited ventricular and atrial septal defects, a thinner right ventricle myocardium, and a bifid cardiac apex. Fate-mapping analysis showed that second heart field contribution to the interventricular septum and right ventricle was deficient in Rac1SHF hearts. Notably, cardiomyocytes had a spherical shape with disrupted F-actin filaments in Rac1SHF compared with elongated and well-aligned cardiomyocytes in littermate controls. Expression of Scrib, a core protein in planar cell polarity, was lost in Rac1SHF hearts with decreased expression of WAVE and Arp2/3, leading to decreased migratory ability. In addition, Rac1-deficient neonatal cardiomyocytes displayed defects in cell projections, lamellipodia formation, and cell elongation. Furthermore, apoptosis was increased and the expression of Gata4, Tbx5, Nkx2.5, and Hand2 transcription factors was decreased in the Rac1SHF right ventricle myocardium. Conclusions-Deficiency of Rac1 in the second heart field impairs elongation and cytoskeleton organization of cardiomyocytes and results in congenital septal defects, thin right ventricle myocardium, and a bifid cardiac apex. Our study suggests that Rac1 signaling is critical to cardiomyocyte polarity and embryonic heart development

Rac1 activation induces tumour necrosis factor-α expression and cardiac dysfunction in endotoxemia

Induction of tumour necrosis factor-α (TNF-α) expression leads to myocardial depression during sepsis. However, the underlying molecular mechanisms are not fully understood. The aim of this study was to investigate the role of Rac1 in TNF-α expression and cardiac dysfunction during endotoxemia and to determine the involvement of phosphoinositide-3 kinase (PI3K) in lipopolysaccharide (LPS)-induced Rac1 activation. Our results showed that LPS-induced Rac1 activation and TNF-α expression in cultured neonatal mouse cardiomyocytes. The response was inhibited in Rac1 deficient cardiomyocytes or by a dominant-negative Rac1 (Rac1N17). To determine whether PI3K regulates Rac1 activation, cardiomyocytes were treated with LY294002, a PI3K selective inhibitor. Treatment with LY294002 decreased Rac1 activity as well as TNF-α expression stimulated by LPS. Furthermore, inhibition of PI3K and Rac1 activity decreased LPS-induced superoxide generation which was associated with a significant reduction in ERK1/2 phosphorylation. To investigate the role of Rac1 in myocardial depression during endotoxemiain vivo, wild-type and cardiomyocyte-specific Rac1 deficient mice were treated with LPS (2 mg/kg, i.p.). Deficiency in Rac1 significantly decreased myocardial TNF-α expression and improved cardiac function during endotoxemia. We conclude that PI3K-mediated Rac1 activation is required for induction of TNF-α expression in cardiomyocytes and cardiac dysfunction during endotoxemia. The effect of Rac1 on TNF-α expression seems to be mediated by increased NADPH oxidase activity and ERK1/2 phosphorylation. © 2011 The Authors Journal of Cellular and Molecular Medicine © 2011 Foundation for Cellular and Molecular Medicine/Blackwell Publishing Ltd

Myocardial infarction in neonatal mice, a model of cardiac regeneration

Myocardial infarction induced by coronary artery ligation has been used in many animal models as a tool to study the mechanisms of cardiac repair and regeneration, and to define new targets for therapeutics. For decades, models of complete heart regeneration existed in amphibians and fish, but a mammalian counterpart was not available. The recent discovery of a postnatal window during which mice possess regenerative capabilities has led to the establishment of a mammalian model of cardiac regeneration. A surgical model of mammalian cardiac regeneration in the neonatal mouse is presented herein. Briefly, postnatal day 1 (P1) mice are anesthetized by isoflurane and placed on an ice pad to induce hypothermia. After the chest is opened, and the left anterior descending coronary artery (LAD) is visualized, a suture is placed around the LAD to inflict myocardial ischemia in the left ventricle. The surgical procedure takes 10-15 min. Visualizing the coronary artery is crucial for accurate suture placement and reproducibility. Myocardial infarction and cardiac dysfunction are confirmed by triphenyl-tetrazolium chloride (TTC) staining and echocardiography, respectively. Complete regeneration 21 days post myocardial infarction is verified by histology. This protocol can be used to as a tool to elucidate mechanisms of mammalian cardiac regeneration after myocardial infarction

Say NO to ROS: Their roles in embryonic heart development and pathogenesis of congenital heart defects in maternal diabetes

Congenital heart defects (CHDs) are the most prevalent and serious birth defect, occurring in 1% of all live births. Pregestational maternal diabetes is a known risk factor for the development of CHDs, elevating the risk in the child by more than four-fold. As the prevalence of diabetes rapidly rises among women of childbearing age, there is a need to investigate the mechanisms and potential preventative strategies for these defects. In experimental animal models of pregestational diabetes induced-CHDs, upwards of 50% of offspring display congenital malformations of the heart, including septal, valvular, and outflow tract defects. Specifically, the imbalance of nitric oxide (NO) and reactive oxygen species (ROS) signaling is a major driver of the development of CHDs in offspring of mice with pregestational diabetes. NO from endothelial nitric oxide synthase (eNOS) is crucial to cardiogenesis, regulating various cellular and molecular processes. In fact, deficiency in eNOS results in CHDs and coronary artery malformation. Embryonic hearts from diabetic dams exhibit eNOS uncoupling and oxidative stress. Maternal treatment with sapropterin, a cofactor of eNOS, and antioxidants such as N-acetylcysteine, vitamin E, and glutathione as well as maternal exercise have been shown to improve eNOS function, reduce oxidative stress, and lower the incidence CHDs in the offspring of mice with pregestational diabetes. This review summarizes recent data on pregestational diabetes-induced CHDs, and offers insights into the important roles of NO and ROS in embryonic heart development and pathogenesis of CHDs in maternal diabetes

A charge-sensing region in the stromal interaction molecule 1 luminal domain confers stabilization-mediated inhibition of soce in response to s-nitrosylation

Store-operated Ca2 entry (SOCE) is a major Ca2 signaling pathway facilitating extracellular Ca2 influx in response to the initial release of intracellular endo/sarcoplasmic reticulum (ER/ SR) Ca2 stores. Stromal interaction molecule 1 (STIM1) is the Ca2 sensor that activates SOCE following ER/SR Ca2 depletion. The EF-hand and the adjacent sterile -motif (EFSAM) domains of STIM1 are essential for detecting changes in luminal Ca2 concentrations. Low ER Ca2 levels trigger STIM1 destabilization and oligomerization, culminating in the opening of Orai1-composed Ca2 channels on the plasma membrane. NO-mediated S-nitrosylation of cysteine thiols regulates myriad protein functions, but its effects on the structural mechanisms that regulate SOCE are unclear. Here, we demonstrate that S-ni-trosylation of Cys49 and Cys56 in STIM1 enhances the thermodynamic stability of its luminal domain, resulting in suppressed hydrophobic exposure and diminished Ca2 depletion– dependent oligomerization. Using solution NMR spectroscopy, we pinpointed a structural mechanism for STIM1 stabilization driven by complementary charge interactions between an electropositive patch on the core EFSAM domain and the S-nitrosy-lated nonconserved region of STIM1. Finally, using live cells, we found that the enhanced luminal domain stability conferred by either Cys49 and Cys56 S-nitrosylation or incorporation of negatively charged residues into the EFSAM electropositive patch in the full-length STIM1 context significantly suppresses SOCE. Collectively, our results suggest that S-nitrosylation of STIM1 inhibits SOCE by interacting with an electropositive patch on the EFSAM core, which modulates the thermodynamic stability of the STIM1 luminal domain

Therapeutic Potential of Annexins in Sepsis and COVID-19

Sepsis is a continuing problem in modern healthcare, with a relatively high prevalence, and a significant mortality rate worldwide. Currently, no specific anti-sepsis treatment exists despite decades of research on developing potential therapies. Annexins are molecules that show efficacy in preclinical models of sepsis but have not been investigated as a potential therapy in patients with sepsis. Human annexins play important roles in cell membrane dynamics, as well as mediation of systemic effects. Most notably, annexins are highly involved in anti-inflammatory processes, adaptive immunity, modulation of coagulation and fibrinolysis, as well as protective shielding of cells from phagocytosis. These discoveries led to the development of analogous peptides which mimic their physiological function, and investigation into the potential of using the annexins and their analogous peptides as therapeutic agents in conditions where inflammation and coagulation play a large role in the pathophysiology. In numerous studies, treatment with recombinant human annexins and annexin analogue peptides have consistently found positive outcomes in animal models of sepsis, myocardial infarction, and ischemia reperfusion injury. Annexins A1 and A5 improve organ function and reduce mortality in animal sepsis models, inhibit inflammatory processes, reduce inflammatory mediator release, and protect against ischemic injury. The mechanisms of action and demonstrated efficacy of annexins in animal models support development of annexins and their analogues for the treatment of sepsis. The effects of annexin A5 on inflammation and platelet activation may be particularly beneficial in disease caused by SARS-CoV-2 infection. Safety and efficacy of recombinant human annexin A5 are currently being studied in clinical trials in sepsis and severe COVID-19 patients

Nitric oxide synthase-3 promotes embryonic development of atrioventricular valves.

Nitric oxide synthase-3 (NOS3) has recently been shown to promote endothelial-to-mesenchymal transition (EndMT) in the developing atrioventricular (AV) canal. The present study was aimed to investigate the role of NOS3 in embryonic development of AV valves. We hypothesized that NOS3 promotes embryonic development of AV valves via EndMT. To test this hypothesis, morphological and functional analysis of AV valves were performed in wild-type (WT) and NOS3(-/-) mice at postnatal day 0. Our data show that the overall size and length of mitral and tricuspid valves were decreased in NOS3(-/-) compared with WT mice. Echocardiographic assessment showed significant regurgitation of mitral and tricuspid valves during systole in NOS3(-/-) mice. These phenotypes were all rescued by cardiac specific NOS3 overexpression. To assess EndMT, immunostaining of Snail1 was performed in the embryonic heart. Both total mesenchymal and Snail1(+) cells in the AV cushion were decreased in NOS3(-/-) compared with WT mice at E10.5 and E12.5, which was completely restored by cardiac specific NOS3 overexpression. In cultured embryonic hearts, NOS3 promoted transforming growth factor (TGFβ), bone morphogenetic protein (BMP2) and Snail1expression through cGMP. Furthermore, mesenchymal cell formation and migration from cultured AV cushion explants were decreased in the NOS3(-/-) compared with WT mice. We conclude that NOS3 promotes AV valve formation during embryonic heart development and deficiency in NOS3 results in AV valve insufficiency