Fibronectin and transforming growth factor beta contribute to erythropoietin resistance and maladaptive cardiac hypertrophy

The use of recombinant human erythropoietin (rhEPO) to promote repair and minimize cardiac hypertrophy after myocardial infarction has had disappointing outcomes in clinical trials. We hypothesized that the beneficial non-hematopoietic effects of rhEPO against cardiac hypertrophy could be offset by the molecular changes initiated by rhEPO itself, leading to rhEPO resistance or maladaptive hypertrophy. This hypothesis was investigated using an isoproterenol-induced model of myocardial infarct and cardiac remodelling with emphasis on hypertrophy. In h9c2 cardiomyocytes, rhEPO decreased isoproterenol-induced hypertrophy, and the expression of the pro-fibrotic factors fibronectin, alpha smooth muscle actin and transforming growth factor beta-1 (TGF-β1). In contrast, by itself, rhEPO increased the expression of fibronectin and TGF-β1. Exogenous TGF-β1 induced a significant increase in hypertrophy, which was further potentiated by rhEPO. Exogenous fibronectin not only induced hypertrophy of cardiomyocytes, but also conferred resistance to rhEPO treatment. Based on these findings we propose that the outcome of rhEPO treatment for myocardial infarction is determined by the baseline concentrations of fibronectin and TGF-β1. If endogenous fibronectin or TGF-β levels are above a certain threshold, they could cause resistance to rhEPO therapy and enhancement of cardiac hypertrophy, respectively, leading to maladaptive hypertrophy.     

Sodium channels contribute to action potential generation in canine and human pancreatic islet B cells

Summary Pancreatic islet B cells depolarize and display trains of action potentials in response to stimulatory concentrations of glucose. Based on data from rodent islets these action potentials are considered to be predominantly Ca²⁺ dependent. Here we describe Na⁺-dependent action potentials and Na⁺ currents recorded from canine and human pancreatic islet B cells. Current-clamp recording using the nystatin perforated-patch technique demonstrates that B cells from both species display tetrodotoxin-sensitive Na⁺ action potentials in response to modest glucose-induced depolarization. In companion whole-cell voltage-clamp experiments on canine B cells, the underlying Na⁺ current displays steep voltage-dependent activation and inactivation over the range of –50 to –40 mV. The Na⁺ current is sensitive to tetrodotoxin block with aK ₁=3.2nm and has a reversal potential which changes with [Na⁺] _o as predicted by the Nernst equation. These results suggest that a voltage-dependent Na⁺ current may contribute significantly to action potential generation in some species outside the rodent family.     

Actin and myosin contribute to mammalian mitochondrial DNA maintenance

Mitochondrial DNA maintenance and segregation are dependent on the actin cytoskeleton in budding yeast. We found two cytoskeletal proteins among six proteins tightly associated with rat liver mitochondrial DNA: non-muscle myosin heavy chain IIA and β-actin. In human cells, transient gene silencing of MYH9 (encoding non-muscle myosin heavy chain IIA), or the closely related MYH10 gene (encoding non-muscle myosin heavy chain IIB), altered the topology and increased the copy number of mitochondrial DNA; and the latter effect was enhanced when both genes were targeted simultaneously. In contrast, genetic ablation of non-muscle myosin IIB was associated with a 60% decrease in mitochondrial DNA copy number in mouse embryonic fibroblasts, compared to control cells. Gene silencing of β-actin also affected mitochondrial DNA copy number and organization. Protease-protection experiments and iodixanol gradient analysis suggest some β-actin and non-muscle myosin heavy chain IIA reside within human mitochondria and confirm that they are associated with mitochondrial DNA. Collectively, these results strongly implicate the actomyosin cytoskeleton in mammalian mitochondrial DNA maintenance.     

RAD18 and RAD54 cooperatively contribute to maintenance of genomic stability in vertebrate cells

Translesion DNA synthesis (TLS) and homologous DNA recombination (HR) are two major pathways that account for survival after post-replicational DNA damage. TLS functions by filling gaps on a daughter strand that remain after DNA replication caused by damage on the mother strand, while HR can repair gaps and breaks using the intact sister chromatid as a template. The RAD18 gene, which is conserved from lower eukaryotes to vertebrates, is essential for TLS in Saccharomyces cerevisiae. To investigate the role of RAD18, we disrupted RAD18 by gene targeting in the chicken B-lymphocyte line DT40. RAD18(-/-) cells are sensitive to various DNA-damaging agents including ultraviolet light and the cross-linking agent cisplatin, consistent with its role in TLS. Interestingly, elevated sister chromatid exchange, which reflects HR- mediated post-replicational repair, was observed in RAD18(-/-) cells during the cell cycle. Strikingly, double mutants of RAD18 and RAD54, a gene involved in HR, are synthetic lethal, although the single mutant in either gene can proliferate with nearly normal kinetics. These data suggest that RAD18 plays an essential role in maintaining chromosomal DNA in cooperation with the RAD54-dependent DNA repair pathway.     

All joint moments significantly contribute to trunk angular acceleration

Computationally advanced biomechanical analyses of gait demonstrate the often counter-intuitive roles of joint moments on various aspects of gait such as propulsion, swing initiation, and balance. Each joint moment can produce linear and angular acceleration of all body segments (including those on which the moment does not directly act) due to the dynamic coupling inherent in the interconnected musculoskeletal system. This study presents quantitative relationships between individual joint moments and trunk control with respect to balance during gait to show that the ankle, knee, and hip joint moments all affect the angular acceleration of the trunk. We show that trunk angular acceleration is affected by all joints in the leg with varying degrees of dependence during the gait cycle. Furthermore, it is shown that inter-planar coupling exists and a two-dimensional analysis of trunk balance neglects important out-of-plane joint moments that affect trunk angular acceleration.     

Specific monoclonal antibodies against the surface of rat islet beta cells

Type 1 diabetes arises from the autoimmune destruction of islet beta cells, with the participation of both arms of the immune system. To better characterize the beta cell membrane, we have raised monoclonal antibodies to the surface of the INS-1 insulinoma cell line. Twenty-two such antibodies were produced, 21 of the IgG class, all reactive to different cell membrane proteins from INS-1 and neonatal islet cells, yielding identical electrophoresis patterns, with molecular weights mainly between 45 and 60 kD. We have focused on three such antibodies that recognize different protein targets, and are specific for islet beta cells. The target protein of antibody AA4, also found on monkey islets, is expressed at significantly higher levels on beta cells (55.8 vs 30.6% of cells, plus 3-4 fold increase in average fluorescence intensity per cell) when neonatal rat islet cells are incubated with high (16 mM vs 3mM) glucose concentrations. Further identification of the target antigens is in progress and is expected to shed more light on the properties of beta cell membrane proteins, and their probable participation in various disease processes.     

Selective deletion of Pten in pancreatic beta cells leads to increased islet mass and resistance to STZ-induced diabetes

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a lipid phosphatase. PTEN inhibits the action of phosphatidylinositol-3-kinase and reduces the levels of phosphatidylinositol triphosphate, a crucial second messenger for cell proliferation and survival, as well as insulin signaling. In this study, we deleted Pten specifically in the insulin producing beta cells during murine pancreatic development. Pten deletion leads to increased cell proliferation and decreased cell death, without significant alteration of beta-cell differentiation. Consequently, the mutant pancreas generates more and larger islets, with a significant increase in total beta-cell mass. PTEN loss also protects animals from developing streptozotocin-induced diabetes. Our data demonstrate that PTEN loss in beta cells is not tumorigenic but beneficial. This suggests that modulating the PTEN-controlled signaling pathway is a potential approach for beta-cell protection and regeneration therapies.     

CNS midline cells contribute to maintenance of the initial dorsoventral patterning of the Drosophila ventral neuroectoderm

Dorsoventral patterning of the Drosophila ventral neuroectoderm is established by the expression of three evolutionarily conserved homeodomain genes: ventral nervous system defective (vnd), intermediate neuroblasts defective (ind), and muscle segment homeobox (msh) in the medial, intermediate, and lateral columns of the ventral neuroectoderm, respectively. It was not clear whether extrinsic factor(s) from the CNS midline cells influence the initial dorsoventral patterning by controlling the expression of the dorsoventral patterning genes. We show here that the CNS midline cells, specified by single-minded (sim), are essential for maintaining expression of the dorsoventral patterning genes. Ectopic expression of sim in the ventral neuroectoderm during the blastoderm stage repressed expression of the three homeodomain genes in the ventral neuroectoderm. This indicates that the identity of the CNS midline cells is established by a series of repressions of the three homeodomain genes in the ventral neuroectoderm. Ectopic expression of sim in the ventral neuroectoderm during initial neurogenesis induced ectopic ind expression in the medial column in addition to that in the intermediate column via EGFR signaling between the ventral neuroectoderm and midline cells. In contrast, it repressed the expression of vnd and msh in the medial and lateral columns, respectively. Our findings demonstrate that the CNS midline cells provide extrinsic positional information via EGFR signaling that maintains the initial subdivision of the ventral neuroectoderm into three dorsoventral columns during initial neurogenesis.     

Persistent expression of HNF6 in islet endocrine cells causes disrupted islet architecture and loss of beta cell function

We used transgenesis to explore the requirement for downregulation of hepatocyte nuclear factor 6 (HNF6) expression in the assembly, differentiation, and function of pancreatic islets. In vivo, HNF6 expression becomes downregulated in pancreatic endocrine cells at 18. 5 days post coitum (d.p.c.), when definitive islets first begin to organize. We used an islet-specific regulatory element (pdx1(PB)) from pancreatic/duodenal homeobox (pdx1) gene to maintain HNF6 expression in endocrine cells beyond 18.5 d.p.c. Transgenic animals were diabetic. HNF6-overexpressing islets were hyperplastic and remained very close to the pancreatic ducts. Strikingly, alpha, delta, and PP cells were increased in number and abnormally intermingled with islet beta cells. Although several mature beta cell markers were expressed in beta cells of transgenic islets, the glucose transporter GLUT2 was absent or severely reduced. As glucose uptake/metabolism is essential for insulin secretion, decreased GLUT2 may contribute to the etiology of diabetes in pdx1(PB)-HNF6 transgenics. Concordantly, blood insulin was not raised by glucose challenge, suggesting profound beta cell dysfunction. Thus, we have shown that HNF6 downregulation during islet ontogeny is critical to normal pancreas formation and function: continued expression impairs the clustering of endocrine cells and their separation from the ductal epithelium, disrupts the spatial organization of endocrine cell types within the islet, and severely compromises beta cell physiology, leading to overt diabetes.     

Transforming growth factor beta is a critical regulator of adult human islet plasticity

Tissue plasticity is well documented in the context of pancreatic regeneration and carcinogenesis, with recent reports implicating dedifferentiated islet cells both as endocrine progenitors and as the cell(s) of origin in pancreatic adenocarcinoma. Accordingly, it is noteworthy that accumulating evidence suggests that TGFbeta signaling is essential to pancreatic endocrine development and maintenance, whereas its loss is associated with the progression to pancreatic adenocarcinoma. The aim of this study was to examine the role of TGFbeta in an in vitro model of islet morphogenetic plasticity. Human islets were embedded in a collagen gel and cultured under conditions that induced transformation into duct-like epithelial structures (DLS). Addition of TGFbeta caused a dose-dependent decrease in DLS formation. Although it was demonstrated that collagen-embedded islets secrete low levels of TGFbeta, antibody-mediated neutralization of this endogenously released TGFbeta improved DLS formation rates, suggesting local TGFbeta concentrations may in fact be higher. Time course studies indicated that TGFbeta signaling was associated with an increase in ERK and p38 MAPK phosphorylation, although inhibitor-based studies were consistent with an islet endocrine-stabilizing effect mediated by p38 alone. Localization of TGFbeta signaling molecules suggested that the action of TGFbeta is directly on the beta-cell to inhibit apoptosis and thus stabilize endocrine phenotype.     

Molecular conflicts disrupting centromere maintenance contribute to Xenopus hybrid inviability

1. Download : Download high-res image (231KB)
2. Download : Download full-size image

     

Experimental study of rat beta islet cells cultured under simulated microgravity conditions

To observe the effects of simulated microgravity on beta islet cell culture, we have compared the survival rates and the insulin levels of the isolated rat islet cells cultured at micro- and normal gravity conditions. The survival rates of the cells cultured were determined by acridine orange-propidium iodide double-staining on day 3, 7 and 14. The morphology of the cells was observed by electron microscopy. Insulin levels were measured by radio immuno assays. Our results show that the cell number cultured under the microgravity condition is significantly higher than that under the routine condition (P<0.01). Some tubular structure shown by transmission electron microscopy, possibly for the transport of nutrients, were formed intercellularly in the microgravity cultured group on day 7. There were also abundant secretion particles and mitochondria in the cytoplasm of the cells. Scanning electron microscopy showed that there were holes formed between each islet, possibly connecting with the nutrient trans     

Raf and RhoA cooperate to transform intestinal epithelial cells and induce growth resistance to transforming growth factor beta

Although unregulated activation of the Ras/Raf/mitogen-activated protein kinase kinase/Erk signaling pathway is believed to be a central mechanism by which many cell types undergo oncogenic transformation, recent studies indicate that activation of Raf kinase by oncogenic Ras is not sufficient to cause tumorigenic transformation in intestinal epithelial cells. Thus, identification of signaling proteins and pathways that interact with Raf to transform intestinal epithelial cells may be critical for understanding aberrant growth control in the intestinal epithelium. Functional interactions between Raf and the small GTPase RhoA were studied in RIE-1 cells overexpressing both activated Raf(22W) and activated RhoA(63L). Double transfectants were morphologically transformed, formed colonies in soft agar, grew in nude mice, overexpressed cyclin D1 and cyclooxygenase-2 (COX-2), and were resistant to growth inhibition by transforming growth factor (TGF) beta. RIE-Raf and RIE-RhoA single transfectants showed none of these characteristics. Expression of a dominant-negative RhoA(N19) construct in RIE-Ras(12V) cells was associated with markedly reduced COX-2 mRNA, COX-2 protein, and prostaglandin E2 levels when compared with RIE-Ras(12V) cells transfected with vector alone. However, no change in transformed morphology, growth in soft agar, cyclin D1 expression, TGFalpha expression, or TGFbeta sensitivity was observed. In summary, coexpression of activated Raf and RhoA induces transformation and TGFbeta resistance in intestinal epithelial cells. Although blockade of RhoA signaling reverses certain well-described characteristics of RIE-Ras cells, it is insufficient to reverse the transformed phenotype and restore TGFbeta sensitivity. Blockade of additional Rho family members or alternate Ras effector pathways may be necessary to fully reverse the Ras phenotype.     

Rapid Ca2+ influx and diacylglycerol synthesis in growth hormone-mediated islet beta -cell mitogenesis

Growth hormone (GH) is an important mitogenic stimulus for the insulin-producing beta-cell. We investigated the effects of GH on Ca(2+) handling and diacylglycerol (DAG) and cAMP formation in the beta-cell. GH elicited a rapid increase in the cytoplasmic free [Ca(2+)], which required extracellular Ca(2+) and was also blocked by pertussis toxin or protein kinase C (PKC) inhibition. GH also elevated islet DAG content, which should lead to PKC activation. Pertussis toxin and PKC inhibitors obliterated the mitogenicity of GH, suggesting involvement of GTP-binding proteins. PKC activation stimulated beta-cell proliferation, and it also activated phospholipase D. Islet cAMP content was not elevated by GH. Addition of a specific protein kinase A antagonist failed to influence the mitogenicity of GH, whereas a stimulatory cAMP agonist stimulated beta-cell replication. We conclude that GH rapidly increases the beta-cell cytoplasmic free [Ca(2+)] and also evokes a similar increase in DAG content via a phosphatidylcholine-specific phospholipase C, but does not affect mitogen-activated protein kinases, phospholipase D, or the cAMP signaling pathway. This rise in DAG may be of importance in translation of the stimulatory signal of GH into a proliferative response by the beta-cell, which seems to occur through GTP-binding proteins and PKC-dependent mechanisms.     

Soil and climate equally contribute to changes in the species compositions of Brazilian dry forests across 300 km

了解在不同空间尺度上控制生物多样性分布的因素是保护工作面临的一个关键挑战。生物多样性,反映在不同地点物种组成的差异(β多样性),可以通过物种更替(周转率)获得,并受到多种因素的驱动。在本研究中,我们试图通过研究两个与受威胁的巴西季节性干旱森林相关的问题探讨：I)物种周转对β多样性的贡献是什么? II)哪些因素驱动了林块间物种组成的变化?我们在17个相隔近300公里的干燥森林斑块中对树种进行采样,以及采集环境变量(土壤和气候)。我们使用β多样性划分框架来确定周转率的贡献,采用冗余分析和适合的空间结构来评估环境和空间因素对物种组成变化的贡献。斑块间的β多样性主要以周转组分(98.2%)为代表,Simpson相异度优于国内其他地区 (多位点和两两比较的平均值分别为0.89和0.71)。环境因子对物种组成变化的解释多于空间因素,占物种组成变化的30.3%,其中28.1%是非空间结构的。我们建议,300公里代表一个阈值,在这个阈值上,土壤和气候预测因子在决定群落周转方面具有相似的效应(在不考虑空间结构的情况下,分别为14.9%和12.6%)。因此,应该跨景观考虑保护策略,以有效地保护热带森林多样性,因为即使考虑到不同规模的气候差异, 景观化的土壤种类也是物种周转的重要驱动因素。     

All leg joints contribute to quiet human stance: A mechanical analysis

According to the state of the art model (single inverted pendulum) the regulation of quiet human stance seems to be dominated by ankle joint actions. Recent findings substantiated both in-phase and anti-phase fluctuations of ankle and hip joint kinematics can be identified in quiet human stance. Thus, we explored in an experimental study to what extent all three leg joints actually contribute to the balancing problem of quiet human stance. We also aimed at distinguishing kinematic from torque contributions. Thereto, we directly measured ankle, knee, and hip joint kinematics with high spatial resolution and ground reaction forces. Then, we calculated the six respective joint torques and, additionally, the centre of mass kinematics. We searched for high cross-correlations between all these mechanical variables. Beyond confirming correlated anti-phase kinematics of ankle and hip, the main results are: (i) ankle and knee joint fluctuate tightly (torque) coupled and (ii) the bi-articular muscles of the leg are well suited to fulfil the requirements of fluctuations around static equilibrium. Additionally, we (iii) identified high-frequency oscillations of the shank between about 4 and 8 Hz and (iv) discriminated potentially passive and active joint torque contributions. These results demonstrate that all leg joints contribute actively and concertedly to quiet human stance, even in the undisturbed case. Moreover, they substantiate the single inverted pendulum paradigm to be an invalid model for quiet human stance.