MeCP2 Affects Skeletal Muscle Growth and Morphology through Non Cell-Autonomous Mechanisms

Rett syndrome (RTT) is an autism spectrum disorder mainly caused by mutations in the X-linked MECP2 gene and affecting roughly 1 out of 10.000 born girls. Symptoms range in severity and include stereotypical movement, lack of spoken language, seizures, ataxia and severe intellectual disability. Notably, muscle tone is generally abnormal in RTT girls and women and the Mecp2-null mouse model constitutively reflects this disease feature. We hypothesized that MeCP2 in muscle might physiologically contribute to its development and/or homeostasis, and conversely its defects in RTT might alter the tissue integrity or function. We show here that a disorganized architecture, with hypotrophic fibres and tissue fibrosis, characterizes skeletal muscles retrieved from Mecp2-null mice. Alterations of the IGF-1/Akt/mTOR pathway accompany the muscle phenotype. A conditional mouse model selectively depleted of Mecp2 in skeletal muscles is characterized by healthy muscles that are morphologically and molecularly indistinguishable from those of wild-type mice raising the possibility that hypotonia in RTT is mainly, if not exclusively, mediated by non-cell autonomous effects. Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects. Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain. Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.     

A novel LMNA mutation (R189W) in familial dilated cardiomyopathy: evidence for a 'hot spot' region at exon 3: a case report

Background

To assess the reliability of fetal heart volume measurement by three-dimensional sonography (3DUS) using the eXtended Imaging Virtual Organ Computer-aided AnaLysis (XI VOCAL) method.

Methods

This reliability study enrolled 30 pregnant women with singleton healthy pregnancies between 19 and 34 weeks of gestation. All volume acquirements were performed with a convex volumetric transducer (C3-7ED) coupled to an Accuvix XQ sonography device (Medison, Korea). The XI VOCAL 10 planes was the method of choice for volumetric measurement. 3D datasets were analyzed by two observers (EQSB and HJFM); fetal heart volume was measured twice by the first and once by the second observer to calculate intra and interobserver reproducibility. Statistical analysis used pareated Student's t test (p) and calculated Intraclass correlation coefficients (ICC). Bland-Altman plots were also constructed.

Results

We observed an excellent intra- and interobserver reliability for fetal cardiac volume assessed by XI VOCAL. For the intraobserver the ICC was 0.998 (95% CI: 0.997; 0.999), with mean of differences of 0.12 cm³ (95% limits of agreement: -0.84; +0.84; p = 0.130). For interobserver the ICC was 0.899 (95%CI: 0.996; 0.998), mean of differences 0.05 cm³ (95% limits of agreement: -0.84; +0.84; p = 0.175).

Conclusion

Fetal cardiac volume assessed by 3DUS using XI VOCAL method is highly reproducible between 19 to 34 gestational weeks.     

GSTM1, GSTT1 and CYP1A1 detoxification gene polymorphisms and susceptibility to smoking-related coronary artery disease: a case-only study

Cigarette smoking is a powerful risk factor for coronary artery disease (CAD), leading to the formation of DNA alterations within blood vessels and heart. However, the degree of smoking-related atherosclerosis varies from individual to individual. Genetic polymorphisms of relevant xenobiotic metabolising enzymes may determine the susceptibility of an individual response to environmental toxicants. The purpose of this study was to test the hypothesis that the inheritance of polymorphic genes encoding cytochrome P450 1A1 (CYP1A1 MspI) and glutathione S-transferases (GSTM1(null) and GSTT1(null)) may be causally associated with the presence and severity of smoking-induced CAD. In a case-only design, 222 (179 male, 57.8+/-10.3 years) consecutive smoker patients who had undergone elective and diagnostic coronary angiography were recruited. We found a group (n=169) of smoker patients with significant CAD, defined as>50% reduction in diameter of at least one major vessel, and a group without obstructive CAD (n=53). No significant differences were observed in CYP1A1 genotypes frequencies between CAD and non-CAD smokers (p=0.1). Homozygous deletion of GSTM1 had a frequency of 58.6% among patients with CAD and 45.3% among those without CAD (p=0.08). The frequency of the GSTT1(null) genotype was 43.8% among the patients with CAD and 24.5% among CAD-free subjects (p=0.01). After adjustment for traditional risk factors, the presence of combined GSTM1(null)GSTT1(null) genotypes was significantly associated with an increased risk of CAD (OR=3.9; 95% CI: 1.3-11.4, p=0.01). Moreover, smokers with combined GSTM1(null)GSTT1(null) genotypes had significantly higher number of stenosed vessels than those with the positive genotype (2.3+/-0.9 versus 1.7+/-0.8, p=0.03). Our findings showed that smokers carrying GST deleted genotypes have an increased susceptibility to the smoking related coronary artery disease. Exploring gene-smoking effect provides an excellent model in order to understand gene-environment toxicants interaction and its implications to cardiovascular disease.     

Thiocyanate transport in resting and IL-4-stimulated human bronchial epithelial cells: role of pendrin and anion channels

SCN(-) (thiocyanate) is an important physiological anion involved in innate defense of mucosal surfaces. SCN(-) is oxidized by H(2)O(2), a reaction catalyzed by lactoperoxidase, to produce OSCN(-) (hypothiocyanite), a molecule with antimicrobial activity. Given the importance of the availability of SCN(-) in the airway surface fluid, we studied transepithelial SCN(-) transport in the human bronchial epithelium. We found evidence for at least three mechanisms for basolateral to apical SCN(-) flux. cAMP and Ca(2+) regulatory pathways controlled SCN(-) transport through cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, respectively, the latter mechanism being significantly increased by treatment with IL-4. Stimulation with IL-4 also induced the strong up-regulation of an electroneutral SCN(-)/Cl(-) exchange. Global gene expression analysis with microarrays and functional studies indicated pendrin (SLC26A4) as the protein responsible for this SCN(-) transport. Measurements of H(2)O(2) production at the apical surface of bronchial cells indicated that the extent of SCN(-) transport is important to modulate the conversion of this oxidant molecule by the lactoperoxidase system. Our studies indicate that the human bronchial epithelium expresses various SCN(-) transport mechanisms under resting and stimulated conditions. Defects in SCN(-) transport in the airways may be responsible for susceptibility to infections and/or decreased ability to scavenge oxidants.     

Reorganization of prion protein membrane environment during low potassium-induced apoptosis in primary rat cerebellar neurons

We studied the changes occurring in the membrane environment of prion protein (PrP) during apoptosis induced by low potassium in primary rat cerebellar neurons. Ceramide levels increased during apoptosis-inducing treatment, being doubled with respect to time-matched controls after 24 h. Sphingomyelin levels were parallely decreased, while cholesterol and ganglioside contents were not affected. Changes in ceramide and sphingomyelin composition were exclusively restricted to a detergent-resistant membrane fraction. The pro-apoptotic treatment was accompanied by the down-regulation of PrP and of the non-receptor kinase Fyn. The levels of PrP and Fyn were correspondingly reduced in the detergent-resistant membrane fraction. In control cells, the membrane microenvironment separated by immunoprecipitation with anti-PrP antibody contained 80% of the detergent-resistant PrP and 35% and 38% of the sphingolipids and cholesterol respectively. Upon low potassium treatment, 20% of the PrP originally present in the detergent-resistant fraction was immunoprecipitated, together with 19% of sphingolipids and 22% of cholesterol. Thus, PrP in the immunoprecipitate from apoptotic cells was ninefold less than in control ones, while sphingolipids and cholesterol were about 50% with respect to controls cells. The molar ratio between cholesterol, sphingomyelin and ceramide was 15 : 6 : 1 in the PrP-rich environment from control neurons, and 6 : 2 : 1 in that from apoptotic cells.     

Inhibition of catalase activity as an early response of Arabidopsis thaliana cultured cells to the phytotoxin fusicoccin

In Arabidopsis thaliana cells, fusicoccin (FC) treatment induced an early and marked increase in the extracellular H(2)O(2) level. It also increased the huge hypo-osmotic stress-induced oxidative wave and, in addition, prevented the H(2)O(2) peak drop. These effects were apparently not linked to changes in either cytoplasmic pH or cytoplasmic free calcium concentration, since they occurred independently of the activity state of the plasma membrane (PM) H(+)-ATPase and neither influx nor efflux of (45)Ca(2+) was modified by FC. In the presence of diphenylene iodonium (DPI), inhibiting the PM NADPH oxidase presumably responsible for reactive oxygen species (ROS) production, no apoplastic H(2)O(2) development was detected either with or without FC. However, no increase in DPI-sensitive ferricyanide reduction, but rather a gradual decrease, occurred with FC. These results suggested that the H(2)O(2) increase observed with FC was not due to a overproduction of ROS but, more probably, to a reduced capability of FC-treated cells to degrade the H(2)O(2) formed. This view, at first supported by the finding that FC-treated cells failed to break down exogenously supplied H(2)O(2), was clearly confirmed by a series of measurements on exogenous catalase activity, tested in cell-free media of FC-treated samples. This assay, in fact, allowed ascertainment and partial characterization of an as yet unidentified factor increasingly accumulating in the incubation medium of FC-treated cells, behaving as a non-competitive catalase inhibitor and able to reduce markedly the cell's capability for H(2)O(2) scavenging.     

Antimicrobial Activity of Aroma Compounds against Saccharomyces cerevisiae and Improvement of Microbiological Stability of Soft Drinks as Assessed by Logistic Regression

The combined effects of a mild heat treatment (55°C) and the presence of three aroma compounds [citron essential oil, citral, and (E)-2-hexenal] on the spoilage of noncarbonated beverages inoculated with different amounts of a Saccharomyces cerevisiae strain were evaluated. The results, expressed as growth/no growth, were elaborated using a logistic regression in order to assess the probability of beverage spoilage as a function of thermal treatment length, concentration of flavoring agents, and yeast inoculum. The logit models obtained for the three substances were extremely precise. The thermal treatment alone, even if prolonged for 20 min, was not able to prevent yeast growth. However, the presence of increasing concentrations of aroma compounds improved the stability of the products. The inhibiting effect of the compounds was enhanced by a prolonged thermal treatment. In fact, it influenced the vapor pressure of the molecules, which can easily interact within microbial membranes when they are in gaseous form. (E)-2-Hexenal showed a threshold level, related to initial inoculum and thermal treatment length, over which yeast growth was rapidly inhibited. Concentrations over 100 ppm of citral and thermal treatment longer than 16 min allowed a 90% probability of stability for bottles inoculated with 10⁵ CFU/bottle. Citron gave the most interesting responses: beverages with 500 ppm of essential oil needed only 3 min of treatment to prevent yeast growth. In this framework, the logistic regression proved to be an important tool to study alternative hurdle strategies for the stabilization of noncarbonated beverages.     

Myofilament calcium sensitivity does not affect cross-bridge activation-relaxation kinetics

We employed single myofibril techniques to test whether the presence of slow skeletal troponin-I (ssTnI) is sufficient to induce increased myofilament calcium sensitivity (EC(50)) and whether modulation of EC(50) affects the dynamics of force development. Studies were performed using rabbit psoas myofibrils activated by rapid solution switch and in which Tn was partially replaced for either recombinant cardiac Tn(cTn) or Tn composed of recombinant cTn-T (cTnT) and cTn-C (cTnC), and recombinant ssTnI (ssTnI-chimera Tn). Tn exchange was performed in rigor solution (0.5 mg/ml Tn; 20 degrees C; 2 h) and confirmed by SDS-PAGE. cTnI exchange induced a decrease in EC(50); ssTnI-chimera Tn exchange induced a further decrease in EC(50) (in microM: endogenous Tn, 1.35 +/- 0.08; cTnI, 1.04 +/- 0.13; ssTnI-chimera Tn, 0.47 +/- 0.03). EC(50) was also decreased by application of 100 microM bepridil (control: 2.04 +/- 0.03 microM; bepridil 1.35 +/- 0.03 microM). Maximum tension was not different between any groups. Despite marked alterations in EC(50), none of the dynamic activation-relaxation parameters were affected under any condition. Our results show that 1) incorporation of ssTnI into the fast skeletal sarcomere is sufficient to induce increased myofilament Ca(2+) sensitivity, and 2) the dynamics of actin-myosin interaction do not correlate with EC(50). This result suggests that intrinsic cross-bridge cycling rate is not altered by the dynamics of thin-filament activation.     

Influence of channel subunit composition on L-type Ca2+ current kinetics and cardiac wave stability

Previous studies have demonstrated that the slope of the function relating the action potential duration (APD) and the diastolic interval, known as the APD restitution curve, plays an important role in the initiation and maintenance of ventricular fibrillation. Since the APD restitution slope critically depends on the kinetics of the L-type Ca(2+) current, we hypothesized that manipulation of the subunit composition of these channels may represent a powerful strategy to control cardiac arrhythmias. We studied the kinetic properties of the human L-type Ca(2+) channel (Ca(v)1.2) coexpressed with the alpha(2)delta-subunit alone (alpha(1C) + alpha(2)delta) or in combination with beta(2a), beta(2b), or beta(3) subunits (alpha(1C) + alpha(2)delta + beta), using Ca(2+) as the charge carrier. We then incorporated the kinetic properties observed experimentally into the L-type Ca(2+) current mathematical model of the cardiac action potential to demonstrate that the APD restitution slope can be selectively controlled by altering the subunit composition of the Ca(2+) channel. Assuming that beta(2b) most closely resembles the native cardiac L-type Ca(2+) current, the absence of beta, as well as the coexpression of beta(2a), was found to flatten restitution slope and stabilize spiral waves. These results imply that subunit modification of L-type Ca(2+) channels can potentially be used as an antifibrillatory strategy.     

Physicochemical and biological study of selected hydrophobic polyethylenimine-based polycationic liposomes and their complexes with DNA

Non-viral gene therapy is based on the development of efficient and safe gene carrier systems able to transfer DNA into cells. Polyethylenimine (PEI), the most promising non-viral vector, with its high cationic-charge-density potential is able (1) to compact DNA in complexes (polyplexes) smaller than those formed by liposomes (lipoplexes) and (2) to destabilize the endosomal membrane by a 'proton sponge' effect. Several PEI's hydrophobic modifications were reported in the last several years but in some cases a reduced transfection efficiency was observed. The mechanism underlying this phenomenon is not well understood so far. In order to extensively investigate these mechanisms, we reported a physicochemical and biological study of selected hydrophobic PEI's derivatives grafted with chains of different length and percentages of substitution able to form vesicles (polycationic liposomes) and to bind DNA. Their properties were studied by means of dynamic light scattering, freeze-fracture microscopy, potentiometric titrations, gel retardation assays, polyanion exchange reactions, toxicity assays, in vitro transfections, and fluorescence microscopy. Our results indicate that even if polyplexes are able to pass through the cellular membrane, the stability of PEI's hydrophobic polyplexes likely explain their different transfection efficiency in vitro.