Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43

Healthy cardiomyocytes are electrically coupled at the intercalated discs by gap junctions. In infarcted hearts, adverse gap-junctional remodeling occurs in the border zone, where cardiomyocytes are chemically and electrically influenced by myofibroblasts. The physical movement of these contacts remains unquantified. Using scanning ion conductance microscopy, we show that intercellular contacts between cardiomyocytes and myofibroblasts are highly dynamic, mainly owing to the edge dynamics (lamellipodia) of the myofibroblasts. Decreasing the amount of functional connexin-43 (Cx43) at the membrane through Cx43 silencing, suppression of Cx43 trafficking, or hypoxia-induced Cx43 internalization attenuates heterocellular contact dynamism. However, we found decreased dynamism and stabilized membrane contacts when cellular coupling was strengthened using 4-phenylbutyrate (4PB). Fluorescent-dye transfer between cells showed that the extent of functional coupling between the 2 cell types correlated with contact dynamism. Intercellular calcein transfer from myofibroblasts to cardiomyocytes is reduced after myofibroblast-specific Cx43 down-regulation. Conversely, 4PB-treated myofibroblasts increased their functional coupling to cardiomyocytes. Consistent with lamellipodia-mediated contacts, latrunculin-B decreases dynamism, lowers physical communication between heterocellular pairs, and reduces Cx43 intensity in contact regions. Our data show that heterocellular cardiomyocyte-myofibroblast contacts exhibit high dynamism. Therefore, Cx43 is a potential target for prevention of aberrant cardiomyocyte coupling and myofibroblast proliferation in the infarct border zone.-Schultz, F., Swiatlowska, P., Alvarez-Laviada, A., Sanchez-Alonso, J. L., Song, Q., de Vries, A. A. F., Pijnappels, D. A., Ongstad, E., Braga, V. M. M., Entcheva, E., Gourdie, R. G., Miragoli, M., Gorelik, J. Cardiomyocyte-myofibroblast contact dynamism is modulated by connexin-43.

Ursodeoxycholic acid prevents ventricular conduction slowing and arrhythmia by restoring T-type calcium current in fetuses during cholestasis

Background

Increased maternal serum bile acid concentrations in intrahepatic cholestasis of pregnancy (ICP) are associated with fetal cardiac arrhythmias. Ursodeoxycholic acid (UDCA) has been shown to demonstrate anti-arrhythmic properties via preventing ICP-associated cardiac conduction slowing and development of reentrant arrhythmias, although the cellular mechanism is still being elucidated.

Methods

High-resolution fluorescent optical mapping of electrical activity and electrocardiogram measurements were used to characterize effects of UDCA on one-day-old neonatal and adult female Langendorff-perfused rat hearts. ICP was modelled by perfusion of taurocholic acid (TC, 400μM). Whole-cell calcium currents were recorded from neonatal rat and human fetal cardiomyocytes.

Results

TC significantly prolonged the PR interval by 11.0±3.5% (P<0.05) and slowed ventricular conduction velocity (CV) by 38.9±5.1% (P<0.05) exclusively in neonatal and not in maternal hearts. A similar CV decline was observed with the selective T-type calcium current (I_Ca,T) blocker mibefradil 1μM (23.0±6.2%, P<0.05), but not with the L-type calcium current (I_Ca,L) blocker nifedipine 1μM (6.9±6.6%, NS). The sodium channel blocker lidocaine (30μM) reduced CV by 60.4±4.5% (P<0.05). UDCA co-treatment was protective against CV slowing induced by TC and mibefradil, but not against lidocaine. UDCA prevented the TC-induced reduction in the I_Ca,T density in both isolated human fetal (−10.2±1.5 versus −5.5±0.9 pA/pF, P<0.05) and neonatal rat ventricular myocytes (−22.3±1.1 versus −9.6±0.8 pA/pF, P<0.0001), whereas UDCA had limited efficacy on the I_Ca,L.

Conclusion

Our findings demonstrate that I_Ca,T plays a significant role in ICP-associated fetal cardiac conduction slowing and arrhythmogenesis, and is an important component of the fetus-specific anti-arrhythmic activity of UDCA.

The protective effect of ursodeoxycholic acid in an in vitro model of the human fetal heart occurs via targeting cardiac fibroblasts

Bile acids are elevated in the blood of women with intrahepatic cholestasis of pregnancy (ICP) and this may lead to fetal arrhythmia, fetal hypoxia and potentially fetal death in utero. The bile acid taurocholic acid (TC) causes abnormal calcium dynamics and contraction in neonatal rat cardiomyocytes. Ursodeoxycholic acid (UDCA), a drug clinically used to treat ICP, prevents adverse effects of TC. During development, the fetus is in a state of relative hypoxia. Although this is essential for the development of the heart and vasculature, resident fibroblasts can transiently differentiate into myofibroblasts and form gap junctions with cardiomyocytes in vitro, resulting in cardiomyocyte depolarization. We expanded on previously published work using an in vitro hypoxia model to investigate the differentiation of human fetal fibroblasts into myofibroblasts. Recent evidence shows that potassium channels are involved in maintaining the membrane potential of ventricular fibroblasts and that ATP-dependent potassium (KATP) channel subunits are expressed in cultured fibroblasts. KATP channels are a valuable target as they are thought to have a cardioprotective role during ischaemic and hypoxic conditions. We investigated whether UDCA could modulate fibroblast membrane potential. We established the isolation and culture of human fetal cardiomyocytes and fibroblasts to investigate the effect of hypoxia, TC and UDCA on human fetal cardiac cells. UDCA hyperpolarized myofibroblasts and prevented TC-induced depolarisation, possibly through the activation of KATP channels that are expressed in cultured fibroblasts. Also, similar to the rat model, UDCA can counteract TC-induced calcium abnormalities in human fetal cultures of cardiomyocytes and myofibroblasts. Under normoxic conditions, we found a higher number of myofibroblasts in cultures derived from human fetal hearts compared to cells isolated from neonatal rat hearts, indicating a possible increased number of myofibroblasts in human fetal hearts. Hypoxia further increased the number of human fetal and rat neonatal myofibroblasts. However, chronically administered UDCA reduced the number of myofibroblasts and prevented hypoxia-induced depolarisation. In conclusion, our results show that the protective effect of UDCA involves both the reduction of fibroblast differentiation into myofibroblasts, and hyperpolarisation of myofibroblasts, most likely through the stimulation of potassium channels, i.e. KATP channels. This could be important in validating UDCA as an antifibrotic and antiarrhythmic drug for treatment of failing hearts and fetal arrhythmia.

Multisite phosphorylation of C-Nap1 releases it from Cep135 to trigger centrosome disjunction

During mitotic entry, centrosomes separate to establish the bipolar spindle. Delays in centrosome separation can perturb chromosome segregation and promote genetic instability. However, interphase centrosomes are physically tethered by a proteinaceous linker composed of C-Nap1 (also known as CEP250) and the filamentous protein rootletin. Linker disassembly occurs at the onset of mitosis in a process known as centrosome disjunction and is triggered by the Nek2-dependent phosphorylation of C-Nap1. However, the mechanistic consequences of C-Nap1 phosphorylation are unknown. Here, we demonstrate that Nek2 phosphorylates multiple residues within the C-terminal domain of C-Nap1 and, collectively, these phosphorylation events lead to loss of oligomerization and centrosome association. Mutations in non-phosphorylatable residues that make the domain more acidic are sufficient to release C-Nap1 from the centrosome, suggesting that it is an increase in overall negative charge that is required for this process. Importantly, phosphorylation of C-Nap1 also perturbs interaction with the core centriolar protein, Cep135, and interaction of endogenous C-Nap1 and Cep135 proteins is specifically lost in mitosis. We therefore propose that multisite phosphorylation of C-Nap1 by Nek2 perturbs both oligomerization and Cep135 interaction, and this precipitates centrosome disjunction at the onset of mitosis.

Study on cell survival, induction of apoptosis and micronucleus formation in SCL‐II cells after exposure to the auger electron emitter99mTc

OBJECTIVE

To study the biological effectiveness of Auger electrons emitted by (99m)Tc on cell survival, induction of apoptosis and micronucleus (MN) formation in the human squamous cell carcinoma cell line SCL-II and compare the effects observed to those observed after exposure to external 60Co gamma radiation.

MATERIAL AND METHODS

Cells were either gamma(60Co)-irradiated (0.67 Gy/min) or exposed to (99m)Tc-pertechnetate (0.95-14.3 MBq/ml) for 24 h under cell culture conditions and assayed for cell survival (colony-forming assay), micronucleus formation (cytochalasin B assay) and the frequency of apoptotic cells (fluorescence microscopy). Monte Carlo based dosimetry has been applied to derive the absorbed dose corresponding to the accumulated decays of (99m)Tc under the given geometry.

RESULTS

Absorbed doses up to 0.5 Gy could be achieved after 99mTc-exposure leading to no substantial cell killing in this dose range except at one dose point (0.1 Gy) resulting in an relative biological effectiveness (RBE)SF 0.9 of 0.64 when compared to the 60Co reference radiation. MN formation was described best by a linear dose response and was consistently lower after 99mTc exposure when compared to 60Co irradiated cells resulting in an RBE of 0.37. Apoptosis induction was significantly increased after 99mTc exposure at much lower doses (0.1 Gy) when compared to the reference radiation. The (99m)Tc uptake experiments revealed an activity concentration ratio cells vs. medium of 0.07 after 24 h of exposure.

CONCLUSION

No overall increased biological effectiveness due to the emitted Auger electrons of (99m)Tc, applied as sodium-pertechnetate, could be observed in the investigated cell line when compared to acute external gamma radiation. The RBEs in the range of 0.37-0.64 might be well explained by dose rate effects. The significantly increased apoptotic response after (99m)Tc-exposure at very low doses has to be further investigated.

Analysis of the CONRAD computational problems expressing only stochastic uncertainties: neutrons and protons

Within the scope of CONRAD (A Coordinated Action for Radiation Dosimetry) Work Package 4 on Computational Dosimetry jointly collaborated with the other research actions on internal dosimetry, complex mixed radiation fields at workplaces and medical staff dosimetry. Besides these collaborative actions, WP4 promoted an international comparison on eight problems with their associated experimental data. A first set of three problems, the results of which are herewith summarised, dealt only with the expression of the stochastic uncertainties of the results: the analysis of the response function of a proton recoil telescope detector, the study of a Bonner sphere neutron spectrometer and the analysis of the neutron spectrum and dosimetric quantity H(p)(10) in a thermal neutron facility operated by IRSN Cadarache (the SIGMA facility). A second paper will summarise the results of the other five problems which dealt with the full uncertainty budget estimate. A third paper will present the results of a comparison on in vivo measurements of the (241)Am bone-seeker nuclide distributed in the knee. All the detailed papers will be presented in the WP4 Final Workshop Proceedings.

Mechanical properties of the posterior rotator cuff

BACKGROUND

The infraspinatus is an important active and passive stabilizer of the glenohumeral joint. It functions as external rotator and participates in elevation of the arm. As its main posterior component, it is frequently involved in rotator cuff tears.

OBJECTIVE

The purpose of this study was to determine the structural and mechanical properties of the infraspinatus tendon structure, including the midsubstance and insertion regions, in the superior, mid-superior, mid-inferior, and inferior portions, in two joint positions.

METHODS

The infraspinatus tendons from 22 fresh frozen cadaver shoulders were divided into four strips. The tendons were held in a cryo-jaw and tested with a material-testing machine in 0 degrees or 60 degrees of glenohumeral abduction corresponding to 90 degrees arm abduction. Ultimate load, displacement and failure mode were recorded. Stiffness, ultimate stress and elastic modulus were calculated.

RESULTS

Significant differences between glenohumeral abduction positions were detected only for the elastic modulus. The mid-superior (676.5 N, S.D. 231.0 N) and the inferior portion (549.9 N, S.D. 284.6 N) had the highest failure loads while the superior (462.8 N, S.D. 237.2 N) and the mid-inferior portions (315.3 N, S.D. 181.5 N) were weaker. Similar trends across the tendon strips were shown for stiffness, ultimate stress and elastic modulus.

RELEVANCE

Position dependent changes in mechanical properties of the infraspinatus tendon probably do not play a role in the pathomechanism of posterior shoulder dislocation. Peaks in stiffness in mid-superior and inferior tendon sections explain the low incidence of posterior dislocations. The low ultimate failure loads in the superior portions might explain the frequent extension of rotator cuff ruptures into the infraspinatus tendon.

[Psychological effect of corrective surgery in female patients with structural and functional abnormalities of the jaws]

20 young women (16 to 31 years of age) who underwent orthognatic surgery between 1979 and 1984 were subjected to an evaluation of their dental, orthognatic and psychological catamneses. The psychological results concerning operation motivation, preoperative stress and information, early postoperative condition and subjective assessment of the operative result are reported and discussed. Proposals are made to improve pre- and postoperative treatment of these patients.

Rey-Auditory Verbal Learning and Rey-Osterrieth Complex Figure Design performance in Alzheimer's disease and closed head injury

Performance on the Rey-Auditory Verbal Learning (R-AVL) and Rey-Osterrieth Complex Figure Design (R-O CFD) tests was examined in patients (N = 94) with dementia of the Alzheimer's type (DAT) and closed head injury (CHI). On the R-AVL, DAT patients demonstrated considerably greater impairment than CHI patients, along with a flat learning/retention curve that showed negligible improvement with repeated trials, recency effects only, and an excessive number of word intrusions (confabulation) on the recognition trial. CHI patients demonstrated both a recency and primacy effect along with improvement over repeated trials (positive slope learning curve). Both groups demonstrated impairment R-O CFD recall; the DAT group again displayed substantially greater copying and recall deficits. Clinical guidelines are given for the use of the R-AVL and R-O CFD for these two patient populations.

Tissue distribution and myelotoxicity of daunomycin in the rat: rapid bolus injection vs continuous infusion

The pharmacokinetic and cytotoxic behaviour of daunomycin in rats (7.5 mg/kg) when administered as an i.v. bolus injection were compared with those of a 3-hr infusion. After an i.v. bolus injection, the plasma drug levels decreased triphasically (t1/2 alpha = 0.8 min, t1/2 beta = 29.6 min and t1/2 gamma = 9.9 hr). The organs showed two types of concentration/time curves. One was found in the lungs, liver, kidneys and heart and had an initial high drug concentration followed by a relatively rapid elimination. The other was shown by the hemopoietic tissues (spleen and bone marrow): the drug uptake phase lasted longer (about 1.5 hr) and the elimination was slower. In general, daunomycin infusion led to substantially lower plasma and tissue levels, including in the heart, liver and kidneys. Again the hemopoietic tissues behaved in a different way: in spleen and bone marrow almost equal drug levels were obtained after daunomycin infusion as compared to a bolus injection. The myelotoxicity after daunomycin treatment was assessed by CFU-S (colony forming units-spleen) survival: the bolus injection killed as many CFU-S as did infusion (mean +/- S.D.: 11.8 +/- 5.3 CFU-S survival versus mean +/- S.D.: 13.5 +/- 2.4). Thus, it can be predicted that daunomycin infusion will lead to less cardiotoxicity but to an equal bone marrow suppression.

Dietary characteristics of hyperactive and control boys

The purpose of this study was to examine the relationship between dietary habits and behavioral problems in hyperactive boys and to determine how successful parents are in maintaining their children on sugar-free diets. The mothers of 32 hyperactive boys aged 7 to 12 years and 26 matched controls completed 3-day diet records and food frequency interviews. The hyperactive boys were also evaluated in a playroom for impulsivity, compliance, attention, motor activity, memory, and learning. No differences were found in any of the measures of dietary content between the hyperactive and control groups. The only significant differences between those two groups were a lower socioeconomic status and a greater number of parents attempting sugar-restricted diets in the hyperactive group. Boys on sugar-restricted diets had only one significant dietary difference from those not restricted. Correlations between the information obtained in food frequency interviews and in 3-day diet histories were not significant (r = .06 to .33) for the hyperactive group, but the food frequency interviews were significant for the control group (r = .41 to .47). Four behavioral variables showed significant partial correlations with reported sugar intake. Overall, the results demonstrated that the diets of a group of hyperactive boys were similar to those of a control group. There appeared to be little difference between the diets of the families that attempted to restrict sugar and those that did not.

Glycogen accumulation of the aging human brain

We describe light- and electron-microscopically a new type of intracytoplasmatic inclusions within cell processes of the cerebral cortex and the underlying white matter. These structures measure 5-50 micron in diameter and consist almost exclusively of densely packed alpha- or beta-glycogen granules, which never occur together in any single structure. Within their periphery, electron-dense amorphous spots and cell organelles, especially mitochondria, were seen. No membrane-bound glycogen was observed. We propose to call them granular glycogen bodies. They occur in 4 of 7 examined postmortem specimens of the cerebral cortex of people older than 60 years of age. They were not found in 4 younger controls aged 26-48. Their appearance may reflect a distinct turnover disorder of carbohydrate metabolism, which becomes manifest under diverse pathologic conditions and in the normal aging process.

Effects of sucrose ingestion on the behavior of hyperactive boys

A challenge design was used in two separate studies to investigate the effects of sucrose ingestion on the behavior and learning of hyperactive boys. In both studies, 16 boys were admitted to a clinical research center for 3 successive days, on each of which they were given a sucrose-free diet. On day 1, baseline levels on the learning tasks were established; on days 2 and 3 a challenge drink of either sucrose 1.75 gm/kg or a placebo (aspartame in equivalent sweetness) was presented, in a counterbalanced order. In the first study the challenge drink was administered 1 hour after lunch; in the second study it was given in the morning after an overnight fast. On days 2 and 3 of both studies, 37 behavioral (playroom observation and examiner ratings) and cognitive (learning and memory tasks) measures were collected, starting 1/2 hour after ingestion of the drink. The results of both studies revealed no differences between the boys' performance on the two challenge days. These findings undermine the hypothesis that sucrose plays a major role in accounting for the inappropriate behavior of hyperactive boys.

Repeated daunomycin administration in rats. Pharmacokinetics and bone marrow toxicity

In the experiments described here, rats received three IV bolus injections (7.5 mg/kg) of daunomycin. The plasma data obtained after a single IV injection could be described by a two-compartment open model with t1/2 alpha and t1/2 beta values of 18.4 and 472.1 min. Of the tissues, the lungs contained the most daunomycin per gram of tissue, followed by the kidneys, liver, heart, and spleen. Daunomycinol was the main metabolic product and no substantial differences were found in daunomycinol content among the different organs. For all tissues and plasma, higher drug concentration values than would be expected on the basis of accumulation alone were observed after the second but not after the third injection. The cumulative urine excretion of daunomycin and daunomycinol remained essentially unchanged after one, two, and three daunomycin injections. However, the cumulative bile excretion increased after repeated daunomycin administration. The experiments in which the myelotoxicity was assessed by CFU-S survival after daunomycin treatment showed that three successive daunomycin administrations lead to a proportional reduction in stem cells.

Evidence for a possible dose-dependent pharmacokinetics of Cyclosporin-A in the rat

Cyclosporin-A (Cy-A) was administered to rats intravenously (i.v.) at different dosages (20, 40 and 80 mg/kg body weight). At the lower dose (20 mg/kg), the blood levels decreased biphasically and could be described by an open linear two-compartment model with excretion from the central compartment only. The t 1/2 values for the alpha-distribution and beta-elimination phases were about 6 min and 16.5 h, respectively. At higher dose levels (40 and 80 mg/kg), the involvement of an additional compartment became apparent. The blood concentration/time data sets obtained with 40 and 80 mg/kg doses were best described by an open linear three-compartment model. The 24-h urine and bile excretions were in the order of 10 and 20% of the total administered dose. The values for the normalized areas under the plasma concentration/time curves obtained at different Cy-A doses (20, 40 and 80 mg/kg) were about 1, 3 and 25, respectively.