Homology modelling of human DHCR24 (seladin-1) and analysis of its binding properties through molecular docking and dynamics simulations

Recent biochemical and clinical evidences unveiled that DHCR24 enzyme (3-beta-hydoxysterol-Delta(24)-reductase, also named seladin-1), which catalyzes the last step of the cholesterol biosynthesis, is implicated in relevant neuroprotective processes by modulating the level of cholesterol in membrane. The present study was undertaken with a view to model the DHCR24 enzyme and its catalytic site, analyzing the substrate recognition at an atomic level. A homology model of the enzyme was obtained based on plant Cytokinin Dehydrogenase, and its active site was found to bind the desmosterol plus a set of post-squalenic intermediates of the cholesterol biosynthesis in a binding mode conducive to catalysis, even if the docking results suggested that the enzyme has a clear preference for the last intermediates of such biosynthetic pathway. Since DHCR24 possesses a putative transmembrane segment, the enzyme was, then, inserted in a suitable membrane model and the membrane-anchored structure in complex with desmosterol and cholesterol underwent 10ns MD simulations. Such simulations evidenced a clearly different behavior between substrate and product since the product only completely leaves the catalytic cavity whereas desmosterol firmly conserves its pivotal interactions during all simulation time. This is one of the first reports documenting the enzymatic product egress using simple MD simulations in which all atoms are free to move.

Clinical predictors of cardiac syncope at initial evaluation in patients referred urgently to a general hospital: the EGSYS score

OBJECTIVE

To develop, in patients referred for syncope to an emergency department (ED), a diagnostic score to identify those patients likely to have a cardiac cause.

DESIGN

Prospective cohort study.

SETTING

ED of 14 general hospitals.

PATIENTS

516 consecutive patients with unexplained syncope.

INTERVENTIONS

Subjects underwent a diagnostic evaluation on adherence to Guidelines of the European Society of Cardiology. The clinical features of syncope were analysed using a standard 52-item form. In a validation cohort of 260 patients the predictive value of symptoms/signs was evaluated, a point score was developed and then validated in a cohort of 256 other patients.

MAIN OUTCOME MEASUREMENTS

Diagnosis of cardiac syncope, mortality.

RESULTS

Abnormal ECG and/or heart disease, palpitations before syncope, syncope during effort or in supine position, absence of autonomic prodromes and absence of predisposing and/or precipitating factors were found to be predictors of cardiac syncope. To each variable a score from +4 to -1 was assigned to the magnitude of regression coefficient. A score >or=3 identified cardiac syncope with a sensitivity of 95%/92% and a specificity of 61%/69% in the derivation and validation cohorts, respectively. During follow-up (mean (SD) 614 (73) days) patients with score >or=3 had a higher total mortality than patients with a score <3 both in the derivation (17% vs 3%; p<0.001) and in the validation cohort (21% vs 2%; p<0.001).

CONCLUSIONS

A simple score derived from clinical history can be usefully employed for the triage and management of patients with syncope in an ED.

Retinoic acid reduces human neuroblastoma cell migration and invasiveness: effects on DCX, LIS1, neurofilaments-68 and vimentin expression

BACKGROUND

Neuroblastoma is a severe pediatric tumor, histologically characterised by a variety of cellular phenotypes. One of the pharmacological approaches to neuroblastoma is the treatment with retinoic acid. The mechanism of action of retinoic acid is still unclear, and the development of resistance to this differentiating agent is a great therapy problem.Doublecortin, a microtubule-associated protein involved in neuronal migration, has recently been proposed as a molecular marker for the detection of minimal residual disease in human neuroblastoma. Nevertheless, no information is available on the expression of doublecortin in the different cell-types composing human neuroblastoma, its correlation with neuroblastoma cell motility and invasiveness, and the possible modulations exerted by retinoic acid treatment.

METHODS

We analysed by immunofluorescence and by Western blot analysis the presence of doublecortin, lissencephaly-1 (another protein involved in neuronal migration) and of two intermediate filaments proteins, vimentin and neurofilament-68, in SK-N-SH human neuroblastoma cell line both in control conditions and under retinoic acid treatment. Migration and cell invasiveness studies were performed by wound scratch test and a modified microchemotaxis assay, respectively.

RESULTS

Doublecortin is expressed in two cell subtypes considered to be the more aggressive and that show high migration capability and invasiveness. Vimentin expression is excluded by these cells, while lissencephaly-1 and neurofilaments-68 are immunodetected in all the cell subtypes of the SK-N-SH cell line. Treatment with retinoic acid reduces cell migration and invasiveness, down regulates doublecortin and lissencephaly-1 expression and up regulates neurofilament-68 expression. However, some cells that escape from retinoic acid action maintain migration capability and invasiveness and express doublecortin.

CONCLUSION

a) Doublecortin is expressed in human neuroblastoma cells that show high motility and invasiveness;b) Retinoic acid treatment reduces migration and invasiveness of the more aggressive cell components of SK-N-SH cells;c) The cells that after retinoic acid exposure show migration and invasive capability may be identified on the basis of doublecortin expression.

Evaluation of conventional and real-time PCR assays for detection and differentiation of Spotted Fever Group Rickettsia in dog blood

Spotted Fever Group Rickettsia is important cause of emerging and re-emerging infectious disease in people and dogs. Importantly, dogs can serve as sentinels for disease in people. Sensitive and specific diagnostic tests that differentiate among species of infecting Rickettsia are needed. The objective of this study was to develop a sensitive and specific PCR that differentiates SFG Rickettsia infecting dog blood. Conventional and real-time PCR assays were developed using primers that targeted a small region of the ompA gene. Their sensitivity, determined by testing a cloned target sequence in the presence of host DNA, was 15-30 and 5 copies of DNA, respectively. Testing of Rickettsia cultures and analysis of Rickettsia gene sequences deposited in GenBank verified DNA could be amplified and used to differentiate species. DNA from the blood of infected dogs was also tested. Importantly, Rickettsia DNA was detected before seroconversion in some dogs. The species of infecting Rickettsia was also identified. We conclude these assays may assist in the timely diagnosis of infection with SFG Rickettsia. They may also facilitate the discovery of novel SFG Rickettsia infecting dogs, and in the investigation of dogs as sentinels for emerging rickettsioses.

Calcineurin primes immature gonadotropin-releasing hormone-secreting neuroendocrine cells for migration

During development, many neurons display calcium-dependent migration, but the role of this messenger in regulating gene expression leading to this event has not yet been elucidated. Among the decoders of calcium signals is calcineurin, a Ca(2+)/calmodulin serine/threonine phosphatase that has been involved in both short-term and long-term cellular changes. By using immortalized GnRH-secreting neurons, we now show that, in vitro, Ca(2+)-dependent gene expression, proceeding via calcineurin and the transcription factor nuclear factor of activated T cells, is a key player controlling the chemomigratory potential of developing GnRH-secreting neurons. Furthermore, our data highlight the switch nature of this phosphatase, whose activation or inactivation guides cells to proceed from one genetic program to the next.

Polarization of caveolins and caveolae during migration of immortalized neurons

During CNS development neurons undergo directional migration to achieve their adult localizations. To study neuronal migration, we used a model cell line of immortalized murine neurons (gonadotropin-releasing hormone expressing neurons; GN11), enriched with caveolins and caveolae invaginations that show in vitro chemotaxis upon serum exposure. Cholesterol depletion with methyl-beta-cyclodextrin induced the loss of caveolae and the inhibition of chemotaxis, thus suggesting that GN11 migration depends upon the structural integrity of caveolae. Polarization of proteins and organelles is a hallmark of cell migration. Accordingly, GN11 cells transmigrating through filter pores exhibited a polarized distribution of caveolin-1 isoform (cav-1) in the leading processes. In contrast, during two-dimensional migration cav-1 and caveolae polarized at the trailing edge. As caveolae are enriched with signaling molecules, we suggest that asymmetrical localization of caveolae may spatially orient GN11 neurons to incoming migratory signals thereby transducing them into directional migration.

From nose to fertility: the long migratory journey of gonadotropin-releasing hormone neurons

Gonadotropin-releasing hormone (GnRH) neurons, a small number of cells dispersed in the hypothalamic region of the basal forebrain, play an important role in reproductive function. These neurons originate in the nasal placode and migrate, first in the nasal compartment, then through the cribriform plate and finally through the basal forebrain, before they attain their positions in the hypothalamus. Their movement through changing molecular environments suggests that numerous factors are involved in different phases of their migration. In humans, failure of GnRH neurons to migrate normally results in delayed or absent pubertal maturation and infertility. Advances in genetic and molecular biologic techniques in this decade have allowed us to gain insights into several molecules that affect the migration of GnRH neurons and, consequently, play a role in the establishment and maintenance of reproductive function.

Catheter ablation of isolated premature ventricular contractions arising from the sinus of Valsalva

Monomorphic premature ventricular contractions (PVCs) are a benign phenomenon in patients without structural heart disease. The focal source is usually localised in the right ventricular outflow tract and more rarely in the left ventricular outflow tract. We report two cases of frequent isolated PVCs treated with radiofrequency catheter ablation. Ventricular dysfunction was documented in one patient and the potential contribution of arrhythmia to ventricular dysfunction was suspected. In both patients electroanatomic mapping of the right and left ventricular outflow tracts was performed, which allowed identification of the earliest ventricular activation during PVCs. The site of the earliest ventricular activation was documented in both cases at the left coronary cusp of the aortic valve. Aortography was performed to disclose the relationship between the ablation catheter and the anatomic structure of the aortic root. PVCs were successfully eliminated with radiofrequency application in both patients.

Update in the treatment of neurally-mediated syncope

Syncope is a transient, self-limited loss of consciousness, usually leading to falling. The underlying mechanism is a transient global cerebral hypoperfusion. Since there are many causes of syncope, a specific treatment cannot be administered without knowing of the exact mechanism responsible of loss of consciousness. Drugs are ineffective. The main therapeutic innovations of the most recent years are isometric counter-pressure maneuvres, lower limb compression bandage and therapy guided by implantable loop recorder in patients with recurrent suspected neurally-mediated syncope.

Cardioinhibitory carotid sinus hypersensitivity predicts an asystolic mechanism of spontaneous neurally mediated syncope

AIMS

We correlated the finding of cardioinhibitory carotid sinus hypersensitivity (CSH) with that observed during a spontaneous syncopal relapse by means of an implantable loop recorder (ILR).

METHODS AND RESULTS

We included 18 consecutive patients with suspected recurrent neurally mediated syncope and positive cardioinhibitory response during carotid sinus massage (max pause 5.5 +/- 1.6 s) who had subsequent documentation of a spontaneous syncope by means of an ILR. They were compared with a 2:1 age- and sex-matched group of 36 patients with a clinical diagnosis of recurrent neurally mediated syncope and negative response to carotid sinus massage, tilt testing and ATP test. Asystole >3 s was observed at the time of the spontaneous syncope in 16 (89%) of CSH patients and in 18 (50%) of the control group (P = 0.007). Sinus arrest was the most frequent finding among CSH patients but not among controls (72 vs. 28%, P = 0.003). After ILR documentation, 14 CSH patients with asystole received dual-chamber pacemaker implantation; during 35 +/- 22 months of follow-up, 2 syncopal episodes recurred in 2 patients (14%), and pre-syncope occurred in another 2 patients (14%). Syncope burden decreased from 1.68 (95% confidence interval 1.66 - 1.70) episodes per patient per year before to 0.04 (0.038-0.042) after pacemaker implant (98% relative risk reduction).

CONCLUSIONS

In patients with suspected neurally mediated syncope, the finding of cardioinhibitory CSH predicts an asystolic mechanism at the time of spontaneous syncope and, consequently, suggests a possible benefit of cardiac pacing therapy.

Dexamethasone blocks the migration of the human neuroblastoma cell line SK-N-SH

Glucocorticoids (Gc) influence the differentiation of neural crest-derived cells such as those composing sympathoadrenal tumors like pheochromocytomas, as well as neuroblastomas and gangliomas. In order to obtain further information on the effects of Gc on cells evolving from the neural crest, we have used the human neuroblastoma cell line SK-N-SH to analyze: 1) the presence and the binding characteristics of Gc receptors in these cells, 2) the effect of dexamethasone (Dex) on the migration of SK-N-SH cells, and 3) the effect of Dex on the organization of the cytoskeleton of SK-N-SH cells. We show that: 1) receptors that bind [(3)H]-Dex with high affinity and high capacity (Kd of 9.6 nM, Bmax of 47 fmol/mg cytosolic protein, corresponding to 28,303 sites/cell) are present in cytosolic preparations of SK-N-SH cells, and 2) treatment with Dex (in the range of 10 nM to 1 microM) has an inhibitory effect (from 100% to 74 and 43%, respectively) on the chemotaxis of SK-N-SH cells elicited by fetal bovine serum. This inhibition is completely reversed by the Gc receptor antagonist RU486 (1 microM), and 3) as demonstrated by fluorescent phalloidin-actin detection, the effect of Dex (100 nM) on SK-N-SH cell migration is accompanied by modifications of the cytoskeleton organization that appear with stress fibers. These modifications did not take place in the presence of 1 microM RU486. The present data demonstrate for the first time that Dex affects the migration of neuroblastoma cells as well as their cytoskeleton organization by interacting with specific receptors. These findings provide new insights on the mechanism(s) of action of Gc on cells originating in the neural crest.

Neuropilins and their ligands are important in the migration of gonadotropin-releasing hormone neurons

Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus play an important role in reproductive function. These cells originate in the nasal compartment and migrate into the basal forebrain in association with olfactory/vomeronasal nerves in embryonic life in rodents. Here, we studied the role of neuropilins and their ligands, semaphorins, in the development of the olfactory-GnRH system. We focused on Neuropilin-2 knock-out (Npn-2(-/-)) mice, because they are known to display defasciculation of olfactory nerves and reduced fertility. We found a significant decrease in the number of GnRH neurons in the hypothalamus and a marked reduction in their gonadal size. We then observed an abnormal increase of GnRH neurons in the noses of Npn-2(-/-) mice, indicating that these cells failed to migrate into the forebrain. However, because neuropilins and semaphorins are involved in events of neuronal migration in the brain, we asked whether the observed reduction in GnRH neurons was directly attributable to the action of these molecules. Using fluorescence-activated cell sorting and reverse transcription-PCR on mRNA derived from embryonic green fluorescent protein (GFP)-GnRH transgenic mice, we found expression of class 3 semaphorins and their receptors (neuropilin-1/2 and plexin-A1) in GnRH neurons. Furthermore, double-immunofluorescence experiments showed that migrating GnRH neurons, as well as associated olfactory fibers, express Npn-2 in the nasal region. We then used a line of immortalized GnRH neurons (GN11 cells) that display the same expression patterns for semaphorins and their receptors as GFP-GnRH cells and found that class 3 semaphorins and vascular endothelial growth factors modulate their migratory activity. These studies provide support for the direct involvement of neuropilins and their ligands in the establishment of the GnRH neuroendocrine system.

Leukemia inhibitory factor induces the chemomigration of immortalized gonadotropin-releasing hormone neurons through the independent activation of the Janus kinase/signal transducer and activator of transcription 3, mitogen-activated protein kinase/extracellularly regulated kinase 1/2, and phosphatidylinositol 3-kinase/Akt signaling pathways

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine of the IL-6 superfamily. LIF acts through a cell-surface receptor complex formed by two subunits, the specific LIF receptor beta (LIFRbeta) and the glycoprotein 130. Little is known about LIF involvement in modulating the neuroendocrine circuitry governing the reproductive function and, specifically, the development of GnRH-secreting neurons. In the present study, we evaluated the effect of LIF on the in vitro migration of GN11 cells, a model of immature and migratory GnRH neurons, and the signaling pathways involved in this process. GN11 cells expressed both LIFRbeta and glycoprotein 130 subunits. Exposure of GN11 cells to 100 ng/ml LIF resulted in activation of the Janus kinases (Jaks)/signal transducer and activator of transcription 3, MAPK/ERK1/2, and phosphatidylinositol 3-kinase/protein kinase B/Akt pathways. The selective inhibition of Jaks, MAPK kinase, and phosphatidylinositol 3-kinase indicated that these signaling pathways were activated independently by LIF and that Jak2 is not the main kinase involved in LIF signaling. Exposure of GN11 cells to LIF for 3 h induced a concentration-dependent chemotactic response, with a plateau at 100 ng/ml LIF. LIF was also found to induce chemokinesis of GN11 cells. Furthermore, LIF-promoted GN11 migration was the result of the partial and independent contribution of all the three signaling pathways activated by LIF. The present data, together with the observation that LIF and LIFRbeta are expressed prenatally in the mouse nasal compartment, would suggest that LIF might participate in the migration of GnRH neurons.

Kallmann's syndrome, a neuronal migration defect

Infertility and inability to smell are the phenotypical features of Kallmann's syndrome (KS), a genetic disease which affects 1 in 10,000 males and 1 in 50,000 females, the majority of the cases being sporadic. The molecular pathogenesis of KS is complex but mainly referable to the impairment of olfactory axon development and of the migration of gonadotropin-releasing hormone (GnRH) neurons. Only two different genes have been identified so far as responsible for the disease: KAL1 and KAL2, encoding anosmin-1 and fibroblast growth factor receptor 1 (FGFR1), respectively. In this review we focus our attention on insights evoked by recent studies, which propose a new direct role for anosmin-1 in the migration GnRH neurons, and a fascinating hypothesis of interactions between anosmin-1 and FGFR1 systems.

[Comparative study of results of catheter ablation in ventricular tachycardia of different etiologies]

BACKGROUND

The aim of this study was to assess long-term results and adverse events in patients with ventricular tachycardia from different etiologies.

METHODS

The recurrence rate of tachycardia, consequent further therapies (other catheter ablation procedures, drug therapy and implantable defibrillator) and clinical events have been assessed in 60 consecutive patients undergoing ventricular tachycardia catheter ablation between January 2000 and December 2004.

RESULTS

During a median follow-up of 20 months (interquartile range 13-36 months), tachycardia recurred in 27 patients (45%) after a median of 3 months (interquartile range 1-12 months). A second procedure was performed in 11 patients; it was successful in 8 patients. Four patients underwent pharmacological therapy which was successful in all cases. Overall, after ablation (> or =1 procedures) and pharmacological therapy, tachycardia was cured in 75% of cases. All the 20 patients without structural heart disease were cured with ablation vs. 62% of patients with heart disease (p = 0.001). Patients with dilated cardiomyopathy reported worst results (33% success, p = 0.03). Recurrences were predicted by acute failure of procedure (p = 0.05), presence of heart disease (p = 0.006) and history of atrial arrhythmias (p = 0.02). On a multivariate analysis, only structural heart disease continued to be an independent predictor of ventricular tachycardia recurrence.

CONCLUSIONS

Catheter ablation of ventricular tachycardia has a high percentage of recurrences in patients with heart disease, whereas is curative in subjects without structural heart disease.