The end adjusts the means: Heterochromatin remodelling during terminal cell differentiation

All cells that constitute mature tissues in an eukaryotic organism undergo a multistep process of cell differentiation. At the terminal stage of this process, cells either cease to proliferate forever or rest for a very long period of time. During terminal differentiation, most of the genes that are required for cell ‘housekeeping’ functions, such as proto-oncogenes and other cell-cycle and cell proliferation genes, become stably repressed. At the same time, nuclear chromatin undergoes dramatic morphological and structural changes at the higher-order levels of chromatin organization. These changes involve both constitutively inactive chromosomal regions (constitutive heterochromatin) and the formerly active genes that become silenced and structurally modified to form facultative heterochromatin. Here we approach terminal cell differentiation as a unique system that allows us to combine biochemical, ultrastructural and molecular genetic techniques to study the relationship between the hierarchy of chromatin higher-order structures in the nucleus and its function(s) in dynamic packing of genetic material in a form that remains amenable to regulation of gene activity and other DNA-dependent cellular processes.     

Chromatin condensation in terminally differentiating mouse erythroblasts does not involve special architectural proteins but depends on histone deacetylation

Terminal erythroid differentiation in vertebrates is characterized by progressive heterochromatin formation and chromatin condensation and, in mammals, culminates in nuclear extrusion. To date, although mechanisms regulating avian erythroid chromatin condensation have been identified, little is known regarding this process during mammalian erythropoiesis. To elucidate the molecular basis for mammalian erythroblast chromatin condensation, we used Friend virus-infected murine spleen erythroblasts that undergo terminal differentiation in vitro. Chromatin isolated from early and late-stage erythroblasts had similar levels of linker and core histones, only a slight difference in nucleosome repeats, and no significant accumulation of known developmentally regulated architectural chromatin proteins. However, histone H3(K9) dimethylation markedly increased while histone H4(K12) acetylation dramatically decreased and became segregated from the histone methylation as chromatin condensed. One histone deacetylase, HDAC5, was significantly upregulated during the terminal stages of Friend virus-infected erythroblast differentiation. Treatment with histone deacetylase inhibitor, trichostatin A, blocked both chromatin condensation and nuclear extrusion. Based on our data, we propose a model for a unique mechanism in which extensive histone deacetylation at pericentromeric heterochromatin mediates heterochromatin condensation in vertebrate erythroblasts that would otherwise be mediated by developmentally-regulated architectural proteins in nucleated blood cells. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Dual and opposing roles of presynaptic Ca2+ influx for spontaneous GABA release from rat medial preoptic nerve terminals

Calcium influx into the presynaptic nerve terminal is well established as a trigger signal for transmitter release by exocytosis. By studying dissociated preoptic neurons with functional adhering nerve terminals, we here show that presynaptic Ca²⁺ influx plays dual and opposing roles in the control of spontaneous transmitter release. Thus, application of various Ca²⁺ channel blockers paradoxically increased the frequency of spontaneous (miniature) inhibitory GABA-mediated postsynaptic currents (mIPSCs). Similar effects on mIPSC frequency were recorded upon washout of Cd²⁺ or EGTA from the external solution. The results are explained by a model with parallel Ca²⁺ influx through channels coupled to the exocytotic machinery and through channels coupled to Ca²⁺-activated K⁺ channels at a distance from the release site.     

Fast neurotransmission in the rat medial preoptic nucleus

The functional properties of neurotransmission in the medial preoptic nucleus (MPN) were studied in a brain slice preparation from young male rats. The aims were to evaluate the thin slice preparation for studying evoked synaptic responses in MPN neurons, to characterize the fast responses triggered by activation of presynaptic nerve fibers in the MPN, and to identify the involved receptor types. Presynaptic stimulation within the MPN evoked postsynaptic voltage and current responses that were blocked by 200 microM Cd2+ or by 2.0 microM tetrodotoxin and were attributed to action potential-evoked transmitter release. The relation to stimulus strength and comparison with spontaneous synaptic currents suggested that in many cases only one presynaptic nerve fiber was excited by the stimulus. Furthermore, the transmission was probabilistic in nature, with frequent failures. Thus, response probability, most likely reflecting transmitter release probability, could be evaluated in the thin slice preparation. Evoked excitatory postsynaptic currents recorded under voltage-clamp conditions were, due to kinetics, I-V relation, and pharmacological properties, attributed to AMPA/kainate receptors and NMDA receptors, whereas inhibitory currents were attributed to GABAA receptors. No responses that could be attributed to glycine or other types of primary transmitters were detected. Although serotonin (5-HT) did not appear to function as a primary transmitter, glutamate- as well as GABA-mediated transmission was suppressed by 500 microM 5-HT, with a clear reduction in response probability observed. 5-HT also reduced the frequency, but not the amplitude, of spontaneous postsynaptic currents and was therefore ascribed a presynaptic site of action.     

Carbamazepine-induced drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome: report of four cases and brief review

Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is a rare but severe drug reaction, most commonly to aromatic anticonvulsants with a delayed onset, variable clinical presentation and protracted course. The exact incidence of DRESS syndrome is not known because of the variability in clinical presentation, lack of strict diagnostic criteria and universally accepted nomenclature.
We report four cases of DRESS syndrome associated with the use of carbamazepine. The clinical manifestation was similar: a maculopapular eruption progressing to exfoliative erythroderma, fever, and lymphadenopathy. Leukocytosis, atypical lymphocytes and liver injury (in 2 patients) were also observed. Assessment of causality using the Naranjo algorithm established a "probable" relationship with carbamazepine in three of the cases and a "possible" relationship in one case.
Detection of DRESS syndrome is dependent on the exclusion of a variety of diseases with similar manifestations and may be delayed in time. DRESS syndrome is a potentially life-threatening multisystem adverse drug reaction, and accidental reexposure or drug provocation tests must be avoided.     

Treatment of adverse drug reactions in a dermatology department

The aim of the study was to evaluate the pattern of utilization of systemic drugs used in the management of adverse drug reactions (ADRs) leading to hospitalization. A prospective pharmacovigilance study was carried out among patients admitted to the Clinic of Dermatology and Venereology in Stara Zagora (July 1999–June 2009). ADRs were classified by type, severity and causality. Casecausality was scored according to Naranjo et al. (1981). Drug utilization was measured in defined daily doses (DDDs) per 100 hospital bed days. A total of 144 cutaneous ADRs, predominantly “type B” were the reason for hospitalization. Highest utilization for the management of ADRs was found for the drug groups “Blood and blood forming organs” (406.08 DDDs/100 bed days) and “Respiratory system” (111.15 DDDs/100 bed days). The use of DDD for measuring drug utilization reveals the importance of drug-induced exacerbations of chronic skin diseases like psoriasis which were associated with significant utilization of drugs belonging to the group “Blood and blood forming organs”. Considering the low preventability of “type B” ADRs, our findings suggest that potential reduction of drug-related hospitalizations may be achieved through the rational use of drugs in patients with comorbidities.     

New insights into secondary prevention in post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is unique amongst psychiatric disorders in two ways. Firstly, there is usually a very clear point of onset- the traumatic event The second unique feature of PTSD is that it is characterized by a failure of the normal response to resolve. Given these two characteristics, PTSD appears a good candidate for secondary prevention, ie, interventions immediately after the trauma. Evidence available starting from current concepts and contemporary research of potential secondary prevention interventions are presented. Common practices in the aftermath of trauma such as debriefing and benzodiazepines need to be carefully considered, taking into account their potential harm to the spontaneous recovery process, and the trajectory of PTSD, and not only judging them according to their immediate (comforting) effects. A discussion of the balance required between aiding recovery but not interfering with the potent natural resolution of symptoms (that is expected in most cases), along with potential avenues of future research, are presented. Results of a small pilot study with a single intervention of hydrocortisone immediately after trauma appear to be promising, and clearly indicate the need for further studies.     

Spray‐ and laser‐assisted biomaterial processing for fast and efficient autologous cell‐plus‐matrix tissue engineering

At present, intensive investigation aims at the creation of optimal valvular prostheses. We introduced and tested the applicability and functionality of two advanced cell‐plus‐matrix seeding technologies, spray‐assisted bioprocessing (SaBP) and laser‐assisted bioprocessing (LaBP), for autologous tissue engineering (TE) of bioresorbable artificial grafts. For SaBP, human mesenchymal stem cells (HMSCs), umbilical cord vein endothelial cells (HUVECs) and fibrin were simultaneously spray‐administered on poly(ε‐caprolactone) (PCL) substrates. For LaBP, HUVECs and HMSCs were separately laser‐printed in stripes, followed by fibrin sealing. Three‐leaflet valves were manufactured following TE of electrospun PCL tissue equivalents. Grafts were monitored in vitro under static and dynamic conditions in bioreactors. SaBP and LaBP resulted in TE of grafts with homogeneous cell distribution and accurate cell pattern, respectively. The engineered valves demonstrated immediate sufficient performance, complete cell coating, proliferation, engraftment, HUVEC‐mediated invasion, HMSC differentiation and extracellular matrix deposition. SaBP revealed higher efficiency, with at least 12‐fold shorter processing time than the applied LaBP set‐up. LaBP realized coating with higher cell density and minimal cell–scaffold distance. Fibrin and PCL stability remain issues for improvement. The introduced TE technologies resulted in complete valvular cell‐plus‐matrix coating, excellent engraftment and HMSCs differentiation. SaBP might have potential for intraoperative table‐side TE considering the procedural duration and ease of implementation. LaBP might accelerate engraftment with precise patterns. Copyright © 2012 John Wiley & Sons, Ltd.