A novel nonlinear afterload for ex vivo heart evaluation: Porcine experimental results.

BACKGROUND: Existing working heart models for ex vivo functional evaluation of donor hearts often use cardiac afterloads made up of discrete resistive and compliant elements. This approach limits the practicality of independently controlling systolic and diastolic aortic pressure to safely test the heart under multiple loading conditions. We present and investigate a novel afterload concept designed to enable such control. METHODS: Six ∼70 kg pig hearts were evaluated in vivo, then ex vivo in left-ventricular working mode using the presented afterload. Both in vivo and ex vivo, the hearts were evaluated at two exertion levels: at rest and following a 20 µg adrenaline bolus, while measuring aortic pressure and flow, left ventricular pressure and volume, and left atrial pressure. RESULTS: The afterload gave aortic pressure waveforms that matched the general shape of the in vivo measurements. A wide range of physiological systolic pressures (93 to 160 mm Hg) and diastolic pressures (73 to 113 mm Hg) were generated by the afterload. CONCLUSIONS: With the presented afterload concept, multiple physiological loading conditions could be tested ex vivo, and compared with the corresponding in vivo data. An additional control loop from the set pressure limits to the measured systolic and diastolic aortic pressure is proposed to address discrepancies observed between the set limits and the measured pressures.

Cold non-ischemic heart preservation with continuous perfusion prevents early graft failure in orthotopic pig-to-baboon xenotransplantation.

BACKGROUND: Successful preclinical transplantations of porcine hearts into baboon recipients are required before commencing clinical trials. Despite years of research, over half of the orthotopic cardiac xenografts were lost during the first 48 hours after transplantation, primarily caused by perioperative cardiac xenograft dysfunction (PCXD). To decrease the rate of PCXD, we adopted a preservation technique of cold non-ischemic perfusion for our ongoing pig-to-baboon cardiac xenotransplantation project. METHODS: Fourteen orthotopic cardiac xenotransplantation experiments were carried out with genetically modified juvenile pigs (GGTA1- KO/hCD46/hTBM) as donors and captive-bred baboons as recipients. Organ preservation was compared according to the two techniques applied: cold static ischemic cardioplegia (IC; n = 5) and cold non-ischemic continuous perfusion (CP; n = 9) with an oxygenated albumin-containing hyperoncotic cardioplegic solution containing nutrients, erythrocytes and hormones. Prior to surgery, we measured serum levels of preformed anti-non-Gal-antibodies. During surgery, hemodynamic parameters were monitored with transpulmonary thermodilution. Central venous blood gas analyses were taken at regular intervals to estimate oxygen extraction, as well as lactate production. After surgery, we measured troponine T and serum parameters of the recipient's kidney, liver and coagulation functions. RESULTS: In porcine grafts preserved with IC, we found significantly depressed systolic cardiac function after transplantation which did not recover despite increasing inotropic support. Postoperative oxygen extraction and lactate production were significantly increased. Troponin T, creatinine, aspartate aminotransferase levels were pathologically high, whereas prothrombin ratios were abnormally low. In three of five IC experiments, PCXD developed within 24 hours. By contrast, all nine hearts preserved with CP retained fully preserved systolic function, none showed any signs of PCXD. Oxygen extraction was within normal ranges; serum lactate as well as parameters of organ functions were only mildly elevated. Preformed anti-non-Gal-antibodies were similar in recipients receiving grafts from either IC or CP preservation. CONCLUSIONS: While standard ischemic cardioplegia solutions have been used with great success in human allotransplantation over many years, our data indicate that they are insufficient for preservation of porcine hearts transplanted into baboons: Ischemic storage caused severe impairment of cardiac function and decreased tissue oxygen supply, leading to multi-organ failure in more than half of the xenotransplantation experiments. In contrast, cold non-ischemic heart preservation with continuous perfusion reliably prevented early graft failure. Consistent survival in the perioperative phase is a prerequisite for preclinical long-term results after cardiac xenotransplantation.

Intact endothelial and contractile function of coronary artery after 8 hours of heart preservation.

OBJECTIVES: The aim of the study was to investigate if adequate preservation of coronary artery endothelium-dependent relaxation and contractility may be obtained after 8 hours of non-ischemic heart preservation. DESIGN: Porcine hearts were perfused for 8 hours at 8 °C, either in cycles of 15 minutes perfusion and 60 minutes non-perfusion, or by continuous perfusion. The perfusate consisted of a cardioplegic, hyperoncotic nutrition solution with oxygenated red cells, and the perfusion pressure was 20 mmHg. In organ baths, coronary artery segments from the preserved hearts were studied and compared to fresh controls. RESULTS: Endothelium-dependent relaxation and contractility were fully preserved after both intermittent and continuous perfusion, as compared to fresh controls. No myocardial edema was seen; water content of the myocardium was 79.5 ± 0.2%, 79.0 ± 0.4% and 79.0 ± 0.3% (ns) for fresh controls, intermittently perfused, and continuously perfused hearts, respectively. CONCLUSION: Intact endothelial and contractile function of coronary artery may be obtained after 8 hours of non-ischemic heart preservation.

Safe orthotopic transplantation of hearts harvested 24 hours after brain death and preserved for 24 hours.

OBJECTIVES: The aim of this study was to demonstrate safe orthotopic transplantation of porcine donor hearts harvested 24 hours after brain death and preserved for 24 hours before transplantation. DESIGN: Circulatory normalization of brain dead (decapitated) pigs was obtained using a new pharmacological regimen (n = 10). The donor hearts were perfused at 8 °C in cycles of 15 min perfusion followed by 60 min without perfusion. The perfusate consisted of an albumin-containing hyperoncotic cardioplegic nutrition solution with hormones and erythrocytes. Orthotopic transplantation was done in 10 recipient pigs after 24 hours' preservation. Transplanted pigs were monitored for 24 hours, then an adrenaline stress test was done. RESULTS: All transplanted pigs were stable throughout the 24-hour observation period with mean aortic pressure around 80 mmHg and normal urine production. Mean right and left atrial pressures were in the range of 3-6 and 5-10 mmHg, respectively. Blood gases at 24 hours did not differ from baseline values. The adrenaline test showed a dose dependent response, with aortic pressure increasing from 98/70 to 220/150 mmHg and heart rate from 110 to 185 beats/min. CONCLUSION: Orthotopic transplantation of porcine hearts harvested 24 hours after brain death and preserved for 24 hours can be done safely.

Excitation and contraction of cardiac muscle and coronary arteries of brain-dead pigs.

Excitability and contraction of cardiac muscle from brain-dead donors critically influence the success of heart transplantation. Membrane physiology, Ca2+-handling, and force production of cardiac muscle and the contractile properties of coronary arteries were studied in hearts of brain-dead pigs. Cardiac muscle and vascular function after 12 h brain death (decapitation between C2 and C3) were compared with properties of fresh tissue. In both isolated cardiomyocytes (whole-cell patch clamp) and trabecular muscle (conventional microelectrodes), action potential duration was shorter in brain dead, compared to controls. Cellular shortening and Ca2+ transients were attenuated in the brain dead, and linked to lower mRNA expression of L-type calcium channels and a slightly lower ICa,L, current, as well as to a lower expression of phospholamban. The current-voltage relationship and the current above the equilibrium potential of the inward K+ (IK1) channel were altered in the brain-dead group, associated with lower mRNA expression of the Kir2.2 channel. Delayed K+ currents were detected (IKr, IKs) and were not different between groups. The transient outward K+ current (Ito) was not observed in the pig heart. Coronary arteries exhibited increased contractility and sensitivity to the thromboxane analogue (U46619), and unaltered endothelial relaxation. In conclusion, brain death involves changes in cardiac cellular excitation which might lower contractility after transplantation. Changes in the inward rectifier K+ channel can be associated with an increased risk for arrhythmia. Increased reactivity of coronary arteries may lead to increased risk of vascular spasm, although endothelial relaxant function was well preserved.

Prevention of Ischemic Myocardial Contracture Through Hemodynamically Controlled DCD.

PURPOSE: Ischemic myocardial contracture (IMC) or "stone heart" is a condition with rapid onset following circulatory death. It inhibits transplantability of hearts donated upon circulatory death (DCD). We investigate the effectiveness of hemodynamic normalization upon withdrawal of life-sustaining therapy (WLST) in a large-animal controlled DCD model, with the hypothesis that reduction in cardiac work delays the onset of IMC. METHODS: A large-animal study was conducted comprising of a control group ([Formula: see text]) receiving no therapy upon WLST, and a test group ([Formula: see text]) subjected to a protocol for fully automated computer-controlled hemodynamic drug administration. Onset of IMC within 1 h following circulatory death defined the primary end-point. Cardiac work estimates based on pressure-volume loop concepts were developed and used to provide insight into the effectiveness of the proposed computer-controlled therapy. RESULTS: No test group individual developed IMC within [Formula: see text], whereas all control group individuals did (4/6 within [Formula: see text]). CONCLUSION: Automatic dosing of hemodynamic drugs in the controlled DCD context has the potential to prevent onset of IMC up to [Formula: see text], enabling ethical and medically safe organ procurement. This has the potential to increase the use of DCD heart transplantation, which has been widely recognized as a means of meeting the growing demand for donor hearts.

Manual versus mechanical cardiopulmonary resuscitation. An experimental study in pigs.

BACKGROUND: Optimal manual closed chest compressions are difficult to give. A mechanical compression/decompression device, named LUCAS, is programmed to give compression according to the latest international guidelines (2005) for cardiopulmonary resuscitation (CPR). The aim of the present study was to compare manual CPR with LUCAS-CPR. METHODS: 30 kg pigs were anesthetized and intubated. After a base-line period and five minutes of ventricular fibrillation, manual CPR (n = 8) or LUCAS-CPR (n = 8) was started and run for 20 minutes. Professional paramedics gave manual chest compression's alternating in 2-minute periods. Ventilation, one breath for each 10 compressions, was given to all animals. Defibrillation and, if needed, adrenaline were given to obtain a return of spontaneous circulation (ROSC). RESULTS: The mean coronary perfusion pressure was significantly (p < 0.01) higher in the mechanical group, around 20 mmHg, compared to around 5 mmHg in the manual group. In the manual group 54 rib fractures occurred compared to 33 in the LUCAS group (p < 0.01). In the manual group one severe liver injury and one pressure pneumothorax were also seen. All 8 pigs in the mechanical group achieved ROSC, as compared with 3 pigs in the manual group. CONCLUSIONS: LUCAS-CPR gave significantly higher coronary perfusion pressure and significantly fewer rib fractures than manual CPR in this porcine model.

Non-ischemic Heart Preservation via Hypothermic Cardioplegic Perfusion Induces Immunodepletion of Donor Hearts Resulting in Diminished Graft Infiltration Following Transplantation.

Introduction: Many donor organs contain significant leukocyte reservoirs which upon transplantation activate recipient leukocytes to initiate acute rejection. We aimed to assess whether non-ischemic heart preservation via ex vivo perfusion promotes immunodepletion and alters the inflammatory status of the donor organ prior to transplantation. Methods: Isolated porcine hearts underwent ex vivo hypothermic, cardioplegic perfusion for 8 h. Leukocyte populations were quantified in left ventricle samples by flow cytometry. Cell-free DNA, cytokines, and chemokines were quantified in the perfusate. Tissue integrity was profiled by targeted proteomics and a histological assessment was performed. Heterotopic transplants comparing ex vivo hypothermic preservation and static cold storage were utilized to assess graft infiltration as a solid clinical endpoint. Results:Ex vivo perfusion significantly immunodepleted myocardial tissue. The perfusate displayed a selective, pro-inflammatory cytokine/chemokine pattern dominated by IFN-γ. The tissue molecular profile was improved following perfusion by diminished expression of nine pro-apoptotic and six ischemia-associated proteins. Histologically, no evidence of tissue damage was observed and cardiac troponin I was low throughout perfusion. Cell-free DNA was detected, the source of which may be necrotic/apoptotic leukocytes. Post-transplant graft infiltration was markedly reduced in terms of both leucocyte distribution and intensity of foci. Conclusions: These findings demonstrate that ex vivo perfusion significantly reduced donor heart immunogenicity via loss of resident leukocytes. Despite the pro-inflammatory cytokine pattern observed, a pro-survival and reduced ischemia-related profile was observed, indicating an improvement in graft viability by perfusion. Diminished graft infiltration was observed in perfused hearts compared with those preserved by static cold storage following 48 h of transplantation.

Detection of bronchial function of NHBD lung following one-h warm ischemia by organ bath model.

This study investigated the feasibility and effects of organ bath to be used for detection of bronchial function of non-heart-beating donor (NHBD) lung after 1-h warm ischemia. Sixteen Swedish pigs were divided into two groups randomly: heart-beating donor (HBD) group and NHBD with 1-h warm ischemia (NHBD-1 h) group. The bronchial rings whose lengths and inner diameters were both 1.5 mm were obtained from isolated left lungs of all the pigs. Acetylcholine, arachidonic acid natrium and papaverine were used to test and compare the contractile and relaxant function of bronchial smooth muscles and epithelium-dependent relaxation (EpiDR) response between HBD and NHBD-1 h groups. The results showed that there was no significant difference in the values of bronchial precontraction between HBD and NHBD-1 h groups (5.18+/-0.07 vs 5.10+/-0.11 mN, P>0.05). No significant difference in the values of EpiDR responses between HBD and NHBD-1 h groups (1.26+/-0.05 vs 1.23+/-0.07 mN, P>0.05) was observed either. During the process of EpiDR induction, the rings had no spontaneous relaxation in two groups. In addition, papaverine solution completely relaxed the bronchial smooth muscles of all bronchial rings. It was concluded that after warm ischemia for 1 h, the contractile and relaxant abilities of bronchial smooth muscles, and the epithelium-dependent adjustment both kept intact. Organ bath model could be a liable and scientific way to evaluate the bronchial function of NHBD lung.

Phase-controlled intermittent intratracheal insufflation of oxygen during chest compression-active decompression mCPR improves coronary perfusion pressure over continuous insufflation.

PURPOSE: It has previously been shown that continuous intratracheal insufflation of oxygen (CIO) is superior to intermittent positive pressure ventilation (IPPV) regarding gas exchange and haemodynamics. The purpose of this study was to investigate gas exchange and haemodynamics with a new technique of phase-controlled intermittent insufflation of oxygen (PIIO) compared to CIO. METHOD: Twenty (20) pigs were used, stratified into two groups (CIO, PIIO), with 10 animals each. Upon induction of ventricular fibrillation, standard ventilator support was replaced by either of CIO or PIIO ventilation. Chest compressions were delivered by the LUCAS I mCPR device. Following 20 min of CPR in normothermia, defibrillation was attempted. RESULTS: Return of spontaneous circulation (ROSC) occurrence was not significantly higher (P < 0.16) in the PIIO (9/10) than in the CIO (6/10) group. During the decompression phase the PIIO group showed significant increases in mean (P < 0.01), maximal (P < 0.02) and end-decompression (P < 0.01) coronary perfusion pressure (CPP), compared to the CIO group. PIIO resulted in increased compression phase aortic pressure (P < 0.03). Intratracheal pressure was 5-30 cmH2O within both groups during mCPR, with a significantly lower (P < 0.02) mean for the PIIO group. Arterial and venous blood gas analysis showed comparable results between the groups, when taking base line values into account. An exception was that PIIO resulted in significantly higher (P < 0.05) oxygen partial pressure during mCPR, and lower (P < 0.05) arterial lactate following ROSC. CONCLUSION: PIIO results in significantly higher CPP and compression phase aortic pressure during mCPR in a porcine population. Further studies are needed to validate these findings in humans. Study protocol conforming with ethic approval M174-15, issued by the Malmö/Lunds regionala djurförsöksetiska nämnd (REB).

Closed-Loop Prevention of Hypotension in the Heartbeating Brain-Dead Porcine Model.

Objective: The purpose of this paper is to demonstrate feasibility of a novel closed-loop controlled therapy for prevention of hypertension in the heartbeating brain-dead porcine model. METHODS: Dynamic modeling and system identification were based on in vivo data. A robust controller design was obtained for the identified models. Disturbance attenuation properties and reliability of operation of the resulting control system were evaluated in vivo. RESULTS: The control system responded both predictably and consistently to external disturbances. It was possible to prevent mean arterial pressure to fall below a user-specified reference throughout 24 h of completely autonomous operation. CONCLUSION: Parameter variability in the identified models confirmed the benefit of closed-loop controlled administration of the proposed therapy. The evaluated robust controller was able to mitigate both process uncertainty and external disturbances. SIGNIFICANCE: Prevention of hypertension is critical to the care of heartbeating brain-dead organ donors. Its automation would likely increase the fraction of organs suitable for transplantation from this patient group.

In vivo validation of the coincidence of the peak and end of the T wave with full repolarization of the epicardium and endocardium in swine.

OBJECTIVES/BACKGROUND: Previous in vitro studies have suggested full repolarization of the epicardium coincides with the peak of the T wave (T(peak)) and that of the M cells coincides with the end of the T wave (T(end)). However, in vivo validation of the theory is lacking. METHODS: Monophasic action potentials (MAPs) were recorded using the CARTO mapping system from 51 +/- 10 epicardial sites and 64 +/- 9 endocardial sites of the left ventricle in 10 pigs and from 41 +/- 4 epicardial sites and 53 +/- 2 endocardial sites of the right ventricle in two of the 10 pigs. End of repolarization (EOR) times over the epicardium (EOR(epi)), endocardium (EOR(endo)), and over both (EOR(total)) were obtained. QT(peak) and QT(end) intervals were measured from simultaneously recorded 12-lead ECG. RESULTS: Minimal and maximal EOR(total) were observed in the left ventricle in all pigs. Minimal EOR(total) was on the epicardium in five pigs, and maximal EOR(total) was on the endocardium in nine pigs. Minimal, mean, and maximal QT(peak) intervals all were significantly smaller than maximal EOR(epi) (322 +/- 23 ms, P <.01). No significant difference was found between maximal QT(end) interval (338 +/- 30 ms) and maximal EOR(endo) (339 +/- 24 ms, difference = 1 +/- 19 ms, P =.92), between maximal QT(end) interval and maximal EOR(total) (341 +/- 24 ms, difference = 2 +/- 18 ms, P =.69), or between minimal QT(peak) interval (283 +/- 28 ms) and minimal EOR(total) (282 +/- 20 ms, difference = 0 +/- 15 ms, P =.95). CONCLUSIONS: In in vivo pig models, T(peak) does not coincide with full repolarization of the epicardium but coincides well with the earliest EOR, whereas the T(end) corresponds with the latest EOR. These findings suggest that not only the transmural gradients but also the apicobasal repolarization gradients contribute to genesis of the T wave.

Transplantation of lungs from non-heart-beating donors after functional assessment ex vivo.

BACKGROUND: If lungs from patients dying of heart attacks are to serve as donor organs in a safe way, their function should be properly assessed before transplantation. The aim of this study was to investigate donor lung function evaluation in a realistic large animal model. METHODS: Twelve 60-kg pigs were used. Five minutes after ventricular fibrillation was induced, cardiopulmonary resuscitation was initiated and maintained for 20 minutes. After a 10-min hands-off period, heparin was administered through a central venous catheter followed by 20 chest compressions. Intrapleural cooling was initiated after 65 minutes of warm ischemia. Cooling proceeded for 6 hours within the cadaver, after which lung function was assessed ex vivo. Recipient pigs underwent left lung transplantation followed by right pneumonectomy, thus making these animals 100% dependent for their survival on the function of the donor lungs. RESULTS: The assessment showed that all lungs had adequate function to serve as donor lungs. All recipient animals were in good condition during the 24-hour observation period after the operation. The blood gas function did not differ significantly from that in the healthy donor animals before induction of ventricular fibrillation; pulmonary vascular resistance was within normal range. CONCLUSIONS: Lungs from non-heart-beating donors topically cooled in situ for 6 hours after 65 minutes of warm ischemia were assessed ex vivo and found to have normal function. They were then transplanted and retained normal function during a 24-hour observation period.

Continuous intratracheal insufflation of oxygen improves the efficacy of mechanical chest compression-active decompression CPR.

The aim of the present study was to compare the efficacy of intratracheal continuous insufflation of oxygen (CIO) with intermittent positive pressure ventilation (IPPV) regarding gas exchange and haemodynamics during mechanical chest compression-active decompression cardiopulmonary resuscitation (mCPR) provided by the LUCAS device. Ventricular fibrillation (VF) was induced electrically and ventilation was discontinued in 16 pigs, mean body weight 23 kg (range 22-27 kg). They were randomized into two groups (CIO versus IPPV). After 8 min of VF, mCPR was started and run for 30 min in normothermia, after which defibrillation was attempted during on-going mCPR. Return of spontaneous circulation was obtained in eight of eight CIO pigs and in four of eight IPPV pigs. Arterial oxygen tension (P < 0.05) and coronary perfusion pressure (P < 0.01) were significantly higher in the CIO pigs. Arterial CO(2)-tension was subnormal in both groups and significantly (P < 0.05) lower in the IPPV-pigs (around 4.5 versus 3.0 kPa). The intratracheal pressure differed significantly (P < 0.001) between the two groups. It was negative in each decompression phase in the IPPV pigs in spite of 6 mmHg of PEEP. The CIO pigs had a positive intratracheal pressure during the whole cycle of mCPR, with a minimum pressure of 8 mmHg during each decompression phase. To conclude, mCPR combined with CIO gave adequate ventilation and significantly better oxygenation and coronary perfusion pressure than mCPR combined with IPPV.

The critical importance of minimal delay between chest compressions and subsequent defibrillation: a haemodynamic explanation.

Outcome after prehospital defibrillation remains dire. The aim of the present study was to elucidate the pathophysiology of cardiac arrest and to suggest ways to improve outcome. Ventricular fibrillation (VF) was induced in air-ventilated pigs, after which ventilation was withdrawn. After 6.5 min of VF, ventilation with 100% oxygen was initiated. In six pigs (group I), defibrillation was the only treatment carried out. In another six pigs (group II), mechanical chest compression-decompression CPR (mCPR) was carried out for 3.5 min followed by a 40-s hands-off period before defibrillation. If unsuccessful, mCPR was resumed for a further 30 s before a second or a third, 40-s delayed, shock was given. In a final six pigs (group III) mCPR was applied for 3.5 min after which up to three shocks (if needed) were given during on-going mCPR. Return of spontaneous circulation (ROSC) occurred in none of the pigs in group I (0%), in 1 of six pigs in group II (17%) and in five of six pigs in group III (83%). During the first 3 min of VF arterial blood was transported to the venous circulation, with the consequence that the left ventricle emptied and the right ventricle became greatly distended. It took 2 min of mCPR to establish an adequate coronary perfusion pressure, which was lost when the mCPR was interrupted. During 30 s of mCPR coronary perfusion pressure was negative, but a carotid flow of about 25% of basal value was obtained. In this pig model, VF caused venous congestion, an empty left heart, and a greatly distended right heart within 3 min. Adequate heart massage before and during defibrillation greatly improved the likelihood of return of spontaneous circulation (ROSC).

Evaluation of LUCAS, a new device for automatic mechanical compression and active decompression resuscitation.

LUCAS is a new gas-driven CPR device providing automatic chest compression and active decompression. In an artificial thorax model, superior pressure and flow were obtained with LUCAS compared with manual CPR. In a randomized study on pigs with induced ventricular fibrillation significantly higher cardiac output, carotid artery blood flow, end-tidal CO(2), intrathoracic decompression-phase aortic- and coronary perfusion pressures were obtained with LUCAS-CPR (83% ROSC) compared to manual CPR (0% ROSC). In normothermic fibrillating pigs, the ROSC rate was 100% after 15 min and 38% after 60 min of LUCAS-CPR (no drug treatment). The ROSC rate increased to 75% if surface cooling to 34 degrees C was applied during the first 30 min of the 1-h resuscitation period. Experience with the first 20 patients has shown that LUCAS is light (6.5 kg), easy to handle, quick to apply (10-20 s), maintains a correct position, and works optimally during transport both on stretchers and in ambulances. In one hospital patient with a witnessed asystole where manual CPR failed, LUCAS-CPR achieved ROSC within 3 min. One year later the patient's mental capacity was fully intact. To conclude, LUCAS-CPR gives significantly better circulation during ventricular fibrillation than manual CPR.

MeCP2 suppresses nuclear microRNA processing and dendritic growth by regulating the DGCR8/Drosha complex.

Loss- and gain-of-function mutations of the X-linked gene MECP2 (methyl-CpG binding protein 2) lead to severe neurodevelopmental disorders in humans, such as Rett syndrome (RTT) and autism. MeCP2 is previously known as a transcriptional repressor by binding to methylated DNA and recruiting histone deacetylase complex (HDAC). Here, we report that MeCP2 regulates gene expression posttranscriptionally by suppressing nuclear microRNA processing. We found that MeCP2 binds directly to DiGeorge syndrome critical region 8 (DGCR8), a critical component of the nuclear microRNA-processing machinery, and interferes with the assembly of Drosha and DGCR8 complex. Protein targets of MeCP2-suppressed microRNAs include CREB, LIMK1, and Pumilio2, which play critical roles in neural development. Gain of function of MeCP2 strongly inhibits dendritic and spine growth, which depends on the interaction of MeCP2 and DGCR8. Thus, control of microRNA processing via direct interaction with DGCR8 represents a mechanism for MeCP2 regulation of gene expression and neural development.

A novel, minimally invasive rat model of normothermic cardiopulmonary bypass model without blood priming.

BACKGROUND: Cardiopulmonary bypass (CPB) has been shown to be associated with systemic inflammatory response leading to postoperative organ dysfunction. Elucidating the underlying mechanisms and developing protective strategies for the pathophysiological consequences of CPB have been hampered due to the absence of a satisfactory recovery animal model. The purpose of this study was to establish a novel, minimally invasive rat model of normothermic CPB model without blood priming. METHODS: Twenty adult male Sprague-Dawley rats weighing 450-560 g were randomly divided into CPB group (n = 10) and control group (n = 10). All rats were anaesthetized and mechanically ventilated. The carotid artery and jugular vein were cannulated. The blood was drained from the right atrium via the right jugular and further transferred by a miniaturized roller pump to a hollow fiber oxygenator and back to the rat via the left carotid artery. The volume of the priming solution, composed of 6% HES 130/0.4 and 125 IU heparin, was less than 12 ml. The surface of the hollow fiber oxygenator was 0.075 m(2). CPB was conducted for 60 minutes at a flow rat of 100-120 ml × kg (-1)× min(-1) in CPB group. Oxygen flow/perfusion flow was 0.8 to 1.0, and the mean arterial pressure remained 60-80 mmHg. RESULTS: All CPB processes were successfully achieved. Blood gas analysis and hemodynamic parameters of each time point were in accordance with normal ranges. The vital signs of all rats were stable. CONCLUSIONS: The establishment of CPB without blood priming in rats can be achieved successfully. The nontransthoracic model should facilitate the investigation of pathophysiological processes concerning CPB-related multiple organ dysfunction and possible protective interventions. This novel, recovery, and reproducible minimally invasive CPB model may open the field for various studies on the pathophysiological process of CPB and systemic ischemia-reperfusion injury in vivo.

Intrinsic epigenetic factors cooperate with the steroid hormone ecdysone to govern dendrite pruning in Drosophila.

Pruning that selectively removes unnecessary axons/dendrites is crucial for sculpting neural circuits during development. During Drosophila metamorphosis, dendritic arborization sensory neurons, ddaCs, selectively prune their larval dendrites in response to the steroid hormone ecdysone. However, it is unknown whether epigenetic factors are involved in dendrite pruning. Here, we analyzed 81 epigenetic factors, from which a Brahma (Brm)-containing chromatin remodeler and a histone acetyltransferase CREB-binding protein (CBP) were identified for their critical roles in initiating dendrite pruning. Brm and CBP specifically activate a key ecdysone response gene, sox14, but not EcR-B1. Furthermore, the HAT activity of CBP is important for sox14 expression and dendrite pruning. EcR-B1 associates with CBP in the presence of ecdysone, which is facilitated by Brm, resulting in local enrichment of an active chromatin mark H3K27Ac at the sox14 locus. Thus, specific intrinsic epigenetic factors cooperate with steroid hormones to activate selective transcriptional programs, thereby initiating neuronal remodeling.