ß-Adrenergic Stimulation Induces Histone Deacetylase 5 (HDAC5) Nuclear Accumulation in Cardiomyocytes by B55α-PP2A-Mediated Dephosphorylation.

BACKGROUND: Class IIa histone deacetylase (HDAC) isoforms such as HDAC5 are critical signal-responsive repressors of maladaptive cardiomyocyte hypertrophy, through nuclear interactions with transcription factors including myocyte enhancer factor-2. ß-Adrenoceptor (ß-AR) stimulation, a signal of fundamental importance in regulating cardiac function, has been proposed to induce both phosphorylation-independent nuclear export and phosphorylation-dependent nuclear accumulation of cardiomyocyte HDAC5. The relative importance of phosphorylation at Ser259/Ser498 versus Ser279 in HDAC5 regulation is also controversial. We aimed to determine the impact of ß-AR stimulation on the phosphorylation, localization, and function of cardiomyocyte HDAC5 and delineate underlying molecular mechanisms. METHODS AND RESULTS: A novel 3-dimensional confocal microscopy method that objectively quantifies the whole-cell nuclear/cytoplasmic distribution of green fluorescent protein tagged HDAC5 revealed the ß-AR agonist isoproterenol to induce ß1-AR-mediated and protein kinase A-dependent HDAC5 nuclear accumulation in adult rat cardiomyocytes, which was accompanied by dephosphorylation at Ser259/279/498. Mutation of Ser259/Ser498 to Ala promoted HDAC5 nuclear accumulation and myocyte enhancer factor-2 inhibition, whereas Ser279 ablation had no such effect and did not block isoproterenol-induced nuclear accumulation. Inhibition of the Ser/Thr phosphatase PP2A blocked isoproterenol-induced HDAC5 dephosphorylation. Co-immunoprecipitation revealed a specific interaction of HDAC5 with the PP2A targeting subunit B55α, as well as catalytic and scaffolding subunits, which increased >3-fold with isoproterenol. Knockdown of B55α in neonatal cardiomyocytes attenuated isoproterenol-induced HDAC5 dephosphorylation. CONCLUSIONS: ß-AR stimulation induces HDAC5 nuclear accumulation in cardiomyocytes by a mechanism that is protein kinase A-dependent but requires B55α-PP2A-mediated dephosphorylation of Ser259/Ser498 rather than protein kinase A-mediated phosphorylation of Ser279.

Three methods of manual external chest compressions during microgravity simulation.

INTRODUCTION: Cardiopulmonary resuscitation (CPR) in microgravity is challenging. There are three single-person CPR techniques that can be performed in microgravity: the Evetts-Russomano (ER), Handstand (HS), and Reverse Bear Hug (RBH). All three methods have been evaluated in parabolic flights, but only the ER method has been shown to be effective in prolonged microgravity simulation. All three methods of CPR have yet to be evaluated using the current 2010 guidelines. METHODS: There were 23 male subjects who were recruited to perform simulated terrestrial CPR (+1 G(z)) and the three microgravity CPR methods for four sets of external chest compressions (ECC). To simulate microgravity, the subjects used a body suspension device (BSD) and trolley system. True depth (D(T)), ECC rate, and oxygen consumption (Vo2) were measured. RESULTS: The mean (+/- SD) D(T) for the ER (37.4 +/- 1.5 mm) and RBH methods (23.9 +/- 1.4 mm) were significantly lower than +1 G(z) CPR. However, both methods attained an ECC rate that met the guidelines (105.6 +/- 0.8; 101.3 +/- 1.5 compressions/min). The HS method achieved a superior D(T) (49.3 +/- 1.2 mm), but a poor ECC rate (91.9 +/- 2.2 compressions/min). Vo2 for ER and HS was higher than +1 Gz; however, the RBH was not. CONCLUSION: All three methods have merit in performing ECC in simulated microgravity; the ER and RBH have adequate ECC rates, and the HS method has adequate D(T). However, all methods failed to meet all criteria for the 2010 guidelines. Further research to evaluate the most effective method of CPR in microgravity is needed.

A comparison between the 2010 and 2005 basic life support guidelines during simulated hypogravity and microgravity.

BACKGROUND: Current 2010 terrestrial (1Gz) CPR guidelines have been advocated by space agencies for hypogravity and microgravity environments, but may not be feasible. The aims of this study were to (1) evaluate rescuer performance over 1.5 min of external chest compressions (ECCs) during simulated Martian hypogravity (0.38Gz) and microgravity (µG) in relation to 1Gz and rest baseline and (2) compare the physiological costs of conducting ECCs in accordance with the 2010 and 2005 CPR guidelines. METHODS: Thirty healthy male volunteers, ranging from 17 to 30 years, performed four sets of 30 ECCs for 1.5 min using the 2010 and 2005 ECC guidelines during 1Gz, 0.38Gz and µG simulations (Evetts-Russomano (ER) method), achieved by the use of a body suspension device. ECC depth and rate, range of elbow flexion, post-ECC heart rate (HR), minute ventilation (VE), peak oxygen consumption (VO2peak) and rate of perceived exertion (RPE) were measured. RESULTS: All volunteers completed the study. Mean ECC rate was achieved for all gravitational conditions, but true depth during simulated microgravity was not sufficient for the 2005 (28.5 ± 7.0 mm) and 2010 (32.9 ± 8.7 mm) guidelines, even with a mean range of elbow flexion of 15°. HR, VE and VO2peak increased to an average of 136 ± 22 bpm, 37.5 ± 10.3 L·min-1, 20.5 ± 7.6 mL·kg-1·min-1 for 0.38Gz and 161 ± 19 bpm, 58.1 ± 15.0 L·min-1, 24.1 ± 5.6 mL·kg-1·min-1 for µG from a baseline of 84 ± 15 bpm, 11.4 ± 5.9 L·min-1, 3.2 ± 1.1 mL·kg-1·min-1, respectively. RPE was the only variable to increase with the 2010 guidelines. CONCLUSION: No additional physiological cost using the 2010 basic life support (BLS) guidelines was needed for healthy males performing ECCs for 1.5 min, independent of gravitational environment. This cost, however, increased for each condition tested when the two guidelines were compared. Effective ECCs were not achievable for both guidelines in simulated µG using the ER BLS method. This suggests that future implementation of an ER BLS in a simulated µG instruction programme as well as upper arm strength training is required to perform effective BLS in space.

A conserved tryptophan at the membrane-water interface acts as a gatekeeper for Kir6.2/SUR1 channels and causes neonatal diabetes when mutated.

We identified a novel heterozygous mutation, W68R, in the Kir6.2 subunit of the ATP-sensitive potassium (KATP) channel, in a patient with transient neonatal diabetes. This tryptophan is absolutely conserved in mammalian Kir channels. The functional effects of mutations at residue 68 of Kir6.2 were studied by heterologous expression in Xenopus oocytes, and by homology modelling. We found the Kir6.2-W68R mutation causes a small reduction in ATP inhibition in the heterozygous state and an increase in the whole-cell KATP current. This can explain the clinical phenotype of the patient. The effect of the mutation was not charge or size dependent, the order of potency for ATP inhibition being W

Occult small bowel perforation in a patient with Ehlers Danlos syndrome: a case report and review of the literature.

Patients who present with a co-existing connective tissue disorder add a degree of complexity to operative intervention. We present an unusual case of a 53-year-old Caucasian female patient with Ehlers Danlos syndrome who presented with an occult perforation of the distal ileum. The patient had known small bowel diverticulae yet the perforation occurred within the normal bowel wall. The pre-operative CT only showed malrotation of the large bowel and did not correlate with the intra-operative findings. Our case has highlighted that although small bowel perforation is a rare occurrence, it may be more common in Ehlers Danlos and may present with atypical features. Perforation may also occur alongside normal bowel as well as diverticulae within the bowel. Where diverticulae exists within a patient with Ehlers Danlos syndrome and there is some diagnostic uncertainty, there should be a lower threshold for operative intervention. We present in the discussion a number of salient features and learning points.