PGC-1α regulates myonuclear accretion after moderate endurance training.

The transcriptional demands of skeletal muscle fibres are high and require hundreds of nuclei (myonuclei) to produce specialised contractile machinery and multiple mitochondria along their length. Each myonucleus spatially regulates gene expression in a finite volume of cytoplasm, termed the myonuclear domain (MND), which positively correlates with fibre cross-sectional area (CSA). Endurance training triggers adaptive responses in skeletal muscle, including myonuclear accretion, decreased MND sizes and increased expression of the transcription co-activator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). Previous work has shown that overexpression of PGC-1α in skeletal muscle regulates mitochondrial biogenesis, myonuclear accretion and MND volume. However, whether PGC-1α is critical for these processes in adaptation to endurance training remained unclear. To test this, we evaluated myonuclear distribution and organisation in endurance-trained wild-type mice and mice lacking PGC-1α in skeletal muscle (PGC-1α mKO). Here, we show a differential myonuclear accretion response to endurance training that is governed by PGC-1α and is dependent on muscle fibre size. The positive relationship of MND size and muscle fibre CSA trended towards a stronger correlation in PGC-1a mKO versus control after endurance training, suggesting that myonuclear accretion was slightly affected with increasing fibre CSA in PGC-1α mKO. However, in larger fibres, the relationship between MND and CSA was significantly altered in trained versus sedentary PGC-1α mKO, suggesting that PGC-1α is critical for myonuclear accretion in these fibres. Accordingly, there was a negative correlation between the nuclear number and CSA, suggesting that in larger fibres myonuclear numbers fail to scale with CSA. Our findings suggest that PGC-1α is an important contributor to myonuclear accretion following moderate-intensity endurance training. This may contribute to the adaptive response to endurance training by enabling a sufficient rate of transcription of genes required for mitochondrial biogenesis.

Approaching the adiabatic timescale with machine learning.

The control and manipulation of quantum systems without excitation are challenging, due to the complexities in fully modeling such systems accurately and the difficulties in controlling these inherently fragile systems experimentally. For example, while protocols to decompress Bose-Einstein condensates (BECs) faster than the adiabatic timescale (without excitation or loss) have been well developed theoretically, experimental implementations of these protocols have yet to reach speeds faster than the adiabatic timescale. In this work, we experimentally demonstrate an alternative approach based on a machine-learning algorithm which makes progress toward this goal. The algorithm is given control of the coupled decompression and transport of a metastable helium condensate, with its performance determined after each experimental iteration by measuring the excitations of the resultant BEC. After each iteration the algorithm adjusts its internal model of the system to create an improved control output for the next iteration. Given sufficient control over the decompression, the algorithm converges to a solution that sets the current speed record in relation to the adiabatic timescale, beating out other experimental realizations based on theoretical approaches. This method presents a feasible approach for implementing fast-state preparations or transformations in other quantum systems, without requiring a solution to a theoretical model of the system. Implications for fundamental physics and cooling are discussed.

Reducing dynamin 2 (DNM2) rescues DNM2-related dominant centronuclear myopathy.

Centronuclear myopathies (CNM) are a group of severe muscle diseases for which no effective therapy is currently available. We have previously shown that reduction of the large GTPase DNM2 in a mouse model of the X-linked form, due to loss of myotubularin phosphatase MTM1, prevents the development of the skeletal muscle pathophysiology. As DNM2 is mutated in autosomal dominant forms, here we tested whether DNM2 reduction can rescue DNM2-related CNM in a knock-in mouse harboring the p.R465W mutation (Dnm2RW/+) and displaying a mild CNM phenotype similar to patients with the same mutation. A single intramuscular injection of adeno-associated virus-shRNA targeting Dnm2 resulted in reduction in protein levels 5 wk post injection, with a corresponding improvement in muscle mass and fiber size distribution, as well as an improvement in histopathological CNM features. To establish a systemic treatment, weekly i.p. injections of antisense oligonucleotides targeting Dnm2 were administered to Dnm2RW/+mice for 5 wk. While muscle mass, histopathology, and muscle ultrastructure were perturbed in Dnm2RW/+mice compared with wild-type mice, these features were indistinguishable from wild-type mice after reducing DNM2. Therefore, DNM2 knockdown via two different strategies can efficiently correct the myopathy due to DNM2 mutations, and it provides a common therapeutic strategy for several forms of centronuclear myopathy. Furthermore, we provide an example of treating a dominant disease by targeting both alleles, suggesting that this strategy may be applied to other dominant diseases.

Myostatin inhibition using mRK35 produces skeletal muscle growth and tubular aggregate formation in wild type and TgACTA1D286G nemaline myopathy mice.

Nemaline myopathy (NM) is a heterogeneous congenital skeletal muscle disease with cytoplasmic rod-like structures (nemaline bodies) in muscle tissue. While weakness in NM is related to contractile abnormalities, myofiber smallness is an additional abnormality in NM that may be treatable. We evaluated the effects of mRK35 (a myostatin inhibitor developed by Pfizer) treatment in the TgACTA1D286G mouse model of NM. mRK35 induced skeletal muscle growth that led to significant increases in animal bodyweight, forelimb grip strength and muscle fiber force, although it should be noted that animal weight and forelimb grip strength in untreated TgACTA1D286G mice was not different from controls. Treatment was also associated with an increase in the number of tubular aggregates found in skeletal muscle. These findings suggest that myostatin inhibition may be useful in promoting muscle growth and strength in Acta1-mutant muscle, while also further establishing the relationship between low levels of myostatin and tubular aggregate formation.

Multiple roles of integrin-α3 at the neuromuscular junction.

The neuromuscular junction (NMJ) is the synapse between motoneurons and skeletal muscle, and is responsible for eliciting muscle contraction. Neurotransmission at synapses depends on the release of synaptic vesicles at sites called active zones (AZs). Various proteins of the extracellular matrix are crucial for NMJ development; however, little is known about the identity and functions of the receptors that mediate their effects. Using genetically modified mice, we find that integrin-α3 (encoded by Itga3), an adhesion receptor at the presynaptic membrane, is involved in the localisation of AZ components and efficient synaptic vesicle release. Integrin-α3 also regulates integrity of the synapse - mutant NMJs present with progressive structural changes and upregulated autophagy, features commonly observed during ageing and in models of neurodegeneration. Unexpectedly, we find instances of nerve terminal detachment from the muscle fibre; to our knowledge, this is the first report of a receptor that is required for the physical anchorage of pre- and postsynaptic elements at the NMJ. These results demonstrate multiple roles of integrin-α3 at the NMJ, and suggest that alterations in its function could underlie defects that occur in neurodegeneration or ageing.

Impairments in contractility and cytoskeletal organisation cause nuclear defects in nemaline myopathy.

Nemaline myopathy (NM) is a skeletal muscle disorder caused by mutations in genes that are generally involved in muscle contraction, in particular those related to the structure and/or regulation of the thin filament. Many pathogenic aspects of this disease remain largely unclear. Here, we report novel pathological defects in skeletal muscle fibres of mouse models and patients with NM: irregular spacing and morphology of nuclei; disrupted nuclear envelope; altered chromatin arrangement; and disorganisation of the cortical cytoskeleton. Impairments in contractility are the primary cause of these nuclear defects. We also establish the role of microtubule organisation in determining nuclear morphology, a phenomenon which is likely to contribute to nuclear alterations in this disease. Our results overlap with findings in diseases caused directly by mutations in nuclear envelope or cytoskeletal proteins. Given the important role of nuclear shape and envelope in regulating gene expression, and the cytoskeleton in maintaining muscle fibre integrity, our findings are likely to explain some of the hallmarks of NM, including contractile filament disarray, altered mechanical properties and broad transcriptional alterations.

Effect of PGC1-beta ablation on myonuclear organisation.

Skeletal muscle fibres are large, elongated multinucleated cells. Each nucleus within a myofibre is responsible for generating gene products for a finite volume of cytoplasm-the myonuclear domain (MND). Variation in MND sizes during atrophy, hypertrophy and disease states, are common. The factors that contribute to definitive MND sizes are not yet fully understood. Previous work has shown that peroxisome proliferator-activated receptor gamma coactivator 1α (PGC1-α) modulates MND volume, presumably to support increased biogenesis of mitochondria. The transcriptional co-regulator peroxisome proliferator-activated receptor gamma coactivator 1ß (PGC1-ß) is a homologue of PGC1-α with overlapping functions. To investigate the role of this protein in MND size regulation, we studied a mouse skeletal muscle specific knockout (cKO). Myofibres were isolated from the fast twitch extensor digitorum longus (EDL) muscle, membrane-permeabilised and analysed in 3 dimensions using confocal microscopy. PGC1-ß ablation resulted in no significant difference in MND size between cKO and wild type (WT) mice, however, subtle differences in nuclear morphology were observed. To determine whether these nuclear shape changes were associated with alterations in global transcriptional activity, acetyl histone H3 immunostaining was carried out. We found there was no significant difference in nuclear fluorescence intensity between the two genotypes. Overall, the results suggest that PGC-1α and PGC-1ß play different roles in regulating nuclear organisation in skeletal muscle; however, further work is required to pinpoint their exact functions.

Prostaglandin E2 and an EP4 receptor agonist inhibit LPS-Induced monocyte chemotactic protein 5 production and secretion in mouse cardiac fibroblasts via Akt and NF-κB signaling.

BACKGROUND: Prostaglandin E2 (PGE2) signals through 4 separate G-protein coupled receptor sub-types to elicit a variety of physiologic and pathophysiological effects. We have previously reported that mice lacking the EP4 receptor in the cardiomyocytes develop heart failure with a phenotype of dilated cardiomyopathy. Also, these mice have increased levels of chemokines, like MCP-5, in their left ventricles. We have recently reported that overexpression of the EP4 receptor could improve cardiac function in the myocardial infarction model. Furthermore, we showed that overexpression of EP4 had an anti-inflammatory effect in the whole left ventricle. It has also been shown that PGE2 can antagonize lipopolysaccharide-induced secretion of chemokines/cytokines in various cell types. We therefore hypothesized that PGE2 inhibits lipopolysaccharide (LPS)-induced MCP-5 secretion in adult mouse cardiac fibroblasts via its EP4 receptor. METHODS AND RESULTS: Our hypothesis was tested using isolated mouse adult ventricular fibroblasts (AVF) treated with LPS. Pre-treatment of the cells with PGE2 and the EP4 agonist CAY10598 resulted in reductions of the pro-inflammatory response induced by LPS. Specifically, we observed reductions in MCP-5 secretion. Western blot analysis showed reductions in phosphorylated Akt and IκBα indicating reduced NF-κB activation. The anti-inflammatory effects of PGE2 and EP4 agonist signaling appeared to be independent of cAMP, p-44/42, or p38 pathways. CONCLUSION: Exogenous treatment of PGE2 and the EP4 receptor agonist blocked the pro-inflammatory actions of LPS. Mechanistically, this was mediated via reduced Akt phosphorylation and inhibition of NF-κB.

SIRT1 regulates nuclear number and domain size in skeletal muscle fibers.

Skeletal muscle fibers are giant multinucleated cells wherein individual nuclei govern the protein synthesis in a finite volume of cytoplasm; this is termed the myonuclear domain (MND). The factors that control MND size remain to be defined. In the present study, we studied the contribution of the NAD+ -dependent deacetylase, sirtuin 1 (SIRT1), to the regulation of nuclear number and MND size. For this, we isolated myofibers from mice with tissue-specific inactivation (mKO) or inducible overexpression (imOX) of SIRT1 and analyzed the 3D organisation of myonuclei. In imOX mice, the number of nuclei was increased whilst the average MND size was decreased as compared to littermate controls. Our findings were the opposite in mKO mice. Muscle stem cell (satellite cell) numbers were reduced in mKO muscles, a possible explanation for the lower density of myonuclei in these mice; however, no change was observed in imOX mice, suggesting that other factors might also be involved, such as the functional regulation of stem cells/muscle precursors. Interestingly, however, the changes in the MND volume did not impact the force-generating capacity of muscle fibers. Taken together, our results demonstrate that SIRT1 is a key regulator of MND sizes, although the underlying molecular mechanisms and the cause-effect relationship between MND and muscle function remain to be fully defined.

Catheter ablation for atrial fibrillation on uninterrupted direct oral anticoagulants: A safe approach.

BACKGROUND: Current consensus guidelines suggest direct oral anticoagulants (DOACs) are interrupted periprocedurally for catheter ablation (CA) of atrial fibrillation (AF). However, this may predispose patients to thromboembolic complications. This study investigates the safety of CA for AF on uninterrupted DOACs compared to uninterrupted warfarin. METHODS: This was a single-center, retrospective study of consecutive patients undergoing CA for AF. All patients were heparinized prior to transseptal puncture with a target-activated clotting time (ACT) of 300-350 seconds. Patients who had procedures performed on continuous DOAC were compared to those on continuous warfarin. Clinical, procedural data, and complications occurring up to 3 months were analyzed from a prospective registry with additional review of electronic health records. RESULTS: A total of 1,884 procedures were performed over 28 months: 761 (609 patients) on uninterrupted warfarin and 1,123 (900 patients) on uninterrupted DOAC (rivaroxaban 64%, apixaban 32%, and dabigatran 4%). There was no difference in the composite endpoint of death, thromboembolism, or major bleeding complication (2.2% vs 1.4%, P = 0.20). There was no difference in the complications comprising this, including tamponade, hematoma, pseudoaneurysm, and transfusion (P-values 0.28, 0.13, 0.45, and 0.36). There were no strokes, transient ischemic attacks, or other thromboembolic complications. There was no difference between groups in the proportion of tamponades requiring reversal of oral anticoagulation, the volume of blood lost, the proportion transfused, or the proportion drained percutaneously (P-values 0.50, 0.51, 0.36, and 0.38). CONCLUSION: Catheter ablation for AF can be performed safely and effectively in patients anticoagulated with DOACs and heparinized with a therapeutic ACT. There is no increased risk of periprocedural bleeding when compared to uninterrupted warfarin.

Exploring the Role of PGC-1α in Defining Nuclear Organisation in Skeletal Muscle Fibres.

Muscle fibres are multinucleated cells, with each nucleus controlling the protein synthesis in a finite volume of cytoplasm termed the myonuclear domain (MND). What determines MND size remains unclear. In the present study, we aimed to test the hypothesis that the level of expression of the transcriptional coactivator PGC-1α and subsequent activation of the mitochondrial biogenesis are major contributors. Hence, we used two transgenic mouse models with varying expression of PGC-1α in skeletal muscles. We isolated myofibres from the fast twitch extensor digitorum longus (EDL) and slow twitch diaphragm muscles. We then membrane-permeabilised them and analysed the 3D spatial arrangements of myonuclei. In EDL muscles, when PGC-1α is over-expressed, MND volume decreases; whereas, when PGC-1α is lacking, no change occurs. In the diaphragm, no clear difference was noted. This indicates that PGC-1α and the related mitochondrial biogenesis programme are determinants of MND size. PGC-1α may facilitate the addition of new myonuclei in order to reach MND volumes that can support an increased mitochondrial density. J. Cell. Physiol. 232: 1270-1274, 2017. © 2016 Wiley Periodicals, Inc.

Widely tunable, narrow linewidth external-cavity gain chip laser for spectroscopy between 1.0 - 1.1 µm.

We have developed and characterised a stable, narrow linewidth external-cavity laser (ECL) tunable over 100 nm around 1080 nm, using a single-angled-facet gain chip. We propose the ECL as a low-cost, high-performance alternative to fibre and diode lasers in this wavelength range and demonstrate its capability through the spectroscopy of metastable helium. Within the coarse tuning range, the wavelength can be continuously tuned over 30 pm (7.8 GHz) without mode-hopping and modulated with bandwidths up to 3 kHz (piezo) and 37(3) kHz (current). The spectral linewidth of the free-running ECL was measured to be 22(2) kHz (Gaussian) and 4.2(3) kHz (Lorentzian) over 22.5 ms, while a long-term frequency stability better than 40(20) kHz over 11 hours was observed when locked to an atomic reference.

Preexercise energy drink consumption does not improve endurance cycling performance but increases lactate, monocyte, and interleukin-6 response.

The purpose of this study was to investigate the influence of an energy drink (ED) on cycling performance and immune-related variables. Eleven trained male cyclists (33.4 ± 8.9 years; 81 ± 7.6 kg; maximal VO2, 52 ± 3.4 ml·kg(-1)·min(-1)) consumed 500 ml of (a) ED (2.0 g taurine, 1.2 g glucuronolactone, 160 mg caffeine, 56 g carbohydrate [CHO], and B vitamins), (b) cola matched for caffeine and CHO (CC), or (c) flavored placebo (PL: sparking water and flavoring) 50 minutes before racing in a randomized, crossover design. Performance was measured as time to complete (TTC) a 25-mile simulated road race. Blood was collected at baseline, 30 minutes after drink consumption, during exercise at miles 5 (M5), 15 (M15), and immediately (POEX) and 30 minutes (30minPO) after exercise. TTC was not different (p > 0.05) among trials (ED, 68.6 ± 2.7; CC, 68.9 ± 3.8; PL, 69.6 ± 3.8 minutes). Consumption of CC and ED elicited a mild hypoglycemia elicited a mild hypoglycemia during cycling. POEX interleukin-6 (IL-6) was greatest after ED, whereas CC IL-6 was greater than PL (10.2 ± 1.6, 6.7 ± 0.6, and 4.8 ± 0.7 pg·ml(-1), respectively; p < 0.001). Cycling increased leukocyte number in all conditions with ED leukocyte number greater than that of PL at M15 (9.8 ± 0.6, 8.5 ± 0.3 × 10(6) cells·mL(-1)). Energy drink induced an earlier recruitment of monocytes to the blood stream than CC. Mean fat oxidation was greater in PL compared with CC (0.43 ± 0.06 and 0.28 ± 0.04 g·min(-1); p = 0.033) but did not differ between ED (0.32 ± 0.06) and PL. Lactate was higher in ED compared with CC and PL at M5 and M15 (p = 0.003), but there was no significant influence of either ED or CC on performance. Carbohydrate and caffeine consumption before endurance cycling significantly increased the IL-6 release and leukocytosis, and the additional ingredients in ED seem to have further augmented these responses.

Subcutaneous Oxytocin Injection Reduces Heat Pain: A Randomized-Controlled Trial.

Oxytocin (OT) is a neuropeptide broadly implicated in social relationships and behavior. OT also exerts antinociceptive and pain-reducing effects in both humans and rodents. Recent research in rodents demonstrates that these effects can be peripheral and local. In human studies, intravenous OT has reduced visceral pain, and subcutaneous injection of OT has reduced postsurgical pain. However, the local effects of subcutaneous OT on experimental pain have not been studied. We conducted a 2-session crossover study during which healthy adults received a subcutaneous injection of synthetic OT (4 mcg/2 mL) or saline placebo (isotonic saline 2 mL), in a randomized and double-blinded manner. Eighteen participants completed full study procedures. We hypothesized that 10 minutes after injection, OT would reduce measures of acute mechanical pain, pressure pain, and heat pain perception. Subcutaneous OT significantly reduced ratings of heat pain intensity and unpleasantness (both P < .01), but did not alter mechanical pain, pressure pain, or heat pain threshold (all P > .05). Changes in heat pain were observed only on the injected arm and not on the contralateral arm, confirming a localized mechanism. These findings confirm the ability of OT in or near the skin to modulate nociceptive processes in cutaneous tissues in human adults, opening exciting avenues for further mechanistic research as well as potential clinical applications for acute pain. PERSPECTIVE: This randomized-controlled trial showed that a subcutaneous injection of OT could reduce perception of heat pain tested with a thermode. OT did not alter mechanical or pressure pain or thresholds for perceiving heat pain. These findings are relevant to scientists and clinicians seeking nonaddictive local drug treatments for pain.

Protein engineered variants of hepatocyte growth factor/scatter factor promote proliferation of primary human hepatocytes and in rodent liver.

BACKGROUND & AIMS: Hepatocyte growth factor/scatter factor (HGF/SF) stimulates hepatocyte DNA synthesis and protects against apoptosis; in vivo it promotes liver regeneration and reduces fibrosis. However, its therapeutic value is limited by its complex domain structure, high cost of production, instability, and poor tissue penetration due to sequestration by heparin sulfate proteoglycans (HSPGs). METHODS: Using protein engineering techniques, we created a full-length form of HGF/SF (called HP21) and a form of the small, naturally occurring HGF/SF fragment, NK1 (called 1K1), which have reduced affinity for HSPG. We characterized the stability and proliferative and anti-apoptotic effects of these variants in primary human hepatocytes and in rodents. RESULTS: Analytical ultracentrifugation showed that 1K1 and NK1 were more stable than the native, full-length protein. All 4 forms of HGF/SF induced similar levels of DNA synthesis in human hepatocytes; 1K1 and NK1 required heparin, an HSPG analogue, for full agonistic activity. All the proteins reduced levels of Fas ligand-mediated apoptosis, reducing the activity of caspase-3/7 and cleavage of poly(adenosine diphosphate-ribose) polymerase. 1K1 was more active than NK1 in rodents; in healthy mice, 1K1 significantly increased hepatocyte DNA synthesis, and in mice receiving carbon tetrachloride, it reduced fibrosis. In rats, after 70% partial hepatectomy, daily administration of 1K1 for 5 days significantly increased liver mass and the bromodeoxyuridine labeling index compared with mice given NK1. CONCLUSIONS: 1K1, an engineered form of the small, naturally occurring HGF/SF fragment NK1, has reduced affinity for HSPG and exerts proliferative and antiapoptotic effects in cultured hepatocytes. In rodents, 1K1 has antifibrotic effects and promotes liver regeneration. The protein has better stability and is easier to produce than HGF/SF and might be developed as a therapeutic for acute and chronic liver disease.

Defects in glycosylation impair satellite stem cell function and niche composition in the muscles of the dystrophic Large(myd) mouse.

The dystrophin-associated glycoprotein complex (DGC) is found at the muscle fiber sarcolemma and forms an essential structural link between the basal lamina and internal cytoskeleton. In a set of muscular dystrophies known as the dystroglycanopathies, hypoglycosylation of the DGC component α-dystroglycan results in reduced binding to basal lamina components, a loss in structural stability, and repeated cycles of muscle fiber degeneration and regeneration. The satellite cells are the key stem cells responsible for muscle repair and reside between the basal lamina and sarcolemma. In this study, we aimed to determine whether pathological changes associated with the dystroglycanopathies affect satellite cell function. In the Large(myd) mouse dystroglycanopathy model, satellite cells are present in significantly greater numbers but display reduced proliferation on their native muscle fibers in vitro, compared with wild type. However, when removed from their fiber, proliferation in culture is restored to that of wild type. Immunohistochemical analysis of Large(myd) muscle reveals alterations to the basal lamina and interstitium, including marked disorganization of laminin, upregulation of fibronectin and collagens. Proliferation and differentiation of wild-type satellite cells is impaired when cultured on substrates such as collagen and fibronectin, compared with laminins. When engrafted into irradiated tibialis anterior muscles of mdx-nude mice, wild-type satellite cells expanded on laminin contribute significantly more to muscle regeneration than those expanded on fibronectin. These results suggest that defects in α-dystroglycan glycosylation are associated with an alteration in the satellite cell niche, and that regenerative potential in the dystroglycanopathies may be perturbed.

WITHDRAWN: I feel your pain: Higher empathy is associated with higher posterior default mode network activity.

The authors discovered an error in the primary analysis and have withdrawn the results from this version of the investigation.

Lem2 is essential for cardiac development by maintaining nuclear integrity.

AIMS: Nuclear envelope integrity is essential for the compartmentalization of the nucleus and cytoplasm. Importantly, mutations in genes encoding nuclear envelope (NE) and associated proteins are the second highest cause of familial dilated cardiomyopathy. One such NE protein that causes cardiomyopathy in humans and affects mouse heart development is Lem2. However, its role in the heart remains poorly understood. METHODS AND RESULTS: We generated mice in which Lem2 was specifically ablated either in embryonic cardiomyocytes (Lem2 cKO) or in adult cardiomyocytes (Lem2 iCKO) and carried out detailed physiological, tissue, and cellular analyses. High-resolution episcopic microscopy was used for three-dimensional reconstructions and detailed morphological analyses. RNA-sequencing and immunofluorescence identified altered pathways and cellular phenotypes, and cardiomyocytes were isolated to interrogate nuclear integrity in more detail. In addition, echocardiography provided a physiological assessment of Lem2 iCKO adult mice. We found that Lem2 was essential for cardiac development, and hearts from Lem2 cKO mice were morphologically and transcriptionally underdeveloped. Lem2 cKO hearts displayed high levels of DNA damage, nuclear rupture, and apoptosis. Crucially, we found that these defects were driven by muscle contraction as they were ameliorated by inhibiting myosin contraction and L-type calcium channels. Conversely, reducing Lem2 levels to ∼45% in adult cardiomyocytes did not lead to overt cardiac dysfunction up to 18 months of age. CONCLUSIONS: Our data suggest that Lem2 is critical for integrity at the nascent NE in foetal hearts, and protects the nucleus from the mechanical forces of muscle contraction. In contrast, the adult heart is not detectably affected by partial Lem2 depletion, perhaps owing to a more established NE and increased adaptation to mechanical stress. Taken together, these data provide insights into mechanisms underlying cardiomyopathy in patients with mutations in Lem2 and cardio-laminopathies in general.

Hepatitis C Virus Reflex Testing Protocol in an Emergency Department.

INTRODUCTION: Our aim was to measure hepatitis C virus (HCV) screening and linkage-to-care rates in an urban emergency department (ED) before and after implementing an HCV viral RNA (vRNA) reflex testing protocol within a HCV screening program for at-risk patients. Our hypothesis was that using a reflex testing protocol would increase HCV testing rates of at-risk patients in the ED, which would increase the linkage-to-care rate. METHODS: In August 2018, our institution implemented an automated, electronic health record-based HCV screening protocol in the ED for at-risk patients. In January 2019, we implemented an HCV vRNA reflex testing protocol (reflex testing) for all positive HCV antibody (Ab) tests that were initiated through the screening protocol. We compared completion rates of HCV vRNA testing and the rate of linkage to care for patients with positive HCV Ab test results before and after implementation of reflex testing (five months per study period). RESULTS: Prior to reflex testing implementation, 233/425 (55%) patients with a positive HCV Ab test had an HCV vRNA test performed, whereas 270/323 (84%) patients with a positive HCV Ab test result had vRNA testing after reflex testing implementation (odds ratio [OR], 4.2; 95% confidence interval (CI): 3.0-6.0; P < 0.001). Of the eligible patients with positive HCV Ab test results who could be linked to care, 45 (10.6%) were linked to care before HCV reflex implementation and 46 (14.2%) were linked to care with reflex testing (OR, 1.4; 95% CI: 0.9-2.2; P = 0.13). CONCLUSION: Implementing a reflex testing initiative into an HCV screening program in the ED can result in an increase of the percentage of patients who receive an HCV vRNA test after having had a positive HCV Ab. Hepatitis C virus vRNA reflex testing was not associated with a statistically significant increase in linkage-to-care rates for HCV Ab-positive patients; however, further studies are required.

THE NUCLEUS: Mechanosensing in cardiac disease.

The nucleus provides a physical and selective chemical boundary to segregate the genome from the cytoplasm. The contents of the nucleus are surrounded by the nuclear envelope, which acts as a hub of mechanosensation, transducing forces from the external cytoskeleton to the nucleus, thus impacting on nuclear morphology, genome organisation, gene transcription and signalling pathways. Muscle tissues such as the heart are unique in that they actively generate large contractile forces, resulting in a distinctive mechanical environment which impacts nuclear properties, function and mechanosensing. In light of this, mutations that affect the function of the nuclear envelope (collectively known as nuclear envelopathies and laminopathies) disproportionately result in striated muscle diseases, which include dilated and arrhythmogenic cardiomyopathies. Here we review the nucleus and its role in mechanotransduction, as well as associated defects that lead to cardiac dysfunction.