Site-specific methylation of Notch1 controls the amplitude and duration of the Notch1 response

Physiologically, Notch signal transduction plays a pivotal role in differentiation; pathologically, Notch signaling contributes to the development of cancer. Transcriptional activation of Notch target genes involves cleavage of the Notch receptor in response to ligand binding, production of the Notch intracellular domain (NICD), and NICD migration into the nucleus and assembly of a coactivator complex. Posttranslational modifications of the NICD are important for its transcriptional activity and protein turnover. Deregulation of Notch signaling and stabilizing mutations of Notch1 have been linked to leukemia development. We found that the methyltransferase CARM1 (coactivator-associated arginine methyltransferase 1; also known as PRMT4) methylated NICD at five conserved arginine residues within the C-terminal transactivation domain. CARM1 physically and functionally interacted with the NICD-coactivator complex and was found at gene enhancers in a Notch-dependent manner. Although a methylation-defective NICD mutant was biochemically more stable, this mutant was biologically less active as measured with Notch assays in embryos of Xenopus laevis and Danio rerio. Mathematical modeling indicated that full but short and transient Notch signaling required methylation of NICD.

Electrophysiological characterization of spinal neurons in different models of diabetes type 1- and type 2-induced neuropathy in rats

Diabetic polyneuropathy (DPN) is a devastating complication of diabetes. The underlying pathogenesis of DPN is still elusive and an effective treatment devoid of side effects presents a challenge. There is evidence that in type-1 and -2 diabetes, metabolic and morphological changes lead to peripheral nerve damage and altered central nociceptive transmission, which may contribute to neuropathic pain symptoms. We characterized the electrophysiological response properties of spinal wide dynamic range (WDR) neurons in three diabetic models. The streptozotocin (STZ) model was used as a drug-induced model of type-1 diabetes, and the BioBreeding/Worcester (BB/Wor) and Zucker diabetic fatty (ZDF) rat models were used for genetic DPN models. Data were compared to the respective control group (BB/Wor diabetic-resistant, Zucker lean (ZL) and saline-injected Wistar rat). Response properties of WDR neurons to mechanical stimulation and spontaneous activity were assessed. We found abnormal response properties of spinal WDR neurons in all diabetic rats but not controls. Profound differences between models were observed. In BB/Wor diabetic rats evoked responses were increased, while in ZDF rats spontaneous activity was increased and in STZ rats mainly after discharges were increased. The abnormal response properties of neurons might indicate differential pathological, diabetes-induced, changes in spinal neuronal transmission. This study shows for the first time that specific electrophysiological response properties are characteristic for certain models of DPN and that these might reflect the diverse and complex symptomatology of DPN in the clinic.

The toxic effect of R350P mutant desmin in striated muscle of man and mouse

Mutations of the human desmin gene on chromosome 2q35 cause autosomal dominant, autosomal recessive and sporadic forms of protein aggregation myopathies and cardiomyopathies. We generated R349P desmin knock-in mice, which harbor the ortholog of the most frequently occurring human desmin missense mutation R350P. These mice develop age-dependent desmin-positive protein aggregation pathology, skeletal muscle weakness, dilated cardiomyopathy, as well as cardiac arrhythmias and conduction defects. For the first time, we report the expression level and subcellular distribution of mutant versus wild-type desmin in our mouse model as well as in skeletal muscle specimens derived from human R350P desminopathies. Furthermore, we demonstrate that the missense-mutant desmin inflicts changes of the subcellular localization and turnover of desmin itself and of direct desmin-binding partners. Our findings unveil a novel principle of pathogenesis, in which not the presence of protein aggregates, but disruption of the extrasarcomeric intermediate filament network leads to increased mechanical vulnerability of muscle fibers. These structural defects elicited at the myofiber level finally impact the entire organ and subsequently cause myopathy and cardiomyopathy.

[Human Single Drug Exposures to Non-opioid Analgesics Reported to the Poisons Information Centre Erfurt from 2003 to 2012]

AIM OF THE STUDY

Because of their frequency, non-opioid analgesics (NOA) single drug exposures registered by Poisons Information Centre (PIC) Erfurt have been studied over a decade.

METHODS

A retrospective analysis of frequencies, circumstances of exposure, symptom severity, and age groups in NOA single drug exposures received by the PIC Erfurt from the beginning of 2003 to the end of 2012 was undertaken.

RESULTS

Of all 4749 NOA single drug exposures, the 10 most frequent were caused by paracetamol (n=1 686), ibuprofen (n=1 439), acetylsalicylic acid (n=456), dipyrone (n=274), diclofenac (n=267), flupirtine (n=138), naproxen (n=41), etoricoxib (n=36), indomethacin (n=24), and dexketoprofen (n=19). Paracetamol single drug exposures increased from 158 in 2003 to 216 in 2007 and fell afterwards to 133 in 2012. Ibuprofen single drug exposures continously rose from 57 in 2003 to 258 in 2012. Adults were more often involved in NOA (53.8%) and all single drug exposures (54.1%) than children (45.9% and 45.6%, respectively). Suicidal attempts were more frequent in NOA (43.1%) than in all single drug exposures (34.2%), whereas accidental exposures or exposures in abuse were less often (33.4 and 0.2%, 46.0 and 0.9% respectively). NOA single drug exposures resulted mostly in none to minor symptoms (77.0%) and rarely in moderate (2.1%) or severe symptoms (1.0%). One adult was found dead after probable ingestion of 32 g of acetylsalicylic acid in suicidal intention.

CONCLUSIONS

Because many NOA are over-the-counter drugs, it is difficult to obtain data on their use. PIC data could provide information on the NOA use in the population.

Overlapping and opposing functions of G protein-coupled receptor kinase 2 (GRK2) and GRK5 during heart development

G protein-coupled receptor kinases 2 (GRK2) and 5 (GRK5) are fundamental regulators of cardiac performance in adults but are less well characterized for their function in the hearts of embryos. GRK2 and -5 belong to different subfamilies and function as competitors in the control of certain receptors and signaling pathways. In this study, we used zebrafish to investigate whether the fish homologs of GRK2 and -5, Grk2/3 and Grk5, also have unique, complementary, or competitive roles during heart development. We found that they differentially regulate the heart rate of early embryos and equally facilitate heart function in older embryos and that both are required to develop proper cardiac morphology. A loss of Grk2/3 results in dilated atria and hypoplastic ventricles, and the hearts of embryos depleted in Grk5 present with a generalized atrophy. This Grk5 morphant phenotype was associated with an overall decrease of early cardiac progenitors as well as a reduction in the area occupied by myocardial progenitor cells. In the case of Grk2/3, the progenitor decrease was confined to a subset of precursor cells with a committed ventricular fate. We attempted to rescue the GRK loss-of-function heart phenotypes by downstream activation of Hedgehog signaling. The Grk2/3 loss-of-function embryos were rescued by this approach, but Grk5 embryos failed to respond. In summary, we found that GRK2 and GRK5 control cardiac function as well as morphogenesis during development although with different morphological outcomes.

Automatic zebrafish heartbeat detection and analysis for zebrafish embryos

A fully automatic detection and analysis method of heartbeats in videos of nonfixed and nonanesthetized zebrafish embryos is presented. This method reduces the manual workload and time needed for preparation and imaging of the zebrafish embryos, as well as for evaluating heartbeat parameters such as frequency, beat-to-beat intervals, and arrhythmicity. The method is validated by a comparison of the results from automatic and manual detection of the heart rates of wild-type zebrafish embryos 36-120 h postfertilization and of embryonic hearts with bradycardia and pauses in the cardiac contraction.

Aciculin interacts with filamin C and Xin and is essential for myofibril assembly, remodeling and maintenance

Filamin C (FLNc) and Xin actin-binding repeat-containing proteins (XIRPs) are multi-adaptor proteins that are mainly expressed in cardiac and skeletal muscles and which play important roles in the assembly and repair of myofibrils and their attachment to the membrane. We identified the dystrophin-binding protein aciculin (also known as phosphoglucomutase-like protein 5, PGM5) as a new interaction partner of FLNc and Xin. All three proteins colocalized at intercalated discs of cardiac muscle and myotendinous junctions of skeletal muscle, whereas FLNc and aciculin also colocalized in mature Z-discs. Bimolecular fluorescence complementation experiments in developing cultured mammalian skeletal muscle cells demonstrated that Xin and aciculin also interact in FLNc-containing immature myofibrils and areas of myofibrillar remodeling and repair induced by electrical pulse stimulation (EPS). Fluorescence recovery after photobleaching (FRAP) experiments showed that aciculin is a highly dynamic and mobile protein. Aciculin knockdown in myotubes led to failure in myofibril assembly, alignment and membrane attachment, and a massive reduction in myofibril number. A highly similar phenotype was found upon depletion of aciculin in zebrafish embryos. Our results point to a thus far unappreciated, but essential, function of aciculin in myofibril formation, maintenance and remodeling.

Which criteria demand additive stenting during catheter-directed thrombolysis?

Many factors are necessary for obtaining satisfactory results after catheter-directed thrombolysis (CDT) for iliofemoral deep venous thrombosis (DVT). Selections of patients, composition of the thrombolytic fluid, anticoagulation per- and post-procedural, recognition and treatment of persistent obstructive lesions of the iliac veins are the most important contributors. Stenting has been known for 15 to 20 years. The first publication on CDT in 1991 was combined with ballooning the iliac vein, an additive procedure which has been abandoned as an isolated procedure. This chapter will discuss selection, indication, such as an iliac compression syndrome, and outcome of iliac stenting in combination with CDT. The reported frequency of stenting used after CDT is very inconsistent, therefore this will be discussed in details. It is concluded that selection for stenting is of the greatest importance, when CDT is used for iliofemoral DVT, but strict criteria for stenting are not available in the existing literature. The potential value of intravascular ultrasound (IVUS) is also discussed.

Indications for stenting during thrombolysis

The most important vein segment to thrombolyse after deep venous thrombosis (DVT) is the outflow tract meaning the iliofemoral vein. Iliofemoral DVT is defined as DVT in the iliac vein and the common femoral vein. Spontaneous recanalization is less than 50%, particularly on the left side. The compression from adjacent structures, predominantly on the left side is known as the iliac vein compression syndrome. Therefore, it is essential that supplementary endovenous procedures have to be performed in case of persistent obstructive lesions following catheter-directed thrombolysis. Insertion of a stent in this position is the treatment of choice facilitating the venous flow into an unobstructed outflow tract either from the femoral vein or the deep femoral vein or both. The stent, made of stainless steel or nitinol, has to be self-expandable and flexible with radial force to overcome the challenges in this low-pressure system. The characteristics of the anatomy with external compression and often a curved vein segment with diameter difference make stent placement necessary. Ballooning alone has no place in this area. The proportion of inserted stents varies in the published materials with catheter-directed thrombolysis of iliofemoral deep venous thrombosis.

High-throughput screening of zebrafish embryos using automated heart detection and imaging

Over the past decade, the zebrafish has become a key model organism in genetic screenings and drug discovery. A number of genes have been identified to affect the development of the shape and functioning of the heart, leading to zebrafish mutants with heart defects. The development of semiautomated microscopy systems has allowed for the investigation of drugs that reverse a disease phenotype on a larger scale. However, there is a lack of automated feature detection, and commercially available computer-aided microscopes are expensive. Screening of the zebrafish heart for drug discovery typically includes the identification of heart parameters, such as the frequency or fractional shortening. Until now, screening processes have been characterized by manual handling of the larvae and manual microscopy. Here, an intelligent robotic microscope is presented, which automatically identifies the orientation of a zebrafish in a micro well. A predefined region of interest, such as the heart, is detected automatically, and a video with higher magnification is recorded. Screening of a 96-well plate takes 35 to 55 min, depending on the length of the videos. Of the zebrafish hearts, 75% are recorded accurately without any user interaction. A description of the system, including the graphical user interface, is given.

F-box and leucine-rich repeat protein 22 is a cardiac-enriched F-box protein that regulates sarcomeric protein turnover and is essential for maintenance of contractile function in vivo

RATIONALE

The emerging role of the ubiquitin-proteasome system in cardiomyocyte function and homeostasis implies the necessity of tight regulation of protein degradation. However, little is known about cardiac components of this machinery.

OBJECTIVE

We sought to determine whether molecules exist that control turnover of cardiac-specific proteins.

METHODS AND RESULTS

Using a bioinformatic approach to identify novel cardiac-enriched sarcomere proteins, we identified F-box and leucine-rich repeat protein 22 (Fbxl22). Tissue-specific expression was confirmed by multiple tissue Northern and Western Blot analyses as well as quantitative reverse-transcriptase polymerase chain reaction on a human cDNA library. Immunocolocalization experiments in neonatal and adult rat ventricular cardiomyocytes as well as murine heart tissue located Fbxl22 to the sarcomeric z-disc. To detect cardiac protein interaction partners, we performed a yeast 2-hybrid screen using Fbxl22 as bait. Coimmunoprecipitation confirmed the identified interactions of Fbxl22 with S-phase kinase-associated protein 1 and Cullin1, 2 critical components of SCF (Skp1/Cul1/F-box) E3- ligases. Moreover, we identified several potential substrates, including the z-disc proteins α-actinin and filamin C. Consistently, in vitro overexpression of Fbxl22-mediated degradation of both substrates in a dose-dependent fashion, whereas proteasome inhibition with MG-132 markedly attenuated degradation of both α-actinin and filamin C. Finally, targeted knockdown of Fbxl22 in rat cardiomyocytes as well as zebrafish embryos results in the accumulation of α-actinin associated with severely impaired contractile function and cardiomyopathy in vivo.

CONCLUSIONS

These findings reveal the previously uncharacterized cardiac-specific F-box protein Fbxl22 as a component of a novel cardiac E3 ligase. Fbxl22 promotes the proteasome-dependent degradation of key sarcomeric proteins, such as α-actinin and filamin C, and is essential for maintenance of normal contractile function in vivo.

Smyd2 controls cytoplasmic lysine methylation of Hsp90 and myofilament organization

Protein lysine methylation is one of the most widespread post-translational modifications in the nuclei of eukaryotic cells. Methylated lysines on histones and nonhistone proteins promote the formation of protein complexes that control gene expression and DNA replication and repair. In the cytoplasm, however, the role of lysine methylation in protein complex formation is not well established. Here we report that the cytoplasmic protein chaperone Hsp90 is methylated by the lysine methyltransferase Smyd2 in various cell types. In muscle, Hsp90 methylation contributes to the formation of a protein complex containing Smyd2, Hsp90, and the sarcomeric protein titin. Deficiency in Smyd2 results in the loss of Hsp90 methylation, impaired titin stability, and altered muscle function. Collectively, our data reveal a cytoplasmic protein network that employs lysine methylation for the maintenance and function of skeletal muscle.

The myosin-interacting protein SMYD1 is essential for sarcomere organization

Assembly, maintenance and renewal of sarcomeres require highly organized and balanced folding, transport, modification and degradation of sarcomeric proteins. However, the molecules that mediate these processes are largely unknown. Here, we isolated the zebrafish mutant flatline (fla), which shows disturbed sarcomere assembly exclusively in heart and fast-twitch skeletal muscle. By positional cloning we identified a nonsense mutation within the SET- and MYND-domain-containing protein 1 gene (smyd1) to be responsible for the fla phenotype. We found SMYD1 expression to be restricted to the heart and fast-twitch skeletal muscle cells. Within these cell types, SMYD1 localizes to both the sarcomeric M-line, where it physically associates with myosin, and the nucleus, where it supposedly represses transcription through its SET and MYND domains. However, although we found transcript levels of thick filament chaperones, such as Hsp90a1 and UNC-45b, to be severely upregulated in fla, its histone methyltransferase activity - mainly responsible for the nuclear function of SMYD1 - is dispensable for sarcomerogenesis. Accordingly, sarcomere assembly in fla mutant embryos can be reconstituted by ectopically expressing histone methyltransferase-deficient SMYD1. By contrast, ectopic expression of myosin-binding-deficient SMYD1 does not rescue fla mutants, implicating an essential role for the SMYD1-myosin interaction in cardiac and fast-twitch skeletal muscle thick filament assembly.

Protein kinase D2 controls cardiac valve formation in zebrafish by regulating histone deacetylase 5 activity

BACKGROUND

The molecular mechanisms that guide heart valve formation are not well understood. However, elucidation of the genetic basis of congenital heart disease is one of the prerequisites for the development of tissue-engineered heart valves.

METHODS AND RESULTS

We isolated here a mutation in zebrafish, bungee (bng(jh177)), which selectively perturbs valve formation in the embryonic heart by abrogating endocardial Notch signaling in cardiac cushions. We found by positional cloning that the bng phenotype is caused by a missense mutation (Y849N) in zebrafish protein kinase D2 (pkd2). The bng mutation selectively impairs PKD2 kinase activity and hence Histone deacetylase 5 phosphorylation, nuclear export, and inactivation. As a result, the expression of Histone deacetylase 5 target genes Krüppel-like factor 2a and 4a, transcription factors known to be pivotal for heart valve formation and to act upstream of Notch signaling, is severely downregulated in bungee (bng) mutant embryos. Accordingly, the expression of Notch target genes, such as Hey1, Hey2, and HeyL, is severely decreased in bng mutant embryos. Remarkably, downregulation of Histone deacetylase 5 activity in homozygous bng mutant embryos can rescue the mutant phenotype and reconstitutes notch1b expression in atrioventricular endocardial cells.

CONCLUSIONS

We demonstrate for the first time that proper heart valve formation critically depends on Protein kinase D2-Histone deacetylase 5-Krüppel-like factor signaling.

Targeted next-generation sequencing for the molecular genetic diagnostics of cardiomyopathies

BACKGROUND

Today, mutations in more than 30 different genes have been found to cause inherited cardiomyopathies, some associated with very poor prognosis. However, because of the genetic heterogeneity and limitations in throughput and scalability of current diagnostic tools up until now, it is hardly possible to genetically characterize patients with cardiomyopathy in a fast, comprehensive, and cost-efficient manner.

METHODS AND RESULTS

We established an array-based subgenomic enrichment followed by next-generation sequencing to detect mutations in patients with hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). With this approach, we show that the genomic region of interest can be enriched by a mean factor of 2169 compared with the coverage of the whole genome, resulting in high sequence coverage of selected disease genes and allowing us to define the genetic pathogenesis of cardiomyopathies in a single sequencing run. In 6 patients, we detected disease-causing mutations, 2 microdeletions, and 4 point mutations. Furthermore, we identified several novel nonsynonymous variants, which are predicted to be harmful, and hence, might be potential disease mutations or modifiers for DCM or HCM.

CONCLUSIONS

The approach presented here allows for the first time a comprehensive genetic screening in patients with hereditary DCM or HCM in a fast and cost-efficient manner.

MicroRNA signatures in total peripheral blood as novel biomarkers for acute myocardial infarction

MicroRNAs (miRNAs) are important regulators of adaptive and maladaptive responses in cardiovascular diseases and hence are considered to be potential therapeutical targets. However, their role as novel biomarkers for the diagnosis of cardiovascular diseases still needs to be systematically evaluated. We assessed here for the first time whole-genome miRNA expression in peripheral total blood samples of patients with acute myocardial infarction (AMI). We identified 121 miRNAs, which are significantly dysregulated in AMI patients in comparison to healthy controls. Among these, miR-1291 and miR-663b show the highest sensitivity and specificity for the discrimination of cases from controls. Using a novel self-learning pattern recognition algorithm, we identified a unique signature of 20 miRNAs that predicts AMI with even higher power (specificity 96%, sensitivity 90%, and accuracy 93%). In addition, we show that miR-30c and miR-145 levels correlate with infarct sizes estimated by Troponin T release. The here presented study shows that single miRNAs and especially miRNA signatures derived from peripheral blood, could be valuable novel biomarkers for cardiovascular diseases.

Myomasp/LRRC39, a heart- and muscle-specific protein, is a novel component of the sarcomeric M-band and is involved in stretch sensing

RATIONALE AND OBJECTIVE

The M-band represents a transverse structure in the center of the sarcomeric A-band and provides an anchor for the myosin-containing thick filaments. In contrast to other sarcomeric structures, eg, the Z-disc, only few M-band-specific proteins have been identified to date, and its exact molecular composition remains unclear.

METHODS AND RESULTS

Using a bioinformatic approach to identify novel heart- and muscle-specific genes, we found a leucine rich protein, myomasp (Myosin-interacting, M-band-associated stress-responsive protein)/LRRC39. RT-PCR and Northern and Western blot analyses confirmed a cardiac-enriched expression pattern, and immunolocalization of myomasp revealed a strong and specific signal at the sarcomeric M-band. Yeast 2-hybrid screens, as well as coimmunoprecipitation experiments, identified the C terminus of myosin heavy chain (MYH)7 as an interaction partner for myomasp. Knockdown of myomasp in neonatal rat ventricular myocytes (NRVCMs) led to a significant upregulation of the stretch-sensitive genes GDF-15 and BNP. Conversely, the expression of MYH7 and the M-band proteins myomesin-1 and -2 was found to be markedly reduced. Mechanistically, knockdown of myomasp in NRVCM led to a dose-dependent suppression of serum response factor-dependent gene expression, consistent with earlier observations linking the M-band to serum response factor-mediated signaling. Finally, downregulation of myomasp/LRRC39 in spontaneously beating engineered heart tissue constructs resulted in significantly lower force generation and reduced fractional shortening. Likewise, knockdown of the myomasp/LRRC39 ortholog in zebrafish resulted in severely impaired heart function and cardiomyopathy in vivo.

CONCLUSIONS

These findings reveal myomasp as a previously unrecognized component of an M-band-associated signaling pathway that regulates cardiomyocyte gene expression in response to biomechanical stress.

Strumpellin is a novel valosin-containing protein binding partner linking hereditary spastic paraplegia to protein aggregation diseases

Mutations of the human valosin-containing protein gene cause autosomal-dominant inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia. We identified strumpellin as a novel valosin-containing protein binding partner. Strumpellin mutations have been shown to cause hereditary spastic paraplegia. We demonstrate that strumpellin is a ubiquitously expressed protein present in cytosolic and endoplasmic reticulum cell fractions. Overexpression or ablation of wild-type strumpellin caused significantly reduced wound closure velocities in wound healing assays, whereas overexpression of the disease-causing strumpellin N471D mutant showed no functional effect. Strumpellin knockdown experiments in human neuroblastoma cells resulted in a dramatic reduction of axonal outgrowth. Knockdown studies in zebrafish revealed severe cardiac contractile dysfunction, tail curvature and impaired motility. The latter phenotype is due to a loss of central and peripheral motoneuron formation. These data imply a strumpellin loss-of-function pathogenesis in hereditary spastic paraplegia. In the human central nervous system strumpellin shows a presynaptic localization. We further identified strumpellin in pathological protein aggregates in inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia, various myofibrillar myopathies and in cortical neurons of a Huntington's disease mouse model. Beyond hereditary spastic paraplegia, our findings imply that mutant forms of strumpellin and valosin-containing protein may have a concerted pathogenic role in various protein aggregate diseases.

JunB-CBFbeta signaling is essential to maintain sarcomeric Z-disc structure and when defective leads to heart failure

In muscle cells, a complex network of Z-disc proteins allows proper reception, transduction and transmission of mechanical and biochemical signals. Mutations in genes encoding different Z-disc proteins such as integrin-linked kinase (ILK) and nexilin have recently been shown to cause heart failure by distinct mechanisms such as disturbed mechanosensing, altered mechanotransduction or mechanical Z-disc destabilization. We identified core-binding factor β (CBFβ) as an essential component for maintaining sarcomeric Z-disc and myofilament organization in heart and skeletal muscle. In CBFβ-deficient cardiomyocytes and skeletal-muscle cells, myofilaments are thinned and Z-discs are misaligned, leading to progressive impairment of heart and skeletal-muscle function. Transcription of the gene encoding CBFβ mainly depends on JunB activity. In JunB-morphant zebrafish, which show a heart-failure phenotype similar to that of CBFβ-deficient zebrafish, transcript and protein levels of CBFβ are severely reduced. Accordingly, ectopic expression of CBFβ can reconstitute cardiomyocyte function and rescue heart failure in JunB morphants, demonstrating for the first time an essential role of JunB-CBFβ signaling for maintaining sarcomere architecture and function.

Myozap, a novel intercalated disc protein, activates serum response factor-dependent signaling and is required to maintain cardiac function in vivo

RATIONALE

The intercalated disc (ID) is a highly specialized cell-cell contact structure that ensures mechanical and electric coupling of contracting cardiomyocytes. Recently, the ID has been recognized to be a hot spot of cardiac disease, in particular inherited cardiomyopathy.

OBJECTIVE

Given its complex structure and function we hypothesized that important molecular constituents of the ID still remain unknown.

METHODS AND RESULTS

Using a bioinformatics screen, we discovered and cloned a previously uncharacterized 54 kDa cardiac protein which we termed Myozap (Myocardium-enriched zonula occludens-1-associated protein). Myozap is strongly expressed in the heart and lung. In cardiac tissue it localized to the ID and directly binds to desmoplakin and zonula occludens-1. In a yeast 2-hybrid screen for additional binding partners of Myozap we identified myosin phosphatase-RhoA interacting protein (MRIP), a negative regulator of Rho activity. Myozap, in turn, strongly activates SRF-dependent transcription through its ERM (Ezrin/radixin/moesin)-like domain in a Rho-dependent fashion. Finally, in vivo knockdown of the Myozap ortholog in zebrafish led to severe contractile dysfunction and cardiomyopathy.

CONCLUSIONS

Taken together, these findings reveal Myozap as a previously unrecognized component of a Rho-dependent signaling pathway that links the intercalated disc to cardiac gene regulation. Moreover, its subcellular localization and the observation of a severe cardiac phenotype in zebrafish, implicate Myozap in the pathogenesis of cardiomyopathy.

Nexilin mutations destabilize cardiac Z-disks and lead to dilated cardiomyopathy

Z-disks, the mechanical integration sites of heart and skeletal muscle cells, link anchorage of myofilaments to force reception and processing. The key molecules that enable the Z-disk to persistently withstand the extreme mechanical forces during muscle contraction have not yet been identified. Here we isolated nexilin (encoded by NEXN) as a novel Z-disk protein. Loss of nexilin in zebrafish led to perturbed Z-disk stability and heart failure. To evaluate the role of nexilin in human heart failure, we performed a genetic association study on individuals with dilated cardiomyopathy and found several mutations in NEXN associated with the disease. Nexilin mutation carriers showed the same cardiac Z-disk pathology as observed in nexilin-deficient zebrafish. Expression in zebrafish of nexilin proteins encoded by NEXN mutant alleles induced Z-disk damage and heart failure, demonstrating a dominant-negative effect and confirming the disease-causing nature of these mutations. Increasing mechanical strain aggravated Z-disk damage in nexilin-deficient skeletal muscle, implying a unique role of nexilin in protecting Z-disks from mechanical trauma.

A single serine in the carboxyl terminus of cardiac essential myosin light chain-1 controls cardiomyocyte contractility in vivo

Although it is well known that mutations in the cardiac essential myosin light chain-1 (cmlc-1) gene can cause hypertrophic cardiomyopathy, the precise in vivo structural and functional roles of cMLC-1 in the heart are only poorly understood. We have isolated the zebrafish mutant lazy susan (laz), which displays severely reduced contractility of both heart chambers. By positional cloning, we identified a nonsense mutation within the zebrafish cmlc-1 gene to be responsible for the laz phenotype, leading to expression of a carboxyl-terminally truncated cMLC-1. Whereas complete loss of cMLC-1 leads to cardiac acontractility attributable to impaired cardiac sarcomerogenesis, expression of a carboxyl-terminally truncated cMLC-1 in laz mutant hearts is sufficient for normal cardiac sarcomerogenesis but severely impairs cardiac contractility in a cell-autonomous fashion. Whereas overexpression of wild-type cMLC-1 restores contractility of laz mutant cardiomyocytes, overexpression of phosphorylation site serine 195-deficient cMLC-1 (cMLC-1(S195A)) does not reconstitute cardiac contractility in laz mutant cardiomyocytes. By contrast, introduction of a phosphomimetic amino acid on position 195 (cMLC-1(S195D)) rescues cardiomyocyte contractility, demonstrating for the first time an essential role of the carboxyl terminus and especially of serine 195 of cMLC-1 in the regulation of cardiac contractility.

MicroRNA-21 contributes to myocardial disease by stimulating MAP kinase signalling in fibroblasts

MicroRNAs comprise a broad class of small non-coding RNAs that control expression of complementary target messenger RNAs. Dysregulation of microRNAs by several mechanisms has been described in various disease states including cardiac disease. Whereas previous studies of cardiac disease have focused on microRNAs that are primarily expressed in cardiomyocytes, the role of microRNAs expressed in other cell types of the heart is unclear. Here we show that microRNA-21 (miR-21, also known as Mirn21) regulates the ERK-MAP kinase signalling pathway in cardiac fibroblasts, which has impacts on global cardiac structure and function. miR-21 levels are increased selectively in fibroblasts of the failing heart, augmenting ERK-MAP kinase activity through inhibition of sprouty homologue 1 (Spry1). This mechanism regulates fibroblast survival and growth factor secretion, apparently controlling the extent of interstitial fibrosis and cardiac hypertrophy. In vivo silencing of miR-21 by a specific antagomir in a mouse pressure-overload-induced disease model reduces cardiac ERK-MAP kinase activity, inhibits interstitial fibrosis and attenuates cardiac dysfunction. These findings reveal that microRNAs can contribute to myocardial disease by an effect in cardiac fibroblasts. Our results validate miR-21 as a disease target in heart failure and establish the therapeutic efficacy of microRNA therapeutic intervention in a cardiovascular disease setting.

Regulation of muscle development by DPF3, a novel histone acetylation and methylation reader of the BAF chromatin remodeling complex

Chromatin remodeling and histone modifications facilitate access of transcription factors to DNA by promoting the unwinding and destabilization of histone-DNA interactions. We present DPF3, a new epigenetic key factor for heart and muscle development characterized by a double PHD finger. DPF3 is associated with the BAF chromatin remodeling complex and binds methylated and acetylated lysine residues of histone 3 and 4. Thus, DPF3 may represent the first plant homeodomains that bind acetylated lysines, a feature previously only shown for the bromodomain. During development Dpf3 is expressed in the heart and somites of mouse, chicken, and zebrafish. Morpholino knockdown of dpf3 in zebrafish leads to incomplete cardiac looping and severely reduced ventricular contractility, with disassembled muscular fibers caused by transcriptional deregulation of structural and regulatory proteins. Promoter analysis identified Dpf3 as a novel downstream target of Mef2a. Taken together, DPF3 adds a further layer of complexity to the BAF complex by representing a tissue-specific anchor between histone acetylations as well as methylations and chromatin remodeling. Furthermore, this shows that plant homeodomain proteins play a yet unexplored role in recruiting chromatin remodeling complexes to acetylated histones.

Targeted mutation reveals essential functions of the homeodomain transcription factor Shox2 in sinoatrial and pacemaking development

BACKGROUND

Identifying molecular pathways regulating the development of pacemaking and coordinated heartbeat is crucial for a comprehensive mechanistic understanding of arrhythmia-related diseases. Elucidation of these pathways has been complicated mainly by an insufficient definition of the developmental structures involved in these processes and the unavailability of animal models specifically targeting the relevant tissues. Here, we report on a highly restricted expression pattern of the homeodomain transcription factor Shox2 in the sinus venosus myocardium, including the sinoatrial nodal region and the venous valves.

METHODS AND RESULTS

To investigate its function in vivo, we have generated mouse lines carrying a targeted mutation of the Shox2 gene. Although heterozygous animals did not exhibit obvious defects, homozygosity of the targeted allele led to embryonic lethality at 11.5 to 13.5 dpc. Shox2-/- embryos exhibited severe hypoplasia of the sinus venosus myocardium in the posterior heart field, including the sinoatrial nodal region and venous valves. We furthermore demonstrate aberrant expression of connexin 40 and connexin 43 and the transcription factor Nkx2.5 in vivo specifically within the sinoatrial nodal region and show that Shox2 deficiency interferes with pacemaking function in zebrafish embryos.

CONCLUSIONS

From these results, we postulate a critical function of Shox2 in the recruitment of sinus venosus myocardium comprising the sinoatrial nodal region.

Reduction of atherosclerotic nanoplaque formation and size by Ginkgo biloba (EGb 761) in cardiovascular high-risk patients

Coating a silica surface with the isolated lipoprotein receptor proteoheparan sulfate (HS-PG) from arterial endothelium and vascular matrices and adding both the atherogenic VLDL/IDL/LDL lipid fraction in its native composition and Ca(2+) ions, we could observe in vitro the earliest stages of atherosclerotic plaque development by ellipsometric techniques (patent EP 0 946 876). This so-called nanoplaque formation is represented by the ternary aggregational complex of the HS-PG receptor, lipoprotein particles and calcium ions. The model was validated in several clinical studies on statins in cardiovascular high-risk patients. In eight patients who had undergone an aortocoronary bypass operation, the reduction of atherosclerotic nanoplaque formation amounted to 11.9+/-2.5% (p<0.0078) and of nanoplaque size to 24.4+/-8.1% (p<0.0234), respectively, after a 2-month therapy with Ginkgo biloba extract (2x 120 mg daily, EGb 761). Additionally, superoxide dismutase (SOD) activity was upregulated by 15.7+/-7.0% (p<0.0391), the quotient oxLDL/LDL lowered by 17.0+/-5.5% (p<0.0234) and lipoprotein(a) concentration decreased by 23.4+/-7.9% (p<0.0234) in the patients' blood. The concentration of the vasodilating substances cAMP and cGMP was augmented by 37.5+/-9.1% (p<0.0078) and 27.7+/-8.3% (p<0.0156), respectively. A multiple regression analysis between the patients' VLDL/IDL/LDL lipoprotein fraction applied in the ellipsometry measurements as well as the further risk factors oxLDL/LDL and Lp(a) on the one hand and changes in nanoplaque formation on the other hand reveals a basis for a mechanistic explanation of nanoplaque reduction under ginkgo treatment. The atherosclerosis inhibiting effect is possibly due to an upregulation in the body's own radical scavenging enzymes and an attenuation of the risk factors oxLDL/LDL and Lp(a).

Integrin-linked kinase, a novel component of the cardiac mechanical stretch sensor, controls contractility in the zebrafish heart

The vertebrate heart possesses autoregulatory mechanisms enabling it first to sense and then to adapt its force of contraction to continually changing demands. The molecular components of the cardiac mechanical stretch sensor are mostly unknown but of immense medical importance, since dysfunction of this sensing machinery is suspected to be responsible for a significant proportion of human heart failure. In the hearts of the ethylnitros-urea (ENU)-induced, recessive embryonic lethal zebrafish heart failure mutant main squeeze (msq), we find stretch-responsive genes such as atrial natriuretic factor (anf) and vascular endothelial growth factor (vegf) severely down-regulated. We demonstrate through positional cloning that heart failure in msq mutants is due to a mutation in the integrin-linked kinase (ilk) gene. ILK specifically localizes to costameres and sarcomeric Z-discs. The msq mutation (L308P) reduces ILK kinase activity and disrupts binding of ILK to the Z-disc adaptor protein beta-parvin (Affixin). Accordingly, in msq mutant embryos, heart failure can be suppressed by expression of ILK, and also of a constitutively active form of Protein Kinase B (PKB), and VEGF. Furthermore, antisense-mediated abrogation of zebrafish beta-parvin phenocopies the msq phenotype. Thus, we provide evidence that the heart uses the Integrin-ILK-beta-parvin network to sense mechanical stretch and respond with increased expression of ANF and VEGF, the latter of which was recently shown to augment cardiac force by increasing the heart's calcium transients.

Cardiac myosin light chain-2: a novel essential component of thick-myofilament assembly and contractility of the heart

Although it is well known that mutations in the cardiac regulatory myosin light chain-2 (mlc-2) gene cause hypertrophic cardiomyopathy, the precise in vivo structural and functional roles of MLC-2 in the heart are only poorly understood. We have isolated a mutation in zebrafish, tell tale heart (tel(m225)), which selectively perturbs contractility of the embryonic heart. By positional cloning, we identified tel to encode the zebrafish mlc-2 gene. In contrast to mammals, zebrafish have only 1 cardiac-specific mlc-2 gene, which we find to be expressed in atrial and ventricular cardiomyocytes during early embryonic development, but also in the adult heart. Accordingly, loss of zMLC-2 function cannot be compensated for by upregulation of another mlc-2 gene. Surprisingly, ultrastructural analysis of tel cardiomyocytes reveals complete absence of organized thick myofilaments. Thus, our findings provide the first in vivo evidence that cardiac MLC-2 is required for thick-filament stabilization and contractility in the vertebrate heart.

Catheter Directed Thrombolysis for Treatment of Ilio-femoral Deep Venous Thrombosis is Durable, Preserves Venous Valve Function and May Prevent Chronic Venous Insufficiency

OBJECTIVES

To investigate the results of catheter directed thrombolysis offered to patients with acute femoro-iliac deep venous thrombosis (DVT).

DESIGN

Retrospective analysis of all patients treated with this modality at Gentofte Hospital until December 2003.

MATERIAL

Forty-five consecutive patients treated between June 1999 and December 2003 with a median age of 31 years. All patients had femoro-iliac DVT with an average anamnesis of 6 days.

METHODS

All patients were treated by catheter directed infusion of alteplase into the popliteal vein. After thrombolysis residual venous stenoses were treated by percutaneous balloon angioplasty (PTA) and stenting. Patients were followed with color-duplex scanning for assessment of venous patency and reflux.

RESULTS

Forty-two of 45 (93%) of cases were treated successfully with reopening of the thrombosed vein segments. In 30 of 45 cases a residual stenosis was treated by PTA and stenting. Only one serious complication was observed: Compartment syndrome of the forearm where arterial punctures had been taken. After an average of 24 months follow-up were no cases of re-thrombosis among the 42 patients discharged with open veins. Only two of 41 with presumed normal venous valve function prior to DVT developed reflux during follow-up.

CONCLUSION

In this selected patient group, catheter directed thrombolysis seems effective in treating acute DVT, it appears durable and preserves venous valve function in the majority. The method needs to be tested in a randomised controlled trial.

VEGF-PLCgamma1 pathway controls cardiac contractility in the embryonic heart

The strength of the heart beat can accommodate in seconds to changes in blood pressure or flow. The mechanism for such homeostatic adaptation is unknown. We sought the cause of poor contractility in the heart of the embryonic zebrafish with the mutation dead beat. We find through cloning that this is due to a mutation in the phospholipase C gamma1 (plcgamma1) gene. In mutant embryos, contractile function can be restored by PLCgamma1 expression directed selectively to cardiac myocytes. In other situations, PLCgamma1 is known to transduce the signal from vascular endothelial growth factor (VEGF), and we show here that abrogation of VEGF also interferes with cardiac contractility. Somewhat unexpectedly, FLT-1 is the responsible VEGF receptor. We show that the same system functions in the rat. Blockage of VEGF-PLCgamma1 signaling decreases calcium transients in rat ventricular cardiomyocytes, whereas VEGF imposes a positive inotropic effect on cardiomyocytes by increasing calcium transients. Thus, the muscle of the heart uses the VEGF-PLCgamma1 cascade to control the strength of the heart beat. We speculate that this paracrine system may contribute to normal and pathological regulation of cardiac contractility.

Quantification of feto-maternal haemorrhage (FMH) by flow cytometry: anti-fetal haemoglobin labelling potentially underestimates massive FMH in comparison to labelling with anti-D

Many centres now routinely use flow cytometry to quantify feto-maternal haemorrhage (FMH). However, which flow cytometric method is the most accurate in quantifying FMH is currently unknown. An audit of clinical results in which FMH had been estimated by both directly conjugated monoclonal anti-D and anti-fetal haemoglobin (HbF) labelling suggested that the anti-HbF labelling method may underestimate massive FMH in comparison to labelling with anti-D. Subsequent to this audit, 46 samples of adult D-negative blood were spiked with varying amounts of D-positive cord blood (0.05-10% fetal cells per sample), and the number of fetal cells present was quantified by both labelling methods. The percentage of fetal cells detected by anti-D was not significantly different to the estimated percentage of fetal cells added to each sample (P = 0.636). However, anti-HbF labelling significantly underestimated the percentage of fetal cells present (P = 0.0001). In comparison to anti-D, the percentage of fetal cells detected by anti-HbF was also significantly lower (P < 0.0001). The difference in fetal cell detection between anti-D and anti-HbF labelling was only apparent in the spiked samples containing > or =1% fetal cells per sample. In samples containing < or =0.6% fetal cells, no significant difference in the detection of fetal cells between anti-D and anti-HbF labelling was observed (P = 0.11). To allow adequate immunoprophylaxis in D-negative mothers with massive FMH, we recommend that anti-D labelling should be used in the routine flow cytometric estimation of FMH.

Frequency dependent changes in mechanosensitivity of rat knee joint afferents after antidromic saphenous nerve stimulation

The aim of the present study was to examine the effect of electrical saphenous nerve stimulation (14 V, 1-10 Hz) on the mechanosensitivity of rat knee joint afferents. The responses to passive joint rotations at defined torque were recorded from slowly conducting knee joint afferent nerve fibres (0.6-20.0 m/s). After repeated nerve stimulation with 1 Hz, the mechanosensitivity of about 79% of the units was significantly affected. The effects were most prominent at a torque close to the mechanical threshold. In about 46% of the examined nerve fibres a significant increase was obtained, whereas about 33% reduced their mechanosensitivity. The sensitisation was prevented by an application of 5 microM phentolamine, an alpha-adrenergic receptor blocker, together with a neuropeptide Y receptor blocker. An inhibition of N-type Ca(2+) channels by an application of 1 microM omega-conotoxin GVIA caused comparable changes of the mechanosensitivity during the electrical stimulation. Electrical nerve stimulation with higher frequencies resulted in a further reduction of the mean response to joint rotations. After stimulation with 10 Hz, there was a nearly complete loss of mechanosensitivity.In conclusion, antidromic electrical nerve stimulation leads to a frequency dependent transient decrease of the mechanosensitivity. A sensitisation was only obtained at 1 Hz, but this effect may be based on the influence of sympathetic nerve fibres.

Cortical projection of the rat knee joint innervation and its processing in the somatosensory areas SI and SII

In recent years the rat knee joint has become an important model for the study of nociception of deep tissues. In contrast to the cortical processing of superficial pain, the knowledge about the processing of deep pain evoked by noxious stimuli in tissues such as tendons, bone, and joint is sparse. To obtain a basis for further functional studies, the projections of the knee joint in the cerebral cortex were determined. Cortical surface potentials evoked by electrical stimulation of the posterior articular nerve were recorded by a platinum ball electrode. Evoked activity was found in the primary somatosensory area SI in an area of about 3 x 3 mm on the contralateral side. Its center was located about 3 mm caudal to the bregma and about 3 mm lateral to the superior sagittal sinus. A small projection in SII was found on the lateral side of the cortex about 6 mm lateral from SI. This area had a size of about 1 x 1 mm, and the amplitudes of the potentials were smaller but had similar latencies to those in SI. An additional projection with small potentials and longer latencies was observed in SI on the ipsilateral side. Cooling of the contralateral SI revealed deprivation of the ipsilateral evoked potentials in SI whereas the potentials in SII remained unchanged. These data indicate that information from the knee joint is processed in parallel in SI and SII on the contralateral side and that there is an additional serial processing in SI on the ipsilateral side.

Histological demonstration of voltage dependent calcium channels on calcitonin gene-related peptide-immunoreactive nerve fibres in the mouse knee joint

The afferent (excitability) and efferent functions (release of neuropeptides) of primary afferent nerve fibres are based on Ca(2+)-influx. The aim of the present study was to examine the presence of L- and N-type Ca(2+)-channels at sensory nerve fibres in the mouse knee joint capsule. Specific fluorescent labelled channel blockers and antisera against these channel subtypes were combined with an immunohistochemical staining for calcitonin gene-related peptide (CGRP), a neuropeptide that is widely distributed in primary afferents. There was a nearly complete colocalisation of CGRP immunoreactivity and the binding of omega-conotoxin GVIA (toxin VIA of Conus geographus or BODIPY-verapamil (BODIPY(R) FL verapamil, hydrochloride) demonstrating the presence of N-type and L-type Ca(2+)-channels, respectively. These data were further confirmed by identical results obtained after an immunohistochemical demonstration of the two channel subtypes at the peptidergic nerve fibres.