DYRK1A is a novel negative regulator of cardiomyocyte hypertrophy

Inhibition of DYRK1A attenuates vascular remodeling in pulmonary arterial hypertension via suppressing STAT3/Pim-1/NFAT pathway

Pulmonary arterial hypertension (PAH) is characterized by progressive vascular remodeling caused by the excessive proliferation and survival of pulmonary artery smooth muscle cells (PASMCs). Dual-specificity tyrosine regulated kinase 1A (DYRK1A) is a pleiotropic kinase involved in the regulation of multiple biological functions, including cell proliferation and survival. However, the role and underlying mechanisms of DYRK1A in PAH pathogenesis remain unclear. We found that DYRK1A was upregulated in PASMCs in response to hypoxia, both in vivo and in vitro. Inhibition of DYRK1A by harmine significantly attenuated hypoxia-induced pulmonary hypertension and pulmonary artery remodeling. Mechanistically, we found that DYRK1A promoted pulmonary arterial remodeling by enhancing the proliferation and survival of PASMCs through activating the STAT3/Pim-1/NFAT pathway, because STAT3 gain-of-function via adeno-associated virus serotype 2 (AAV2) carrying the constitutively active form of STAT3 (STAT3C) nearly abolished the protective effect of harmine on PAH. Collectively, our results reveal a significant role for DYRK1A in pulmonary arterial remodeling and suggest it as a drug target with translational potential for the treatment of PAH.

Salivary cardiac-enriched FHL2-interacting protein is associated with higher diastolic-to-systolic-blood pressure ratio, sedentary time and center of pressure displacement in healthy 7-9 years old school-children

Introduction

Cardiac-enriched FHL2-interacting protein (CEFIP) is a recently identified protein, first found in the z-disc of striated muscles, and related to cardiovascular diseases. Our objectives are: 1) to quantify CEFIP in saliva in healthy 7-9 years old school-children; and 2) to assess the associations of salivary CEFIP concentration and blood pressure, physical (in)activity and physical fitness in these children.

Methods

A total of 72 children (7.6 ± 0.3 years) were included in the study, recruited in primary schools in Girona (Spain). A sandwich enzyme-linked immunosorbent assay was used (abx506878; Abbexa, United Kingdom) to quantify CEFIP in saliva. Anthropometric evaluation was performed [body mass, height and body mass index (BMI)]. Systolic and diastolic blood pressure were measured by means of an electronic oscillometer and the diastolic-to-systolic blood pressure ratio (D/S BP ratio) was calculated. Physical (in)activity [sedentary time and time spent in physical activity (PA)] were assessed by means of a triaxial Actigraph GT3X accelerometer (Actigraph, Pensacola, FL, USA) that children were instructed to wear for 24h during 7 conssecutive days. Finally, physical fitness (speed and agility, explosive power of legs, handgrip strength, flexibility and balance) were assessed through validated and standardized testing batteries.

Results

CEFIP was easily detected and measured in all saliva samples (mean concentration: 0.6 ± 0.2 pg/ml). Salivary CEFIP was positively associated with D/S BP ratio (r=0.305, p=0.010) and sedentary time (r=0.317, p=0.012), but negatively associated with PA in 7-9 years old school-children (r=-0.350, p=0.002). Furthermore, salivary CEFIP was related to lower level of balance i.e., higher center of pressure (CoP) displacement in these children (r=0.411, p<0.001). The associations of salivary CEFIP with D/S BP ratio (Beta=0.349, p=0.004), sedentary time (Beta=0.354, p=0.009) and CoP displacement (Beta=0.401, p=0.001), were maintained significant after adjustment for potential confounding variables such as age, gender and BMI in linear regression analyses.

Conclusion

CEFIP can be easily assessed in saliva as a promising biomarker associated with cardiovascular health in 7-9 years old school-children. Interestingly, higher salivary CEFIP concentration was related to higher D/S BP ratio, more sedentary time and higher CoP displacement i.e., lower level of balance in these children.

Rational design and appraisal of selective Cdc2-Like kinase 1 (Clk1) inhibitors as novel autophagy inducers for the treatment of acute liver injury (ALI)

Autophagy inducers are promising agents for treating certain medical illnesses, while no safe autophagy inducers are in clinical applications. Cdc2-like kinase 1 (Clk1) inhibitors induce autophagy efficiently; however, most Clk1 inhibitors lack selectivity, especially against Dyrk1A kinase. Herein, we report a series of 1H-pyrrolo[2,3-b]pyridin-5-amine derivatives as novel Clk1 inhibitors. Through detailed structural modification and structure-activity relationship studies, compound 10ad shows potent and selective inhibition for Clk1, with an IC₅₀ value of 5 nM and over 300-fold selectivity for Dyrk1A. Related kinase screening also validates the selectivity of compound 10ad. Furthermore, compound 10ad potently induces autophagy in vitro and exhibits significant hepatoprotective effects in the acute liver injury model induced by acetaminophen (paracetamol). In general, due to the excellent potency and selectivity, compound 10ad was worth further investigation in the treatment of autophagy-related diseases.

An overview of cdc2-like kinase 1 (Clk1) inhibitors and their therapeutic indications

Over the past decade, Clk1 has been identified as a promising target for the treatment of various diseases, in which deregulated alternative splicing plays a role. First small molecules targeting Clk1 are in clinical trials for the treatment of solid cancer, where variants of oncogenic proteins derived from alternative splicing promote tumor progression. Since many infectious pathogens hi-jack the host cell's splicing machinery to ensure efficient replication, further indications in this area are under investigation, such as Influenza A, HIV-1 virus, and Trypanosoma infections, and more will likely be discovered in the future. In addition, Clk1 was found to contribute to the progression of Alzheimer's disease through causing an imbalance of tau splicing products. Interestingly, homozygous Clk1 knockout mice showed a rather mild phenotype, opposed to what might be expected in view of the profound role of Clk1 in alternative splicing. A major drawback of most Clk1 inhibitors is their insufficient selectivity; in particular, Dyrk kinases and haspin were frequently identified as off-targets, besides the other Clk isoforms. Only few inhibitors were shown to be selective over Dyrk1A and haspin, whereas no Clk1 inhibitor so far achieved selectivity over the Clk4 isoform. In this review, we carefully compiled all Clk1 inhibitors from the scientific literature and summarized their structure-activity relationships (SAR). In addition, we critically discuss the available selectivity data and describe the inhibitor's efficacy in cellular models, if reported. Thus, we provide a comprehensive overview on the current state of Clk1 drug discovery and highlight the most promising chemotypes.

Inhibition of DYRK1A, via histone modification, promotes cardiomyocyte cell cycle activation and cardiac repair after myocardial infarction

BACKGROUND

While the adult mammalian heart undergoes only modest renewal through cardiomyocyte proliferation, boosting this process is considered a promising therapeutic strategy to repair cardiac injury. This study explored the role and mechanism of dual-specificity tyrosine regulated kinase 1A (DYRK1A) in regulating cardiomyocyte cell cycle activation and cardiac repair after myocardial infarction (MI).

METHODS

DYRK1A-knockout mice and DYRK1A inhibitors were used to investigate the role of DYRK1A in cardiomyocyte cell cycle activation and cardiac repair following MI. Additionally, we explored the underlying mechanisms by combining genome-wide transcriptomic, epigenomic, and proteomic analyses.

FINDINGS

In adult mice subjected to MI, both conditional deletion and pharmacological inhibition of DYRK1A induced cardiomyocyte cell cycle activation and cardiac repair with improved cardiac function. Combining genome-wide transcriptomic and epigenomic analyses revealed that DYRK1A knockdown resulted in robust cardiomyocyte cell cycle activation (shown by the enhanced expression of many genes governing cell proliferation) associated with increased deposition of trimethylated histone 3 Lys4 (H3K4me3) and acetylated histone 3 Lys27 (H3K27ac) on the promoter regions of these genes. Mechanistically, via unbiased mass spectrometry, we discovered that WD repeat-containing protein 82 and lysine acetyltransferase 6A were key mediators in the epigenetic modification of H3K4me3 and H3K27ac and subsequent pro-proliferative transcriptome and cardiomyocyte cell cycle activation.

INTERPRETATION

Our results reveal a significant role of DYRK1A in cardiac repair and suggest a drug target with translational potential for treating cardiomyopathy.

FUNDING

This study was supported in part by grants from the National Natural Science Foundation of China (81930008, 82022005, 82070296, 82102834), National Key R&D Program of China (2018YFC1312700), Program of Innovative Research Team by the National Natural Science Foundation (81721001), and National Institutes of Health (5R01DK039308-31, 7R37HL023081-37, 5P01HL074940-11).

Impact of DYRK1A Expression on TNNT2 Splicing and Daunorubicin Toxicity in Human iPSC-Derived Cardiomyocytes

Cardiac troponin T (encoded by TNNT2) is involved in the contraction of cardiomyocytes during beating. The alternative splicing of TNNT2 results in four transcript variants with differential Ca2+ sensitivity. The splicing of TNNT2 involves phosphorylation of the splicing factor SRSF6 by DYRK1A. Altered TNNT2 splicing patterns have been identified in failing human hearts. There is a paucity of studies describing DYRK1A-SRSF6-TNNT2 interplays in human cardiomyocytes. Also, it is not known whether the sensitivity of cardiomyocytes to cardiotoxic anthracyclines is modified in the context of variable DYRK1A-TNNT2 expression. In this study, we investigated the impact of DYRK1A on the endogenous expression of TNNT2 splicing variants in iPSC-derived cardiomyocytes. We also examined whether DYRK1A expression modifies the sensitivity of cardiomyocytes to the cardiotoxic drug daunorubicin (DAU). DYRK1A over-expression increased the abundance of TNNT2 fetal variants by ~ 58% whereas the abundance of the adult cTnT3 variant decreased by ~ 27%. High DYRK1A expression increased the phosphorylation of SRSF6 by ~ 25-65%. DAU cytotoxicity was similar between cardiomyocytes with variable levels of DYRK1A expression. DYRK1A over-expression ameliorated the impact of DAU on beating frequency. This study lays the foundation to further investigate the contribution of variable DYRK1A-TNNT2 expression to Ca2+ handling and beating in human cardiomyocytes.

A Bioinformatics Evaluation of the Role of Dual-Specificity Tyrosine-Regulated Kinases in Colorectal Cancer

Simple Summary

The dual-specificity tyrosine-regulated kinase (DYRK) family has been implicated in various diseases, including cancer. However, its role in colorectal cancer has not been elucidated. In this research, we used publicly available web-based tools to investigate DYRKs status in colorectal cancer. Our results showed that among DYRKs, only DYRK1A was upregulated significantly in late tumor stages, and it is associated with poor prognosis for colorectal cancer patients. These finding comprehensively characterized DYRK1A as a potential new therapeutic approach in CRC, especially in late tumor stages.

Abstract

Colorectal cancer (CRC) is the third most common cancer worldwide and has an increasing incidence in younger populations. The dual-specificity tyrosine-regulated kinase (DYRK) family has been implicated in various diseases, including cancer. However, the role and contribution of the distinct family members in regulating CRC tumorigenesis has not been addressed yet. Herein, we used publicly available CRC patient datasets (TCGA RNA sequence) and several bioinformatics webtools to perform in silico analysis (GTEx, GENT2, GEPIA2, cBioPortal, GSCALite, TIMER2, and UALCAN). We aimed to investigate the DYRK family member expression pattern, prognostic value, and oncological roles in CRC. This study shed light on the role of distinct DYRK family members in CRC and their potential outcome predictive value. Based on mRNA level, DYRK1A is upregulated in late tumor stages, with lymph node and distant metastasis. All DYRKs were found to be implicated in cancer-associated pathways, indicating their key role in CRC pathogenesis. No significant DYRK mutations were identified, suggesting that DYRK expression variation in normal vs. tumor samples is likely linked to epigenetic regulation. The expression of DYRK1A and DYRK3 expression correlated with immune-infiltrating cells in the tumor microenvironment and was upregulated in MSI subtypes, pointing to their potential role as biomarkers for immunotherapy. This comprehensive bioinformatics analysis will set directions for future biological studies to further exploit the molecular basis of these findings and explore the potential of DYRK1A modulation as a novel targeted therapy for CRC.

Harmine suppresses collagen production in hepatic stellate cells by inhibiting DYRK1B

Liver fibrosis is a major consequence of chronic liver disease, where excess extracellular matrix is deposited, due caused by the activation of hepatic stellate cells (HSCs). The suppression of collagen production in HSCs is therefore regarded as a therapeutic target of liver fibrosis. The present study investigated effects of harmine, which is a β-carboline alkaloid and known as an inhibitor of dual-specificity tyrosine-regulated kinases (DYRKs), on the production of collagen in HSCs. LX-2 cells, a human HSC cell line, were treated with harmine (0-10 μM) for 48 h in the presence or absence of TGF-β1 (5 ng/ml). The expression of collagen type I α1 (COL1A1) and DYRK isoforms was investigated by Western blotting, quantitative RT-PCR, or immunofluorescence. The influence of knockdown of each DYRK isoform on the COL1A1 expression was further investigated. The expression of COL1A1 was markedly increased by treating with TGF-β1 for 48 h in LX-2 cells. Harmine (10 μM) significantly inhibited the increased expression of COL1A1. LX-2 cells expressed mRNAs of DYRK1A, DYRK1B, DYRK2, and DYRK4, although the expression of DYRK4 was much lower than the others. Knockdown of DYRK1B, but not DYRK1A or DYRK2, with siRNA significantly suppressed TGF-β1-induced increase in COL1A1 expression. These results suggest that harmine suppresses COL1A1 expression via inhibiting DYRK1B in HSCs and therefore might be effective for the treatment of liver fibrosis.

Harmine is an effective therapeutic small molecule for the treatment of cardiac hypertrophy

Harmine is a β-carboline alkaloid isolated from Banisteria caapi and Peganum harmala L with various pharmacological activities, including antioxidant, anti-inflammatory, antitumor, anti-depressant, and anti-leishmanial capabilities. Nevertheless, the pharmacological effect of harmine on cardiomyocytes and heart muscle has not been reported. Here we found a protective effect of harmine on cardiac hypertrophy in spontaneously hypertensive rats in vivo. Further, harmine could inhibit the phenotypes of norepinephrine-induced hypertrophy in human embryonic stem cell-derived cardiomyocytes in vitro. It reduced the enlarged cell surface area, reversed the increased calcium handling and contractility, and downregulated expression of hypertrophy-related genes in norepinephrine-induced hypertrophy of human cardiomyocytes derived from embryonic stem cells. We further showed that one of the potential underlying mechanism by which harmine alleviates cardiac hypertrophy relied on inhibition of NF-κB phosphorylation and the stimulated inflammatory cytokines in pathological ventricular remodeling. Our data suggest that harmine is a promising therapeutic agent for cardiac hypertrophy independent of blood pressure modulation and could be a promising addition of current medications for cardiac hypertrophy.

Novel DYRK1A Inhibitor Rescues Learning and Memory Deficits in a Mouse Model of Down Syndrome

Down syndrome (DS) is a complex genetic disorder associated with substantial physical, cognitive, and behavioral challenges. Due to better treatment options for the physical co-morbidities of DS, the life expectancy of individuals with DS is beginning to approach that of the general population. However, the cognitive deficits seen in individuals with DS still cannot be addressed pharmacologically. In young individuals with DS, the level of intellectual disability varies from mild to severe, but cognitive ability generally decreases with increasing age, and all individuals with DS have early onset Alzheimer’s disease (AD) pathology by the age of 40. The present study introduces a novel inhibitor for the protein kinase DYRK1A, a key controlling kinase whose encoding gene is located on chromosome 21. The novel inhibitor is well characterized for use in mouse models and thus represents a valuable tool compound for further DYRK1A research.

DYRK1A activates NFATC1 to increase glioblastoma migration

Glioblastoma (GBM) is the most aggressive glioma, and is prone to develop resistance to chemotherapy and radiotherapy; hence, patients with glioblastoma have a high recurrence rate and a low 1-year survival rate. In addition, the pathogenesis of glioblastoma is complex and largely unknown, and the available treatments are limited. Here, we uncovered a fundamental role of DYRK1A in regulating NFATC1 in GBMs. We found that DYRK1A was highly expressed in glioma and glioblastoma cells, and its expression was positively correlated with that of NFATC1. Moreover, inhibition of DYRK1A promoted NFATC1 degradation in GBM cells and sharply reduced the transactivation of NFATC1, not only by decreasing the expression of NFATC1-targeted genes, but also by reducing the luciferase activity, and vice versa. However, DYRK1A had the opposite effect on NFATC2. Most importantly, our data suggest that DYRK1A inhibition reduces glioblastoma migration. Polypeptides derived from the DYRK1A-targeted motif of NFATC1, by competitively blocking DYRK1A kinase activity on NFATC1, clearly destabilized NFATC1 protein and impaired glioblastoma migration. We propose that the recovery of NFATC1 stability is a key oncogenic event in a large proportion of gliomas, and pharmacological inhibition of DYRK1A by polypeptides could represent a promising therapeutic intervention for GBM.

Comprehensive bioinformatics analysis reveals kinase activity profiling associated with heart failure

Heart failure is a complex clinical syndrome originating from cardiac injury, which leads to considerable morbidity and mortality. Among the dynamic molecular adaptations occurring in heart failure development, aggravation of the disease is often attributed to global or local abnormality of the kinase. Therefore, the overall monitoring of kinase activity is indispensable. In this study, a bioinformatics analysis method was developed to conduct deep mining of transcriptome and phosphoproteome in failing heart tissue. A total of 982 differentially expressed genes and 9781 phosphorylation sites on 3252 proteins were identified. Via upstream regulator relations and kinase-substrate relations, a dendrogram of kinases can be constructed to monitor its abnormality. The results show that, on the dendrogram, the distribution of kinases demonstrated complex kinase activity changes and certain rules that occur during heart failure. Finally, we also identified the hub kinases in heart failure and verified the expression of these kinases by reverse-transcription polymerase chain reaction and Western blot analysis. In conclusion, for the first time, we have systematically analyzed the differences in kinases during heart failure and provided an unprecedented breadth of multi-omics data. These results can bring about a sufficient data foundation and novel research perspectives.

Leishmania Protein Kinases: Important Regulators of the Parasite Life Cycle and Molecular Targets for Treating Leishmaniasis

Leishmania is a protozoan parasite of the trypanosomatid family, causing a wide range of diseases with different clinical manifestations including cutaneous, mucocutaneous and visceral leishmaniasis. According to WHO, one billion people are at risk of Leishmania infection as they live in endemic areas while there are 12 million infected people worldwide. Annually, 0.9-1.6 million new infections are reported and 20-50 thousand deaths occur due to Leishmania infection. As current chemotherapy for treating leishmaniasis exhibits numerous drawbacks and due to the lack of effective human vaccine, there is an urgent need to develop new antileishmanial therapy treatment. To this end, eukaryotic protein kinases can be ideal target candidates for rational drug design against leishmaniasis. Eukaryotic protein kinases mediate signal transduction through protein phosphorylation and their inhibition is anticipated to be disease modifying as they regulate all essential processes for Leishmania viability and completion of the parasitic life cycle including cell-cycle progression, differentiation and virulence. This review highlights existing knowledge concerning the exploitation of Leishmania protein kinases as molecular targets to treat leishmaniasis and the current knowledge of their role in the biology of Leishmania spp. and in the regulation of signalling events that promote parasite survival in the insect vector or the mammalian host.

5-Methoxybenzothiophene-2-Carboxamides as Inhibitors of Clk1/4: Optimization of Selectivity and Cellular Potency

Clks have been shown by recent studies to be promising targets for cancer therapy, as they are considered key regulators in the process of pre-mRNA splicing, which in turn affects every aspect of tumor biology. In particular, Clk1 and -4 are overexpressed in several human tumors. Most of the potent Clk1 inhibitors reported in the literature are non-selective, mainly showing off-target activity towards Clk2, Dyrk1A and Dyrk1B. Herein, we present new 5-methoxybenzothiophene-2-carboxamide derivatives with unprecedented selectivity. In particular, the introduction of a 3,5-difluoro benzyl extension to the methylated amide led to the discovery of compound 10b (cell-free IC₅₀ = 12.7 nM), which was four times more selective for Clk1 over Clk2 than the previously published flagship compound 1b. Moreover, 10b showed an improved growth inhibitory activity with T24 cells (GI₅₀ = 0.43 µM). Furthermore, a new binding model in the ATP pocket of Clk1 was developed based on the structure-activity relationships derived from new rigidified analogues.

DYRK1A: a down syndrome-related dual protein kinase with a versatile role in tumorigenesis

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a dual kinase that can phosphorylate its own activation loop on tyrosine residue and phosphorylate its substrates on threonine and serine residues. It is the most studied member of DYRK kinases, because its gene maps to human chromosome 21 within the Down syndrome critical region (DSCR). DYRK1A overexpression was found to be responsible for the phenotypic features observed in Down syndrome such as mental retardation, early onset neurodegenerative, and developmental heart defects. Besides its dual activity in phosphorylation, DYRK1A carries the characteristic of duality in tumorigenesis. Many studies indicate its possible role as a tumor suppressor gene; however, others prove its pro-oncogenic activity. In this review, we will focus on its multifaceted role in tumorigenesis by explaining its participation in some cancer hallmarks pathways such as proliferative signaling, transcription, stress, DNA damage repair, apoptosis, and angiogenesis, and finally, we will discuss targeting DYRK1A as a potential strategy for management of cancer and neurodegenerative disorders.

The E3 ubiquitin ligase HectD3 attenuates cardiac hypertrophy and inflammation in mice

Myocardial inflammation has recently been recognized as a distinct feature of cardiac hypertrophy and heart failure. HectD3, a HECT domain containing E3 ubiquitin ligase has previously been investigated in the host defense against infections as well as neuroinflammation; its cardiac function however is still unknown. Here we show that HectD3 simultaneously attenuates Calcineurin-NFAT driven cardiomyocyte hypertrophy and the pro-inflammatory actions of LPS/interferon-γ via its cardiac substrates SUMO2 and Stat1, respectively. AAV9-mediated overexpression of HectD3 in mice in vivo not only reduced cardiac SUMO2/Stat1 levels and pathological hypertrophy but also largely abolished macrophage infiltration and fibrosis induced by pressure overload. Taken together, we describe a novel cardioprotective mechanism involving the ubiquitin ligase HectD3, which links anti-hypertrophic and anti-inflammatory effects via dual regulation of SUMO2 and Stat1. In a broader perspective, these findings support the notion that cardiomyocyte growth and inflammation are more intertwined than previously anticipated.

Rangrez et al. show that overexpression of the HECT domain E3 ubiquitin protein ligase 3 (HectD3) reduces cardiac hypertrophy while reducing macrophage infiltration in mice. This study provides a cardioprotective mechanism, where HectD3 targets SUMO2 and Stat1 to exert its anti-hypertrophic and anti-inflammatory effects.

DYRK1A Kinase Positively Regulates Angiogenic Responses in Endothelial Cells

Angiogenesis is a highly regulated process essential for organ development and maintenance, and its deregulation contributes to inflammation, cardiac disorders, and cancer. The Ca2+/nuclear factor of activated T cells (NFAT) signaling pathway is central to endothelial cell angiogenic responses, and it is activated by stimuli like vascular endothelial growth factor (VEGF) A. NFAT phosphorylation by dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs) is thought to be an inactivating event. Contrary to expectations, we show that the DYRK family member DYRK1A positively regulates VEGF-dependent NFAT transcriptional responses in primary endothelial cells. DYRK1A silencing reduces intracellular Ca2+ influx in response to VEGF, which dampens NFAT activation. The effect is exerted at the level of VEGFR2 accumulation leading to impairment in PLCγ1 activation. Notably, Dyrk1a heterozygous mice show defects in developmental retinal vascularization. Our data establish a regulatory circuit, DYRK1A/ Ca2+/NFAT, to fine-tune endothelial cell proliferation and angiogenesis.

Dual-specificity tyrosine phosphorylation-regulated kinase 2 regulates osteoclast fusion in a cell heterotypic manner

Monocyte fusion into osteoclasts, bone resorbing cells, plays a key role in bone remodeling and homeostasis; therefore, aberrant cell fusion may be involved in a variety of debilitating bone diseases. Research in the last decade has led to the discovery of genes that regulate osteoclast fusion, but the basic molecular and cellular regulatory mechanisms underlying the fusion process are not completely understood. Here, we reveal a role for Dyrk2 in osteoclast fusion. We demonstrate that Dyrk2 down regulation promotes osteoclast fusion, whereas its overexpression inhibits fusion. Moreover, Dyrk2 also promotes the fusion of foreign-body giant cells, indicating that Dyrk2 plays a more general role in cell fusion. In an earlier study, we showed that fusion is a cell heterotypic process initiated by fusion-founder cells that fuse to fusion-follower cells, the latter of which are unable to initiate fusion. Here, we show that Dyrk2 limits the expansion of multinucleated founder cells through the suppression of the fusion competency of follower cells.

The novel cardiac z-disc protein CEFIP regulates cardiomyocyte hypertrophy by modulating calcineurin signaling

The z-disc is a structural component at the lateral borders of the sarcomere and is important for mechanical stability and contractility of both cardiac and skeletal muscles. Of note, the sarcomeric z-disc also represents a nodal point in cardiomyocyte function and signaling. Mutations of numerous z-disc proteins are associated with cardiomyopathies and muscle diseases. To identify additional z-disc proteins that might contribute to cardiac disease, we employed an in silico screen for cardiac-enriched cDNAs. This screen yielded a previously uncharacterized protein named cardiac-enriched FHL2-interacting protein (CEFIP), which exhibited a heart- and skeletal muscle-specific expression profile. Importantly, CEFIP was located at the z-disc and was up-regulated in several models of cardiomyopathy. We also found that CEFIP overexpression induced the fetal gene program and cardiomyocyte hypertrophy. Yeast two-hybrid screens revealed that CEFIP interacts with the calcineurin-binding protein four and a half LIM domains 2 (FHL2). Because FHL2 binds calcineurin, a phosphatase controlling hypertrophic signaling, we examined the effects of CEFIP on the calcineurin/nuclear factor of activated T-cell (NFAT) pathway. These experiments revealed that CEFIP overexpression further enhances calcineurin-dependent hypertrophic signal transduction, and its knockdown repressed hypertrophy and calcineurin/NFAT activity. In summary, we report on a previously uncharacterized protein CEFIP that modulates calcineurin/NFAT signaling in cardiomyocytes, a finding with possible implications for the pathogenesis of cardiomyopathy.

Development of Selective Clk1 and -4 Inhibitors for Cellular Depletion of Cancer-Relevant Proteins

In cancer cells, kinases of the Clk family control the supply of full-length, functional mRNAs coding for a variety of proteins essential to cell growth and survival. Thus, inhibition of Clks might become a novel anticancer strategy, leading to a selective depletion of cancer-relevant proteins after turnover. On the basis of a Weinreb amide hit compound, we designed and synthesized a diverse set of methoxybenzothiophene-2-carboxamides, of which the N-benzylated derivative showed enhanced Clk1 inhibitory activity. Introduction of a m-fluorine in the benzyl moiety eventually led to the discovery of compound 21b, a potent inhibitor of Clk1 and -4 (IC₅₀ = 7 and 2.3 nM, respectively), exhibiting an unprecedented selectivity over Dyrk1A. 21b triggered the depletion of EGFR, HDAC1, and p70S6 kinase from the cancer cells, with potencies in line with the measured GI₅₀ values. In contrast, the cellular effects of congener 21a, which inhibited Clk1 only weakly, were substantially lower.

Myeloid leukemia factor-1 is a novel modulator of neonatal rat cardiomyocyte proliferation

The present study focuses on the identification of the gene expression profile of neonatal rat cardiomyocytes (NRVCMs) after dynamic mechanical stretch through microarrays of RNA isolated from cells stretched for 2, 6 or 24h. In this analysis, myeloid leukemia factor-1 (MLF1) was found to be significantly downregulated during the course of stretch. We found that MLF1 is highly expressed in the heart, however, its cardiac function is unknown yet. In line with microarray data, MLF1 was profoundly downregulated in in vivo mouse models of cardiomyopathy, and also significantly reduced in the hearts of human patients with dilated cardiomyopathy. Our data indicates that the overexpression of MLF1 in NRVCMs inhibited cell proliferation while augmenting apoptosis. Conversely, knockdown of MLF1 protected NRVCMs from apoptosis and promoted cell proliferation. Moreover, we found that knockdown of MLF1 protected NRVCMs from hypoxia-induced cell death. The observed accelerated apoptosis is attributed to the activation of caspase-3/-7/PARP-dependent apoptotic signaling and upregulation of p53. Most interestingly, MLF1 knockdown significantly upregulated the expression of D cyclins suggesting its possible role in cyclin-dependent cell proliferation. Taken together, we, for the first time, identified an important role for MLF1 in NRVCM proliferation.

Understanding the Multifaceted Role of Human Down Syndrome Kinase DYRK1A

The dual-specificity tyrosine (Y) phosphorylation-regulated kinase DYRK1A, also known as Down syndrome (DS) kinase, is a dosage-dependent signaling kinase that was originally shown to be highly expressed in DS patients as a consequence of trisomy 21. Although this was evident some time ago, it is only in recent investigations that the molecular roles of DYRK1A in a wide range of cellular processes are becoming increasingly apparent. Since initial knowledge on DYRK1A became evident through minibrain mnb, the Drosophila homolog of DYRK1A, this review will first summarize the scientific reports on minibrain and further expand on the well-established neuronal functions of mammalian and human DYRK1A. Recent investigations across the current decade have provided rather interesting and compelling evidence in establishing nonneuronal functions for DYRK1A, including its role in infection, immunity, cardiomyocyte biology, cancer, and cell cycle control. The latter part of this review will therefore focus in detail on the emerging nonneuronal functions of DYRK1A and summarize the regulatory role of DYRK1A in controlling Tau and α-synuclein. Finally, the emerging role of DYRK1A in Parkinson's disease will be outlined.

Dyrk1a regulates the cardiomyocyte cell cycle via D-cyclin-dependent Rb/E2f-signalling

AIMS

Down syndrome-associated dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A) is a ubiquitously expressed protein kinase. Up to date a variety of targets have been identified, establishing a key role for Dyrk1a in selected signalling pathways. In cardiomyocytes, Dyrk1a acts as a negative regulator of hypertrophy by phosphorylating transcription factors of the NFAT family, but its mechanistic function in the heart remains poorly understood. This study was designed to investigate a potential protective role of Dyrk1a in cardiac hypertrophy in vivo.

METHODS AND RESULTS

We generated transgenic mice with cardiac-specific overexpression of Dyrk1a. Counterintuitively, these mice developed severe dilated cardiomyopathy associated with congestive heart failure and premature death. In search for the cause of this unexpected phenotype, we found that Dyrk1a interacts with all members of the D-cyclin family and represses their protein levels in vitro and in vivo. Particularly, forced expression of Dyrk1a leads to increased phosphorylation of Ccnd2 on Thr280 and promotes its subsequent proteasomal degradation. Accordingly, cardiomyocytes overexpressing Dyrk1a display hypo-phosphorylated Rb1, suppression of Rb/E2f-signalling, and reduced expression of E2f-target genes, which ultimately results in impaired cell cycle progression.

CONCLUSIONS

We identified Dyrk1a as a novel negative regulator of D-cyclin-mediated Rb/E2f-signalling. As dysregulation of this pathway with impaired cardiomyocyte proliferation leads to cardiomyopathy, dose-specific Dyrk1a expression and activity appears to be critical for the hyperplastic and hypertrophic growth of the developing heart.

Overexpression of Dyrk1A regulates cardiac troponin T splicing in cells and mice

The human heart expresses four isoforms of cardiac troponin T (cTnT) through alternative splicing of exons 4 and 5 of the cTnT gene. Alternative splicing of cTnT exon 5 is developmentally regulated. cTnT isoforms containing exon 5 are expressed in the fetal and neonatal heart but not in the mature heart. SRp55 is an essential splicing factor involved in cTnT exon 5 splicing and it is phosphorylated by Dyrk1A (dual specificity tyrosine phosphorylation regulated kinase 1A). In the present study, we found Dyrk1A interacted with SRp55 and enhanced its promotion of cTnT exon 5 inclusion. The shift from cTnT exon 5 inclusion to exclusion during development was delayed in the heart of Ts65Dn mice due to Dyrk1A overexpression. These results provide new insight into the role of Dyrk1A in the neonatal cardiac development.

Systematic diversification of benzylidene heterocycles yields novel inhibitor scaffolds selective for Dyrk1A, Clk1 and CK2

The dual-specificity tyrosine-regulated kinase 1A (Dyrk1A) has gathered much interest as a pharmacological target in Alzheimer's disease (AD), but it plays a role in malignant brain tumors as well. As both diseases are multi-factorial, further protein kinases, such as Clk1 and CK2, were proposed to contribute to the pathogenesis. We designed a new class of α-benzylidene-γ-butyrolactone inhibitors that showed low micromolar potencies against Dyrk1A and/or Clk1 and a good selectivity profile among the most frequently reported off-target kinases. A systematic replacement of the heterocyclic moiety gave access to further inhibitor classes with interesting selectivity profiles, demonstrating that the benzylidene heterocycles provide a versatile tool box for developing inhibitors of the CMGC kinase family members Dyr1A/1B, Clk1/4 and CK2. Efficacy for the inhibition of Dyrk1A-mediated tau phosphorylation was demonstrated in a cell-based assay. Multi-targeted but not non-specific kinase inhibitors were also obtained, that co-inhibited the lipid kinases PI3Kα/γ. These compounds were shown to inhibit the proliferation of U87MG cells in the low micromolar range. Based on the molecular properties, the inhibitors described here hold promise for CNS activity.

Dyrk1A-ASF-CaMKIIδ Signaling Is Involved in Valsartan Inhibition of Cardiac Hypertrophy in Renovascular Hypertensive Rats

OBJECTIVES

It is known that the expression, activity and alternative splicing of Ca2+/calmodulin-dependent protein kinase IIδ (CaMKIIδ) are dysregulated in the cardiac remodeling process. Recently, we found a further signaling pathway, by which dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) regulates the alternative splicing of CaMKIIδ via the alternative splicing factor (ASF), i.e., Dyrk1A-ASF-CaMKIIδ. In this study, we aimed to investigate whether Dyrk1A-ASF-CaMKIIδ signaling was involved in valsartan inhibition of cardiac hypertrophy in renovascular hypertensive rats.

METHODS

Rats were subjected to two kidney-one clip (2K1C) surgery and then treated with valsartan (30 mg/kg/day) for 8 weeks. Hypertrophic parameter analysis was then performed. Western blot analysis was used to determine the protein expression of Dyrk1A and ASF and RT-PCR was used to analyze the alternative splicing of CaMKIIδ in the left ventricular (LV) sample.

RESULTS

Valsartan attenuated cardiac hypertrophy in 2K1C rats but without impairment of cardiac systolic function. Increased protein expression of Dyrk1A and decreased protein expression of ASF were observed in the LV sample of 2K1C rats. Treatment of 2K1C rats with valsartan reversed the changes in Dyrk1A and ASF expression in the LV sample. Valsartan adjusted the 2K1C-induced imbalance in alternative splicing of CaMKIIδ by upregulating the mRNA expression of CaMKIIδC and downregulating the mRNA expression of CaMKIIδA and CaMKIIδB.

CONCLUSIONS

Valsartan inhibition of cardiac hypertrophy in renovascular hypertensive rats was mediated, at least partly, by Dyrk1A-ASF-CaMKIIδ signaling.

Involvement of the dual-specificity tyrosine phosphorylation-regulated kinase 1A-alternative splicing factor-calcium/calmodulin-dependent protein kinase IIδ signaling pathway in myocardial infarction-induced heart failure of rats

BACKGROUND

Alternative splicing factor (ASF)-regulated alternative splicing of calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) plays an important role in pathologic cardiac remodeling. ASF can be phosphorylated by dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A). This study aimed to investigate the possible involvement of the Dyrk1A-ASF-CaMKIIδ signaling pathway in the progression of myocardial infarction (MI)-induced heart failure (HF).

METHODS AND RESULTS

MI in rats was induced by means of left anterior descending coronary artery ligation. Seven weeks after MI, the increase in left ventricular internal diameter at end-diastole (LVIDd), and the decrease in both ejection fraction (EF) and fractional shortening (FS) indicated that MI rats had developed HF. Quantitative real time reverse-transcription polymerase chain reaction indicated the dysregulation of CaMKIIδ alternative splicing, ie, up-regulation of CaMKIIδA and CaMKIIδC and down-regulation of CaMKIIδB in the hearts of HF rats. Electrophoresis and immunostaining revealed that HF activated the phosphorylation of ASF and affected its subcellular localization. Western blot analysis demonstrated a significant elevation in the activity and expression of Dyrk1A in HF rats. Inversely, treatment of MI-induced HF rats with Dyrk1A inhibitor, either harmine or EGCG, improved the symptoms of HF, reversed the molecular changes of Dyrk1A and ASF, and regulated alternative splicing of CaMKIIδ in HF rats.

CONCLUSIONS

Enhanced activation of Dyrk1A-ASF-CaMKIIδ signaling pathway may underlie the mechanisms of HF after MI, and Dyrk1A inhibition may contribute to inactivation of this pathway and thereby retard the progression of MI-induced HF.

Design and synthesis of a potent inhibitor of class 1 DYRK kinases as a suppressor of adipogenesis

Dysregulation of dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) has been demonstrated in several pathological conditions, including Alzheimer's disease and cancer progression. It has been recently reported that a gain of function-mutation in the human DYRK1B gene exacerbates metabolic syndrome by enhancing obesity. In the previous study, we developed an inhibitor of DYRK family kinases (INDY) and demonstrated that INDY suppresses the pathological phenotypes induced by overexpression of DYRK1A or DYRK1B in cellular and animal models. In this study, we designed and synthesized a novel inhibitor of DYRK family kinases based on the crystal structure of the DYRK1A/INDY complex by replacing the phenol group of INDY with dibenzofuran to produce a derivative, named BINDY. This compound exhibited potent and selective inhibitory activity toward DYRK family kinases in an in vitro assay. Furthermore, treatment of 3T3-L1 pre-adipocytes with BINDY hampered adipogenesis by suppressing gene expression of the critical transcription factors PPARγ and C/EBPα. This study indicates the possibility of BINDY as a potential drug for metabolic syndrome.

B-RAF and its novel negative regulator reticulocalbin 1 (RCN1) modulates cardiomyocyte hypertrophy

AIM

Activation of the kinase RAF and its downstream targets leads to cardiomyocyte hypertrophy. It has been hypothesized that B-RAF might be the main activator of MEK in various cell types. Therefore, the aim of this study was to investigate the role of B-RAF and its modulating factors in cardiomyocyte hypertrophy.

METHODS AND RESULTS

Neonatal rat cardiomyocytes were pre-treated with and without the specific B-RAF inhibitor SB590885 and then stimulated with phenylephrine to induce hypertrophy. Inhibition of B-RAF completely impeded the hypertrophic response and led to a significant reduction of MEK1/2 phosphorylation. By applying a eukaryotic cDNA expression screen, based on a dual-luciferase reporter assay for B-RAF activity measurement, we identified RCN1 as a new negative modulator of B-RAF activity. Adenovirus-mediated overexpression of reticulocalbin 1 (RCN1) completely impeded phenylephrine-induced hypertrophy and led to significantly reduced MEK1/2 phosphorylation. Conversely, adenoviral knockdown of RCN1 with a specific synthetic miRNA induced cardiomyocyte hypertrophy and significantly increased MEK1/2 phosphorylation.

CONCLUSIONS

In summary, our results show that the inhibition of B-RAF abolishes cardiomyocyte hypertrophy and we identified RCN1 as novel negative modulator of cardiomyocyte hypertrophy by inhibition of the mitogen-activated protein kinase signalling cascade. Our results show that B-RAF kinase activity is essential for cardiac hypertrophy and RCN1, its newly identified negative regulator, abolishes hypertrophic response of cardiomyocytes in vitro.

Key role of ERK1/2 molecular scaffolds in heart pathology

The ability of cardiomyocytes to detect mechanical and humoral stimuli is critical for adaptation of the myocardium in response to new conditions and for sustaining the increased workload during stress. While certain stimuli mediate a beneficial adaptation to stress conditions, others result in maladaptive remodelling, ultimately leading to heart failure. Specific signalling pathways activating either adaptive or maladaptive cardiac remodelling have been identified. Paradoxically, however, in a number of cases, the transduction pathways involved in such opposing responses engage the same signalling proteins. A notable example is the Raf-MEK1/2-ERK1/2 signalling pathway that can control both adaptive and maladaptive remodelling. ERK1/2 signalling requires a signalosome complex where a scaffold protein drives the assembly of these three kinases into a linear pathway to facilitate their sequential phosphorylation, ultimately targeting specific effector molecules. Interestingly, a number of different Raf-MEK1/2-ERK1/2 scaffold proteins have been identified, and their role in determining the adaptive or maladaptive cardiac remodelling is a promising field of investigation for the development of therapeutic strategies capable of selectively potentiating the adaptive response.

DYRK2 negatively regulates cardiomyocyte growth by mediating repressor function of GSK-3β on eIF2Bε

BACKGROUND

A prerequisite of hypertrophic response of the myocardium is an increase in protein synthesis. A central regulator of translation initiation is Eukaryotic initiation factor 2B (eIF2B). Here we assessed the hypothesis that regulation of protein synthesis via eIF2Bε is essential to cardiac hypertrophic response in vivo.

METHODS

Two transgenic mouse lines were generated with cardiac restricted overexpression of eIF2Bε or its mutant eIF2Bε-eIFS(535)A, which cannot be inactivated by phosphorylation through GSK-3β.

RESULTS

(1) Under baseline conditions eIF2Bε transgenic mice showed no difference in cardiac phenotype compared to wild type, whereas in the mutant eIF2Bε-S(535)A an increase in LV/tibia length (7.5 ± 0.4 mg/mm vs. 6.2 ± 0.2 mg/mm, p<0.001) and cardiomyocyte cross sectional area (13004 ± 570 vs. 10843 ± 347 RU, p<0.01) was observed. (2) Cardiac overexpression of eIF2Bε did not change the response of the heart to pathologic stress induced by chronic isoproterenol treatment. (3) Cardiac overexpression of the eIF2Bε transgene was followed by overexpression of DYRK2 which is known to prime the inhibitory action of GSK-3β on eIF2Bε, while DYRK1A and GSK-3β itself were not increased. (4) In C57BL/6 mice after 48 h of isoproterenol-stimulation or aortic banding, eIF2Bε was increased and DYRK2 was concomitantly decreased. (5) In line with these in vivo findings, siRNA knockdown of DYRK2 in cultured cardiomyocytes resulted in decreased levels of p(S535)- eIF2Bε, (6) whereas adenoviral induced overexpression of DYRK2 was accompanied by clearly increased phosphorylation of eIF2Bε, indicating a coordinated response pattern (7) Adenoviral induced overexpression of DYRK2 leads to significantly reduced cardiomyocyte size and diminishes hypertrophic response to adrenergic stimulation.

CONCLUSIONS

The interaction of GSK-3β and its priming kinase DYRK2 regulate the activity of eIF2Bε in cardiac myocytes. DYRK2 is a novel negative regulator of cardiomyocyte growth. DYRK2 could serve as a therapeutic option to regulate myocardial growth.

The role of the paracrine/autocrine mediator endothelin-1 in regulation of cardiac contractility and growth

Endothelin-1 (ET-1) is a critical autocrine and paracrine regulator of cardiac physiology and pathology. Produced locally within the myocardium in response to diverse mechanical and neurohormonal stimuli, ET-1 acutely modulates cardiac contractility. During pathological cardiovascular conditions such as ischaemia, left ventricular hypertrophy and heart failure, myocyte expression and activity of the entire ET-1 system is enhanced, allowing the peptide to both initiate and maintain maladaptive cellular responses. Both the acute and chronic effects of ET-1 are dependent on the activation of intracellular signalling pathways, regulated by the inositol-trisphosphate and diacylglycerol produced upon activation of the ET(A) receptor. Subsequent stimulation of protein kinases C and D, calmodulin-dependent kinase II, calcineurin and MAPKs modifies the systolic calcium transient, myofibril function and the activity of transcription factors that coordinate cellular remodelling. The precise nature of the cellular response to ET-1 is governed by the timing, localization and context of such signals, allowing the peptide to regulate both cardiomyocyte physiology and instigate disease.

LINKED ARTICLES

This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

ADAM17 silencing by adenovirus encoding miRNA-embedded siRNA revealed essential signal transduction by angiotensin II in vascular smooth muscle cells

Small interfering RNA (siRNA) mediated gene silencing has been utilized as a powerful molecular tool to study the functional significance of a specific protein. However, due to transient gene silencing and insufficient transfection efficiency, this approach can be problematic in primary cell culture such as vascular smooth muscle cells. To overcome this weakness, we utilized an adenoviral-encoded microRNA (miRNA)-embedded siRNA "mi/siRNA"-based RNA interference. Here, we report the results of silencing a disintegrin and metalloprotease 17 (ADAM17) in cultured rat vascular smooth muscle cells and its functional mechanism in angiotensin II signal transduction. 3 distinct mi/siRNA sequences targeting rat ADAM17 were inserted into pAd/CMV/V5-DEST and adenoviral solutions were obtained. Nearly 90% silencing of ADAM17 was achieved when vascular smooth muscle cells were infected with 100 multiplicity of infection of each ADAM17 mi/siRNA encoding adenovirus for 3days. mi/siRNA-ADAM17 but not mi/siRNA-control inhibited angiotensin II-induced epidermal growth factor receptor trans-activation and subsequent extracellular signal-regulated kinase activation and hypertrophic response in the cells. mi/siRNA-ADAM17 also inhibited angiotensin II-induced heparin-binding epidermal growth factor-like factor shedding. This inhibition was rescued with co-infection of adenovirus encoding mouse ADAM17 but not by its cytosolic domain deletion mutant or cytosolic Y702F mutant. As expected, angiotensin II induced tyrosine phosphorylation of ADAM17 in the cells. In conclusion, ADAM17 activation via its tyrosine phosphorylation contributes to heparin-binding epidermal growth factor-like factor shedding and subsequent growth promoting signals induced by angiotensin II in vascular smooth muscle cells. An artificial mi/siRNA-based adenoviral approach appears to be a reliable gene-silencing strategy for signal transduction research in primary cultured vascular cells.

Dyrk1A, a serine/threonine kinase, is involved in ERK and Akt activation in the brain of hyperhomocysteinemic mice

Hyperhomocysteinemia due to cystathionine beta synthase (CBS) deficiency is associated with diverse brain disease. Whereas the biological actions linking hyperhomocysteinemia to the cognitive dysfunction are not well understood, we tried to establish relationships between hyperhomocysteinemia and alterations of signaling pathways. In the brain of CBS-deficient mice, a murine model of hyperhomocysteinemia, we previously found an activation of extracellular signal-regulated kinase (ERK) pathway and an increase of Dyrk1A, a serine/threonine kinase involved in diverse functions ranging from development and growth to apoptosis. We then investigated the relationship between Dyrk1A and the signaling pathways initiated by receptor tyrosine kinases (RTK), the ERK and PI3K/Akt pathways. We found a significant increase of phospho-ERK, phospho-MEK, and phospho-Akt in the brain of CBS-deficient and Dyrk1a-overexpressing mice. This increase was abolished when CBS-deficient and Dyrk1A-transgenic mice were treated with harmine, an inhibitor of Dyrk1A kinase activity, which emphasizes the role of Dyrk1A activity on ERK and Akt activation. Sprouty 2 protein level, a negative feedback loop modulator that limits the intensity and duration of RTK activation, is decreased in the brain of CBS-deficient mice, but not in the brain of Dyrk1A transgenic mice. Furthermore, a reduced Dyrk1A and Grb2 binding on sprouty 2 and an increased interaction of Dyrk1A with Grb2 were found in the brain of Dyrk1A transgenic mice. The consequence of Dyrk1A overexpression on RTK activation seems to be a decreased interaction of sprouty 2/Grb2. These observations demonstrate ERK and Akt activation induced by Dyrk1A in the brain of hyperhomocysteinemic mice and open new perspectives to understand the basis of the cognitive defects in hyperhomocysteinemia.

Weighted pedigree-based statistics for testing the association of rare variants

BACKGROUND

With the advent of next-generation sequencing (NGS) technologies, researchers are now generating a deluge of data on high dimensional genomic variations, whose analysis is likely to reveal rare variants involved in the complex etiology of disease. Standing in the way of such discoveries, however, is the fact that statistics for rare variants are currently designed for use with population-based data. In this paper, we introduce a pedigree-based statistic specifically designed to test for rare variants in family-based data. The additional power of pedigree-based statistics stems from the fact that while rare variants related to diseases or traits of interest occur only infrequently in populations, in families with multiple affected individuals, such variants are enriched. Note that while the proposed statistic can be applied with and without statistical weighting, our simulations show that its power increases when weighting (WSS and VT) are applied.

RESULTS

Our working hypothesis was that, since rare variants are concentrated in families with multiple affected individuals, pedigree-based statistics should detect rare variants more powerfully than population-based statistics. To evaluate how well our new pedigree-based statistics perform in association studies, we develop a general framework for sequence-based association studies capable of handling data from pedigrees of various types and also from unrelated individuals. In short, we developed a procedure for transforming population-based statistics into tests for family-based associations. Furthermore, we modify two existing tests, the weighted sum-square test and the variable-threshold test, and apply both to our family-based collapsing methods. We demonstrate that the new family-based tests are more powerful than corresponding population-based test and they generate a reasonable type I error rate.To demonstrate feasibility, we apply the newly developed tests to a pedigree-based GWAS data set from the Framingham Heart Study (FHS). FHS-GWAS data contain approximately 5000 uncommon variants with frequencies less than 0.05. Potential association findings in these data demonstrate the feasibility of the software PB-STAR (note, PB-STAR is now freely available to the public).

CONCLUSION

Our tests show that when analyzing for rare variants, a pedigree-based design is more powerful than a population-based case-control design. We further demonstrate that a pedigree-based statistic's power to detect rare variants increases in direct relation to the proportion of affected individuals within the pedigree.

MicroRNAs Are Involved in End-Organ Damage During Hypertension

Even in the new millennium, arterial hypertension remains a serious condition, with considerable morbidity and mortality worldwide. Crucial in managing the disease is not only lowering arterial blood pressure but also preventing or treating the typical end-organ damage caused by long-lasting and inadequately treated hypertension. In the past decade, it has been shown that microRNAs (miRs) are involved in several hypertension-related pathologies, such as cardiac hypertrophy and fibrosis, hypertensive heart failure, renal fibrosis, kidney failure, and, to a lesser extent, eye disease and hemorrhagic stroke. Whereas others extensively reviewed the role of miRs in atherosclerosis and vascular disease, this review focuses on their role in target organ damage during arterial hypertension. We emphasize the involvement of miRs in pathological end-organ remodeling processes and try to demonstrate some common miR signatures in distinct end organs. Hence, we aimed to provide proof of arterial hypertension being a systemic disease, similar to diabetes mellitus or metabolic syndrome. Furthermore, miRs that act on one particular process in different end organs are interesting therapeutic targets. Some future perspectives in miR research are highlighted with respect to novel therapeutic strategies in the cardiovascular field.

The function of miRNA in cardiac hypertrophy

Cardiac hypertrophy is an adaptive enlargement of the myocardium in response to altered stress or injury. The cellular responses of cardiomyocytes and non-cardiomyocytes to various signaling pathways should be tightly and delicately regulated to maintain cardiac homeostasis and prevent pathological cardiac hypertrophy. MicroRNAs (miRNAs) are endogenous, single-stranded, short non-coding RNAs that act as regulators of gene expression by promoting the degradation or inhibiting the translation of target mRNAs. Recent studies have revealed expression signatures of miRNAs associated with pathological cardiac hypertrophy and heart failure in humans and mouse models of heart diseases. Increasing evidence indicates that dysregulation of specific miRNAs could alter the cellular responses of cardiomyocytes and non-cardiomyocytes to specific signaling upon the pathological hemodynamic overload, leading to cardiac hypertrophy and heart failure. This review summarizes the cell-autonomous functions of cardiomyocyte miRNAs regulated by different pathways and the roles of non-cardiomyocyte miRNAs in cardiac hypertrophy. The therapeutic effects of a number of miRNAs in heart diseases are also discussed.

Coculture with hematopoietic stem cells protects cardiomyocytes against apoptosis via paracrine activation of AKT

Background

Previous experimental studies concluded that stem cells (SC) may exert their beneficial effects on the ischemic heart by paracrine activation of antiapoptotic pathways. In order to identify potential cardioprotective mediators, we performed a systematic analysis of the differential gene expression of hematopoietic SC after coculture with cardiomyocytes (CM).

Methods

After 48 h of coculture with neonatal rat ventricular CM (NRVCM), two consecutive cell sorting steps generated a highly purified population of conditioned murine hematopoietic SC (>99%). Next, a genome-wide microarray analysis of cocultured vs. monocultured hematopoietic SC derived from three independent experiments was performed. The analysis of differentially expressed genes was focused on products that are secretable and/or membrane-bound and potentially involved in antiapoptotic signalling.

Results

We found CCL-12, Macrophage Inhibitory Factor, Fibronectin and connexin 40 significantly upregulated in our coculture model. An ELISA of cell culture supernatants was performed to confirm secretion of candidate genes and showed that coculture supernatants revealed markedly higher CCL-12 concentrations. Moreover, we stimulated NRVCM with concentrated coculture supernatants which resulted in a significant reduction of apoptosis compared to monoculture-derived supernatant. Mechanistically, NRVCMs stimulated with coculture supernatants showed a higher level of AKT-phosphorylation, consistent with enhanced antiapoptotic signaling.

Conclusion

In summary, our results show that the interaction between hematopoietic SC and NRVCM led to a modified gene expression and induction of antiapoptotic pathways. These findings may thus at least in part explain the cardioprotective effects of hematopoietic SC.

Cardiomyocyte calcineurin signaling in subcellular domains: from the sarcolemma to the nucleus and beyond

The serine-threonine phosphatase calcineurin is activated in cardiac myocytes in the diseased heart and induces pathological hypertrophy. Calcineurin activity is mainly triggered by calcium/calmodulin binding but also through calpain mediated cleavage. How controlled calcineurin activation is possible in cardiac myocytes, which typically show a 10-fold difference in cytosolic calcium concentration with every heartbeat, has remained enigmatic. It is now emerging that calcineurin activation and signaling occur in subcellular microdomains, in which it is brought together with target proteins and exceedingly high concentrations of calcium in order to induce downstream signaling. We review current evidence of subcellular calcineurin mainly at the sarcolemma and the nucleus, but also in association with the sarcoplasmic reticulum and mitochondria. We also suggest that knowledge about subcellular signaling could help to develop inhibitors of calcineurin in specific microdomains to avoid side-effects that may arise from complete calcineurin inhibition.

The small molecule harmine regulates NFATc1 and Id2 expression in osteoclast progenitor cells

Small molecule compounds that potently affect osteoclastogenesis could be useful as chemical probes for elucidating the mechanisms of various biological phenomena and as effective therapeutic strategies against bone resorption. An osteoclast progenitor cell-based high-throughput screening system was designed to target activation of NFAT, which is a key event for osteoclastogenesis. Orphan ligand library screening using this system identified the β-carboline derivative harmine, which is a highly potent inhibitor of dual-specificity tyrosine-phosphorylation regulated kinase 1A (DYRK1A), to be an NFAT regulator in osteoclasts. RAW264.7 cells highly expressed DYRK1A protein, and in vitro phosphorylation assay demonstrated that harmine directly inhibited the DYRK1A-mediated phosphorylation (in-activation) of NFATc1. Harmine promoted the dephosphorylation (activation) of NFATc1 in RAW264.7 cells within 24h, and it significantly increased the expression of NFATc1 in RAW264.7 cells and mouse primary bone marrow macrophages (BMMs) both in the presence and absence of RANKL stimulation. Although harmine promoted NFATc1 expression and stimulated target genes for osteoclastogenesis, cell-cell fusion and the formation of TRAP-positive multinucleated osteoclasts from RAW264.7 cells and BMMs was significantly inhibited by harmine treatment. Meanwhile, harmine remarkably promoted the expression of inhibitor of DNA binding/differentiation-2 (Id2), which is a negative regulator for osteoclastogenesis, in RAW264.7 cells and BMMs. An Id2-null-mutant showed slightly increased osteoclast formation from BMMs, and the harmine-mediated inhibition of osteoclast formation was abolished in the BMMs of Id2-null-mutant mice. These results suggest that harmine is a potent activator of NFATc1 that interferes with the function of DYRK1A in osteoclast precursors and also up-regulates Id2 protein, which may dominantly inhibit expression pathways associated with cell-cell fusion, thereby leading to the disruption of the fusion events mediating osteoclastogenesis. The small molecule harmine is therefore expected to provide an experimental tool for investigating signaling cascades in osteoclastogenesis, especially those centered on DYRK1A-mediated NFATc1 and Id2 regulation.

Enhanced expression of DYRK1A in cardiomyocytes inhibits acute NFAT activation but does not prevent hypertrophy in vivo

AIMS

The calcineurin and nuclear factor of activated T cells (NFAT) pathway can mediate pro-hypertrophic signalling in the heart. Recently, it has been shown that dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) phosphorylates NFAT, which limits calcineurin/NFAT signal transduction in T cells and hypertrophy in cultured cardiomyocytes. The hypothesis tested in this study was that DYRK1A prevents calcineurin/NFAT-mediated cardiac hypertrophy in vivo.

METHODS AND RESULTS

In cultured rat cardiomyocytes, adenovirus-mediated overexpression of DYRK1A antagonized calcineurin-mediated nuclear NFAT translocation and the phenylephrine-induced hypertrophic growth response. To test the ability of DYRK1A to reduce hypertrophic cardiac growth in vivo, we created tetracycline-repressible Dyrk1a transgenic mice to avoid the cardiac developmental defects associated with embryonic DYRK1A expression. However, in the mouse model, histological determination of myocyte diameter, heart weight/body weight ratio, and echocardiographic measurements revealed that myocardial expression of DYRK1A failed to reduce hypertrophy induced via aortic banding or co-expression of calcineurin. This discrepancy is explained, at least in part, by insufficient long-term inhibition of NFAT and the activation of DYRK1A-resistant maladaptive genes in vivo.

CONCLUSION

Isolated augmentation of DYRK1A can be compensated for in vivo, and this may significantly limit anti-hypertrophic interventions aimed at enhancing DYRK1A activity.

Tapping the brake on cardiac growth-endogenous repressors of hypertrophic signaling

Cardiac hypertrophy is considered an early hallmark during the clinical course of heart failure and an important risk factor for cardiac morbidity and mortality. Although hypertrophy of individual cardiomyocytes in response to pathological stimuli has traditionally been considered as an adaptive response required to sustain cardiac output, accumulating evidence from studies in patients and animal models suggests that in most instances hypertrophy of the heart also harbors maladaptive aspects. Major strides have been made in our understanding of the pathways that convey pro-hypertrophic signals from the outside of the cell to the nucleus. In recent years it also has become increasingly evident that the heart possesses a variety of endogenous feedback mechanisms to counterbalance this growth response. These repressive mechanisms are of particular interest since they may provide valuable therapeutic options. In this review we summarize currently known endogenous repressors of pathological cardiac growth as they have been studied by gene targeting in mice. Many of the repressors that function in signal transduction appear to regulate calcineurin (e.g. PICOT, calsarcin, RCAN) and JNK signaling (e.g. CDC42, MKP-1) and some will be described in greater detail in this review. In addition, we will focus on factors such as Kruppel-like factors (KLF4, KLF15 and KLF10) and histone deacetylases (HDACs), which constitute a relevant group of nuclear proteins that repress transcription of the hypertrophic gene program in cardiomyocytes.

DYRK family of protein kinases: evolutionary relationships, biochemical properties, and functional roles

Dual-specificity tyrosine-regulated kinases (DYRKs) comprise a family of protein kinases within the CMGC group of the eukaryotic kinome. Members of the DYRK family are found in 4 (animalia, plantae, fungi, and protista) of the 5 main taxa or kingdoms, and all DYRK proteins studied to date share common structural, biochemical, and functional properties with their ancestors in yeast. Recent work on DYRK proteins indicates that they participate in several signaling pathways critical for developmental processes and cell homeostasis. In this review, we focus on the DYRK family of proteins from an evolutionary, biochemical, and functional point of view and discuss the most recent, relevant, and controversial contributions to the study of these kinases.

Activation, regulation, and inhibition of DYRK1A

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a protein kinase with diverse functions in neuronal development and adult brain physiology. Higher than normal levels of DYRK1A are associated with the pathology of neurodegenerative diseases and have been implicated in some neurobiological alterations of Down syndrome, such as mental retardation. It is therefore important to understand the molecular mechanisms that control the activity of DYRK1A. Here we review the current knowledge about the initial self-activation of DYRK1A by tyrosine autophosphorylation and propose that this mechanism presents an ancestral feature of the CMGC group of kinases. However, tyrosine phosphorylation does not appear to regulate the enzymatic activity of DYRK1A. Control of DYRK1A may take place on the level of gene expression, interaction with regulatory proteins and regulated nuclear translocation. Finally, we compare the properties of small molecule inhibitors that target DYRK1A and evaluate their potential application and limitations. The β-carboline alkaloid harmine is currently the most selective and potent inhibitor of DYRK1A and has proven very useful in cellular assays.

MicroRNA-199b targets the nuclear kinase Dyrk1a in an auto-amplification loop promoting calcineurin/NFAT signalling

MicroRNAs (miRs) are a class of single-stranded, non-coding RNAs of about 22 nucleotides in length. Increasing evidence implicates miRs in myocardial disease processes. Here we show that miR-199b is a direct calcineurin/NFAT target gene that increases in expression in mouse and human heart failure, and targets the nuclear NFAT kinase dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1a (Dyrk1a), constituting a pathogenic feed forward mechanism that affects calcineurin-responsive gene expression. Mutant mice overexpressing miR-199b, or haploinsufficient for Dyrk1a, are sensitized to calcineurin/NFAT signalling or pressure overload and show stress-induced cardiomegaly through reduced Dyrk1a expression. In vivo inhibition of miR-199b by a specific antagomir normalized Dyrk1a expression, reduced nuclear NFAT activity and caused marked inhibition and even reversal of hypertrophy and fibrosis in mouse models of heart failure. Our results reveal that microRNAs affect cardiac cellular signalling and gene expression, and implicate miR-199b as a therapeutic target in heart failure.