Notch signaling modulates the electrical behavior of cardiomyocytes

Notch2 Signaling Drives Cardiac Hypertrophy by Suppressing Purine Nucleotide Metabolism

Gain-of-function mutations of Notch2 cause the rare autosomal dominant disorder known as Hajdu-Cheney syndrome (HCS). Most patients with HCS develop congenital heart disease; however, the precise mechanisms remain elusive. Here, a murine model expressing the human Notch2 intracellular domain (hN2ICD) in cardiomyocytes (hN2ICD-TgCM) was generated and the mice spontaneously developed ventricular diastolic dysfunction with preserved ejection fraction and cardiac hypertrophy. Ectopic hN2ICD expression promoted cardiomyocyte hypertrophy by suppressing adenylosuccinate lyase (ADSL)-mediated adenosine 5'-monophosphate (AMP) generation, which further enhanced the activation of the mammalian target of rapamycin complex 1 pathway by reducing AMP-activated kinase activity. Hairy and enhancer of split 1 silencing abrogated hN2ICD-induced cardiomyocyte hypertrophy by increasing Adsl transcription. Importantly, pharmacological activation of AMP-activated kinase ameliorated cardiac hypertrophy and dysfunction in hN2ICD-TgCM mice. The frameshift mutation in Notch2 exon 34 (c.6426dupT), which causes early-onset HCS, induces AC16 human cardiomyocyte hypertrophy through suppressing ADSL-mediated AMP generation. Thus, targeting Notch2-mediated purine nucleotide metabolism may be an attractive therapeutic approach to heart failure treatment.

The cAMP/PKA signaling pathway conditions cardiac performance in experimental animals with metabolic syndrome

Metabolic syndrome (MetS) increases the risk of coronary artery disease, but effects of this condition on the working myocardium remain to be fully elucidated. In the present study we evaluated the consequences of diet-induced metabolic disorders on cardiac function and myocyte performance using female mice fed with Western diet. Animals maintained on regular chow were used as control (Ctrl). Mice on the Western diet (WesD) had increased body weight, impaired glucose metabolism, preserved diastolic and systolic function, but increased left ventricular (LV) mass, with respect to Ctrl animals. Moreover, WesD mice had reduced heart rate variability (HRV), indicative of altered cardiac sympathovagal balance. Myocytes from WesD mice had increased volume, enhanced cell mechanics, and faster kinetics of contraction and relaxation. Moreover, levels of cAMP and protein kinase A (PKA) activity were enhanced in WesD myocytes, and interventions aimed at stabilizing cAMP/PKA abrogated functional differences between Ctrl and WesD cells. Interestingly, in vivo β-adrenergic receptor (β-AR) blockade normalized the mechanical properties of WesD myocytes and revealed defective cardiac function in WesD mice, with respect to Ctrl. Collectively, these results indicate that metabolic disorders induced by Western diet enhance the cAMP/PKA signaling pathway, a possible adaptation required to maintain cardiac function.

Phosphorylation of cardiac sodium channel at Ser571 anticipates manifestations of the aging myopathy

Diastolic dysfunction and delayed ventricular repolarization are typically observed in the elderly, but whether these defects are intimately associated with the progressive manifestation of the aging myopathy remains to be determined. In this regard, aging in experimental animals is coupled with increased late Na+ current (INa,L) in cardiomyocytes, raising the possibility that INa,L conditions the modality of electrical recovery and myocardial relaxation of the aged heart. For this purpose, aging male and female wild-type (WT) C57Bl/6 mice were studied together with genetically engineered mice with phosphomimetic (gain of function, GoF) or ablated (loss of function, LoF) mutations of the sodium channel Nav1.5 at Ser571 associated with, respectively, increased and stabilized INa,L. At ∼18 mo of age, WT mice developed prolonged duration of the QT interval of the electrocardiogram and impaired diastolic left ventricular (LV) filling, defects that were reversed by INa,L inhibition. Prolonged repolarization and impaired LV filling occurred prematurely in adult (∼5 mo) GoF mutant mice, whereas these alterations were largely attenuated in aging LoF mutant animals. Ca2+ transient decay and kinetics of myocyte shortening/relengthening were delayed in aged (∼24 mo) WT myocytes, with respect to adult cells. In contrast, delayed Ca2+ transients and contractile dynamics occurred at adult stage in GoF myocytes and further deteriorated in old age. Conversely, myocyte mechanics were minimally affected in aging LoF cells. Collectively, these results document that Nav1.5 phosphorylation at Ser571 and the late Na+ current modulate the modality of myocyte relaxation, constituting the mechanism linking delayed ventricular repolarization and diastolic dysfunction.NEW & NOTEWORTHY We have investigated the impact of the late Na current (INa,L) on cardiac and myocyte function with aging by using genetically engineered animals with enhanced or stabilized INa,L, due to phosphomimetic or phosphoablated mutations of Nav1.5. Our findings support the notion that phosphorylation of Nav1.5 at Ser571 prolongs myocardial repolarization and impairs diastolic function, contributing to the manifestations of the aging myopathy.

The characteristics of proliferative cardiomyocytes in mammals

Better understanding of the mechanisms regulating the proliferation of pre-existing cardiomyocyte (CM) should lead to better options for regenerating injured myocardium. The absence of a perfect research model to definitively identify newly formed mammalian CMs is lacking. However, methodologies are being developed to identify and enrich proliferative CMs. These methods take advantages of the different proliferative states of CMs during postnatal development, before and after injury in the neonatal heart. New approaches use CMs labeled in lineage tracing animals or single cell technique-based CM clusters. This review aims to provide a timely update on the characteristics of the proliferative CMs, including their structural, functional, genetic, epigenetic and metabolic characteristics versus non-proliferative CMs. A better understanding of the characteristics of proliferative CMs should lead to the mechanisms for inducing endogenous CMs to self-renew, which is a promising therapeutic strategy to treat cardiac diseases that cause CM death in humans.

KV Channel-Interacting Proteins in the Neurological and Cardiovascular Systems: An Updated Review

K_V channel-interacting proteins (KChIP1-4) belong to a family of Ca²⁺-binding EF-hand proteins that are able to bind to the N-terminus of the K_V4 channel α-subunits. KChIPs are predominantly expressed in the brain and heart, where they contribute to the maintenance of the excitability of neurons and cardiomyocytes by modulating the fast inactivating-K_V4 currents. As the auxiliary subunit, KChIPs are critically involved in regulating the surface protein expression and gating properties of K_V4 channels. Mechanistically, KChIP1, KChIP2, and KChIP3 promote the translocation of K_V4 channels to the cell membrane, accelerate voltage-dependent activation, and slow the recovery rate of inactivation, which increases K_V4 currents. By contrast, KChIP4 suppresses K_V4 trafficking and eliminates the fast inactivation of K_V4 currents. In the heart, I_Ks, I_Ca,L, and I_Na can also be regulated by KChIPs. I_Ca,L and I_Na are positively regulated by KChIP2, whereas I_Ks is negatively regulated by KChIP2. Interestingly, KChIP3 is also known as downstream regulatory element antagonist modulator (DREAM) because it can bind directly to the downstream regulatory element (DRE) on the promoters of target genes that are implicated in the regulation of pain, memory, endocrine, immune, and inflammatory reactions. In addition, all the KChIPs can act as transcription factors to repress the expression of genes involved in circadian regulation. Altered expression of KChIPs has been implicated in the pathogenesis of several neurological and cardiovascular diseases. For example, KChIP2 is decreased in failing hearts, while loss of KChIP2 leads to increased susceptibility to arrhythmias. KChIP3 is increased in Alzheimer's disease and amyotrophic lateral sclerosis, but decreased in epilepsy and Huntington's disease. In the present review, we summarize the progress of recent studies regarding the structural properties, physiological functions, and pathological roles of KChIPs in both health and disease. We also summarize the small-molecule compounds that regulate the function of KChIPs. This review will provide an overview and update of the regulatory mechanism of the KChIP family and the progress of targeted drug research as a reference for researchers in related fields.

A perspective on Notch signalling in progression and arrhythmogenesis in familial hypertrophic and dilated cardiomyopathies

In this perspective, we discussed emerging data indicating a role for Notch signalling in inherited disorders of the heart failure with focus on hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) linked to variants of genes encoding mutant proteins of the sarcomere. We recently reported an upregulation of elements in the Notch signalling cascade in cardiomyocytes derived from human inducible pluripotent stem cells expressing a TNNT2 variant encoding cardiac troponin T (cTnT-I79N+/-), which induces hypertrophy, remodelling, abnormalities in excitation-contraction coupling and electrical instabilities (Shafaattalab S et al. 2021 Front. Cell Dev. Biol. 9, 787581. (doi:10.3389/fcell.2021.787581)). Our search of the literature revealed the novelty of this finding and stimulated us to discuss potential connections between the Notch signalling pathway and familial cardiomyopathies. Our considerations focused on the potential role of these interactions in arrhythmias, microvascular ischaemia, and fibrosis. This finding underscored a need to consider the role of Notch signalling in familial cardiomyopathies which are trigged by sarcomere mutations engaging mechano-signalling pathways for which there is evidence of a role for Notch signalling with crosstalk with Hippo signalling. Our discussion included a role for both cardiac myocytes and non-cardiac myocytes in progression of HCM and DCM. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Modulation of Notch Signaling at Early Stages of Differentiation of Human Induced Pluripotent Stem Cells to Dopaminergic Neurons

Elaboration of protocols for differentiation of human pluripotent stem cells to dopamine neurons is an important issue for development of cell replacement therapy for Parkinson's disease. A number of protocols have been already developed; however, their efficiency and specificity still can be improved. Investigating the role of signaling cascades, important for neurogenesis, can help to solve this problem and to provide a deeper understanding of their role in neuronal development. Notch signaling plays an essential role in development and maintenance of the central nervous system after birth. In our study, we analyzed the effect of Notch activation and inhibition at the early stages of differentiation of human induced pluripotent stem cells to dopaminergic neurons. We found that, during the first seven days of differentiation, the cells were not sensitive to the Notch inhibition. On the contrary, activation of Notch signaling during the same time period led to significant changes and was associated with an increase in expression of genes, specific for caudal parts of the brain, a decrease of expression of genes, specific for forebrain, as well as a decrease of expression of genes, important for the formation of axons and dendrites and microtubule stabilizing proteins.

lncRNA-TCONS_00008552 expression in patients with pulmonary arterial hypertension due to congenital heart disease

Long noncoding RNAs (lncRNAs) are potential regulators of a variety of cardiovascular diseases. Therefore, there is a series of differentially expressed lncRNAs in pulmonary arterial hypertension (PAH) that may be used as markers to diagnose PAH and even predict the prognosis. However, their specific mechanisms remain largely unknown. Therefore, we investigated the biological role of lncRNAs in patients with PAH. First, we screened patients with PAH secondary to ventricular septal defect (VSD) and those with VSD without PAH to assess differences in lncRNA and mRNA expression between the two groups. Our results revealed the significant upregulation of 813 lncRNAs and 527 mRNAs and significant downregulation of 541 lncRNAs and 268 mRNAs in patients with PAH. Then, we identified 10 hub genes in a constructed protein-protein interaction network. Next, we performed bioinformatics analyses, including Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis and subsequently constructed coding-noncoding co-expression networks. We screened lncRNA-TCONS_00008552 and lncRNA-ENST00000433673 as candidate genes and verified the expression levels of the lncRNAs using quantitative reverse-transcription PCR. Although expression levels of lncRNA-TCONS_00008552 in the plasma from the PAH groups were significantly increased compared with the control groups, there was no significant difference in the expression of lncRNA-ENST00000433673 between the two groups. This study bolsters our understanding of the role of lncRNA in PAH occurrence and development and indicates that lncRNA-TCONS_00008552 is a novel potential molecular marker for PAH.

The Role of the Notch Signaling Pathway in Recovery of Cardiac Function after Myocardial Infarction

Myocardial infarction (MI) is a pathological process, evidencing as massive death of cardiomyocytes associated with hypoxic and oxidative stress. The formation of areas of fibrosis ultimately leads to heart failure. There are some mechanisms that contribute to the functional repair of the heart. In most mammals, including humans, the Notch signaling pathway has cardioprotective effects. It is involved in the formation of the heart in embryogenesis and in the restoration of cardiac function after MI due to: (1) reducing oxidative stress; (2) prevention of apoptosis; (3) regulation of inflammation; (4) containment of fibrosis and hypertrophy of cardiomyocytes; (5) tissue revascularization; and (6) regulation of proliferation and differentiation of cardiomyocytes. In addition, the Notch signaling pathway interacts with other signaling cascades involved in the pathogenesis of MI and subsequent cardiac repair. In this review, we consider the Notch signaling pathway as a potential target for therapeutic approaches aimed at improving cardiac recovery after MI.

Scn1b expression in the adult mouse heart modulates Na+ influx in myocytes and reveals a mechanistic link between Na+ entry and diastolic function

Voltage-gated sodium channels (VGSCs) are macromolecular assemblies composed of a number of proteins regulating channel conductance and properties. VGSCs generate Na+ current (INa) in myocytes and play fundamental roles in excitability and impulse conduction in the heart. Moreover, VGSCs condition mechanical properties of the myocardium, a process that appears to involve the late component of INa. Variants in the gene SCN1B, encoding the VGSC β1- and β1B-subunits, result in inherited neurological disorders and cardiac arrhythmias. But the precise contributions of β1/β1B-subunits and VGSC integrity to the overall function of the adult heart remain to be clarified. For this purpose, adult mice with cardiac-restricted, inducible deletion of Scn1b (conditional knockout, cKO) were studied. Myocytes from cKO mice had increased densities of fast (+20%)- and slow (+140%)-inactivating components of INa, with respect to control cells. By echocardiography and invasive hemodynamics, systolic function was preserved in cKO mice, but diastolic properties and ventricular compliance were compromised, with respect to control animals. Importantly, inhibition of late INa with GS967 normalized left ventricular filling pattern and isovolumic relaxation time in cKO mice. At the cellular level, cKO myocytes presented delayed kinetics of Ca2+ transients and cell mechanics, defects that were corrected by inhibition of INa. Collectively, these results document that VGSC β1/β1B-subunits modulate electrical and mechanical function of the heart by regulating, at least in part, Na+ influx in cardiomyocytes.NEW & NOTEWORTHY We have investigated the consequences of deletion of Scn1b, the gene encoding voltage-gated sodium channel β1-subunits, on myocyte and cardiac function. Our findings support the notion that Scn1b expression controls properties of Na+ influx and Ca2+ cycling in cardiomyocytes affecting the modality of cell contraction and relaxation. These effects at the cellular level condition electrical recovery and diastolic function in vivo, substantiating the multifunctional role of β1-subunits in the physiology of the heart.

Heart Rate Variability Reveals Altered Autonomic Regulation in Response to Myocardial Infarction in Experimental Animals

The analysis of beating rate provides information on the modulatory action of the autonomic nervous system on the heart, which mediates adjustments of cardiac function to meet hemodynamic requirements. In patients with myocardial infarction, alterations of heart rate variability (HRV) have been correlated to the occurrence of arrhythmic events and all-cause mortality. In the current study, we tested whether experimental rodent models of myocardial infarction recapitulate dynamics of heart rate variability observed in humans, and constitute valid platforms for understanding mechanisms linking autonomic function to the development and manifestation of cardiovascular conditions. For this purpose, HRV was evaluated in two engineered mouse lines using electrocardiograms collected in the conscious, restrained state, using a tunnel device. Measurements were obtained in naïve mice and animals at 3-∼28 days following myocardial infarction, induced by permanent coronary artery ligation. Two mouse lines with inbred and hybrid genetic background and, respectively, homozygous (Homo) and heterozygous (Het) for the MerCreMer transgene, were employed. In the naïve state, Het female and male mice presented prolonged RR interval duration (∼9%) and a ∼4-fold increased short- and long-term RR interval variability, with respect to sex-matched Homo mice. These differences were abrogated by pharmacological interventions inhibiting the sympathetic and parasympathetic axes. At 3-∼14 days after myocardial infarction, RR interval duration increased in Homo mice, but was not affected in Het animals. In contrast, Homo mice had minor modifications in HRV parameters, whereas substantial (> 50%) reduction of short- and long-term RR interval variation occurred in Het mice. Interestingly, ex vivo studies in isolated organs documented that intrinsic RR interval duration increased in infarcted vs. non-infarcted Homo and Het hearts, whereas RR interval variation was not affected. In conclusion, our study documents that, as observed in humans, myocardial infarction in rodents is associated with alterations in heart rhythm dynamics consistent with sympathoexcitation and parasympathetic withdrawal. Moreover, we report that mouse strain is an important variable when evaluating autonomic function via the analysis of HRV.

Bioengineering Systems for Modulating Notch Signaling in Cardiovascular Development, Disease, and Regeneration

The Notch intercellular signaling pathways play significant roles in cardiovascular development, disease, and regeneration through modulating cardiovascular cell specification, proliferation, differentiation, and morphogenesis. The dysregulation of Notch signaling leads to malfunction and maldevelopment of the cardiovascular system. Currently, most findings on Notch signaling rely on animal models and a few clinical studies, which significantly bottleneck the understanding of Notch signaling-associated human cardiovascular development and disease. Recent advances in the bioengineering systems and human pluripotent stem cell-derived cardiovascular cells pave the way to decipher the role of Notch signaling in cardiovascular-related cells (endothelial cells, cardiomyocytes, smooth muscle cells, fibroblasts, and immune cells), and intercellular crosstalk in the physiological, pathological, and regenerative context of the complex human cardiovascular system. In this review, we first summarize the significant roles of Notch signaling in individual cardiac cell types. We then cover the bioengineering systems of microfluidics, hydrogel, spheroid, and 3D bioprinting, which are currently being used for modeling and studying Notch signaling in the cardiovascular system. At last, we provide insights into ancillary supports of bioengineering systems, varied types of cardiovascular cells, and advanced characterization approaches in further refining Notch signaling in cardiovascular development, disease, and regeneration.

Analysis of Molecular Mechanism of YiqiChutan Formula Regulating DLL4-Notch Signaling to Inhibit Angiogenesis in Lung Cancer

In order to explore the specific mechanism of YiqiChutan formula (YQCTF) in inhibiting the angiogenesis of lung cancer and its relationship with delta-like ligand 4- (DLL4-) Notch signaling, 30 healthy BALB/c-nu/nu rats were selected and divided into three groups: A549 group (implanted with lung adenocarcinoma cell line A549), NCI-H460 group (implanted with human lung large-cell carcinoma cell line NCI-H460), and NCI-H446 group (implanted with human lung small cell carcinoma cell line NCI-H446) for constructing lung cancer transplanted tumor models. After modeling, the group treated with normal saline was taken as control group, 200 mg/kg of YQCTF was adopted for intervention, and the tumor volume and growth inhibition rate were compared with the vascular targeted inhibitor Sorafenib. HE staining, CD31 fluorescent antibody staining, and microelectron microscopy were adopted to observe the neovascular endothelial cells of the transplanted tumor. The expression of VEGF, HIF-1α, DLL4, and Notch-1 in the transplanted tumors in each group was detected by Western blot and RT-PCR at the protein level or mRNA level. Compared with the control group, the YQCTF-treated group had obvious inhibitory effect on lung cancer transplanted tumor and lung cancer angiogenesis. In the YQCTF-treated group, the density of angiogenesis decreased significantly and the vascular lumen structure also decreased, and the expression levels of VEGF, HIF-1α, DLL4, and Notch-1 in the YQCTF-treated group were all lower than those in the control group. YQCTF could inhibit the growth of lung cancer transplanted tumor through antiangiogenesis, and it could also reduce the amount of angiogenesis in lung cancer transplanted tumor. In addition, the generation of lumen structure was also hindered, which was realized through the VEGF signaling pathway and DLL4-Notch signaling pathway.

Sodium channel β1 subunits participate in regulated intramembrane proteolysis-excitation coupling

Loss-of-function (LOF) variants in SCN1B, encoding voltage-gated sodium channel β1 subunits, are linked to human diseases with high risk of sudden death, including developmental and epileptic encephalopathy and cardiac arrhythmia. β1 Subunits modulate the cell-surface localization, gating, and kinetics of sodium channel pore-forming α subunits. They also participate in cell-cell and cell-matrix adhesion, resulting in intracellular signal transduction, promotion of cell migration, calcium handling, and regulation of cell morphology. Here, we investigated regulated intramembrane proteolysis (RIP) of β1 by BACE1 and γ-secretase and show that β1 subunits are substrates for sequential RIP by BACE1 and γ-secretase, resulting in the generation of a soluble intracellular domain (ICD) that is translocated to the nucleus. Using RNA sequencing, we identified a subset of genes that are downregulated by β1-ICD overexpression in heterologous cells but upregulated in Scn1b-null cardiac tissue, which lacks β1-ICD signaling, suggesting that the β1-ICD may normally function as a molecular brake on gene transcription in vivo. We propose that human disease variants resulting in SCN1B LOF cause transcriptional dysregulation that contributes to altered excitability. Moreover, these results provide important insights into the mechanism of SCN1B-linked channelopathies, adding RIP-excitation coupling to the multifunctionality of sodium channel β1 subunits.

Transcriptomic uniqueness and commonality of the ion channels and transporters in the four heart chambers

Myocardium transcriptomes of left and right atria and ventricles from four adult male C57Bl/6j mice were profiled with Agilent microarrays to identify the differences responsible for the distinct functional roles of the four heart chambers. Female mice were not investigated owing to their transcriptome dependence on the estrous cycle phase. Out of the quantified 16,886 unigenes, 15.76% on the left side and 16.5% on the right side exhibited differential expression between the atrium and the ventricle, while 5.8% of genes were differently expressed between the two atria and only 1.2% between the two ventricles. The study revealed also chamber differences in gene expression control and coordination. We analyzed ion channels and transporters, and genes within the cardiac muscle contraction, oxidative phosphorylation, glycolysis/gluconeogenesis, calcium and adrenergic signaling pathways. Interestingly, while expression of Ank2 oscillates in phase with all 27 quantified binding partners in the left ventricle, the percentage of in-phase oscillating partners of Ank2 is 15% and 37% in the left and right atria and 74% in the right ventricle. The analysis indicated high interventricular synchrony of the ion channels expressions and the substantially lower synchrony between the two atria and between the atrium and the ventricle from the same side.

Rhythm dynamics of the aging heart: an experimental study using conscious, restrained mice

Heart rate variability (HRV) is a measure of variation in time interval between heartbeats and reflects the influence of autonomic nervous system and circulating/locally released factors on sinoatrial node discharge. Here, we tested whether electrocardiograms (ECGs) obtained in conscious, restrained mice, a condition that affects sympathovagal balance, reveal alterations of heart rhythm dynamics with aging. Moreover, based on emergence of sodium channels as modulators of pacemaker activity, we addressed consequences of altered sodium channels on heart rhythm. C57Bl/6 mice and mice with enhanced late sodium current due to Nav1.5 mutation at Ser571 (S571E) at ~4 to ~24 mo of age, were studied. HRV was assessed using time- and frequency-domain and nonlinear parameters. For C57Bl/6 and S571E mice, standard deviation of RR intervals (SDRR), total power of RR interval variation, and nonlinear standard deviation 2 (SD2) were maximal at ~4 mo and decreased at ~18 and ~24 mo, together with attenuation of indexes of sympathovagal balance. Modulation of sympathetic and/or parasympathetic divisions revealed attenuation of autonomic tone at ~24 mo. At ~4 mo, S571E mice presented lower heart rate and higher SDRR, total power, and SD2 with respect to C57Bl/6, properties reversed by late sodium current inhibition. At ~24 mo, heart rate decreased in C57Bl/6 but increased in S571E, a condition preserved after autonomic blockade. Collectively, our data indicate that aging is associated with reduced HRV. Moreover, sodium channel function conditions heart rate and its age-related adaptations, but does not interfere with HRV decline occurring with age.NEW & NOTEWORTHY We have investigated age-associated alterations of heart rate properties in mice using conscious electrocardiographic recordings. Our findings support the notion that aging is coupled with altered sympathovagal balance with consequences on heart rate variability. Moreover, by using a genetically engineered mouse line, we provide evidence that sodium channels modulate heart rate and its age-related adaptations.

Novel Methods for High-resolution Assessment of Cardiac Action Potential Repolarization

The profile of the action potential (AP) of cardiomyocytes contributes to the modality of ventricular repolarization of the heart. Experimentally, the examination of the AP in isolated cardiomyocytes provides information on their electrical properties, adaptations to physiological and pathological conditions, and putative ionic mechanisms involved in the process. Currently, there are no available platforms for automated assessment of AP properties and standard methodologies restrict the examination of the AP repolarization to discrete, user-defined ranges, neglecting significant intervals of the electrical recovery. This study proposes two automatic methods to assess AP profile throughout the entire repolarization phase. One method is based on AP data inversion and direct extraction of patterns describing beat-to-beat dynamics. The second method is based on evolutive singular value decomposition (ESVD), which identifies common patterns in a series of consecutive APs. The two methodologies were employed to analyze electrical signals collected from cardiomyocites obtained from healthy mice and animals with diabetes, a condition associated with alterations of AP properties in cardiac cells. Our methodologies revealed that the duration of the early repolarization phase of the AP tended to become progressively longer during a stimulation train, whereas the late repolarization progressively shortened. Although this behavior was comparable in the two groups of cells, alterations in AP dynamics occurred at distinct repolarization levels, a feature highlighted by the ESVD approach. In conclusion, the proposed methodologies allow detailed, automatic analysis of the AP repolarization and identification of critical alterations occurring in the electrical behavior of myocytes under pathological conditions.

Neurosurgical Management of Lateral Meningocele Syndrome: A Clinical Update for the Pediatric Neurosurgeon

BACKGROUND

Lateral meningocele syndrome (LMS) is an exceedingly rare connective tissue disease with phenotypic anomalies similar to those seen in Marfan syndrome, Ehler-Danlos syndrome, and Loeys-Dietz syndrome. However, this syndrome is invariably associated with the presence of multiple lateral thoracolumbar spinal meningoceles: a distinct point of phenotypic divergence from other connective tissue disorders. The etiopathogenesis of this syndrome has recently been linked to truncating mutations within exon 33 of NOTCH3. Despite numerous reports, neurosurgical management of multiple spinal meningoceles remains poorly defined in the literature. We conducted a literature review to provide insight into the nosology, clinical significance, and neurosurgical management strategies of this distinct connective tissue disorder.

SUMMARY

Our literature search revealed 11 articles (16 cases) of LMS, which included 9 males and 7 females, belonging to 14 different families. Half of these cases underwent genetic screening: all of which were discovered to exhibit a truncating mutation within exon 33 of NOTCH3. All patients exhibited multiple lateral thoracolumbar spinal meningoceles with craniofacial dysmorphisms. Other clinical characteristics included pathologic changes in spine morphology, Chiari I malformation, syringomyelia, hydrocephalus, and tethered cord. Operative management of multiple spinal meningoceles in LMS is complicated by the presence of such coexisting structural neurologic pathologies, which may alter cerebrospinal fluid flow dynamics and, ultimately, impact operative intervention. Key Messages: LMS is an exceedingly rare connective tissue disorder with severe spinal dural involvement. Neurosurgical management of multiple spinal meningoceles is complex, which is further complicated by the presence of coexisting neuropathology, such as pathologic transformation of spine morphology and Chiari I malformation. Patients with a connective tissue disorder phenotype found to have multiple spinal meningoceles on imaging studies may benefit from evaluation by a medical geneticist and a pediatric neurosurgeon.

Podoplanin neutralization improves cardiac remodeling and function after acute myocardial infarction

Podoplanin, a small mucine-type transmembrane glycoprotein, has been recently shown to be expressed by lymphangiogenic, fibrogenic and mesenchymal progenitor cells in the acutely and chronically infarcted myocardium. Podoplanin binds to CLEC-2, a C-type lectin-like receptor 2 highly expressed by CD11bhigh cells following inflammatory stimuli. Why podoplanin expression appears only after organ injury is currently unknown. Here, we characterize the role of podoplanin in different stages of myocardial repair after infarction and propose a podoplanin-mediated mechanism in the resolution of post-MI inflammatory response and cardiac repair. Neutralization of podoplanin led to significant improvements in the left ventricular functions and scar composition in animals treated with podoplanin neutralizing antibody. The inhibition of the interaction between podoplanin and CLEC-2 expressing immune cells in the heart enhances the cardiac performance, regeneration and angiogenesis post MI. Our data indicates that modulating the interaction between podoplanin positive cells with the immune cells after myocardial infarction positively affects immune cell recruitment and may represent a novel therapeutic target to augment post-MI cardiac repair, regeneration and function.

Cardiac injections of AntagomiRs as a novel tool for knockdown of miRNAs during heart development

BACKGROUND

Studying microRNA networks during heart development is essential to obtain a better understanding of developmental defects and diseases associated with the heart and to identify novel opportunities for therapeutics. Here we highlight the advantages of chicken embryos as a vertebrate model for studying intermediate processes of heart development. Avians develop a four-chambered heart closely resembling human anatomy and they develop ex utero, which makes them easily accessible. Furthermore, embryos are available all year with a steady supply.

RESULTS

In this report we established a novel method for the knockdown of microRNA function by microinjecting AntagomiRs into the chicken heart in ovo. Our approach enables the targeted delivery of antagomirs into a locally restricted area and is not impacted by circulation. After further embryo development the successful miRNA knockdown was confirmed. Loss of function phenotypes can be evaluated rapidly, compared to more time-consuming genetic ablation experiments. The local application avoids potential systemic effects of microRNA knockdown, therefore allowing the assessment of impacts on heart development only. The method can be adjusted for different stages of chicken embryos (HH13-HH18) as well as for knockdown or targeted overexpression of coding genes.

CONCLUSION

In conclusion our method allows targeted and locally restricted delivery of Antagomirs to the heart leading to successful knockdown of microRNA function. This method enables rapid phenotypic assessment, for example by gene expression analysis of multiple cardiac genes.