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Ricardo E. Dolmetsch - One of the best experts on this subject based on the ideXlab platform.
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aberrant calcium channel splicing drives defects in cortical differentiation in Timothy Syndrome
2019Co-Authors: Sergiu P Pasca, Thomas Portmann, Theo D Palmer, Georgia Panagiotakos, Christos Haveles, Arpana Arjun, Ralitsa Petrova, Anshul Rana, Ricardo E. DolmetschAbstract:The syndromic autism spectrum disorder (ASD) Timothy Syndrome (TS) is caused by a point mutation in the alternatively spliced exon 8A of the calcium channel Cav1.2. Using mouse brain and human induced pluripotent stem cells (iPSCs), we provide evidence that the TS mutation prevents a normal developmental switch in Cav1.2 exon utilization, resulting in persistent expression of gain-of-function mutant channels during neuronal differentiation. In iPSC models, the TS mutation reduces the abundance of SATB2-expressing cortical projection neurons, leading to excess CTIP2+ neurons. We show that expression of TS-Cav1.2 channels in the embryonic mouse cortex recapitulates these differentiation defects in a calcium-dependent manner and that in utero Cav1.2 gain-and-loss of function reciprocally regulates the abundance of these neuronal populations. Our findings support the idea that disruption of developmentally regulated calcium channel splicing patterns instructively alters differentiation in the developing cortex, providing important in vivo insights into the pathophysiology of a syndromic ASD.
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Alteration in basal and depolarization induced transcriptional network in iPSC derived neurons from Timothy Syndrome
2014Co-Authors: Yuan Tian, Ricardo E. Dolmetsch, Sergiu P Pasca, Irina Voineagu, Hyejung Won, Vijayendran Chandran, Steve Horvath, Daniel H GeschwindAbstract:Background Common genetic variation and rare mutations in genes encoding calcium channel subunits have pleiotropic effects on risk for multiple neuropsychiatric disorders, including autism spectrum disorder (ASD) and schizophrenia. To gain further mechanistic insights by extending previous gene expression data, we constructed co-expression networks in Timothy Syndrome (TS), a monogenic condition with high penetrance for ASD, caused by mutations in the L-type calcium channel, Ca_v1.2. Methods To identify patient-specific alterations in transcriptome organization, we conducted a genome-wide weighted co-expression network analysis (WGCNA) on neural progenitors and neurons from multiple lines of induced pluripotent stem cells (iPSC) derived from normal and TS (G406R in CACNA1C) individuals. We employed transcription factor binding site enrichment analysis to assess whether TS associated co-expression changes reflect calcium-dependent co-regulation. Results We identified reproducible developmental and activity-dependent gene co-expression modules conserved in patient and control cell lines. By comparing cell lines from case and control subjects, we also identified co-expression modules reflecting distinct aspects of TS, including intellectual disability and ASD-related phenotypes. Moreover, by integrating co-expression with transcription factor binding analysis, we showed the TS-associated transcriptional changes were predicted to be co-regulated by calcium-dependent transcriptional regulators, including NFAT, MEF2, CREB, and FOXO, thus providing a mechanism by which altered Ca^2+ signaling in TS patients leads to the observed molecular dysregulation. Conclusions We applied WGCNA to construct co-expression networks related to neural development and depolarization in iPSC-derived neural cells from TS and control individuals for the first time. These analyses illustrate how a systems biology approach based on gene networks can yield insights into the molecular mechanisms of neural development and function, and provide clues as to the functional impact of the downstream effects of Ca^2+ signaling dysregulation on transcription.
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alteration in basal and depolarization induced transcriptional network in ipsc derived neurons from Timothy Syndrome
2014Co-Authors: Yuan Tian, Ricardo E. Dolmetsch, Sergiu P Pasca, Irina Voineagu, Hyejung Won, Vijayendran Chandran, Steve Horvath, Daniel H GeschwindAbstract:Common genetic variation and rare mutations in genes encoding calcium channel subunits have pleiotropic effects on risk for multiple neuropsychiatric disorders, including autism spectrum disorder (ASD) and schizophrenia. To gain further mechanistic insights by extending previous gene expression data, we constructed co-expression networks in Timothy Syndrome (TS), a monogenic condition with high penetrance for ASD, caused by mutations in the L-type calcium channel, Cav1.2. To identify patient-specific alterations in transcriptome organization, we conducted a genome-wide weighted co-expression network analysis (WGCNA) on neural progenitors and neurons from multiple lines of induced pluripotent stem cells (iPSC) derived from normal and TS (G406R in CACNA1C) individuals. We employed transcription factor binding site enrichment analysis to assess whether TS associated co-expression changes reflect calcium-dependent co-regulation. We identified reproducible developmental and activity-dependent gene co-expression modules conserved in patient and control cell lines. By comparing cell lines from case and control subjects, we also identified co-expression modules reflecting distinct aspects of TS, including intellectual disability and ASD-related phenotypes. Moreover, by integrating co-expression with transcription factor binding analysis, we showed the TS-associated transcriptional changes were predicted to be co-regulated by calcium-dependent transcriptional regulators, including NFAT, MEF2, CREB, and FOXO, thus providing a mechanism by which altered Ca2+ signaling in TS patients leads to the observed molecular dysregulation. We applied WGCNA to construct co-expression networks related to neural development and depolarization in iPSC-derived neural cells from TS and control individuals for the first time. These analyses illustrate how a systems biology approach based on gene networks can yield insights into the molecular mechanisms of neural development and function, and provide clues as to the functional impact of the downstream effects of Ca2+ signaling dysregulation on transcription.
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state dependent signaling by cav1 2 regulates hair follicle stem cell function
2013Co-Authors: Gozde Yucel, Ricardo E. Dolmetsch, Georgia Panagiotakos, Anshul Rana, Banu Altindag, Natalia Gomezospina, Maria Fernanda Lara, Anthony E OroAbstract:The signals regulating stem cell activation during tissue regeneration remain poorly understood. We investigated the baldness associated with mutations in the voltage-gated calcium channel (VGCC) Cav1.2 underlying Timothy Syndrome (TS). While hair follicle stem cells express Cav1.2, they lack detectable voltage-dependent calcium currents. Cav1.2(TS) acts in a dominant-negative manner to markedly delay anagen, while L-type channel blockers act through Cav1.2 to induce anagen and overcome the TS phenotype. Cav1.2 regulates production of the bulge-derived BMP inhibitor follistatin-like1 (Fstl1), derepressing stem cell quiescence. Our findings show how channels act in nonexcitable tissues to regulate stem cells and may lead to novel therapeutics for tissue regeneration.
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Modeling Timothy Syndrome with iPS Cells
2013Co-Authors: Masayuki Yazawa, Ricardo E. DolmetschAbstract:Genetic mutations in ion channel genes that are associated with cardiac arrhythmias have been identified over the past several decades. However, little is known about the pathophysiological processes. An important limitation has been the difficulty of using human cardiomyocytes to study arrhythmias and identify drugs. To circumvent this issue, we have developed a method using human-induced pluripotent stem cells to generate cardiomyocytes from individuals with Timothy Syndrome (TS), a genetic disorder characterized by QT prolongation, ventricular tachycardia, and autism. The TS ventricular-like cardiomyocytes exhibit deficits in contraction, electrical signaling, and calcium handling, as revealed by live cell imaging and electrophysiological studies. We tested candidate drugs in TS cardiomyocytes and found that roscovitine could successfully rescue these cellular phenotypes. The use of a human cellular model of cardiac arrhythmias provides a useful new platform not only to study disease mechanisms but also to develop new therapies to treat cardiac arrhythmias.
David Chitayat - One of the best experts on this subject based on the ideXlab platform.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is described as an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities, and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet, and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures, and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.
Charles Antzelevitch - One of the best experts on this subject based on the ideXlab platform.
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novel Timothy Syndrome mutation leading to increase in cacna1c window current
2015Co-Authors: Nicole J Boczek, David J Tester, Michael J Ackerman, Charles Antzelevitch, Erin M Miller, Vladislav V Nesterenko, Richard J Czosek, Stephanie M WareAbstract:Background Timothy Syndrome (TS) is a rare multisystem genetic disorder characterized by a myriad of abnormalities, including QT prolongation, syndactyly, and neurologic symptoms. The predominant genetic causes are recurrent de novo missense mutations in exon 8/8A of the CACNA1C- encoded L-type calcium channel; however, some cases remain genetically elusive. Objective The purpose of this study was to identify the genetic cause of TS in a patient who did not harbor a CACNA1C mutation in exon 8/A, and was negative for all other plausible genetic substrates. Methods Diagnostic exome sequencing was used to identify the genetic substrate responsible for our case of TS. The identified mutation was characterized using whole-cell patch-clamp technique, and the results of these analyses were modeled using a modified Luo–Rudy dynamic model to determine the effects on the cardiac action potential. Results Whole exome sequencing revealed a novel CACNA1C mutation, p.Ile1166Thr, in a young male with diagnosed TS. Functional electrophysiologic analysis identified a novel mechanism of TS-mediated disease, with an overall loss of current density and a gain-of-function shift in activation, leading to an increased window current. Modeling studies of this variant predicted prolongation of the action potential as well as the development of spontaneous early afterdepolarizations. Conclusion Through expanded whole exome sequencing, we identified a novel genetic substrate for TS, p.Ile1166Thr-CACNA1C. Electrophysiologic experiments combined with modeling studies have identified a novel TS mechanism through increased window current. Therefore, expanded genetic testing in cases of TS to the entire CACNA1C coding region, if initial targeted testing is negative, may be warranted.
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a cacna1c mutation that causes a subset of Timothy Syndrome phenotypes correlates
2013Co-Authors: Jessica A Hennessey, Charles Antzelevitch, Yonghui Jiang, J D Miller, Harriett A Stadt, W Patrick, Ryan Pfeiffer, Ronald J Kanter, Geoffrey S PittAbstract:Background Timothy Syndrome (TS) is a rare congenital long QT Syndrome (LQTS) associated with extracardiac manifestations including craniofacial dysmorphia and dental abnormalities. The locus for TS is CACNA1C , which encodes the Ca V 1.2 L-type Ca 2+ channel, for which canonical mutations lead to a decrease in voltage-dependent inactivation (VDI). However, a recent report of a patient with LQTS in isolation and a CACNA1C mutation that did not affect VDI raised the question whether altered VDI is necessary for extracardiac phenotypes. In a patient with a maternally inherited microdeletion with a chromosomal translocation who presented with LQTS and associated ventricular tachyarrhythmias (Figure A), a subset of TS phenotypes, and a skeletal myopathy not readily explained by the translocation, we sought to identify a causative mutation for the TS phenotypes. Methods A candidate gene approach identified a mutation in CACNA1C that was absent in the mother. We performed electrophysiologic studies on the mutant and characterized CACNA1C expression in skeletal muscle with a mouse CACNA1C reporter line. Results We identified a glycine to arginine mutation at position 1911 (G1911R) in Ca V 1.2. Functional studies revealed that G1911R increased Ca V 1.2 channel availability (Figures B and C) and decreased VDI (Figure D). The CACNA1C reporter mouse showed no Ca V 1.2 expression in skeletal muscle. Conclusions We describe a CACNA1C mutation that leads to a subset of TS phenotypes. In the context of a recently described CACNA1C mutation that does not affect VDI in an LQTS patient without extracardiac phenotypes, these data suggest that the extracardiac phenotypes seen in TS require effects on VDI.
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case scenario anesthesia related cardiac arrest in a child with Timothy Syndrome
2012Co-Authors: Aruna Nathan, Charles Antzelevitch, Lisa M Montenegro, Victoria L VetterAbstract:The long QT Syndrome (LQTS) is characterized by prolonged ventricular repolarization, the electrocardiographic appearance of long QT intervals, an atypical polymorphic ventricular tachycardia known as torsades de pointes (TdP), and an increased risk for sudden cardiac death. Patients with LQTS can suffer severe cardiac events resulting in syncope, seizures, and sudden cardiac death during times of physical and emotional stress and when exposed to certain pharmacological agents. The perioperative management of patients with LQTS has been reviewed1,2; however, the individual risk posed by exposure to perioperative and anesthetic medications and interventions has not been quantified by prospective studies.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is described as an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities, and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet, and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures, and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.
Masayuki Yazawa - One of the best experts on this subject based on the ideXlab platform.
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Timothy Syndrome ipsc modeling
2020Co-Authors: Ramsey Bekdash, Alison D Klein, Masayuki YazawaAbstract:L-type voltage-gated calcium channels play an essential role in various physiological systems including neuronal excitation and any mutation or dysfunction in the channel has significant impact on human brain function resulting in psychiatric diseases. Particular gain-of-function mutations in CACNA1C encoding CaV1.2 have been associated with Timothy Syndrome, a devastating disease with a multi-organ phenotype. Efforts to understand the underlying pathophysiology and find therapeutic strategy have been spurred recently with the advances in stem cell technology, in particular those arising from patient-derived sources. In this review, we report on the recent advances in Timothy Syndrome research and on the methods used to study this disease.
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inhibition of cdk5 alleviates the cardiac phenotypes in Timothy Syndrome
2017Co-Authors: Loujin Song, Seonhye E Park, Yehuda Isseroff, Kumi Morikawa, Masayuki YazawaAbstract:L-type calcium channel CaV1.2 plays an essential role in cardiac function. The gain-of-function mutations in CaV1.2 have been reported to be associated with Timothy Syndrome, a disease characterized by QT prolongation and syndactyly. Previously we demonstrated that roscovitine, a cyclin-dependent kinase (CDK) inhibitor, could rescue the phenotypes in induced pluripotent stem cell-derived cardiomyocytes from Timothy Syndrome patients. However, exactly how roscovitine rescued the phenotypes remained unclear. Here we report a mechanism potentially underlying the therapeutic effects of roscovitine on Timothy Syndrome cardiomyocytes. Our results using roscovitine analogs and CDK inhibitors and constructs demonstrated that roscovitine exhibits its therapeutic effects in part by inhibiting CDK5. The outcomes of this study allowed us to identify a molecular mechanism whereby CaV1.2 channels are regulated by CDK5. This study provides insights into the regulation of cardiac calcium channels and the development of future therapeutics for Timothy Syndrome patients.
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Using iPS cell-derived neurons to uncover cellular phenotypes associated with Timothy Syndrome
2016Co-Authors: Sergiu P Pasca, Masayuki Yazawa, Thomas Portmann, Irina Voineagu, Anca M Pasca, Theo D Palmer, Sachiko Chikahisa, En Cord, Nishino Seiji, Jonathan A BernsteinAbstract:Monogenic neurodevelopmental disorders provide key insights into the pathogenesis of disease and help us understand how specific genes control the development of the human brain. Timothy Syndrome is caused by a missense mutation in the L-type calcium channel Cav1.2 that is associated with developmental delay and autism 1. We generated cortical neuronal precursor cells and neurons from induced pluripotent stem cells derived from individuals with Timothy Syndrome. Cells from these individuals have defects in calcium (Ca2+) signaling and activity-dependent gene expression. They also show abnormalities in differentiation, including decreased expression of genes that are expressed in lower cortical layers and in callosal projection neurons. In addition, neurons derived from individuals with Timothy Syndrome show abnormal expression of tyrosine hydroxylase and increased production of norepinephrine and dopamine. This phenotype can be reversed by treatment with roscovitine, a cyclin-dependent kinase inhibitor and atypical L-type–channel blocker 2, 3, 4. These findings provide strong evidence that Cav1.2 regulates the differentiation of cortical neurons in humans and offer new insights into the causes of autism in individuals with Timothy Syndrome
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Modeling Timothy Syndrome with iPS Cells
2013Co-Authors: Masayuki Yazawa, Ricardo E. DolmetschAbstract:Genetic mutations in ion channel genes that are associated with cardiac arrhythmias have been identified over the past several decades. However, little is known about the pathophysiological processes. An important limitation has been the difficulty of using human cardiomyocytes to study arrhythmias and identify drugs. To circumvent this issue, we have developed a method using human-induced pluripotent stem cells to generate cardiomyocytes from individuals with Timothy Syndrome (TS), a genetic disorder characterized by QT prolongation, ventricular tachycardia, and autism. The TS ventricular-like cardiomyocytes exhibit deficits in contraction, electrical signaling, and calcium handling, as revealed by live cell imaging and electrophysiological studies. We tested candidate drugs in TS cardiomyocytes and found that roscovitine could successfully rescue these cellular phenotypes. The use of a human cellular model of cardiac arrhythmias provides a useful new platform not only to study disease mechanisms but also to develop new therapies to treat cardiac arrhythmias.
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Timothy Syndrome is associated with activity-dependent dendritic retraction in rodent and human neurons.
2013Co-Authors: Jocelyn F Krey, Aleksandr Shcheglovitov, Masayuki Yazawa, Sergiu Pasca, Rachel Schwemberger, Randall L. Rasmusson, Ricardo E. DolmetschAbstract:L-type voltage gated calcium channels have an important role in neuronal development by promoting dendritic growth and arborization. A point mutation in the gene encoding Ca(V)1.2 causes Timothy Syndrome, a neurodevelopmental disorder associated with autism spectrum disorders (ASDs). We report that channels with the Timothy Syndrome alteration cause activity-dependent dendrite retraction in rat and mouse neurons and in induced pluripotent stem cell (iPSC)-derived neurons from individuals with Timothy Syndrome. Dendrite retraction was independent of calcium permeation through the mutant channel, was associated with ectopic activation of RhoA and was inhibited by overexpression of the channel-associated GTPase Gem. These results suggest that Ca(V)1.2 can activate RhoA signaling independently of Ca(2+) and provide insights into the cellular basis of Timothy Syndrome and other ASDs.
Jane Gillis - One of the best experts on this subject based on the ideXlab platform.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is described as an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.
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long qt syndactyly joint contractures stroke and novel cacna1c mutation expanding the spectrum of Timothy Syndrome
2012Co-Authors: Jane Gillis, Charles Antzelevitch, Elena Burashnikov, Susan Blaser, Gil J Gross, Lesley Turner, Riyana Babulhirji, David ChitayatAbstract:Timothy Syndrome (TS) is an autosomal dominant condition with the constellation of features including prolonged QT interval, hand and foot abnormalities, and mental retardation or autism. Splawski et al. [2004] previously described two phenotypes associated with TS distinguished by two unique and different mutations within the CACNA1C gene. We report on a newborn who presented with prolonged QT interval and associated polymorphic ventricular tachycardia, dysmorphic facial features, syndactyly of the hands and feet, and joint contractures, suggestive of TS. He developed a stroke, subsequent intractable seizures, and was found to have cortical blindness and later profound developmental delay. Initial targeted mutation analysis did not identify either of the previously described TS associated mutations; however, full gene sequencing detected a novel CACNA1C gene mutation (p.Ala1473Gly). The clinical and genetic findings in our case expand both the clinical and molecular knowledge of TS.