Michael Gotthardt

Universitätsklinikum Tübingen, Tübingen, Baden-Württemberg, Germany

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Publications (58)429.67 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: ShcA (Src Homology and Collagen A) is an adaptor protein that binds to tyrosine kinase receptors. Its germ line deletion is embryonic lethal with abnormal cardiovascular system formation, and its role in cardiovascular development is unknown. To investigate its functional role in cardiovascular development in mice, ShcA was deleted in cardiomyocytes and vascular smooth muscle cells by crossing ShcA flox mice with SM22a-Cre transgenic mice. Conditional mutant mice developed signs of severe dilated cardiomyopathy, myocardial infarctions, and premature death. No evidence of a vascular contribution to the phenotype was observed. Histological analysis of the heart revealed aberrant sarcomeric Z-disk and M-band structures, and misalignments of T-tubules with Z-disks. We find that not only the ErbB3/Neuregulin signaling pathway but also the baroreceptor reflex response, which have been functionally associated, are altered in the mutant mice. We further demonstrate that ShcA interacts with Caveolin-1 and the costameric protein plasma membrane Ca2+/calmodulin-dependent ATPase (PMCA), and that its deletion leads to abnormal dystrophin signaling. Collectively, these results demonstrate that ShcA interacts with crucial proteins and pathways that link Z-disk and costamere. Copyright © 2014, The American Society for Biochemistry and Molecular Biology.
    The Journal of biological chemistry. 12/2014;
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    ABSTRACT: Congenital core myopathies (CM) remain genetically unexplained in many cases. Heart disease is not considered part of the typical CM spectrum. Childhood-onset dilated cardiomyopathy (DCM) was reported in two families with minicores and homozygous TTN mutations. TTN encodes the giant sarcomere protein titin. Relatively few titin mutations (mostly heterozygous and associated to adult-onset cardiac or skeletal muscle disease) have been reported, TTN size and complexity precluding full screening before NGS. Thus, the prevalence and spectrum of titinopathies is probably underestimated. Here we report the analysis of 23 families with CM and primary heart disease using TTN M-line targeted sequencing followed in selected patients by whole-exome sequencing and functional studies. We found 7 novel homozygous or compound heterozygous TTN mutations (5 in the M-line, 5 truncating) in 5 patients. All heterozygous parents were healthy. We identified 4 novel phenotypes previously unreported or non-associated with TTN, including several congenital cardiopathies. The first antenatal-onset titinopathy presented with multi-minicore disease (MmD), arthrogryposis, left ventricular non-compaction and ventricular septal defect, and was associated with the first-reported absence of a functional titin kinase domain in humans. Other novel phenotypes associate MmD with auricular and/or ventricular septal defects, Rigid Spine, Emery-Dreifuss phenotype and/or adult-onset DCM. The histological pattern consistently showed minicores, central nuclei and structural lesions. Conversely, the spectrum of severity and heart disease was large. Thus, we demonstrate that TTN M-line truncating mutations are typically recessive and represent a significant cause of MmD with heart disease. Our results represent the first series of recessive titinopathies, expand TTN mutational and phenotypic spectrum, and identify TTN as a candidate gene in arthrogryposis, EDMD and pediatric heart defects.
    Neuromuscular Disorders 10/2014; 24(s 9–10):804–805. · 3.46 Impact Factor
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    ABSTRACT: Cardiac titin is the main determinant of sarcomere stiffness during diastolic relaxation. To explore whether titin stiffness affects the kinetics of cardiac myofibrillar contraction and relaxation, we used subcellular myofibrils from left ventricles of homozygous (KO) and heterozygous (HET) N2B-KO mice which express truncated cardiac titins lacking the unique elastic N2B region. Compared to myofibrils from wildtype (WT) mice, myofibrils from KO and HET mice exhibit increased passive myofibrillar stiffness. To determine the kinetics of Ca(2+)-induced force development (rate constant kACT), myofibrils from KO, HET and WT mice were stretched to the same sarcomere length (2.3 µm) and rapidly Ca(2+) activated. Additionally, mechanically-induced force redevelopment kinetics (rate constant kTR) was determined by slackening and re-stretching myofibrils during Ca(2+) activation. Myofibrils from KO mice exhibited significant higher kACT, kTR and maximum Ca(2+) activated tension than myofibrils from WT. In contrast, the kinetic parameters of biphasic force relaxation induced by rapidly reducing [Ca(2+)] were not significantly different among the three genotypes. These results indicate that increased titin stiffness promotes myocardial contraction by accelerating the formation of force-generating cross-bridges without decelerating relaxation.
    Journal of cell science. 06/2014;
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    ABSTRACT: Mutations in the gene encoding the RNA-binding protein RBM20 have been implicated in dilated cardiomyopathy (DCM), a major cause of chronic heart failure, presumably through altering cardiac RNA splicing. Here, we combined transcriptome-wide crosslinking immunoprecipitation (CLIP-seq), RNA-seq, and quantitative proteomics in cell culture and rat and human hearts to examine how RBM20 regulates alternative splicing in the heart. Our analyses revealed the presence of a distinct RBM20 RNA-recognition element that is predominantly found within intronic binding sites and linked to repression of exon splicing with RBM20 binding near 3' and 5' splice sites. Proteomic analysis determined that RBM20 interacts with both U1 and U2 small nuclear ribonucleic particles (snRNPs) and suggested that RBM20-dependent splicing repression occurs through spliceosome stalling at complex A. Direct RBM20 targets included several genes previously shown to be involved in DCM as well as genes not typically associated with this disease. In failing human hearts, reduced expression of RBM20 affected alternative splicing of several direct targets, indicating that differences in RBM20 expression may affect cardiac function. Together, these findings identify RBM20-regulated targets and provide insight into the pathogenesis of human heart failure.
    The Journal of clinical investigation. 06/2014;
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    ABSTRACT: The coxsackievirus and adenovirus receptor (CAR) is a cell contact protein with an important role in virus uptake. Its extracellular immunoglobulin domains mediate the binding to coxsackie and adenoviruses as well as homophilic and heterophilic interactions between cells. The cytoplasmic tail links CAR to the cytoskeleton and intracellular signaling cascades. In the heart, CAR is crucial for embryonic development, electrophysiology, and coxsackievirus B infection. Non-cardiac functions are less well understood, in part due to the lack of suitable animal models. Here we generated a transgenic mouse that rescued the otherwise embryonic lethal CAR-knockout (KO) phenotype by expressing chicken CAR exclusively in the heart. Using this rescue model we addressed interspecies differences in coxsackievirus uptake and non-cardiac functions of CAR. Survival of the non-cardiac CAR KO mouse (ncKO) indicates an essential role for CAR in the developing heart, but not in other tissues. In adult animals cardiac activity was normal, suggesting that chicken CAR can replace the physiological functions of mouse CAR in the cardiomyocyte. However, chicken CAR did not mediate virus entry in vivo so that hearts expressing chicken- instead of mouse CAR were protected from infection and myocarditis. Comparison of sequence homology and modeling of the D1 domain indicate differences between mammalian and chicken CAR that relate to the sites important for virus binding but not those involved in homodimerization. Thus, CAR-directed anti-coxsackieviral therapy with only minor adverse effects in non-cardiac tissue could be further improved by selectively targeting the virus-host interaction while maintaining cardiac function. Coxsackievirus B3 (CVB3) is one of the most common human pathogens causing myocarditis. Its receptor CAR does not only mediate virus uptake but also relates to cytoskeletal organization and intracellular signaling. Animals without CAR die prenatally with major cardiac malformations. In the adult heart CAR is important for virus entry and electrical conduction, but its non-muscle functions are largely unknown. Here we show that chicken CAR expression exclusively in the heart can rescue the otherwise embryonic lethal CAR knockout phenotype but does not support CVB3 infection of adult cardiomyocytes. Our findings have implication for the evolution of virus/host versus physiological interactions involving CAR and could help to improve future coxsackievirus directed therapies inhibiting virus replication while maintaining CAR's cellular functions.
    Journal of Virology 04/2014; · 5.08 Impact Factor
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    ABSTRACT: Core myopathies (CM), the main non-dystrophic myopathy in childhood, remain genetically unexplained in many cases. Heart disease is not considered part of the typical CM spectrum. No congenital heart defect has been reported, and childhood-onset cardiomyopathy has been documented in only two CM families with homozygous mutations of the TTN gene. TTN encodes titin, a giant protein of striated muscles. Recently, heterozygous TTN truncating mutations have also been reported as a major cause of dominant dilated cardiomyopathy. However, relatively few TTN mutations and phenotypes are known, and titin pathophysiological role in cardiac and skeletal muscle conditions is incompletely understood.We analyzed a series of 23 families with congenital CM and primary heart disease using TTN M-line targeted sequencing followed in selected patients by whole-exome sequencing and functional studies. We identified 7 novel homozygous or compound-heterozygous TTN mutations (5 in the M-line, 5 truncating) in 17% patients. Heterozygous parents were healthy. Phenotype analysis identified four novel titinopathies, including cardiac septal defects, left ventricular non-compaction, Emery-Dreifuss muscular dystrophy or arthrogryposis. Additionally, in vitro studies documented the first-reported absence of the titin kinase domain in humans, leading to a severe antenatal phenotype.We establish that CM are associated with a large range of heart conditions of which TTN mutations are a major cause, thereby expanding TTN mutational and phenotypic spectrum. Additionally, our results suggest titin kinase implication in cardiac morphogenesis and demonstrate that heterozygous TTN truncating mutations may not manifest unless associated with a second mutation, reassessing the paradigm of their dominant expression.
    Human Molecular Genetics 10/2013; · 7.69 Impact Factor
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    ABSTRACT: Objectives To investigate the modulatory effect of the Coxsackie and adenovirus receptor (CAR) on ventricular conduction and arrhythmia vulnerability in the setting of myocardial ischemia. Background A heritable component in risk for ventricular fibrillation (VF) during myocardial infarction (MI) has been well established. A recent genome-wide association study (GWAS) for VF during acute MI has led to the identification of a locus on chromosome 21q21 (rs2824292) in the vicinity of the CXADR gene. CXADR encodes the coxsackie and adenovirus receptor (CAR), a cell adhesion molecule predominantly located at intercalated discs of the cardiomyocyte. Methods The correlation between CAR transcript levels and rs2824292 genotype was investigated in human left ventricular samples. Electrophysiological studies and molecular analyses were performed CAR haploinsufficient mice (CAR+/-). Results In human left ventricular samples, the risk allele at the chr21q21 GWAS locus was associated with lower CXADR mRNA levels, suggesting that decreased cardiac levels of CAR predispose to ischemia-induced VF. Hearts from CAR+/- mice displayed ventricular conduction slowing in addition to an earlier onset of ventricular arrhythmias during the early phase of acute myocardial ischemia following LAD ligation. Connexin43 expression and distribution was unaffected, but CAR+/- hearts displayed increased arrhythmia susceptibility upon pharmacological electrical uncoupling. Patch-clamp analysis of isolated CAR+/- myocytes showed reduced sodium current magnitude specifically at the intercalated disc. Moreover, CAR co-precipitated with NaV1.5 in vitro, suggesting that CAR affects sodium channel function through a physical interaction with NaV1.5. Conclusion We identify CAR as a novel modifier of ventricular conduction and arrhythmia vulnerability in the setting of myocardial ischemia. Genetic determinants of arrhythmia susceptibility (such as CAR) may constitute future targets for risk stratification of potentially lethal ventricular arrhythmias in patients with coronary artery disease
    Journal of the American College of Cardiology 01/2013; · 14.09 Impact Factor
  • Biophysical Journal 01/2013; 104(2):310-. · 3.67 Impact Factor
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    ABSTRACT: The cellular basis of the Frank-Starling "Law of the Heart" is the length-dependence of activation, but the mechanisms by which the sarcomere detects length changes and converts this information to altered calcium sensitivity has remained elusive. Here the effect of titin-based passive tension on the length-dependence of activation (LDA) was studied by measuring the tension-pCa relation in skinned mouse LV muscle at two sarcomere lengths (SLs). N2B KO myocardium, where the N2B spring element in titin is deleted and passive tension is elevated, was compared to WT myocardium. Myofilament lattice structure was studied with low-angle X-ray diffraction; the myofilament lattice spacing (d(10)) was measured as well as the ratio of the intensities of the 1,1 and 1,0 diffraction peaks (I(11)/I(10)) as an estimate of the degree of association of myosin heads with the thin filaments. Experiments were carried out in skinned muscle in which the lattice spacing was reduced with Dextran-T500. Experiments with and without lattice compression were also carried out following PKA phosphorylation of the skinned muscle. Under all conditions that were tested, LDA was significantly larger in N2B KO myocardium compared to WT myocardium, with the largest differences following PKA phosphorylation. A positive correlation between passive tension and LDA was found that persisted when the myofilament lattice was compressed with Dextran and that was enhanced following PKA phosphorylation. Low-angle X-ray diffraction revealed a shift in mass from thin filaments to thick filaments as sarcomere length was increased. Furthermore, a positive correlation was obtained between myofilament lattice spacing and passive tension and the change in I(11)/I(10) and passive tension and these provide possible explanations for how titin-based passive tension might regulate calcium sensitivity.
    Archives of Biochemistry and Biophysics 12/2012; · 3.37 Impact Factor
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    ABSTRACT: Alternative splicing has a major role in cardiac adaptive responses, as exemplified by the isoform switch of the sarcomeric protein titin, which adjusts ventricular filling. By positional cloning using a previously characterized rat strain with altered titin mRNA splicing, we identified a loss-of-function mutation in the gene encoding RNA binding motif protein 20 (Rbm20) as the underlying cause of pathological titin isoform expression. The phenotype of Rbm20-deficient rats resembled the pathology seen in individuals with dilated cardiomyopathy caused by RBM20 mutations. Deep sequencing of the human and rat cardiac transcriptome revealed an RBM20-dependent regulation of alternative splicing. In addition to titin (TTN), we identified a set of 30 genes with conserved splicing regulation between humans and rats. This network is enriched for genes that have previously been linked to cardiomyopathy, ion homeostasis and sarcomere biology. Our studies emphasize the key role of post-transcriptional regulation in cardiac function and provide mechanistic insights into the pathogenesis of human heart failure.
    Nature medicine 04/2012; 18(5):766-73. · 27.14 Impact Factor
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    ABSTRACT: Titin (also known as connectin) is an intrasarcomeric muscle protein that functions as a molecular spring and generates passive tension upon muscle stretch. The N2B element is a cardiac-specific spring element within titin's extensible region. Our goal was to study the contribution of the N2B element to the mechanical properties of titin, particularly its hypothesized role in limiting energy loss during repeated stretch (diastole)-shortening (systole) cycles of the heart. We studied energy loss by measuring hysteresis from the area between the stretch and release passive force-sarcomere length curves and used both wild-type (WT) mice and N2B knockout (KO) mice in which the N2B element has been deleted. A range of protocols was used, including those that mimic physiological loading conditions. KO mice showed significant increases in hysteresis. Most prominently, in tissue that had been preconditioned with a physiological stretch-release protocol, hysteresis increased significantly from 320 ± 46 pJ/mm(2)/sarcomere in WT to 650 ± 94 pJ/mm(2)/sarcomere in N2B KO myocardium. These results are supported by experiments in which oxidative stress was used to mechanically inactivate portions of the N2B-Us of WT titin through cysteine cross-linking. Studies on muscle from which the thin filaments had been extracted (using the actin severing protein gelsolin) showed that the difference in hysteresis between WT and KO tissue cannot be explained by filament sliding-based viscosity. Instead the results suggest that hysteresis arises from within titin and most likely involves unfolding of immunoglobulin-like domains. These studies support that the mechanical function of the N2B element of titin includes reducing hysteresis and increasing the efficiency of the heart.
    Biophysical Journal 09/2011; 101(6):1385-92. · 3.67 Impact Factor
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    ABSTRACT: Viscosity is proposed to modulate diastolic function, but only limited understanding of the source(s) of viscosity exists. In vitro experiments have shown that the proline-glutamic acid-valine-lysine (PEVK) rich element of titin interacts with actin, causing a viscous force in the sarcomere. It is unknown whether this mechanism contributes to viscosity in vivo. We tested the hypothesis that PEVK-actin interaction causes cardiac viscosity and is important in vivo via an integrative physiological study on a unique PEVK knockout (KO) model. Both skinned cardiomyocytes and papillary muscle fibers were isolated from wildtype (WT) and PEVK KO mice and passive viscosity was examined using stretch-hold-release and sinusoidal analysis. Viscosity was reduced by ~60% in KO myocytes and ~50% in muscle fibers at room temperature. The PEVK-actin interaction was not modulated by temperature or diastolic calcium, but was increased by lattice compression. Stretch-hold and sinusoidal frequency protocols on intact isolated mouse hearts showed a smaller, 30-40% reduction in viscosity, possibly due to actomyosin interactions, and showed that microtubules did not contribute to viscosity. Transmitral Doppler echocardiography similarly revealed a 40% decrease in LV chamber viscosity in the PEVK KO in vivo. This integrative study is the first to quantify the influence of a specific molecular (PEVK-actin) viscosity in vivo and shows that PEVK-actin interactions are an important physiological source of viscosity.
    Journal of Molecular and Cellular Cardiology 06/2011; 51(3):428-34. · 5.15 Impact Factor
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    ABSTRACT: The giant muscle protein titin is an essential structural component of the sarcomere. It forms a continuous periodic backbone along the myofiber that provides resistance to mechanical strain. Thus, the titin filament has been regarded as a blueprint for sarcomere assembly and a prerequisite for stability. Here, a novel titin-eGFP knockin mouse provided evidence that sarcomeric titin is more dynamic than previously suggested. To study the mobility of titin in embryonic and neonatal cardiomyocytes, we used fluorescence recovery after photobleaching and investigated the contribution of protein synthesis, contractility, and calcium load to titin motility. Overall, the kinetics of lateral and longitudinal movement of titin-eGFP were similar. Whereas protein synthesis and developmental stage did not alter titin dynamics, there was a strong, inhibitory effect of calcium on titin mobility. Our results suggest a model in which the largely unrestricted movement of titin within and between sarcomeres primarily depends on calcium, suggesting that fortification of the titin filament system is activity dependent.
    The Journal of Cell Biology 05/2011; 193(4):785-98. · 10.82 Impact Factor
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    ABSTRACT: Cardiac muscle expresses predominantly larger N2BA titin isoforms at embryonic and prenatal stages of development, and these are mostly replaced with a smaller N2B isoform in adults. We have previously discovered a mutation in rats that dramatically alters titin splicing (Greaser et al J Mol Cell Cardiol 44:982, 2008). To determine the mechanism responsible for this change in titin splicing, we performed genetic linkage analysis with 191 animals from two different backcrosses. The titin splicing factor mutation was mapped to the long arm of chromosome 1 using a 10K SNP chip. PCR verified that the mutation occurs as a large deletion of an RS type splicing factor. The deletion was further verified by Southern blot, qPCR, and western blot analysis. Immunofluorescence staining of cardiomyocytes and HL1 cells indicated that the splicing factor was localized in the nucleus. Insertion of adenovirus constructs of the factor into homozygous mutant cardiomyocytes restored wild type titin splicing. The mutant rats show significantly larger left ventricle (LV) diameter in diastole and lower ejection fractions. Heart rate response to dobutamine was blunted in both heterozygote and homozygote mutants compared to wild type. Histological observations after Masson trichrome staining showed that fibrosis was significantly increased in LV from the same groups as compared to wild type hearts. An increased percentage in sudden death occurred in heterozygotes and homozygous mutants after 10 months of age. The splicing factor is mainly expressed in cardiac muscle and skeletal muscle as determined by Western blotting. Although heterozygote and homozygote mutants survive and reproduce, the titin splicing factor is required for normal cardiac structure and function. Supported by NIH HL77196.
    Biophysical Journal 03/2011; 100(3):287a. · 3.67 Impact Factor
  • Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • Joshua Nedrud, Michael Gotthardt, Henk Granzier
    Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
  • Biophysical Journal 01/2011; 100(3). · 3.67 Impact Factor
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    ABSTRACT: Previous work suggests that titin-based passive tension is a factor in the Frank-Starling mechanism of the heart, by increasing length-dependent activation (LDA) through an increase in calcium sensitivity at long sarcomere length. We tested this hypothesis in a mouse model (N2B KO model) in which titin-based passive tension is elevated as a result of the excision of the N2B element, one of cardiac titin's spring elements. LDA was assessed by measuring the active tension-pCa (-log[Ca(2+)]) relationship at sarcomere length (SLs) of 1.95, 2.10, and 2.30 microm in WT and N2B KO skinned myocardium. LDA was positively correlated with titin-based passive tension due to an increase in calcium sensitivity at the longer SLs in the KO. For example, at pCa 6.0, the KO:WT tension ratio was 1.28+/-0.07 and 1.42+/-0.04 at SLs of 2.1 and 2.3 microm, respectively. There was no difference in protein expression or total phosphorylation of sarcomeric proteins. We also measured the calcium sensitivity after PKA treating the skinned muscle and found that titin-based passive tension was also now correlated with LDA, with a slope that was significantly increased compared to no PKA treatment. Finally, we performed isolated heart experiments and measured the Frank-Starling relation (slope of developed wall stress-LV volume relation) as well as diastolic stiffness (slope of diastolic wall stress-volume relation). The FSM was more pronounced in the N2B KO hearts and the slope of the FSM correlated with diastolic stiffness. These findings support that titin-based passive tension triggers an increase in calcium sensitivity at long sarcomere length, thereby playing an important role in the Frank-Starling mechanism of the heart.
    Journal of Molecular and Cellular Cardiology 09/2010; 49(3):449-58. · 5.15 Impact Factor
  • Biophysical Journal 01/2010; 98(3). · 3.67 Impact Factor
  • Joshua Nedrud, Michael Gotthardt, Henk Granzier
    Biophysical Journal 01/2010; 98(3). · 3.67 Impact Factor

Publication Stats

3k Citations
429.67 Total Impact Points

Institutions

  • 2014
    • Universitätsklinikum Tübingen
      • Division of Molecular Pathology
      Tübingen, Baden-Württemberg, Germany
  • 2006–2014
    • Max-Delbrück-Centrum für Molekulare Medizin
      • Research Team Neuromuscular and Cardiovascular Cell Biology
      Berlín, Berlin, Germany
  • 2012
    • University of Wisconsin, Madison
      • Muscle Biology Laboratory
      Madison, MS, United States
  • 2009–2012
    • The University of Arizona
      • Department of Physiology
      Tucson, AZ, United States
    • Max Planck Institute of Molecular Cell Biology and Genetics
      Dresden, Saxony, Germany
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 2008
    • Institut für Pharmakologie und Toxikologie der Bundeswehr
      München, Bavaria, Germany
  • 2003–2007
    • Washington State University
      • Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology (VCAPP)
      Pullman, WA, United States
    • University of Texas at Dallas
      Richardson, Texas, United States
  • 2004
    • University of Strasbourg
      Strasburg, Alsace, France
  • 1996–2003
    • University of Texas Southwestern Medical Center
      • Department of Molecular Genetics
      Dallas, TX, United States
  • 1998
    • Howard Hughes Medical Institute
      Ashburn, Virginia, United States