Sian Harding

Publications (3)17.73 Total impact

• Article: Investigation of a transgenic mouse model of familial dilated cardiomyopathy.

  Weihua Song, Emma Dyer, Daniel Stuckey, Man-Ching Leung, Massimiliano Memo, Catherine Mansfield, Michael Ferenczi, Ke Liu, Charles Redwood, Kristen Nowak, Sian Harding, Kieran Clarke, Dominic Wells, Steven Marston
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  ABSTRACT: We have investigated a transgenic mouse model of inherited dilated cardiomyopathy that stably expresses the ACTC E361G mutation at around 50% of total actin in the heart. F-actin isolated from ACTC E361G mouse hearts was incorporated into thin filaments with native human tropomyosin and troponin and compared with NTG mouse actin by in vitro motility assay. There was no significant difference in sliding speed, fraction of filaments motile or Ca(2+)-sensitivity (ratio EC(50) E361G/NTG=0.95+/-0.08). The Ca(2+)-sensitivity of force in skinned trabeculae from ACTC E361G mice was slightly higher than NTG (EC(50) E361G/NTG=0.78+/-0.04). The molecular phenotype was revealed when troponin was dephosphorylated; Ca(2+)-sensitivity of E361G-containing thin filaments was now lower than NTG (EC(50) E361G(dPTn)/NTG(dPTn)=2.15+/-0.09). We demonstrated that this was due to uncoupling of Ca(2+)-sensitivity from troponin I phosphorylation by comparing Ca(2+)-sensitivity of phosphorylated and dephosphorylated thin filaments. For NTG actin-containing thin filaments EC(50) native/dPTn=3.0+/-0.3 but for E361G-containing thin filaments EC(50) native/dPTn=1.04+/-0.07.We studied contractility in isolated myocytes and found no significant differences under basal conditions. We measured cardiac performance by cine-MRI, echocardiography and with a conductance catheter over a period of 4 to 18 months and found minimal systematic differences between NTG and ACTC E361G mice under basal conditions. However, the increase in septal thickening, ejection fraction, heart rate and cardiac output following dobutamine treatment was significantly less in ACTC E361G mice compared with NTG. We propose that the ACTC E361G mutation uncouples myofilament Ca(2+)-sensitivity from Troponin I phosphorylation and blunts the response to adrenergic stimulation, leading to a reduced cardiac reserve with consequent contractile dysfunction under stress, leading to dilated cardiomyopathy.
  Journal of Molecular and Cellular Cardiology 09/2010; 49(3):380-9. · 5.17 Impact Factor
• Article: The potential of cardiac stem cell therapy for heart failure.

  Alexander Lyon, Sian Harding
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  ABSTRACT: Cardiac failure is characterised by the loss of cardiomyocytes, and several strategies to replace the lost cell mass are being developed. Animal models have demonstrated the therapeutic potential of several cell types, and both autologous skeletal myoblasts and bone marrow progenitor cells have been tested in preliminary clinical trials. However functional improvements have been modest and the mechanism of benefit is unclear, although myocardial regeneration is not a significant factor. Alternative strategies using autologous resident cardiac progenitor cells or embryonic stem cell-derived cardiomyocytes could recreate de novo myocardium with higher efficiency, although various hurdles must be overcome before these strategies are translated to the clinic.
  Current Opinion in Pharmacology 05/2007; 7(2):164-70. · 6.86 Impact Factor
• Article: Overexpression of wild-type Galpha(i)-2 suppresses beta-adrenergic signaling in cardiac myocytes.

  Thomas Rau, Monika Nose, Ute Remmers, Joachim Weil, Astrid Weissmüller, Kerry Davia, Sian Harding, Karsten Peppel, Walter J Koch, Thomas Eschenhagen
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  ABSTRACT: The role of Galpha(i)-2 overexpression in desensitization of beta-adrenergic signaling in heart failure is controversial. An adenovirus-based approach was used to investigate whether overexpression of Galpha(i)-2 impairs beta-adrenergic stimulation of adenylyl cyclase (AC) activity and cAMP levels in neonatal rat cardiac myocytes (NRCM) and cell shortening of adult rat ventricular myocytes (ARVM). Infection of NRCM with Ad5Galpha(i)-2 increased Galpha(i)-2 by 50-600% in a virus dose-dependent manner. Overexpression was paralleled by suppression of GTP- and isoprenaline-stimulated AC by 10-72% (P<0.001) in a PTX-sensitive manner. Isoprenaline-stimulated shortening of Ad5Galpha(i)-2-infected ARVM was attenuated by 34% (P<0.01). Ad5Galpha(i)-2/GFP (Galpha(i)-2, green fluorescent protein; bicistronic) was constructed to monitor transfection homogeneity and target Galpha(i)-2 overexpression to levels found in heart failure. At Galpha(i)-2 levels of 93% above control, isoprenaline-stimulated AC activity and cAMP levels were reduced by 17% and 40% (P<0.02), respectively. Beta1- and beta2-adrenergic stimulation was reduced similarly. Our results suggest that (a) the Galpha(i)-2 system exhibits tonic inhibition of stimulated AC in cardiac myocytes, (b) Galpha(i)-2-mediated inhibition is concentration-dependent and occurs at Galpha(i)-2 levels seen in heart failure, and (c) Galpha(i)-2-mediated inhibition affects both beta1- and beta2-adrenergic stimulation of AC. The data argue for an important, independent role of the Galpha(i)-2 increase in heart failure.
  The FASEB Journal 03/2003; 17(3):523-5. · 5.71 Impact Factor