MYOCARDIAL DYSFUNCTION IN HYPERTROPHIC CARDIOMYOPATHY: PRIMARY EFFECTS OF SARCOMERIC MUTATIONS VERSUS SECONDARY EC-COUPLING REMODELLING.

Raffaele Coppini1, Cecilia Ferrantini2, Francesca Gentile2, Luca Mazzoni1, Benedetta Tosi2, Manuel J. Pioner1, Beatrice Scellini2, Nicoletta Piroddi2, Jil C. Tardiff3, Chiara Tesi2, Elisabetta Cerbai1, Corrado Poggesi2. 1University of Florence, Firenze, Italy 2University of Arizona, Tucson, USA.

In cardiac muscle from HCM patients primary changes in myofilament function, related to the presence of disease-causing mutations in sarcomeric proteins, are always associated with secondary abnormalities due to adverseremodeling of cardiomyocyte EC-coupling(Coppini et al,Circulation 2013). The latter are likely major contributorsof the mechanical dysfunction and arrhythmogeneity of HCM human hearts. Here we characterize the changes insarcomere function and EC-coupling that occur in two HCM mouse models carrying different mutations in cTnT(R92Q and E163R). Echocardiography showed LV hypertrophy, enhanced contractility, diastolic dysfunction andenlarged left atria in both HCM models; the phenotype was more pronounced in the R92Q mice. In E163Rventricular myofibrils, in spite of a significant increase in the rate of the initial isometric slow phase of relaxation,overall relaxation from maximal activation was impaired and prolonged vs WT and R92Q myofibrils that exhibitedsimilar relaxation kinetics. Resting tension was higher in the E163Q compared to WT and R92Q myofibrils.Isometric ATPase both at rest and at maximal Ca2+-activation and the energy cost of tension generation wereincreased in E163R vs WT and R92Q skinned trabeculae. Myofilament Ca2+-sensitivity was increased in bothmutant lines compared to WT; the change was larger in the R92Q preparations. R92Q intact cardiomyocytes andtrabeculae compared to WT and E163R preparations showed blunted response to inotropic interventions, reducedamplitude and slower decay of Ca2+-transients with reduced SERCA function. Twitch kinetics were prolonged inboth HCM mouse models, despite Ca2+-transient kinetics was faster and SERCA function unchanged in theE163R mice. Intact preparations of both HCM mouse models showed increased probability of arrhythmogenicbehavior that increased in response to isoproterenol. The results suggest that similar HCM phenotypes can begenerated through different pathogenic pathways. Grant Telethon-GGP13162.

ABSTRACTIntact trabeculae mechanics

Intracellular Calcium Fluxes

BACKGROUND AND AIM

RESULTS

METHODS

We aimed to characterize changes in sarcomere function and in E-Ccoupling in two HCM mouse models carrying two different cTnT mutations.

SUMMARY and CONCLUSIONSThe cardiac phenotypes of R92Q and E163R cTnT mouse models areessentially similar and recapitulate the features of the human HCM.

In E163 mice the mutant protein is associated with major impairment ofmyofilament function (increased CB dissociation rate & increased energeticcost of tension generation, impaired mechanism that switches contraction off& impaired sarcomere relaxation) that can be directly related to themechanical dysfunction of the in vivo heart.

In R92Q mice no major changes in myofilament function (a part from theincreased Ca2+-sensitivity) are observed suggesting that additionalpathogenic mechanisms may be involved in the mechanical dysfunction of thein vivo heart.

In R92Q mice increased myofilament Ca2+ sensitivity is associated with alarge spectrum of E-C coupling changes which appear to be the majorcontributor to the observed mechanical dysfunction and arrhythmogeneicityresembling the advanced human disease (Coppini et al., Circulation 2013).

In E163R mice impairment of myofilament function appears to be theleading element determining mechanical abnormalities. In the absence ofmajor E-C coupling changes, the increased arrhythmogeneicity in E163Rmyocardium may be a direct consequence of the increased myofilament Ca2sensitivity.

ACKNOWLEDGEMENTS

Telethon Italy grant 13162Gileas Sciences Inc.

Ca2+sensitivity ATP

consumed

Altered CB mechanics& kinetics

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Sarcoplasmic reticulum

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Invitro

Echocardiography Systolic/diastolic function

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Manning, Tardiff et al. J Mol Biol. 2012

~30micepergroup,810months

KITransgenicMice

Coppini R. et al, Circulation 2013Ferrantini C. et al. J Cardiovasc Trasl Res 2009

Echocardiography

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