Genotype-Driven Pathogenesis of Atrial Fibrillation in Hypertrophic Cardiomyopathy: The Case of Different TNNT2 Mutations

Figures

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  FIGURE 1. Sites and carrier numerosity of individual mutations in 45 TNNT2-positive Hypertrophic CardioMyopathy patients (HCM). (A) Representation of TNNT2 exons (top panel) and structural and functional cTnT protein domains (bottom panel) showing hot (big red bold numbers) and sporadic (small black numbers) mutation sites. For mutations carried by more than one patient, the total number of carriers is indicated. (B) Pie chart of data reported in A: Six hot-spot mutation sites and nine sporadic ones are identified. Data modified and updated from Coppini et al., 2014.

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  FIGURE 2. Echocardiographic measurements in WT and cTnT mutant mouse models. (A) Representative echocardiographic images of left atrial area (LA) of WT, R92Q and E163R mice. (B) Comparison of LA areas, maximal anteroposterior left atrial diameter measured from parasternal long axis view, ratio between E and A waves (E/A ratio), isovolumic relaxation time (IVRT), E-wave and A wave in mice from the three study cohorts. Statistical tests: One-way ANOVA with Tukey correction. Data are Means ± S.E.M. from 10 mice per group. * = 0.05>p > 0.01; ** = 0.01 > p > 0.001.

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  FIGURE 3. Mechanics and energetics of permeabilized atrial trabeculae from WT and cTnT mutant mouse models. (A) Picture of one permeabilized atrial trabecula with a scheme of the method used to calculate the volume of the trabecula assumed to be a cylinder between two elliptical cones (B) Representative tension (top) and ATPase activity (bottom) traces from wild-type (WT), R92Q, and E163R trabeculae that were maximally Ca2+-activated (pCa 4.5) at 20°C. Tension cost can be estimated as the ratio between the maximal Ca2+-activated ATPase activity and isometric tension (see Table 2). (C) Relationship between isometric tension and ATPase activity measured at different pCa’s in permeabilized atrial trabeculae from the three groups of mice. The tension cost can be measured from the slope of the ATPase-tension relationship; mean tension cost values are reported at the right. Mean ± SE of tension cost was calculated at 20°C. from WT (N = 6, n = 10), R92Q (N = 3, n = 6) and E163R (N = 4, n = 8) mice: N = number of animals, n = number of trabeculae. Statistical test see below (D) pCa-Tension curves (left) and mean values of pCa at half-maximal activation (pCa50, right) from WT (N = 5, n = 10), R92Q…

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  FIGURE 4. Comparison of isometric twitch amplitude and kinetics of intact atrial trabeculae from WT, R92Q and E163Rmice. (A) Left: representative tension traces of twitches from intact atrial trabeculae of WT, R92Q and E163R mice under control experimental conditions (30°C, 2 mM external [Ca2+], stimulation frequency 1 Hz). Right: relationship between stimulation frequency and peak isometric twitch tension in the three groups of intact atrial trabeculae. (B) Left: normalized superimposed twitches at 1 Hz stimulation frequency to highlight kinetics differences. Center: average time to peak at different stimulation frequencies in atrial trabeculae from the three groups. Right: average time from peak to 50% relaxation (RT50) in atrial trabeculae from the three groups. (C) Inotropic interventions in atrial trabeculae. Left: superimposed traces under control conditions and following addition of isoproterenol 1 µM (ISO) or 6 mM external [Ca2+] in trabeculae from WT, R92Q, and E163R mice. Right: variation of the peak twitch force from our control conditions following ISO, 6 mM external [Ca2+] and post rest potentiation. * = p < 0.05 ** = p < 0.01; One-way ANOVA with Tukey correction. WT (N = 9, n…

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  FIGURE 5. Spontaneous activity in R92Q atrial trabeculae. (A) Representative traces showing the stimulation protocol that may induce spontaneous activity upon stimulation pauses following a train of high frequency stimuli. R92Q but not E163R and WT trabeculae showed significant occurrence of spontaneous triggered activity during the resting pauses. (B) Percentage of trabeculae showing spontaneous activity during long pauses. One-way ANOVA with Tukey correction. * = p < 0.05. WT (N = 9, n = 14), R92Q (N = 4, n = 10) and E163R (N = 5, n = 10) mice. N = number of animals, n = number of trabeculae.

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  FIGURE 6. Atrial myopathy in cTnT-HCM: different pathogenesis of atrial cardiomyopathy, different genotype-driven therapeutical strategies for AF. Left: Atrial myopathy in E163R cTnT-HCM is likely a consequence of increased LV filling pressures as in secondary hypertrophy and other chronic LV conditions. In this case, AF would be predominantly sustained by atrial tissue structural remodeling and associated micro and macro reentrant conduction and first class antiarrhythmics to slow down conduction velocity and catheter ablation could be the recommended first choice treatments. Right: Atrial myopathy in R92Q cTnT-HCM is likely a direct effect of the mutation as in other genetic-based forms of AF. We identified the increased atrial and ventricular myofilament calcium sensitivity associated to this mutation as the trigger for cellular arrhythmias determined by calcium handling dysregulation, as previously demonstrated for other cTnT mutations. In this case drugs that directly decrease sarcomere calcium sensitivity or ameliorate cell calcium homeostasis can be more beneficial compared to classical antiarrhythmics and invasive treatments.