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Enhanced cardiac TBC1D10C expression lowers heart rate and enhances exercise capacity and survival

View Article: PubMed Central - PubMed

ABSTRACT

TBC1D10C is a protein previously demonstrated to bind and inhibit Ras and Calcineurin. In cardiomyocytes, also CaMKII is inhibited and all three targeted enzymes are known to promote maladaptive cardiomyocyte hypertrophy. Here, in accordance with lack of Calcineurin inhibition in vivo, we did not observe a relevant anti-hypertrophic effect despite inhibition of Ras and CaMKII. However, cardiomyocyte-specific TBC1D10C overexpressing transgenic mice exhibited enhanced longevity. Ejection fraction and exercise capacity were enhanced in transgenic mice, but shortening of isolated cardiomyocytes was not increased. This suggests longevity resulted from enhanced cardiac performance but independent of cardiomyocyte contractile force. In further search for mechanisms, a transcriptome-wide analysis revealed expressional changes in several genes pertinent to control of heart rate (HR) including Hcn4, Scn10a, Sema3a and Cacna2d2. Indeed, telemetric holter recordings demonstrated slower atrial conduction and significantly lower HR. Pharmacological reduction of HR was previously demonstrated to enhance survival in mice. Thus, in addition to inhibition of stress signaling, TBC1D10C economizes generation of cardiac output via HR reduction, enhancing exercise capacity and survival. TBC1D10C may be a new target for HR reduction and longevity.

No MeSH data available.


Related in: MedlinePlus

Phenotype of TBC1D10C TG mice.(a) Western blot displaying overexpression levels of TBC1D10C in WT vs. TG mice in myocardial tissue (n = 4). The full length membrane of this cropped blot is displayed in Supplemental Fig. 6. (b) Heart weight to body weight ratio (hw/bw) (WT: n = 16, TG: n = 12; n.s.). (c) Echo-cardiography in 9-week-old mice revealed similar anterior wall thickness (AWThd) and left ventricular inner diameter (LVIDd), significantly increased fractional area shortening (FAS), ejection fraction (EF), stroke volume (SV), reduced heart rate (HR) and similar cardiac output (CO) in the TG (WT: n = 33, TG: n = 39 mice; P < 0.05). (d) Telemetric ECG recordings in conscious mice confirmed significantly reduced heart rate (HR) and revealed a prolonged PR interval and equal QRS and QTc intervals in TBC1D10C TG vs. WT mice (n = 7 per group; P < 0.05). (e) Fractional shortening (left) and calcium transient measurements in isolated left ventricular cardiomyocytes from WT and TG mice (n = 7 mice per group, 6–10 cells each; P < 0.05; two-way ANOVA).
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f1: Phenotype of TBC1D10C TG mice.(a) Western blot displaying overexpression levels of TBC1D10C in WT vs. TG mice in myocardial tissue (n = 4). The full length membrane of this cropped blot is displayed in Supplemental Fig. 6. (b) Heart weight to body weight ratio (hw/bw) (WT: n = 16, TG: n = 12; n.s.). (c) Echo-cardiography in 9-week-old mice revealed similar anterior wall thickness (AWThd) and left ventricular inner diameter (LVIDd), significantly increased fractional area shortening (FAS), ejection fraction (EF), stroke volume (SV), reduced heart rate (HR) and similar cardiac output (CO) in the TG (WT: n = 33, TG: n = 39 mice; P < 0.05). (d) Telemetric ECG recordings in conscious mice confirmed significantly reduced heart rate (HR) and revealed a prolonged PR interval and equal QRS and QTc intervals in TBC1D10C TG vs. WT mice (n = 7 per group; P < 0.05). (e) Fractional shortening (left) and calcium transient measurements in isolated left ventricular cardiomyocytes from WT and TG mice (n = 7 mice per group, 6–10 cells each; P < 0.05; two-way ANOVA).

Mentions: We generated TG mice with moderately enhanced cardiomyocyte-specific expression of TBC1D10C (Fig. 1a). TG mice were healthy and of equal weight and their hearts did not exhibit macroscopic differences. Echocardiographic analysis of a large cohort of 9-week-old mice revealed a substantial increase in fractional area shortening (FAS) (wild-type [WT]: 56.6 ± 1.6%, n = 33; TG: 63.4 ± 2.0%, n = 39; P < 0.005), ejection fraction (EF) (WT: 63.3 ± 1.4%, n = 33; TG: 69.1 ± 1.1%, n = 39; P < 0.005) and stroke volume (SV) (WT: 41.0 ± 1.5 μL, n = 33; TG: 45.2 ± 1.4 μL, n = 39; P < 0.05) whereas heart rate (HR) was significantly decreased (WT: 449 ± 9 beats/min, n = 33; TG: 421 ± 7 beats/min, n = 39; P < 0.05) (Fig. 1b,c). The reciprocal relationship between HR and SV resulted in a neutral effect on echocardiographically determined cardiac output (CO) (WT: 18.5 ± 0.8 mL/min, n = 33; TG: 19.0 ± 0.6 mL/min, n = 39; n.s.). Of note, structural and morphological parameters (left ventricular internal diameter at end diastole [LVIDd], diastolic anterior wall thickness [AWThd] and heart weight/body weight ratio [HW/BW]) remained identical between WT and TG littermates. This phenotype was largely preserved in a second, independently generated TG mouse line with relatively lower expression of TBC1D10C (Supplemental Fig. 1a,b), in which FAS and EF were also significantly enhanced. HR was also reduced in this second line (line 2); although the reduction did not reach statistical significance (HR: WT: 407 ± 12 beats/min, n = 15; TG: 384 ± 13 beats/min, n = 15; n.s.), a similar CO was observed in WT and TG mice despite significantly higher EF (WT: 54.1 ± 2.3%, n = 15; TG: 60.7 ± 2.8%, n = 15; P < 0.05) (Supplemental Fig. 1c). Owing to lower TBC1D10C overexpression, less reduction of HR, and less increase in SV in line2, line1 was chosen for additional studies.


Enhanced cardiac TBC1D10C expression lowers heart rate and enhances exercise capacity and survival
Phenotype of TBC1D10C TG mice.(a) Western blot displaying overexpression levels of TBC1D10C in WT vs. TG mice in myocardial tissue (n = 4). The full length membrane of this cropped blot is displayed in Supplemental Fig. 6. (b) Heart weight to body weight ratio (hw/bw) (WT: n = 16, TG: n = 12; n.s.). (c) Echo-cardiography in 9-week-old mice revealed similar anterior wall thickness (AWThd) and left ventricular inner diameter (LVIDd), significantly increased fractional area shortening (FAS), ejection fraction (EF), stroke volume (SV), reduced heart rate (HR) and similar cardiac output (CO) in the TG (WT: n = 33, TG: n = 39 mice; P < 0.05). (d) Telemetric ECG recordings in conscious mice confirmed significantly reduced heart rate (HR) and revealed a prolonged PR interval and equal QRS and QTc intervals in TBC1D10C TG vs. WT mice (n = 7 per group; P < 0.05). (e) Fractional shortening (left) and calcium transient measurements in isolated left ventricular cardiomyocytes from WT and TG mice (n = 7 mice per group, 6–10 cells each; P < 0.05; two-way ANOVA).
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f1: Phenotype of TBC1D10C TG mice.(a) Western blot displaying overexpression levels of TBC1D10C in WT vs. TG mice in myocardial tissue (n = 4). The full length membrane of this cropped blot is displayed in Supplemental Fig. 6. (b) Heart weight to body weight ratio (hw/bw) (WT: n = 16, TG: n = 12; n.s.). (c) Echo-cardiography in 9-week-old mice revealed similar anterior wall thickness (AWThd) and left ventricular inner diameter (LVIDd), significantly increased fractional area shortening (FAS), ejection fraction (EF), stroke volume (SV), reduced heart rate (HR) and similar cardiac output (CO) in the TG (WT: n = 33, TG: n = 39 mice; P < 0.05). (d) Telemetric ECG recordings in conscious mice confirmed significantly reduced heart rate (HR) and revealed a prolonged PR interval and equal QRS and QTc intervals in TBC1D10C TG vs. WT mice (n = 7 per group; P < 0.05). (e) Fractional shortening (left) and calcium transient measurements in isolated left ventricular cardiomyocytes from WT and TG mice (n = 7 mice per group, 6–10 cells each; P < 0.05; two-way ANOVA).
Mentions: We generated TG mice with moderately enhanced cardiomyocyte-specific expression of TBC1D10C (Fig. 1a). TG mice were healthy and of equal weight and their hearts did not exhibit macroscopic differences. Echocardiographic analysis of a large cohort of 9-week-old mice revealed a substantial increase in fractional area shortening (FAS) (wild-type [WT]: 56.6 ± 1.6%, n = 33; TG: 63.4 ± 2.0%, n = 39; P < 0.005), ejection fraction (EF) (WT: 63.3 ± 1.4%, n = 33; TG: 69.1 ± 1.1%, n = 39; P < 0.005) and stroke volume (SV) (WT: 41.0 ± 1.5 μL, n = 33; TG: 45.2 ± 1.4 μL, n = 39; P < 0.05) whereas heart rate (HR) was significantly decreased (WT: 449 ± 9 beats/min, n = 33; TG: 421 ± 7 beats/min, n = 39; P < 0.05) (Fig. 1b,c). The reciprocal relationship between HR and SV resulted in a neutral effect on echocardiographically determined cardiac output (CO) (WT: 18.5 ± 0.8 mL/min, n = 33; TG: 19.0 ± 0.6 mL/min, n = 39; n.s.). Of note, structural and morphological parameters (left ventricular internal diameter at end diastole [LVIDd], diastolic anterior wall thickness [AWThd] and heart weight/body weight ratio [HW/BW]) remained identical between WT and TG littermates. This phenotype was largely preserved in a second, independently generated TG mouse line with relatively lower expression of TBC1D10C (Supplemental Fig. 1a,b), in which FAS and EF were also significantly enhanced. HR was also reduced in this second line (line 2); although the reduction did not reach statistical significance (HR: WT: 407 ± 12 beats/min, n = 15; TG: 384 ± 13 beats/min, n = 15; n.s.), a similar CO was observed in WT and TG mice despite significantly higher EF (WT: 54.1 ± 2.3%, n = 15; TG: 60.7 ± 2.8%, n = 15; P < 0.05) (Supplemental Fig. 1c). Owing to lower TBC1D10C overexpression, less reduction of HR, and less increase in SV in line2, line1 was chosen for additional studies.

View Article: PubMed Central - PubMed

ABSTRACT

TBC1D10C is a protein previously demonstrated to bind and inhibit Ras and Calcineurin. In cardiomyocytes, also CaMKII is inhibited and all three targeted enzymes are known to promote maladaptive cardiomyocyte hypertrophy. Here, in accordance with lack of Calcineurin inhibition in vivo, we did not observe a relevant anti-hypertrophic effect despite inhibition of Ras and CaMKII. However, cardiomyocyte-specific TBC1D10C overexpressing transgenic mice exhibited enhanced longevity. Ejection fraction and exercise capacity were enhanced in transgenic mice, but shortening of isolated cardiomyocytes was not increased. This suggests longevity resulted from enhanced cardiac performance but independent of cardiomyocyte contractile force. In further search for mechanisms, a transcriptome-wide analysis revealed expressional changes in several genes pertinent to control of heart rate (HR) including Hcn4, Scn10a, Sema3a and Cacna2d2. Indeed, telemetric holter recordings demonstrated slower atrial conduction and significantly lower HR. Pharmacological reduction of HR was previously demonstrated to enhance survival in mice. Thus, in addition to inhibition of stress signaling, TBC1D10C economizes generation of cardiac output via HR reduction, enhancing exercise capacity and survival. TBC1D10C may be a new target for HR reduction and longevity.

No MeSH data available.


Related in: MedlinePlus