Myocardial contractile and metabolic properties of familial hypertrophic cardiomyopathy caused by cardiac troponin I gene mutations: a simulation study

Genetic association between 1425G/A SNP in PRKCH and hypertrophic cardiomyopathy in a Chinese population

Hypertrophic cardiomyopathy is a heterogeneous myocardial disorder with a broad spectrum of clinical presentation and morphologic features. Previous reports indicated that protein kinase C pathway as a major determinant of cardiac hypertrophy and heart failure. Population-based analyses of the association between PRKCH gene (encoded PKCη) and HCM has not been performed yet. The purpose of this study is to investigate the association of the nonsynonymous SNP (1425G/A) in PRKCH gene and hypertrophic cardiomyopathy in a Chinese population. 323 patients with HCM and 326 controls were examined using a case-control methodology. The 1425G/A SNP in PRKCH was genotyped by allele-specific real-time PCR assay. The 1425G/A SNP in PRKCH increased the risk of HOCM (hypertrophic obstructive cardiomyopathy) (OR=1.427, 95% confidence interval, 1.013 to 2.012, P=0.046) under a dominant model. After age- and sex-adjustment, the significant associations remained in HOCM (for GG +AG versus AA, OR= 2.497, 95% confidence interval, 1.01 to 6.17; P=0.047). The 1425G/A SNP in PRKCH increases the risk of hypertrophic obstructive cardiomyopathy in the Chinese population.

Proteasome dysfunction in cardiomyopathies

The ubiquitin-proteasome system (UPS) plays a critical role in removing unwanted intracellular proteins and is involved in protein quality control, signalling and cell death. Because the heart is subject to continuous metabolic and mechanical stress, the proteasome plays a particularly important role in the heart, and proteasome dysfunction has been suggested as a causative factor in cardiac dysfunction. Proteasome impairment has been detected in cardiomyopathies, heart failure, myocardial ischaemia, and hypertrophy. Proteasome inhibition is also sufficient to cause cardiac dysfunction in healthy pigs, and patients using a proteasome inhibitor for cancer therapy have a higher incidence of heart failure. In this Topical Review we discuss the experimental data which suggest UPS dysfunction is a common feature of cardiomyopathies, with an emphasis on hypertrophic cardiomyopathy caused by sarcomeric mutations. We also propose potential mechanisms by which cardiomyopathy-causing mutations may lead to proteasome impairment, such as altered calcium handling and increased oxidative stress due to mitochondrial dysfunction.

17β-estradiol prevents cardiac diastolic dysfunction by stimulating mitochondrial function: a preclinical study in a mouse model of a human hypertrophic cardiomyopathy mutation

OBJECTIVE

We investigated the effect of ovariectomy (OVX) and 17β-estradiol (E2) replacement on both mitochondrial and myocardial function in cTnT-Q92 transgenic mice generated by cardiac-restricted expression of a human hypertrophic cardiomyopathy (HCM) mutation.

METHODS

The cTnT-Q92 mice were ovariectomized at twenty weeks of age and were treated with either placebo (OVX group) or E2 (OVX+E2 group) for twelve weeks before being sacrificed. Wild-type and cTnT-Q92 female mice receiving sham operation were used as controls. Indices of diastolic function such as mitral early (E) and late (A) inflow as well as isovolumic relaxation time (IVRT) were measured by echocardiography. A Clark-type electrode was used to detect respiratory control, and ATP levels were determined at the mitochondrial level using HPLC. Key components related to mitochondrial energy metabolism, such as peroxisome proliferator-activated receptor α (PPARα), PPARγ coactivator 1α (PGC-1α) and nuclear respiratory factor-1 (NRF-1), were also analyzed using Western blot and RT-PCR. The levels of oxidative stress markers were determined by measuring malondialdehyde (MDA) using the thiobarbituric acid assay.

RESULTS

The cTnT-Q92 mice had impaired diastolic function compared with wild-type mice (E/A ratio, 1.39 ± 0.04 vs. 1.21 ± 0.01, p<0.001; IVRT, 19.17 ± 0.85 vs. 22.15 ± 1.43 ms, p=0.028). In response to ovariectomy, cardiac function further decreased compared with that observed in cTnT-Q92 mice that received the sham operation (E/A ratio, 1.15 ± 0.04 vs. 1.21 ± 0.01, p<0.001; IVRT, 28.31 ± 0.39 vs. 22.15 ± 1.43 ms, p=0.002). Myocardial energy metabolism, as determined by ATP levels (3.49 ± 0.31 vs. 5.07 ± 0.47 μmol/g, p<0.001), and the mitochondrial respiratory ratio (2.04 ± 0.10 vs. 2.63 ± 0.11, p=0.01) also decreased significantly. By contrast, myocardial concentrations of MDA increased significantly in the OVX group, and PGC-1α, PPARα and NRF-1decreased significantly. E2 supplementation significantly elevated myocardial ATP levels (4.55 ± 0.21 vs. 3.49 ± 0.31 μmol/g, p=0.003) and mitochondrial respiratory function (3.93 ± 0.05 vs. 2.63 ± 0.11, p=0.001); however, it reduced the MDA level (0.21 ± 0.02 vs. 0.36 ± 0.03 nmol/g, p<0.001), which subsequently improved diastolic function (E/A ratio, 1.35 ± 0.06 vs. 1.15 ± 0.04, p<0.001; IVRT, 18.22 ± 1.16 vs. 28.31 ± 0.39 ms, p=0.007).

CONCLUSIONS

Our study has shown that 17β-estradiol improved myocardial diastolic function, prevented myocardial energy dysregulation, and reduced myocardial oxidative stress in cTnT-Q92 mice.