Sex differences in myosin heavy chain isoforms of human failing and nonfailing atria

Myosins and MyomiR Network in Patients with Obstructive Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy. The molecular mechanisms determining HCM phenotypes are incompletely understood. Myocardial biopsies were obtained from a group of patients with obstructive HCM (n = 23) selected for surgical myectomy and from 9 unused donor hearts (controls). A subset of tissue-abundant myectomy samples from HCM (n = 10) and controls (n = 6) was submitted to laser-capture microdissection to isolate cardiomyocytes. We investigated the relationship among clinical phenotype, cardiac myosin proteins (MyHC6, MyHC7, and MyHC7b) measured by optimized label-free mass spectrometry, the relative genes (MYH7, MYH7B and MYLC2), and the MyomiR network (myosin-encoded microRNA (miRs) and long-noncoding RNAs (Mhrt)) measured using RNA sequencing and RT-qPCR. MyHC6 was lower in HCM vs. controls, whilst MyHC7, MyHC7b, and MyLC2 were comparable. MYH7, MYH7B, and MYLC2 were higher in HCM whilst MYH6, miR-208a, miR-208b, miR-499 were comparable in HCM and controls. These results are compatible with defective transcription by active genes in HCM. Mhrt and two miR-499-target genes, SOX6 and PTBP3, were upregulated in HCM. The presence of HCM-associated mutations correlated with PTBP3 in myectomies and with SOX6 in cardiomyocytes. Additionally, iPSC-derived cardiomyocytes, transiently transfected with either miR-208a or miR-499, demonstrated a time-dependent relationship between MyomiRs and myosin genes. The transfection end-stage pattern was at least in part similar to findings in HCM myectomies. These data support uncoupling between myosin protein/genes and a modulatory role for the myosin/MyomiR network in the HCM myocardium, possibly contributing to phenotypic diversity and providing putative therapeutic targets.

Effect of Myosin Isoforms on Cardiac Muscle Twitch of Mice, Rats and Humans

To understand how pathology-induced changes in contractile protein isoforms modulate cardiac muscle function, it is necessary to quantify the temporal-mechanical properties of contractions that occur under various conditions. Pathological responses are much easier to study in animal model systems than in humans, but extrapolation between species presents numerous challenges. Employing computational approaches can help elucidate relationships that are difficult to test experimentally by translating the observations from rats and mice, as model organisms, to the human heart. Here, we use the spatially explicit MUSICO platform to model twitch contractions from rodent and human trabeculae collected in a single laboratory. This approach allowed us to identify the variations in kinetic characteristics of α- and β-myosin isoforms across species and to quantify their effect on cardiac muscle contractile responses. The simulations showed how the twitch transient varied with the ratio of the two myosin isoforms. Particularly, the rate of tension rise was proportional to the fraction of α-myosin present, while the β-isoform dominated the rate of relaxation unless α-myosin was >50%. Moreover, both the myosin isoform and the Ca2+ transient contributed to the twitch tension transient, allowing two levels of regulation of twitch contraction.

Human heart disease: lessons from human pluripotent stem cell-derived cardiomyocytes

Technical advances in generating and phenotyping cardiomyocytes from human pluripotent stem cells (hPSC-CMs) are now driving their wider acceptance as in vitro models to understand human heart disease and discover therapeutic targets that may lead to new compounds for clinical use. Current literature clearly shows that hPSC-CMs recapitulate many molecular, cellular, and functional aspects of human heart pathophysiology and their responses to cardioactive drugs. Here, we provide a comprehensive overview of hPSC-CMs models that have been described to date and highlight their most recent and remarkable contributions to research on cardiovascular diseases and disorders with cardiac traits. We conclude discussing immediate challenges, limitations, and emerging solutions.

Sex Differences in Metabolic Cardiomyopathy

In contrast to ischemic cardiomyopathies which are more common in men, women are over-represented in diabetic cardiomyopathies. Diabetes is a risk factor for cardiovascular disease; however, there is a sexual dimorphism in this risk factor: heart disease is five times more common in diabetic women but only two-times more common in diabetic men. Heart failure with preserved ejection fraction, which is associated with metabolic syndrome, is also more prevalent in women. This review will examine potential mechanisms for the sex differences in metabolic cardiomyopathies. Sex differences in metabolism, calcium handling, nitric oxide, and structural proteins will be evaluated. Nitric oxide synthase and PPARα exhibit sex differences and have also been proposed to mediate the development of hypertrophy and heart failure. We focused on a role for these signalling pathways in regulating sex differences in metabolic cardiomyopathies.

The Importance of Biological Sex and Estrogen in Rodent Models of Cardiovascular Health and Disease

Nearly one-third of deaths in the United States are caused by cardiovascular disease (CVD) each year. In the past, CVD was thought to mainly affect men, leading to the exclusion of women and female animals from clinical studies and preclinical research. In light of sexual dimorphisms in CVD, a need exists to examine baseline cardiac differences in humans and the animals used to model CVD. In humans, sex differences are apparent at every level of cardiovascular physiology from action potential duration and mitochondrial energetics to cardiac myocyte and whole-heart contractile function. Biological sex is an important modifier of the development of CVD with younger women generally being protected, but this cardioprotection is lost later in life, suggesting a role for estrogen. Although endogenous estrogen is most likely a mediator of the observed functional differences in both health and disease, the signaling mechanisms involved are complex and are not yet fully understood. To investigate how sex modulates CVD development, animal models are essential tools and should be useful in the development of therapeutics. This review will focus on describing the cardiovascular sexual dimorphisms that exist both physiologically and in common animal models of CVD.

GSK-3β heterozygous knockout is cardioprotective in a knockin mouse model of familial dilated cardiomyopathy

Glycogen synthase kinase-3β (GSK-3β) plays a central role in both cardiac physiology and pathology. Herein we want to clarify the role of GSK-3β in familial dilated cardiomyopathy. We generated a mouse model carrying a heterozygous knockout mutation of GSK-3β (GSK-3β(+/-) KO), together with a ΔK210 knockin mutation in cardiac troponin T (ΔK210 cTnT KI), which was proved to be one of the genetic causes of familial dilated cardiomyopathy (DCM). GSK-3β(+/-) KO prevented the slow and rapid deterioration in left ventricular systolic function accompanying heart failure (HF) in DCM mice with heterozygous and homozygous ΔK210 cTnT KI mutations, respectively. GSK-3β(+/-) KO also prevented cardiac enlargement, myocardial fibrosis, and cardiomyocyte apoptosis and markedly reduced the expression of cardiac β-myosin heavy chain isoform, indicative of HF, in DCM mice with homozygous ΔK210 cTnT KI mutation. GSK-3β(+/-) KO also extended the life span of these DCM mice. This study suggests that the inhibition of GSK-3β is cardioprotective in familial DCM associated with ΔK210 cTnT mutation.

Impact of Genotype on the Occurrence of Atrial Fibrillation in Patients With Hypertrophic Cardiomyopathy

Genes associated with hypertrophic cardiomyopathy (HC) are not uniformly expressed in the atrial myocardium. Whether this may impact susceptibility to atrial fibrillation (AF) is unresolved. To analyze the prevalence and clinical correlates of AF in relation to genotype in a large HC cohort, prevalence and clinical profile of AF were assessed in 237 patients with HC, followed for 14 ± 10 years. Patients were divided into 3 genetic subgroups: (1) MYBPC3 (58%), (2) MYH7 (28%), and (3) "other genotypes" (14%; comprising TNNT2, TNNI3, TPM1, MYL2, complex genotypes, Z-line, and E-C coupling genes). Left atrial size was similar in the 3 subsets. AF occurred in 74 patients with HC (31%), with no difference among groups (31% in MYBPC3, 37% in MYH7 and 18% in other genotypes, p = 0.15), paroxysmal/persistent AF (12%, 18%, and 12%, respectively; p = 0.53), paroxysmal/persistent evolved to permanent (12%, 12%, and 3%, p = 0.36) or permanent AF (7%, 7%, and 3%, p = 0.82). Age at AF onset was younger in the group with other genotypes (37 ± 10 years) compared to the first 2 groups (53 ± 14 and 51 ± 17, respectively; p = 0.05) because of early onset associated with complex genotypes and a specific JPH2 mutation associated with abnormal intracellular calcium handling. At multivariate analysis, independent predictors of AF were atrial diameter (p ≤0.05) and age at diagnosis (p = 0.09), but not genetic subtype (p = 0.35). In conclusion, in patients with HC, genetic testing cannot be used in clinical decision making with regard to management strategies for AF. Genotype is not predictive of onset or severity of AF, which appears rather driven by hemodynamic determinants of atrial dilatation. Exceptions are represented by rare genes suggesting specific molecular pathways for AF in genetic cardiomyopathies.

Knock-in mice harboring a Ca(2+) desensitizing mutation in cardiac troponin C develop early onset dilated cardiomyopathy

The physiological consequences of aberrant Ca(2+) binding and exchange with cardiac myofilaments are not clearly understood. In order to examine the effect of decreasing Ca(2+) sensitivity of cTnC on cardiac function, we generated knock-in mice carrying a D73N mutation (not known to be associated with heart disease in human patients) in cTnC. The D73N mutation was engineered into the regulatory N-domain of cTnC in order to reduce Ca(2+) sensitivity of reconstituted thin filaments by increasing the rate of Ca(2+) dissociation. In addition, the D73N mutation drastically blunted the extent of Ca(2+) desensitization of reconstituted thin filaments induced by cTnI pseudo-phosphorylation. Compared to wild-type mice, heterozygous knock-in mice carrying the D73N mutation exhibited a substantially decreased Ca(2+) sensitivity of force development in skinned ventricular trabeculae. Kaplan-Meier survival analysis revealed that median survival time for knock-in mice was 12 weeks. Echocardiographic analysis revealed that knock-in mice exhibited increased left ventricular dimensions with thinner walls. Echocardiographic analysis also revealed that measures of systolic function, such as ejection fraction (EF) and fractional shortening (FS), were dramatically reduced in knock-in mice. In addition, knock-in mice displayed electrophysiological abnormalities, namely prolonged QRS and QT intervals. Furthermore, ventricular myocytes isolated from knock-in mice did not respond to β-adrenergic stimulation. Thus, knock-in mice developed pathological features similar to those observed in human patients with dilated cardiomyopathy (DCM). In conclusion, our results suggest that decreasing Ca(2+) sensitivity of the regulatory N-domain of cTnC is sufficient to trigger the development of DCM.