Rationale High-myofilament Ca2+-sensitivity has been proposed as trigger of disease pathogenesis in familial hypertrophic cardiomyopathy (HCM) based on in vitro and transgenic mice studies. However, myofilament Ca2+-sensitivity depends on protein phosphorylation and muscle length, and at present, data in human are scarce. Objective To investigate whether high-myofilament Ca2+-sensitivity and perturbed length-dependent activation are characteristics for human HCM with mutations in thick- and thin-filament proteins. Methods and Results Cardiac samples from patients with HCM harboring mutations in genes encoding thick (MYH7, MYBPC3) and thin (TNNT2, TNNI3, TPM1) filament proteins were compared with sarcomere mutation-negative HCM and nonfailing donors. Cardiomyocyte force measurements showed higher myofilament Ca2+-sensitivity in all HCM samples and low phosphorylation of protein kinase A (PKA)-targets compared with donors. After exogenous PKA treatment, myofilament Ca2+-sensitivity was either similar (MYBPC3mut, TPM1mut, sarcomere mutation-negative HCM), higher (MYH7mut, TNNT2mut), or even significantly lower (TNNI3mut) compared with donors. Length-dependent activation was significantly smaller in all HCM than in donor samples. PKA treatment increased phosphorylation of PKA-targets in HCM myocardium and normalized length-dependent activation to donor values in sarcomere mutation-negative HCM and HCM with truncating MYBPC3 mutations, but not in HCM with missense mutations. Replacement of mutant by wild-type troponin in TNNT2mut and TNNI3mut corrected length-dependent activation to donor values. Conclusions High-myofilament Ca2+-sensitivity is a common characteristic of human HCM and partly reflects hypophosphorylation of PKA-targets compared with donors. Length-dependent sarcomere activation is perturbed by missense mutations, possibly via post-translational modifications other than PKA-hypophosphorylation or altered protein–protein interactions, and represents a common pathomechanism in HCM.

Cardiac muscle cells are equipped with specialized biochemical machineries for the rapid generation of force and movement central to the work generated by the heart. During each heart beat cardiac muscle cells perceive and experience changes in length and load, which reflect one of the fundamental principles of physiology known as the Frank-Starling law of the heart. Cardiac muscle cells are unique mechanical stretch sensors that allow the heart to increase cardiac output, and adjust it to new physiological and pathological situations. In the present review we discuss the mechano-sensory role of the cytoskeletal proteins with respect to their tight interaction with the sarcolemma and extracellular matrix. The role of contractile thick and thin filament proteins, the elastic protein titin, and their anchorage at the Z-disc and M-band, with associated proteins are reviewed in physiologic and pathologic conditions leading to heart failure. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé

Background An enhanced inflammatory response predicts worse outcomes in heart failure (HF). We hypothesized that administration of Interleukin-1 (IL-1) receptor antagonist (anakinra) could inhibit the inflammatory response and improve peak aerobic exercise capacity in patients with recently decompensated systolic HF. Methods and Results We randomly assigned 60 patients with reduced left ventricular ejection fraction (<50%) and elevated C-reactive protein (CRP) levels (>2 mg/L), within 14 days of hospital discharge, to daily subcutaneous injections with anakinra 100 mg for 2 weeks, 12 weeks, or placebo. Patients underwent measurement of peak oxygen consumption (VO2 [mL•kg−1•min−1]) and ventilatory efficiency (the VE/VCO2 slope). Treatment with anakinra did not affect peak VO2 or VE/VCO2 slope at 2 weeks. At 12 weeks, patients continued on anakinra showed an improvement in peak VO2 from 14.5 [10.5–16.6] to 16.1 [13.2–18.6] mL•kg−1•min−1 (P=0.009 for within-group changes), whereas no significant changes occurred within the anakinra 2-week or placebo groups. The between groups differences, however, were not statistically significant. The incidence of death or re-hospitalization for HF at 24 weeks was 6%, 31%, and 30%, in the anakinra 12-week, anakinra 2-week and placebo groups, respectively (Log-rank test P=0.10). Conclusions No change in peak VO2 occurred at 2 weeks in patients with recently decompensated systolic HF treated with anakinra, whereas an improvement was seen in those patients in whom anakinra was continued for 12 weeks. Additional larger studies are needed to validate the effects of prolonged anakinra on peak VO2 and re-hospitalization for HF.

Female patients with HCM are older at the time of myectomy and show greater impairment of diastolic function. Furthermore, left ventricular and left atrial remodeling is increased in women when corrected for body surface area. At a cellular level, HCM women showed increased compliant titin and a larger degree of interstitial fibrosis.

A, Toldo S. A mouse model of heart failure with preserved ejection fraction due to chronic infusion of a low subpressor dose of angiotensin II. Am J Physiol Heart Circ Physiol 309: H771-H778, 2015. First published July 17, 2015; doi:10.1152/ajpheart.00282.2015.-Heart failure (HF) with preserved ejection fraction (HFpEF) is a clinical syndrome of HF symptoms associated with impaired diastolic function. Although it represents ϳ50% of patients with HF, the mechanisms of disease are poorly understood, and therapies are generally ineffective in reducing HF progression. Animal models of HFpEF not due to pressure or volume overload are lacking, therefore limiting in-depth understanding of the pathophysiological mechanisms and the development of novel therapies. We hypothesize that a continuous infusion of low-dose angiotensin II (AT II) is sufficient to induce left ventricular (LV) diastolic dysfunction and HFpEF, without increasing blood pressure or inducing LV hypertrophy or dilatation. Osmotic pumps were implanted subcutaneously in 8-wk-old male mice assigned to the AT II (0.2 mg·kg Ϫ1 ·day Ϫ1 ) or volume-matched vehicle (N ϭ 8/group) for 4 wk. We measured systolic and diastolic arterial blood pressures through a tail-cuff transducer, LV dimensions and ejection fraction through echocardiography, and LV relaxation through pulsed-wave Doppler and LV catheterization. Myocardial fibrosis and cardiomyocyte cross-sectional area were measured. AT II infusion had no effects on systemic arterial blood pressure. ATII induced significant impairment in LV diastolic function, as measured by an increase (worsening) in LV isovolumetric relaxation time, myocardial performance index, isovolumetric relaxation time constant, and LV end-diastolic pressure without altering LV dimensions, mass, or ejection fraction. Chronic infusion of low-dose AT II recapitulates the HFpEF phenotype in the mouse, without increasing systemic arterial blood pressure. This mouse model may provide insight into the mechanisms of HFpEF.heart failure with preserved ejection fraction; diastolic dysfunction; animal model; angiotensin II; end-diastolic pressure; isovolumetric relaxation time NEW & NOTEWORTHY Chronic infusion of low-dose angiotensin II in the mouse induces diastolic dysfunction and HFpEF in the absence of pressure overload, LV systolic dysfunction, LV dilatation or hypertrophy, and metabolic abnormalities. This model may be considered a novel tool for mechanistic preclinical studies in HFpEF with translational potential.HEART FAILURE (HF) WITH PRESERVED ejection fraction (HFpEF) is a clinical syndrome of symptoms of HF, such as breathlessness and exercise intolerance, associated with impaired left ventricular (LV) diastolic function in the presence of a normal LV ejection fraction (LVEF Ͼ 50%) (2). HFpEF carries significant morbidity and mortality burdens, and the prevalence of the disease has increased over the past 30 yr (2, 17). To date, the mechanisms underlying diastolic dysfunction and the progression of HFpEF are poorly understood. The path...

The pathological progression of hypertrophic cardiomyopathy (HCM) is sex dimorphic such that male HCM mice develop phenotypic indicators of cardiac disease well before female HCM mice. Here, we hypothesized that alterations in myofilament function underlies, in part, this sex dimorphism in HCM disease development. Firstly, 10–12 month female HCM (harboring a mutant [R403Q] myosin heavy chain) mice presented with proportionately larger hearts than male HCM mice. Next, we determined Ca2+-sensitive tension development in demembranated cardiac trabeculae excised from 10–12 month female and male HCM mice. Whereas HCM did not impact Ca2+-sensitive tension development in male trabeculae, female HCM trabeculae were more sensitive to Ca2+ than wild-type (WT) counterparts and both WT and HCM males. We hypothesized that the underlying cause of this sex difference in Ca2+-sensitive tension development was due to changes in Ca2+ handling and sarcomeric proteins, including expression of SR Ca2+ ATPase (2a) (SERCA2a), β-myosin heavy chain (β-MyHC) and post-translational modifications of myofilament proteins. Female HCM hearts showed an elevation of SERCA2a and β-MyHC protein whereas male HCM hearts showed a similar elevation of β-MyHC protein but a reduced level of cardiac troponin T (cTnT) phosphorylation. We also measured the distribution of cardiac troponin I (cTnI) phosphospecies using phosphate-affinity SDS–PAGE. The distribution of cTnI phosphospecies depended on sex and HCM. In conclusion, female and male HCM mice display sex dimorphic myofilament function that is accompanied by a sex- and HCM-dependent distribution of sarcomeric proteins and cTnI phosphospecies.

The heart adapts to exercise stimuli in a sex-dimorphic manner when mice are fed the traditional soy-based chow. Females undergo more voluntary exercise (4 wk) than males and exhibit more cardiac hypertrophy per kilometer run (18, 32). We have found that diet plays a critical role in cage wheel exercise and cardiac adaptation to the exercise stimulus in this sex dimorphism. Specifically, feeding male mice a casein-based, soy-free diet increases daily running distance over soy-fed counterparts to equal that of females. Moreover, casein-fed males have a greater capacity to increase their cardiac mass in response to exercise compared with soy-fed males. To further explore the biochemical mechanisms for these differences, we performed a candidate-based RT-PCR screen on genes previously implicated in diet- or exercise-based cardiac hypertrophy. Of the genes screened, many exhibit significant exercise, diet, or sex effects but only transforming growth factor-β1 shows a significant three-way interaction with no genes showing a two-way interaction. Finally, we show that the expression and activity of adenosine monophosphate-activated kinase-α2 and acetyl-CoA carboxylase is dependent on exercise, diet, and sex.

There is a growing appreciation that our microbial environment in the gut plays a critical role in the maintenance of health and the pathogenesis of disease. Probiotic, beneficial gut microbes, administration can directly attenuate cardiac injury and post-myocardial infarction (MI) remodelling, yet the mechanisms of cardioprotection are unknown. We hypothesised that administration of Bifidobacterium animalis subsp. lactis 420 (B420), a probiotic with known anti-inflammatory properties, to mice will mitigate the pathological impact of MI, and that anti-inflammatory T regulatory (Treg) immune cells are necessary to impart protection against MI as a result of B420 administration. Wild-type male mice were administered B420, saline or Lactobacillus salivarius 33 (Ls-33) by gavage daily for 14 or 35 days, and underwent ischemia/reperfusion (I/R). Pretreatment with B420 for 10 or 28 days attenuated cardiac injury from I/R and reduced levels of inflammatory markers. Depletion of Treg cells by administration of anti-CD25 monoclonal antibodies eliminated B420-mediated cardio-protection. Further cytokine analysis revealed a shift from a pro-inflammatory to an anti-inflammatory environment in the probiotic treated post-MI hearts compared to controls. To summarise, B420 administration mitigates the pathological impact of MI. Next, we show that Treg immune cells are necessary to mediate B420-mediated protection against MI. Finally, we identify putative cellular, epigenetic and/or post-translational mechanisms of B420-mediated protection against MI.