Transverse aortic constriction (TAC) is a well-established model of pressure overload-induced cardiac hypertrophy and failure in mice. The degree of constriction “tightness” dictates the TAC severity and is determined by the gauge (G) of needle used. Though many reports use the TAC model, few studies have directly compared the range of resulting phenotypes. In this study adult male mice were randomized to receive TAC surgery with varying degrees of tightness: mild (25G), moderate (26G) or severe (27G) for 4 weeks, alongside sham-operated controls. Weekly echocardiography and terminal haemodynamic measurements determined cardiac remodelling and function. All TAC models induced significant, severity-dependent left ventricular hypertrophy and diastolic dysfunction compared to sham mice. Mice subjected to 26G TAC additionally exhibited mild systolic dysfunction and cardiac fibrosis, whereas mice in the 27G TAC group had more severe systolic and diastolic dysfunction, severe cardiac fibrosis, and were more likely to display features of heart failure, such as elevated plasma BNP. We also observed renal atrophy in 27G TAC mice, in the absence of renal structural, functional or gene expression changes. 25G, 26G and 27G TAC produced different responses in terms of cardiac structure and function. These distinct phenotypes may be useful in different preclinical settings.

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Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disorder affecting 1 in 500 people in the general population. Characterized by asymmetric left ventricular hypertrophy, cardiomyocyte disarray and cardiac fibrosis, HCM is a highly complex disease with heterogenous clinical presentation, onset and complication. While mutations in sarcomere genes can account for a substantial proportion of familial cases of HCM, 40%–50% of HCM patients do not carry such sarcomere variants and the causal mutations for their diseases remain elusive. Recently, we identified a novel variant of the alpha-crystallin B chain (CRYABR123W) in a pair of monozygotic twins who developed concordant HCM phenotypes that manifested over a nearly identical time course. Yet, how CRYABR123W promotes the HCM phenotype remains unclear. Here, we generated mice carrying the CryabR123W knock-in allele and demonstrated that hearts from these animals exhibit increased maximal elastance at young age but reduced diastolic function with aging. Upon transverse aortic constriction, mice carrying the CryabR123W allele developed pathogenic left ventricular hypertrophy with substantial cardiac fibrosis and progressively decreased ejection fraction. Crossing of mice with a Mybpc3 frame-shift model of HCM did not potentiate pathological hypertrophy in compound heterozygotes, indicating that the pathological mechanisms in the CryabR123W model are independent of the sarcomere. In contrast to another well-characterized CRYAB variant (R120G) which induced Desmin aggregation, no evidence of protein aggregation was observed in hearts expressing CRYABR123W despite its potent effect on driving cellular hypertrophy. Mechanistically, we uncovered an unexpected protein-protein interaction between CRYAB and calcineurin. Whereas CRYAB suppresses maladaptive calcium signaling in response to pressure-overload, the R123W mutation abolished this effect and instead drove pathologic NFAT activation. Thus, our data establish the CryabR123W allele as a novel genetic model of HCM and unveiled additional sarcomere-independent mechanisms of cardiac pathological hypertrophy.

Background: Mineralocorticoid receptor (MR) antagonists decrease heart failure (HF) hospitalization and mortality, but the mechanisms are unknown. Preclinical studies reveal that the benefits on cardiac remodeling and dysfunction are not completely explained by inhibition of MR in cardiomyocytes, fibroblasts, or endothelial cells. The role of MR in smooth muscle cells (SMCs) in HF has never been explored. Methods: Male mice with inducible deletion of MR from SMCs (SMC-MR-knockout) and their MR-intact littermates were exposed to HF induced by 27-gauge transverse aortic constriction versus sham surgery. HF phenotypes and mechanisms were measured 4 weeks later using cardiac ultrasound, intracardiac pressure measurements, exercise testing, histology, cardiac gene expression, and leukocyte flow cytometry. Results: Deletion of MR from SMC attenuated transverse aortic constriction-induced HF with statistically significant improvements in ejection fraction, cardiac stiffness, chamber dimensions, intracardiac pressure, pulmonary edema, and exercise capacity. Mechanistically, SMC-MR-knockout protected from adverse cardiac remodeling as evidenced by decreased cardiomyocyte hypertrophy and fetal gene expression, interstitial and perivascular fibrosis, and inflammatory and fibrotic gene expression. Exposure to pressure overload resulted in a statistically significant decline in cardiac capillary density and coronary flow reserve in MR-intact mice. These vascular parameters were improved in SMC-MR-knockout mice compared with MR-intact littermates exposed to transverse aortic constriction. Conclusions: These results provide a novel paradigm by which MR inhibition may be beneficial in HF by blocking MR in SMC thereby improving cardiac blood supply in the setting of pressure overload–induced hypertrophy thereby mitigating the adverse cardiac remodeling that contributes to HF progression and symptoms.

Background: Augmentation of NP (natriuretic peptide) receptor and cyclic guanosine monophosphate (cGMP) signaling has emerged as a therapeutic strategy in heart failure (HF). cGMP-specific PDE9 (phosphodiesterase 9) inhibition increases cGMP signaling and attenuates stress-induced hypertrophic heart disease in preclinical studies. A novel cGMP-specific PDE9 inhibitor, CRD-733, is currently being advanced in human clinical studies. Here, we explore the effects of chronic PDE9 inhibition with CRD-733 in the mouse transverse aortic constriction pressure overload HF model. Methods: Adult male C57BL/6J mice were subjected to transverse aortic constriction and developed significant left ventricular (LV) hypertrophy after 7 days ( P <0.001). Mice then received daily treatment with CRD-733 (600 mg/kg per day; n=10) or vehicle (n=17), alongside sham-operated controls (n=10). Results: CRD-733 treatment reversed existing LV hypertrophy compared with vehicle ( P <0.001), significantly improved LV ejection fraction ( P =0.009), and attenuated left atrial dilation ( P <0.001), as assessed by serial echocardiography. CRD-733 prevented elevations in LV end diastolic pressures ( P =0.037) compared with vehicle, while lung weights, a surrogate for pulmonary edema, were reduced to sham levels. Chronic CRD-733 treatment increased plasma cGMP levels compared with vehicle ( P <0.001), alongside increased phosphorylation of Ser 273 of cardiac myosin binding protein-C, a cGMP-dependent protein kinase I phosphorylation site. Conclusions: The PDE9 inhibitor, CRD-733, improves key hallmarks of HF including LV hypertrophy, LV dysfunction, left atrial dilation, and pulmonary edema after pressure overload in the mouse transverse aortic constriction HF model. Additionally, elevated plasma cGMP may be used as a biomarker of target engagement. These findings support future investigation into the therapeutic potential of CRD-733 in human HF.