Ivabradine (Iva) has shown beneficial structural and functional effects in clinical and experimental heart failure (HF), but its action in combination with mechanical unloading (MU), such as during treatment with left ventricular assist devices (LVAD), is unknown. The aim of this study was to investigate the effects of Iva during MU, in a rodent model of HF. We studied the chronic effects (4 weeks) of Iva (10 mg/kg/day) alone and in combination with MU [induced by heterotopic abdominal heart transplantation (HATx)] on whole-heart and cellular structure, function, and excitation–contraction (E–C) coupling in a rodent (rat) model of HF, 12 weeks post-left coronary artery (LCA) ligation. Effects of Iva were compared with those of β-blockade using metoprolol [(Met), 250 mg/kg/day]. Iva, but not Met, reversed myocardial fibrosis, alone and in combination with MU. MU-induced restoration of deranged E–C coupling was enhanced by Iva to a greater extent than Met: both Iva and Met enhanced the recovery of the Ca²⁺ transient amplitude and the sarcoplasmic reticulum (SR) Ca²⁺ content, but Iva alone maintained MU-induced normalization of L-type Ca²⁺ current and t-tubule abnormalities. Met prevented MU-induced reduction in the myocardial size (myocardial atrophy); Iva had no effect on this parameter. Iva shows beneficial structural and E–C coupling effects during MU: Iva reverses myocardial fibrosis and enhances the restoration of deranged E–C coupling, displaying more beneficial effects than that of Met. These results suggest that Iva may prove effective in enhancing functional recovery in heart failure patients receiving LVAD therapy.

Organ transplantation is often lifesaving, but the long‐term deleterious effects of combinatorial immunosuppression regimens and allograft failure cause significant morbidity and mortality. Long‐term graft survival in the absence of continuing immunosuppression, defined as operational tolerance, has never been described in the context of multiple major histocompatibility complex (MHC) mismatches. Here, we show that miR‐142 deficiency leads to indefinite allograft survival in a fully MHC mismatched murine cardiac transplant model in the absence of exogenous immunosuppression. We demonstrate that the cause of indefinite allograft survival in the absence of miR‐142 maps specifically to the T cell compartment. Of therapeutic relevance, temporal deletion of miR‐142 in adult mice prior to transplantation of a fully MHC mismatched skin allograft resulted in prolonged allograft survival. Mechanistically, miR‐142 directly targets Tgfbr1 for repression in regulatory T cells (T_REG). This leads to increased T_REG sensitivity to TGF‐β and promotes transplant tolerance via an augmented peripheral T_REG response in the absence of miR‐142. These data identify manipulation of miR‐142 as a promising approach for the induction of tolerance in human transplantation.

BACKGROUND: Changes in the phenotype and genotype in hypertrophic cardiomyopathy (HCM) are thought to involve the myocardium as well as extracardiac tissues. Here, we describe the structural and functional changes in the ascending aorta of obstructive patients with HCM. METHODS: Changes in the aortic wall were studied in a cohort of 101 consecutive patients with HCM undergoing myectomy and 9 normal controls. Biopsies were examined histologically, immunohistochemically, and by electron microscopy. Changes in protein expression were quantified using morphometry and Western blotting. Pulse wave velocity was measured using cardiac magnetic resonance in 85 patients with HCM and compared with 117 age-matched normal controls. RESULTS: In HCM, the number of medial lamellar units was significantly decreased, associated with an increase in interlamellar distance and aortic wall thickness, as compared with controls. Electron microscopy showed an altered lamellar structure with disorientation of elastin fibers from the circumferential direction. There was a significant decrease in collagen content, α-smooth muscle actin, smooth muscle myosin, smooth muscle 22 and integrin β1, as well as a significant increase in calponin and caspase-3. Fibulins 1, 2, and 5 showed reduced expression in HCM-aortic biopsies. Functionally, pulse wave velocity was significantly higher in patients with HCM compared with healthy controls, with an association between higher pulse wave velocity and more severe molecular and clinical parameters. CONCLUSIONS: The increased wall stiffness observed in the aortas of obstructive patients with HCM is associated with structural alterations in the medial lamellar unit, including changes in smooth muscle cells and the extracellular matrix, indicating potential arterial dysfunction.

Cardiac fibrosis is associated with disruptions of the myocardial architecture through changes in volume, composition and organisation of the extracellular matrix. Ivabradine (IVA), a selective inhibitor of the pacemaker current, has shown to have beneficial effects on pathological remodelling. As fibroblasts are the predominant mediators of fibrosis we investigated whether IVA has direct effects on fibroblasts. Heart failure (HF) was induced by permanent coronary artery ligation in rats; sham-operated animals (S) were used as controls. After 12 weeks, HF animals were treated either with IVA or saline (HF-S) for a further 4 weeks. Discoidin domain-containing receptor-2 (DDR-2) and α-smooth muscle actin (α-SMA) were measured as markers of fibroblasts and activated fibroblasts respectively. IVA reduced the DDR-2 (in arbitrary units (a.u.), S: 0.33 ± 0.03, n = 4; HF-S: 0.77 ± 0.06, n = 5; HF-IVA: 0.57 ± 0.02, n = 5; p < 0.05) and α-SMA (S: 0.50 ± 0.13, n = 5; HF-S: 1.00 ± 0.13, n = 6; HF-IVA: 0.44 ± 0.08, n = 4; p < 0.05) expression observed in HF to sham levels. Chronic effects (4 weeks) of IVA (30 nM and 1 uM) were assessed on left ventricular fibroblasts isolated from a patient with dilated cardiomyopathy investigating α-SMA expression. IVA decreased α-SMA expression in fibroblasts (control: 535 ± 41; IVA 30 nM: 363 ± 20; IVA 1 uM: 181 ± 36; n = 4; p < 0.05). Expression of TGF-b1 (S: 0.26 ± 0.03, n = 4; HF-S: 0.49 ± 0.02, n = 5; HF-IVA: 0.34 ± 0.01, n = 4; p < 0.05) and SMAD-2 (S: 0.23 ± 0.01, n = 4; HF-S: 0.40 ± 0.04, n = 5; HF-IVA: 0.25 ± 0.03, n = 5; p < 0.05) was up-regulated during HF but IVA normalised this to sham levels. Our results on reduced TGF-b1 and α-SMA expression highlight a beneficial role of IVA in the reparative process of the failing heart.