Early expression of monocyte chemoattractant protein-1 correlates with the onset of isoproterenol-induced cardiac fibrosis in rats with distinct angiotensin-converting enzyme polymorphism

Simultaneous targeting of oxidative stress and fibrosis reverses cardiomyopathy-induced ventricular remodelling and dysfunction

BACKGROUND AND PURPOSE

Oxidative stress and fibrosis are hallmarks of cardiomyopathy-induced heart failure yet are not effectively targeted by current frontline therapies. Here, the therapeutic effects of the anti-oxidant, N-acetylcysteine (NAC), were compared and combined with an acute heart failure drug with established anti-fibrotic effects, serelaxin (RLX), in a murine model of cardiomyopathy.

EXPERIMENTAL APPROACH

Adult male 129sv mice were subjected to repeated isoprenaline (25 mg·kg^-1 )-induced cardiac injury for five consecutive days and then left to undergo fibrotic healing until Day 14. Subgroups of isoprenaline-injured mice were treated with RLX (0.5 mg·kg^-1 ·day^-1 ), NAC (25 mg·kg^-1 ·day^-1 ) or both combined, given subcutaneously via osmotic minipumps from Day 7 to 14. Control mice received saline instead of isoprenaline.

KEY RESULTS

Isoprenaline-injured mice showed increased left ventricular (LV) inflammation (~5-fold), oxidative stress (~1-2.5-fold), cardiomyocyte hypertrophy (~25%), cardiac remodelling, fibrosis (~2-2.5-fold) and dysfunction by Day 14 after injury. NAC alone blocked the cardiomyopathy-induced increase in LV superoxide levels, to a greater extent than RLX. Additionally, either treatment alone only partly reduced several measures of LV inflammation, remodelling and fibrosis. In comparison, the combination of RLX and NAC prevented the cardiomyopathy-induced LV macrophage infiltration, remodelling, fibrosis and cardiomyocyte size, to a greater extent than either treatment alone after 7 days. The combination therapy also restored the isoprenaline-induced reduction in LV function, without affecting systolic BP.

CONCLUSION AND IMPLICATIONS

These findings demonstrated that the simultaneous targeting of oxidative stress and fibrosis is key to treating the pathophysiology and dysfunction induced by cardiomyopathy.

Lumican-null mice are susceptible to aging and isoproterenol-induced myocardial fibrosis

With aging and stress, the myocardium undergoes structural remodeling, often leading to fibrosis. The purpose of this study is to examine whether lumican, one of the class II small leucine-rich proteoglycans, has a protective role in cardiac remodeling and fibrosis. In attempts to elucidate the hypothesis that lumican may have a protective role in cardiac remodeling and fibrosis, we compared the cardiac phenotypes of young (3-month-old) and elder (6-month- and 12-month-old) lumican-null (Lum^-/-) mice. Extra-cellular matrix remodeling and apoptosis are examined to determine the roles of lumican on age-dependent cardiac fibrosis induced by isoproterenol. Compared to wild type littermates, Lum^-/- mice exhibited higher mortality due to significantly impaired systolic function, which was associated with an increase of atrial natriuretic peptide (ANP) secreted by the ventricles in response to excessive stretching of myocytes. Masson's Trichrome and silver stains showed significantly more severe ventricle fibrosis in Lum^-/- mice. Interestingly, rate of cell death mediated via apoptosis illustrated by the expression of caspase 3 and TUNEL assay was lower in Lum^-/- mice after isoproterenol infusion. In addition, Lum^-/- mice exhibited higher levels of TGF-β, collagen I/III, and membrane-type matrix metalloproteinase-1 (MT1-MMP/MMP-14) during cardiac remodeling. This study shows that alternations of lumican might be implicated in the pathogenesis of cardiac fibrosis and suggests lumican as novel targets for cardiac fibrosis therapy. Further studies are required to define the mechanism by which lumican modulates cardiac remodeling.

mTOR Complexes Repress Hypertrophic Agonist-Stimulated Expression of Connective Tissue Growth Factor in Adult Cardiac Muscle Cells

Connective tissue growth factor (CTGF) is a fibrogenic cytokine that promotes fibrosis in various organs. In the heart, both cardiomyocytes (CM) and cardiac fibroblasts have been reported as a source of CTGF expression, aiding cardiac fibrosis. Although the mammalian target of rapamycin (mTOR) forms 2 distinct complexes, mTORC1 and mTORC2, and plays a central role in integrating biochemical signals for protein synthesis and cellular homeostasis, we explored its role in CTGF expression in adult feline CM. CM were stimulated with 10 μM phenylephrine (PE), 200 nM angiotensin (Ang), or 100 nM insulin for 24 hours. PE and Ang, but not insulin, caused an increase in CTGF mRNA expression with the highest expression observed with PE. Inhibition of mTOR with torin1 but not rapamycin significantly enhanced PE-stimulated CTGF expression. Furthermore, silencing of raptor and rictor using shRNA adenoviral vectors to suppress mTORC1 and mTORC2, respectively, or blocking phosphatidylinositol 3-kinase (PI3K) signaling with LY294002 (LY) or Akt signaling by dominant-negative Akt expression caused a substantial increase in PE-stimulated CTGF expression as measured by both mRNA and secreted protein levels. However, studies with dominant-negative delta isoform of protein kinase C demonstrate that delta isoform of protein kinase C is required for both agonist-induced CTGF expression and mTORC2/Akt-mediated CTGF suppression. Finally, PE-stimulated CTGF expression was accompanied with a corresponding increase in Smad3 phosphorylation and pretreatment of cells with SIS3, a Smad3 specific inhibitor, partially blocked the PE-stimulated CTGF expression. Therefore, a PI3K/mTOR/Akt axis plays a suppressive role on agonist-stimulated CTGF expression where the loss of this mechanism could be a contributing factor for the onset of cardiac fibrosis in the hypertrophying myocardium.

EPAC expression and function in cardiac fibroblasts and myofibroblasts

In the heart, cardiac fibroblasts (CF) and cardiac myofibroblasts (CMF) are the main cells responsible for wound healing after cardiac insult. Exchange protein activated by cAMP (EPAC) is a downstream effector of cAMP, and it has been not completely studied on CF. Moreover, in CMF, which are the main cells responsible for cardiac healing, EPAC expression and function are unknown. We evaluated in both CF and CMF the effect of transforming growth factor β1 (TGF-β1) on EPAC-1 expression. We also studied the EPAC involvement on collagen synthesis, adhesion, migration and collagen gel contraction.

METHOD

Rat neonatal CF and CMF were treated with TGF-β1 at different times and concentrations. EPAC-1 protein levels and Rap1 activation were measured by western blot and pull down assay respectively. EPAC cellular functions were determined by adhesion, migration and collagen gel contraction assay; and collagen expression was determined by western blot.

RESULTS

TGF-β1 through Smad and JNK significantly reduced EPAC-1 expression in CF, while in CMF this cytokine increased EPAC-1 expression through ERK1/2, JNK, p38, AKT and Smad3. EPAC activation was able to induce higher Rap1-GTP levels in CMF than in CF. EPAC and PKA, both cAMP effectors, promoted CF and CMF adhesion on fibronectin, as well as CF migration; however, this effect was not observed in CMF. EPAC but not PKA activation mediated collagen gel contraction in CF, while in CMF both PKA and EPAC mediated collagen gel contraction. Finally, the EPAC and PKA activation reduced collagen synthesis in CF and CMF.

CONCLUSION

TGF-β1 differentially regulates the expression of EPAC in CF and CMF; and EPAC regulates differentially CF and CMF functions associated with cardiac remodeling.

The role of TWEAK/Fn14 in cardiac remodeling

The pathophysiological basis of heart failure is cardiac remodeling, a process that comprises structural and functional changes including cardiomyocyte proliferation, hypertrophy, necrosis, apoptosis, autophagy, interstitial fibrosis, contractile dysfunction and ventricular dilatation. Accumulating evidence demonstrate that tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is involved in the process by binding its receptor fibroblast growth factor-inducible molecule 14 (Fn14). In this review, we will discuss the potential role of the TWEAK/Fn14 axis in cardiac remodeling, elucidate its possible mechanisms and explore new therapeutic targets for heart failure.

Exercise training inhibits inflammatory cytokines and more than prevents myocardial dysfunction in rats with sustained beta-adrenergic hyperactivity

Myocardial hypertrophy and dysfunction occur in response to excessive catecholaminergic drive. Adverse cardiac remodelling is associated with activation of proinflammatory cytokines in the myocardium. To test the hypothesis that exercise training can prevent myocardial dysfunction and production of proinflammatory cytokines induced by beta-adrenergic hyperactivity, male Wistar rats were assigned to one of the following four groups: sedentary non-treated (Con); sedentary isoprenaline treated (Iso); exercised non-treated (Ex); and exercised plus isoprenaline (Iso+Ex). Echocardiography, haemodynamic measurements and isolated papillary muscle were used for functional evaluations. Real-time RT-PCR and Western blot were used to quantify tumour necrosis factor alpha, interleukin-6, interleukin-10 and transforming growth factor beta(1) (TGF-beta(1)) in the tissue. NF-B expression in the nucleus was evaluated by immunohistochemical staining. The Iso rats showed a concentric hypertrophy of the left ventricle (LV). These animals exhibited marked increases in LV end-diastolic pressure and impaired myocardial performance in vitro, with a reduction in the developed tension and maximal rate of tension increase and decrease, as well as worsened recruitment of the Frank-Starling mechanism. Both gene and protein levels of tumour necrosis factor alpha and interleukin-6, as well as TGF-beta(1) mRNA, were increased. In addition, the NF-B expression in the Iso group was significantly raised. In the Iso+Ex group, the exercise training had the following effects: (1) it prevented LV hypertrophy; (ii) it improved myocardial contractility; (3) it avoided the increase of proinflammatory cytokines and improved interleukin-10 levels; and (4) it attenuated the increase of TGF-beta(1) mRNA. Thus, exercise training in a model of beta-adrenergic hyperactivity can avoid the adverse remodelling of the LV and inhibit inflammatory cytokines. Moreover, the cardioprotection is related to beneficial effects on myocardial performance.