Rip2 modifies VEGF-induced signalling and vascular permeability in myocardial ischaemia.

AIMS: In myocardial ischaemia, vascular endothelial growth factor (VEGF) induces permeability by activating a signalling pathway that includes VEGF receptor 2 (VEGFR2), resulting in increased oedema and inflammation and thereby expanding the area of tissue damage. In this study, we investigated the role of receptor-interacting protein 2 (Rip2) in VEGF signalling and myocardial ischaemia/reperfusion injury. METHODS AND RESULTS: To determine whether Rip2 has a role in VEGF signalling, we used cultured endothelial cells in which Rip2 was or was not inactivated. In Rip2-deficient endothelial cells, stimulation with VEGF resulted in more rapid kinetics of VEGFR2 phosphorylation than in control cells. Rip2 deficiency also enhanced VEGF-induced activation of ERK1/2, suggesting an increased propensity for endothelial permeability. In a mouse model of myocardial ischaemia, Rip2 deficiency resulted in enhanced vascular permeability, increased oedema and expanding area of myocardial damage, and markedly reduced heart function after long-term follow-up. CONCLUSION: Our results show that Rip2 modifies VEGF-induced signalling and vascular permeability in myocardial ischaemia. These findings indicate that Rip2 may be a promising novel therapeutic target to reduce excess vascular permeability in ischaemic heart disease.

Myocardial KRAS(G12D) expression does not cause cardiomyopathy in mice.

AIMS: Germ-line mutations in genes encoding components of the RAS/mitogen-activated protein kinase (MAPK) pathway cause developmental disorders called RASopathies. Hypertrophic cardiomyopathy (HCM) is the most common myocardial pathology and a leading cause of death in RASopathy patients. KRAS mutations are found in Noonan and cardio-facio-cutaneous syndromes. KRAS mutations, unlike mutations of RAF1 and HRAS, are rarely associated with HCM. This has been attributed to the fact that germ-line KRAS mutations cause only a moderate up-regulation of the MAPK pathway. Highly bioactive KRAS mutations have been hypothesized to cause severe cardiomyopathy incompatible with life. The aim of this study was to define the impact of KRAS(G12D) expression in the heart. METHODS AND RESULTS: To generate mice with endogenous cardiomyocyte-specific KRAS(G12D) expression (cKRAS(G12D) mice), we bred mice with a Cre-inducible allele expressing KRAS(G12D) from its endogenous promoter (Kras2(LSL)) to mice expressing Cre under control of the cardiomyocyte-specific α-myosin heavy chain promoter (αMHC-Cre). cKRAS(G12D) mice showed high levels of myocardial ERK and AKT signalling. However, surprisingly, cKRAS(G12D) mice were born in Mendelian ratios, appeared healthy, and had normal function, size, and histology of the heart. CONCLUSION: Mice with cardiomyocyte-specific KRAS(G12D) expression do not develop heart pathology. These results challenge the view that the level of MAPK activation correlates with the severity of HCM in RASopathies and suggests that MAPK-independent strategies may be of interest in the development of new treatments for these syndromes.

Novel rat model reveals important roles of ß-adrenoreceptors in stress-induced cardiomyopathy.

BACKGROUND: Stress-induced cardiomyopathy (SIC), also known as Takotsubo cardiomyopathy, is an acute cardiac syndrome with substantial morbidity and mortality. The unique hallmark of SIC is extensive ventricular akinesia involving apical segments with preserved function in basal segments. Adrenergic overstimulation plays an important role in initiating SIC but the pathophysiological pathways and receptors involved are unknown. METHODS: Sprague Dawley rats (~300 g) were injected with a single dose of the ß-adrenergic agonist isoprenaline (ISO, i.p.) and echocardiography was used to study cardiac function. The akinetic part of the left ventricle was biopsied in six SIC patients. Amount of intracellular lipid and glycogen as well as degree of permanent cardiac damage were assessed by histology. RESULTS: In rats, ISO at doses ≥ 50 mg/kg induced severe SIC-like regional akinesia that completely resolved within seven days. Intracellular lipid content was higher in akinetic, but not in normokinetic myocardium in both SIC patients and rats. ß2-receptor blockade or Gi-pathway inhibition was associated with less widespread akinesia and low lipid accumulation but significantly increased acute mortality. CONCLUSIONS: We provide a novel rat model of SIC that supports the hypothesis of circulating catecholamines as initiators of SIC. We propose that the ß-adrenoreceptor pathway is important in the setting of severe catecholamine overstimulation and that perturbations of cardiac metabolism occur in SIC.

TNFalpha-antagonist neither improve cardiac remodelling or cardiac function at early stage of heart failure in diabetic rats.

OBJECTIVES: Despite tumor necrosis factor alpha (TNFalpha) has been shown to be a prognostic marker in patients with heart failure and previous preclinical study with TNFalpha-antagonist has been demonstrated to improve cardiac function in acute heart failure, recent clinical trials using TNFalpha-antagonist in patients with chronic severe heart failure have been disappointing. The aim was to study why TNFalpha-antagonist may not work during long-term treatment in chronic heart failure (CHF) in experimental model. METHODS: 49 rats were used at the age of 26 weeks: healthy Whistar Kyoto rats (WKY, n = 26) and diabetic (WKY+D, n = 23). Rats in each group received either a 12-week treatment with TNFalpha-antagonist (Etanercept) or NaCl injections. RESULTS: In diabetic rats, there were increased plasma glucose level and blood pressure. By use of echocardiography diabetic rats displayed not only enlarged and thinned left ventricles but also decreased both systolic and diastolic functions. Moreover, there are increased interleukin-6 (IL6) mRNA levels. However, TNFalpha-antagonist, etanercept, does not improve either cardiac remodelling or cardiac function. IL6 mRNA level remained unchanged after treatment of etanercept. CONCLUSION: Chronic treatment of TNFalpha-antagonist has no favourable effect on either cardiac remodelling or cardiac function. It is therefore inappropriate to use TNFalpha-antagonist in CHF in diabetes as underlying cause.