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Background: Heart failure is one of the leading causes of mortality and is primarily the final stage of several overload cardiomyopathies, preceded by an early adaptive hypertrophic response and characterized by coordinated cardiomyocyte growth, angiogenesis, and inflammation. Therefore, growth factors and cytokines have to be critically regulated during cardiac response to transverse aortic constriction. Interestingly, the dual properties of placental growth factor as an angiogenic factor and cytokine make it a candidate to participate in cardiac remodeling in response to hemodynamic overload., Methods and Results: After transverse aortic constriction, placental growth factor knockout mice displayed a dysregulation of cardiac remodeling, negatively affecting muscle growth. Molecular insights underscored that this effect was ascribable mainly to a failure in the establishment of adequate inflammatory response owing to an impaired activity of tumor necrosis factor-α-converting enzyme. Interestingly, after transverse aortic constriction, placental growth factor knockout mice had strongly increased levels of tissue inhibitor of metalloproteinases-3, the main natural TACE inhibitor, thus indicating an unbalance of the tissue inhibitor of metalloproteinases-3/tumor necrosis factor-α-converting enzyme axis. Strikingly, when we used an in vivo RNA interference approach to reduce tissue inhibitor of metalloproteinases-3 levels in placental growth factor knockout mice during transverse aortic constriction, we obtained a complete phenotype rescue of early dilated cardiomyopathy., Conclusions: Our results demonstrate that placental growth factor finely tunes a balanced regulation of the tissue inhibitor of metalloproteinases-3/tumor necrosis factor-α-converting enzyme axis and the consequent TNF-α activation in response to transverse aortic constriction, thus allowing the establishment of an inflammatory response necessary for adaptive cardiac remodeling.

Aims: The Raf-MEK1/2-ERK1/2 (ERK1/2-extracellular signal-regulated kinases 1/2) signalling cascade is crucial in triggering cardiac responses to different stress stimuli. Scaffold proteins are key elements in coordinating signalling molecules for their appropriate spatiotemporal activation. Here, we investigated the role of IQ motif-containing GTPase-activating protein 1 (IQGAP1), a scaffold for the ERK1/2 cascade, in heart function and remodelling in response to pressure overload., Methods and Results: IQGAP1-null mice have unaltered basal heart function. When subjected to pressure overload, IQGAP1-null mice initially develop a compensatory hypertrophy indistinguishable from that of wild-type (WT) mice. However, upon a prolonged stimulus, the hypertrophic response develops towards a thinning of left ventricular walls, chamber dilation, and a decrease in contractility, in an accelerated fashion compared with WT mice. This unfavourable cardiac remodelling is characterized by blunted reactivation of the foetal gene programme, impaired cardiomyocyte hypertrophy, and increased cardiomyocyte apoptosis. Analysis of signalling pathways revealed two temporally distinct waves of both ERK1/2 and AKT phosphorylation peaking, respectively, at 10 min and 4 days after aortic banding in WT hearts. IQGAP1-null mice show strongly impaired phosphorylation of MEK1/2-ERK1/2 and AKT following 4 days of pressure overload, but normal activation of these kinases after 10 min. Pull-down experiments indicated that IQGAP1 is able to bind the three components of the ERK cascade, namely c-Raf, MEK1/2, and ERK1/2, as well as AKT in the heart., Conclusion: These data demonstrate, for the first time, a key role for the scaffold protein IQGAP1 in integrating hypertrophy and survival signals in the heart and regulating long-term left ventricle remodelling upon pressure overload.