Cardiac-specific blockade of NF-κB in cardiac pathophysiology:: differences between acute and chronic stimuli in vivo

The role of NF-kappa B in cardiac physiology and pathophysiology has been difficult to delineate due to the inability to specifically block NF-kappa B signaling in the heart. Cardiac-specific transgenic models have recently been developed that repress NF-kappa B activation by preventing phosphorylation at specific serine residues of the inhibitory kappa B (I kappa B) protein isoform I kappa B alpha. However, these models are unable to completely block NF-kappa B because of a second signaling pathway that regulates NF-kappa B function via Tyr42 phosphorylation of I kappa B alpha. We report the development of transgenic (3M) mouse lines that express the mutant I kappa B alpha((S32A,S36A,Y42F)) in a cardiac-specific manner. NF-kappa B activation in cardiomyopathic TNF-1.6 mice is completely blocked by the 3M transgene but only partially blocked (70-80%) by the previously described double-mutant 2M [I kappa B alpha((S32A, S36A))] transgene, which demonstrates the action of two proximal pathways for NF-kappa B activation in TNF-alpha-induced cardiomyopathy. In contrast, after acute stimuli including administration of TNF-alpha and ischemia-reperfusion (I/R), NF-kappa B activation is blocked in both 2M and 3M transgenic mice. This result suggests that phosphorylation of the regulatory Ser32 and Ser36 predominantly mediates NF-kappa B activation in these situations. We show that infarct size after I/R is reduced by 70% in 3M transgenic mice, which conclusively demonstrates that NF-kappa B is involved in I/R injury. In summary, we have engineered novel transgenic mice that allow us to distinguish two major proximal pathways for NF-kappa B activation. Our results demonstrate that the serine and tyrosine phosphorylation pathways are differentially activated during different pathophysiological processes (cardiomyopathy and I/R injury) and that NF-kappa B contributes to infarct development after I/R.