Activation of p38 Mitogen-Activated Protein Kinase Contributes to the Early Cardiodepressant Action of Tumor Necrosis Factor Original Research Article

Objectives The purpose of this study was to determine whether p38 mitogen-activated protein kinase (p38-MAPK) contributes to tumor necrosis factor-alpha (TNFα)-induced contractile depression. Background Tumor necrosis factor has both beneficial and detrimental consequences that may result from the activation of different downstream pathways. Tumor necrosis factor activates p38-MAPK, a stress-responsive kinase implicated in contractile depression and cardiac injury. Methods In isolated hearts from mice lacking the p38-MAPK activator, MAPK kinase 3 (MKK3), perfused at constant coronary pressure or flow, we measured the left ventricular developed pressure (LVDP) and the relationship between end-diastolic volume and LVDP in the presence and absence of 10 ng/ml TNFα. Results Within 15 min at constant pressure, TNFα significantly reduced LVDP and coronary flow in outbred and mkk3+/+ mice. This early negative inotropic effect was associated with a marked phosphorylation of both p38-MAPK and its indirect substrate, HSP27. In hearts lacking MKK3, TNFα failed to activate p38-MAPK or to cause significant contractile dysfunction. The actions of TNFα were similarly attenuated in MAPK-activated protein kinase 2 (MK2)-deficient hearts, which have a marked reduction in myocardial p38-MAPK protein content, and by the p38-MAPK catalytic site inhibitor SB203580 (1 μmol/l). Under conditions of constant coronary flow, the p38-MAPK activation and contractile depression induced by TNFα, though attenuated, remained sensitive to the absence of MKK3 or the presence of SB203580. The role of p38-MAPK in TNFα-induced contractile depression was confirmed in isolated murine cardiac myocytes exposed to SB203580 or lacking MKK3. Conclusions Tumor necrosis factor activates p38-MAPK in the intact heart and in isolated cardiac myocytes through MKK3. This activation likely contributes to the early cardiodepressant action of TNFα.