Immunohistochemical study of the phosphorylated and activated form of c-Jun NH2-terminal kinase in human aorta.

c-Jun NH2-terminal kinase is a key enzyme mediating the cellular response to a variety of extracellular stimuli. In the present study, we performed immunohistochemical studies of the expression of the phosphorylated form of the kinase in 51 human aortas of various ages. The phosphorylated kinase immunoreactivity was strongly detected in vascular smooth muscle cells of the medial vessel layer of atherosclerotic lesions from adults. Immunoreactivity was also strongly detected in similar cells of the intima. On the other hand, immunoreactive phosphorylated kinase was only weakly detected in the medial vascular smooth muscle cells of non-atherosclerotic lesions from adults. We also investigated the expression of the phosphorylated kinase in infant aortas. In contrast to its weak immunoreactivity in adult non-atherosclerotic lesions, the kinase immunoreactivity was detected in high amounts in vascular smooth muscle cells of non-atherosclerotic lesions from infants. Thus, the abundant expression of the phosphorylated kinase in these cells in atherosclerotic lesions of adults and non-atherosclerotic lesions of infants suggests that the activation of c-Jun NH2-terminal kinase may be an important element initiating the proliferation of vascular smooth muscle cells during atherogenesis and aortic development.