Yoshihito Takimoto

Differential expression of three types of nitric oxide synthase in both infarcted and non-infarcted left ventricles after myocardial infarction in the rat

In the present report we investigated the differential expression of three types of nitric oxide synthase (NOS) in the left ventricle after myocardial infarction in rats. One, 3, 7, 14, 28 and 56 days (n=6-12 for each group) after ligation of a coronary artery, tissue samples were obtained from infarcted and non-infarcted tissues. The mRNA and protein levels of neuronal (n) NOS, endothelial (e) NOS and inducible (i) NOS were sequentially determined by semi-quantitative reverse transcription-polymerase chain reaction and Western blotting. Progressive left ventricular dilatation and gradual reduction in fractional shortening were confirmed by echocardiography. The expression levels of nNOS were significantly increased 1, 3 and 7 days post-infarct compared to those of sham-operated rats in both the infarcted (P<0.01) and non-infarcted regions (P<0.01). Immunohistochemical analysis showed that nNOS was localized in nerve fibers in the left ventricle and that the number of positive fibers after myocardial infarction had increased compared to that in sham-operated rats. With regard to eNOS, no significant changes in expression levels were detected between infarcted hearts and sham-operated controls. The level of iNOS expression peaked three days post-infarct and then decreased in the infarcted tissue, whereas it increased one day post-infarct, peaked at 14 and 28 days post-infarct and was still elevated in the chronic stage in the ventricular septum. iNOS immunoreactivity was detected in spared cardiomyocytes and macrophages in the infarcted region, and in cardiomyocytes in the ventricular septum. The expressions of three types of NOS were differentially regulated and iNOS produced in the non-infarcted region may contribute to the progression of heart failure after myocardial infarction in rats.

TISSUE FACTOR PATHWAY INHIBITOR-2 IS A NOVEL MITOGEN FOR VASCULAR SMOOTH MUSCLE CELLS

A mitogen for growth-arrested cultured bovine aortic smooth muscle cells was purified to homogeneity from the supernatant of cultured human umbilical vein endothelial cells by heparin affinity chromatography and reverse-phase high performance liquid chromatography. This mitogen was revealed to be tissue factor pathway inhibitor-2 (TFPI-2), which is a Kunitz-type serine protease inhibitor. TFPI-2 was expressed in baby hamster kidney cells using a mammalian expression vector. Recombinant TFPI-2 (rTFPI-2) stimulated DNA synthesis and cell proliferation in a dose-dependent manner (1–500 nm). rTFPI-2 activated mitogen-activated protein kinase (MAPK) activity and stimulated early proto-oncogene c-fos mRNA expression in smooth muscle cells. MAPK, c-fos expression and the mitogenic activity were inhibited by a specific inhibitor of MAPK kinase, PD098059. Thus, the mitogenic function of rTFPI-2 is considered to be mediated through MAPK pathway. TFPI has been reported to exhibit antiproliferative action after vascular smooth muscle injury in addition to the ability to inhibit activation of the extrinsic coagulation cascade. However, structurally similar TFPI-2 was found to have a mitogenic activity for the smooth muscle cell.