Smooth muscle myosin heavy chains (MHC) exist in multiple isoforms. Rabbit smooth muscle contain at least three types of MHC isoforms ; SM1 (204 kDa), SM2 (200 kDa) and SMemb (200 kDa). SM1 and SM2 are specific to smooth muscle, but SMemb is a nonmuscle-type MHC abundantly expressed in the embryonic aorta and in activated mesenchymal cells. We previously reported that these three MHC isoforms are differentially expressed in rabbit during normal vascular development and in experimental arteriosclerosis and demonstrated that MHC isoforms are excellent markers for smooth muscle phenotype. In order to clarify the clinical significance of MHC isoforms, this article will focus on the expression of smooth muscle MHC isoforms in normally developing and atherosclerotic human arteries, especially in coronary arteries. We recently isolated and characterized three cDNA clones encoding human SM1, SM2, and SMemb. The expression of SM2 mRNA in the human fetal aorta was significantly lower as compared to SM1 mRNA but the ratio of SM2-to SM1-mRNA was increased after birth. SMemb mRNA in the aorta was decreased after birth. lmmuno-histologically, SM1 was constitutively positive from the fetal stage to adulthood in the apparently normal media of the aorta and coronary arteries, whereas SM2 was not detected in fetal arteries of early gestational stage. SM2 was recognized in well-differentiated smooth muscle after perinatal stage. In the human aorta or coronary arteries, unlike in rabbit, SMemb was detected even in the adult. Mild diffuse intimal thickening in the major coronary arteries of the young was found to be composed of smooth muscle cells, reacting equally to three antibodies for MHC isoforms. In thickened but non-atheromatous intima, the expression of well-differentiated smooth muscle-specific MHC (SM2) was reduced, especially in the deeper layer. With progression of atherosclerosis, intimal smooth muscle diminished the expression of not only SM2 but also SM1, whereas α-smooth muscle actin was well preserved. We conclude from these results that smooth muscle MHC isoforms are important molecular markers for studying human vascular smooth muscle cell differentiation as well as the cellular mechanisms of atherosclerosis. J Atheroscler Thromb, 1995 ; 2 : 14-23.

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Platelet binding to an endothelial monolayer was examined after denudation. The binding increased for up to 10 min and thereafter declined gradually. Antibodies against von Willebrand factor (vWF) inhibited the binding. Production of prostacyclin (PGI₂) occurred 10 min after endothelial denudation. This study suggests that vWF is involved in the binding during the first 10 min and that PGI2 suppresses the binding thereafter. J Atheroscler Thromb, 1995 ; 2 : 37-40.

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Nitric oxide (NO) and prostacyclin (PGI₂) have vasodilative and anti-proliferative effects on smooth muscle cells (SMC) and an anti-aggregating action on platelets. The present study was designed to elucidate the influence of modified low density lipoprotein (LDL) on the release of NO and PGI₂ from rat peritoneal macrophages. Cholesteryl ester (CE) content in macrophages markedly increased on incubation with acetylated LDL (ac-LDL), while NO release did not change. Although incubation with mildly oxidized LDL (m-ox-LDL) and highly oxidized LDL (h-ox-LDL) increased CE content in macrophages, only incubation with h-ox-LDL reduced NO release. PGI₂ release from macrophages was not affected by incubation with ac-LDL, m-ox-LDL or h-ox-LDL. These results indicate that the degree of suppression of NO release in macrophages by modified LDL is related to the extent of oxidative modification of LDL itself, but not to the extent of the accumulation of CE in macrophages. Although the role of NO released from macrophages in atherosclerosis is still unclear, the observation of reduced production of NO from macrophages in response to ox-LDL may provide new insight into the role of ox-LDL in the pathogenesis of atherosclerosis. J Atheroscler Thromb, 1995 ; 2 : 41-45.

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Time courses of synthesis and secretion of lipoprotein lipase (LPL) were examined in 3T3-L1 adipocytes. LPL was glycosylated in the endoplasmic reticulum (ER) within 10 min after synthesis, and was transported after 20-30 min to the trans Golgi where it was converted to the mature form with M_r= 55, 000-58, 000, which was resistant to endoglycosidase H (endo H). LPL subunits with M_r= 55, 000-58, 000 appeared in the medium within 30 min after synthesis. The effects of brefeldin A (BFA), which inhibits transport of glycoproteins in various types of cells, on secretion and glycosylation of LPL were also examined. BFA completely blocked release of LPL activity into the medium, causing accumulation of the activity in cells. The suppressive effect of BFA on release of LPL activity was reversible. BFA-treated cells synthesized LPL with M_r= 53, 000-55, 000 consisting of 2 types of subunits, the main type being totally endo H-sensitive and the other partially endo H-sensitive. No LPL subunits were secreted into the medium by BFA-treated cells. J Atheroscler Thromb, 1995 ; 2 : 46-52.

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A total of 155 Japanese subjects (79 men and 76 women) who were classified as having normal or borderline glucose tolerance, according to the criteria for the 50-g oral glucose tolerance test (GTT) of the Japanese Diabetes Society, were analyzed for factors related to serum high density lipoprotein (HDL) -cholesterol concentration, especially the responses of insulin and free fatty acid (FFA) after a glucose challenge. In men, significant negative univariate correlations were observed with body mass index (P<0.01), the summed values of triceps and subscapular skin-folds (P<0.01), serum insulin concentration at all time intervals, and serum FFA at 30 and 60 min of GTT. Serum insulin at 60, 120, and 180 min, sum insulin, and FFA at 30 and 60 min of GTT were significantly related to serum HDL-cholesterol after adjustment for body mass index and triglyceride concentration. Multiple linear regression analysis with the step-forward method showed that sum insulin (P<0.01), FFA at 60 min of GTT (P<0.001), and alcohol consumption (P<0.01) were independently related to serum HDL-cholesterol concentration. Only the triglyceride concentration was inversely correlated (P<0.05) with HDL-cholesterol concentration in women. These data indicate that both insulin and FFA concentrations, as markers of insulin resistance, apparently influence on HDL kinetics in men, but not in women. The lack of this association in women was appeared to related to the degree of obesity. J Atheroscler Thromb, 1995 ; 2 : 53-59.

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To study exogenous sterol metabolism during the suppression or stimulation of cholesterol biosynthesis induced by treatments for hyperlipidemia, we determined plasma plant sterol concentrations before and after administration of an HMG-CoA reductase inhibitor, pravastatin, and compared these with changes in these plasma sterol levels by the bile-sequestrating resin, cholestyramine. The effects of the drugs were also studied in a sitosterolemic patient who has had increased plasma levels of plant sterols. Plasma cholesterol levels determined by the HPLC method were decreased significantly after administration of pravastatin. Plasma plant sterol (sitosterol and campesterol) as well as cholestanol concentrations were also significantly reduced. Cholestyramine administration decreased plasma levels of cholesterol, but did not change those of plant sterols in the hypercholesterolemic subjects. Pravastatin had little effect in a sitosterolemic patient on plasma levels of sterols, where cholestyramine decreased the plasma levels of both cholesterol and cholestanol. These results indicate that treatment with the HMG-CoA reductase inhibitor decreases plasma plant sterol concentrations, and suggest that the increased plasma plant sterol levels in sitosterolemia might not be due to the decreased cholesterol biosynthesis in vivo. J Atheroscier Thromb, 1995 ; 2 : 60-65.

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A 41-year-old female patient with muscle dystrophy, hepatosplenomegaly and tendinous xanthoma showed mild hypertriglyceridemia. The lipoprotein profile in blood showed increases in triglycerides in VLDL and LDL, and a marked decrease of cholesterol in HDL. Chylomicronemia was found, but was not severe. Both lipoprotein lipase and hepatic triglyceride lipase activities were reduced to a level that was only a few percent of the control. Immunoblotting study revealed that the IgG autoantibody in her serum was apparently reactable with hepatic triglyceride lipase and weakly with lipoprotein lipase. Hypertriglyceridemia in this patient is suggested to be due to the autoantibody to these lipases. J Atheroscler Thromb, 1995 ; 2 : 66-69.

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