Rationale: Sphingomyelin synthase (SMS)2 contributes to de novo sphingomyelin (SM) biosynthesis and plasma membrane SM levels. SMS2 deficiency in macrophages diminishes nuclear factor B and mitogen-activated protein kinase activation induced by inflammatory stimuli. Objective: The effects of SMS2 deficiency on the development of atherosclerosis are investigated. Methods and Results: We measured cholesterol efflux from macrophages of wild-type (WT) and SMS2 knockout (KO) mice. We transplanted SMS2 KO mouse bone marrow into low-density lipoprotein (LDL) receptor (LDLr) knockout mice (SMS2 ؊/؊ 3 LDLr ؊/؊ ), creating a mouse model of SMS2 deficiency in the macrophages. We found that SMS2 deficiency caused significant induction of cholesterol efflux in vitro and in vivo. Moreover, we found that SMS2 KO mice had less interleukin-6 and tumor necrosis factor ␣ in the circulation before and after endotoxin stimulation, compared with controls. More importantly, after 3 months on a western-type diet, SMS2 ؊/؊ 3 LDLr ؊/؊ mice showed decreased atherosclerotic lesions in the aortic arch, root (57%, P<0.001), and the entire aorta (42%, P<0.01), compared with WT3 LDLr ؊/؊ mice. Analysis of plaque morphology revealed that SMS2 ؊/؊ 3 LDLr ؊/؊ mice had significantly less necrotic core area (71%, P<0.001), less macrophage content (37%, P<0.01), and more collagen content (35%, P<0.05) in atherosclerotic lesions. We also found that SMS2 ؊/؊ 3 LDLr ؊/؊ mice had significantly lower free cholesterol and cholesteryl ester levels in the brachiocephalic artery than WT3 LDLr Key Words: macrophage sphingomyelin synthase deficiency Ⅲ sphingomyelin biosynthesis Ⅲ cholesterol efflux Ⅲ inflammation Ⅲ atherosclerosis F oam cell formation caused by excessive accumulation of cholesterol in the macrophages is a pathological hallmark of atherosclerosis, 1 which is also known to be an inflammatory disease. 2 The accumulation of macrophage-derived foam cells in the vessel wall is always accompanied by the production of a wide range of chemokines and cytokines that regulate the turnover and differentiation of immigrating and resident cells and subsequent plaque development. 2 Thus, promoting cholesterol efflux from cholesterol-laden macrophages, as well as diminishing their inflammatory response, can both be significant antiatherogenic approaches.The interaction between sphingomyelin (SM), cholesterol, and glycosphingolipid drives the formation of plasma membrane rafts, 3 and in some cells, caveolae. 4,5 SM is synthesized by sphingomyelin synthase (SMS), which transfers the phosphorylcholine moiety from phosphatidylcholine (PC) onto ceramide. 6 Two SMS genes, SMS1 and SMS2, have been cloned, and their subcellular localization characterized. 7,8 SMS1 is found in the trans-Golgi apparatus, whereas SMS2 is predominantly located in the plasma membranes. 7,9 Our laboratory and others have shown that SMS1 and SMS2 expression levels correlate positively with those of SM in the lipid rafts. 10 -12 Furthermore, SMS1 has been implicated in the regulation of lipi...

Background-It has been proposed that plasma sphingomyelin (SM) plays a very important role in plasma lipoprotein metabolism and atherosclerosis. Sphingomyelin synthase (SMS) is the last enzyme for SM de novo biosynthesis. Two SMS genes, SMS1 and SMS2, have been cloned and characterized. Methods and Results-To evaluate the in vivo role of SMS2 in SM metabolism, we prepared SMS2 knockout (KO) and SMS2 liver-specific transgenic (LTg) mice and studied their plasma SM and lipoprotein metabolism. On a chow diet, SMS2 KO mice showed a significant decrease in plasma SM levels (25%, PϽ0.05), but no significant changes in total cholesterol, total phospholipids, or triglyceride, compared with wild-type (WT) littermates. On a high-fat diet, SMS2 KO mice showed a decrease in plasma SM levels (28%, PϽ0.01), whereas SMS2LTg mice showed a significant increase in those levels (29%, PϽ0.05), but no significant changes in other lipids, compared with WT littermates. Atherogenic lipoproteins from SMS2LTg mice displayed a significantly stronger tendency toward aggregation after mammalian sphingomyelinase treatment, compared with controls. Moreover, SMS2 deficiency significantly increased plasma apoE levels (2.0-fold, PϽ0.001), whereas liver-specific SMS2 overexpression significantly decreased those levels (1.8-fold, PϽ0.01). Finally, SMS2 KO mouse plasma promoted cholesterol efflux from macrophages, whereas SMS2LTg mouse plasma prevented it. Conclusions-We therefore believe that regulation of liver SMS2 activity could become a promising treatment for atherosclerosis. Key Words: SMS2 knockout mice Ⅲ SMS2 liver-specific transgenic mice Ⅲ plasma sphingomyelin Ⅲ plasma lipoproteins Ⅲ plasma cholesterol S phingomyelin (SM), which is the second most abundant phospholipid in mammalian plasma, appears in all major lipoproteins, where it is part of the monolayer of polar lipids and cholesterol that surrounds a core of neutral lipids. Up to 18% of total plasma phospholipid exists as SM, 1 with the ratio of phosphatidylcholine (PC)/SM varying widely among lipoprotein subclasses. 2 Atherogenic lipoproteins such as VLDL remnants accumulating in cholesterol-fed rabbits tend to be SM-enriched. 3 The SM content of atherosclerotic lesions is higher than that of normal arterial tissue, and SM accumulation is disproportionate to that of PC. 4 However, the role of SM deposited or synthesized in atheromata still remains undefined.It has been suggested that subendothelial retention and aggregation of atherogenic lipoproteins play a very important role in atherogenesis. 5 SM-rich LDL retained in atherosclerotic lesions is acted on by an arterial wall sphingomyelinase, which appears to promote aggregation, initiating the early phase of atherosclerosis development. 4 We have found that plasma SM levels in apoE KO mice are 4-fold higher than in WT mice, 6 and this may partially explain the increased atherosclerosis found in these animals. 7 Our laboratory and others have also discovered that inhibition of SM biosynthesis significantly decreases plasma SM and ...

When expressed through baculovirus, the ORF1 polyprotein of HEV was processed into smaller proteins that correlated with their proposed functional domains. Though the involvement of non-cysteine protease(s) could not be be ruled out, this processing mainly depended upon a cysteine protease.