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ABSTRACT: OBJECTIVE: Sphingolipid de novo biosynthesis is related to nonalcoholic fatty liver disease or hepatic steatosis. However, the mechanism is still unclear. Sphingomyelin synthase (SMS), using ceramide as one of the substrates to produce sphingomyelin, sits at the crossroads of sphingolipid biosynthesis. SMS has 2 isoforms: SMS1 and SMS2. SMS2 is the major isoform in liver. APPROACH AND RESULTS: To investigate the relationship between liver SMS2 activity-mediated sphingolipid changes and hepatic steatosis, we used 2 mouse models: SMS2 liver-specific transgenic and SMS2 knockout mice. We found that SMS2 liver-specific transgenic livers have lower ceramide and higher sphingomyelin, whereas SMS2 knockout livers have higher ceramide and lower sphingomyelin. We also found that liver SMS2 overexpression promoted fatty acid uptake and liver steatosis, whereas SMS2 deficiency had an opposite effect in comparison with their respective controls. Importantly, the exogenous ceramide supplementation to Huh7 cells, a human hepatoma cell line, reduced the expression of proliferator-activated receptor γ2 and its target genes, CD36 and FSP27. Proliferator-activated receptor γ reporter analysis confirmed this phenomenon. Furthermore, proliferator-activated receptor γ antagonist treatment significantly decreased triglyceride accumulation in SMS2 liver-specific transgenic liver. CONCLUSIONS: We attributed these effects to ceramide that can suppress proliferator-activated receptor γ2, thus reducing the expression of CD36 and FSP27 and reducing liver steatosis. After all, SMS2 inhibition in the liver could diminish liver steatosis.
Arteriosclerosis Thrombosis and Vascular Biology 05/2013; · 6.37 Impact Factor
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ABSTRACT: Sphingomyelin synthase (SMS), the last enzyme involved in the biosynthesis of sphingomyelin (SM), plays a critical role in the constitution of cell membrane and has impact on the expression of membrane proteins. SMS2, one of two SMS enzymes, is predominantly located in the plasma membrane, and is mainly expressed in the brain. Therefore, it is conceivable that SMS2 deficiency may have impact on expression of some membrane proteins, such as membrane-bound drug transporters. Using SMS2 gene deficient mouse brain tissues, we studied the gene and protein expression profiles of drug transporters, ERM proteins (ezrin/radixin/moesin) and the cytoskeleton protein, β-actin, in mouse brain by RT-PCR, western blot and immunohistochemistry analysis. We found that the mRNA expression of Mdr1 rather than the other drug transporters was significantly decreased in the SMS2 deficient brain. Accordingly, the expression and the function of Pgp (Mdr1/P-glycoprotein) were significantly downregulated in brain. In addition, the substantially downregulated expression of ezrin and β-actin was also observed in the SMS2 deficient brain. The immunohistochemistry analysis further revealed the suppressed expression of Pgp, ezrin and β-actin in both cortex and paraventricular areas of SMS2 knockout mice. Furthermore, both Pgp and β-actin were found to be co-immunoprecipitated with ezrin from the total brain lysate, suggesting the association between Pgp, ezrin and β-actin in the brain. These results indicate that SMS2 participates in the expression regulation of drug transporters, particularly Pgp, and suggest that SMS2 may be a potential target for enhancing drug access to the brain.
Biochemical pharmacology 04/2011; 82(3):287-94. · 4.25 Impact Factor
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ABSTRACT: Studies have shown that plasma high density lipoprotein cholesterol levels are negatively correlated with the development of atherosclerosis, whereas epidemiological studies have also shown that plasma sphingomyelin level is an independent risk factor for atherosclerosis.
To evaluate the relationship between cellular sphingomyelin level and cholesterol metabolism, we created two cell lines that overexpressed sphingomyelin synthase 1 or 2 (SMS1 or SMS2), using the Tet-off expression system.
We found that SMS1 or SMS2 overexpression in Huh7 cells, a human hepatoma cell line, significantly increased the levels of intracellular sphingomyelin, cholesterol, and apolipoprotein A-I and decreased levels of apolipoprotein A-I and cholesterol in the cell culture medium, implying a defect in both processes.
Our findings indicate that the manipulation of sphingomyelin synthase activity could influence the metabolism of sphingomyelin, cholesterol and apolipoprotein A-I.
Lipids in Health and Disease 03/2011; 10:46. · 2.17 Impact Factor
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ABSTRACT: Sphingomyelin synthase 2 (SMS2) contributes to de novo sphingomyelin (SM) biosynthesis. Its activity is related to SM levels in the plasma and the cell membrane. In this study, we investigated the possibility of a direct relationship between SMS and atherosclerosis.
The Adenovirus containing SMS2 gene was given into 10-week ApoE KO C57BL/6J mice by femoral intravenous injection. In the control group, the Adenovirus containing GFP was given. To confirm this model, we took both mRNA level examination (RT-PCR) and protein level examination (SMS activity assay).
We generated recombinant adenovirus vectors containing either human SMS2 cDNA (AdV-SMS2) or GFP cDNA (AdV-GFP). On day six after intravenous infusion of 2 × 10(11) particle numbers into ten-week-old apoE KO mice, AdV-SMS2 treatment significantly increased liver SMS2 mRNA levels and SMS activity (by 2.7-fold, 2.3-fold, p < 0.001, respectively), compared to AdV-GFP treated mice. Moreover, plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and sphingomyelin (SM) levels were significantly increased by 39% (p < 0.05), 42% (p < 0.05), 68% (p < 0.001), and 45% (p < 0.05), respectively. Plasma high-density lipoprotein cholesterol (HDL-C), phosphatidylcholine (PC), and PC/SM ratio were decreased by 42% (p < 0.05), 18% (p < 0.05), and 45% (p < 0.05), respectively. On day 30, the atherosclerotic lesions on the aortic arch of AdV-SMS2 treated mice were increased, and the lesion areas on the whole aorta and in the aortic root were significantly increased (p < 0.001). Furthermore, the collagen content in the aorta root was significantly decreased (p < 0.01).
Our results present direct morphological evidence for the pro-atherogenic capabilities of SMS2. SMS2 could be a potential target for treating atherosclerosis.
Lipids in Health and Disease 01/2011; 10:7. · 2.17 Impact Factor
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ABSTRACT: We used the sphingomyelin (SM) synthase 2 (Sms2) gene knockout (KO) approach to test our hypothesis that selectively decreasing plasma lipoprotein SM can play an important role in preventing atherosclerosis.
The sphingolipid de novo synthesis pathway is considered a promising target for pharmacological intervention in atherosclerosis. However, its potential is hampered because the substance's atherogenic mechanism is not completely understood. We prepared Sms2 and apolipoprotein E (Apoe) double-KO mice. They showed a significant decrease in plasma lipoprotein SM levels (35%, P<0.01) and a significant increase in ceramide and dihydroceramide levels (87.5% and 27%, respectively; P<0.01) but no significant changes in other tested sphingolipids, cholesterol, and triglyceride. Non-high-density lipoproteins from the double-KO mice showed a reduction of SM, but not cholesterol, and displayed less tendency toward aortic sphingomyelinase-mediated lipoprotein aggregation in vitro and retention in aortas in vivo when compared with controls. More important, at the age of 19 weeks, Sms2 KO/Apoe KO mice showed a significant reduction in atherosclerotic lesions of the aortic arch and root (52%, P<0.01) compared with controls. The Sms2 KO/Apoe KO brachiocephalic artery contained significantly less SM, ceramide, free cholesterol, and cholesteryl ester (35%, 32%, 58%, and 60%, respectively; P<0.01) than that of the Apoe KO brachiocephalic artery.
Decreasing plasma SM levels through decreasing SMS2 activity could become a promising treatment for atherosclerosis.
Arteriosclerosis Thrombosis and Vascular Biology 11/2010; 30(11):2114-20. · 6.37 Impact Factor
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ABSTRACT: Sphingomyelin synthase 1 (SMS1) and SMS2 are two isoforms of SMS, the last enzyme for sphingomyelin (SM) biosynthesis. To evaluate the role of SMS in vivo in terms of plasma lipoprotein metabolism, we generated recombinant adenovirus vectors containing human SMS1 cDNA (AdV-SMS1), SMS2 cDNA (AdV-SMS2), or the reporter LacZ cDNA (AdV-LacZ) as a control. On day 7 after intravenous infusion of 2 x 10(11) particles of both AdV-SMS1 and AdV-SMS2 into mice, liver SMS1 and SMS2 mRNA levels as well as SMS activity were significantly increased (2.5-, 2.7-, 2.1-, and 2.3-fold, respectively; P < 0.001). Lipoprotein analysis indicated that AdV-SMS1 and AdV-SMS2 treatment caused no changes of total SM and cholesterol levels but significantly decreased HDL-SM and HDL-cholesterol (42% and 38%, and 27% and 25%, respectively; P < 0.05). It also significantly increased non-HDL-SM and non-HDL-cholesterol levels (50% and 35%, and 64% and 61%, respectively; P < 0.05) compared with AdV-LacZ controls. SDS-PAGE showed a significant increase in apolipoprotein B (apoB; P < 0.01) but no changes in apoA-I levels. Moreover, we found that non-HDL from both AdV-SMS1- and AdV-SMS2-treated mice was significantly aggregated after treatment with a mammalian sphingomyelinase, whereas lipoproteins from control animals did not aggregate. To investigate the mechanism of HDL changes, we measured liver scavenger receptor class B type I (SR-BI) levels by Western blot. We found that AdV-SMS1 and AdV-SMS2 mouse liver homogenates contained 50% and 55% higher SR-BI levels than in controls, whereas no change was observed in hepatic ABCA1 levels. An HDL turnover study revealed an increase of plasma clearance rates for [3H]cholesteryl oleyl ether-HDL but not for [125I]HDL in both AdV-SMS1 and AdV-SMS2 mice compared with controls. In conclusion, adenovirus-mediated SMS1 and SMS2 overexpression increased lipoprotein atherogenic potential. Such an effect may contribute to the increased plasma SM levels observed in animal models of atherosclerosis and in human patients with coronary artery disease.
The Journal of Lipid Research 06/2006; 47(6):1307-14. · 5.56 Impact Factor
