Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P43026 (lipopolysaccharide)
 62,215 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sphingomyelin synthase (SMS), the last enzyme in the sphingomyelin (SM) biosynthetic pathway, uses ceramide and phosphatidylcholine as substrates to produce SM and diacylglycerol (DAG). To evaluate the role of SMS in apoptosis, we generated Chinese hamster ovary cells that stably express human SMS1 or SMS2. We found that SMS1 or SMS2 overexpression results in a significant increase in cellular levels of SM (24% or 20%) and DAG (35% or 31%), respectively, compared with controls. Cells overexpressing SMS1 or SMS2 were more likely to undergo lysis mediated by lysenin (a protein that causes lysis through its affinity with SM-rich microdomains in the plasma membrane) than were controls, indicating SM enrichment of the plasma membrane. SMS1 and SMS2 overexpression also led to higher retention of DiIC16 fluorescence compared with wild-type cells, indicating an increased number of detergent-insoluble microdomains and significantly increased tumor necrosis factor-alpha-mediated apoptosis. To further evaluate the relationship between SMS activity and cell apoptosis, we used SMS1 and SMS2 small interfering RNA (siRNA) to knock down their mRNA in THP-1-derived macrophages. We found that SMS1 or SMS2 siRNA significantly reduces intracellular SM (by 20% or 23%), plasma membrane SM (as indicated by the rate of lysenin-mediated cell lysis), and DAG levels (24% or 20%), respectively, while significantly reducing lipopolysaccharide-mediated apoptosis compared with controls. These results indicate that SMS1 and SMS2 are key factors in the control of SM and DAG levels within the cell and thus influence apoptosis.
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PMID:SMS overexpression and knockdown: impact on cellular sphingomyelin and diacylglycerol metabolism, and cell apoptosis. 1798 38

Sphingomyelin synthase (SMS) catalyzes the synthesis of sphingomyelin (SM) and is required for maintenance of plasma membrane microdomain fluidity. Of the two isoforms of mammalian SMS, SMS1 is mostly present in the trans-Golgi apparatus, whereas SMS2 is predominantly found at the plasma membrane. SMS2 has a role in receptor mediated response to inflammation in macrophages, however, the role of SMS2 in vascular permeability, pulmonary edema, and lung injury have not been investigated. To define the role of SMS activation in lung injury, we utilized a lipopolysaccharide (LPS)-induced lung edema model. SMS activity was measured and correlated with the severity of lung injury. Within 4 h of LPS treatment, SMS activity was increased significantly and remained upregulated up to 24 h. Comparison of LPS-induced lung injury in SMS2 knockout (SMS2(-/-)) and wild-type littermate control mice showed that inflammation, cytokine induction, and lung injury were significantly inhibited in SMS2(-/-) mice. Our results suggest that a deficiency of SMS2 can diminish the extent of pulmonary edema and lung injury. Furthermore, we show that depletion of SMS2 was sufficient to decrease MAP kinase-JNK activation, severity of LPS-induced pulmonary neutrophil influx, and inflammation, suggesting a novel role of SMS2 activation in lung injury.
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PMID:Sphingomyelin synthase 2 (SMS2) deficiency attenuates LPS-induced lung injury. 2119 Nov 8

Sepsis is characterized by a severe inflammatory response to infection. With the spread of sepsis, various tissues, including the lungs, liver and kidney, may be damaged. This may finally develop into multiple organ dysfunction syndrome. Sphingomyelin and cholesterol are two main lipids involved in sepsis. The metabolism of sphingomyelin and cholesterol in the livers of mice with sepsis needs to be clarified. To achieve this, the present study intraperitoneally injected mice with PBS, lipopolysaccharide (LPS; 10 mg/kg) and LPS + pyrrolidine dithiocarbamate (PDTC; 30 mg/kg). Subsequently, sphingomyelin and cholesterol content were measured using kits, the sphingomyelin synthase (SMS) activity was measured using thin layer chromatography, and the expression levels of SMS1 and 2, hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), ATP binding cassette subfamily A member 1 (ABCA1), scavenger receptor class B member 1 (SR-B1) and apolipoprotein A1 (Apo A1) were determined by western blotting in the livers of mice. Results demonstrated that, in the LPS group, sphingomyelin and cholesterol content was significantly increased (P<0.001; n=6), the SMS activity significantly enhanced (P<0.001; n=6), the expression levels of SMS2, HMGCR, ABCA1 and SR-B1 were augmented (P<0.05; n=6), and the expression of Apo A1 was decreased (P<0.05; n=6), whereas SMS1 level only slightly increased with no statistical significance (P>0.05; n=6), compared to the levels in the control group. However, PDTC was able to attenuate these alterations. These results indicated that sphingomyelin and cholesterol content may increase in the liver dysfunction of sepsis by increasing the expression of SMS2, HMGCR, SR-B1 and ABCA1, and downregulating Apo A1.
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PMID:Effects of sepsis on the metabolism of sphingomyelin and cholesterol in mice with liver dysfunction. 2928 3

Bacterial lipopolysaccharide (LPS) is recognized by CD14 protein and the Toll-like receptor (TLR)4/MD2 complex localized in the plasma membrane of immune cells. TLR4 triggers two signaling pathways engaging the MyD88 and TRIF adaptor proteins which lead to production of various pro-inflammatory cytokines. These processes are likely to be modulated by sphingomyelin, as the CD14 - TLR4 interaction takes place in plasma membrane rafts enriched in this lipid. To verify this assumption, we analyzed the influence of tricyclodecane-9-yl xanthogenate (D609), which was proven here to be an SMS inhibitor, and silencing of sphingomyelin synthase (SMS) 1 and/or SMS2 on LPS-induced signaling in macrophages. LPS up-regulated the expression and activity of SMS while exposure to D609 or silencing of SMS1 and SMS2 counteracted this action and led (except for SMS2 silencing) to a depletion of sphingomyelin in cells. Concomitantly, the MyD88- and TRIF-dependent signaling pathways of TLR4 were inhibited with the latter being especially sensitive to the reduction of the SMS1 and/or SMS2 activity. The D609 treatment and SMS1 and/or SMS2 depletion all reduced the level of CD14 protein in cells, which likely was an important determinant of the reduction of the LPS-induced pro-inflammatory responses.
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PMID:Sphingomyelin synthase activity affects TRIF-dependent signaling of Toll-like receptor 4 in cells stimulated with lipopolysaccharide. 3167 13