Lysophosphatidic acid (LPA) is a bioactive lipid mediator. Concentrations of the major LPA species in mouse plasma decreased uniformly following administration of a potent selective inhibitor of the ...LPA-generating lysophospholipase D autotaxin, identifying an active mechanism for removal of LPA from the circulation. LPA, akylglycerol phosphate (AGP), sphingosine 1-phosphate (S1P), and a variety of structural mimetics of these lipids, including phosphatase-resistant phosphonate analogs of LPA, were rapidly eliminated (t1/2 < 30 s) from the circulation of mice following intravenous administration of a single bolus dose without significant metabolism in situ in the blood. These lipids accumulated in the liver. Elimination of intravenously administered LPA was blunted by ligation of the hepatic circulation, and ~90% of LPA administered through the portal vein was accumulated by the isolated perfused mouse liver at first pass. At early times following intravenous administration, more LPA was associated with a nonparenchymal liver cell fraction than with hepatocytes. Primary cultures of nonparenchymal liver cells rapidly assimilated exogenously provided LPA. Our results identify hepatic uptake as an important determinant of the bioavailability of LPA and bioactive lysophospholipid mimetics and suggest a mechanism to explain changes in circulating LPA levels that have been associated with liver dysfunction in humans.
Flavonoids, such as the tea catechin epigallocatechin-gallate (EGCG), can protect against atherosclerosis by decreasing vascular endothelial cell inflammation. Heme oxygenase-1 (HO-1) is an enzyme ...that plays an important role in vascular physiology, and its induction may provide protection against atherosclerosis. Heme oxygenase-1 can be compartmentalized in caveolae in endothelial cells. Caveolae are plasma microdomains important in vesicular transport and the regulation of signaling pathways associated with the pathology of vascular diseases. We hypothesize that caveolae play a role in the uptake and transport of EGCG and mechanisms associated with the anti-inflammatory properties of this flavonoid. To test this hypothesis, we explored the effect of EGCG on the induction of NF-E2-related factor (Nrf2) and HO-1 in endothelial cells with or without functional caveolae. Treatment with EGCG activated Nrf2 and increased HO-1 expression and cellular production of bilirubin. In addition, EGCG rapidly accumulated in caveolae, which was associated with caveolin-1 displacement from the plasma membrane towards the cytosol. Similar to EGCG treatment, silencing of caveolin-1 by siRNA technique also resulted in up-regulation of Nrf2, HO-1 and bilirubin production. These data suggest that EGCG-induced caveolin-1 displacement may reduce endothelial inflammation.
The isolation and structure elucidation of six new bacterial metabolites spoxazomicin D (2), oxachelins B and C (4, 5), and carboxamides 6–8 and 11 previously reported bacterial metabolites (1, 3, ...9–12a, and 14–18) from Streptomyces sp. RM-14-6 is reported. Structures were elucidated on the basis of comprehensive 1D and 2D NMR and mass spectrometry data analysis, along with direct comparison to synthetic standards for 2, 11, and 12a,b. Complete 2D NMR assignments for the known metabolites lenoremycin (9) and lenoremycin sodium salt (10) were also provided for the first time. Comparative analysis also provided the basis for structural revision of several previously reported putative aziridine-containing compounds exemplified by madurastatins A1, B1, C1 (also known as MBJ-0034), and MBJ-0035 as phenol-dihydrooxazoles. Bioactivity analysis including antibacterial, antifungal, cancer cell line cytotoxicity, unfolded protein response (UPR) modulation, and EtOH damage neuroprotection revealed 2 and 5 as potent neuroprotectives and lenoremycin (9) and its sodium salt (10) as potent UPR modulators, highlighting new functions for phenol-oxazolines/salicylates and polyether pharmacophores.
Dephosphorylation of phosphatidic acid (PA) is the penultimate step in triglyceride synthesis. Adipocytes express soluble intracellular PA-specific phosphatases (Lipins) and broader specificity ...membrane-associated lipid phosphate phosphatases (LPPs) that can also dephosphorylate PA. Inactivation of lipin1 causes lipodystrophy in mice due to defective developmental adipogenesis. Triglyceride synthesis is diminished but not ablated by inactivation of lipin1 in differentiated adipocytes implicating other PA phosphatases in this process. To investigate the possible role of LPPs in adipocyte lipid metabolism and signaling we made mice with adipocyte-targeted inactivation of LPP3 encoded by the Plpp3(Ppap2b) gene. Adipocyte LPP3 deficiency resulted in blunted ceramide and sphingomyelin accumulation during diet-induced adipose tissue expansion, accumulation of the LPP3 substrate sphingosine 1- phosphate, and reduced expression of serine palmitoyl transferase. However, adiposity was unaffected by LPP3 deficiency on standard, high fat diet or Western diets, although Western diet-fed mice with adipocyte LPP3 deficiency exhibited improved glucose tolerance. Our results demonstrate functional compartmentalization of lipid phosphatase activity in adipocytes and identify an unexpected role for LPP3 in the regulation of diet-dependent sphingolipid synthesis that may impact on insulin signaling.
The lipid phosphate phosphatase 3 (LPP3) degrades bioactive lysophospholipids, including lysophosphatidic acid and sphingosine-1-phosphate, and thereby terminates their signaling effects. Although ...emerging evidence links lysophosphatidic acid to atherosclerosis and vascular injury responses, little is known about the role of vascular LPP3. The goal of this study was to determine the role of LPP3 in the development of vascular neointima formation and smooth muscle cells (SMC) responses.
We report that LPP3 is expressed in vascular SMC after experimental arterial injury. Using gain- and loss-of-function approaches, we establish that a major function of LPP3 in isolated SMC cells is to attenuate proliferation (extracellular signal-regulated kinases) activity, Rho activation, and migration in response to serum and lysophosphatidic acid. These effects are at least partially a consequence of LPP3-catalyzed lysophosphatidic acid hydrolysis. Mice with selective inactivation of LPP3 in SMC display an exaggerated neointimal response to injury.
Our observations suggest that LPP3 serves as an intrinsic negative regulator of SMC phenotypic modulation and inflammation after vascular injury, in part, by regulating lysophospholipid signaling. These findings may provide a mechanistic link to explain the association between a PPAP2B polymorphism and coronary artery disease risk.
Appalachian active coal fire sites were selected for the isolation of bacterial strains belonging to the class actinobacteria. A comparison of high-resolution electrospray ionization mass ...spectrometry (HRESIMS) and ultraviolet (UV) absorption profiles from isolate extracts to natural product databases suggested Streptomyces sp. RM-4-15 to produce unique metabolites. Four new pyranonaphthoquinones, frenolicins C–F (1–4), along with three known analogues, frenolicin (6), frenolicin B (7), and UCF76-A (8), were isolated from the fermentation of this strain. An additional new analogue, frenolicin G (5), along with two known compounds, deoxyfrenolicin (9) and UCF 13 (10), were isolated from the fermentation supplied with 18 mg/L of scandium chloride, the first example, to the best of our knowledge, wherein scandium chloride supplementation led to the confirmed production of new bacterial secondary metabolites. Structures 1–5 were elucidated on the basis of spectral analysis and chemical modification. While frenolicins are best known for their anticoccidial activity, the current study revealed compounds 6–9 to exhibit moderate cytotoxicity against the human lung carcinoma cell line (A549) and thereby extends the anticancer SAR for this privileged scaffold.
Brown adipose tissue is a thermogenic organ that dissipates stored energy as heat to maintain body temperature. This process may also provide protection from development of diet-induced obesity. We ...report that the bioactive lipid mediator lysophosphatidic acid (LPA) markedly decreases differentiation of cultured primary brown adipocyte precursors, whereas potent selective inhibitors of the LPA-generating enzyme autotaxin (ATX) promote differentiation. Transgenic mice overexpressing ATX exhibit reduced expression of brown adipose tissue-related genes in peripheral white adipose tissue and accumulate significantly more fat than wild-type controls when fed a high-fat diet. Our results indicate that ATX and its product LPA are physiologically relevant negative regulators of brown fat adipogenesis and are consistent with a model in which a decrease in mature peripheral brown adipose tissue results in increased susceptibility to diet-induced obesity in mice.
Background
Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA has recently been associated with increased risk of cardiovascular disease (CVD) in multiple ...large‐scale human population studies, but the underlying mechanisms remain elusive. We previously reported that BPA activates the pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism and has pro‐atherogenic effects in animal models upon activation. Interestingly, BPA is a potent agonist of human PXR but does not activate mouse or rat PXR signaling, which confounds the use of rodent models to evaluate mechanisms of BPA‐mediated CVD risk. This study aimed to investigate the atherogenic mechanism of BPA using a PXR‐humanized mouse model.
Methods and Results
A PXR‐humanized ApoE deficient (huPXR•ApoE−/−) mouse line was generated that respond to human PXR ligands and feeding studies were performed to determine the effects of BPA exposure on atherosclerosis development. Exposure to BPA significantly increased atherosclerotic lesion area in the aortic root and brachiocephalic artery of huPXR•ApoE−/− mice by 104% (P<0.001) and 120% (P<0.05), respectively. By contrast, BPA did not affect atherosclerosis development in the control littermates without human PXR. BPA exposure did not affect plasma lipid levels but increased CD36 expression and lipid accumulation in macrophages of huPXR•ApoE−/− mice.
Conclusion
These findings identify a molecular mechanism that could link BPA exposure to increased risk of CVD in exposed individuals. PXR is therefore a relevant target for future risk assessment of BPA and related environmental chemicals in humans.
Lipins are phosphatidic acid phosphatases with a pivotal role in regulation of triglyceride and glycerophospholipid metabolism. Lipin1 is also an amplifier of PGC-1α, a nuclear coactivator of PPAR-α ...responsive gene transcription. Lipins do not contain recognized membrane-association domains, but interaction of these enzymes with cellular membranes is necessary for access to their phospholipid substrate. We identified a role for a conserved polybasic amino acid motif in an N-terminal domain previously implicated as a determinant of nuclear localization in selective binding of lipin1β to phosphatidic acid, using blot overlay assays and model bilayer membranes. Studies using lipin1β polybasic motif variants establish that this region is also critical for nuclear import and raise the possibility that nuclear/cytoplasmic shuttling of lipin1β is regulated by PA. We used pharmacological agents and lipin1β polybasic motif mutants to explore the role of PA-mediated membrane association and nuclear localization on lipin1β function in phospholipid metabolism and adipogenic differentiation. We identify a role for the lipin1 polybasic motif as both a lipid binding motif and a primary nuclear localization sequence. These two functions are necessary for full expression of the biological activity of the protein in intracellular lipid metabolism and transcriptional control of adipogenesis.
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