No abstract

Supplementary key words cholesterol • lipoprotein • low density lipoprotein • autotaxin • mass spectrometryLysophosphatidic acids (LPAs) are a class of small receptor active phospholipid signaling molecules that promote the growth, survival, and motility of many cell types. LPA, its receptors and enzymes involved in LPA generation and inactivation are implicated in many pathologies including cardiovascular, pulmonary, and neurological diseases, and cancer (1-3). These observations underscore the importance of identifying the sources and mechanisms regulating the bioavailability and signaling actions of LPA that underlie this association with disease processes. LPA is abundant in plasma where it is primarily generated by hydrolysis of lysophospholipids [notably lysophosphatidylcholine (LPC)] by the secreted phospholipase, autotaxin (ATX) (4, 5), and can be degraded by phospholipases and lipid phosphatases, which may contribute to turnover of circulating LPA pools (3, 4). There is significant inter-individual variability in plasma LPA levels in humans (6). Despite some provocative observations, efforts to associate plasma LPA levels with human disease risk have largely been unsuccessful (7). Plasma LPA is prominently associated with serum albumin (6). Lysophospholipids are present in HDLs and LDLs (8); and LDL, particularly oxidized LDL, contains bioactive LPA (9, 10). This association of LPA with LDL is particularly relevant to the possible role of LPA in cardiovascular disease because of the central role played by LDL in atherosclerosis. However, at present, little is known about the metabolism and function of LDL-associated LPA.Understanding the regulation of LPA metabolism and signaling in cardiovascular disease is important because, in humans, heritable variants of the PLPP3 gene encoding lipid phosphate phosphatase 3 (LPP3), an enzyme that can Abstract Lysophosphatidic acids (LPAs) are bioactive radyl hydrocarbon-substituted derivatives of glycerol 3-phosphate. LPA metabolism and signaling are implicated in heritable risk of coronary artery disease. Genetic and pharmacological inhibition of these processes attenuate experimental atherosclerosis. LPA accumulates in atheromas, which may be a consequence of association with LDLs. The source, regulation, and biological activity of LDL-associated LPA are unknown. We examined the effects of experimental hyperlipidemia on the levels and distribution of circulating LPA in mice. The majority of plasma LPA was associated with albumin in plasma from wild-type mice fed normal chow. LDL-associated LPA was increased in plasma from high-fat Western diet-fed mice that are genetically prone to hyperlipidemia (LDL receptor knockout or activated proprotein convertase subtilisin/kexin type 9-overexpressing C57Bl6). Adipose-specific deficiency of the ENPP2 gene encoding the LPA-generating secreted lysophospholipase D, autotaxin (ATX), attenuated these Western diet-dependent increases in LPA. ATX-dependent increases in LDLassociated LPA were observed in isolated incubated plasma. ...

We previously reported that high levels of plasma neurotensin (NT), a gut hormone released from enteroendocrine cells of the small bowel, contribute to obesity and comorbid conditions. Gut microbiota has been implicated in the obesity development. Paneth cells are critical in maintaining gut microbiota composition and homeostasis by releasing antimicrobial proteins including α‐defensins. The purpose of our current study was to determine the possible role of NT in gut microbiota composition and α‐defensin gene expression associated with obesity. Here we show that the ratio of Firmicutes/Bacteroidetes (F/B ratio) and intestinal proinflammatory cytokines is significantly increased in NT+/+ mice fed with a high‐fat diet (HFD) which were improved in NT‐deficient mice. HFD disrupted the intestinal Mmp7/α‐defensin axis, which was completely prevented in NT−/− mice. In addition, NT treatment inhibited DEFA5 expression and concurrent NF‐κB activity, which was blocked by a pan PKC inhibitor (Gö6983) or an inhibitor for atypical PKCs (CRT0066854). More importantly, the shRNA‐mediated knockdown of atypical PKCτ reversed NT‐attenuated DEFA5 expression and increased NF‐κB activity. NT contributes to the HFD‐induced disruption of gut microbiota composition and α‐defensin expression. PKCτ/λ plays a central role in NT‐mediated α‐defensin gene expression which might be mediated through the inhibition of NF‐κB signaling pathways in Paneth cells.

Studies demonstrate a role for neurotensin (NT) in obesity and related comorbidities.Bile acid (BA) homeostasis alterations are associated with obesity. We determined the effect of NT on BA metabolism in obese and non-obese conditions. Plasma and fecal BA profiles were analyzed by LC-MS/MS in male and female NT +/+ and NT −/− mice fed low-fat (LFD) or high-fat diet (HFD) for 6 weeks (early stage of obesity) or greater than 20 weeks (late stage of obesity). The nuclear farnesoid X receptor (FXR) and BA transporter mRNA expression were assessed in ileum, mouse enteroids, and human cell lines. HFD decreased plasma primary and secondary BAs in NT +/+ mice; HFD-induced decrease of plasma BAs was improved in NT-deficient mice. In NT +/+ mice, HFD inhibited ileal FXR and BA transporter expression; HFD-decreased expression of FXR and BA transporters was prevented in NT −/− mice. Compared with LFD-fed NT +/+ mice, LFD-fed NT −/− mice had relatively lower levels of ileal FXR and BA transporter expression. Moreover, NT stimulates the expression of FXR and BA transporters in Caco-2 cells; however, stimulated expression of BA transporters was attenuated in NT −/− enteroids. Therefore, we demonstrate that HFD disrupts the BA metabolism and ileal FXR and BA transporter axis which are improved in the absence of NT, suggesting that NT contributes to HFD-induced disruption of BA metabolism and plays an inhibitory role in the regulation of ileal FXR and BA transporter signaling under obese conditions. Conversely, NT positively regulates the expression of ileal FXR and BA transporters under non-obese conditions. Therefore, NT plays a dual role in obese and non-obese conditions, suggesting possible therapeutic strategies for obesity control.