Lipocalin-type prostaglandin D2 synthase (L-PGDS) modulates beneficial metabolic effects of vertical sleeve gastrectomy.

BACKGROUND: Vertical sleeve gastrectomy (VSG) ameliorates metabolic complications in obese and diabetic patients through unknown mechanisms. OBJECTIVE: The objective of this study was to investigate the role of lipocalin-type prostaglandin D2 synthase (L-PGDS) in glucose regulation in response to VSG using L-PGDS knock-out (KO), knock-in (KI), and C57BL/6 (wild type) mice. SETTING: Winthrop University Hospital Research Institute. METHODS: Animals were divided into 6 groups: L-PGDS KO sham/VSG (n = 5), L-PGDS KI sham/VSG (n = 5), and C57BL/6 (wild type) sham/VSG (n = 5). Related parameters were measured in fasting animals after 10 weeks. RESULTS: Our intraperitoneal glucose tolerance tests and homeostatic model assessment insulin resistance results showed significant glycemic improvement 10 weeks post-VSG in both C57BL/6 and KI groups compared with the sham group. In contrast, the KO group developed glucose intolerance and insulin resistance similar to or greater than the sham group 10 weeks post-VSG. Interestingly, weight gain was insignificant 10 weeks post-VSG in all the groups and even trended higher in the KO group compared with sham. Peptide YY levels in the KO group post-VSG were slightly increased but significantly less than other groups. Similarly, the KO group showed significantly less leptin sensitivity in response to VSG compared with the KI group. Total cholesterol level remained unchanged in all groups irrespective of sham or surgery but interestingly, the KO group had significantly higher cholesterol levels. In parallel, adipocyte size was also found to be significantly increased in the KO group post-VSG compared with the sham group. CONCLUSION: Our findings propose that L-PGDS plays an important role in the beneficial metabolic effects observed after VSG.

Roux-en-Y gastric bypass attenuates the progression of cardiometabolic complications in obese diabetic rats via alteration in gastrointestinal hormones.

BACKGROUND: Roux-en-Y gastric bypass (RYGB) ameliorates type 2 diabetes (T2DM) and obesity through alteration in gastrointestinal (GI) hormones. OBJECTIVE: The objective of this study was to investigate the effect of RYGB on GI hormones and cardiometabolic parameters in Zucker diabetic fatty (ZDF) rodents. SETTING: Winthrop University Hospital, Research and Academic Center METHODS: Animals were divided into 3 groups, pair-fed (n = 4), ad lib (n = 4), and RYGB (n = 5). This study was carried out for 4 weeks and all related parameters were measured pre- and postsurgery in fasted obese diabetic Zucker rodents. RESULTS: Postoperatively, RYGB significantly decreased fasting blood glucose by 32% compared with ad lib. Plasma insulin and leptin levels were also found to be significantly decreased, by 66% and 38%, respectively, after surgery. Moreover, both glucose-dependent insulinotropic polypeptide (GIP) and peptide tyrosine-tyrosine (PYY) were significantly increased after RYGB-by 300% and 51%, respectively. Glucagon-like peptide-1 (GLP-1) levels were also increased, but the increase was not statistically significant. Total cholesterol levels of the RYGB group remained unchanged for 4 weeks. However, total cholesterol in the ad lib and pair-fed groups increased by 25% and 34%, respectively, compared with initial levels. The cholesterol/high-density lipoprotein (HDL) ratio was decreased in the RYGB group by 14% and 30% compared with the ad lib and pair-fed group, respectively. The RYGB group had a significant decrease in aortic wall thickness of 25% compared with the ad lib and pair-fed groups. Similarly, the RYGB group had a 20-unit (mm Hg) decrease in systolic blood pressure compared with the presurgical value. CONCLUSION: RYGB has beneficial cardiometabolic effects through alterations in GI hormones in a severely obese and diabetic rodent model.

Role of Lipocalin-type prostaglandin D2 synthase (L-PGDS) and its metabolite, prostaglandin D2, in preterm birth.

The objective of the study was to investigate the role of prostaglandin D2 during pregnancy and its mediator Lipocalin-type prostaglandin D2 synthase (L-PGDS) as a predictor of preterm birth (PTB). Transgenic L-PGDS (+/+), L-PGDS (-/-) and C57BL/6 control pregnant mice models were used to determine the effect of DP1 and DP2 receptor antagonists in lipopolysaccharide (LPS)-induced PTB mice. In addition, L-PGDS levels were measured in the cervicovaginal secretions (CVS) of 370 pregnant women using ELISA and further processed for isoform detection using 2-D gel electrophoresis. Our results found that C57BL/6 control mice (n = 26), transgenic L-PGDS (+/+) (n = 26), demonstrated an 89% and 100% preterm birth in LPS (intraperitoneal injection, 20mg/kg) induced mice model respectively. Interestingly, the incidence of PTB was significantly reduced to 40% in L-PGDS (-/-) knockout mice (n = 26). DP1 and DP2 receptor antagonists (0.264 µg/day, dose of 0.1 µg/µl with the flow of 0.11 µl/h for 28 day using Alzet pumps) were used to investigate the effect in LPS-induced PTB in C57BL/6 mice and found 3.3-fold increase in viable pups after LPS-induction. In addition, L-PGDS levels were measured in CVS samples and found that PTB women (n = 296) had two-fold higher levels compared to full term births (n = 74) and established a significant inverse correlation between levels of L-PGDS and days to expected delivery by using 370 preterm birth CVS samples. Elevated L-PGDS levels in the CVS of women may be considered as a potential biomarker for PTB in future. Secondly, the use of DP1 and DP2 receptor antagonists may represent novel tocolytic agents for the treatment of PTB.

Targeting steroid receptor coactivator 1 with antisense oligonucleotides increases insulin-stimulated skeletal muscle glucose uptake in chow-fed and high-fat-fed male rats.

The steroid receptor coactivator 1 (SRC1) regulates key metabolic pathways, including glucose homeostasis. SRC1(-/-) mice have decreased hepatic expression of gluconeogenic enzymes and a reduction in the rate of endogenous glucose production (EGP). We sought to determine whether decreasing hepatic and adipose SRC1 expression in normal adult rats would alter glucose homeostasis and insulin action. Regular chow-fed and high-fat-fed male Sprage-Dawley rats were treated with an antisense oligonucleotide (ASO) against SRC1 or a control ASO for 4 wk, followed by metabolic assessments. SRC1 ASO did not alter basal EGP or expression of gluconeogenic enzymes. Instead, SRC1 ASO increased insulin-stimulated whole body glucose disposal by ~30%, which was attributable largely to an increase in insulin-stimulated muscle glucose uptake. This was associated with an approximately sevenfold increase in adipose expression of lipocalin-type prostaglandin D2 synthase, a previously reported regulator of insulin sensitivity, and an approximately 70% increase in plasma PGD2 concentration. Muscle insulin signaling, AMPK activation, and tissue perfusion were unchanged. Although GLUT4 content was unchanged, SRC1 ASO increased the cleavage of tether-containing UBX domain for GLUT4, a regulator of GLUT4 translocation. These studies point to a novel role of adipose SRC1 as a regulator of insulin-stimulated muscle glucose uptake.

Diminished lipocalin-type prostaglandin D(2) synthase expression in human lung tumors.

Previously, we demonstrated that lipocalin-type prostaglandin D(2) synthase (L-PGDS) induces apoptosis and prevents cell cycle progression in several cell types. In this study we determined the expression of L-PGDS in a variety of human lung tumor types. While L-PGDS expression was evident in the surrounding margins, we observed significantly decreased protein and gene expression in the tumor tissue. Using RT-PCR we demonstrated that L-PGDS gene expression decreased proportionately with tumor progression. In addition, we demonstrated that exogenously added L-PGDS could suppress the hyperproliferation and PDGF-stimulated migration of A549 cells, a cultured carcinomic human alveolar basal epithelial cell line. We conclude that L-PGDS may play a key role in modulating lung cancer growth and may offer a novel diagnostic and therapeutic approach for treatment.

Lipocalin-type prostaglandin D(2) synthase stimulates glucose transport via enhanced GLUT4 translocation.

Previously, we demonstrated that lipocalin-type prostaglandin D(2) synthase (L-PGDS) knockout mice become glucose intolerant and display signs of diabetic nephropathy and accelerated atherosclerosis. In the current study we sought to explain the link between L-PGDS and glucose tolerance. Using the insulin-sensitive rat skeletal muscle cell line, L6, we showed that L-PGDS could stimulate glucose transport approximately 2-fold as well as enhance insulin-stimulated glucose transport, as measured by 2-deoxy-[(3)H]-glucose uptake. The increased glucose transport was not attributed to increased GLUT4 production but rather the stimulation of GLUT4 translocation to the plasma membrane, a phenomenon that was lost when cells were cultured under hyperglycemic (20 mM) conditions or pretreated with wortmannin. There was however, an increase in GLUT1 expression as well as a 3-fold increase in hexokinase III expression, which was increased to nearly 5-fold in the presence of insulin, in response to L-PGDS at 20 mM glucose. In addition, adipocytes isolated from L-PGDS knockout mice were significantly less sensitive to insulin-stimulated glucose transport than wild-type. We conclude that L-PGDS, via production of prostaglandin D(2), is an important mediator of muscle and adipose glucose transport which is modulated by glycemic conditions and plays a significant role in the glucose intolerance associated with type 2 diabetes.

Complex rheological properties of a water-soluble extract from the fronds of the black tree fern, Cyathea medullaris.

A water-soluble extract was obtained from the fronds of a New Zealand native black tree fern (Cyathea medullaris or Mamaku in Maori). The extract exhibited complex rheological behavior. Newtonian, shear-thinning, shear-thickening, thixotropic, antithixotropic, and viscoelastic behaviors were observed depending on polymer concentration, shear rate, and shear history. The extract also displayed rod-climbing and self-siphoning properties typical of viscoelastic fluids. Such complex rheological properties have been reported in synthetic or chemically modified polymers but are less frequent in unmodified biopolymers. Although Mamaku extract obtained from the pith of the fern has been traditionally used by the Maori in New Zealand for treating wounds and diarrhea among other ailments, this material has never been characterized before. This study reports on the chemical composition of the extract and on its viscoelastic properties through rotational and oscillatory rheological measurements. Explanations of the mechanism behind the rheological properties were based on transient network models for associating polymers.

Post-translational modification regulates prostaglandin D2 synthase apoptotic activity: characterization by site-directed mutagenesis.

Lipocalin-type prostaglandin D(2) synthase (L-PGDS) is a highly glycosylated protein found in several body fluids. Elevated L-PGDS levels have been observed in the serum of patients with renal impairment, diabetes mellitus, and hypertension. Recently, we demonstrated the ability of L-PGDS to induce apoptosis in a variety of cell types including epithelial cells, neuronal cells, and vascular smooth muscle cells (VSMCs). The aim of this study was to investigate the effect several site-directed mutations had on L-PGDS-induced apoptosis in order to identify potential sites of regulation. Point mutations created in a glycosylation site (Asn51), a protein kinase C phosphorylation site (Ser106), and the enzymatic active site (Cys65) all inhibited L-PGDS-induced apoptosis as determined by both terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) and caspase3 activity. We also compared the L-PGDS isoforms present in GK rat serum to WKY control serum using two-dimensional gel electrophoresis and observed distinct differences which vanished after PNGase F glycolytic digestion. We conclude that post-translational modification of L-PGDS, by either glycosylation or phosphorylation, enhances its apoptotic activity and inhibits VSMC hyperproliferation and postulate that this process is altered in type 2 diabetes.

Rheological and light scattering properties of flaxseed polysaccharide aqueous solutions.

Polysaccharides isolated from flaxseed meals using ethanol consisted of a soluble ( approximately 7.5% w/w) and an insoluble fraction (2% w/w). The soluble fraction was dialyzed in various salt concentrations and characterized using viscometry and light scattering techniques. Observations using a size-exclusion column coupled to a multiangle laser light scattering (SEC-MALLS) revealed three molecular weight fractions consisting of a small amount ( approximately 17%) of large molecular weight species (1.0 x 10(6)) and a large amount ( approximately 69%) of small molecular weight species (3.1 x 10(5) Da). Dynamic light scattering measurements indicated the presence of very small molecules (hydrodynamic radius approximately 10 nm) and a very large molecular species (hydrodynamic radius in excess of 100 nm); the latter were probably aggregates. The intrinsic viscosity, [eta], of the polysaccharide in Milli-Q water was 1030 +/- 20 mL/g. The viscosity was due largely to the large molecular weight species since viscosity is influenced by the hydrodynamic volume of molecules in solution. The Smidsrod parameter B obtained was approximately 0.018, indicating that the molecules adopted a semi-flexible conformation. This was also indicated by the slope ( approximately 0.56) from the plot of root-mean-square (RMS) radius versus molar mass (M(w)).

Viscoelastic behaviour aids extrusion from and reabsorption of the liquid phase into the digesta plug: creep rheometry of hindgut digesta in the common brushtail possum Trichosurus vulpecula.

Temporal variation in the rheometric properties of the proximal and distal colonic digesta of an arboreal marsupial folivore, the common brushtail possum, was examined to assess flow behaviour during peristalsis, segmentation and other aspects of intestinal motility. The time-dependent rheometric characteristics on application of a constant shear stress within the physiological range showed an initial elastic and subsequent viscoelastic phase, which fitted Burger's model of creep compliance. Similarly, the time-dependent rheometric characteristics on recovery from shear stress fitted with a generalised two-component Maxwell model of elastic and viscoelastic components for creep recovery. Differences in the relative magnitudes of the viscoelastic components during recovery from those during shear indicated that the physical properties of the digesta plug changed with sustained shear stress, a phenomenon, which is likely to result from extrusion of the liquid phase from the solid elements of the digesta plug. There was significant viscoelastic recovery during the initial 4 s following cessation of stress, which would allow for prompt concomitant reabsorption of the liquid phase into the digesta plug. This supports a hypothesis of alternate extrusion and reabsorption of the liquid phase of the digesta plug. This would promote both nutrient absorption across the intestinal wall (from liquid extrusion) and enzyme permeation and digestion (from liquid absorption into the plug). However, the presence of a slower component of viscoelastic recovery indicates that liquid phase reabsorption into the digesta plug is incomplete if the interval before a subsequent contraction is less than 150 s, in which case unreabsorbed liquid may be driven either orally or aborally. This would at least partly account for differences in retention times of liquid and solid phase digesta markers reported for the gastrointestinal tracts of numerous vertebrate species.

Accelerated glucose intolerance, nephropathy, and atherosclerosis in prostaglandin D2 synthase knock-out mice.

Type 2 diabetics have an increased risk of developing atherosclerosis, suggesting the mechanisms that cause this disease are enhanced by insulin resistance. In this study we examined the effects of gene knock-out (KO) of lipocalin-type prostaglandin D(2) synthase (L-PGDS), a protein found at elevated levels in type 2 diabetics, on diet-induced glucose tolerance and atherosclerosis. Our results show that L-PGDS KO mice become glucose-in-tolerant and insulin-resistant at an accelerated rate when compared with the C57BL/6 control strain. Adipocytes were significantly larger in the L-PGDS KO mice compared with controls on the same diets. Cell culture data revealed significant differences between insulin-stimulated mitogen-activated protein kinase phosphatase-2, protein-tyrosine phosphatase-1D, and phosphorylated focal adhesion kinase expression levels in L-PGDS KO vascular smooth muscle cells and controls. In addition, only the L-PGDS KO mice developed nephropathy and an aortic thickening reminiscent to the early stages of atherosclerosis when fed a "diabetogenic" high fat diet. We conclude that L-PGDS plays an important role regulating insulin sensitivity and atherosclerosis in type 2 diabetes and may represent a novel model of insulin resistance, atherosclerosis, and diabetic nephropathy.

Periodic fluid extrusion and models of digesta mixing in the intestine of a herbivore, the common brushtail possum (Trichosurus vulpecula).

The digesta in four gut compartments (proximal and distal halves of small intestine, caecum, and proximal colon) of a wild hindgut fermenting herbivore, the common brushtail possum (Trichosurus vulpecula), were investigated by rheometry and permeametry. Digesta from all compartments were highly viscous and exhibited shear-thinning. Apparent viscosity was positively related to dry matter content, and increased from proximal small intestine to colon. Dynamic rheological measurements showed that in small intestinal digesta the elastic modulus was greater than the viscous modulus and their ratios were characteristic of weak gels, indicating that digesta could sustain compression. The apparent viscosity of distal small intestinal digesta was markedly lower when measured by capillary viscometry than by rotatory viscometry, indicating that plug flow was likely to be facilitated by lubrication from a peripheral layer of less viscous fluid; i.e., there was an augmented plug flow. Permeametry showed that fluid was extruded from all digesta on compression at physiological pressures, that there was significant permeability of proximal and distal small intestinal digesta, but that digesta became progressively compacted during permeation, with a concomitant reduction in permeability as dry matter content increased. It is proposed that conditions within the small intestine differ from those of an ideal plug flow reactor as radial mixing and turbulence cannot occur. Instead, we suggest that segmentation and peristalsis aid radial mixing of the fluid phase by compressing the solid phase, with extrusion of fluid through the digesta plug. This extrusion may be followed by resorption of fluid back into the plug when the elasticity of the solid phase of digesta is Hookean, thus aiding the mixing of secreted enzymes with insoluble substrates within the plug.

Negative regulation of midline vascular development by the notochord.

The negative regulation of vascular patterning is one of the least understood processes in vascular biology. In amniotes, blood vessels develop throughout the embryonic disc, except for a midline region surrounding the notochord. Here we show that the notochord is the primary signaling center for the inhibition of vessel formation along the embryonic midline. Notochord ablation in quail embryos results in vascular plexus formation at midline. Implantation of the notochord into paraxial and lateral mesoderm inhibits vessel formation locally. The notochord-expressed BMP antagonists Chordin and Noggin inhibit endothelial cell migration in vitro, and their ectopic expression in vivo results in a local disruption of vessel formation. Conversely, BMP-4 activates endothelial cell migration in vitro, and its ectopic expression along the notochord induces vascular plexus formation at midline. These data indicate an inhibitory role of the notochord in defining an avascular zone at the embryonic midline, in part via BMP antagonism.

Hemodynamic-dependent patterning of endothelin converting enzyme 1 expression and differentiation of impulse-conducting Purkinje fibers in the embryonic heart.

Impulse-conducting Purkinje fibers differentiate from myocytes during embryogenesis. The conversion of contractile myocytes into conduction cells is induced by the stretch/pressure-induced factor, endothelin (ET). Active ET is produced via proteolytic processing from its precursor by ET-converting enzyme 1 (ECE1) and triggers signaling by binding to its receptors. In the embryonic chick heart, ET receptors are expressed by all myocytes, but ECE1 is predominantly expressed in endothelial cells of coronary arteries and endocardium along which Purkinje fiber recruitment from myocytes takes place. Furthermore, co-expression of exogenous ECE1 and ET-precursor in the embryonic heart is sufficient to ectopically convert cardiomyocytes into Purkinje fibers. Thus, localized expression of ECE1 defines the site of Purkinje fiber recruitment in embryonic myocardium. However, it is not known how ECE1 expression is regulated in the embryonic heart. The unique expression pattern of ECE1 in the embryonic heart suggests that blood flow-induced stress/stretch may play a role in patterning ECE1 expression and subsequent induction of Purkinje fiber differentiation. We show that gadolinium, an antagonist for stretch-activated cation channels, downregulates the expression of ECE1 and a conduction cell marker, Cx40, in ventricular chambers, concurrently with delayed maturation of a ventricular conduction pathway. Conversely, pressure-overload in the ventricle by conotruncal banding results in a significant expansion of endocardial ECE1 expression and Cx40-positive putative Purkinje fibers. Coincident with this, an excitation pattern typical of the mature heart is precociously established. These in vivo data suggest that biomechanical forces acting on, and created by, the cardiovascular system during embryogenesis play a crucial role in Purkinje fiber induction and patterning.