Elsevier

Life Sciences

Volume 86, Issues 21–22, 22 May 2010, Pages 781-790
Life Sciences

Carbaprostacyclin, a PPARδ agonist, ameliorates excess lipid accumulation in diabetic rat placentas

https://doi.org/10.1016/j.lfs.2010.03.008Get rights and content

Abstract

Aims

Maternal diabetes impairs placental development and metabolism. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors relevant in metabolic homeostasis. We investigated the concentrations of PPARδ and its endogenous agonist prostacyclin (PGI2), as well as the effects of carbaprostacylin (cPGI2, a PPARδ agonist) on lipid metabolism in placentas from control and streptozotocin-induced diabetic rats on day 13.5 of gestation.

Main methods

The placentas were explanted to evaluate PPARδ expression and PGI2 concentrations, and cultured with cPGI2 for further analysis of lipid metabolism (concentrations and 14C-acetate derived synthesis of triglycerides, cholesteryl esters, phospholipids, cholesterol and free fatty acids; release of glycerol and lipid peroxidation).

Key findings

Reduced PGI2 concentrations were found in the placentas from diabetic rats when compared to controls. cPGI2 additions reduced the concentrations and synthesis of several lipid species, increased lipid catabolism and reduced lipid peroxidation in the placenta. These effects were more marked in diabetic tissues, which presented alterations in the lipid metabolic parameters evaluated. cPGI2 additions increased placental PPARδ and acyl-CoA oxidase expression, which are changes possibly involved in the catabolic effects observed.

Significance

The present study reveals the capability of cPGI2 to regulate placental lipid metabolism and PPARδ expression, and suggests that preserving appropriate PGI2 concentrations in the placenta may help to metabolize maternal derived lipid overload in diabetic gestations.

Introduction

The altered metabolic environment in maternal diabetes during pregnancy impairs fetal and placental development (Jawerbaum and Gonzalez, 2006, Melamed and Hod, 2009). Placental alterations in morphology, function and metabolism are found in both human and experimental diabetic pregnancies (Capobianco et al., 2008, Daskalakis et al., 2008, Desoye and Shafrir, 1996, Yu et al., 2008). Impaired nutrient transfer through the placenta leads to lipid overaccumulation in the placenta and the fetus, a feature that characterizes the macrosomic fetus in both human and various experimental models (Diamant et al., 1982, Herrera and Amusquivar, 2000, Khan, 2007). In addition, a pro-inflammatory environment is a feature in diabetic pregnancies, and several markers of pro-inflammation, including increased lipid peroxidation, have been observed both in fetuses and in the placenta (Jawerbaum and Gonzalez, 2006, Pustovrh et al., 2005, Radaelli et al., 2003).

The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that regulate the expression of several genes involved in metabolic homeostasis, developmental processes and the regulation of pro-inflammatory processes (Bensinger and Tontonoz, 2008, Desvergne et al., 2004, Wieser et al., 2008). PPAR ligands are well known to induce the expression of several genes involved in both peroxisomal and mitochondrial β-oxidation, and to amplify their signalling pathways through the increase of PPAR expression (Limor et al., 2008, Nagasawa et al., 2006, Reddy and Rao, 2006).

There are three PPAR isotypes identified (PPARα, PPARγ and PPARδ) which form a functional transcriptional unit upon heterodimerization with retinoid X receptors and activation by their ligands (Hihi et al. 2002). PPAR ligands are various fatty acids, with greater preference for monounsaturated and polyunsaturated fatty acids. Indeed, the arachidonic acid metabolites leukotriene B4 (LTB4), 15deoxyΔ12,14prostaglandinJ2 (15dPGJ2) and prostacyclin (PGI2) have been shown to respectively activate PPARα, PPARγ and PPARδ (Forman et al., 1997, Hihi et al., 2002, Wise, 2003). Synthetic analogues of PGI2 such as carbaprostacyclin (cPGI2) are also able to bind and act as agonists of PPARδ (Forman et al., 1997, Wise, 2003). Although it is well known that PGI2 can classically act through membrane prostacyclin receptors (IP), PGI2 activation of PPARδ has been shown to be involved in several biological processes such as angiogenesis, lipid homeostasis in cardiomyocytes and skeletal muscle, stem cell proliferation, decidualization and embryo implantation (Barish et al., 2006, de Lange et al., 2008, He et al., 2008, Kim and Han, 2008, Lim and Dey, 2000, Wang et al., 2007).

We have previously found reduced PPARδ and PGI2 concentrations in the embryos from diabetic rats during early organogenesis, which are alterations related to impairments in the synthesis of lipids and in the production of PGE2 needed for proper embryo morphogenesis (Higa et al. 2007). Reduced concentrations of PGI2 have also been found in term placentas from diabetic patients and diabetic experimental models, an alteration related to the impaired vascular function of the placenta (Jawerbaum et al., 1997, Kuhn et al., 1990, Saldeen et al., 1998).

PPARδ is highly expressed in the syncytial trophoblast layer in the human placenta and its expression increases during labour (Berry et al., 2003, Wang et al., 2002). In human trophoblast cells cultured in vitro, cPGI2 regulates the expression of 11-β-hydroxysteroid dehydrogenase type 2, an enzyme that metabolizes maternal derived glucocorticoids and is related to fetal growth (Julan et al. 2005).

PPARδ is expressed in the three layers of the mouse placenta and regulates the differentiation of trophoblast giant cells, which play a critical role in the establishment of the placental structure, fulfil an important endocrine function, and are an important site of lipid accumulation during development (Nadra et al. 2006). PPARδ null mice are not viable due to severe impairments in placental development, as a result of an altered differentiation of the trophoblast giant cells, spongiotrophoblasts and glycogen trophoblast cells (Barak et al., 2002, Nadra et al., 2006, Wang et al., 2007). These developmental alterations are different from those found in the PPARγ null mice, in which defective placental vascularization leads to an impaired fetal cardiac development and function (Barak et al. 1999). PPARα null mice are viable but present several metabolic impairments and an increased abortion rate (Yessoufou et al. 2006). These data suggest that the three PPAR isotypes have specific roles in placental development (Barak et al. 2008).

We have recently identified PPARγ and PPARα as regulators of lipid metabolic processes in the rat placenta (Capobianco et al., 2008, Martinez et al., 2008). Moreover, in a mild diabetic rat model obtained through neonatal administration of streptozotocin (Portha et al. 1979), thoroughly characterized throughout gestation (Jawerbaum and Gonzalez 2005), the concentrations of PPARγ and PPARα isoforms and the concentrations of 15dPGJ2 and LTB4 (PPARγ and PPARα respective endogenous ligands) are altered in the placenta, and the activation of these nuclear receptors results in different metabolic functions in the diabetic placenta (Capobianco et al., 2008, Martinez et al., 2008). The aim of the present study was to assess the expression of PPARδ, the concentrations of PGI2 and the effect of carbaprostacyclin (a PGI2 analogue that activates PPARδ) in lipid concentrations, synthesis, catabolism and peroxidation in placentas of pregnant control and diabetic rats at day 13.5 of gestation. The results revealed that the PPARδ agonist cPGI2 also has a specific regulatory function in the regulation of lipid homeostasis in both control and diabetic placentas.

Section snippets

Animals

Albino Wistar rats bred in the laboratory were fed ad libitum with commercial rat chow (Asociación Cooperativa Argentina, Buenos Aires, Argentina). At 2 days of age neonates were injected with either streptozotocin (90 mg/kg s.c., Sigma-Aldrich) in citrate buffer (0.05 M, pH 4.5) (diabetic experimental model) or buffer alone (controls) (Portha et al. 1979). The reproductive characteristics of this diabetic experimental model have been reported previously (Jawerbaum and Gonzalez 2005). Control and

Prostacyclin concentrations and PPARδ expression

In the diabetic experimental model evaluated, pregnant rats on day 13.5 of gestation showed marked hyperglycemia (control: 100 ± 11 mg/dl, diabetic: 221 ± 25 mg/dl; p < 0.001) and triglyceridemia (control: 1.06 ± 0.15 g/l, diabetic: 2.06 ± 0.41 g/l; p < 0.05). In the placentas from diabetic animals there were no changes in PPARδ mRNA when compared to controls (Fig. 1A). PPARδ protein content was also similar in placentas from control and diabetic rats (Fig. 1B). The concentrations of PGI2, an endogenous PPARδ

Discussion

In the present study, we identified a novel role of cPGI2, a PPARδ agonist, as a regulator of lipid metabolism and peroxidation in the placentas from diabetic rats. These results, together with the observed reduction in PGI2 concentration in the placentas from these diabetic animals, contribute to the understanding of the altered regulatory pathways of placental lipid metabolism that could lead to fetal impairments in maternal diabetes.

Indeed, placental lipid transfer is critical for normal

Conclusions

The present work provides evidence of abnormal PGI2 concentrations in the diabetic rat placenta in a post-implantation stage, a reduction that may lead to alterations in its signalling pathway through PPARδ, as no changes in the expression of this nuclear receptor were observed. Besides, the PPARδ agonist cPGI2 has been shown to be a potent regulator of lipid concentrations, synthesis, catabolism and peroxidation and to upregulate PPARδ mRNA, providing clues that PPARδ activation and/or

Conflict of interest statement

There is no conflict of interest.

Acknowledgements

This work was supported by grants from Agencia de Promoción Científica y Tecnológica de Argentina (PICT 05-32268 and PICT 06-00084).

References (65)

  • H. Ohkawa et al.

    Assay for lipid peroxides in animal tissues by thiobarbituric acid reaction

    Analytical Biochemistry

    (1979)
  • P.E. Poleni et al.

    Agonists of peroxisome proliferators-activated receptors (PPAR) alpha, beta/delta or gamma reduce transforming growth factor (TGF)-beta-induced proteoglycans' production in chondrocytes

    Osteoarthritis and Cartilage / OARS, Osteoarthritis Research Society

    (2007)
  • S.M. Reilly et al.

    PPAR delta as a therapeutic target in metabolic disease

    FEBS Letters

    (2008)
  • P. Saldeen et al.

    Prostanoid production in the umbilicoplacental arterial tree relative to impaired glucose tolerance

    Early Human Development

    (1998)
  • N. Suwaki et al.

    Expression and potential role of peroxisome proliferator-activated receptor gamma in the placenta of diabetic pregnancy

    Placenta

    (2007)
  • H. Wang et al.

    Stage-specific integration of maternal and embryonic peroxisome proliferator-activated receptor delta signaling is critical to pregnancy success

    The Journal of Biological Chemistry

    (2007)
  • Q. Wang et al.

    Expression of PPAR and RXR isoforms in the developing rat and human term placentas

    Placenta

    (2002)
  • K.K. Wu et al.

    Cellular and molecular biology of prostacyclin synthase

    Biochemical and Biophysical Research Communications

    (2005)
  • Y. Xu et al.

    Effect of placental fatty acid metabolism and regulation by peroxisome proliferator activated receptor on pregnancy and fetal outcomes

    Journal of Pharmaceutical Sciences

    (2007)
  • D.A. Young et al.

    A novel method for measurement of triglyceride lipase activity: suitable for microgram and nanogram quantities of tissue

    Journal of Lipid Research

    (1988)
  • K. Asayama et al.

    Increased peroxisomal fatty acid beta-oxidation and enhanced expression of peroxisome proliferator-activated receptor-alpha in diabetic rat liver

    Molecular and Cellular Biochemistry

    (1999)
  • Y. Barak et al.

    Effects of peroxisome proliferator-activated receptor delta on placentation, adiposity, and colorectal cancer

    Proceedings of the National Academy of Sciences of the United States of America

    (2002)
  • Y. Barak et al.

    PPAR signaling in placental development and function

    PPAR Research

    (2008)
  • G.D. Barish et al.

    PPAR delta: a dagger in the heart of the metabolic syndrome

    The Journal of Clinical Investigation

    (2006)
  • S.J. Bensinger et al.

    Integration of metabolism and inflammation by lipid-activated nuclear receptors

    Nature

    (2008)
  • E.B. Berry et al.

    Peroxisome proliferator-activated receptor isoform expression changes in human gestational tissues with labor at term

    Molecular Pharmacology

    (2003)
  • O. Braissant et al.

    Differential expression of peroxisome proliferator-activated receptor-alpha, -beta, and -gamma during rat embryonic development

    Endocrinology

    (1998)
  • E. Capobianco et al.

    15-deoxy-delta(12,14)-prostaglandin J2 and peroxisome proliferator-activated receptor gamma (PPARgamma) levels in term placental tissues from control and diabetic rats: modulatory effects of a PPARgamma agonist on nitridergic and lipid placental metabolism

    Reproduction, Fertility, and Development

    (2005)
  • E. Capobianco et al.

    Effects of natural ligands of PPARgamma on lipid metabolism in placental tissues from healthy and diabetic rats

    Molecular Human Reproduction

    (2008)
  • G. Daskalakis et al.

    Placental pathology in women with gestational diabetes

    Acta Obstetricia et Gynecologica Scandinavica

    (2008)
  • P. de Lange et al.

    Peroxisome proliferator-activated receptor delta: a conserved director of lipid homeostasis through regulation of the oxidative capacity of muscle

    PPAR Research

    (2008)
  • G. Desoye et al.

    The human placenta in diabetic pregnancy

    Diabetic Reviews

    (1996)
  • Cited by (0)

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