Elsevier

Placenta

Volume 35, Issue 10, October 2014, Pages 802-807
Placenta

Fatty Acid Binding Protein-4 is expressed in the mouse placental labyrinth, yet is dispensable for placental triglyceride accumulation and fetal growth

https://doi.org/10.1016/j.placenta.2014.07.008Get rights and content

Highlights

  • FABP4 regulates lipid trafficking in human trophoblasts. Its role in the placenta in vivo is unknown.

  • FABP4 is expressed in the mouse placental labyrinthine layer, mainly in endothelial cells.

  • The level of mouse placental FABP4 is highest at E16.5.

  • FABP4 is dispensable for murine feto-placental growth and placental lipid accumulation.

Abstract

Introduction

Fatty Acid Binding Protein-4 (FABP4) is a member of a family of FABP proteins that regulate intracellular lipid trafficking in diverse tissues. We recently showed that FABP4 regulates triglyceride accumulation in primary human trophoblasts. To assess the function of placental FABP4 in vivo, we tested the hypothesis that FABP4 is expressed in the murine placenta, and regulates placenta triglyceride accumulation.

Methods

C57Bl/6 wild type or Fabp4-null mice were time-bred, and fetuses and placentas harvested at different time points during pregnancy. Placental FABP4 expression was assessed at different gestational ages, using quantitative PCR, immunohistochemistry, immunofluorescence and western immunoblotting. FABPs expression was examined by RT-qPCR. Placental lipids were extracted using the Folch method and triglyceride levels determined using a colorimetric quantification kit.

Results

Using immunohistochemistry, we found that FABP4 was expressed in the placental labyrinthine layer, predominantly in endothelial cells in association with CD31 positive fetal capillaries. The level of placental FABP4 mRNA and protein increased from E12.5 to E16.5 and slightly decreased at E18.5. Breeding of Fabp4 heterozygous mice resulted in embryonic genotypes that followed a Mendelian distribution and exhibited normal weight and morphology, triglyceride content, and expression of other FABP family members. Exposure to hypoxia (O2 = 12%) between E12.5–E18.5 did not uncover a difference between wild type and Fabp4-null mice.

Conclusions

FABP4 is expressed in the mouse placental labyrinth, with highest expression at E16.5. FABP4 is dispensable for feto-placental growth and placental lipid accumulation.

Introduction

The trans-placental maternal-to-fetal transport of nutrients is essential for normal growth and development of the eutherian embryo. Fetal growth restriction that results from fetal hypo-nutrition has been associated with intrauterine fetal death, neonatal and childhood morbidity, and the adult metabolic syndrome with its consequences [1]. Among nutrients that support intrauterine growth, fatty acids are germane, particularly during the second half of pregnancy, when fetal growth accelerates and fat accretion increases exponentially [2], [3], [4], [5]. Fatty acids are also essential for organ development–for instance, in the brain, retina, heart and lungs [6], [7], [8], [9], [10], [11]–where they serve as a source of calories and membrane building blocks and also as precursors for the production of eicosanoids, phospholipids, and their derivatives [12], [13].

The major fraction of fatty acids that circulate in the maternal blood is covalently bound by triglycerides and lipoproteins, with a smaller fraction circulating as free fatty acids bound by albumin, VLDL, or chylomicron. Fatty acids are released for placental uptake by the action of triglyceride hydrolases and transported across the trophoblastic microvillous membrane, with kinetics that depend on biochemical characteristics such as chain length, lipid solubility, and affinity to carrier proteins [14], [15], [16], [17], [18], [19]. Within cells, cytoplasmic fatty acids are bound by fatty acid binding proteins (FABPs). These small (132 aa) proteins mediate intracellular fatty acid transport to lipid droplets for storage, to mitochondria or peroxisomes for oxidation and energy production, to the endoplasmic reticulum for membrane synthesis and cell signaling, and to the nucleus for regulation of gene expression [20].

We have previously determined that FABP1, FABP3, FABP4, FABP5, and FABPpm are the dominant FABP forms expressed in human placental trophoblasts [21], [22]. Importantly, we found that hypoxia selectively upregulated the expression of FABP1, FABP3 and FABP4 and that fatty acids enhance the expression of FABP4. These changes were associated with increased lipid droplet and triglyceride accumulation in primary human trophoblasts (PHT) and were attenuated by inhibition of FABP4 [21], [22]. Coupled with the known function of FABP4 (also known as adipocyte FABP4, AFABP4, adipocyte protein 2, and aP2) as a fatty acid chaperone [23], [24], [25], our findings led us to propose the hypothesis that FABP4 is a key regulator of trophoblastic lipid transport and accumulation. To assess the function of FABP4 in vivo, we sought to determine the expression of FABP4 in the mouse placenta, and determine the impact of Fabp4 ablation in mice on feto-placental development and triglyceride accumulation.

Section snippets

Animals and breeding

Our experiments were performed using either wild type (wt) C57Bl/6 mice, obtained from Jackson Laboratory, or C57Bl/6 mice that harbor a targeted mutation in the Fabp4 gene, which were provided by Dr. G. Hotamisligil (Harvard University) [26]. Our experimental protocols were approved by the Institutional Animal Care and Use Committee of the University of Pittsburgh. We performed timed breeding by pairing heterozygous males and females overnight, with the morning after mating labeled as

Results

To gain insight into the role of placental FABP4 in vivo, we initially sought to examine the expression of FABP4 in placentas of wild type C57Bl/6 mice. Using immunohistochemistry (Fig. 1), we confirmed that FABP4 is highly expressed in the maternal decidua, as previously shown [29]. Importantly, within the placenta proper, we found that FABP4 is primarily expressed in the labyrinthine layer and not in the junctional zone (Fig. 1, Fig. 2J). Using immunofluorescent co-staining for the

Discussion

We previously found that FABP4 is expressed in human placental trophoblasts. We also found that exposure of PHT cells to either fatty acids or hypoxia in vitro enhanced the expression of FABP4 and that pharmacological or siRNA-mediated inhibition of FABP4 markedly reduced the accumulation of triglycerides in trophoblasts [21], [22]. Notably, FABP4 was previously shown to be highly expressed in the mouse decidua as early as E5, with a major increase in expression on E7–8 [29], yet the expression

Conflict of interest

None declared.

Financial support

This project was supported by R01-HD045675, P01-HD069316, and R01-ES011597 (to YS).

Disclosure

The authors have nothing to disclose.

Acknowledgments

We thank Dr. Dr. Gokhan Hotamisligil (Harvard School of Public Health) for generously providing the Fabp4 heterozygous mice. We thank Judy Ziegler and Sun Huijie for technical assistance, Lori Rideout for assistance in manuscript preparation, and Bruce Campbell for editing. The project was supported by NIH grants R01-HD045675, P01-HD069316, and R01-ES011597 (to YS).

References (33)

  • D.A. Bernlohr et al.

    Evidence for an increase in transcription of specific mRNAs during differentiation of 3T3-L1 preadipocytes

    J Biol Chem

    (1985)
  • N.R. Coe et al.

    Targeted disruption of the adipocyte lipid-binding protein (aP2 protein) gene impairs fat cell lipolysis and increases cellular fatty acid levels

    J Lipid Res

    (1999)
  • J. Folch et al.

    A simple method for the isolation and purification of total lipides from animal tissues

    J Biol Chem

    (1957)
  • P. Haggarty

    Fatty acid supply to the human fetus

    Annu Rev Nutr

    (2010)
  • P. Haggarty

    Meeting the fetal requirement for polyunsaturated fatty acids in pregnancy

    Curr Opin Clin Nutr Metab Care

    (2014)
  • E. Herrera

    Lipid metabolism in pregnancy and its consequences in the fetus and newborn

    Endocrine

    (2002)
  • Cited by (23)

    • Placental hypoxia: What have we learnt from small animal models?

      2021, Placenta
      Citation Excerpt :

      However, overall, only select transport mechanisms and transporters have been investigated in the placenta in response to MIH and RUPP. Thus, it is likely that other placental transport mechanisms, such as those for lipids, ions, micronutrients, vitamins and water may also be altered [101–103]. Alongside its transport function, the placenta signals fetal needs for nutrients and oxygen to the mother via the secretion of hormones and growth factors [104].

    • Perinatal lipid nutrition

      2020, Molecular Nutrition: Mother and Infant
    • Variation in the FABP4 gene affects carcass and growth traits in sheep

      2018, Meat Science
      Citation Excerpt :

      The effects of FABP4 variation on birth-weight, growth and muscle yield might also be explained by other phenomenon. Besides being predominantly expressed within adipocytes, FABP4 is also expressed in the placenta in humans (Scifres, Chen, Nelson, & Sadovsky, 2011) and mice (Makkar, Mishima, Chang, Scifres, & Sadovsky, 2014). The latter report suggested that FABP4 may be involved in foeto-placental growth and placental lipid accumulation.

    • Effect of maternal hypoglycaemia during gestation on materno-foetal nutrient transfer and embryo-foetal development: Evidence from experimental studies focused primarily on the rat

      2018, Reproductive Toxicology
      Citation Excerpt :

      Intracellular fatty acid binding proteins (FABP), mainly FABP-3 in mice and rats placenta, but also FABP-5 at low levels in mice, facilitate further delivery to transporters in the membranes facing the foetal circulation [17,168,171,172,180–182]. Transport from placental tissue into the foetal circulation is most likely maintained by FABP-4, which is predominantly present in foetal vascular endothelial cells in mice [183], although, fabp-4 knock-out does not affect embryo-foetal growth in mice [183]. FABP-3 has been identified as the major FABP expressed in mouse trophoblast cells [180].

    • Modulation of FABP4 hypomethylation by DNMT1 and its inverse interaction with miR-148a/152 in the placenta of preeclamptic rats and HTR-8 cells

      2016, Placenta
      Citation Excerpt :

      Bound antibodies were viewed under a confocal microscope (Olympus Fluoview 1000, Japan). Lipids were extracted from placental tissues or HTR-8 cells by the Folch method [21]. Chloroform/methanol mix based on the Folch method was also used to extract lipids from the maternal serum.

    View all citing articles on Scopus
    View full text