Characterization of cardiac fatty-acid-binding protein from human placenta. Comparison with placenta hepatic types

Transport of Docosahexaenoic Acid via the Human Placenta: A Theoretical Study

The high demand of the fetus for Docosahexaenoic acid, DHA, is satisfied by a concert of several mechanisms that take place in the placental terminal villi. Scarcity of laboratory data makes the detailed description of these mechanisms elusive. Here, the DHA transport across the placenta is modeled as a boundary value problem that accounts for diffusion, reactions with fatty acids binding proteins, FABPs, and metabolic consumption within the Syncytiotrophoblast, ST. For any given DHA fluxes at the bordering membranes, analytical and numerical solutions yield the DHA concentration profile within the ST. We find that in order to comply with adequate DHA delivery to the fetus and with physiological DHA concentrations in the maternal and fetal circulations, it is essential to have a significant rise of DHA concentration at the microvillus membrane, MVM and a rapid dissociation of the DHA from the FABP. The model establishes the relations between the concentrations of the FABPs in the ST, their equilibrium dissociation constant from the DHA, and the placental DHA metabolic degradation rate, hitherto unknown. We conclude that the bound (to the protein) DHA molecule is degraded at a rate of 0.3-0.45 s^-1.

Fatty acid transporting proteins: Roles in brain development, aging, and stroke

Polyunsaturated fatty acids are required for the brain development and significantly impact aging and stroke. Due to the hydrophobicity of fatty acids, fatty acids transportation related proteins that include fatty acid binding proteins (FABPs), long chain acyl-coA synthase (ACS), fatty acid transportation proteins (FATPs), fatty acid translocase (FAT/CD36) and newly reported major facilitator superfamily domain-containing protein (Mfsd2a) play critical roles in the uptake of various fatty acids, especially polyunsaturated fatty acids. They are not only involved in neurodevelopment, but also have great impact on neurological disease, such as aging related dementia and stroke.

Fatty Acid Binding Protein 3 Is Involved in n-3 and n-6 PUFA transport in mouse trophoblasts

BACKGROUND

Low placental fatty acid (FA) transport during the embryonic period has been suggested to result in fetal developmental disorders and various adult metabolic diseases, but the molecular mechanism by which FAs are transported through the placental unit remains largely unknown.

OBJECTIVE

The aim of this study was to examine the distribution and functional relevance of FA binding protein (FABP), a cellular chaperone of FAs, in the mouse placenta.

METHODS

We clarified the localization of FABPs and sought to examine their function in placental FA transport through the phenotypic analysis of Fabp3-knockout mice.

RESULTS

Four FABPs (FABP3, FABP4, FABP5, and FABP7) were expressed with spatial heterogeneity in the placenta, and FABP3 was dominantly localized to the trophoblast cells. In placentas from the Fabp3-knockout mice (both sexes), the transport coefficients for linoleic acid (LA) were significantly reduced compared with those from wild-type mice by 25% and 44% at embryonic day (E) 15.5 and E18.5, respectively, whereas those for α-linolenic acid (ALA) were reduced by 19% and 17%, respectively. The accumulation of LA (18% and 27% at E15.5 and E18.5) and ALA (16% at E15.5) was also significantly less in the Fabp3-knockout fetuses than in wild-type fetuses. In contrast, transport and accumulation of palmitic acid (PA) were unaffected and glucose uptake significantly increased by 23% in the gene-ablated mice compared with wild-type mice at E18.5. Incorporation of LA (51% and 52% at 1 and 60 min, respectively) and ALA (23% at 60 min), but not PA, was significantly less in FABP3-knockdown BeWo cells than in controls, whereas glucose uptake was significantly upregulated by 51%, 50%, 31%, and 33% at 1, 20, 40, and 60 min, respectively.

CONCLUSIONS

Collectively FABP3 regulates n-3 (ω-3) and n-6 (ω-6) polyunsaturated FA transport in trophoblasts and plays a pivotal role in fetal development.

Hypoxia regulates the expression of fatty acid-binding proteins in primary term human trophoblasts

OBJECTIVE

Fatty acids (FAs) are essential for fetal development. Cellular FA uptake is modulated by fatty acid-binding proteins (FABPs). We hypothesized that hypoxia regulates the expression of FABPs in human trophoblasts.

STUDY DESIGN

Primary term human trophoblasts were cultured for 72 hours in either standard (O2 = 20%) or hypoxic (O2 < 1%) conditions. FABP expression was interrogated using polymerase chain reaction and Western immunoblotting. Trophoblast lipid droplets were examined using dipyrromethene boron difluoride 493/503 staining.

RESULTS

We detected the expression of FABP1, -3, -4, -5, and pm but not FABP2 or FABP6-9 subtypes in trophoblasts. Exposure to hypoxia markedly increased lipid droplet accumulation in trophoblasts. Consistent with this observation, hypoxia enhanced the expression of FABP1, -3, and -4. Lastly, agonists of peroxisome proliferator-activated receptor-gamma enhanced the expression of FABP1 and -4 in trophoblasts.

CONCLUSION

Hypoxia enhances the expression of FABP1, -3, and -4 in term human trophoblasts, suggesting that FABPs support fat accumulation in the hypoxic placenta.

Effect of maternal triglycerides and free fatty acids on placental LPL in cultured primary trophoblast cells and in a case of maternal LPL deficiency

Maternal hypertriglyceridemia is a normal condition in late gestation and is an adaptation to ensure an adequate nutrient supply to the fetus. Placental lipoprotein lipase (LPL) is involved in the initial step in transplacental fatty acid transport as it hydrolyzes maternal triglycerides (TG) to release free fatty acids (FFA). We investigated LPL activity and protein (Western blot) and mRNA expression (real-time RT-PCR) in the placenta of an LPL-deficient mother with marked hypertriglyceridemia. The LPL activity was fourfold lower, LPL protein expression 50% lower, and mRNA expression threefold higher than that of normal, healthy placentas at term (n = 4-7). To further investigate the role of maternal lipids in placental LPL regulation, we isolated placental cytotrophoblasts from term placentas and studied LPL activity and protein and mRNA expression after incubation in Intralipid (as a source of TG) and oleic, linoleic, and a combination of oleic, linoleic, and arachidonic acids as well as insulin. Intralipid (40 and 400 mg/dl) decreased LPL activity by approximately 30% (n = 10-14, P < 0.05) and 400 microM linoleic and linoleic-oleic-arachidonic acid (n = 10) decreased LPL activity by 37 and 34%, respectively. No major changes were observed in LPL protein or mRNA expression. We found no effect of insulin on LPL activity or protein expression in the cultured trophoblasts. To conclude, the activity of placental LPL is reduced by high levels of maternal TG and/or FFA. This regulatory mechanism may serve to counteract an excessive delivery of FFA to the fetus in conditions where maternal TG levels are markedly increased.

Expression pattern of fatty acid transport protein-1 (FATP-1), FATP-4 and heart-fatty acid binding protein (H-FABP) genes in human term placenta

Placental tissue from five women undergoing elective caesarean did not present differences in fatty acids or mRNA expression of FATP-1, FATP-4 and H-FABP in different placental locations. mRNA expression of FATP-1 and FATP-4 was significantly higher than H-FABP. The expression of L-FABP was too low in placenta for accurate quantification.

Gestational and hormonal regulation of human placental lipoprotein lipase

The fetal demand for FFA increases as gestation proceeds, and LPL represents one potential mechanism for increasing placental lipid transport. We examined LPL activity and protein expression in first trimester and term human placenta. The LPL activity was 3-fold higher in term (n = 7; P < 0.05) compared with first trimester (n = 6) placentas. The LPL expression appeared lower in microvillous membrane from first trimester (n = 2) compared with term (n = 2) placentas. We incubated isolated placental villous fragments with a variety of effectors [GW 1929, estradiol, insulin, cortisol, epinephrine, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha] for 1, 3, and 24 h to investigate potential regulatory mechanisms. Decreased LPL activity was observed after 24 h of incubation with estradiol (1 micro g/ml), insulin, cortisol, and IGF-1 (n = 12; P < 0.05). We observed an increase in LPL activity after 3 h of incubation with estradiol (20 ng/ml) or hyperglycemic medium plus insulin (n = 7; P < 0.05). To conclude, we suggest that the gestational increase in placental LPL activity represents an important mechanism to enhance placental FFA transport in late pregnancy. Hormonal regulation of placental LPL activity by insulin, cortisol, IGF-1, and estradiol may be involved in gestational changes and in alterations in LPL activity in pregnancies complicated by altered fetal growth.

Implication of ATP and sodium in arachidonic acid incorporation by placental syncytiotrophoblast brush border and basal plasma membranes in the human

The human placental syncytiotrophoblast is the main site of exchange of nutrients and minerals between the mother and her fetus. In order to characterize the placental transport of some fatty acids, we studied the incorporation of arachidonic acid, a fetal primordial fatty acid, in purified bipolar syncytiotrophoblast brush border (BBM) and basal plasma membranes (BPM) from human placenta. The basal arachidonic acid incorporation in BBM and BPM was time dependent and reached maximal values of 0.75+/-0.10 and 0.48+/-0.18 pmol/mg protein, respectively, after 2.5 min. The presence of adenosine triphosphate (ATP) (3 m m) increases significantly the maximal incorporation of arachidonic acid by sixfold (4.75+/-0.35 pmol/mg) and ninefold (4.40+/-0.84 pmol/mg) in BBM and BPM, respectively. Moreover, an increase in the arachidonic acid incorporation was also obtained in the presence of sodium where the values achieved 7.68+/-0.98 (10x) and 6.53 pmol/mg (13.6x) for BBM and BPM, respectively. We also showed that the combination of both Na(+)and ATP increases significantly the maximal incorporation of arachidonic acid in BPM to 7.89+/-0.15 pmol/mg protein, while in BBM it did not modify its incorporation (8.18+/-0.25 pmol/mg protein), as compared to the presence of sodium alone. Our results demonstrate that arachidonic acid is incorporated by both placental syncytiotrophoblast membranes, and is ATP and sodium-linked. However, different mechanisms seem to be involved in this fatty acid incorporation through BBM and BPM, since the presence of Na(+)or ATP increased it, while the association of these two elements increased it only in BPM. We also demonstrated by osmolarity experiments that both membranes bind arachidonic acid, potentially involving one or more fatty acids binding proteins.

Composition and permeability of syncytiotrophoblast plasma membranes in pregnancies complicated by intrauterine growth restriction

The objective of this study was to determine placental membrane permeabilities to water, urea and mannitol in intrauterine growth restriction (IUGR) and compare them to normal gestational age matched controls. Further, we wished to investigate whether potential changes in permeability were related to changes in membrane fluidity, cholesterol or phospholipid fatty acid content of the membranes. Syncytiotrophoblast microvillous (MVM) and basal membranes (BM) were isolated from normal and IUGR placentas at term. Passive permeability to water, urea, and mannitol showed no significant alterations in IUGR compared to controls. Cholesterol content in BM, but not in MVM, was lower in placentas from pregnancies complicated by IUGR. However, membrane fluidity did not change in these pregnancies. The phospholipid fatty acid composition of the plasma membranes isolated from all placentas showed a predominance of unsaturated fatty acid species in the BM and saturated species in the MVM. In the MVM from IUGR, mead acid (20:3), behenic acid (22:0) and nervonic acid (24:1) constituted higher percentages of the total when compared to normally grown controls. In the BM from IUGR, mead acid (20:3) was increased relative to the total phospholipid fatty acid content. In conclusion, the syncytiotrophoblast membranes exhibit only minor changes in passive permeability and composition when the pregnancy is complicated by IUGR.

Detection and cellular localization of plasma membrane-associated and cytoplasmic fatty acid-binding proteins in human placenta

The aim of this study was to investigate location and the types of membrane-associated and cytoplasmic fatty acid-binding proteins in human placental trophoblasts using monospecific polyclonal antibodies. Western blot analysis demonstrated the presence of multiple membrane and cytoplasmic fatty acid transport/binding proteins in human placenta. In addition to previously reported placental membrane fatty acid-binding (p-FABPpm, 40 kDa), fatty acid translocase (FAT, 88 kDa) and fatty acid transport protein (FATP, 62 kDa) were detected in both microvillous and basal membranes of the human placenta. Among the cytoplasmic proteins, heart (H) and liver (L) type FABP were detected in the cytosol of the human placental primary trophoblasts as well as in human placental choriocarcinoma (BeWo) cells. The immunoreactivity of epidermal type (E)-FABP was not detected in trophoblasts or BeWo cells despite its presence in human placental cytosol. Location of FAT and FATP on the both sides of the bipolar placental cells may favour transport of free fatty acids (FFA) pool in both directions i.e. from the mother to the fetus and vice versa. However, p-FABPpm, because of its exclusive location on the microvillous membranes, may favour the unidirectional flow of maternal plasma long-chain polyunsaturated fatty acids present in the FFA pool to the fetus, due to binding specificity for these fatty acids. Although the roles of these proteins in placental fatty acid uptake and metabolism are yet to be understood fully, their complex interaction may be involved in the uptake of maternal FFA by the placenta for delivery to the fetus.

Long-chain polyunsaturated fatty acid transport across the perfused human placenta

The role of the placenta in controlling the supply of fatty acids to the fetus was investigated in term placentae (n = 9) from normal pregnancies. The maternal side was perfused ex vivo for 90 min with a modified Krebs Ringer solution containing a physiological mixture of fatty acids and ratio of fatty acid to human albumin. There was no evidence of chain elongation and desaturation of the essential fatty acids. Relative to the value for oleic acid, the rate of transfer to the fetal circulation was: 1.30 +/- 0.02 (P < 0.001) for linoleic acid, 1.61 +/- 0.09 (P = 0.002) for alpha-linolenic acid, 0.67 +/- 0.10 (P = 0.033) for arachidonic acid and 2.10 +/- 0.16 (P = 0.003) for docosahexaenoic acid. For tissue accumulation the values were 1.47 +/- 0.39 (P < 0.001) for linoleic acid, 2.24 +/- 0.37 (P = 0.027) for alpha-linolenic acid, 9.84 +/- 1.03 (P = 0.001) for arachidonic acid, and 3.01 +/- 0.79 (P = 0.064) for docosahexaenoic acid. The order of selectivity for transfer from the maternal to the fetal circulation was docosahexaenoic > alpha-linolenic > linoleic > oleic > arachidonic acid. Such a mechanism would allow the preferential transfer of docosahexaenoic acid and the essential fatty acids to the fetal circulation, thereby protecting the polyunsaturated fatty acid supply to the fetus during a critical period of development.

Endothelial cells of the human microvasculature express epidermal fatty acid-binding protein

Epidermal fatty acid-binding protein (E-FABP), previously characterized in human keratinocytes, is a cytoplasmic protein of 15 kD that specifically binds fatty acids (FAs). Previous PAGE-immunoblotting studies indicated that several human tissues display an immunoreactive band with an electrophoretic mobility identical to that of E-FABP. The aim of this study was to determine in which cells, other than keratinocytes, E-FABP might be expressed. By immunohistochemistry, we show that E-FABP is expressed in endothelial cells of the microvasculature of the placenta, heart, skeletal muscle, small intestine, lung, and renal medulla. Interestingly, in lung, a tissue of endodermal origin, E-FABP staining was also localized to secretory cells, ie, Clara cells, goblet cells, and probably a subpopulation of pneumocytes. RNA isolated from cultured human umbilical vein and normal human dermal microvascular endothelial cells was analyzed by reverse-transcriptase polymerase chain reaction (RT-PCR). Southern blotting and sequencing of the cloned RT-PCR products demonstrate that endothelial E-FABP is identical to keratinocyte E-FABP. These data suggest that E-FABP-mediated FA transport occurs at the level of the microvasculature in several FA target organs.

Fatty acid compositions of colostrum, cord blood, maternal blood and major infant formulas in Japan

Lipid profiles in colostrum, cord blood, maternal blood and major infant formulas in Japan were analyzed. In the first part of the study, colostrum obtained from 36 normal delivery women and six kinds of infant formulas provided by three major milk companies were analyzed for their fatty acid composition using capillary gas-lipid chromatography. Although enriched with docosahexaenoic acid (DHA), the percent composition of DHA in the six infant formulas (0.15-0.21%) was significantly lower than that in the colostrum (1.1 +/- 0.54). Arachidonic acid (AA) and eicosapentaenoic acid (EPA) were present in the colostrum but not detectable in the infant formulas. It is recommended that although the exact amount of specific fatty acids needed in the infant diet was not completely known, to be as close as possible to natural breast milk, the level of DHA, EPA and AA should be raised in the infant formulas. In the second part of the study, 19 pairs of maternal and cord blood were analyzed for their lipid profile. All samples were from normal vaginal delivery. The measurement of cholesterol, triglycerides, phospholipids and free fatty acids was performed with commercially available enzymatic methods on an automated discrete random access analyzer. Total fatty acid was determined as described in the first part of the study. The results were analyzed with Spearman's rank correlation coefficient. No correlation could be found between maternal and fetal concentrations of cholesterol, triglycerides, phospholipids or total fatty acids. Correlation could be found in non-esterified fatty acids, in palmitic acids, and oleic acid levels. It was concluded that the lipid transport and metabolism in the fetal-placenta unit is complex and further delicate investigation is required.

Linoleic acid transport by human placental syncytiotrophoblast membranes

The placenta syncytiotrophoblast is the site of exchange of nutrients, lipids and minerals between the mother and the fetus. In order to characterize the transport of fatty acids by the placenta, we purified bipolar syncytiotrophoblast brush border and basal plasma membranes from human placenta. These purified brush border and basal plasma membranes enriched 3-fold and 22-fold, respectively, in sodium/potassium-ATPase and 27-fold and 6-fold in alkaline phosphatase activity, compared with the placental homogenates. Fatty acid transport was performed at different fatty acid/albumin ratios to evaluate the optimal uptake conditions. The maximal transport efficiency, for linoleic acid bound to albumin by sonication, was obtained with a 6:1 fatty acid/albumin ratio in brush border and basal plasma membranes. The linoleic acid transport observed with brush border membranes followed Michaelis-Menten kinetics, with a Michaelis constant of 7.89 +/- 0.01 microM and a maximal incorporation rate of 30.80 +/- 6.39 pmol.mg-1.min-1. Linoleic acid transport was very low in basal plasma membranes and we obtained a Michaelis constant of 0.95 +/- 0.01 microM and a maximal incorporation rate of 1.62 +/- 5.06 pmol.mg-1.min-1. In order to show that linoleic acid accumulated within brush border and plasma membrane vesicles, and to eliminate the possibility of a non-specific binding of fatty acid to these membranes, we demonstrated by an osmolarity experiment, the decrease of the linoleic acid transport in brush border and basal plasma membranes obtained in the presence of 455 microM essential fatty acid at 23 degrees C for 180 min. The results presented in this study suggest that linoleic acid is transported significantly by syncytiotrophoblast brush border membranes and basal plasma membranes. Thus, it may represent a unidirectional transport from mother to fetus through the brush border membranes facing the mother, followed by transport at a slower rate through basal plasma membranes facing the fetus.

Purification, characterization and partial sequencing of the heart fatty acid-binding protein from Bufo arenarum

A 15.7 kDa fatty acid-binding protein from toad heart was purified by gel-filtration chromatography on Sephadex G-75 followed by anion-exchange chromatography on a Mono-Q column. Purity was confirmed by gel electrophoresis and isoelectric focusing. Molecular mass, isoelectric point, amino acid composition and partial internal sequence showed that the protein is related to mammalian heart fatty acid-binding proteins.

Characterization and binding properties of human fetal lung fatty acid-binding proteins

When delipidated Mr > 10,000 cut-off human fetal lung cytosol was separated on gel filtration and ion-exchange chromatography on Auto-FPLC system, two fatty acid-binding proteins (FABPs) of pI 6.9 and pI 5.4 were purified to homogeneity. On Western blotting analysis with the anti-human fetal lung pI 6.9 FABP, these two proteins showed immunochemical cross reactivity with each other and with purified hepatic FABPs but not with cardiac or gut FABP. These two FABPs have identical molecular mass of 15.2 kDa, which is slightly higher than that of the hepatic proteins (14.2 kDa). Carbohydrate covalently linked to FABPs, that may substantially add to the molecular mass, was not detected in the purified protein preparations. Amino acid analysis revealed that both the proteins have same amino acid composition each containing one Trp residue that is lacking in hepatic FABP. Different isoforms of lung FABP exhibited different binding ability for their natural ligands. These proteins bind palmitoyl CoA with higher affinity than oleic acid. pI 6.9 FABP can more rapidly and efficiently transfer fatty acid than can pI 5.4 FABP from unilammelar liposomes. Thus these FABPs may play a critical role in fatty acid transport during human fetal lung development.