Physiological and pathological regulation of feto/placento/maternal leptin expression

Abstract

There is clear evidence of placental leptin production, as shown recently in trophoblast cultures and by dual in vitro placenta perfusion (median production of 225 pg/min per g of tissue; 98.4% released into the maternal and 1.6% into the fetal circulation). However, the physiological impact for the mother and the fetus is unclear. The classical role of leptin is to provide information about energy stores to the central nervous system, and to reduce appetite if the energy stores are full. In pregnancy, maternal plasma leptin concentrations are elevated, and lack the well established correlation with body fat energy stores that is observed in non-pregnant women, indicating an alternative function for leptin during pregnancy and fetal development. Maternal and fetal plasma leptin levels are dysregulated in pathological conditions such as gestational diabetes, pre-eclampsia and intra-uterine growth retardation, representing an effect or a cause of disturbances in the feto/placento/maternal unit.

Full text

Biochemical Society Transactions (2001) Volume 29, part 2
Physiological and pathological regulation of feto/placento/maternal
leptin expression
K. Linnemann*, A. Malek†, H. Schneider† and C. Fusch*
1
*Neonatology, Department of Pediatrics, Ernst-Moritz-Arndt University, D-17489 Greifswald, Germany, and
†Department of Obstetrics and Gynecology, Inselspital, University of Bern, CH-3012 Bern, Switzerland
Abstract
There is clear evidence of placental leptin pro-
duction, as shown recently in trophoblast cultures
and by dual in vitro placenta perfusion (median
production of 225 pg\min per g of tissue; 98.4 %
released into the maternal and 1.6 % into the fetal
circulation). However, the physiological impact
for the mother and the fetus is unclear. The
classical role of leptin is to provide information
about energy stores to the central nervous system,
and to reduce appetite if the energy stores are full.
In pregnancy, maternal plasma leptin concen-
trations are elevated, and lack the well established
correlation with body fat energy stores that is
observed in non-pregnant women, indicating an
alternative function for leptin during pregnancy
and fetal development. Maternal and fetal plasma
leptin levels are dysregulated in pathological con-
ditions such as gestational diabetes, pre-eclampsia
and intra-uterine growth retardation, representing
an effect or a cause of disturbances in the feto\
placento\maternal unit.
Findings suggesting placental leptin
production
Leptin plays a key role in weight-control mechan-
isms by signalling information on total body
energy stores to the central nervous system (CNS)
[1]. This information is mediated by the long form
of the leptin receptor, which is expressed in many
tissues, including the CNS and the placenta [2,3].
In addition, leptin originating from adipose tissue
has a number of roles in reproduction : leptin
seems to trigger the onset of puberty, and is
necessary for ovulation, as it signals nutritional
status to the reproductive axis [4,5].
During pregnancy, leptin levels show marked
changes, suggesting the placenta as a putative
source of production of leptin in addition to
Key words: fetal growth retardation, placenta, pre-eclampsia,
perfusion, hypoxia.
Abbreviations used : CNS, central nervous system; hCG, human
chorionic gonadotropin; hPL, human placental lactogen ; IUGR,
intra-uterine growth retardation.
1
To whom correspondence should be addressed (e-mail
fusch!mail.uni-greifswald.de).
adipose tissue. Maternal plasma leptin levels rise
sharply during the first trimester [6–10] and
decline back to normal values after delivery
[11–13]. Maternal leptin levels increase by a factor
of 2–4 in early pregnancy [14,15] and are about
2–5-fold higher than fetal levels at term (Table 1)
[16–19]. In the fetus, leptin concentrations are
higher in venous than in arterial cord blood. After
birth, neonatal serum leptin decreases markedly,
again suggesting the placenta as an additional
source of leptin during pregnancy [20,21]. How-
ever, the classical role of increased leptin levels of
diminishing appetite in adults as a feedback signal
from increased body energy stores to the CNS
seems unlikely in pregnancy, so a new approach is
required for a better understanding of the impact
of elevated leptin levels in the feto\placento\
maternal unit.
Evidence for placental leptin
production
The suspected placental production of leptin was
confirmed in cell culture experiments using tro-
phoblasts and BeWo cells : the syncytiotrophoblast
could be identified as the leptin-producing cell in
the placental tissue. Green et al. [22] and Masuzaki
and co-workers [23] described leptin production
in the placenta, BeWo cells, a choriocarcinoma cell
line and trophoblasts maturing to syncytiotropho-
blasts. The expression of placental leptin was
demonstrated by detection of leptin mRNA in
early-gestation, mid-gestation and term placentas
[24]. The transcripts of leptin and its receptor
were localized in the syncytiotrophoblasts, and the
expression of leptin mRNA declined during ges-
tation [24], which is in contrast with increasing
maternal plasma leptin levels in pregnancy.
Cell culture experiments, however, do not
allow the precise quantification of placental leptin
production or assessment of the extent to which
leptin is released into the fetal and maternal
circulations. Recently we demonstrated substan-
tial leptin release in the dual-closed-loop in vitro
perfusion model of the term placenta [25–27].
Briefly, in this study ten placentas from normal
pregnancies were perfused for 240–840 min (me-
# 2001 Biochemical Society 86

Cytokines and Cytokine Receptors in Fetal Growth and Development
Table 1
Fetal and maternal plasma leptin levels at term
Leptin concentration (ng/ml)
Study Number of subjects Maternal plasma Fetal cord blood
Helland et al. [16] 166 17.7 (35th week) Girls 10.8; boys 7.6
Schubring et al. [14] 27 20.0 Vein 8.9; artery 9.7
Yura et al. [21] 38 29.5 Vein 12.9 ; artery 9.8
Geary et al. [17] 39 11.8 4.2*
McCarthy et al. [19] 24 27.0 5.4*
Lin et al. [20] 42 22.36 Vein 5.7; artery 0.6
*Origin not specified.
dian 480 min) with NCTC 135 and Earl ’s buffer
(1: 2, v\v), and leptin release into the fetal and
maternal circuits was measured separately by RIA
(Mediagnost, Tubingen, Germany). The total
placental production rate was 225 pg of leptin\min
per g of placental tissue, with 98.4 % of total
release into the maternal circulation and 1.6 %
into the fetal circulation. When compared with the
release of other placental proteohormones such as
human chorionic gonadotropin (hCG) and human
placental lactogen (hPL), measured simultaneous-
ly in the same perfusion experiments, the relative
release of leptin into the fetal circulation was
considerably greater than expected for the mol-
ecular mass (leptin, 16 kDa, 1.6%; hCG, 39 kDa,
0.05% ; hPL, 22 kDa, 0.05 %) (Figure 1). As-
suming that specific placental transport of leptin
does not occur, this finding may be explained by
leptin production by placental villous tree en-
Figure 1
Maternal () and fetal () release of leptin,
hPL and hCG
Release is expressed as a percentage of total release. Note the
logarithmic scale on the y-axis. From Linnemann, K., Malek, A.,
Sager, R., Blum, W. F., Schneider, H. and Fusch, C. (2000) Leptin
production and release in the dually in vitro perfused human
placenta. J. Clin. Endocrinol. Metab. 85(11), 4298–4301 ; # The
Endocrine Society, with permission.
dothelial cells as an additional possible source of
augmented leptin release into the fetal circuit [28].
Physiological regulation of leptin
production in the
feto/placento/maternal unit
Maternal
The observed increase in maternal leptin levels
during pregnancy is presumably caused by
placental leptin production, as well as increased
leptin production by the adipose tissue. The
contribution of placental leptin to plasma levels is
only about 15% (estimated from our in vitro
perfusion data [25]), and cannot explain the up to
2–4-fold increase in leptin levels of pregnant
women at term. The residual leptin supply must
come from maternal adipose tissue, possibly due
to stimulation by placental hormones. Hardie et al.
[12] showed a significant correlation between
circulating oestradiol, hCG and leptin levels dur-
ing pregnancy. Stimulatory effects on leptin pro-
duction were also described for 17β-oestradiol and
hCG in cell culture experiments [10,29]. hCG
and leptin appear to stimulate each other‘s pro-
duction in a mutual manner, as hCG production
was also increased by leptin, as demonstrated in
cytotrophoblastic cell culture in the presence or
absence of Cetrorelix, an antagonist of luteinizing-
hormone-releasing hormone which inhibits
leptin-induced hCG secretion [29].
Insulin is another hormone involved in the
regulation of placental leptin. Placental leptin
mRNA and protein levels are elevated in insulin-
treated diabetic pregnacies : fetal concentrations of
leptin and insulin are increased in venous cord
blood without modification of maternal circulating
leptin levels [30]. In fact, cord blood leptin levels
are elevated in infants of diabetic mothers and in
# 2001 Biochemical Society87

Biochemical Society Transactions (2001) Volume 29, part 2
large-for-gestational-age newborns ; from the cur-
rent data it cannot be deduced whether this rise in
leptin is caused by increased leptin production due
to increased fetal fat mass or if a primary increase
in leptin production stimulated by insulin may act
as a fetal growth factor, therefore giving rise to
large-for-gestational-age infants [31,32]. In adi-
pocyte cell culture experiments, insulin adminis-
tration provoked a dose-dependent increase in
leptin protein production, and cortisol was found
to potentiate this effect of insulin [33]. The
physiological role of hyperleptinaemia with regard
to maternal feeding behaviour during pregnancy is
not fully understood, but animal data suggest that
pregnancy is a maternal leptin-resistant state
[34,35].
Fetal
Fetal plasma leptin is derived from the placenta
(leptin mRNA is detected from early gestation, i.e.
weeks 7–14, up to term [24]) and from fetal adipose
tissue, which appears and develops progessively
from 14 weeks of gestation to term [36]. Fetal
plasma leptin increases during development in
utero [37], and studies have shown a significant
correlation with birth weight [31,38–40]. Gender
differences (lower leptin levels in males when
compared with females with identical amounts of
body fat) are already present at birth, and persist
during later life [11,40,41]. These gender-specific
differences may be due to the fact that testosterone
seems to suppress leptin production. In fact, a
negative correlation between leptin and testos-
terone levels has been demonstrated [11].
Very few investigations have been carried out
into leptin regulation in the fetus. It is generally
accepted that fetal leptin reflects fetal fat mass, as
it does in the adult [39,42].
Insulin levels are correlated with leptin levels
in large-for-gestational-age infants, and leptin is
overexpressed in placentas of diabetic pregnancies
[30,43]. In pre-term infants a 3-fold elevation of
cord blood leptin levels was seen when mothers
had received steroids antenatally compared with
untreated pregnancies of the same gestational age
[31]. This finding confirms the stimulatory effects
of steroids on leptin production. It is likely that
placental leptin release is more important for fetal
than for maternal leptin levels: almost all hCG is
released into the maternal circulation, thus stimu-
lating leptin production by maternal adipose
tissue. Only a very small amount of the hCG
produced is released into fetal blood [25], and
therefore stimulation of leptin production by hCG
in fetal adipose tissue does not occur.
Fetal leptin levels are also correlated with
fetal growth ; leptin levels in growth-retarded
fetuses are lower than in controls [43–45]. The
high level of expression of leptin (and its receptor
[3]) in fetal bone suggests a role for leptin in bone
or cartilage development, as well as in the develop-
ment of ossification and haematopoiesis during
intra-uterine development [3]. The presence of
mature leptin protein in several tissues of the
fetus contrasts with the absence of leptin from
the corresponding adult tissues [3,46]; this
suggests that leptin is a growth factor in fetal
development, rather than acting as a signal of fetal
energy stores to the fetal CNS, as it does in adults.
In addition to factors known to be directly
involved in fetal growth, recently other factors,
such as retinoids, have been identified to have an
impact on leptin production, at least in cell
cultures. The physiological significance of these
findings remains unclear [47].
Pathological regulation of leptin
production in the
feto/placento/maternal unit
Pre-eclampsia and hypoxia
Maternal and fetal plasma leptin levels are
increased in pre-eclampsia [19,48]; however,
the causes of elevated leptin production are
unknown. Pre-eclampsia is considered to be a
hypoxia-associated placental disorder. It has been
established that hypoxia is involved in the regu-
lation of leptin expression, and may therefore
contribute to elevated plasma leptin levels in
pre-eclampsia [49]. On the other hand, pro-
inflammatory cytokines (e.g. interleukin-1, inter-
leukin-6) seem to be involved in the multifactorial
pathogenesis of pre-eclampsia. Stimulatory effects
of interleukin-1 and interleukin-6 on leptin pro-
duction have been observed [29,50], suggesting
that elevated pro-inflammatory activity in pre-
eclampsia promotes augmented leptin production.
Intra-uterine growth retardation (IUGR)
IUGR may be caused by nutritional, genetic or
placental vascular factors [51–53]. Failure of ad-
equate leptin production and regulation may be an
additional cause of IUGR; fetal leptin levels are
significantly decreased in IUGR [17,37,44,45] and
leptin is thought to be a growth factor in fetal
development [28,32]. Recently, Lea et al. [54]
# 2001 Biochemical Society 88

Cytokines and Cytokine Receptors in Fetal Growth and Development
reported a twin pregnancy where one infant was
of appropriate size for gestational age and the
other was growth-retarded. In situ hybridization
and immunostaining of the placental tissue from
these twins showed lower leptin expression in the
growth-retarded infant. On the other hand, de-
creased fetal leptin levels could also be a con-
sequence of reduced body fat mass resulting in
reduced leptin production by fetal adipose tissue.
Conclusion
During pregnancy and at birth there is evidence
for augmented maternal and fetal leptin levels.
This increase is explained in part by leptin
production by the placenta. A number of factors
have been identified that are involved in the
regulation of leptin production in the feto\
placento\maternal unit, such as hCG, β-oes-
tradiol, insulin and cortisol. So far, the role of
increased leptin production during pregnancy
remains unclear. It may be hypothesized that
increased leptin levels during pregnancy are part
of a teleologically old and redundant system
ensuring fetal growth and development, even in
periods of reduced maternal energy supply.
References
1 Schwartz, M. W., Woods, S. C., Porte, Jr, D., Seeley, R. J. and
Baskin, D. G. (2000) Nature (London) 404, 661–671
2 Tartaglia, L. A., Dembski, M., Weng, X., Deng, N.,
Culpepper, J., Devos, R., Richards, G. J., Campfield, L. A.,
Clark, F. T. and Deeds, J. (1995) Cell 83, 1263–1271
3 Hoggard, N., Hunter, L., Duncan, J. S., Williams, L. M.,
Trayhurn, P. and Mercer, J. G. (1997) Proc. Natl. Acad. Sci.
U.S.A. 94, 11073–11078
4 Cunningham, M. J., Clifton, D. K. and Steiner, R. A. (1999)
Biol. Reprod. 60, 216–222
5 Foster, D. L. and Nagatani, S. (1999) Biol. Reprod. 60,
205–215
6 Highman, T. J., Friedman, J. E., Huston, L. P., Wong, W. W.
and Catalano, P. M. (1998) Am. J. Obstet. Gynecol. 178,
1010–1015
7 Lage, M., Garcia-Mayor, R. V., Tome, M. A., Cordido, F.,
Valle-Inclan, F., Considine, R. V., Caro, J. F., Dieguez, C. and
Casanueva, F. F. (1999) Clin. Endocrinol. 50, 211–216
8 Mukherjea, R., Castonguay, T. W., Douglass, L. W. and
Moser-Veillon, P. (1999) Life Sci. 65, 1183–1193
9 Sattar, N., Greer, I. A., Pirwani, I., Gibson, J. and Wallace,
A. M. (1998) Acta Obstet. Gynecol. Scand. 77, 278–283
10 Sivan, E., Whittaker, P. G., Sinha, D., Homko, C. J., Lin, M.,
Reece, E. A. and Boden, G. (1998) Am. J. Obstet. Gynecol.
179, 1128–1132
11 Ertl, T., Funke, S., Sarkany, I., Szabo, I., Rascher, W., Blum,
W. F. and Sulyok, E. (1999) Biol. Neonate 75, 167–176
12 Hardie, L., Trayhurn, P., Abramovich, D. and Fowler, P.
(1997) Clin. Endocrinol. 47, 101–106
13 Hytinantti, T., Koistinen, H. A., Koivisto, V. A., Karonen, S. L.
and Andersson, S. (1999) Pediatr. Res. 45, 197–201
14 Schubring, C., Kiess, W., Englaro, P., Rascher, W., Dotsch, J.,
Hanitsch, S., Attanasio, A. and Blum, W. F. (1997) J. Clin.
Endocrinol. Metab. 82, 1480–1483
15 Sivan, E., Lin, W. M., Homko, C. J., Reece, E. A. and Boden,
G. (1997) Diabetes 46, 917–919
16 Helland, I. B., Reseland, J. E., Saugstad, O. D. and Drevon,
C. A. (1998) Pediatrics 101, E12
17 Geary, M., Pringle, P. J., Persaud, M., Wilshin, J., Hindmarsh,
P. C., Rodeck, C. H. and Brook, C. G. (1999) Br. J. Obstet.
Gynaecol. 106, 1054–1060
18 Gomez, L., Carrascosa, A., Yeste, D., Potau, N., Rique, S.,
Ruiz-Cuevas, P. and Almar, J. (1999) Horm. Res. 51,10–14
19 McCarthy, J. F., Misra, D. N. and Roberts, J. M. (1999) Am. J.
Obstet. Gynecol. 180, 731–736
20 Lin, K. C., Hsu, S. C., Kuo, C. H. and Zhou, J. Y. (1999)
Gaoxiong Yixue Kexue Zazhi 15, 679–685
21 Yura, S., Sagawa, N., Mise, H., Mori, T., Masuzaki, H., Ogawa,
Y. and Nakao, K. (1998) Am. J. Obstet. Gynecol. 178,
926–930
22 Green, E. D., Maffei, M., Braden, V. V., Proenca, R., DeSilva,
U., Zhang, Y., Chua, Jr, S. C., Leibel, R. L., Weissenbach, J.
and Friedman, J. M. (1995) Genome Res. 5,5–12
23 Masuzaki, H., Ogawa, Y., Sagawa, N., Hosoda, K.,
Matsumoto, T., Mise, H., Nishimura, H., Yoshimasa, Y.,
Tanaka, I., Mori, T. and Nakao, K. (1997) Nat. Med. (N. Y.)
3, 1029–1033
24 Henson, M. C., Swan, K. F. and O ’Neil, J. S. (1998) Obstet.
Gynecol. 92, 1020–1028
25 Linnemann, K., Malek, A., Sager, R., Blum, W. F., Schneider,
H. and Fusch, C. (2000) J. Clin. Endocrinol. Metab. 85,
4298–4301
26 Schneider, H. and Huch, A. (1985) Contrib. Gynecol.
Obstet. 13,40–47
27 Schneider, H., Panigel, M. and Dancis, J. (1972) Am. J.
Obstet. Gynecol. 114, 822–828
28 Ashworth, C. J., Hoggard, N., Thomas, L., Mercer, J. G.,
Wallace, J. M. and Lea, R. G. (2000) Rev. Reprod. 5,18–24
29 Chardonnens, D., Cameo, P., Aubert, M. L., Pralong, F. P.,
Islami, D., Campana, A., Gaillard, R. C. and Bischof, P. (1999)
Mol. Hum. Reprod. 5, 1077–1082
30 Lepercq, J., Cauzac, M., Lahlou, N., Timsit, J., Girard, J.,
Auwerx, J. and Hauguel-de Mouzon, S. (1998) Diabetes 47,
847–850
31 Shekhawat, P. S., Garland, J. S., Shivpuri, C., Mick, G. J.,
Sasidharan, P., Pelz, C. J. and McCormick, K. L. (1998)
Pediatr. Res. 43, 338–343
32 Hassink, S. G., de Lancey, E., Sheslow, D. V., Smith-Kirwin,
S. M., O’Connor, D. M., Considine, R. V., Opentanova, I.,
Dostal, K., Spear, M. L., Leef, K. et al. (1997) Pediatrics 100,
E1
33 Wabitsch, M., Jensen, P. B., Blum, W. F., Christoffersen, C. T.,
Englaro, P., Heinze, E., Rascher, W., Teller, W., Tornqvist, H.
and Hauner, H. (1996) Diabetes 45, 1435–1438
34 Garcia, M. D., Casanueva, F. F., Dieguez, C. and Senaris,
R. M. (2000) Biol. Reprod. 62, 698–703
35 Mounzih, K., Qiu, J., Ewart-Toland, A. and Chehab, F. F.
(1998) Endocrinology 139, 5259–5262
36 Poissonnet, C. M., Burdi, A. R. and Garn, S. M. (1984) Early
Hum. Dev. 10,1–11
37 Cetin, I., Morpurgo, P. S., Radaelli, T., Taricco, E., Cortelazzi,
D., Bellotti, M., Pardi, G. and Beck-Peccoz, P. (2000) Pediatr.
Res. 48, 646–651
# 2001 Biochemical Society89

Biochemical Society Transactions (2001) Volume 29, part 2
38 Shaarawy, M. and el Mallah, S. Y. (1999) J. Soc. Gynecol.
Invest. 6,70–73
39 Clapp, III, J. F. and Kiess, W. (1998) J. Soc. Gynecol. Invest. 5,
300–303
40 Matsuda, J., Yokota, I., Iida, M., Murakami, T., Naito, E., Ito,
M., Shima, K. and Kuroda, Y. (1997) J. Clin. Endocrinol.
Metab. 82, 1642–1644
41 Blum, W. F., Englaro, P., Hanitsch, S., Juul, A., Hertel, N. T.,
Muller, J., Skakkebaek, N. E., Heiman, M. L., Birkett, M.,
Attanasio, A. M. et al. (1997) J. Clin. Endocrinol. Metab. 82,
2904–2910
42 Fusch, C., Keisker, A., Blum, W. F. and Moessinger, A. C.
(1997) Pediatr. Res. 41, 231A
43 Wolf, H. J., Ebenbichler, C. F., Huter, O., Bodner, J.,
Lechleitner, M., Foger, B., Patsch, J. R. and Desoye, G. (2000)
Eur. J. Endocrinol. 142, 623–629
44 Varvarigou, A., Mantzoros, C. S. and Beratis, N. G. (1999)
Clin. Endocrinol. 50, 177–183
45 Koistinen, H. A., Koivisto, V. A., Andersson, S., Karonen, S. L.,
Kontula, K., Oksanen, L. and Teramo, K. A. (1997) J. Clin.
Endocrinol. Metab. 82, 3328–3330
46 Holness, M. J., Munns, M. J. and Sugden, M. C. (1999) Mol.
Cell. Endocrinol. 157,11–20
47 Guibourdenche, J., Tarrade, A., Laurendeau, I., Rochette-Egly,
C., Chambon, P., Vidaud, M. and Evain-Brion, D. (2000)
J. Clin. Endocrinol. Metab. 85, 2550–2555
48 Laivuori, H., Kaaja, R., Koistinen, H., Karonen, S. L.,
Andersson, S., Koivisto, V. and Ylikorkala, O. (2000) Metab.
Clin. Exp. 49, 259–263
49 Mise, H., Sagawa, N., Matsumoto, T., Yura, S., Nanno, H.,
Itoh, H., Mori, T., Masuzaki, H., Hosoda, K., Ogawa, Y. and
Nakao, K. (1998) J. Clin. Endocrinol. Metab. 83, 3225–3229
50 Meisser, A., Cameo, P., Islami, D., Campana, A. and Bischof,
P. (1999) Mol. Hum. Reprod. 5, 1055–1058
51 Wollmann, H. A. (1998) Horm. Res. 49 (Suppl. 2), 1–6
52 Lin, C. C. and Santolaya-Forgas, J. (1998) Obstet. Gynecol.
92, 1044–1055
53 Lin, C. C. and Santolaya-Forgas, J. (1999) Obstet. Gynecol.
93, 140–146
54 Lea, R. G., Howe, D., Hannah, L. T., Bonneau, O., Hunter, L.
and Hoggard, N. (2000) Mol. Hum. Reprod. 6, 763–769
Received 27 November 2000
# 2001 Biochemical Society 90