| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
INSERM U-344, Endocrinologie Moléculaire, Faculté de Médecine Necker (P.C.-L., V.G., B.B., N.B., P.A.K.), 75730 Paris Cedex 15, France; Cancer Research Program, Garvan Institute of Medical Research (C.O.), Darlinghurst, New South Wales 2010, Sydney, Australia; Hoechst Marion Roussel, Inc.-France (L.L., M.G.-K., R.B.), 93235 Romainville, France; the Division of Clinical Pathophysiology, World Health Organization Collaborating Center for Osteoporosis and Bone Diseases, Department of Internal Medicine, University Hospital (P.A.), Geneva, Switzerland; Service Anatomo-Pathologie, Hôpital Necker-Enfants Malades, Université René Descartes Paris V (D.D.), 75015 Paris, France; and the Departments of Cell Biology and Orthopedics, Yale University School of Medicine (M.A., R.B.), New Haven, Connecticut 06510
Address all correspondence and requests for reprints to: Dr. Paul A. Kelly, INSERM U-344, Endocrinologie Moléculaire, Faculté de Médecine Necker, 156 rue de Vaugirard, 75730 Paris Cedex 15, France. E-mail: kelly{at}necker.fr
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
PRL is synthesized and secreted by lactotrophic cells of the anterior pituitary gland of all vertebrates and by various extrapituitary sites including decidual cells of the placenta (11, 12). PRL is mainly involved in actions such as induction and maintenance of lactation, reproduction, osmoregulation, and immunomodulation. However, this hormone has been shown to have multiple functions in various vertebrate species, including actions resembling those of a growth factor (12). The PRL receptor is a single chain protein with only one transmembrane domain, belonging to the class I cytokine receptor superfamily. The activation of the PRL receptor occurs by ligand-induced homodimerization (13, 14). In the mouse, the PRL receptor is expressed as three short forms (S1-PRLR, S2-PRLR, and S3-PRLR) and one long (L-PRLR) form, differing in the length and sequence of their cytoplasmic tails due to alternative splicing of a single PRL receptor gene (15, 16, 17). The long and short receptor forms share identical extracellular, transmembrane, and membrane proximal cytoplasmic domain sequences, but diverge in their carboxyl-terminal cytoplasmic sequences (15, 18). The different cytoplasmic domains of these receptor forms may connect to distinct signaling pathways. Although both forms of the PRL receptor are dimerized by the binding of a single molecule of PRL to activate the tyrosine kinase Jak2 and can stimulate cell growth, only the long form of the receptor leads to activation of the transcription factor STAT5 (signal transducer and activator of transcription-5) and initiates milk protein gene transcription (19, 20, 21). In addition, PRL receptors are the targets of at least three hormones in mouse: PRL, placental lactogen I (PL-I), and PL-II (14, 22).
In our laboratory, mice carrying a germline null mutation of the PRL receptor have been produced by gene targeting in embryonic stem cells (16). In this knockout model, exon 5 of the gene encoding the PRL receptor was replaced with neomycin resistance gene cassette, resulting in a PRL receptor transcript deleted of 169 bp (size of exon 5) and, if translated, would generate a very short peptide unable to bind PRL. We have previously observed in heterozygous females the failure of mammary development and lactation after the first pregnancy and in PRL receptor-deficient (-/-) female mice complete sterility due to multiple causes, including failure of blastocyst implantation (16). We have also identified altered maternal behavior in -/- animals (23). This mouse model has been used here to examine the putative effects of PRL in bone metabolism.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Cell culture
Osteoblasts from calvaria were prepared and characterized as
previously described (23A ). Briefly, neonatal mouse calvaria
were dissected free from adherent soft tissue, washed in PBS, and
sequentially digested with 0.2% dispase (Boehringer Mannheim) and
0.1% collagenase (Sigma Chemical Co., L’Isle d’Abeau,
France; five times for 15 min each time). Cells released by the
last three enzymatic digestions were washed and grown in 
MEM
(Sigma Chemical Co.) containing 10% FBS and
antibiotics.
PRL receptor +/+ and PRL receptor -/- osteoclast-like cells were
obtained from cocultures of wild-type osteoblastic cells and bone
marrow cells from either PRL receptor-deficient mice or their wild-type
littermates in the presence of 10 nM
1,25-dihydroxyvitamin D3 (Hoechst Marion Roussel, Inc., Romainville, France) for 5 days. Osteoclast-like
cells were purified by 0.1% (type 1a) collagenase (Sigma Chemical Co.) and 0.2% dispase (Boehringer Mannheim) treatment
(24). All cultures were maintained at 37 C in a humidified atmosphere
of 5% CO2.
RNA extraction and RT-PCR analysis
Total cellular RNA was extracted as previously described (25).
First strand complementary DNA was synthesized from 1 µg total RNA
using 200 U Moloney murine leukemia virus reverse transcriptase (RT;
Promega Corp., Madison, WI) for 2 h at 37 C after
oligo(deoxythymidine) priming (250 ng). One microliter of the RT
product was submitted to PCR for amplification of mPRL receptor
sequences. The reaction mixture (50 µl) contained 25 pmol of each
primer for PRL receptor, 0.2 mM deoxy-NTPs, 50
mM KCl, 2 mM MgCl2, and 1 U
Taq DNA polymerase. For PCR of different PRL receptor
transcripts, amplification was performed using the Gem Amply PCR System
2400 (Perkin Elmer, Norwalk, CT) with the following
profiles: 94 C for 5 min for 1 cycle; 94 C for 30 sec, 67 C for 1 min,
and 72 C for 1.5 min for 30 cycles; and 72 C for 5 min for 1 cycle. For
PCR performed with osteoclast-like cell mRNA extracts, amplification
was performed with the following profiles: 94 C for 5 min for 1 cycle;
94 C for 45 sec, 62 C for 1 min, and 72 C for 45 sec for 35 cycles; and
72 C for 5 min for 1 cycle. Amplification products were resolved on 1%
agarose gels. The specificity of the reaction was confirmed by Southern
transfer onto Hybond N+ membranes (Amersham) and
hybridization with a 32P-labeled specific
oligonucleotide.
Oligonucleotide probes
Specific probes, complementary to different forms of PRL
receptor mRNAs, were used as follows (synthesis by Genentech, Inc., Eurogentec, Seraino, Belgium). Wsm
(5'-CATGGATACTGGAGTAGATGGGGC-3') is complementary to the extracellular
domain of the mouse PRL receptor. S1 (5'-CAACTGGAGAATAGAACACCAGAG-3'),
S2 (5'-CTTGTATTTGCTTGGAGAGCCAGT-3'), and S3
(5'-TTCAAGTTGCTCTTTGTTGTGAAC-3') are oligonucleotides specific to the
cytoplasmic domains of the three different short forms of the mPRL
receptor deduced from sequences previously published (18). mLF2
(5'-TTGCACAGCCACTTCTTCCTCTCC-3') is complementary to the 529- to 553-bp
sequence of the cytoplasmic domain of the long form of the mPRL
receptor (15). The sequence of the oligonucleotide used for Southern
analysis is 5'-GATGACAGCAGAGAGAACGGCACA-3'. For PCR performed with
osteoclast-like cell mRNA extracts, two oligonucleotides derived from
exons 2 and 7 were used: exon 2 primer, 5'-TGAGCATCGCAG ATGTTTTGCAC-3';
and exon 7 primer, 5'-TTGATGACCTGTGAAGTGGAT-3'. Oligonucleotides
derived from exons 4 and 5 were used to identify the resulting bands by
Southern analysis (exon 4 probe, 5'-GGTCAGATGGAGGACTCCCCACCA-3'; and
exon 5 probe, 5'-GAGAAAAAC ACCTATGAATGTC-3').
Western blot analysis
Total osteoblast proteins were solubilized in Tris-HCl (pH 7.4)
and 10 mM MgCl2-0.5% Triton X-100 at 4 C for
1 h. Osteoblasts from four petri dishes (100 mm) were washed three
times with cold PBS, scraped from plates, and collected into PBS on
ice. Cells were pelleted and resuspended in 1.2 ml lysis buffer [50
mM Tris-HCl (pH 8.0), 150 mM NaCl, 5
mM MgCl2, 1% Triton X-100, 0,5% sodium
deoxycholate, 0.1% SDS, 0.5 mM
phenylmethylsulfonylfluoride, 10 µg/ml of leupeptin, 10 µg/ml
aprotinin, and 10 µg/ml pepstatin] at 4 C on a wheel stirrer for 30
min. The extracts were centrifuged, and the supernatant was incubated
overnight with 2 µg U5-specific mouse monoclonal antibody against the
PRL receptor (26) before the addition of goat antimouse IgG antibodies
immobilized on agarose beads. The beads were collected by
centrifugation and washed three times in Tris-HCl (pH 7.4), 10
mM MgCl2, and Triton X-100 before denaturation
by boiling 5 min in 3% SDS and 5% ß-mercaptoethanol in 12
mM Tris-HCl (pH 6.8). Samples were electrophorised and
electrotransferred to enhanced chemiluminescence (ECL) nylon membranes.
Membranes were incubated with 2 µg/ml U5 antibody in 50
mM Tris-HCl (pH 7.5), 200 mM NaCl, 0.05%
Tween-20, and 1% BSA (AB) for 2 h at room temperature with gentle
rocking. Membranes were washed three times for 15 min each time in 50
ml 50 mM Tris-HCl (pH 7.5), 200 mM NaCl, and
0.05% Tween-20 (WB) before incubation with goat antimouse IgG linked
to peroxidase in AB for 1 h and washed four times for 20 min each
time in 50 ml WB. Bands were visualized using x-ray film and the ECL
chemiluminescence kit.
Histological examination of calvaria
Calvaria from E18.5 embryos were fixed in 4% formalin solution
and processed for conventional histology. Calvaria were embedded in
paraffin examined on 20 noncontiguous 5-µm-thick sections colored
with hematoxylin-eosin-safran, or von Kossa’s stain.
Histomorphometry of long bone
Double labeling was performed as described previously (27). The
first calcein injection (2 mg/kg BW) was followed by the same dose of
calcein 7 days later. Eight-week-old animals were killed 2 days after
the second injection, and their tibia and femora were dissected and
fixed in PBS-buffered formaldehyde (pH 7.0). After embedding in
methyl-methacrylate, and sectioning at 10 µm, a blind analysis of the
unstained samples was conducted under fluorescent light. Measurements
of the mineral apposition rate and the bone formation rate and
quantification of the percentage of mineralizing surface were performed
in wild-type (+/+) and mutant (-/-) littermates. Histomorphometric
parameters, such as osteoid tissue, bone volume, osteoblast surface,
and osteoclast number, were analyzed following the recommended
nomenclature (28). These parameters were determined in an area of 300
µm in length from the chondro-osseous junction to the diaphysis
surrounded by cortical bone on both sides.
Bone mass measurements by dual energy x-ray absorptiometry
Techniques measuring bone mineral density (BMD) and bone mineral
content (BMC) using energy x-ray absorptiometry with Hologic QDR 1000
instruments (Waltham, MA) were adapted for application in the mouse. An
ultra high resolution mode was used with a collimator 0.09 cm in
diameter as previously described (29). Histomorphometric parameters
follow the recommended nomenclature (28).
Serum mineral analysis
Serum calcium, phosphate, and magnesium levels were measured in
samples from individual males or females (4 months old) by absorption
spectrophotometry. All measurements were assayed on a Hitachi 400
automatic analyzer (Hitachi, Tokyo, Japan). Calcium levels were
confirmed and validated by simultaneous serum albumin measurements.
Hormone concentration determinations
Estradiol, progesterone, and testosterone were
measured in individual serum samples from 4-month-old animals using
human RIA kits (Immunotech, Paris, France; reference no.
1663, 1188, and 1087, respectively). Serum levels of estradiol and
progesterone were measured on the morning of estrous. The
estrous cycle was confirmed by vaginal smears. The serum concentration
of PTH was measured in individual serum samples of 4-month-old animals
using a rat PTH immunoradiometric assay kit (Nichols Institute Diagnostics, Avon, France).
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
shows coronal sections of
calvaria of 18.5-day-old +/+ and -/- embryos (total n = 3; three
different litters). Clearly, less ossified tissue is seen in sections
of -/- calvaria colored with either hematoxylin-eosin-safran (A and
B) or von Kossa’ s stain (C and D). This reduced calcification did not
affect postnatal cranial development.
|
, A–D; data not shown for
heterozygotes). When results were tabulated for four (+/+) and six
(-/-) mice per group from three litters, trabecular and cortical
mineral apposition rates were significantly decreased in long bones
(tibiae and femora) of PRL receptor-/- mice. On the other
hand, there was no modification in mineralizing surface between +/+ and
-/- mice (Table 1). Consequently, there
was a 60% decrease in the bone formation rate in knockout animals
compared with that in wild-type littermates, indicating that the lack
of PRL receptor leads to a profound slowing down of bone formation
(Table 1). Interestingly, considering the decrease in mineral
apposition rates and bone formation rates, osteoblast surface, which is
a reliable indicator of the number of osteoblasts and osteoid surface,
was not significantly diminished in the knockout animals (Table 1).
There was also no significant difference between the number of
osteoclasts and the bone volume in -/- mice compared with those in
wild-type controls. Thus, the bone formation rate is decreased in PRL
knockout animals, whereas the number of resorbing cells is maintained,
a situation that could lead to a diminished bone mass. The bone
alterations observed could be due to a problem in osteoblast activity
rather than a decrease in osteoblast number. This is in accordance with
the unaltered mineralizing surface. No radiographic evidence of
skeletal malformation was seen in adult -/- mice at 6 and 10 weeks of
age. In addition, radiographic analysis of long bones of 6-, 9-, and
16-week-old wild-type and knockout animals revealed no difference in
the overall size of -/- mice.
|
|
, A and B).
|
). The
increase in serum calcium levels has been validated by simultaneous
albumin measurements. Levels of serum albumin were not modified in
knockout mice compared with those in wild-type animals [25.83 ±
2.93 g/liter (n = 6) vs. 25.50 ± 2.35 g/liter
(n = 6) for wild-type and knockout mice, respectively]. Urinary
calcium was measured and standardized with creatinine levels. No
modifications were observed [3.61 ± 0.49 mmol/liter (n =
10) vs. 3.42 ± 0.29 mmol/liter (n = 10) for
wild-type and knockout mice, respectively].
|
along with testosterone levels in males
and PTH levels in males and females. Major modifications were seen in
calciotropic and some steroid hormones. Homozygous mutants exhibited an
elevation in serum PTH levels. The levels of estradiol and
progesterone in females were clearly decreased; this was
especially evident for progesterone. These was no evident
modification in testosterone levels in males. Finally, the serum PRL
level was greatly increased (40-fold) in PRL receptor-/-
males and females (data not shown). Heterozygous mice were
indistinguishable from their wild-type littermates with respect to
hormone and bone status.
|
). The specificity of the
PCR products was confirmed by Southern blot analysis with a common
transmembrane (exon 8) probe (Fig. 5B).
|
). We used monoclonal
antibody U5 to the rat PRL receptor (26), which recognizes an
extracellular epitope of the receptor located in a region of the
protein encoded by gene sequences after the exon 5 deletion introduced
in -/- mice. Positive controls were performed using human breast
cancer cells (T-47D; long form), rat liver microsomes (short form;
Fig. 5C), and 293 cells expressing short, long, and intermediate forms
of the rat PRL receptor (Fig. 5D).
Lack of expression of PRL receptor transcripts in wild-type murine
osteoclast-like cells
To determine whether PRL receptor mRNA was also expressed in
osteoclasts, osteoclast-like cells were prepared by coculturing primary
cultured osteoblasts from PRL receptor knockout mice with bone marrow
cells from wild-type (+/+) mice, or conversely, in the presence of
1,25-dihydroxyvitamin D3 (24). RNA from osteoclast-like
cells was reverse transcribed, and the resulting complementary DNA was
used for PCR amplification of a region spanning the exon 5 deletion, by
primers located in exons 2 and 7 (Fig. 6A). After +/+ osteoclast-like cells were
produced by coculture with osteoblasts from -/- animals, and RT-PCR
was performed on osteoclast-like cells mRNA, only a single band was
observed, the size of which corresponded to the 169-bp deletion of exon
5, as expected for a -/- transcript (Fig. 6B). Internal 20-mer probes
derived from exons 4 and 5 were used to identify the resulting bands by
Southern analysis. These results indicate that PRL receptor transcripts
are totally absent from murine osteoclast-like cells (or other minority
cells derived from precursor bone marrow cells after coculture and
purification), and that osteoblasts represent the only potential
target of PRL in bone (Fig. 6, C and D).
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Bone status in PRL receptor knockout mice
Histomorphometric observations on embryonic calvaria and the
reduction in bone formation rates without a comparable decrease in
osteoblast or osteoid surface in adults suggest that functional
activity, rather than bone-forming cell populations, is altered.
Evaluations of the functional activities of osteoblasts isolated from
knockout animals are in progress. In addition, BMD and BMC were
significantly reduced in proximal and total tibia in PRL
receptor-deficient mice compared with those in control mice, confirming
that PRL receptor knockout mice are osteopenic. These in
vivo observations suggest the implication of PRL in bone
metabolism sometimes evoked in physiological studies involving PRL. In
the last decade, clinical studies have attempted to correlate plasma
PRL levels with osteopenia observed during lactation, weaning, or
postmenopausal states (3, 6, 30).
Prolonged administration of PRL decreased calcium excretion in mature rats and increased bone formation and tibia calcium content in growing rats (31). PRL enhanced calcium turnover in both compact and trabecular bones of mature rats. Young rats responded to PRL by increasing the rate of mineral deposit, whereas weaned rats increased calcium release (32, 33). The analysis of bone metabolic parameters, bone turnover, bone formation, and bone resorption showed an increase during hyperprolactinemia.
During lactation and postweaning, BMD and markers of bone remodeling are modified in women (3, 6). The skeletal changes occurring during lactation can be quite dramatic in some species. In the first reproductive cycle of rats, there can be a substantial loss of metaphyseal cancellous bone, particularly in long bones, with a bone turnover rate considerably elevated (34). There are also changes in cortical bone during the reproductive cycle in rats, including periosteal and endocortical expansion, with a significant increase in the medullar cavity area (34).
In all of these studies, hypogonadism associated with hyperprolactinemia has been evoked to explain the final decrease in BMC (4, 35). The main mechanism of BMD loss in these cases probably involved in part hypoestrogenemia, but a direct effect of PRL cannot be excluded. On this point, our in vitro results are in agreement with the hypothesis of a direct role of PRL in bone metabolism.
PRL receptor expression in murine bone
The presence of short and long forms of PRL receptor mRNAs in
osteoblasts confirms the potential of a direct action of PRL on murine
osteoblasts but not on osteoclasts. The presence of PRL receptor
transcripts in two human osteoblastic lines (MG63 and Saos-2) and the
regulation of these transcripts by vitamin D3 and
dexamethasone have also recently been reported (10). In addition, PRL
receptor mRNA and protein levels have been shown to increase during
gestation in a number of fetal rat bone tissues (7). The presence of
PRL receptor in such tissues and more specifically in osteoblasts is
consistent with our results.
The expression of the long form of the PRL receptor protein in murine osteoblasts and the demonstration of a negative effect on bone metabolism resulting from the null mutation of the PRL receptor strongly indicate that the PRL receptor plays a role in bone formation. The long form of the receptor appears to be the active form in bone and has been shown previously to be functionally active in terms of transcription of PRL-stimulated genes (13, 14). Interestingly, the short form of the PRL receptor protein could not be detected in normal murine osteoblasts under our experimental conditions. This absence could be due to the relatively low level of short form transcript or the reduced stability of this mRNA, but we cannot exclude the possibility of short form expression only under certain physiological conditions, whereas its role remains unknown for now.
PRL receptors have been localized in maturing chondrocytes, tooth buds, and developing vertebrae (9). The cellular distribution and developmental expression of the PRL receptor were examined by in situ hybridization, immunohistochemistry, and radioligand binding. The studies of PRL receptor expression in human and rat fetal tissues (respectively, between 7.5–14.5 weeks and 12.5–20.5 days of age) show the appearance in early fetal development of intense PRL receptor immunoreactivity in tissues, including long bones, vertebrae, and ribs (7, 8, 9). Thus, the possible role of the PRL receptor in embryonic bone development is potentially of importance in almost all species (including humans) in view of the fact that the PRL receptor is also a target of placental lactogens. From approximately embryonic day 8.5 until birth in the mouse, during the period of substantial fetal growth and development, it is possible that placental lactogen, first PL-I and then PL-II, functionally activate PRL receptors (9, 22). Thus, even in the absence of pituitary PRL, PRL receptors could be involved in bone formation. A recent paper describing inactivation of the PRL gene did not specifically report any alteration in bone development (36). Either more detailed studies of these mice will be required or perhaps PLs can compensate for the lack of PRL in these mice. We propose that the PRL receptor plays a role in fetal bone development with consequences on bone status in adults.
Hormonal status of PRL receptor knockout mice
The increase in serum calcium levels observed in knockout animals
remains obscure, but it is well known that mineral homeostasis is under
the control of hormones such as PTH, estradiol, or calcitriol, which
have been suggested to be directly or indirectly involved with PRL
metabolism (5, 37, 38). All mineral abnormalities could be explained by
estrogen and progesterone deficiency or/and the high level
of PTH. This high level of PTH in knockout mice (males or females)
could also explain the calcium and bone abnormalities. In addition, the
active form of 1,25-dihydroxyvitamin D is PRL regulated, so it will be
interesting in the future to measure the level of 1,25-hydroxyvitamin
D. In summary, the hormonal status of the knockout mice are perturbed,
resulting in several potential consequences, not only for bone
formation but also for reproductive status and behavior.
Others groups have demonstrated the importance of hormones such as estradiol, GH, or progesterone directly on bone cells or at least in bone metabolism (39, 40, 41). Despite the possible direct effect of PRL in osteoblasts demonstrated in the present report, we cannot rule out a potential indirect systemic effect of PRL via interactions with the regulation of hormones implicated in bone metabolism. The PRL receptor knockout mouse may be a useful model to study such actions. A number of other phenotypes have been reported in this model: sterility, due in part to a failure of blastocyst implantation, and modification of maternal behavior (16, 23). Our results demonstrate that the hormonal status of the knockout mice is clearly altered, with several potential consequences on bone. Although it is difficult to make any general interpretations, both the potential systemic effects of hormonal alterations and the potential direct effects due to the absence of PRL receptor in knockout mice must be considered. In vitro approaches with normal and PRL receptor-deficient osteoblasts should allow us to better understand the role of PRL in bone and to separate direct and indirect actions of the PRL receptor. The balance between PRL and estradiol, progesterone, and PTH will be important to better understand the mineral status of the animals and the regulation of the total mineral stock. The potential hormonal dysregulation in this mouse model, especially concerning estradiol and/or progesterone, represents one of the interesting questions to be addressed.
It is noteworthy that there is convergence of certain genes regulating bone remodeling, linked to tight attachment of osteoclasts to the bone matrix, and oocyte implantation in the endometrial matrix. After fecondation, progesterone stimulates calcitonin (42), insulin-like growth factor I (43), and basic fibroblast growth factor (39) secretion in the uterus. These proteins are also implicated in bone metabolism. Moreover, some researchers have observed a local synthesis of PTH and integrins in the implantation area of the oocyte (44, 45). The reproductive dysfunctions seen in PRL receptor-deficient mice could open new fields of investigation concerning progesterone and hormonal regulation in general and interactions between cells and the extracellular matrix in bone metabolism in particular.
Secondly, we must evoke the possible interactions between PRL and estradiol and their effects on bone turnover in PRL receptor-deficient mice. Recently, it has been reported that alterations in maternal estrogen levels during pregnancy can influence early phases of fetal bone development and subsequently result in permanent changes in the skeleton (46). One approach would be to ovariectomize PRL receptor knockout mice and evaluate a change in bone formation in the context of an estrogen deficiency.
Finally, PTH-related peptide (PTH-rP) was recently shown to be expressed in human mammary tissue, and elevated circulating PTH-rP levels as well as concomitant hypercalcemia have been described during lactation (5). Some data support the hypothesis that PTH-rP is an alternative mechanism associated with bone loss and recovery during and subsequent to lactation with associated low serum estradiol levels (5). Overexpression of PTH-rP in myoepithelial cells in mammary glands of transgenic mice has been reported to result in a form of mammary hypoplasia characterized by a profound defect in branching morphogenesis of the developing mammary duct system (47). PTH-rP, which is a mature product of mammary epithelial and myoepithelial cells, may participate in normal mammary development, perhaps as a locally secreted growth inhibitor. These data support the hypothesis of an interaction between PRL and PTH-rP during lactation and their putative association in bone loss (38). Despite this, an increase in PTH or/and PTH-rP could explain the increase in serum calcium, but not the decrease in bone formation.
Conclusions
Our data suggest that the bone alterations observed in PRL
receptor knockout mice represent a delay in bone formation, leading to
minor osteopenia. Although there have been some reports suggesting that
PRL might play a role in bone development, the results described in the
present manuscript are the first to clearly demonstrate that the
presence of a lactogen receptor could be important for normal bone
remodeling. On the basis of these results, it is possible to define new
axes of investigation concerning the effects of PRL and its hormonal
consequence on bone metabolism. In vitro studies also
represent a means to analyze the direct effects of PRL on bone, in
particular signal transduction and biological responses in osteoblasts.
These studies should to be of broad general interest to basic
scientists and clinicians, because they help in the understanding of
bone disorders observed during pregnancy, lactation, and under certain
pathological conditions such as hyperprolactinemia.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
2 C. J. Martin fellow of the National Health and Medical Research
Council of Australia.
Received May 13, 1998.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
This article has been cited by other articles:
 |
|
 |
|
  M K. Javaid and R. I. Holt Understanding osteoporosis J Psychopharmacol, March 1, 2008; 22(2_suppl): 38 - 45. [Abstract] [PDF]
|
|
|
|
 |
|
 M. J. LeBaron, T. J. Ahonen, M. T. Nevalainen, and H. Rui In Vivo Response-Based Identification of Direct Hormone Target Cell Populations Using High-Density Tissue Arrays Endocrinology, March 1, 2007; 148(3): 989 - 1008. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Charoenphandhu, K. Tudpor, K. Thongchote, W. Saengamnart, S. Puntheeranurak, and N. Krishnamra High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats Am J Physiol Endocrinol Metab, February 1, 2007; 292(2): E443 - E452. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A J Craven, A J Nixon, M G Ashby, C J Ormandy, K Blazek, R J Wilkins, and A J Pearson Prolactin delays hair regrowth in mice. J. Endocrinol., November 1, 2006; 191(2): 415 - 425. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C Zermeno, J Guzman-Morales, Y Macotela, G Nava, F Lopez-Barrera, J B Kouri, C Lavalle, G M. de la Escalera, and C Clapp Prolactin inhibits the apoptosis of chondrocytes induced by serum starvation. J. Endocrinol., May 1, 2006; 189(2): R1 - R8. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Kedzia, L. Lacroix, N. Ameur, T. Ragot, P. A. Kelly, B. Caillou, and N. Binart Medullary Thyroid Carcinoma Arises in the Absence of Prolactin Signaling Cancer Res., September 15, 2005; 65(18): 8497 - 8503. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. C. Miller, B. L. Anderson, and B. M. Bowman Weaning Initiates a Rapid and Powerful Anabolic Phase in the Rat Maternal Skeleton Biol Reprod, July 1, 2005; 73(1): 156 - 162. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Fleenor, J. Oden, P. A. Kelly, S. Mohan, S. Alliouachene, M. Pende, S. Wentz, J. Kerr, and M. Freemark Roles of the Lactogens and Somatogens in Perinatal and Postnatal Metabolism and Growth: Studies of a Novel Mouse Model Combining Lactogen Resistance and Growth Hormone Deficiency Endocrinology, January 1, 2005; 146(1): 103 - 112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. N. VanHouten and J. J. Wysolmerski Low Estrogen and High Parathyroid Hormone-Related Peptide Levels Contribute to Accelerated Bone Resorption and Bone Loss in Lactating Mice Endocrinology, December 1, 2003; 144(12): 5521 - 5529. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. J. Yarram, M. J. Perry, T. J. Christopher, K. Westby, N. L. Brown, T. Lamminen, S. B. Rulli, F.-P. Zhang, I. Huhtaniemi, J. R. Sandy, et al. Luteinizing Hormone Receptor Knockout (LuRKO) Mice and Transgenic Human Chorionic Gonadotropin (hCG)-Overexpressing Mice (hCG {alpha}{beta}+) Have Bone Phenotypes Endocrinology, August 1, 2003; 144(8): 3555 - 3564. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. G. Robertson, J. Harris, M. J. Naylor, S. R. Oakes, J. Kindblom, K. Dillner, H. Wennbo, J. Tornell, P. A. Kelly, J. Green, et al. Prostate Development and Carcinogenesis in Prolactin Receptor Knockout Mice Endocrinology, July 1, 2003; 144(7): 3196 - 3205. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Foitzik, K. Krause, A. J. Nixon, C. A. Ford, U. Ohnemus, A. J. Pearson, and R. Paus Prolactin and Its Receptor Are Expressed in Murine Hair Follicle Epithelium, Show Hair Cycle-Dependent Expression, and Induce Catagen Am. J. Pathol., May 1, 2003; 162(5): 1611 - 1621. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. J. Ormandy, M. Naylor, J. Harris, F. Robertson, N. D. Horseman, G. J. Lindeman, J. Visvader, and P. A. Kelly Investigation of the Transcriptional Changes Underlying Functional Defects in the Mammary Glands of Prolactin Receptor Knockout Mice Recent Prog. Horm. Res., January 1, 2003; 58(1): 297 - 323. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. J. Allan, E. Tonner, M. C. Barber, M. T. Travers, J. H. Shand, R. G. Vernon, P. A. Kelly, N. Binart, and D. J. Flint Growth Hormone, Acting in Part through the Insulin-Like Growth Factor Axis, Rescues Developmental, But Not Metabolic, Activity in the Mammary Gland of Mice Expressing a Single Allele of the Prolactin Receptor Endocrinology, November 1, 2002; 143(11): 4310 - 4319. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. E. Cruz-Soto, M. D. Scheiber, K. A. Gregerson, G. P. Boivin, and N. D. Horseman Pituitary Tumorigenesis in Prolactin Gene-Disrupted Mice Endocrinology, November 1, 2002; 143(11): 4429 - 4436. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. F. Gevers, N. Loveridge, and I. C. A. F. Robinson Bone Marrow Adipocytes: A Neglected Target Tissue for Growth Hormone Endocrinology, October 1, 2002; 143(10): 4065 - 4073. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Freemark, I. Avril, D. Fleenor, P. Driscoll, A. Petro, E. Opara, W. Kendall, J. Oden, S. Bridges, N. Binart, et al. Targeted Deletion of the PRL Receptor: Effects on Islet Development, Insulin Production, and Glucose Tolerance Endocrinology, April 1, 2002; 143(4): 1378 - 1385. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L.-y. Yu-Lee Stimulation of interferon regulatory factor-1 by prolactin Lupus, October 1, 2001; 10(10): 691 - 699. [Abstract] [PDF]
|
|
|
|
|
|
L. Welniak, S. Richards, and W. Murphy Effects of prolactin on hematopoiesis Lupus, October 1, 2001; 10(10): 700 - 705. [Abstract] [PDF]
|
|
|
|
|
|
S. Bernichtein, S. Kinet, S. Jeay, M. Llovera, D. Madern, J. A. Martial, P. A. Kelly, and V. Goffin S179D-Human PRL, a Pseudophosphorylated Human PRL Analog, Is an Agonist and Not an Antagonist Endocrinology, September 1, 2001; 142(9): 3950 - 3963. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. J. Craven, C. J. Ormandy, F. G. Robertson, R. J. Wilkins, P. A. Kelly, A. J. Nixon, and A. J. Pearson Prolactin Signaling Influences the Timing Mechanism of the Hair Follicle: Analysis of Hair Growth Cycles in Prolactin Receptor Knockout Mice Endocrinology, June 1, 2001; 142(6): 2533 - 2539. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Freemark, D. Fleenor, P. Driscoll, N. Binart, and P. A. Kelly Body Weight and Fat Deposition in Prolactin Receptor-Deficient Mice Endocrinology, February 1, 2001; 142(2): 532 - 537. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. A. McClellan, F. G. Robertson, J. Kindblom, H. Wennbo, J. Törnell, B. Bouchard, P. A. Kelly, and C. J. Ormandy Investigation of the Role of Prolactin in the Development and Function of the Lacrimal and Harderian Glands Using Genetically Modified Mice Invest. Ophthalmol. Vis. Sci., January 1, 2001; 42(1): 23 - 30. [Abstract] [Full Text]
|
|
|
|
|
|
D. Coss, L. Yang, C. B. Kuo, X. Xu, R. A. Luben, and A. M. Walker Effects of prolactin on osteoblast alkaline phosphatase and bone formation in the developing rat Am J Physiol Endocrinol Metab, December 1, 2000; 279(6): E1216 - E1225. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Ling, G. Hellgren, M. Gebre-Medhin, K. Dillner, H. Wennbo, B. Carlsson, and H. Billig Prolactin (PRL) Receptor Gene Expression in Mouse Adipose Tissue: Increases during Lactation and in PRL-Transgenic Mice Endocrinology, October 1, 2000; 141(10): 3564 - 3572. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Binart, C. Helloco, C. J. Ormandy, J. Barra, P. Clement-Lacroix, N. Baran, and P. A. Kelly Rescue of Preimplantatory Egg Development and Embryo Implantation in Prolactin Receptor-Deficient Mice after Progesterone Administration Endocrinology, July 1, 2000; 141(7): 2691 - 2697. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Bouchard, C. J. Ormandy, J. P. Di Santo, and P. A. Kelly Immune System Development and Function in Prolactin Receptor-Deficient Mice J. Immunol., July 15, 1999; 163(2): 576 - 582. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Freemark Editorial: The Fetal Adrenal and the Maturation of the Growth Hormone and Prolactin Axes Endocrinology, May 1, 1999; 140(5): 1963 - 1965. [Full Text]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |
