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Original Studies |
Department of Obstetrics and Gynecology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
Address correspondence and requests for reprints to: Jo Kitawaki, M.D., Ph.D., Department of Obstetrics and Gynecology, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kamigyo-ku, Kyoto 602-8566, Japan. E-mail: kitawaki{at}koto.kpu-m.ac.jp
| Abstract |
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| Introduction |
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A recent finding that led us to reevaluate the endometrial 17ßHSD2 is that the mRNA and protein of aromatase cytochrome P450, the enzyme responsible for estrogen biosynthesis, are not present in the endometrium of disease-free uterus (16, 17, 18, 19), but present in the eutopic endometrium of patients with endometriosis, adenomyosis, and/or leiomyomas (18, 19). Although histologically the eutopic endometria of patients with benign uterine diseases resemble the endometria of disease-free uterus, the estrogen metabolism may be remarkably different (18, 19). However, the "normal" endometrial specimens used in the previous 17ßHSD studies had been obtained mostly by hysterectomy conducted for various benign diseases including endometriosis, adenomyosis, and leiomyomas, but not necessarily for disease-free uteri.
The present study was, therefore, conducted to analyze the mRNA expression and activity of 17ßHSD2 in the endometrium during the menstrual cycle. The groups were divided as disease-free endometria that were defined as only those obtained from normal menstruating women with cervical cancer in situ but showing no other gynecological disease and diseased endometria that were defined as those obtained from patients with endometriosis, adenomyosis, and/or leiomyomas.
| Materials and Methods |
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Endometrial biopsy specimens were obtained for diagnostic purposes from patients scheduled for laparotomy or laparoscopy at the Department of Obstetrics and Gynecology, Kyoto Prefectural University of Medicine. This study protocol was approved by the Kyoto Prefectural University of Medicine institutional review board, and informed consent was obtained from each patient. All patients were of reproductive age with normal menstrual cycles. The patients were not receiving any endocrine therapy, such as GnRH analog, danazol, or pseudopregnancy therapy. Endometrial specimens were classified into disease groups as described previously (19). Endometriosis, adenomyosis, and/or leiomyomas were diagnosed by histological examination using excised uteri or laparoscopy. Endometria obtained from patients with cervical cancer in situ but showing no other gynecological disease (n = 23), or those obtained from patients with tubal occlusion or adhesion but without endometriosis, adenomyosis, or leiomyomas (n = 9) were defined as "disease free." The following cases were excluded from the study: malignant neoplasms other than cervical carcinoma in situ, ovarian neoplasms, pelvic inflammation, and pregnancy. A total of 65 patients met the criteria; nineteen patients in the proliferative phase and 13 patients in the secretory phase with endometriosis, adenomyosis, and/or leiomyomas, and 20 patients in the proliferative phase and 13 patients in the secretory phase without disease. The mean age was 38.9 ± 8.3 yr (mean ± SD, 2648 yr), and the mean body mass index (BMI) was 21.5 ± 2.2 (16.924.8), respectively. There was no significant difference in the mean ages or BMI among the groups with endometriosis, adenomyosis, leiomyomas, and disease free. Endometrial specimens were obtained according to chronological dating, basal body temperature, and transvaginal ultrasound sonography and were histologically diagnosed according to the criteria of Noyes et al. (20). Fresh tissue samples were divided into two portions: one was frozen immediately at -80 C and stored for total RNA extraction and 17ßHSD2 assay, and the other was fixed with 4% paraformaldehyde for histological diagnosis.
RNA isolation and RT-PCR
Total RNA was extracted using Trizol (Life Technologies, Inc., Gaithersburg, MD), and the first-strand cDNA synthesis from total RNA was catalyzed by Superscript II RT (Life Technologies, Inc.) using oligo(deoxythimidine)1218, as described previously (18). The resulting first-strand cDNA was used for PCR amplification with the following primers: 5'-CTGAGGAATTGCGAAGAACC-3' (forward, nucleotides 445464) and 5'-GAAGTCCTTGCTGGCTAACG-3' (reverse, nucleotides 10371018) (21) for human 17ßHSD2; and human G3PDH amplimer set for glyceraldehyde-3-phosphate dehydrogenase (G3PDH) (CLONTECH Laboratories, Inc., Palo Alto, CA). Because the 17ßHSD2 gene encodes two alternatively spliced mRNAs (22), the primer set for 17ßHSD2 is designed to detect the mRNA encoding the previously identified 17ßHSD type 2A protein that has enzymatic activity, but not the mRNA encoding 17ßHSD type 2B protein that lacks enzymatic activity. The PCR mixture comprised 1 µL first-strand cDNA, 0.2 µmol/L of each of the primers mentioned above, 0.2 mmol/L dNTP, and 1 µL AdvanTaq DNA polymerase (CLONTECH Laboratories, Inc.), in a total volume of 50 µL PCR buffer provided by the manufacturer. After an initial denaturation at 95 C for 1 min, PCR was carried out for 35 cycles at 95 C for 30 sec, at 60 C (for 17ßHSD2) or 55 C (for G3PDH) for 30 sec, and at 68 C for 30 sec.
Northern blot analysis
Northern blotting was performed as described previously (23).
Briefly, 20 µg total RNA was electrophoresed in a 1%
agarose/formaldehyde gel and transferred to a nylon membrane (Hybond
N+; Amersham Pharmacia Biotech,
Piscataway, NJ) by capillary blotting and UV cross-linked. Membranes
were prehybridized for 1 h at 65 C in 0.5 mol/L
Na2HPO4/H3PO4
buffer (pH 7.2) containing 1 mmol/L EDTA and 7% SDS. The radiolabeled
probes for 17ßHSD2 and G3PDH were
derived from the amplified cDNA fragments produced in the RT-PCR of
term placental tissues. DNA bands were excised from the agarose gel and
extracted using a NucleoTrap DNA purification kit (CLONTECH Laboratories, Inc.). Aliquots of the DNA products were sequenced
by the dye terminator method using a model 100 DNA analyzer (PE Applied Biosystems, Inc., Foster City, CA) and the sequence for
17ßHSD2 was confirmed to be equal to the
sequence reported in the Genbank databank. The probes were radiolabeled
with [
-32P]dCTP using a Random primer plus
extension labeling system (NEN Life Science Products,
Boston, MA). After hybridization for 24 h at 60 C, membranes were
washed three times for 5 min each at 65 C, followed by a wash for 15
min at 65 C in 0.04 mol/L
Na2HPO4/H3PO4
buffer (pH 7.2) containing 1% SDS. The hybridized signal was analyzed
using a bioimazing analyzer (BAS 2000; Fujix, Tokyo, Japan).
Assay of 17ßHSD2 activity
17ßHSD2 activity was measured according to the methods of
Tseng and Gurpide (6), with modification (12). The endometrial
specimens were homogenized in 0.05 mol/L Tris-HCl buffer (pH 8.0) and
centrifuged at 800 x g. The resulting supernatant
(
0.8 mg protein/mL) was incubated for 60 min at 37 C in air with
[6, 7-3H]E2 (NEN Life Science Products; 1.5 x 106
dpm, 37 µmol/L) and nicotinamide adenine dinucleotide
(NAD+; Sigma, St. Louis, MO) (1.4
mmol/L) in a total incubation volume of 0.4 mL. The reaction was
stopped by the addition of 2 mL diethyl ether containing
[4-14C]E1 (NEN Life Science Products; 2x103 dpm) as well as
nonradioactive standards E1 and
E2 (0.2 mg each). The organic phase was extracted
three times with diethyl ether, and the tritiated
E1 formed was isolated by thin-layer
chromatography using Silicagel 60 F254 (0.25 mm;
E. Merck, Darmstadt, Germany) in the systems of chloroform-ethyl
acetate (4:1, v/v) and benzene-ethyl acetate (1:1, v/v). The
radioactivity of the control incubation without
NAD+ was subtracted; however, it was usually
negligible. The specific activity was calculated from the
3H/14C ratio of
E1 formed.
For kinetic studies, the 800 x g supernatant of the endometrial homogenate was incubated for 10 min with varying concentration of [3H]E2 and NAD+ (1.4 mmol/L) in a total incubation volume of 0.4 mL. The protein concentration of the reaction mixture was determined by Bio-Rad Laboratories, Inc. Protein Assay Kit (Bio-Rad Laboratories, Inc., Hercules, CA), with BSA as the standard.
Organ culture
Organ culture of endometrial tissues were performed as described
previously (12, 24). Briefly, the endometrial tissue was washed
immediately after sampling and cut into
1-mm cubes in ice-cold HBSS
(Life Technologies, Inc.). The tissue fragments were
placed on several pieces of l-cm cubes of Spongel (Yamanouchi
Pharmaceuticals, Tokyo, Japan), which were immersed in 10 mL
DMEM/Hams F12 medium (1:1) with 15 nmol/L HEPES buffer without Phenol
red (Life Technologies, Inc.) supplemented with 10% FBS
(Life Technologies, Inc.), penicillin (100 IU/mL),
streptomycin (100 µg/mL), and fungizone (0.25 µg/mL). The FBS had
been treated twice with charcoal (6.25 mg/mL) and Dextran T-70 (0.625
mg/mL) and then incubated at 56 C for 30 min to remove endogenous
cytokines and steroids. The tissue fragments were cultured with or
without steroid for 48 h in a humidified atmosphere of 5%
CO2-95% air. The fragments were washed with
saline and were subjected to the enzyme assay.
Statistics
Differences in ages, BMI, 17ßHSD2 activity, and mRNA levels among groups were analyzed with the one-factor ANOVA, and multiple comparisons were performed using Scheffés procedure. The relation between 17ßHSD2 activity and age and between 17ßHSD2 activity and BMI was analyzed by Spearmans correlation coefficient by rank test.
| Results |
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| Discussion |
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The discrepancy demonstrated in the present study could be attributed to two possibilities. First, the expression status of the progesterone receptors may be different in disease-free and diseased endometria. It is well established that the progesterone receptor concentration in the endometrium increases during the proliferative phase. The concentration remains high during the early secretory phase and declines in the mid- to late secretory phase (25, 26). Recently, the cyclic variation for the two splice variant isoforms, progesterone receptors A and B, has been demonstrated immunohistochemically (27, 28). However, these studies were performed without distinguishing disease-free from diseased endometrium. Whereas the eutopic endometrium of patients with endometriosis shows a cyclic change in the 17ßHSD2 activity, the endometriotic implants obtained from the same patients lack 17ßHSD2 expression (29). Because the estrogen and progesterone receptors are also expressed in the endometriotic tissues, this difference may not be explained only by the steroid receptor status. Second, another unknown factor that may be present in diseased endometrium but not in disease-free endometrium could be needed for action with progestin to stimulate 17ßHSD2 mRNA transcription. The 5'-flanking region of the 17ßHSD2 gene contains several known transcription factor-binding sites, including an inverse progesterone receptor-binding site, PEA3 binding sites, AP1 sites, and an ISGF2 recognition site (22). However, the postprogesterone receptor mechanism by which progestins induce 17ßHSD2 has not been elucidated. Additional studies on the molecular mechanism of induction are required.
Taken together with the finding that aromatase cytochrome P450 is
absent in disease-free endometrium (16, 17, 18, 19) and present in diseased
endometrium (18, 19), the estrogen metabolism in the human endometrium
should be reevaluated. In disease-free endometrium during the secretory
phase, the local E2 concentration may be higher
than that in diseased endometrium, despite the fact that local
E1 synthesized by aromatase is negligible.
E1 is further inactivated to
E1-sulfate by sulfotransferase. Although the
converse reaction of E1-sulfate to
E1 catalyzed by sulfatase occurs simultaneously
and that the activities of sulfotransferase (30) and sulfatase (31)
have been shown to elevate in the secretory phase, conjugation occurs
predominantly in the secretory endometrium. In addition to the
inactivation of E2, 17ßHSD2 simultaneously
possesses 20
-hydroxysteroid dehydrogenase activity, which oxidates
20
-dihydroprogesterone to the more active progestin progesterone (4, 6). In disease-free endometrium during the secretory phase, the local
progesterone concentration may be lower than that in diseased
endometrium. Conversely, empiric evidence supports administration of
progestins during the secretory phase, so-called luteal support, may
improve the pregnancy rate. This discrepancy should also be elucidated.
The accumulation of information on the distinction of pathologic
endometria contributes to the better understanding of
estrogen-dependent diseases.
Received March 3, 2000.
Revised May 11, 2000.
Accepted June 7, 2000.
| References |
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-hydroxysteroid dehydrogenase activity. J Biol
Chem. 268:1296412969.
-dihydroprogesterone dehydrogenase activities in human endometrium
during the menstrual cycle. Endocrinology. 94:419423.
-dihydroprogesterone dehydrogenase activities in human endometrial
glands and stroma: progestin induction of steroid dehydrogenase
activities in vitro is restricted to the glandular
epithelium. Endocrinology. 111:743749.This article has been cited by other articles:
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