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The Journal of Clinical Endocrinology & Metabolism Vol. 83, No. 1 187-194
Copyright © 1998 by The Endocrine Society

Original Studies

Expression of Types 1, 2, and 3 17ß-Hydroxysteroid Dehydrogenase in Subcutaneous Abdominal and Intra-Abdominal Adipose Tissue of Women

Anne M. Corbould, Stephen J. Judd and Raymond J. Rodgers

Department of Medicine, Flinders University, Bedford Park, South Australia, 5042, Australia

Address all correspondence and requests for reprints to: Raymond J. Rodgers, Department of Medicine, Flinders University, Bedford Park, South Australia, 5042, Australia.


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Human adipose tissue is known to have 17ß-oxidoreductase activity, interconverting estrone (E1) and estradiol (E2), as well as androstenedione (A) and testosterone (T). We examined both the subcutaneous abdominal and intra-abdominal (visceral) adipose tissue of women for expression of types 1, 2, and 3 17ß-hydroxysteroid dehydrogenase (17ß-HSD) using ribonuclease (RNase) protection assay and RT-PCR/Southern blotting. Type 1 17ß-HSD, which encodes the enzyme responsible for the conversion of E1 to E2 in the placenta and ovary, was expressed in the subcutaneous abdominal and intra-abdominal adipose tissue of women, but the messenger RNA transcripts were predominantly incompletely spliced and therefore unlikely to encode an active protein. A pseudogene for type 1 17ß-HSD was also expressed in these tissues, but messenger RNA transcripts were again unspliced. Type 2 17ß-HSD, which encodes an enzyme that can catalyze the conversion of T to A and E2 to E1, was expressed in both the subcutaneous abdominal and intra-abdominal adipose tissue of women. Type 3 17ß-HSD was also expressed in adipose tissue from both sites studied. Type 3 17ß-HSD encodes the enzyme that catalyzes the conversion of A to T in the testis and also converts E1 to E2. Together with aromatase, which is known to be expressed in adipose tissue, the expression of types 2 and 3 17ß-HSD indicates that sex steroid production in the adipose tissue of women is a complex process. The association of visceral obesity with the development of insulin resistance and dyslipidaemia raises the question of the role of steroid production in adipose tissue in the pathogenesis of these disorders.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
HUMAN adipose tissue is a site of both synthesis and inactivation of sex steroids. All of the estrogen in postmenopausal women (1) and more than 50% of circulating testosterone (T) in normal premenopausal women (2, 3) is produced in peripheral tissues, probably mainly adipose tissue. In addition to their endocrine role, sex steroids synthesized in adipose tissue may also have important effects at a local tissue level (4, 5) including intracrine effects (6). Human adipose tissue possesses 17ß-hydroxysteroid oxidoreductase activity: interconversion of the weak estrogen, estrone (E1), and the strong estrogen, estradiol (E2), has been shown to occur in adipose tissue in vitro (7, 8). Likewise, interconversion of androstenedione (A), and the potent androgen, T, has been demonstrated in human adipose tissue (7, 8). In contrast to cytochrome P450 aromatase, the catalyst for conversion of androgens to estrogens, which has been extensively investigated in this tissue, little is known about the enzymes known as 17ß-hydroxysteroid dehydrogenases (17ß-HSD), which are responsible for the 17ß-hydroxy-steroid oxidoreductase activity in human adipose tissue.

Several 17ß-HSD genes have now been characterized in the human. Type 1 17ß-HSD, which was cloned from placenta by several groups (9, 10, 11), is the only 17ß-HSD that has been detected in adipose tissue to date (8, 12). This 17ß-HSD, which is also expressed in granulosa cells and a number of other tissues, encodes an enzyme that primarily catalyzes the conversion of E1 to E2 (13). Type 1 17ß-HSD also catalyzes conversion of dehydroepiandrosterone (DHEA) to androstenediol (Adiol) (13) and A to T (14) but with significantly lower efficiency. The gene for type 1 17ß-HSD (h17ß-HSDII) has been assigned to the q11-q21 region of chromosome 17 (11). An in-tandem pseudogene (h17ß-HSDI) has also been identified (12). The nucleotide sequences of the two genes show 89% homology.

Type 2 17ß-HSD, cloned from prostate and shown to be expressed in liver, placenta, endometrium, and small intestine, catalyzes the conversion of E2 to E1 and T to A, as well as 20{alpha}-dihydroprogesterone to progesterone (15). The enzyme responsible for catalyzing the conversion of A to T in the testis is type 3 17ß-HSD (16). This enzyme also catalyzes conversion of DHEA to Adiol and E1 to E2. To date, type 3 17ß-HSD has been shown to be expressed only in testis. Type 4 17ß-HSD, which is expressed in many tissues with highest levels in liver, heart, prostate and testis, has been shown to convert E2 to E1 and Adiol to DHEA (17). Recently, type 5 17ß-HSD has been cloned from human placenta. Preliminary reports suggest that this enzyme catalyzes the conversion of A to T (referred to in Ref.18).

The aims of this study were to examine, in detail, the expression of types 1, 2, and 3 17ß-HSD in human adipose tissue. We examined the splicing of type 1 17ß-HSD transcripts and also looked for evidence of expression of the related pseudogene. Although the subcutaneous adipose tissue of women has been reported to convert A to T (7) and is likely to be the peripheral tissue responsible for extraglandular T production in normal women, much less is known of the steroidogenic potential of visceral adipose tissue. Androgen metabolism in visceral adipose tissue may be of particular relevance however, because of the direct venous drainage of this tissue to the liver and the association of visceral obesity with metabolic disorders such as insulin resistance and dyslipidaemia (19).


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Tissues

One to three grams of subcutaneous abdominal adipose tissue and visceral adipose tissue (omentum) were collected from women (age 16–78 yr, body mass index 20–36 kg/m2) undergoing elective laparotomy for hysterectomy, colectomy, or cholecystectomy. Women taking the oral contraceptive pill or hormonal replacement therapy during the prior 3 months were excluded. Human term placenta, a pool of granulosa cells from women undergoing oocyte retrieval in an in vitro fertilization (IVF) program, and testes from patients undergoing bilateral orchidectomy for prostate carcinoma were also obtained. This study was approved by the Committee for Clinical Investigations at Flinders Medical Centre, and the subjects gave written informed consent.

Northern blotting

RNA was isolated and subjected to electophoresis in a formaldehyde/agarose gel by the method of Sambrook et al. (20), then electroblotted onto a nylon filter (Hybond-N; Amersham Australia, North Ryde, Australia), as reported previously in detail (21). Hybridization was by standard methods (20) in 50% formamide at 42 C for 18 h using 32P-labeled DNA probes. The probes were prepared from the 975-bp Eco I-SacI fragment of type 1 17ß-HSD complementary DNA (cDNA), the 658-bp PstI-SacI fragment of the clone (9) of type 2 17ß-HSD cDNA, and the full-length type 3 17ß-HSD cDNA using the random priming method with incorporation of [{alpha}-32P]deoxycytidine triphosphate (Gigaprime Kit; Bresatec, Thebarton, SA, Australia). Stringency washes were in 0.1 x SSC with 0.1% SDS solution at 42 C.

RNase protection assay

The 975-bp EcoRI to SacI fragment of type 1 17ß-HSD cDNA was subcloned from pPUC 18 (9) into the corresponding sites of pBluescript S/K (Stratagene, La Jolla, CA). The 658-bp PstI to SacI fragment of type 2 17ß-HSD cDNA (15) and the cDNA encoding the entire 1153-bp coding region for human type 3 17ß-HSD (16) were subcloned from pCMV6 into the PstI and SacI and the HindIII and BamHI sites of pBluescript S/K, respectively. The subclones were linearized with HinfI in the case of type 1 17ß-HSD and RsaI for types 2 and 3 17ß-HSD; antisense RNA probes were generated by incorporating [{alpha}-32P]uridine triphosphate (Bresatec) with T3 RNA polymerase using a Promega riboprobe kit (Promega, Madison, WI) (probe sizes 470, 275, and 579 nucleotides, respectively). Total RNA (20 µg) from omental adipose tissues, term placenta, testes, and postmenopausal ovary was analyzed as published previously (21).

RT-PCR and Southern blotting

RNA (1 µg) from each tissue was reverse transcribed using random hexameric primers (Promega) and Moloney murine leukemia virus reverse transcriptase 200 U/µg RNA (Gibco-BRL, Gaithersburg, MD). For each tissue sample, RNA was incubated in the RT mix without the addition of reverse transcriptase for use as a negative control. The RT reaction (1 µL) was amplified by PCR using Taq DNA polymerase (Promega) in an OmniGene temperature cycler (Hybaid, Middlesex, UK) for 35 cycles of 94 C for 30 sec, 60 C for 30 sec for type 1 17ß-HSD, 57 C for 30 sec for type 2 17ß-HSD, 55 C for 30 sec for type 3 17ß-HSD, 72 C for 30 sec, and on the final cycle, 72 C for 15 min. The primers used for type 1 17ß-HSD were 5'-CTTCAAAGTGTATGCCACGTTGAG-3' and 5'-TACTACATTCACGTCCAGCACAGAG-3', for type 2 17ß-HSD were 5'- CGGTGCTCCAAATGGACATCAC-3' and 5'-GGATGGAAGCAACTTTAATTCCCC-3', and the primers used for type 3 17ß-HSD were S1 (5'-AGCCTCATCCATTGTAACATCACC-3') and two reverse primers used in different reactions; AS1 (5'-AAGCCCGCCAAGATTTCATG-3') and AS2 (5'-AGAAAGCCCGCCAAGATTTC-3'). The primers for ß-actin were 5'-TGTACGCCAACACAGTGCTGTCT-3' and 5'-CGTCATACTCCTGCTTGCTGATCC-3'. Southern blots were carried out using standard methods (20), with stringency washes of 0.1 x SSC at 65 C. DNA probes were prepared as for Northern blots.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Northern blots confirmed the expression of type 1 17ß-HSD in placenta and granulosa cells, type 2 17ß-HSD in placenta, and type 3 17ß-HSD in testis, but no signal was detectable in 10 µg total RNA samples of three subcutaneous abdominal and three omental adipose tissues for types 1 and 2 17ß-HSD, and two subcutaneous abdominal and two omental adipose tissues for type 3 17ß-HSD (results not shown).

Using the more sensitive technique of RNase protection assay, type 1 17ß-HSD (results not shown) and type 2 17ß-HSD (Fig. 1Go, A) messenger RNA (mRNA) transcripts were not detectable in omental adipose tissue samples. In the RNase protection assay for type 3 17ß-HSD, a protected band of predicted size (513 nucleotides) was present in testis as expected, and a protected band of the same size was also detected in the omental adipose tissue samples (Fig. 1Go, C).



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  		Figure 1. RNase protection assay for type 2 17ß-HSD (A) and type 3 17ß-HSD (C) using RNA (20 µg) from omental adipose tissue samples (O16, O17), placenta (P), pooled IVF granulosa cells (G), postmenopausal ovary (Ov), and testes (T1, T2). Upper arrow indicates location of probe (275 nucleotides for type 2, 576 nucleotides for type 3) and lower arrow indicates location of protected band (256 nucleotides for type 2 and 513 nucleotides for type 3). Integrity and purity of RNA (0.5 µg) was assessed on a nondenaturing gel stained with ethidium bromide (B and D).

 
RT-PCR followed by Southern blotting was also used to examine the expression of the three types of 17ß-HSD in subcutaneous and omental adipose tissue samples. With primers for type 1 17ß-HSD, a product of expected size (262 bp) was seen in placenta, but in the six of seven subcutaneous adipose tissue samples (Fig. 2AGo) and six of eight omental samples (Fig. 3AGo) where a band was visible on the gel, the product was larger than expected (409 bp), consistent with inclusion of the intron. This intron between exons 2 and 3 is 147 bp (12). When these products were analyzed using Southern blotting, it was apparent that although the major band in the subcutaneous and omental adipose tissue samples was the 409-bp product, several samples also showed a small amount of the 262-bp product (three of the five positive subcutaneous samples and two of the five positive omental samples had detectable 262-bp product in addition to the 409-bp product) (Figs. 2DGo and 3DGo). When the type 1 17ß-HSD PCR products were digested with StyI, for which there is a recognition site only in the intron between exons 2 and 3 (Fig. 4AGo), the placenta and granulosa cell bands did not change in size, but the 409-bp product in adipose tissue was digested to give bands of size 206 and 203 bp, consistent with cutting of the intron (Figs. 4Go, B and C). To determine whether the 409-bp band was possibly a product of the homologous pseudogene, the PCR products were digested with HinfI, which has a recognition site in the functional gene and not in the pseudogene (Fig. 4AGo). Digestion of the 409-bp product from the functional gene with HinfI would be predicted to result in bands of size 293 and 116 bp (Fig. 4BGo). Except in one omental sample in which there was no digestion of the 409-bp product, there was part digestion of the 409-bp band, consistent with expression of both the type 1 17ß-HSD functional gene and related pseudogene (Fig. 4DGo). Thus in adipose tissue, the 409-bp product derived from both the type 1 17ß-HSD functional gene and the pseudogene represents unspliced RNA.



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  		Figure 2. RT-PCR and Southern blot analyses of expression of type 1 17ß-HSD in subcutaneous abdominal adipose tissue. RT-PCR of subcutaneous abdominal adipose tissue samples from seven women (samples 1–7), placenta (P), pooled IVF granulosa cells (G), testis (T), and no RNA N) using primers specific for type 1 17ß-HSD (A). B, Same as A except that reverse transcriptase was omitted from reaction mix. RT-PCR of same tissues as in A using primers for ß-actin (C). Agarose gels

 


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  		Figure 3. RT-PCR and Southern blot analyses of expression of type 1 17ß-HSD in omental adipose tissue. RT-PCR of omental adipose tissue samples from women (samples 8–15), placenta (P), pooled IVF granulosa cells (G), testis (T), and no RNA (N) using primers specific for type 1 17ß-HSD (A). B, Same as A except that reverse transcriptase was omitted from reaction mix. RT-PCR of same tissue as in A using primers for ß-actin (C). Agarose gels (A, B, and C) were stained with ethidium bromide. D, E, and F, Southern blots using type 1 17ß-HSD probe. D and E, Same PCR products as in A and B, respectively. F, RT-PCR products generated using primers for type 3 17ß-HSD. Spliced RNA results in a PCR product of 262 bp. For unspliced RNA, product size is 409 bp. Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

 


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  		Figure 4. Analysis of gene expression and mRNA splicing of type 1 17ß-HSD in omental and subcutaneous abdominal adipose tissue. A, Partial maps of functional type 1 17ß-HSD gene and pseudogene showing location of restriction enzyme sites for HinfI in functional gene only and StyI sites in intron between exons II and III in both genes. PCR priming sites are indicated (arrows). B, Predicted size of products (bp) following PCR amplification and restriction enzyme digestion from spliced and unspliced functional gene and pseudogene. C and D, Products (separated on agarose gels and stained with ethidium bromide) following RT-PCR amplification and digestion with StyI (C) and HinfI (D). Sizes of these products are indicated (arrows, bp). Samples are omental (8–11) and subcutaneous abdominal adipose tissues (2, 3, 5, 6), placenta (P), and pooled IVF granulosa cells (G). Molecular weight markers (M) are HpaII-digested pUC19.

 
Using primers for type 2 17ß-HSD, a product of predicted size (384 bp) was detected in placenta as expected (Figs. 5AGo and 6AGo). Of six subcutaneous adipose tissue samples analyzed using RT-PCR, faint products of expected size were visible in two samples on an ethidium bromide gel (Fig. 5AGo) but on Southern blotting of the PCR products, a signal was detected in five of the samples (Fig. 5CGo). In seven of eight omental adipose tissue samples analyzed by the same method, a 384-bp band was visible on an ethidium bromide gel (Fig. 6AGo), and all of these seven samples were hybridizable with cDNA for type 2 17ß-HSD (Fig. 6CGo).



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  		Figure 5. RT-PCR and Southern blot analyses of expression of type 2 17ß-HSD in subcutaneous abdominal adipose tissue. RT-PCR of subcutaneous abdominal adipose tissue samples from women (samples 1–7), placenta (P), testis (T), and no RNA (N) using primers specific for type 2 17ß-HSD (A). B, Same as A except that reverse transcriptase was omitted from reaction mix. Agarose gels (A and B) were stained with ethidium bromide. C, D, and E, Southern blots using type 2 17ß-HSD probe. C and D, Same PCR products as in A and B, respectively. E, RT-PCR products generated using primers for type 1 17ß-HSD. Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

 


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  		Figure 6. RT-PCR and Southern blot analyses of expression of type 2 17ß-HSD in omental adipose tissue. RT-PCR of omental adipose tissue samples from women (samples 8–15), placenta (P), testis (T), and no RNA (N) using primers specific for type 2 17ß-HSD (A). B, Same as A except that reverse transcriptase was omitted from reaction mix. Agarose gels (A and B) were stained with ethidium bromide. C, D, and E, Southern blots using type 2 17ß-HSD probe. C and D, Same PCR products as in A and B, respectively. E, RT-PCR products generated using primers for type 1 17ß-HSD. Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

 
Using primers for type 3 17ß-HSD, a product of predicted size (380 bp) was detected in testis as expected and also in all of seven subcutaneous abdominal adipose tissue samples from women (Fig. 7AGo). These bands were hybridizable with cDNA of type 3 17ß-HSD (Fig. 6CGo). RT-PCR/Southern blotting using two sets of primers confirmed the expression of type 3 17ß-HSD in 11 of 13 omental adipose tissue samples (Fig. 8Go, A, E, and F).



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  		Figure 7. RT-PCR and Southern blot analyses of expression of type 3 17ß-HSD in subcutaneous abdominal adipose tissue. RT-PCR of subcutaneous abdominal adipose tissue samples from seven women (samples 1–7), placenta placenta (P), testis (T), and no RNA (N) using primers specific for type 3 17ß-HSD (A). B, Same as A except that reverse transcriptase was omitted from reaction mix. Agarose gels (A and B) were stained with ethidium bromide. C, D, and E, Southern blots using type 3 17ß-HSD probe. C and D, Same PCR products as in A and B, respectively. E, RT-PCR products generated using primers for type 1 17ß-HSD. Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

 


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  		Figure 8. RT-PCR and Southern blot analyses of expression of type 3 17ß-HSD in omental adipose tissue samples. RT-PCR of omental adipose tissue samples from 13 women (samples 8, 11–15, and 17–23), placenta (P), pooled IVF granulosa cells (G), testis (T), and no RNA (N) using two different primer sets specific for type 3 17ß-HSD. Primers S1 and AS1 (see Methods) were used in A and B, and S1 and AS2 were used in E, F, and G. B, Same samples as A; G, same samples as in E and F, except that reverse transcriptase was omitted from reaction mix of B and G. C and H, RT-PCR products generated using primers for type 1 17ß-HSD and hybridized with type 3 17ß-HSD probe as used in A, B, F, and G. D and E, Ethidium bromide-stained gels of RT-PCR products generated using ß-actin primers (D) and type 3 17ß-HSD primers (E). Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

(A, B, and C) were stained with ethidium bromide. D, E, and F, Southern blots using type 1 17ß-HSD probe. D and E, Same PCR products as on A and B, respectively, except that pooled granulosa cells (G1, G2) are different samples. F, RT-PCR products generated using primers for type 3 17ß-HSD (sample 9 is subcutaneous abdominal adipose tissue). Spliced RNA results in a PCR product of 262 bp. For unspliced RNA, product size is 409 bp. Molecular weight markers (M) are HpaII-digested pUC19, and product sizes (bp) are arrowed.

 
In these experiments, rigorous controls were included. No PCR products were detected when the RT step was omitted (e.g. Fig. 2Go, B and E). Thus the PCR products observed from the reverse transcribed mRNA were in fact derived from mRNA and not DNA. The labeled cDNA probes used were specific: PCR products generated using primers for type 3 17ß-HSD were not hybridizable with cDNA of type 1 17ß-HSD (Fig. 2FGo and 3FGo). Type 1 17ß-HSD PCR products were not hybridizable with cDNA of type 2 17ß-HSD (Figs. 5EGo and 6EGo) or with cDNA of type 3 17ß-HSD (Figs. 7EGo, and 8Go, C and H).


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
This study demonstrated that types 1, 2, and 3 17ß-HSD are expressed in the adipose tissue of women taken from both the subcutaneous abdominal and omental sites. In vitro studies with human adipose tissue have demonstrated its capacity to interconvert steroids with reduction of E1 to E2 and A to T being the favored reactions (7, 8, 22). The conversion of E1 to E2 is strongly catalyzed by type 1 17-HSD, but our studies suggest that in contrast to the placenta, adipose tissue does not contain the active enzyme. Our studies show that whether a product of the functional gene (h17ß-HSDII) or the in-tandem pseudogene for type 1 17ß-HSD (h17ß-HSDI), the mRNAs for type 1 17ß-HSD in adipose tissue are predominantly incompletely spliced. Because of in-frame stop codons in the intron that we observed to be retained in adipose tissue mRNA, translation of the unspliced mRNA would result in production of a truncated protein encoding only the first 27% of the type 1 17ß-HSD. This protein is unlikely to be active. If the type 1 17ß-HSD pseudogene was transcribed and correctly spliced, it would also encode a truncated protein because of a G substituted for a T with creation of a TAA stop codon at position 218 (12). The h17ß-HSDI gene has been shown to be transcribed in benign and malignant breast tissue, endometrium, placenta, and in a variety of cell lines (23), although its function, if any, is unknown. Initial reports of type 1 17ß-HSD expression in human abdominal adipose tissue (the gender of origin and whether subcutaneous or visceral was not stated) were based on a Northern blot analysis of a single sample (12) and an RNase protection assay of one sample (8). In that RNase protection assay, the probe used was derived from within a single exon of the type 1 17ß-HSD gene, which would not have been able to distinguish unspliced from correctly spliced mRNA. In the absence of the functional type 1 17ß-HSD isozyme in adipose tissue, we propose that type 3 17ß-HSD is the catalyst for E1 to E2 conversion in this tissue.

We have shown for the first time that type 3 17ß-HSD is expressed in adipose tissue. The level of expression was sufficiently high in the omental adipose tissue of women to be detectable by RNase protection assay. Type 3 17ß-HSD has potent activity in converting A to T via the {Delta}4 pathway (16). This enzyme may be responsible for the conversion of A to T in the peripheral tissues of women: this constitutes an important source of circulating T in premenopausal women, contributing approximately 100 µg or 50% of total T production each day (2, 3). Type 3 17ß-HSD when expressed in COS cells also catalyzes the conversion of DHEA to Adiol by the {Delta}5 pathway, although with less efficiency than it converts A to T (16). The conversion of DHEA to Adiol has been demonstrated in vitro in subcutaneous abdominal adipose tissue of women (24), and administration of oral DHEA to postmenopausal women results in a dramatic rise in plasma T (25). Because 3ß-HSD activity has been shown to be present in adipose tissue, at least in the rhesus monkey (26), the production of T from DHEA in adipose tissue could be catalyzed by type 3 17ß-HSD through either the {Delta}4 or {Delta}5 pathway.

The ultimate fate of A delivered to adipose tissue will depend on the relative activities of type 2 17ß-HSD, type 3 17ß-HSD, and aromatase. Estrogen production would be favored by a high aromatase/type 3 17ß-HSD ratio, and androgen production by a low ratio. Our current studies did not determine the relative levels of expression of these enzymes or whether this differs in adipose tissue from different sites. However, we did find that in omental adipose tissue, type 3 17ß-HSD could be detected by RNase protection assay, but type 2 17ß-HSD could only be detected by the more sensitive RT-PCR/Southern blotting methods, suggesting that the former is more highly expressed. Similarly, in subcutaneous abdominal adipose tissue, PCR products for type 3 17ß-HSD were readily detected in ethidium bromide-stained gels, whereas Southern blotting was often required to detect type 2 17ß-HSD PCR products.

Regional differences in adipose tissue steroidogenesis may be important given the association in women of abdominal obesity, but not peripheral obesity, with elevated plasma T, insulin resistance, and dyslipidaemia (27, 28, 29). These metabolic abnormalities appear to be associated specifically with an increase in visceral adipose tissue (30). Killinger et al. (31) reported that in cultured stromal cells derived from human subcutaneous abdominal and omental adipose tissue, the formation of 5{alpha}-reduced androgens from A was 10-fold greater than the formation of E1, suggesting predominance of type 3 17ß-HSD, whereas in adipose tissue from the buttock and upper thigh, the production of 5{alpha}-reduced androgens and E1 were equivalent. This observation has major clinical importance because although T produced in visceral adipose tissue would not be likely to increase circulating T levels significantly (32), transport directly to the liver by the portal circulation would expose the liver to higher levels of T: this may have important effects in inducing hyperinsulinaemia and dyslipidaemia (33, 34). Production of T by adipose tissue may also have important local actions, including intracrine effects (6). For example, T has been shown to increase the expression of adipocyte ß-adrenergic receptors, activation of which leads to lipolysis (4, 5). Replication and differentiation of preadipocytes may also be influenced by sex steroids (35, 36). Thus, local T production may potentially influence lipolytic activity or even the size of adipose tissue deposits.

In conclusion, both the subcutaneous abdominal and omental adipose tissue of women express type 1 17ß-HSD, but unlike placenta, this appears to be predominantly unspliced RNA and thus is unlikely to encode an active protein. Both types 2 and 3 17ß-HSD are expressed in the subcutaneous abdominal and omental adipose tissue of women. The adipose tissue of women is recognized as an important source of circulating sex steroids, both androgens and estrogens. Sex steroid production in adipose tissue may also be important for the regulation of functions of that tissue, including lipolysis and preadipocyte replication. The complex enzymology of 17ß-HSDs in human adipose tissue and the interactions between these enzymes and aromatase are clearly worthy of further study, especially in view of the important role of distribution of body fat in the determination of metabolic complications of obesity.


   Acknowledgments
 
The cDNA for the type 1 17ß-HSD was kindly supplied by Professor R. Vihko, Clinical Chemistry Department, University of Oulo, Oulo, Finland. The cDNAs for the types 2 and 3 17ß-HSD were kindly supplied by Dr. S. Andersson, The Cecil H. and Ida Green Center for Reproductive Biology Sciences, The University of Texas, Southwestern Medical Center, Dallas, TX. We are very grateful to Dr. D. Wattchow and Dr. N. Rieger, Department of Surgery, Flinders Medical Centre, for collection of the adipose tissue samples.

Received May 7, 1997.

Revised July 22, 1997.

Accepted September 23, 1997.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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