IN PREVIOUS investigations we found that plasma

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1 X/81/ $02.00/0 Journal of Clinical Endocrinology and Metabolism Copyright 1981 by The Endocrine Society Vol. 52, No. 6 Printed in U.S.A. The Role of Cyclic Adenosine 3',5'-Monophosphate in Cholesterol Metabolism and Steroidogenesis by the Human Fetal Adrenal Gland* BRUCE R. CARR, MASAO OHASHI, C. R. PARKER, JR., AND EVAN R. SIMPSON Cecil H. and Ida Green Center for Reproductive Biology Sciences, and the Departments of Obstetrics- Gynecology and Biochemistry, University of Texas Southwestern Medical School, Dallas, Texas ABSTRACT. In the present investigation we studied the role of camp as a mediator of ACTH action in human fetal adrenal (HFA) tissue. We have characterized the response to ACTH, dibutyryl adenosine 3',5'-cyclic monophosphoric acid (dbcamp), and cholera toxin (CT) with respect to steroidogenesis, low density lipoprotein (LDL) binding, degradation of LDL, and the rate of de novo synthesis of cholesterol. The rate of dehydroisoandrosterone sulfate secretion was similar in HFA tissue maintained in the presence of ACTH, dbcamp, or CT. In contrast, cortisol secretion by HFA tissue was more sensitive to dbcamp and CT than to ACTH. In membrane preparations obtained from HFA tissue maintained in the presence of ACTH, dbcamp, or CT, there was a 2 to 3-fold increase of specific binding of [ 125 I]iodo-LDL. In HFA tissue maintained in the presence of ACTH or CT, the rate of degradation of LDL was significantly increased compared to tissue maintained in the lipoprotein-poor serum alone. Finally, in HFA tissue maintained in the presence of ACTH, dbcamp, or CT there was a 6- to 10- fold stimulation of the rate of incorporation of [ 14 C]acetate into cholesterol. We conclude that steroidogenesis, LDL binding, and degradation, as well as de novo synthesis of cholesterol, are probably stimulated in HFA tissue via a camp-mediated pathway. ( J Clin Endocrinol Metab 52: 1124, 1981) IN PREVIOUS investigations we found that plasma lipoproteins, and specifically low density lipoprotein (LDL), serve as a major source of the cholesterol that is required to maintain the high rate of steroid secretion by the human fetal adrenal (HFA) gland (1,2). Furthermore, we have demonstrated that ACTH causes an increase in the number of high affinity binding sites for LDL on HFA membrane preparations (Ohashi, M., B. R. Carr, and E. R. Simpson, unpublished observations). ACTH stimulates the metabolism of LDL (3) as well as the de novo synthesis of cholesterol (4) to supply optimal precursor for steroidogenesis in the HFA gland. The role of camp as a mediator or second messenger of ACTH action to stimulate steroidogenesis in adrenal cells of nonhuman species has been well characterized, and has been the topic of recent reviews (5, 6). In the present investigation, we sought to define the role of camp as a mediator of ACTH action in HFA tissue. Specifically, we sought to characterize the response of HFA tissue to dibutyryl adenosine 3',5'-cyclic monophosphoric acid (dbcamp) and cholera toxin (CT), which Received September 29, Address correspondence and requests for reprints to: Bruce R. Carr, M.D., Cecil H. and Ida Green Center for Reproductive Biology Sciences 5323 Harry Hines Boulevard Dallas, Texas * This work was supported in part by USPHS Grant Nos. 2-R01- HD and 5-P50-HD stimulates adenylate cyclase activity (6), with respect to steroidogenesis, LDL binding, degradation of LDL, and de novo synthesis of cholesterol. Adrenal glands Materials and Methods HFA glands were obtained from first and second trimester abortuses. Tissues were obtained in accordance with the Donors Anatomical Gift Act of the State of Texas after obtaining consent in writing from the woman to be aborted, using a consent form and protocol approved by the Human Research Review Committee of the University of Texas Health Science Center at Dallas, Texas. Abortion was accomplished by dilatation and extraction or else occurred spontaneously. The adrenal tissue was placed immediately in Waymouth-Gey's culture medium containing 1% antibiotics, and within one hour was minced into pieces of approximately 1 mm 3. Tissue culture Four fragments of fetal adrenal tissue were placed on lens paper that was supported by a stainless steel grid in each organ culture dish (60 X 15 mm; Falcon Plastics, Cockeysville, MD). To each dish was added 1 ml medium containing 60 vol Waymouth's MB 752/1 medium, 40 vol Gey's balanced salt solution (Grand Island Biological Company, Grand Island, NY) and 10 vol lipoprotein-poor serum () or 10 vol pooled human 1124

2 ROLE OF camp IN HFA TISSUE 1125 serum (HS). Synthetic ACTH-(1-24) (Cortrosyn), obtained from Organon (West Orange, NJ), was added to the culture medium of some dishes to achieve a concentration of 1 /xg ml" 1. dbcamp and CT obtained from Sigma Chemical Co. (St. Louis, MO) were added to the culture medium of other dishes to achieve concentrations of 1 mg/ml and 10 /xg/ml, respectively. The tissue fragments were maintained at 37 C in a humidified atmosphere of 5% CO 2-95% air. The medium was changed every 24 h. Steroid measurements In experiments designed to determine the rates of steroid secretion, tissue was incubated in medium containing 10% HS alone or 10% HS plus ACTH, dbcamp, or CT. The medium was removed and replaced with fresh medium every 24 h. The media were frozen at 20 C until assayed. Cortisol and dehydroisoandrosterone sulfate (DS) were quantified by RIA (7, 8). At the end of the culture period, the tissue fragments were rinsed two times and homogenized in 1.0 ml NaCl (0.15 M). Aliquots of the homogenates were assayed for protein by the method of Lowry et al. (9). Each experimental condition was replicated in quintuplicate, and the results are expressed as the mean ± SE of the daily secretion rate of DS or cortisol (micrograms steroid mg" 1 protein 24 h" 1 ). Lipoproteins LDL (density, g ml" 1 ) and were prepared as described previously (2). [ 125 I]Iodo-LDL was prepared according to the procedure of Bilheimer et al. (10) as adapted by Goldstein and Brown (11). The final specific activity of [ 125 I]- iodo-ldl ranged from cpm ng" 1 protein. Preparations of membrane fractions from HFA tissues On day 3 of culture, the tissue fragments from 5-10 dishes were pooled, suspended in 3 ml Tris-chloride (10 IM) buffer, ph 7.4, containing NaCl (150 mm) and CaCl 2 (1 mil), and centrifuged at 800 X g for 5 min at 4 C. The washed tissue pellet was suspended in 3 ml of the same buffer and homogenized with a tightly fitting Teflon glass homogenizer (15 strokes). The homogenate was centrifuged at 800 X g for 10 min at 4 C. The resultant pellet was suspended in 3 ml of the same buffer and centrifuged under the same conditions. The supernatant fractions were combined and centrifuged at 100,000 X g for 60 min at 4 C. The resulting pellet was stored in a liquid nitrogen freezer. Binding of [ 125 IJiodo-LDL to membrane fractions Membrane-bound [ 125 I]iodo-LDL was assayed by a modification of the method of Basu et al. (12). The binding assays were conducted in 1.5 ml polyethylene microfuge tubes (Brinkman Instruments, Palo Alto, CA) that had been precoated with 1% Siliclad (Clay-Adams, Inc., Parsippany, NJ). The usual binding assay was performed at a final ph of 7.5 in 100 /il Trischloride (50 mm) buffer containing NaCl (100 mm), CaCl 2 (0.5 mm), bovine serum albumin (20 mg ml" 1 ) and the indicated amounts of membrane protein, and [ 125 I]iodo-LDL (10 /zg protein ml '), with or without nonradiolabeled LDL (2 mg protein ml" 1 ). Before use, the stock solution of [ 125 I]iodo-LDL and nonradiolabeled LDL were passed through a Millipore filter (0.45 /xm; Millipore Corp., Bedford, MA). The binding reactions were initiated by the addition of [ 125 I]iodo-LDL, and the reaction mixtures were incubated for 60 min at 0 C in an ice water bath. To quantify the amount of membrane-bound [ 125 I]iodo-LDL, an aliquot (70 jul) of the reaction mixture was layered onto 150 /il 100% fetal calf serum in a thick cellulose proprionate tube (7.0 X 21.0 mm,; Beckman Instruments, Palo Alto, CA) that had been precoated with 1% Siliclad. The tubes were centrifuged at 100,000 X g for 20 min in a Beckman LP42Ti rotor. The supernatant fluid was discarded, and the surface of the pellet was washed by rinsing four times with 100 /il 100% fetal calf serum without suspending the pellet. After a final washing, the bottom portion of the tube was cut off with a hot razor blade and placed in a glass tube for radioactivity assay employing a Micromedic 4/600 series counter (Micromedic Systems, Niles, IL). The protein content of each membrane fraction was assayed by the method of Lowry et al. (9). Each value presented in the figure is the average of the results of triplicate assays. Degradation of lipoproteins by HFA tissue The tissue fragments were maintained in organ culture as described above. On the third day of culture the fragments were rinsed twice with 0.15 M NaCl. Fresh medium containing (10% vol/vol) and 10 jug [ 125 I]iodo-LDL was added to each dish. The incubation was continued at 37 C for 24 h. The rate of degradation of [ 125 I]iodo-LDL was determined as described (3). The results are expressed as nanograms [ 125 I]iodo-LDL degraded mg" 1 protein 24 h" 1 and are the mean ± SE of quintuplicate replicates. Statistical analysis of the data was performed utilizing the Students' t test. Incorporation of [ U CJacetate into cholesterol by HFA tissue The rate of incorporation of [ H C]acetate into cholesterol was determined in adrenal tissues on the third day of culture as described (4). The results are expressed as nanomoles mg" 1 protein h" 1, and each value represents the average of duplicate measurements. Steroid secretion rates Results The rate of secretion of DS by HFA tissue (maintained in culture medium containing 10% HS) as a function of days in culture is presented in Fig. 1. In the absence of ACTH, dbcamp, or CT, the rate of DS secretion by HFA tissue fragments remained low. In the presence of ACTH, the secretion rate of DS was high on the first day in culture. Thereafter, DS secretion declined and subsequently was maintained at a steady rate, 5- to 8-fold greater than that obtained in HFA tissue maintained in the presence of HS alone. A similar pattern of DS secretion was observed in tissue maintained in the presence of

3 1126 CARR ET AL. JCE & M 1981 Vol 52 No 6 E x CP CO Q ft % HS 10% HS 10% HS 10% HS + ACTH + dbcamp +C.T. DAYS IN CULTURE FIG. 1. Secretion rate of DS by HFA tissue as a function of days in culture. The tissue was maintained in the presence of HS (E), HS plus ACTH (ea), HS plus dbcamp (eg) and HS plus CT M. The medium was changed daily and analyzed for steroids. The results presented are the mean ± SE offive replicates and are expressed as jug DS mg"' tissue protein 24 h" 1. Adrenal tissue as represented in Fig. 1 and 2 was obtained from a single abortus. - 7 CM X I 5 Specific binding of LDL to membrane preparations of HFA tissue The specific binding of [ 125 I]iodo-LDL (total binding minus binding when excess nonradiolabeled LDL was added) by membrane preparations of HFA prepared from tissue previously maintained in the presence of 10% and in the presence or absence of ACTH, dbcamp, or CT are presented in Fig. 3. The specific binding of [ 125 I]iodo-LDL by HFA tissues that were maintained in culture medium containing ACTH, dbcamp, or CT was 2- to 3-fold greater than the specific binding by membranes prepared from nontreated tissues. Degradation of [ nb I]iodo-LDL The rates of degradation of [ 125 I]iodo-LDL by HFA maintained in the presence of 10%, and in the presence or absence of ACTH, dbcamp, or CT, are presented in Fig. 4. In the presence of ACTH or CT there was a 2-fold greater rate of degradation of LDL than in the presence of alone (P < 0.01 and P < 0.05, respectively). In tissue maintained in the presence of dbcamp there was a greater rate of degradation of LDL compared to that in tissue maintained in the presence of alone, but this difference was not statistically significant % HS 10% HS 10% HS 10% HS + ACTH +dbcamp +C.T. DAYS IN CULTURE FIG. 2. Secretion rate of cortisol by human fetal adrenal tissue as a function of days in culture. See Fig. 1 for details. dbcamp or CT. The rate of secretion of cortisol, as a function of days in culture, is presented in Fig. 2. Again, in the absence of ACTH, dbcamp, and CT, cortisol secretion remained low. In the presence of ACTH, cortisol secretion increased gradually throughout the culture period. In the presence of dbcamp or CT, cortisol secretion rates were higher on the first day in culture (4.4 ± 0.7 and 3.2 ± 0.3 /xg mg" 1 protein 24 h" 1, respectively) compared to those in HFA tissue maintained in the presence of ACTH (0.9 ±0.1 /xg mg" 1 protein 24 h" 1 ). However, by the third day in culture, cortisol secretion rates in HFA tissue maintained in the presence of dbcamp and CT were comparable to those observed in the presence of ACTH. \ Incorporation of [ U C] acetate into cholesterol The rates of incorporation of [ 14 C]acetate into cholesterol by HFA tissue maintained in the presence of 10% and in the presence or absence of ACTH, dbcamp, or CT are presented in Fig. 5. The rate of de novo, synthesis of cholesterol in HFA tissue maintained in the 300 r Z> ^ o E H N» T7E yyyyyyyy + ACTH + dbcamp FIG. 3. Effect of ACTH, dbcamp, and CT on specific binding of [ 125 I]iodo-LDL by HFA membrane fractions. Membrane fractions were prepared as described in the text from tissue fragments that had been maintained for 72 h in medium containing (o), plus ACTH (a), plus dbcamp (ta), and plus CT ( ). See Materials and Methods for details. Each data bar represents the mean of triplicate assays of specific binding of [ 125 I]iodo-LDL. Adrenal tissue obtained from a single abortus was utilized for this experiment.

4 ROLE OF camp IN HFA TISSUE r «400 to CM 200 p< ACTH p< dbcamp +C.T. FIG. 4. Effect of ACTH, dbcamp, and CT on the degradation of [ 125 I]iodo-LDL by HFA tissue. Tissue fragments were maintained for 72 h in medium containing (ea), plus ACTH (ea), plus dbcamp (El), and plus CT (mi). Thereafter, tissue fragments were incubated with [ 125 I]iodo-LDL (10 jug LDL-protein ml" 1 ) for an additional 24 h. The rate of degradation of [ l25 I]iodo-LDL was assessed as described in the text. Each value represents the mean ± SE of five replicate dishes of adrenal tissue from one abortus. O ac ^ ffix _) c O <u r ACTH + dbcamp +C.T. FIG. 5. Effect of ACTH, dbcamp, and CT on the rate of incorporation of [ 14 C]acetate into cholesterol by HFA tissue. Tissue fragments were maintained for 72 h in medium containing (m), plus ACTH (a), plus dbcamp (ra), and plus CT (mi). Thereafter tissue fragments were incubated for 6 h with [ 14 C]acetate (592 JUM), and the rate of incorporation into cholesterol was assessed as described in the text. Each data bar represents the mean of results obtained with duplicate incubations. Adrenal tissue utilized for this experiment was obtained from one abortus. presence of ACTH, dbcamp, or CT was 6 to 10-fold greater than that in the tissue maintained in the presence of alone. Discussion camp has been characterized as the intracellular second messenger of ACTH action in the stimulation of steroidogenesis in adrenal tissue. In the present investigation we found that steroidogenesis was stimulated in HFA tissue maintained in the presence of ACTH, dbcamp, or CT. In the presence of ACTH, dbcamp, or CT, DS secretion was found to be high after 24 h of treatment, followed by a decline on the second day of treatment. Thereafter, DS secretion remained steady through the remainder of the culture period. This pattern of DS secretion is similar qualitatively to that observed in previous experiments (1, 2). The secretory pattern of cortisol by HFA tissue maintained in the presence of ACTH was similar to that previously reported (1, 2), namely, the rate of cortisol secretion increased gradually over a 5- to 6-day period in the presence of ACTH. In contrast, in HFA tissue maintained in the presence of dbcamp or CT, the rate of cortisol secretion initially was 4-5 times the rate of cortisol secretion by HFA tissue maintained in the presence or absence of ACTH, and thereafter remained relatively constant. Adrenal cells comprising the neocortex or adult zone of the HFA gland secrete large quantities of cortisol and minimal quantities of DS, whereas adrenal cells from the fetal zone secrete only small amounts of cortisol but larger quantities of DS (13). If neocortex cells are deficient in the number of ACTH receptors of refractory to ACTH during the first few days in culture, this could explain the difference in cortisol secretion in the presence of ACTH as compared to dbcamp or CT. Furthermore, it would follow that since similar secretion rates of DS by HFA tissue were observed in the presence of ACTH, dbcamp, or CT, fetal zone tissue appears not to be refractory to ACTH or deficient in ACTH receptors. Others have found that cortisol secretion by HFA cells in monolayer culture was stimulated by dbcamp but noted a 3-day lag period in the secretion rates of cortisol in the presence of ACTH or dbcamp (14, 15). The difference in cortisol and DS secretion rates obtained in the present study compared to the results described by others (14, 15) might be explained by the use of higher concentrations of ACTH and dbcamp or the use of tissue fragments in organ culture rather than cells in monolayer culture. We have previously described the responsiveness of the HFA gland to ACTH during the first week of culture (16). The behavior of HFA tissue in organ culture may reflect more closely the in vivo pattern of steroid secretion. The use of collagenase to disperse adrenal cells of the HFA gland may lead to alteration in membrane components, leading to a delay for a few days before a response to ACTH action could become manifest (14). In previous experiments we found that LDL serves as the major source of cholesterol that is utilized by HFA to maintain steroidogenesis. In the present study we sought to ascertain whether camp would cause increased binding and degradation of LDL by HFA tissue in a fashion similar to that of ACTH. We found that either ACTH, dbcamp, or CT caused an increase in the specific binding of LDL by membrane fractions prepared from

5 1128 CARR ET AL. JCE & M < HFA. In addition, these compounds also stimulated degradation of LDL in HFA tissue. Furthermore, the rate of de novo synthesis of cholesterol by HFA tissue was stimulated in the presence of dbcamp, CT, or ACTH. In summary, the stimulation of steroidogenesis, cholesterol biosynthesis, and LDL metabolism in HFA tissue maintained in the presence of ACTH also was observed in tissues maintained in the presence of dbcamp or CT. We envision the role of ACTH and camp in steroidogenesis and cholesterol metabolism in the HFA gland as follows: ACTH binds to its receptor on the surface of the cells of the HFA gland and as a consequence, adenylate cyclase is activated to form camp from ATP. This causes activation of protein kinase that leads, in turn, to phosphorylation of specific proteins. It has been demonstrated recently that a number of proteins of rat adrenal are phosphorylated in response to ACTH (17). This leads, presumably, to the iniation of reactions that give rise to increased levels of key enzymes and proteins involved in adrenal cell cholesterol metabolism such as the cholesterol side chain cleavage enzyme system, 3-hydroxy-3- methylglutaryl coenzyme A (human menopausal gonadotropin Co A reductase), and the LDL receptor. In this fashion an optimal supply of cholesterol for steroid hormone production in the HFA gland is assured. Acknowledgments The authors gratefully acknowledge the skilled technical assistance of Paul Randolph, Warren Hatley, Kathy Ebenhack, and Julie Morrison, and thank Vicki Rankin for expert editorial assistance. References 1. Simpson ER, Carr BR, Parker Jr CR, Milewich L, Porter JC, MacDonald PC 1979 The role of serum lipoproteins in steroidogenesis by the human fetal adrenal cortex. J Clin Endocrinol Metab 49: Vol 52«No 6 2. Carr BR, Parker Jr CR, Milewich L, Porter JC, MacDonald PC, Simpson ER 1980 The role of low density, high density and very low density lipoproteins in steroidogenesis by the human fetal adrenal gland. Endocrinology 106: Carr BR, Porter JC, MacDonald PC, Simpson ER 1980 Metabolism of low density lipoprotein by human fetal adrenal tissue. Endocrinology 107: Carr BR, MacDonald PC, Simpson ER 1980 The regulation of de novo synthesis of cholesterol in the human fetal adrenal gland by low density lipoprotein and ACTH. Endocrinology 107: Schulster D 1974 Adrenocorticotrophic hormone and the control of adrenal corticosteroidogenesis. In: Briggs MH, Christie GA (eds) Advances in Steroid Biochemistry and Pharmacology. Academic Press, London and New York, vol 4: Gill GN 1979 ACTH regulation of the adrenal cortex. In: Gill NG (ed) Pharmacology of Adrenal Cortical Hormones. Pergamon Press, Oxford, p Gomez-Sanchez C, Milewich L, Holland OB 1977 Radioiodinated derivatives for steroid radioimmunoassay. Application to the radioimmunoassay of cortisol. J Lab Clin Med 89: Buster JE, Abraham GE 1972 Radioimmunoassay of plasma dehydroepiandrosterone sulfate. Anal Lett 5: Lowry OH, Rosebrough NJ, Farr AL, Randall RJ 1951 Protein measurement with the Folin phenol reagent. J Biol Chem 193: Bilheimer DW, Eisenberg S, Levy RI1972 The metabolism of very low density lipoproteins. I. Preliminary in vitro and in vivo observations. Biochim Biophys Acta 260: Goldstein JL, Brown MS 1974 Binding and degradation of low density lipoproteins by cultured human fibroblasts. J Biol Chem 249: Basu SK, Goldstein JL, Brown MS 1978 Characterization of the low density lipoprotein receptor in membranes prepared from human fibroblasts. J Biol Chem 253: Seron-Ferre M, Lawrence CC, Siiteri PK, Jaffe RB 1978 Steroid production by definitive and fetal zones of the human fetal adrenal gland. J Clin Endocrinol Metab 47: Baird AC, Brisson G, Kan KW, Duguid WC, Solomon S 1978 Control of steroid synthesis in human fetal adrenals in monolayer culture. Can J Biochem 56: Roos BA 1974 Effect of ACTH and camp on human adrenocortical growth and function in vitro. Endocrinology 94: Carr BR, Parker Jr CR, Milewich L, Porter JC, MacDonald PC, Simpson ER 1980 Steroid secretion by ACTH-stimulated human fetal adrenal tissue during the first week in organ culture. Steroids 36: Koroscil TM, Gallant S 1980 On the mechanism of action of adrenocorticotropic hormone. J Biol Chem 255:6276