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Gonadotropin-releasing hormone: potential role in autoimmunity
International Immunopharmacology 1 Ž2001. 1077–1083 www.elsevier.comrlocaterintimp
Review
Gonadotropin-releasing hormone: potential role in autoimmunity Jill D. Jacobson Section of Endocrinology, Children’s Mercy Hospital, UniÕersity of Missouri-Kansas City School of Medicine, Kansas City, MO, USA Received 22 May 2000; received in revised form 31 July 2000; accepted 14 August 2000
Gonadotropin-releasing hormone ŽGnRH., also known as luteinizing hormone releasing hormone ŽLHRH., is a decapeptide that is produced in the hypothalamus. It is delivered by the hypothalamic pituitary portal system to the gonadotropic cells of the anterior pituitary. It modulates the release of both luteinizing hormone ŽLH. and follicle stimulating hormone ŽFSH.. The GnRH molecule is highly conserved among species. GnRH exerts its actions through a seven transmembrane domain receptor that is coupled to G proteins. Its signal transducers include the stimulatory G protein G a s and two homologous stimulatory G proteins termed G a q and G a 11 w1x. Binding studies have confirmed the presence of the GnRH receptor in whole spleens and thymuses in rats and mice w2,3x. Porcine, human, rat, and murine immune cells express GnRH receptor mRNA w2,4–6x. GnRH possesses potent immune actions: studies in mice, rats, and humans show that GnRH exerts stimulatory influences on IFN-g production, on expression of the interleukin-2 receptor, on B and T lymphocyte proliferation, and on serum IgG levels w2,3,7–10x. Moreover, immune cells from rats and humans produce peptides with GnRH immunoreactivity and bioactivity w11,12x. Fig. 1 diagrams the known interactions of GnRH and the immune system. Most studies of GnRH production have utilized whole lymphoid organs, i.e. spleens and thymuses.
Therefore, it remains unclear as to which immune subsets produce GnRH. One study demonstrated that GnRH was produced in similar proportions in unfractionated peripheral blood T lymphocytes and in CD4 q and CD8 q subsets in humans, suggesting that GnRH is produced by multiple immune subsets w13x. Given that GnRH possesses direct immunostimulatory actions, we hypothesized that GnRH might play a role in the exacerbation of autoimmune disease. The administration of GnRH antagonists led to a reduction in autoantibody levels, total immunoglobulin levels, renal disease, and survival in a mouse model of systemic lupus erythematosus ŽSLE.. Disease severity was ameliorated in intact and gonadectomized mice, in male and female mice, and in estradiol-treated mice, demonstrating that the protective effects of the GnRH antagonists were independent of gonadal steroids w9x. Fig. 2 demonstrates survival in males and females. Interestingly, the survival in females treated with a GnRH antagonist mimicked the survival curve in males treated with vehicle. In contrast to the effects of GnRH antagonists, GnRH agonists exerted sexually dimorphic actions, even in gonadectomized mice. Although GnRH antagonist was effective in reducing disease severity Žas measured by anti-DNA antibody levels. levels in both males and females, GnRH agonist administration exerted effects on autoantibody levels in females
1567-5769r01r$ - see front matter q 2001 Published by Elsevier Science B.V. PII: S 1 5 6 7 - 5 7 6 9 Ž 0 1 . 0 0 0 3 8 - 8
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J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
Fig. 1. GnRH itself has been shown to be immunostimulatory. Immune cells from rats and humans produce immunoreactive and bioactive GnRH w11,12x. Porcine and human immune cells express receptors for GnRH w4,5x. Acute treatment with GnRH increases expression of GnRH receptor mRNA in thymocytes in mice w6x. Studies in mice and rats show that GnRH exerts stimulatory influences on expression of the interleukin-2 receptor, on B and T lymphocyte proliferation, and on serum IgG levels w2,3,8–10x. Figure is from Jacobson et al. w48x and reprinted with permission.
only w3x. Fig. 3 demonstrates anti-DNA antibody levels in males and females after 30 weeks of exposure to vehicle, GnRH antagonist or GnRH. The effects of GnRH waned over time in females. This could be attributable to tachyphylaxis to GnRH. GnRH is known to downregulate its receptor at the level of the pituitary whenever it is administered in a nonpulsatile fashion w14x. If GnRH plays a role in the modulation of autoimmune diseases, one might speculate that clinical conditions associated with elevated GnRH might display a high incidence of autoimmune disease. In fact, gonadal failure, regardless of etiology, is associated with a high incidence of autoimmune diseases, including autoimmune thyroid disease. Gonadal failure leads to loss of negative feedback on GnRH at the level of the hypothalamus. In the clinical conditions of Turner syndrome and premature ovarian failure ŽPOF., patients have, by definition of disease, ovarian failure and loss of estrogen production; yet, the incidence of autoimmune thyroid disease is extremely high Ž30%. w15,16x. Klinefelter syndrome and Down syndrome also display both gonadal fail-
ure a 30% incidence of autoimmune thyroid disease w17–19x. Data exist that patients with systemic lupus erythematosus ŽSLE., a prototypic autoimmune disease, display significantly elevated gonadotropin levels compared to controls w20,21x. It remains possible that GnRH’s immune actions are mediated, at least in part, through gonadotropins. Several studies demonstrating immune alterations following gonadotropin administration were performed in non-gonadectomized humans. These studies have generally attributed the immune actions of gonadotropins to alterations in androgens and estrogens w22,23x. The literature contains little evidence for direct immune actions of gonadotropins, for expression of gonadotropin receptors, or for production of gonadotropins by immune cells. Production of GnRH at the level of the hypothalamus and responsiveness to GnRH at the level of the pituitary are sexually dimorphic. The feedback effects of estradiol on hypothalamic release of GnRH are complex: whereas chronic estrogen exposure exerts negative feedback effects on GnRH release, rising estrogen levels stimulate GnRH release w24x.
J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
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Fig. 2. Survival in gonadectomized females treated with GnRH antagonist or vehicle. The horizontal axis represents weeks of age. Survival was assessed by Mantel–Haenzel methodology ŽGnRH antagonist, n s 40; vehicle, n s 42.. Survival is prolonged with GnRH antagonist Ž p s 0.0025..
Estrogen exposure increases the expression of the GnRH receptor and increases GnRH responsiveness at the level of the pituitary w25–27x. In contrast, GnRH production, release, and action are generally negatively regulated by androgens w28–31x. Androgens have been shown to decrease GnRH receptor
mRNA and protein w32–34x. This increase in GnRH production and increased GnRH action observed in females may play a role in the earlier timing of puberty in females. Little is known about modulatory effects of gonadal steroids or gender on GnRH production or
Fig. 3. Anti-DNA antibody levels in ovariectomized ŽSWR = NZB. F1 hybrid female and male mice after various weeks of treatment with vehicle, GnRH, or GnRH antagonist. Serum anti-DNA antibody levels were measured by a standard ELISA technique and expressed as optical density ŽO.D... Results are mean " S.E.M. Ž n s 14–22.. ) Significantly different from Ž p - 0.05. than vehicle. Figure is modified from Jacobson et al. w3x and reprinted with permission.
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J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
action at the level of the immune system. A recent study demonstrated that gonadectomy increases GnRH concentration in the thymus in rats. Exposure to testosterone prevented this increase w35x. This is the first demonstration that immune production of GnRH can be modulated by gonadal steroids. Fig. 4 diagrams the known interactions between the hypothalamic–pituitary–gonadal axis and the immune system. In retrospect, it appears that the studies demonstrating immunostimulatory properties of GnRH were done exclusively in female rats. A contradictory study that demonstrated immunosuppressive effects of GnRH on lymphocyte proliferation in vitro utilized lymphocytes from male volunteers w36x. A possible unifying explanation for the above reports is that the immune actions of GnRH are
gender-specific. In fact, we have demonstrated that splenocytes obtained from male and female mice exhibit divergent in vitro T lymphocyte proliferative responses to mitogen in the presence of GnRH w37x. Splenocytes from male mice respond to GnRH with a decrease in T lymphocyte proliferation compared to controls, whereas splenocytes from females respond with an increase. The differences in in vitro T cell proliferation persist even in long-term gonadectomized mice Žunpublished observations.. One possible mechanism for the observed gender differences in immunological responsiveness to GnRH might relate to increased GnRH receptor expression in immune cells in females. Binding studies from our laboratory demonstrate that splenic populations from female mice express more GnRH receptor than splenocytes from males w3x. Both estrogen and
Fig. 4. Estradiol ŽE 2 ., especially cyclical estradiol Žrepresented by dashed lines., as seen in women during the reproductive years, leads to increased GnRH production at the level of the hypothalamus and increased GnRH responsiveness at the level of the pituitary w24–27x. Androgens, e.g. testosterone ŽT., exert suppressive effects on GnRH production at the level of the hypothalamus and action at the level of the pituitary w28–34x. Estrogens are known to increase GnRH receptor mRNA at the level of the immune cell in mice w6x. Androgens have been shown to prevent the increase in GnRH levels that are demonstrable in the thymus following castration of male rats w35x. Thus, androgens and estrogens may alter production and responsiveness to GnRH similarly in the immune system as they do in the central nervous system.
J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
GnRH further increase the expression of the GnRH receptor mRNA in whole splenic populations. Several investigators have shown that gender differences in GnRH responsiveness in pituitary cells does not correlate directly with the expression of the GnRH receptor. Authors have suggested that post-receptor differences may explain these observations w27,38,39x. GnRH is known to exert its actions largely through specific G proteins, namely G a qr11 and G a s , at least in pituitary cell culture systems w40–42x. We have recently demonstrated splenocytes from female mice express more mRNA for G a qr11 mRNA and protein than splenocytes from males after in vivo exposure to GnRH w3x. Functional studies of G protein activity show that antisense oligonucleotides to G a qr11 and to G a s eliminate the gender differences in T cell proliferation w43,44x. G a qr11 exerts actions largely through inositol 3-phosphate ŽIP3 .. Gender differences exist in production of inositol 3-phosphate in normal DBAr2 mice in response to in vitro exposure to GnRH w45x. The literature contains few reports of gender differences in G protein expression. One study demonstrated increased G a s protein levels and increased G a s activity in response to b-adrenergic stimulation in female compared to male rats. Estradiol exposure augmented G a s activity in both male and female rats w46x. A recent study suggests that progesterone, testosterone, estradiol and GnRH all modulate G protein activity in rat pituitary cells w47x. Beyond these studies, little is known about hormonal modulation of G proteins. In summary, GnRH is produced by lymphocytes and exerts potent immunomodulatory actions. GnRH has been shown to exert gender restricted immune actions in vitro and in vivo. These gender differences correlate with gender differences in expression of the GnRH receptor and with gender differences in expression of the G proteins through which GnRH acts. We speculate that these gender differences in G proteins may contribute to the gender differences in the expression of autoimmune disease.
Acknowledgements This study was supported by NIH grant 1R29AR43152, by a grant from the Lupus Founda-
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tion of America, and by a career development award from Pharmacia Upjohn.
References w1x Stanislaus D, Ponder S, Ji TH, Conn PM. Gonadotropini-releasing hormone receptor couples to multiple G proteins in rat gonadotrophs and in GGH3 cells: evidenced from palmitoylation and overexpression of G proteins. Biol Reprod 1998;59:579–86. w2x Marchetti B, Guarcello V, Morale MC, Bartoloni G, Raiti F, Palumbo Jr. G, et al. Luteinizing hormone-releasing hormone ŽLHRH. agonist restoration of age-associated decline of thymus weight, thymic LHRH receptors, and thymocyte proliferative capacity. Endocrinology 1989;125:1037–45. w3x Jacobson JD, Ansari MA, Kinealy M, Muthukrishnan V. Gender specific exacerbation of murine lupus by gonadotropin-releasing hormone: potential role of G alpha qr11. Endocrinology 1999;140:3429–37. w4x Weesner GD, Becker BA, Matteri RL. Expression of luteinizing hormone-releasing hormone and its receptor in porcine immune tissues. Life Sci 1997;61:1643–9. w5x Chen H, Jeung E, Stephenson M, Leung PCK. Human peripheral blood mononuclear cells express gonadotropin-releasing hormone ŽGnRH.,GnRH receptor, and interleukin-2 receptor g-chain messenger ribonucleic acids that are regulated by GnRH in vitro. J Clin Endocrinol Metab 1999; 84:743–50. w6x Jacobson JD, Crofford LJ, Sun L, Wilder RL. Cyclical expression of GnRH and GnRH receptor mRNA in lymphoid organs. Neuroendocrinology 1998;67:117–25. w7x Grasso G, Massai L, De Leo L, Musccettola M. The effect of LHRH and TRH on human interferon-gamma production in vivo and in vitro. Life Sci 1998;62:2005–14. w8x Morale MC, Batticane N, Bartoloni G, Guarcello V, Farinella Z, Galasso MG, et al. Blockade of central and peripheral luteinizing hormone-releasing hormone ŽLHRH. receptors in neonatal rats with a potent LHRH-antagonist inhibits the morphofunctional development of the thymus and maturation of the cell-mediated and humoral immune responses. Endocrinology 1991;128:1073–85. w9x Jacobson JD, Nisula BC, Steinberg AD. Modulation of the expression of murine lupus by gonadotropin-releasing hormone analogs. Endocrinology 1994;134:2516–23. w10x Batticane N, Morale MC, Gallo F, Farinella Z, Marchetti B. Luteinizing hormone-releasing hormone signaling at the lymphocyte involves stimulation of interleukin-2 receptor expression. Endocrinology 1991;129:277–86. w11x Emanuele NV, Emanuele MA, Tentler J, Kirsteins L, Azad N, Lawrence AM. Rat spleen lymphocytes contain an immunoactive and bioactive luteinizing hormone-releasing hormone. Endocrinology 1990;126:2482–6. w12x Maier CC, Marchetti B, Le Boeuf RD, Blalock JE. Thymocytes express a mRNA that is identical to hypothalamic
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J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083 luteinizing hormone-releasing hormone mRNA. Cell Mol Neurobiol 1992;12:447–54. Azad N, La Paglia N, Jurgens KA, Kirsteins L, Emanuele NV, Kelley MR, et al. Immunoactivation enhances the concentration of luteinizing hormone-releasing hormone peptide and its gene expression in human peripheral T-lymphocytes. Endocrinology 1993;133:215–23. Beltchetz PE, Plant TM, Nakai Y, Keogh EJ, Knobil E. Hypophysial responses to continuous and intermittent delivery of hypothalamic gonadotropin-releasing hormone. Science 1978;202:631–3. William ED, Engel E, Forbes AP. Thyroiditis and gonadal agenesis. NEJM 1964;270:805–10. Belvisi L, Bombelli F, Sironi L, Doldi N. Organ-specific autoimmunity in patients with premature ovarian failure. J Endocrinol Invest 1993;16:889–92. McKeown DA, Doty RL, Perl DP, Frye RE, Simms I, Mester A. Olfactory function in young adolescents with Down’s syndrome. J Neurol Neurosurg Psych 1996;61:412–4. Otten BJ, Wit JM. wGrowth hormone therapy in dysmorphic syndromes and chronic diseasex. wwGroeihormoontherapie bij dysmorfe syndromen en chronische ziekten.xx Tijdschr Kindergeneeskd 1992;60:183–91. Fraser GR. Goitre in Klinefelter’s syndrome. Br Med J 1963;1:1284. Athreya BH, Pletcher J, Zulian F, Weiner DB, Williams WV. Subset-specific effects of sex hormones and pituitary gonadotropins on human lymphocyte proliferation in vitro wpublished erratum appears in Clin Immunol Immunopathol 1993 Jul; 68Ž1.:93x. Clin Immunol Immunopathol 1993;66:201–11. Athreya BH, Seghal GS, Lahita RG. Adenohypophyseal and sex hormones in pediatric rheumatic diseases. J Rheumatol 1994;21:725–30. Yesilova Z, Ozat M, Kocar IH, Turan M, Pekel A, Senguil A, et al. The effects of gonadotropin treatment on the immunological features of male patients with idiopathic hypogonadotpropic hypogonadism. J Clin Endocrinol Metab 2000;85:66–70. Ho HN, Chen HF, Chen SU, Chao KH, Yang YS, Huang SC, et al. Gonadotropin releasing hormone ŽGnRH. agonist induces down-regulation of the CD3qCD25q lymphocyte subpopulation in peripheral blood. Am J Reprod Immunol 1995;33:243–52. Leadem CA, Kalra SP. Stimulation with estrogen and progesterone of luteinizing hormone ŽLH.-releasing hormone release from perifused adult female rat hypothalami: correlation with the LH surge. Endocrinology 1984;114:51–6. Quinones-Jenab V, Jenab S, Ogawa S, Funabashi T, Weesner GD, Pfaff DW. Estrogen regulation of gonadotropin-releasing hormone receptor messenger RNA in female rat pituitary tissue. Brain Res Mol Brain Res 1996;38:243–50. Bauer-Dantoin AC, Weiss J, Jameson JL. Roles of estrogen, progesterone, and gonadotropin-releasing hormone ŽGnRH. in the control of pituitary GnRH receptor gene expression at the time of the preovulatory gonadotropin surges. Endocrinology 1995;136:1014–9. Colin IM, Bauer-Dantoin AC, Sundaresan S, Kopp P, Jame-
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son JL. Sexually dimorphic transcriptional responses to gonadotropin-releasing hormone require chronic in vivo exposure to estradiol. Endocrinology 1996;137:2300–7. Veldhuis JD, Urban RJ, Dufau ML. Evidence that androgen negative feedback regulates hypothalamic gonadotropin-releasing hormone impulse strength and the burst-like secretion of biologically active luteinizing hormone in men. J Clin Endocrinol Metab 1992;74:1227–35. Kalra PS, Kalra SP. Discriminative effects of testosterone on hypothalamic luteinizing hormone-releasing hormone levels and luteinizing hormone secretion in castrated male rats: analyses of dose and duration characteristics. Endocrinology 1982;111:24–9. Roselli CE, Resko JA. Regulation of hypothalamic luteinizing hormone-releasing hormone levels by testosterone and estradiol in male rhesus monkeys. Brain Res 1990;509:343–6. Fattinger KE, Verotta D, Porchet HC, Munafo A, Le Cotonnec JY, Sheiner LB. Modeling a bivariate control system: LH and testosterone response to the GnRH antagonist Antide. Am J Physiol 1996;271:E775–87. McArdle CA, Schomerus E, Groner I, Poch A. Estradiol regulates gonadotropin-releasing hormone receptor number, growth and inositol phosphate production in alpha T3-1 cells. Mol Cell Endocrinol 1992;87:95–103. Jennes L, Brame B, Centers A, Janovick JA, Conn PM. Regulation of hippocampal gonadotropin releasing hormone ŽGnRH. receptor mRNA and GnRH-stimulated inositol phosphate production by gonadal steroid hormones. Brain Res Mol Brain Res 1995;33:104–10. Yasin M, Dalkin AC, Haisenleder DJ, Kerrigan JR, Marshall JC. Gonadotropin-releasing hormone ŽGnRH. pulse pattern regulates GnRH receptor gene expression: augmentation by estradiol. Endocrinology 1995;136:1559–64. Azad N, Lapaglia N, Agrawal L, Steiner J, Uddin S, Williams DW, et al. The role of gonadectomy and testoterone replacement on thymic luteinizing hormone-releasing hormone production. J Endocrinol 1998;158:229–35. Varma S, Sabharwal P, Malarkey W. Human splenocytes secrete LHRH, which inhibits lymphocyte proliferation. Prog NeuroEndocrinImmunol 1992;5:187–91. Jacobson JD, Baker JC, Sun L. Gender differences in immune responsiveness to gonadotropin-releasing hormone in mice. Pediatr Res 1996;39:90A, Abstract. Laws SC, Webster JC, Miller WL. Estradiol alters the effectiveness of gonadotropin-releasing hormone ŽGnRH. in ovine pituitary cultures: GnRH receptors vs. responsiveness to GnRH. Endocrinology 1990;127:381–6. Baldwin DM, Bourne GA, Marshall JC. Pituitary LH responsiveness to GnRH in vitro as related to GnRH receptor number. Am J Physiol 1984;247:E651–56. Stanislaus D, Janovick JA, Brothers S, Conn PM. Regulation of GŽqr11. alpha by the gonadotropin-releasing hormone receptor. Mol Endocrinol 1997;11:738–46. Stanislaus D, Pinter JH, Janovick JA, Conn PM. Mechanisms mediating multiple physiological responses to gonadotropinreleasing hormone. Mol Cell Endocrinol 1998;144:1–10. Cornea A, Janovick JA, Stanislaus D, Conn PM. Redistribu-
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tion of Gqr11a in the pituitary gonadotrope in response to a gonadotropin-releasing hormone agonist. Endocrinology 1998;139:397–402. Jacobson JD, Muthukrishnan VY, Kinealy M, Jagarlamudi S, Ansari MA. Gender specific immune actions of GnRH parallel G aqr11 activity. FASEB 1998;12:A124, Abstract. Jacobson JD, Muthukrishnan VY, Kinealy M, Ansari MA. Gender differences in expression of G alpha s parallel immune responsiveness to GnRH. Endocr Soc 1998;1:119, Abstract. Ansari MA, Jacobson JD. Gender-specific changes in G qr11 protein and its mediators in murine spleen cells. Soc Neurosci 1999;25Ž1.:943, Abstract.
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w46x Yagami T, Tohkin M, Matsubara T. The involvement of the stimulatory G protein in sexual dimorphism of beta-adrenergic receptor-mediated functions in rat liver. Biochim Biophys Acta 1994;1222:257–64. w47x Ravindra R, Aronstam RS. Progesterone, testosterone and estradiol-17 beta inhibit gonadotropin-releasing hormone stimulation of G protein GTPase activity in plasma membranes from rat anterior pituitary lobe. Acta Endocrinol ŽCopenhagen. 1992;126:345–9. w48x Jacobson JD, Ansari MA, Mansfield ME, McArthur CP, Clement LT. Gonadotropin-releasing hormone increases CD4 q T-lymphocyte numbers in an animal model of immunodeficiency. J Allergy Clin Immunol 1999;104:653–8.
Review
Gonadotropin-releasing hormone: potential role in autoimmunity Jill D. Jacobson Section of Endocrinology, Children’s Mercy Hospital, UniÕersity of Missouri-Kansas City School of Medicine, Kansas City, MO, USA Received 22 May 2000; received in revised form 31 July 2000; accepted 14 August 2000
Gonadotropin-releasing hormone ŽGnRH., also known as luteinizing hormone releasing hormone ŽLHRH., is a decapeptide that is produced in the hypothalamus. It is delivered by the hypothalamic pituitary portal system to the gonadotropic cells of the anterior pituitary. It modulates the release of both luteinizing hormone ŽLH. and follicle stimulating hormone ŽFSH.. The GnRH molecule is highly conserved among species. GnRH exerts its actions through a seven transmembrane domain receptor that is coupled to G proteins. Its signal transducers include the stimulatory G protein G a s and two homologous stimulatory G proteins termed G a q and G a 11 w1x. Binding studies have confirmed the presence of the GnRH receptor in whole spleens and thymuses in rats and mice w2,3x. Porcine, human, rat, and murine immune cells express GnRH receptor mRNA w2,4–6x. GnRH possesses potent immune actions: studies in mice, rats, and humans show that GnRH exerts stimulatory influences on IFN-g production, on expression of the interleukin-2 receptor, on B and T lymphocyte proliferation, and on serum IgG levels w2,3,7–10x. Moreover, immune cells from rats and humans produce peptides with GnRH immunoreactivity and bioactivity w11,12x. Fig. 1 diagrams the known interactions of GnRH and the immune system. Most studies of GnRH production have utilized whole lymphoid organs, i.e. spleens and thymuses.
Therefore, it remains unclear as to which immune subsets produce GnRH. One study demonstrated that GnRH was produced in similar proportions in unfractionated peripheral blood T lymphocytes and in CD4 q and CD8 q subsets in humans, suggesting that GnRH is produced by multiple immune subsets w13x. Given that GnRH possesses direct immunostimulatory actions, we hypothesized that GnRH might play a role in the exacerbation of autoimmune disease. The administration of GnRH antagonists led to a reduction in autoantibody levels, total immunoglobulin levels, renal disease, and survival in a mouse model of systemic lupus erythematosus ŽSLE.. Disease severity was ameliorated in intact and gonadectomized mice, in male and female mice, and in estradiol-treated mice, demonstrating that the protective effects of the GnRH antagonists were independent of gonadal steroids w9x. Fig. 2 demonstrates survival in males and females. Interestingly, the survival in females treated with a GnRH antagonist mimicked the survival curve in males treated with vehicle. In contrast to the effects of GnRH antagonists, GnRH agonists exerted sexually dimorphic actions, even in gonadectomized mice. Although GnRH antagonist was effective in reducing disease severity Žas measured by anti-DNA antibody levels. levels in both males and females, GnRH agonist administration exerted effects on autoantibody levels in females
1567-5769r01r$ - see front matter q 2001 Published by Elsevier Science B.V. PII: S 1 5 6 7 - 5 7 6 9 Ž 0 1 . 0 0 0 3 8 - 8
1078
J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
Fig. 1. GnRH itself has been shown to be immunostimulatory. Immune cells from rats and humans produce immunoreactive and bioactive GnRH w11,12x. Porcine and human immune cells express receptors for GnRH w4,5x. Acute treatment with GnRH increases expression of GnRH receptor mRNA in thymocytes in mice w6x. Studies in mice and rats show that GnRH exerts stimulatory influences on expression of the interleukin-2 receptor, on B and T lymphocyte proliferation, and on serum IgG levels w2,3,8–10x. Figure is from Jacobson et al. w48x and reprinted with permission.
only w3x. Fig. 3 demonstrates anti-DNA antibody levels in males and females after 30 weeks of exposure to vehicle, GnRH antagonist or GnRH. The effects of GnRH waned over time in females. This could be attributable to tachyphylaxis to GnRH. GnRH is known to downregulate its receptor at the level of the pituitary whenever it is administered in a nonpulsatile fashion w14x. If GnRH plays a role in the modulation of autoimmune diseases, one might speculate that clinical conditions associated with elevated GnRH might display a high incidence of autoimmune disease. In fact, gonadal failure, regardless of etiology, is associated with a high incidence of autoimmune diseases, including autoimmune thyroid disease. Gonadal failure leads to loss of negative feedback on GnRH at the level of the hypothalamus. In the clinical conditions of Turner syndrome and premature ovarian failure ŽPOF., patients have, by definition of disease, ovarian failure and loss of estrogen production; yet, the incidence of autoimmune thyroid disease is extremely high Ž30%. w15,16x. Klinefelter syndrome and Down syndrome also display both gonadal fail-
ure a 30% incidence of autoimmune thyroid disease w17–19x. Data exist that patients with systemic lupus erythematosus ŽSLE., a prototypic autoimmune disease, display significantly elevated gonadotropin levels compared to controls w20,21x. It remains possible that GnRH’s immune actions are mediated, at least in part, through gonadotropins. Several studies demonstrating immune alterations following gonadotropin administration were performed in non-gonadectomized humans. These studies have generally attributed the immune actions of gonadotropins to alterations in androgens and estrogens w22,23x. The literature contains little evidence for direct immune actions of gonadotropins, for expression of gonadotropin receptors, or for production of gonadotropins by immune cells. Production of GnRH at the level of the hypothalamus and responsiveness to GnRH at the level of the pituitary are sexually dimorphic. The feedback effects of estradiol on hypothalamic release of GnRH are complex: whereas chronic estrogen exposure exerts negative feedback effects on GnRH release, rising estrogen levels stimulate GnRH release w24x.
J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
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Fig. 2. Survival in gonadectomized females treated with GnRH antagonist or vehicle. The horizontal axis represents weeks of age. Survival was assessed by Mantel–Haenzel methodology ŽGnRH antagonist, n s 40; vehicle, n s 42.. Survival is prolonged with GnRH antagonist Ž p s 0.0025..
Estrogen exposure increases the expression of the GnRH receptor and increases GnRH responsiveness at the level of the pituitary w25–27x. In contrast, GnRH production, release, and action are generally negatively regulated by androgens w28–31x. Androgens have been shown to decrease GnRH receptor
mRNA and protein w32–34x. This increase in GnRH production and increased GnRH action observed in females may play a role in the earlier timing of puberty in females. Little is known about modulatory effects of gonadal steroids or gender on GnRH production or
Fig. 3. Anti-DNA antibody levels in ovariectomized ŽSWR = NZB. F1 hybrid female and male mice after various weeks of treatment with vehicle, GnRH, or GnRH antagonist. Serum anti-DNA antibody levels were measured by a standard ELISA technique and expressed as optical density ŽO.D... Results are mean " S.E.M. Ž n s 14–22.. ) Significantly different from Ž p - 0.05. than vehicle. Figure is modified from Jacobson et al. w3x and reprinted with permission.
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J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
action at the level of the immune system. A recent study demonstrated that gonadectomy increases GnRH concentration in the thymus in rats. Exposure to testosterone prevented this increase w35x. This is the first demonstration that immune production of GnRH can be modulated by gonadal steroids. Fig. 4 diagrams the known interactions between the hypothalamic–pituitary–gonadal axis and the immune system. In retrospect, it appears that the studies demonstrating immunostimulatory properties of GnRH were done exclusively in female rats. A contradictory study that demonstrated immunosuppressive effects of GnRH on lymphocyte proliferation in vitro utilized lymphocytes from male volunteers w36x. A possible unifying explanation for the above reports is that the immune actions of GnRH are
gender-specific. In fact, we have demonstrated that splenocytes obtained from male and female mice exhibit divergent in vitro T lymphocyte proliferative responses to mitogen in the presence of GnRH w37x. Splenocytes from male mice respond to GnRH with a decrease in T lymphocyte proliferation compared to controls, whereas splenocytes from females respond with an increase. The differences in in vitro T cell proliferation persist even in long-term gonadectomized mice Žunpublished observations.. One possible mechanism for the observed gender differences in immunological responsiveness to GnRH might relate to increased GnRH receptor expression in immune cells in females. Binding studies from our laboratory demonstrate that splenic populations from female mice express more GnRH receptor than splenocytes from males w3x. Both estrogen and
Fig. 4. Estradiol ŽE 2 ., especially cyclical estradiol Žrepresented by dashed lines., as seen in women during the reproductive years, leads to increased GnRH production at the level of the hypothalamus and increased GnRH responsiveness at the level of the pituitary w24–27x. Androgens, e.g. testosterone ŽT., exert suppressive effects on GnRH production at the level of the hypothalamus and action at the level of the pituitary w28–34x. Estrogens are known to increase GnRH receptor mRNA at the level of the immune cell in mice w6x. Androgens have been shown to prevent the increase in GnRH levels that are demonstrable in the thymus following castration of male rats w35x. Thus, androgens and estrogens may alter production and responsiveness to GnRH similarly in the immune system as they do in the central nervous system.
J.D. Jacobsonr International Immunopharmacology 1 (2001) 1077–1083
GnRH further increase the expression of the GnRH receptor mRNA in whole splenic populations. Several investigators have shown that gender differences in GnRH responsiveness in pituitary cells does not correlate directly with the expression of the GnRH receptor. Authors have suggested that post-receptor differences may explain these observations w27,38,39x. GnRH is known to exert its actions largely through specific G proteins, namely G a qr11 and G a s , at least in pituitary cell culture systems w40–42x. We have recently demonstrated splenocytes from female mice express more mRNA for G a qr11 mRNA and protein than splenocytes from males after in vivo exposure to GnRH w3x. Functional studies of G protein activity show that antisense oligonucleotides to G a qr11 and to G a s eliminate the gender differences in T cell proliferation w43,44x. G a qr11 exerts actions largely through inositol 3-phosphate ŽIP3 .. Gender differences exist in production of inositol 3-phosphate in normal DBAr2 mice in response to in vitro exposure to GnRH w45x. The literature contains few reports of gender differences in G protein expression. One study demonstrated increased G a s protein levels and increased G a s activity in response to b-adrenergic stimulation in female compared to male rats. Estradiol exposure augmented G a s activity in both male and female rats w46x. A recent study suggests that progesterone, testosterone, estradiol and GnRH all modulate G protein activity in rat pituitary cells w47x. Beyond these studies, little is known about hormonal modulation of G proteins. In summary, GnRH is produced by lymphocytes and exerts potent immunomodulatory actions. GnRH has been shown to exert gender restricted immune actions in vitro and in vivo. These gender differences correlate with gender differences in expression of the GnRH receptor and with gender differences in expression of the G proteins through which GnRH acts. We speculate that these gender differences in G proteins may contribute to the gender differences in the expression of autoimmune disease.
Acknowledgements This study was supported by NIH grant 1R29AR43152, by a grant from the Lupus Founda-
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tion of America, and by a career development award from Pharmacia Upjohn.
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