Jukka Kero

GPR109A (PUMA-G/HM74A) mediates nicotinic acid–induced flushing

Nicotinic acid (niacin) has long been used as an antidyslipidemic drug. Its special profile of actions, especially the rise in HDL-cholesterol levels induced by nicotinic acid, is unique among the currently available pharmacological tools to treat lipid disorders. Recently, a G-protein-coupled receptor, termed GPR109A (HM74A in humans, PUMA-G in mice), was described and shown to mediate the nicotinic acid-induced antilipolytic effects in adipocytes. One of the major problems of the pharmacotherapeutical use of nicotinic acid is a strong flushing response. This side effect, although harmless, strongly affects patient compliance. In the present study, we show that mice lacking PUMA-G did not show nicotinic acid-induced flushing. In addition, flushing in response to nicotinic acid was also abrogated in the absence of cyclooxygenase type 1, and mice lacking prostaglandin D(2) (PGD(2)) and prostaglandin E(2) (PGE(2)) receptors had reduced flushing responses. The mouse orthologue of GPR109A, PUMA-G, is highly expressed in macrophages and other immune cells, and transplantation of wild-type bone marrow into irradiated PUMA-G-deficient mice restored the nicotinic acid-induced flushing response. Our data clearly indicate that GPR109A mediates nicotinic acid-induced flushing and that this effect involves release of PGE(2) and PGD(2), most likely from immune cells of the skin.

Elevated luteinizing hormone induces expression of its receptor and promotes steroidogenesis in the adrenal cortex

Transgenic (TG) female mice expressing bLHbeta-CTP (a chimeric protein derived from the beta-subunit of bovine luteinizing hormone [LH] and a fragment of the beta-subunit of human chorionic gonadotropin [hCG]) exhibit elevated serum LH, infertility, polycystic ovaries, and ovarian tumors. In humans, increased LH secretion also occurs in infertility and polycystic ovarian syndrome, often concomitant with adrenocortical dysfunction. We therefore investigated adrenal function in LH overexpressing bLHbeta-CTP female mice. The size of their adrenals was increased by 80% with histological signs of cortical stimulation. Furthermore, adrenal steroid production was increased, with up to 14-fold elevated serum corticosterone. Primary adrenal cells from TG and control females responded similarly to ACTH stimulation, but, surprisingly, the TG adrenals responded to hCG with significantly increased cAMP, progesterone, and corticosterone production. LH receptor (LHR) expression and activity were also elevated in adrenals from female TG mice, but gonadectomized TG females showed no increase in corticosterone, suggesting that the dysfunctional ovaries of the intact TG females promote adrenocortical hyperfunction. We suggest that, in intact TG females, enhanced ovarian estrogen synthesis causes increased secretion of prolactin (PRL), which elevates LHR expression. Chronically elevated serum LH, augmented by enhanced PRL production, induces functional LHR expression in mouse adrenal cortex, leading to elevated, LH-dependent, corticosterone production. Thus, besides polycystic ovaries, the bLHbeta-CTP mice provide a useful model for studying human disorders related to elevated LH secretion and adrenocortical hyperfunction.

Nicotinic acid inhibits progression of atherosclerosis in mice through its receptor GPR109A expressed by immune cells

Nicotinic acid (niacin) is a drug used to reduce the progression of atherosclerosis. Its antiatherosclerotic activity is believed to result from lipid-modifying effects, including its ability to decrease LDL cholesterol and increase HDL cholesterol levels in plasma. Here, we report that in a mouse model of atherosclerosis, we found that nicotinic acid inhibited disease progression under conditions that left total cholesterol and HDL cholesterol plasma levels unaffected. The antiatherosclerotic effect was not seen in mice lacking the receptor for nicotinic acid GPR109A. Surprisingly, transplantation of bone marrow from GPR109A-deficient mice into atherosclerosis-prone animals also abrogated the beneficial effect of nicotinic acid. We detected expression of GPR109A in macrophages in atherosclerotic plaques. In macrophages from WT mice, but not from GPR109A-deficient animals, nicotinic acid induced expression of the cholesterol transporter ABCG1 and promoted cholesterol efflux. Furthermore, activation of GPR109A by nicotinic acid inhibited MCP-1-induced recruitment of macrophages into the peritoneal cavity and impaired macrophage recruitment to atherosclerotic plaques. In contrast with current models, our data show that nicotinic acid can reduce the progression of atherosclerosis independently of its lipid-modifying effects through the activation of GPR109A on immune cells. We conclude therefore that GPR109A mediates antiinflammatory effects, which may be useful for treating atherosclerosis and other diseases.

Mode of Delivery and Asthma – Is There a Connection?

Genetic factors cannot explain the recent rapid increase in the incidence of atopic diseases. The phenomenon has been explained by environmental factors, and there are data for and against the hypothesis that a decline in the pressure of microbial stimulation early in life could be behind the allergy epidemic. Changes have also occurred in maternity care, among them a rise in the caesarean section rate, which could diminish initial microbial exposure and thereby alter T helper 1 cell/T helper-2 cell development and affect the risk of developing atopy. In this study, we sought to establish whether mode of delivery does influence the development of atopic asthma. Finnish 1987 Medical Birth Register (n = 59,927 live births) information was linked between several national health registers to obtain information on asthma and mode of delivery in children registered. The data were adjusted for maternal age, previous deliveries, childs sex, and birth size. Atopy was evaluated in the second study (Turku Birth Cohort), which involved 219 children born by vaginal delivery (n = 106) or caesarean section (n = 113); history of atopic symptoms was established by questionnaire and a clinical examination was conducted, including skin prick testing and determination of total and allergen-specific IgE in serum. The register study showed the cumulative incidence of asthma at the age of seven to be significantly higher in children born by caesarean section (4.2%) than in those vaginally delivered (3.3%), the adjusted odds ratio (OR) for confounding variables being 1.21 (1.08–1.36), p < 0.01. In the second study, significantly more positive allergy tests were reported in questionnaires in the caesarean (22%) than in the vaginal delivery group (11%), OR 2.22 (1.06–4.64), p < 0.01, and a trend toward more positive skin prick reactions was documented at clinical examination; 41%versus 29%, OR 1.31 (0.65–2.65), p = 0.11. In conclusion, these results suggest that caesarean section delivery may be associated with an increased prevalence of atopic asthma.

Thyrocyte-specific Gq/G11 deficiency impairs thyroid function and prevents goiter development

The function of the adult thyroid is regulated by thyroid-stimulating hormone (TSH), which acts through a G protein-coupled receptor. Overactivation of the TSH receptor results in hyperthyroidism and goiter. The Gs-mediated stimulation of adenylyl cyclase-dependent cAMP formation has been regarded as the principal intracellular signaling mechanism mediating the action of TSH. Here we show that the Gq/G11-mediated signaling pathway plays an unexpected and essential role in the regulation of thyroid function. Mice lacking the alpha subunits of Gq and G11 specifically in thyroid epithelial cells showed severely reduced iodine organification and thyroid hormone secretion in response to TSH, and many developed hypothyroidism within months after birth. In addition, thyrocyte-specific Galphaq/Galpha11-deficient mice lacked the normal proliferative thyroid response to TSH or goitrogenic diet, indicating an essential role of this pathway in the adaptive growth of the thyroid gland. Our data suggest that Gq/G11 and their downstream effectors are promising targets to interfere with increased thyroid function and growth.

Biphasic Action of Prolactin in the Regulation of Murine Leydig Tumor Cell Functions1

We investigated in this study the effects of ovine PRL on endocrine functions of cultured murine Leydig tumor cells (mLTC-1). The parameters studied were the activation of signal transduction systems involving cAMP and intracellular free Ca, the expression of Janus kinase 2 (JAK2), expression and function of LH and PRL receptors (R), expression of the steroidogenic acute regulatory (StAR) protein, and stimulation of steroidogenesis. Very similar biphasic doseand timedependent responses of all the parameters studied were found upon PRL stimulation, comprising a fast inhibition within 24 h in response to high PRL doses (

High levels of luteinizing hormone analog stimulate gonadal and adrenal tumorigenesis in mice transgenic for the mouse inhibin- α -subunit promoter/Simian virus 40 T-antigen fusion gene

30 mg/liter), and a slow stimulation, between 48–72 h, in response to lower PRL doses (1–10 mg/liter). In addition, extracellular Ca (1.5 mmol/liter) increased the effect of PRL on human CG (hCG)-stimulated StAR messenger RNA expression and progesterone (P) production. Importantly, the biphasic effects of PRL on LHR gene expression and hCG-mediated P production were abolished in the presence of anti-PRL antiserum, demonstrating specificity of PRL action. The PRL effects on StAR expression, and steroid and cAMP production, apparently reflect its effects on LHR function. The relevance of the PRL effects observed in mLTC-1 cells was supported by demonstration of similar PRL responses in hCG-stimulated testosterone production of isolated mouse Leydig cells. Collectively, these findings clearly demonstrate the biphasic regulatory actions of PRL, and clarify some facets of the controversial role of this hormone in Leydig cell function. (Endocrinology 142: 308–318, 2001) T ROLE of PRL in the regulation of gonadal functions remains controversial (1, 2). Numerous studies have elucidated effects of PRL on testis, in particular on Leydig cells, although the exact nature and regulatory pathways involved in these actions are still poorly understood. A confounding factor affecting the results could be the heterologous nature of PRL preparations used, although there are also genuine differences in effects of PRL on Leydig cells of different species. For example, some studies demonstrate that PRL stimulates Leydig cells, and in particular the LHR function, whereas others demonstrate inhibitory actions on the same parameters. Induction of hypoprolactinemia by bromocriptine is known to suppress the LHR levels in rat testes (3–5). PRL treatment has been shown to increase the number of Leydig cells and LHR in hypophysectomized immature rats (6–8), as well as testicular LH-mediated testosterone production (9, 10). However, hyperprolactinemia in men is known to be associated with azoospermia (1, 11), hypogonadism (12), and impaired gonadal function (13), and it induces direct inhibitory effects on Leydig cell steroidogenesis in the rat (14). A reason for such apparently conflicting findings may lie in the fact that the nature of PRL actions on Leydig cells is dependent on their functional state, in addition to being time and dose dependent. PRL is known to induce a biphasic effect on hCG-stimulated steroid production in MA-10 mouse Leydig tumor cells (15, 16). Further aspects of the apparently biphasic effects of PRL on Leydig cell steroidogenesis have yet to be investigated. The steroidogenic acute regulatory (StAR) protein, a novel 30-kDa mitochondrial factor, has recently been purified, cloned, and characterized in MA-10 cells (17). The rate-limiting and regulated step in steroid hormone biosynthesis is the transport of cholesterol from the outer to the mitochondrial inner membrane (18, 19), which has recently been found to be mediated by StAR protein. It has also been demonstrated that StAR protein is intimately associated with the acute regulation of steroidogenesis in steroidogenic cells (20–23). Recently, we demonstrated that human CG (hCG) markedly enhanced the StAR protein and StAR messenger RNA (mRNA) levels, which were consistent with progesterone (P) production in mLTC-1 cells (22). The possible connections of PRL and StAR protein actions are not known in the regulation of steroidogenesis. The PRL action is mediated through its binding to a plasma membrane receptor, a member of the cytokine/PRL/GH receptor family, including those of GH, and a large number of lymphokines and related growth factors (24–26). This receptor family is characterized by a single transmembrane domain and conserved homology in the extracellular domain (25, 26). In the testis, PRL receptors are expressed in Leydig (27–29), Sertoli, and spermatogenic cells (30). Several receptors of this family, including those of PRL, were found to induce tyrosine phosphorylation and activation of receptorassociated tyrosine kinases of the Janus kinase (JAK) family (31, 32). In addition, PRL is known to activate the cytoplasmic signal transducers and activators of transcription (STATs), possibly through direct phosphorylation by the JAK2 tyrosine kinase (33). An important pathway of PRL actions is Received April 5, 2000. Address all correspondence and requests for reprints to: Ilpo T. Huhtaniemi, M.D., Ph.D., Department of Physiology, University of Turku, FIN-20520 Turku, Finland. E-mail: ilpo.huhtaniemi@utu.fi. * This study was supported by a research grant from the Sigrid Jusélius Foundation. † Equal contributors to this study. 0013-7227/01/

Transgenic and knockout mouse models for the study of luteinizing hormone and luteinizing hormone receptor function

03.00/0 Vol. 142, No. 1 Endocrinology Printed in U.S.A. Copyright

Common Respiratory Infections Early in Life May Reduce the Risk of Atopic Dermatitis

Transgenic (TG) mice expressing the Simian virus 40 T-antigen under the control of the murine inhibin-α promoter (Inhα/Tag) develop granulosa and Leydig cell tumors at the age of 5–6 months, with 100% penetrance. When these mice are gonadectomized, they develop adrenocortical tumors. Suppression of gonadotropin secretion inhibits the tumorigenesis in the gonads of intact animals and in the adrenals after gonadectomy. To study further the role of luteinizing hormone (LH) in gonadal and adrenal tumorigenesis, a double TG mouse model was generated by crossing the Inhα/Tag mice with mice producing constitutively elevated levels of LH (bLHβ-CTP mice). Our results show that in double TG mice (bLHβ-CTP/Inhα/Tag), gonadal tumorigenesis starts earlier and progresses faster than in Inhα/Tag mice. Both ovarian and testicular tumors were histologically comparable with the tumors found in Inhα/Tag mice. In addition, adrenal tumorigenesis was found in intact double TG females, but not in Inhα/Tag females. Inhibin-α and LH receptor (LHR) were highly expressed in tumorigenic gonadal tissues, and the elevated LH levels were shown to be associated with ectopic LHR and high inhibin-α expression in the female adrenals. We conclude that in the Inhα/Tag tumor mouse model, elevated LH levels act as a tumor promoter, advancing gonadal and adrenal tumorigenesis.

Differential expression and regulation of the retinoblastoma family of proteins during testicular development and spermatogenesis : roles in the control of germ cell proliferation, differentiation and apoptosis

The main functions of luteinizing hormone (LH) are concerned with regulation of gonadal function, and these functions are today well delineated through previous physiological studies. However, novel information of less well-known aspects of actions of this hormone is currently emerging from studies on genetically modified mouse models, with either enhanced or suppressed LH/LH receptor (LHR) function. The novel functions of LH include its role, in specific situations, as promoter of formation and growth of gonadal and extragonadal tumors. Chronically elevated LH levels in transgenic (TG) mice can also induce responses to this hormone in extragonadal tissues. The knockout (KO) mouse for the LHR has elucidated various less well-known details in the function of LH during ontogeny and adult life. Finally, studies on LHR promoter function have revealed that the expression of this gene occurs in age, sex and tissues-specific fashion. The purpose of this brief review is to summarize some of our recent findings upon studies of TG and KO mice with altered function of LH or its receptor.