This thesis reports the results of studies on steroid metabolism in a subject with an adrenocortical carcinoma and hypoglycemia, in the testes obtained from a subject with virilizing male pseudohermaphroditism and in the testes of the normal rat. Incubations of cell-free homogenates of an adrenocortical carcinoma from a 51 year old female with severe hypoglycemia were performed using ³H-pregnenolone and ¹⁴C-progesterone as substrates. Transformation of ³H-pregnenolone to progesterone, dehydroepiandrosterone and androstenedione was observed; no metabolites of ¹⁴C-progesterone were detected. The excretion rate in urine of 3α ,17,21-trihydroxy-5β -pregnan-20-one, a metabolite of cortexolone, was elevated which suggests that a defect in 11β -hydroxylase activity was present. The excretion rates in urine of total 17-ketosteroids, 17-hydroxycorticoids and 17-ketogenic steroids were elevated; the excretion rates of testosterone, dehydroepiandrosterone, pregnandiol, pregnanetriol and free cortisol were not elevated. The etiology of the hypoglycemia that may accompany some adrenocortical tumors remains unknown. It was not possible to relate the results of the investigations of steroid metabolism reported herein to the hypoglycemia that was present. Steroid biosynthesis in vitro was investigated in testes obtained during puberty from a 14 year old subject with virilizing male pseudohermaphroditism. Cell-free homogenates of gonadal tissue efficiently metabolized ³H-pregnenolone, ¹⁴C-progesterone and ¹⁴C-androstenedione to testosterone; formation of estrone and estradiol-17β was not detected. 16α-Htdroxyprogesterone was formed from both ³H-pregnenolone and ¹⁴C-progesterone. The results are similar to those of others who have investigated the steroidogenic capacity of gonadal tissue in patients with male pseudohermaphroditism and feminization at puberty. A defect in the formation of progesterone from pregnenolone has been suggested to explain the results of a previous study in which the gonadal tissue obtained from a patient with virilizing male pseudohermaphroditism was incubated with ³H-pregnenolone as substrate. In the investigations reported herein, transformations of ³H-pregnenolone to testosterone and androstenedione occurred both via 17-hydroxypregnenolone and dehydroepiandrosterone and via progesterone and 17-hydroxyprogesterone. The failure of patients with virilizing male pseudohermaphroditism to masculinize during embryonic development contrasts with the virilization that occurs during puberty. A biochemical abnormality may exert a transient effect during embryonic development. Alternatively, the sensitivity to androgenic hormones may be subnormal in certain tissues and normal in other tissues of patients with virilizing male pseudohermaphroditism. The biosynthesis of testosterone from progesterone and pregnenolone was investigated in the rat testis. Time studies were performed using cell-free homogenates and ³H-progesterone and ¹⁴C-17-hydroxyprogesterone in combination as substrates. It was demonstrated that the side-chain cleavage of 17-hydroxyprogesterone is the rate-limiting reaction in the biosynthesis of testosterone from progesterone and the evidence suggested that 17-hydroxyprogesterone was present as a bound intermediate (at least in part). The progesterone 17-hydroxylase and the 17-hydroxyprogesterone side- chain cleavage enzyme of the rat testis can be solubilized by treatment of lyophilized microsomes with Triton N-101. Both enzymes displayed maximal activity at pH 6.8 and at 37°. Progesterone rather than pregnenolone is the preferred substrate for the 17α-hydroxylase. Either NADH or NADPH can serve as the reductant for active 17-hydroxylation of progesterone and for side-chain cleavage of 17-hydroxyprogesterone. The soluble fraction contains NADPH dehydrogenase, non-heme iron protein and cytochrome P-450. The presence of these compounds in association with the 17α-hydroxylase and the side-chain cleavage enzyme activities suggests that these reactions are catalyzed by elaborate enzymatic systems analogous to those required for 11β-hydroxylation and cholesterol side-chain cleavage in adrenal mitochondria / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Production of hormones in the ovary is controlled by endocrine, paracrine, autocrine and intracrine influences. Similar controls may exist in the placenta. I wished to investigate the involvement of second messengers in the action of hormones in control of hormonogenesis in rat ovary and human placenta. The second messengers involved in the action of gonadotropin-releasing hormone (GnRH) and prostaglandin (PG) F₂[formula omitted] were investigated in rat granulosa and luteal cells. As well, the endocrine role of GnRH in the placenta and the possible second messengers involved were investigated. Monolayer cultures of rat granulosa and luteal cells and human placental cells were prepared. Rat granulosa cells were mechanically dispersed; rat luteal cells were enzymatically dispersed with collagenase and DNase. Rat granulosa cells were treated during the first 24 hours in culture; rat luteal cells were treated up to 3 days after dispersion. Radioimmunoassay of medium was used to determine the effect of treatments on hormone production. Studies which examined the effect of hormones on the intracellular free calcium concentration ([Ca²⁺]i) in single cells using the calcium sensitive fluorescent dye, Fura-2, were done in monolayer rat granulosa and luteal cell cultures. Human placental cells, from first trimester and term placentae, were dispersed using trypsin-DNase or collagenase-DNase. Cells were cultured for 2 days prior to treatment. The effects of treatments on production of steroid (progesterone and estrogen), glycoprotein (human chorionic gonadotropin; hCG) and protein (human placental lactogen; hPL) hormones were determined by radioimmunoassay of the medium. In rat granulosa and luteal cell cultures, I examined the effect of a number of hormones and second messengers. Effects of follicle-stimulating hormone (FSH), luteinizing hormone (LH), cyclic adenosine monophosphate (cAMP), GnRH and PGF₂[formula omitted] on ovarian hormonogenesis have been previously reported. Changes in cytosolic free calcium concentrations ([Ca²⁺]i) in response to PGF₂[formula omitted] were measured in single rat granulosa and luteal cells. I found that in 34% of granulosa cells, and 53% of luteal cells, there was a 3 to 4 fold increase in resting [Ca²⁺]i within 30 seconds of administration of PGF₂[formula omitted]. Many cells which responded to PGF₂[formula omitted] also responded to GnRH (39% of granulosa cells; 67% of luteal cells). The immediate source of the increased [Ca²⁺]i appeared to be common intracellular stores. No change in hormone production in response to GnRH in placental cell cultures was seen. Trypsin dispersion may have damaged cell surface receptors, therefore the effect of second messengers on hormone production in these cultures was examined. In term and first trimester trophoblast cultures, I observed the following effects with 8-bromo-cyclic adenosine monophosphate (8-br-cAMP): inhibited estrogen production from the supplied androgen precursors; stimulated hCG production; stimulated hPL production in first trimester placental cell cultures (hPL was not measured in enough term cultures to determine the effect of 8-br-cAMP), and stimulated progesterone production. I also investigated the effects of activators and inhibitors of the phosphoinositide (PtdIns(4,5)P₂) breakdown second messenger pathway (TPA, A23187, arachidonic acid); no effects of these agents were seen. Other hormones suspected of having endocrine, paracrine or autocrine effects in the placenta were tested without effect. I conclude that GnRH and PGF₂[formula omitted] cause increases in [Ca²]i in rat ovarian cells, from common intracellular stores of calcium, and that the production of hormones by the human placenta may be under regulation of an agent or agents which induce production of cAMP. / Medicine, Faculty of / Obstetrics and Gynaecology, Department of / Graduate

Steroidogenic factor (SF1) is an orphan nuclear receptor that is essential for steroid hormone-biosynthesis and endocrine development. Recent studies have demonstrated that phospholipids are ligands for SF1. In the present study our aim was to identify endogenous ligands for SF1 and characterize their functional significance in mediating cAMP-dependent transcription of human CYP17. Using mass spectrometry we show that in H295R adrenocortical cells SF1 is bound to sphingosine (SPH) under basal conditions and that cAMP stimulation decreases the amount of SPH bound to the receptor. We also show that silencing both acid and neutral ceramidases using siRNA induces CYP17 mRNA expression, suggesting that SPH acts as an inhibitory ligand. In vitro analysis of ligand binding using scintillation proximity assays show that several sphingolipids and phospholipids, including phosphatidic acid (PA), can compete with [3H]SPH for binding to SF1, suggesting that SF1 may have more than one ligand and binding specificity may change with the changes in intracellular fluxes of phospholipids. Further, phosphatidic acid (PA) induces SF1-dependent transcription of CYP17 reporter constructs. Inhibition of diacyglycerol kinase (DAGK) activity using R59949 and silencing DAGK- expression attenuates SF1-dependent CYP17 transcriptional. We propose that PA is an activating ligand for SF1 and that cAMP-stimulated activation of SF1 takes place by displacement of SPH.

No description available.

Les espèces réactives de l’oxygène ont initialement été identifiées comme des produits délétères dérivés du métabolisme aérobie. Il est maintenant accepté que ces espèces sont produites de manière régulée par des enzymes et interviennent dans des fonctions cellulaires telles que la défense immunitaire, la signalisation intracellulaire, la biosynthèse des hormones et la modification de matrice extracellulaire. Les NADPH (Nicotinamide Adénine Dinucléotide Phosphate) oxydases (NOX) forment une famille d’enzymes transmembranaires capables de former de l’anion superoxyde (O2.-) par transfert d’électrons du NADPH à l’oxygène moléculaire (O2). DUOX1 et DUOX2 sont deux des sept membres composant cette famille qui génèrent directement de l’H2O2 comme produit de réduction de l’O2.<p>Initialement clonés à partir de la thyroïde dans notre laboratoire, les ADNc codant pour les protéines DUOX ont été identifiées dans d’autres tissus, comme par exemple la prostate ou l’épithélium respiratoire où DUOX1 est majoritaire. DUOX2 se retrouve également dans les glandes salivaires, dans la muqueuse rectale et tout le long du tractus digestif. D’autre part, un orthologue de DUOX, appelé Udx1, a été identifié en 2004 au niveau de la membrane ovocytaire chez l’oursin. Dans chacun de ces tissus, l’H2O2 produit par les protéines joue un rôle clef. <p>Le mécanisme d’activation de DUOX dans tous ces tissus n’a été identifié que récemment. En effet, pour être exprimé sous forme active à la surface cellulaire, les protéines DUOX nécessitent un facteur de maturation spécifique. Ces facteurs, appelés DUOXA1 et 2 pour « DUOX activator », suivent l’expression tissulaire de leur DUOX respectif. Nous avons montré que la région COOH-terminale de DUOXA1 est responsable de l’activité génératrice d’H2O2 de DUOX1. DUOX2 peut produire de l’H2O2 ou de l’O2.-. L’extrémité NH2-terminale de DUOXA2 est critique dans cette activité et détermine le type de dérivé oxygéné produit. Dans notre système, DUOXA2 n’est pas détecté à la surface cellulaire, sauf en cas de modification de son extrémité amino-terminale par l’addition d’un épitope. DUOXA1 peut être exprimé à la membrane plasmique mais sa présence n’est pas nécessaire au sein du complexe formé avec DUOX pour que ce dernier soit actif. Les facteurs de maturation jouent donc un rôle de protéine chaperonne, induisant la maturation et la translocation d’une protéine DUOX active à la surface cellulaire. <p>Dans la thyroïde, l’H2O2 produit par les protéines DUOX constitue le cofacteur de la thyroperoxydase catalysant l’oxydation de l’iode et le couplage de sa forme oxydée sur des résidus tyrosines de la thyroglobuline menant in fine à la synthèse des hormones thyroïdiennes T3 et T4 et leur relarguage dans la circulation sanguine. Plusieurs mutations dans le gène DUOX2 ont déjà été décrites chez des patients atteints de dyshormonogenèse transitoire ou permanente. Nous avons mis en évidence qu’une inactivation totale de la protéine DUOX2 était compatible avec un état hypothyroïdien peu sévère et transitoire, indiquant l’intervention probable de DUOX1 dans la synthèse des hormones thyroïdiennes. Le défaut génétique identifié est composé d’une délétion génomique partielle d’un allèle associée à une mutation faux-sens (G1518S) sur l’autre allèle du patient hypothyroïdien. Cette mutation, située dans le site catalytique de l’enzyme, mène à une abolition de l’activité de l’enzyme qui est néanmoins exprimée partiellement à la surface cellulaire. <p>Les messagers des DUOX ont été identifiés récemment dans les tractus digestif et respiratoire. Le rôle joué par l’H2O2 dans ces tissus semble avant tout être un rôle de défense contre les micro-organismes en mettant en jeu la lactoperoxydase oxydant le thiocyanate en composé bactéricide actif. Nous avons montré que l’H2O2 produit par DUOX exerce un effet répulsif sur les bactéries. En effet, l’invasion de cellules CHO exprimant de manière stable DUOX2 et DUOXA2 par Salmonella Typhimurium est diminuée lorsque la production d’H2O2 de ces cellules est stimulée. Cet effet répulsif constituerait un rôle primordial pour DUOX au niveau des muqueuses respiratoire et digestive.<p>Lors de la fertilisation, une explosion respiratoire a lieu et de l’H2O2 est produit. Cet H2O2 fourni à l’ovoperoxydase permettrait la formation d’une enveloppe rigide autour de l’ovocyte, bloquant ainsi l’entrée de spermatozoïdes surnuméraires. Ce phénomène a été largement étudié dans l’ovocyte d’oursin, dans lequel la NADPH oxydase responsable de la production d’H2O2 a été caractérisée: il s’agit de Udx1, l’orthologue de DUOX. Chez les mammifères, le phénomène existe mais le mécanisme est en grande partie inconnu. Nous avons montré que les ARNm des DUOX sont exprimés dans l’ovocyte humain ;ceci nous permet d’émettre l’hypothèse que l’inhibition de la polyspermie chez l’homme pourrait être similaire à celle de l’oursin. <p> / Doctorat en Sciences biomédicales et pharmaceutiques / info:eu-repo/semantics/nonPublished