Fetal exposure to excess glucocorticoids has been proposed as a key determinant of pregnancy outcome, as well as a predictor of long term health of the offspring through a phenomenon known as ‘developmental programming’. Obesity and ‘stress’ during pregnancy are two potential sources of altered fetal exposure to glucocorticoids. One in five pregnant women is obese at antenatal booking, and maternal obesity increases risk of offspring complications including higher birth weight, potentially leading to long-term programming effects on the offspring. Likewise, maternal anxiety during pregnancy has been identified as a programming factor, increasing the risk of psychopathology in the offspring. This thesis tests the hypothesis that in humans this association is mediated by altered action of glucocorticoids, by examining circulating levels of maternal glucocorticoids during pregnancy and through measurement of key genes in the placenta regulating fetal glucocorticoid exposure. Serum cortisol levels were measured at 16, 28 and 36 weeks gestation in n=173 class III obese (BMI 44.0±4.5kg/m2) and n=107 lean (BMI 22.8±1.6kg/m2) pregnant women. Serial corticosteroid binding globulin (CBG) concentrations were measured in a subset (n=39 lean, 26 obese) and free cortisol levels calculated using Coolen’s equation. CRH concentrations were measured at the same time points in obese (n=20) and lean (n=22) pregnant women Salivary cortisol was measured in samples collected at bed-time, waking and 30 minutes after waking. mRNA levels of candidate genes regulating glucocorticoids and fetal/placental growth including 11-beta hydroxysteroid dehydrogenase type 2 (11βHSD2), which inactivates cortisol, insulin-like growth factor 2 (IGF2) and glucocorticoid receptor (GR) were measured in first trimester (n=32), second trimester (n=15) and term (n=60) placental samples. DNA methylation of key regions controlling the expression of the IGF2, GR and 11βHSD2 genes was measured by pyrosequencing in first trimester and term samples. Levels of mRNAs encoding 11βHSD1, 11βHSD2, GR and MR were measured in term placentas collected from women from Helsinki, Finland in whom anxiety during pregnancy had been prospectively assessed using validated questionnaires. Term placental samples from a subset of the obese and lean women who had also completed stress questionnaires during pregnancy were used to examine replication of findings. Cortisol levels rose similarly during pregnancy in obese and lean but were significantly lower throughout pregnancy in obese women (p<0.05). The diurnal rhythm of cortisol was maintained. CBG levels also increased, though this change was lower in obese (1.21-fold (±0.9) vs 1.56-fold (±0.07), p<0.01). In obese women, lower calculated free cortisol at 16 weeks gestation was associated with higher birth weight after adjustment for other factors (r=-0.46, p<0.05). Placental mRNA encoding 11βHSD2 increased in association with increasing obesity in early pregnancy (r=0.44, p<0.01) and was highest in term placenta in obese women with macrosomic (>4000g) offspring (p<0.05). Placental transcript abundance of GR also increased in association with increasing obesity in early pregnancy (r=0.38, p<0.05), but was lowest in term placenta from obese with macrosomic offspring (p<0.05). IGF2 mRNA abundance was lower in the placentas of obese women with macrosomic offspring at term compared to both lean women and obese women with normal weight offspring (p<0.01). Methylation results are reported. Placental mRNA levels encoding 11βHSD1 (which converts inactive cortisone to active cortisol) at term was found to positively associate with maternal anxiety measured in the first trimester of pregnancy in a group of pregnant Finnish women (β=0.3, p<0.05). Findings were similar in the replication sample in lean women only (β=4.6, p<0.05). Lower circulating and bioavailable cortisol levels in early pregnancy, together with a greater placental ‘barrier’ to maternal glucocorticoids represent key mechanisms contributing to higher birth weight in offspring of obese women. Regeneration of active glucocorticoids in placenta and increasing placental sensitivity to glucocorticoids increases fetal glucocorticoid exposure and offers insight into the biological mechanisms underlying adverse offspring effects of maternal prenatal anxiety.

In recent years there has been an explosion in the rates of obesity, defined as a body mass index greater than 30kg/ m2, and associated cardiovascular disease. Alterations in peripheral glucocorticoid metabolism have been suggested to play a role in the development of obesity. Obesity occurs in both sexes, but the risk of associated metabolic disturbance and vascular dysfunction is greater in men. Although there is no accepted definition of obesity in rodents, the term is used to describe animals with a significant increase in fat pad mass often achieved by feeding a high fat diet. Although animal models of obesity have been useful in delineating potential mechanisms linking obesity with its metabolic and vascular sequelae, most studies have been in male animals and, thus, have not addressed sex differences. Additionally, emerging evidence shows that obesity during pregnancy is associated with increased cardio-metabolic and vascular disease in offspring, although the processes underlying such ‘programming’ effects are unclear. This thesis addresses the hypothesis that exposure to postnatal, or maternal obesity will alter both metabolism and vascular function in mice. Male and female mice maintained on a high fat and sugar diet from 5 weeks of age had increased adipose tissue deposition in adulthood. However there were striking sex differences in glucose homeostasis, mRNA levels and glucocorticoid metabolism, with males being more severely affected. Treatment of male mice with 17β-estradiol ameliorated a number of the effects of the high fat diet, including weight gain and altered glucose homeostasis; additionally estradiol altered glucocorticoid metabolism in the adipose so that it resembled that of females. Suprisingly, given the changes in metabolism, obesity in adult mice produced only small changes in vascular function and did not alter vascular remodelling following injury. The effects of maternal obesity were studied using male offspring aged 3 and 6 months. The offspring of obese mothers had similar body weight, adiposity, plasma lipid and plasma hormone concentrations to controls. In contrast, exposure to obesity in utero was associated with receptor specific changes in agonist-mediated contraction and decreased endothelium-dependent relaxation in male offspring. Despite these changes in vascular function, no alterations in blood pressure or vascular remodelling following injury were present. These results demonstrate that the more profound changes in glucose-insulin homeostasis associated with obesity in male humans can be recapitulated in rodent models and imply that estradiol plays a role in protecting the metabolism of female mice, potentially by alteration of glucocorticoid metabolism. Despite altered metabolism in postnatal obesity vascular function remained normal suggesting metabolic and vascular dysfunction are not intrinsically linked. Conversely, maternal obesity did not cause any overt changes in offspring metabolism but caused vascular dysfunction implying these parameters can be programmed independently.

The structural and functional decline of the ageing human brain varies by brain region, cognitive function and individual. The underlying biological mechanisms are poorly understood. One potentially important mechanism is exposure to glucocorticoids (GCs; cortisol in humans); GC production is increasingly varied with age in humans, and chronic exposure to high levels is hypothesised to result in cognitive decline via cerebral remodelling. However, studies of GC exposure in humans are scarce and methodological differences confound cross-study comparison. Furthermore, there has been little focus on the effects of GCs on the frontal lobes and key white matter tracts in the ageing brain. This thesis therefore examines relationships among cortisol levels, structural brain measures and cognitive performance in 90 healthy, elderly community-dwelling males from the Lothian Birth Cohort 1936. Salivary cortisol samples characterised diurnal (morning and evening) and reactive profiles (before and after a cognitive test battery). Structural variables comprised Diffusion Tensor Imaging measures of major brain tracts and a novel manual parcellation method for the frontal lobes. The latter was based on a systematic review of current manual methods in the context of putative function and cytoarchitecture. Manual frontal lobe brain parcellation conferred greater spatial and volumetric accuracy when compared to both single- and multi-atlas parcellation at the lobar level. Cognitive ability was assessed via tests of general cognitive ability, and neuropsychological tests thought to show differential sensitivity to the integrity of frontal lobe sub-regions. The majority of, but not all frontal lobe test scores shared considerable overlap with general cognitive ability, and cognitive scores correlated most consistently with the volumes of the anterior cingulate. This is discussed in light of the diverse connective profile of the cingulate and a need to integrate information over more diffuse cognitive networks according to proposed de-differentiation or compensation in ageing. Individuals with higher morning, evening or pre-test cortisol levels showed consistently negative relationships with specific regional volumes and tract integrity. Participants whose cortisol levels increased between the start and end of cognitive testing showed selectively larger regional volumes and lower tract diffusivity (correlation magnitudes <.44). The significant relationships between cortisol levels and cognition indicated that flatter diurnal slopes or higher pre-test levels related to poorer test performance. In contrast, higher levels in the morning generally correlated with better scores (correlation magnitudes <.25). Interpretation of all findings was moderated by sensitivity to type I error, given the large number of comparisons conducted. Though there were limited candidates for mediation analysis, cortisol-function relationships were partially mediated by tract integrity (but not sub-regional frontal volumes) for memory and post-error slowing. This thesis offers a novel perspective on the complex interplay among glucocorticoids, cognition and the structure of the ageing brain. The findings suggest some role for cortisol exposure in determining age-related decline in complex cognition, mediated via brain structure.

7-Oxysterols constitute the major component (40%) of oxidized low-density lipoprotein (oxLDL). They arise in the body via auto-oxidation of cholesterol and are known to induce endothelial dysfunction, oxidative stress and apoptosis in the vascular wall, prior to development of atherosclerosis. A novel pathway has been described for hepatic inter-conversion of 7-ketocholesterol (7-KC) and 7β -hydroxycholesterol (7β OHC) by the enzyme 11β-hydroxysteroid dehydrogenase type-1 (11β HSD1), better known for metabolizing glucocorticoids. Inhibition of 11βHSD1 is atheroprotective and the potential underlying mechanism for this may involve altered metabolism and actions of glucocorticoids. However, alterations in the metabolism of 7-oxysterols may also play an important role in this atheroprotective effect. The work described here addresses the hypotheses that (i) 7-oxysterols are substrates for murine 11βHSD1; (ii) inhibition of 11β HSD1 may abolish cellular metabolism of 7-oxysterols; (iii) this route of metabolism may modulate the actions of 7-oxysterols and glucocorticoids on murine vascular physiology. Murine 11β HSD1 inter-converted 7-oxysterols (Km=327.6±98ìM, Vmax=0.01±0.001pmol/ìg/min) but the regulation of reaction direction is different from that for glucocorticoids. Predominant dehydrogenation of 7β OHC to 7-KC was quantified in several models (recombinant protein, cultured cells stably transfected with 11β HSD1), in which predominant reduction of glucocorticoids was measured. Furthermore, in murine hepatic microsomes, dehydrogenation of 7β OHC occurred exclusively. In aortic rings in culture, however, both reduction and dehydrogenation of 7-oxysterols were evident. 7-Oxysterols and glucocorticoid substrates competed for metabolism by 11β HSD1, with 7β OHC inhibiting dehydrogenation of glucocorticoids (Ki=908±53nM). The circulating concentrations of 7-oxysterols in the plasma of C57Bl6 and 11β HSD1-/- mice were in the ìM range (0.02 – 0.13ìM). The disruption of 11β HSD1 has resulted in increased ratios of 7-KC and 7β OHC over total plasma cholesterol levels (*p<0.05). This finding suggested that 11β HSD1 is involved in metabolizing and determining the plasma levels of 7-KC and 7β OHC. To assess the consequences of these alterations for vascular function, studies were undertaken in aortic rings. Prolonged incubation with 7-oxysterols (20-25 ìM) showed a tendency to attenuate noradrenaline-mediated contractions of C57Bl6 aortae, but had no effect on contractions in response to 5-hydroxytryptamine or KCl. Similarly, endothelium-dependent and -independent relaxations of murine aortae were unaltered after exposure to 7-oxysterols. Thus in the mouse, 11β HSD1 may influence the balance of circulating and cellular 7-oxysterols which may have consequential effects on glucocorticoid action. Although this work suggests that concentrations present in murine tissues are unlikely to cause vascular dysfunction, they may influence further cellular events as yet undescribed. Under pathological conditions where high concentrations of 7-oxysterols occur, 11β HSD1 may influence the extracellular-transport and delivery of 7-KC and 7β OHC to the plaque. This work therefore proposes that inhibition of metabolism of 7-oxysterols by 11β HSD1 inhibitors, may contribute to the atheroprotective effects of these drugs.

Alterations in glucocorticoid (GC) biosynthesis and metabolism are associated with a variety of pathophysiological disorders including cholestasis, diabetes and other metabolic disorders. Bile acids (BA) are also important modulators of metabolic functions and regulate cholesterol, triglyceride and glucose homeostasis as well as being critical for dietary fat digestion, enterohepatic function, and postprandial thermogenesis. In intact cells and in vivo, the 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme converts inactive GC precursors (cortisone in humans, and 11-dehydrocorticosterone in mice and rats) into their active forms (cortisol and corticosterone, respectively) thereby amplifying local intracellular GC levels. Interconversion by 11β-HSD1 of other sterols has also been described. These include conversions of 7keto-cholesterol to 7β-hydroxycholesterol, 7-oxodehydroepiandrosterone (7-oxo-DHEA) to 7α-hydroxy- and 7β-hydroxy DHEA, 7- oxo-lithocholic acid (LCA, a bile acid; BA) to chenodeoxycholic acid (CDCA, a 7α- hydroxylated BA) and ursodeoxycholic acid (UDCA, a 7β-hydroxylated BA) in human liver microsomes. In the liver, BA inhibit 11β-HSD1 but whether 11β-HSD1 regulates BA homeostasis is unclear. Evidence of molecular regulation of the enterohepatic recycling of bile acids by liver glucocorticoid receptor (GR) in mice does suggest a role for 11β-HSD1. It was therefore hypothesised that disruption of 11β-HSD1 expression in mice would impair BA recycling and might affect the relative concentrations of BA within the enterohepatic circuit. The primary objective of the current work was to investigate the impact of altered 11β-HSD1 on BA homeostasis. This was achieved using genetically modified mouse models with altered 11β-HSD1 expression, either globally or restricted to hepatocytes. BA are stored in the gall bladder and are released postprandially, to aid digestion. It was hypothesised that 11β-HSD1 deficiency might the affect the process of postprandial gall bladder emptying/refilling. Mice with global 11β-HSD1 knockout (Hsd11b1-/-) and age-matched control mice (C57Bl/6) were either fasted for 4h and culled or fasted for 4h and re-fed for another 4h before culling. Their response to fasting and re-feeding was assessed with specific focus on organs associated with BA recycling in the enterohepatic circuit (liver, gall bladder, serum and small intestine). Gall bladders of fasted Hsd11b1-/- and C57Bl/6 mice had similar volumes of bile but in fasted Hsd11b1-/- mice, BA concentrations were higher in serum and liver. As expected, re-feeding caused gall bladder emptying in C57Bl/6 mice with consequent increased serum and liver bile acid concentrations. In Hsd11b1-/- mice, the gall bladder did not empty and serum and liver BA concentrations were similar to the fasted state. To explore possible reasons for this, levels of mRNA encoding proteins known to be involved in hepatic BA transport were quantified using real-time q-PCR. Levels of mRNA encoding NTCP/ SCL10A1/ SCL10A1, the transporter responsible for most hepatocyte BA uptake, were increased in livers of fasted Hsd11b1-/- mice whereas levels of Slc51b mRNA, encoding the OST- transporter that facilitates BA removal from liver to the systemic circulation, and levels of Mrp2 and Atp8b1/FIC1 mRNAs (both encoding proteins which transport BA from liver into gall bladder) were decreased. This suggests that in fasted Hsd11b1-/- mice, BA transporter expression is altered to increase BA influx into hepatocytes and decrease efflux, to compensate for reduced levels of liver BA. These data together imply that bile acid recycling is controlled by 11β-HSD1 activity which regulates gall bladder emptying, hepatic BA concentration and BA transporter activity to ensure continuity of BA recycling within the enterohepatic circuit compartments. These changes may also affect digestion of lipids and fat-soluble micronutrients. Because 11β-HSD1 can directly metabolise secondary BA, it was predicted that 11β-HSD1 deficiency would lead to changes in the BA profile. Profiling of BA in the gall bladder was performed using mass spectrophotometry. In Hsd11b1-/- mice, 7α-hydroxylated BA predominated (cholic acid [CA]>α-muricholic acid [α- MCA]>CDCA>others), in contrast to C57Bl/6 mice in which 7β-hydroxylated BA predominated (ω-MCA>β-MCA>UDCA>others). The ratio of 7α:7β acids was therefore >100-fold greater in Hsd11b1-/- mice. This suggests that 11β-HSD1 either directly or indirectly controls the epimerisation of 7α- to 7β- hydroxylated BAs. Measurement of mRNAs encoding proteins important for hepatic BA biosynthesis in livers of fasted Hsd11b1-/- mice showed decreased expression of Scarb1/SR-B1, Cyp39a1 and Cyp27a1 (though with no change in levels of CDCA, the product of CYP27A1, in liver or bile fluid), compared to fasted control mice. Hepatic levels of Gpbar1/TGR5/GPBAR1 and Cyp3a11 mRNAs, encoding proteins important in BA detoxification, were increased and decreased, respectively. This suggests that Gpbar1/TGR5/GPBAR1, encoding G-protein coupled bile acid receptor (also called TGR5/GPBAR1) and an FXR target, could be induced to detoxify 7α-hydroxylated BA whereas expression of Cyp3a11, which catalyses the conversion of LCA to hyodeoxycholic acid (HDCA) is decreased; bile fluid of Hsd11b1-/- mice contained lower levels of LCA and little to no HDCA, though LCA and HDCA levels in liver were unaltered. Currently, the functional differences between 7α- and 7β- hydroxylated BA are not clear. However, these findings could have significant implications for bile acid-mediated transcription which, in turn, might affect lipid and sterol metabolism. Also, alterations in BA composition may have other physiological consequences via other pathways. Because cholesterol is the precursor of BA synthesis, it was hypothesised that western diet (WD) (containing cholesterol) would exacerbate and/or alter the phenotype of Hsd11b1-/- mice. Gall bladder weights of fasted Hsd11b1-/- and control C57Bl/6 mice did not change with western diet compared to chow diet. In control C57Bl/6 mice, the total BA concentration in the gall bladder increased in response to WD in comparison to chow diet. In contrast, Hsd11b1-/- mice showed no change in total BA concentration when fed on WD in comparison to chow. These data indicate that 11β-HSD1 is required by mice for the normal increase in total BA concentration in bile in response to dietary cholesterol. BA profiling of bile from control mice fed on WD showed no difference in the relative amounts of 7β-hydroxylated BA and 7α-hydroxylated BA to littermates fed on chow diet with the exception of β–MCA which increased, and α–MCA which decreased. Like chow-fed Hsd11b1-/- mice, BA profiling of bile from WD-fed Hsd11b1-/- mice showed a significant decrease in relative levels of 7β-hydroxylated BA (UDCA < β-MCA < others) and an increase in percentage of 7α-hydroxylated BAs (CA>α-MCA>CDCA>others) compared to C57Bl/6 controls. These data show that Hsd11b1-/- mice fail to show the normal increase in 7β-hydroxylated BA and decrease in 7α-hydroxylated BA observed in control mice in response to a cholesterol containing diet, suggesting 11β-HSD1 deficiency blunts the influence of cholesterol on BA composition. Measurement of hepatic mRNAs encoding BA transporters suggest that hepatocyte uptake of BA is decreased in C57Bl/6 on WD compared to those mice on chow diet, whereas this was not the case in Hsd11b1-/- mice where hepatic expression did not change with diet. Thus, Hsd11b1-/- mice failed to increase expression of Ntcp/ Scl10a1/ Scl10a1 appropriately, suggesting impaired hepatic BA uptake, while Slc51b (encoding OST-β) expression was increased, compared to control mice, possibly to reduce hepatic BA concentration by transporting BA out of hepatocytes into the systemic circulation. Therefore, Hsd11b1-/- mice may adapt to a cholesterol-induced increase in hepatic BA by blunting hepatic BA uptake via NTCP/ SCL10A1/ SCL10A1 and increasing hepatic efflux via OST-β. The effects of 11β-HSD1 deficiency upon BA recycling and BA profile and concentration within the enterohepatic circuit, could reflect 11β-HSD1 action within the liver or could be due to actions in other tissues. / To investigate the role of hepatic 11β-HSD1 specifically, 11β-HSD1 liver-specific knockout (Hsd11b1LKO), 11β- HSD1 liver-specific over-expressors (Hsd11b1LOE) and control mice with exon 3 of the Hsd11b1 gene “floxed” (Hsd11b1F) were studied. Findings from this study indicate a role for 11β-HSD1 in adaption to dietary cholesterol and suggest that hepatic 11β-HSD1 (as opposed to 11β-HSD1 in extra-hepatic tissues) is the main factor regulating BA metabolism. Also, work from this thesis demonstrates 11β-HSD1 is an important regulator of gall bladder emptying and filling, an important component of enterohepatic bile acid recycling. Based on these findings it is anticipated that therapeutic use of 11β-HSD1 inhibitors will result in BA imbalances within the enterohepatic circuit and therefore BA homeostasis. Care must therefore be observed when implementing therapeutic use of 11β-HSD1 inhibitors, with particular focus on patients with cholestasis, Addison’s disease and critically ill patients who already have known BA imbalances in their enterohepatic system.

No description available.

5a-Reductase 1 (5aR1) metabolises steroids such as glucocorticoids and androgens and is highly expressed in the livers of mice. Genetic disruption of 5aR1 leads to adverse metabolic consequences in mice and pharmacological inhibition in humans induces peripheral insulin resistance. I hypothesised that these effects are due to increased hepatic glucocorticoid action and firstly set up an experimental paradigm using A-348441, a liver-selective glucocorticoid receptor antagonist, to assess the contribution of hepatic glucocorticoid action. A-348441 was then utilised to assess whether changes in hepatic glucocorticoid signalling underpinned metabolic changes in: 1) a genetic model where the gene for 5aR1 has been disrupted, and 2) a pharmacological model using dutasteride, a dual 5aR1, R2 inhibitor. Previous work with A-348441 has demonstrated it can lower blood glucose levels in ob/ob mice. However, monogenic models of obesity are not fully representative of idiopathic obesity, which is commonly related to diet. Therefore, I utilised a mouse model of high fat dietary challenge to determine the effects of A-348441 in a more relevant model. High fat diet worsened metabolic indices such as body weight and weight gain, adipose tissue depot mass, fasting insulin and insulin response to a glucose challenge. A-348441 improved metabolic health of mice on high fat diet, preventing high fat-induced body weight gain, total white adipose depot weight gain and attenuating high fat-induced elevations in fasting plasma insulin, fasting glucose and insulin response to a glucose tolerance test. Importantly, hepatic glucocorticoid receptor antagonism did not change plasma corticosterone concentrations, indicating that glucocorticoid receptor antagonism was limited to the liver and thus demonstrating that hepatic glucocorticoid action plays a major role in high fat dietinduced metabolic phenotype. Using A-348441, I then went on to test the contribution of hepatic glucocorticoid action to the adverse metabolic phenotype in wild-type and 5aR1 knockout mice also under a high fat dietary challenge; two timescales were explored – 10 weeks with A- 348441 administered from the start and 6 months with A-348441 introduced after 5 months of high fat diet. 5aR1 knockout mice were overall more insulin resistant and had fattier livers than the wild-type mice at 10 weeks regardless of diet consumed. High fat diet overall worsened metabolic indices - increasing body weight, weight gain, adipose tissue depot mass, fasting insulin and insulin response to a glucose challenge in both genotypes and at both time points. Hepatic glucocorticoid receptor antagonism in 5aR1 knockout mice prevented high fat diet-induced metabolic consequences as expected in the 10-week high fat diet model, but not in the 6-month experiment; hyperinsulinaemia and weight gain were attenuated in the 10-week high fat diet model but not the 6-month high fat diet model, suggesting hepatic glucocorticoid receptor antagonism can prevent, but not reverse, high fat diet-induced metabolic consequences. However, A-348441 did not have a bigger effect on ameliorating the worsened metabolic state of the 5αR1 knockout mice. This suggests that increased hepatic glucocorticoid action does not underpin the adverse phenotype reported in the 5aR1 knockout mice. Dutasteride is a dual 5aR inhibitor prescribed to men for benign prostate hyperplasia or prostate cancer. I then recapitulated the human experiment where 5aR was pharmacologically inhibited and investigated the effects of dutasteride in mice. Inhibition of 5aRs in mice impaired insulin sensitivity, with increased insulin response to glucose tolerance test and also increased liver triglyceride levels; body weight, total adipose depot weight, fasting insulin, fasting glucose or glucose response to a glucose tolerance test were not changed by dutasteride. A-348441 reduced this hyperinsulinaemia but, as in other models, did not reduce the increased liver triglyceride levels. This suggests hepatic glucocorticoid action plays a substantial role in the development of insulin resistance caused by 5aR inhibition, but not in the development of hepatic steatosis. Therefore, adverse metabolic changes as a result of 5aR1 inhibition with dutasteride may be driven by altered hepatic glucocorticoid metabolism. Furthermore, metabolic changes caused by lifelong 5aR1 disruption are not responsive to short-term hepatic glucocorticoid receptor antagonism and altered androgen signalling may play a greater role. In conclusion, targeting the hepatic glucocorticoid receptor may be beneficial in restoring metabolic homeostasis in diet-induced obesity.

Increased circulating levels of glucocorticoids observed in many catabolic conditions play a major role in the induction of muscle atrophy. Indeed, inhibition of glucocorticoid action by glucocorticoid receptor antagonist attenuates and, in some cases, abolishes muscle atrophy. Circulating and tissue levels of IGF-I, a growth factor that stimulates the development of muscle mass, are frequently reduced in response to glucocorticoids. This decline could therefore trigger muscle atrophy in catabolic conditions. Indeed, systemic administration of IGF-I prevents glucocorticoid-induced muscle atrophy. However, use of systemic IGF-I administration is limited by its hypoglycemic and cardiac hypertrophic actions. Moreover, local IGF-I seems to play a more important role in the regulation of muscle mass than systemic IGF-I. Therefore, to limit loss of muscle mass observed in catabolic states, IGF-I administration must mimic as close as possible the autocrine production of IGF-I. The aim of this thesis was to investigate whether the restoration of IGF-I muscle content could reverse muscle atrophy induced by glucocorticoids. In this work we have tested the hypothesis that the local decrease in muscle IGF-I content might be responsible for the muscular atrophy induced by glucocorticoids. In our work, we have demonstrated that localized overexpression of IGF-I by gene electrotransfer prevents muscle atrophy in glucocorticoid-treated rats. High rate of fiber transfection and long term gene expression were obtained by combining multiple injection sites of DNA with electroporation. Human IGF-I gene electrotransfer using this optimised protocol resulted in increased muscle IGF-I mRNA and protein levels together with prevention of loss of skeletal muscle mass. Furthermore, alterations in the Akt/GSK-3â/â-catenin signaling pathway caused by glucocorticoids were prevented by local IGF-I gene overexpression. Finally, muscle overexpression of caAkt, dnGSK-3b and ÄNb-catenin was sufficient to mimic the anti-atrophic effect of IGF-I supporting the role of this signalling pathway in muscle atrophy caused by glucocorticoids. Taken together, our results show, for the first time in vivo, the role of the IGF-I/Akt/GSK-3b/b-catenin pathway in the skeletal muscle atrophy caused by glucocorticoids. In conclusion, our work highlights the crucial role of decreased muscle IGF-I in glucocorticoid-induced muscle atrophy. Indeed, the data presented in this thesis support the fact that the atrophic action of glucocorticoids is in part due to the downregulation of IGF-I, leading to the inhibition of its signalling pathways while restoration of muscle IGF-I levels is able to counteract totally muscle atrophy.

No description available.

In mammals distinct steroid hormones termed mineralocorticoids (MCs) and glucocorticoids (GCs) regulate hydromineral balance and the stress response, respectively. In contrast, it is thought that a single corticosteroid, 1[alpha]-hydroxycorticosterone (1[alpha]-B) serves as both a GC and MC in elasmobranchs. I investigated the putative dual MC and GC roles of 1[alpha]-B by examining ex vivo regulation of interrenal 1[alpha]-B synthesis by osmoregulatory and stress hormones in the euryhaline stingray Dasyatis sabina. A commercial enzyme-linked immunoassay was adapted for the quantification of 1[alpha]-B. I also isolated cDNA sequences encoding two rate-limiting steroidogenic enzymes, the steroidogenic acute regulatory protein (StAR) and P450 cholesterol side-chain cleavage (P450scc), and characterized the steroidogenic activity of the encoded proteins using a heterologous expression system. Both the stress hormone adrenocorticotropic hormone (ACTH) and the antinatriuretic peptide angiotensin II (ANG II) were potently steroidogenic in ex vivo interrenal cultures, whereas C-type natriuretic peptide (CNP) inhibited 1[alpha]-B synthesis. StAR and P450scc mRNA levels were increased by 24 h incubation with ACTH and decreased by both ANG II and CNP. To examine changes in osmoregulatory hormone systems that impinge upon 1[alpha]-B synthesis, I also isolated the cDNA sequences of the ANG II and CNP receptors, AT and NPR-B. Both AT and NPR-B mRNA levels were significantly elevated in osmoregulatory tissues of freshwater (FW; Lake Monroe, FL) versus saltwater (SW; Corpus Christi Bay, TX) populations of D. sabina. Interrenal StAR and NPR-B mRNA levels were also significantly higher in FW individuals. The physiological roles of 1[alpha]-B were further investigated in vivo by examining the effects of stress and FW transfer on interrenal synthesis of 1[alpha]-B. Plasma 1[alpha]-B and glucose were significantly elevated by hook-and-line capture stress, indicating that 1[alpha]-B acts in classical GC fashion to facilitate the stress response. In contrast, 1[alpha]-B was significantly decreased 24 h after SW-FW transfer. In light of the osmotic strategy of euryhaline elasmobranchs, this result is consistent with a MC role for 1[alpha]-B. Taken together, the results of this research strongly support a dual role for 1[alpha]-B in facilitating both hydromineral balance and the stress response in elasmobranchs. / text