Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2009. / Title from PDF t.p. (viewed on Jul 8, 2010). Source: Dissertation Abstracts International, Volume: 70-10, Section: B, page: 5920. Adviser: Gregory E. Demas.

Thesis (Ph.D.)--University of California, San Francisco, 2009. / Source: Dissertation Abstracts International, Volume: 71-02, Section: B, page: . Adviser: Keith R. Yamamoto.

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abstract: The impact of urbanization on wildlife is becoming an important topic in conservation. However little is known concerning the proximate mechanisms involved which enable some species to persist in cities, while others perish. Adapting to novel city environments requires individuals to maintain a functional physiological response to stressful stimuli, while concurrently using the necessary resources (food) needed to persist. A primary function of the stress response is the mobilization of intrinsic energy resources, and thus both requirements (energy and stress) are explicably linked. This dissertation investigates the interaction of energetic reserves and the physiological stress response in a native bird species, the Curve-billed Thrasher, within the context of this species' colonization of Phoenix, Arizona. This research uses a combination of comparative studies, statistical modeling, and experimental approaches conducted in field and captive settings to demonstrate how urban and desert populations of these species differ in energetic state and stress physiology. These studies reveal that the current energetic status of an individual bird influences the secretion of glucocorticoids (primary stress hormones) and can alter how energy reserves are used for gluconeogenesis to produce energy during acute stress. In addition, this research also identifies how differing levels of a hypothalamic neuropeptide (vasotocin) may play a role in mediating differences in stress physiology between populations. The quantity of food available and even temporal variability in its abundance may alter how native birds respond to stress. Increased body condition offsets the costs of maintaining the stress response in urban areas. / Dissertation/Thesis / Ph.D. Biology 2010

The goal of this research project is to understand how a high sugar diet may affect pancreatic beta cell function. High glucose concentrations lead to an increase in lipid droplets and TORC1 in beta cells, which promote high basal secretion of insulin (Erion K.A. et al., JBC, 2015). SREBP is a key regulator of cholesterol and lipid synthesis and depends on TORC1 activity. The active form of SREBP is located in the nucleus. Does glucose-induced lipid synthesis in beta cells increase via SREBP? To answer this question, we propose: 1) To test the effect of high glucose (11mM) on nuclear SREBP in INS-1 cells in comparison to physiological glucose (4mM). 2) To determine if nuclear SREBP is affected when PIP4Kgamma (a regulator of TORC1) is suppressed. SREBP translocation from the cytosol to the nucleus was measured by immunofluorescence. SREBP processing was measured by western blot. SREBP1 activation increased in response to prolonged exposure to excess glucose after at least 48hrs. Both translocation and processing increased in 11mM glucose compared to 4mM glucose. When PIP4Kgamma was suppressed in INS-1 cells, SREBP translocation was inhibited. Lipid droplet accumulation was measured by nile red staining and it was found that de novo lipid synthesis only contributes to a small fraction of total lipid droplets. In conclusion, SREBP is activated in beta cells when in excess glucose. This may allow for lipid accumulation and basal hypersecretion of insulin due to over nutrition.

Increased sugar consumption is considered to be a contributor to the worldwide epidemics of obesity and diabetes and the consequent cardio metabolic risks. These include a significant increase for Type II diabetes and associated multiple comorbidities such as non-alcoholic fatty liver disease (NAFLD). The accumulation of excess triglycerides characterizes NAFL with a prevalence of up to 53% in morbidly obese populations. While in itself benign, fatty liver can progress to non-alcoholic steatohepatitis (NASH), which is characterized by apoptosis, inflammation and fibrosis in 10-20% of individuals. Progression to NASH increases the risk of further deterioration to cirrhosis and hepatocellular carcinoma (HCC). However, progression is unpredictable in any given individual and no risk factors predisposing to progression have been identified. Variation in a limited number of genes, such as patatin-like phospholipase (PNPLA3) and transmembrane 6 superfamily member 2 (TM6SF2), have been linked to an increased susceptibility to NAFLD. Recently, fibroblast growth factor 21 (FGF21) was reported to be a potential predictor for NAFLD as it significantly increases in patients with obesity and NAFL. Multiple lines of evidence indicate that FGF21 plays an important role in liver metabolism in mice and humans, playing a key role in carbohydrate and lipid metabolism. FGF21 was originally identified as an endocrine member of the fibroblast growth factor family as it can be released into the circulation. FGF21 was initially assigned a purely metabolic role as infusions led to weight loss and increased glucose clearance through induced expression of the GLUT1 transporter. However, FGF21 biology is now understood to be extremely complex, as it is expressed in many metabolically active tissues including, liver, white (WAT) and brown adipose tissue (BAT), muscle and pancreas. Functions of FGF21 are distinct in all these tissues. In the previous studies from our lab, we have seen fructose consumption, but not glucose, leads to an increase in serum FGF21 levels both in humans and mice. In general, sugar is typically consumed by humans in the form of sucrose or high fructose corn syrup (HFCS), both of which consist of nearly equal amounts of the simple sugars, glucose and fructose. Although attention has been focused on sucrose and fructose in many studies, no direct comparison was found to study fructose, glucose and sucrose. The current study aims to expand on the role of FGF21 in mediating the effects of chronic consumption of these refined sugars in mice. Wildtype (WT) and FGF21 knockout (KO) mice were fed with one of these diets for 20 weeks and in general, mice eating diets with high refined sugars gained less weight than mice eating chow, although calorie consumption was the same. In terms of body composition, sucrose fed FGF21 KO mice had less fat mass compared to chow fed animals. Dextrose fed and fructose fed mice had comparable fat mass reduction in WT and KO mice. Interestingly, glucose tolerance tests (GTT) showed increased glucose sensitivity in dextrose fed WT and KO mice after four weeks, however glucose tolerance decayed after 12 weeks on the diet. At 16 weeks fructose fed KO mice had significant increased glucose sensitivity compared to controls. Insulin tolerance tests showed similar results between all cohorts and a larger sample size would be needed to elicit any differences. Pyruvate tolerance tests (PTT) showed significantly increased hepatic gluconeogenesis in fructose fed KO mice compared to controls but not in dextrose or sucrose fed mice. Energy expenditure was measured by indirect calorimetry. No significance changes were observed in dextrose fed mice compared to chow controls in terms of VO2 or heat production. Both WT and KO dextrose fed mice had a higher RER, consistent with utilization of carbohydrates over fat for baseline energy expenditure. Sucrose fed mice showed marked increases in VO2 over an averaged 24-hour period and similarly fructose fed mice FGF21 KO mice had increased energy expenditure. Significant increases in RER were observed in both WT and KO sucrose fed mice controls and a similar trend was observed in WT and KO fructose fed mice. Overall, we see differential metabolic effects of all the high carbohydrate diets on the mice. Chronic consumption of dextrose only affected glucose sensitivity. Whereas chronic consumption of sucrose influences glucose and insulin sensitivity and energy expenditure suggesting internal metabolic changes while fructose consumption additionally showed increased hepatic gluconeogenesis without the marked increase in insulin sensitivity. However, detailed tissue analysis is required to determine specific physiological and molecular changes between refined sugar cohorts and the role of FGF21 in this context.

Ames dwarf mice have a spontaneous homozygous Prophet of Pituitary Factor 1 (Prop1) loss-of-function mutation. The Prop1 mutation results in a lack of differentiation of lactotrophs, thyrotrophs, and somatotrophs in the anterior pituitary. Without these endocrine cell types, Ames dwarf mice have essentially no circulating levels of growth hormone (GH), thyroid-stimulating hormone (TSH), and prolactin, and exhibit downstream hormonal deficiencies including insulin-like growth factor 1 (IGF-1), 3’,3,5-triiodothyronine (T3), and thyroxine (T4). Ames dwarf mice are exceptionally long-lived (40% to over 60% depending on sex and diet). They are also extremely insulin sensitive, have a delayed incidence of cancer, and have improved energy metabolism. While the extended lifespan and the many characteristics of an extended healthspan have been known for some time in Ames dwarf mice, the revelation that dwarf mice have improved energy metabolism was less than a decade ago. This finding came about at the molecular level (improved efficiency of the electron transport chain) and at the whole-animal level (increased oxygen consumption and decreased respiratory quotient). To date, however, few studies have been directed at furthering our understanding of the possible mechanism(s) by which Ames dwarf mice have altered energy metabolism. The goal of the studies presented in this dissertation is to delineate these mechanisms and to lay the groundwork for future studies that broaden our understanding of the role(s) of energy metabolism in the aging process. Project 1 examines the effects of early-life T4 replacement therapy in Ames dwarf mice. Previous work established that life-long T4 replacement therapy shortens lifespan in Snell dwarf mice (these mice have endocrine deficits that are essentially identical to those of Ames dwarf mice), while short-term replacement therapy during the early postnatal period of Ames dwarf mice does not. We hypothesized that T4 replacement therapy causes transient impairment of energy metabolism, which is why long-term T4 replacement therapy shortens longevity, and short-term replacement therapy does not. Supporting our hypothesis, we showed that short-term T4 replacement therapy during the early postnatal period transiently impaired energy metabolism as measured by indirect calorimetry. Following early-life T4 replacement therapy, we also observed an accelerated rate of sexual development, as well as lasting effects on bone physiology. Project 2 continued our investigation of energy metabolism by examining a highly metabolic tissue: brown adipose tissue (BAT), which is responsible for non-shivering thermogenesis. Our laboratory has already demonstrated functional alterations in visceral adipose tissue of Ames dwarf mice, and given the altered energy metabolism of Ames dwarf mice, we hypothesized that BAT may also be functionally unique compared to their normal littermates. Supporting our hypothesis, we observed alterations in gene expression, relative weight, and histological structure of BAT in Ames dwarf mice. Moreover, surgical removal of the interscapular BAT depot resulted in a unique physiological response, where Ames dwarf mice lost adiposity in their subcutaneous, perirenal, and epididymal white adipose tissue depots, thus contrasting with normal mice that gained adiposity. Project 3 built upon the findings of our second study, where we continued to examine the role of non-shivering thermogenesis and core body temperature in Ames dwarf mice. To further understand the role of non-shivering thermogenesis in glucose homeostasis and energy metabolism, we housed a cohort of Ames dwarf mice and their normal littermates at room temperature (23˚C), and another cohort at thermoneutrality (for mice this is 30˚C). We found that Ames dwarf mice placed at thermoneutrality had impaired glucose homeostasis and energy metabolism. This is an important finding because we and others believe both of these metabolic processes are important factors for longevity. Taken together, these studies indicate that the improved energy metabolism in Ames dwarf mice is dependent upon several factors, including a loss of thyroid hormone signaling and improved non-shivering thermogenesis.

O efeito de refeições ricas em carboidratos e lipídeos sobre a sensibilidade à insulina foi avaliado. Além disso, investigou-se o conteúdo da proteína GLUT4 em músculo esquelético e tecido adiposo branco. Ratos foram realimentados por 1, 2, 4 e 6 horas com: refeição balanceada (B); rica em carboidrato (C) e rica em lipídeo (L). O índice glicose/insulina revelou que C e L apresentavam resistência à insulina 2 horas após o início da ingestão. No teste de tolerância à insulina, uma redução (~47%) na sensibilidade à insulina foi observada em C após 2 e 4 horas de realimentação. O teste de tolerância à glicose confirmou a resistência à insulina em C e L após 2 horas de ingestão. Não houve alteração no conteúdo de GLUT4, nos momentos em que se verificou alteração na sensibilidade à insulina. Tais resultados indicam que, em ratos, refeições não balanceadas (alto teor de carboidrato ou alto teor de lipídeo), induzem menor sensibilidade à insulina 2 horas após o início da ingestão, e este fenômeno não envolve alterações no conteúdo de GLUT4 nos tecidos avaliados. / The effect of high carbohydrate and fat meals on the insulin sensitivity was evaluated. Furthermore, it was investigated the content of GLUT4 protein on the skeletal muscle and white adipose tissue. Rats were refed for 1, 2, 4 and 6 hours with: balanced meal (B); high carbohydrate meal (C) and high fat meal (L). The glucose/insulin index shows that C and L meals exhibited insulin resistance after 2 hours of ingestion. In the insulin tolerance test, a reduction (~47%) in the insulin sensitivity was observed in C group after 2 and 4 hours of refeeding. The glucose tolerance test confirmed the insulin resistance in C and L-groups after 2 hours of ingestion and such phenomena did not involve alterations in the GLUT4 content on both skeletal muscle or white adipose tissue.

Soy based products are growing in popularity in food supplementation, and a larger population of the world is consuming soy on a regular basis. Soy contains phytoestrogens, plant based mimics of the hormone estrogen. Estrogen has many functions in humans, but one relatively unexplored function is its ability to regulate the levels of the hormone oxytocin (OT) and its receptor (OTR) in the brain. OT is a hormone traditionally known for its role in birth, but recently has been as a key regulator in many different behaviors. These behaviors that OT may affect include increased maternal behaviors, increased sexual behaviors, increased social interactions, increased trust, decreased anxiety, and increased potential for pair bonding. Key phytoestrogens found in soy are of the isoflavone family, and genistein and diadzein are the main two isoflavones that have been shown to exert physiologic effects when ingested by binding to estrogen receptors in the brain. The isoflavones can be estrogen agonists or estrogen antagonists, based on the preexisting, endogenous levels of estrogen in the individual. For men and postmenopausal women, it is believed that ingesting soy can cause an increase in production of OT and OTR, resulting in an increased in OT driven behaviors. For premenopausal women, there is a high endogenous level of estrogen present, so the ingested soy can cause a decrease in production of OT and OTR in the brain, resulting in a decrease in OT driven behaviors. While there is strong evidence to suggest that this may in fact occur in humans, more human based studies, rather than animal models, must be conducted to further verify and validate this hypothesis. An important area yet unexplored is the onset and duration of these OT driven behaviors. It is unclear if these are transient, or more long lasting effects, and future studies must be done to answer this question. This area of research is certainly more relevant as soy based diets are becoming more common; moving forward additional research is needed to determine the extent of oxytocin's ability to alter behaviors in individuals in a significant way.

The hypothalamic-pituitary-interrenal (HPI) axis in fishes controls the production of cortisol in response to a stressor. To study HPI axis regulation during chronic stress, pairs of juvenile rainbow trout (Oncorhynchus mykiss) were allowed to form dominance hierarchies. Subordinate trout experience chronic social stress associated with a sustained elevation in circulating cortisol levels. Circulating cortisol levels reflect the balance between negative feedback regulation of the HPI axis and cortisol clearance, both of which lower cortisol levels, and cortisol production via HPI axis activation. The capacity for negative feedback and cortisol clearance appeared to be intact in subordinate fish, based on the rapid decline in cortisol after cortisol injection or during recovery from social stress. In addition, corticosteroid receptor transcript and protein abundances throughout the HPI axis did not differ between dominant and subordinate trout. Elevated transcript abundances of 11β-hydroxysteroid dehydrogenase type 2 (11βhsd2) in the preoptic area (POA) and pituitary of subordinate fish suggested an enhanced role for this cortisol-inactivating enzyme during chronic social stress. Steroidogenesis occurs in the interrenal cells of the head kidney, and appeared to be a primary driver of increased plasma cortisol levels in subordinate trout. Transcript abundances of the HPI axis effectors corticotropin releasing factor (crf) and pro-opiomelanocortin (pomc) were not elevated in the POA or pituitary, respectively, of subordinate trout. However, rate-limiting components of head kidney steroidogenesis were elevated, including steroidogenic acute regulatory protein (star) and P450 side chain cleavage enzyme (p450scc). A novel finding in the head kidney was increased transcript abundance of steroidogenic factor 1, which regulates steroidogenic enzyme transcription in mammals. Accordingly, head kidney preparations from subordinate trout exhibited increased basal cortisol production in vitro. Despite this elevation in basal steroidogenesis, subordinate rainbow trout demonstrated attenuated cortisol production in response to stimulation by exogenous adrenocorticotropic hormone (ACTH) both in vivo and in vitro. A similar attenuation was observed with cAMP, suggesting that impairment of acute cortisol production arises downstream of cAMP in the ACTH signalling pathway. The regulation of crf in the POA during chronic social stress was probed in more detail by measuring the abundance of selected microRNAs (miRNA) predicted to target and reduce crf or 11βhsd2 mRNA, but these were not found to play a role. Methylation of the crf promoter revealed significantly decreased methylation at two loci in dominant trout, but the functional significance of this methylation pattern requires further study. Collectively, the present thesis used an array of experimental approaches to provide a comprehensive picture of HPI axis regulation during chronic social stress in rainbow trout.