Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 160-183).

A recently discovered peptide hormone, pituitary adenylate cyclase-activating polypeptide (PACAP) regulates several endocrine systems affecting essential physiological processes such as metabolism, growth, reproduction, and the stress response. PACAP acts as a hypophysiotropic factor, is a potent secretogogue of insulin, regulates production and release of catecholamines from the adrenal medulla and acts as a neuromodulator in the sympathetic and parasympathetic nervous system. The primary structure of PACAP has been highly conserved during the evolution of chordates suggesting it plays an important physiological role. The objective of my thesis was to identify PACAP’s primary physiological function and to determine if it is essential for survival by generating a mouse line deficient in PACAP through targeted disruption of the PACAP gene locus. Postnatal PACAP expression was examined to determine sites of peripheral PACAP production. In addition, several splice variants of the PACAP gene with alternate 5’untranslated regions were identified suggesting a complex system for regulating expression of the mouse PACAP gene. A targeting vector that allows tissue specific or developmental stage specific knockout of the PACAP gene was constructed in the event that PACAP gene deletion resulted in embryonic lethality. PACAP null mice were generated from homologously recombined embryonic stem cells. Initial characterization of the PACAP null mice determined that in the absence of PACAP, mice died within the first two postnatal weeks with abnormal lipid metabolism. Lipid accumulation was present in liver, heart and skeletal muscle and serum lipids were high. Mitochondrial dysfunction in the liver was not the cause of the lipid accumulation, as P-oxidative function was normal. I conclude that PACAP null mice are unable to regulate lipid release from white adipose tissue stores, resulting in a flood of lipids to non-adipose tissues. The abnormal distribution of lipids observed in the PACAP null mice is characteristic of diabetes type 2, yet classical insulin resistance is not observed. Thus, elevated insulin levels were accompanied by low blood glucose levels and the response to a glucose challenge was normal. The uncontrolled release of free fatty acids may result if glucose that is taken up by cells can not be utilized and an alternate energy source is required or if white adipocytes only are insulin resistant. The PACAP null mice were temperature sensitive, in that when raised at 21“C they exhibited metabolic dysfunction and died by two weeks of age. At 24°C most (85%) of the mice survived to adulthood with no obvious signs of metabolic dysfunction. We have determined that the inability of the PACAP null pups to thermoregulate normally when exposed to a lower environmental temperature may be associated with decreased norepinephrine levels to the brown adipose tissue. PACAP may be important for the production and release of catecholamines in the adrenal gland or within the sympathetic nervous system in times of prolonged stress. A mechanistic connection between the lipid abnormalities and the temperature sensitivity in the PACAP null pups has yet to be made. Catecholamines affect a wide range of tissues and the problems associated with insulin regulation within the PACAP null mice may be due to the imbalance in catecholamine production. As one of two main stress response systems, the sympathetic nervous system elicits a vital coping mechanism in times of stress and PACAP’s ability to regulate this system may explain why the primary structure of PACAP has remained so highly conserved. PACAP is a wide acting hormone and therefore the metabolic problems seen in the PACAP null mice may result from altered regulation of several endocrine systems at once. Targeted disruption of the PACAP gene in mouse has revealed a role for PACAP in the regulation of lipid metabolism and in the sympathetic control of thermoregulation. / Graduate

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Thesis (M.S.)--Michigan State University. Dept. of Physiology, 2008. / "Committee members, Weiming Li, Richard Miksicek, and Cheryl Sisk"--Acknowledgments. Title from PDF t.p. (viewed on Aug. 4, 2009) Includes bibliographical references (p. 51-54). Also issued in print.

Multiple Endocrine Neoplasia Type 1 (MEN1) is an autosomal dominant disorder characterized by the combined occurrence of pituitary, pancreatic islet and parathyroid tumours. MEN1-associated tumours show loss of heterozygosity and the MEN1 gene encodes a putative tumour-suppressor, menin, whose over-expression in vitro inhibits cell proliferation. MEN1-associated tumours present earlier, are more aggressive and more difficult to treat than sporadic endocrine tumours. Strategies for earlier identification of index cases and novel therapies may contribute towards reduced morbidity and mortality from the condition. In this study, I first investigated the safety and efficacy of MEN1 gene replacement therapy using a modified adenoviral vector in pituitary tumours of heterozygous Men1 knockout mice. This revealed that MEN1 gene replacement was safe, effective and induced reduction of tumour cell proliferation. I also performed an in vivo phage-displayed peptide library screening study in heterozygous Men1 knockout mice to identify novel peptides that specifically bind pancreatic islet tumours. This identified one peptide sequence that likely targets pancreatic islet tumours. To further elucidate the role of menin I carried out phenotypic characterization of the mouse model for MEN1 in two mouse strains to investigate the effect of different genetic backgrounds and the potential for genetic modifiers on tumour phenotype. The frequency of pituitary and adrenal tumours was significantly influenced by the mouse strain, demonstrating the importance of genetic background on MEN1 tumour occurrence, implicating the role of genetic modifiers. Finally, I investigated the prevalence of MEN1 mutations in a cohort of patients presenting with primary hyperparathyroidism under 40 years of age. This revealed that 6% of under 40 year-olds with apparently sporadic parathyroid tumours have MEN1 mutations, and are likely to present with multiple parathyroid tumours. Pre-operative genetic screening of under 40 year-old patients with multiglandular parathyroid disease may reduce post-operative recurrence of hyperparathyroidism in those patients with MEN1 mutations.