Item – Theses Canada

​
OCLC number
1019491746
Link(s) to full text
LAC copy
Author
Fick, Laura J.
Title
Molecular mechanisms involved in the regulation of circadian clock gene and neuropeptide transcription : influence of palmitate.
Degree
Ph. D. -- University of Toronto, 2010
Publisher
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, 2013.
Description
1 online resource
Notes
Includes bibliographical references.
Abstract
<?Pub Inc> Canadians live in a society where the sun does not dictate the workday. Our lifestyles must shift to cater to the 24-hour demands of a fast paced global community. As a result our circadian rhythms are altered, leading to dysregulation of key physiological processes responsible for the maintenance of essential functions like energy homeostasis. Energy homeostasis is controlled by neuropeptide-expressing neurons within the hypothalamus. These neurons are affected by circulating hormone and nutrient levels in addition to their endogenous molecular clock machinery that controls cellular processes. Therefore, hypotheses were generated that non-SCN hypothalamic neurons express orexigenic neuropeptides in a rhythmic fashion without external influence from the SCN as a result of internal rhythmicity; and that elevated concentrations of palmitate, a ubiquitous saturated FFA common in a high fat diet, have direct influence on the mRNA levels of circadian clock components 'Bmal1, Clock, Per2, Rev-erb'[alpha] and the potent orexigenic neuropeptides ' NPY, AgRP' and 'ppGhrelin' through mechanisms related to HAT, SIRT1 and AMPK. Using the mHypoE-44 neurons, a well characterized cell line that expresses the molecular clock and specific neuropeptides these hypotheses were explored in four studies. Neuropeptide expression within the mHypoE-44 neurons was determined to be rhythmic. 'NPY' and 'NT' demonstrate significant 24-hour rhythms. 'CRH' and 'ppGhrelin' mRNA cycled significantly in an ultradian fashion, oscillating approximately every 18 h. 'AgRP' mRNA did not show a significant rhythm. We identified rhythmic binding of BMAL1 to the 'NPY' promoter, suggesting clock-mediated control of neuropeptide expression. 'Bmal1' and 'Clock' mRNA levels were elevated with palmitate, whereas 'Per2' and 'Rev-erb'[alpha] mRNA showed significant decreases following palmitate treatment. Palmitate increased the acetylation of both BMAL1 and PER2 proteins. Alteration of AMPK activity altered the mRNA levels of all clock genes assayed and AMPK activation diminished the palmitate-induced changes in 'Bmal1' mRNA. Palmitate significantly elevated both 'NPY' and 'ppGhrelin' mRNA levels. Chemical modifiers that decrease acetylation altered these systems. AMPK activation reduced the palmitate-induced changes in 'NPY' mRNA levels. These findings demonstrate that non-SCN neurons have rhythmic neuropeptide transcript levels. This thesis elucidates a direct effect of palmitate on the molecular clock and neuropeptide expression at the level of the hypothalamic neuron; and these findings highlight a role for HAT/SIRT1 activation and AMPK in these important processes, which ultimately contribute to the understanding of circadian dysregulation and energy balance.
ISBN
9780494976876
049497687X
9780494976876