Neurological - Molecular Interface in Food Intake and Metabolism in Birds and Mammals
Obesity is a physiological consequence of dysregulated energy homeostasis. Energy homeostasis depends on energy intake and energy expenditure. Factors controlling the development of different adipose tissue deposits in the body and their distinct metabolic phenotypes are of considerable interest from both an agricultural and biomedical perspective. Following the literature review, the first chapter was devoted to studies designed to bridge the neural-adipose interface in understanding the relationship between appetite regulation and adipose tissue deposition in chickens, using chickens selected for low or high juvenile body weight as a model. Appetite regulation in the brain, particularly the hypothalamus, is the main factor governing food intake. Neuropeptide Y (NPY), known as a potent orexigenic factor, also promotes energy storage in fat in mammals and thus has a dual role in promoting energy intake via appetite regulation in the brain and energy storage/expenditure via direct effects on adipose tissue function. There have been no reports of the effects of NPY on adipose tissue function in any avian species. By exposing chicken preadipocytes to different concentration of NPY, we found that NPY enhances both proliferation and differentiation and thus appears to play a major role in chicken adipogenesis, an effect that has not yet been reported, to our knowledge. In the body weight selected chicken lines, we found that NPY and receptor sub-type expression was elevated in the abdominal fat of chickens from the high body weight chicken line and expression of these genes displayed heterosis in the reciprocal crosses of the parental lines as compared to both the high and low body weight selected lines. Intriguingly, expression of those same genes was greater in the low weight than high weight chickens in the hypothalamus. Hypothalamic transcriptomic profiling revealed that genes involved in serotonergic and dopaminergic systems may also play an important role in both appetite regulation and insulin-regulated energy homeostasis in the body weight chicken lines. Intracerebroventricular injection of serotonin in broiler chicks was associated with a dose and time dependent reduction in food intake that was coupled with the activation of the ventromedial hypothalamus and arcuate nucleus, as determined by c-fos immunoreactivity. The remainder of this dissertation project describes the effects of knocking down expression of a recently discovered transcription factor, ZBED6, on mouse preadipocyte proliferation and differentiation. The dissertation ends with a study using diet-induced porcine prepubertal obesity as a model to examine differences in adipokine gene expression between different fat depots from pigs that consumed diets that differed in carbohydrate composition. Overall, we conclude that both NPY and monoamines such as serotonin and dopamine are of importance in the regulation of energy balance in chickens. Moreover, we propose that NPY is a factor that mediates hypothalamus and adipose tissue crosstalk in chickens. An understanding of this system may provide a new avenue for the treatment of obesity and associated disease complications by re-orchestrating the neuronal outputs or adiposity inputs. This information may also be of value in developing strategies to improve feed conversion and meat yield in commercial broilers.