Molecular, immunohistochemical and functional characterization of the vertebrate hormones, nesfatin-1 and peptide YY

The endocrine system is composed of neurons and specialized secretory cells which provide efficient communication through the secretion of a multitude of different chemical messengers. Amino-acid linked chains, known as peptides, are among the most diverse group of these intercellular chemical messengers. In most multicellular eukaryotic organisms, including fish and mammals, peptides are crucial to the regulation and integration of the nervous system and organs. This thesis furthers our understanding of the appetite regulatory peptide hormones peptide YY (PYY) and nesfatin-1. This work presents the first examination of the composition, distribution and physiological role of NUCB2/nesfatin-1 and the first functional studies of PYY and dipeptidyl peptidase-4 (DPP4) in a non-mammalian vertebrate. Both NUCB2 and PYY mRNA are abundantly expressed centrally within the brain, digestive organs and reproductive system. This research indicates that both appetite regulatory peptides are nutrient responsive. In addition, nesfatin-1-like immunoreactivity (IR) was prominent in the hypothalamus, pituitary and gastrointestinal tract. Furthermore, intraperitoneal and intracerebroventricular injections of nesfatin-1 and PYY provide the first evidence that nesfatin-1 and PYY are anorexigenic peptides in goldfish. In addition, this thesis provides evidence indicating that nesfatin-1 mediates hypophysiotropic regulation of LH and GH secretion in vivo. In rodents, nesfatin-1 is a recently discovered multifunctional metabolic hormone abundantly expressed in the pancreatic islets. This work identifies the effects of nesfatin-1 on insulin secretion, glucose utilization and whole-body energy homeostasis in rodents. These studies are the first to characterize the co-localization of nesfatin-1 IR with insulin within the pancreatic islets of C57BL/6 mice and Fischer 344 rats. In addition, these studies show a direct effect of nesfatin-1 on insulin secretion in vitro using mouse insulinoma cells, and with isolated islets from C57BL/6 mice as well as Fischer 344 rats. Combining gene expression and immunohistochemical morphological analysis this thesis unveils that endogenous pancreatic islet nesfatin-l-IR is altered in diabetes and diet induced obesity. Furthermore, nesfatin-1 was found to inhibit insulin-mediated glucose uptake in L6 skeletal muscle cells, while stimulating glucose uptake in primary adipocytes from rats. Nesfatin-1 increased spontaneous physical activity and whole-body fat oxidation, but reduced cumulative food intake. Collectively, this work indicates that glucose responsive nesfatin-1 regulates insulin secretion, glucose homeostasis and whole-body energy balance in rats. Furthermore, both nesfatin-1 and PYY are nutrient responsive hormones with multiple neuroendocrine and metabolic effects in vertebrates.