Osteoporosis is a growing health concern, characterised by deterioration of bone and increased fracture incidence. Anabolic treatments for reversing bone loss are presently limited. A bone anabolic response was recently reported following deletion of hypothalamic neuropeptide Y2 receptors in mice. In contrast, no discernable bone phenotype was observed in Y4 receptor knockout (Y4-/-) mice, revealing specificity between the Y receptors in their control of bone formation. Studies in this thesis revealed a second anabolic response in the absence of another Y receptor subtype; the Y1 receptor. The potential interaction between the Y1 and Y2- anabolic pathways with each other and with Y4 was investigated through the generation of mouse models lacking multiple Y receptor subtypes. Interestingly, no synergistic elevation in bone volume was observed in Y1-/-Y2-/- double knockout mice, indicative of shared mechanisms of action. In contrast, the synergistic elevation in bone volume of male Y2-/- Y4-/- mice was likely due to additive effects of leptin signalling. Consequentially, potential interaction between Y receptors and leptin was investigated by crossing the Y receptor knockouts onto the leptin deficient ob/ob background, revealing differential responses of the Y receptor pathways to leptin deficiency, with the anabolic response of the Y2-/- model retained in Y2-/-/ob mice but abolished in Y1-/-/ob mice compared to Y1-/-. Differential responses of these two pathways were also revealed following gonadectomy of Y1-/- and Y2-/- mice. Importantly, these studies also demonstrated the ability of the central Y2- anabolic pathway to halt gonadectomy-induced bone loss. Interestingly, cultured stromal cells from germline Y2-/- mice exhibited an enhanced ability to undergo mineralisation and adipocyte differentiation, associated with a greater number of mesenchymal progenitor cells present within the bone of Y2-/- mice, suggesting a potential mechanism for the greater mineralisation of the Y2-/- model in vitro and in vivo. Y1 receptor expression was also detected in stromal cells from wild type mice, but was nearly abolished in Y2-/- mice. Together these findings demonstrate an important therapeutic potential for these pathways in the treatment of osteoporosis and indicate that modulation of Y receptor signalling within the bone microenvironment may alter proportions of mesenchymal progenitor populations with effects on bone formation.

In the heart, neuropeptide Y (NPY) released during stimulation of the sympathetic nerve attenuates vagal-evoked bradycardia for a prolonged period. The inhibitory action of NPY is proposed as being Y2 receptor mediated. In rat and mouse, anaesthetised with sodium pentobarbitone, the selective Y2 receptor antagonist BIIE0246 reduced the inhibition of cardiac vagal activity evoked by a Y2 agonist, N-acetyl [Leu28, 31] NPY 24-36. BIIE0246 also reduced the inhibitory effect on vagal action evoked by stimulation of the sympathetic nerve. Deletion of the receptor in Y2 receptor-knockout mice abolished all NPY mediated inhibition of cardiac vagal-evoked bradycardia. These findings strongly support the proposal that NPY released during stimulation of the sympathetic nerve acts via Y2 receptors on the vagus nerve to decrease the slowing effect on the heart evoked by vagal stimulation. Examination of the structural components within NPY, using NPY, related PP peptides and structurally altered analogs, showed proline residues in the N-terminal polyproline region of NPY were found to influence the level of presynaptic activity while residues in the PP fold region further enhanced activity. NPY fragments, as long or longer than 3-36 NPY, possessed full inhibitory activity whereas short C-terminal analogs, such as 24-36 did not. The two leucine residues in agonist N-acetyl [Leu28, 31] NPY 24-36 was found to alter the structure and enhance the amphipathic nature of the a-helix in the shortened fragment. Arginine residues in the helix were also found to be important for activity. The leucine residues in N-acetyl [Leu28, 31] NPY 24-36 are proposed to stabilise the molecule producing an over all linear conformation. Although the conformation adopted by NPY at the receptor is unknown, it is plausible to suggest that the interaction between the proline residues and the a-helix stabilise the molecule in the same way that leucine substitution does in N-acetyl [Leu28, 31] NPY 24-36. Results obtained in Y2 receptor-knockout mice infer by their faster heart rates, an inhibitory role for the receptor in regions of the brain able to effect sympathetic outflow to the heart. Therefore knowledge of the structural requirements required of agonists and antagonists for Y2 receptor activation is likely to be of practical significance in drug design for the treatment of diseases affecting both parasympathetic and sympathetic innervation of the heart.

Thesis (M.S.)--Case Western Reserve University, 2008. / [School of Medicine] Department of Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of New South Wales, 2003. / Also available online.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [56]-65).

published_or_final_version / abstract / Medicine / Master / Master of Philosophy

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.