Novel Role of Y1 Receptors in the Coordinated Regulation of Bone and Energy Homeostasis

Amanda Sainsbury,Shu Lin,Ronaldo F Enriquez,En-Ju D Lin,John A Eisman,Matthew J During,Michelle M Mcdonald,Edith M Gardiner,Nicola J Lee,Herbert Herzog,Pernilla Lundberg,Lei Zhang,Susan J Allison,David G Little,Paul A Baldock,Katy Slack,Ernie Yulyaningsih

doi:10.1074/jbc.m700644200

Abstract

The importance of neuropeptide Y (NPY) and Y2 receptors in the regulation of bone and energy homeostasis has recently been demonstrated. However, the contributions of the other Y receptors are less clear. Here we show that Y1 receptors are expressed on osteoblastic cells. Moreover, bone and adipose tissue mass are elevated in Y1(-/-) mice with a generalized increase in bone formation on cortical and cancellous surfaces. Importantly, the inhibitory effects of NPY on bone marrow stromal cells in vitro are absent in cells derived from Y1(-/-) mice, indicating a direct action of NPY on bone cells via this Y receptor. Interestingly, in contrast to Y2 receptor or germ line Y1 receptor deletion, conditional deletion of hypothalamic Y1 receptors in adult mice did not alter bone homeostasis, food intake, or adiposity. Furthermore, deletion of both Y1 and Y2 receptors did not produce additive effects in bone or adiposity. Thus Y1 receptor pathways act powerfully to inhibit bone production and adiposity by nonhypothalamic pathways, with potentially direct effects on bone tissue through a single pathway with Y2 receptors.

Highlights

The Y receptor system is complex, consisting of five Y receptors (Y1, Y2, Y4, Y5, and y6), each with varying distributions across peripheral and central tissues, including the hypothalamus
Given the clear involvement of Y1 receptors in the regulation of energy homeostasis as well as new evidence of a putative role for Y1 receptors on osteoblast-like cells, we investigated the effect of germ line and conditional deletion of Y1 receptors in mice
Similar to Y2Ϫ/Ϫ mice, bone formation rate was greater in Y1Ϫ/Ϫ mice compared with wild-type mice with enhanced mineral apposition rate (MAR) in both sexes, but no change in mineralizing surface (Fig. 2)

Summary

EXPERIMENTAL PROCEDURES

Animal Care—All research and animal care procedures were approved by the Garvan Institute/St. Generation of Y1Ϫ/Ϫ and Y1Ϫ/ϪY2Ϫ/Ϫ Double Mutant Mice —A targeting vector for the Y1 and Y2 receptor genes (Npy1r and Npy2r, respectively) has been used to produce both germ line (Y1Ϫ/Ϫ or Y2Ϫ/Ϫ) and conditional (floxed, Y1lox/lox or Y2lox/lox) knock-out mice, as previously published [2, 14]. Injection with adeno-associated viral vector (rAAV) expressing Cre-recombinase produced hypothalamus-specific Y1 receptor knock-out mice (Y1Hyp). Gene Expression in Mouse Calvarial Osteoblast Cultures— Bone cells were isolated from calvariae of 2- to 3-day-old CsA mice using a modified time sequential enzyme-digestion technique [19]. Isolation and Culture of Bone Marrow Stromal Cells—Bone marrow stromal cells were isolated from 5- to 9-week-old male wild-type and germ line Y1Ϫ/Ϫ mice as previously described (see accompanying report [39]).

RESULTS

89 Ϯ 6 97 Ϯ 13

DISCUSSION