title: Pregnane X receptor knockout mice display osteopenia with reduced bone formation and enhanced bone resorption.
abstract: The steroid and xenobiotic receptor (SXR) and its murine ortholog pregnane X receptor (PXR) are nuclear receptors that are expressed mainly in the liver and intestine where they function as xenobiotic sensors. In addition to its role as a xenobiotic sensor, previous studies in our laboratories and elsewhere have identified a role for SXR/PXR as a mediator of bone homeostasis. Here, we report that systemic deletion of PXR results in marked osteopenia with mechanical fragility in female mice as young as 4 months old. Bone mineral density (BMD) of PXR knockout (PXRKO) mice was significantly decreased compared with the BMD of wild-type (WT) mice. Micro-computed tomography analysis of femoral trabecular bones revealed that the three-dimensional bone volume fraction of PXRKO mice was markedly reduced compared with that of WT mice. Histomorphometrical analysis of the trabecular bones in the proximal tibia showed a remarkable reduction in bone mass in PXRKO mice. As for bone turnover of the trabecular bones, bone formation is reduced, whereas bone resorption is enhanced in PXRKO mice. Histomorphometrical analysis of femoral cortical bones revealed a larger cortical area in WT mice than that in PXRKO mice. WT mice had a thicker cortical width than PXRKO mice. Three-point bending test revealed that these morphological phenotypes actually caused mechanical fragility. Lastly, serum levels of phosphate, calcium, and alkaline phosphatase were unchanged in PXRKO mice compared with WT. Consistent with our previous results, we conclude that SXR/PXR promotes bone formation and suppresses bone resorption thus cementing a role for SXR/PXR as a key regulator of bone homeostasis.
authors.affiliation: Department of Geriatric Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Azuma
authors.forename: Stephanie C
authors.initials: SC
authors.lastname: Casey
authors.forename: Masako
authors.initials: M
authors.lastname: Ito
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Urano
authors.forename: Kuniko
authors.initials: K
authors.lastname: Horie
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Ouchi
authors.forename: Séverine
authors.initials: S
authors.lastname: Kirchner
authors.forename: Bruce
authors.initials: B
authors.lastname: Blumberg
authors.forename: Satoshi
authors.initials: S
authors.lastname: Inoue
mesh_terms: D000469:Alkaline Phosphatase / Q000097:blood; D000818:Animals; D015519:Bone Density / Q000235:genetics; D001851:Bone Diseases, Metabolic / Q000000981:diagnostic imaging / Q000235:genetics* / Q000473:pathology; D001862:Bone Resorption / Q000235:genetics*; D002118:Calcium / Q000097:blood; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging; D006706:Homeostasis / Q000502:physiology; D051379:Mice; D057507:Mice, 129 Strain; D018345:Mice, Knockout; D010012:Osteogenesis / Q000235:genetics*; D010710:Phosphates / Q000097:blood; D000077297:Pregnane X Receptor; D011859:Radiography; D011987:Receptors, Steroid / Q000235:genetics* / Q000502:physiology
chemical_list: D010710:Phosphates; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D000469:Alkaline Phosphatase; D002118:Calcium