title: Osteoblast-derived FGF9 regulates skeletal homeostasis.
abstract: FGF9 has complex and important roles in skeletal development and repair. We have previously observed that Fgf9 expression in osteoblasts (OBs) is regulated by G protein signaling and therefore the present study was done to determine whether OB-derived FGF9 was important in skeletal homeostasis. To directly test this idea, we deleted functional expression of Fgf9 gene in OBs using a 2.3kb collagen type I promoter-driven Cre transgenic mouse line (Fgf9OB-/-). Both Fgf9 knockout (Fgf9OB-/-) and the Fgf9 floxed littermates (Fgf9fl/fl) mice were fully backcrossed and maintained in an FBV/N background. Three month old Fgf9OB-/-mice displayed a significant decrease in cancellous bone and bone formation in the distal femur and a significant decrease in cortical thickness at the TFJ. Strikingly, female Fgf9OB-/-mice did not display altered bone mass. Continuous treatment of mouse BMSCs with exogenous FGF9 inhibited mouse BMSC mineralization while acute treatment increased the proliferation of progenitors, an effect requiring the activation of Akt1. Our results suggest that mature OBs are an important source of FGF9, positively regulating skeletal homeostasis in male mice. Osteoblast-derived FGF9 may serve a paracrine role to maintain the osteogenic progenitor cell population through activation of Akt signaling.
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA; Department of Medicine, University of California, San Francisco, CA, USA.
authors.forename: Liping
authors.initials: L
authors.lastname: Wang
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA.
authors.forename: Theresa
authors.initials: T
authors.lastname: Roth
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA.
authors.forename: Marcia
authors.initials: M
authors.lastname: Abbott
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA.
authors.forename: Linh
authors.initials: L
authors.lastname: Ho
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA; Division of Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Thai Red Cross Society, Bangkok, Thailand; King Chulalongkorn Memorial Hospital, Bangkok, Thailand.
authors.forename: Lalita
authors.initials: L
authors.lastname: Wattanachanya
authors.affiliation: Endocrine Unit, VA Medical Center, San Francisco, CA, USA; Department of Medicine, University of California, San Francisco, CA, USA. Electronic address: Robert.Nissenson@ucsf.edu.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Nissenson
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D005260:Female; D051525:Fibroblast Growth Factor 9 / Q000172:deficiency / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology*; D015151:Immunoblotting; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis / Q000502:physiology*; D016133:Polymerase Chain Reaction; D055114:X-Ray Microtomography
chemical_list: C496460:Fgf9 protein, mouse; D051525:Fibroblast Growth Factor 9
keywords: Akt; Bone formation; FGF9; Osteoblasts; Stem cells