title: Disruption of Kif3a in osteoblasts results in defective bone formation and osteopenia.
abstract: We investigated whether Kif3a in osteoblasts has a direct role in regulating postnatal bone formation. We conditionally deleted Kif3a in osteoblasts by crossing osteocalcin (Oc; also known as Bglap)-Cre with Kif3a(flox/null) mice. Conditional Kif3a-null mice (Kif3a(Oc-cKO)) had a 75% reduction in Kif3a transcripts in bone and osteoblasts. Conditional deletion of Kif3a resulted in the reduction of primary cilia number by 51% and length by 27% in osteoblasts. Kif3a(Oc-cKO) mice developed osteopenia by 6 weeks of age unlike Kif3a(flox/+) control mice, as evidenced by reductions in femoral bone mineral density (22%), trabecular bone volume (42%) and cortical thickness (17%). By contrast, Oc-Cre;Kif3a(flox/+) and Kif3a(flox/null) heterozygous mice exhibited no skeletal abnormalities. Loss of bone mass in Kif3a(Oc-cKO) mice was associated with impaired osteoblast function in vivo, as reflected by a 54% reduction in mineral apposition rate and decreased expression of Runx2, osterix (also known as Sp7 transcription factor 7; Sp7), osteocalcin and Dmp1 compared with controls. Immortalized osteoblasts from Kif3a(Oc-cKO) mice exhibited increased cell proliferation, impaired osteoblastic differentiation, and enhanced adipogenesis in vitro. Osteoblasts derived from Kif3a(Oc-cKO) mice also had lower basal cytosolic calcium levels and impaired intracellular calcium responses to fluid flow shear stress. Sonic hedgehog-mediated Gli2 expression and Wnt3a-mediated β-catenin and Axin2 expression were also attenuated in Kif3a(Oc-cKO) bone and osteoblast cultures. These data indicate that selective deletion of Kif3a in osteoblasts disrupts primary cilia formation and/or function and impairs osteoblast-mediated bone formation through multiple pathways including intracellular calcium, hedgehog and Wnt signaling.
authors.affiliation: Department of Medicine, the University of Tennessee Health Science Center, Memphis, TN 38165, USA.
authors.forename: Ni
authors.initials: N
authors.lastname: Qiu
authors.forename: Zhousheng
authors.initials: Z
authors.lastname: Xiao
authors.forename: Li
authors.initials: L
authors.lastname: Cao
authors.forename: Meagan M
authors.initials: MM
authors.lastname: Buechel
authors.forename: Valentin
authors.initials: V
authors.lastname: David
authors.forename: Esra
authors.initials: E
authors.lastname: Roan
authors.forename: L Darryl
authors.initials: LD
authors.lastname: Quarles
mesh_terms: D000818:Animals; D001851:Bone Diseases, Metabolic / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D002454:Cell Differentiation; D005260:Female; D020868:Gene Silencing; D006801:Humans; D016547:Kinesins / Q000235:genetics* / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis
chemical_list: C490202:Kif3a protein, mouse; D016547:Kinesins