title: CXCL12/CXCR4 signaling in the osteoblast regulates the mesenchymal stem cell and osteoclast lineage populations.
abstract: The chemokine CXCL12 and its receptor CXCR4 play a key role in regulation of hematopoietic stem cells and cell migratory function during morphogenesis. Osteoblasts express both the ligand and the receptor, but little is known about the role of CXCL12-CXCR4 signaling in maintaining skeletal homeostasis. Using Cre-Lox technology to delete CXCR4 in mature osteoblasts in mice, we show here a significant decrease in bone mass and alterations in cancellous bone structure. CXCR4 gene ablation increased the number of colony-forming units (CFU), CFU-positive for alkaline phosphatase (CFU-AP(+)), and mineralizing nodules in bone marrow stromal cell (BMSC) cultures. The adipocyte precursor population decreased in BMSCs harvested from the KO animals. The nonadherent population of BMSCs harvested from the long bone diaphysis of KO animals formed more osteoclasts, a finding that was associated with increased circulatory levels of pyridinoline, a marker of bone resorption. Our data show that osteoblast-specific CXCR4 deletion has profound effects on the mesenchymal stem cell pool and allocation to the osteoblastic and adipocytic cell lineages. They also show that CXCL12/CXCR4 signaling in the mature osteoblast can feedback to regulate the osteoclast precursor pool size and play a multifunctional role in regulating bone formation and resorption.
authors.affiliation: Division of Endocrinology, Veterans Affairs Medical Center, 4150 Clement St., San Francisco, CA 94123, USA.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shahnazari
authors.forename: Vivian
authors.initials: V
authors.lastname: Chu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Wronski
authors.forename: Robert A
authors.initials: RA
authors.lastname: Nissenson
authors.forename: Bernard P
authors.initials: BP
authors.lastname: Halloran
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002465:Cell Movement / Q000187:drug effects; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000378:metabolism* / Q000494:pharmacology; D005838:Genotype; D007150:Immunohistochemistry; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000235:genetics / Q000378:metabolism*; D055114:X-Ray Microtomography
chemical_list: C514936:CXCR4 protein, mouse; D054377:Chemokine CXCL12; D019718:Receptors, CXCR4
keywords: bone; chemokine; skeletal homeostasis