Acute phosphate restriction leads to impaired fracture healing and resistance to BMP-2.
Hypophosphatemia leads to rickets and osteomalacia, the latter of which results in decreased biomechanical integrity of bones, accompanied by poor fracture healing. Impaired phosphate-dependent apoptosis of hypertrophic chondrocytes is the molecular basis for rickets. However, the underlying pathophysiology of impaired fracture healing has not been characterized previously. To address the role of phosphate in fracture repair, mice were placed on a phosphate-restricted diet 2 days prior to or 3 days after induction of a mid-diaphyseal femoral fracture to assess the effects of phosphate deficiency on the initial recruitment of mesenchymal stem cells and their subsequent differentiation. Histologic and micro-computed tomographic (microCT) analyses demonstrated that both phosphate restriction models dramatically impaired fracture healing primarily owing to a defect in differentiation along the chondrogenic lineage. Based on Sox9 and Sox5 mRNA levels, neither the initial recruitment of cells to the callus nor their lineage commitment was effected by hypophosphatemia. However, differentiation of these cells was impaired in association with impaired bone morphogenetic protein (BMP) signaling. In vivo ectopic bone-formation assays and in vitro investigations in ST2 stromal cells confirmed that phosphate restriction leads to BMP-2 resistance. Marrow ablation studies demonstrate that hypophosphatemia has different effects on injury-induced intramembranous bone formation compared with endochondral bone formation. Thus phosphate plays an important role in the skeleton that extends beyond mineralized matrix formation and growth plate maturation and is critical for endochondral bone repair.
Wigner
Nathan A
NA
Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Boston University Medical Center, Boston, MA, USA.
Luderer
Hilary F
HF
Cox
Megan K
MK
Sooy
Karen
K
Gerstenfeld
Louis C
LC
Demay
Marie B
MB
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D002146:Bony Callus / Q000378:metabolism; D002454:Cell Differentiation; D002465:Cell Movement; D004032:Diet; D005269:Femur / Q000293:injuries*; D017102:Fracture Healing; D050723:Fractures, Bone / Q000378:metabolism*; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010710:Phosphates / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D055758:SOX9 Transcription Factor / Q000032:analysis; D055755:SOXD Transcription Factors / Q000032:analysis
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D010710:Phosphates; D012333:RNA, Messenger; D055758:SOX9 Transcription Factor; D055755:SOXD Transcription Factors; C089186:Sox5 protein, mouse; C527933:Sox9 protein, mouse