title: Acute skeletal injury is necessary for human adipose-derived stromal cell-mediated calvarial regeneration.
abstract: BACKGROUND
  Studies have demonstrated that human adipose-derived stromal cells (ASCs) are able to repair acute calvarial injuries. The more clinically relevant repair of an established skeletal defect, however, has not been addressed. The authors sought to determine whether human ASCs could heal chronic (established) calvarial defects.
  
  
  METHODS
  Critical-sized (4 mm) mouse parietal defects were created. Human ASCs were engrafted either immediately postoperatively (acute defect) or 8 weeks following defect creation (established defect). Methods of analysis included microcomputer tomography scans, histology, and in situ hybridization. Finally, human ASCs were treated in vitro with platelet-rich plasma to simulate an acute wound environment; proliferation and osteogenic differentiation were assessed (alkaline phosphatase, alizarin red, and quantitative reverse transcriptase polymerase chain reaction).
  
  
  RESULTS
  Nearly complete osseous healing was observed when calvarial defects were immediately engrafted with human ASCs. In contrast, when human ASCs were engrafted into established defects, little bone formation occurred. Histological analysis affirmed findings by microcomputer tomography, showing more robust staining for alkaline phosphatase and picrosirius red in an acute than in an established human ASC-engrafted defect. In situ hybridization and quantitative reverse transcriptase polymerase chain reaction showed an increase in bone morphogenetic protein (BMP) expression (BMP-2, BMP-4, and BMP-7) acutely following calvarial defect creation. Finally, in vitro treatment of human ASCs with platelet-rich plasma enhanced osteogenic differentiation and increased BMP-2 expression.
  
  
  CONCLUSIONS
  Although human ASCs can be utilized to heal an acute mouse calvarial defect, they do not enhance healing of an established (or chronic) defect. Endogenous BMP signaling activated after injury may explain these differences in healing. Platelet-rich plasma enhances osteogenic differentiation of human ASCs in vitro and may prove a promising therapy for future skeletal tissue engineering efforts.
authors.affiliation: Stanford and Los Angeles, Calif. From the Hagey Laboratory for Pediatric Regenerative Medicine, Department of Surgery, Plastic and Reconstructive Surgery Division, Stanford University School of Medicine; Division of Advanced Prosthodontics, Biomaterials, and Hospital Dentistry, University of California, Los Angeles, School of Dentistry; and Department of Bioengineering, University of California, Los Angeles, Engineering and Applied Sciences.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Levi
authors.forename: Aaron W
authors.initials: AW
authors.lastname: James
authors.forename: Emily R
authors.initials: ER
authors.lastname: Nelson
authors.forename: Michelle
authors.initials: M
authors.lastname: Peng
authors.forename: Derrick C
authors.initials: DC
authors.lastname: Wan
authors.forename: George W
authors.initials: GW
authors.lastname: Commons
authors.forename: Min
authors.initials: M
authors.lastname: Lee
authors.forename: Benjamin
authors.initials: B
authors.lastname: Wu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Longaker
mesh_terms: D000273:Adipose Tissue / Q000166:cytology*; D000818:Animals; D049109:Cell Proliferation; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008875:Middle Aged; D010012:Osteogenesis / Q000502:physiology*; D010294:Parietal Bone / Q000293:injuries / Q000601:surgery*; D019651:Plastic Surgery Procedures / Q000379:methods*; D012887:Skull Fractures / Q000601:surgery*; D033581:Stem Cell Transplantation / Q000379:methods*; D017154:Stromal Cells / Q000166:cytology*