title: Pro-inflammatory M1 macrophages promote Osteogenesis by mesenchymal stem cells via the COX-2-prostaglandin E2 pathway.
abstract: Bone fractures are among the most common orthopaedic problems that affect individuals of all ages. Immediately after injury, activated macrophages dynamically contribute to and regulate an acute inflammatory response that involves other cells at the injury site, including mesenchymal stem cells (MSCs). These macrophages and MSCs work in concert to modulate bone healing. In this study, we co-cultured undifferentiated M0, pro-inflammatory M1, and anti-inflammatory M2 macrophages with primary murine MSCs in vitro to determine the cross-talk between polarized macrophages and MSCs and their effects on osteogenesis. After 4 weeks of co-culture, MSCs grown with macrophages, especially M1 macrophages, had enhanced bone mineralization compared to MSCs grown alone. The level of bone formation after 4 weeks of culture was closely associated with prostaglandin E2 (PGE2) secretion early in osteogenesis. Treatment with celecoxib, a cyclooxygenase-2 (COX-2) selective inhibitor, significantly reduced bone mineralization in all co-cultures but most dramatically in the M1-MSC co-culture. We also found that the presence of macrophages reduced the secretion of osteoprotegerin (OPG), the decoy RANKL receptor, suggesting that macrophages may indirectly modulate osteoclast activity in addition to enhancing bone formation. Taken together, these findings suggest that an initial pro-inflammatory phase modulated by M1 macrophages promotes osteogenesis in MSCs via the COX-2-PGE2 pathway. Understanding the complex interactions between macrophages and MSCs provide opportunities to optimize bone healing and other regenerative processes via modulation of the inflammatory response. This study provides one possible biological mechanism for the adverse effects of non-steroidal anti-inflammatory drugs on fracture healing and bone regeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2378-2385, 2017.
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Laura Y
authors.initials: LY
authors.lastname: Lu
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Florence
authors.initials: F
authors.lastname: Loi
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Karthik
authors.initials: K
authors.lastname: Nathan
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Tzu-Hua
authors.initials: TH
authors.lastname: Lin
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Jukka
authors.initials: J
authors.lastname: Pajarinen
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.|Laboratoire de Biomécanique et Biomatériaux Ostéo-Articulaires - UMR CNRS 7052, Faculté de Médecine - Université Paris7, Paris, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Gibon
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Akira
authors.initials: A
authors.lastname: Nabeshima
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.|Department of Oral and Maxillofacial Surgery, University of Chile, Santiago, Chile.
authors.forename: Luis
authors.initials: L
authors.lastname: Cordova
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.|Department of Medicine, Clinicum, University of Helsinki, and Helsinki University Hospital, Helsinki, Finland.
authors.forename: Eemeli
authors.initials: E
authors.lastname: Jämsen
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Yao
authors.affiliation: Department of Orthopaedic Surgery, Stanford University, Stanford, California.|Department of Bioengineering, Stanford University, Stanford, California.
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Goodman
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002113:Calcification, Physiologic; D018920:Coculture Techniques; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D015232:Dinoprostone / Q000378:metabolism*; D008264:Macrophages / Q000502:physiology*; D008297:Male; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D051379:Mice; D010012:Osteogenesis; D053244:Osteoprotegerin / Q000378:metabolism; D061251:Primary Cell Culture; D020239:Receptor Cross-Talk
chemical_list: D053244:Osteoprotegerin; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D000469:Alkaline Phosphatase; D015232:Dinoprostone
keywords: fracture healing; mesenchymal stem cells; osteogenesis; polarized macrophages