title: Megakaryocytes are mechanically responsive and influence osteoblast proliferation and differentiation.
abstract: Maintenance of bone mass and geometry is influenced by mechanical stimuli. Paradigms suggest that osteocytes embedded within the mineralized matrix and osteoblasts on the bone surfaces are the primary responders to physical forces. However, other cells within the bone marrow cavity, such as megakaryocytes (MKs), are also subject to mechanical forces. Recent studies have highlighted the potent effects of MKs on osteoblast proliferation as well as bone formation in vivo. We hypothesize that MKs are capable of responding to physical forces and that the interactions between these cells and osteoblasts can be influenced by mechanical stimulation. In this study, we demonstrate that two MK cell lines respond to fluid shear stress in culture. Furthermore, using laser capture microdissection, we isolated MKs from histologic sections of murine tibiae that were exposed to compressive loads in vivo. C-fos, a transcription factor shown to be upregulated in response to load in various tissue types, was increased in MKs from loaded relative to non-loaded limbs at a level comparable to that of osteocytes from the same limbs. We also developed a co-culture system to address whether mechanical stimulation of MKs in culture would impact osteoblast proliferation and differentiation. The presence of MKs in co-culture, but not conditioned media, had dramatic effects on proliferation of preosteoblast MC3T3-E1 cells in culture. Our data suggests a minimal decrease in proliferation as well as an increase in mineralization capacity of osteoblasts co-cultured with MKs exposed to shear compared to co-cultures with unstimulated MKs.
authors.affiliation: Orthopaedic Research Laboratories, University of Michigan, Room 2003 Biomedical Sciences Research Building, 109 Zina Pitcher Place, Ann Arbor, MI 48109, USA.
authors.forename: Constance P
authors.initials: CP
authors.lastname: Soves
authors.affiliation: Orthopaedic Research Laboratories, University of Michigan, Room 2003 Biomedical Sciences Research Building, 109 Zina Pitcher Place, Ann Arbor, MI 48109, USA.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Miller
authors.affiliation: Orthopaedic Research Laboratories, University of Michigan, Room 2003 Biomedical Sciences Research Building, 109 Zina Pitcher Place, Ann Arbor, MI 48109, USA.
authors.forename: Dana L
authors.initials: DL
authors.lastname: Begun
authors.affiliation: Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, 1011 North University Ave., Ann Arbor, MI 48109, USA.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Taichman
authors.affiliation: Department of Clinical Studies-New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Room 145 Myrin Bldg, Kennett Square PA; Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia PA.
authors.forename: Kurt D
authors.initials: KD
authors.lastname: Hankenson
authors.affiliation: Orthopaedic Research Laboratories, University of Michigan, Room 2003 Biomedical Sciences Research Building, 109 Zina Pitcher Place, Ann Arbor, MI 48109, USA. Electronic address: stevegld@umich.edu.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Goldstein
mesh_terms: D000818:Animals; D000880:Anthraquinones / Q000378:metabolism; D001696:Biomechanical Phenomena; D002113:Calcification, Physiologic; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D049109:Cell Proliferation; D018920:Coculture Techniques; D006801:Humans; D020014:K562 Cells; D008533:Megakaryocytes / Q000166:cytology*; D051379:Mice; D042282:Microdissection; D010006:Osteoblasts / Q000166:cytology*; D010011:Osteocytes / Q000166:cytology; D033081:Shear Strength; D013314:Stress, Mechanical; D013977:Tibia / Q000166:cytology / Q000502:physiology; D016474:Weight-Bearing
chemical_list: D000880:Anthraquinones; C010078:alizarin; D002118:Calcium
keywords: Fluid shear; Laser capture microdissection; Mechanotransduction; Megakaryocyte