Pyk2 regulates megakaryocyte-induced increases in osteoblast number and bone formation.
Preclinical and clinical evidence from megakaryocyte (MK)-related diseases suggests that MKs play a significant role in maintaining bone homeostasis. Findings from our laboratories reveal that MKs significantly increase osteoblast (OB) number through direct MK-OB contact and the activation of integrins. We, therefore, examined the role of Pyk2, a tyrosine kinase known to be regulated downstream of integrins, in the MK-mediated enhancement of OBs. When OBs were co-cultured with MKs, total Pyk2 levels in OBs were significantly enhanced primarily because of increased Pyk2 gene transcription. Additionally, p53 and Mdm2 were both decreased in OBs upon MK stimulation, which would be permissive of cell cycle entry. We then demonstrated that OB number was markedly reduced when Pyk2-/- OBs, as opposed to wild-type (WT) OBs, were co-cultured with MKs. We also determined that MKs inhibit OB differentiation in the presence and absence of Pyk2 expression. Finally, given that MK-replete spleen cells from GATA-1-deficient mice can robustly stimulate OB proliferation and bone formation in WT mice, we adoptively transferred spleen cells from these mice into Pyk2-/- recipient mice. Importantly, GATA-1-deficient spleen cells failed to stimulate an increase in bone formation in Pyk2-/- mice, suggesting in vivo the important role of Pyk2 in the MK-induced increase in bone volume. Further understanding of the signaling pathways involved in the MK-mediated enhancement of OB number and bone formation will facilitate the development of novel anabolic therapies to treat bone loss diseases.
Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA.
Ying-Hua
YH
Cheng
R Adam
RA
Hooker
Khanh
K
Nguyen
Rita
R
Gerard-O'Riley
David L
DL
Waning
Brahmananda R
BR
Chitteti
Tomas E
TE
Meijome
Hui Lin
HL
Chua
Artur P
AP
Plett
Christie M
CM
Orschell
Edward F
EF
Srour
Lindsey D
LD
Mayo
Fredrick M
FM
Pavalko
Angela
A
Bruzzaniti
Melissa A
MA
Kacena
D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D051418:Focal Adhesion Kinase 2 / Q000235:genetics / Q000378:metabolism*; D008533:Megakaryocytes / Q000166:cytology / Q000201:enzymology*; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts / Q000166:cytology / Q000201:enzymology*; D010012:Osteogenesis / Q000502:physiology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
D016159:Tumor Suppressor Protein p53; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D051418:Focal Adhesion Kinase 2; C496053:Ptk2b protein, mouse