The immunomodulatory adapter proteins DAP12 and Fc receptor gamma-chain (FcRgamma) regulate development of functional osteoclasts through the Syk tyrosine kinase.
Osteoclasts, the only bone-resorbing cells, are central to the pathogenesis of osteoporosis, yet their development and regulation are incompletely understood. Multiple receptors of the immune system use a common signaling paradigm whereby phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) within receptor-associated adapter proteins recruit the Syk tyrosine kinase. Here we demonstrate that a similar mechanism is required for development of functional osteoclasts. Mice lacking two ITAM-bearing adapters, DAP12 and the Fc receptor gamma-chain (FcRgamma), are severely osteopetrotic. DAP12(-/-)FcRgamma(-/-) bone marrow cells fail to differentiate into multinucleated osteoclasts or resorb bone in vitro and show impaired phosphorylation of the Syk tyrosine kinase. syk(-/-) progenitors are similarly defective in osteoclast development and bone resorption. Intact SH2-domains of Syk, introduced by retroviral transduction, are required for functional reconstitution of syk(-/-) osteoclasts, whereas intact ITAM-domains on DAP12 are required for reconstitution of DAP12(-/-) FcRgamma(-/-) cells. These data indicate that recruitment of Syk to phosphorylated ITAMs is critical for osteoclastogenesis. Although DAP12 appears to be primarily responsible for osteoclast differentiation in cultures directly stimulated with macrophage-colony stimulating factor and receptor activator of NF-kappaB ligand cytokines, DAP12 and FcRgamma have overlapping roles in supporting osteoclast development in osteoblast-osteoclast cocultures, which mirrors their overlapping functions in vivo. These results provide new insight into the biology of osteoclasts and suggest novel therapeutic targets in diseases of bony remodeling.
Mócsai
Attila
A
Department of Laboratory Medicine, University of California, San Francisco, CA 94143, USA.
Humphrey
Mary Beth
MB
Van Ziffle
Jessica A G
JA
Hu
Yongmei
Y
Burghardt
Andrew
A
Spusta
Steven C
SC
Majumdar
Sharmila
S
Lanier
Lewis L
LL
Lowell
Clifford A
CA
Nakamura
Mary C
MC
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western; D001862:Bone Resorption; D018920:Coculture Techniques; D004792:Enzyme Precursors / Q000378:metabolism / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D016173:Macrophage Colony-Stimulating Factor / Q000008:administration & dosage; D051379:Mice; D010006:Osteoblasts / Q000166:cytology*; D010022:Osteopetrosis / Q000235:genetics; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology*; D011961:Receptors, Fc / Q000235:genetics / Q000502:physiology*; D011971:Receptors, Immunologic / Q000235:genetics / Q000502:physiology*; D000072377:Syk Kinase
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D011961:Receptors, Fc; D011971:Receptors, Immunologic; C484963:Tyrobp protein, mouse; D016173:Macrophage Colony-Stimulating Factor; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse