Maintenance of bone mass requires the integrated activity of osteoclasts (OCs) and osteoblasts (OBs). While they are functionally distinct, both are polarized and execute their activities by regulated secretion of bone-degrading and -synthesizing molecules, respectively. Bone resorption necessitates extracellular proton transport as a result of insertion of the vacuolar H+ATPase into the bone-apposed OC plasma membrane and targeted secretion of the collagenolytic enzyme cathepsin K. Similarly, skeletal synthesis involves secretion of specific matrix proteins such as type 1 collagen onto existing bone surfaces. Thus, the exocytic capacity of bone cells is fundamental to skeletal homeostasis. Regulated secretion, also called exocytosis, requires cell polarity in which intracellular, cargo-containing vesicles are delivered, by organization of the cytoskeleton, to an exocytic plasma membrane domain, which in OCs and OBs is that apposed to bone. Upon arrival at the site of exocytosis, the cargo-containing vesicles fuse with the plasma membrane via a number of linked steps, including high affinity binding of a synaptotagmin, a family of vesicle-associated adaptors, with several plasma membrane-residing proteins. We show data that synaptotagmin VII regulates exocytosis by OCs and OBs in a cell-autonomous manner. In consequence, mice lacking synaptotagmin VII have decreased remodeling and are a model for type II or low turnover osteoporosis. Cell polarity, a pre-requisite for exocytosis, is regulated by a conserved signaling pathway wherein activated cdc42 recruits an atypical protein kinase C, which phosphorylates essential downstream targets, including atypical PKCs such as PKC;. We find that RANKL-mediated organization of the OC cytoskeleton, and the cell's capacity to resorb bone, involve activation of the cdc42/PKC;pathway. Providing additional support for this posture, mice whose OCs express increased levels of active cdc42 are osteoporotic and those lacking the small GTPase have osteopetrosis. Similarly, cell-specific deletion of PKC;generates OCs that fail to polarize or resorb bone. These observations suggest a model in which 1) PKC;, activated by cdc42, promotes OC polarization and 2) following polarization, synaptotagmin VII controls exocytosis of bone- regulating molecules by OCs. Additionally Syt VII regulates OB exocytosis. Hence, our specific aims are to determine the mechanisms by which 1) PKC;signaling promotes OC polarization and 2) synaptotagmin VII controls exocytosis by OCs and OBs.

Public Health Relevance

Maintenance of bone mass requires optimal and coordinated function of the cells regulating this parameter. We have identified novel proteins that individually control bone turnover. We propose to identify the mechanisms by which these two proteins control bone mass, with the view of generating novel drugs to treat diseases such as osteoporosis.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR057037-05
Application #
8493782
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Chen, Faye H
Project Start
2009-06-01
Project End
2014-05-31
Budget Start
2013-06-01
Budget End
2014-05-31
Support Year
5
Fiscal Year
2013
Total Cost
$308,785
Indirect Cost
$105,637
Name
Washington University
Department
Pathology
Type
Schools of Medicine
DUNS #
068552207
City
Saint Louis
State
MO
Country
United States
Zip Code
63130
Su, Xinming; Esser, Alison K; Amend, Sarah R et al. (2016) Antagonizing Integrin β3 Increases Immunosuppression in Cancer. Cancer Res 76:3484-95
Fukunaga, Tomohiro; Zou, Wei; Rohatgi, Nidhi et al. (2015) An insulin-sensitizing thiazolidinedione, which minimally activates PPARγ, does not cause bone loss. J Bone Miner Res 30:481-8
Izawa, Takashi; Rohatgi, Nidhi; Fukunaga, Tomohiro et al. (2015) ASXL2 Regulates Glucose, Lipid, and Skeletal Homeostasis. Cell Rep 11:1625-37
Warren, Julia T; Zou, Wei; Decker, Corinne E et al. (2015) Correlating RANK ligand/RANK binding kinetics with osteoclast formation and function. J Cell Biochem 116:2476-83
Zou, Wei; Teitelbaum, Steven L (2015) Absence of Dap12 and the αvβ3 integrin causes severe osteopetrosis. J Cell Biol 208:125-36
Fukunaga, Tomohiro; Zou, Wei; Warren, Julia T et al. (2014) Vinculin regulates osteoclast function. J Biol Chem 289:13554-64
Zhu, Tingting; Chappel, Jean C; Hsu, Fong-Fu et al. (2013) Type I phosphotidylinosotol 4-phosphate 5-kinase γ regulates osteoclasts in a bifunctional manner. J Biol Chem 288:5268-77
Zou, Wei; Croke, Monica; Fukunaga, Tomohiro et al. (2013) Zap70 inhibits Syk-mediated osteoclast function. J Cell Biochem 114:1871-8
Zou, Wei; Izawa, Takashi; Zhu, Tingting et al. (2013) Talin1 and Rap1 are critical for osteoclast function. Mol Cell Biol 33:830-44
Izawa, Takashi; Zou, Wei; Chappel, Jean C et al. (2012) c-Src links a RANK/ýývýý3 integrin complex to the osteoclast cytoskeleton. Mol Cell Biol 32:2943-53

Showing the most recent 10 out of 23 publications