Submitted on May 12, 2006
Accepted on November 21, 2006
ATP Reduces Gel Compaction in Osteoblast-Populated Collagen Gels
Jie Qi1, Liqun Chi2, James E. Faber3, Beverly H. Koller4, and Albert J Banes1*
1 Flexcell International Corporation, Hillsborough, North Carolina, United States; Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North carolina State University, Chapel Hill, North Carolina, United States
2 Flexcell International Corporation, Hillsborough, North Carolina, United States
3 Department of Physiology, University of North Carolina, Chapel Hill,, North Carolina, United States
4 Genetics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
* To whom correspondence should be addressed. E-mail: ajbvault{at}med.unc.edu.
Bone remodeling is a localized process, but regulated by systemic signals such as hormones, cytokines and mechanical loading. The mechanism by which bone cells convert these systemic signals into local signals is not completely understood. It is broadly accepted that the "prestress" in cytoskeleton of cells affects the magnitude of cellular response to mechanical stimuli. Prestress derives from stiff cytoskeletal proteins and their connections within the cell and from cell contractility upon attaching to matrix. In an in vitro model of three dimensional gel compaction, the relative cellular prestress levels in the same matrix environment were determined by matrix compaction rate: a greater compaction rate resulted in a higher level of prestress. In the present study, the effects of ATP on the prestress of osteoblasts were studied using mouse MC3T3-E1 cells grown in 3D, bioartificial tissues (BATs). ATP (
100 µM) reduced the compaction rate of BATs in a dose-dependent manner. ADP, BzBzATP and UTP, but not 
, 
-methylene ATP, also reduced the compaction rate, but to a lesser extent. PPADS did not block the effect of ATP on BAT compaction rate. These results indicate that both P2X and P2Y receptors are involved in ATP-induced reduction of BAT compaction rate. Steady fluid flow and RT-PCR results showed that ATP reduced cell attachment on type I collagen by down-regulating the expression of integrin 1. These results suggest a potential role for P2 receptors in matrix remodeling and repair and as a potential drug target in the treatment of bone diseases.
