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Rac-GTPase, osteoclast cytoskeleton and bone resorption
S Razzouk1, M Lieberherr, G Cournot
1CNRS-UPR 1524, INRA-LNSA-Bât 221, Jouy en Josas/France.
European Journal of Cell Biology
|June 1, 1999
Summary
Rac-GTPases (Rac1 and Rac2) and PAK1 kinase regulate osteoclast cytoskeleton and bone resorption. These proteins influence actin organization and resorptive activity but not NADPH diaphorase activity in rat osteoclasts.
Area of Science:
- Cell Biology
- Biochemistry
- Bone Biology
Background:
- Rho-GTPases, including Rac1 and Rac2, are key regulators of cytoskeleton organization and are targets of p21-activated kinases (PAKs).
- Rac1 and Rac2 are integral components of NADPH oxidase, an enzyme generating free radicals, which can influence bone resorption.
- Osteoclast cytoskeleton organization is critical for bone adhesion and resorption, and these cells exhibit NADPH diaphorase activity.
Purpose of the Study:
- To investigate the role of Rac1, Rac2, and PAK1 in regulating the cytoskeleton, resorptive activity, and NADPH diaphorase activity of rat osteoclasts.
- To determine if Rac-GTPases and PAK1 influence actin organization and bone resorption by osteoclasts.
Main Methods:
- Disaggregated rat osteoclasts were permeabilized with saponin.
- Specific antibodies against Rac1, Rac2, and PAK1 were introduced to assess their effects.
- Actin organization was visualized using Rhodamine-phalloidin staining.
- Osteoclast resorptive activity was quantified using the bone-slice method.
Main Results:
- Incubation with anti-Rac antibodies induced dose- and time-dependent alterations in osteoclast cytoskeleton, including cell rounding, retraction fiber formation, disruption of actin rings, and peripheral actin dots.
- Anti-PAK1 antibody treatment resulted in similar cytoskeletal changes.
- Osteoclast resorptive activity was significantly reduced following treatment with anti-Rac or anti-PAK1 antibodies, evidenced by decreased total resorbed area and mean pit area.
- None of the tested antibodies affected the NADPH diaphorase activity of the osteoclasts.
Conclusions:
- Rac-GTPases (Rac1 and Rac2) are present in rat osteoclasts and play a crucial role in organizing the actin cytoskeleton.
- These GTPases are involved in regulating osteoclast resorptive activity, potentially through mediation by PAK1 kinase.
- The study found no evidence that Rac-GTPases or PAK1 influence osteoclast NADPH diaphorase activity.