Filamin A regulates monocyte migration through Rho small GTPases during osteoclastogenesis
Bibliographic record
Abstract
Osteoclastogenesis (OCG) results from the fusion of monocytes after stimulation with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kappaB ligand (RANKL). Migration of monocytes into close proximity precedes critical fusion events that are required for osteoclast formation. Cellular migration requires leading-edge actin cytoskeleton assembly that drives cellular locomotion. Filamin A (FLNa) cross-links F-actin filaments in the leading edge of migrating cells and also has been shown to regulate signal transduction during cell migration. However, little is known about the possible role of FLNa in osteoclastogenesis. Our objective in this study was to investigate the role of FLNa in osteoclastogenesis. Bone marrow monocytes isolated from the tibiae and femora of wild type (WT) and Flna-null mice were cultured for 6 days with M-CSF and RANKL, and osteoclasts were identified by tartrate-resistant acid phosphatase (TRACP) staining. The Flna-null mouse skeletal phenotype was characterized using dual-energy X-ray absorptiometry (DXA) to analyze the skeleton, as well as tests on blood chemistry. Osteoclast levels in vivo were quantified by counting of TRACP-stained histologic sections of distal femora. To elucidate the mechanisms by which Flna regulates osteoclastogenesis, migration, actin polymerization, and activation of Rho GTPases, Rac1, Cdc42, and RhoA were assessed in monocytes during in vitro OCG. Deficiencies in migration were rescued using constitutively active Rac1 and Cdc42 TAT fusion proteins. The RANKL signaling pathway was evaluated for activation by monitoring nuclear translocation of NF kappaB and c-jun and expression of key osteoclast genes using quantitative real-time polymerase chain reaction (qRT-PCR). Our results show that Flna-null monocytes formed fewer osteoclasts in vitro, and those that were formed were smaller with fewer nuclei. Decreased OCG was reflected in vivo in TRACP-stained histologic bone sections. Flna-null monocytes experienced impaired migratory ability. When OCG was performed at increasing starting cellular plating densities in order to decrease intercellular distances, there was progressive rescue of Flna-null osteoclast formation comparable with WT levels, confirming that Flna regulates monocyte migration prefusion. Activation of the actin cytoskeleton regulators Rac1, Cdc42, and RhoA and actin free-barbed end generation were partially or completely abrogated in Flna-null monocytes; however, monocyte migration was restored on rescuing with constitutively active Rac1 and Cdc42 TAT fusion proteins. We conclude that filamin A is required for osteoclastogenesis by regulating actin dynamics via Rho GTPases that control monocyte migration.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".