A Novel Role for Thrombin in Hematopoietic Stem/Progenitor Cell Homing.
Bibliographic record
Abstract
Abstract Thrombin, an important serine protease, not only plays a pivotal role in platelet aggregation and coagulation, but also through activation of its receptor, seven transmembrane, G-protein-coupled receptor PAR-1, elicits numerous cellular responses in platelets and endothelial cells such as induction of adhesion molecules, production of chemokines, activation of matrix metalloproteinase (MMP)-2, cytoskeletal reorganization and migration. Thrombin is also one of the inflammatory molecules elevated during G-CSF mobilization of hematopoietic stem/progenitor cells (HSPC) and their collection by leukapheresis. We recently reported that components of leukapheresis products including thrombin enhance in vitro chemotaxis of CD34+ cells towards an SDF-1 gradient and in vivo homing to bone marrow (BM) niches in a murine model (Blood2005; 105:40). In this study we investigated whether thrombin enhances the homing-related responses of human HSPC (CD34+ cells) through MMPs, especially membrane-type (MT)1-MMP which is known to be localized on the leading edge of migrating cells and both activates latent proMMPs (MMP-2, -9) and itself has strong pericellular proteolytic activity. We found that stimulation of CD34+ cells with thrombin upregulates mRNA for MT1-MMP and MMP-9 as well as MT1-MMP protein expression (Western blot, flow cytometry) and proMMP-2 and proMMP-9 secretion (zymography). Thrombin was also found to (i) prime trans-Matrigel chemoinvasion of CD34+ cells towards a low SDF-1 gradient (20 ng/mL), which was inhibited by epigallocatechin-3-gallate, a potent inhibitor of MT1-MMP, and (ii) activate MMP-2 in of co-cultures of CD34+ cells with stromal cells (BM fibroblasts and HUVEC) which secrete proMMP-2. We also found that SDF-1 upregulates mRNA and protein expression of MT1-MMP. Moreover, using confocal microscopy we demonstrate for the first time that in CD34+ cells, PAR-1, like CXCR4, is localized in the GM1 fraction of lipid rafts and stimulation of these cells with thrombin as well as SDF-1 increases incorporation of MT1-MMP into membrane lipid rafts. Furthermore, disruption of lipid raft formation by the cholesterol-depleting agent methyl-b-cyclodextrin inhibits MT1-MMP incorporation into membrane lipid rafts and also trans-Matrigel chemoinvasion of CD34+ cells towards SDF-1. Thus we conclude that thrombin, through PAR-1 signalling and the SDF-1-CXCR4 axis, upregulates the incorporation of MT1-MMP into membrane lipid rafts and the interaction of these axes enhances the homing-related responses of HSPC towards SDF-1.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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 | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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 source (direct Gemma or distilled Codex), 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".