Apolipoprotein(a)-Dependent Inhibition of Pericellular Plasminogen Activation Is Mediated by Specific Cellular Receptors
Bibliographic record
Abstract
Abstract Abstract 2236 Lipoprotein(a) [Lp(a)] has been identified as an independent risk factor for cardiovascular diseases such as coronary heart disease. Lp(a) levels vary over 1000-fold within the human population and Lp(a) possesses both proatherogenic and prothrombotic properties due to the LDL-like moiety and apolipoprotein(a) [apo(a)] components, respectively. Apo(a) is highly homologous to plasminogen and thus can potentially interfere with plasminogen activation. Plasmin generated in the context of fibrin mediates the breakdown of blood clots, which are the causative factors in heart attacks and strokes. Plasmin generated on the surface of vascular cells plays a role in cell migration and proliferation, two of the fibroproliferative inflammatory events that underlie atherosclerosis. Previous studies have suggested that apo(a) may inhibit pericellular plasminogen activation on the basis of observations that apo(a) decreases plasminogen binding to cells. We have undertaken analysis of the mechanism by which apo(a) may interfere with pericellular plasminogen activation to allow for a more definitive description of the role of Lp(a) within the vasculature. Plasminogen activation was found to be markedly inhibited by the recombinant apo(a) variant 17K, in a dose dependent manner, on human umbilical vein endothelial cells (HUVECs), human monocytic leukemia cells (THP-1), THP-1 macrophages, and smooth muscle cells. The strong lysine binding site in kringle IV type 10, as well as kringle V appear to be required for this effect since apo(a) variants lacking these elements (17KΔAsp and 17KΔV, respectively) failed to inhibit activation. However, the role of lysine-dependent binding of apo(a) itself to the cells is not clear. Carboxypeptidase treatment of cells did not decrease apo(a) binding, and apo(a) does not compete directly for plasminogen binding to the cells. Rather, apo(a) and plasminogen may bind to the cells as a complex. We next attempted to identify the cell-surface receptor(s) that mediate plasminogen activation on the cell surface as well as its inhibition by apo(a). Urokinase-type plasminogen activator receptor (uPAR) has been previously shown to bind to urokinase-type plasminogen activator (uPA), vitronectin, and β3 integrins. uPAR is involved in the remodeling of the extracellular matrix (ECM) through regulation of plasminogen activation. We found evidence that uPAR is a potential receptor for both plasminogen and apo(a). Knockdown of uPAR in HUVECs results in decreased binding of plasminogen, 17K and, to a lesser extent, 17KΔAsp and 17KΔV. Similar experiments in SMCs revealed no changes in binding. A decrease in tPA-mediated plasminogen activation following uPAR knockdown occurred in HUVECs, and addition of 17K did not result in any further decrease. Overexpression of uPAR in THP-1 macrophages leads to greater than a two fold increase in 17K and plasminogen binding. Plasminogen activation increases over two-fold as a result of overexpression of uPAR, while 17K blunts the effect of uPAR overexpression. These results indicate that uPAR plays a crucial role in both plasminogen and apo(a) binding to the cell surface of specific cells and inhibition by apo(a) of plasminogen activation. Macrophage-1-antigen (Mac-1) receptor consists of CD11b (αM) and CD18 (β2) integrin and has been previously shown to recognize uPA and control migration and adhesion. Furthermore, αVβ3 has been previously shown to bind to vitronectin and the uPA-uPAR complex which promotes cell adhesion through binding of both vitronectin and αVβ3 integrins. We found that blocking the αM, β2, or αVβ3 receptors with monoclonal antibodies in THP-1 cells leads to a decrease in plasminogen activation, as well as a blunting of the inhibitory effects of apo(a) on plasminogen activation. These results indicate a role for Mac-1 and αVβ3 in apo(a) binding and inhibition of plasminogen activation. In conclusion, we have demonstrated, for the first time, the role of specific receptors in binding of apo(a) to vascular cell surfaces and in mediating the inhibitory effect of apo(a) on pericellular plasminogen activation. Disclosures: No relevant conflicts of interest to declare.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".