Abstract 380: PDI and ERp57 Localization in Platelets Is Regulated by Actin Polymerization
Bibliographic record
Abstract
Introduction: PDI and ERp57 are members of the thiol isomerase family of enzymes that are released to the platelet surface where they contribute to a range of platelet responses. PDI has been reported to be present in subcellular structures in resting platelets, although it is excluded from α - and δ -granules, and lysosomes. It was, however, recently shown to co-localise with TLR9 in T-granules, intracellular bodies underlying the plasma membrane. The subcellular localisation of other platelet thiol isomerases or their mechanisms of translocation to the cell surface have not been established. Hypothesis and Methods: Using spinning disk confocal microscopy we sought to explore whether platelet thiol isomerases ERp57 and PDI are co-localised in resting and activated platelets and to test the hypothesis that translocation of thiol isomerases to the platelet surface is dependent on actin polymerization. Results and Conclusions: In resting platelets, PDI and ERp57 were organized in punctate structures both on the platelet surface and in the cytoplasm. They did not colocalise with P-selectin consistent with them residing outside α -granules. In contrast to expectations, TLR9 did not colocalize with PDI and ERp57, suggesting their exclusion from T-granules. Partial colocalization was observed in resting platelets between PDI and ERp57 in granule-like structures. Upon platelet activation, this degree of co-distribution persisted with PDI and ERp57 migrating to the platelet surface. Latrunculin A, an inhibitor of actin polymerization, decreased P-selectin exposure on the platelet surface, as measured by flow cytometry, and agonist-stimulated platelets treated with this agent retained a rounded shape, as shown by tubulin staining. Importantly, latrunculin A also blocked the translocation of PDI and ERp57 from internal granule-like structures to the platelet surface. We conclude that in resting platelets PDI and ERp57 are organized, and partially co-localised, in punctuate structures unlikely to represent α- or T-granules. The polymerization of actin during platelet activation exerts a fundamental role in the relocalization of PDI and ERp57 from these cytoplasmic structures to the platelet surface.
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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".