Transendothelial migration of the Lyme disease spirochete involves spirochete internalization as an intermediate step through a transcellular pathway that involves Cdc42 and Rac1
Bibliographic record
Abstract
ABSTRACT Despite its importance in pathogenesis, the hematogenous dissemination pathway of B. burgdorferi is still largely uncharacterized. To probe the molecular details of transendothelial migration more easily, we studied this process using cultured primary or telomerase-immortalized human microvascular endothelial cells in a medium that maintains both the human cells and the spirochetes. In B. burgdorferi infected monolayers we observed ∼55% of wild-type spirochetes crossing the monolayer. Microscopic characterization revealed entrance points across the cellular surface rather than at cellular junctions, supporting a transcellular route. In support of this pathway, locking the endothelial junctions using a VE-PTP inhibitor did not reduce transendothelial migration. We also used inhibitors to block the most common endocytic pathways to elucidate effectors that might be involved in B. burgdorferi uptake and/or transmigration. Directly inhibiting Cdc42 reduced spirochete transmigration by impeding internalization. However, blocking Rac1 alone dramatically reduced transmigration and resulted in a concomitant increase in spirochete accumulation in the cell. Our combined results support that B. burgdorferi internalization is an intermediate step in the transendothelial migration process which requires both Cdc42 and Rac1; Cdc42 is needed for spirochete internalization while Rac1 is required for cellular egress. These are the first two host proteins implicated in B. burgdorferi transmigration across endothelial cells. IMPORTANCE Lyme borreliosis is caused by Borrelia burgdorferi and related bacteria. It is the most common tick-transmitted illness in the Northern Hemisphere. The ability of this pathogen to spread to a wide variety of locations results in a diverse set of clinical manisfestations, yet little is known regarding vascular escape of the spirochete, an important pathway for dissemination. Our current work has studied the traversal of B. burgdorferi across a monolayer of microvascular endothelial cells grown in culture. We show that this occurs by passage of the spirochetes directly through these cells rather than at cellular junctions and that internalization of B. burgdorferi is an intermediate step in the transmigration process. We also identify the first two host proteins, Cdc42 and Rac1, that are used by the spirochetes to promote traversal of the cellular monolayer. Our new experimental system also provides a new avenue for further studies of this important process.
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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) | 0.001 | 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 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".