Investigating the role of lysosomal exocytosis in Alzheimer’s disease
Bibliographic record
Abstract
Abstract Background Many studies have implicated the endosomal‐lysosomal system in the production of beta‐amyloid (Aβ), but the actual compartments involved in Aβ secretion have never been visualized. Although lysosomes are expected to be a site of Aβ clearance, studies have also shown them to be a site of Aβ accumulation. Lysosomal exocytosis is well recognized as a major secretory pathway in non‐neuronal cells but is virtually unstudied in neurons. This project investigates the role and mechanism of lysosomal secretion in neurons. We hypothesize that lysosomal exocytosis is a pathway for Aβ release and could be modulated by Rab27b in iPSC‐derived human neurons. Method To study lysosomal exocytosis in a neuronal system, our lab established normal and mutant APP Swedish expressing iPSC‐neurons. The involvement of lysosome‐related secretory proteins (Rab27b, Munc13‐4 and synaptotagmin‐7) were examined using siRNA, dominant‐negative or shRNA constructs. Cells were co‐transduced with a pH‐sensitive dual‐fluorescent lysosomal marker (pHluorin‐LAMP1‐mAppleFP) to identify and track lysosomes. Cells were also loaded with fluorescent exogenous Aβ or a dye to mark endogenous Aβ, and then treated with ionomycin to induce exocytosis. Total internal reflection fluorescence (TIRF) microscopy was performed to capture videos of molecular events occurring within 250nm from the plasma membrane. Imaris software was used to analyze co‐localization of LAMP‐1 with Aβ, and the number and timing of lysosomal secretory events. Result In untreated cells, loaded Aβ accumulated in lysosomes. After treatment with ionomycin, a dramatic decrease of lysosomal Aβ was observed. In live cells, TIRF microscopy captured lysosomes docking and fusing with the plasma membrane over 150 seconds after ionomycin treatment. This was visualized by pHluorin‐LAMP1 (which is normally dark in an acidic pH) fluorescing green upon lysosomal fusion with the plasma membrane. Overexpression of Rab27b N133I mutant significantly increased lysosomal exocytosis of Aβ compared to wild‐type, and Rab27b shRNA dramatically reduced lysosomal exocytosis and Aβ secretion. Conclusion Our results demonstrate that lysosomal exocytosis is a novel secretion pathway in human neurons and identify potential pharmacological targets that regulate clearance of toxic Aβ.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".