RhoA and Its Downstream Effectors ROCK/Cofilin and Formin Trigger Mitochondrial Fragmentation in PKD
Bibliographic record
Abstract
Background: Polycystic kidney disease (PKD) is the most prevalent genetic renal disorder, caused by the loss/loss of function of polycistin-1 (PC1) or 2 (PC2), and characterized by excessive cyst formation and fibrosis. A key cellular feature of PKD is the fragmentation of mitochondria, but the underlying mechanism is unknown. Our previous studies have shown that PC loss induces RhoA- dependent nuclear translocation of myocardin-related transcription factor, leading to fibrogenesis. Based on this scenario, we asked whether PC1/2 loss-induced mitochondrial fragmentation might also be a mediated by RhoA. Methods: Mitochondrial morphology was quantified by volumetric confocal microcopy in mitoRFP-transfected LLC-PK1 tubular cells. RhoA activity was measured by RhoA G-LISA. The manipulation of expression/activation of proteins is described at the corresponding results. Results: RhoA activation by constitutively active RhoA or RhoA II activator toxin induced robust mitochondrial fragmentation. Importantly, PC1 or PC2 silencing triggered RhoA activation and mitochondrial fragmentation, which was prevented/reversed by downregulation/inhibition of RhoA (siRNA, dominant negative (DN) RhoA, or C3 toxin). Fission was catalyzed by dynamin-related protein 1 (Drp1), as a) PC loss promoted RhoA-dependent mitochondrial Drp1 translocation; and b) fragmentation was prevented/reversed by Drp1 silencing or inhibition (mDivi or DN-Drp1). PC loss provoked cofilin phosphorylation (inhibition) via Rho kinase (ROCK) and its target LIM kinase. Inhibition of ROCK or LIMK reduced fragmentation. Mitochondrial fission also required the other major RhoA effector pathway, the activation of formins. Mitochondrially targeted active formins, like DIAPH3, but not its actin polymerization-deficient mutant induced fission, while the pan-formin inhibitor SMIFH2 abolished PC loss-provoked fragmentation. Importantly, the human PKD cell line WT 9-12 exhibited fragmented mitochondrial network, which was restored by SMIFH2. Fragmentation facilitated PC1/2 loss-induced fibrogenic gene expression. Conclusion: Thus, PC1/2 loss leads to mitochondrial fragmentation by activation of RhoA and its effectors, which promote F-actin polymerization by decreased severing (cofilin inhibition) and increased assembly (formin activation).
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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 | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".