Modulating α‐actinin‐4 dynamics in podocytes
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Bibliographic record
Abstract
Podocytes are epithelial cells that line the outer aspect of renal blood vessels and provide a platform for the kidney's filtering apparatus, the slit diaphragm. Mutations in alpha-actinin-4, an actin bundling protein highly expressed in podocytes, result in increased affinity for actin and cause a familial form of focal segmental glomerulosclerosis. We hypothesized that such gain-of-affinity mutations would override alpha-actinin-4's sensitivity to regulatory factors such as calcium (acting via two EF-hand motifs), and phosphoinositides. We generated calcium- (mutEF) and phosphoinositide- (mutPI) insensitive variants of alpha-actinin-4, comparing their properties to a disease-associated mutant (K256E) and to the wildtype (wt) protein. alpha-Actinin-4(mutPI) displayed increased affinity for actin, while the affinity of alpha-actinin-4(mutEF) was unchanged. Addition of calcium to actin sedimentation assays caused a decrease in the association of alpha-actinin-4(wt) with filamentous actin, while phosphoinositides generally increased this association. Similar to alpha-actinin-4(K256E), alpha-actinin-4(mutPI) was mislocalized in cultured podocytes, being preferentially associated with filamentous actin and focal adhesions. Fluorescence recovery after photobleaching experiments revealed a rapid turnover of alpha-actinin-4(wt) and alpha-actinin-4(mutEF) along stress fibers and focal adhesions, while the turnover of alpha-actinin-4(K256E) and alpha-actinin-4(mutPI) was dramatically reduced at these subcellular locales. Equibiaxial mechanical stimulation of podocytes, a mimic of intraglomerular forces, reduced podocyte surface area by 50%; this decrease was more severe (70%) in the presence of high-affinity mutants of alpha-actinin-4. These data suggest that dynamic regulation of alpha-actinin-4/actin interactions may be necessary for maintaining podocyte structure in response to glomerular hydrostatic forces.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 it