Investigating the Urinary Salt Losing Phenotype in R607H and L919X Mutant Mice with Distal Renal Tubular Acidosis
Bibliographic record
Abstract
Introduction: The renal collecting duct consists of two cell types: principal and intercalated cells (ICs, alpha- and beta-type). These cells play a crucial role in regulating fluid, electrolyte, and acid-base homeostasis. Specifically, alpha-ICs promote secretion of protons into the urine through an apical proton ATPase while enabling the reabsorption of bicarbonate into the blood via the basolateral protein, kidney anion exchanger 1 (kAE1). Genetic mutations that impact IC cell function can lead to a condition called distal renal tubular acidosis (dRTA). Patients with dRTA typically exhibit alkaline urine, metabolic acidosis, electrolyte imbalances, and urinary ion loss. Study Objective and Hypothesis: Some dRTA patients continue to exhibit impaired conservation of sodium, despite sustained correction of their acidosis. The mechanisms that lead to this impairment need further investigation. Our lab has two dRTA kAE1 knock in (KI) mouse models, L919X (LX) and R607H (RH), that recapitulate classical metabolic acidosis seen in human patients. We hypothesize that these mice serve as an effective model for studying the cause behind the persistent urinary ion loss. The objectives of our work are to 1) determine whether our mouse models accurately reflect the urinary ion loss seen in dRTA patients, 2) comprehensively characterise the previously unpublished mouse line, kAE1 KI L919X, and 3) elucidate the mechanism behind this urinary salt loss. Methods: To test our hypothesis, we fed wild-type (WT) and dRTA mutant mice a low NaCl, acid, or combination (NaCl + acid) diet, to mirror conditions previously studied in human patients. We collected urine and plasma from the mice to measure ion concentrations and pH. We harvested and processed their kidney and gut tissues for analysis through qRT-PCR, immunoblot, and immunofluorescence to investigate acid-base and salt transports in the collecting duct and thick ascending limb. We aimed to identify potential alterations in these transporters between WT and KI mice. Results: On the low NaCl diet, there were little differences between WT and KI mice, either in comparison to each other or relative to their baseline conditions. However, the combination diet revealed a urinary salt losing phenotype in the RH and LX KI mice. These KI mice also displayed hypernatremia, hyperchloremia, and a failure to secrete potassium and to properly concentrate their urine. qRT-PCR analysis of whole kidney tissues revealed a surprising increase in the paracellular transport pathways, including claudin-4 and claudin-10b in the KI compared to WT. Initial immunoblots indicate a concordant upregulation and downregulation of protein expression that aligns with transcriptional changes seen at the mRNA level. Conclusion: Our current findings suggest a defective collecting duct function in the KI mice, thus validating our hypothesis. Additionally, there appears to be a compensatory mechanism at play in earlier nephron segments to rescue ion homeostasis. The results from this research may contribute to improved treatment options for patients that suffer with this severe disease. It will also deepen the understanding of the interconnected and complex functions of the nephron, aiding in treatment of other major conditions like hypertension or end-stage renal disease. Canadian Institutes of Health Research (CIHR), Canada Graduate Scholarship - Master's CIHR, and Kidney Foundation of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
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How this classification was reachedexpand
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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".