Sexually divergent potassium handling following adaptation of tubule-specific kallikrein-1 knockout mice to a short term, low sodium diet

Background: We previously identified kallikrein-1, encoded by the gene Klk1, as (1) the predominant isoform of tissue kallikrein expressed in the kidney and (2) a top differentially expressed protease gene in mice following kidney-specific deletion of the mineralocorticoid receptor (MR). We recently developed a mouse model with deletion of Klk1 along the aldosterone-sensitive nephron (Klk1 flx/flx Calb1 -Cre) and found that kallikrein-1 contributes to gamma-ENaC cleavage upon treatment with a short term, low sodium, high potassium diet. We hypothesized that kallikrein-1 mediates gamma-ENaC cleavage in response to MR signaling. However, it remained unclear whether differences in kallikrein-1 regulation of gamma-ENaC cleavage occur between states of Na + depletion and dietary K + excess, so we sought to generate an inducible, kidney specific model to test for differences in dietary treatments. Methods: Following induction with doxycycline (2 weeks, 2mg/mL doxycycline hyclate in 5% sucrose drinking water), Klk1 flx/flx Pax8 + Cre + (KS- Klk1 KO) or matched littermates treated with vehicle (controls) were placed in metabolic cages for 24-hour urine collection. Animals were fed a control diet (0.33% Na, 1.16% K) for 2 days, then switched to a sodium deficient diet (LS, 0.03% Na, 1.16% K) for 5 days. Urine was collected daily. Following day 5 of LS, mice were harvested for plasma and kidney tissue. Plasma metabolic panel was measured using an iSTAT handheld blood analyzer, and urine electrolytes were measured by flame photometry. Whole kidney lysates were analyzed using western blotting to quantify protein expression normalized to protein loading. Results are expressed as mean +/- SEM and analyzed using two-tailed t-test. Results: We detected a 90% reduction in renal kallikrein-1 protein expression in KS- Klk1 KO compared with controls (p < 0.001). Following day 5 of LS, female KS-Klk1-KO mice (n=5) were found to have reduced urine K+ excretion (KO 0.031+/-0.002 mmol/gbw/24hr vs. WT 0.049+/-0.002 mmol/gbw/24hr, p = 0.01), however there was no change in plasma K+ (KO 4.5+/-0.3 mmol/L vs. WT 5.0+/-0.5 mmol/L, p = 0.39). There was no difference in either urine K+ excretion (KO 0.044+/-0.007 mmol/gbw/24hr vs. WT 0.037+/-0.006 mmol/gbw/24hr, p = 0.45) or plasma K+ (KO 4.2+/0.3 mmol/L vs. WT 4.4+/-0.3mmol/L, p = 0.62) in male KS- Klk1 KO mice (n = 3). Importantly, we did not find any difference in the ratio of cleaved:uncleaved gamma-ENaC (F, p = 0.49; M, p = 0.07). Conclusions: Female, but not male, KS- Klk1 KO animals exhibited reduced urinary K+ compared with controls following 5 days of LS. In contrast with our previous model of renal Klk1 deletion, which used a combined low sodium, high potassium diet, differences in gamma-ENaC cleavage were not detected in either sex. Further studies are needed to better resolve all cleaved species of gamma-ENaC, and to test the hypothesis that kallikrein-1 effects on gamma-ENaC cleavage become more pronounced in response to dietary K + loading. This work was supported by DK051496. Additionally, JNC is supported by L70DK140988 and T32-HL166128-01A1 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.