Decreased klotho is associated with the activation of renin-angiotensin system in kidneys of the rats with doxorubicin-induced nephrosis

Background: Klotho, an anti-aging hormone predominantly produced in the renal distal convoluted tubules, is diminished in various kidney disease models. The renin-angiotensin system (RAS) is not only crucial in the development of hypertension but also influences the progression of numerous renal disorders. The relationship between klotho expression and RAS regulation, however, remains elusive. To investigate this, we utilized a doxorubicin (Dox)-induced nephrotic rat model to determine the interplay between klotho and the renin-angiotensin system (RAS) activation. Methods: 1. Male Sprague-Dawley (SD) rats, aged 8-9 weeks, were administered Dox at a dosage of 6 mg/kg via tail-vein injection or an equivalent volume of vehicle. Two weeks after the injection, Dox-treated rats were randomly assigned to receive either the angiotensin II type 1 receptor (AT1R) blocker Candesartan (1 mg/kg, IP) or saline daily for an additional week. The animals were then euthanized with over-anesthesia, and their kidney, serum, and urine samples were collected for according measurements. 2. Data are presented as the mean ± SEM, and a P-value of less than 0.05 was considered statistically significant, as determined by one-way ANOVA followed by the Holm-Sidak test for multiple comparisons. Results: Compared to the vehicle control group, Dox-treated rats displayed proteinuria (22.39±2.4 vs 14.94±1.9 μg/24h), hypoalbuminemia (18.1±1.0 vs 32.68±0.9 g/L), and azotemia (serum creatinine, SCr, 85 ± 26.3 vs 23.2 ± 5 μmol/L). Kidney klotho protein levels were reduced (20.25±9.1% of control, same as below). Renin (180.76±28.2%), angiotensin-converting-enzyme (ACE, 130.37±10.5%)and AT1 receptor (197.34±20.7%) levels were elevated while renal AT2 receptor expression was decreased (29.3±4.7%).The levels of angiotensinogen and ACE2 remained unchanged. Candesartan treatment ameliorated nephrosis, as evidenced by reduced decreased urine total protein excretion (9.17±1.9 μg/24h) and SCr (18.08±0.8 μmol/L), concurrent with an increase in serum albumin (25.84 ±1.8g/L). Renal klotho levels returned to normal upon treatment(70.26 ± 7.8 %). In addition, Candesartan had no effect on renal klotho levels in normal SD male rats, spontaneously hypertensive male rats and male/female C57Bl6/J mice. Conclusion: The reduction in klotho expression is associated with the activation of the renin-angiotensin system in the kidneys of rats with doxorubicin-induced nephrosis. Further studies will be conducted on other renal disease models. The direct interactions between renal klotho and RAS components remain to be established. Postgraduate Research & Practice Innovation Program of Jiangsu Province (Grant No.SJCX24-0758) 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.