Objectives: To establish an improved reversible ureteral obstruction (RUUO) mouse model that more accurately recapitulates progressive renal interstitial fibrosis by addressing key limitations of conventional UUO/RUUO models—namely unilateral compensation, rapid and non-physiologic injury, excessive tubular damage, and high variability. This model is designed to enable earlier detection of fibrosis, more reliable functional assessment, and better evaluation of therapeutic interventions. Methods: C57BL/6 mice were randomly divided into three groups: New model 1 group (new bilateral RUUO model), model 2 group (RUUO with contralateral nephrectomy), and model 3 (RUUO with intact contralateral kidney). In model 1, the left ureter was clamped for 4 days, then released. After a 3-day recovery, the right ureter underwent the same procedure. In model 2, the left ureter was clamped as in Model 1, but the unclamped right kidney was removed via nephrectomy. In model 3, the left ureter was clamped for 7 days and then released, with the contralateral kidney left intact. Plasma and urine samples collection started at 24 hours after the final procedure and continued for 28 days. Kidney tissues were harvested at the end of experiment, and the kidney weight was weighted. Kidney injury, fibrosis, and function (in Model 1) were evaluated using PAS, Masson’s Trichrome staining, immunohistochemistry, RT-PCR and Western blotting. Results: Our new RUUO Model 1 demonstrated gradually developing fibrosis, as shown by Masson’s Trichrome and α-SMA staining, with clear collagen deposition. Glomerular filtration rate (GFR), measured via transcutaneous FITC-Sinistrin clearance, indicated that Model 1 mice had moderately impaired kidney function. Compared to conventional RUUO Model 2, Model 1 exhibited less severe tubular injury within 24 hours of model induction and on days 7 and 14, reflected by more than 50% lower plasma creatinine and BUN levels. Model 2 showed the highest plasma creatinine on day 1 (0.24 ± 0.13, p < 0.001, n = 5). Histopathological analysis revealed that new model 1 developed more homogeneous interstitial fibrosis and tubular atrophy by the end of the experiment Than model 2 and 3. Western blot analysis of α-SMA, F4/80, fibronectin, and TGF-β1 showed detectable collagen accumulation and fibrotic matrix remodeling in Model 1, accompanied by only mild inflammatory responses, in contrast to the excessive inflammation observed in Models 2 and 3. Conclusions: We developed a reliable mouse model of kidney fibrosis using alternatively repeated ureteral clamping. This model produces slowly progressive fibrosis, measurable kidney injury, and functional decline, overcoming the contralateral compensation seen in conventional models. It better recapitulates both the pathophysiology and functional consequences of human chronic kidney disease and provides an improved platform to study early fibrosis, assess renal function decline, reduce surgical variability, and evaluate preventive or therapeutic interventions. This abstract was presented at the American Physiology Summit 2026 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.
Tran et al. (2026) studied this question.