Renal Fibrosis Models: UUO, Adenine, IRI & More
Compare UUO, adenine diet, 5/6 nephrectomy, IRI, and diabetic nephropathy for CKD. Includes flowchart and endpoint guidance by research objective.
Introduction: Overview of Renal Fibrosis Models and the Importance of Model Selection
Chronic kidney disease (CKD) affects approximately 10% of the global population, and renal interstitial fibrosis—the final common pathway of CKD—is one of the major histopathological correlates of declining kidney function. In drug discovery for CKD therapeutics, selecting the appropriate animal model that recapitulates the fibrotic process is a decisive factor in the success of preclinical studies.
However, the range of animal models available for inducing renal fibrosis is extensive, and each model has distinct mechanisms, timelines, and evaluable endpoints. The key to successful clinical translation lies not in asking "which model is the best?" but rather "which model best fits the research objective?"
This article provides a comprehensive comparison of the major renal fibrosis models used in preclinical research and offers guidance for selecting the optimal model based on your research goals. For in-depth details on individual models, please refer to the dedicated articles linked throughout.
1. Overview and Comparison Table of Major Models
The table below summarizes the key characteristics of the representative renal fibrosis models used in preclinical studies.
| Model | Induction Method | Fibrosis Type | Duration | Renal Function Decline | Surgery Required | Clinical Relevance |
|---|---|---|---|---|---|---|
| UUO | Unilateral ureteral ligation | Interstitial fibrosis (obstructive) | 1–2 weeks | No | Yes | Context-dependent (obstructive nephropathy) |
| Adenine diet | Adenine-containing diet / oral gavage | Tubulointerstitial fibrosis | 4–8 weeks | Yes | No | Relatively high |
| 5/6 Nephrectomy | Nephrectomy + remnant kidney resection/infarction | Glomerulosclerosis + interstitial fibrosis | 8–12 weeks | Yes | Yes (high difficulty) | Relatively high (resembles CKD progression) |
| IRI | Renal artery clamping | Interstitial fibrosis (post-AKI) | 4–8 weeks | Yes (acute phase) | Yes | Relatively high (AKI-to-CKD) |
| db/db | Genetic (leptin receptor deficiency) | Glomerulosclerosis + mesangial expansion | 12–24 weeks | Yes (gradual) | No | Relatively high (type 2 diabetic nephropathy) |
| STZ-induced | Streptozotocin administration | Glomerulosclerosis + interstitial fibrosis | 12–24 weeks | Yes | No | Context-dependent (type 1 diabetic nephropathy) |
| BTBR ob/ob | Genetic (leptin deficiency + background strain) | Glomerulosclerosis + nodular lesions | 12–20 weeks | Yes | No | Relatively high (nodular glomerulosclerosis) |
| Repeated cisplatin | Intraperitoneal cisplatin injection | Tubulointerstitial fibrosis | 4–8 weeks | Yes | No | Limited (drug-induced nephrotoxicity) |
| Alport syndrome mice | Genetic (Col4a3/a4/a5 mutation) | GBM abnormalities + interstitial fibrosis | 8–20 weeks | Yes (progressive) | No | Relatively high (hereditary nephritis) |
"Clinical relevance" is a qualitative indication of which aspects of human CKD each model recapitulates, not a quantitative correlation coefficient. In addition, duration, dose, and lesion severity vary substantially with species, background strain, diet, route of administration, and analysis timepoint, so the values in the table should be treated as representative ranges rather than standard values.
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2. Detailed Description of Each Model
2.1 UUO (Unilateral Ureteral Obstruction) Model
The fastest and most reproducible renal fibrosis model
The UUO model induces rapid interstitial fibrosis in the obstructed kidney through surgical ligation of one ureter. Because surgery provides a clear-cut trigger, the "start point" of fibrosis is precisely defined, and robust fibrosis is established by Day 7–14.
- Advantages: Short duration (1–2 weeks), high reproducibility, and clear distinction between prophylactic and therapeutic dosing designs
- Considerations: The contralateral kidney compensates, so serum creatinine and BUN do not increase. Hydronephrosis (ureteral dilation and renal pelvic enlargement) accompanies the fibrosis, introducing pathological elements beyond pure fibrosis
- Recommended use: Initial screening of anti-fibrotic compounds, mechanistic studies
- Key endpoints: Sirius Red staining, hydroxyproline assay, α-SMA IHC
[!TIP] For a detailed timeline, protocol, and guidance on when to choose UUO vs. adenine models, see the Complete Guide to the UUO Renal Fibrosis Model.
2.2 Adenine Diet-Induced CKD Model
A non-invasive model with gradual fibrosis progression
Dietary administration of adenine (representative protocols use 0.2–0.25% adenine-containing chow; concentration and feeding duration vary with species, background strain, and diet) or oral gavage leads to the deposition of 2,8-dihydroxyadenine (DHA) crystals within renal tubules, driving inflammation and fibrosis.
- Advantages: No surgery required, elevated BUN/creatinine enables assessment of renal function, and fibrosis develops progressively
- Considerations: The mechanism involves non-physiological crystal deposition. With dietary administration, palatability issues may reduce food intake, increasing inter-animal variability. Oral gavage provides better dose accuracy but requires daily handling
- Recommended use: Efficacy evaluation including renal function improvement, disease modeling closer to human CKD
- Duration: 4–8 weeks (mice), 4–6 weeks (rats)
[!NOTE] For more details on the adenine model, see the Complete Guide to the Adenine-Induced CKD Model.
2.3 5/6 Nephrectomy (Remnant Kidney) Model
A classical CKD-progression model with glomerular hyperfiltration, proteinuria, and renal function decline
This model involves unilateral nephrectomy combined with resection (or infarction via renal artery branch ligation) of approximately two-thirds of the contralateral kidney. The resulting overload on remaining nephrons drives glomerular hyperfiltration → glomerulosclerosis → interstitial fibrosis—a sequence that closely mirrors human CKD progression.
- Advantages: Recapitulates both glomerulosclerosis and interstitial fibrosis, accompanied by hypertension, proteinuria, and renal function decline; high pathological similarity to human CKD
- Considerations: Requires two-stage surgery with high technical demands. Variability in the amount of tissue resected directly impacts data variability, making outcomes highly dependent on operator skill. Relatively high mortality (10–20%)
- Recommended use: Mechanistic studies of CKD progression, efficacy evaluation of renoprotective agents such as RAS inhibitors
- Duration: 8–12 weeks (more commonly performed in rats)
- Key endpoints: BUN/creatinine, proteinuria, glomerulosclerosis score, Masson's trichrome staining
2.4 Ischemia-Reperfusion Injury (IRI) Model
A clinically relevant model for AKI-to-CKD transition
Temporary clamping of the renal artery (typically 25–45 minutes) followed by reperfusion induces ischemia-reperfusion injury. The model recapitulates the AKI-to-CKD transition—from acute tubular necrosis through incomplete repair to chronic interstitial fibrosis.
- Advantages: Recapitulates the clinically important AKI-to-CKD transition. Enables evaluation of both the acute phase (inflammation, necrosis) and chronic phase (fibrosis, maladaptive repair)
- Considerations: Precise control of ischemia time is critical (even a few minutes' difference significantly affects disease severity). Core body temperature management also strongly influences reproducibility. Unilateral IRI with contralateral nephrectomy allows renal function assessment but increases mortality
- Recommended use: Mechanistic studies of AKI-to-CKD transition, evaluation of renoprotective and pro-regenerative agents
- Duration: 24–72 hours for acute-phase assessment, 4–8 weeks for chronic fibrosis evaluation
- Key endpoints: Acute phase (BUN/Cr, KIM-1, NGAL), chronic phase (Sirius Red, collagen deposition area, α-SMA)
2.5 Diabetic Kidney Disease (DKD) Models
Renal fibrosis models in the context of diabetes
Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease worldwide, making it a critically important target area for drug development. Several models are used depending on the specific research question.
db/db Mice
A type 2 diabetes model caused by leptin receptor deficiency. These mice spontaneously develop obesity, hyperglycemia, and insulin resistance, and by 20–24 weeks of age exhibit mesangial expansion, glomerular basement membrane thickening, and mild-to-moderate albuminuria.
- Advantages: Faithfully recapitulates the metabolic background of human type 2 diabetes. Non-invasive
- Considerations: Fibrosis is mild, and advanced human DKD features (nodular sclerosis) are difficult to reproduce. The C57BLKS/J background yields relatively stable nephropathy
STZ (Streptozotocin)-Induced Model
STZ administration destroys pancreatic β-cells, inducing type 1 diabetes. Maintaining animals under hyperglycemic conditions for 12–24 weeks may lead to glomerulosclerosis and interstitial fibrosis (lesion severity depends on STZ direct nephrotoxicity, diabetes phenotype, and background strain). Combining low-dose STZ with a high-fat diet (HFD) can produce a type 2 diabetes-like phenotype.
- Advantages: Can be induced in any strain and at any age. Low cost
- Considerations: Direct nephrotoxicity of STZ may confound results. Low-dose repeated administration is preferred over single high-dose injection
BTBR ob/ob Mice
This model introduces leptin deficiency (ob/ob) onto the BTBR background strain. It is one of the few mouse models capable of recapitulating nodular glomerulosclerosis (Kimmelstiel-Wilson nodule-like lesions), a hallmark of human DKD.
- Advantages: One of the representative models that readily recapitulate the histopathological features of human DKD (nodular sclerosis, mesangial expansion, GBM thickening)
- Considerations: Limited availability and high maintenance costs for the BTBR strain. Low breeding efficiency
2.6 Repeated Cisplatin Model
A drug-induced nephrotoxicity fibrosis model
Repeated low-dose cisplatin administration (e.g., 7 mg/kg once weekly for 4 weeks) induces cycles of acute tubular necrosis → maladaptive repair → interstitial fibrosis. Unlike the traditional single high-dose model (acute kidney injury model), this protocol enables evaluation of chronic fibrosis progression.
- Advantages: No surgery required, relatively straightforward protocol. Directly models chemotherapy-associated nephrotoxicity as seen clinically
- Considerations: Systemic toxicity of cisplatin (weight loss, myelosuppression) must be monitored. Effects are not kidney-specific, and deterioration of overall health may confound data
- Recommended use: Evaluation of preventive/therapeutic agents for chemotherapy-related nephrotoxicity, AKI-to-CKD transition research
2.7 Alport Syndrome Mice (Col4a3 Knockout)
A genetic model of progressive renal fibrosis
Col4a3 knockout mice recapitulate human Alport syndrome, progressing through glomerular basement membrane structural abnormalities → proteinuria → glomerulosclerosis → interstitial fibrosis to renal failure along a predictable timeline.
- Advantages: Spontaneously progressive hereditary renal fibrosis. Disease progression is predictable with high reproducibility. No surgery required
- Considerations: Requires specific genetically modified mice (limited availability, cost). Rate of progression varies significantly by background strain (129Sv background shows rapid progression; C57BL/6 background is more gradual)
- Recommended use: Therapeutic evaluation for hereditary kidney diseases, long-term assessment of progressive fibrosis
3. Model Selection Flowchart by Research Objective
Use the following decision framework to select the optimal model based on your research goals.
Step 1: What Do You Want to Evaluate?
A. Initial screening of anti-fibrotic compounds (short-duration, high-throughput) → UUO model (results in 1–2 weeks)
B. Comprehensive efficacy evaluation including renal function improvement → Adenine diet model or 5/6 nephrectomy model
C. Prevention/treatment of AKI-to-CKD transition → IRI model (continuous evaluation from acute to chronic phase)
D. Therapeutic evaluation for diabetic kidney disease (DKD) → db/db (type 2 DM) / STZ (type 1 DM) / BTBR ob/ob (nodular sclerosis)
E. Mechanistic studies and therapeutic evaluation for hereditary kidney diseases → Alport syndrome mice
Step 2: Time, Cost, and Technical Constraints
| Constraint | Recommended Model |
|---|---|
| Results needed within 2 weeks | UUO |
| No surgical capability | Adenine diet, STZ, db/db, repeated cisplatin |
| Renal function markers (BUN/Cr) required | Adenine diet, 5/6 nephrectomy, IRI, DKD models |
| Reproducing classical CKD progression (glomerulosclerosis + interstitial fibrosis) | 5/6 nephrectomy, BTBR ob/ob |
| Minimize cost | UUO (short duration), adenine diet (no procedures) |
Step 3: Recommended Two-Stage Strategy
[!TIP] A commonly used staged design: Conduct initial screening with the UUO model for rapid results, then validate promising candidates using the adenine diet model or 5/6 nephrectomy model in a two-stage strategy—a time- and cost-efficient approach in practice. The rationale parallels the tiered use of CDA-HFD and GAN models in MASH drug discovery.
4. Endpoint Comparison
Below are the key evaluation endpoints used in renal fibrosis models and their applicability across models.
4.1 Renal Function Markers
| Endpoint | UUO | Adenine | 5/6 Nx | IRI | DKD Models |
|---|---|---|---|---|---|
| Serum creatinine | ✕ | ○ | ○ | ○ (acute) | ○ |
| BUN | ✕ | ○ | ○ | ○ (acute) | ○ |
| Proteinuria/albuminuria | ✕ | △ | ○ | △ | ○ |
| KIM-1 (urine/serum) | △ | ○ | ○ | ○ | ○ |
| GFR (inulin clearance, etc.) | ✕ | ○ | ○ | ○ | ○ |
In the UUO model, the contralateral kidney compensates, so serum renal function markers remain unchanged. Choose a model other than UUO when renal function assessment is required in your study design.
4.2 Histological and Biochemical Endpoints
| Endpoint | What It Measures | Priority | Common to All Models | Detailed Article |
|---|---|---|---|---|
| Sirius Red staining | Collagen deposition area (%) | Core | ○ | Protocol & Quantification |
| Masson's trichrome staining | Fibrosis area | Core | ○ | Staining Protocol |
| Hydroxyproline assay | Total collagen content | Core | ○ | Assay Guide |
| α-SMA IHC | Activated myofibroblasts | Recommended | ○ | ImageJ Quantification |
| PAS staining | Glomerulosclerosis / tubular injury | Recommended | ○ (especially DKD) | — |
| F4/80 IHC | Macrophage infiltration | Optional | ○ | — |
| RT-qPCR | Col1a1, Acta2, Tgfb1, Fn1, etc. | Recommended | ○ | — |
4.3 Recommended Endpoint Combinations by Model
| Model | Primary Endpoints | Secondary Endpoints |
|---|---|---|
| UUO | Sirius Red + hydroxyproline | α-SMA IHC, RT-qPCR, kidney weight ratio |
| Adenine | BUN/Cr + Sirius Red | Hydroxyproline, Masson's trichrome |
| 5/6 Nx | BUN/Cr + proteinuria + glomerulosclerosis score | Sirius Red, Masson's trichrome |
| IRI | Acute: BUN/Cr + KIM-1 / Chronic: Sirius Red | NGAL, α-SMA, F4/80 |
| DKD | Albuminuria + PAS staining (glomerulosclerosis) | Mesangial expansion score, Sirius Red |
5. Practical Considerations for Model Selection
5.1 Species and Strain Differences
The choice of animal species and strain is also a critical variable in model selection.
- Mouse vs. rat: The 5/6 nephrectomy model is predominantly used in rats (due to technical ease of surgery and kidney size), whereas UUO and adenine models are widely used in mice
- Strain effects are model-specific: Renal injury, fibrosis, and mortality differ across C57BL/6, BALB/c, FVB/N, and 129 strains, and cross-organ generalizations (e.g., "C57BL/6 is Th1-dominant and more fibrosis-prone") do not always hold. In renal models, for instance, C57BL/6 mice are relatively resistant to cisplatin-induced injury and require a higher dose to induce fibrosis (Sears SM et al. Am J Physiol Renal Physiol. 2020). The background strain should be fixed and justified, and pilot induction is often needed even with the same induction method (see the Species and Strain Differences in Fibrosis Models Guide for details)
- Background strain for DKD models: db/db mice on the C57BLKS/J background develop the most consistent nephropathy. On the C57BL/6 background, nephropathy tends to be milder
5.2 Combination Models
To overcome the limitations of single models, combination approaches that integrate multiple induction methods have been developed.
- STZ + high-fat diet (HFD): Adds metabolic dysfunction to a type 1 diabetes model, producing a phenotype closer to type 2 DKD
- Unilateral IRI + contralateral nephrectomy: Enables evaluation of post-AKI chronicity along with changes in renal function
- UUO + STZ: Evaluates obstructive nephropathy against a diabetic background
5.3 The 3Rs (Replacement, Reduction, Refinement)
- Replacement: Minimize animal use through integration with in vitro kidney slice cultures and renal organoids
- Reduction: Reduce required sample sizes by minimizing data variability through microsurgical techniques (see the UUO article for details)
- Refinement: Prioritize non-invasive models (adenine diet, genetic models)
Summary: Matching the Right Model to Your Research Question Is the Key to Drug Discovery Success
Each renal fibrosis model has its own strengths and limitations. The critical point is not to search for the "best model" but to select the one that best addresses your specific research question.
| Objective | First Choice | Second Choice |
|---|---|---|
| Rapid screening of anti-fibrotic compounds | UUO | Adenine diet |
| Efficacy evaluation including renal function improvement | Adenine diet | 5/6 nephrectomy |
| AKI-to-CKD transition research | IRI | Repeated cisplatin |
| DKD therapeutic development | db/db / BTBR ob/ob | STZ + HFD |
| Long-term evaluation of progressive CKD | 5/6 nephrectomy | Alport syndrome mice |
By leveraging this guide during the design phase of preclinical studies, selecting the appropriate model and endpoint combination will increase the likelihood of successful clinical translation.
Related Articles
- Complete Guide to the UUO Renal Fibrosis Model
- Complete Guide to the Adenine-Induced CKD Model
- Fibrosis Quantitative Assessment Hub
- Sirius Red Staining Protocol
- Hydroxyproline Assay Guide
- Masson's Trichrome Staining Protocol
- Species and Strain Differences in Fibrosis Models Guide
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- Cosgrove D, et al. "Collagen COL4A3 knockout: a mouse model for autosomal Alport syndrome." Genes Dev. 1996;10(23):2981-2992. PubMed
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