Modeling Principle

The C57 mouse bleomycin pulmonary fibrosis model is a SCI gold-standard standardized rodent interstitial pulmonary fibrosis model established by single intratracheal instillation of bleomycin (BLM). It accurately recapitulates the complete pathological cascade of clinical idiopathic pulmonary fibrosis (IPF), including alveolar epithelial injury, chronic pulmonary inflammation, myofibroblast activation, massive collagen deposition and lung tissue remodeling, and serves as a global universal standard model for pulmonary fibrosis pathogenesis research and anti-fibrotic drug evaluation.

As a broad-spectrum anti-tumor antibiotic, bleomycin exerts strong lung-targeted cytotoxicity. Intratracheal administration directly acts on type Ⅰ and type Ⅱ alveolar epithelial cells, destroys the integrity of epithelial barrier, induces DNA fragmentation and mitochondrial oxidative stress burst, accumulates massive oxidative damage products ROS and MDA, and drives apoptosis and necrosis of alveolar epithelial cells. Damaged epithelium continuously releases damage-associated molecular patterns (DAMPs), recruits massive infiltration of alveolar macrophages, neutrophils and lymphocytes into pulmonary interstitium, activates NF-κB inflammatory pathway, and secretes pro-inflammatory factors such as TNF-α, IL-6 and IL-1β to form a persistent chronic pulmonary inflammatory microenvironment. Sustained stimulation of chronic inflammation transforms resting pulmonary fibroblasts into myofibroblasts, abnormally activates the canonical TGF-β1/Smad fibrotic signaling axis, and upregulates massive synthesis and deposition of extracellular matrix proteins including type Ⅰ/Ⅲ collagen, fibronectin and laminin. Alveolar structures collapse, alveolar septa thicken, and normal lung parenchyma is replaced by fibrous scars, gradually forming progressive lesions including early alveolitis, middle-stage fibroplasia and late-stage dense fibrosis, which fully recapitulates the progressive and irreversible interstitial injury characteristics of human idiopathic pulmonary fibrosis.

Inbred C57BL/6 mice possess homogenous and unified genetic background, stable response to bleomycin pulmonary toxicity, clear temporal sequence of pulmonary fibrosis progression and minimal intra-group individual differences without spontaneous pulmonary fibrotic lesions. It can completely distinguish three-stage pathological phenotypes of inflammatory phase, fibroproliferative phase and terminal lung remodeling phase, and is applicable to preclinical pharmacodynamic evaluation of lung injury inflammation regulation, epithelial repair, anti-fibrotic target excavation, small molecules, traditional Chinese medicines and biological agents.

Modeling Success Criteria

Macroscopic Lung Gross Phenotype

The bilateral lungs of blank control group were soft, uniformly light pink, smooth on surface without white plaques or congested nodules. On Day 21 terminal point, lung tissues of model group shrank in volume, hardened in texture, covered with diffuse gray-white fibrous scar plaques on lobe surface, with significantly elevated pulmonary organ coefficient, pulmonary congestion and edema accompanied by focal consolidation. Macroscopic fibrotic plaques were clearly visible to naked eye, with extremely significant difference from blank group, confirming preliminary successful model construction.

Core Serum and Pulmonary Fibrosis Biochemical Indexes

The pulmonary TGF-β1 content of model group was extremely significantly upregulated compared with blank group, serving as core quantitative gold standard for fibrosis initiation. Meanwhile, mRNA and protein expression of type Ⅰ and Ⅲ collagen in lung tissues were greatly elevated with excessive extracellular matrix deposition. Pro-inflammatory factors TNF-α, IL-6 and IL-1β in serum and lung tissues were persistently highly expressed with sustained activation of chronic alveolar inflammation, fully matching the core biochemical characteristics of "preceding inflammation followed by secondary fibrosis" in clinical IPF patients.

Pulmonary Histopathological Characteristics

Combined HE, Masson and Sirius red staining of lung tissues showed typical IPF-like fibrotic pathological changes:

1. Day 7 inflammatory phase: obviously widened alveolar septa, diffuse massive infiltration of neutrophils, macrophages and lymphocytes, increased exudation in alveolar lumen, degeneration and shedding of alveolar epithelium;
2. Day 14 proliferative phase: massive proliferation of fibroblasts, slight collagen fiber deposition, initial destruction and collapse of alveolar structures;
3. Day 21 terminal fibrotic phase: large-area damage of normal alveolar structures with honeycomb changes, extremely thickened alveolar septa, extensive accumulation of massive blue/red stained collagen fibers forming dense fibrous scars and reduced inflammatory cell infiltration, which fully recapitulates the classic pathological grading characteristics of human idiopathic pulmonary fibrosis.

Core Oxidative Stress and Fibrotic Pathway Indexes

The levels of oxidative damage products ROS and MDA in lung tissues of model group were significantly increased, while the activities of antioxidant enzymes SOD and GSH-Px were significantly decreased, resulting in severe alveolar epithelial oxidative stress imbalance. The TGF-β1/Smad2/3 fibrotic pathway was persistently overactivated, and the expression of α-SMA myofibroblast marker was significantly upregulated, which fully conforms to the complete pathogenic mechanism of bleomycin induction: epithelial oxidative injury-chronic inflammation-myofibroblast activation-collagen deposition, serving as core academic criterion for confirming successful modeling.

Model Advantages

This model is a SCI-recognized gold-standard mouse model of bleomycin-induced pulmonary fibrosis with standardized modeling operation and stable lesion formation via single intratracheal instillation, which fully recapitulates the whole inflammation-fibrosis course of human IPF within 21 days. C57 mice possess consistent genetic background, uniform fibrosis progression gradient, extremely low intra-group data dispersion and excellent experimental reproducibility. It has pure modeling mechanism relying only on drug alveolar epithelial toxicity to initiate injury without confounding interference such as exogenous surgery and gene editing, with clear targets. It is specially applied to preclinical pharmacodynamic screening of anti-fibrotic small molecules, traditional Chinese medicine extracts, biological agents and pulmonary epithelial protective agents. It features low experimental cost, simple animal feeding and large sample size, with data recognized by all high-score respiratory SCI journals, suitable for fund declaration, master/doctor project opening, graduation thesis and basic & translational medical research of pulmonary fibrosis.

Research Applications

The C57 mouse bleomycin pulmonary fibrosis model is corely applied to basic research on alveolar epithelial oxidative injury mechanism, chronic inflammation-mediated pulmonary fibrosis, TGF-β/Smad myofibroblast activation and abnormal extracellular matrix deposition. It is specially used for screening and evaluating traditional Chinese medicine compounds, natural active products, small chemical molecules and targeted biological preparations with effects of protecting alveolar epithelium, inhibiting chronic pulmonary inflammation, blocking TGF-β fibrotic signal, reducing collagen accumulation and delaying lung tissue remodeling. It is widely adopted for excavation of pathogenic targets of idiopathic pulmonary fibrosis, verification of pharmacological mechanisms of anti-fibrotic drugs and in-vivo preclinical evaluation of pulmonary injury repair preparations, serving as the most widely used standardized rodent gold-standard model in the fields of respiratory pharmacology, interstitial lung disease and fibrotic translational research.

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