Chronic Obstructive Pulmonary Disease (COPD) is the most prevalent chronic respiratory disorder, marked by persistent respiratory symptoms and irreversible progressive airflow restriction (Safiri et al., 2022). COPD is responsible for at least 3 million deaths globally each year, ranking as the third leading cause of mortality worldwide. Prolonged exposure to harmful gases and particles is the primary driver of COPD onset and progression (Soriano et al., 2018). This exposure can trigger inflammation in both large and small airways, leading to epithelial cell metaplasia, loss of ciliated epithelial cells, goblet cell hyperplasia, hypertrophy/hyperplasia of submucosal glands and smooth muscles, and increased mucus secretion, ultimately resulting in alveolar wall destruction and emphysema (Hill et al., 2022; Long et al., 2024). Current pharmacological treatments for COPD include bronchodilators, corticosteroids, β2-agonists, and theophylline, which can alleviate clinical symptoms and improve quality of life but do not significantly slow disease progression (Wing et al., 2021). Previous studies have shown that these treatments have limited efficacy and are associated with significant side effects, such as steroid insensitivity and an increased risk of pneumonia (Shah et al., 2023). Therefore, there is an urgent need to develop safe and effective treatments for COPD.

Airway mucus, a thin liquid layer covering the airway surface, is composed of water, ions, mucins (MUC), and other macromolecules (X. Li et al., 2025; Mettler et al., 2024). It facilitates the clearance of inhaled foreign particles through mucociliary clearance, thereby offering effective lung protection (Münzel et al., 2020). Exogenous harmful gases and particles, such as cigarette smoke, stimulate the excessive proliferation of goblet cells and hypertrophy of submucosal glands, leading to increased mucin secretion in respiratory patients, causing airway obstruction and persistent lung damage (Takezawa et al., 2016). MUC5AC and MUC5B are the primary types of airway mucins, directly reflecting the extent of airway mucus secretion (Kesimer, 2022; Radicioni et al., 2021). Studies have shown significantly elevated levels of MUC5AC and MUC5B in the sputum of COPD patients, resulting in high mucin secretion, persistent coughing, sputum production, and impaired lung function. In a mouse model of cigarette smoke-induced COPD, levels of MUC5AC and MUC5B in lung tissue were significantly elevated (Hoang et al., 2022). Additionally, in airway epithelial cells exposed to cigarette smoke, MUC5AC and MUC5B were highly expressed, resulting in increased epithelial cell inflammation (Xu et al., 2023). Therefore, effectively inhibiting mucus hypersecretion in the airways can alleviate chronic airway inflammation, delay the progressive decline in lung function, and improve outcomes for COPD patients.

Ubiquitination is a crucial post-translational modification of proteins that regulates protein degradation and participates in various pathological and physiological processes, such as airway inflammation (Agrata and Komander, 2025; Fan et al., 2020). Under the action of ubiquitin-activating enzyme E1, ubiquitin-conjugating enzyme E2, and ubiquitin ligase E3, the C-terminal amino acid of the ubiquitin molecule is linked to the lysine residue on the target protein via an isopeptide bond. E3 ubiquitin ligases containing the RING domain are part of the Tripartite Motif (TRIM) protein family (Huang et al., 2024; Wang et al., 2025). TRIM56, a member of this family, catalyzes the ubiquitination of proteins such as Vimentin, DVL2 (Dishevelled-2), ERα, SAP18 (Sin3A-associated protein 18), IκBα, STING, cGAS, and TGF-β-activated kinase 1 (TAK1) (Liu et al., 2022; Wang et al., 2024). These processes are implicated in carcinogenesis, innate immunity, autophagy, and signal transduction (Vertegaal, 2022; Yang et al., 2022). As an E3 ubiquitin ligase, TRIM56 enhances the antiviral response to cytosolic DNA by catalyzing K63-linked ubiquitination of STING to promote its dimerization, as well as monoubiquitination of cGAS to facilitate its stable dimerization and DNA-binding activity (Guan et al., 2024; Seo et al., 2018). Furthermore, TRIM56 positively regulates the TLR3-mediated antiviral signaling pathway (Xu et al., 2022). Although the role of TRIM56 in innate immunity is well-established, it remains unclear whether it can regulate the expression of mucins such as MUC5AC.

Traditional Chinese Medicine (TCM) has been extensively used in the clinical management of Chronic Obstructive Pulmonary Disease (COPD), showing significant clinical efficacy in alleviating symptoms, reducing the frequency of acute exacerbations, and improving overall quality of life. According to TCM theory, lung qi deficiency is a primary syndrome associated with COPD (Cao et al., 2023; Tao et al., 2025). The Bu Fei formula (BFF), a Chinese herbal medicine, is specifically prescribed for patients with this syndrome. Research has shown that it can improve lung function, significantly reduce acute exacerbations, and extend the 6-min walk distance in COPD patients. Furthermore, it is effective in alleviating chronic cough, sputum production, wheezing, chest tightness, shortness of breath, fatigue, and cyanosis (J. Li et al., 2025). This study aims to establish COPD mouse models and airway epithelial cell cultures to investigate the role of the BFF in the TRIM56-mediated ubiquitination pathway and to elucidate its mechanism for suppressing airway mucus hypersecretion.