Danlong oral liquid alleviates airway remodeling in asthma by targeting the S1PR2/ROCK1/YAP signaling pathway in airway smooth muscle cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Danlong Oral Liquid (DLOL) is a proprietary Traditional Chinese Medicine (TCM) with documented clinical efficacy against asthma, yet its underlying mechanism of action remains incompletely understood. The bioactive sphingolipid mediator sphingosine-1-phosphate (S1P) and its receptor S1PR2 signaling axis are critically implicated in asthma pathogenesis, particularly in driving airway smooth muscle cell (ASMC) remodeling, a key pathological feature of asthma. Despite this, the mechanistic involvement of DLOL in this specific pathway has not been explored.

AIM OF THE STUDY: This study aimed to validate the effect of DLOL against asthma-associated airway remodeling and to elucidate whether its mechanism of action involves the modulation of the S1PR2/ROCK1/YAP signaling pathway in ASMCs.

MATERIALS AND METHODS: The therapeutic effects and mechanisms of DLOL were investigated using a combination of in vivo and in vitro approaches. An in vivo rat model of allergic asthma was induced by ovalbumin (OVA) sensitization and challenge. We assessed airway hyperresponsiveness (AHR) and performed inflammatory cell counts in bronchoalveolar lavage fluid (BALF) using Wright-Giemsa staining. Lung histopathology was evaluated by Hematoxylin and Eosin (H&E) staining, Periodic Acid-Schiff (PAS) staining, and Masson's trichrome staining to assess inflammation, goblet cell hyperplasia, and collagen deposition. Levels of S1P and cytokines (IL-4, IL-5, IL-13) in BALF and serum, along with OVA-IgE in serum, were measured by enzyme-linked immunosorbent assay (ELISA). The protein and gene expression of key molecules in the S1PR2/ROCK1/YAP signaling pathway were analyzed by Western blotting (WB), immunohistochemistry (IHC), and Real-time quantitative polymerase chain reaction (RT-qPCR). For in vitro studies, primary rat ASMCs were stimulated with S1P. The impact of DLOL-containing serum (DL-CS) on proliferation was assessed using the Cell Counting Kit-8 (CCK-8) and 5-Ethynyl-2'-deoxyuridine (EdU) incorporation assays. Cell migration and contraction were evaluated by scratch assay and collagen gel contraction assay, respectively. Underlying mechanisms were further examined by WB, RT-qPCR, and immunofluorescence (IF).

RESULTS: DLOL administration significantly alleviated AHR, airway inflammation, and remodeling in a rat model of asthma. Mechanistically, DLOL downregulated the S1PR2/ROCK1/YAP signaling axis in lung tissues, inhibiting the expression of S1PR2, RhoA, and ROCK1, promoting YAP inactivation, and suppressing the downstream targets FOXM1 and CyclinD1. Consistently, DL-CS potently inhibited S1P-induced proliferation, migration, and contraction of ASMCs in vitro, further confirming its robust anti-remodeling activity.

CONCLUSIONS: Our integrated findings demonstrate that DLOL alleviates allergic asthma and airway remodeling by inhibiting the S1PR2/ROCK1/YAP signaling pathway in ASMCs, thereby restraining their pro-remodeling phenotypes. This work not only provides a solid mechanistic basis for the clinical application of DLOL but also positions it as a promising multi-targeted therapy for asthma.