Gq-coupled G protein-coupled receptors (GPCRs) regulate airway smooth muscle tone, and their excessive stimulation can lead to airway hyperresponsiveness (AHR). This is a key feature of asthma. This study investigates the effects of FR900359 (FR) on AHR, fibroblast proliferation, mucus production, and collagen deposition because current anti-inflammatory treatment fails to reverse the structural airway changes.
This study aimed to examine whether pharmacological inhibition of Gq protein signaling using the selective inhibitor FR might prevent airway remodeling in asthma. This study demonstrated that inhibition of Gq significantly decreases airway remodeling, offering a potential novel treatment method for chronic asthma. The research used a chronic asthma mouse model, asthmatic lung issues, and various human cell lines.
For the in vivo model, a chronic asthma model was established in female Balb/c mice by using ovalbumin (OVA) sensitization and repeated aerosol exposure. FR was injected intratracheally before every OVA exposure. FlexiVent was used for AHR. Lung tissue was analyzed by using histological staining, and real-time polymerase chain reaction (qPCR) was used for remodeling markers.
For the in vitro model, human lung fibroblasts (HFL1) were stimulated with asthma-related growth factors and Gq agonists with or without FR to evaluate cell proliferation. Air-liquid interface (ALI) cultures of human bronchial epithelial cells (HBECs) were utilized to assess the mucus secretion and production with interleukin-13 (IL-13) and Gq agonist stimulation, with FR or tiotropium treatment. Global cells were counted using Alcian blue staining. MUC5AC secretion was assessed by enzyme-linked immunosorbent assay (ELISA). The mucoepidermoid NCI-H292 cell line was utilized to assess mucus gene expression after EGF and thrombin stimulation, with or without FR. Precision-cut lung slices (PCLS) from asthmatic donors received treatment with FR. MUC5AC levels in medium culture were evaluated to detect the ex vivo effect on mucus secretion.
Statistical analyses were conducted by GraphPad Prism, which involved one-way or two-way ANOVA with Tukey’s or Bonferroni’s post hoc tests and unpaired two-tailed t-tests. A p-value of < 0.05 was considered statistically significant.
Inhibition of Gq proteins with FR significantly reduced airway remodeling in the chronic OVA-induced asthma mouse model. Mice receiving intratracheal FR showed reduced AHR during the methacholine challenge. This indicates the improved airway tone regulation. Notably, FR did not change cytokine levels or eosinophilic inflammation in the bronchoalveolar lavage (BAL), suggesting its effects are independent of inflammatory pathways.
Histological analysis showed that FR decreased peribronchial collagen deposition and goblet cell metaplasia. Staining methods like Sirius Red, PAS, and MUC5AC validated fewer mucus-producing cells. Gene expression studies found decreased MUC5AC mRNA. Transcription factors linked with goblet cell differentiation (Spdef, Foxa2, Scgb1a1) did not change. This indicates FR mostly affects mucus production rather than differentiation.
Similar to in vivo, FR suppressed the proliferation of human lung fibroblasts (HFL1) treated with asthma-related growth factors and Gq agonists linked to asthma in vitro. In ALI cultures of the HBECs, FR inhibited mucus secretion induced by IL-13 and Gq agonists. Ex vivo lung tissue and NCI-H292 cells from asthmatic patients showed comparable results. FR successfully targets airway remodeling elements, independent of inflammatory suppression, and shows relevance to human asthma treatment.
This study highlights the potential of FR, a selective Gq protein inhibitor, to reduce airway remodeling, such as mucus overproduction, goblet cell metaplasia, fibroblast proliferation, and collagen buildup. However, a key limitation of this study is the uncertainty regarding whether these benefits are directly from inhibition of Gq or indirectly from reduced AHR. Long-term safety and systemic effects of FR remain unclear, and in vitro and ex vivo models do not fully replicate the complexity of in vivo biology. Nonetheless, FR shows promise as a novel treatment method for asthma and needs further evaluation in clinical and preclinical studies.
References: Dietrich JM, Matthey M, Simon A, et al. Pharmacological Gq targeting prevents asthmatic airway remodeling. Mol Ther. 2025. doi:10.1016/j.ymthe.2025.07.032
