PLK1 Mediates the Proliferation and Contraction of Airway Smooth Muscle Cells and Has a Role in T2-High Asthma with Neutrophilic Inflammation Model.

Background: Type 2 (T2)-high asthma with neutrophilic inflammation is characterized by airway eosinophilic and neutrophilic infiltration, hyperresponsiveness, remodeling, and insensitivity to steroid treatment. Sphingosine-1-phosphate (S1P), which has a crucial role in the development of asthma, promotes the proliferation and contraction of airway smooth muscle cells (ASMCs), contributing to the pathophysiological processes of asthma. However, the downstream mediator of S1P remains unclear, as does its role in T2-high asthma with neutrophilic inflammation. Methods: Ovalbumin- and ozone-induced murine models were used to replicate T2-high asthma with neutrophilic inflammation and primary ASMCs were applied to explore the underlying effects. Through transcriptomic analysis, PLK1 was identified as a potential key molecule associated with S1P-induced proliferation and contraction. Functional studies were performed both in vitro and in vivo by pharmacological inhibition to validate the role of PLK1 and to evaluate the therapeutic effects of PLK1 inhibition. Results: S1P level was elevated in the bronchoalveolar lavage fluid (BALF) of T2-high asthma with neutrophilic inflammation model, and promoted ASMCs proliferation and contraction. PLK1 expression increased in S1P-stimulated ASMCs and asthmatic lung tissues. Inhibition of PLK1 blocked S1P-induced ASMCs proliferation and contraction. In vivo, PLK1 inhibition reduced airway inflammation (particularly neutrophilic infiltration), airway remodeling (airway smooth muscle proliferation and collagen deposition), and airway hyperresponsiveness and resistance, improving lung function (of both large and small airways), with superior therapeutic effects to those of dexamethasone. In addition, PLK1 inhibition markedly reduced the BALF levels of IL-17A, IL-21 and IL-6, suggesting that PLK1 might exert its effects mainly through the regulation of Th17 pathway. Conclusion: PLK1 mediates S1P-induced ASMC proliferation and contraction, and plays an important part in T2-high asthma with neutrophilic inflammation model, making it a potential therapeutic target for treating T2-high asthma with neutrophilic inflammation.