Mechanism of SMND-309 against lung injury induced by chronic intermittent hypoxia

Obstructive sleep apnea–hypopnea syndrome (OSAHS) is a common sleep disorder that causes severe physiological disturbance. Evidence showed that OSAHS is an important associated comorbidity that can affect the survival of patients with pulmonary fibrosis. Until now, the potential mechanisms by which OSAHS accelerates the progression of lung fibrosis remain unclear. By constructing a pathological model of chronic intermittent hypoxia (CIH), the present study aimed to explore the pathological progress and potential mechanism of lung injury caused by OSAHS. Meanwhile, SMND-309 was given for treatment to evaluate its potential therapeutic role in CIH-induced lung injury. Mice were randomly divided into (C57BL/6 wild-type) WT+(room air) RA, WT + CIH, SMND-309 + RA, and SMND-309 + CIH groups. The WT + CIH and SMND-309 + CIH groups were exposed to CIH condition for 12 weeks, while the other groups were processed in normal oxygen at the same time. The SMND-309 + RA and SMND-309 + CIH groups were intraperitoneally injected with SMND-309 at the last week of the modeling period. After 12 weeks of treatment, three mice from each group were perfused through the heart. Lung tissues were isolated, fixed, sectioned, and stained with H&E, Masson, and immunofluorescence stain. The rest of the lung tissues were harvested for Western blot and ELISA assays. CIH treatment increased the expression of pro-inflammatory factors (TNF-α and IL-6), resulting in lung tissue structure disorder, inflammatory cell infiltration, increased pulmonary capillary permeability, and pulmonary edema. The activation of the NF-κB signaling pathway played a crucial role in the process of inflammation. Noticeably, we observed M2 macrophage accumulation in the lung after CIH exposure, which promoted epithelial–mesenchymal transition (EMT) and pulmonary tissue fibrosis. ELISA assays showed the increased expression of TGF-β, IL-10, and IL-4 in the CIH group. SMND-309 inhibited pulmonary inflammation, reduced the accumulation of M2 macrophage, alleviated collagen deposition and lung damage. CIH could induce chronic lung inflammation, promote the activation of M2 macrophages, trigger the occurrence of EMT, and accelerate the deposition of lung collagen, eventually leading to lung tissue damage. This study presents a possible explanation by which interstitial lung diseases, particularly idiopathic pulmonary fibrosis (IPF) with OSAHS, are usually associated with fast progress and poor prognosis. SMND-309 showed a good protective effect on CIH-induced lung damage.