Background Existing studies have confirmed that fine particulate matter (PM_2.5)is one of the important factors inducing pulmonary fibrosis. Pulmonary fibrosis is the terminal stage of a major category of lung diseases characterized by the destruction of tissue structure, and eventually leading lung ventilation and ventilation dysfunction. No effective pulmonary fibrosis treatment is available yet. Objective To investigate the protective effect of salidroside on pulmonary fibrosis induced by the exposure of PM_2.5 and its molecular mechanism. Methods Seventy 7-week-old male C57BL/6 mice were randomly divided into four groups: control group (intratracheal instillation of normal saline + saline by gavage, n=25), Sal group (intratracheal instillation of normal saline + Sal 60 mg·kg⁻¹ by gavage, n=10), PM_2.5 group (intratracheal instillation of PM_2.5 5 mg·kg⁻¹ + saline by gavage, n=10), and Sal + PM_2.5 group (intratracheal instillation of PM_2.5 5 mg·kg⁻¹ +Sal 60 mg·kg⁻¹ by gavage, n=10). The mice were administered by gavage once daily, intratracheal instillation once every 3 d, and every 3 d constituted an experimental cycle. At the end of the 26-30th cycles, 3 mice in the control group and 3 mice in the PM_2.5 group were randomly sacrificed, and the lung tissues were collected for Masson staining to verify whether the pulmonary fibrosis model was successfully established. After 30 cycles, the model was successfully constructed. After 1 week of continuous observation, the mice were sacrificed, and the blood and lung tissues of the mice were collected to make lung tissue sections. Assay kits were correspondingly employed to detect oxidative stress indicators such as serum malondialdehyde (MDA) and superoxide dismutase (SOD). Western blotting was used to detect the expression of fibrosis-related proteins (Collagen-III, α-SMA), mitochondrial dynamics-related proteins (MFN1, Drp1), and mitophagy-related proteins (PINK1, Parkin, and LC3). Results Compared with the control group, the weight gain rate of the PM_2.5 group was slowed down (P<0.05), which was alleviated by the Sal intervention (P<0.05). The lung coefficient increased after the PM_2.5 exposure (P<0.05), which was alleviated by Sal intervention. Compared with the control group, the PM_2.5 group showed severe alveolar structure damage, inflammatory cell infiltration, and blue collagen deposition, and significantly increased the lung injury score, collagen volume fraction (CVF), Szapiel score, and Ashcroft score (P<0.05), as well as serum oxidative stress levels (P<0.05). The protein expression levels of Collagen-III, α-SMA, Drp1, PINK1, Parkin, and LC3 II/I were increased (P<0.05), and the expression of MFN1 was decreased (P<0.05). Compared with the PM_2.5 group, the Sal intervention alleviated lung injury, reduced inflammatory cell infiltration and collagen deposition, showing decreased lung injury score, CVF, Szapiel score, and Ashcroft score (P<0.05), and decreased serum oxidative stress levels (P<0.05); the protein expression levels of Collagen-III, α-SMA, PINK1, Parkin, and LC3 II/I were decreased (P<0.05), the expression level of Drp1 was decreased, and the expression level of MFN1 was increased. Conclusion In the process of pulmonary fibrosis induced by PM_2.5 exposure in mice, Sal may affect mitochondrial autophagy through PINK1/Parkin pathway and play a protective role. The specific mechanism needs to be further verified.

Background Salidroside (SAL) has a protective effect on multiple organ systems. Exposure to fine particulate matter (PM_2.5) in the atmosphere may lead to disruptions in gut microbiota and impact intestinal health. The regulatory effect of SAL on the gut microbiota of mice exposed to PM_2.5 requires further investigation. Objective To evaluate gut microbiota disruption in mice after being exposed to PM_2.5 and the potential effect of SAL. Methods Forty male C57BL/6 mice, aged 6 to 8 weeks, were randomly divided into four groups: a control group, an SAL group, a PM_2.5 group, and an SAL+PM_2.5 group, each containing 10 mice. In the SAL group and the SAL+PM_2.5 group, the mice were administered SAL (60 mg·kg⁻¹) by gavage, while in the control group and the PM_2.5 group, sterile saline (10 mL·kg⁻¹) was administered by gavage. In the PM_2.5 group and the SAL+PM_2.5 group, PM_2.5 suspension (8 mg·kg⁻¹) was intratracheally instilled, and in the control group and SAL group, sterile saline (1.5 mL·kg⁻¹) was intratracheally administered. Each experiment cycle spanned 2 d, with a total of 10 cycles conducted over 20 d. Histopathological changes in the ileum tissue of the mice were observed after HE staining. Colon contents were collected for gut microbiota sequencing and short-chain fatty acids (SCFAs) measurements. Results The PM_2.5 group showed infiltration of inflammatory cells in the ileum tissue, while the SAL+PM_2.5 group exhibited only a small amount of inflammatory cell infiltration. Compared to the control group, the PM_2.5 group showed decreased Shannon index (P<0.05) and increased Simpson index (P<0.05), indicating that the diversity of gut microbiota in this group was decreased; the SAL+PM_2.5 group showed increased Shannon index compared to the PM_2.5 group (P<0.05) and decreased Simpson index (P<0.05), indicating that the diversity of gut microbiota in mice intervened with SAL was increased. The principal coordinates analysis (PCoA) revealed a significant separation between the PM_2.5 group and the control group, while the separation trend was less evident among the control group, the SAL group, and the SAL+PM_2.5 group. The unweighted pair-group method with arithmetic means (UPGMA) clustering tree results showed that the control group and the SAL group clustered together first, followed by clustering with the SAL+PM_2.5 group, and finally, the three groups clustered with the PM_2.5 group. The PCoA and UPGMA clustering results indicated that the uniformity and similarity of the microbiota in the PM_2.5 group were significantly decreased. Compared to the control group, the PM_2.5 group showed decreased abundance of phylum Bacteroidetes and Candidatus_Saccharimonas (P<0.05) and increased abundance of phylum Proteobacteria, genus Escherichia, genus Bacteroides, genus Prevotella, genus Enterococcus, and genus Proteus (P<0.05). Compared to the PM_2.5 group, the SAL+PM_2.5 group showed decreased abundance of phylum Proteobacteria, phylum Actinobacteria, genus Prevotella, and genus Proteus (P<0.05), and increased abundance of Candidatus_Saccharimonas (P<0.05). The PM_2.5 group showed reduced levels of propionic acid, valeric acid, and hexanoic acid compared to the control group (P<0.05), while the SAL+PM_2.5 group showed increased levels of propionic acid, isobutyric acid, butyric acid, valeric acid, and hexanoic acid compared to the PM_2.5 group (P<0.05). Conclusion Exposure to PM_2.5 can cause pathological alterations, microbial dysbiosis, and disturbing production of SCFAs in intestinal tissue in mice. However, SAL can provide a certain degree of protective effect against these changes.