Significant Role of Thrombospondin-2 in Acute Lung Injury and Its Underlying Molecular Mechanisms

Acute lung injury (ALI) is associated with high mortality. Thrombospondin-2 (THBS2), a member of the THBS family, has been implicated in multiple diseases, but its role in ALI remains unclear. The study aimed to explore the role of THBS2 in ALI and its regulatory mechanisms. A549 cells were treated with 1 μg/mL lipopolysaccharide (LPS) for 24 h to establish an in vitro cellular model of ALI. THBS2 siRNA was used to knockdown THBS2 and investigate its role. Changes in cell viability and apoptosis were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry, respectively. Malondialdehyde (MDA), superoxide dismutase (SOD), reactive oxygen species (ROS), and catalase (CAT) levels were quantified. Interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-alpha (TNF-α) levels were measured by enzyme-linked immunosorbent assay. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed to determine gene and protein expression, respectively. THBS2 expression was increased in LPS-induced A549 cells. LPS significantly reduced cell viability, enhanced cell apoptosis, increased cleaved caspase-3 expression and the cleaved caspase-3/caspase-3 ratio, increased ROS and MDA levels, decreased SOD and CAT activity, and promoted IL-6, IL-1β, and TNF-α levels in A549 cells. Meanwhile, LPS activated the toll-like receptor 4 (TLR4)/NF-κB pathway, but these changes were reversed by THBS2 siRNA. The results also demonstrated that TLR4 plasmid reversed the protective effects of THBS2 siRNA against LPS-induced injury in A549 cells. THBS2 was upregulated in ALI in vitro model, and its knockdown attenuated LPS-induced injury in A549 cells by inhibiting the TLR4/NF-κB signaling pathway.