Transcriptomic analysis identifies upregulation of secreted phosphoprotein 1 in silicotic rats

Silicosis is caused by exposure to crystalline silica and the molecular mechanism of silicotic fibrosis remains unclear. Therefore, the present study investigated the mRNA profiles of rats exposed to crystalline silica. RNA-sequencing techniques were used to observe differential expression of mRNAs in silicotic rats induced by chronic inhalation of crystalline silica particulates. Prediction of mRNA functions and signaling pathways was conducted using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Certain differentially expressed mRNAs were verified in lung tissue of silicotic rats by quantitative polymerase chain reaction (qPCR). Secreted phosphoprotein 1 (SPP1) was measured in serum from silicosis patients, lungs of silicotic rats and NR8383 macrophages treated with silica. A total of 1,338 mRNAs were revealed to be differentially expressed in silicotic rat lungs, including 912 upregulated and 426 downregulated mRNAs. In GO analysis of significant changes in mRNAs, the most affected processes were the defense response, extracellular space and chemokine activity in terms of biological process, cellular component and molecular function. In KEGG pathway analysis, dysregulated mRNAs were involved in systemic lupus erythematosus, staphylococcus aureus infection, complement and coagulation cascades, alcoholism and pertussis. qPCR demonstrated that expression of Spp1, Mmp12, Ccl7, Defb5, Fabp4 and Slc26a4 was increased in silicotic rats, while Lpo, Itln1, Lcn2 and Dlk1 expression was decreased. It was also found that SPP1 was increased in serum from silicosis patients, silicotic rats and silica-treated NR8383 macrophages. The expression of mRNAs was altered significantly in silicotic rats, which suggested that certain genes are novel targets for the diagnosis and treatment of silicosis.