Porcine respiratory disease complex induces pulmonary fibrosis related to the aberrant sphingolipid metabolism

Porcine respiratory disease complex (PRDC) is a common syndrome in the modern swine industry worldwide, and its pathogenesis remains unclear to date. Our study aimed to investigate PRDC-induced pulmonary fibrosis and sphingolipid metabolism, and their relationship. Mouse and cell line (A549 and 3D4/21) models exposed to bleomycin and/or transforming growth factor-β1 (TGF-β1) were developed. Histopathological and immunohistochemical staining, colorimetry, lipidomics analysis and pharmacologic intervention assays were used to analyse lung fibrosis and sphingolipid profiles. PRDC was validated by the presence of alveolar epithelial cell (AEC) injury and hyperplasia, inflammatory infiltrates, asymmetric macrophage polarization and mast cell phenotypic changes, TGF-β1 and fibroblast growth factor 2 (FGF-2) overproduction, extensive collagen deposition, foci of fibroblast/myofibroblast with stress fibres (α-SMA, γ-SMA and γ2 actin), cell interaction with increasing frequency, proliferation, apoptosis and autophagy dysregulation, and mucin 6 release—all of which are characteristics of pulmonary fibrosis. Based on the sphingolipidomics and pharmacologic interventions data—the dysregulated sphingolipids, including sphingomyelin (SM), ceramide (Cer), sphingosine-1-phosphate (S1P) and cerebroside (Cb), possibly due to serine palmitoyltransferase (SPT; SPTLC1), ceramide synthase (CerS; CerS2, CerS4), sphingomyelin synthase (SMS; SMS1), neutral sphingomyelinase (NSMase), acid sphingomyelinase (ASMase; SMPDL3B) and sphingosine kinase (SphK; SphK1, SphK2), were found to be closely related to pulmonary fibrosis. Furthermore, d18:1 24:1 SM and 18:1 S1P may be conserved biomarkers and tiamulin fumarate (TF) changes have anti-fibrotic activity. Overall, PRDC induces pulmonary fibrosis, related to the aberrant sphingolipid metabolism, where conserved sphingolipid biomarkers and anti-fibrotic candidates have been found.