Raw data of Figs 1–6 in this study.

Background
Larval invasion of gut mucosa is a crucial procedure in Trichinella spiralis infection. Previous studies showed that T. spiralis excretory-secretory proteins (ESP) disrupted gut epithelial integrity and promoted larval invasion by inducing apoptosis. However, the key molecules of the ESPs involved in this process are unknown. A serine protease (TsSPc) in T. spiralis ESPs was identified to be capable of promoting larval invasion. The aim of this study was to investigate whether TsSPc induces gut epithelial apoptosis, disrupts the barrier function, promotes larval invasion, and elucidates its acting mechanism.
Methodology/principal findings
The results of DAPI, TUNEL and Annexin V/PI staining, immunofluorescence test (IFT) and flow cytometry showed that rTsSPc triggered Caco-2 cell apoptosis. The results of qPCR and Western blot revealed that rTsSPc significantly up-regulated the expression of Caco-2 cell apoptosis-related proteins (Caspase 3, Caspase 9 and Caspase 8, Bax and Cytochrome c), activated the apoptosis pathway, and thereby induced Caco-2 apoptosis. rTsSPc bound and interacted with PGAM5 receptor in Caco-2 cells and induced apoptosis, reduced the tight junctions (TJs) expression levels and damaged the Caco-2 monolayer integrity and barrier function, and promoted larval invasion. When gut epithelial PGAM5 receptor and apoptosis were inhibited by PGAM5-specific siRNA, inhibitor (LFHP-1c) and apoptosis inhibitor (Z-VAD-FMK), trans-epithelial electrical resistance (TEER) and TJs expression were obviously increased, and intestinal permeability was evidently decreased. Additionally, larval invasion of Caco-2 monolayer was also decreased by siPGAM5 and inhibitor pretreatment. These findings indicated that inhibition of PGAM5 receptor and apoptosis prevented rTsSPc from damaging gut epithelial integrity and larval invasion.
Conclusions
rTsSPc binding and interacting with PGAM5 triggered gut epithelial apoptosis, reduced the TJs expression and damaged gut barrier function, thereby mediated larval invasion. TsSPc might be a candidate vaccine target to interdict larval invasion and T. spiralis infection.