STAT1/MUC4 activation promotes antimicrobial peptide production to reduce intestinal epithelium barrier injury caused by enteropathogenic infection.

INTRODUCTION

Antimicrobial peptides (AMPs) are endogenous peptides that have been identified to alleviate intestinal epithelial barrier inflammation and dysfunction caused by enteropathogenic (EPEC) infection; nonetheless, the upstream molecular mechanism of the production of AMPs is poorly understood.

MATERIAL AND METHODS

The binding of signal transducer and activator of transcription (STAT) 1 (STAT1) to mucin 4 (MUC4) was examined by co-immunoprecipitation assay. To detect the influence of STAT1 and MUC4 expression, a C57BL/6 mouse model of EPEC infection and an EPEC infected intestinal epithelial cell (IEC) in model were established. Expression levels of STAT1, MUC4, phosphorylated (p)-STAT1, proinflammatory cytokines, zonula occludens-1 (ZO-1) and AMP-related genes in mouse ileum and/or IEC were analyzed by immunohistochemical test, immunofluorescence assay, Western blot, and/or qRT-PCR. Meanwhile, IEC viability and apoptosis were measured using CCK-8 assay and flow cytometry.

RESULTS

p-STAT1, MUC4, ZO-1 and AMP-related genes were lowly expressed in the ileum of EPEC-infected mice. p-STAT1 and MUC4 bound to each other. The expression levels of STAT1 and MUC4 were decreased in EPEC-infected IEC. STAT1 overexpression counteracted the EPEC-induced reduction of viability, apoptosis promotion, ZO-1 activity inhibition, release of proinflammatory cytokines, and downregulation of MUC4 and AMP-related genes in IEC. MUC4 knockdown partly counteracted the effect of STAT1 overexpression, but did not affect the forced STAT1 overexpression in EPEC-infected IEC.

CONCLUSIONS

STAT1/MUC4 pathway activation promotes AMP production to mitigate intestinal epithelium barrier injury caused by EPEC infection.