Polyamines are required for expression of Toll-like receptor 2 modulating intestinal epithelial barrier integrity

The Toll-like receptors (TLRs) allow mammalian intestinal epithelium to detect various microbes and activate innate immunity after infection. TLR2 and TLR4 have been identified in intestinal epithelial cells (IECs) as fundamental components of the innate immune response to bacterial pathogens, but the exact mechanism involved in control of TLR expression remains unclear. Polyamines are implicated in a wide variety of biological functions, and regulation of cellular polyamines is a central convergence point for the multiple signaling pathways driving different epithelial cell functions. The current study determined whether polyamines regulate TLR expression, thereby modulating intestinal epithelial barrier function. Depletion of cellular polyamines by inhibiting ornithine decarboxylase (ODC) with alpha-difluoromethylornithine decreased levels of TLR2 mRNA and protein, whereas increased polyamines by ectopic overexpression of the ODC gene enhanced TLR2 expression. Neither intervention changed basal levels of TLR4. Exposure of normal IECs to low-dose (5 microg/ml) LPS increased ODC enzyme activity and stimulated expression of TLR2 but not TLR4, while polyamine depletion prevented this LPS-induced TLR2 expression. Decreased TLR2 in polyamine-deficient cells was associated with epithelial barrier dysfunction. In contrast, increased TLR2 by the low dose of LPS enhanced epithelial barrier function, which was abolished by inhibition of TLR2 expression with specific, small interfering RNA. These results indicate that polyamines are necessary for TLR2 expression and that polyamine-induced TLR2 activation plays an important role in regulating epithelial barrier function.