Inhibition of keratinocyte migration by lipopolysaccharide

A critical process in cutaneous wound healing is reepithelialization by keratinocytes that closes the breach in the epidermis. Chronic wounds fail to reepithelialize despite the presence of activated and proliferative keratinocytes around the wound perimeter. This type of wound is generally colonized to a greater or lesser extent by bacteria. This study examines the possibility that bacterial products might directly inhibit keratinocyte migration. Using conventional scratch assays, we observed a dose-dependent inhibition of keratinocyte migration by lipopolysaccharide (LPS) derived from either Pseudomonas aeruginosa or Escherichia coli. Although the P. aeruginosa preparation appeared to be slightly more inhibitory, both gave half-maximal inhibition at 0.5-0.6 ng/mL. Migration of fibroblasts was not inhibited. The result could not be attributed to a cytotoxic effect of the LPS. LPS inhibition of migration was relieved by neutralizing antibodies to toll-like receptors (TLR), 40% by anti-TLR2 and 75% by anti-TLR4. We conclude that keratinocyte migration is inhibited by bacterial products, detected through TLR4 and also through TLR2. Because chronic wounds always show some presence of bacteria, these findings provide a possible explanation for the lack of healing found in ulcers.