Cytokeratins mediate epithelial innate defense through their antimicrobial properties

Abstract

Epithelial cells express antimicrobial proteins in response to invading pathogens, although little is known regarding epithelial defense mechanisms during healthy conditions. Here we report that epithelial cytokeratins have innate defense properties because they constitutively produce cytoprotective antimicrobial peptides. Glycine-rich C-terminal fragments derived from human cytokeratin 6A were identified in bactericidal lysate fractions of human corneal epithelial cells. Structural analysis revealed that these keratin-derived antimicrobial peptides (KDAMPs) exhibited coil structures with low α-helical content. Synthetic analogs of these KDAMPS showed rapid bactericidal activity against multiple pathogens and protected epithelial cells against bacterial virulence mechanisms, while a scrambled peptide showed no bactericidal activity. However, the bactericidal activity of a specific KDAMP was somewhat reduced by glycine-alanine substitutions. KDAMP activity involved bacterial binding and permeabilization, but the activity was unaffected by peptide charge or physiological salt concentration. Knockdown of cytokeratin 6A markedly reduced the bactericidal activity of epithelial cell lysates in vitro and increased the susceptibility of murine corneas to bacterial adherence in vivo. These data suggest that epithelial cytokeratins function as endogenous antimicrobial peptides in the host defense against infection and that keratin-derived antimicrobials may serve as effective therapeutic agents.

Keratin 16 regulates innate immunity in response to epidermal barrier breach

“…Expression of KRT6 paralogs (a and b) was also markedly elevated ( Fig. 1C), consistent with their wound-inducible nature (25) and their newly proposed status as DAMPs (26). Such a DAMP-centric profile occurs independently of the disease-causing mutation and is strikingly similar to our findings in Krt16 −/− front-paw calluses, suggesting that the misregulation of barrier-related genes is a general feature of PC-related palmoplantar keratoderma.…”

Keratin 1 maintains skin integrity and participates in an inflammatory network in skin via interleukin-18

“…In support of this, absence of Krt17 was reported to attenuate inflammation in models of acute dermatitis, characterized by a change in inflammatory cytokines from a Th1-and Th17-to a Th2-dominated inflammatory response (Depianto et al, 2010). More recently, antimicrobial activity of fragments of Krt6A in corneal keratinocyte extracts was reported (Tam et al, 2012). Given the slightly elevated fragility of Krt1/IL-18 2/2 epidermis, such an activity, if conserved in mouse epidermal keratinocytes, might contribute to the absence of strong inflammation in surviving animals.…”

The Importance of the Pseudomonas aeruginosa Type III Secretion System in Epithelium Traversal Depends upon Conditions of Host Susceptibility

“…The susceptibility of MyD88 Ϫ/Ϫ corneas to ExsA-independent traversal led us to investigate if MyD88 deficiency impaired antimicrobial activity of the corneal epithelium. Our choice to focus on antimicrobial activity, rather than other potential defense factors, was based on our earlier discoveries that corneally expressed antimicrobials (including mBD3 and keratin-derived antimicrobial peptides [KDAMPs]) contribute to maintaining the corneal epithelial barrier against P. aeruginosa (49,59). Thus, the corneal epithelium of normal healthy wild-type and MyD88…”