Abstract
Soil- and waterborne bacteria such as Pseudomonas aeruginosa are constantly challenging body surfaces. Since infections of healthy skin are unexpectedly rare, we hypothesized that the outermost epidermis, the stratum corneum, and sweat glands directly control the growth of P. aeruginosa by surface-provided antimicrobials. Due to its high abundance in the upper epidermis and eccrine sweat glands, filaggrin-2 (FLG2), a water-insoluble 248 kDa S100 fused-type protein, might possess these innate effector functions. Indeed, recombinant FLG2 C-terminal protein fragments display potent antimicrobial activity against P. aeruginosa and other Pseudomonads. Moreover, upon cultivation on stratum corneum, P. aeruginosa release FLG2 C-terminus-containing FLG2 fragments from insoluble material, indicating liberation of antimicrobially active FLG2 fragments by the bacteria themselves. Analyses of the underlying antimicrobial mechanism reveal that FLG2 C-terminal fragments do not induce pore formation, as known for many other antimicrobial peptides, but membrane blebbing, suggesting an alternative mode of action. The association of the FLG2 fragment with the inner membrane of treated bacteria and its DNA-binding implicated an interference with the bacterial replication that was confirmed by in vitro and in vivo replication assays. Probably through in situ-activation by soil- and waterborne bacteria such as Pseudomonads, FLG2 interferes with the bacterial replication, terminates their growth on skin surface and thus may contributes to the skin’s antimicrobial defense shield. The apparent absence of FLG2 at certain body surfaces, as in the lung or of burned skin, would explain their higher susceptibility towards Pseudomonas infections and make FLG2 C-terminal fragments and their derivatives candidates for new Pseudomonas-targeting antimicrobials.
Highlights
Human skin and mucosal surfaces harbor and encounter a high number of diverse microorganisms [1,2], but are rarely infected
Filaggrin-2 Targets Bacterial Replication unexpectedly resistant towards P. aeruginosa infections, it constitutes a promising source of new antimicrobials
We identified fragments of the insoluble skin protein filaggrin-2 as P. aeruginosa-bactericidal proteins that can be released by the action of P. aeruginosa from the outermost skin layer
Summary
Human skin and mucosal surfaces harbor and encounter a high number of diverse microorganisms [1,2], but are rarely infected. Apart from the physical skin barrier of the stratum corneum (reviewed in ref.[3]), a “chemical barrier”, consisting of various antimicrobial peptides and proteins (AMPs), was described to act as innate defense barrier and contributes to the control of microbial growth at body surfaces [4,5]. Ubiquitous Pseudomonads are highly abundant on human skin [12] but cause skin infections only when the cutaneous barrier is disturbed, such as in toe web infections [13] or hot tub folliculitis [14]. Under conditions where the cutaneous barrier is completely missing as in burn wounds, Pseudomonas aeruginosa is a major cause of morbidity and mortality [15]
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