Staphylococcus aureus Induces Increased Serine Protease Activity in Keratinocytes

Abstract

Bacteria that reside on the skin can influence the behavior of the cutaneous immune system, but the mechanisms responsible for these effects are incompletely understood. Colonization of the skin by Staphylococcus aureus (S. aureus) is increased in atopic dermatitis (AD) and can result in increased severity of the disease. In this study we show that S. aureus stimulates human keratinocytes to increase their endogenous protease activity, including specific increases in trypsin activity. This increased protease activity coincided with increased expression of mRNA for kallikreins (KLKs), with KLK6, 13, and 14 showing the greatest induction after exposure to S. aureus. Suppression of mRNA for these KLKs in keratinocytes by targeted siRNA silencing prior to S. aureus exposure blocked the increase in protease activity. Keratinocytes exposed to S. aureus showed enhanced degradation of desmoglein-1 (DSG-1) and filaggrin (FLG) while siRNA for KLK6, KLK13, and KLK14 partially blocked this degradation. These data illustrate how S. aureus directly influences the skin barrier integrity by stimulating endogenous proteolytic activity and defines a previously unknown mechanism by which S. aureus may influence skin diseases.

Biphasic influence of Staphylococcus aureus on human epidermal tight junctions

“…The discrepancy with the protease/hemolysin effects mentioned above might be the use of human primary keratinocytes compared with immortalized cells. In a recent paper, it was shown that S. aureus induces keratinocyte‐intrinsic serine protease activity (e.g., kallikreins and trypsin) . However, the authors concluded that TLR activation was not involved in the induction, but rather secreted virulence factors .…”

Staphylococcus aureus: Master Manipulator of the Skin

“…Interestingly, this penetration of S. aureus into the skin may be linked to the differences Liu et al (2017) observed in subcutaneous versus epicutaenous S. aureus infections. Furthermore, we have shown that a secreted S. aureus factor(s) can stimulate human keratinocytes to increase expression of epithelial serine proteases that further damage the skin barrier (Williams et al, 2017). These S. aureus -induced serine proteases have been shown to stimulate the protease-activated receptor 2 (PAR-2) in keratinocytes to induce IL-1-type cytokines.…”

Evidence that Human Skin Microbiome Dysbiosis Promotes Atopic Dermatitis

“…Although in vitro studies of the effect of S. aureus on skin cells is important mechanistically, in vivo murine models of live S. aureus colonization have provided even stronger evidence that S. aureus colonization can induce AD skin phenotypes. We have shown that colonization of murine skin by S. aureus directly induces serine protease activity that disrupts the epidermal barrier (Williams et al, 2017) and that expression of T helper type 2 cytokines in the skin (a hallmark of the AD phenotype) is dependent on proteases secreted by S. aureus (Nakatsuji et al, 2016). Additionally, Nakamura et al (2013) have observed that S. aureus delta toxin increases allergic responses and promotes both inflammation and desquamation of the skin surface.…”