Staphylococcus aureus Proteases: Orchestrators of Skin Inflammation

Abstract

Skin homeostasis relies on a delicate balance between host proteases and protease inhibitors along with those secreted from microbial communities, as disruption to this harmony contributes to the pathogenesis of inflammatory skin disorders, including atopic dermatitis and Netherton’s syndrome. In addition to being a prominent cause of skin and soft tissue infections, the gram-positive bacterium Staphylococcus aureus is a key player in inflammatory skin conditions due to its array of 10 secreted proteases. Herein we review how S. aureus proteases augment the development of inflammation in skin disorders. These mechanisms include degradation of skin barrier integrity, immune dysregulation and pruritis, and impairment of host defenses. Delineating the diverse roles of S. aureus proteases has the potential to reveal novel therapeutic strategies, such as inhibitors of proteases or their cognate target, as well as neutralizing vaccines to alleviate the burden of inflammatory skin disorders in patients.

Main Text

The gram-positive bacterium, Staphylococcus aureus, colonizes various niches in the body, including the skin and mucous membranes. It is the leading cause of skin and soft tissue infections, driving a spectrum of skin infections from mild conditions (e.g., folliculitis and impetigo) to life-threatening diseases (e.g., cellulitis, abscesses, and toxic shock syndrome) (Turner et al., 2019). S. aureus colonization is associated with various inflammatory skin conditions such as prurigo nodularis (PN) (Tutka et al., 2023), bullous pemphigoid (BP) (Belheouane et al., 2023; Messingham et al., 2022), psoriasis (Ng et al., 2017), atopic dermatitis (AD) (Kong et al., 2012; Paller et al., 2019; Saheb Kashaf et al., 2023), and Netherton’s syndrome (NS) (Renner et al., 2009).

A pivotal role in S. aureus pathogenesis and fitness is played by 10 proteases, whose expression is under strict positive and negative regulation by agr and sar, respectively (Dunman et al., 2001; Kolar et al., 2013; Zielinska et al., 2012): Two cysteine proteases (ScpA, Staphopain A; SspB, Staphopain B), a serine glutamyl endopeptidase (SspA, V8), a metalloproteinase (Aur, Aureolysin), and six serine-like proteases (splABCDEF). These proteases are zymogens and undergo activation by extracellular autocatalysis (Aur and ScpA) or by each other (Aur activates V8 which then cleaves SspB)—except for the Spls, which are active upon secretion (Drapeau, 1978; Massimi et al., 2002; Nickerson et al., 2010; Nickerson et al., 2008; Nickerson et al., 2007). Host proteases such as the Kallikreins regulate many processes such as skin barrier function and desquamation (outermost skin layer shedding), wound healing, tissue remodeling by matrix metalloproteinases (MMPs), inflammatory responses, and defense mechanisms, for example, antimicrobial peptides (AMPs) (Nauroy and Nystrom, 2019, Yamasaki et al., 2006). Skin homeostasis therefore relies on a delicate balance between host proteases and protease inhibitors, as well as microbial proteases, as disruptions contribute to skin inflammation (De Veer et al., 2014). For example, S. aureus-mediated skin inflammation is associated with increased Kallikrein protease expression in keratinocytes, and deleterious mutations in the serine protease inhibitor, LEKTI (Spink5), lead to NS development (Chavanas et al., 2000; Koziel and Potempa, 2013; Nauroy and Nystrom, 2019; Williams et al., 2017). Unsurprisingly, secreted S. aureus proteases are associated with the pathology of many skin conditions, for example, psoriasis (Chang et al., 2018), AD (Kline et al., 2024; Nakatsuji et al., 2016; Williams et al., 2019), skin abscesses (Kolar et al., 2013), and NS (Sillanpaa et al., 2021, Williams et al., 2020).

The mechanisms of action of S. aureus proteases are multifaceted (Fig. 1). First, with the skin being the initial barrier that pathogens face, proteases aid invasion by degrading key components of skin integrity (e.g., desmogleins, occludins, collagen) (Hirasawa et al., 2010; Imamura et al., 2005; Kline et al., 2024; Koziel and Potempa, 2013; Lehman et al., 2019; Nakatsuji et al., 2016; Ohbayashi et al., 2011; Ohnemus et al., 2008; Potempa et al., 1988; Sillanpaa et al., 2021; Williams et al., 2020). Recently, we found in an AD-like skin inflammation model in mice that S. aureus proteases contributed to loss of skin barrier function as measured by increased transepidermal water loss (TEWL) and decreased filaggrin and desmoglein-1 expression, recapitulating features of AD skin (Demessant-Flavigny et al., 2023; Kline et al., 2024; Williams et al., 2017). Because increased protease activity is reported in filaggrin-deficient skin and S. aureus strains isolated from AD patients exhibit elevated proteolytic activity, a strong connection exists between staphylococcal proteases and skin conditions such as AD (Miedzobrodzki et al., 2002; Nakatsuji et al., 2016).

FIG. 1.

The role of Staphylococcus aureus proteases in skin inflammation. The mechanisms of action of S. aureus proteases in the skin are multifaceted. Proteases directly degrade skin barrier proteins like filaggrin and desmoglein-1, as well as dermal collagen and elastin, promoting skin infection and inflammation. In addition, S. aureus proteases induce the production of pro-inflammatory cytokines in the skin, including keratinocyte-derived IL-36α and CCL7. CCL7 further recruits eosinophils, which results in IL-17 cytokine production and inflammation. Importantly, the S. aureus V8 protease directly activates cutaneous neurons, inducing pruritis and further skin damage from scratching. Finally, S. aureus proteases impair neutrophil function (e.g., chemotaxis and phagocytosis) and numerous host defense components such as AMPs, immunoglobulins, and complement, which contributes to bacterial survival in the skin. Ker, keratinocytes; Eos, eosinophils; AMP, antimicrobial peptides; ScpA, staphopain A; SspB, staphopain B; Aur, aureolysin; V8, serine protease V8. Created with Biorender.com

Second, S. aureus proteases orchestrate immune dysregulation in the skin, affecting cytokine and chemokine expression inducing a pro-inflammatory milieu, potentiating tissue damage (Jusko et al., 2014; Kline et al., 2024; Nakatsuji et al., 2016; Smagur et al., 2009a; Sieprawska-Lupa et al., 2004). For example, S. aureus proteases induce keratinocyte-derived interleukin (IL)-36α production, correlating with disease severity and skin inflammation in mice (Kline et al., 2024; Liu et al., 2017; Patrick et al., 2021). This finding is relevant to humans, as dysregulated IL-36 expression patterns are reported in the skin of patients with psoriasis, PN, and BP (Johnston et al., 2017; Maglie et al., 2023; Patrick et al., 2021; Tongmuang et al., 2024; Tsoi et al., 2022). Moreover, we uncovered a previously unrecognized role for S. aureus proteases in triggering eosinophil-mediated skin inflammation through CCL7-induced eosinophil recruitment and IL-17 cytokine production (Kline et al., 2024). A deeper understanding on how proteases induce cell-mediated skin inflammation is needed, as eosinophilia and staphylococcal presence are emerging as common factors in various skin disorders (e.g., AD, BP, NS, and PN) (Farnaghi et al., 2020; Johansson et al., 2000; Paluel-Marmont et al., 2017; Saheb Kashaf et al., 2023; Simpson et al., 2018; Williams et al., 2020).

Finally, staphylococcal proteases cleave a plethora of host defense components such as AMPs, immunoglobulins, and complement proteins, all of which serve to impair host defenses and facilitate bacterial survival (Deng et al., 2023; Frey et al., 2021; Laarman et al., 2011; Mcgavin et al., 1997; Singh and Phukan, 2019; Smagur et al., 2009a). Moreover, a new role for S. aureus V8 protease to directly activate cutaneous neurons and induce itch was discovered, which worsened skin pathology due to increased scratching (Deng et al., 2023). Herein, we will breakdown the roles of specific S. aureus proteases in inflammatory skin disorders, summarized in Table 1.

Table 1.

Summary of Staphylococcus aureus Proteases in Disease Processes

Protease type	Protease, gene	Target	Outcome	Relevant disease	References
Cysteine protease	Staphopain A (ScpA), scpA	Collagen, elastin	Skin degradation, S. aureus dissemination	NS, AD	(Massimi et al., 2002; Nakatsuji et al., 2016, Williams et al., 2020; Potempa et al., 1988, Sillanpaa et al., 2021; Ohbayashi et al., 2011)
		Complement	Host immune defense evasion	Unknown	(Jusko et al., 2014)
		Chemerin	Neutrophil chemotaxis inhibition	Psoriasis	(Albanesi et al., 2009; Zhang et al., 2024, Luangsay et al., 2009; Wittamer et al., 2003; Cash et al., 2008; Lin et al., 2022; Chen et al., 2024; Skrzeczynska-Moncznik et al., 2009; Kong et al., 2023)
		CXCR2	Neutrophil activation and chemotaxis inhibition	Unknown	(Laarman et al., 2012)
	Staphopain B (SspB), sspB	Collagen, elastin	Skin degradation, S. aureus dissemination	NS, AD	(Massimi et al., 2002; Nakatsuji et al., 2016, Williams et al., 2020; Potempa et al., 1988, Sillanpaa et al., 2021; Ohbayashi et al., 2011)
		Fibrinogen	S. aureus dissemination	Unknown	(Imamura et al., 2005; Massimi et al., 2002)
		Complement (C3b)	Host immune defense evasion	Unknown	(Jusko et al., 2014)
		Cathelicidin LL-37	NF-κB mediated immune activation reduction	AD	(Sonesson et al., 2017; Reinholz et al., 2012)
		Chemerin	Neutrophil chemotaxis inhibition	Psoriasis, skin infection	(Albanesi et al., 2009; Zhang et al., 2024, Luangsay et al., 2009; Wittamer et al., 2003; Cash et al., 2008; Lin et al., 2022; Chen et al., 2024; Skrzeczynska-Moncznik et al., 2009; Kong et al., 2023)
		CD11b, CD16, CD31	Neutrophil and monocyte phagocytosis inhibition	Unknown	(Smagur et al., 2009a; Smagur et al., 2009b)
		Galectin-3	Neutrophil transmigration and ROS generation inhibition	Unknown, skin infection	(Elmwall et al., 2017; Bhaumik et al., 2013, Nieminen et al., 2008; Larsen et al., 2011, Karlsson et al., 1998)
Metallo-proteinase	Aureolysin (Aur), aur	Collagen, pro-MMP9, MMP9	Skin degradation, S. aureus dissemination	Unknown	(Lehman et al., 2019)
		Cathelicidin LL-37	Decreased bacterial killing	NS, psoriasis, AD	(Sieprawska-Lupa et al., 2004; Zingkou et al., 2020; Yamasaki et al., 2007; Lande et al., 2007, Reinholz et al., 2012; Williams et al., 2017)
		Complement (C3b, C5a)	Opsonophagocytosis inhibition	Unknown	(Laarman et al., 2011)
Serine glutamyl endopeptidase	Serine protease V8 (V8), sspA	Claudin, occludin, desmoglein	Epidermal barrier dysfunction, IgE response	AD	(Ohnemus et al., 2008; Hirasawa et al., 2010; Wang et al., 2017)
		Immunoglobulins, complement, protease inhibitors	Host immune defense evasion	Unknown	(Frey et al., 2021; Jusko et al., 2014; Kolar et al., 2013; Prokesova et al., 1992; Singh and Phukan, 2019)
		Fibronectin binding protein	Biofilm degradation, S. aureus dissemination	Unknown	(Mcgavin et al., 1997)
		Protease-activated receptors	Pruritis	AD, psoriasis	(Weidinger and Novak, 2016; Deng et al., 2023; Wang.and Kim, 2020; Misery et al., 2023)
Serine-like protease	Serine-like protease A (SplA), splA	Mucin 16	Lung epithelial barrier disruption	Pneumonia, asthma	(Singh and Phukan, 2019; Stentzel et al., 2017; Pietrocola et al., 2017; Paharik et al., 2016)
	Serine-like protease B (SplB), splB	Complement (C3b, C5b-C9)	Opsonophagocytosis inhibition	Asthma	(Singh and Phukan, 2019; Stentzel et al., 2017; Dasari et al., 2022)
	Serine-like protease C (SplC), splC	Unknown	Unknown	Unknown	(Singh and Phukan, 2019)
	Serine-like protease D (SplD), splD	Unknown	Eosinophilia and Th2 response	Asthma	(Stentzel et al., 2017; Singh and Phukan, 2019; Teufelberger et al., 2018)
	Serine-like protease E (SplE), splE	Unknown	Unknown	Unknown	(Singh and Phukan, 2019)
	Serine-like protease F(SplF), splF	Unknown	Eosinophilia and Th2 response	Asthma	(Singh and Phukan, 2019; Stentzel, Teufelberger et al. 2017)

AD, atopic dermatitis; NS, Netherton’s syndrome; ROS, reactive oxygen species; MMP, matrix metalloproteinases.

Staphopains A and B

The staphopains are the most highly secreted proteases of S. aureus and exhibit broad activity, including barrier destruction and host defense evasion (Imamura et al., 2005; Laarman et al., 2012; Ohbayashi et al., 2011; Potempa et al., 1988; Smagur et al., 2009a). Skin and tissue degradation in NS and AD patients is directly caused by staphopains, with 10 nM concentrations being sufficient for collagen destruction (Nakatsuji et al., 2016; Ohbayashi et al., 2011; Sillanpaa et al., 2021; Williams et al., 2020). In a mouse model of epicutaneous S. aureus exposure, a combined deletion of both scpA and sspB rather than individual deletions led to decreased skin inflammation and increased TEWL (Williams et al., 2020). Concordantly, increased scpA and sspB transcript levels are observed in lesional versus nonlesional or healthy skin in NS patients (Williams et al., 2020). Both ScpA and SspB degrade elastin and connective skin tissue, but SspB also degrades fibrinogen, all of which enable S. aureus dissemination (Potempa et al., 1988, Massimi et al., 2002, Imamura et al., 2005).

Staphopains also exacerbate skin pathologies by dampening immune responses. Both staphopains interfere with complement components, with SspB exerting high C3b specificity (Jusko et al., 2014). In AD lesions, local production of SspB degrades LL-37, protecting the bacteria from cathelicidin-mediated damage (Sonesson et al., 2017). Moreover, LL-37 fragments may have immune modulatory effects such as NF-κB activation, enhancing inflammation (Reinholz et al., 2012; Sonesson et al., 2017). Initially discovered in psoriatic lesions, the AMP chemerin, like LL-37, requires proteolytic cleavage and induces cutaneous neutrophil infiltration and inflammation (Albanesi et al., 2009; Cash et al., 2008; Lin et al., 2022; Luangsay et al., 2009, Wittamer et al., 2003). Despite high levels of chemerin and pro-inflammatory cytokines in psoriatic skin, the staphopain–chemerin relationship necessitates further investigation (Kong et al., 2023; Skrzeczynska-Moncznik et al., 2009; Zhang et al., 2024). In a murine intradermal S. aureus infection model, chemerin proteolysis by SspB leads to increased skin pathology due to decreased neutrophil infiltration and control of S. aureus, since neutrophilia is paramount for bacterial clearance (Chen et al., 2024). ScpA inhibits neutrophil activation and chemotaxis in vitro by cleaving CXCR2, whereas SspB aids in immune evasion by blocking phagocytosis through CD11b, CD16, and CD31 degradation on neutrophils and monocytes (Laarman et al., 2012; Smagur et al., 2009a; Smagur et al., 2009b).

Another proteolytic target for SspB is the lectin galactin-3, resulting in inhibition of its antimicrobial capabilities and increased skin pathology in a murine S. aureus infection model (Elmwall et al., 2017). Produced by epithelial and immune cells, galectin-3 facilitates cutaneous neutrophil transmigration and activation from the blood during early inflammation (Bhaumik et al., 2013; Larsen et al., 2011; Nieminen et al., 2008). Moreover, galectin-3 induces NADPH oxidase activation and subsequent reactive oxygen species generation and, consequentially, the potential for skin inflammation (Karlsson et al., 1998). Clinical S. aureus isolates from invasive and superficial skin infections exhibited increased galectin-3 proteolytic activity, further underlining their translational importance (Elmwall et al., 2017).

Aureolysin

The metalloprotease Aur contributes to skin disorders by targeting various host components, including skin barrier proteins and immune system responses. Aur facilitates S. aureus penetration by cleaving pro-MMP-9 and MMP-9, destroying collagen (Lehman et al., 2019). Aur also cleaves and inactivates the AMP LL-37, leading to bacterial persistence (Sieprawska-Lupa et al., 2004; Williams et al., 2017). Furthermore, dysregulation of LL-37 has been implicated in a variety of skin conditions such as NS (Zingkou et al., 2020), rosacea (Yamasaki et al., 2007), psoriasis (Lande et al., 2007), and AD (Reinholz et al., 2012); therefore, the impact of Aur may be far reaching. Aur also increases bacterial survival by interfering with complement-mediated opsonophagocytosis through C3 cleavage, thereby inhibiting C3b deposition and C5a release (Laarman et al., 2011). Along with α-toxin, Aur enhances bacterial survival within macrophages (Kubica et al., 2008), and heightened levels are detected in phagocytosed-S. aureus within human neutrophils (Burlak et al., 2007). Finally, Aur is responsible for activating V8, causing a variety of downstream skin pathologies (Nickerson et al., 2008).

Serine protease V8

Initially discovered in 1972, V8 is emerging as a prominent S. aureus protease causing skin damage and pathogenesis (Drapeau et al., 1972). V8 disrupts skin barrier integrity through the degradation of tight junctions (e.g., claudins, occludins, desmogleins) and increased TEWL, thus contributing to AD development (Hirasawa et al., 2010; Ohnemus et al., 2008; Wang et al., 2017). Of note, purified V8 when applied to murine skin enhances IgE responses and epidermal barrier dysfunction, hallmarks of AD (Hirasawa et al., 2010). V8 mediates immune evasion and increased bacterial survival by targeting a myriad of host and bacterial proteins, for example, complement components C3 and C5, protease inhibitors, the Fc region of immunoglobulins, and fibronectin (Fn)-binding protein, leading to biofilm degradation and greater bacterial dissemination (Frey et al., 2021; Jusko et al., 2014; Kolar et al., 2013; Mcgavin et al., 1997; Prokesova et al., 1992; Singh and Phukan, 2019).

A hallmark of skin conditions such as AD and psoriasis that are commonly associated with S. aureus dysbiosis is pruritus—the sensation of itch—long thought to exacerbate tissue injury and pathology (Weidinger and Novak, 2016). Recent studies found that pathological tissue damage is the result of itch behavior orchestrated by S. aureus V8, incurring a fitness benefit for S. aureus (Deng et al., 2023). In a murine AD-like model of S. aureus infection, V8 directly caused pruritus, with S. aureus localizing to peripheral itch-inducing pruriceptive neurons—specific neurons responsive to stimuli such as cytokines and histamines (Misery et al., 2023; Wang and Kim, 2020). Specifically, V8 cleaved protease-activated receptor 1 (PAR1) on the pruriceptors, thereby triggering pruritus, in line with increased SspA levels detected in AD patient lesions (Deng et al., 2023).

Serine protease-like proteins (SplABCDEF)

Despite significant amino acid homology to V8, the role of Spls in skin inflammation is unclear (Singh and Phukan, 2019). A longitudinal expression study of S. aureus proteases upon human skin contact revealed an upregulation of all agr-regulated genes, with splA transcription peaking during late colonization, in contrast with scpA, sspB, sspA, and aur whose levels were stable throughout (Burian et al., 2021). Therefore, SplA’s role may be involved in persistence rather than initial colonization. Recent in vitro work revealed that SplB, in addition to Aur, blocks complement deposition (C3b and C5b-9) on the bacterial surface, leading to opsonophagocytosis inhibition, further enabling S. aureus survival (Dasari et al., 2022).

Knowledge on the Spl family garnered during lung inflammation may help frame future dermatological work (Pietrocola et al., 2017). SplA aids in bacterial invasion and dissemination in the lung by cleaving mucin 16, an epithelial barrier glycosylated protein (Paharik et al., 2016). Since mucin 16 is also present at ocular and reproductive tract epithelial surfaces, splA may disrupt epithelial integrity there too (Govindarajan et al., 2012). The Spls, especially SplD and SplF, are frequently reported in the context of airway allergic responses where they trigger Th2 responses, eosinophilia, and IgE production following allergen exposure (Singh and Phukan, 2019; Stentzel et al., 2017; Teufelberger et al., 2018). Alongside the pore-forming α-hemolysin, Spls induce epithelial breakdown, enabling allergen exposure and subsequent allergic responses (Stentzel et al., 2017). Interestingly, elevated titers of SplA, SplB, SplD, and SplF-specific IgE were detected in asthmatic patient serum, suggestive of an allergen role (Stentzel et al., 2017). Furthermore, increased levels of Spl-binding IgG were also detected in S. aureus-colonized nasal polyps (Stentzel et al., 2017). SplD also has allergen capabilities as its intratracheal administration without adjuvant led to the SplD-specific IgE production, bronchial hyperreactivity, eosinophilia, and a Th2 cytokine response in mice (Stentzel et al., 2017; Teufelberger et al., 2018). This response was IL-33-dependent but neutrophil elastase induced IL-33 maturation, not SplD (Lefrancais et al., 2012; Teufelberger et al., 2018). PAR2 levels were also increased, but occurred independent of SplD in contrast to V8, suggestive of alternative PAR2 activation mechanisms (Deng et al., 2023; Teufelberger et al., 2018). Further studies are needed to determine the applicability of these Spl findings to inflammatory skin disorders.

S. epidermidis protease

EcpA, a cysteine protease from the related bacterium S. epidermidis, is often found in AD lesions where its presence correlates with disease severity, and induces skin inflammation by activating the virulence factor, PSM-δ (Cau et al., 2021; Williams et al., 2023). Using synthetic peptides, these studies found that PSM-δ exhibited similar inflammatory gene expression profiles as PSM-α from S. aureus, including the upregulation of IL-17 responses, CXCL chemokines, and IL-1 cytokines, all contributing to skin inflammation (Williams et al., 2023). Whether S. aureus staphopains act similarly with downstream PSM-α activation warrants investigation (Nakatsuji et al., 2016; Williams et al., 2019).

Conclusions

Uncovering the role of S. aureus proteases in skin inflammation has provided valuable insights into the pathogenesis of inflammatory skin disorders and has potential in the development of novel therapeutic approaches to help mitigate the burden of S. aureus-associated skin diseases. For example, natural or synthetic protease inhibitors are an untapped opportunity to treat conditions exacerbated by S. aureus protease activity, as previous work has primarily focused on targeting host proteases (e.g., kallikreins in NS) (Liddle et al., 2021). In pruritic skin disorders, reducing itch may be achievable by inhibiting the V8 protease target, PAR1, by repurposing an FDA-approved PAR1 blocking drug, vorapaxar (Deng et al., 2023). Furthermore, staphylococcal proteases present promising targets for vaccine development—either by neutralizing protease activity directly or decreasing the bacterium’s ability for invasion, immune evasion, colonization, and infection. Moreover, a better understanding of S. aureus proteases in the skin may help target other bacterial proteases inducing skin inflammation such as Esp and EcpA of S. epidermidis (Cau et al., 2021; Rademacher et al., 2022), SpeB from Streptococcus pyogenes (Lukomski et al., 1999), or PIV and elastase from Pseudomonas aeruginosa (Kim et al., 2021; Schmidtchen et al., 2003). Collectively, expanding our knowledge of bacterial proteases not only paves the way for innovative treatments but also enhances our overall understanding of microbial contributions to skin health and disease.

Footnotes

Authors’ Contributions

Conceptualization, S.N.K. and N.K.A.; Writing—Original Draft, S.N.K. and N.K.A.; Writing—Review & Editing, S.N.K., Y.S., N.K.A.; and Funding Acquisition, N.K.A.

Disclosure Statement

N.K.A. has received previous grant support from Pfizer and Boehringer Ingelheim and was a paid consultant for Janssen Pharmaceuticals. The remaining authors state no conflict of interest.

Funding Information

This study was funded, in part, by grants R01AI111205 (N.K.A.) from the United States National Institute of Allergic and Infectious Diseases, as well as grant LF-OC-22–000953 (N.K.A.) from the LEO Foundation. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

References

Albanesi

, Scarponi

, Pallotta

, et al. Chemerin expression marks early psoriatic skin lesions and correlates with plasmacytoid dendritic cell recruitment. J Exp Med, 2009; 206(1):249–258.

Belheouane

, Hermes

, VAN Beek

, et al. Characterization of the skin microbiota in bullous pemphigoid patients and controls reveals novel microbial indicators of disease. J Adv Res, 2023; 44:71–79.

Bhaumik

, St-Pierre

, Milot

, et al. Galectin-3 facilitates neutrophil recruitment as an innate immune response to a parasitic protozoa cutaneous infection. Journal of Immunology (Baltimore, Md). 1950, 2013; 190(2):630–640.

Burian

, Plange

, Schmitt

, et al. Adaptation of staphylococcus aureus to the human skin environment identified using an ex vivo tissue model. Front Microbiol, 2021; 12:728989.

Burlak

, Hammer

, Robinson

, et al. Global analysis of community-associated methicillin-resistant Staphylococcus aureus exoproteins reveals molecules produced in vitro and during infection. Cell Microbiol, 2007; 9(5):1172–1190.

Cash

, Hart

, Russ

, et al. Synthetic chemerin-derived peptides suppress inflammation through ChemR23. J Exp Med, 2008; 205(4):767–775.

Cau

, Williams

, Butcher

, et al. Staphylococcus epidermidis protease EcpA can be a deleterious component of the skin microbiome in atopic dermatitis. J Allergy Clin Immunol, 2021; 147(3):955–966.e16.

Chang

, Yan

, Singh

, et al. Alteration of the cutaneous microbiome in psoriasis and potential role in Th17 polarization. Microbiome, 2018; 6(1):154.

Chavanas

, Bodemer

, Rochat

, et al. Mutations in SPINK5, encoding a serine protease inhibitor, cause netherton syndrome. Nat Genet, 2000; 25(2):141–142.

10.

Chen

, Song

, Wang

, et al. The chemerin-CMKLR1 axis in keratinocytes impairs innate host defense against cutaneous Staphylococcus aureus infection. Cell Mol Immunol, 2024; 21(6):533–545.

11.

Dasari

, Nordengrun

, Vilhena

, et al. The protease SplB of staphylococcus aureus targets host complement components and inhibits complement-mediated bacterial opsonophagocytosis. J Bacteriol, 2022; 204(1):e0018421–21.

12.

DE Veer

, Furio

, Harris

, et al. Proteases: Common culprits in human skin disorders. Trends Mol Med, 2014; 20(3):166–178.

13.

Demessant-Flavigny

, Connetable

, Kerob

, et al. Skin microbiome dysbiosis and the role of Staphylococcus aureus in atopic dermatitis in adults and children: A narrative review. Acad Dermatol Venereol, 2023; 37(S5):3–17.

14.

Deng

, Costa

, Blake

, et al. S. aureus drives itch and scratch-induced skin damage through a V8 protease-PAR1 axis. Cell, 2023; 186(24):5375–5393.e25.

15.

Drapeau

. Role of metalloprotease in activation of the precursor of staphylococcal protease. J Bacteriol, 1978; 136(2):607–613.

16.

Drapeau

, Boily

, Houmard

. Purification and properties of an extracellular protease of Staphylococcus aureus. J Biol Chem, 1972; 247(20):6720–6726.

17.

Dunman

, Murphy

, Haney

, et al. Transcription profiling-based identification of Staphylococcus aureus genes regulated by the agr and/or sarA loci. J Bacteriol, 2001; 183(24):7341–7353.

18.

Elmwall

, Kwiecinski

, NA

, et al. Galectin-3 is a target for proteases involved in the virulence of Staphylococcus aureus. Infect Immun, 2017; 85(7):e00177–17.

19.

Farnaghi

, Ehsani

, Kamyab-Hesary

, et al. Correlation of dermal and blood eosinophilia with bullous pemphigoid disease severity. Int J Womens Dermatol, 2020; 6(3):171–175.

20.

Frey

, Chaput

, Shaw

. Insight into the human pathodegradome of the V8 protease from Staphylococcus aureus. Cell Rep, 2021; 35(1):108930.

21.

Govindarajan

, Menon

, Spurr-Michaud

, et al. A metalloproteinase secreted by Streptococcus pneumoniae removes membrane mucin MUC16 from the epithelial glycocalyx barrier. PLoS One, 2012; 7(3):e32418.

22.

Hirasawa

, Takai

, Nakamura

, et al. Staphylococcus aureus extracellular protease causes epidermal barrier dysfunction. J Invest Dermatol, 2010; 130(2):614–617.

23.

Imamura

, Tanase

, Szmyd

, et al. Induction of vascular leakage through release of bradykinin and a novel kinin by cysteine proteinases from Staphylococcus aureus. J Exp Med, 2005; 201(10):1669–1676.

24.

Johansson

, Liang

, Marcusson

, et al. Eosinophil cationic protein- and eosinophil-derived neurotoxin/eosinophil protein X-immunoreactive eosinophils in prurigo nodularis. Arch Dermatol Res, 2000; 292(8):371–378.

25.

Johnston

, Xing

, Wolterink

, et al. IL-1 and IL-36 are dominant cytokines in generalized pustular psoriasis. J Allergy Clin Immunol, 2017; 140(1):109–120.

26.

Jusko

, Potempa

, Kantyka

, et al. Staphylococcal proteases aid in evasion of the human complement system. J Innate Immun, 2014; 6(1):31–46.

27.

Karlsson

, Follin

, Leffler

, et al. Galectin-3 activates the NADPH-oxidase in exudated but not peripheral blood neutrophils. Blood, 1998; 91(9):3430–3438.

28.

Kim

, Li

, Lee

. Alleviation of pseudomonas aeruginosa infection by propeptide-mediated inhibition of protease IV. Microbiol Spectr, 20212021;9(2):e0078221–21.

29.

Kline

, Orlando

, Lee

, et al. Staphylococcus aureus proteases trigger eosinophil-mediated skin inflammation. Proc Natl Acad Sci U S A, 2024; 121(6):e2309243121.

30.

Kolar

, Ibarra

, Rivera

, et al. Extracellular proteases are key mediators of Staphylococcus aureus virulence via the global modulation of virulence-determinant stability. Microbiologyopen, 2013; 2(1):18–34.

31.

Kong

, Oh

, Deming

, et al. NISC COMPARATIVE SEQUENCE PROGRAM. Temporal shifts in the skin microbiome associated with disease flares and treatment in children with atopic dermatitis. Genome Research, 2012; 22(5):850–859.

32.

Kong

, Sun

, Cui

, et al. Chemerin exacerbates psoriasis by stimulating keratinocyte proliferation and cytokine production. Curr Med Sci, 2023; 43(2):399–408.

33.

Koziel

, Potempa

. Protease-armed bacteria in the skin. Cell Tissue Res, 2013; 351(2):325–337.

34.

Kubica

, Guzik

, Koziel

, et al. A potential new pathway for Staphylococcus aureus dissemination: The silent survival of S. aureus phagocytosed by human monocyte-derived macrophages. PLoS One, 2008; 3(1):e1409.

35.

Laarman

, Mijnheer

, Mootz

, et al. Staphylococcus aureus staphopain a inhibits CXCR2-dependent neutrophil activation and chemotaxis. Embo J, 2012; 31(17):3607–3619.

36.

Laarman

, Ruyken

, Malone

, et al. Staphylococcus aureus metalloprotease aureolysin cleaves complement C3 to mediate immune evasion. Journal of Immunology Baltimore, Md, 2011; 186(11):6445–6453.

37.

Lande

, Gregorio

, Facchinetti

, et al. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature, 2007; 449(7162):564–569.

38.

Larsen

, Chen

, Saegusa

, et al. Galectin-3 and the skin. J Dermatol Sci, 2011; 64(2):85–91.

39.

Lefrancais

, Roga

, Gautier

, et al. IL-33 is processed into mature bioactive forms by neutrophil elastase and cathepsin G. Proc Natl Acad Sci U S A, 2012; 109(5):1673–1678.

40.

Lehman

, Nuxoll

, Yamada

, et al. Protease-Mediated growth of staphylococcus aureus on host proteins is opp3 dependent. mBio, 2019; 10(2):e02553–18.

41.

Liddle

, Beneton

, Benson

, et al. A potent and selective kallikrein-5 inhibitor delivers high pharmacological activity in skin from patients with netherton syndrome. J Invest Dermatol, 2021; 141(9):2272–2279.

42.

Lin

, Cai

, Luo

, et al. Epithelial chemerin-CMKLR1 signaling restricts microbiota-driven colonic neutrophilia and tumorigenesis by up-regulating lactoperoxidase. Proc Natl Acad Sci U S A, 2022; 119(29):e2205574119.

43.

Liu

, Archer

, Dillen

, et al. Staphylococcus aureus epicutaneous exposure drives skin inflammation via IL-36-Mediated T cell responses. Cell Host Microbe, 2017; 22(5):653–666.e5.

44.

Luangsay

, Wittamer

, Bondue

, et al. Mouse ChemR23 is expressed in dendritic cell subsets and macrophages, and mediates an anti-inflammatory activity of chemerin in a lung disease model. Journal of Immunology (Baltimore, Md). 1950, 2009; 183(10):6489–6499.

45.

Lukomski

, Montgomery

, Rurangirwa

, et al. Extracellular cysteine protease produced by Streptococcus pyogenes participates in the pathogenesis of invasive skin infection and dissemination in mice. Infect Immun, 1999; 67(4):1779–1788.

46.

Maglie

, Mercurio

, Morelli

, et al. Interleukin-36 cytokines are overexpressed in the skin and sera of patients with bullous pemphigoid. Exp Dermatol, 2023; 32(6):915–921.

47.

Massimi

, Park

, Rice

, et al. Identification of a novel maturation mechanism and restricted substrate specificity for the SspB cysteine protease of Staphylococcus aureus. J Biol Chem, 2002; 277(44):41770–41777.

48.

Mcgavin

, Zahradka

, Rice

, et al. Modification of the Staphylococcus aureus fibronectin binding phenotype by V8 protease. Infect Immun, 1997; 65(7):2621–2628.

49.

Messingham

, Cahill

, Kilgore

, et al. TSST-1(+)Staphylococcus aureus in bullous pemphigoid. J Invest Dermatol, 2022; 142(4):1032–1039.e6.

50.

Miedzobrodzki

, Kaszycki

, Bialecka

, et al. Proteolytic activity of Staphylococcus aureus strains isolated from the colonized skin of patients with acute-phase atopic dermatitis. Eur J Clin Microbiol Infect Dis, 2002; 21(4):269–276.

51.

Misery

, Pierre

, Le Gall-Ianotto

, et al. Basic mechanisms of itch. J Allergy Clin Immunol, 2023; 152(1):11–23.

52.

Nakatsuji

, Chen

, Two

, et al. Staphylococcus aureus exploits epidermal barrier defects in atopic dermatitis to trigger cytokine expression. J Invest Dermatol, 2016; 136(11):2192–2200.

53.

Nauroy

, Nystrom

. Kallikreins: Essential epidermal messengers for regulation of the skin microenvironment during homeostasis, repair and disease. Matrix Biol Plus, 2019; 6–7:100019.

54.

, Huang

, Chu

, et al. Risks for Staphylococcus aureus colonization in patients with psoriasis: A systematic review and meta-analysis. Br J Dermatol, 2017; 177(4):967–977.

55.

Nickerson

, Ip

, Passos

, et al. Comparison of staphopain A (ScpA) and B (SspB) precursor activation mechanisms reveals unique secretion kinetics of proSspB (staphopain B), and a different interaction with its cognate staphostatin, SspC. Mol Microbiol, 2010; 75(1):161–177.

56.

Nickerson

, Joag

, Mcgavin

. Rapid autocatalytic activation of the M4 metalloprotease aureolysin is controlled by a conserved N-terminal fungalysin-thermolysin-propeptide domain. Mol Microbiol, 2008; 69(6):1530–1543.

57.

Nickerson

, Prasad

, Jacob

, et al. Activation of the SspA serine protease zymogen of Staphylococcus aureus proceeds through unique variations of a trypsinogen-like mechanism and is dependent on both autocatalytic and metalloprotease-specific processing. J Biol Chem, 2007; 282(47):34129–34138.

58.

Nieminen

, St-Pierre

, Bhaumik

, et al. Role of galectin-3 in leukocyte recruitment in a murine model of lung infection by Streptococcus pneumoniae. Journal of Immunology (Baltimore, Md). 1950, 2008; 180(4):2466–2473.

59.

Ohbayashi

, Irie

, Murakami

, et al. Degradation of fibrinogen and collagen by staphopains, cysteine proteases released from Staphylococcus aureus. Microbiology (Reading), 2011; 157(Pt 3):786–792.

60.

Ohnemus

, Kohrmeyer

, Houdek

, et al. Regulation of epidermal tight-junctions (TJ) during infection with exfoliative toxin-negative Staphylococcus strains. J Invest Dermatol, 2008; 128(4):906–916.

61.

Paharik

, Salgado-Pabon

, Meyerholz

, et al. The spl serine proteases modulate staphylococcus aureus protein production and virulence in a rabbit model of pneumonia. mSphere, 2016; 1(5):e00208.

62.

Paller

, Kong

, Seed

, et al. The microbiome in patients with atopic dermatitis. J Allergy Clin Immunol, 2019; 143(1):26–35.

63.

Paluel-Marmont

, Bellon

, Barbet

, et al. Eosinophilic esophagitis and colonic mucosal eosinophilia in netherton syndrome. J Allergy Clin Immunol, 2017; 139(6):2003–2005.e1.

64.

Patrick

, LIU

, Alphonse

, Dikeman , et al. Epicutaneous Staphylococcus aureus induces IL-36 to enhance IgE production and ensuing allergic disease. J Clin Invest, 2021; 131(5):e143334; doi: 10.1172/JCI143334

65.

Pietrocola

, Nobile

, Rindi

, et al. Staphylococcus aureus manipulates innate immunity through own and host-expressed proteases. Front Cell Infect Microbiol, 2017; 7:166.

66.

Potempa

, Dubin

, Korzus

, et al. Degradation of elastin by a cysteine proteinase from Staphylococcus aureus. J Biol Chem, 1988; 263(6):2664–2667.

67.

Prokesova

, Potuznikova

, Potempa

, et al. Cleavage of human immunoglobulins by serine proteinase from Staphylococcus aureus. Immunol Lett, 1992; 31(3):259–265.

68.

Rademacher

, Bartels

, Glaser

, et al. Staphylococcus epidermidis-Derived protease esp mediates proteolytic activation of pro–IL-1beta in human keratinocytes. J Invest Dermatol, 2022; 142(10):2756–2765.e8.

69.

Reinholz

, Ruzicka

, Schauber

. Cathelicidin LL-37: An antimicrobial peptide with a role in inflammatory skin disease. Ann Dermatol, 2012; 24(2):126–135.

70.

Renner

, Hartl

, Rylaarsdam

, et al. Comel-Netherton syndrome defined as primary immunodeficiency. J Allergy Clin Immunol, 2009; 124(3):536–543.

71.

Saheb Kashaf

, Harkins

, Deming

, et al. NISC COMPARATIVE SEQUENCING PROGRAM. Staphylococcal diversity in atopic dermatitis from an individual to a global scale. Cell Host & Microbe, 2023; 31(4):578–592.e6.

72.

Schmidtchen

, Holst

, Tapper

, et al. Elastase-producing Pseudomonas aeruginosa degrade plasma proteins and extracellular products of human skin and fibroblasts, and inhibit fibroblast growth. Microb Pathog, 2003; 34(1):47–55.

73.

Sieprawska-Lupa

, Mydel

, Krawczyk

, et al. Degradation of human antimicrobial peptide LL-37 by Staphylococcus aureus-derived proteinases. Antimicrob Agents Chemother, 2004; 48(12):4673–4679.

74.

Sillanpaa

, Soratto

TAT

, Eranko

, et al. Skin microbiota and clinical associations in netherton syndrome. JID Innov, 2021; 1(2):100008.

75.

Simpson

, Villarreal

, Jepson

, et al. Patients with atopic dermatitis colonized with staphylococcus aureus have a distinct phenotype and endotype. J Invest Dermatol, 2018; 138(10):2224–2233.

76.

Singh

, Phukan

. Interaction of host and Staphylococcus aureus protease-system regulates virulence and pathogenicity. Med Microbiol Immunol, 2019; 208(5):585–607.

77.

Skrzeczyńska-Moncznik

, Wawro

, Stefańska

, et al. Potential role of chemerin in recruitment of plasmacytoid dendritic cells to diseased skin. Biochem Biophys Res Commun, 2009; 380(2):323–327.

78.

Smagur

, Guzik

, Bzowska

, et al. Staphylococcal cysteine protease staphopain B (SspB) induces rapid engulfment of human neutrophils and monocytes by macrophages. Biol Chem, 2009a;390(4):361–371.

79.

Smagur

, Guzik

, Magiera

, et al. A new pathway of staphylococcal pathogenesis: Apoptosis-like death induced by staphopain B in human neutrophils and monocytes. J Innate Immun, 2009b;1(2):98–108.

80.

Sonesson

, Przybyszewska

, Eriksson

, et al. Identification of bacterial biofilm and the Staphylococcus aureus derived protease, staphopain, on the skin surface of patients with atopic dermatitis. Sci Rep, 2017; 7(1):8689–8682.

81.

Stentzel

, Teufelberger

, Nordengrun

, et al. Staphylococcal serine protease-like proteins are pacemakers of allergic airway reactions to Staphylococcus aureus. J Allergy Clin Immunol, 2017; 139(2):492–500.e8.

82.

Teufelberger

, Nordengrun

, Braun

, et al. The IL-33/ST2 axis is crucial in type 2 airway responses induced by Staphylococcus aureus-derived serine protease-like protein D. J Allergy Clin Immunol, 2018; 141(2):549–559.e7.

83.

Tongmuang

, Cai

, An

, et al. Floxed Il1rl2 locus with mCherry reporter element reveals distinct expression patterns of the IL-36 receptor in barrier tissues. Cells, 2024; 13(9):787; doi: 10.3390/cells13090787

84.

Tsoi

, Hacini-Rachinel

, Fogel

, et al. Transcriptomic characterization of prurigo nodularis and the therapeutic response to nemolizumab. J Allergy Clin Immunol, 2022; 149(4):1329–1339.

85.

Turner

, Sharma-Kuinkel

, Maskarinec

, et al. Methicillin-resistant Staphylococcus aureus: An overview of basic and clinical research. Nat Rev Microbiol, 2019; 17(4):203–218.

86.

Tutka

, Żychowska

, Żaczek

, et al. Skin microbiome in prurigo nodularis. Int J Mol Sci, 2023; 24(8):7675; doi: 10.3390/ijms24087675

87.

Wang

, Kim

. Itch: A paradigm of neuroimmune crosstalk. Immunity, 2020; 52(5):753–766.

88.

Wang

, Mchugh

, Qureshi

, et al. IL-1beta-Induced protection of keratinocytes against Staphylococcus aureus-Secreted proteases is mediated by human beta-Defensin 2. J Invest Dermatol, 2017; 137(1):95–105.

89.

Weidinger

, Novak

. Atopic dermatitis. Lancet (London, England), 2016; 387(10023):1109–1122.

90.

Williams

, Bagood

, Enroth

, et al. Staphylococcus epidermidis activates keratinocyte cytokine expression and promotes skin inflammation through the production of phenol-soluble modulins. Cell Rep, 2023; 42(9):113024.

91.

Williams

, Cau

, Wang

, et al. Interplay of staphylococcal and host proteases promotes skin barrier disruption in netherton syndrome. Cell Rep, 2020; 30(9):2923–2933.e7.

92.

Williams

, Costa

, Zaramela

, et al. Quorum sensing between bacterial species on the skin protects against epidermal injury in atopic dermatitis. Sci Transl Med, 2019; 11(490):eaat8329; doi: 10.1126/scitranslmed.aat8329

93.

Williams

, Nakatsuji

, Sanford

, et al. Staphylococcus aureus induces increased serine protease activity in keratinocytes. J Invest Dermatol, 2017; 137(2):377–384.

94.

Wittamer

, Franssen

, Vulcano

, et al. Specific recruitment of antigen-presenting cells by chemerin, a novel processed ligand from human inflammatory fluids. J Exp Med, 2003; 198(7):977–985.

95.

Yamasaki

, DI Nardo

, Bardan

, et al. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med, 2007; 13(8):975–980.

96.

Yamasaki

, Schauber

, Coda

, et al. Kallikrein-mediated proteolysis regulates the antimicrobial effects of cathelicidins in skin. Faseb J, 2006; 20(12):2068–2080.

97.

Zhang

, Zheng

, Ye

, et al. Microbiome: Role in inflammatory skin diseases. J Inflamm Res, 2024; 17:1057–1082.

98.

Zielinska

, Beenken

, Mrak

, et al. sarA-mediated repression of protease production plays a key role in the pathogenesis of Staphylococcus aureus USA300 isolates. Mol Microbiol, 2012; 86(5):1183–1196.

99.

Zingkou

, Pampalakis

, Sotiropoulou

. Cathelicidin represents a new target for manipulation of skin inflammation in netherton syndrome. Biochim Biophys Acta Mol Basis Dis, 2020; 1866(10):165831.