Viral afterlife: SARS-CoV-2 as a reservoir of immunomimetic peptides that reassemble into proinflammatory supramolecular complexes.

It is unclear how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection leads to the strong but ineffective inflammatory response that characterizes severe Coronavirus disease 2019 (COVID-19), with amplified immune activation in diverse cell types, including cells without angiotensin-converting enzyme 2 receptors necessary for infection. Proteolytic degradation of SARS-CoV-2 virions is a milestone in host viral clearance, but the impact of remnant viral peptide fragments from high viral loads is not known. Here, we examine the inflammatory capacity of fragmented viral components from the perspective of supramolecular self-organization in the infected host environment. Interestingly, a machine learning analysis to SARS-CoV-2 proteome reveals sequence motifs that mimic host antimicrobial peptides (xenoAMPs), especially highly cationic human cathelicidin LL-37 capable of augmenting inflammation. Such xenoAMPs are strongly enriched in SARS-CoV-2 relative to low-pathogenicity coronaviruses. Moreover, xenoAMPs from SARS-CoV-2 but not low-pathogenicity homologs assemble double-stranded RNA (dsRNA) into nanocrystalline complexes with lattice constants commensurate with the steric size of Toll-like receptor (TLR)-3 and therefore capable of multivalent binding. Such complexes amplify cytokine secretion in diverse uninfected cell types in culture (epithelial cells, endothelial cells, keratinocytes, monocytes, and macrophages), similar to cathelicidin's role in rheumatoid arthritis and lupus. The induced transcriptome matches well with the global gene expression pattern in COVID-19, despite using <0.3% of the viral proteome. Delivery of these complexes to uninfected mice boosts plasma interleukin-6 and CXCL1 levels as observed in COVID-19 patients.

Microencapsulated Benzoyl Peroxide for Rosacea in Context: A Review of the Current Treatment Landscape.

Rosacea, a chronic skin condition affecting millions of people in the USA, leads to significant social and professional stigmatization. Effective management strategies are crucial to alleviate symptoms and improve patients' quality of life. Encapsulated benzoyl peroxide 5% (E-BPO 5%) is a newly FDA-approved topical treatment for rosacea that shows promise in enhancing therapeutic response and minimizing skin irritation. This review aims to assess the role of recently FDA approved E-BPO 5% in the current treatment landscape for rosacea management, as it is not yet included in clinical guidelines that predominantly rely on older approved therapies. The review focuses on randomized controlled trials conducted in English-speaking adults. It evaluates the efficacy, safety, and tolerability of various US Food and Drug Administration (FDA)-approved agents used for rosacea treatment, including E-BPO cream, metronidazole gel, azelaic acid gel and foam, ivermectin cream, minocycline foam, oral doxycycline, brimonidine gel, and oxymetazoline HCl cream. Existing therapies have been effective in reducing papulopustular lesions and erythema associated with rosacea for many years. E-BPO 5% offers a promising addition to the treatment options due to its microencapsulation technology, which prolongs drug delivery time and aims to improve therapeutic response while minimizing skin irritation. Further research is necessary to determine the exact role of E-BPO 5% in the therapeutic landscape for rosacea. However, based on available evidence, E-BPO 5% shows potential as a valuable treatment option for managing inflammatory lesions of rosacea, and it may offer benefits to patients including: rapid onset of action, demonstrated efficacy by Week 2, excellent tolerability, and sustained long-term results for up to 52 weeks of treatment.

Regulation of Epidermal Ferritin Expression Influences Systemic Iron Homeostasis.

Absorption of dietary iron is largely regulated by the liver hormone hepcidin, which is released under conditions of iron overload and inflammation. Although hepcidin-dependent regulation of iron uptake and circulation is well-characterized, recent studies have suggested that the skin may play an important role in iron homeostasis, including transferrin receptor-mediated epidermal iron uptake and direct hepcidin production by keratinocytes. In this study, we characterized direct keratinocyte responses to conditions of high and low iron. We observed potent iron storage capacity by keratinocytes in vitro and in vivo and the effects of iron on epidermal differentiation and gene expression associated with inflammation and barrier function. In mice, systemic iron was observed to be coupled to epidermal iron content. Furthermore, topical inflammation, as opposed to systemic inflammation, resulted in a primary iron-deficiency phenotype associated with low liver hepcidin. These studies suggest a role for keratinocytes and epidermal iron storage as regulators of iron homeostasis with direct contribution by the cutaneous inflammatory state.

Staphylococcus epidermidis activates keratinocyte cytokine expression and promotes skin inflammation through the production of phenol-soluble modulins.

Staphylococcus epidermidis is a common microbe on human skin and has beneficial functions in the skin microbiome. However, under conditions of allergic inflammation, the abundance of S. epidermidis increases, establishing potential danger to the epidermis. To understand how this commensal may injure the host, we investigate phenol-soluble modulin (PSM) peptides produced by S. epidermidis that are similar to peptides produced by Staphylococcus aureus. Synthetic S. epidermidis PSMs induce expression of host defense genes and are cytotoxic to human keratinocytes. Deletion mutants of S. epidermidis lacking these gene products support these observations and further show that PSMs require the action of the EcpA bacterial protease to induce inflammation when applied on mouse skin with an intact stratum corneum. The expression of PSMδ from S. epidermidis is also found to correlate with disease severity in patients with atopic dermatitis. These observations show how S. epidermidis PSMs can promote skin inflammation.

Reduction of Erythema in Moderate-Severe Rosacea by a Low Molecular Weight Heparan Sulfate Analog (HSA).

Rosacea changes are a result of an immune mediated response and the angiogenic properties of the LL-37 peptide. This peptide induces an inflammatory signal that activates the NLRP3-mediated inflammasome, triggering rosacea pathogenesis. Research findings show that LL-37 peptide is inhibited by binding to a cell surface glycosaminoglycan, heparan sulfate. Heparan Sulfate Analog (HSA) is a proprietary low molecular weight analog of heparan sulfate that has been formulated into a Dermal Repair Cream (DRC), specifically to aid in such immune mediated responses. Herein, in vitro studies using human epidermal keratinocytes showed an increase in HSA decreased LL-37 toxicity and IL-8 cytokine release. A single-center, randomized double-blind trial included 16 subjects (Fitzpatrick skin types I-IV) with a clinical diagnosis of type 1 rosacea and moderate to severe facial erythema, who were undergoing Pulsed Dye Laser (PDL) treatment. The clinical improvements of their facial erythema were assessed at baseline, 2 weeks, 4 weeks, and 8 weeks. Results revealed that low molecular weight HSA significantly improves the clinical signs of rosacea during the 8 weeks of use likely resulting from inhibition of LL-37 induced IL-8 cytokine release. These findings support the use of DRC in rosacea topical treatment regimens as it demonstrates visible skin benefits and improves tolerability of PDL therapy in a shorter duration of time as compared with PDL alone.George R, Gallo RL, Cohen JL, et al. Reduction of erythema in moderate-severe rosacea by a low molecular weight Heparan Sulfate Analog (HSA). J Drugs Dermatol. 2023;22(6):546-553. doi:10.36849/JDD.7494.

TREM2 macrophages induced by human lipids drive inflammation in acne lesions.

Acne affects 1 in 10 people globally, often resulting in disfigurement. The disease involves excess production of lipids, particularly squalene, increased growth of Cutibacterium acnes, and a host inflammatory response with foamy macrophages. By combining single-cell and spatial RNA sequencing as well as ultrahigh-resolution Seq-Scope analyses of early acne lesions on back skin, we identified TREM2 macrophages expressing lipid metabolism and proinflammatory gene programs in proximity to hair follicle epithelium expressing squalene epoxidase. We established that the addition of squalene induced differentiation of TREM2 macrophages in vitro, which were unable to kill C. acnes. The addition of squalene to macrophages inhibited induction of oxidative enzymes and scavenged oxygen free radicals, providing an explanation for the efficacy of topical benzoyl peroxide in the clinical treatment of acne. The present work has elucidated the mechanisms by which TREM2 macrophages and unsaturated lipids, similar to their involvement in atherosclerosis, may contribute to the pathogenesis of acne.

The Ubiquitous Human Skin Commensal Staphylococcus hominis Protects against Opportunistic Pathogens.

Staphylococcus hominis is frequently isolated from human skin, and we hypothesize that it may protect the cutaneous barrier from opportunistic pathogens. We determined that S. hominis makes six unique autoinducing peptide (AIP) signals that inhibit the major virulence factor accessory gene regulator (agr) quorum sensing system of Staphylococcus aureus. We solved and confirmed the structures of three novel AIP signals in conditioned medium by mass spectrometry and then validated synthetic AIP activity against all S. aureus agr classes. Synthetic AIPs also inhibited the conserved agr system in a related species, Staphylococcus epidermidis. We determined the distribution of S. hominis agr types on healthy human skin and found S. hominis agr-I and agr-II were highly represented across subjects. Further, synthetic AIP-II was protective in vivo against S. aureus-associated dermonecrotic or epicutaneous injury. Together, these findings demonstrate that a ubiquitous colonizer of human skin has a fundamentally protective role against opportunistic damage. IMPORTANCE Human skin is home to a variety of commensal bacteria, including many species of coagulase-negative staphylococci (CoNS). While it is well established that the microbiota as a whole maintains skin homeostasis and excludes pathogens (i.e., colonization resistance), relatively little is known about the unique contributions of individual CoNS species to these interactions. Staphylococcus hominis is the second most frequently isolated CoNS from healthy skin, and there is emerging evidence to suggest that it may play an important role in excluding pathogens, including Staphylococcus aureus, from colonizing or infecting the skin. Here, we identified that S. hominis makes 6 unique peptide inhibitors of the S. aureus global virulence factor regulation system (agr). Additionally, we found that one of these peptides can prevent topical or necrotic S. aureus skin injury in a mouse model. Our results demonstrate a specific and broadly protective role for this ubiquitous, yet underappreciated skin commensal.

Mechanisms for control of skin immune function by the microbiome.

The skin represents the largest area for direct contact between microbes and host immunocytes and is a site for constant communication between the host and this diverse and essential microbial community. Coagulase-negative staphylococci are an abundant bacterial genus on the human skin and are regulated through various mechanisms that include the epidermal barrier environment and innate and adaptive immune systems within the epidermis and dermis. In turn, some species and strains of these bacteria produce beneficial products that augment host immunity by exerting specifically targeted antimicrobial, anti-inflammatory, or anti-neoplastic activity while also promoting broad innate and adaptive immune responses. The use of selected skin commensals as a therapeutic has shown promise in recent human clinical trials. This emerging concept of bacteriotherapy is defining mechanisms of action and validating the dependence on the microbiome for maintenance of immune homeostasis.

Update on Facial Erythema in Rosacea.

Dermatologists are cognizant of the multiple clinical manifestations of rosacea, particularly persistent facial erythema, which has been deemed to be the most prevalent diagnostic feature and often poses a significant negative impact on quality of life. To address the need to recognize rosacea as a single disease with multiple potential phenotypes, a new classification system has been developed by 28 clinical and scientific experts worldwide.

Staphylococcus epidermidis protease EcpA can be a deleterious component of the skin microbiome in atopic dermatitis.

BACKGROUND: Staphylococcus aureus and Staphylococcus epidermidis are the most abundant bacteria found on the skin of patients with atopic dermatitis (AD). S aureus is known to exacerbate AD, whereas S epidermidis has been considered a beneficial commensal organism. OBJECTIVE: In this study, we hypothesized that S epidermidis could promote skin damage in AD by the production of a protease that damages the epidermal barrier. METHODS: The protease activity of S epidermidis isolates was compared with that of other staphylococcal species. The capacity of S epidermidis to degrade the barrier and induce inflammation was examined by using human keratinocyte tissue culture and mouse models. Skin swabs from atopic and healthy adult subjects were analyzed for the presence of S epidermidis genomic DNA and mRNA. RESULTS: S epidermidis strains were observed to produce strong cysteine protease activity when grown at high density. The enzyme responsible for this activity was identified as EcpA, a cysteine protease under quorum sensing control. EcpA was shown to degrade desmoglein-1 and LL-37 in vitro, disrupt the physical barrier, and induce skin inflammation in mice. The abundance of S epidermidis and expression of ecpA mRNA were increased on the skin of some patients with AD, and this correlated with disease severity. Another commensal skin bacterial species, Staphylococcus hominis, can inhibit EcpA production by S epidermidis. CONCLUSION: S epidermidis has commonly been regarded as a beneficial skin microbe, whereas S aureus has been considered deleterious. This study suggests that the overabundance of S epidermidis found on some atopic patients can act similarly to S aureus and damage the skin by expression of a cysteine protease.

Role of Epigenetics in the Regulation of Immune Functions of the Skin.

This review is intended to illuminate the emerging understanding of epigenetic modifications that regulate both adaptive and innate immunity in the skin. Host defense of the epidermis and dermis involves the interplay of many cell types to enable homeostasis; tolerance to the external environment; and appropriate response to transient microbial, chemical, and physical insults. To understand this process, the study of cutaneous immunology has focused on immune responses that reflect both adaptive learned and genetically programmed innate defense systems. However, recent advances have begun to reveal that epigenetic modifications of chromatin structure also have a major influence on the skin immune system. This deeper understanding of how enzymatic changes in chromatin structure can modify the skin immune system and may explain how environmental exposures during life, and the microbiome, lead to both short-term and long-term changes in cutaneous allergic and other inflammatory processes. Understanding the mechanisms responsible for alterations in gene and chromatin structure within skin immunocytes could provide key insights into the pathogenesis of inflammatory skin diseases that have thus far evaded understanding by dermatologists.

Standard management options for rosacea: The 2019 update by the National Rosacea Society Expert Committee.

In 2017, a National Rosacea Society Expert Committee developed and published an updated classification of rosacea to reflect current insights into rosacea pathogenesis, pathophysiology, and management. These developments suggest that a multivariate disease process underlies the various clinical manifestations of the disorder. The new system is consequently based on phenotypes that link to this process, providing clear parameters for research and diagnosis as well as encouraging clinicians to assess and treat the disorder as it may occur in each individual. Meanwhile, a range of therapies has become available for rosacea, and their roles have been increasingly defined in clinical practice as the disorder has become more widely recognized. This update is intended to provide a comprehensive summary of management options, including expert evaluations, to serve as a guide for tailoring treatment and care on an individual basis to achieve optimal patient outcomes.

Cathelicidin preserves intestinal barrier function in polymicrobial sepsis.

OBJECTIVES: The intestinal epithelium compartmentalizes the sterile bloodstream and the commensal bacteria in the gut. Accumulating evidence suggests that this barrier is impaired in sepsis, aggravating systemic inflammation. Previous studies reported that cathelicidin is differentially expressed in various tissues in sepsis. However, its role in sepsis-induced intestinal barrier dysfunction has not been investigated. DESIGN: To examine the role of cathelicidin in polymicrobial sepsis, cathelicidin wild-(Cnlp+/+) and knockout (Cnlp-/-) mice underwent cecal-ligation and puncture (CLP) followed by the assessment of septic mortality and morbidity as well as histological, biochemical, immunological, and transcriptomic analyses in the ileal tissues. We also evaluated the prophylactic and therapeutic efficacies of vitamin D3 (an inducer of endogenous cathelicidin) in the CLP-induced murine polymicrobial sepsis model. RESULTS: The ileal expression of cathelicidin was increased by three-fold after CLP, peaking at 4 h. Knockout of Cnlp significantly increased 7-day mortality and was associated with a higher murine sepsis score. Alcian-blue staining revealed a reduced number of mucin-positive goblet cells, accompanied by reduced mucin expression. Increased number of apoptotic cells and cleavage of caspase-3 were observed. Cnlp deletion increased intestinal permeability to 4kD fluorescein-labeled dextran and reduced the expression of tight junction proteins claudin-1 and occludin. Notably, circulating bacterial DNA load increased more than two-fold. Transcriptome analysis revealed upregulation of cytokine/inflammatory pathway. Depletion of Cnlp induced more M1 macrophages and neutrophils compared with the wild-type mice after CLP. Mice pre-treated with cholecalciferol (an inactive form of vitamin D3) or treated with 1alpha, 25-dihydroxyvitamin D3 (an active form of VD3) had decreased 7-day mortality and significantly less severe symptoms. Intriguingly, the administration of cholecalciferol after CLP led to worsened 7-day mortality and the associated symptoms. CONCLUSIONS: Endogenous cathelicidin promotes intestinal barrier integrity accompanied by modulating the infiltration of neutrophils and macrophages in polymicrobial sepsis. Our data suggested that 1alpha, 25-dihydroxyvitamin D3 but not cholecalciferol is a potential therapeutic agent for treating sepsis.

Innate Immune Dysfunction in Rosacea Promotes Photosensitivity and Vascular Adhesion Molecule Expression.

Rosacea is a chronic skin disease characterized by photosensitivity, abnormal dermal vascular behavior, inflammation, and enhanced expression of the antimicrobial peptide LL-37. We observed that dermal endothelial cells in rosacea had an increased expression of VCAM1 and hypothesized that LL-37 could be responsible for this response. The digestion of double-stranded RNA from keratinocytes exposed to UVB blocked the capacity of these cells to induce adhesion molecules on dermal microvascular endothelial cells. However, a synthetic noncoding snoU1RNA was only capable of increasing adhesion molecules on endothelial cells in the presence of LL-37, suggesting that the capacity of UVB exposure to promote both double-stranded RNA and LL-37 was responsible for the endothelial response to keratinocytes. Sequencing of RNA from the endothelial cells uncovered the activation of Gene Ontology (GO) pathways relevant to the human disease, such as type I and II interferon signaling, cell-cell adhesion, leukocyte chemotaxis, and angiogenesis. Functional relevance was demonstrated as double-stranded RNA and LL-37 promoted adhesion and transmigration of monocytes across the endothelial cell monolayers. Gene knockdown of TLR3, RIGI, or IRF1 decreased monocyte adhesion in endothelial cells, confirming the role of the double-stranded RNA recognition pathways. These observations show how the expression of LL-37 can lead to enhanced sensitivity to UVB radiation in rosacea.

A mouse model for vitamin D-induced human cathelicidin antimicrobial peptide gene expression.

In humans and other primates, 1,25(OH)2vitamin D3 regulates the expression of the cathelicidin antimicrobial peptide (CAMP) gene via toll-like receptor (TLR) signaling that activates the vitamin D pathway. Mice and other mammals lack the vitamin D response element (VDRE) in their CAMP promoters. To elucidate the biological importance of this pathway, we generated transgenic mice that carry a genomic DNA fragment encompassing the entire human CAMP gene and crossed them with Camp knockout (KO) mice. We observed expression of the human transgene in various tissues and innate immune cells. However, in mouse CAMP transgenic macrophages, TLR activation in the presence of 25(OH)D3 did not induce expression of either CAMP or CYP27B1 as would normally occur in human macrophages, reinforcing important species differences in the actions of vitamin D. Transgenic mice did show increased resistance to colonization by Salmonella typhimurium in the gut. Furthermore, the human CAMP gene restored wound healing in the skin of Camp KO mice. Topical application of 1,25(OH)2vitamin D3 to the skin of CAMP transgenic mice induced CAMP expression and increased killing of Staphylococcus aureus in a wound infection model. Our model can help elucidate the biological importance of the vitamin D-cathelicidin pathway in both pathogenic and non-pathogenic states.

Response to Comment on "A commensal strain of Staphylococcus epidermidis protects against skin neoplasia" by Nakatsuji et al.

Kozmin et al. contend that observations previously reported regarding the antimicrobial and antitumor activities of 6-N-hydroxy aminopurine (6-HAP) were incorrect. Their conclusions rely on poorly characterized reagents and focus strictly on in vitro techniques without validation in relevant mammalian model systems. We are pleased to be able to illuminate the weaknesses in their technical comment. The totality of current results continues to support our original conclusion that a strain of the common human commensal skin bacterium, Staphylococcus epidermidis, produces 6-HAP that can inhibit tumor growth.

Retinoids Enhance the Expression of Cathelicidin Antimicrobial Peptide during Reactive Dermal Adipogenesis.

A subset of dermal fibroblasts undergo rapid differentiation into adipocytes in response to infection and acutely produce the cathelicidin antimicrobial peptide gene Camp Vitamin A and other retinoids inhibit adipogenesis yet can show benefit to skin disorders, such as cystic acne, that are exacerbated by bacteria. We observed that retinoids potently increase and sustain the expression of Camp in preadipocytes undergoing adipogenesis despite inhibition of markers of adipogenesis, such as Adipoq, Fabp4, and Rstn Retinoids increase cathelicidin in both mouse and human preadipocytes, but this enhancement of antimicrobial peptide expression did not occur in keratinocytes or a sebocyte cell line. Preadipocytes undergoing adipogenesis more effectively inhibited growth of Staphylococcus aureus when exposed to retinoic acid. Whole transcriptome analysis identified hypoxia-inducible factor 1-α (HIF-1α) as a mechanism through which retinoids mediate this response. These observations uncouple the lipid accumulation element of adipogenesis from the innate immune response and uncover a mechanism, to our knowledge previously unsuspected, that may explain therapeutic benefits of retinoids in some skin disorders.

Photoimmunology: how ultraviolet radiation affects the immune system.

Ultraviolet (UV) radiation is a ubiquitous component of the environment that has important effects on a wide range of cell functions. Short-wavelength UVB radiation induces sunburn and is a potent immunomodulator, yet longer-wavelength, lower-energy UVA radiation also has effects on mammalian immunity. This Review discusses current knowledge regarding the mechanisms by which UV radiation can modify innate and adaptive immune responses and how this immunomodulatory capacity can be both beneficial in the case of inflammatory and autoimmune diseases, and detrimental in the case of skin cancer and the response to several infectious agents.

Quorum sensing between bacterial species on the skin protects against epidermal injury in atopic dermatitis.

Colonization of the skin by Staphylococcus aureus is associated with exacerbation of atopic dermatitis (AD), but any direct mechanism through which dysbiosis of the skin microbiome may influence the development of AD is unknown. Here, we show that proteases and phenol-soluble modulin α (PSMα) secreted by S. aureus lead to endogenous epidermal proteolysis and skin barrier damage that promoted inflammation in mice. We further show that clinical isolates of different coagulase-negative staphylococci (CoNS) species residing on normal skin produced autoinducing peptides that inhibited the S. aureus agr system, in turn decreasing PSMα expression. These autoinducing peptides from skin microbiome CoNS species potently suppressed PSMα expression in S. aureus isolates from subjects with AD without inhibiting S. aureus growth. Metagenomic analysis of the AD skin microbiome revealed that the increase in the relative abundance of S. aureus in patients with active AD correlated with a lower CoNS autoinducing peptides to S. aureus ratio, thus overcoming the peptides' capacity to inhibit the S. aureus agr system. Characterization of a S. hominis clinical isolate identified an autoinducing peptide (SYNVCGGYF) as a highly potent inhibitor of S. aureus agr activity, capable of preventing S. aureus-mediated epithelial damage and inflammation on murine skin. Together, these findings show how members of the normal human skin microbiome can contribute to epithelial barrier homeostasis by using quorum sensing to inhibit S. aureus toxin production.