Recognition of Propionibacterium acnes by human TLR2 heterodimers

Phenylacetaldehyde attenuates Cutibacterium acnes-induced inflammation in keratinocytes and monocytes

Cutibacterium acnes (C. acnes)-induced inflammation is the key driver of acne vulgaris. C. acnes stimulates keratinocytes to secrete pro-inflammatory cytokines, subsequently triggering monocytes to produce additional cytokines. Although synthetic antibacterials, such as antibiotics, are commonly used to treat this disorder, the development of resistance has greatly diminished their effectiveness in the treatment of acne. This study aimed to evaluate whether phenylacetaldehyde (PAA), a natural compound, attenuates C. acnes-mediated inflammation without exerting antibacterial activity. The results confirmed that PAA exhibited no antibacterial activity against C. acnes at concentrations below 200 μM, as determined by the broth microdilution method. Furthermore, PAA significantly inhibited the mRNA and protein levels of pro-inflammatory cytokines in C. acnes-treated keratinocytes, as measured by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assays, respectively. Additionally, PAA reduced the activation of nuclear factor kappa B (NF-κB) following exposure to C. acnes, as verified by western blot and luciferase reporter assays. Notably, the inhibitory action of PAA on C. acnes-induced inflammatory cytokine production was largely abolished by a protein kinase A inhibitor. Preliminary validation in monocytes further suggested that PAA suppressed the pro-inflammatory cytokine responses triggered by C. acnes. In conclusion, PAA effectively mitigated C. acnes-stimulated inflammation in keratinocytes as well as monocytes without exhibiting bactericidal activity, suggesting its potential as a supplementary therapeutic option for acne management.

Molecular Mechanisms of Intervertebral Disc Degeneration Induced by Propionibacterium acnes

Intervertebral disc degeneration (IVDD), a prevalent degenerative disorder with substantial socioeconomic impacts, is closely linked to endplate inflammation and chronic low back pain. Its pathogenesis involves multifactorial mechanisms, including long-term chronic mechanical loading, external trauma, and hereditary factors. Emerging evidence highlights Propionibacterium acnes (P. acnes), a gram-positive bacterium with potent proinflammatory properties, as a key contributor to IVDD progression. This review systematically analyses the latest literature on related studies, focusing on the molecular mechanisms of IVDD induced by P. acnes. Three molecules play an important role in the induction of IVDD by P. acnes, namely, IL-1β, MIF, and MMP. In addition, P. acnes induces IVDD through three core mechanisms, namely, proinflammatory (activation of TLR2, production of large amounts of ROS to promote inflammation), pyroptosis (production of large amounts of NLRP3 through the TXNIP-NLRP3 axis and the ROS-NLRP3 axis), and apoptosis (promotion of Bax and inhibition of Bcl-2 expression through the TLR2-JNK pathway). The dissection of these related important molecules and pathogenic mechanisms can lead to a better understanding of the role of P. acnes in IVDD. It can provide an important theoretical basis for future research. However, the current study's lack of large-scale clinical validation, unresolved colonization controversies, and limited experimental methods are limitations. Therefore, in the future, it is still necessary to improve the relevant theories and resolve the current controversies through more advanced experimental methods and higher quality clinical studies. In conclusion, the study of P. acnes-induced IVDD is promising, and further research can be conducted in the future, which is expected to develop novel therapeutic approaches for P. acnes, thus effectively slowing down the development of IVDD.

The Secretion of Inflammatory Cytokines Triggered by TLR2 Through Calcium-Dependent and Calcium-Independent Pathways in Keratinocytes

Keratinocytes can be activated by Cutibacterium acnes, leading to the production of proinflammatory cytokines via toll-like receptors (TLRs) 2 and 4. Although several studies have investigated keratinocytes, the mechanism of calcium-mediated activation remains unclear. Herein, we investigated whether calcium influx via TLR2 and TLR4 stimulation was involved in cytokine secretion by keratinocytes in HaCaT cells. Although TLR2 stimulation by peptidoglycan (PGN) increased intracellular calcium influx, TLR4 stimulation by lipopolysaccharide (LPS) did not increase it, as analyzed using flow cytometry with the calcium indicator Fluo-3. However, activation by either TLR2 or TLR4 ligands upregulated the intracellular calcium influx in THP-1 monocytes. Additionally, the expression of major proinflammatory cytokines and chemokines, such as interleukin (IL)-6, IL-8, IL-1α, granulocyte-macrophage colony-stimulating factor (GM-CSF), and monocyte chemoattractant protein-1 (MCP-1), was significantly increased by TLR2 in HaCaT cells. Moreover, treatment with the intracellular calcium chelator, BAPTA-AM, disrupted PGN-mediated induction of IL-6, IL-8, and MCP-1 production. Real-time quantitative polymerase chain reaction (PCR) and western blotting revealed that TLR2 stimulation induced expression of the epidermal differentiation marker keratin 1. In conclusion, TLR2-induced intracellular calcium influx plays a pivotal role in the secretion of proinflammatory cytokines, such as IL-6 and MCP-1, in keratinocytes. Moreover, the continuous influx of calcium via TLR2 activation leads to keratinization. In vitro studies using HaCaT cells provide basic research on the effect of TLR2-induced calcium on C. acnes-mediated inflammation in keratinocytes. These studies are limited in their ability to clinically predict what happens in human keratinocytes. Clinical studies on patients with acne, including three-dimensional (3D) cultures of primary keratinocytes, are required to develop new diagnostic markers for determining the severity of acne vulgaris.

Label-free biosensor assay decodes the dynamics of Toll-like receptor signaling

The discovery of Toll-like receptors (TLRs) represented a significant breakthrough that paved the way for the study of host-pathogen interactions in innate immunity. However, there are still major gaps in understanding TLR function, especially regarding the early dynamics of downstream TLR pathways. Here, we present a label-free optical biosensor-based assay as a method for detecting TLR activation in a native and label-free environment and defining the dynamics of TLR pathway activation. This technology is sufficiently sensitive to detect TLR signaling and readily discriminates between different TLR signaling pathways. We define pharmacological modulators of cell surface and endosomal TLRs and downstream signaling molecules and uncover TLR signaling signatures, including potential biased receptor signaling. These findings highlight that optical biosensor assays complement traditional assays that use a single endpoint and have the potential to facilitate the future design of selective drugs targeting TLRs and their downstream effector cascades.

Octahydroindolizine alkaloid Homocrepidine A from Dendrobium crepidatum attenuate P. acnes-induced inflammatory in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Dendrobium crepidatum Lindl. ex Paxton is a perennial epiphyte of Dendrobium genus, distributed in southern China, and utilized as the traditional Chinese medicine "Shihu" in Yunnan Province. Due to its heat-clearing and detoxicating properties, it is formulated as the "XiaoCuoWan" as recorded in the China Pharmacopoeia, and specially used to treat chronic skin inflammatory diseases, such as acne.

AIM OF THE STUDY

This research aimed to estimate impact of the octahydroindoline alkaloid Homocrepidine A (HCA), isolated from D. crepidatum, on acne inflammation using both human THP-1 cells and mouse models. Furthermore, the potential anti-inflammatory mechanism of HCA has been analyzed through molecular biology methods and computer simulation.

MATERIALS AND METHODS

THP-1 cells and mouse models induced by live Propionibacterium acnes (P. acnes) were employed to evaluate the anti-inflammatory properties of crude extract of D. crepidatum (DCE) and HCA. ELISA was utilized to detect the release of inflammatory cytokines in both cellular and murine ear tissues. RNAseq was used to screen the pathways associated with HCA-mediated inflammatory inhibition, while Western blot, RT-qPCR, and immunofluorescence were utilized to detect the expression of relevant proteins. Additionally, molecular docking simulations and cellular thermal shift assays were employed to confirm the target of HCA.

RESULTS

Our research shows that DCE and HCA can effectively alleviate acne inflammation. HCA inhibits TLR2 expression by interacting with amino acid residues in the TIR domain of hTLR2, including Pro-681, Asn-688, Trp-684, and Ile-685. Moreover, HCA disrupts inflammatory signal transduction mediated by MAPK and NF-κB pathways through MyD88-dependent pathway. Additionally, HCA treatment facilitates Nrf2 nuclear translocation and upregulates HO-1 expression, thereby inhibiting NLRP3 inflammasomes activation. In vivo experiments further revealed that HCA markedly attenuated erythema and swelling caused by P. acnes in mice ears, while also decreasing the expression of pro-inflammatory cytokines IL-1β and IL-8.

CONCLUSIONS

Our research highlights the protective effects of D. crepidatum and its bioactive compound HCA against acne inflammation, marking the first exploration of its potential in this context. The discoveries indicate that HCA treatment may represent a promising functional approach for acne therapy.

Cutibacterium acnes contamination does not enhance the proinflammatory profile of platelet concentrates

BACKGROUND

Cutibacterium acnes, a common anaerobic platelet concentrate (PC) contaminant, has been associated with rare mild adverse transfusion reactions and is often considered a harmless commensal. Notably, C. acnes can cause chronic infections and has been shown to induce the release of proinflammatory cytokines by immune cells. Since elevated concentrations of proinflammatory factors in PCs have been linked to noninfectious adverse reactions, this study aimed to assess whether C. acnes could elicit the release and accumulation of proinflammatory factors during PC storage, thereby enhancing the risk of such reactions.

STUDY DESIGN/METHODS

Four ABO-matched buffy coat PCs were pooled and split into six units, each were inoculated with either saline (negative control), a Staphylococcus aureus isolate (positive control, 30 colony forming units [CFU]/unit), or four C. acnes PC isolates (10 CFU/mL) and stored at 20-24°C with agitation. Bacterial counts, platelet activation, and concentration of proinflammatory factors were assessed on days 0, 3, and 5. N = 3.

RESULTS

C. acnes counts remained stable, while S. aureus proliferated reaching 108CFU/mL by the end of PC storage. By day 5, no significant differences in platelet activation or proinflammatory cytokine profiles were observed in C. acnes-contaminated PCs compared to the negative control (p > .05), while there was a significant increase (p ≤ .05) in sCD40L concentration (day 3), and platelet activation and IL-8 concentration (day 5) in S. aureus-contaminated units.

DISCUSSION

C. acnes contamination does not promote the accumulation of proinflammatory factors in the absence of proliferation during storage and may not enhance the risk of inflammatory reactions when transfused to patients.

Anti-CAMP1 IgG promotes macrophage phagocytosis of Cutibacterium acnes type II

Among 5 types of the Christie-Atkins-Munch-Petersen factor (CAMP) of Cutibacterium acnes, CAMP1 is highly expressed in phylotype II as well as IB, and thought to be a virulence factor of opportunistic but fatal blood, soft tissue, and implant-related infections. The target of a human single-chain variable antibody fragment (scFv), recently isolated from a phage display library, has been identified as CAMP1 of phylotype II, using immunoprecipitation followed by mass spectrometry, phage display peptide biopanning, 3D-modelling, and ELISA. The IgG1 format of the antibody could enhance phagocytosis of C. acnes DMST 14916 by THP-1 human monocytes. Our results suggest that the antibody-dependent phagocytosis process is mediated by the caveolae membrane system and involves the induction of IL-1β. This is the first report on the study of a human antibody against CAMP1 of C. acnes phylotype II, of which a potential use as therapeutic antibody against virulence C. acnes infection is postulated.

Induction of IL-32 in the immune response of keratinocytes to Mycobacterium marinum infection

Keratinocytes are the predominant cell type in the skin epidermis, and they not only protect the skin from the influence of external physical factors but also function as an immune barrier against microbial invasion. However, little is known regarding the immune defence mechanisms of keratinocytes against mycobacteria. Here, we performed single-cell RNA sequencing (scRNA-seq) on skin biopsy samples from patients with Mycobacterium marinum infection and bulk RNA sequencing (bRNA-seq) on M. marinum-infected keratinocytes in vitro. The combined analysis of scRNA-seq and bRNA-seq data revealed that several genes were upregulated in M. marinum-infected keratinocytes. Further in vitro validation of these genes by quantitative polymerase chain reaction and western blotting assay confirmed the induction of IL-32 in the immune response of keratinocytes to M. marinum infection. Immunohistochemistry also showed the high expression of IL-32 in patients' lesions. These findings suggest that IL-32 induction is a possible mechanism through which keratinocytes defend against M. marinum infection; this could provide new targets for the immunotherapy of chronic cutaneous mycobacterial infections.

Regulation of cell cycle and differentiation markers by pathogenic, non-pathogenic and opportunistic skin bacteria

Skin is the first line of defense against the physical, chemical and the biological environment. It is an ideal organ for studying molecular responses to biological infections through a variety of skin cells that specialize in immune responses. Comparative analysis of skin response to pathogenic, non-pathogenic, and commensal bacteria would help in the identification of disease specific pathways for drug targets. In this study, we investigated human breast reduction skin responses to Cutibacterium acnes (C. acnes), Staphylococcus aureus (S. aureus), Staphylococcus epidermidis (S. epidermidis), and TLR1/2 agonist using Affymetrix microarray chips. The Pam3CSK4 solution and bacterial cultures were prepared and inoculated in steel rings, that were placed on the acetone treated epidermis in a petri dish. After 24 h incubation, 8 mm punch biopsies were taken from the center of the ring, and RNA was extracted. The genome-wide expression was then analyzed using Affymetrix HG-133A gene chip microarray. We found that the C. acnes and S. aureus boosted the production of extracellular matrix components and attenuated the expression of differentiation markers. The above responses were mediated through the TLR2 pathway. Skin also responded to S. aureus and C. acnes by inducing the genes of the cell cycle machinery; this response was not TLR2-dependent. S. aureus induced, whereas C. acnes suppressed the genes associated with apoptosis; this was also not TLR2-dependent. Moreover, S. epidermis apparently did not lead to changes in gene expression. We conclude that the breast reduction skin is a very useful model to study the global gene expression in response to bacterial treatments.

A Janus-Faced Bacterium: Host-Beneficial and -Detrimental Roles of Cutibacterium acnes

The bacterial species Cutibacterium acnes (formerly known as Propionibacterium acnes) is tightly associated with humans. It is the dominant bacterium in sebaceous regions of the human skin, where it preferentially colonizes the pilosebaceous unit. Multiple strains of C. acnes that belong to phylogenetically distinct types can co-exist. In this review we summarize and discuss the current knowledge of C. acnes regarding bacterial properties and traits that allow host colonization and play major roles in host-bacterium interactions and also regarding the host responses that C. acnes can trigger. These responses can have beneficial or detrimental consequences for the host. In the first part of the review, we highlight and critically review disease associations of C. acnes, in particular acne vulgaris, implant-associated infections and native infections. Here, we also analyse the current evidence for a direct or indirect role of a C. acnes-related dysbiosis in disease development or progression, i.e., reduced C. acnes strain diversity and/or the predominance of a certain phylotype. In the second part of the review, we highlight historical and recent findings demonstrating beneficial aspects of colonization by C. acnes such as colonization resistance, immune system interactions, and oxidant protection, and discuss the molecular mechanisms behind these effects. This new insight led to efforts in skin microbiota manipulation, such as the use of C. acnes strains as probiotic options to treat skin disorders.

Cutibacterium acnes Phylotype I and II Strains Interact Differently With Human Skin Cells

Acne vulgaris is one of the most common skin disorders and affects the pilosebaceous units. Although the exact pathogenesis of acne is still unknown, Cutibacterium acnes (formerly known as Propionibacterium acnes) is considered one of the key contributing factors. In fact, a significant association exists between C. acnes strains belonging to phylotype I and acne. However, there is still heavy debate on the exact role of C. acnes in acne and its behavior in the pilosebaceous unit, and more specifically its interactions with the human skin cells. In this study, key elements of the host-pathogen interaction were studied for a collection of C. acnes strains, belonging to phylotype I and II, including association with HaCaT keratinocytes and SZ95 sebocytes, the effect of C. acnes on keratinocyte tight junctions in a HaCaT monoculture and in an additional keratinocyte-sebocyte co-culture model, and C. acnes invasion through the keratinocyte cell layer. Our data showed association of all C. acnes strains to both skin cell lines, with a significantly higher association of type I strains compared to type II strains. Microscopic imaging and western blot analysis of the tight junction protein ZO-1, together with transepithelial electrical resistance (TEER) measurements revealed an initial induction of keratinocyte tight junctions after 24 h infection but a degradation after 48 h, demonstrating a decline in cell lining integrity during infection. Subsequently, C. acnes was able to invade after 48 h of infection, although invasion frequency was significantly higher for type II strains compared to type I strains.

Cutibacterium acnes Infection Induces Type I Interferon Synthesis Through the cGAS-STING Pathway

Cutibacterium (previously Propionibacterium) acnes is an anaerobic, Gram-positive commensal of the human body. The bacterium has been associated with a variety of diseases, including acne vulgaris, prosthetic joint infections, prostate cancer, and sarcoidosis. The accumulation of C. acnes in diseases such as acne and prostate cancer has been shown to correlate with enhanced inflammation. While the C. acnes-induced proinflammatory axis, via NF-κB and MAPK signaling and inflammasome activation, has been investigated over the last few decades, the potential role of C. acnes in triggering the type I interferon (IFN-I) pathway has not been addressed. Our results show that C. acnes induces the IFN-I signaling axis in human macrophages by triggering the cGAS-STING pathway. In addition, IFN-I signaling induced by C. acnes strongly depends on the adapter protein TRIF in a non-canonical manner; these signaling events occurred in the absence of any detectable intracellular replication of the bacterium. Collectively, our results provide important insight into C. acnes-induced intracellular signaling cascades in human macrophages and suggest IFN-I as a factor in the etiology of C. acnes-induced diseases. This knowledge may be valuable for developing novel therapies targeting C. acnes in diseases where the accumulation of the bacterium leads to an inflammatory pathology.

Biological Characterization, Mechanistic Investigation and Structure-Activity Relationships of Chemically Stable TLR2 Antagonists

Toll-like receptors (TLRs) build the first barrier in the innate immune response and therefore represent promising targets for the modulation of inflammatory processes. Recently, the pyrogallol-containing TLR2 antagonists CU-CPT22 and MMG-11 were reported; however, their 1,2,3-triphenol motif renders them highly susceptible to oxidation and excludes them from use in extended experiments under aerobic conditions. Therefore, we have developed a set of novel TLR2 antagonists (1-9) based on the systematic variation of substructures, linker elements, and the hydrogen-bonding pattern of the pyrogallol precursors by using chemically robust building blocks. The novel series of chemically stable and synthetically accessible TLR2 antagonists (1-9) was pharmacologically characterized, and the potential binding modes of the active compounds were evaluated structurally. Our results provide new insights into structure-activity relationships and allow rationalization of structural binding characteristics. Moreover, they support the hypothesis that this class of TLR ligands bind solely to TLR2 and do not directly interact with TLR1 or TLR6 of the functional heterodimer. The most active compound from this series (6), is chemically stable, nontoxic, TLR2-selective, and shows a similar activity with regard to the pyrogallol starting points, thus indicating the variability of the hydrogen bonding pattern.

Identification and validation of a novel dual small-molecule TLR2/8 antagonist

Toll-like receptor 2 (TLR2) and TLR8 are involved in the recognition of bacterial and viral components and are linked not only to protective antimicrobial immunity but also to inflammatory diseases. Recently, increasing attention has been paid to the receptor crosstalk between TLR2 and TLR8 to fine-tune innate immune responses. In this study, we report a novel dual TLR2/TLR8 antagonist, compound 24 that was developed by a modeling-guided synthesis approach. The modulator was optimized from the previously reported 1,3-benzothiazole derivative, compound 8. Compound 24 was pharmacologically characterized for the ability to inhibit TLR2- and TLR8-mediated responses in TLR-overexpressing reporter cells and THP-1 macrophages. The modulator showed high efficacy with IC₅₀ values in the low micromolar range for both TLRs, selectivity towards other TLRs and low cytotoxicity. At TLR2, a slight predominance for the TLR2/1 heterodimer was found in reporter cells selectively expressing TLR2/1 or TLR2/6 heterodimers. Concentration ratio analysis in the presence of Pam₃CSK₄ or Pam₂CSK₄ indicated non-competitive antagonist behavior at hTLR2. In computational docking studies, a plausible alternative binding mode of compound 24 was predicted for both TLR2 and TLR8. Our results provide evidence that it is feasible to simultaneously and selectively target endosomal- and surface-located TLRs. We identified a small-molecule dual TLR2/8 antagonist that may serve as a valuable pharmacological tool to decipher the role of TLR2/8 co-signaling in inflammation.

Lubricin expression in the lumbar endplate and its association with Modic changes

Objective

To explore the expression of lubricin in the lumbar endplate and its association with Modic changes (MCs).

Methods

Human endplate specimens harvested from patients undergoing surgery for thoracolumbar spine fractures ​or lumbar interbody fusion were divided into two groups: MCs group and normal group. Lubricin expression was examined by immunohistochemistry, and differences between the groups were analysed using quantitative polymerase chain reaction (qPCR). Lubricin expression and differences between endplates with MCs and normal endplates were confirmed using a rabbit model. In a final experiment, rabbit endplate chondrocytes were cocultured with Propionibacteria acnes (P. acnes) supernatant, and the expression of lubricin and endplate degeneration related genes were evaluated. In addition, the expression of matrix metalloproteinase 1(MMP-1), A disintegrin-like and metalloproteinase with thrombospondin type 5 motif (ADAMTS5) and inflammatory factors (Interleukin- 1β (IL-1β) and Interleukin-6 (IL-6)) were evaluated after lubricin overexpression.

Results

Lubricin was found in human lumbar endplates and its expression was lower in the MCs group compared to the normal group. In the rabbit model, lubricin was also found in the endplate. In rabbits injected with P. acnes (the MCs group), lubricin expression of endplate decreased compared to the normal group. In the culture of rabbit endplate chondrocytes with P. acnes supernatant, the expression of lubricin, aggrecan, sox9 and collagen type-II decreased significantly, while that of MMP-1 and ADAMTS5 increased significantly. Moreover, lubricin overexpression could downregulate the expression of MMP-1, ADAMTS5 and inflammatory factors (IL-1β and IL-6) compared to negative control.

Conclusion

Lubricin is present in the lumbar endplate where it may have an anti-inflammatory role. P. acnes infection inhibits lubricin expression by cartilage endplate cells and this may facilitate the progression of MCs and endplate degeneration.

The translational potential of this article

Lubricin may have an anti-inflammatory role. P. acnes infection inhibits lubricin expression by cartilage endplate cells and this may facilitate the progression of MCs and endplate degeneration.

The novel small-molecule antagonist MMG-11 preferentially inhibits TLR2/1 signaling

Toll-like receptor 2 (TLR2) forms heterodimers with either TLR1 or TLR6 to induce protective early inflammatory responses to pathogen- and damage-associated molecular patterns. However, excessive activation is associated with inflammatory and metabolic diseases. Several TLR2 antagonists have been described but pharmacological characterization is still at an early stage. Previously, we identified the potent and selective TLR2 antagonist MMG-11 by computational modelling and experimental validation. Here, we characterized the TLR2 antagonists MMG-11 and CU-CPT22 as well as the TIR-domain binding TLR2 antagonist C29 in TLR-overexpressing promoter cells as well as human and mouse macrophages. In line with our recent studies, MMG-11 abrogated pro-inflammatory cytokine secretion and NF-κB activation induced by different bacterial TLR2 agonists. MMG-11 preferentially inhibited TLR2/1 signaling in promoter cells stably expressing TLR2 heterodimers and mouse macrophages. Furthermore, the TLR2 antagonist blocked ligand-induced interaction of TLR2 with MyD88 and reduced MAP kinase and NF-κB activation. MMG-11 and CU-CPT22 but not C29 displaced Pam₃CSK₄ in an indirect binding assay confirming the competitive mode of action of MMG-11 and CU-CPT22. Isobologram analysis revealed additive and synergistic effects when the non-competitive antagonist C29 was combined with the competitive antagonist MMG-11 or CU-CPT22, respectively. In conclusion, we provide evidence that MMG-11 acts as a competitive antagonist with a predominance for the TLR2/1 heterodimer in human and mouse cells. Our results also indicate that MMG-11 is a model compound for studying TLR2 signaling.

Toll-like receptor 2 plays an essential role in electroacupuncture analgesia in a mouse model of inflammatory pain

BACKGROUND

Inflammatory pain occurs when local tissue injury activates macrophages and neutrophils, hence increasing pro-inflammatory cytokine and chemokine levels. Toll-like receptor 2 (TLR2) antagonism reportedly suppresses neuropathic and inflammatory pain.

AIMS

In the present study, we investigated the effect of electroacupuncture (EA) on TLR2 and related signalling molecules in a complete Freund's adjuvant (CFA)-induced mouse model of inflammatory pain to determine whether EA can attenuate inflammatory pain via the TLR2 signalling pathway.

METHODS

EA significantly reduced mechanical and thermal hyperalgesia in the animal model. A similar effect was produced by TLR2 antagonism induced by CU-CPT22 injection.

RESULTS

TLR2 expression in the dorsal root ganglia, spinal cord and thalamus increased following induction of inflammation. Expression levels of downstream molecules such as pPI3K, pAkt and pmTOR also increased, as did those of MAPK subfamily members such as pERK, pp38 and pJNK. Transcription factors (pCREB and pNFκB) and nociceptive ion channels (Nav1.7 and Nav1.8) were also involved.

CONCLUSION

Increased expression of the above molecules was attenuated by both EA and TLR2 antagonism. Our results show that EA attenuates inflammatory pain via TLR2 signalling.

Cutibacterium acnes phylotypes diversity loss: a trigger for skin inflammatory process

BACKGROUND

Acne has long been understood as a multifactorial chronic inflammatory disease of the pilosebaceous follicle, where Cutibacterium acnes (subdivided into six main phylotypes) is a crucial factor. In parallel, the loss of microbial diversity among the skin commensal communities has recently been shown as often accompanied by inflammatory skin disorders.

OBJECTIVE

This study investigated the association of C. acnes phylotype diversity loss and the impact on Innate Immune System (IIS) activation.

METHODS

The IIS response of skin after incubation with phylotypes IA1, II or III individually and with the combination of IA1 + II + III phylotypes, was studied in an in vitro skin explant system. The inflammatory response was monitored by immunohistochemistry and ELISA assays, targeting a selection of Innate Immune Markers (IIMs) (IL-6, IL-8, IL-10, IL-17, TGF-β).

RESULTS

IIMs were significantly upregulated in skin when being incubated with phylotype IA1 alone compared with the combination IA1 + II + III. In parallel, ELISA assays confirmed these results in supernatants for IL-17, IL-8 and IL-10.

CONCLUSION

We identify the loss of C. acnes phylotype diversity as a trigger for IIS activation, leading to cutaneous inflammation. These innovative data underline the possibility to set up new approaches to treat acne. Indeed, maintaining the balance between the different phylotypes of C. acnes may be an interesting target for the development of drugs.

Target Proteins of Phloretin for Its Anti-Inflammatory and Antibacterial Activities Against Propionibacterium acnes-Induced Skin Infection

Phloretin is a natural chalcone with antibacterial and anti-inflammatory effects. This study investigated the anti-acne activity of phloretin against Propionibacterium acnes-induced skin infection and the potential target proteins of its anti-inflammatory and antibacterial effects. Phloretin potently inhibited the growth of P. acnes and P. acnes-induced Toll-like receptor (TLR) 2-mediated inflammatory signaling in human keratinocytes. Secreted embryonic alkaline phosphatase assay confirmed that the anti-inflammatory activity of phloretin is associated with the P. acnes-stimulated TLR2-mediated NF-κB signaling pathway. Phloretin significantly decreased the level of phosphorylated c-Jun N-terminal kinase (JNK), showing a binding affinity of 1.184 × 10⁻⁵ M⁻¹. We also found that phloretin binds with micromolar affinity to P. acnes β-ketoacyl acyl carrier protein (ACP) synthase III (KAS III), an enzyme involved in fatty acid synthesis. Conformation-sensitive native polyacrylamide gel electrophoresis showed that phloretin reduced KAS III-mediated 3-ketoacyl ACP production by over 66%. A docking study revealed that phloretin interacts with the active sites of JNK1 and KAS III, suggesting their involvement in P. acnes-induced inflammation and their potential as targets for the antibacterial activity of phloretin. These results demonstrate that phloretin may be useful in the prevention or treatment of P. acnes infection.

Suppression of Propionibacterium acnes-stimulated proinflammatory cytokines by Chinese bayberry extracts and its active constituent myricetin in human sebocytes in vitro

Myrica rubra Sieb. et Zucc. (Myricaceae), known as Chinese bayberry, is traditionally used as folk medicine in Asian countries. The interaction of Propionibacterium acnes signalling with sebocytes is considered important in the pathogenesis of acne. In the present study, extracts and active compounds of Chinese bayberry were used to determine chemical antioxidant activity and anti-inflammatory effects in P. acnes-stimulated human SZ95 sebocytes. A high-performance liquid chromatography with electrochemical detection system was used to analyse the phenolic composition of bayberry extracts. Accordingly, the flavonols, myricitrin and myricetin, were found to be abundant in the unhydrolysed and hydrolysed extracts of Chinese bayberry fruits, respectively. The anthocyanin cyanidin-3-glucoside was also predominantly found in the unhydrolysed extracts. Quantification of human inflammatory cytokines indicated that cell-free extracts of P. acnes stimulated IL-8 and IL-6 production, which was inhibited by myricetin, rather than its glycoside or anthocyanin. Myricetin also exhibited inhibitory effects in P. acnes-stimulated gene expression of Toll-like receptor (TLR) 2 and protein phosphorylation of p70 S6 kinase. In conclusion, myricetin shows a suppressive effect on P. acnes-induced cytokine production through regulation of the TLR and mammalian target of rapamycin pathways. Myricetin goes beyond previous research findings to potentially modulate inflammatory signalling in human sebocytes. These results will be valuable in developing anti-inflammatory agents against skin acne.

The impact of Cymbopogon martinii essential oil on Cutibacterium (formerly Propionibacterium) acnes strains and its interaction with keratinocytes

OBJECTIVES

The human skin microbiota is mainly composed of bacteria belonging to the genera Staphylococcus, Cutibacterium, Micrococcus and Corynebacterium, but on the skin of the face and back, ca. 50% of the total microbiota is represented by the bacterium Cutibacterium acnes. The aim of this research was to evaluate the impact of C. martini EO and its major compound, geraniol, on C. acnes.

METHODS

The minimum inhibitory concentration against C. acnes strains, phenotypic changes and responses of the proteome was determined. In addition, was assessed the effect of compounds in RNA-binding assay, on C. acnes-exposed keratinocytes and on the C. acnes type distribution on shoulder skin.

KEY FINDINGS

The range of the MIC was 0.7 to 1.6 mg/ml for the three main C. acnes types. There were no cytotoxic effects of compounds in the absence or presence of C. acnes; after 7 days of exposure to C. martini EO, we could not detect a major shift of the C. acnes types on shoulder skin that was found to be dominated by C. acnes strains of types II and IA2.

CONCLUSIONS

Our work gives novel insight into the skin microbiota-interacting properties of C. martini EO.

Calprotectin can play an inflammatory role in acne vulgaris

Introduction

Acne vulgaris (AV) is a chronic inflammatory disorder of the pilosebaceous unit. Although various mechanisms have been indicated in the etiopathogenesis of acne vulgaris, the exact pathophysiology is still unknown.

Aim

To investigate the level of calprotectin in acne vulgaris and its levels relationship with disease severity.

Material and methods

A total of 66 AV patients, who were divided into 33 mild and 33 moderate–severe cases, and 30 healthy controls were enrolled in the study. Disease severity was assessed using the Global Acne Score. According to this scale, patients whose Global Acne Score was 1–18 had mild acne, those with a score of 19–30 had moderate acne, those with a score of 31–38 had severe acne, and those with a score greater than 39 had very severe acne. Serum calprotectin levels of all participants were measured by enzyme-linked immunosorbent assay method.

Results

The serum calprotectin levels in the moderate–severe AV group were significantly higher than that of the mild AV group (p < 0.001). In addition, the serum calprotectin level in the mild AV group was significantly higher than that of the healthy control group (p = 0.047). However, in the Spearman’s correlation analysis, the serum calprotectin level and GAS were not correlated in AV patients (p = 0.171, r = 0.179).

Conclusions

Serum calprotectin levels are increased in mild and moderate AV patients.

SIG1459: A novel phytyl-cysteine derived TLR2 modulator with in vitro and clinical anti-acne activity

Cutibacterium (formerly Propionibacterium acnes) is a major contributor to the pathogenesis of acne. C. acnes initiates an innate immune response in keratinocytes via recognition and activation of toll-like receptor-2 (TLR2), a key step in comedogenesis. Tetramethyl-hexadecenyl-cysteine-formylprolinate (SIG1459), a novel anti-acne isoprenylcysteine (IPC) small molecule, is shown in this study to have direct antibacterial activity and inhibit TLR2 inflammatory signalling. In vitro antibacterial activity of SIG1459 against C. acnes was established demonstrating minimal inhibitory concentration (MIC = 8.5 μmol\L), minimal bactericidal concentration (MBC = 16.1 μmol\L) and minimal biofilm eradication concentration (MBEC = 12.5 μmol\L). To assess SIG1459's anti-inflammatory activity, human keratinocytes were exposed to C. acnes and different TLR2 ligands (peptidoglycan, FSL-1, Pam3CSK4) that induce pro-inflammatory cytokine IL-8 and IL-1α production. Results demonstrate SIG1459 inhibits TLR2-induced IL-8 release from TLR2/TLR2 (IC₅₀  = 0.086 μmol\L), TLR2/6 (IC₅₀  = 0.209 μmol\L) and IL-1α from TLR2/TLR2 (IC₅₀  = 0.050 μmol\L). To assess the safety and in vivo anti-acne activity of SIG1459, a vehicle controlled clinical study was conducted applying 1% SIG1459 topically (n = 35 subjects) in a head-to-head comparison against 3% BPO (n = 15 subjects). Utilizing the Investigator Global Assessment scale for acne as primary endpoint, results demonstrate 1% SIG1459 significantly outperformed 3% BPO over 8 weeks, resulting in 79% improvement as compared to 56% for BPO. Additionally, 1% SIG1459 was well tolerated. Thus, SIG1459 and phytyl IPC compounds represent a novel anti-acne technology that provides a safe dual modulating benefit by killing C. acnes and reducing the inflammation it triggers via TLR2 signalling.

Toll-Like Receptor 2 Signaling and Current Approaches for Therapeutic Modulation in Synucleinopathies

The innate immune response in the central nervous system (CNS) is implicated as both beneficial and detrimental to health. Integral to this process are microglia, the resident immune cells of the CNS. Microglia express a wide variety of pattern-recognition receptors, such as Toll-like receptors, that detect changes in the neural environment. The activation of microglia and the subsequent proinflammatory response has become increasingly relevant to synucleinopathies, including Parkinson's disease the second most prevalent neurodegenerative disease. Within these diseases there is evidence of the accumulation of endogenous α-synuclein that stimulates an inflammatory response from microglia via the Toll-like receptors. There have been recent developments in both new and old pharmacological agents designed to target microglia and curtail the inflammatory environment. This review will aim to delineate the process of microglia-mediated inflammation and new therapeutic avenues to manage the response.

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

Propionibacterium acnes induces intervertebral disc degeneration by promoting nucleus pulposus cell apoptosis via the TLR2/JNK/mitochondrial-mediated pathway

Evidence suggests that intervertebral disc degeneration (IVDD) can be induced by Propionibacterium acnes (P. acnes), although the underlying mechanisms are unclear. In this study, we analyzed the pathological changes in degenerated human intervertebral discs (IVDs) infected with P. acnes. Compared with P. acnes-negative samples, P. acnes-positive IVDs showed increased apoptosis of nucleus pulposus cells (NPCs) concomitant with severe IVDD. Then, a P. acnes-inoculated IVD animal model was established, and severe IVDD was induced by P. acnes infection by promoting NPC apoptosis. The results suggested that P.acnes-induced apoptosis of NPCs via the Toll-like receptor 2 (TLR2)/c-Jun N-terminal kinase (JNK) pathway and mitochondrial-mediated cell death. In addition, P. acnes was found to activate autophagy, which likely plays a role in apoptosis of NPCs. Overall, these findings further validated the involvement of P. acnes in the pathology of IVDD and provided evidence that P. acnes-induced apoptosis of NPCs via the TLR2/JNK pathway is likely responsible for the pathology of IVDD.

Modulation of Toll Like Receptor-2 on sebaceous gland by the treatment of adult female acne

Adult female acne is a chronic inflammatory, immune-mediated disease that affects the pilosebaceous unit in women in their 20s to 40s, and is considered different from acne vulgaris. Propionibacterium acnes is recognized by TLR-2, resulting in activation of this receptor and an inflammatory response through the NFκ B pathway. This therapeutic, interventional, open, randomized, evaluator-blinded and comparative trial included 38 adult women with moderate facial acne and 10 age-matched controls, all aged between 26 and 44 years. Two treatments were performed over six months: 15% azelaic acid gel (AA) bid (n = 18) and oral contraceptive (COC) drospirenone 3 mg/ethinylestradiol .02 mg (n = 20). Biopsies were taken at baseline (control, lesion, perilesional) and at the conclusion (lesion and perilesional) of the study to evaluate TLR-2 expression by immunohistochemistry. Lesion count and blind photographic evaluation were used for efficacy. The groups were homogeneous: 70% of lesions were located in the submandibular area, 95% of participants had inflammatory lesions; of these, 50% had persistent and 50% had late-onset acne. The mean ages were 33.7 ± 5.5 and 33.1 ± 5.3 years (COC and AA group, respectively). A moderate clinical improvement was observed in both groups. No difference in TLR-2 expression in the lesion or perilesional areas was observed; however, reduced TLR-2 expression was seen in the control group. A significant reduction in expression was observed after both treatments, with no difference between the groups. This finding suggests an anti-inflammatory effect of COCs and AA in adult female acne, via modulation of the TLR-2 receptor.

Glucocorticoids and Toll-like receptor 2 cooperatively induce acute-phase serum amyloid A

Serum amyloid A (SAA) is a highly conserved acute-phase protein and extrahepatic produced SAA1/2 contributes to cutaneous inflammation. Prolonged systemic or topical treatment with glucocorticoids can provoke skin diseases such as steroid-induced acne. Glucocorticoids increase Toll-like receptor 2 (TLR2) expression, however, an inflammatory mediator linked to this side effect remains elusive. We report that TLR2 agonists in combination with dexamethasone substantially increase SAA expression and production in human keratinocytes and epithelial cells. Dexamethasone-mediated SAA1 induction depends on the glucocorticoid receptor (GR). In response to Propionibacterium acnes, TLR2-activated signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB (NF-κB) signaling pathways are critically involved in dexamethasone-induced SAA1 production. The formation of transcription factor complexes between GR or p300 and phospho-STAT3 was confirmed by co-immunoprecipitation in dexamethasone- and P. acnes-stimulated keratinocytes. Furthermore, dexamethasone and P. acnes-increased TLR2 and mitogen-activated protein kinase phosphatase-1 (MKP-1) contribute to induction of SAA1 and 2. Likewise, tumor necrosis factor (TNF) induces SAA1 in combination with dexamethasone. GR, transcription factors STAT3 and NF-κB, but not MKP-1, mediate TNF- and dexamethasone-induced SAA1. Conclusively, we provide evidence that glucocorticoids promote SAA1 production under infectious and sterile inflammatory conditions which may provide significant insights to the pathogenesis of steroid-induced acne.

Cell type-specific regulatory effects of glucocorticoids on cutaneous TLR2 expression and signalling

Glucocorticoids (GCs) induce Toll-like receptor (TLR) 2 expression and synergistically upregulate TLR2 with pro-inflammatory cytokines or bacteria. These paradoxical effects have drawn attention to the inflammatory initiating or promoting effects of GCs, as GC treatment can provoke inflammatory skin diseases. Here, we aimed to investigate the regulatory effects of GCs in human skin cells of different epidermal and dermal layers. We found that Dex induced TLR2 expression mainly in undifferentiated and less in calcium-induced differentiated keratinocytes but not in HaCaT cells or fibroblasts, however, Dex reduced TLR1/6 expression. Stimulation with Dex under inflammatory conditions further increased TLR2 but not TLR1 or TLR6 levels in keratinocytes. Increased ligand-induced interaction of TLR2 with MyD88 and expression of the adaptor protein TRAF6 indicated enhanced TLR2 signalling, whereas TLR2/1 or TLR2/6 signalling was not increased in Dex-pretreated keratinocytes. GC-increased TLR2 expression was negatively regulated by JNK MAPK signalling when stimulated with Propionibacterium acnes. Our results provide novel insights into the molecular mechanisms of glucocorticoid-mediated expression and function of TLR2 in human skin cells and the understanding of the mechanisms of corticosteroid side effects.