Platelet activation and aggregation by the opportunistic pathogen Cutibacterium (Propionibacterium) acnes

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.

Comprehensive lipidomic analysis of the genus Cutibacterium

Cutibacterium are part of the human skin microbiota and are opportunistic microorganisms that become pathogenic in immunodeficient states. These lipophilic bacteria willingly inhabit areas of the skin where sebaceous glands are abundant; hence, there is a need to thoroughly understand their metabolism. Lipids are no longer considered only structural elements but also serve as signaling molecules and may have antigenic properties. Lipidomics remains a major research challenge, mainly due to the diverse physicochemical properties of lipids. Therefore, this study aimed to perform a large comparative lipidomic analysis of eight representatives of the Cutibacterium genus, including four phylotypes of C. acnes and two strains of C. granulosum, C. avidum, and C. namnetense. Lipidomic analysis was performed by liquid chromatography‒mass spectrometry (LC-MS) in both positive and negative ion modes, allowing the detection of the widest range of metabolites. Fatty acid analysis by gas chromatography‒mass spectrometry (GC-MS) corroborated the lipidomic data. As a result, 128 lipids were identified, among which it was possible to select marker compounds, some of which were characteristic even of individual C. acnes phylotypes. These include phosphatidylcholine PC 30:0, sphingomyelins (SM 33:1, SM 35:1), and phosphatidylglycerol with an alkyl ether substituent PG O-32:0. Moreover, cardiolipins and fatty acid amides were identified in Cutibacterium spp. for the first time. This comparative characterization of the cutibacterial lipidome with the search for specific molecular markers reveals its diagnostic potential for clinical microbiology.

IMPORTANCE

Cutibacterium (previously Propionibacterium) represents an important part of the human skin microbiota, and its role in clinical microbiology is growing due to opportunistic infections. Lipidomics, apart from protein profiling, has the potential to prove to be a useful tool for defining the cellular fingerprint, allowing for precise differentiation of microorganisms. In this work, we presented a comparative analysis of lipids found in eight strains of the genus Cutibacterium, including a few C. acnes phylotypes. Our results are one of the first large-scale comprehensive studies regarding the bacterial lipidome, which also enabled the selection of C. acnes phylotype-specific lipid markers. The increased role of lipids not only as structural components but also as diagnostic markers or potential antigens has led to new lipid markers that can be used as diagnostic tools for clinical microbiology. We believe that the findings in our paper will appeal to a wide range of researchers.

Complement C3b contributes to Escherichia coli-induced platelet aggregation in human whole blood

Introduction

Platelets have essential functions as first responders in the immune response to pathogens. Activation and aggregation of platelets in bacterial infections can lead to life-threatening conditions such as arterial thromboembolism or sepsis-associated coagulopathy.

Methods

In this study, we investigated the role of complement in Escherichia coli (E. coli)-induced platelet aggregation in human whole blood, using Multiplate^® aggregometry, flow cytometry, and confocal microscopy.

Results and Discussion

We found that compstatin, which inhibits the cleavage of complement component C3 to its components C3a and C3b, reduced the E. coli-induced platelet aggregation by 42%-76% (p = 0.0417). This C3-dependent aggregation was not C3a-mediated as neither inhibition of C3a using a blocking antibody or a C3a receptor antagonist, nor the addition of purified C3a had any effects. In contrast, a C3b-blocking antibody significantly reduced the E. coli-induced platelet aggregation by 67% (p = 0.0133). We could not detect opsonized C3b on platelets, indicating that the effect of C3 was not dependent on C3b-fragment deposition on platelets. Indeed, inhibition of glycoprotein IIb/IIIa (GPIIb/IIIa) and complement receptor 1 (CR1) showed that these receptors were involved in platelet aggregation. Furthermore, aggregation was more pronounced in hirudin whole blood than in hirudin platelet-rich plasma, indicating that E. coli-induced platelet aggregation involved other blood cells. In conclusion, the E. coli-induced platelet aggregation in human whole blood is partly C3b-dependent, and GPIIb/IIIa and CR1 are also involved in this process.

Tumour cell-activated platelets modulate the immunological activity of CD4+, CD8+, and NK cells, which is efficiently antagonized by heparin

Platelets, key players in haemostasis, are progressively investigated with respect to their role in immunity and inflammation. Although the platelet support to haematogenous cancer cell metastasis has been the subject of multiple studies, their impact on anti-cancer immunity remains unaddressed. Here, we investigated the immunomodulatory potential of platelets upon their activation by MDA-MB-231 breast cancer cells in various in vitro approaches. We provide evidence that platelets as well as their tumour cell-induced releasates increased the ratio of regulatory T cells, shaping an immunosuppressive phenotype in isolated CD4⁺ cultures. The influence on CD8⁺ T cells was assessed by detecting the expression of activation markers CD25/CD69 and release of cytolytic and pro-inflammatory proteins. Notably, the platelet preparations differentially influenced CD8⁺ T cell activation, while platelets were found to inhibit the activation of CD8⁺ T cells, platelet releasates, in contrast, supported their activation. Furthermore, the NK cell cytolytic activity was attenuated by platelet releasates. Low molecular weight heparin (LMWH), the guideline-based anticoagulant for cancer-associated thrombotic events, is known to interfere with tumour cell-induced platelet activation. Thus, we aimed to investigate whether, unfractionated heparin, LMWH or novel synthetic heparin mimetics can also reverse the immunosuppressive platelet effects. The releasate-mediated alteration in immune cell activity was efficiently abrogated by heparin, while the synthetic heparin mimetics partly outperformed the commercial heparin derivatives. This is the first report on the effects of heparin on rebalancing immunosuppression in an oncological context emerging as a novel aspect in heparin anti-tumour activities.

A Specific Host/Microbial Signature of Plasma-Derived Extracellular Vesicles Is Associated to Thrombosis and Marrow Fibrosis in Polycythemia Vera

Simple Summary

Patients with polycythemia vera, a myeloproliferative neoplasm, are at increased risk of thrombosis and progression to myelofibrosis. However, no disease-specific risk factors have been identified so far. Extracellular vesicles, released from a broad variety of cells, are receiving increasing attention for their effects on cell-to-cell communication. In addition, they play a role in cancer and thrombosis. Interestingly, circulating microbial components/microbes have been recently indicated as potential modifiers of inflammation and coagulation. Here, we identified a signature of thrombosis history and marrow fibrosis by analyzing the phenotype and the microbial DNA cargo of the circulating extracellular vesicles after isolation from the plasma of patients with polycythemia vera. These data may support the role of extracellular vesicles as liquid biomarkers of aggressive disease, thus contributing to refining the prognosis of polycythemia vera.

Abstract

Polycythemia vera is a myeloproliferative neoplasm with increased risk of thrombosis and progression to myelofibrosis. However, no disease-specific risk factors have been identified so far. Circulating extracellular vesicles (EVs) are mostly of megakaryocyte (MK-EVs) and platelet (PLT-EVs) origin and, along with phosphatidylethanolamine (PE)-EVs, play a role in cancer and thrombosis. Interestingly, circulating microbial components/microbes have been recently indicated as potential modifiers of inflammation and coagulation. Here, we investigated phenotype and microbial DNA cargo of EVs after isolation from the plasma of 38 patients with polycythemia vera. Increased proportion of MK-EVs and reduced proportion of PLT-EVs identify patients with thrombosis history. Interestingly, EVs from patients with thrombosis history were depleted in Staphylococcus DNA but enriched in DNA from Actinobacteria members as well as Anaerococcus. In addition, patients with thrombosis history had also lower levels of lipopolysaccharide-associated EVs. In regard to fibrosis, along with increased proportion of PE-EVs, the EVs of patients with marrow fibrosis were enriched in DNA from Collinsella and Flavobacterium. Here, we identified a polycythemia-vera-specific host/microbial EV-based signature associated to thrombosis history and marrow fibrosis. These data may contribute to refining PV prognosis and to identifying novel druggable targets.

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.

Platelet and neutrophil responses to Porphyromonas gingivalis in human whole blood

Porphyromonas gingivalis is a causative agent for periodontal disease. Binding of platelets to this gram-negative anaerobe can regulate host hemostatic (thrombus forming) and immune (neutrophil interacting) responses during bacterial infection. Additionally, in response to bacterial pathogens neutrophils can release their DNA, forming highly prothrombotic neutrophil extracellular traps (NETs), which then further enhance platelet responses. This study evaluates the role of P. gingivalis on platelet expression of CD62P, platelet-neutrophil interactions, and labeled neutrophil-associated DNA. Human whole blood was preincubated with varying P. gingivalis concentrations, with or without subsequent addition of adenosine diphosphate (ADP). Flow cytometry was employed to measure platelet expression of CD62P using PerCP-anti-CD61 and PE-anti-CD62P, platelet-neutrophil interactions using PerCP-anti-CD61 and FITC-anti-CD16, and the release of neutrophil DNA using FITC-anti-CD16 and Sytox Blue labeling. Preincubation with a high (6.25 × 10⁶  CFU/mL) level of P. gingivalis significantly increased platelet expression of CD62P in ADP treated and untreated whole blood. In addition, platelet-neutrophil interactions were significantly increased after ADP stimulation, following 5-22 min preincubation of blood with high P. gingivalis CFU. However, in the absence of added ADP, platelet-neutrophil interactions increased in a manner dependent on the preincubation time with P. gingivalis. Moreover, after ADP addition, 16 min preincubation of whole blood with P. gingivalis led to increased labeling of neutrophil-associated DNA. Taken together, the results suggest that the presence of P. gingivalis alters platelet and neutrophil responses to increase platelet activation, platelet interactions with neutrophils, and the level of neutrophil antimicrobial NETs.

Cutibacterium acnes as an Opportunistic Pathogen: An Update of Its Virulence-Associated Factors

Cutibacterium acnes is a member of the skin microbiota found predominantly in regions rich in sebaceous glands. It is involved in maintaining healthy skin and has long been considered a commensal bacterium. Its involvement in various infections has led to its emergence as an opportunist pathogen. Interactions between C. acnes and the human host, including the human skin microbiota, promote the selection of C. acnes strains capable of producing several virulence factors that increase inflammatory capability. This pathogenic property may be related to many infectious mechanisms, such as an ability to form biofilms and the expression of putative virulence factors capable of triggering host immune responses or enabling C. acnes to adapt to its environment. During the past decade, many studies have identified and characterized several putative virulence factors potentially involved in the pathogenicity of this bacterium. These virulence factors are involved in bacterial attachment to target cells, polysaccharide-based biofilm synthesis, molecular structures mediating inflammation, and the enzymatic degradation of host tissues. C. acnes, like other skin-associated bacteria, can colonize various ecological niches other than skin. It produces several proteins or glycoproteins that could be considered to be active virulence factors, enabling the bacterium to adapt to the lipophilic environment of the pilosebaceous unit of the skin, but also to the various organs it colonizes. In this review, we summarize current knowledge concerning characterized C. acnes virulence factors and their possible implication in the pathogenicity of C. acnes.

Platelet plug formation in whole blood is enhanced in the presence of Porphyromonas gingivalis

Porphyromonas gingivalis is a gram-negative anaerobic bacterium and an etiologic agent of adult periodontitis. By inducing a dysbiotic state within the host microbiota it contributes to a chronic inflammatory environment in the oral cavity. Under some circumstances, the oral bacteria may gain access to systemic circulation. While the most widely recognized function of platelets is to reduce hemorrhage in case of vascular damage, it is known that platelets are also involved in the hematologic responses to bacterial infections. Some pathogenic bacteria can interact with platelets, triggering their activation and aggregation. The aim of this study was to assess platelet responses to the presence of P. gingivalis in whole blood. Human whole blood was pretreated with P. gingivalis and then platelet plug formation was measured under high shear conditions using the PFA-100. In the presence of P. gingivalis, time for a platelet plug to occlude the aperture in the collagen/ADP cartridge was shortened in a manner dependent on bacterial concentration and the duration of bacterial preincubation of blood. P. gingivalis enhances thrombus forming potential of platelets in whole blood.

Regulation of Monospecies and Mixed Biofilms Formation of Skin Staphylococcus aureus and Cutibacterium acnes by Human Natriuretic Peptides

Staphylococcus aureus and Cutibacterium acnes are common representatives of the human skin microbiome. However, when these bacteria are organized in biofilm, they could be involved in several skin disorders such as acne or psoriasis. They inhabit in hollows of hair follicles and skin glands, where they form biofilms. There, they are continuously exposed to human hormones, including human natriuretic peptides (NUPs). We first observed that the atrial natriuretic peptide (ANP) and the C-type natriuretic peptide (CNP) have a strong effect S. aureus and C. acnes biofilm formation on the skin. These effects are significantly dependent on the aero-anaerobic conditions and temperature. We also show that both ANP and CNP increased competitive advantages of C. acnes toward S. aureus in mixed biofilm. Because of their temperature-dependent effects, NUPs appear to act as a thermostat, allowing the skin to modulate bacterial development in normal and inflammatory conditions. This is an important step toward understanding how human neuroendocrine systems can regulate the cutaneous microbial community and should be important for applications in fundamental sciences, medicine, dermatology, and cosmetology.