Immune modulation by molecules of Staphylococcus aureus

Dissertation ist gesperrt bis 22. Mai 2022 !Staphylococcus aureus, a major human pathogen, is the source or various infections ranging from mild skin abscesses to severe endocarditis and sepsis. The pathogenesis of S. aureus is based on the production of a wide variety of toxins and immune modulators, which can support bacterial immune evasion but also immune activation. For example, S. aureus releases the cytolytic phenol-soluble modulins (PSMs), which impair leukocyte membrane integrity, activate the human formyl-peptide receptor 2 (FPR2) and influence the release of immune-stimulatory lipoproteins (Lpps). Lpps are membrane-anchored proteins that are abundant in the S. aureus secretome although they lack a specific release system. We observed here that S. aureus membrane vesicles (MVs) contain Lpps and represent a vehicle for Lpp release. MV formation was strongly enhanced by an external turgor pressure as well as the presence of the surfactant-like PSMs, which enhanced membrane fluidity. The immune stimulatory component of Lpps is the lipid-anchor, by which Lpps are anchored in MVs. For an effective Toll-like receptor 2 (TLR2) activation, this lipid anchor has to be liberated. We could demonstrate that increasing PSM concentrations induces MV disruption and thus the release of Lpps, PSMs and other MV-associated proteins, which induce TLR2 and FPR2 activation, respectively. However, also bacterial metabolites can interact with the human immune system. Short carboxylic acids with less than six carbon atoms are the major products of bacterial fermentation or the phosphotransacetylase-acetate kinase (Pta-AckA) pathway. This group of molecules is referred to as short chain fatty acids (SCFAs) and have been described to activate the neutrophilic free-fatty acid receptor GPR43 (FFAR2). Here we could show that GPR43 activation by the SCFA member acetate transferred neutrophils into a primed state, which is characterized by an increased immune reaction towards subsequent bacterial stimulation. GPR43-dependent priming led, after restimulation with activating ligands, to increased chemotaxis and cytokine / ROS release. Furthermore, priming via GPR43 resulted in enhanced expression of Fc- and complement receptors and in improved bacterial elimination. This acetate-dependent priming was also observed in an in vivo murine sepsis model, where a GPR43-mediated priming resulted in drastically reduced bacterial loads and disease severity. In summary, in the first part we could show that S. aureus releases TLR2-activating Lpps through PSM- and turgor-driven MV-release. And in the second part we demonstrated that acetate activates neutrophils in a GPR43-dependent manner and thereby enhances the immune reaction against S. aureus

Short-Chain Fatty Acid and FFAR2 Activation - A New Option for Treating Infections?

The human innate immune system is equipped with multiple mechanisms to detect microbe-associated molecular patterns (MAMPs) to fight bacterial infections. The metabolite short-chain fatty acids (SCFAs) acetate, propionate and butyrate are released by multiple bacteria or are food ingredients. SCFA production, especially acetate production, is usually essential for bacteria, and knockout of pathways involved in acetate production strongly impairs bacterial fitness. Because host organisms use SCFAs as MAMPs and alter immune reactions in response to SCFAs, interventions that modulate SCFA levels can be a new strategy for infection control. The interaction between SCFAs and host cells has been primarily investigated in the intestinal lumen because of the high local levels of SCFAs released by bacterial microbiome members. However, members of not only the intestinal microbiome but also the skin microbiome produce SCFAs, which are known ligands of the seven-transmembrane G-protein-coupled receptor FFAR2. In addition to enterocytes, FFAR2 is expressed on other human cell types, including leukocytes, especially neutrophils. This finding is in line with other research that determined that targeted activation of FFAR2 diminishes susceptibility toward various types of infection by bacteria such as Klebsiella pneumonia, Citrobacter rodentium, and Staphylococcus aureus but also by viruses such as respiratory syncytial and influenza viruses. Thus, our immune system appears to be able to use FFAR2-dependent detection of SCFAs for perceiving and even averting severe infections. We summarize recent advances in understanding the role of SCFAs and FFAR2 in various infection types and propose the manipulation of this receptor as an additional therapeutic strategy to fight infections

Acetate sensing by GPR43 alarms neutrophils and protects from severe sepsis

Katja Schlatterer et al. use mouse models to show that elevated serum acetate concentrations prime human neutrophils in a GPR43-dependent fashion, and rescue mice from severe sepsis. These results suggest microbiome-, diet-, or pathogen-derived short-chain fatty acids govern the defense capacities of immune cells, potentially hinting at the therapeutic potential of GPR43 in treating sepsis

Staphylococcus aureus Depends on Eap Proteins for Preventing Degradation of Its Phenol-Soluble Modulin Toxins by Neutrophil Serine Proteases

Neutrophil granulocytes act as a first line of defense against pathogenic staphylococci. However, Staphylococcus aureus has a remarkable capacity to survive neutrophil killing, which distinguishes it from the less-pathogenic Staphylococcus epidermidis. Both species release phenol-soluble modulin (PSM) toxins, which activate the neutrophil formyl-peptide receptor 2 (FPR2) to promote neutrophil influx and phagocytosis, and which disrupt neutrophils or their phagosomal membranes at high concentrations. We show here that the neutrophil serine proteases (NSPs) neutrophil elastase, cathepsin G and proteinase 3, which are released into the extracellular space or the phagosome upon neutrophil FPR2 stimulation, effectively degrade PSMs thereby preventing their capacity to activate and destroy neutrophils. Notably, S. aureus, but not S. epidermidis, secretes potent NSP-inhibitory proteins, Eap, EapH1, EapH2, which prevented the degradation of PSMs by NSPs. Accordingly, a S. aureus mutant lacking all three NSP inhibitory proteins was less effective in activating and destroying neutrophils and it survived less well in the presence of neutrophils than the parental strain. We show that Eap proteins promote pathology via PSM-mediated FPR2 activation since murine intraperitoneal infection with the S. aureus parental but not with the NSP inhibitors mutant strain, led to a significantly higher bacterial load in the peritoneum and kidneys of mFpr2-/- compared to wild-type mice. These data demonstrate that NSPs can very effectively detoxify some of the most potent staphylococcal toxins and that the prominent human pathogen S. aureus has developed efficient inhibitors to preserve PSM functions. Preventing PSM degradation during infection represents an important survival strategy to ensure FPR2 activation

Staphylococcus aureus Depends on Eap Proteins for Preventing Degradation of Its Phenol-Soluble Modulin Toxins by Neutrophil Serine Proteases

Neutrophil granulocytes act as a first line of defense against pathogenic staphylococci. However, Staphylococcus aureus has a remarkable capacity to survive neutrophil killing, which distinguishes it from the less-pathogenic Staphylococcus epidermidis. Both species release phenol-soluble modulin (PSM) toxins, which activate the neutrophil formyl-peptide receptor 2 (FPR2) to promote neutrophil influx and phagocytosis, and which disrupt neutrophils or their phagosomal membranes at high concentrations. We show here that the neutrophil serine proteases (NSPs) neutrophil elastase, cathepsin G and proteinase 3, which are released into the extracellular space or the phagosome upon neutrophil FPR2 stimulation, effectively degrade PSMs thereby preventing their capacity to activate and destroy neutrophils. Notably, S. aureus, but not S. epidermidis, secretes potent NSP-inhibitory proteins, Eap, EapH1, EapH2, which prevented the degradation of PSMs by NSPs. Accordingly, a S. aureus mutant lacking all three NSP inhibitory proteins was less effective in activating and destroying neutrophils and it survived less well in the presence of neutrophils than the parental strain. We show that Eap proteins promote pathology via PSM-mediated FPR2 activation since murine intraperitoneal infection with the S. aureus parental but not with the NSP inhibitors mutant strain, led to a significantly higher bacterial load in the peritoneum and kidneys of mFpr2-/- compared to wild-type mice. These data demonstrate that NSPs can very effectively detoxify some of the most potent staphylococcal toxins and that the prominent human pathogen S. aureus has developed efficient inhibitors to preserve PSM functions. Preventing PSM degradation during infection represents an important survival strategy to ensure FPR2 activation

Staphylococcus aureus Depends on Eap Proteins for Preventing Degradation of Its Phenol-Soluble Modulin Toxins by Neutrophil Serine Proteases

Neutrophil granulocytes act as a first line of defense against pathogenic staphylococci. However, Staphylococcus aureus has a remarkable capacity to survive neutrophil killing, which distinguishes it from the less-pathogenic Staphylococcus epidermidis. Both species release phenol-soluble modulin (PSM) toxins, which activate the neutrophil formyl-peptide receptor 2 (FPR2) to promote neutrophil influx and phagocytosis, and which disrupt neutrophils or their phagosomal membranes at high concentrations. We show here that the neutrophil serine proteases (NSPs) neutrophil elastase, cathepsin G and proteinase 3, which are released into the extracellular space or the phagosome upon neutrophil FPR2 stimulation, effectively degrade PSMs thereby preventing their capacity to activate and destroy neutrophils. Notably, S. aureus, but not S. epidermidis, secretes potent NSP-inhibitory proteins, Eap, EapH1, EapH2, which prevented the degradation of PSMs by NSPs. Accordingly, a S. aureus mutant lacking all three NSP inhibitory proteins was less effective in activating and destroying neutrophils and it survived less well in the presence of neutrophils than the parental strain. We show that Eap proteins promote pathology via PSM-mediated FPR2 activation since murine intraperitoneal infection with the S. aureus parental but not with the NSP inhibitors mutant strain, led to a significantly higher bacterial load in the peritoneum and kidneys of mFpr2-/- compared to wild-type mice. These data demonstrate that NSPs can very effectively detoxify some of the most potent staphylococcal toxins and that the prominent human pathogen S. aureus has developed efficient inhibitors to preserve PSM functions. Preventing PSM degradation during infection represents an important survival strategy to ensure FPR2 activation

Staphylococcus aureus Depends on Eap Proteins for Preventing Degradation of Its Phenol-Soluble Modulin Toxins by Neutrophil Serine Proteases

Neutrophil granulocytes act as a first line of defense against pathogenic staphylococci. However, Staphylococcus aureus has a remarkable capacity to survive neutrophil killing, which distinguishes it from the less-pathogenic Staphylococcus epidermidis. Both species release phenol-soluble modulin (PSM) toxins, which activate the neutrophil formyl-peptide receptor 2 (FPR2) to promote neutrophil influx and phagocytosis, and which disrupt neutrophils or their phagosomal membranes at high concentrations. We show here that the neutrophil serine proteases (NSPs) neutrophil elastase, cathepsin G and proteinase 3, which are released into the extracellular space or the phagosome upon neutrophil FPR2 stimulation, effectively degrade PSMs thereby preventing their capacity to activate and destroy neutrophils. Notably, S. aureus, but not S. epidermidis, secretes potent NSP-inhibitory proteins, Eap, EapH1, EapH2, which prevented the degradation of PSMs by NSPs. Accordingly, a S. aureus mutant lacking all three NSP inhibitory proteins was less effective in activating and destroying neutrophils and it survived less well in the presence of neutrophils than the parental strain. We show that Eap proteins promote pathology via PSM-mediated FPR2 activation since murine intraperitoneal infection with the S. aureus parental but not with the NSP inhibitors mutant strain, led to a significantly higher bacterial load in the peritoneum and kidneys of mFpr2(-/-) compared to wild-type mice. These data demonstrate that NSPs can very effectively detoxify some of the most potent staphylococcal toxins and that the prominent human pathogen S. aureus has developed efficient inhibitors to preserve PSM functions. Preventing PSM degradation during infection represents an important survival strategy to ensure FPR2 activation