Protective Role of an Initial Low-Dose Septic Challenge against Lethal Sepsis in Neonatal Mice: A Pilot Study

Neonatal sepsis is characterized by systemic bacterial invasion followed by a massive inflammatory response. At present, no therapeutic strategy has been found that significantly reduces the mortality of neonatal sepsis. We aimed to investigate the protective role of an initial low-dose septic challenge for the prevention of subsequent lethal sepsis in a mouse model. A stock cecal slurry (CS) solution was prepared from adult ceca. The LD83 (1.5 mg CS/g) was used for all animals. An initial challenge of normal saline (NS) or 0.5 mg CS/g (non-lethal dose) was administered at four days of age, then 1.5 mg CS/g was administered intraperitoneally at seven days of age (72 h post-initial challenge), and survival was monitored. Initial exposure to NS (n = 10) resulted in 90% mortality following exposure to the LD83 CS dose in contrast to an initial exposure to CS (n = 16), which significantly decreased mortality to 6% (p < 0.0001), reduced blood bacterial counts, attenuated inflammatory responses, and suppressed lipid mediators. Initial exposure to a non-lethal CS dose prior to exposure to a lethal CS dose significantly reduces sepsis mortality, a protective effect that might be mediated by modulating abnormal systemic inflammatory responses.

Sestrin2 protects against lethal sepsis by suppressing the pyroptosis of dendritic cells

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sestrin2 (SESN2), a highly evolutionarily conserved protein, is critically involved in the cellular response to various stresses and has been confirmed to maintain the homeostasis of the internal environment. However, the potential effects of SESN2 in regulating dendritic cells (DCs) pyroptosis in the context of sepsis and the related mechanisms are poorly characterized. In this study, we found that SESN2 was capable of decreasing gasdermin D (GSDMD)-dependent pyroptosis of splenic DCs by inhibiting endoplasmic reticulum (ER) stress (ERS)-related nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3)-mediated ASC pyroptosome formation and caspase-1 (CASP-1) activation. Furthermore, SESN2 deficiency induced NLRP3/ASC/CASP-1-dependent pyroptosis and the production of proinflammatory cytokines by exacerbating the PERK–ATF4–CHOP signaling pathway, resulting in an increase in the mortality of septic mice, which was reversed by inhibiting ERS. These findings suggest that SESN2 appears to be essential for inhibiting NLRP3 inflammasome hyperactivation, reducing CASP-1-dependent pyroptosis, and improving sepsis outcomes through stabilization of the ER. The present study might have important implications for exploration of novel potential therapeutic targets for the treatment of sepsis complications.

Inhibition of iNOS protects against the deleterious effects of sub-lethal sepsis and ethanol in the cardiorenal system

We tested the hypothesis that ethanol would aggravate the deleterious effects of sub-lethal cecal ligation and puncture (SL-CLP) sepsis in the cardiorenal system and that inhibition of iNOS would prevent such response. Male C57BL/6 mice were treated with ethanol for 12 weeks. One hour before SL-CLP surgery, mice were treated with N6-(1-Iminoethyl)-lysine (L-NIL, 5 mg/kg, i.p), a selective inhibitor of iNOS. A second dose of L-NIL was administered 24 h after SL-CLP surgery. Mice were killed 48 h post-surgery and blood, the renal cortex and left ventricle (LV) were collected for biochemical analysis. L-NIL attenuated the increase in serum creatinine levels induced by ethanol, but not by SL-CLP. Ethanol, but not SL-CLP increased creatine kinase (CK)-MB activity and L-NIL did not prevent this response. In the renal cortex, L-NIL prevented the redox imbalance induced by ethanol and SL-CLP. Inhibition of iNOS also decreased lipoperoxidation induced by ethanol and SL-CLP in the LV. L-NIL prevented the increase of pro-inflammatory cytokines and reactive oxygen species (ROS) induced by ethanol and/or SL-CLP in the cardiorenal system, suggesting that iNOS modulated some of the molecular mechanisms that underlie the deleterious effects of both conditions in the cardiorenal system.

Feeding-induced resistance to acute lethal sepsis is dependent on hepatic BMAL1 and FXR signalling

In mice, time of day strongly influences lethality in response to LPS, with survival greatest at the beginning compared to the end of the light cycle. Here we show that feeding, rather than light, controls time-of-day dependent LPS sensitivity. Mortality following LPS administration is independent of cytokine production and the clock regulator BMAL1 expressed in myeloid cells. In contrast, deletion of BMAL1 in hepatocytes globally disrupts the transcriptional response to the feeding cycle in the liver and results in constitutively high LPS sensitivity. Using RNAseq and functional validation studies we identify hepatic farnesoid X receptor (FXR) signalling as a BMAL1 and feeding-dependent regulator of LPS susceptibility. These results show that hepatocyte-intrinsic BMAL1 and FXR signalling integrate nutritional cues to regulate survival in response to innate immune stimuli. Understanding hepatic molecular programmes operational in response to these cues could identify novel pathways for targeting to enhance endotoxemia resistance.

SLAMF7 Regulates Inflammatory Response In Macrophage During Polymicrobial Sepsis

Uncontrolled microbe-triggered inflammation results in multiple organ injury and shock in sepsis. However, the regulatory mechanisms that restrict cytokine storm are still elusive. Using gene screening, we identified an immunoglobulin-like receptor called Signaling Lymphocyte Activation Molecular Family-7 (SLAMF7), as a key regulator of inflammation during sepsis. We found that the expression of SLAMF7 on monocytes and macrophages was significantly elevated in sepsis subjects and septic mice. SLAMF7 attenuated TLR dependent MAPKs and NF-κB signaling activation by co-operating with Src homology 2-containing inositol‑5'‑phosphatase1 (SHIP1). Furthermore, SLAMF7 interacted with SHIP1 and TNF receptor associated factor 6 (TRAF6) to inhibite K63 ubiquitination of TRAF6. In addition, we found that intracellular domain tyrosine phosphorylation sites of SLAMF7 and phosphatase domain of SHIP1 were indispensable for the interaction of SLAMF7/SHIP1/TRAF6 and the modulation of cytokines production. Finally, recombinant murine SLAMF7 peptide agonist or genetic knockout of SLAMF7 in mice demonstrated that SLAMF7 confered protection against lethal sepsis and endotoxemia by suppressing inflammatory cytokines. Taken together, our findings reveal a critical negative regulatory role of SLAMF7 on cytokine storm in macrophages during polymicrobial sepsis, and therefore provide new sights into a novel diagnostic marker and therapeutic target for sepsis.

Type IV pilus retraction enables sustained bacteremia and plays a key role in the outcome of meningococcal sepsis in a humanized mouse model

Neisseria meningitidis (the meningococcus) remains a major cause of bacterial meningitis and fatal sepsis. This commensal bacterium of the human nasopharynx can cause invasive diseases when it leaves its niche and reaches the bloodstream. Blood-borne meningococci have the ability to adhere to human endothelial cells and rapidly colonize microvessels. This crucial step enables dissemination into tissues and promotes deregulated inflammation and coagulation, leading to extensive necrotic purpura in the most severe cases. Adhesion to blood vessels relies on type IV pili (TFP). These long filamentous structures are highly dynamic as they can rapidly elongate and retract by the antagonistic action of two ATPases, PilF and PilT. However, the consequences of TFP dynamics on the pathophysiology and the outcome of meningococcal sepsis in vivo have been poorly studied. Here, we show that human graft microvessels are replicative niches for meningococci, that seed the bloodstream and promote sustained bacteremia and lethality in a humanized mouse model. Intriguingly, although pilus-retraction deficient N. meningitidis strain (ΔpilT) efficiently colonizes human graft tissue, this mutant did not promote sustained bacteremia nor induce mouse lethality. This effect was not due to a decreased inflammatory response, nor defects in bacterial clearance by the innate immune system. Rather, TFP-retraction was necessary to promote the release of TFP-dependent contacts between bacteria and, in turn, the detachment from colonized microvessels. The resulting sustained bacteremia was directly correlated with lethality. Altogether, these results demonstrate that pilus retraction plays a key role in the occurrence and outcome of meningococcal sepsis by supporting sustained bacteremia. These findings open new perspectives on the role of circulating bacteria in the pathological alterations leading to lethal sepsis.

CBP Bromodomain Inhibition Rescues Mice From Lethal Sepsis Through Blocking HMGB1-Mediated Inflammatory Responses

CREB binding protein (CBP), a transcriptional coactivator and acetyltransferase, is involved in the pathogenesis of inflammation-related diseases. High mobility group box-1 protein (HMGB1) is a critical mediator of lethal sepsis, which has prompted investigation for the development of new treatment for inflammation. Here, we report that the potent and selective inhibition of CBP bromodomain by SGC-CBP30 blocks HMGB1-mediated inflammatory responses in vitro and in vivo. Our data suggest that CBP bromodomain inhibition suppresses LPS-induced expression and release of HMGB1, when the inhibitor was given 8 h post LPS stimulation; moreover, CBP bromodomain inhibition attenuated pro-inflammatory activity of HMGB1. Furthermore, our findings provide evidence that SGC-CBP30 down-regulated rhHMGB1-induced activation of MAPKs and NF-κB signaling by triggering the reactivation of protein phosphatase 2A (PP2A) and the stabilization of MAPK phosphatase 1 (MKP-1). Collectively, these results suggest that CBP bromodomain could serve as a candidate therapeutic target for the treatment of lethal sepsis via inhibiting LPS-induced expression and release of HMGB1 and suppressing the pro-inflammatory activity of HMGB1.

Targeting adaptor protein SLP76 of RAGE as a therapeutic approach for lethal sepsis

Accumulating evidence shows that RAGE has an important function in the pathogenesis of sepsis. However, the mechanisms by which RAGE transduces signals to downstream kinase cascades during septic shock are not clear. Here, we identify SLP76 as a binding partner for the cytosolic tail of RAGE both in vitro and in vivo and demonstrate that SLP76 binds RAGE through its sterile α motif (SAM) to mediate downstream signaling. Genetic deficiency of RAGE or SLP76 reduces AGE-induced phosphorylation of p38 MAPK, ERK1/2 and IKKα/β, as well as cytokine release. Delivery of the SAM domain into macrophages via the TAT cell-penetrating peptide blocks proinflammatory cytokine production. Furthermore, administration of TAT-SAM attenuates inflammatory cytokine release and tissue damage in mice subjected to cecal ligation and puncture (CLP) and protects these mice from the lethality of sepsis. These findings reveal an important function for SLP76 in RAGE-mediated pro-inflammatory signaling and shed light on the development of SLP76-targeted therapeutics for sepsis.

The Role of Plasmin/Plasminogen in Experimental Polymicrobial Sepsis

Introduction: Sepsis is characterized by systemic inflammation and increased coagulation. Although plasmin activity is increased at the onset of sepsis, increased levels of plasminogen activator inhibitor-1 can counter-regulate it triggering an imbalance of the procoagulant and fibrinolytic systems, which results in disseminated intravascular coagulation. Objective: To evaluate the role of the plasminogen/plasmin (Plg/Pla) system in experimental sepsis. Material and Methods: Plg-deficient (Plg-/-) mice, Plg+/+ littermate controls and wild-type (WT) C57Bl/6 mice were subjected to Cecal Ligation and Puncture (CLP) to induce sepsis. In this model, a double puncture is made through the cecum using either a 30 or 18-gauge needle to induce sub-lethal or lethal sepsis, respectively. Survival rates were assessed. Inflammatory parameters and bacterial counts were evaluated in peritoneal lavage fluid and blood 12h after CLP. In other experiments WT mice were treated with Pla or Plg, employing two different therapeutic protocols. Results: In WT mice, the survival rate in sub-lethal sepsis was more than 80% at 6 days after CLP, while lethal sepsis all mice died by 2 days. Increased inflammatory infiltrates were found in peritoneal cavities of mice subjected to lethal sepsis compared to sub-lethal sepsis. The plasma levels of Plg were reduced in lethal sepsis when compared to sub-lethal sepsis, while the levels of a marker for sepsis severity, IL-6, increased. In the sub-lethal model of sepsis, the survival rate of Plg-/- mice was 40% while all Plg+/+ mice survived. In this model, increased inflammatory infiltration, predominantly neutrophils and M1 macrophages, was present in peritoneal cavities of Plg-/- mice 12h after CLP, accompanied by increased IL-6 and ALT levels, compared with Plg+/+ littermates. No genotype-dependent difference in the levels of TNF-α and IL-10 were observed. The bacterial clearance in Plg-/- mice and Plg+/+ littermates were similar. In WT mice, exogenous Pla (10 µg/mice, i.p.) administered 3h after lethal sepsis did not modify the lethality rate, but decreased inflammatory infiltration (neutrophils and M1 macrophages) at the infectious site with reduced levels of CXCL1 and ALT. No differences in the levels of TNF-α, IL-1-6 and IL-10 were observed after Pla treatment. Pla administration reduced bacterial counts in blood with no differences in peritoneal fluid. In a separate protocol, administration of Pla or Plg (10 µg/mouse, i.p.) in two bolus injections, at both 6 and 12h after lethal CLP, resulted in a significant reduction in lethality rate (~30% survival) when compared to the vehicle group (no survival). Interestingly, co-injection of Plg in combination with a broad-spectrum antibiotic (imipenem 30mg/kg, i.p.) protected approximately 80% of mice, compared with 60% protection with antibiotic alone. Conclusion: Plg/Pla exhibit a protective effect in sepsis by reducing inflammatory parameters, neutrophil recruitment and tissue damage. Keywords: sepsis, plasmin, plasminogen system, CLP model. Disclosures No relevant conflicts of interest to declare.