Identification and transcriptomic assessment of latent profile pediatric septic shock phenotypes.

BACKGROUND: Sepsis poses a grave threat, especially among children, but treatments are limited owing to heterogeneity among patients. We sought to test the clinical and biological relevance of pediatric septic shock subclasses identified using reproducible approaches. METHODS: We performed latent profile analyses using clinical, laboratory, and biomarker data from a prospective multi-center pediatric septic shock observational cohort to derive phenotypes and trained a support vector machine model to assign phenotypes in an internal validation set. We established the clinical relevance of phenotypes and tested for their interaction with common sepsis treatments on patient outcomes. We conducted transcriptomic analyses to delineate phenotype-specific biology and inferred underlying cell subpopulations. Finally, we compared whether latent profile phenotypes overlapped with established gene-expression endotypes and compared survival among patients based on an integrated subclassification scheme. RESULTS: Among 1071 pediatric septic shock patients requiring vasoactive support on day 1 included, we identified two phenotypes which we designated as Phenotype 1 (19.5%) and Phenotype 2 (80.5%). Membership in Phenotype 1 was associated with ~ fourfold adjusted odds of complicated course relative to Phenotype 2. Patients belonging to Phenotype 1 were characterized by relatively higher Angiopoietin-2/Tie-2 ratio, Angiopoietin-2, soluble thrombomodulin (sTM), interleukin 8 (IL-8), and intercellular adhesion molecule 1 (ICAM-1) and lower Tie-2 and Angiopoietin-1 concentrations compared to Phenotype 2. We did not identify significant interactions between phenotypes, common treatments, and clinical outcomes. Transcriptomic analysis revealed overexpression of genes implicated in the innate immune response and driven primarily by developing neutrophils among patients designated as Phenotype 1. There was no statistically significant overlap between established gene-expression endotypes, reflective of the host adaptive response, and the newly derived phenotypes, reflective of the host innate response including microvascular endothelial dysfunction. However, an integrated subclassification scheme demonstrated varying survival probabilities when comparing patient endophenotypes. CONCLUSIONS: Our research underscores the reproducibility of latent profile analyses to identify pediatric septic shock phenotypes with high prognostic relevance. Pending validation, an integrated subclassification scheme, reflective of the different facets of the host response, holds promise to inform targeted intervention among those critically ill.

External validation of the modified sepsis renal angina index for prediction of severe acute kidney injury in children with septic shock.

BACKGROUND: Acute kidney injury (AKI) occurs commonly in pediatric septic shock and increases morbidity and mortality. Early identification of high-risk patients can facilitate targeted intervention to improve outcomes. We previously modified the renal angina index (RAI), a validated AKI prediction tool, to improve specificity in this population (sRAI). Here, we prospectively assess sRAI performance in a separate cohort. METHODS: A secondary analysis of a prospective, multicenter, observational study of children with septic shock admitted to the pediatric intensive care unit from 1/2019 to 12/2022. The primary outcome was severe AKI (≥ KDIGO Stage 2) on Day 3 (D3 severe AKI), and we compared predictive performance of the sRAI (calculated on Day 1) to the original RAI and serum creatinine elevation above baseline (D1 SCr > Baseline +). Original renal angina fulfillment (RAI +) was defined as RAI ≥ 8; sepsis renal angina fulfillment (sRAI +) was defined as RAI ≥ 20 or RAI 8 to < 20 with platelets < 150 × 103/µL. RESULTS: Among 363 patients, 79 (22%) developed D3 severe AKI. One hundred forty (39%) were sRAI + , 195 (54%) RAI + , and 253 (70%) D1 SCr > Baseline + . Compared to sRAI-, sRAI + had higher risk of D3 severe AKI (RR 8.9, 95%CI 5-16, p < 0.001), kidney replacement therapy (KRT) (RR 18, 95%CI 6.6-49, p < 0.001), and mortality (RR 2.5, 95%CI 1.2-5.5, p = 0.013). sRAI predicted D3 severe AKI with an AUROC of 0.86 (95%CI 0.82-0.90), with greater specificity (74%) than D1 SCr > Baseline (36%) and RAI + (58%). On multivariable regression, sRAI + retained associations with D3 severe AKI (aOR 4.5, 95%CI 2.0-10.2, p < 0.001) and need for KRT (aOR 5.6, 95%CI 1.5-21.5, p = 0.01). CONCLUSIONS: Prediction of severe AKI in pediatric septic shock is important to improve outcomes, allocate resources, and inform enrollment in clinical trials examining potential disease-modifying therapies. The sRAI affords more accurate and specific prediction than context-free SCr elevation or the original RAI in this population.

AC6 regulates the microtubule-depolymerizing kinesin KIF19A to control ciliary length in mammals.

Motile cilia are hairlike structures that line the respiratory and reproductive tracts and the middle ear and generate fluid flow in these organs via synchronized beating. Cilium growth is a highly regulated process that is assumed to be important for flow generation. Recently, Kif19a, a kinesin residing at the cilia tip, was identified to be essential for ciliary length control through its microtubule depolymerization function. However, there is a lack of information on the nature of proteins and the integrated signaling mechanism regulating growth of motile cilia. Here, we report that adenylate cyclase 6 (AC6), a highly abundant AC isoform in airway epithelial cells, inhibits degradation of Kif19a by inhibiting autophagy, a cellular recycling mechanism for damaged proteins and organelles. Using epithelium-specific knockout mice of AC6, we demonstrated that AC6 knockout airway epithelial cells have longer cilia compared with the WT cells because of decreased Kif19a protein levels in the cilia. We demonstrated in vitro that AC6 inhibits AMP-activated kinase (AMPK), an important modulator of cellular energy-conserving mechanisms, and uncouples its binding with ciliary kinesin Kif19a. In the absence of AC6, activation of AMPK mobilizes Kif19a into autophagosomes for degradation in airway epithelial cells. Lower Kif19a levels upon pharmacological activation of AMPK in airway epithelial cells correlated with elongated cilia and vice versa. In all, the AC6-AMPK pathway, which is tunable to cellular cues, could potentially serve as one of the crucial ciliary growth checkpoints and could be channeled to develop therapeutic interventions for cilia-associated disorders.

Deficiency of AMPKα1 Exacerbates Intestinal Injury and Remote Acute Lung Injury in Mesenteric Ischemia and Reperfusion in Mice.

Mesenteric ischemia and reperfusion (I/R) injury can ensue from a variety of vascular diseases and represents a major cause of morbidity and mortality in intensive care units. It causes an inflammatory response associated with local gut dysfunction and remote organ injury. Adenosine monophosphate-activated protein kinase (AMPK) is a crucial regulator of metabolic homeostasis. The catalytic α1 subunit is highly expressed in the intestine and vascular system. In loss-of-function studies, we investigated the biological role of AMPKα1 in affecting the gastrointestinal barrier function. Male knock-out (KO) mice with a systemic deficiency of AMPKα1 and wild-type (WT) mice were subjected to a 30 min occlusion of the superior mesenteric artery. Four hours after reperfusion, AMPKα1 KO mice exhibited exaggerated histological gut injury and impairment of intestinal permeability associated with marked tissue lipid peroxidation and a lower apical expression of the junction proteins occludin and E-cadherin when compared to WT mice. Lung injury with neutrophil sequestration was higher in AMPKα1 KO mice than WT mice and paralleled with higher plasma levels of syndecan-1, a biomarker of endothelial injury. Thus, the data demonstrate that AMPKα1 is an important requisite for epithelial and endothelial integrity and has a protective role in remote organ injury after acute ischemic events.

miR-145a Regulation of Pericyte Dysfunction in a Murine Model of Sepsis.

BACKGROUND: Sepsis is a life-threatening systemic disease with severe microvascular dysfunction. Pericytes preserve vascular homeostasis. To our knowledge, the potential roles of microRNAs in sepsis-induced pericyte dysfunction have not been explored. METHODS: We determined lung pericyte expression of miR-145a in cecal ligation and puncture (CLP)-induced sepsis. Mouse lung pericytes were isolated and transfected with a miR-145a mimic, followed by stimulation with lipopolysaccharide (LPS). We measured inflammatory cytokine levels. To assess the functions of miR-145a in vivo, we generated a pericyte-specific miR-145a-knockout mouse and determined sepsis-induced organ injury, lung and renal vascular leakage, and mouse survival rates. We used RNA sequencing and Western blotting to analyze the signaling pathways regulated by miR-145a. RESULTS: CLP led to decreased miR-145a expression in lung pericytes. The miR-145a mimic inhibited LPS-induced increases in cytokines. In CLP-induced sepsis, pericytes lacking miR-145a exhibited increased lung and kidney vascular leakage and reduced survival rates. We found that miR-145a could suppress LPS-induced NF-κB activation. In addition, we confirmed that the transcription factor Friend leukemia virus integration 1 (Fli-1) is a target of miR-145a and that Fli-1 activates NF-κB signaling. CONCLUSION: Our results demonstrated that pericyte miR-145a mediates sepsis-associated microvascular dysfunction, potentially by means of Fli-1-mediated modulation of NF-κB signaling.

The olfactomedin-4 positive neutrophil has a role in murine intestinal ischemia/reperfusion injury.

Olfactomedin-4 (OLFM4) identifies a subset of neutrophils conserved in both mouse and man, associated with worse outcomes in several inflammatory conditions. We investigated the role of OLFM4-positive neutrophils in murine intestinal ischemia/reperfusion (IR) injury. Wild-type (WT) C57Bl/6 and OLFM4 null mice were subjected to intestinal IR injury and then monitored for survival or tissues harvested for further analyses. In vivo intestinal barrier function was determined via functional assay of permeability to FITC-dextran. OLFM4 null mice had a significant 7-d survival benefit and less intestinal barrier dysfunction compared with WT. Early after IR, WT mice had worse mucosal damage on histologic examination. Experiments involving adoptive transfer of bone marrow demonstrated that the mortality phenotype associated with OLFM4-positive neutrophils was transferrable to OLFM4 null mice. After IR injury, WT mice also had increased intestinal tissue activation of NFκB and expression of iNOS, 2 signaling pathways previously demonstrated to be involved in intestinal IR injury. In combination, these experiments show that OLFM4-positive neutrophils are centrally involved in the pathologic pathway leading to intestinal damage and mortality after IR injury. This may provide a therapeutic target for mitigation of intestinal IR injury in a variety of common clinical situations.-Levinsky, N. C., Mallela, J., Opoka, A., Harmon, K., Lewis, H. V., Zingarelli, B., Wong, H. R., Alder, M. N. The olfactomedin-4 positive neutrophil has a role in murine intestinal ischemia/reperfusion injury.

Autophagy and mitochondrial biogenesis impairment contribute to age-dependent liver injury in experimental sepsis: dysregulation of AMP-activated protein kinase pathway.

Age is an independent risk factor of multiple organ failure in patients with sepsis. However, the age-related mechanisms of injury are not known. AMPK is a crucial regulator of energy homeostasis, which controls mitochondrial biogenesis by activation of peroxisome proliferator-activated receptor-γ coactivator-α (PGC-1α) and disposal of defective organelles by autophagy. We investigated whether AMPK dysregulation might contribute to age-dependent liver injury in young (2-3 mo) and mature male mice (11-13 mo) subjected to sepsis. Liver damage was higher in mature mice than in young mice and was associated with impairment of hepatocyte mitochondrial function, structure, and biogenesis and reduced autophagy. At molecular analysis, there was a time-dependent nuclear translocation of the active phosphorylated catalytic subunits AMPKα1/α2 and PGC-1α in young, but not in mature, mice after sepsis. Treatment with the AMPK activator 5-amino-4-imidazolecarboxamide riboside-1-ß-d-ribofuranoside (AICAR) improved liver mitochondrial structure in both age groups compared with vehicle. In loss-of-function studies, young knockout mice with systemic deficiency of AMPKα1 exhibited greater liver injury than did wild-type mice after sepsis. Our study suggests that AMPK is important for liver metabolic recovery during sepsis. Although its function may diminish with age, pharmacological activation of AMPK may be of therapeutic benefit.-Inata, Y., Kikuchi, S., Samraj, R. S., Hake, P. W., O'Connor, M., Ledford, J. R., O'Connor, J., Lahni, P., Wolfe, V., Piraino, G., Zingarelli, B. Autophagy and mitochondrial biogenesis impairment contribute to age-dependent liver injury in experimental sepsis: dysregulation of AMP-activated protein kinase pathway.

Exosomes from endothelial progenitor cells improve outcomes of the lipopolysaccharide-induced acute lung injury.

BACKGROUND: The acute respiratory distress syndrome (ARDS) is characterized by disruption of the alveolar-capillary barrier resulting in accumulation of proteinaceous edema and increased inflammatory cells in the alveolar space. We previously found that endothelial progenitor cell (EPC) exosomes prevent endothelial dysfunction and lung injury in sepsis in part due to their encapsulation of miRNA-126. However, the effects of EPC exosomes in acute lung injury (ALI) remain unknown. METHODS: To determine if EPC exosomes would have beneficial effects in ALI, intratracheal administration of lipopolysaccharide (LPS) was used to induce ALI in mice. Lung permeability, inflammation, and the role of miRNA-126 in the alveolar-epithelial barrier function were examined. RESULTS: The intratracheal administration of EPC exosomes reduced lung injury following LPS-induced ALI at 24 and 48 h. Compared to placebo, intratracheal administration of EPC exosomes significantly reduced the cell number, protein concentration, and cytokines/chemokines in the bronchoalveolar lavage fluid (BALF), indicating a reduction in permeability and inflammation. Further, EPC exosomes reduced myeloperoxidase (MPO) activity, lung injury score, and pulmonary edema, demonstrating protection against lung injury. Murine fibroblast (NIH3T3) exosomes, which do not contain abundant miRNA-126, did not provide these beneficial effects. In human small airway epithelial cells (SAECs), we found that overexpression of miRNA-126-3p can target phosphoinositide-3-kinase regulatory subunit 2 (PIK3R2), while overexpression of miRNA-126-5p inhibits the inflammatory alarmin HMGB1 and permeability factor VEGFα. Interestingly, both miR-126-3p and 5p increase the expression of tight junction proteins suggesting a potential mechanism by which miRNA-126 may mitigate LPS-induced lung injury. CONCLUSIONS: Our data demonstrated that human EPC exosomes are beneficial in LPS-induced ALI mice, in part through the delivery of miRNA-126 into the injured alveolus.

Age-Dependent Myocardial Dysfunction in Critically Ill Patients: Role of Mitochondrial Dysfunction.

Myocardial dysfunction is common in septic shock and post-cardiac arrest but manifests differently in pediatric and adult patients. By conventional echocardiographic parameters, biventricular systolic dysfunction is more prevalent in children with septic shock, though strain imaging reveals that myocardial injury may be more common in adults than previously thought. In contrast, diastolic dysfunction in general and post-arrest myocardial systolic dysfunction appear to be more widespread in the adult population. A growing body of evidence suggests that mitochondrial dysfunction mediates myocardial depression in critical illness; alterations in mitochondrial electron transport system function, bioenergetic production, oxidative and nitrosative stress, uncoupling, mitochondrial permeability transition, fusion, fission, biogenesis, and autophagy all may play key pathophysiologic roles. In this review we summarize the epidemiologic and clinical phenotypes of myocardial dysfunction in septic shock and post-cardiac arrest and the multifaceted manifestations of mitochondrial injury in these disease processes. Since neonatal and pediatric-specific data for mitochondrial dysfunction remain sparse, conclusive age-dependent differences are not clear; instead, we highlight what evidence exists and identify gaps in knowledge to guide future research. Finally, since focal ischemic injury (with or without reperfusion) leading to myocardial infarction is predominantly an atherosclerotic disease of the elderly, this review focuses specifically on septic shock and global ischemia-reperfusion injury occurring after resuscitation from cardiac arrest.

Fli-1 Governs Pericyte Dysfunction in a Murine Model of Sepsis.

Background: Pericytes are vascular mural cells and are embedded in the basement membrane of the microvasculature. Recent studies suggest a role for pericytes in lipopolysaccharide (LPS)-induced microvascular dysfunction and mortality, but the mechanisms of pericyte loss in sepsis are largely unknown. Methods: By using a cecal ligation and puncture (CLP)-induced murine model of sepsis, we observed that CLP led to lung and renal pericyte loss and reduced lung pericyte density and pericyte/endothelial cell (EC) coverage. Results: Up-regulated Friend leukemia virus integration 1 (Fli-1) messenger ribonucleic acid (RNA) and protein levels were found in lung pericytes from CLP mice in vivo and in LPS-stimulated lung pericytes in vitro. Knockout of Fli-1 in Foxd1-derived pericytes prevented CLP-induced pericyte loss, vascular leak, and improved survival. Disrupted Fli-1 expression by small interfering RNA inhibited LPS-induced inflammatory cytokines and chemokines in cultured lung pericytes. Furthermore, CLP-induced pericyte pyroptosis was mitigated in pericyte Fli-1 knockout mice. Conclusions: Our findings suggest that Fli-1 is a potential therapeutic target in sepsis.

Age-dependent cardiac function during experimental sepsis: effect of pharmacological activation of AMP-activated protein kinase by AICAR.

Age represents a major risk factor for multiple organ failure, including cardiac dysfunction, in patients with sepsis. AMP-activated protein kinase (AMPK) is a crucial regulator of energy homeostasis that controls mitochondrial biogenesis by activation of peroxisome proliferator-activated receptor-γ coactivator-1α and disposal of defective organelles by autophagy. We investigated whether AMPK dysregulation contributes to age-dependent cardiac injury in young (2-3 mo) and mature adult (11-13 mo) male mice subjected to sepsis by cecal ligation and puncture and whether AMPK activation by 5-amino-4-imidazole carboxamide riboside affords cardioprotective effects. Plasma proinflammatory cytokines and myokine follistatin were similarly elevated in vehicle-treated young and mature adult mice at 18 h after sepsis. However, despite equivalent troponin I and T levels compared with similarly treated young mice, vehicle-treated mature adult mice exhibited more severe cardiac damage by light and electron microscopy analyses with more marked intercellular edema, inflammatory cell infiltration, and mitochondrial derangement. Echocardiography revealed that vehicle-treated young mice exhibited left ventricular dysfunction after sepsis, whereas mature adult mice exhibited a reduction in stroke volume without apparent changes in load-dependent indexes of cardiac function. At molecular analysis, phosphorylation of the catalytic subunits AMPK-α1/α2 was associated with nuclear translocation of peroxisome proliferator-activated receptor-γ coactivator-1α in vehicle-treated young but not mature adult mice. Treatment with 5-amino-4-imidazole carboxamide riboside ameliorated cardiac architecture derangement in mice of both ages. These cardioprotective effects were associated with attenuation of the systemic inflammatory response and amelioration of cardiac dysfunction in young mice only, not in mature adult animals. NEW & NOTEWORTHY Our data suggest that sepsis-induced cardiac dysfunction manifests with age-dependent characteristics, which are associated with a distinct regulation of AMP-activated protein kinase-dependent metabolic pathways. Consistent with this age-related deterioration, pharmacological activation of AMP-activated protein kinase may afford cardioprotective effects allowing a partial recovery of cardiac function in young but not mature age.

Correction to: Minimum Quality Threshold in Pre-Clinical Sepsis Studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.

The original version of this article unfortunately contained mistakes.

Minimum Quality Threshold in Pre-Clinical Sepsis Studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.

PURPOSE: Pre-clinical animal studies precede the majority of clinical trials. While the clinical sepsis definitions and recommended treatments are regularly updated, a systematic review of pre-clinical models of sepsis has not been done and clear modeling guidelines are lacking. To address this deficit, a Wiggers-Bernard Conference on pre-clinical sepsis modeling was held in Vienna in May, 2017. The conference goal was to identify limitations of pre-clinical sepsis models and to propose a set of guidelines, defined as the "Minimum Quality Threshold in Pre-Clinical Sepsis Studies" (MQTiPSS), to enhance translational value of these models. METHODS: 31 experts from 13 countries participated and were divided into 6 thematic Working Groups (WG): (1) Study Design, (2) Humane modeling, (3) Infection types, (4) Organ failure/dysfunction, (5) Fluid resuscitation and (6) Antimicrobial therapy endpoints. As basis for the MQTiPSS discussions, the participants conducted a literature review of the 260 most highly cited scientific articles on sepsis models (2002-2013). RESULTS: Overall, the participants reached consensus on 29 points; 20 at "recommendation" (R) and 9 at "consideration" (C) strength. This Executive Summary provides a synopsis of the MQTiPSS consensus (Tables 1, 2 and 3). CONCLUSIONS: We believe that these recommendations and considerations will serve to bring a level of standardization to pre-clinical models of sepsis and ultimately improve translation of pre-clinical findings. These guideline points are proposed as "best practices" that should be implemented for animal sepsis models. In order to encourage its wide dissemination, this article is freely accessible in Shock, Infection and Intensive Care Medicine Experimental.

Age-Dependent Changes in AMPK Metabolic Pathways in the Lung in a Mouse Model of Hemorrhagic Shock.

The development of multiple organ failure in patients with hemorrhagic shock is significantly influenced by patient age. Adenosine monophosphate-activated protein kinase (AMPK) is a crucial regulator of energy homeostasis, which coordinates metabolic repair during cellular stress. We investigated whether AMPK-regulated signaling pathways are age-dependent in hemorrhage-induced lung injury and whether AMPK activation by 5-amino-4-imidazole carboxamide riboside (AICAR) affords lung protective effects. Male C57/BL6 young mice (3-5 mo), mature adult mice (9-12 mo), and young AMPKα1 knockout mice (3-5 mo) were subjected to hemorrhagic shock by blood withdrawing, followed by resuscitation with shed blood and lactated Ringer's solution. Plasma proinflammatory cytokines were similarly elevated in C57/BL6 young and mature adult mice after hemorrhagic shock. However, mature adult mice exhibited more severe lung edema and neutrophil infiltration, and higher mitochondrial damage in alveolar epithelial type II cells, than did young mice. No change in autophagy was observed. At molecular analysis, the phosphorylation of the catalytic subunit AMPKα1 was associated with nuclear translocation of peroxisome proliferator-activated receptor γ co-activator-α in young, but not mature, adult mice. Treatment with AICAR ameliorated the disruption of lung architecture in mice of both ages; however, effects in mature adult mice were different than young mice and also involved inhibition of nuclear factor-κB. In young AMPKα1 knockout mice, AICAR failed to improve hypotension and lung neutrophil infiltration. Our data demonstrate that during hemorrhagic shock, AMPK-dependent metabolic repair mechanisms are important for mitigating lung injury. However, these mechanisms are less competent with age.

Metformin ameliorates gender-and age-dependent hemodynamic instability and myocardial injury in murine hemorrhagic shock.

Severity of multiple organ failure is significantly impacted by age and gender in patients with hemorrhagic shock. However, the molecular mechanisms underlying the enhanced organ injury are not fully understood. AMP-activated protein kinase (AMPK) is a pivotal orchestrator of metabolic responses during stress. We investigated whether hemorrhage-induced myocardial injury is age and gender dependent and whether treatment with metformin, an AMPK activator, affords cardioprotective effects. C57/BL6 young (3-5months) and mature (9-12months) male and female mice were subjected to hemorrhagic shock by blood withdrawing followed by resuscitation with blood and Lactated Ringer's solution. Vehicle-treated young and mature mice of both genders had a similar elevation of plasma inflammatory cytokines at 3h after resuscitation. However, vehicle-treated male mature mice experienced hemodynamic instability and higher myocardial damage than young male mice, as evaluated by echocardiography, histology and cardiovascular injury biomarkers. There was also a gender-dependent difference in cardiovascular injury in the mature group as vehicle-treated male mice exhibited more severe organ injury than female mice. At molecular analysis, vehicle-treated mature mice of both genders exhibited a marked downregulation of AMPKα activation and nuclear translocation of peroxisome proliferator-activated receptor γ co-activator α when compared with young mice. Treatment with metformin improved cardiovascular function and survival in mature animals of both genders. However, specific cardioprotective effects of metformin were gender-dependent. Metformin did not affect hemodynamic or inflammatory responses in young animals. Thus, our data suggest that targeting metabolic recovery with metformin may be a potential treatment approach in severe hemorrhage in adult population.

Role of matrix metalloproteinase-8 as a mediator of injury in intestinal ischemia and reperfusion.

Acute mesenteric ischemia is associated with high morbidity and mortality. In recent studies, we found that the intestine is an important source of matrix metalloproteinase (MMP)8 during intestinal injury. We hypothesized that genetic ablation or pharmacological inhibition of MMP8 would reduce intestinal injury in mice subjected to intestinal ischemia-reperfusion (I/R) injury. Male mice aged 8-12 wk were subjected to intestinal I/R injury by transient occlusion of the superior mesenteric artery for 30 min. MMP8 was inhibited by genetic and pharmacological approaches. In vivo study endpoints included several functional, histological, and biochemical assays. Intestinal sections were assessed for barrier function and expression of tight junction proteins. I/R injury led to increased intestinal and systemic expression of MMP8. This increase was associated with increased intestinal neutrophil infiltration, epithelial injury, and permeability. I/R injury was associated with increased systemic inflammation and weight loss. These parameters were ameliorated by inhibiting MMP8. I/R injury caused a loss of the tight junction protein claudin-3, which was ameliorated by genetic ablation of MMP8. MMP8 plays an important role in intestinal I/R injury through mechanisms involving increased inflammation and loss of claudin-3. Inhibition of MMP8 is a potential therapeutic strategy in this setting.-Daly, M. C., Atkinson, S. J., Varisco, B. M., Klingbeil L., Hake, P., Lahni, P., Piraino, G., Wu, D., Hogan, S. P., Zingarelli, B., Wong, H. R. Role of matrix metalloproteinase-8 as a mediator of injury in intestinal ischemia and reperfusion.

Blockade of exosome generation with GW4869 dampens the sepsis-induced inflammation and cardiac dysfunction.

Sepsis is an infection-induced severe inflammatory disorder that leads to multiple organ failure. Amongst organs affected, myocardial depression is believed to be a major contributor to septic death. While it has been identified that large amounts of circulating pro-inflammatory cytokines are culprit for triggering cardiac dysfunction in sepsis, the underlying mechanisms remain obscure. Additionally, recent studies have shown that exosomes released from bacteria-infected macrophages are pro-inflammatory. Hence, we examined in this study whether blocking the generation of exosomes would be protective against sepsis-induced inflammatory response and cardiac dysfunction. To this end, we pre-treated RAW264.7 macrophages with GW4869, an inhibitor of exosome biogenesis/release, followed by endotoxin (LPS) challenge. In vivo, we injected wild-type (WT) mice with GW4869 for 1h prior to endotoxin treatment or cecal ligation/puncture (CLP) surgery. We observed that pre-treatment with GW4869 significantly impaired release of both exosomes and pro-inflammatory cytokines (TNF-α, IL-1ß, IL-6) in RAW264.7 macrophages. At 12h after LPS treatment or CLP surgery, WT mice pre-treated with GW4869 displayed lower amounts of exosomes and pro-inflammatory cytokines in the serum than control PBS-injected mice. Accordingly, GW4869 treatment diminished the sepsis-induced cardiac inflammation, attenuated myocardial depression and prolonged survival. Together, our findings indicate that blockade of exosome generation in sepsis dampens the sepsis-triggered inflammatory response and thereby, improves cardiac function and survival.

A Stromal Cell-Derived Factor 1α Analogue Improves Endothelial Cell Function in Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome.

Endothelial cell (EC) dysfunction is a critical mediator of the acute respiratory distress syndrome (ARDS). Recent studies have demonstrated that stromal cell-derived factor 1α (SDF-1α) promotes EC barrier integrity. Our previous studies used a SDF-1α analogue CTCE-0214 (CTCE) in experimental sepsis and demonstrated that it attenuated vascular leak and modulated microRNA (miR) levels. We examined the hypothesis that CTCE improves EC function in lipopolysaccharide (LPS)-induced ARDS through increasing miR-126 expression. Human microvascular endothelial cells (HMVECs) were treated with thrombin to disrupt the EC integrity followed by incubation with CTCE or SDF-1α. Barrier function was determined by trans-endothelial electrical resistance assay. CTCE-induced alterations in miRNA expression and signaling pathways involved in barrier function were determined. Thrombin-induced vascular leak was abrogated by both CTCE and SDF-1α. CTCE also prevented thrombin-induced decreases of vascular endothelial (VE)-cadherin cell surface expression and expansion of the intercellular space. CTCE increased miR-126 levels and induced activation of AKT/Rac 1 signaling. Cotreatment with a miR-126 inhibitor blocked the protective effects of CTCE on AKT activation and endothelial permeability. In subsequent in vivo studies, ARDS was induced by intratracheal instillation of LPS. Intravenous injection of CTCE diminished the injury severity as evidenced by significant reductions in protein, immune cells, inflammatory cytokines and chemokines in the bronchoalveolar lavage fluid, increased miR-126 expression and decreased pulmonary vascular leak and alveolar edema. Taken together, our data show that CTCE improves endothelial barrier integrity through increased expression of miR-126 and activation of Rac 1 signaling and represents an important potential therapeutic strategy in ARDS.

Matrix Metalloproteinase-8 Augments Bacterial Clearance in a Juvenile Sepsis Model.

Genetic ablation or pharmacologic inhibition of matrix metalloproteinase-8 (MMP8) improves survival in an adult murine sepsis model. Because developmental age influences the host inflammatory response, we hypothesized that developmental age influences the role of MMP8 in sepsis. First, we compared sepsis survival between wild type (WT, C57BL/6) and MMP8 null juvenile-aged mice (12-14 days) after intraperitoneal injection of a standardized cecal slurry. Second, peritoneal lavages collected at 6 and 18 hours after cecal slurry injection were analyzed for bacterial burden, leukocyte subsets, and inflammatory cytokines. Third, juvenile WT mice were pretreated with an MMP8 inhibitor prior to cecal slurry injection; analysis of their bacterial burden was compared to vehicle-injected animals. Fourth, the phagocytic capacity of WT and MMP8 null peritoneal macrophages was compared. Finally, peritoneal neutrophil extracellular traps (NETs) were compared using immunofluorescent imaging and quantitative image analysis. We found that juvenile MMP8 null mice had greater mortality and higher bacterial burden than WT mice. Leukocyte counts and cytokine concentrations in the peritoneal fluid were increased in the MMP8 null mice, relative to the wild type mice. Peritoneal macrophages from MMP8 null mice had reduced phagocytic capacity compared to WT macrophages. There was no quantitative difference in NET formation, but fewer bacteria were adherent to NETs from MMP8 null animals. In conclusion, in contrast to septic adult mice, genetic ablation of MMP8 increased mortality following bacterial peritonitis in juvenile mice. The increase in mortality in MMP8 null juvenile mice was associated with reduced bacterial clearance and reduced NET efficiency. We conclude that developmental age influences the role of MMP8 in sepsis.