GM-CSF Administration Improves Defects in Innate Immunity and Sepsis Survival in Obese Diabetic Mice

Bioinformatics analysis of neutrophil-associated hub genes and ceRNA network construction in septic cardiomyopathy

Septic cardiomyopathy (SCM) is a critical sepsis complication characterized by reversible cardiac depression during early septic shock. Neutrophils, integral to innate immunity, can mediate organ damage when abnormal, but their specific role in sepsis-induced myocardial damage remains elusive. Our study focuses on elucidating the role of Neutrophil-Related Genes (NRGs) in SCM, finding early diagnosis and treatment biomarkers. We identified shared differentially expressed genes (DEGs) from datasets GSE79962 and GSE44363 and pinpointed hub DEGs using the cytoHubba plugin in Cytoscape software. The Neutrophil-Related Hub Gene (NRHG) MRC1 was identified via intersecting hub DEGs with NRGs from WGCNA. We validated MRC1's abnormal expression in SCM using our data and external datasets. Furthermore, a neutrophil-related ceRNA network (AC145207.5/ miR-23a-3p/MRC1) was constructed and validated. Our findings reveal MRC1 as a potential NRHG in SCM pathogenesis, offering insights into neutrophil-mediated mechanisms in SCM and providing a novel molecular target for early diagnosis and intervention in SCM.

Sepsis in elderly patients: the role of neutrophils in pathophysiology and therapy

Sepsis is among the most important causes of mortality, particularly within the elderly population. Sepsis prevalence is on the rise due to different factors, including increasing average population age and the concomitant rise in the prevalence of frailty and chronic morbidities. Recent investigations have unveiled a "trimodal" trajectory for sepsis-related mortality, with the ultimate zenith occurring from 60 to 90 days until several years after the original insult. This prolonged temporal course ostensibly emanates from the sustained perturbation of immune responses, persevering beyond the phase of clinical convalescence. This phenomenon is particularly associated with the aging immune system, characterized by a broad dysregulation commonly known as "inflammaging." Inflammaging associates with a chronic low-grade activation of the innate immune system preventing an appropriate response to infective agents. Notably, during the initial phases of sepsis, neutrophils-essential in combating pathogens-may exhibit compromised activity. Paradoxically, an overly zealous neutrophilic reaction has been observed to underlie multi-organ dysfunction during the later stages of sepsis. Given this scenario, discovering treatments that can enhance neutrophil activity during the early phases of sepsis while curbing their overactivity in the later phases could prove beneficial in fighting pathogens and reducing the detrimental effects caused by an overactive immune system. This narrative review delves into the potential key role of neutrophils in the pathological process of sepsis, focusing on how the aging process impacts their functions, and highlighting possible targets for developing immune-modulatory therapies. Additionally, the review includes tables that outline the principal potential targets for immunomodulating agents.

Sepsis and obesity: a scoping review of diet-induced obesity murine models

BACKGROUND

Sepsis, the life-threatening host response to infection, is a major cause of mortality. Obesity increases vulnerability to sepsis; however, some degree of obesity may be protective, called the "obesity paradox". This scoping review systematically maps the literature on outcomes associated with diet-induced obesity and sepsis-induced organ injury, focusing on non-transgenic murine models.

METHODS

A literature search of primary articles was conducted from database inception to June 2023. Eligible articles compared diet-induced obesity to non-obese mice in sepsis models involving live pathogens. Two reviewers screened articles and extracted data on obesogenic and sepsis models utilized, and organ injury outcomes, including physiological dysfunction, histological alterations, and biochemical changes.

RESULTS

Seventeen studies met eligibility criteria; 82% used male C57BL/6 mice, and 88% used cecal ligation and puncture to induce sepsis. Most studies used 60% high-fat diets compared to 10-16% fat in controls. Seven (64%) studies reported increased mortality in obese septic mice, one (9%) observed a decrease, and three (37%) found no significant difference. The liver, lungs, and kidneys were the most studied organs. Alanine transaminase results were inconclusive. Myeloperoxidase levels were increased in the livers of two studies and inconclusive in the lungs of obese septic mice. Creatinine and neutrophil gelatinase-associated lipocalin were elevated in obese septic mice.

CONCLUSIONS

There is variability in the methodology and measured outcomes in murine models of diet-induced obesity and sepsis and a lack of studies in female mice. The absence of standardized models has produced conflicting findings on the impact of obesity on sepsis outcomes.

Recombinant GM-CSF enhances the bactericidal ability of PMNs by increasing intracellular IL-1β and improves the prognosis of secondary Pseudomonas aeruginosa pneumonia in sepsis

This study tested the hypothesis that recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) enhances polymorphonuclear neutrophils (PMNs) via interleukin (IL)-1β to improve the prognosis of secondary infection in sepsis. The latter stage of sepsis is prone to induce immunosuppression, resulting in secondary fatal infections. Recombinant GM-CSF has become a way for sepsis-induced immunosuppression due to its immunomodulatory effect. However, the functional impact of GM-CSF on PMNs in sepsis remains obscure. This study aimed to study the role of recombinant GM-CSF on the bactericidal ability of PMNs in septic mice, assessing its effect on the prognosis of secondary pneumonia, and explore the mechanism of recombinant GM-CSF by intervening PMNs in patients with sepsis. The C57BL/6J sepsis mouse model was induced by cecal ligation and puncture. Recombinant murine GM-CSF (rmGM-CSF) was used in vivo when mice developed immunosuppression, which was characterized by abnormal bactericidal function of PMNs in peripheral blood. rmGM-CSF improved the prognosis of secondary pneumonia and reversed the function of PMNs. PMNs isolated by Percoll from septic patients were treated by recombinant human GM-CSF (rhGM-CSF) in vitro. The expression of CD11b, reactive oxygen species, phagocytosis, and neutrophil extracellular trap release in PMNs were enhanced by rhGM-CSF treatments. Whole-transcriptomic sequencing of mouse PMNs indicated that recombinant GM-CSF increased the expression of Il1b gene in PMNs. Blocking and inhibiting IL-1β release effectively counteracted the enhancing effect of GM-CSF on the bactericidal function of PMNs. rmGM-CSF enhances the bactericidal function of PMNs in vivo and improves the prognosis of secondary pneumonia in septic mice, and recombinant GM-CSF increases IL-1β precursor reserves, which, if stimulated, can rapidly enhance the bactericidal capacity of PMNs.

Pneumosepsis survival in the setting of obesity leads to persistent steatohepatitis and metabolic dysfunction

BACKGROUND

As critical care practice evolves, the sepsis survivor population continues to expand, often with lingering inflammation in many organs, including the liver. Given the concurrently increasing population of patients with NAFLD, in this study, we aimed to understand the long-term effect of sepsis on pre-existing NAFLD and hyperglycemia.

METHODS

Male mice were randomized to a high-fat diet or a control diet (CD). After 24 weeks on diet, mice were inoculated with Klebsiella pneumoniae (Kpa). Serial glucose tolerance tests, and insulin and pyruvate challenge tests were performed 1 week before infection and at 2 and 6 weeks after infection. Whole tissue RNA sequencing and histological evaluation of the liver were performed. To test whether persistent inflammation could be reproduced in other abnormal liver environments, mice were also challenged with Kpa after exposure to a methionine-choline-deficient high-fat diet. Finally, a retrospective cohort of 65,139 patients was analyzed to evaluate whether obesity was associated with liver injury after sepsis.

RESULTS

After Kpa inoculation, high-fat diet mice had normalized fasting blood glucose without a change in insulin sensitivity but with a notable decrease in pyruvate utilization. Liver examination revealed focal macrophage collections and a unique inflammatory gene signature on RNA analysis. In the clinical cohort, preobesity, and class 1 and class 2 obesity were associated with increased odds of elevated aminotransferase levels 1-2 years after sepsis.

CONCLUSIONS

The combination of diet-induced obesity and pneumosepsis survival in a murine model resulted in unique changes in gluconeogenesis and liver inflammation, consistent with the progression of benign steatosis to steatohepatitis. In a cohort study, obese patients had an increased risk of elevated aminotransferase levels 1-2 years following sepsis.

Negative correlation between circulating integrin α4+ group 3 innate lymphoid cells and the severity of type 2 diabetes

BACKGROUND

Impaired intestinal barrier and immune dysfunction promote the development of type 2 diabetes (T2D). Group 3 innate lymphoid cells (ILC3s), which are enriched in the intestinal lamina propria, are key for intestinal barrier integrity. However, there is a paucity of data on circulating ILC3s in patients with T2D.

PURPOSE

To examine the characteristics of ILC3s in patients with T2D and identify the relationship between ILC3s and clinical indicators of T2D.

METHODS

Fifty-nine patients with T2D and thirty controls were enrolled in this retrospective study. Peripheral blood mononuclear cells were isolated and analyzed by flow cytometry and plasma cytokine levels were measured by enzyme-linked immunosorbent assays.

RESULTS

The proportion of circulating ILC3s in the T2D group was significantly lower than that in controls and showed a negative correlation with fasting glucose and glycated hemoglobin and a positive correlation with granulocyte-macrophage colony-stimulating factor (GM-CSF). Similarly, the proportion of circulating integrin α4⁺ ILC3s was also significantly lower in the T2D group and showed a negative correlation with fasting glucose and glycated hemoglobin and a positive correlation with GM-CSF. Moreover, the level of circulating integrin α4⁺ ILC3s showed a positive correlation with the proportion of circulating dendritic cells (DCs), which was also decreased in patients with T2D and positively associated with GM-CSF.

CONCLUSION

ILC3s, especially integrin α4⁺ ILC3s, were decreased in patients with T2D and showed a negative correlation with disease severity. These cell subsets may delay the progression of T2D by promoting DC differentiation via the secretion of GM-CSF.

Innate immune response to peritoneal bacterial infection

Spontaneous and secondary peritoneal infections, mostly of bacterial origin, easily spread to cause severe sepsis. Cellular and humoral elements of the innate immune system are constitutively present in peritoneal cavity and omentum, and play an important role in peritonitis progression and resolution. This review will focus on the description of the anatomic characteristics of the peritoneal cavity and the composition and function of such innate immune elements under both steady-state and bacterial infection conditions. Potential innate immune-based therapeutic interventions in bacterial peritonitis alternative or adjunctive to classical antibiotic therapy will be briefly discussed.

Diet-induced obesity in mice impairs host defense against Klebsiella pneumonia in vivo and glucose transport and bactericidal functions in neutrophils in vitro

Obesity impairs host defense against Klebsiella pneumoniae, but responsible mechanisms are incompletely understood. To determine the impact of diet-induced obesity on pulmonary host defense against K. pneumoniae, we fed 6-wk-old male C57BL/6j mice a normal diet (ND) or high-fat diet (HFD) (13% vs. 60% fat, respectively) for 16 wk. Mice were intratracheally infected with Klebsiella, assayed at 24 or 48 h for bacterial colony-forming units, lung cytokines, and leukocytes from alveolar spaces, lung parenchyma, and gonadal adipose tissue were assessed using flow cytometry. Neutrophils from uninfected mice were cultured with and without 2-deoxy-d-glucose (2-DG) and assessed for phagocytosis, killing, reactive oxygen intermediates (ROI), transport of 2-DG, and glucose transporter (GLUT1-4) transcripts, and protein expression of GLUT1 and GLUT3. HFD mice had higher lung and splenic bacterial burdens. In HFD mice, baseline lung homogenate concentrations of IL-1β, IL-6, IL-17, IFN-γ, CXCL2, and TNF-α were reduced relative to ND mice, but following infection were greater for IL-6, CCL2, CXCL2, and IL-1β (24 h only). Despite equivalent lung homogenate leukocytes, HFD mice had fewer intraalveolar neutrophils. HFD neutrophils exhibited decreased Klebsiella phagocytosis and killing and reduced ROI to heat-killed Klebsiella in vitro. 2-DG transport was lower in HFD neutrophils, with reduced GLUT1 and GLUT3 transcripts and protein (GLUT3 only). Blocking glycolysis with 2-DG impaired bacterial killing and ROI production in neutrophils from mice fed ND but not HFD. Diet-induced obesity impairs pulmonary Klebsiella clearance and augments blood dissemination by reducing neutrophil killing and ROI due to impaired glucose transport.

Molecular Level Insights Into the Structural and Dynamic Factors Driving Cytokine Function

Cytokines are key mediators of cellular communication and regulators of biological advents. The timing, quantity and localization of cytokines are key features in producing specific biological outcomes, and thus have been thoroughly studied and reviewed while continuing to be a focus of the cytokine biology community. Due to the complexity of cellular signaling and multitude of factors that can affect signaling outcomes, systemic level studies of cytokines are ongoing. Despite their small size, cytokines can exhibit structurally promiscuous and dynamic behavior that plays an equally important role in biological activity. In this review using case studies, we highlight the recent insight gained from observing cytokines through a molecular lens and how this may complement a system-level understanding of cytokine biology, explain diversity of downstream signaling events, and inform therapeutic and experimental development.

Application of Peak Glucose Range and Diabetes Status in Mortality Risk Stratification in Critically Ill Patients with Sepsis

The effects of diabetes and glucose on the outcomes of patients with sepsis are somewhat conflicting. This retrospective study enrolled 1214 consecutive patients with sepsis, including a subpopulation of 148 patients with immune profiles. The septic patients were stratified according to their Diabetes mellitus (DM) status or peak glucose level (three-group tool; P1: ≤140 mg/dL, P2: 141–220 mg/dL, P3: >220 mg/dL) on day 1. Although the DM group had a lower hazard ratio (HR) for 90-day mortality compared to non-DM patients, the adjusted HRs were insignificant. The modified sequential organ failure assessment-glucose (mSOFA-g) score can predict 90-day survival in patients with and without diabetes (β = 1.098, p < 0.001; β = 1.202, p < 0.001). The goodness of fit of the mSOFA-g score was 5% higher than the SOFA score of the subgroup without diabetes. The SOFA score and human leukocyte antigen-D-related (HLA-DR) expression were comparable between the groups. The P3 group had lower HLA-DR expression on days 1 and 3 and a higher 90-day mortality. The three-group tool was useful for predicting 90-day mortality in patients with separate Kaplan-Meier survival curves and mortality HRs in the construction and validation cohorts. The peak glucose level, instead of diabetes status, can be used as an easy adjunctive tool for mortality risk stratification in critically ill septic patients.

Innate Immune System Orchestrates Metabolic Homeostasis and Dysfunction in Visceral Adipose Tissue During Obesity

Arising incidence of metabolic disorders and related diseases caused by obesity is a global health concern. Elucidating the role of the immune system in this process will help to understand the related mechanisms and develop treatment strategies. Here, we have focused on innate immune cells in visceral adipose tissue (VAT) and summarized the roles of these cells in maintaining the homeostasis of VAT. Furthermore, this review reveals the importance of quantitative and functional changes of innate immune cells when the metabolic microenvironment changes due to obesity or excess lipids, and confirms that these changes eventually lead to the occurrence of chronic inflammation and metabolic diseases of VAT. Two perspectives are reviewed, which include sequential changes in various innate immune cells in the steady state of VAT and its imbalance during obesity. Cross-sectional interactions between various innate immune cells at the same time point are also reviewed. Through delineation of a comprehensive perspective of VAT homeostasis in obesity-induced chronic inflammation, and ultimately metabolic dysfunction and disease, we expect to clarify the complex interactive networks among distinct cell populations and propose that these interactions should be taken into account in the development of biotherapeutic strategies.

A Bittersweet Response to Infection in Diabetes; Targeting Neutrophils to Modify Inflammation and Improve Host Immunity

Chronic and recurrent infections occur commonly in both type 1 and type 2 diabetes (T1D, T2D) and increase patient morbidity and mortality. Neutrophils are professional phagocytes of the innate immune system that are critical in pathogen handling. Neutrophil responses to infection are dysregulated in diabetes, predominantly mediated by persistent hyperglycaemia; the chief biochemical abnormality in T1D and T2D. Therapeutically enhancing host immunity in diabetes to improve infection resolution is an expanding area of research. Individuals with diabetes are also at an increased risk of severe coronavirus disease 2019 (COVID-19), highlighting the need for re-invigorated and urgent focus on this field. The aim of this review is to explore the breadth of previous literature investigating neutrophil function in both T1D and T2D, in order to understand the complex neutrophil phenotype present in this disease and also to focus on the development of new therapies to improve aberrant neutrophil function in diabetes. Existing literature illustrates a dual neutrophil dysfunction in diabetes. Key pathogen handling mechanisms of neutrophil recruitment, chemotaxis, phagocytosis and intracellular reactive oxygen species (ROS) production are decreased in diabetes, weakening the immune response to infection. However, pro-inflammatory neutrophil pathways, mainly neutrophil extracellular trap (NET) formation, extracellular ROS generation and pro-inflammatory cytokine generation, are significantly upregulated, causing damage to the host and perpetuating inflammation. Reducing these proinflammatory outputs therapeutically is emerging as a credible strategy to improve infection resolution in diabetes, and also more recently COVID-19. Future research needs to drive forward the exploration of novel treatments to improve infection resolution in T1D and T2D to improve patient morbidity and mortality.

Metabolic dysfunction and immunometabolism in COVID-19 pathophysiology and therapeutics

The COVID-19 pandemic has emerged as a public health crisis and has placed a significant burden on healthcare systems. Patients with underlying metabolic dysfunction, such as type 2 diabetes mellitus and obesity, are at a higher risk for COVID-19 complications, including multi-organ dysfunction, secondary to a deranged immune response, and cellular energy deprivation. These patients are at a baseline state of chronic inflammation associated with increased susceptibility to the severe immune manifestations of COVID-19, which are triggered by the cellular hypoxic environment and cytokine storm. The altered metabolic profile and energy generation of immune cells affect their activation, exacerbating the imbalanced immune response. Key immunometabolic interactions may inform the development of an efficacious treatment for COVID-19. Novel therapeutic approaches with repurposed drugs, such as PPAR agonists, or newly developed molecules such as the antagomirs, which block microRNA function, have shown promising results. Those treatments, alone or in combination, target both immune and metabolic pathways and are ideal for septic COVID-19 patients with an underlying metabolic condition.

The Essential Involvement of the Omentum in the Peritoneal Defensive Mechanisms During Intra-Abdominal Sepsis

Although the abilities of the omentum to alleviate inflammation and prevent infection have been revealed over the past decades, the underlying mechanisms remain largely unelucidated. Here, we demonstrated that the mortality of mice exposed to cecal ligation and puncture (CLP) and omentectomy was remarkably increased compared to those treated with CLP alone. Moreover, the efficacy of the omentum was associated with an impairment in intraperitoneal bacterial clearance together with an increase in the expression of proinflammatory cytokines. Besides, in response to peritoneal infections, the size and quantity of the omental milky spots (MSs) were increased tremendously and they also support innate-like B1 cell responses and local IgM production in the peritoneal cavity. Furthermore, not only the migration but also the functional activities of neutrophils were diminished in the absence of the omentum. These data collectively show that the omentum contributes more to peritoneal immune responses during septic peritonitis than has heretofore been recognized. Thus, harnessing the function of MS-containing omentum to increase its protective effectiveness may exert important biological and therapeutic implications for the control of intra-abdominal infections.

The Collision of Meta-Inflammation and SARS-CoV-2 Pandemic Infection

The coronavirus disease 2019 (COVID-19) pandemic has forced us to consider the physiologic role of obesity in the response to infectious disease. There are significant disparities in morbidity and mortality by sex, weight, and diabetes status. Numerous endocrine changes might drive these varied responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, including hormone and immune mediators, hyperglycemia, leukocyte responses, cytokine secretion, and tissue dysfunction. Studies of patients with severe COVID-19 disease have revealed the importance of innate immune responses in driving immunopathology and tissue injury. In this review we will describe the impact of the metabolically induced inflammation (meta-inflammation) that characterizes obesity on innate immunity. We consider that obesity-driven dysregulation of innate immune responses may drive organ injury in the development of severe COVID-19 and impair viral clearance.

Different roles of intracellular and extracellular reactive oxygen species of neutrophils in type 2 diabetic mice with invasive aspergillosis

Diabetic patients have an increased risk of invasive aspergillosis (IA), but the mechanism is still unclear. Reactive oxygen species (ROS) produced by neutrophils play a key role in defense against Aspergillus infection. Since diabetes mellitus affects the production of ROS from neutrophils, the purpose of this study is to investigate whether this effect is related to the susceptibility of diabetic mice to IA. C57BL/6 mice were used to establish type 2 diabetes mellitus (T2DM) model, and IA was induced by airway infection with Aspergillus fumigatus. After infection, the fungal load, neutrophil count and ROS content in the lung tissues of T2DM mice were higher than those in the control mice, and the inflammation of the lung tissue was more serious. After being exposed to hyphae in vitro, compared with the control group, neutrophils in T2DM mice had higher apoptosis rate and intracellular ROS content, as well as lower viability, extracellular ROS content and fungicidal ability. In summary, after T2DM mice are infected with A. fumigatus, the reduction of extracellular ROS produced by neutrophils may lead to a decrease in fungicidal ability, while the increase of intracellular ROS is related to neutrophil and lung tissue damage.

"Shielding" of Cytokine Induction by the Periodontal Microbiome in Patients with Periodontitis Associated with Type 2 Diabetes Mellitus

Periodontal diseases, especially those with polymicrobial etiology, are often associated with type 2 diabetes mellitus, proceeding more severely and affecting the course of diabetes mellitus. Recently, this feature has been associated with the ability of periodontopathogen microflora to cause not only a local infectious process in the oral cavity, but also to interact with the human immune system and induce various systemic effects. We investigated changes in the salivary cytokine profile of patients with chronic periodontitis, associated and not associated with type 2 diabetes mellitus. We observed a statistically significant decrease of MCP-1/CCL2, GM-CSF, IL-5, IL-6, and IFN-γ in the saliva of patients with chronic periodontitis associated with type 2 diabetes mellitus in comparison with patients with chronic periodontitis only. All of these cytokines are associated with macrophage activation. These data are an important contribution to the elucidation of the mechanism of periodontopathogens involvement in the manifestation of the systemic effects of type 2 diabetes.