Age-associated accumulation of B cells promotes macrophage inflammation and inhibits lipolysis in adipose tissue during sepsis

Unraveling immunosenescence in sepsis: from cellular mechanisms to therapeutics

Sepsis is a life-threatening multiple organ dysfunction resulting from a dysregulated host response to infection, and patients with sepsis always exhibit a state of immune disorder characterized by both overwhelming inflammation and immunosuppression. The aging of immune system, namely "immunosenescence", has been reported to be correlated with high morbidity and mortality in elderly patients with sepsis. Initially, immunosenescence was considered as a range of age-related alterations in the immune system. However, increasing evidence has proven that persistent inflammation or even a short-term inflammatory challenge during sepsis could trigger accelerated aging of immune cells, which might further exacerbate inflammatory cytokine storm and promote the shift towards immunosuppression. Thus, premature immunosenescence is found in young sepsis individuals, which further aggravates immune disorders and induces the progression of sepsis. Furthermore, in old sepsis patients, the synergistic effects of both sepsis and aging may cause immunosenescence-associated alterations more significantly, resulting in more severe immune dysfunction and a worse prognosis. Therefore, it is necessary to explore the potential therapeutic strategies targeting immunosenescence during sepsis.

Aging-associated changes in immunological parameters: Implications for COVID-19 immune response in the elderly

Aging has a profound impact on the immune system, leading to a gradual decline in its function and increased systemic inflammation, collectively known as immunosenescence and inflammaging. These changes make older adults more susceptible to infections, including COVID-19, and contribute to worse clinical outcomes, such as higher morbidity and mortality rates. This review explores immunological changes associated with aging, including impaired innate immune responses, reduced T- and B-cell function, and altered cytokine profiles. A comprehensive literature search identified relevant studies on the topic, and inclusion criteria focused on studies addressing age-related immune changes and their impact on responses to COVID-19. The findings underscore the need for targeted healthcare strategies to mitigate the negative effects of aging on immunity and improve immune resilience, and ultimately clinical outcomes and quality of life for this vulnerable population.

From fat storage to immune hubs: the emerging role of adipocytes in coordinating the immune response to infection

Adipose tissue is a rich source of diverse cell populations, including immune cells, adipocytes and stromal cells. Interactions between these different cell types are now appreciated to be critical for maintaining tissue structure and function, by governing processes such as adipogenesis, lipolysis and differentiation of white to beige adipocytes. Interactions between these cells also drive inflammation in obesity, leading to an expansion of adipose tissue immune cells, and the secretion of proinflammatory cytokines from immune cells and from adipocytes themselves. However, in evolutionary terms, obesity is a recent phenomenon, raising the question of why adipocytes evolved to express factors that influence the immune response. Studies of various pathogens indicate that adipocytes are highly responsive to infection, altering their metabolic profiles in a way that can be used to release nutrients and fuel the immune response. In the case of infection with the extracellular parasite Trypanosoma brucei, attenuating the ability of adipocytes to sense the cytokine IL-17 results in a loss of control of the local immune response and an increased pathogen load. Intriguingly, comparisons of the adipocyte response to infection suggest that the immune responses of these cells occur in a pathogen-dependent manner, further confirming their complexity. Here, with a focus on murine adipose tissue, we discuss the emerging concept that, in addition to their canonical function, adipocytes are immune signalling hubs that integrate and disseminate signals from the immune system to generate a local environment conducive to pathogen clearance.

B-cell interleukin 1 receptor 1 modulates the female adipose tissue immune microenvironment during aging

Myeloid cell production of interleukin-1β (IL-1β) drives inflammaging in visceral white adipose tissue (vWAT) and contributes to the expansion of interleukin-1 receptor 1 (Il1r1)-positive aged adipose B cells (AABs). AABs promote metabolic dysfunction and inflammation under inflammatory challenges. However, whether IL-1β contributes to AAB-associated inflammation during aging is unclear. Using a B-cell-specific knockout of Il1r1 (BKO mice), we characterized old vWAT in the absence of IL-1β-B-cell signaling. In addition to sex-specific metabolic improvements in females, we identified a reduction in the proportion of B cells and a sex-specific increase in the B1/B2 B-cell ratio in BKO vWAT. Using single-cell RNA sequencing of vWAT immune cells, we observed that BKO differentially affected inflammatory signaling in vWAT immune cells. These data suggest that IL-1β-B-cell signaling supports the inflammatory response in multiple cell types and provides insight into the complex microenvironment in aged vWAT.

The Fifth Annual Symposium of the Midwest Aging Consortium

As the healthcare burden caused by an increasingly aging population rapidly rises, a pressing need exists for innovative geroscience research that can elucidate aging mechanisms and precipitate the development of therapeutic interventions to support healthy aging. The Fifth Annual Midwest Aging Consortium Aging Research symposium, held from April 28 to 30, 2024, was hosted by The Ohio State University in Columbus, Ohio, and featured presentations from investigators across the Midwestern United States. This report summarizes the research presented at the symposium, whose topics included cellular senescence and the aging brain, metabolism and metabolic interventions, nutrition, redox mechanisms and biomarkers, and stress mechanisms. Abstract presentations and short talks highlighted early-stage and young investigators, whereas 2 keynote presentations anchored the symposium. Overall, this symposium showed the robustness of aging research in the Midwest and underscored the advantages of a collaborative approach to geroscience research.

Function and Regulation of Age-Associated B Cells in Diseases

The aging process often leads to immune-related diseases, including infections, tumors, and autoimmune disorders. Recently, researchers identified a special subpopulation of B cells in elderly female mice that increases with age and accumulates prematurely in mouse models of autoimmune diseases or viral infections; these B cells are known as age-related B cells (ABCs). These cells possess distinctive cell surface phenotypes and transcriptional characteristics, and the cell population is widely recognized as CD11c+CD11b+T-bet+CD21-CD23- cells. Research has shown that ABCs are a heterogeneous group of B cells that originate independently of the germinal center and are insensitive to B-cell receptor (BCR) and CD40 stimulation, differentiating and proliferating in response to toll-like receptor 7 (TLR7) and IL-21 stimulation. Additionally, they secrete self-antibodies and cytokines to regulate the immune response. These issues have aroused widespread interest among researchers in this field. This review summarizes recent research progress on ABCs, including the functions and regulation of ABCs in aging, viral infection, autoimmune diseases, and organ transplantation.

The impact of glucose metabolism on inflammatory processes in sepsis-induced acute lung injury

Acute lung injury (ALI) is a prevalent and critical complication of sepsis, marked by high incidence and mortality rates, with its pathogenesis still not being fully elucidated. Recent research has revealed a significant correlation between the metabolic reprogramming of glucose and sepsis-associated ALI (S-ALI). Throughout the course of S-ALI, immune cells, including macrophages and dendritic cells, undergo metabolic shifts to accommodate the intricate demands of immune function that emerge as sepsis advances. Indeed, glucose metabolic reprogramming in S-ALI serves as a double-edged sword, fueling inflammatory immune responses in the initial stages and subsequently initiating anti-inflammatory responses as the disease evolves. In this review, we delineate the current research progress concerning the pathogenic mechanisms linked to glucose metabolic reprogramming in S-ALI, with a focus on the pertinent immune cells implicated. We encapsulate the impact of glucose metabolic reprogramming on the onset, progression, and prognosis of S-ALI. Ultimately, by examining key regulatory factors within metabolic intermediates and enzymes, We have identified potential therapeutic targets linked to metabolic reprogramming, striving to tackle the inherent challenges in diagnosing and treating Severe Acute Lung Injury (S-ALI) with greater efficacy.

Sex-Specific Metabolic Effects of Gestational Chronodisruption and Maternal Melatonin Supplementation in Rat Offspring

Gestational chronodisruption, increasingly common due to irregular light exposure, disrupts maternal-fetal circadian signaling, leading to long-term health issues in offspring. We utilized a chronic photoperiod shifting model (CPS) in pregnant rats to induce chronodisruption and investigated the potential mitigating effects of maternal melatonin supplementation (CPS + Mel). Male and female offspring were evaluated at 3 ages (90, 200, and 400 days of age) for metabolic profiles, hormonal responses, cytokine levels, and adipose tissue activity. Our findings indicate that gestational chronodisruption leads to increased birth weight by approximately 15% in male and female offspring and increased obesity prevalence in male offspring, accompanied by a 30% reduction in nocturnal melatonin levels and a significant disruption in corticosterone rhythms. Male CPS offspring also exhibited decreased lipolytic activity in white adipose tissue, with a 25% reduction in glycerol release compared to controls, indicating impaired metabolic flexibility. In contrast, female offspring, while less affected metabolically, showed a 25% increase in adipose tissue lipolytic activity and higher levels of pro-inflammatory cytokines such as IL-6 (increased by 40%). Scheduled melatonin supplementation in chronodisrupted mothers, administered throughout gestation, effectively normalized birth weights in both sexes, reduced obesity prevalence in males by 18%, and improved lipolytic activity in male offspring, bringing it closer to control levels. In females, melatonin supplementation moderated cytokine levels, reducing IL-6 by 35% and restoring IL-10 levels to near-control values. These results highlight the importance of sex-specific prenatal interventions, particularly the role of melatonin in preventing disruptions to fetal metabolic and inflammatory pathways caused by gestational chronodisruption. Melatonin treatment would prevent maternal circadian rhythm misalignment, thereby supporting healthy fetal development. This study opens new avenues for developing targeted prenatal care strategies that align maternal and fetal circadian rhythms, mitigating the long-term health risks associated with chronodisruption during pregnancy.

GDF3 promotes adipose tissue macrophage-mediated inflammation via altered chromatin accessibility during aging

Age-related susceptibility to sepsis and endotoxemia is poorly defined, although hyperactivation of the immune system and the expansion of the visceral adipose as an immunological reservoir are underlying features. Macrophages from older organisms exhibit substantial changes, including chronic NLRP3 inflammasome activation, genomic remodeling and a dysfunctional, amplified inflammatory response upon new exposure to pathogen. However, the mechanisms by which old macrophages maintain their inflammatory phenotype during endotoxemia remains elusive. We previously identified Gdf3 , a TGFβ superfamily cytokine, as a top-regulated gene by age and the NLRP3 inflammasome in adipose tissue macrophages (ATMs). Here, we demonstrate that endotoxemia increases inflammatory (CD11c + ) ATMs in a Gdf3- dependent manner in old mice. Lifelong systemic or myeloid-specific deletion of Gdf3 leads to reduced endotoxemia- induced inflammation, with decreased CD11c + ATMs and inflammatory cytokines, and protection from hypothermia. Moreover, acute blockade of Gdf3 using JQ1, a BRD4 inhibitor, phenocopies old mice with lifelong Gdf3- deficiency. We show that GDF3 promotes the inflammatory phenotype in ATMs by phosphorylating SMAD2/3. Mechanistically, the differential chromatin landscape of ATMs from old mice with or without myeloid-driven Gdf3 indicates that GDF3- SMAD2/3 signaling axis shifts the chromatin accessibility of ATMs towards an inflammatory state during aging. Furthermore, pharmaceutical inhibition of SMAD3 with a specific inhibitor of SMAD3 (SIS3) mimics Gdf3 deletion. SIS3 reduces endotoxemia-mediated inflammation with fewer CD11c + ATMs and less severe hypothermia in old, but not young mice, as well as reduced mortality. In human adipose tissue, age positively correlates with GDF3 level, while inflammation correlates with pSMAD2/3 level. Overall, these results highlight the importance of GDF3-SMAD2/3 axis in driving inflammation in older organisms and identify this signaling axis as a promising therapeutic target for mitigating endotoxemia-related inflammation in the aged.

Lactate's impact on immune cells in sepsis: unraveling the complex interplay

Lactate significantly impacts immune cell function in sepsis and septic shock, transcending its traditional view as just a metabolic byproduct. This review summarizes the role of lactate as a biomarker and its influence on immune cell dynamics, emphasizing its critical role in modulating immune responses during sepsis. Mechanistically, key lactate transporters like MCT1, MCT4, and the receptor GPR81 are crucial in mediating these effects. HIF-1α also plays a significant role in lactate-driven immune modulation. Additionally, lactate affects immune cell function through post-translational modifications such as lactylation, acetylation, and phosphorylation, which alter enzyme activities and protein functions. These interactions between lactate and immune cells are central to understanding sepsis-associated immune dysregulation, offering insights that can guide future research and improve therapeutic strategies to enhance patient outcomes.

Protocol to examine murine visceral adipose tissue immune cells using fluorescence-based flow cytometry

Adipose tissue immune cells are heterogeneous and dynamic, alter metabolism, and drive immune responses. Here, we present a protocol for assessment and characterization of murine adipose tissue immune cells using fluorescence-based flow cytometry and sorting into pure populations. We describe steps for isolation of the stromovascular fraction, antibody staining, and data collection by flow cytometry. We also discuss common issues and troubleshooting steps. For complete details on the use and execution of this protocol, please refer to Carey et al.1.

Role for BLT1 in regulating inflammation within adipose tissue immune cells of aged mice

BACKGROUND

Aging is a complex biological process characterized by obesity and immunosenescence throughout the organism. Immunosenescence involves a decline in immune function and the increase in chronic-low grade inflammation, called inflammaging. Adipose tissue expansion, particularly that of visceral adipose tissue (VAT), is associated with an increase in pro-inflammatory macrophages that play an important role in modulating immune responses and producing inflammatory cytokines. The leukotriene B4 receptor 1 (BLT1) is a regulator of obesity-induced inflammation. Its ligand, LTB4, acts as a chemoattractant for immune cells and induces inflammation. Studies have shown that BLT1 is crucial for cytokine production during lipopolysaccharide (LPS) endotoxemia challenge in younger organisms. However, the expression patterns and function of BLT1 in older organisms remains unknown.

RESULTS

In this study, we investigated BLT1 expression in immune cell subsets within the VAT of aged male and female mice. Moreover, we examined how antagonizing BLT1 signaling could alter the inflammatory response to LPS in aged mice. Our results demonstrate that aged mice exhibit increased adiposity and inflammation, characterized by elevated frequencies of B and T cells, along with pro-inflammatory macrophages in VAT. BLT1 expression is the highest in VAT macrophages. LPS and LTB4 treatment result in increased BLT1 in young and aged bone marrow-derived macrophages (BMDMs). However, LTB4 treatment resulted in amplified Il6 from aged, but not young BMDMs. Treatment of aged mice with the BLT1 antagonist, U75302, followed by LPS-induced endotoxemia resulted in an increase in anti-inflammatory macrophages, reduced phosphorylated NFκB and reduced Il6.

CONCLUSIONS

This study provides valuable insights into the age- and sex- specific changes in BLT1 expression on immune cell subsets within VAT. This study offers support for the potential of BLT1 in modulating inflammation in aging.

Fat-associated lymphoid clusters: Supporting visceral adipose tissue B cell function in immunity and metabolism

It is now widely understood that visceral adipose tissue (VAT) is a highly active and dynamic organ, with many functions beyond lipid accumulation and storage. In this review, we discuss the immunological role of this tissue, underpinned by the presence of fat-associated lymphoid clusters (FALCs). FALC's distinctive structure and stromal cell composition support a very different immune cell mix to that found in classical secondary lymphoid organs, which underlies their unique functions of filtration, surveillance, innate-like immune responses, and adaptive immunity within the serous cavities. FALCs are important B cell hubs providing B1 cell-mediated frontline protection against infection and supporting B2 cell-adaptative immune responses. Beyond these beneficial immune responses orchestrated by FALCs, immune cells within VAT play important homeostatic role. Dysregulation of immune cells during obesity and aging leads to chronic pathological "metabolic inflammation", which contributes to the development of cardiometabolic diseases. Here, we examine the emerging and complex functions of B cells in VAT homeostasis and the metabolic complications of obesity, highlighting the potential role that FALCs play and emphasize the areas where further research is needed.

M2 macrophage-derived TGF-β induces age-associated loss of adipogenesis through progenitor cell senescence

OBJECTIVES

Adipose tissue is an endocrine and energy storage organ composed of several different cell types, including mature adipocytes, stromal cells, endothelial cells, and a variety of immune cells. Adipose tissue aging contributes to the pathogenesis of metabolic dysfunction and is likely induced by crosstalk between adipose progenitor cells (APCs) and immune cells, but the underlying molecular mechanisms remain largely unknown. In this study, we revealed the biological role of p16high senescent APCs, and investigated the crosstalk between each cell type in the aged white adipose tissue.

METHODS

We performed the single-cell RNA sequencing (scRNA-seq) analysis on the p16high adipose cells sorted from aged p16-CreERT2/Rosa26-LSL-tdTomato mice. We also performed the time serial analysis on the age-dependent bulk RNA-seq datasets of human and mouse white adipose tissues to infer the transcriptome alteration of adipogenic potential within aging.

RESULTS

We show that M2 macrophage-derived TGF-β induces APCs senescence which impairs adipogenesis in vivo. p16high senescent APCs increase with age and show loss of adipogenic potential. The ligand-receptor interaction analysis reveals that M2 macrophages are the donors for TGF-β and the senescent APCs are the recipients. Indeed, treatment of APCs with TGF-β1 induces senescent phenotypes through mitochondrial ROS-mediated DNA damage in vitro. TGF-β1 injection into gonadal white adipose tissue (gWAT) suppresses adipogenic potential and induces fibrotic genes as well as p16 in APCs. A gWAT atrophy is observed in cancer cachexia by APCs senescence, whose induction appeared to be independent of TGF-β induction.

CONCLUSIONS

Our results suggest that M2 macrophage-derived TGF-β induces age-related lipodystrophy by APCs senescence. The TGF-β treatment induced DNA damage, mitochondrial ROS, and finally cellular senescence in APCs.