B Cells with a Senescent-Associated Secretory Phenotype Accumulate in the Adipose Tissue of Individuals with Obesity

Finding a Link between Obesity and Senescence: A Systematic Review and Meta-Analysis

Background

Cell aging is associated with changes in telomeres due to DNA damage arising from chronic inflammation in obese patients. The aim of the systematic review and meta-analysis was to find the relationship between obesity and aging or senescence.

Methods

The systematic review was conducted through PRISMA guideline, beginning with literature search within 2012-2022 in several databases (PubMed, EBSCOHost, Science Direct, Scopus, and Cochrane) followed by screening process using predetermined PICO criteria. Original studies on the topic of obesity and senescence (aging), from preclinical studies to clinical research (cohort or cross-sectional studies) that were published within the last ten years. All studies were appraised using SYRCLE risk of bias tool for preclinical studies and Newcastle-Ottawa Scale (NOS) for cross-sectional and cohort studies. The data extraction on the studies' characteristic and outcome on aging or senescence were followed by quantitative analysis using MetaXL process on prevalence ratio and hazard ratio of obesity to comorbidities and mortality.

Results

Fifteen studies were enrolled. Obesity and white adipose tissue cause increased levels of pro-inflammatory and pro-senescence cytokine and macrophage whilst the aging process lowers metabolism with increased insulin resistance and linked to increased risk of obesity. Obesity occurs in 22% (95% CI 18%-26%) of elderly population with higher prevalence rate in the women population. Obesity is associated with significant increased risk of multimorbidity by 56% (OR = 1.58 [95% CI 1.48-1.96]).

Conclusion

The obesity and aging or senescence has reciprocal relationship between each other.

From the Sun to the Cell: Examining Obesity through the Lens of Vitamin D and Inflammation

Obesity affects more than one billion people worldwide and often leads to cardiometabolic chronic comorbidities. It induces senescence-related alterations in adipose tissue, and senescence is closely linked to obesity. Fully elucidating the pathways through which vitamin D exerts anti-inflammatory effects may improve our understanding of local adipose tissue inflammation and the pathogenesis of metabolic disorders. In this narrative review, we compiled and analyzed the literature from diverse academic sources, focusing on recent developments to provide a comprehensive overview of the effect of vitamin D on inflammation associated with obesity and senescence. The article reveals that the activation of the NF-κB (nuclear factor kappa B subunit 1) and NLRP3 inflammasome (nucleotide-binding domain, leucine-rich-containing, pyrin domain-containing-3) pathways through the toll-like receptors, which increases oxidative stress and cytokine release, is a common mechanism underlying inflammation associated with obesity and senescence, and it discusses the potential beneficial effect of vitamin D in alleviating the development of subclinical inflammation. Investigating the main target cells and pathways of vitamin D action in adipose tissue could help uncover complex mechanisms of obesity and cellular senescence. This review summarizes significant findings related to opportunities for improving metabolic health.

Atypical B cells consist of subsets with distinct functional profiles

Atypical B cells are a population of activated B cells that are commonly enriched in individuals with chronic immune activation but are also part of a normal immune response to infection or vaccination. To better define the role of atypical B cells in the human adaptive immune response, we performed single-cell sequencing of transcriptomes, cell surface markers, and B cell receptors in individuals with chronic exposure to the malaria parasite Plasmodium falciparum, a condition known to lead to accumulation of circulating atypical B cells. We identified three previously uncharacterized populations of atypical B cells with distinct transcriptional and functional profiles and observed marked differences among these three subsets in their ability to produce immunoglobulin G upon T-cell-dependent activation. Our findings help explain the conflicting observations in prior studies regarding the function of atypical B cells and highlight their different roles in the adaptive immune response in chronic inflammatory conditions.

High Fat Diet-Induced Obesity Dysregulates Splenic B Cell Mitochondrial Activity

Diet-induced obesity impairs mitochondrial respiratory responses in tissues that are highly metabolically active, such as the heart. However, less is known about the impact of obesity on the respiratory activity of specific cell types, such as splenic B cells. B cells are of relevance, as they play functional roles in obesity-induced insulin resistance, inflammation, and responses to infection. Here, we tested the hypothesis that high-fat-diet (HFD)-induced obesity could impair the mitochondrial respiration of intact and permeabilized splenic CD19+ B cells isolated from C57BL/6J mice and activated ex vivo with lipopolysaccharide (LPS). High-resolution respirometry was used with intact and permeabilized cells. To reveal potential mechanistic targets by which HFD-induced obesity dysregulates B cell mitochondria, we conducted proteomic analyses and 3D serial block face scanning electron microscopy (SBFEM). High-resolution respirometry revealed that intact LPS-stimulated B cells of obese mice, relative to controls, displayed lower ATP-linked, as well as maximal uncoupled, respiration. To directly investigate mitochondrial function, we used permeabilized LPS-stimulated B cells, which displayed increased H2O2 emission and production with obesity. We also examined oxidative phosphorylation efficiency simultaneously, which revealed that oxygen consumption and ATP production were decreased in LPS-stimulated B cells with obesity relative to controls. Despite minimal changes in total respiratory complex abundance, in LPS-stimulated B cells of obese mice, three of the top ten most downregulated proteins were all accessory subunits of respiratory complex I. SBFEM showed that B cells of obese mice, compared to controls, underwent no change in mitochondrial cristae integrity but displayed increased mitochondrial volume that was linked to bioenergetic function. Collectively, these results establish a proof of concept that HFD-induced obesity dysregulates the mitochondrial bioenergetic metabolism of activated splenic B cells.

Immune Diseases Associated with Aging: Molecular Mechanisms and Treatment Strategies

Aging is associated with a decline in immune function, thereby causing an increased susceptibility to various diseases. Herein, we review immune diseases associated with aging, focusing on tumors, atherosclerosis, and immunodeficiency disorders. The molecular mechanisms underlying these conditions are discussed, highlighting telomere shortening, tissue inflammation, and altered signaling pathways, e.g., the mammalian target of the rapamycin (mTOR) pathway, as key contributors to immune dysfunction. The role of the senescence-associated secretory phenotype in driving chronic tissue inflammation and disruption has been examined. Our review underscores the significance of targeting tissue inflammation and immunomodulation for treating immune disorders. In addition, anti-inflammatory medications, including corticosteroids and nonsteroidal anti-inflammatory drugs, and novel approaches, e.g., probiotics and polyphenols, are discussed. Immunotherapy, particularly immune checkpoint inhibitor therapy and adoptive T-cell therapy, has been explored for its potential to enhance immune responses in older populations. A comprehensive analysis of immune disorders associated with aging and underlying molecular mechanisms provides insights into potential treatment strategies to alleviate the burden of these conditions in the aging population. The interplay among immune dysfunction, chronic tissue inflammation, and innovative therapeutic approaches highlights the importance of elucidating these complex processes to develop effective interventions to improve the quality of life in older adults.

Obesity accelerates age defects in B cells, and weight loss improves B cell function

BACKGROUND

We have previously shown that obesity accelerates age-associated defects in B cell function and antibody production leading to decreased secretion of protective antibodies and increased autoimmunity. We wanted to evaluate if obese adults enrolled in a voluntary weight reduction program had higher protective and lower autoimmune antibody responses similar to those observed in lean adults.

METHODS

Experiments were performed using blood isolated from an established cohort of female lean adult and elderly individuals, as well as from the blood of female adults with obesity, before and after a voluntary weight reduction program in which their Body Mass Index (BMI) was reduced 10-34% in 12 months. All participants were vaccinated with the Trivalent Inactivated Influenza vaccine. Serum samples were evaluated for the presence of pro-inflammatory cytokines and adipokines, vaccine-specific antibodies and autoimmune antibodies. We evaluated the composition of the B cell pool by flow cytometry, the expression of RNA for class switch transcription factors and pro-inflammatory markers by qPCR, the in vitro secretion of pro- and anti-inflammatory cytokines and their capacity to induce pro-inflammatory T cells.

RESULTS

Obesity, similar to aging, induced increased serum levels of pro-inflammatory cytokines and autoimmune antibodies, while vaccine-specific antibodies were reduced. In agreement with the serum results, the B cell pool of obese adults and elderly individuals was enriched in pro-inflammatory B cell subsets and was characterized by higher expression of markers associated with cell senescence, higher levels of T-bet, the transcription factor for autoimmune antibodies and lower levels of E47, the transcription factor associated with protective responses to the influenza vaccine. B cells from obese adults and elderly individuals were also able to secrete inflammatory cytokines and support the generation of inflammatory T cells. All these pro-inflammatory characteristics of B cells from obese individuals were significantly attenuated, but not completely reversed, by weight loss.

CONCLUSIONS

Although the results from our small observational study show that obesity-induced dysfunctional B cell responses, similar to those occurring during aging, are ameliorated in some but not all obese individuals after weight loss, the effects of body weight loss on mechanistic pathways are largely missing and deserve further investigation.

The link between lymphocyte subpopulations in peripheral blood and metabolic variables in patients with severe obesity

Background

Obesity, a public health problem, is a state of metainflammation that influences the development of chronic degenerative diseases, particularly in patients with severe obesity.

Objective

The objective of this study was to evidence immunometabolic differences in patients with different degrees of obesity, including severe obesity, by determining correlations between lymphocyte subpopulations and metabolic, body composition, and clinical variables.

Methods

Peripheral blood immune cells (CD4+, CD8+ memory and effector T lymphocytes) were analyzed, and measures of body composition, blood pressure, and biochemical composition (glucose, glycated hemoglobin (HbA1c), insulin, C-reactive protein (CRP), and the lipid profile) were carried out in patients with different degrees of obesity.

Results

The patients were classified according to total body fat (TBF) percentage as normal body fat, class 1 and 2 obesity, class 3 obesity, and class 4 obesity. The greater the TBF percentage, the more pronounced the differences in body composition (such as a decrease in the fat-free mass (FFM) that is defined as sarcopenic obesity) and the immunometabolic profile. There was an increase of CD3+ T lymphocytes (mainly CD4+, CD4+CD62-, and CD8+CD45RO+ T lymphocytes) and an increase in the TBF percentage (severity of obesity).

Conclusions

The correlations between lymphocyte subpopulations and metabolic, body composition, and clinical variables demonstrated the existence of a chronic, low-intensity inflammatory process in obesity. Therefore, measuring the immunometabolic profile by means of lymphocyte subpopulations in patients with severe obesity could be useful to determine the severity of the disease and the increased risk of presenting obesity-associated chronic degenerative diseases.

Heat-Killed Lacticaseibacillus paracasei Repairs Lipopolysaccharide-Induced Intestinal Epithelial Barrier Damage via MLCK/MLC Pathway Activation

Intestinal epithelial barrier function is closely associated with the development of many intestinal diseases. Heat-killed Lacticaseibacillus paracasei (HK-LP) has been shown to improve intestinal health and enhance immunity. However, the function of HK-LP in the intestinal barrier is still unclear. This study characterized the inflammatory effects of seven HK-LP (1 μg/mL) on the intestinal barrier using lipopolysaccharide (LPS) (100 μg/mL)-induced Caco-2 cells. In this study, HK-LP 6105, 6115, and 6235 were selected, and their effects on the modulation of inflammatory factors and tight junction protein expression (claudin-1, zona occludens-1, and occludin) were compared. The effect of different cultivation times (18 and 48 h) was investigated in response to LPS-induced intestinal epithelial barrier dysfunction. Our results showed that HK-LP 6105, 6115, and 6235 improved LPS-induced intestinal barrier permeability reduction and transepithelial resistance. Furthermore, HK-LP 6105, 6115, and 6235 inhibited the pro-inflammatory factors (TNF-α, IL-1β, IL-6) and increased the expression of the anti-inflammatory factors (IL-4, IL-10, and TGF-β). HK-LP 6105, 6115, and 6235 ameliorated the inflammatory response. It inhibited the nuclear factor kappa B (NF-κB) signaling pathway-mediated myosin light chain (MLC)/MLC kinase signaling pathway by downregulating the Toll-like receptor 4 (TLR4)/NF-κB pathway. Thus, the results suggest that HK-LP 6150, 6115, and 6235 may improve intestinal health by regulating inflammation and TJ proteins. Postbiotics produced by these strains exhibit anti-inflammatory properties that can protect the intestinal barrier.

Cellular Senescence in Obesity and Associated Complications: a New Therapeutic Target

PURPOSE OF REVIEW

Obesity has increased worldwide recently and represents a major global health challenge. This review focuses on the obesity-associated cellular senescence in various organs and the role of these senescent cells (SnCs) in driving complications associated with obesity. Also, the ability to target SnCs pharmacologically with drugs termed senotherapeutics as a therapy for these complications is discussed.

RECENT FINDINGS

Several studies have shown a positive correlation between obesity and SnC burden in organs such as adipose tissue, liver, and pancreatic-β-cells. These SnCs produce several secretory factors which affect other cells and tissues in a paracrine manner resulting in organ dysfunction. The accumulation of SnCs in adipocytes affects their lipid storage and impairs adipogenesis. The inflammatory senescence-associated secretory phenotype (SASP) of SnCs downregulates the antioxidant capacity and mitochondrial function in tissues. Senescent hepatocytes cannot oxidize fatty acids, which leads to lipid deposition and senescence in β-cells decrease function. These and other adverse effects of SnCs contribute to insulin resistance and type-2 diabetes. The reduction in the SnC burden genetically or pharmacologically improves the complications associated with obesity. The accumulation of SnCs with age and disease accelerates aging. Obesity is a key driver of SnC accumulation, and the complications associated with obesity can be controlled by reducing the SnC burden. Thus, senotherapeutic drugs have the potential to be an effective therapeutic option.

Dicer1 deficient mice exhibit premature aging and metabolic perturbations in adipocytes

Age-related diseases are major concern in developed countries. To avoid disabilities that accompany increased lifespan, pharmaceutical approaches are considered. Therefore, appropriate animal models are required for a better understanding of aging processes and potential in vivo assays to evaluate the impact of molecules that may delay the occurrence of age-related diseases. Few mouse models exhibiting pathological aging exist, but currently, none of them reproducibly mimics human diseases like osteoporosis, cognitive dysfunctions or sarcopenia that can be seen in some, but not all, elders. Here, we describe the premature aging phenotypes of Dicer-deficient mature animals, which exhibit an overall deterioration of many organs and tissues (skin, heart, and adipose tissue) ultimately leading to a significant reduction of their lifespan. Molecular characterization of transcriptional responses focused on the adipose tissue suggested that both canonical and non-canonical functions of DICER are involved in this process and highlight potential actionable pathways to revert it.

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Dicer1-deficient mice have a reduced lifespan with early age-related symptoms

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Mutant mice are resistant to high fat diet-induced disorders

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Myokines FGF21 and GDF15 are likely key regulators of adipocytes metabolism

T-bet B or not T-bet B, is that the question in obesity-related metabolic disease?

Obesity is linked to inflammation and downstream metabolic dysregulation. In this issue of Cell Metabolism, Hägglöf et al. show that iNKT cells enable the accumulation of T-bet⁺ B cells in white adipose tissue, which in turn produce chemokine and antibody mediators that exacerbate the onset and severity of metabolic disease.

Metformin Enhances B Cell Function and Antibody Responses of Elderly Individuals With Type-2 Diabetes Mellitus

Our previous work has shown that young and elderly patients with Type-2 Diabetes Mellitus (T2DM) treated with Metformin have optimal B cell function and serum antibodies specific for the seasonal influenza vaccine. In this paper, we have evaluated B cell function and the metabolic requirements of B cell antibody responses in elderly T2DM patients (E_T2DM) taking or not Metformin, and compared to those of healthy elderly (E_H) and healthy young (Y_H) individuals. Results show that Metformin significantly increases in vivo B cell function, measured by influenza vaccine-specific serum antibodies, in E_T2DM patients to the levels observed in E_H and more importantly in Y_H individuals. Metformin also decreases the frequencies of pro-inflammatory B cell subsets, as well as intrinsic inflammation and metabolic requirements of peripheral B cells from E_T2DM. This hyper-metabolic phenotype of B cells from E_T2DM is needed to support intrinsic inflammation, measured by the expression of transcripts for markers of the senescence-associated secretory phenotype (SASP), and the secretion of autoimmune antibodies. Importantly, B cell function in E_T2DM patients taking Metformin is not only increased as compared to that in E_T2DM patients not taking Metformin, but is comparable to B cell function measured in Y_H individuals. These results altogether strongly support the anti-aging effects of Metformin on humoral immunity.

Immune Senescence, Immunosenescence and Aging

With aging, there is increased dysfunction of both innate and adaptive immune responses, which contributes to impaired immune responses to pathogens and greater mortality and morbidity. This age-related immune dysfunction is defined in general as immunosenescence and includes an increase in the number of memory T cells, loss of ability to respond to antigen and a lingering level of low-grade inflammation. However, certain features of immunosenescence are similar to cellular senescence, which is defined as the irreversible loss of proliferation in response to damage and stress. Importantly, senescence cells can develop an inflammatory senescence-associated secretory phenotype (SASP), that also drives non-autonomous cellular senescence and immune dysfunction. Interestingly, viral infection can increase the extent of immune senescence both directly and indirectly, leading to increased immune dysfunction and inflammation, especially in the elderly. This review focuses on age-related immune dysfunction, cellular senescence and the impaired immune response to pathogens.

Obesity Accelerates Age-Associated Defects in Human B Cells Through a Metabolic Reprogramming Induced by the Fatty Acid Palmitate

We have measured the secretion of autoimmune antibodies in plasma samples and in culture supernatants of blood-derived B cells from four groups of individuals: young lean (Y_L), elderly lean (E_L), young obese (Y_O) and elderly obese (E_O). We found secretion comparable in Y_O and E_L individuals, suggesting that obesity accelerates age-associated defects in circulating B cells. To define at least one possible molecular pathway involved, we used an in vitro model in which B cells from Y_L and E_L individuals have been stimulated with the Fatty Acid (FA) palmitate, the most common saturated FA in the human body. The rationale to use palmitate is that there is a chronic increase in circulating levels of palmitate, due to increased spontaneous lipolysis occurring during aging and obesity, and this may induce autoimmune B cells. Results herein show that in vitro incubation of B cells from Y_L and E_L individuals with the FA palmitate induces mRNA expression of T-bet, the transcription factor for autoimmune antibodies, as well as secretion of autoimmune IgG antibodies, with B cells from Y_L individuals looking similar to B cells from E_L individuals, confirming our initial hypothesis. The generation of autoimmune B cells in the presence of the FA palmitate was found to be associated with a metabolic reprogramming of B cells from both Y_L and E_L individuals. These results altogether show the critical role of the FA palmitate in inducing human B cell immunosenescence and show for the first time the importance of metabolic pathways in this process.

Targeting immune dysfunction in aging

Human aging is a multifactorial phenomenon that affects numerous organ systems and cellular processes, with the immune system being one of the most dysregulated. Immunosenescence, the gradual deterioration of the immune system, and inflammaging, a chronic inflammatory state that persists in the elderly, are among the plethora of immune changes that occur during aging. Almost all populations of immune cells change with age in terms of numbers and/or activity. These alterations are in general highly detrimental, resulting in an increased susceptibility to infections, reduced healing abilities, and altered homeostasis that promote the emergence of age-associated diseases such as cancer, diabetes, and other diseases associated with inflammation. Thanks to recent developments, several strategies have been proposed to target central immunological processes or specific immune subpopulations affected by aging. These therapeutic approaches could soon be applied in the clinic to slow down or even reverse specific age-induced immune changes in order to rejuvenate the immune system and prevent or reduce the impact of various diseases. Due to its systemic nature and interconnection with all the other systems in the body, the immune system is an attractive target for aging intervention because relatively targeted modifications to a small set of cells have the potential to improve the health of multiple organ systems. Therefore, anti-aging immune targeting therapies could represent a potent approach for improving healthspan. Here, we review aging changes in the major components of the immune system, we summarize the current immune-targeting therapeutic approaches in the context of aging and discuss the future directions in the field of immune rejuvenation.