SenNet recommendations for detecting senescent cells in different tissues.

Once considered a tissue culture-specific phenomenon, cellular senescence has now been linked to various biological processes with both beneficial and detrimental roles in humans, rodents and other species. Much of our understanding of senescent cell biology still originates from tissue culture studies, where each cell in the culture is driven to an irreversible cell cycle arrest. By contrast, in tissues, these cells are relatively rare and difficult to characterize, and it is now established that fully differentiated, postmitotic cells can also acquire a senescence phenotype. The SenNet Biomarkers Working Group was formed to provide recommendations for the use of cellular senescence markers to identify and characterize senescent cells in tissues. Here, we provide recommendations for detecting senescent cells in different tissues based on a comprehensive analysis of existing literature reporting senescence markers in 14 tissues in mice and humans. We discuss some of the recent advances in detecting and characterizing cellular senescence, including molecular senescence signatures and morphological features, and the use of circulating markers. We aim for this work to be a valuable resource for both seasoned investigators in senescence-related studies and newcomers to the field.

Apoptotic stress causes mtDNA release during senescence and drives the SASP.

Senescent cells drive age-related tissue dysfunction partially through the induction of a chronic senescence-associated secretory phenotype (SASP)1. Mitochondria are major regulators of the SASP; however, the underlying mechanisms have not been elucidated2. Mitochondria are often essential for apoptosis, a cell fate distinct from cellular senescence. During apoptosis, widespread mitochondrial outer membrane permeabilization (MOMP) commits a cell to die3. Here we find that MOMP occurring in a subset of mitochondria is a feature of cellular senescence. This process, called minority MOMP (miMOMP), requires BAX and BAK macropores enabling the release of mitochondrial DNA (mtDNA) into the cytosol. Cytosolic mtDNA in turn activates the cGAS-STING pathway, a major regulator of the SASP. We find that inhibition of MOMP in vivo decreases inflammatory markers and improves healthspan in aged mice. Our results reveal that apoptosis and senescence are regulated by similar mitochondria-dependent mechanisms and that sublethal mitochondrial apoptotic stress is a major driver of the SASP. We provide proof-of-concept that inhibition of miMOMP-induced inflammation may be a therapeutic route to improve healthspan.

Kidney inflammaging is promoted by CCR2+ macrophages and tissue-derived micro-environmental factors.

The incidence of disorders associated with low inflammatory state, such as chronic kidney disease, increases in the elderly. The accumulation of senescent cells during aging and the senescence-associated secretory phenotype, which leads to inflammaging, is known to be deleterious and account for progressive organ dysfunction. To date, the cellular actors implicated in chronic inflammation in the kidney during aging are still not well characterized. Using the DECyt method, based on hierarchical clustering of flow cytometry data, we showed that aging was associated with significant changes in stromal cell diversity in the kidney. In particular, we identified two cell populations up-regulated with aging, the mesenchymal stromal cell subset (kMSC) expressing CD73 and the monocyte-derived Ly6C+ CCR2+ macrophage subset expressing pro-inflammatory cytokines. Aged CD73+ kMSCs depicted senescence associated features with low proliferation rate, increased DNA damage foci and Ccl2 expression. Using co-cultures experiments, we showed that aged CD73+ kMSC promoted monocyte activation and secretion of inflammatory cytokines albeit less efficiently than young CD73+ kMSCs. In the context of ageing, increased frequency of CD73+ kMSC subpopulations could provide additional niche factors to newly recruited monocytes favoring a positive regulatory loop in response to local inflammation. Interfering with such partnership during aging could be a valuable approach to regulate kidney inflammaging and to limit the risk of developing chronic kidney disease in the elderly.

Selective Cardiomyocyte Oxidative Stress Leads to Bystander Senescence of Cardiac Stromal Cells.

Accumulation of senescent cells in tissues during normal or accelerated aging has been shown to be detrimental and to favor the outcomes of age-related diseases such as heart failure (HF). We have previously shown that oxidative stress dependent on monoamine oxidase A (MAOA) activity in cardiomyocytes promotes mitochondrial damage, the formation of telomere-associated foci, senescence markers, and triggers systolic cardiac dysfunction in a model of transgenic mice overexpressing MAOA in cardiomyocytes (Tg MAOA). However, the impact of cardiomyocyte oxidative stress on the cardiac microenvironment in vivo is still unclear. Our results showed that systolic cardiac dysfunction in Tg MAOA mice was strongly correlated with oxidative stress induced premature senescence of cardiac stromal cells favoring the recruitment of CCR2+ monocytes and the installation of cardiac inflammation. Understanding the interplay between oxidative stress induced premature senescence and accelerated cardiac dysfunction will help to define new molecular pathways at the crossroad between cardiac dysfunction and accelerated aging, which could contribute to the increased susceptibility of the elderly to HF.

Apoptotic Epitope-Specific CD8+ T Cells and Interferon Signaling Intersect in Chronic Hepatitis C Virus Infection.

CD8(+) T cells specific to caspase-cleaved antigens derived from apoptotic T cells represent a principal player in chronic immune activation. Here, we found that both apoptotic epitope-specific and hepatitis C virus (HCV)-specific CD8(+) T cells were mostly confined within the effector memory (EM) or terminally differentiated EM CD45RA(+) cell subsets expressing a dysfunctional T-helper 1-like signature program in chronic HCV infection. However, apoptotic epitope-specific CD8(+) T cells produced tumor necrosis factor α and interleukin 2 at the intrahepatic level significantly more than HCV-specific CD8(+) T cells, despite both populations expressing high levels of programmed death 1 receptor. Contextually, only apoptotic epitope-specific CD8(+) T cells correlated with both interferon-stimulated gene levels in T cells and hepatic fibrosis score. Together, these data suggest that, compared with HCV-specific CD8(+) T cells, apoptotic epitope-specific CD8(+) T cells can better sustain chronic immune activation, owing to their capacity to produce tumor necrosis factor α, and exhibit greater resistance to inhibitory signals during chronic HCV infection.

From T cell apoptosis to chronic immune activation in inflammatory diseases.

A variety of physiological and pathological conditions may induce cell death. Therefore, it is reasonable that apoptotic cells send different signals promoting either tolerance or immune responses. Many factors influence the type of response, such as the quality (e.g. bearing or released factors, activation state), the timing and the site of cell death. In particular, the activation state of apoptotic lymphocytes (CD40L expression) may be crucial in determining the fate of their cross-presentation, i.e. cross-tolerance versus cross-priming. The cross-presentation of apoptotic activated CD40L+ T cells determines the cross-priming of apoptotic epitope-specific CD8+ T cells. These autoreactive CD8+ T cells are observed in diseases with a sustained component of chronic inflammation such as chronic viral infections and systemic autoimmune diseases. We have explored this phenomenon in HIV and chronic hepatitis C virus infections as well as in multiple sclerosis and rheumatoid arthritis, all conditions where these CD8+ T cells participate in the maintenance of a low-level state of inflammation.

Senescent cell transplantation into the skin induces age-related peripheral dysfunction and cognitive decline.

Cellular senescence is an established cause of cell and tissue aging. Senescent cells have been shown to increase in multiple organs during aging, including the skin. Here we hypothesized that senescent cells residing in the skin can spread senescence to distant organs, thereby accelerating systemic aging processes. To explore this hypothesis, we initially observed an increase in several markers of senescence in the skin of aging mice. Subsequently, we conducted experiments wherein senescent fibroblasts were transplanted into the dermis of young mice and assessed various age-associated parameters. Our findings reveal that the presence of senescent cells in the dermal layer of young mice leads to increased senescence in both proximal and distal host tissues, alongside increased frailty, and impaired musculoskeletal function. Additionally, there was a significant decline in cognitive function, concomitant with increased expression of senescence-associated markers within the hippocampus brain area. These results support the concept that the accumulation of senescent cells in the skin can exert remote effects on other organs including the brain, potentially explaining links between skin and brain disorders and diseases and, contributing to physical and cognitive decline associated with aging.

Mitochondrial RNA cytosolic leakage drives the SASP.

Senescent cells secrete proinflammatory factors known as the senescence-associated secretory phenotype (SASP), contributing to tissue dysfunction and aging. Mitochondrial dysfunction is a key feature of senescence, influencing SASP via mitochondrial DNA (mtDNA) release and cGAS/STING pathway activation. Here, we demonstrate that mitochondrial RNA (mtRNA) also accumulates in the cytosol of senescent cells, activating RNA sensors RIG-I and MDA5, leading to MAVS aggregation and SASP induction. Inhibition of these RNA sensors significantly reduces SASP factors. Furthermore, BAX and BAK plays a key role in mtRNA leakage during senescence, and their deletion diminishes SASP expression in vitro and in a mouse model of Metabolic Dysfunction Associated Steatohepatitis (MASH). These findings highlight mtRNA's role in SASP regulation and its potential as a therapeutic target for mitigating age-related inflammation.

Increased CD8+ T cell responses to apoptotic T cell-associated antigens in multiple sclerosis.

BACKGROUND: Here, we evaluated the hypothesis that CD8+ T cell responses to caspase-cleaved antigens derived from effector T cells undergoing apoptosis, may contribute to multiple sclerosis (MS) immunopathology. METHODS: The percentage of autoreactive CD8+ T effector cells specific for various apoptotic T cell-associated self-epitopes (apoptotic epitopes) were detected in the peripheral blood and cerebrospinal fluid (CSF) by both enzyme-linked immunospot and dextramers of class I molecules complexed with relevant apoptotic epitopes. Moreover, the capacity of dextramer+ CD8+ T cells to produce interferon (IFN)-γ and/or interleukin (IL)-17 in response to the relevant apoptotic epitopes was evaluated by the intracellular cytokine staining. Cross-presentation assay of apoptotic T cells by dendritic cells was also evaluated ex vivo. RESULTS: We found that polyfunctional (IFN-γ and/or IL-17 producing) autoreactive CD8+ T cells specific for apoptotic epitopes were represented in MS patients with frequencies significantly higher than in healthy donors. These autoreactive CD8+ T cells with a strong potential to produce IFN-γ or IL-17 in response to the relevant apoptotic epitopes were significantly accumulated in the CSF from the same patients. In addition, the frequencies of these autoreactive CD8+ T cells correlated with the disease disability. Cross-presentation assay revealed that caspase-cleaved cellular proteins are required to activate apoptotic epitope-specific CD8+ T cells ex vivo. CONCLUSION: Taken together, these data indicate that apoptotic epitope-specific CD8+ T cells with strong inflammatory potential are recruited at the level of the inflammatory site, where they may be involved in MS immunopathology through the production of high levels of inflammatory cytokines.

Cellular senescence: all roads lead to mitochondria.

Senescence is a multi-functional cell fate, characterized by an irreversible cell-cycle arrest and a pro-inflammatory phenotype, commonly known as the senescence-associated secretory phenotype (SASP). Emerging evidence indicates that accumulation of senescent cells in multiple tissues drives tissue dysfunction and several age-related conditions. This has spurred the academic community and industry to identify new therapeutic interventions targeting this process. Mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence which plays important roles not only in the senescence growth arrest but also in the development of the SASP and resistance to cell-death. Here, we review the evidence that supports a role for mitochondria in the development of senescence and describe the underlying mechanisms. Finally, we propose that a detailed road map of mitochondrial biology in senescence will be crucial to guide the future development of senotherapies.

Effectiveness of immunoglobulin replacement therapy on clinical outcome in patients with primary antibody deficiencies: results from a multicenter prospective cohort study.

A 5-years multicenter prospective study on 201 patients with common variable immunodeficiencies and 101 patients with X-linked agammaglobulinemia over a cumulative follow-up period of 1,365 patient-years was conducted to identify prognostic markers and risk factors for associated clinical co-morbidities, the effects of long-term immunoglobulin treatment and the IgG trough level to be maintained over time required to minimise infection risk. Overall, 21% of the patients with common variable immunodeficiencies and 24% of patients with X-linked agammaglobulinemia remained infection free during the study. A reduction of pneumonia episodes has been observed after initiation of Ig replacement. During the observation time, pneumonia incidence remained low and constant over time. Patients with pneumonia did not have significant lower IgG trough levels than patients without pneumonia, with the exception of patients whose IgG trough levels were persistently <400 mg/dL. In X-linked agammaglobulinemia, the only co-morbidity risk factor identified for pneumonia by the final multivariable model was the presence of bronchiectasis. In common variable immunodeficiencies, our data allowed us to identify a clinical phenotype characterised by a high pneumonia risk: patients with low IgG and IgA levels at diagnosis; patients who had IgA level <7 mg/dL and who had bronchiectasis. The effect of therapy with immunoglobulins at replacement dosage for non-infectious co-morbidities (autoimmunity, lymphocytic hyperplasia and enteropathy) remains to be established. A unique general protective trough IgG level in antibody deficiency patients will remain undefined because of the major role played by the progression of lung disease in X-linked agammaglobulinemia and in a subset of patients with common variable immunodeficiencies.

Aging induces cardiac mesenchymal stromal cell senescence and promotes endothelial cell fate of the CD90 + subset.

Aging is a major risk factor in the development of chronic diseases, especially cardiovascular diseases. Age-related organ dysfunction is strongly associated with the accumulation of senescent cells. Cardiac mesenchymal stromal cells (cMSCs), deemed part of the microenvironment, modulate cardiac homeostasis through their vascular differentiation potential and paracrine activity. Transcriptomic analysis of cMSCs identified age-dependent biological pathways regulating immune responses and angiogenesis. Aged cMSCs displayed a senescence program characterized by Cdkn2a expression, decreased proliferation and clonogenicity, and acquisition of a senescence-associated secretory phenotype (SASP). Increased CCR2-dependent monocyte recruitment by aged cMSCs was associated with increased IL-1ß production by inflammatory macrophages in the aging heart. In turn, IL-1ß induced senescence in cMSCs and mimicked age-related phenotypic changes such as decreased CD90 expression. The CD90+ and CD90- cMSC subsets had biased vascular differentiation potentials, and CD90+ cMSCs were more prone to acquire markers of the endothelial lineage with aging. These features were related to the emergence of a new cMSC subset in the aging heart, expressing CD31 and endothelial genes. These results demonstrate that cMSC senescence and SASP production are supported by the installation of an inflammatory amplification loop, which could sustain cMSC senescence and interfere with their vascular differentiation potentials.

Monoamine oxidase-A is a novel driver of stress-induced premature senescence through inhibition of parkin-mediated mitophagy.

Cellular senescence, the irreversible cell cycle arrest observed in somatic cells, is an important driver of age-associated diseases. Mitochondria have been implicated in the process of senescence, primarily because they are both sources and targets of reactive oxygen species (ROS). In the heart, oxidative stress contributes to pathological cardiac ageing, but the mechanisms underlying ROS production are still not completely understood. The mitochondrial enzyme monoamine oxidase-A (MAO-A) is a relevant source of ROS in the heart through the formation of H2 O2 derived from the degradation of its main substrates, norepinephrine (NE) and serotonin. However, the potential link between MAO-A and senescence has not been previously investigated. Using cardiomyoblasts and primary cardiomyocytes, we demonstrate that chronic MAO-A activation mediated by synthetic (tyramine) and physiological (NE) substrates induces ROS-dependent DNA damage response, activation of cyclin-dependent kinase inhibitors p21cip , p16ink4a , and p15ink4b and typical features of senescence such as cell flattening and SA-ß-gal activity. Moreover, we observe that ROS produced by MAO-A lead to the accumulation of p53 in the cytosol where it inhibits parkin, an important regulator of mitophagy, resulting in mitochondrial dysfunction. Additionally, we show that the mTOR kinase contributes to mitophagy dysfunction by enhancing p53 cytoplasmic accumulation. Importantly, restoration of mitophagy, either by overexpression of parkin or inhibition of mTOR, prevents mitochondrial dysfunction and induction of senescence. Altogether, our data demonstrate a novel link between MAO-A and senescence in cardiomyocytes and provides mechanistic insights into the potential role of MAO-dependent oxidative stress in age-related pathologies.

CD8+ T Cells Specific to Apoptosis-Associated Antigens Predict the Response to Tumor Necrosis Factor Inhibitor Therapy in Rheumatoid Arthritis.

CD8+ T cells specific to caspase-cleaved antigens derived from apoptotic T cells (apoptotic epitopes) represent a principal player in chronic immune activation, which is known to amplify immunopathology in various inflammatory diseases. The purpose of the present study was to investigate the relationship involving these autoreactive T cells, the rheumatoid arthritis immunopathology, and the response to tumor necrosis factor-α inhibitor therapy. The frequency of autoreactive CD8+ T cells specific to various apoptotic epitopes, as detected by both enzyme-linked immunospot assay and dextramers of major histocompatibility complex class I molecules complexed with relevant apoptotic epitopes, was longitudinally analyzed in the peripheral blood of rheumatoid arthritis patients who were submitted to etanercept treatment (or other tumor necrosis factor inhibitors as a control). The percentage of apoptotic epitope-specific CD8+ T cells was significantly higher in rheumatoid arthritis patients than in healthy donors, and correlated with the disease activity. More important, it was significantly more elevated in responders to tumor necrosis factor-α inhibitor therapy than in non-responders before the start of therapy; it significantly dropped only in the former following therapy. These data indicate that apoptotic epitope-specific CD8+ T cells may be involved in rheumatoid arthritis immunopathology through the production of inflammatory cytokines and that they may potentially represent a predictive biomarker of response to tumor necrosis factor-α inhibitor therapy to validate in a larger cohort of patients.

Health related quality of life in common variable immunodeficiency.

PURPOSE: To quantify the health related quality of life in primary immunodeficiency patients. MATERIALS AND METHODS: We used generic health status and general psychological health questionnaires to determine the range of issues that needed to be considered in examining the burden of common variable immunodeficiency (CVID). RESULTS: The health status of patients with CVID was lower than that observed in normal subjects. Overall, Role-Physical and General Health scales correlated with a poorer clinical status. Surprisingly, the duration of disease did not influence health status. Being female, older, General Health Questionnaire-positive and alexithymic proved to be major risk factors associated with a poor health status. Patients with chronic lung disease and chronic diarrhea had the lowest values on the Medical Outcome Study, Short Form SF-36 (SF-36) scales. Disease severity perception was associated with the General Health Questionnaire and alexithymia status. Limitations in daily activities as a result of lower physical health were the major problems facing common variable immunodeficiency patients. CONCLUSION: Our data underlined the importance of conducting a periodical health related quality of life assessment on patients with primary antibody deficiencies and, moreover, stressed the necessity of providing psychological support to at risk patients.

Current trends in management of hepatitis B virus reactivation in the biologic therapy era.

Hepatitis B virus (HBV) reactivation represents an emerging cause of liver disease in patients undergoing treatment with biologic agents. In particular, the risk of HBV reactivation is heightened by the use monoclonal antibodies, such as rituximab (anti-CD20) and alemtuzumab (anti-CD52) that cause profound and long-lasting immunosuppression. Emerging data indicate that HBV reactivation could also develop following the use of other biologic agents, such as tumor necrosis factor (TNF)-α inhibitors. When HBV reactivation is diagnosed, it is mandatory to suspend biologic treatment and start antiviral agents immediately. However, pre-emptive antiviral therapy prior to monoclonal antibody administration is crucial in preventing HBV reactivation and its clinical consequences. Several lines of evidence have shown that risk of HBV reactivation is greatly reduced by the identification of high-risk patients and the use of prophylactic antiviral therapy. In this article, we discuss current trends in the management of HBV reactivation in immunosuppressed patients receiving biologic therapy, such as rituximab, alemtuzumab and TNF-α antagonists.

Lung MRI as a possible alternative to CT scan for patients with primary immune deficiencies and increased radiosensitivity.

BACKGROUND: Patients with common variable immunodeficiency (CVID) suffer from respiratory infections leading over time to permanent lung damage. Increased radiosensitivity has been described, and clinicians should consider a risk-benefit assessment when ordering a CT scan, in that the exact level of "safe" radiation exposure is unknown. METHODS: Twenty-one patients with CVID were evaluated with chest CT scan, MRI, and pulmonary function tests on the same day. MRI protocol included a T2-weighted rotating blade-like k-space covering sequence (time repetition, 2,000; echo train = 27; field of view, 400 mm; flip angle, 150; slice thickness, 5 mm) on axial and coronal planes. The bronchial and parenchymal abnormalities were compared with those identified by CT scan applying a modified Bhalla scoring system to assess bronchiectasis, bronchial wall thickening, number of bronchial generations involved, mucous plugging, consolidations, emphysema, bullae, and nodules. RESULTS: CT scan and MRI findings were comparable for moderate to severe degrees of bronchial and parenchymal alterations. A low concordance was found between MRI and CT scan for lower scores of bronchial abnormalities. CT scan allowed a better identification of peripheral airways abnormalities. CONCLUSIONS: Lung alterations in patients with higher radiation sensitivity, such as patients with CVID, might be evaluated by MRI, a radiation-free technique alternative to CT scan.

Prospective study on CVID patients with adverse reactions to intravenous or subcutaneous IgG administration.

INTRODUCTION: The multicenter prospective study provides information on adverse reactions to intravenous and subcutaneous immunoglobulin treatment in a cohort of 262 patients with common variable immunodeficiency. Severe adverse reactions are a rare but unpredictable event that might occur also in patients who tolerate substitutive intravenous or subcutaneous immunoglobulin therapy for months or years. RESULTS: Subcutaneous therapy has been proved to be a safe option in the 13 patients who had to stop intravenous treatment and who remained out of immunoglobulin replacement for long periods of time. However, severe reactions to subcutaneous therapy occurred at the first or after several subcutaneous immunoglobulin administrations in 2 out of 13 patients. CONCLUSION: Therefore, patients with previous severe reactions to intravenous immunoglobulin should be considered at particularly high risk for reaction to subcutaneous administration. In these cases, switching from in-hospital administration to home self-administration should be done with extreme care.