Essential role for autophagy in the maintenance of immunological memory against influenza infection

Dependence on Autophagy for Autoreactive Memory B Cells in the Development of Pristane-Induced Lupus

The production of autoantibodies by autoreactive B cells plays a major role in the pathogenesis of lupus. Increases in memory B cells have been observed in human lupus patients and autoimmune lpr mice. Autophagy is required for the maintenance of memory B cells against viral infections; however, whether autophagy regulates the persistence of autoantigen-specific memory B cells and the development of lupus remains to be determined. Here we show that memory B cells specific for autoantigens can be detected in autoimmune lpr mice and a pristane-induced lupus mouse model. Interestingly, B cell-specific deletion of Atg7 led to significant loss of autoreactive memory B cells and reduced autoantibody production in pristane-treated mice. Autophagy deficiency also attenuated the development of autoimmune glomerulonephritis and pulmonary inflammation after pristane treatment. Adoptive transfer of wild type autoreactive memory B cells restored autoantibody production in Atg7-deficient recipients. These data suggest that autophagy is important for the persistence of autoreactive memory B cells in mediating autoantibody responses. Our results suggest that autophagy could be targeted to suppress autoreactive memory B cells and ameliorate humoral autoimmunity.

Srag Regulates Autophagy via Integrating into a Preexisting Autophagy Pathway in Testis

Spermatogenesis is an essential process for producing sperm cells. Reproductive strategy is successfully evolved for a species to adapt to a certain ecological system. However, roles of newly evolved genes in testis autophagy remain unclear. In this study, we found that a newly evolved gene srag (Sox9-regulated autophagy gene) plays an important role in promoting autophagy in testis in the lineage of the teleost Monopterus albus. The gene integrated into an interaction network through a two-way strategy of evolution, via Sox9-binding in its promoter and interaction with Becn1 in the coding region. Its promoter region evolved a cis element for binding of Sox9, a transcription factor for male sex determination. Both in vitro and in vivo analyses demonstrated that transcription factor Sox9 could bind to and activate the srag promoter. Its coding region acquired ability to interact with key autophagy initiation factor Becn1 via the conserved C-terminal, indicating that srag integrated into preexisting autophagy network. Moreover, we determined that Srag enhanced autophagy by interacting with Becn1. Notably, srag transgenic zebrafish revealed that Srag exerted the same function by enhancing autophagy through the Srag–Becn1 pathway. Thus, the new gene srag regulated autophagy in testis by integrated into preexisting autophagy network.

Bioinformatic Analyses Identify a Prognostic Autophagy-Related Long Non-coding RNA Signature Associated With Immune Microenvironment in Diffuse Gliomas

Background

Autophagy and long non-coding RNA (lncRNA) play a critical role in tumor progression and microenvironment. However, the role of autophagy-related lncRNAs (ARLs) in glioma microenvironment remains unclear.

Methods

A total of 988 diffuse glioma samples were extracted from TCGA and CGGA databases. Consensus clustering was applied to reveal different subgroups of diffuse gliomas. Kaplan-Meier analysis was used to evaluate survival differences between groups. The infiltration of immune cells was estimated by ssGSEA, TIMER, and CIBERSORT algorithms. The construction of ARL signature was conducted using principal component analysis.

Results

Consensus clustering revealed two clusters of diffuse gliomas, in which cluster 1 was associated with poor prognosis and enriched with malignant subtypes of gliomas. Moreover, cluster 1 exhibited high apoptotic and immune characteristics, and it had a low purity and high infiltration of several immune cells. The constructed ARL signature showed a promising accuracy in predicting the prognosis of glioma patients. ARL score was significantly elevated in the malignant subtype of glioma and the high ARL score indicated a poor prognosis. Besides, the high ARL score notably indicated low tumor purity and high infiltration of macrophages and neutrophils.

Conclusion

Our study developed and validated a novel ARL signature for the classification of diffuse glioma, which was closely associated with glioma immune microenvironment and could serve as a promising prognostic biomarker for glioma patients.

Considerations for a Respiratory Syncytial Virus Vaccine Targeting an Elderly Population

Respiratory syncytial virus (RSV) is most commonly associated with acute lower respiratory tract infections in infants and children. However, RSV also causes a high disease burden in the elderly that is often under recognized. Adults >65 years of age account for an estimated 80,000 RSV-associated hospitalizations and 14,000 deaths in the United States annually. RSV infection in aged individuals can result in more severe disease symptoms including pneumonia and bronchiolitis. Given the large disease burden caused by RSV in the aged, this population remains an important target for vaccine development. Aging results in lowered immune responsiveness characterized by impairments in both innate and adaptive immunity. This immune senescence poses a challenge when developing a vaccine targeting elderly individuals. An RSV vaccine tailored towards an elderly population will need to maximize the immune response elicited in order to overcome age-related defects in the immune system. In this article, we review the hurdles that must be overcome to successfully develop an RSV vaccine for use in the elderly, and discuss the vaccine candidates currently being tested in this highly susceptible population.

B Cell Metabolism and Autophagy in Autoimmunity

B cells are central to the pathogenesis of multiple autoimmune diseases, through antigen presentation, cytokine secretion, and the production of autoantibodies. During development and differentiation, B cells undergo drastic changes in their physiology. It is emerging that these are accompanied by equally significant shifts in metabolic phenotype, which may themselves also drive and enforce the functional properties of the cell. The dysfunction of B cells during autoimmunity is characterised by the breaching of tolerogenic checkpoints, and there is developing evidence that the metabolic state of B cells may contribute to this. Determining the metabolic phenotype of B cells in autoimmunity is an area of active study, and is important because intervention by metabolism-altering therapeutic approaches may represent an attractive treatment target.

Adaptive immunity at the crossroads of autophagy and metabolism

The function of lymphocytes is dependent on their plasticity, particularly their adaptation to energy availability and environmental stress, and their protein synthesis machinery. Lymphocytes are constantly under metabolic stress, and macroautophagy/autophagy is the primary metabolic pathway that helps cells overcome stressors. The intrinsic role of autophagy in regulating the metabolism of adaptive immune cells has recently gained increasing attention. In this review, we summarize and discuss the versatile roles of autophagy in regulating cellular metabolism and the implications of autophagy for immune cell function and fate, especially for T and B lymphocytes.

B Cell Response to Vaccination

As one of the most important weapons against infectious diseases, vaccines have saved countless lives since their first use in the late eighteenth century. Antibodies produced by effector B cells upon vaccination play a critical role in mediating protection. The past several decades of research have led to a revolution in our understanding of B cell response to vaccination. Vaccines against SARS-CoV-2 coronavirus were developed at an unprecedented speed to power our global fight against COVID-19 pandemic. Nevertheless, we still face many challenges in the development of vaccines against many other deadly viruses, such as human immunodeficiency virus (HIV) and influenza virus. In this review, we summarize the latest findings on B cell response to vaccination and pathogen infection. We also discuss the current challenges in the field and the potential strategies targeting B cell response to improve vaccine efficacy.Key abbreviations box: BCR: B cell receptor; bNAb: broadly neutralizing antibody; DC: dendritic cells; DZ: dark zone; EF response: extrafollicular response; FDC: follicular dendritic cell; GC: germinal center; HIV: human immunodeficiency virus; IC: immune complex; LLPC: long-lived plasma cell; LZ: light zone; MBC: memory B cell; SLPB: short-lived plasmablast; TFH: T follicular helper cells; TLR: Toll-like receptor.

Emerging role of autophagy in anti-tumor immunity: Implications for the modulation of immunotherapy resistance

Immunotherapies such as CAR-T cell transfer and antibody-targeted therapy have produced promising clinical outcomes in patients with advanced and metastatic cancer that are resistant to conventional therapies. However, with increasing use of cancer immunotherapy in clinical treatment, multiple therapy-resistance mechanisms have gradually emerged. The tumor microenvironment (TME), an integral component of cancer, can significantly influence the therapeutic response. Thus, it is worth exploring the potential of TME in modulating therapy resistance, in the hope to devise novel strategies to reinforcing anti-cancer treatments such as immunotherapy. As a crucial recycling process in the complex TME, the role of autophagy in tumor immunity has been increasingly appreciated. Firstly, autophagy in tumor cells can affect their immune response through modulating MHC-I-antigen complexes, thus modulating immunogenic tumor cell death, changing functions of immune cells via secretory autophagy, reducing the NK- and CTL-mediated cell lysis and degradation of immune checkpoint proteins. Secondly, autophagy is critical for the differentiation, maturation and survival of immune cells in the TME and can significantly affect the immune function of these cells, thereby regulating the anti-tumor immune response. Thirdly, alteration of autophagic activity in stromal cells, especially in fibroblasts, can reconstruct the three-dimensional stromal environment and metabolic reprogramming in the TME. A number of studies have demonstrated that optimal induction or inhibition of autophagy may lead to effective therapeutic regimens when combined with immunotherapy. This review discusses the important roles of autophagy in tumor cells, immune cells and stromal cells in the context of tumor immunity, and the potential of combining the autophagy-based therapy with immunotherapy as novel therapeutic approaches against cancer.

Cell death pathways and viruses: Role of microRNAs

Viral infections lead to the death of more than a million people each year around the world, both directly and indirectly. Viruses interfere with many cell functions, particularly critical pathways for cell death, by affecting various intracellular mediators. MicroRNAs (miRNAs) are a major example of these mediators because they are involved in many (if not most) cellular mechanisms. Virus-regulated miRNAs have been implicated in three cell death pathways, namely, apoptosis, autophagy, and anoikis. Several molecules (e.g., BECN1 and B cell lymphoma 2 [BCL2] family members) are involved in both apoptosis and autophagy, while activation of anoikis leads to cell death similar to apoptosis. These mechanistic similarities suggest that common regulators, including some miRNAs (e.g., miR-21 and miR-192), are involved in different cell death pathways. Because the balance between cell proliferation and cell death is pivotal to the homeostasis of the human body, miRNAs that regulate cell death pathways have drawn much attention from researchers. miR-21 is regulated by several viruses and can affect both apoptosis and anoikis via modulating various targets, such as PDCD4, PTEN, interleukin (IL)-12, Maspin, and Fas-L. miR-34 can be downregulated by viral infection and has different effects on apoptosis, depending on the type of virus and/or host cell. The present review summarizes the existing knowledge on virus-regulated miRNAs involved in the modulation of cell death pathways. Understanding the mechanisms for virus-mediated regulation of cell death pathways could provide valuable information to improve the diagnosis and treatment of many viral diseases.

AMPK Metabolism in the B Lineage Modulates Humoral Responses

A large and growing body of evidence supports functions of enzymes that regulate or effect cellular metabolism in governing the development, survival, and effector functions of immune cells—especially T cells, macrophages, and dendritic cells. Among these proteins, adenosine monophosphate-activated protein kinase (AMPK) is a conserved ATP and nutrient sensor that regulates multiple metabolic pathways to promote energy homeostasis. Although AMPK had been shown to regulate aspects of CD4⁺ and CD8⁺ T cell biology, its function in B lymphocytes has been less clear. Here, we review recent advances in our understanding of the role of AMPK in the metabolism, function, and maintenance of the B lineage.

Transcriptional and Metabolic Control of Memory B Cells and Plasma Cells

For many infections and almost all vaccines, neutralizing-antibody-mediated immunity is the primary basis and best functional correlate of immunological protection. Durable long-term humoral immunity is mediated by antibodies secreted by plasma cells that preexist subsequent exposures and by memory B cells that rapidly respond to infections once they have occurred. In the midst of the current pandemic of coronavirus disease 2019, it is important to define our current understanding of the unique roles of memory B cells and plasma cells in immunity and the factors that control the formation and persistence of these cell types. This fundamental knowledge is the basis to interpret findings from natural infections and vaccines. Here, we review transcriptional and metabolic programs that promote and support B cell fates and functions, suggesting points at which these pathways do and do not intersect.

Redox regulation of immunometabolism

Metabolic pathways and redox reactions are at the core of life. In the past decade(s), numerous discoveries have shed light on how metabolic pathways determine the cellular fate and function of lymphoid and myeloid cells, giving rise to an area of research referred to as immunometabolism. Upon activation, however, immune cells not only engage specific metabolic pathways but also rearrange their oxidation-reduction (redox) system, which in turn supports metabolic reprogramming. In fact, studies addressing the redox metabolism of immune cells are an emerging field in immunology. Here, we summarize recent insights revealing the role of reactive oxygen species (ROS) and the differential requirement of the main cellular antioxidant pathways, including the components of the thioredoxin (TRX) and glutathione (GSH) pathways, as well as their transcriptional regulator NF-E2-related factor 2 (NRF2), for proliferation, survival and function of T cells, B cells and macrophages.

Autophagy in the Regulation of Tissue Differentiation and Homeostasis

Autophagy is a constitutive pathway that allows the lysosomal degradation of damaged components. This conserved process is essential for metabolic plasticity and tissue homeostasis and is crucial for mammalian post-mitotic cells. Autophagy also controls stem cell fate and defective autophagy is involved in many pathophysiological processes. In this review, we focus on established and recent breakthroughs aimed at elucidating the impact of autophagy in differentiation and homeostasis maintenance of endothelium, muscle, immune system, and brain providing a suitable framework of the emerging results and highlighting the pivotal role of autophagic response in tissue functions, stem cell dynamics and differentiation rates.

AMPKα1 in B Cells Dampens Primary Antibody Responses yet Promotes Mitochondrial Homeostasis and Persistence of B Cell Memory

Emerging evidence indicates that metabolic programs regulate B cell activation and Ab responses. However, the metabolic mediators that support the durability of the memory B cell and long-lived plasma cell populations are not fully elucidated. Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionary conserved serine/threonine kinase that integrates cellular energy status and nutrient availability to intracellular signaling and metabolic pathways. In this study, we use genetic mouse models to show that loss of ΑMPKα1 in B cells led to a weakened recall Ab response associated with a decline in the population of memory-phenotype B cells. AMPKα1-deficient memory B lymphocytes exhibited aberrant mitochondrial activity, decreased mitophagy, and increased lipid peroxidation. Moreover, loss of AMPKα1 in B lymphoblasts was associated with decreased mitochondrial spare respiratory capacity. Of note, AMPKα1 in B cells was dispensable for stability of the bone marrow-resident, long-lived plasma cell population, yet absence of this kinase led to increased rates of Ig production and elevated serum Ab concentrations elicited by primary immunization. Collectively, our findings fit a model in which AMPKα1 in B cells supports recall function of the memory B cell compartment by promoting mitochondrial homeostasis and longevity but restrains rates of Ig production.

FunRes: resolving tissue-specific functional cell states based on a cell-cell communication network model

The functional specialization of cell types arises during development and is shaped by cell-cell communication networks determining a distribution of functional cell states that are collectively important for tissue functioning. However, the identification of these tissue-specific functional cell states remains challenging. Although a plethora of computational approaches have been successful in detecting cell types and subtypes, they fail in resolving tissue-specific functional cell states. To address this issue, we present FunRes, a computational method designed for the identification of functional cell states. FunRes relies on scRNA-seq data of a tissue to initially reconstruct the functional cell-cell communication network, which is leveraged for partitioning each cell type into functional cell states. We applied FunRes to 177 cell types in 10 different tissues and demonstrated that the detected states correspond to known functional cell states of various cell types, which cannot be recapitulated by existing computational tools. Finally, we characterize emerging and vanishing functional cell states in aging and disease, and demonstrate their involvement in key tissue functions. Thus, we believe that FunRes will be of great utility in the characterization of the functional landscape of cell types and the identification of dysfunctional cell states in aging and disease.

Wiskott Aldrich syndrome protein regulates non-selective autophagy and mitochondrial homeostasis in human myeloid cells

The actin cytoskeletal regulator Wiskott Aldrich syndrome protein (WASp) has been implicated in maintenance of the autophagy-inflammasome axis in innate murine immune cells. Here, we show that WASp deficiency is associated with impaired rapamycin-induced autophagosome formation and trafficking to lysosomes in primary human monocyte-derived macrophages (MDMs). WASp reconstitution in vitro and in WAS patients following clinical gene therapy restores autophagic flux and is dependent on the actin-related protein complex ARP2/3. Induction of mitochondrial damage with CCCP, as a model of selective autophagy, also reveals a novel ARP2/3-dependent role for WASp in formation of sequestrating actin cages and maintenance of mitochondrial network integrity. Furthermore, mitochondrial respiration is suppressed in WAS patient MDMs and unable to achieve normal maximal activity when stressed, indicating profound intrinsic metabolic dysfunction. Taken together, we provide evidence of new and important roles of human WASp in autophagic processes and immunometabolic regulation, which may mechanistically contribute to the complex WAS immunophenotype.

Integrating DNA damage response and autophagy signalling axis in ultraviolet-B induced skin photo-damage: a positive association in protecting cells against genotoxic stress

The skin acts as both physical as well as an immunological barrier against hazardous agents from the outside environment and protects the internal organs against damage. Skin ageing is a dynamic process caused by the influence of various external factors, including damage from ultraviolet (UV-B) radiation, which is known as photo-ageing, and due to internal chronological mechanisms. A normal ageing process requires several orchestrated defense mechanisms to diverse types of stress responses, the concomitant renewal of cellular characteristics, and the homeostasis of different cell types that directly or indirectly protect the integrity of skin. Cumulative oxidative and endoplasmic reticulum (ER) stress responses and their adverse impact on biological systems in the skin are a common mechanism of the ageing process, negatively impacting DNA by causing mutations that lead to many physiological, functional, and aesthetic changes in the skin, culminating in the development of many diseases, including photo-damage and photo-carcinogenesis. Exposure of the skin to ultraviolet-(B) elicits the activation of signal transduction pathways, including DNA damage response, autophagy, and checkpoint signal adaptations associated with clearing radiation-induced DNA damage. Recent experimental reports suggest that autophagy is involved in maintaining skin homeostasis upon encountering different stresses, notably genotoxic stress. It has also been revealed that autophagy positively regulates the recognition of DNA damage by nucleotide excision repair and that skin ageing is associated with defects in the autophagy process. Moreover, autophagy is constitutively active in the skin epithelium, imparting protection to skin cells against a diverse range of outside insults, thus increasing resistance to environmental stressors. It has also been found that the stress-induced suppression of the autophagy response in experimental settings leads to enhanced apoptosis during photo-ageing upon UV-B exposure and that the maintenance of homeostasis depends on cellular autophagy levels. More recent reports in this domain claim that relieving the oxidative-stress-mediated induction of the ER stress response upon UV-B irradiation protects skin cells from photo-damage effects. The integration of autophagy and the DNA damage response under genotoxic stress is being considered as a meaningful partnership for finding novel molecular targets and devising suitable therapeutic strategies against photo-ageing disorders. Here, we summarize and review the current understanding of the mechanisms governing the intricate interplay between autophagy and the DNA damage response and its regulation by UV-B, the roles of autophagy in regulating the cellular response to UV-B-induced photodamage, and the implications of the modulation of autophagy as a meaningful partnership in the treatment and prevention of photoaging disorders.

NIX-Mediated Mitophagy Promotes Effector Memory Formation in Antigen-Specific CD8+ T Cells

Autophagy plays a critical role in the maintenance of immunological memory. However, the molecular mechanisms involved in autophagy-regulated effector memory formation in CD8⁺ T cells remain unclear. Here we show that deficiency in NIX-dependent mitophagy leads to metabolic defects in effector memory T cells. Deletion of NIX caused HIF1α accumulation and altered cellular metabolism from long-chain fatty acid to short/branched-chain fatty acid oxidation, thereby compromising ATP synthesis during effector memory formation. Preventing HIF1α accumulation restored long-chain fatty acid metabolism and effector memory formation in antigen-specific CD8⁺ T cells. Our study suggests that NIX-mediated mitophagy is critical for effector memory formation in T cells.

Gupta et al. demonstrate that mitophagy mediated by NIX, a mitochondrial outer membrane protein, plays a critical role in CD8⁺ T cell effector memory formation by regulating mitochondrial superoxide-dependent HIF1α protein accumulation and fatty acid metabolism. These findings elucidate the molecular mechanisms regulating T cell effector memory formation against viruses.

Clearance of HIV infection by selective elimination of host cells capable of producing HIV

The RNA genome of the human immunodeficiency virus (HIV) is reverse-transcribed into DNA and integrated into the host genome, resulting in latent infections that are difficult to clear. Here we show an approach to eradicate HIV infections by selective elimination of host cells harboring replication-competent HIV (SECH), which includes viral reactivation, induction of cell death, inhibition of autophagy and the blocking of new infections. Viral reactivation triggers cell death specifically in HIV-1-infected T cells, which is promoted by agents that induce apoptosis and inhibit autophagy. SECH treatments can clear HIV-1 in >50% mice reconstituted with a human immune system, as demonstrated by the lack of viral rebound after withdrawal of treatments, and by adoptive transfer of treated lymphocytes into uninfected humanized mice. Moreover, SECH clears HIV-1 in blood samples from HIV-1-infected patients. Our results suggest a strategy to eradicate HIV infections by selectively eliminating host cells capable of producing HIV.

New chimeric TLR7/NOD2 agonist is a potent adjuvant to induce mucosal immune responses

Background

PRR (Pattern Recognition Receptor) agonists have been widely tested as potent vaccine adjuvants. TLR7 (Toll-Like Receptor 7) and NOD2 (nucleotide-binding oligomerization domain 2) are key innate receptors widely expressed at mucosal levels.

Methods

Here, we evaluated the immunostimulatory properties of a novel hybrid chemical compound designed to stimulate both TLR7 and NOD2 receptors.

Finding

The combined TLR7/NOD2 agonist showed increase efficacy than TLR7L or NOD2L agonists alone or combined in different in vitro models. Dual TLR7/NOD2 agonist efficiently stimulates TLR7 and NOD2, and promotes the maturation and reprogramming of human dendritic cells, as well as the secretion of pro-inflammatory or adaptive cytokines. This molecule also strongly induces autophagy in human cells which is a major intracellular degradation system that delivers cytoplasmic constituents to lysosomes in both MHC class I and II-restricted antigen presentation. In vivo, TLR7/NOD2L agonist is a potent adjuvant after intranasal administration with NP-p24 HIV vaccine, inducing high-quality humoral and adaptive responses both in systemic and mucosal compartments. Use of TLR7/NOD2L adjuvant improves very significantly the protection of mice against an intranasal challenge with a vaccinia virus expressing the p24.

Interpretation

Dual TLR7/NOD2L agonist is a very potent and versatile vaccine adjuvant and promote very efficiently both systemic and mucosal immunity.

Funding

This work was supported by 10.13039/100009060Sidaction.

Role of Autophagy in Lung Inflammation

Autophagy is a cellular recycling system found in almost all types of eukaryotic organisms. The system is made up of a variety of proteins which function to deliver intracellular cargo to lysosomes for formation of autophagosomes in which the contents are degraded. The maintenance of cellular homeostasis is key in the survival and function of a variety of human cell populations. The interconnection between metabolism and autophagy is extensive, therefore it has a role in a variety of different cell functions. The disruption or dysfunction of autophagy in these cell types have been implicated in the development of a variety of inflammatory diseases including asthma. The role of autophagy in non-immune and immune cells both lead to the pathogenesis of lung inflammation. Autophagy in pulmonary non-immune cells leads to tissue remodeling which can develop into chronic asthma cases with long term effects. The role autophagy in the lymphoid and myeloid lineages in the pathology of asthma differ in their functions. Impaired autophagy in lymphoid populations have been shown, in general, to decrease inflammation in both asthma and inflammatory disease models. Many lymphoid cells rely on autophagy for effector function and maintained inflammation. In stark contrast, autophagy deficient antigen presenting cells have been shown to have an activated inflammasome. This is largely characterized by a T_H17 response that is accompanied with a much worse prognosis including granulocyte mediated inflammation and steroid resistance. The cell specificity associated with changes in autophagic flux complicates its targeting for amelioration of asthmatic symptoms. Differing asthmatic phenotypes between T_H2 and T_H17 mediated disease may require different autophagic modulations. Therefore, treatments call for a more cell specific and personalized approach when looking at chronic asthma cases. Viral-induced lung inflammation, such as that caused by SARS-CoV-2, also may involve autophagic modulation leading to inflammation mediated by lung resident cells. In this review, we will be discussing the role of autophagy in non-immune cells, myeloid cells, and lymphoid cells for their implications into lung inflammation and asthma. Finally, we will discuss autophagy's role viral pathogenesis, immunometabolism, and asthma with insights into autophagic modulators for amelioration of lung inflammation.

Antiviral responses of ATG13 to the infection of peste des petits ruminants virus through activation of interferon response

Not only are autophagy-related (ATG) proteins the essential orchestrators of the autophagy machinery, but also they regulate many other cellular pathways. Here, we demonstrated that ATG13 exerted an obviously antiviral activity against the infection of peste des petits ruminants virus (PPRV) in cell culture model. We found that PPRV infection or the treatment with interferon (IFN) against PPRV infection significantly induced ATG13 expression. Mechanistically, ATG13 stimulated interferon expression and the subsequent activation of the JAK-STAT cascade. These activations triggered the transcription of interferon-stimulated genes (ISGs) to exert antiviral activity. Conversely, the loss of ATG13 significantly attenuated the potency of RIG-IN in activating IFN responses. In summary, we have demonstrated that basal ATG13 was involved in host antiviral activities against PPRV infection and the over-expression of ATG13 activated IFN production to inhibit PPRV replication in an unconventional fashion.

Metabolic Reprogramming in CD8+ T Cells During Acute Viral Infections

CD8+ T cells represent one of the most versatile immune cells critical for clearing away viral infections. Due to their important role, CD8+ T cell activation and memory formation during viral infection have been the focus of several studies recently. Although CD8+ T cell activation and memory formation have been associated with metabolic alterations, the molecular understanding behind T cells choosing one type of metabolism over others based on their differentiation stage is still unclear. This review focuses on how the signaling molecules and cellular processes that are characteristic of CD8+ T cell activation and memory formation also play a critical role in selecting specific type of metabolism during viral infections. In addition, we will summarize the epigenetic factors regulating these metabolic alterations.

Maintenance of Germinal Center B Cells by Caspase-9 through Promotion of Apoptosis and Inhibition of Necroptosis

In response to T cell-dependent Ag encounter, naive B cells develop into germinal center (GC) B cells, which can further differentiate into Ab-secreting plasma cells or memory B cells. GC B cells are short lived and are prone to caspase-mediated apoptosis. However, how apoptotic caspases regulate GC B cell fate has not been fully characterized. In this study, we show that mice with B cell-specific knockout of caspase-9 had decreases in GC B cells and Ab production after immunization. Caspase-9-deficient B cells displayed defects in caspase-dependent apoptosis but increases in necroptosis signaling. Additional deletion of Ripk3 restored GC B cells and Ab production in mice with B cell-specific knockout of caspase-9. Our results indicate that caspase-9 plays an important role in the maintenance of Ab responses by promoting apoptosis and inhibiting necroptosis in B cells.

Host-Virus Interaction: How Host Cells Defend against Influenza A Virus Infection

Influenza A viruses (IAVs) are highly contagious pathogens infecting human and numerous animals. The viruses cause millions of infection cases and thousands of deaths every year, thus making IAVs a continual threat to global health. Upon IAV infection, host innate immune system is triggered and activated to restrict virus replication and clear pathogens. Subsequently, host adaptive immunity is involved in specific virus clearance. On the other hand, to achieve a successful infection, IAVs also apply multiple strategies to avoid be detected and eliminated by the host immunity. In the current review, we present a general description on recent work regarding different host cells and molecules facilitating antiviral defenses against IAV infection and how IAVs antagonize host immune responses.

Autophagy in immunity

The molecular machinery of macroautophagy consists of Atg proteins and supports cytoplasmic constituent degradation in lysosomes as its canonical function, phagosome maturation and exocytosis. These different biological processes contribute to cell intrinsic, innate and adaptive immunity. For the respective immune responses, Atg proteins mediate direct pathogen degradation, inflammation restriction, antigen presentation on MHC molecules and survival of memory lymphocyte populations. During adaptive immunity MHC class II presentation of antigens is supported and MHC class I presentation restricted by the macroautophagy machinery. Considering these various functions might allow us to predict the outcome of interventions that manipulate the machinery of Atg proteins as immunotherapies for the benefit of human health.

Regulation of Selective B Cell Autophagy by the Pro-oxidant Adaptor p66SHC

p66SHC is a pro-oxidant member of the SHC family of protein adaptors that acts as a negative regulator of cell survival. In lymphocytes p66SHC exploits both its adaptor and its reactive oxygen species (ROS)-elevating function to antagonize mitogenic and survival signaling and promote apoptosis. As a result, p66SHC deficiency leads to the abnormal expansion of peripheral T and B cells and lupus-like autoimmunity. Additionally, a defect in p66SHC expression is a hallmark of B cell chronic lymphocytic leukemia, where it contributes to the accumulation of long-lived neoplastic cells. We have recently provided evidence that p66SHC exerts a further layer of control on B cell homeostasis by acting as a new mitochondrial LC3-II receptor to promote the autophagic demise of dysfunctional mitochondria. Here we discuss this finding in the context of the autophagic control of B cell homeostasis, development, and differentiation in health and disease.

The role of metabolic checkpoint regulators in B cell survival and transformation

In response to mitogenic stimulation, B cells activate different pro-anabolic signaling pathways such as c-Myc- and mTORC1-dependent networks to satisfy the energetic demands of biomass synthesis and proliferation. In order to preserve viability and function, cell growth cannot progress unchecked and must be adjusted according to the availability of nutrients. Nutrient-sensing proteins such as AMPK antagonize mTORC1 activity in response to starvation. If pro-anabolic signaling pathways are aberrantly activated, B cells may lack the metabolic capacity to accommodate their energetic needs, which can lead to cell death. On the other hand, metabolic hyperactivation is a salient feature of cancer cells, suggesting that mechanisms exist, which allow B cells to cope with metabolic stress. The aim of this review is to discuss how B cells respond to a mismatch between energy supply and demand and what the consequences are of metabolic dysregulation in normal and malignant B cells.

Immune metabolism regulation of the germinal center response

The humoral immune response requires germinal centers to produce high-affinity antigen-specific antibodies that counter pathogens. Numerous studies have provided a better understanding of how metabolic pathways regulate the development, activation and functions of immune cells. Germinal centers are transient, highly dynamic microanatomic structures that develop in lymphoid organs during a T-cell-dependent humoral immune response. Analysis of germinal centers provides an opportunity to understand how metabolic programs control the differentiation and function of highly specialized germinal center B cells and follicular helper CD4⁺ T cells. Targeting immunometabolism during the germinal center response may afford the possibility to improve vaccine design and to develop new therapies to alleviate autoimmunity. In this review, we discuss the major metabolic pathways that are used by germinal center B and T cells, as well as the plasma cells that they produce, all of which are influenced by the microenvironment of this unique structure of the adaptive immune system.

Studies of the metabolic mechanisms involved in antibody production will inform vaccine design and autoimmune disease treatments. Germinal centers (GCs) are transient sites in lymph nodes and the spleen, formed when white blood cells called T-cell lymphocytes respond to infection. GCs act as factories where another lymphocyte group, B cells, proliferates and mutates before producing infection-appropriate antibodies. GCs therefore play a critical role in adaptive immunity, but the metabolic pathways involved are unclear. Laurence Morel and Seung-Chui Choi at the University of Florida, Gainesville, USA, reviewed understanding of the metabolic pathways used by T cells, B cells and the antibodies they produce. The cells within GCs require different energy sources and metabolic pathways according to their developmental stage, to ensure optimal immune responses. The researchers call for extensive profiling of this complex metabolic system.

Plasma cells: You are what you eat

Plasma cells are terminally differentiated B lymphocytes that constitutively secrete antibodies. These antibodies can provide protection against pathogens, and their quantity and quality are the best clinical correlates of vaccine efficacy. As such, plasma cell lifespan is the primary determinant of the duration of humoral immunity. Yet dysregulation of plasma cell function can cause autoimmunity or multiple myeloma. The longevity of plasma cells is primarily dictated by nutrient uptake and non-transcriptionally regulated metabolic pathways. We have previously shown a positive effect of glucose uptake and catabolism on plasma cell longevity and function. In this review, we discuss these findings with an emphasis on nutrient uptake and its effects on respiratory capacity, lifespan, endoplasmic reticulum stress, and antibody secretion in plasma cells. We further discuss how some of these pathways may be dysregulated in multiple myeloma, potentially providing new therapeutic targets. Finally, we speculate on the connection between plasma cell intrinsic metabolism and systemic changes in nutrient availability and metabolic diseases.

Autophagy in the renewal, differentiation and homeostasis of immune cells

Across all branches of the immune system, the process of autophagy is fundamentally important in cellular development, function and homeostasis. Strikingly, this evolutionarily ancient pathway for intracellular recycling has been adapted to enable a high degree of functional complexity and specialization. However, although the requirement for autophagy in normal immune cell function is clear, the mechanisms involved are much less so and encompass control of metabolism, selective degradation of substrates and organelles and participation in cell survival decisions. We review here the crucial functions of autophagy in controlling the differentiation and homeostasis of multiple immune cell types and discuss the potential mechanisms involved.

Polyamines Control eIF5A Hypusination, TFEB Translation, and Autophagy to Reverse B Cell Senescence

Failure to make adaptive immune responses is a hallmark of aging. Reduced B cell function leads to poor vaccination efficacy and a high prevalence of infections in the elderly. Here we show that reduced autophagy is a central molecular mechanism underlying immune senescence. Autophagy levels are specifically reduced in mature lymphocytes, leading to compromised memory B cell responses in old individuals. Spermidine, an endogenous polyamine metabolite, induces autophagy in vivo and rejuvenates memory B cell responses. Mechanistically, spermidine post-translationally modifies the translation factor eIF5A, which is essential for the synthesis of the autophagy transcription factor TFEB. Spermidine is depleted in the elderly, leading to reduced TFEB expression and autophagy. Spermidine supplementation restored this pathway and improved the responses of old human B cells. Taken together, our results reveal an unexpected autophagy regulatory mechanism mediated by eIF5A at the translational level, which can be harnessed to reverse immune senescence in humans.

Autophagy in T Cell Function and Aging

Dysregulation of autophagy with age has been identified as a central mechanism of aging affecting many cells and tissues. T cells do also show decreased activity with age of different autophagic pathways. Here, we will review the current knowledge of the different functions that autophagy has in the regulation of T cell homeostasis, differentiation and function and explore how the age-associated decreased in autophagy activity may contribute to the altered T cell responses that characterize T cell immunosenescence.

Targeting ATG4 in Cancer Therapy

Autophagy is a lysosome-mediated degradation pathway that enables the degradation and recycling of cytoplasmic components to sustain metabolic homoeostasis. Recently, autophagy has been reported to have an astonishing number of connections to cancer, as tumor cells require proficient autophagy in response to metabolic and therapeutic stresses to sustain cell proliferation. Autophagy-related gene 4 (ATG4) is essential for autophagy by affecting autophagosome formation through processing full-length microtubule-associated protein 1A/1B-light chain 3 (pro-LC3) and lipidated LC3. An increasing amount of evidence suggests that ATG4B expression is elevated in certain types of cancer, implying that ATG4B is a potential anticancer target. In this review, we address the central roles of ATG4B in the autophagy machinery and in targeted cancer therapy. Specifically, we discuss how pharmacologically inhibiting ATG4B can benefit cancer therapies.

Emerging views of mitophagy in immunity and autoimmune diseases

Mitophagy is a vital form of autophagy for selective removal of dysfunctional or redundant mitochondria. Accumulating evidence implicates elimination of dysfunctional mitochondria as a powerful means employed by autophagy to keep the immune system in check. The process of mitophagy may restrict inflammatory cytokine secretion and directly regulate mitochondrial antigen presentation and immune cell homeostasis. In this review, we describe distinctive pathways of mammalian mitophagy and highlight recent advances relevant to its function in immunity. In addition, we further discuss the direct and indirect evidence linking mitophagy to inflammation and autoimmunity underlying the pathogenesis of autoimmune diseases including inflammatory bowel diseases (IBD), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC).Abbreviations: AICD: activation induced cell death; AIM2: absent in melanoma 2; ALPL/HOPS: alkaline phosphatase, biomineralization associated; AMA: anti-mitochondrial antibodies; AMFR: autocrine motility factor receptor; ATG: autophagy-related; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CARD: caspase recruitment domain containing; CASP1: caspase 1; CD: Crohn disease; CGAS: cyclic GMP-AMP synthase; CXCL1: C-X-C motif chemokine ligand 1; DEN: diethylnitrosamine; DLAT/PDC-E2: dihydrolipoamide S-acetyltransferase; DNM1L/Drp1: dynamin 1 like; ESCRT: endosomal sorting complexes required for transport; FKBP8: FKBP prolyl isomerase 8; FUNDC1: Fun14 domain containing 1; GABARAP: GABA type A receptor-associated protein; HMGB1: high mobility group box 1; HPIV3: human parainfluenza virus type 3; IBD: inflammatory bowel diseases; IEC: intestinal epithelial cell; IFN: interferon; IL1B/IL-1β: interleukin 1 beta; iNK: invariant natural killer; IRGM: immunity related GTPase M; LIR: LC3-interacting region; LPS: lipopolysaccharide; LRRK2: leucine rich repeat kinase 2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCH5: membrane associated ring-CH-type finger 5; MAVS: mitochondrial antiviral signaling protein; MDV: mitochondria-derived vesicle; MFN1: mitofusin 1; MHC: major histocompatibility complex; MIF: macrophage migration inhibitory factor; mtAP: mitochondrial antigen presentation; mtDNA: mitochondrial DNA; MTOR: mechanistic target of rapamycin kinase; mtROS: mitochondrial ROS; MUL1: mitochondrial E3 ubiquitin protein ligase 1; NBR1: NBR1 autophagy cargo receptor; NFKB/NF-ĸB: nuclear factor kappa B subunit; NK: natural killer; NLR: NOD-like receptor; NLRC4: NLR family CARD domain containing 4; NLRP3: NLR family pyrin domain containing 3; OGDH: oxoglutarate dehydrogenase; OMM: outer mitochondrial membrane; OPTN: optineurin; ox: oxidized; PARK7: Parkinsonism associated deglycase; PBC: primary biliary cirrhosis; PEX13: peroxisomal biogenesis factor 13; PHB/PHB1: prohibitin; PHB2: prohibitin 2; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced kinase 1; PLEKHM1: pleckstrin homology and RUN domain containing M1; PRKN/PARK2: parkin RBR E3 ubiquitin protein ligase; RAB: member RAS oncogene family; RHEB: Ras homolog: mTORC1 binding; RIPK2: receptor interacting serine/threonine kinase 2; RLR: DDX58/RIG-I like receptor; ROS: reactive oxygen species; SBD: small bile ducts; SLC2A1/GLUT1: solute carrier family 2 member 1; SLE: systemic lupus erythematosus; SMURF1: SMAD specific E3 ubiquitin protein ligase 1; SQSTM1/p62: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TCR: T cell receptor; TFAM: transcription factor A: mitochondrial; Th17: T helper 17; TLR9: toll like receptor 9; TMEM173/STING: transmembrane protein 173; TNF/TNF-α: tumor necrosis factor; Ub: ubiquitin; UC: ulcerative colitis; ULK1: unc-51 like autophagy activating kinase 1; WIPI: WD repeat domain: phosphoinositide interacting; ZFYVE1/DFCP1: zinc finger FYVE-type containing 1.

Autophagy: roles in intestinal mucosal homeostasis and inflammation

The intestinal mucosa is a site of multiple stressors and forms the barrier between the internal and external environment. In the intestine, a complex interplay between the microbiota, epithelial barrier and the local immune system maintains homeostasis and promotes a healthy gut. One of the major cellular catabolic processes that regulate this homeostasis is autophagy. Autophagy is required to maintain anti-microbial defense, epithelial barrier integrity and mucosal immune response. Dysregulation of the autophagy process causes disruption of several aspects of the intestinal epithelium and the immune system that can lead to an inappropriate immune response and subsequent inflammation. Genome-wide association studies have found an association between several risk loci in autophagy genes and inflammatory bowel disease. The aim of the current review is to provide an update on the role of autophagy in intestinal mucosal physiology and in the control of inappropriate inflammation.

High ambient temperature dampens adaptive immune responses to influenza A virus infection

Although climate change may expand the geographical distribution of several vector-borne diseases, the effects of environmental temperature in host defense to viral infection in vivo are unknown. Here, we demonstrate that exposure of mice to the high ambient temperature of 36 °C impaired adaptive immune responses against infection with viral pathogens, influenza, Zika, and severe fever with thrombocytopenia syndrome phlebovirus. Following influenza virus infection, the high heat-exposed mice failed to stimulate inflammasome-dependent cytokine secretion and respiratory dendritic cell migration to lymph nodes. Although commensal microbiota composition remained intact, the high heat-exposed mice decreased their food intake and increased autophagy in lung tissue. Induction of autophagy in room temperature-exposed mice severely impaired virus-specific CD8 T cells and antibody responses following respiratory influenza virus infection. In addition, we found that administration of glucose or dietary short-chain fatty acids restored influenza virus-specific adaptive immune responses in high heat-exposed mice. These findings uncover an unexpected mechanism by which ambient temperature and nutritional status control virus-specific adaptive immune responses.

Therapeutic Modulation of Autophagy in Leukaemia and Lymphoma

Haematopoiesis is a tightly orchestrated process where a pool of hematopoietic stem and progenitor cells (HSPCs) with high self-renewal potential can give rise to both lymphoid and myeloid lineages. The HSPCs pool is reduced with ageing resulting in few HSPC clones maintaining haematopoiesis thereby reducing blood cell diversity, a phenomenon called clonal haematopoiesis. Clonal expansion of HSPCs carrying specific genetic mutations leads to increased risk for haematological malignancies. Therefore, it comes as no surprise that hematopoietic tumours develop in higher frequency in elderly people. Unfortunately, elderly patients with leukaemia or lymphoma still have an unsatisfactory prognosis compared to younger ones highlighting the need to develop more efficient therapies for this group of patients. Growing evidence indicates that macroautophagy (hereafter referred to as autophagy) is essential for health and longevity. This review is focusing on the role of autophagy in normal haematopoiesis as well as in leukaemia and lymphoma development. Attenuated autophagy may support early hematopoietic neoplasia whereas activation of autophagy in later stages of tumour development and in response to a variety of therapies rather triggers a pro-tumoral response. Novel insights into the role of autophagy in haematopoiesis will be discussed in light of designing new autophagy modulating therapies in hematopoietic cancers.

Molecular regulation of peripheral B cells and their progeny in immunity

In this review, Boothby et al. summarize some salient advances toward elucidation of the molecular programming of the fate choices and function of B cells in the periphery. They also note unanswered questions that pertain to differences among subsets of B lymphocytes and plasma cells.

Mature B lymphocytes are crucial components of adaptive immunity, a system essential for the evolutionary fitness of mammals. Adaptive lymphocyte function requires an initially naïve cell to proliferate extensively and its progeny to have the capacity to assume a variety of fates. These include either terminal differentiation (the long-lived plasma cell) or metastable transcriptional reprogramming (germinal center and memory B cells). In this review, we focus principally on the regulation of differentiation and functional diversification of the “B2” subset. An overview is combined with an account of more recent advances, including initial work on mechanisms that eliminate DNA methylation and potential links between intracellular metabolites and chromatin editing.

Autophagy and Immune Tolerance

The immune system plays a critical role in defense against invading pathogens, and its function must be strictly controlled to maintain intracellular homeostasis. Once suffering microbial invasion or receiving danger signals, the immune system initiates the responses timely. After the threat removal, the immune system should be shut down to avoid the harm caused by excessive immune activation. Additionally, the immune system needs to be internally adjusted so that it does not respond to self-antigens to avoid autoimmune diseases. The states of nonresponse in immunity are termed as immune tolerance. Numerous studies indicated that macroautophagy (hereafter named as autophagy) is involved in T cells and B cells related immune tolerance. Recently, more and more researches demonstrated that autophagy is not only capable of nonselective degradation of cellular macromolecular components but also responsible for sorting and transporting autophagic substrates through a group of cargo receptors for selective degradation, which is called as selective autophagy. Recent studies indicated that selective autophagy can effectively regulate the immune tolerance and avoid over-activation of immune response by targeting multiple receptors and effectors of immune cells. In this chapter, we will focus on how autophagy participates explicitly in the adaptive and innate immune tolerance.

Autophagy and Immune-Related Diseases

Autophagy is an intracellular degradation and recycling machinery by which cellular materials are delivered to the lysosome for disposal. Beyond lysosomal degradation, autophagy genes play additional roles in secretion and membrane-trafficking pathways. Ranging from cell-intrinsic and cell-type-specific regulation of innate inflammatory signaling pathways to intercellular cross talk through secretion of soluble factors (e.g., shaping the MHC immunopeptidome for T cell response, etc.), autophagy exerts multiple functions in driving inflammation and modulating the pathological progression of immune-related disorders such as neurodegenerative diseases, inflammatory bowel diseases, autoimmunity, and metabolic diseases. Notably, owing to the complexity of autophagy process involving multiple proteins and stepwise assembly of protein complexes, noncanonical forms of autophagy or autophagic proteins, which function beyond autophagy, are equally important in the maintenance of cellular homeostasis and pathogenesis. This chapter summarizes the most up-to-date findings of autophagy proteins in the regulation of immune-related diseases. Understanding of the autophagy machinery offers therapeutic strategies for treating inflammatory diseases.

Cross-talk between signal transduction and metabolism in B cells

Mounting evidence demonstrates that specific metabolic adaptations are needed to support B cell development and differentiation and to enable B cells to thrive in different environments. Mitogen induced activation of intracellular signaling pathways triggers nutrient uptake and metabolic remodeling to meet the cells' current needs. Reciprocally, changes in the metabolic composition of the environment, or in intracellular metabolite levels, can modulate signal transduction and thus shape cell fate and function. In summary, signal transduction and metabolic pathways operate within an integrated network to cooperatively define cellular outcomes.

Regulation of metabolic supply and demand during B cell activation and subsequent differentiation

B cell activation and differentiation are associated with marked changes in proliferative and effector functions. Each stage of B cell differentiation thus has unique metabolic demands. New studies have provided insight on how nutrient uptake and usage by B cells are regulated by B cell receptor signals, autophagy, mammalian target of rapamycin, and transcriptional control of transporters and rate-limiting enzymes. A recurring theme is that these pathways play distinct roles ranging from survival to antibody production, depending on the B cell fate. We review recently published data that define how these pathways control metabolic flux in B cells, with a particular emphasis on genetic and in vivo evidence. We further discuss how lessons from T cells can guide future directions.

ATG5 is required for B cell polarization and presentation of particulate antigens

The involvement of macroautophagy/autophagy proteins in B-cell receptor (BCR) trafficking, although suspected, is not well understood. We show that ATG5 (autophagy related 5) contributes to BCR polarization after stimulation and internalization into LAMP1 (lysosomal-associated membrane protein 1)⁺ and major histocompatibility complex class II (MHC-II)⁺ compartments. BCR polarization is crucial in the context of immobilized antigen processing. Moreover, antigen presentation to cognate T cells is decreased in the absence of ATG5 when the model antigen OVAL/ovalbumin is provided in an immobilized form in contrast to the normal presentation of soluble OVAL. We further show that ATG5 is required for centrosome polarization and actin nucleation in the immune synapse area. This event is accompanied by an increased interaction between ATG16L1 (autophagy related 16-like 1 [S. cerevisiae]) and the microtubule-organizing center-associated protein PCM1 (pericentriolar material 1). In the human B cell line BJAB, PCM1 is required for BCR polarization after stimulation. We thus propose that the ATG12 (autophagy related 12)-ATG5-ATG16L1 complex under BCR stimulation allows its interaction with PCM1 and consequently facilitates centrosome relocalization to the immune synapse, optimizing the presentation of particulate antigens. Abbreviations: ACTB: actin beta; ACTR2/3: ARP2/3 actin-related protein 2/3; APC: antigen-presenting cells; ATG: autophagy-related; BCR: B cell receptor; BECN1/Beclin 1: beclin 1, autophagy related; CDC42: cell division cycle 42; Cr2: complement receptor 2; CSFE: carboxyfluorescein succinimidyl ester; DAPI: 4',6-diamidino-2-phenylindole dihydrochloride; EEA1: early endosome antigen 1; ELISA: enzyme-linked immunosorbent assay; FITC: fluorescein isothyocyanate; GC: germinal center; GJA1/CX3: gap junction protein, alpha 1; Ig: immunoglobulin; LAMP1: lysosomal-associated membrane protein 1; LAP: LC3-associated phagocytosis; LM: littermate; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK/ERK: mitogen activated protein kinase; MHC-II: major histocompatibility complex class II; MIIC: MHC class II compartment; OVAL: ovalbumin; PBS: phosphate-buffered saline; PCM1: pericentriolar material 1; PtdIns3K: phosphatidylinositol 3-kinase; PTPRC/CD45RB/B220; Protein tyrosine phosphatase, receptor type, C; SYK: spleen tyrosine kinase; TBS: Tris-buffered saline; TCR: T cell receptor; ULK1: unc-51 like kinase 1.

The pro-oxidant adaptor p66SHC promotes B cell mitophagy by disrupting mitochondrial integrity and recruiting LC3-II

Macroautophagy/autophagy has emerged as a central process in lymphocyte homeostasis, activation and differentiation. Based on our finding that the p66 isoform of SHC1 (p66SHC) pro-apoptotic ROS-elevating SHC family adaptor inhibits MTOR signaling in these cells, here we investigated the role of p66SHC in B-cell autophagy. We show that p66SHC disrupts mitochondrial function through its CYCS (cytochrome c, somatic) binding domain, thereby impairing ATP production, which results in AMPK activation and enhanced autophagic flux. While p66SHC binding to CYCS is sufficient for triggering apoptosis, p66SHC-mediated autophagy additionally depends on its ability to interact with membrane-associated LC3-II through a specific binding motif within its N terminus. Importantly, p66SHC also has an impact on mitochondria homeostasis by inducing mitochondrial depolarization, protein ubiquitination at the outer mitochondrial membrane, and local recruitment of active AMPK. These events initiate mitophagy, whose full execution relies on the role of p66SHC as an LC3-II receptor which brings phagophore membranes to mitochondria. Importantly, p66SHC also promotes hypoxia-induced mitophagy in B cells. Moreover, p66SHC deficiency enhances B cell differentiation to plasma cells, which is controlled by intracellular ROS levels and the hypoxic germinal center environment. The results identify mitochondrial p66SHC as a novel regulator of autophagy and mitophagy in B cells and implicate p66SHC-mediated coordination of autophagy and apoptosis in B cell survival and differentiation. Abbreviations: ACTB: actin beta; AMPK: AMP-activated protein kinase; ATP: adenosine triphosphate; ATG: autophagy-related; CYCS: cytochrome c, somatic; CLQ: chloroquine; COX: cyclooxygenase; CTR: control; GFP: green fluorescent protein; HIFIA/Hif alpha: hypoxia inducible factor 1 subunit alpha; IMS: intermembrane space; LIR: LC3 interacting region; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR/mTOR: mechanistic target of rapamycin kinase; OA: oligomycin and antimycin A; OMM: outer mitochondrial membrane; PHB: prohibitin; PBS: phosphate-buffered saline; PINK1: PTEN induced putative kinase 1; RFP: red fluorescent protein; ROS: reactive oxygen species; SHC: src Homology 2 domain-containing transforming protein; TMRM: tetramethylrhodamine, methyl ester; TOMM: translocase of outer mitochondrial membrane; ULK1: unc-51 like autophagy activating kinase 1; WT: wild-type.