Metabolic gatekeepers to safeguard against autoimmunity and oncogenic B cell transformation

Fuelling B cells: dynamic regulation of B cell metabolism

B cells experience extreme alterations in their metabolism throughout their life cycle, from naïve B cells, which have minimal activity, to germinal centre (GC) B cells, which proliferate at the fastest rate of all cells, to long-lived plasma cells with very high levels of protein production that can persist for decades. The underpinning of these transitions remains incompletely understood, and a key question is how utilisation of fuel source supports B cell metabolism. For example, GC B cells, unlike almost all rapidly proliferating cells, mainly use fatty acid oxidation rather than glycolysis. However, following differentiation to plasma cells, their metabolism switches towards a high rate of glucose consumption to aid antibody production. In this review, we discuss the key metabolic pathways in B cells, linking them to cellular signalling events and placing them in the context of disease and therapeutic potential.

Metabolic regulation of the immune system in health and diseases: mechanisms and interventions

Metabolism, including glycolysis, oxidative phosphorylation, fatty acid oxidation, and other metabolic pathways, impacts the phenotypes and functions of immune cells. The metabolic regulation of the immune system is important in the pathogenesis and progression of numerous diseases, such as cancers, autoimmune diseases and metabolic diseases. The concept of immunometabolism was introduced over a decade ago to elucidate the intricate interplay between metabolism and immunity. The definition of immunometabolism has expanded from chronic low-grade inflammation in metabolic diseases to metabolic reprogramming of immune cells in various diseases. With immunometabolism being proposed and developed, the metabolic regulation of the immune system can be gradually summarized and becomes more and more clearer. In the context of many diseases including cancer, autoimmune diseases, metabolic diseases, and many other disease, metabolic reprogramming occurs in immune cells inducing proinflammatory or anti-inflammatory effects. The phenotypic and functional changes of immune cells caused by metabolic regulation further affect and development of diseases. Based on experimental results, targeting cellular metabolism of immune cells becomes a promising therapy. In this review, we focus on immune cells to introduce their metabolic pathways and metabolic reprogramming, and summarize how these metabolic pathways affect immune effects in the context of diseases. We thoroughly explore targets and treatments based on immunometabolism in existing studies. The challenges of translating experimental results into clinical applications in the field of immunometabolism are also summarized. We believe that a better understanding of immune regulation in health and diseases will improve the management of most diseases.

Exploration of the underlying mechanism of Astragaloside III in attenuating immunosuppression via network pharmacology and vitro/vivo pharmacological validation

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus mongholicus Bunge (AM, recorded in http://www.worldfloraonline.org, 2023-08-03) is a kind of medicine food homology plant with a long medicinal history in China. Astragaloside III (AS-III) has immunomodulatory effects and is one of the most active components in AM. However, its underlying mechanism of action is still not fully explained.

AIM OF THE STUDY

The research was designed to discuss the protective effects of AS-III on immunosuppression and to elucidate its prospective mechanism.

MATERIALS AND METHODS

Molecular docking methods and network pharmacology analysis were used to comprehensively investigate potential targets and relative pathways for AS-III and immunosuppression. In order to study and verify the pharmacological activity and mechanism of AS-III in alleviating immunosuppression, immunosuppression mouse model induced by cyclophosphamide (CTX) in vivo and macrophage RAW264.7 cell model induced by hypoxia/lipopolysaccharide (LPS) in vitro were used.

RESULTS

A total of 105 common targets were obtained from the AS-III-related and immunosuppression-related target networks. The results of network pharmacology and molecular docking demonstrate that AS-III may treat immunosuppression through by regulating glucose metabolism-related pathways such as regulation of lipolysis in adipocytes, carbohydrate digestion and absorption, cGMP-PKG signaling pathway, central carbon metabolism in cancer together with HIF-1 pathway. The results of molecular docking showed that AS-III has good binding relationship with LDHA, AKT1 and HIF1A. In CTX-induced immunosuppressive mouse model, AS-III had a significant protective effect on the reduction of body weight, immune organ index and hematological indices. It can also protect immune organs from damage. In addition, AS-III could significantly improve the expression of key proteins involved in energy metabolism and serum inflammatory factors. To further validate the animal results, an initial inflammatory/immune response model of macrophage RAW264.7 cells was constructed through hypoxia and LPS. AS-III improved the immune function of macrophages, reduced the release of NO, TNF-α, IL-1β, PDHK-1, LDH, lactate, HK, PK and GLUT-1, and restored the decrease of ATP caused by hypoxia. Besides, AS-III was also demonstrated that it could inhibit the increase of HIF-1α, PDHK-1 and LDH by adding inhibitors and agonists.

CONCLUSIONS

In this study, the main targets of AS-III for immunosuppressive therapy were initially analyzed. AS-III was systematically confirmed to attenuates immunosuppressive state through the HIF-1α/PDHK-1 pathway. These findings offer an experimental foundation for the use of AS-III as a potential candidate for the treatment of immunosuppression.

BAFF neutralization impairs the autoantibody-mediated clearance of dead adipocytes and aggravates obesity-induced insulin resistance

B cell-activating factor (BAFF) is a critical TNF-family cytokine that regulates homeostasis and peripheral tolerance of B2 cells. BAFF overproduction promotes autoantibody generation and autoimmune diseases. During obesity, BAFF is predominantly produced by white adipose tissue (WAT), and IgG autoantibodies against adipocytes are identified in the WAT of obese humans. However, it remains to be determined if the autoantibodies formed during obesity affect WAT remodeling and systemic insulin resistance. Here, we show that IgG autoantibodies are generated in high-fat diet (HFD)-induced obese mice that bind to apoptotic adipocytes and promote their phagocytosis by macrophages. Next, using murine models of obesity in which the gonadal WAT undergoes remodeling, we found that BAFF neutralization depleted IgG autoantibodies, increased the number of dead adipocytes, and exacerbated WAT inflammation and insulin resistance. RNA sequencing of the stromal vascular fraction from the WAT revealed decreased expression of immunoglobulin light-chain and heavy-chain variable genes suggesting a decreased repertoire of B cells after BAFF neutralization. Further, the B cell activation and the phagocytosis pathways were impaired in the WAT of BAFF-neutralized mice. In vitro, plasma IgG fractions from BAFF-neutralized mice reduced the phagocytic clearance of apoptotic adipocytes. Altogether, our study suggests that IgG autoantibodies developed during obesity, at least in part, dampens exacerbated WAT inflammation and systemic insulin resistance.

IL-17B alleviates the pathogenesis of systemic lupus erythematosus by inhibiting FASN-mediated differentiation of B cells

The interleukin 17 (IL-17) family of cytokines has emerged as a critical player in autoimmune disease, including systemic lupus erythematosus (SLE). However, the role of IL-17B, a poorly understood cytokine, in the pathogenesis of SLE is still not known. In this study, we investigated the role of IL-17B in the activation and differentiation of B cells, and the pathogenesis of SLE. Intriguingly, IL-17B deficiency aggravated disease in lupus-prone mice and promoted the activation of B cells and the differentiation of germinal center B cells and plasma cells, while recombinant mouse IL-17B (rmIL-17B) significantly alleviated disease in lupus-prone mice. Mechanistically, rmIL-17B inhibited the activation of the Toll-like receptor and interferon pathways in B cells by downregulating fatty acid synthase-mediated (FASN-mediated) lipid metabolism. Loss of FASN significantly alleviated the disease in lupus-prone mice and inhibited the activation and differentiation of B cells. In addition, B cells had greater FASN expression and lower IL-17RB levels in patients with SLE than in healthy controls. Our study describes the role of IL-17B in regulating B cell activation and differentiation, and alleviating the onset of SLE. These findings will lay a theoretical foundation for further understanding of the pathogenesis of SLE.

Concepts in B cell acute lymphoblastic leukemia pathogenesis

B cell acute lymphoblastic leukemia (B-ALL) arises from genetic alterations impacting B cell progenitors, ultimately leading to clinically overt disease. Extensive collaborative efforts in basic and clinical research have significantly improved patient prognoses. Nevertheless, a subset of patients demonstrate resistance to conventional chemotherapeutic approaches and emerging immunotherapeutic interventions. This review highlights the mechanistic underpinnings governing B-ALL transformation. Beginning with exploring normative B cell lymphopoiesis, we delineate the influence of recurrent germline and somatic genetic aberrations on the perturbation of B cell progenitor differentiation and protumorigenic signaling, thereby facilitating the neoplastic transformation underlying B-ALL progression. Additionally, we highlight recent advances in the multifaceted landscape of B-ALL, encompassing metabolic reprogramming, microbiome influences, inflammation, and the discernible impact of socioeconomic and racial disparities on B-ALL transformation and patient survival.

Mitochondria: the gatekeepers between metabolism and immunity

Metabolism and immunity are crucial monitors of the whole-body homeodynamics. All cells require energy to perform their basic functions. One of the most important metabolic skills of the cell is the ability to optimally adapt metabolism according to demand or availability, known as metabolic flexibility. The immune cells, first line of host defense that circulate in the body and migrate between tissues, need to function also in environments in which nutrients are not always available. The resilience of immune cells consists precisely in their high adaptive capacity, a challenge that arises especially in the framework of sustained immune responses. Pubmed and Scopus databases were consulted to construct the extensive background explored in this review, from the Kennedy and Lehninger studies on mitochondrial biochemistry of the 1950s to the most recent findings on immunometabolism. In detail, we first focus on how metabolic reconfiguration influences the action steps of the immune system and modulates immune cell fate and function. Then, we highlighted the evidence for considering mitochondria, besides conventional cellular energy suppliers, as the powerhouses of immunometabolism. Finally, we explored the main immunometabolic hubs in the organism emphasizing in them the reciprocal impact between metabolic and immune components in both physiological and pathological conditions.

B Cells Dynamic in Aging and the Implications of Nutritional Regulation

Aging negatively affects B cell production, resulting in a decrease in B-1 and B-2 cells and impaired antibody responses. Age-related B cell subsets contribute to inflammation. Investigating age-related alterations in the B-cell pool and developing targeted therapies are crucial for combating autoimmune diseases in the elderly. Additionally, optimal nutrition, including carbohydrates, amino acids, vitamins, and especially lipids, play a vital role in supporting immune function and mitigating the age-related decline in B cell activity. Research on the influence of lipids on B cells shows promise for improving autoimmune diseases. Understanding the aging B-cell pool and considering nutritional interventions can inform strategies for promoting healthy aging and reducing the age-related disease burden.

PD-1 instructs a tumor-suppressive metabolic program that restricts glycolysis and restrains AP-1 activity in T cell lymphoma

The PDCD1-encoded immune checkpoint receptor PD-1 is a key tumor suppressor in T cells that is recurrently inactivated in T cell non-Hodgkin lymphomas (T-NHLs). The highest frequencies of PDCD1 deletions are detected in advanced disease, predicting inferior prognosis. However, the tumor-suppressive mechanisms of PD-1 signaling remain unknown. Here, using tractable mouse models for T-NHL and primary patient samples, we demonstrate that PD-1 signaling suppresses T cell malignancy by restricting glycolytic energy and acetyl coenzyme A (CoA) production. In addition, PD-1 inactivation enforces ATP citrate lyase (ACLY) activity, which generates extramitochondrial acetyl-CoA for histone acetylation to enable hyperactivity of activating protein 1 (AP-1) transcription factors. Conversely, pharmacological ACLY inhibition impedes aberrant AP-1 signaling in PD-1-deficient T-NHLs and is toxic to these cancers. Our data uncover genotype-specific vulnerabilities in PDCD1-mutated T-NHL and identify PD-1 as regulator of AP-1 activity.

Elevated glucose metabolism driving pro-inflammatory response in B cells contributes to the progression of type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease characterized by the immune system's failure to maintain self-tolerance, resulting in the autoimmune destruction of pancreatic beta cells. Although T1D has conventionally been viewed as a T-cell-dominant disease, recent research has emphasized the contribution of B cells in the onset of the disease. However, the mechanism underlying aberrant B cell responses remains unknown. B cell metabolism is a crucial prerequisite for B cell function and the development of adaptive immune responses. Here, we investigated the metabolic features of B cells, first in a cross-sectional cohort and subsequently in non-obese diabetic (NOD) mice, and revealed that there is an increased frequency of high-glucose-avidity (2-NBDGhigh) B cell population that may contribute to T1D progression. Further characterization of the metabolic, transcriptional and functional phenotype of B cells in NOD mice found that elevated glucose avidity is associated with a greater capacity for co-stimulation, proliferation and inflammatory cytokine production. Mechanistically, elevated Myc signaling orchestrated the glucose metabolism and the pro-inflammatory response of B cells in T1D. In vitro experiments demonstrated that pharmacological inhibition of glucose metabolism using metformin and 2-DG reduced pro-inflammatory cytokine production and B cell proliferation. Moreover, the combination of these inhibitors successfully delayed insulitis development, onset of diabetes, and improved high blood glucose levels in streptozotocin (STZ)-induced diabetic mice model. Taken together, our work has uncovered these high-glucose-avidity B cells as novel adjuvant diagnostic and therapeutic targets for T1D.

B cell metabolism in autoimmune diseases: signaling pathways and interventions

Autoimmune diseases are heterogeneous disorders believed to stem from the immune system's inability to distinguish between auto- and foreign- antigens. B lymphocytes serve a crucial role in humoral immunity as they generate antibodies and present antigens. Dysregulation of B cell function induce the onset of autoimmune disorders by generating autoantibodies and pro-inflammatory cytokines, resulting in an imbalance in immune regulation. New research in immunometabolism shows that cellular metabolism plays an essential role in controlling B lymphocytes immune reactions by providing the energy and substrates for B lymphocytes activation, differentiation, and function. However, dysregulated immunometabolism lead to autoimmune diseases by disrupting self-tolerance mechanisms. This review summarizes the latest research on metabolic reprogramming of B lymphocytes in autoimmune diseases, identifying crucial pathways and regulatory factors. Moreover, we consider the potential of metabolic interventions as a promising therapeutic strategy. Understanding the metabolic mechanisms of B cells brings us closer to developing novel therapies for autoimmune disorders.

Distinct metabolic requirements regulate B cell activation and germinal center responses

Following infection or vaccination, activated B cells at extrafollicular sites or within germinal centers (GCs) undergo vigorous clonal proliferation. Proliferating lymphocytes have been shown to undertake lactate dehydrogenase A (LDHA)-dependent aerobic glycolysis; however, the specific role of this metabolic pathway in a B cell transitioning from a naïve to a highly proliferative, activated state remains poorly defined. Here, we deleted LDHA in a stage-specific and cell-specific manner. We find that ablation of LDHA in a naïve B cell did not profoundly affect its ability to undergo a bacterial lipopolysaccharide-induced extrafollicular B cell response. On the other hand, LDHA-deleted naïve B cells had a severe defect in their capacities to form GCs and mount GC-dependent antibody responses. In addition, loss of LDHA in T cells severely compromised B cell-dependent immune responses. Strikingly, when LDHA was deleted in activated, as opposed to naïve, B cells, there were only minimal effects on the GC reaction and in the generation of high-affinity antibodies. These findings strongly suggest that naïve and activated B cells have distinct metabolic requirements that are further regulated by niche and cellular interactions.

ARID5B regulates fatty acid metabolism and proliferation at the Pre-B cell stage during B cell development

During B cell development in bone marrow, large precursor B cells (large Pre-B cells) proliferate rapidly, exit the cell cycle, and differentiate into non-proliferative (quiescent) small Pre-B cells. Dysregulation of this process may result in the failure to produce functional B cells and pose a risk of leukemic transformation. Here, we report that AT rich interacting domain 5B (ARID5B), a B cell acute lymphoblastic leukemia (B-ALL) risk gene, regulates B cell development at the Pre-B stage. In both mice and humans, we observed a significant upregulation of ARID5B expression that initiates at the Pre-B stage and is maintained throughout later stages of B cell development. In mice, deletion of Arid5b in vivo and ex vivo exhibited a significant reduction in the proportion of immature B cells but an increase in large and small Pre-B cells. Arid5b inhibition ex vivo also led to an increase in proliferation of both Pre-B cell populations. Metabolic studies in mouse and human bone marrow revealed that fatty acid uptake peaked in proliferative B cells then decreased during non-proliferative stages. We showed that Arid5b ablation enhanced fatty acid uptake and oxidation in Pre-B cells. Furthermore, decreased ARID5B expression was observed in tumor cells from B-ALL patients when compared to B cells from non-leukemic individuals. In B-ALL patients, ARID5B expression below the median was associated with decreased survival particularly in subtypes originating from Pre-B cells. Collectively, our data indicated that Arid5b regulates fatty acid metabolism and proliferation of Pre-B cells in mice, and reduced expression of ARID5B in humans is a risk factor for B cell leukemia.

IGFBP7 Fuels the Glycolytic Metabolism in B-Cell Precursor Acute Lymphoblastic Leukemia by Sustaining Activation of the IGF1R-Akt-GLUT1 Axis

Increased glycolytic metabolism plays an important role in B-cell precursor Acute Lymphoblastic Leukemia (BCP-ALL). We previously showed that IGFBP7 exerts mitogenic and prosuvival effects in ALL by promoting IGF1 receptor (IGF1R) permanence on the cell surface, thus prolonging Akt activation upon IGFs/insulin stimulation. Here, we show that sustained activation of the IGF1R-PI3K-Akt axis concurs with GLUT1 upregulation, which enhances energy metabolism and increases glycolytic metabolism in BCP-ALL. IGFBP7 neutralization with a monoclonal antibody or the pharmacological inhibition of the PI3K-Akt pathway was shown to abrogate this effect, restoring the physiological levels of GLUT1 on the cell surface. The metabolic effect described here may offer an additional mechanistic explanation for the strong negative impact seen in ALL cells in vitro and in vivo after the knockdown or antibody neutralization of IGFBP7, while reinforcing the notion that it is a valid target for future therapeutic interventions.

Enhanced protein synthesis is a defining requirement for neonatal B cell development

The LIN28B RNA binding protein exhibits an ontogenically restricted expression pattern and is a key molecular regulator of fetal and neonatal B lymphopoiesis. It enhances the positive selection of CD5+ immature B cells early in life through amplifying the CD19/PI3K/c-MYC pathway and is sufficient to reinitiate self-reactive B-1a cell output when ectopically expressed in the adult. In this study, interactome analysis in primary B cell precursors showed direct binding by LIN28B to numerous ribosomal protein transcripts, consistent with a regulatory role in cellular protein synthesis. Induction of LIN28B expression in the adult setting is sufficient to promote enhanced protein synthesis during the small Pre-B and immature B cell stages, but not during the Pro-B cell stage. This stage dependent effect was dictated by IL-7 mediated signaling, which masked the impact of LIN28B through an overpowering stimulation on the c-MYC/protein synthesis axis in Pro-B cells. Importantly, elevated protein synthesis was a distinguishing feature between neonatal and adult B cell development that was critically supported by endogenous Lin28b expression early in life. Finally, we used a ribosomal hypomorphic mouse model to demonstrate that subdued protein synthesis is specifically detrimental for neonatal B lymphopoiesis and the output of B-1a cells, without affecting B cell development in the adult. Taken together, we identify elevated protein synthesis as a defining requirement for early-life B cell development that critically depends on Lin28b. Our findings offer new mechanistic insights into the layered formation of the complex adult B cell repertoire.

Proteomic Profiling of Cryoglobulinemia

Objective

We aimed to explore and identify candidate protein biomarkers of cryoglobulinemia (CGE) in disease control patients with negative cryoglobulin (DC) or healthy controls (HCs).

Methods

The tandem mass tag (TMT)-labeled serum quantitative proteomics approach was used to identify differentially expressed proteins between the CGE and DC groups. Ingenuity pathway analysis was used for functional annotation of differentially expressed proteins. Biomarker candidates were validated in another cohort using the parallel reaction monitoring (PRM) method. Apolipoprotein A1 (APOA1), apolipoprotein CIII (APOC3), adiponectin, and proprotein convertase subtilisin/kexin type-9 (PCSK9), which represent key proteins involved in the cholesterol metabolism pathway, were further verified in an increased number of samples by enzyme-linked immunosorbent assay (ELISA).

Results

A total of 1004 proteins were identified, of which 109 proteins were differentially expressed between the CGE and DC groups. These differentially expressed proteins were primarily involved in hepatic fibrosis/hepatic stellate cell activation and immune/inflammation-related pathways. In the disease and biofunction analysis, these proteins were mainly associated with the adhesion of blood cells, leukocyte migration, cholesterol transport, and transport of lipids. Twelve candidate biomarkers were validated by PRM-based proteomics, and proteins involved in the cholesterol metabolism pathway were further verified. APOA1, APOC3, adiponectin and PCSK9 concentrations were increased in CGE patients compared with healthy controls (P=0.0123, 0.1136, 0.5760, and 0.0019, respectively).

Conclusion

This report describes the first application of a TMT-PRM-ELISA workflow to identify and validate CGE-specific biomarkers in serum. APOA1 and PCSK9 have been confirmed to be increased in CGE patients, demonstrating that proteins involved in cholesterol metabolism are also implicated in the development of CGE. These findings contribute to pathogenesis research and biomarker discovery in CGE.

B cell-specific deletion of Crif1 drives lupus-like autoimmunity by activation of IL-17, IL-6, and pathogenic Tfh cells

OBJECTIVE

CR6-interacting factor 1 (Crif1) is a nuclear transcriptional regulator and a mitochondrial inner membrane protein; however, its functions in B lymphocytes have been poorly defined. In this study, we investigated the effects of Crif1 on B-cell metabolic regulation, cell function, and autoimmune diseases.

METHODS

Using mice with B cell-specific deletion of Crif1 (Crif1^ΔCD19 ), we assessed the relevance of Crif1 function for lupus disease parameters including anti-double-stranded DNA, cytokines, and kidney pathology. RNA sequencing was performed on B cells from Crif1^ΔCD19 mice. The phenotypic and metabolic changes in immune cells were evaluated in Crif1^ΔCD19 mice. Roquin^san/+ mice crossed with Crif1^ΔCD19 mice were monitored to assess the functionality of Crif1-deficient B cells in lupus development.

RESULTS

Crif1^ΔCD19 mice showed an autoimmune lupus-like phenotype, including high levels of autoantibodies to double-stranded DNA and severe lupus nephritis with increased mesangial hypercellularity. While loss of Crif1 in B cells showed impaired mitochondrial oxidative function, Crif1-deficient B cells promoted the production of IL-17 and IL-6 and was more potent in helping T cells develop into T follicular helper cells. In an autoimmune lupus mouse model, depletion of Crif1 in B cells exacerbated lupus severity and Crif1 overexpression prevented lupus development in Roquin^san/san mice.

CONCLUSION

These results showed that Crif1 was negatively correlated with disease severity, and overexpression of Crif1 ameliorated disease development. Our findings suggest that Crif1 is essential for preventing lupus development by maintaining B cell self-tolerance.

Metabolic Program of Regulatory B Lymphocytes and Influence in the Control of Malignant and Autoimmune Situations

Metabolic pathways have been studied for a while in eukaryotic cells. During glycolysis, glucose enters into the cells through the Glut1 transporter to be phosphorylated and metabolized generating ATP molecules. Immune cells can use additional pathways to adapt their energetic needs. The pentose phosphate pathway, the glutaminolysis, the fatty acid oxidation and the oxidative phosphorylation generate additional metabolites to respond to the physiological requirements. Specifically, in B lymphocytes, these pathways are activated to meet energetic demands in relation to their maturation status and their functional orientation (tolerance, effector or regulatory activities). These metabolic programs are differentially involved depending on the receptors and the co-activation molecules stimulated. Their induction may also vary according to the influence of the microenvironment, i.e. the presence of T cells, cytokines … promoting the expression of particular transcription factors that direct the energetic program and modulate the number of ATP molecule produced. The current review provides recent advances showing the underestimated influence of the metabolic pathways in the control of the B cell physiology, with a particular focus on the regulatory B cells, but also in the oncogenic and autoimmune evolution of the B cells.

Deletion of Glut1 in early postnatal cartilage reprograms chondrocytes toward enhanced glutamine oxidation

Glucose metabolism is fundamental for the functions of all tissues, including cartilage. Despite the emerging evidence related to glucose metabolism in the regulation of prenatal cartilage development, little is known about the role of glucose metabolism and its biochemical basis in postnatal cartilage growth and homeostasis. We show here that genetic deletion of the glucose transporter Glut1 in postnatal cartilage impairs cell proliferation and matrix production in growth plate (GPs) but paradoxically increases cartilage remnants in the metaphysis, resulting in shortening of long bones. On the other hand, articular cartilage (AC) with Glut1 deficiency presents diminished cellularity and loss of proteoglycans, which ultimately progress to cartilage fibrosis. Moreover, predisposition to Glut1 deficiency severely exacerbates injury-induced osteoarthritis. Regardless of the disparities in glucose metabolism between GP and AC chondrocytes under normal conditions, both types of chondrocytes demonstrate metabolic plasticity to enhance glutamine utilization and oxidation in the absence of glucose availability. However, uncontrolled glutamine flux causes collagen overmodification, thus affecting extracellular matrix remodeling in both cartilage compartments. These results uncover the pivotal and distinct roles of Glut1-mediated glucose metabolism in two of the postnatal cartilage compartments and link some cartilage abnormalities to altered glucose/glutamine metabolism.

PON2 subverts metabolic gatekeeper functions in B cells to promote leukemogenesis

Unlike other cell types, developing B cells undergo multiple rounds of somatic recombination and hypermutation to evolve high-affinity antibodies. Reflecting the high frequency of DNA double-strand breaks, adaptive immune protection by B cells comes with an increased risk of malignant transformation. B lymphoid transcription factors (e.g., IKZF1 and PAX5) serve as metabolic gatekeepers by limiting glucose to levels insufficient to fuel transformation. We here identified aberrant expression of the lactonase PON2 in B cell acute lymphoblastic leukemia (B-ALL) as a mechanism to bypass metabolic gatekeeper functions. Compared to normal pre-B cells, PON2 expression was elevated in patient-derived B-ALL samples and correlated with poor clinical outcomes in pediatric and adult cohorts. Genetic deletion of Pon2 had no measurable impact on normal B cell development. However, in mouse models for BCR-ABL1 and NRAS^G12D-driven B-ALL, deletion of Pon2 compromised proliferation, colony formation, and leukemia initiation in transplant recipient mice. Compromised leukemogenesis resulted from defective glucose uptake and adenosine triphosphate (ATP) production in PON2-deficient murine and human B-ALL cells. Mechanistically, PON2 enabled glucose uptake by releasing the glucose-transporter GLUT1 from its inhibitor stomatin (STOM) and genetic deletion of STOM largely rescued PON2 deficiency. While not required for glucose transport, the PON2 lactonase moiety hydrolyzes the lactone-prodrug 3OC12 to form a cytotoxic intermediate. Mirroring PON2 expression levels in B-ALL, 3OC12 selectively killed patient-derived B-ALL cells but was well tolerated in transplant recipient mice. Hence, while B-ALL cells critically depend on aberrant PON2 expression to evade metabolic gatekeeper functions, PON2 lactonase activity can be leveraged as synthetic lethality to overcome drug resistance in refractory B-ALL.

Single-cell ATAC-seq reveals GATA2-dependent priming defect in myeloid and a maturation bottleneck in lymphoid lineages

Germline heterozygous mutations in GATA2 are associated with a syndrome characterized by cytopenias, atypical infections, and increased risk of hematologic malignancies. Here, we generated a zebrafish mutant of gata2b that recapitulated the myelomonocytopenia and B-cell lymphopenia of GATA2 deficiency syndrome. Using single-cell assay for transposase accessible chromatin with sequencing of marrow cells, we showed that loss of gata2b led to contrasting alterations in chromosome accessibility in early myeloid and lymphoid progenitors, associated with defects in gene expression. Within the myeloid lineage in gata2b mutant zebrafish, we identified an attenuated myeloid differentiation with reduced transcriptional priming and skewing away from the monocytic program. In contrast, in early lymphoid progenitors, gata2b loss led to accumulation of B-lymphoid transcription factor accessibility coupled with increased expression of the B-cell lineage-specification program. However, gata2b mutant zebrafish had incomplete B-cell lymphopoiesis with loss of lineage-specific transcription factor accessibility in differentiating B cells, in the context of aberrantly reduced oxidative metabolic pathways. Our results establish that transcriptional events in early progenitors driven by Gata2 are required to complete normal differentiation.

Metabolic determinants of B-cell selection

B-cells are antibody-producing cells of the adaptive immune system. Approximately 75% of all newly generated B-cells in the bone marrow are autoreactive and express potentially harmful autoantibodies. To prevent autoimmune disease, the immune system has evolved a powerful mechanism to eliminate autoreactive B-cells, termed negative B-cell selection. While designed to remove autoreactive clones during early B-cell development, our laboratory recently discovered that transformed B-cells in leukemia and lymphoma are also subject to negative selection. Indeed, besides the risk of developing autoimmune disease, B-cells are inherently prone to malignant transformation: to produce high-affinity antibodies, B-cells undergo multiple rounds of somatic immunoglobulin gene recombination and hypermutation. Reflecting high frequencies of DNA-breaks, adaptive immune protection by B-cells comes with a dramatically increased risk of development of leukemia and lymphoma. Of note, B-cells exist under conditions of chronic restriction of energy metabolism. Here we discuss how these metabolic gatekeeper functions during B-cell development provide a common mechanism for the removal of autoreactive and premalignant B-cells to safeguard against both autoimmune diseases and B-cell malignancies.

EBF1 and PAX5 control pro-B cell expansion via opposing regulation of the Myc gene

Genes encoding B lineage-restricted transcription factors are frequently mutated in B-lymphoid leukemias, suggesting a close link between normal and malignant B-cell development. One of these transcription factors is early B-cell factor 1 (EBF1), a protein of critical importance for lineage specification and survival of B-lymphoid progenitors. Here, we report that impaired EBF1 function in mouse B-cell progenitors results in reduced expression of Myc. Ectopic expression of MYC partially rescued B-cell expansion in the absence of EBF1 both in vivo and in vitro. Using chromosome conformation analysis in combination with ATAC-sequencing, chromatin immunoprecipitation-sequencing, and reporter gene assays, six EBF1-responsive enhancer elements were identified within the Myc locus. CRISPR-Cas9-mediated targeting of EBF1-binding sites identified one element of key importance for Myc expression and pro-B cell expansion. These data provide evidence that Myc is a direct target of EBF1. Furthermore, chromatin immunoprecipitation-sequencing analysis revealed that several regulatory elements in the Myc locus are targets of PAX5. However, ectopic expression of PAX5 in EBF1-deficient cells inhibits the cell cycle and reduces Myc expression, suggesting that EBF1 and PAX5 act in an opposing manner to regulate Myc levels. This hypothesis is further substantiated by the finding that Pax5 inactivation reduces requirements for EBF1 in pro-B-cell expansion. The binding of EBF1 and PAX5 to regulatory elements in the human MYC gene in a B-cell acute lymphoblastic leukemia cell line indicates that the EBF1:PAX5:MYC regulatory loop is conserved and may control both normal and malignant B-cell development.

Lipid Droplets as Regulators of Metabolism and Immunity

Abstract

A hallmark of sterile and nonsterile inflammation is the increased accumulation of cytoplasmic lipid droplets (LDs) in non-adipose cells. LDs are ubiquitous organelles specialized in neutral lipid storage and hydrolysis. Originating in the ER, LDs are comprised of a core of neutral lipids (cholesterol esters, triglycerides) surrounded by a phospholipid monolayer and several LD-associated proteins. The perilipin (PLIN1-5) family are the most abundant structural proteins present on the surface of LDs. While PLIN1 is primarily expressed in adipocytes, PLIN2 and PLIN3 are ubiquitously expressed. LDs also acquire a host of enzymes and proteins that regulate LD metabolism. Amongst these are neutral lipases and selective lipophagy factors that promote hydrolysis of LD-associated neutral lipid. In addition, LDs physically associate with other organelles such as mitochondria through inter-organelle membrane contact sites that facilitate lipid transport. Beyond serving as a source of energy storage, LDs participate in inflammatory and infectious diseases, regulating both innate and adaptive host immune responses. Here, we review recent studies on the role of LDs in the regulation of immunometabolism.

Pathogenesis of ANCA-associated vasculitis: an emerging role for immunometabolism

ANCA-associated vasculitis (AAV) is a severe systemic autoimmune disease. A key feature of AAV is the presence of Anti-Neutrophil Cytoplasmic Antibodies (ANCA) directed against myeloperoxidase (MPO) or proteinase-3 (PR3). ANCA are key to the pathogenesis of AAV, where they activate innate immune cells to drive inflammation. Pre-activation or 'priming' of immune cells appears to be important for complete cellular activation in AAV. The burgeoning field of immunometabolism has illuminated the governance of immune cell function by distinct metabolic pathways. There is ample evidence that the priming events synonymous with AAV alter immune cell metabolism. In this review we discuss the pathogenesis of AAV and its intersection with recent insights into immune cell metabolism.

Prediction of the development of islet autoantibodies through integration of environmental, genetic, and metabolic markers

BACKGROUND

The Environmental Determinants of the Diabetes in the Young (TEDDY) study has prospectively followed, from birth, children at increased genetic risk of type 1 diabetes. TEDDY has collected heterogenous data longitudinally to gain insights into the environmental and biological mechanisms driving the progression to persistent islet autoantibodies.

METHODS

We developed a machine learning model to predict imminent transition to the development of persistent islet autoantibodies based on time-varying metabolomics data integrated with time-invariant risk factors (eg, gestational age). The machine learning was initiated with 221 potential features (85 genetic, 5 environmental, 131 metabolomic) and an ensemble-based feature evaluation was utilized to identify a small set of predictive features that can be interrogated to better understand the pathogenesis leading up to persistent islet autoimmunity.

RESULTS

The final integrative machine learning model included 42 disparate features, returning a cross-validated receiver operating characteristic area under the curve (AUC) of 0.74 and an AUC of ~0.65 on an independent validation dataset. The model identified a principal set of 20 time-invariant markers, including 18 genetic markers (16 single nucleotide polymorphisms [SNPs] and two HLA-DR genotypes) and two demographic markers (gestational age and exposure to a prebiotic formula). Integration with the metabolome identified 22 supplemental metabolites and lipids, including adipic acid and ceramide d42:0, that predicted development of islet autoantibodies.

CONCLUSIONS

The majority (86%) of metabolites that predicted development of islet autoantibodies belonged to three pathways: lipid oxidation, phospholipase A2 signaling, and pentose phosphate, suggesting that these metabolic processes may play a role in triggering islet autoimmunity.

Developmental changes in the rules for B cell selection

The autoimmune checkpoint during B cell maturation eliminates self-antigen reactive specificities from the mature B cell repertoire. However, an exception to this rule is illustrated by B-1 cells, an innate-like self-reactive B cell subset that is positively selected into the mature B cell pool in a self-antigen-driven fashion. The mechanisms by which B-1 cells escape central tolerance have puzzled the field for decades. A key clue comes from their restricted developmental window during fetal and neonatal life. Here we use B-1 cells as a prototypic early life derived B cell subset to explore developmental changes in the constraints of B cell selection. We discuss recent advancements in the understanding of the molecular program, centered around the RNA binding protein Lin28b, that licenses self-reactive B-1 cell output during ontogeny. Finally, we speculate on the possible link between the unique rules of early life B cell tolerance and the establishment of B cell - microbial mutualism to propose an integrated model for how developmental and environmental cues come together to create a protective layer of B cell memory involved in neonatal immune imprinting.

Metabolic Gatekeepers of Pathological B Cell Activation

Unlike other cell types, B cells undergo multiple rounds of V(D)J recombination and hypermutation to evolve high-affinity antibodies. Reflecting high frequencies of DNA double-strand breaks, adaptive immune protection by B cells comes with an increased risk of malignant transformation. In addition, the vast majority of newly generated B cells express an autoreactive B cell receptor (BCR). Thus, B cells are under intense selective pressure to remove autoreactive and premalignant clones. Despite stringent negative selection, B cells frequently give rise to autoimmune disease and B cell malignancies. In this review, we discuss mechanisms that we term metabolic gatekeepers to eliminate pathogenic B cell clones on the basis of energy depletion. Chronic activation signals from autoreactive BCRs or transforming oncogenes increase energy demands in autoreactive and premalignant B cells. Thus, metabolic gatekeepers limit energy supply to levels that are insufficient to fuel either a transforming oncogene or hyperactive signaling from an autoreactive BCR.

Philadelphia Chromosome-Positive Leukemia in the Lymphoid Lineage-Similarities and Differences with the Myeloid Lineage and Specific Vulnerabilities

Philadelphia chromosome (Ph) results from a translocation between the breakpoint cluster region (BCR) gene on chromosome 9 and ABL proto-oncogene 1 (ABL1) gene on chromosome 22. The fusion gene, BCR-ABL1, is a constitutively active tyrosine kinase which promotes development of leukemia. Depending on the breakpoint site within the BCR gene, different isoforms of BCR-ABL1 exist, with p210 and p190 being the most prevalent. P210 isoform is the hallmark of chronic myeloid leukemia (CML), while p190 isoform is expressed in majority of Ph-positive B cell acute lymphoblastic leukemia (Ph+ B-ALL) cases. The crucial component of treatment protocols of CML and Ph+ B-ALL patients are tyrosine kinase inhibitors (TKIs), drugs which target both BCR-ABL1 isoforms. While TKIs therapy is successful in great majority of CML patients, Ph+ B-ALL often relapses as a drug-resistant disease. Recently, the high-throughput genomic and proteomic analyses revealed significant differences between CML and Ph+ B-ALL. In this review we summarize recent discoveries related to differential signaling pathways mediated by different BCR-ABL1 isoforms, lineage-specific genetic lesions, and metabolic reprogramming. In particular, we emphasize the features distinguishing Ph+ B-ALL from CML and focus on potential therapeutic approaches exploiting those characteristics, which could improve the treatment of Ph+ B-ALL.

Regulation and repurposing of nutrient sensing and autophagy in innate immunity

Nutrients not only act as building blocks but also as signaling molecules. Nutrient-availability promotes cell growth and proliferation and suppresses catabolic processes, such as macroautophagy/autophagy. These effects are mediated by checkpoint kinases such as MTOR (mechanistic target of rapamycin kinase), which is activated by amino acids and growth factors, and AMP-activated protein kinase (AMPK), which is activated by low levels of glucose or ATP. These kinases have wide-ranging activities that can be co-opted by immune cells upon exposure to danger signals, cytokines or pathogens. Here, we discuss recent insight into the regulation and repurposing of nutrient-sensing responses by the innate immune system during infection. Moreover, we examine how natural mutations and pathogen-mediated interventions can alter the balance between anabolic and autophagic pathways leading to a breakdown in tissue homeostasis and/or host defense.Abbreviations: AKT1/PKB: AKT serine/threonine kinase 1; ATG: autophagy related; BECN1: beclin 1; CGAS: cyclic GMP-AMP synthase; EIF2AK4/GCN2: eukaryotic translation initiation factor 2 alpha kinase 4; ER: endoplasmic reticulum; FFAR: free fatty acid receptor; GABARAP: GABA type A receptor-associated protein; IFN: interferon; IL: interleukin; LAP: LC3-associated phagocytosis; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MAPK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NLR: NOD (nucleotide-binding oligomerization domain) and leucine-rich repeat containing proteins; PI3K, phosphoinositide 3-kinase; PRR: pattern-recognition receptor; PtdIns3K: phosphatidylinositol 3-kinase; RALB: RAS like proto-oncogene B; RHEB: Ras homolog, MTORC1 binding; RIPK1: receptor interacting serine/threonine kinase 1; RRAG: Ras related GTP binding; SQSTM1/p62: sequestosome 1; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; STK11/LKB1: serine/threonine kinase 11; TBK1: TANK binding kinase 1; TLR: toll like receptor; TNF: tumor necrosis factor; TRAF6: TNF receptor associated factor 6; TRIM: tripartite motif protein; ULK1: unc-51 like autophagy activating kinase 1; V-ATPase: vacuolar-type H⁺-proton-translocating ATPase.

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.

Glucose Metabolism on Tumor Plasticity, Diagnosis, and Treatment

Malignant cells support tumor proliferation and progression by adopting to metabolic changes. Tumor cells altered metabolism by increasing glucose uptake and fermentation of glucose to lactate, even in the aerobic state and the presence of functioning mitochondria. Glucose metabolism in tumor plasticity has attracted great interests by clinicians and scientists in the past decades. This review discusses the previous and emerging researches on the tumor plasticity altered by changing glucose metabolism in different cancer cells, including cancer stem cells (CSCs). In addition, we summarize the rising applications of glucose metabolism in tumor diagnosis and treatment. Our objective is to direct future investigation on this altered metabolic phenotype and its application in patient care.

Celebrating 20 Years of IGHV Mutation Analysis in CLL

The division of CLL into 2 broad subsets with highly significant differences in clinical behavior was reported in 2 landmark papers in Blood in 1999.^1,2 The simple analysis of the mutational status of the IGV regions provided both a prognostic indicator and an insight into the cellular origins. Derivation from B cells with very low or no IGV mutations generally leads to a more aggressive disease course than derivation from B cells with higher levels. This finding focused attention on surface Ig (sIg), the major B-cell receptor, and revealed dynamic antigen engagement in vivo as a tumor driver. It has also led to new drugs aimed at components of the intracellular activation cascades. After 20 years, the 2 senior authors of those papers have looked at the history of the observations and at the increasing understanding of the role of sIg in CLL that have emanated from them. As in the past, studies of CLL have provided a link between biology and the clinic, enabling more precise targeting which attacks critical pathways but minimizes side effects.

Regulatory Factor X 7 and its Potential Link to Lymphoid Cancers

Alterations in the Regulatory factor X 7 (RFX7) gene have recurrently been reported in lymphoid cancers. Uncharacterized until recently, this transcription factor regulates genes important for ciliogenesis and for limiting cellular metabolic activity. Here we discuss these observations and conjecture on the links between the reported functions of RFX7 and its potential role in lymphoid cancers, encouraging future studies in these directions.

LncRNAs: The Regulator of Glucose and Lipid Metabolism in Tumor Cells

Metabolism is a complex network of regulatory system. Cells often alter their metabolism in response to the changes in their environment. These adaptive changes are particularly pronounced in tumor cells, known as metabolic reprogramming. Metabolic reprogramming is considered to be one of the top 10 characteristics of tumor cells. Glucose and lipid metabolism are important components of metabolic reprogramming. A large number of experimental studies have shown that long non-coding RNAs (lncRNAs) play an important role in glucose and lipid metabolism. The current review briefly introduces the regulatory effect of lncRNAs on glucose and lipid metabolism of tumor cells, and the significance of lncRNA-mediated metabolism in tumor therapy, hoping to provide new strategies for clinical targeting tumor therapy.