B-cell-activating factor is a regulator of adipokines and a possible mediator between adipocytes and macrophages

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.

Targeting adipocyte-immune cell crosstalk to control breast cancer progression

Adipocytes are crucial components of breast cancer and are involved in regulating the progression, therapeutic efficacy, and prognosis of breast cancer patients. Characterized by storing energy and producing a variety of secretory factors, adipocytes are responsible for inducing obesity and regulating the tumor immune activity. Adipocytes communicate with tumor infiltrating immune cells through the secreted adipokines, cytokines, and exosomes in the breast cancer TIME, which shapes the tumor supporting environment to facilitate the immune escape of tumor cells. In-depth studies of the crosstalk between adipocytes and TIME can not only provide a more comprehensive regulatory landscape of TIME, but also be conducive to screening novel targets for future precision targeted therapy. The aim of this review is to discuss recent studies for understanding the role of crosstalk between adipocytes and immune cells in shaping the breast cancer immune microenvironment.

An insight into major signaling pathways and protein-protein interaction networks involved in the pathogenesis of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is associated with the increase of glucose in the blood rather than being absorbed by the cells. A better understanding of the signaling pathways is necessary to understand the pathophysiology of GDM. This study provides details about a series of signaling pathways and protein-protein interactions involved in the pathogenesis of GDM and their evaluations in GDM development. Protein-protein interactions were found between proteins of several signaling pathways that suggest interlink between these signaling pathways. Protein-protein interactions were generated with high confidence interaction scores based on textmining, co-occurrence, coexpression, neighborhood, gene fusion, experiments and databases. The dysregulation of signaling pathways may also contribute to the increased risk of complications associated with GDM in the mother and child. Further, studies on signaling pathways involved in the pathogenesis of GDM would help in the development of an effective intervention to prevent GDM along with the identification of key targets for effective therapies in the future. This article is protected by copyright. All rights reserved.

B cell activating factor regulates periodontitis development by suppressing inflammatory responses in macrophages

Background

B cell activating factor (BAFF) is a member of the tumor necrosis factor (TNF) superfamily with immunomodulatory effects on both innate and adaptive immune responses. Periodontitis is an inflammatory disease characterized by periodontal soft tissue inflammation and the progressive loss of periodontal ligament and alveolar bone. Macrophages are closely related to periodontitis progression. However, the role of BAFF in periodontitis development and macrophage polarization and the underlying mechanism remain unknown.

Methods

In vivo, a ligation-induced mouse model of periodontitis for BAFF blockade was established to investigate the expression of inducible nitric oxide synthase (iNOS) through real-time PCR (RT-PCR) and immunohistochemistry. In addition, the level of TNF-α in the periodontium, the number of osteoclasts, and alveolar bone resorption were observed. In vitro, RAW 264.7 macrophage cells were treated with 100 ng/mL Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS) in either the presence or absence of 50 nM small interfering RNA (siRNA) targeting BAFF, followed by further incubation for 24 h. These cells and supernatants were collected and stored for RT-PCR, enzyme-linked immunosorbent assay, western blotting and immunofluorescence microscopy.

Results

In vivo, BAFF blockade decreased the levels of TNF-α in the periodontium in a ligature-induced mouse periodontitis model. Reduced osteoclast formation and lower alveolar bone loss were also observed. In addition, BAFF blockade was related to the expression of polarization signature molecules in macrophages. In vitro, BAFF knockdown notably suppressed the production of TNF-α in RAW 264.7 cells stimulated by P. gingivalis LPS. Moreover, BAFF knockdown attenuated the polarization of RAW 264.7 cells into classically activated macrophages (M1), with reduced expression of iNOS.

Conclusions

Based on our limited evidence, we showed BAFF blockade exhibits potent anti-inflammatory properties in mice experimental periodontitis in vivo and in P. gingivalis LPS-treated RAW 264.7 cells in vitro, and macrophage polarization may be responsible for this effect.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01788-6.

B cell activating factor (BAFF): Structure, functions, autoimmunity and clinical implications in Systemic Lupus Erythematosus (SLE)

The B cell activating factor (BAFF), or B lymphocyte stimulator (BLyS), is a B cell survival factor which supports autoreactive B cells and prevents their deletion. BAFF expression is closely linked with autoimmunity and is enhanced by genetic alterations and viral infections. Furthermore, BAFF seems to be involved in adipogenesis, atherosclerosis, neuro-inflammatory processes and ischemia reperfusion (I/R) injury. BAFF is commonly overexpressed in Systemic Lupus Erythematosus (SLE) and strongly involved in the pathogenesis of the disease. The relationship between BAFF levels, disease activity and damage accrual in SLE is controversial, but growing evidence is emerging on its role in renal involvement. Belimumab, a biologic BAFF inhibitor, has been the first biologic agent licensed for SLE therapy so far. As Rituximab (RTX) has been shown to increase BAFF levels following B cell depletion, the combination therapy of RTX plus belimumab (being evaluated in two RCT) seems to be a valuable option for several clinical scenarios. In this review we will highlight the growing body of evidence of immune and non-immune related BAFF expression in experimental and clinical settings.

Methylglyoxal, Glycated Albumin, PAF, and TNF-α: Possible Inflammatory and Metabolic Biomarkers for Management of Gestational Diabetes

Background: In gestational diabetes mellitus (GDM), pancreatic β-cell breakdown can result from a proinflammatory imbalance created by a sustained level of cytokines. In this study, we investigated the role of specific cytokines, such as B-cell activating factor (BAFF), tumor necrosis factor α (TNF-α), and platelet-activating factor (PAF), together with methylglyoxal (MGO) and glycated albumin (GA) in pregnant women affected by GDM. Methods: We enrolled 30 women whose inflammation and metabolic markers were measured at recruitment and after 12 weeks of strict dietetic therapy. We compared these data to the data obtained from 53 randomly selected healthy nonpregnant subjects without diabetes, hyperglycemia, or any condition that can affect glycemic metabolism. Results: In pregnant women affected by GDM, PAF levels increased from 26.3 (17.4–47.5) ng/mL to 40.1 (30.5–80.5) ng/mL (p < 0.001). Their TNF-α levels increased from 3.0 (2.8–3.5) pg/mL to 3.4 (3.1–5.8) pg/mL (p < 0.001). The levels of methylglyoxal were significantly higher in the women with GDM (p < 0.001), both at diagnosis and after 12 weeks (0.64 (0.46–0.90) μg/mL; 0.71 (0.47–0.93) μg/mL, respectively) compared to general population (0.25 (0.19–0.28) μg/mL). Levels of glycated albumin were significantly higher in women with GDM (p < 0.001) only after 12 weeks from diagnosis (1.51 (0.88–2.03) nmol/mL) compared to general population (0.95 (0.63–1.4) nmol/mL). Conclusion: These findings support the involvement of new inflammatory and metabolic biomarkers in the mechanisms related to GDM complications and prompt deeper exploration into the vicious cycle connecting inflammation, oxidative stress, and metabolic results.

Editor’s Pick: Systemic Sclerosis: The Role of YAP/TAZ in Disease Pathogenesis

Systemic sclerosis (SSc) is a systemic autoimmune condition of unknown cause. Yes-Associated Protein/Tafazzin (YAP/TAZ) are transcriptional coactivators previously demonstrated to be involved in cellular stretch biology, and form the principal effector molecules of the Hippo signalling pathway. The association between YAP/TAZ and stretch is contingent upon their cytoplasmic localisation (with nuclear translocation, the cell adopts a relaxed state). The author weighs the evidence for a central role for YAP/TAZ signalling in scleroderma spanning the major clinical features of the condition. Several of the features unique to SSc are mediated by cytoplasmic localisation of YAP/TAZ, including the stretch phenotype (through binding to NF-2), arterial lumenal obliteration (through their binding to angiomotin), the promotion of hypergammaglobulinaemia (via feedback to the upstream Hippo signalling molecule Mammalian Ste20-like Kinase 1), and the induction of B-Lymphocyte-Induced Maturation Protein-1 leading to the adoption of Th2 lineage, prominent in SSc. One observes that the induction of the fibrotic phenotype of scleroderma is mediated through GLI1/GLI2 (the effector molecules of the Hedgehog pathway). GLI1/GLI2 are induced to reciprocally enter the nucleus when YAP/TAZ is intracytoplasmic. The latter explains the characteristically increased connective tissue growth factor 2 and endothelin-1 expression. In this article, the author references some examples of the role of YAP/TAZ in the biophysically similar condition nephrogenic systemic fibrosis and suggests a role of YAP/TAZ cytoplasmic sequestration in programmed cell death protein 1-ligand antagonist-induced scleroderma.

B Cell-Activating Factor Is Associated with Testosterone and Smoking Status in Non-Ambulatory Men with Chronic Spinal Cord Injury

B cell-mediated autoimmunity may contribute to poor neurological outcomes after spinal cord injury (SCI). B cell-activating factor (BAFF) is a key cytokine involved in B cell development, proliferation, activation, and survival whose expression is elevated in men with chronic SCI. The aim of this study was to assess factors associated with circulating BAFF in non-ambulatory males with chronic SCI. We assessed the association between clinical and demographic factors, health habits, and circulating BAFF levels in a convenience sample of 43 non-ambulatory men with chronic spinal cord injury (≥ 1 year post-injury). Serum BAFF and total testosterone levels were quantified by enzyme-linked immunosorbent assay. Body composition was determined by whole body dual-energy X-ray absorptiometry. In multivariable models, active smokers had significantly greater BAFF levels than former/nonsmokers (871 pg/mL vs. 665 pg/ml, p = 0.002). BAFF decreased 36 ± 11.1 pg/mL for every 1 ng/mL increase in total testosterone (p = 0.002). This model explained 41% of the variation in circulating BAFF levels (model p < 0.0001). Our findings suggest that modifiable health habits may be associated with elevated BAFF levels in men with non-ambulatory chronic SCI. Further, the significant and independent negative association between testosterone levels and BAFF would suggest a link between androgen deficiency and autoimmunity observed in SCI via modulation of BAFF and B cell numbers. This points toward BAFF as a potential biomarker of injury severity and a target of therapies designed to reduce neuroinflammation and improve neurological outcomes after SCI.

Cutting Edge: BAFF Overexpression Reduces Atherosclerosis via TACI-Dependent B Cell Activation

Patients with systemic lupus erythematosus exhibit accelerated atherosclerosis, a chronic inflammatory disease of the arterial wall. The impact of B cells in atherosclerosis is controversial, with both protective and pathogenic roles described. For example, natural IgM binding conserved oxidized lipid epitopes protect against atherosclerosis, whereas anti-oxidized low-density lipoprotein (oxLDL) IgG likely promotes disease. Because BAFF promotes B cell class-switch recombination and humoral autoimmunity, we hypothesized that excess BAFF would accelerate atherosclerosis. In contrast, BAFF overexpression markedly reduced hypercholesterolemia and atherosclerosis in hyperlipidemic mice. BAFF-mediated atheroprotection required B cells and was associated with increased protective anti-oxLDL IgM. Surprisingly, high-titer anti-oxLDL IgM production and reduced atherosclerosis was dependent on the BAFF family receptor transmembrane activator and CAML interactor. In summary, we identified a novel role for B cell-specific, BAFF-dependent transmembrane activator and CAML interactor signals in atherosclerosis pathogenesis, of particular relevance to the use of BAFF-targeted therapies in systemic lupus erythematosus.

CsBAFF, a Teleost B Cell Activating Factor, Promotes Pathogen-Induced Innate Immunity and Vaccine-Induced Adaptive Immunity

B cell activating factor (BAFF) is a member of the tumor necrosis factor family that is known to play an important role in B cell activation, proliferation, and differentiation in mammals. However, studies of BAFF in teleosts are very limited and its function, in particular that under in vivo conditions, is essentially unknown. In this study, we conducted in vivo as well as in vitro functional analyses of a BAFF homologue (CsBAFF) from the teleost fish tongue sole (Cynoglossus semilaevis). CsBAFF is composed of 261 residues and shares moderate sequence identities with known BAFFs of other teleosts. CsBAFF expression was most abundant in immune organs and was upregulated during bacterial infection. Purified recombinant CsBAFF (rCsBAFF) bound to tongue sole lymphocytes and promoted cellular proliferation and survival. The results of an in vivo study showed that CsBAFF overexpression in tongue sole significantly enhanced macrophage activation and reduced bacterial infection in fish tissues, whereas knockdown of CsBAFF expression resulted in increased bacterial dissemination and colonization in fish tissues. Furthermore, vaccination studies showed that CsBAFF enhanced the immunoprotection of a DNA vaccine and augmented the production of specific serum antibodies. Taken together, these results provide the first in vivo evidence to indicate that teleost BAFF is an immunostimulator that significantly contributes to the innate antibacterial immune response and vaccine-induced adaptive immune response.

BAFF knockout improves systemic inflammation via regulating adipose tissue distribution in high-fat diet-induced obesity

Obesity is recognized as a chronic low-grade inflammatory state due to adipose tissue expansion being accompanied by an increase in the production of proinflammatory adipokines. Our group is the first to report that B-cell-activating factor (BAFF) is produced from adipocytes and functions as a proinflammatory adipokine. Here, we investigated how loss of BAFF influenced diet-induced obesity in mice by challenging BAFF^−/− mice with a high-fat diet for 10 weeks. The results demonstrated that weight gain in BAFF^−/− mice was >30% than in control mice, with a specific increase in the fat mass of the subcutaneous region rather than the abdominal region. Expression of lipogenic genes was examined by quantitative real-time PCR, and increased lipogenesis was observed in the subcutaneous adipose tissue (SAT), whereas lipogenesis in the epididymal adipose tissue (EAT) was reduced. A significant decrease in EAT mass resulted in the downregulation of inflammatory gene expression in EAT, and more importantly, overall levels of inflammatory cytokines in the circulation were reduced in obese BAFF^−/− mice. We also observed that the macrophages recruited in the enlarged SAT were predominantly M2 macrophages. 3T3-L1 adipocytes were cultured with adipose tissue conditioned media (ATCM), demonstrating that EAT ATCM from BAFF^−/− mice contains antilipogenic and anti-inflammatory properties. Taken together, BAFF^−/− improved systemic inflammation by redistributing adipose tissue into subcutaneous regions. Understanding the mechanisms by which BAFF regulates obesity in a tissue-specific manner would provide therapeutic opportunities to target obesity-related chronic diseases.

Phloretin and phlorizin promote lipolysis and inhibit inflammation in mouse 3T3-L1 cells and in macrophage-adipocyte co-cultures

SCOPE

Previous studies found that phloretin (PT) and phlorizin (PZ) could inhibit glucose transport, with PT being a better inhibitor of lipid peroxidation. This study aimed to evaluate the antiobesity effects of PT and PZ in 3T3-L1 cells and if they can modulate the relationship between adipocytes and macrophages.

METHODS AND RESULTS

Differentiated 3T3-L1 cells were treated with PT or PZ. Subsequently, transcription factors of adipogenesis and lipolysis proteins were measured. In addition, RAW 264.7 macrophages treated with PT or PZ were cultured in differentiated media from 3T3-L1 cells to analyze inflammatory mediators and signaling pathways. PT significantly enhanced glycerol release and inhibited the adipogenesis-related transcription factors. PT also promoted phosphorylation of AMP-activated protein kinase and increased activity of adipose triglyceride lipase and hormone-sensitive lipase. PT suppressed the nuclear transcription factor kappa-B and mitogen-activated protein kinase pathways when RAW 264.7 cells were cultured in differentiated media from 3T3-L1 cells. PZ improved lipolysis and inhibited the macrophage inflammatory response less effectively than PT.

CONCLUSION

This study suggests that PT is more effective than PZ at increasing lipolysis in adipocytes. In addition, PT also suppresses inflammatory response in macrophage that is stimulated by differentiated media from 3T3-L1 cells.

The BAFF/APRIL system: emerging functions beyond B cell biology and autoimmunity

The BAFF system plays a key role in the development of autoimmunity, especially in systemic lupus erythematosus (SLE). This often leads to the assumption that BAFF is mostly a B cell factor with a specific role in autoimmunity. Focus on BAFF and autoimmunity, driven by pharmaceutical successes with the recent approval of a novel targeted therapy Belimumab, has relegated other potential roles of BAFF to the background. Far from being SLE-specific, the BAFF system has a much broader relevance in infection, cancer and allergy. In this review, we provide the latest views on additional roles of the BAFF system in health and diseases, as well as an update on BAFF and autoimmunity, with particular focus on current clinical trials.