Fn14-Fc suppresses germinal center formation and pathogenic B cells in a lupus mouse model via inhibition of the TWEAK/Fn14 Pathway

Roles of interferon regulatory factor 4 in the AKI-CKD transition, glomerular diseases and kidney allograft rejection

Interferon regulatory factor 4 (IRF4) is expressed in immune cells and is a member of the interferon regulatory factor family. Recently, it has been found that IRF4 plays important roles in the acute kidney injury (AKI)-chronic kidney disease (CKD) transition, glomerular diseases and kidney allograft rejection. In particular, the relationship between IRF4 and the AKI-CKD transition has attracted widespread attention. Furthermore, it was also found that the deficiency of IRF4 hindered the transition from AKI to CKD through the suppression of macrophage-to-fibroblast conversion, inhibition of M1-M2 macrophage polarization, and reduction in neutrophil inward flow. Additionally, an examination of the crucial role of IRF4 in glomerular disease was conducted. It was reported that inhibiting IRF4 could alleviate the progression of glomerular disease, and potential physiopathology mechanisms associated with IRF4 were postulated. Lastly, IRF4 was found to have detrimental effects on the development of antibody-mediated rejection (ABMR) and T-cell-mediated rejection (TCMR).

Targeted Therapy for SLE-What Works, What Doesn't, What's Next

For many years, the failure of randomized controlled trials (RCTs) has prevented patients with systemic lupus erythematosus (SLE) from benefiting from biological drugs that have proved to be effective in other rheumatological diseases. Only two biologics are approved for SLE, however they can only be administered to a restricted proportion of patients. Recently, several phase II RCTs have evaluated the efficacy and safety of new biologics in extra-renal SLE and lupus nephritis. Six drug trials have reported encouraging results, with an improvement in multiple clinical and serological outcome measures. The possibility of combining B-cell depletion and anti-BLyS treatment has also been successfully explored.

Targeting fibroblast growth factor (FGF)-inducible 14 (Fn14) for tumor therapy

Fibroblast growth factor-inducible 14 (Fn14) is a member of the tumor necrosis factor (TNF) receptor superfamily (TNFRSF) and is activated by its ligand TNF-like weak inducer of apoptosis (TWEAK). The latter occurs as a homotrimeric molecule in a soluble and a membrane-bound form. Soluble TWEAK (sTWEAK) activates the weakly inflammatory alternative NF-κB pathway and sensitizes for TNF-induced cell death while membrane TWEAK (memTWEAK) triggers additionally robust activation of the classical NF-κB pathway and various MAP kinase cascades. Fn14 expression is limited in adult organisms but becomes strongly induced in non-hematopoietic cells by a variety of growth factors, cytokines and physical stressors (e.g., hypoxia, irradiation). Since all these Fn14-inducing factors are frequently also present in the tumor microenvironment, Fn14 is regularly found to be expressed by non-hematopoietic cells of the tumor microenvironment and most solid tumor cells. In general, there are three possibilities how the tumor-Fn14 linkage could be taken into consideration for tumor therapy. First, by exploitation of the cancer associated expression of Fn14 to direct cytotoxic activities (antibody-dependent cell-mediated cytotoxicity (ADCC), cytotoxic payloads, CAR T-cells) to the tumor, second by blockade of potential protumoral activities of the TWEAK/Fn14 system, and third, by stimulation of Fn14 which not only triggers proinflammtory activities but also sensitizes cells for apoptotic and necroptotic cell death. Based on a brief description of the biology of the TWEAK/Fn14 system and Fn14 signaling, we discuss the features of the most relevant Fn14-targeting biologicals and review the preclinical data obtained with these reagents. In particular, we address problems and limitations which became evident in the preclinical studies with Fn14-targeting biologicals and debate possibilities how they could be overcome.

Emerging role of TWEAK-Fn14 axis in lupus, a disease related to autoimmunity and fibrosis

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder. Lupus nephritis (LN) is one of the severe clinical implications in SLE, and this was relates to fibrosis in the kidney. As an important marker in the tumor necrosis factor (TNF) superfamily, TNF-like weak inducer of apoptosis (TWEAK) has been given much attention with respect to its role in regulating pro-inflammatory immune response. Fibroblast growth factor-inducible 14 (Fn14), the sole receptor for TWEAK, has been found expressed in different immune and non-immune cells. TWEAK binds to Fn14, and then regulates inflammatory components production via downstream signaling pathways. To date, dysregulated expression of TWEAK, Fn14 has been reported in SLE, LN patients, and in vivo, in vitro studies have discussed the significant role of TWEAK-Fn14 axis in SLE, LN pathogenesis, partly through mediating the fibrosis process. In this review, we will discuss the association of TWEAK-Fn14 axis in lupus. Understanding the relationship will better realize the potential for making TWEAK-Fn14 as a marker for the diseases, and will help to give many clues for targeting them in treatment of lupus in the future.

Pro-Inflammatory and B Cell Regulating Capacities of TWEAK in Rainbow Trout (Oncorhynchus mykiss)

Tumor necrosis factor (TNF)-like weak inducer of apoptosis or TWEAK is a member of the TNF superfamily involved in the regulation of many biological processes. In mammals, TWEAK has been shown to play a role in some autoimmune or inflammatory conditions, but its immune role is not yet clearly defined. In teleost fish, although a few studies have identified homologues to mammalian TWEAK, their biological effects have never been investigated. In the current study, we have studied the transcriptional regulation of two TWEAK homologues (TWEAK 1 and 2) identified in rainbow trout (Oncorhynchus mykiss) throughout different tissues, in response to parasitic or viral infections, or in head kidney (HK) leukocytes stimulated with different stimuli. Although the transcription of both homologues was modulated when HK leukocytes were exposed to several immune stimuli, only TWEAK 1 was significantly modulated upon pathogenic exposure. Thus, we performed a characterization of the functions exerted by this cytokine in HK leukocytes. Recombinant TWEAK 1 strongly up-regulated the transcription of pro-inflammatory genes and antimicrobial peptides in HK leukocytes, with differential transcriptional effects in IgM⁺ B cells, IgM^- lymphocytes and myeloid cells. TWEAK 1 also increased the survival and promoted the differentiation of B cells in HK leukocyte cultures. Our results demonstrate that in teleost fish, TWEAK 1 is involved in the response to different types of pathogens, through the modulation of antimicrobial and pro-inflammatory genes in different leukocytes subsets. Furthermore, a role for TWEAK as a B cell differentiation factor has also been established in rainbow trout.

Dysregulated translational factors and epigenetic regulations orchestrate in B cells contributing to autoimmune diseases

B cells play a crucial role in antigen presentation, antibody production and pro-/anti-inflammatory cytokine secretion in adaptive immunity. Several translational factors including transcription factors and cytokines participate in the regulation of B cell development, with the cooperation of epigenetic regulations. Autoimmune diseases are generally characterized with autoreactive B cells and high-level pathogenic autoantibodies. The success of B cell depletion therapy in mouse model and clinical trials has proven the role of B cells in pathogenesis of autoimmune diseases. The failure of B cell tolerance in immune checkpoints results in accumulated autoreactive naïve B (B_N) cells with aberrant B cell receptor signaling and dysregulated B cell response, contributing to self-antibody-mediated autoimmune reaction. Dysregulation of translational factors and epigenetic alterations in B cells has been demonstrated to correlate with aberrant B cell compartment in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome, multiple sclerosis, diabetes mellitus and pemphigus. This review is intended to summarize the interaction of translational factors and epigenetic regulations that are involved with development and differentiation of B cells, and the mechanism of dysregulation in the pathogenesis of autoimmune diseases.

Fibroblast growth factor inducible 14 signaling facilitates anti-dsDNA IgG penetration into mesangial cells

Anti-double-stranded DNA (dsDNA) antibodies induce renal damage in patients with systemic lupus erythematosus by triggering fibrotic processes in kidney cells. However, the precise mechanism underlying penetration of anti-dsDNA immunoglubolin G (IgG) into cells remains unclear. This study was designed to investigate the effect of tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor inducible 14 (Fn14) signaling on anti-dsDNA IgG penetration into cells. Mesangial cells were cultured in vitro, and stimulated with TWEAK and anti-dsDNA IgG. The results revealed that TWEAK dose-dependently enhanced cellular internalization of anti-dsDNA IgG and the expression of high-mobility group box 1 (HMGB1). In addition, TWEAK and anti-dsDNA IgG synthetically downregulate suppressor of cytokine signaling 1, and induce the expression of various fibrotic factors. Furthermore, inhibition of HMGB1 attenuates the enhancement effect of TWEAK on anti-dsDNA IgG internalization. The TWEAK upregulation of HMGB1 involves the nuclear factor-κB and phosphatidylinositide 3-kinase/protein kinase B pathways. Therefore, TWEAK/Fn14 signaling contributes to the penetration of anti-dsDNA IgG and relevant fibrotic processes in mesangial cells.

Toll-like receptor 7 agonist imiquimod prevents the progression of SLE in MRL/lpr mice via inhibiting the differentiation of T follicular helper cells

Previous research has recently indicated that TLR7 is able to induce CD4⁺T cell anergy, which is the opposite of the role it plays in innate immune cells. Therefore, TLR7 ligands may be used as a manner in which to induce CD4⁺T cells "tolerance" in autoimmune diseases. T follicular helper (Tfh) cells were demonstrated to be a subset of CD4⁺T cells that help B cells produce antibodies. The abnormal activity of Tfh cells, though, is their function as a primary pathogenic factor in systemic lupus erythematosus (SLE). However, the role of TLR7 in Tfh cells is not clear. Our study was aimed at determining the influence of TLR7 on Tfh cells in a murine model of SLE (MRL/lpr mice). We were surprised to find that the frequency of Tfh cells and germinal center (GC) B cells was significantly reduced after treatment with the TLR7 agonist imiquimod. Imiquimod also significantly reduced the expression of inducible costimulatory molecule (ICOS) and programmed death 1(PD-1) in Tfh cells and decreased IL-21 secretion. Moreover, imiquimod significantly reduced the mRNA expression of several transcription factors, including Bcl-6, c-Maf, Batf3, Nfatc2 and Stat3, and enhanced the expression of Prdm1 and Stat5b in CD4⁺T cells. Imiquimod also ameliorated the progression of SLE in MRL/lpr mice by inhibiting anti-dsDNA antibodies and antinuclear antibody (ANA) secretion in the serum. Our findings indicated that TLR7 inhibited the development of Tfh cells both in vivo and ex vivo, which depended on many transcription factors aside from Bcl-6. Our results demonstrated that a TLR7 agonist has the potential to be used to inhibit Tfh cell responses during SLE.

LRRK2 is involved in the pathogenesis of system lupus erythematosus through promoting pathogenic antibody production

Background

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the presence of pathogenic autoantibodies associated with polyclonal B cell hyperreactivity. Previous study reported that autophagy-related gene Leucine-rich repeat kinase 2 (LRRK2) was likely a susceptible gene for SLE. However, the pathogenic function of LRRK2 in SLE is undefined.

Methods

Using quantitative PCR, we compared the expression levels of LRRK2 in B cells between SLE patients and healthy controls. The expression levels of LRRK2 in in vitro induced CD19^hi B cells and naïve B cells were compared as well based on RNA-seq assay. A pristane-induced lupus-like mouse model was used to explore the effects of LRRK2 on the development of SLE. IgG level, B cell subsets in the spleens and bone marrows and pathological features in the kidneys were compared between wildtype (WT) and Lrrk2^−/− littermates.

Results

It was obvious that LRRK2 expression was dramatically up-regulated in primary B cells from SLE patients compared to those from healthy controls, as well as in activated CD19^hi B cells. More significantly, LRRK2 expression in B cells was positively correlated with system lupus erythematosus disease activity index (SLEDAI), an indicator for disease severity, and serum IgG levels in SLE patients. Negative correlations were observed between LRRK2 expression and serum C3 or C4 levels, two clinical features associated with SLE-related nephritis. LRRK2 deficiency reduced the death rate of pristane treated mice. Decreased levels of total IgG and autoantibody were detected in the serum with less deposition of immune complexes and attenuated pathological symptoms in the kidneys of Lrrk2^−/− mice. Consistent with the reduction in IgG production, the percentages of germinal center B cells and plasma cells decreased significantly as well with LRRK2 deficiency.

Conclusions

Our study demonstrates that LRRK2 expression is upregulated in B cells from SLE patients with strong correlations to disease severity. LRRK2 deficiency largely attenuates the pathogenic progress of lupus-like features in pristane-induced mice. This is probably achieved through affecting B cell terminal differentiation and subsequent immunoglobulin production.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1786-6) contains supplementary material, which is available to authorized users.

Pregnancy probabilistically augments potential precursors to chronic, immune-mediated or autoimmune lacrimal gland infiltrates

PURPOSE

This study asked whether pregnancy, a risk factor for dry eye disease associated with both chronic, immune-mediated- and autoimmune etiologies, augments development of clusters of coordinately functioning cells (CCFC) that may be precursors to pathological lacrimal gland infiltrates.

METHODS

Lacrimal glands were from six virgin- and six term-pregnant rabbits of the same age and environmental exposure history. Seventy-two immune response-related gene transcripts were assayed by real time RT-PCR. Principal component (PC) analysis identified transcript signatures of CCFC contributing negative (^⊖) or positive (^⊕) PC loadings and determined gland PC projections, which reflect levels of CCFC development.

RESULTS

Three CCFC were of interest as potential precursors to pathological infiltrates. CCFC 1^⊖ was suggestive of an ectopic lymphoid structure with resting T cells and B cells. CCFC 1^⊕ was suggestive of an immune-mediated infiltrate with T_H1 cells and mature, cytotoxic B cells. CCFC 2^⊖ was suggestive of an ectopic lymphoid structure with activated T cells, mature B cells, germinal center, and plasmacytes. CCFC 4^⊖ and CCFC 5^⊖ also included plasmacytes. Pregnancy augmented CCFC 1^⊖ in some glands; augmented CCFC 1^⊕ in others; and augmented CCFC 2^⊖, CCFC 4^⊖, and CCFC 5^⊖ different combinations.

CONCLUSIONS

Potential precursors of pathological infiltrates form in the lacrimal glands by the time of sexual maturity. Pregnancy augments lacrimal gland plasmacyte populations, and it can augment development of potential precursors to either chronic, immune-mediated infiltrates or autoimmune infiltrates of various phenotypes. Systemic and strictly local, probabilistic phenomena interact with pregnancy to determine which combinatorial phenotypes are favored.