Iron metabolism and arthritis:Exploring connections and therapeutic avenues

Iron is indispensable for the viablility of nearly all living organisms,and it is imperative for cells,tissues,and organisms to acquire this essential metal sufficiently and maintain its metabolic stability for survival.Disruption of iron homeostasis can lead to the development of various diseases.There is a robust connection between iron metabolism and infection,immunity,inflammation,and aging,suggesting that disorders in iron metabolism may contribute to the pathogenesis of arthritis.Numerous studies have focused on the significant role of iron metabolism in the development of arthritis and its potential for targeted drug therapy.Targeting iron metabolism offers a promising approach for individualized treatment of arthritis.Therefore,this review aimed to investigate the mechanisms by which the body maintains iron metabolism and the impacts of iron and iron metabolism disorders on arthritis.Furthermore,this review aimed to identify potential therapeutic targets and active substances related to iron metabolism,which could provide promising research directions in this field.

Coming of age:the formation and function of age-associated B cells

B cells are generated in the bone marrow during ontogeny and migrate to peripheral lymphoid organs,where they encounter antigens to elicit humoral immunity.During the past decade,many novel B-cell subsets with distinct phenotypes and functions have been identified,and among these subsets,age-associated B cells(ABCs)were first characterized as a B-cell subset that accumulates with age[1].

B1-cell-produced anti-phosphatidylserine antibodies contribute to lupus nephritis development via TLR-mediated Syk activation

Autoantibodies produced by B cells play a pivotal role in the pathogenesis of systemic lupus erythematosus (SLE). However, both the cellular source of antiphospholipid antibodies and their contributions to the development of lupus nephritis (LN) remain largely unclear. Here, we report a pathogenic role of anti-phosphatidylserine (PS) autoantibodies in the development of LN. Elevated serum PS-specific IgG levels were measured in model mice and SLE patients, especially in those with LN. PS-specific IgG accumulation was found in the kidney biopsies of LN patients. Both transfer of SLE PS-specific IgG and PS immunization triggered lupus-like glomerular immune complex deposition in recipient mice. ELISPOT analysis identified B1a cells as the main cell type that secretes PS-specific IgG in both lupus model mice and patients. Adoptive transfer of PS-specific B1a cells accelerated the PS-specific autoimmune response and renal damage in recipient lupus model mice, whereas depletion of B1a cells attenuated lupus progression. In culture, PS-specific B1a cells were significantly expanded upon treatment with chromatin components, while blockade of TLR signal cascades by DNase I digestion and inhibitory ODN 2088 or R406 treatment profoundly abrogated chromatin-induced PS-specific IgG secretion by lupus B1a cells. Thus, our study has demonstrated that the anti-PS autoantibodies produced by B1 cells contribute to lupus nephritis development. Our findings that blockade of the TLR/Syk signaling cascade inhibits PS-specific B1-cell expansion provide new insights into lupus pathogenesis and may facilitate the development of novel therapeutic targets for the treatment of LN in SLE.

A Common Functional Variant at the Enhancer of the Rheumatoid Arthritis Risk Gene ORMDL3 Regulates its Expression Through Allele-Specific JunD Binding

Genome-wide association studies(GWASs)have identified over 100 loci associated with rheumatoid arthritis(RA);how-ever,the functionally affected genes and the underlying molecular mechanisms contributing to these associations are often unknown.In this study,we conducted an integrative genomic analysis incorporating multiple“omics”data and identified a functional regulatory DNA variant,rs56199421,and a plausible mechanism by which it regulates the expression of a puta-tive RA risk gene,ORMDL Sphingolipid Biosynthesis Regulator 3(ORMDL3).The T allele of rs56199421,located in the enhancer region of ORMDL3,exhibited stronger direct binding ability than the other C allele of rs56199421 did in vitro with the transcription factor JunD and demonstrated higher transcriptional activity.Moreover,the T allele of rs56199421 is associated with elevated RA risk,and ORMDL3 expression is increased in RA patients.Thus,these findings suggest that the T allele of rs56199421 enhances JunD transcription factor binding,increases enhancer activity,and elevates the expression of the RA risk gene ORMDL3.

Aryl hydrocarbon receptor activation drives polymorphonuclear myeloid-derived suppressor cell response and efficiently attenuates experimental Sjögren’s syndrome

Myeloid-derived suppressor cells(MDSCs)comprise heterogeneous myeloid cell populations with immunosuppressive capacity that contribute to immune regulation and tolerance induction.We previously reported impaired MDSC function in patients with primary Sjögren’s syndrome(pSS)and mice with experimental SS(ESS).However,the molecular mechanisms underlying MDSC dysfunction remain largely unclear.In this study,we first found that aryl hydrocarbon receptor(AhR)was highly expressed by human and murine polymorphonuclear MDSCs(PMN-MDSCs).Indole-3-propionic acid(IPA),a natural AhR ligand produced from dietary tryptophan,significantly promoted PMN-MDSC differentiation and suppressive function on CD4^(+)T cells.In contrast,feeding a tryptophan-free diet resulted in a decreased PMN-MDSC response,a phenotype that could be reversed by IPA supplementation.The functional importance of PMN-MDSCs was demonstrated in ESS mice by using a cell-depletion approach.Notably,AhR expression was reduced in PMN-MDSCs during ESS development,while AhR antagonism resulted in exacerbated ESS pathology and dysregulated T effector cells,which could be phenocopied by a tryptophan-free diet.Interferon regulatory factor 4(IRF4),a repressive transcription factor,was upregulated in PMN-MDSCs during ESS progression.Chromatin immunoprecipitation analysis revealed that IRF4 could bind to the promoter region of AhR,while IRF4 deficiency markedly enhanced AhR-mediated PMN-MDSC responses.Furthermore,dietary supplementation with IPA markedly ameliorated salivary glandular pathology in ESS mice with restored MDSC immunosuppressive function.Together,our results identify a novel function of AhR in modulating the PMN-MDSC response and demonstrate the therapeutic potential of targeting AhR for the treatment of pSS.

Epigenetic regulation of B cells and its role in autoimmune pathogenesis

B cells play a pivotal role in the pathogenesis of autoimmune diseases.Although previous studies have shown many genetic polymorphisms associated with B-cell activation in patients with various autoimmune disorders,progress in epigenetic research has revealed new mechanisms leading to B-cell hyperactivation.Epigenetic mechanisms,including those involving histone modifications,DNA methylation,and noncoding RNAs,regulate B-cell responses,and their dysregulation can contribute to the pathogenesis of autoimmune diseases.Patients with autoimmune diseases show epigenetic alterations that lead to the initiation and perpetuation of autoimmune inflammation.Moreover,many clinical and animal model studies have shown the promising potential of epigenetic therapies for patients.In this review,we present an up-to-date overview of epigenetic mechanisms with a focus on their roles in regulating functional B-cell subsets.Furthermore,we discuss epigenetic dysregulation in B cells and highlight its contribution to the development of autoimmune diseases.Based on clinical and preclinical evidence,we discuss novel epigenetic biomarkers and therapies for patients with autoimmune disorders.