Deubiquitination of aryl hydrocarbon receptor (AhR) by USP21 negatively regulates Th17 cells differentiation.

Aryl hydrocarbon receptor (AhR) is a key transcription factor that modulates the differentiation of T helper 17 (Th17) cells. How AhR is regulated at the post-translational level in Th17 cells remains largely unclear. Here we identify USP21 as a newly defined deubiquitinase of AhR. We demonstrate that USP21 interacts with and stabilizes AhR by removing the K48-linked polyubiquitin chains from AhR. Interestingly, USP21 inhibits the transcriptional activity of AhR in a deubiquitinating-dependent manner. USP21 deubiquitinates AhR at the K432 residue, and the maintenance of ubiquitination on this site is required for the intact transcriptional activity of AhR. Moreover, the deficiency of USP21 promotes the differentiation of Th17 cells both in vitro and in vivo. Consistently, adoptive transfer of USP21 deficient naïve CD4+ T cells elicits more severe colitis in Rag1-/- recipients. Therefore, our study reveals a novel mechanism in which USP21 deubiquitinates AhR and negatively regulates the differentiation of Th17 cells.

Iron metabolism and arthritis: Exploring connections and therapeutic avenues.

ABSTRACT: 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.

Rapid and Sustained Effect of Ixekizumab on Patient Global, Spinal Pain, Stiffness, and Fatigue in Chinese Patients with Radiographic Axial Spondyloarthritis.

INTRODUCTION: Ixekizumab, an interleukin 17A (IL-17A) inhibitor, has demonstrated rapid and sustained improvement in the signs and symptoms in patients with active radiographic axial spondyloarthritis (r-axSpA) in global and Chinese populations. We studied the effect of ixekizumab on patient-reported outcomes (PROs) (including patient global, spinal pain, stiffness, and fatigue) and overall health-related quality of life (HRQoL) of ixekizumab in the phase 3 study in China. METHODS: In this Chinese phase 3, randomized, double-blind, placebo-controlled study, patients with r-axSpA were randomized (1:1) to receive ixekizumab 80 mg every 4 weeks (IXEQ4W; starting dose 160 mg) or placebo for 16 weeks. At week 16, patients receiving placebo were switched to IXEQ4W, and those receiving IXEQ4W continued, until week 52. Data for patient global, spinal pain, spinal pain at night, stiffness, and fatigue were collected through week 52. Minimally clinical important differences (MCIDs) were determined for spinal pain and spinal pain at night. The subgroup analyses by baseline disease duration since diagnosis and baseline C-reactive protein (CRP) level were conducted post hoc. RESULTS: Compared with placebo, patients treated with IXEQ4W reported significantly greater improvement with a rapid onset in changes from baseline of PROs (patient global, spinal pain, spinal pain at night, stiffness, and fatigue) through week 16. Improvements were maintained through week 52. A similar trend of improvement was also observed in MCID response in spinal pain and spinal pain at night. The improvement in overall HRQoL was supported by EQ-5D-5L assessment. Subgroup analyses demonstrated that IXEQ4W provided significantly greater efficacy at week 16 compared with placebo, irrespective of baseline disease duration or baseline CRP level. CONCLUSION: IXEQ4W provided rapid and sustained improvement in clinically relevant PROs and overall HRQoL through 1-year treatment in Chinese patients with r-axSpA. Regardless of the baseline disease duration or baseline CRP level, consistent efficacy was observed. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT04285229.

Establishment and validation of prediction model for atherosclerotic cardiovascular disease in patients with hyperuricemia.

OBJECTIVE: To construct a risk prediction model for atherosclerotic cardiovascular disease (ASCVD) in patients with hyperuricemia. METHODS: Data in this study were obtained from the National Health and Nutrition Examination Survey (NHANES) (2007-2010). Participants from Huashan Hospital were included as an external validation. Logistic regression analysis was used to explore the relevant factors of ASCVD in patients with hyperuricemia. The discriminability of the model was evaluated using the area under the curve (AUC) statistic of the receiver operating characteristic curve. Hosmer-Lemeshow test, correction curve and decision curve analysis (DCA) were used to evaluate the model. RESULTS: A total of 389 patients collected from the NHANES were included in the final analysis. Logistic regression analysis showed that age, creatinine (Cr), glucose (Glu), serum uric acid (SUA), and history of gout were predictive factors for ASCVD in hyperuricemia (HUA) patients. These predictive factors were used to construct a nomogram. And 157 patients from NHANES were in the internal validation group and 136 patients from Huashan Hospital were in the external validation group. The AUC values of the three groups were 0.943, 0.735, and 0.664. The p values of the Hosmer-Lemeshow test were .568, .600, and .763. The calibration curve showed consistency between the nomogram and the actual observed values. The DCA curve indicated that the model has good clinical practicality. CONCLUSION: This study constructed the ASCVD risk prediction model for HUA patients, which is beneficial for medical staff to detect high-risk populations of ASCVD in the early stage.

Upregulation of GPX4 drives ferroptosis resistance in scleroderma skin fibroblasts.

The pathogenesis of systemic sclerosis (SSC) fibrosis involves the rapid proliferation of skin fibroblasts, and current anti-fibrotic treatments are limited. This study investigated the relationship between ferroptosis and SSC skin fibroblasts. We observed that erastin-induced ferroptosis was suppressed in SSC fibroblasts. RSL3, a direct inhibitor of Glutathione Peroxidase 4 (GPX4), significantly reduced the viability of the fibroblasts, and upregulation of GPX4 in the SSC fibroblasts contributed to ferroptosis resistance. Furthermore, we demonstrated that transferrin receptor 1 (TfR1) was a crucial transporter for iron deposition in the fibroblasts. Collectively, our results highlight that GPX4 inhibition could enhance the sensitivity to ferroptosis by SSC fibroblasts, which showed distinct characteristics of iron metabolism that were not observed in normal fibroblasts in this study. Taken together, these results suggest that targeting ferroptosis could be a therapeutic strategy for the treatment of SSC.

Higher Dietary Inflammatory Index and Increased Mortality Rate of Adults With Hyperuricemia: Findings From the National Health and Nutritional Examination Survey (2001-2018).

OBJECTIVE: This study aimed to assess the association between Dietary Inflammatory Index (DII) score and death among adults with hyperuricemia. METHODS: We collected data from the 2001 to 2018 cohorts of the National Health and Nutritional Examination Survey. Death information was obtained based on death certificate records from the National Death Index through December 31, 2019. The associations between DII score and all-cause, cardiovascular disease (CVD), and cancer death were investigated by using Cox proportional hazards regression models. RESULTS: We enrolled 7,786 participants with hyperuricemia in this study. The DII score ranged from -4.42 to 4.61. Higher DII score was significantly associated with higher levels of body mass index, glycohemoglobin, glucose, low-density lipoprotein-cholesterol, and C-reactive protein (all P < 0.05). During 67,851 person-years of follow-up, deaths of 1,456 participants were identified, including 532 CVD deaths and 246 cancer deaths. After adjusting for potential variables, significant higher risk of all-cause (hazard ratio [HR] 1.18, 95% confidence interval [95% CI] 1.03-1.36, P = 0.01) and CVD (HR 1.30, 95% CI 1.03-1.63, P = 0.02) death was observed for individuals with higher DII scores. Considering the DII score as a continuous variable, the risk of all-cause and CVD death increases 5% (HR 1.05, 95% CI 1.01-1.08) and 8% (HR 1.08, 95% CI 1.02-1.15) with each one-unit increment in DII score, respectively. Subgroup analysis indicated that the association between DII score and all-cause death among participants with hyperuricemia was more significant in males. CONCLUSION: DII score is found to be positively associated with all-cause and CVD death of adults with hyperuricemia. Controlling the intake of proinflammatory food might be a potential strategy to reduce the mortality rate.

Identification and validation of anti-protein arginine methyltransferase 5 (PRMT5) antibody as a novel biomarker for systemic sclerosis (SSc).

OBJECTIVES: In the complex panorama of autoimmune diseases, the characterisation of pivotal contributing autoantibodies that are involved in disease progression remains challenging. This study aimed to employ a global antibody profiling strategy to identify novel antibodies and investigate their association with systemic sclerosis (SSc). METHODS: We implemented this strategy by conducting immunoprecipitation (IP) following on-bead digestion with the sera of patients with SSc or healthy donors, using antigen pools derived from cell lysates. The enriched antigen-antibody complex was proceeded with mass spectrometry (MS)-based quantitative proteomics and over-represented by bioinformatics analysis. The candidate antibodies were then orthogonally validated in two independent groups of patients with SSc. Mice were immunised with the target antigen, which was subsequently evaluated by histological examination and RNA sequencing. RESULTS: The IP-MS analysis, followed by validation in patients with SSc, revealed a significant elevation in anti-PRMT5 antibodies among patients with SSc. These antibodies exhibited robust diagnostic accuracy in distinguishing SSc from healthy controls and other autoimmune conditions, including systemic lupus erythematosus and Sjögren's syndrome, with an area under the curve ranging from 0.900 to 0.988. The elevation of anti-PRMT5 antibodies was verified in a subsequent independent group with SSc using an additional method, microarray. Notably, 31.11% of patients with SSc exhibited seropositivity for anti-PRMT5 antibodies. Furthermore, the titres of anti-PRMT5 antibodies demonstrated a correlation with the progression or regression trajectory in SSc. PRMT5 immunisation displayed significant inflammation and fibrosis in both the skin and lungs of mice. This was concomitant with the upregulation of multiple proinflammatory and profibrotic pathways, thereby underscoring a potentially pivotal role of anti-PRMT5 antibodies in SSc. CONCLUSIONS: This study has identified anti-PRMT5 antibodies as a novel biomarker for SSc.

Attenuation of fibroblast activation and fibrosis by adropin in systemic sclerosis.

Fibrotic diseases impose a major socioeconomic challenge on modern societies and have limited treatment options. Adropin, a peptide hormone encoded by the energy homeostasis-associated (ENHO) gene, is implicated in metabolism and vascular homeostasis, but its role in the pathogenesis of fibrosis remains enigmatic. Here, we used machine learning approaches in combination with functional in vitro and in vivo experiments to characterize adropin as a potential regulator involved in fibroblast activation and tissue fibrosis in systemic sclerosis (SSc). We demonstrated consistent down-regulation of adropin/ENHO in skin across multiple cohorts of patients with SSc. The prototypical profibrotic cytokine TGFß reduced adropin/ENHO expression in a JNK-dependent manner. Restoration of adropin signaling by therapeutic application of bioactive adropin34-76 peptides in turn inhibited TGFß-induced fibroblast activation and fibrotic tissue remodeling in primary human dermal fibroblasts, three-dimensional full-thickness skin equivalents, mouse models of bleomycin-induced pulmonary fibrosis and sclerodermatous chronic graft-versus-host-disease (sclGvHD), and precision-cut human skin slices. Knockdown of GPR19, an adropin receptor, abrogated the antifibrotic effects of adropin in fibroblasts. RNA-seq demonstrated that the antifibrotic effects of adropin34-76 were functionally linked to deactivation of GLI1-dependent profibrotic transcriptional networks, which was experimentally confirmed in vitro, in vivo, and ex vivo using cultured human dermal fibroblasts, a sclGvHD mouse model, and precision-cut human skin slices. ChIP-seq confirmed adropin34-76-induced changes in TGFß/GLI1 signaling. Our study characterizes the TGFß-induced down-regulation of adropin/ENHO expression as a potential pathomechanism of SSc as a prototypical systemic fibrotic disease that unleashes uncontrolled activation of profibrotic GLI1 signaling.

Xanthohumol attenuates collagen synthesis in scleroderma skin fibroblasts by ROS/Nrf2/TGFß1/Smad3 pathway.

Skin fibrosis, the most obvious clinical manifestation of systemic sclerosis (SSc), has a high unmet need for treatment. Xanthohumol (Xn) has been shown to have beneficial effects on fibrotic diseases, but its efficacy in SSc remains unreported. This study aims to elucidate the effects and mechanisms of Xn on collagen synthesis in SSc skin fibroblasts (SScF). We found increased collagen production in SScF cultured in vitro, accompanied by dysregulated levels of oxidative stress. Cell experiments showed that Xn inhibited cell proliferation and promoted apoptosis. In addition, Xn was shown for the first time to upregulate reactive oxygen species (ROS) and nuclear factor erythroid 2-related factor 2 (Nrf2)levels in SScF, and when combined with the ROS scavenger N-acetylcysteine (NAC), Nrf2 expression was decreased. Importantly, we demonstrated that Xn significantly attenuated collagen synthesis by blocking the fibrotic classical transforming growth factor beta 1 (TGFß1)/Smad3 pathway, which interestingly was upregulated when combined with the Nrf2 inhibitor 385. Taken together, Xn suppressed the TGFß1/Smad3 pathway to ameliorate collagen overproduction by promoting ROS-induced oxidative stress damage and activating Nrf2, suggesting that Xn administration may be an emerging therapeutic strategy for skin fibrosis in SSc.

Ixekizumab for Active Radiographic Axial Spondyloarthritis in Chinese Patients: 16- and 52-Week Results from a Phase III, Randomized, Double-Blind, Placebo-Controlled Study.

INTRODUCTION: Ixekizumab, an interleukin-17A inhibitor, was efficacious and well tolerated for the treatment of active radiographic axial spondyloarthritis (r-axSpA) in international clinical studies. This phase III study aimed to determine the efficacy and safety of ixekizumab for treating Chinese patients with active r-axSpA. METHODS: Adults with active r-axSpA naïve to biologic disease-modifying antirheumatic drugs (bDMARDs), or with an inadequate response/intolerance to one tumor necrosis factor inhibitor, were randomized (1:1), double-blind, to receive ixekizumab 80 mg every 4 weeks (IXEQ4W; starting dose 160 mg), or placebo, for 16 weeks. Patients receiving placebo were then switched to IXEQ4W, and those receiving IXEQ4W continued, until week 52. The primary endpoint was the proportion of bDMARD-naïve patients achieving an Assessment of SpondyloArthritis International Society 40 (ASAS40) response at week 16. RESULTS: In total, 147 patients were randomized to receive placebo (n = 73) or IXEQ4W (n = 74). At week 16, more bDMARD-naive patients achieved ASAS40 in the IXEQ4W group (n = 66; 40.9%) than the placebo group (n = 64, 7.8%; p < 0.001). In the overall study population, ASAS40 was also achieved by more patients in the IXEQ4W group (37.8%) than the placebo group (8.2%; p < 0.001) at week 16, with a significant difference observed as early as week 1. There were significant improvements in all key secondary endpoints at week 16 with IXEQ4W versus placebo. Efficacy was sustained at week 52 in patients who continued IXEQ4W and there were also clinical improvements from weeks 16 to 52 in patients switched to IXEQ4W. The safety profile of ixekizumab was consistent with that described previously. Infections and injection-site reactions were the most frequently reported events of special interest. CONCLUSIONS: IXEQ4W was associated with rapid and significant improvements in the signs and symptoms of active r-axSpA in Chinese patients at week 16 that were sustained at week 52, with no new safety signals. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT04285229.

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); however, 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 putative 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. Supplementary Information: The online version contains supplementary material available at 10.1007/s43657-023-00107-z.

Association of visceral adipose tissue with gout: Observational and Mendelian randomization analyses.

BACKGROUND: The causal relationship between visceral adipose tissue (VAT) and gout is still unclear. We aimed to examine the potential association between them using observational and Mendelian randomization (MR) analyses. METHODS: In the observational analyses, a total of 11,967 participants (aged 39.5 ± 11.5 years) were included from the National Health and Nutrition Examination Survey. Logistic regression models were used to investigate the association between VAT mass and the risk of gout. In two-sample MR analyses, 211 VAT mass-related independent genetic variants (derived from genome-wide association studies in 325,153 UK biobank participants) were used as instrumental variables. The random-effects inverse-variance weighted (IVW) method was used as the primary analysis. Additional sensitivity analyses were also performed to validate our results. RESULTS: Observational analyses found that an increase in VAT mass (per standard deviation) was associated with a higher risk of gout after controlling for confounding factors (odds ratio [OR] = 1.27, 95% confidence intervals [CI] = 1.11-1.45). The two-sample MR analyses demonstrated a causal relationship between increased VAT mass and the risk of gout in primary analyses (OR = 1.78, 95% CI = 1.57-2.03). Sensitivity analyses also showed similar findings, including MR-Egger, weighted median, simple mode, weighted mode, and leave-one-out analyses. CONCLUSIONS: Observational analyses showed a robust association of VAT mass with the risk of gout. Meanwhile, MR analyses also provided evidence of a causal relationship between them. In summary, our findings suggested that targeted interventions for VAT mass may be beneficial to prevent gout.

Progress in research on mesenchymal stem cells and their extracellular vesicles for treating fibrosis in systemic sclerosis.

Systemic sclerosis (SSc) refers to an autoimmune disease characterized by immune dysfunction, vascular endothelial damage, and multi-organ fibrosis. Thus far, this disease is incurable, and its high mortality rate is significantly correlated with fibrotic events. Fibrosis has been confirmed as a difficult clinical treatment area that should be urgently treated in clinical medicine. Mesenchymal stem cells (MSCs) exhibit immunomodulatory, pro-angiogenic, and anti-fibrotic functions. MSCs-derived extracellular vesicles (EVs) have aroused rising interest as a cellular component that retains the functions of MSCs while circumventing the possible adverse effects of MSCs. Moreover, EVs have great potential in treating SSc. In this study, the current research progress on MSCs and their EVs for treating fibrosis in SSc was reviewed, with an aim to provide some reference for future MSCs and their EVs in treating SSc.

Blockade of IL-11 Trans-Signaling or JAK2/STAT3 Signaling Ameliorates the Profibrotic Effect of IL-11.

OBJECTIVES: Systemic sclerosis (SSc) is a rare rheumatic disease characterized by vascular damage, dysregulated immune response, and fibrosis. Interleukin-11 (IL-11) is upregulated in SSc. This study aimed to investigate the pathological and therapeutic role of the IL-11 trans-signaling pathway in SSc. METHODS: Plasma IL-11 level was evaluated in 32 patients with SSc and 15 healthy controls, while the expression levels of ADAM10, ADAM17, IL-11, IL-11 Rα, or IL-11 co-stained with CD3 or CD163 in the skin of SSc patients and healthy controls were analyzed. Fibroblasts were treated with IL-11 and ionomycin to evaluate the profibrotic effect of IL-11 trans-signaling pathway. TJ301 (sgp130Fc) and WP1066 (a JAK2/STAT3 inhibitor) intervention groups were set up to investigate the antifibrotic effect of targeting IL-11. RESULTS: Levels of plasma IL-11 were extremely low in most SSc patients and healthy controls. In contrast, levels of IL-11, IL-11 Rα, and ADAM10, but not ADAM17, were significantly elevated in the skin of SSc patients. Moreover, the numbers of IL-11+ CD3+ cells and IL-11+ CD163+ cells were increased in the skin of SSc patients. Besides, IL-11 and ADAM10 were also elevated in the skin and pulmonary of bleomycin-induced SSc mouse. Fibroblasts co-stimulated with IL-11 and ionomycin showed increased expression of COL3 and phosphorylation of STAT3, which could be inhibited by TJ301 or WP1066. TJ301 also ameliorated skin and lung fibrosis in BLM-induced SSc mouse. CONCLUSIONS: IL-11 induces fibrosis in SSc by regulating the trans-signaling pathway. Blockage of sgp130Fc or inhibition of the JAK2/STAT3 pathway could ameliorate the profibrotic effect of IL-11.

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.

Intestinal uric acid excretion contributes to serum uric acid decrease during acute gout attack.

OBJECTIVE: Spontaneous serum uric acid (SUA) decrease has been found in many patients during acute gout attacks, but its mechanism remains unclear. METHODS: The spontaneous regulation of SUA during a gout attack and its possible causes were evaluated in patients with gout. The mechanism of the spontaneous SUA decrease was further studied in Caco2 cells and a monosodium urate (MSU)-induced gout model of wild-type mice and ABCG2-/- mice. The urate transport function of intestinal epithelial cells was detected by transwell culture of Caco2 cells. Expression of ATP-binding cassette super-family G member 2 (ABCG2), IL-1ß and phosphoinositide 3-kinase (PI3K)/Akt was analysed using real-time PCR, western blotting, or immunofluorescence assays. RESULTS: SUA decreased during acute gout attacks in both the gout patients and MSU-induced gouty mice. Increased serum CRP and IL-1ß levels were correlated with the SUA decrease. Intestinal uric acid excretion and expression of ABCG2 were upregulated in the mice during acute gout attacks. In the ABCG2-/- mice, intestinal uric acid excretion significantly decreased during gout attacks. In an in vitro study of a transwell culture, ABCG2 and its upstream PI3K/Akt pathway were significantly upregulated in intestinal epithelial cells. However, ABCG2 expression and its associated intestinal uric acid transport were inhibited when PI3K/Akt was blocked by a PI3K inhibitor, LY294002. CONCLUSIONS: Increased intestinal urate excretion resulted in spontaneous SUA downregulation during acute gout attacks. Inflammation-induced PI3K/Akt activation and ABCG2 expression in epithelial cells might contribute to the upregulation of intestinal uric acid excretion.

L-shaped association between serum 25-hydroxyvitamin D and all-cause mortality of individuals with rheumatoid arthritis.

OBJECTIVE: We aimed to examine the relationship between serum 25-hydroxyvitamin D and all-cause, cause-specific mortality of patients with RA. METHODS: This cohort study included 1466 patients with RA from The National Health and Nutrition Examination Survey (NHANES) 2001-14. Mortality status was obtained according to death certificate records from the National Death Index. Cox proportional risk models were used to estimate hazard ratios (HR) and 95% CI for mortality. A generalized additive model, smooth curve fitting and 2-piecewise Cox proportional hazards models were established to address the nonlinearity between serum 25-hydroxyvitamin D and mortality. RESULTS: A total of 1466 patients [mean (s.d.) 59.89 (14.14) years old; 58.94% female] were enrolled. The weighted mean level of 25-hydroxyvitamin D was 59.26 (24.99) nmol/l and 38.95% were found with deficient (or severe deficient) vitamin D (<50.00 nmol/l). During 10453 person-years of follow-up, 268 patients were documented for all-cause death, including 52 cardiovascular disease （CVD）deaths and 48 cancer deaths. Compared with patients with serum 25-hydroxyvitamin D <25.00 nmol/l, patients with higher serum 25-hydroxyvitamin D were more likely to have lower rate of all-cause mortality. Nonlinear and L-shaped association between serum 25-hydroxyvitamin D and all-cause mortality was found, and decreased serum 25-hydroxyvitamin D was significantly associated with increased risk of all-cause mortality in patients with serum 25-hydroxyvitamin D <37.30 nmol/l [HR 0.95 (0.92, 0.98); P < 0.01]. CONCLUSION: An L-shaped association between serum 25-hydroxyvitamin D and all-cause mortality was found among patients with RA, indicating that serum 25-hydroxyvitamin D should be improved to a certain level for the prevention of premature death.