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CXCL7 enhances RANKL-induced osteoclastogenesis via the activation of ERK/NFATc1 signaling pathway in inflammatory arthritis

Arthritis Research & Therapy volume 27, Article number: 34 (2025) Cite this article

Abstract

Background

Rheumatoid arthritis (RA) with anti-citrullinated protein/peptide antibodies (ACPA + RA) demonstrates more significant radiographic damage compared to ACPA-negative RA (ACPA- RA). Chemokine-activated signaling pathways contribute to the regulation of the bone formation and resorption. The potential role of C-X-C motif chemokine ligand 7 (CXCL7) in bone erosion and its viability as a therapeutic target for RA merit further investigation.

Methods

Plasma CXCL7 concentration was quantified using enzyme-linked immunosorbent assay (ELISA). The effect of CXCL7 on receptor activator of NF-κB ligand (RANKL)-induced osteoclastogeneis was assessed through tartrate-resistant acid phosphates (TRAP) staining and F-actin ring immunofluorescence. Western blotting analysis was used to identify the signaling pathways activated by CXCL7. To investigate the potential therapeutic effect by targeting Cxcl7, Cxcl7 neutralizing antibodies were administrated intraperitoneally to mice with collagen-induced arthritis (CIA). Histopathology and micro-computed tomography (micro-CT) scanning were utilized to assess joint inflammation and bone destruction in CIA mice.

Results

The plasma CXCL7 concentration was significantly higher in ACPA + RA compared with ACPA- RA and healthy controls. The level of CXCL7 was positively correlated with disease activity and bone erosion in RA patients. It was discovered that CXCL7 promoted RANKL-induced osteoclastogenesis in CD14 + monocytes derived from RA patients. Mechanistically, the addition of Cxcl7 significantly enhanced RANKL-induced phosphorylation of ERK1/2 and NFATc1 expresssion. Cxcl7 neutralizing antibody alleviated arthritis severity in CIA by reducing the inflammatory response, osteoclasts numbers, and bone destruction in CIA mice joints.

Conclusion

CXCL7 contributes to the bone erosion in RA by enhancing RANKL-induced osteoclastogenesis via the activation of ERK/NFATc1 signaling pathways. CXCL7 could potentially be targeted for therapeutic interventions in RA.

Introduction

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovitis and bone destruction [1], which can lead to joint deformity and disability, imposing a significant burden on both society and families [2, 3]. To date, the precise pathogenesis of RA remains incompletely elucidated. Over the past two decades, the introduction of biologic agents, small-molecule targeted drugs, and the clinical application of treat-to-target strategy has significantly improved the prognosis of RA patients [4]. However, a certain proportion of patients remain poorly controlled and unresponsive to existing therapies. To address the unmet clinical needs, further investigation into the pathogenesis of RA and identification of novel therapeutic targets are imperative.

Antibodies against citrullinated protein/peptide autoantibodies (ACPA) are highly specific in RA, which have been used as biomarkers for the diagnosis and prognosis of the disease [5, 6]. Based on the presence or absence of ACPA, RA can be divided into two subtypes, namely ACPA-positive (ACPA+) and ACPA-negative (ACPA-). ACPA + RA patients usually show more severe joint damage and radiographic lesions [7,8,9]. Previous studies have found that there are significant differences in susceptibility gene loci of ACPA + RA and ACPA- RA [10, 11]. Our previous studies have found distinct gene expression profiles in peripheral blood mononuclear cell (PBMC) from ACPA + RA and ACPA- RA patients. Chemokines such as C-X-C motif chemokine ligand 2 (CXCL2) and C-X-C motif chemokine ligand 7 (CXCL7) are highly expressed in PBMC from treatment-naïve ACPA + RA patients. Functional studies revealed that CXCL2 could enhance osteoclastogenesis in RA [12]. The potential role of CXCL7 in the pathogenesis of RA warrants further clarificaiton.

CXCL7 belongs to the family of CXC chemokines, which can be produced by platelets, megakaryocytes, monocytes, lymphocytes and neutrophils [13]. CXCL7 participate in various biological processes, including angiogenesis and biological behavior of malignant tumors [14]. In 2009, it was discovered that Cxcl7 could increase the number of osteoclasts generated by bone marrow-derived macrophage (BMM) [15]. Administration of Cxcl7 neutralizing antibodies in vitro lead to a reduction in osteoclast numbers [16]. In human multiple myeloma, bone-lining mesenchymal stromal cells exhibit high levels of MMP-13 expression. Analysis of soluble factors from both wild type and MMP-13-null mesenchymal stromal cells revealed CXCL7 as a novel MMP-13 substrate and regulator of osteoclastogenesis [17].

Given the research background, we proposed that CXCL7 might aggravate bone destruction in RA by influencing osteoclastogenesis. This hypothesis partially elucidates the mechanism of bone destruction in ACPA + RA, and offers insights into further understanding the pathogenesis of RA.

Materials and methods

Participants

Blood samples were collected from 132 RA patients who admitted to the Rheumatology and Immunology Department of Peking University Third Hospital from 2018 to 2021. All patients fulfilled the 2010 European League against Rheumatism/American College of Rheumatology Classification criteria [6]. Patients with conditions such as pregnancy, infection, other autoimmune diseases, tumor, heart failure, or other organ dysfunctions were excluded. The clinical and laboratory data of the patients were extracted from the electronic medical records. 68 healthy participants were recruited from the Physical Examination Center of Peking University Third Hospital during the same period. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Peking University Third Hospital (No.2020369-01). All procedures involving human specimens are performed with the informed consent of each patient.

Cell culture

PBMCs were separated from the blood of RA patients by Ficoll-Paque Plus (GE Healthcare, Sweden). CD14 + monocytes were positively selected by magnetic-activated cell sorting (Miltenyi Biotec, Germany) and were cultured in 48-well plates (1.5 × 105 cells/well) or 6-well plates (1 × 106 cells/well) in RPMI-1640 medium containing 10% heat-inactivated fetal bovine serum (FBS). Osteoclast differentiation was primed with macrophage colony-stimulating factor (M-CSF, 50 ng/ml), RANKL (100 ng/ml), and various concentrations of CXCL7 (10, 50 or 100 ng/ml). RAW264.7 macrophages (1.0 × 104 cells/well in 48-well plates or 4.5 × 104 cells/well in 12-well plates) were incubated in DMEM media containing 10% FBS and treated with M-CSF (10 ng/ml), RANKL (50 ng/ml) and Cxcl7(10, 50 or 100ng/ml).

Enzyme-linked immunosorbent assay

The plasma levels of CXCL7 in human and mouse were measured using CXCL7 ELISA kits according to the manufacturer’s instructions.

TRAP staining

TRAP staining was conducted using a leukocyte acid phosphatase kit (Sigma-Aldrich) according to the instructions. TRAP-positive cells containing three or more nuclei were counted in at least 5 random fields under a light microscope.

F-actin ring immunofluorescence

To detect the formation of F-actin rings, cells were fixed and incubated with FITC-conjugated anti-actin antibody for 1 h. Then the cells were stained with DAPI for 5 min and observed under Olympus BX51 microscope (Tokyo, Japan).

Bone resorption assay

The CD14 + monocytes were plated at a density of 7.5 × 104 cells/well onto the bone slices. After 28 days of culture, the bone slices (bovine origin) were fixed, dehydrated and sputtered with gold. Then the resorption pits were visualized under a scanning electron microscope (JEOL, JSM7900F, Japan). The area of resorption pits in at least five random fields was quantified using Image J software.

Quantitative PCR

Total RNA was isolated using TRIzol reagent (Invitrogen) and single-stranded cDNA was synthesized from 1 μg of total RNA using reverse transcriptase (Tiangen Biotech). RT-PCR was performed using the Talent qPCR PreMix (SYBR Green) (Tiangen Biotech) and results were detected using a QuantStudio™ 5 Real-Time PCR System (Thermo Fisher Scientific). The primer sequences used are listed in the supplementary material, Table S1.

Western blotting

The RAW264.7 cells were lysed in RIPA Lysis Buffer (Applygen). Total protein (40 μg per lane) was separated by 10% sodium dodecyl sulphate-polyacrylamide gel and transferred onto polyvinylidene fluoride membranes (Merck Millipore). After blocking with 5% milk, the membranes were incubated with specific antibodies for 12–16 h at 4 °C. Secondary antibody coupled with horseradish peroxidase was incubated for 1 h at room temperature, bands were displayed by chemiluminescence development, and data quantitative analysis was performed by the ImageJ software. Details regarding the antibodies used in this study was listed in the supplementary material, Table S2.

CIA model

DBA/1 male mice aged 6–8 weeks were obtained from Beijing Vital River Laboratory Animal Technology Co., Ltd. Animal experiments were approved by the Animal Protection and Ethics Committee of Peking University Health Science Center (Ethics number: LA2020486). Mice were injected subcutaneously into the tail of 100 μg bovine type II collagen (1 mg/mL) mixed with Complete Freund’s Adjuvant. After 21 days, 50 μg bovine type II collagen mixed with Incomplete Freund’s Adjuvant was injected. Blood was collected from the inner canthus to detect the Cxcl7 level in plasma of mice. Isotype antibody and Cxcl7 neutralizing antibody were intraperitoneally injected at the dose of 10 mg/kg on 3, 6, 9, 12, 15 and 18 days after secondary immunization. The neutralizing antibody (catalog number AF793) was obtained from RD Systems. The sample size for each group is 6.

Clinical and histological evaluation of arthritis

Arthritis scores were assessed daily after secondary immunization. Each paw was scored individually based on a 0–4 scale, with 4 indicating the most severe inflammation [18]. On day 42, the joint tissues were fixed, embedded and sliced to prepare for HE staining. HE staining results of ankles were scored from grade 0 to grade 4 according to the intensity of the lining layer hyperplasia and mononuclear cell infiltration [19].

Micro-computed tomography (micro-CT) scanning

The hind paw of mice were fixed on the Micro-CT special scanning pad, with scanning voltage of 80 KV and scanning current of 500 μA. 3D reconstruction by Inveon Research Workplace was applied to acquire bone volume/tissue volume (BV/TV), bone surface area/bone volume, trabecular number (Tb.N) and trabecular thickness (Tb.Th).

Statistical analysis

Data are presented as the mean ± standard deviation or the median with interquartile range. Statistical analyses were performed using Spearman correlation, Mann-Whitney test and one-way analysis of variance followed by Tukey’s test for multiple comparisons. p < 0.05 was considered to be statistically significant.

Results

Increased plasma CXCL7 concentrations were positively correlated with disease activity in RA patients

The concentration of CXCL7 in plasma was detected in 97 ACPA + RA patients, 35 ACPA- RA patients and 68 healthy controls. Age and sex were matched among the three groups. There were no significant differences in the disease activity score of 28 joints (DAS28), duration of disease, CRP, ESR, proportion of bone destruction, and medication between ACPA + RA patients and ACPA- RA patients (Table S3). Median levels of plasma CXCL7 in RA patients (392.2, (208.8, 720.6) ng/ml) was significantly higher than that in healthy controls (135.1, (75.61, 297.9) ng/mL) (p < 0.001, Fig. 1A). Significant elevation of plasma CXCL7 concentration was found in ACPA + RA patients (427.5, (223.2, 790.3) ng/mL) compared to ACPA- RA patients (243.4, (124.6, 495.0) ng/mL) (p < 0.05, Fig. 1B). Plasma CXCL7 concentration was significantly higher in RA patients with bone erosion (573.7, (244.4, 1422) ng/mL) than that in RA without bone erosion (295.6, (195.9, 490.5)ng/mL) (p < 0.01, Fig. 1C). Positive correlations were observed between CXCL7 concentration and DAS28 (r = 0.3744, p < 0.001), ESR (r = 0.2171, p < 0.05) and CRP (r = 0.2775, p < 0.01) (Fig. 1D-F). The expression level of CXCL7 was not correlated with the RF titer (r = 0.1541, p = 0.1494) (Fig. 1G).

Fig. 1
figure 1

The expression of CXCL7 in RA patients and correlations between CXCL7 and clinical parameters. (A) Levels of CXCL7 in the plasma of RA patients (n = 132) and healthy controls (n = 68). (B) Levels of CXCL7 in the plasma of ACPA+ (n = 97) and ACPA- (n = 35) RA patients. (C) Levels of CXCL7 in the plasma of RA patients with (n = 42) or without bone erosion (n = 63). (D-G). Correlation between CXCL7 and ESR (n = 132), CRP (n = 132), DAS28 (n = 132) and RF (n = 89). Data are expressed as median with interquartile range. Statistical analyses were conducted using Mann-Whitney U test (A and C) and the Kruskal-Wallis H test (B). *P < 0.05, **P < 0.01, ***P < 0.001. Correlation analysis was performed using the Spearman test (D, E, F and G)

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CXCL7 promoted osteoclastogenesis and bone resorption in CD14 + monocyte from RA patients

TRAP staining showed that CXCL7 (50 ng/ml) enhanced RANKL-induced osteoclastogenesis of CD14 + monocytes from RA patients (Fig. 2A and D). Immunofluorescence microscopy revealed that CXCL7 (50 ng/ml) promoted the formation of F-actin ring in the presence of M-CSF and RANKL (p < 0.001) (Fig. 2B and E). CD14 + monocytes were cultured on bone slices to measure the function of osteoclast by lacunar resorption assay system. The results showed that the resorption area was increased in bone slices exposed to CXCL7 (50 ng/ml) (p < 0.01) (Fig. 2C). CXCL7 (50 ng/mL) increased the transcription level of RANK (p < 0.01). Expression of the osteoclast markers including cathepsin K (p < 0.05) and TRAP (p < 0.05) was also significantly increased after 3 days of stimulation with the CXCL7 (50 ng/mL) (Fig. 2F).

Fig. 2
figure 2

CXCL7 enhanced osteoclast differentiation and bone resorption in RA patients. CD14 + monocytes isolated from RA patients were cultured with M-CSF, RANKL and CXCL7 at specified concentrations. (A )and (B). Representative images of TRAP and F-actin staining. (C). Exemplary scanning electron microscopy images of bone resorption pits. The proportion of resorption pit area in 5 random fields per group was measured. (D). The ratio of osteoclast number to control group in 5 random fields each well in TRAP staining. (E). The ratio of F-actin ring number to control group in 5 random fields each well in F-actin staining. F. Transcription levels of TRAP, cathepsin K, and RANK after 3 days. Each group consisted of three samples. Data are presented as mean ± SD. Statistical analyses were conducted using one-way ANOVA. *P < 0.05, **P < 0.01, ***P < 0.001. Scale bar in A is 200 μm. Scale bar in B is 100 μm. Scale bar in C is 10 μm

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Cxcl7 promoted osteoclastogenesis via ERK/NFATc1 signaling pathways

Cxcl7 (50 ng/mL) significantly increased the nucleus number of each osteoclast (p < 0.05) without effecting the overall osteoclasts count (Fig. 3A). The transcription level of RANK (p < 0.001), cathepsin K and TRAP (p < 0.05, Fig. 3B) were increased in Cxcl7 (50 ng/mL) group after 3 days. RAW264.7 cells were incubated to explore the signal pathways involved in the osteoclastogenesis. The results showed that Cxcl7 significantly increased the expression of NFATc1 in RAW264.7 cells (p < 0.01, Fig. 3D), with no effect on the c-Fos. The phosphorylation of p65 and ERK1/2 were detected by Western blotting at different time-points. The results showed that addition of Cxcl7 significantly increased phosphorylation of ERK1/2 at 10 min and 15 min (p < 0.05, p < 0.01), with no effect on the phosphorylation of p65 (Fig. 3C).

Fig. 3
figure 3

Cxcl7 enhanced osteoclast differentiation via ERK/NFATc1 signaling pathways in RAW264.7 cells. (A) RAW264.7 cells were cultured in the presence of M-CSF and RANKL with Cxcl7 at the indicated concentrations. After 5 days, cells were fixed and stained for TRAP. Number of osteoclasts and number of nuclei in each osteoclast were counted. (B) After 3 days, transcription levels of TRAP, cathepsin K, and RANK were detected. (C) Cxcl7 increased the activation of the p-ERK at 10 and 15 min, with no effect on p-p65. (D) Cxcl7 induced the mRNA expression of NFATc1 in RAW264.7 cells at 3 days, with no effect on c-Fos. Values shown represent the mean ± SD from three separate experiments. Statistical analyses were conducted using one-way ANOVA. *P < 0.05, **P < 0.01, ***P < 0.001. Scale bar is 100 μm

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Dynamic changes of Cxcl7 expression in peripheral blood of CIA mice

The level of plasma Cxcl7 in control and CIA group were detected at 0, 3, 7, 14 and 21 days after secondary immunization. As shown in the figure S1, compared with the control group, the level of plasma Cxcl7 of CIA mice significantly increased which reached a peak on the 7th day (p < 0.001) (Fig.S1).

Cxcl7 neutralizing antibody ameliorated the inflammatory arthritis and osteoclast formation in CIA mice

The CIA mice exhibited joint swelling approximately one week after the second immunization, and the arthritis index score gradually increased as the disease progressed. The arthritis score in Cxcl7 neutralizing antibody group began to be lower than that in the CIA group on the 16th day and continued to 21th day after the second immunization (p < 0.05) (Fig. 4A). On the 21st day after the second immunization, the ankle joints were collected and embedded in paraffin for HE and TRAP staining. The group treated with Cxcl7 neutralizing antibody showed a significant decrease in inflammatory cell infiltration and synovial tissue hyperplasia compared to the CIA group (p < 0.05) (Fig. 4B). The average number of osteoclasts per field was significantly lower in Cxcl7 neutralizing antibody group compared to CIA group (7 ± 1.79 vs. 16.5 ± 3.27, p < 0.001) (Fig. 4C).

Fig. 4
figure 4

Cxcl7 neutralizing antibody ameliorated inflammation and osteoclast formation in CIA mice. (A) Representative pictures of the hind paws and score of the articular index of the different groups. The arthritis score was presented as mean ± standard error. (B) HE staining of representative ankle sections 21 days after secondary immunization. Synovial hyperplasia and inflammatory cell infiltration were graded. (C) TRAP staining of representative ankle sections (black arrows represented osteoclast). 5 fields were selected for each section and the number of TRAP positive multinucleated cells in each field was calculated. n = 6 per group. Data are presented as mean ± SD. Statistical analyses were conducted using one-way ANOVA. *P < 0.05, **P < 0.01, ***P < 0.001. Scale bar is 100 μm

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Cxcl7 neutralizing antibody mitigated bone destruction in CIA mice

Micro-CT scanning and three-dimensional reconstruction were applied to assess the degree of bone damage. Cortical bone defects and bone loss were observed in the metacarpophalangeal and interphalangeal joint of CIA group, which were reduced in the Cxcl7 neutralizing antibody group (Fig. 5A). Bone mass and bone surface area of tarsal bone (in red box) were measured and the results showed that Cxcl7 neutralizing antibody significantly increased bone volume fraction (Bv/Tv) (p < 0.01) and decreased bone surface area volume ratio (Bs/Bv) (p < 0.01). The number of trabeculae (Tb.N) (p < 0.05) and trabeculae thickness (Tb.Th) (p < 0.01) in Cxcl7 neutralizing antibody group were also increased compared to CIA group (Fig. 5B).

Fig. 5
figure 5

Cxcl7 neutralizing antibody mitigated bone destruction in CIA mice. (A) Representative micro-CT scanning images of the hind paw in different groups. Bone mass and bone surface area of the tarsus (inside red frame) were measured to observe bone mass and bone erosion. (B) Calculation of the microarchitectural parameters was performed. BV/TV = bone volume/tissue volume; Tb.N = trabecular number; Tb.Th = trabecular thickness, Bs/Bv = bone surface/bone volume. n = 6 per group. Data are presented as mean ± SD. Statistical analyses were conducted using one-way ANOVA. *P < 0.05, **P < 0.01

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Discussion

Bone destruction is a prominent pathological feature of RA. In the present study, CXCL7 was demonstrated to enhance the osteoclast differentiation and bone resorption activity through the activation of MAPK-ERK pathway. Treatment with Cxcl7 neutralizing antibody reduced the arthritis score and alleviated the bone destruction in CIA mice, indicating a potential novel therapeutic approach for RA.

Previous studies have found that CXCL7 was highly expressed in the synovium of early RA, which can help to distinguish early RA from remitting arthritis [20]. Platelet‑derived extracellular vesicles containing CXCL7 promoted invasion and migration of RA fibroblast‑like synoviocytes [21]. Consistent with previous studies, we found that the concentration of plasma CXCL7 in RA was significantly elevated compared to healthy controls, especially in RA patients with bone erosion. Cxcl7 has been found to regulate the process of osteoclastogenesis in mouse BMM [15,16,17]. In our study, higher levels of CXCL7 were found in RA patients with bone erosions on radiograph, suggesting that CXCL7 may play a role in the bone destruction of RA. To further investigate the effect of CXCL7 on osteolastogenesis, CD14 + monocytes were isolated from the peripheral blood of RA patients and cultured in vitro. The results showed that CXCL7 enhanced osteoclastogenesis by increasing the number of osteoclasts derived from CD14 + monocytes and expanding the bone resorption area. The current study provides a new clue to investigate the bone destruction mechanism of RA.

RANKL is a critical stimulator in the process of osteoclast formation, binding of RANKL to RANK induces trimerization of RANK, and then recruits tumor necrosis factor receptor associated factor to initiate the downstream signaling cascade [22]. CXCL7 increased the transcription levels of RANK in CD14 + monocytes, which might enhance the stimulating effect of RANKL. Cathepsin belongs to cysteine protease which effectively degrades extracellular matrix proteins in bone. Cathepsin K is expressed at the highest level among the known cathepsins in osteoclasts [23]. We detected the transcription levels of Cathepsin K and found that it was increased upon stimulation with Cxcl7, which may contribute to enhance the function of bone resorption.

It has been shown that Cxcl7 can increase the number of small osteoclasts (3 ≤ number of nuclei ≤ 20) generated by mouse BMM, suggesting that Cxcl7 may play a promoting role in the early stage of osteoclast differentiation [15]. However, we found that Cxcl7 increased the number of nuclei in each osteoclast without increasing the number of osteoclasts generated by RAW264.7 cells, suggesting that Cxcl7 may promote the fusion of osteoclasts in the late stage of osteoclast differentiation. This inconsistency may be due to the application of different osteoclast precursors in different studies. NF-κB and MAPK signaling pathways are known to be critical downstream pathways of RANKL activation, and NFATc1 and c-Fos are critical transcription factors in the regulation of osteoclast differentiation [24]. Our results showed that Cxcl7 significantly promoted phosphorylation of ERK1/2 and mRNA expression of NFATc1, with no effect on phosphorylation of p65 and mRNA expression of c-Fos. Therefore, the above results imply that Cxcl7 could potentially enhance osteoclastogenesis and bone resorption by regulating ERK/NFATc1 signaling pathways.

The activity of CXCL7 is facilitated through C-X-C motif chemokine receptor 2 (CXCR2), a member of the G-protein-coupled receptor family with seven structural transmembrane domains [25]. Previous studies have specifically examined the effect of CXCR2 on arthritis models. It was discovered that CXCR2 receptor blocker DF2162 could reduce arthritis score and paw swelling in adjuvant-induced arthritis [26] and CIA [27]. In comparison to the wild-type mice, the Cxcr2 knockout mice exhibited a significant improvement in joint scores in serum-transferred arthritis models [28]. However, another group found that Cxcr2-/- mice had lower body weight, smaller bone trabecular volume, and worse mechanical properties of long bone compared to wild-type mice. There was also a delay in the healing of skull defects in Cxcr2-/- mice [29]. Briefly, the effects of Cxcr2 knockout on bone metabolism presents variability across studies, which may be related to the pleiotropic function of Cxcr2, including the regulation of osteoclast differentiation and the promotion of angiogenesis during bone remodeling.

Given that CXCR2 binds to multiple chemokines with different functions, directly targeting of CXCR2 could potentially influence its physiological function. Therefore, we applied Cxcl7 neutralizing antibody to evaluate its therapeutic potential in CIA model, with a particular focus on its effect on bone destruction. A significant increase in plasma Cxcl7 levels of CIA mice was observed, commencing on the third day after the secondary immunization, and reaching a peak on the seventh day. The inflammatory response and the degree of bone destruction in CIA mice was alleviated by the Cxcl7 neutralizing antibody, suggesting that targeting CXCL7 might serve as a new therapeutic strategy for RA. However, targeting CXCL7 may reduce inflammation, the dampening in inflammation does not exclude the hypothesis that the number of macrophages/monocytes present in the joint is affected, thereby limiting the precursor cells for osteoclastogenesis. The alleviation of inflammation can also reduce various inflammatory factors, potentially influencing the osteoclastogenesis process. The osteoclastogenesis is a complex process, regulated jointly by a network of various cytokines in vivo.

The mRNA levels of Cxcl1 and Cxcl2 were found to be increased in the ankle joints of mice injected intra-articularly with ACPA [30], and CXCL8 was released by human osteoclasts in response to ACPA stimulation [31]. Our study revealed a significant elevation in plasma CXCL7 levels in ACPA + RA patients compared to those with ACPA- RA. Whether ACPA can regulate the expression of CXCL7 and then participate in the regulation of osteoclast differentiation needs to be further clarified in future studies.

Conclusion

In summary, the current study indicates that CXCL7 may facilitate the osteoclast differentiation of CD14 + monocytes from RA patients. Targeting Cxcl7 by neutralizing antibody resulted in a reduction of arthritis score and mitigated bone destruction in CIA mice. This study enhances our comprehension of the role of CXCL7 in the pathogenesis of RA, and provides experimental basis for identifying new therapeutic target for RA.

Data availability

No datasets were generated or analysed during the current study.

Abbreviations

ACPA:

Anti-citrullinated protein/peptide autoantibodies

BMM:

Bone marrow-derived macrophage

CIA:

Collagen-induced arthritis

CXCL2:

C-X-C motif chemokine ligand 2

CXCL7:

C-X-C motif chemokine ligand 7

CXCR2:

C-X-C motif chemokine receptor 2

DAS28:

Disease activity score of 28 joints

ELISA:

Enzyme-linked immunosorbent assay

M-CSF:

Macrophage colony-stimulating factor

Micro-CT:

Micro-computed tomography

RA:

Rheumatoid arthritis

RANKL:

Receptor activator of NF-κB ligand

TRAP:

Tartrate-resistant acid phosphates

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Acknowledgements

We gratefully thank the Medical Research Center of Peking University Third Hospital for providing experimental equipment and technical support.

Funding

This work was supported by the National Natural Science Foundation of China (No.82271825), and Beijing Municipal Natural Science Foundation (No.7222264).

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Author notes

  1. Xinyu Wang and Lin Sun contributed equally to this work as co-first authors.

Authors and Affiliations

  1. Department of Rheumatology and Immunology, Peking University Third Hospital, Beijing, 100191, China

    Xinyu Wang, Lin Sun, Zhuo An, Changhong Li & Jinxia Zhao

  2. Department of General Medicine, Beijing Chaoyang Hospital, Capital Medical University, Beijing, China

    Xinyu Wang

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  1. Xinyu Wang
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  2. Lin Sun
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  3. Zhuo An
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Contributions

XW, LS and ZA carried out the molecular biochemical studies. XW and LS drafted the manuscript and performed the statistical analysis. CL and JZ participated in the design of the study and helped to draft manuscript. All authors have read and approved the final manuscript.

Corresponding authors

Correspondence to Changhong Li or Jinxia Zhao.

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Ethics approval and consent to participate

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Ethics Committee of Peking University Third Hospital (No.2020369-01). All procedures involving human specimens are performed with the informed consent of each patient. Animal experiments were approved by the Animal Protection and Ethics Committee of Peking University Health Science Center (Ethics number: LA2020486).

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The authors declare no competing interests.

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Wang, X., Sun, L., An, Z. et al. CXCL7 enhances RANKL-induced osteoclastogenesis via the activation of ERK/NFATc1 signaling pathway in inflammatory arthritis. Arthritis Res Ther 27, 34 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13075-025-03502-1

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  • DOI: https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13075-025-03502-1

Keywords

Arthritis Research & Therapy

ISSN: 1478-6362

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