Expression of LRRC15 is upregulated in human RA synovial tissues. (A) Gene Expression Omnibus (GEO) database screening for differentially expressed genes in RA synovial tissues. (B) Expression of LRRC15 in the GEO database. Expression of LRRC15 in collected synovial tissues of RA patients (n = 20) and normal controls (n = 10) by RT-qPCR (C) and immunohistochemistry (IHC) (D). Data are presented as mean ± SD. Statistical significance was determined using unpaired t-tests for independent data. *P < 0.05 vs control group. LRRC15, leucine-rich repeat containing 15; RA, rheumatoid arthritis; HC, healthy controls.|@|~(^,^)~|@|Depletion of LRRC15 protects RA-FLS from proliferation and inflammation. Detection of LRRC15 expression in RA-FLS and Control-FLS by RT-qPCR (A) and western blot (B). (C) The inhibition efficiency of shRNAs of LRRC15 by RT-qPCR. (D) The proliferative capacity of RA-FLS by CCK8 assay. (E) The DNA synthesis of RA-FLS by EdU staining. (F) Pro-inflammatory cytokine concentrations in RA-FLS by ELISA. Data are presented as mean ± SD of the mean of at least 3 independent experiments. Statistical significance was determined using unpaired t-tests for independent data. Multiple groups of samples were analyzed by one-way or two-way ANOVA, and pairwise comparisons were adjusted by Tukey’s method. *P < 0.05 vs Control-FLS. ^#P < 0.05 vs sh-NC. LRRC15, leucine-rich repeat containing 15; RA-FLS, rheumatoid arthritis-associated fibroblast-like synoviocytes; OD, optical density; NC, negative control.|@|~(^,^)~|@|Depletion of LRRC15 inhibits RA-FLS migration, invasion, and angiogenesis. (A) RA-FLS migration by Transwell assay. (B) RA-FLS invasion by Transwell assay. (C) Angiogenic capacity of RA-FLS by angiogenesis assay. Data are presented as mean ± SD of the mean of at least 3 independent experiments. Statistical significance was determined using unpaired t-tests for independent data. *P < 0.05 vs sh-NC. LRRC15, leucine-rich repeat containing 15; RA-FLS, rheumatoid arthritis-associated fibroblast-like synoviocytes; NC, negative control.|@|~(^,^)~|@|Depletion of LRRC15 alleviates CIA in mice. (A) The flow chart of mouse treatment: DBA/1J mice induced with CIA (phosphate-buffered saline [PBS] as control) were further administrated with AAV-shLRRC15 or AAV-NC (2 × 10¹¹ GC/ml). (B) Arthritis scores of each group of mice and representative images of the joints of mice on day 56. (C) Immunohistochemical (IHC) staining of LRRC15 expression in mouse synovial tissues. (D) Detection of IL-6, IL-1β in mouse synovial tissues by ELISA. (E) Detection of pathological changes in mouse synovial tissues by H&E staining. (F) Erosion and destruction of bone tissues in mice detected by Safranin O-fast green staining. Data are presented as mean ± SD (n = 5). Multiple groups of samples were analyzed by one-way or two-way ANOVA, and pairwise comparisons were adjusted by Tukey’s method. *P < 0.05 vs Control. ^#P < 0.05 vs AAV-NC. LRRC15, leucine-rich repeat containing 15; CIA, collagen-induced arthritis; AAV, adeno-associated viruses; NC, negative control; IL, interleukin.|@|~(^,^)~|@|Epigenetic suppression of LRRC15 by RUNX1 is identified in RA-FLS. (A) Pathway enrichment analysis of transcription factors that transcriptionally regulate LRRC15. (B) Intersecting genes in the enriched pathways. (C) RUNX1 expression in the GSE77298 dataset. Detection of RUNX1 expression in RA-FLS by RT-qPCR (D) and western blot (E). (F) Binding relationship of RUNX1 to LRRC15 promoter predicted in the Cistrome Data Browser. (G) The enrichment ability of RUNX1 on LRRC15 promoter by ChIP-qPCR. (H) RUNX1, CBF-β, and LRRC15 protein expression in RA-FLS in response to oe-RUNX1 or oe-RUNX1 + RO5-3335 by western blot. (I) Binding site of RUNX1 on LRRC15 promoter predicted in Jaspar. (J) The regulatory effect of RUNX1 on the transcriptional activity of LRRC15 promoter by dual-luciferase reporter assays. Data are presented as mean ± SD of at least 3 independent experiments. Statistical significance was determined using unpaired t-tests for independent data. Multiple groups of samples were analyzed by one-way or two-way ANOVA, and pairwise comparisons were adjusted by Tukey’s method. *P < 0.05 vs Control-FLS. ^#P < 0.05 vs IgG. ^&P < 0.05 vs oe-NC. ^@P < 0.05 vs oe-RUNX1 + DMSO. LRRC15, leucine-rich repeat containing 15; RUNX1, runt-related transcription factor 1; RA-FLS, rheumatoid arthritis-associated fibroblast-like synoviocytes; HC, healthy controls; CBF-β, core-binding factor subunit beta; NC, negative control; DMSO, dimethyl sulfoxide.|@|~(^,^)~|@|RUNX1-CBF--mediated inhibition of LRRC15 leads to RA-FLS phenotypic changes. β(A) Overexpression efficiency of oe-LRRC15 by RT-qPCR. (B) The proliferative capacity of RA-FLS by CCK8 assay. (C) The DNA synthesis of RA-FLS by EdU staining. (D) Pro-inflammatory cytokine concentrations in RA-FLS by ELISA. (E) RA-FLS migration capacity by Transwell assay. (F) RA-FLS invasion capacity by Transwell assay. (G) Angiogenic capacity of RA-FLS by angiogenesis assay. Data are presented as mean ± SD of at least 3 independent experiments. Statistical significance was determined using unpaired t-tests for independent data. Multiple groups of samples were analyzed by one-way or two-way ANOVA, and pairwise comparisons were adjusted by Tukey’s method. *P < 0.05 vs oe-NC. ^#P < 0.05 vs oe-RUNX1 + oe-NC. ^&P < 0.05 vs oe-RUNX1 + DMSO. RUNX1, runt-related transcription factor 1; CBF-β, core-binding factor subunit beta; LRRC15, leucine-rich repeat containing 15; RA-FLS, rheumatoid arthritis-associated fibroblast-like synoviocytes; NC, negative control; DMSO, dimethyl sulfoxide; OD, optical density; IL, interleukin; CM, conditioned medium.|@|~(^,^)~|@|RUNX1-CBF-mediated inhibition of LRRC15 ameliorates joint damage in CIA mice. β(A) The flow chart of mouse treatment: CIA mice were further administrated with AAV-RUNX1 (2 × 10¹¹ GC/ml), AAV-RUNX1 + AAV-LRRC15, or AAV-RUNX1 + RO5-3335. (B) Arthritis scores of each group of mice and representative images of the joints of mice on day 56. (C) Immunohistochemical (IHC) staining of RUNX1 and LRRC15 expression in mouse synovial tissues. (D) Detection of IL-6 and IL-1β in mouse synovial tissues by ELISA. (E) Detection of pathological changes in mouse synovial tissues by H&E staining. (F) Erosion and destruction of bone tissues in mice detected by Safranin O-fast green staining. Data are presented as mean ± SD (n = 5). Multiple groups of samples were analyzed by one-way or two-way ANOVA, and pairwise comparisons were adjusted by Tukey’s method. *P < 0.05 vs AAV-NC. ^#P < 0.05 vs AAV-RUNX1. RUNX1, runt-related transcription factor 1; LRRC15, leucine-rich repeat containing 15; CIA, collagen-induced arthritis; AAV, adeno-associated viruses; NC, negative control; IL, interleukin.|@|~(^,^)~|@|Schematic representation of LRRC15 involvement in RA pathogenesis. RUNX1 represses the transcriptional expression of LRRC15 by binding to CBF-β, thereby inhibiting the FLS proliferation and ameliorating joint damage in RA. LRRC15, leucine-rich repeat containing 15; RA, rheumatoid arthritis; RUNX1, runt-related transcription factor 1; CBF-β, core-binding factor subunit beta; FLS, fibroblast-like synoviocytes. Plotted by Figdraw (https://www.figdraw.com/).

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