Notch ligands are biomarkers of anti-TNF response in RA patients

Notch and its ligands play a critical role in rheumatoid arthritis (RA) pathogenesis. Hence, studies were conducted to delineate the functional significance of the Notch pathway in RA synovial tissue (ST) cells and the influence of RA therapies on their expression. Morphological studies reveal that JAG1, DLL4, and Notch1 are highly enriched in RA ST lining and sublining CD68+CD14+ MΦs. JAG1 and DLL4 transcription is jointly upregulated in RA MΦs reprogrammed by TLR4/5 ligation and TNF, whereas Syntenin-1 exposure expands JAG1, DLL4, and Notch1 expression levels in these cells. Single-cell RNA-seq data exhibit that JAG1 and Notch3 are overexpressed on all fibroblast-like synoviocyte (FLS) subpopulations, in parallel, JAG2, DLL1, and Notch1 expression levels are modest on RA FLS and are predominately potentiated by TLR4 ligation. Intriguingly, JAG1, DLL1/4, and Notch1/3 are presented on RA endothelial cells, and their expression is mutually reconfigured by TLR4/5 ligation in the endothelium. Synovial JAG1/JAG2/DLL1 or Notch1/3 transcriptomes were unchanged in patients who received disease-modifying anti-rheumatic drugs (DMARDs) or IL-6R Ab therapy regardless of disease activity score. Uniquely, RA MΦs and endothelial cells rewired by IL-6 displayed DLL4 transcriptional upregulation, and IL-6R antibody treatment disrupted RA ST DLL4 transcription in good responders compared to non-responders or moderate responders. Nevertheless, the JAG1/JAG2/DLL1/DLL4 transcriptome was diminished in anti-TNF good responders with myeloid pathotype and was unaltered in the fibroid pathotype except for DLL4. Taken together, our findings suggest that RA myeloid Notch ligands can serve as markers for anti-TNF responsiveness and trans-activate Notch receptors expressed on RA FLS and/or endothelial cells.

Metabolic reprogramming by Syntenin-1 directs RA FLS and endothelial cell-mediated inflammation and angiogenesis

A novel rheumatoid arthritis (RA) synovial fluid protein, Syntenin-1, and its receptor, Syndecan-1 (SDC-1), are colocalized on RA synovial tissue endothelial cells and fibroblast-like synoviocytes (FLS). Syntenin-1 exacerbates the inflammatory landscape of endothelial cells and RA FLS by upregulating transcription of IRF1/5/7/9, IL-1β, IL-6, and CCL2 through SDC-1 ligation and HIF1α, or mTOR activation. Mechanistically, Syntenin-1 orchestrates RA FLS and endothelial cell invasion via SDC-1 and/or mTOR signaling. In Syntenin-1 reprogrammed endothelial cells, the dynamic expression of metabolic intermediates coincides with escalated glycolysis along with unchanged oxidative factors, AMPK, PGC-1α, citrate, and inactive oxidative phosphorylation. Conversely, RA FLS rewired by Syntenin-1 displayed a modest glycolytic-ATP accompanied by a robust mitochondrial-ATP capacity. The enriched mitochondrial-ATP detected in Syntenin-1 reprogrammed RA FLS was coupled with mitochondrial fusion and fission recapitulated by escalated Mitofusin-2 and DRP1 expression. We found that VEGFR1/2 and Notch1 networks are responsible for the crosstalk between Syntenin-1 rewired endothelial cells and RA FLS, which are also represented in RA explants. Similar to RA explants, morphological and transcriptome studies authenticated the importance of VEGFR1/2, Notch1, RAPTOR, and HIF1α pathways in Syntenin-1 arthritic mice and their obstruction in SDC-1 deficient animals. Consistently, dysregulation of SDC-1, mTOR, and HIF1α negated Syntenin-1 inflammatory phenotype in RA explants, while inhibition of HIF1α impaired synovial angiogenic imprint amplified by Syntenin-1. In conclusion, since the current therapies are ineffective on Syntenin-1 and SDC-1 expression in RA synovial tissue and blood, targeting this pathway and its interconnected metabolic intermediates may provide a novel therapeutic strategy.

IRAK4 inhibitor mitigates joint inflammation by rebalancing metabolism malfunction in RA macrophages and fibroblasts

Recent studies show a connection between glycolysis and inflammatory response in rheumatoid arthritis (RA) macrophages (MΦs) and fibroblasts (FLS). Yet, it is unclear which pathways could be targeted to rebalance RA MΦs and FLS metabolic reprogramming. To identify novel targets that could normalize RA metabolic reprogramming, TLR7-mediated immunometabolism was characterized in RA MΦs, FLS and experimental arthritis. We uncovered that GLUT1, HIF1α, cMYC, LDHA and lactate were responsible for the TLR7-potentiated metabolic rewiring in RA MΦs and FLS, which was negated by IRAK4i. While in RA FLS, HK2 was uniquely expanded by TLR7 and negated by IRAK4i. Conversely, TLR7-driven hypermetabolism, non-oxidative PPP (CARKL) and oxidative phosphorylation (PPARγ) were narrowly dysregulated in TLR7-activated RA MΦs and FLS and was reversed by IRAK4i. Consistently, IRAK4i therapy disrupted arthritis mediated by miR-Let7b/TLR7 along with impairing a broad-range of glycolytic intermediates, GLUT1, HIF1α, cMYC, HK2, PFKFB3, PKM2, PDK1 and RAPTOR. Notably, inhibition of the mutually upregulated glycolytic metabolites, HIF1α and cMYC, was capable of mitigating TLR7-induced inflammatory imprint in RA MΦs and FLS. In keeping with IRAK4i, treatment with HIF1i and cMYCi intercepted TLR7-enhanced IRF5 and IRF7 in RA MΦs, distinct from RA FLS. Interestingly, in RA MΦs and FLS, IRAK4i counteracted TLR7-induced CARKL reduction in line with HIF1i. Whereas, cMYCi in concordance with IRAK4i, overturned oxidative phosphorylation via PPARγ in TLR7-activated RA MΦs and FLS. The blockade of IRAK4 and its interconnected intermediates can rebalance the metabolic malfunction by obstructing glycolytic and inflammatory phenotypes in RA MΦs and FLS.

Metabolic regulation of RA macrophages is distinct from RA fibroblasts and blockade of glycolysis alleviates inflammatory phenotype in both cell types

Recent studies have shown the significance of metabolic reprogramming in immune and stromal cell function. Yet, the metabolic reconfiguration of RA macrophages (MΦs) is incompletely understood during active disease and in crosstalk with other cell types in experimental arthritis. This study elucidates a distinct regulation of glycolysis and oxidative phosphorylation in RA MΦs compared to fibroblast (FLS), although PPP (Pentose Phosphate pathway) is similarly reconfigured in both cell types. 2-DG treatment showed a more robust impact on impairing the RA M1 MΦ-mediated inflammatory phenotype than IACS-010759 (IACS, complexli), by reversing ERK, AKT and STAT1 signaling, IRF8/3 transcription and CCL2 or CCL5 secretion. This broader inhibitory effect of 2-DG therapy on RA M1 MΦs was linked to dysregulation of glycolysis (GLUT1, PFKFB3, LDHA, lactate) and oxidative PPP (NADP conversion to NADPH), while both compounds were ineffective on oxidative phosphorylation. Distinctly, in RA FLS, 2-DG and IACS therapies constrained LPS/IFNγ-induced AKT and JNK signaling, IRF5/7 and fibrokine expression. Disruption of RA FLS metabolic rewiring by 2-DG or IACS therapy was accompanied by a reduction of glycolysis (HIF1α, PFKFB3) and suppression of citrate or succinate buildup. We found that 2-DG therapy mitigated CIA pathology by intercepting joint F480+iNOS+MΦ, Vimentin+ fibroblast and CD3+T cell trafficking along with downregulation of IRFs and glycolytic intermediates. Surprisingly, IACS treatment was inconsequential on CIA swelling, cell infiltration, M1 and Th1/Th17 cytokines (IFN-γ/IL-17) and joint glycolytic mediators. Collectively, our results indicate that blockade of glycolysis is more effective than inhibition of complex 1 in CIA, in part due to its effectiveness on the MΦ inflammatory phenotype.

Tofacitinib therapy intercepts macrophage metabolic reprogramming instigated by SARS-CoV-2 Spike protein

The molecular mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein was characterized to identify novel therapies. The impact of tofacitinib, IL-6R Ab, or TNFi therapy was determined on Spike protein or LPS/IFN-γ-induced signaling, inflammation, and metabolic reprogramming in MΦs and/or rheumatoid arthritis (RA) fibroblast-like synoviocyte (FLS). ACE2 frequency was markedly expanded in MΦs compared to T cells and RA FLS. Tofacitinib suppresses Spike protein potentiated STAT1 signaling, whereas this function was unchanged by TNFi. Tofacitinib impairs IL-6/IFN/LPS-induced STAT1 and STAT3 phosphorylation in RA MΦs and FLS. Interestingly, tofacitinib had a broader inhibitory effect on the monokines, glycolytic regulators, or oxidative metabolites compared to IL-6R Ab and TNFi in Spike-protein-activated MΦs. In contrast, all three therapies disrupted IFN-α and IFN-β secretion in response to Spike protein; nonetheless, the IFN-γ was only curtailed by tofacitinib or IL-6R Ab. While tofacitinib counteracted MΦ metabolic rewiring instigated by Spike protein, it was inconsequential on the glycolysis expansion mediated via HK2 and/or LDHA in the activated RA MΦ and FLS. Nevertheless, the potentiated inflammatory response and the diminished oxidative phosphorylation modulated by Spike protein and/or LPS/IFN-γ stimulation in MΦs or RA FLS were reversed by tofacitinib. In conclusion, tofacitinib suppresses MΦ inflammation and immunometabolism triggered by Spike protein and may provide a promising strategy for COVID-19 patients.

FOXM1/LINC00152 feedback loop regulates proliferation and apoptosis in rheumatoid arthritis fibroblast-like synoviocytes via Wnt/β-catenin signaling pathway

Rheumatoid arthritis (RA), a chronic systemic disease, is featured with inflammatory synovitis, which can lead to destruction on bone and cartilage and even cause disability. Emerging studies demonstrated that Fibroblast-like synoviocytes (FLS) is a vital cellular participant in RA progression. Long non-coding RNAs (lncRNAs) are also reported to participate in the pathogenesis of RA. In our present study, lncRNA microarray analysis was applied to screen out lncRNAs differentially expressed in RA FLS. Among which, cytoskeleton regulator RNA (LINC00152) presented biggest fold change. Gain- or loss-of function assays were further carried out in RA FLS, and the results revealed that LINC00152 promoted proliferation but induced apoptosis in RA FLS. Furthermore, up-regulation of LINC00152 may induce promotion of Wnt/β-catenin signaling pathway in RA FLS. Mechanistically, we found that forkhead box M1 (FOXM1) transcriptionally activated LINC00152 in RA FLS. Additionally, LINC00152 positively regulated FOXM1 via sponging miR-1270. In conclusion, the present study focused on elucidating the function of FOXM1/LINC00152 positive feedback loop in RA FLS and its association with Wnt/β-catenin signaling.

A protocol for humanized synovitis mice model

Rheumatoid arthritis (RA) is a debilitating autoimmune disease that causes progressive chronic inflammation of the joints and destruction of articular cartilage and bone erosion. Cartilage destruction is a key characteristic in patients with RA. RA fibroblast-like synoviocytes (FLS) mainly contributes to local production of cytokines, inflammatory mediators and MMPs, and to migrate and destruct joint cartilage. Here, we summarized a detailed protocol for developing a humanized synovitis animal model. A cartilage-sponge complex without RA FLS was implanted under the left flank skin of a SCID mouse primarily, two weeks later, cartilage-sponge complex containing RA FLS was inserted under the right skin of the contralateral flank. The H&E staining clearly helps to identify the cartilage damage on the day 45 after second implantation. This model is highly significant to investigate the role and mechanisms of agents or cells in targeting RA FLS in vivo.