Association of gut commensal translocation with autoantibody production in systemic lupus erythematosus.

OBJECTIVE: Bacterial translocation across the gut barrier has been implicated in the pathogenesis of systemic lupus erythematosus (SLE), though underlying mechanisms remain unclear. This study aimed to investigate the role of translocated bacteria in the context of molecular mimicry by utilizing lupus model mice and blood samples from untreated SLE patients. METHODS: Bacterial translocation was evaluated using nonselective cultured mesenteric lymph nodes (MLNs) from B6SKG mice, a lupus model characterized by impaired TCR signalling and gut dysbiosis. The relationships of detected pathobionts with autoantibody production were examined using in vivo experiments, enzyme-linked immunosorbent assay, immunoblotting, and epitope mapping. RESULTS: Culture-based bacterial profiling in MLNs demonstrated that Lactobacillus murinus was enriched in B6SKG mice with elevated anti-dsDNA IgG levels. Subcutaneous injection of heat-killed L. murinus induced anti-dsDNA IgG production without altering T- or B cell subset composition. Immunoblotting and mass spectrometry analysis identified a peptide ATP-binding cassette (ABC) transporter as a molecular mimicry antigen, with its cross-reactivity in lupus mice confirmed by serological assays and in vivo immunization. The L. murinus ABC transporter exhibited surface epitopes that were cross-reactive with sera from lupus mice and patients. The ABC transporter from R. gnavus, known for its pathogenic role in lupus patients, had a similar epitope sequence to that of the L. murinus ABC transporter and reacted with lupus sera. CONCLUSION: ABC transporters from gut bacteria can serve as cross-reactive antigens that may promote anti-dsDNA antibody production in genetically susceptible mice. These findings underscore the role of commensal-derived molecular mimicry and bacterial translocation in lupus pathogenesis.

Peficitinib improves bone fragility by recovering bone turnover imbalance in arthritic mice.

Peficitinib, a pan-JAK inhibitor, is known to suppress the activation of fibroblast-like synoviocytes (FLSs) and thereby reduces joint inflammation associated with rheumatoid arthritis (RA). However, the effect on osteoporosis in RA remains to be elucidated. In this study, the effect of peficitinib or etanercept on joint inflammation, and consequently decreased bone mineral density (BMD) was evaluated in mice with collagen-induced arthritis (CIA). Additionally, the effect on RANKL production from osteoblasts differentiated from the mesenchymal stem cells of RA patients was evaluated. Administration of peficitinib for established CIA ameliorated arthritis and improved BMD in the femoral metaphysis, but not in the femoral diaphysis. Conversely, etanercept suppressed an increase in synovial inflammatory markers but did not improve arthritic conditions or the reduction of BMD in either region. All elevated bone formation and bone resorption markers were decreased with peficitinib but only partially decreased with etanercept. Furthermore, production of RANKL by human osteoblasts was suppressed by peficitinib but enhanced by etanercept. Unlike etanercept, peficitinib is thought to increase BMD by ameliorating the high bone turnover associated with RA states, resulting in improvement of bone fragility. Our data provide evidence that peficitinib would be expected to show efficacy for osteoporosis associated with RA.

Constitutive Activation of Integrin α9 Augments Self-Directed Hyperplastic and Proinflammatory Properties of Fibroblast-like Synoviocytes of Rheumatoid Arthritis.

Despite advances in the treatment of rheumatoid arthritis (RA), currently approved medications can have significant side effects due to their direct immunosuppressive activities. Additionally, current therapies do not address residual synovial inflammation. In this study, we evaluated the role of integrin α9 and its ligand, tenascin-C (Tn-C), on the proliferative and inflammatory response of fibroblast-like synoviocytes (FLSs) from RA patients grown in three-dimensional (3D)-micromass culture. FLSs from osteoarthritis patients, when grown in the 3D-culture system, formed self-directed lining-like structures, whereas FLSs from RA tissues (RA-FLSs) developed an abnormal structure of condensed cellular accumulation reflective of the pathogenic features of RA synovial tissues. Additionally, RA-FLSs grown in 3D culture showed autonomous production of proinflammatory mediators. Predominant expression of α9 and Tn-C was observed in the condensed lining, and knockdown of these molecules abrogated the abnormal lining-like structure formation and suppressed the spontaneous expression of matrix metalloproteinases, IL-6, TNFSF11/RANKL, and cadherin-11. Disruption of α9 also inhibited expression of Tn-C, suggesting existence of a positive feedback loop in which the engagement of α9 with Tn-C self-amplifies its own signaling and promotes progression of synovial hyperplasia. Depletion of α9 also suppressed the platelet-derived growth factor-induced hyperplastic response of RA-FLSs and blunted the TNF-α-induced expression of matrix metalloproteinases and IL-6. Finally, α9-blocking Ab also suppressed the formation of the condensed cellular lining by RA-FLSs in 3D cultures in a concentration-related manner. This study demonstrates the central role of α9 in pathogenic behaviors of RA-FLSs and highlights the potential of α9-blocking agents as a nonimmunosuppressive treatment for RA-associated synovitis.

Role of JAK-STAT signaling in the pathogenic behavior of fibroblast-like synoviocytes in rheumatoid arthritis: Effect of the novel JAK inhibitor peficitinib.

Rheumatoid arthritis (RA) fibroblast-like synoviocytes (RA-FLS) play a crucial role in the pathogenesis of RA. RA-FLS display passive pro-inflammatory responses and self-directed aggressive responses, such as pro-inflammatory mediator production, reduced apoptosis and formation of a thickened synovial lining. Evidence suggests a role for Janus kinase (JAK)-signal transducer and transcriptional activator (STAT) signaling in the passive response but the aggressive behavior of RA-FLS is poorly understood. The pharmacologic effects of the novel JAK inhibitor, peficitinib, on cytokine-induced intracellular signaling and self-directed aggressive behavior of RA-FLS (e.g., increased expression of apoptosis-resistant genes and sodium nitroprusside-induced apoptosis) were investigated and compared with approved JAK inhibitors. RA-FLS assembly to form a lining-like structure and pro-inflammatory mediator production was investigated in three-dimensional (3D)-micromass culture. Peficitinib inhibited STAT3 phosphorylation in RA-FLS following induction by interferon (IFN)-α2b, IFN-γ, interleukin (IL)-6, oncostatin M, and leukemia inhibitory factor in a concentration-related manner, and was comparable to approved JAK inhibitors, tofacitinib and baricitinib. Peficitinib and tofacitinib suppressed autocrine phosphorylation of STAT3 and expression of apoptosis-resistant genes, and promoted cell death. In 3D-micromass culture, peficitinib reduced multi-layered RA-FLS cells to a thin monolayer, an effect less pronounced with tofacitinib. Both compounds attenuated production of vascular endothelial growth factor-A, matrix metalloproteinases, IL-6 and tumor necrosis factor superfamily-11. This study confirmed the pathogenic role of uncontrolled JAK-STAT signaling in the aggressive and passive responses of RA-FLS that are critical for RA progression. The novel JAK inhibitor peficitinib suppressed the pro-inflammatory behavior of RA-FLS, accelerated cell death and abrogated thickening of the synovium.

Nuclear Smad7 Overexpressed in Mesenchymal Cells Acts as a Transcriptional Corepressor by Interacting with HDAC-1 and E2F to Regulate Cell Cycle.

Smad family proteins are essential intracellular mediators that regulate transforming growth factor-ß (TGF-ß) ligand signaling. In response to diverse stimuli, Smad7 is rapidly expressed and acts as a cytoplasmic inhibitor that selectively interferes with signals elicited from TGF-ß family receptors. In addition, earlier works have indicated that retrovirally transduced Smad7 induces long-lasting cell proliferation arrest in a variety of mesenchymal cells through down-regulation of G1 cyclins. However, the molecular mechanisms underlying the cytostatic effects of Smad7 remain unknown. We show here that Smad7 can form a complex with endogenous histone deacetylase proteins HDAC-1 and HDAC-3 in NIH 3T3 mouse fibroblast cells. By contrast, forced expression of a dominant-negative variant of HDAC-1 efficiently protected cells against Smad7 proliferation inhibition, suggesting that Smad7 depends on the deacetylase activity of its associated HDAC-1 to arrest the cell cycle. Furthermore, Smad7 caused HDAC-1 bind to E2F-1 to form a ternary complex on chromosomal DNA containing an E2F-binding motif and leading to repression in the activity of the E2F target genes. Smad7 mutations that prevented its binding to either HDAC-1 or E2F-1 resulted in a significant decrease in Smad7-mediated inhibition of cell proliferation. The present results strongly suggest that nuclear Smad7 is a transcriptional corepressor for E2F, providing a molecular basis for the Smad7-induced arrest of the cell cycle.

Smad7 induces G0/G1 cell cycle arrest in mesenchymal cells by inhibiting the expression of G1 cyclins.

The major Smad pathways serve in regulating the expression of genes downstream of TGFbeta signals. In this study, we examined the effects of sustained Smad7 expression in cultured cells. Interestingly, Smad7 caused various mesenchymal cells, including NIH3T3 fibroblast and ST2 bone-marrow stromal cells, to undergo a marked morphological alteration into a flattened cell shape, but kept them alive for as long as 60 days. Furthermore, Smad7 arrested the proliferation of the cells even before they reached confluence. These cells became quiescent in G0/G1 phase and accumulated a hypophosphorylated form of retinoblastoma. The cytostatic effect of Smad7 was closely associated with a preceding decrease in the levels of G1 cyclins, such as cyclin D1 and cyclin E. Accordingly, ectopic cyclin E was able to overcome the Smad7-induced arrest of proliferation. These results indicate that Smad7 functions upstream of G1 cyclins and suggest a novel role for Smad7 as an antiproliferative factor. In contrast to the growth of mesenchymal cells, that of epithelial cells was little susceptible to Smad7. The present findings raise the possibility that a link between Smad7 and the G1 to S phase transition may also contribute to the cell cycle control by certain Smad7-inducing stimuli in a cell-type-dependent fashion.