Differentiation of Functional Osteoclasts from Human Peripheral Blood CD14+ Monocytes.

Osteoclasts (OCs) are bone-resorbing cells that play a pivotal role in skeletal development and adult bone remodeling. Several bone disorders are caused by increased differentiation and activation of OCs, so the inhibition of this pathobiology is a key therapeutic principle.Two key factors drive the differentiation of OCs from myeloid precursors: macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor kappa-B ligand (RANKL). Human circulating CD14+ monocytes have long been known to differentiate into OCs in vitro. However, the exposure time and the concentration of RANKL influence the differentiation efficiency. Indeed, protocols for the generation of human OCs in vitro have been described, but they often result in a poor and lengthy differentiation process. Herein, a robust and standardized protocol for generating functionally active mature human OCs in a timely manner is provided. CD14+ monocytes are enriched from human peripheral blood mononuclear cells (PBMCs) and primed with M-CSF to upregulate RANK. Subsequent exposure to RANKL generates OCs in a dose- and time-dependent manner. OCs are identified and quantified by staining with tartrate acid-resistant phosphatase (TRAP) and light microscopy analysis. Immunofluorescence staining of nuclei and F-actin is used to identify functionally active OCs. In addition, OSCAR+CD14- mature OCs are further enriched via flow cytometry cell sorting, and OC functionality quantified by mineral (or dentine/bone) resorption assays and actin ring formation. Finally, a known OC inhibitor, rotenone, is used on mature OCs, demonstrating that adenosine triphosphate (ATP) production is essential for actin ring integrity and OC function. In conclusion, a robust assay for differentiating high numbers of OCs is established in this work, which in combination with actin ring staining and an ATP assay provides a useful in vitro model to evaluate OC function and to screen for novel therapeutic compounds that can modulate the differentiation process.

Systems-biology analysis of rheumatoid arthritis fibroblast-like synoviocytes implicates cell line-specific transcription factor function.

Rheumatoid arthritis (RA) is an immune-mediated disease affecting diarthrodial joints that remains an unmet medical need despite improved therapy. This limitation likely reflects the diversity of pathogenic pathways in RA, with individual patients demonstrating variable responses to targeted therapies. Better understanding of RA pathogenesis would be aided by a more complete characterization of the disease. To tackle this challenge, we develop and apply a systems biology approach to identify important transcription factors (TFs) in individual RA fibroblast-like synoviocyte (FLS) cell lines by integrating transcriptomic and epigenomic information. Based on the relative importance of the identified TFs, we stratify the RA FLS cell lines into two subtypes with distinct phenotypes and predicted active pathways. We biologically validate these predictions for the top subtype-specific TF RARα and demonstrate differential regulation of TGFß signaling in the two subtypes. This study characterizes clusters of RA cell lines with distinctive TF biology by integrating transcriptomic and epigenomic data, which could pave the way towards a greater understanding of disease heterogeneity.

Caspase-8 Variant G Regulates Rheumatoid Arthritis Fibroblast-Like Synoviocyte Aggressive Behavior.

OBJECTIVE: Fibroblast-like synoviocytes (FLS) play a pivotal role in rheumatoid arthritis (RA) by contributing to synovial inflammation and progressive joint damage. An imprinted epigenetic state is associated with the FLS aggressive phenotype. We identified CASP8 (encoding for caspase-8) as a differentially marked gene and evaluated its pathogenic role in RA FLSs. METHODS: RA FLS lines were obtained from synovial tissues at arthroplasty and used at passage 5-8. Caspase-8 was silenced using small interfering RNA, and its effect was determined in cell adhesion, migration and invasion assays. Quantitative reverse transcription PCR and western blot were used to assess gene and protein expression, respectively. A caspase-8 selective inhibitor was used determine the role of enzymatic activity on FLS migration and invasion. Caspase-8 isoform transcripts and epigenetic marks in FLSs were analyzed in FLS public databases. Crystal structures of caspase-8B and G were determined. RESULTS: Caspase-8 deficiency in RA FLSs reduced cell adhesion, migration, and invasion independent of its catalytic activity. Epigenetic and transcriptomic analyses of RA FLSs revealed that a specific caspase-8 isoform, variant G, is the dominant isoform expressed (~80% of total caspase-8) and induced by PDGF. The crystal structures of caspase-8 variant G and B were identical except for a unique unstructured 59 amino acid N-terminal domain in variant G. Selective knockdown of caspase-8G was solely responsible for the effects of caspase-8 on calpain activity and cell invasion in FLS. CONCLUSION: Blocking caspase-8 variant G could decrease cell invasion in diseases like RA without the potential deleterious effects of nonspecific caspase-8 inhibition.

TNF is a homoeostatic regulator of distinct epigenetically primed human osteoclast precursors.

OBJECTIVES: Circulating myeloid precursors are responsible for post-natal osteoclast (OC) differentiation and skeletal health, although the exact human precursors have not been defined. Enhanced osteoclastogenesis contributes to joint destruction in rheumatoid arthritis (RA) and tumour necrosis factor (TNF) is a well-known pro-osteoclastogenic factor. Herein, we investigated the interplay between receptor activator of nuclear factor kappa-Β ligand (RANK-L), indispensable for fusion of myeloid precursors and the normal development of OCs, and TNF in directing the differentiation of diverse pre-OC populations derived from human peripheral blood. METHODS: Flow cytometric cell sorting and analysis was used to assess the potential of myeloid populations to differentiate into OCs. Transcriptomic, epigenetic analysis, receptor expression and inhibitor experiments were used to unravel RANK-L and TNF signalling hierarchy. RESULTS: TNF can act as a critical homoeostatic regulator of CD14+ monocyte (MO) differentiation into OCs by inhibiting osteoclastogenesis to favour macrophage development. In contrast, a distinct previously unidentified CD14-CD16-CD11c+ myeloid pre-OC population was exempt from this negative regulation. In healthy CD14+ MOs, TNF drove epigenetic modification of the RANK promoter via a TNFR1-IKKß-dependent pathway and halted osteoclastogenesis. In a subset of patients with RA, CD14+ MOs exhibited an altered epigenetic state that resulted in dysregulated TNF-mediated OC homoeostasis. CONCLUSIONS: These findings fundamentally re-define the relationship between RANK-L and TNF. Moreover, they have identified a novel pool of human circulating non-MO OC precursors that unlike MOs are epigenetically preconditioned to ignore TNF-mediated signalling. In RA, this epigenetic preconditioning occurs in the MO compartment providing a pathological consequence of failure of this pathway.

Treatment of Active Crohn's Disease With an Ordinary Food-based Diet That Replicates Exclusive Enteral Nutrition.

BACKGROUND & AIMS: Exclusive enteral nutrition (EEN) is the only established dietary treatment for Crohn's disease (CD), but its acceptability is limited. There is a need for novel dietary treatments for CD. METHODS: We evaluated the effects of an individualized food-based diet (CD-TREAT), with similar composition to EEN, on the gut microbiome, inflammation, and clinical response in a rat model, healthy adults, and children with relapsing CD. Twenty-five healthy adults randomly received EEN or CD-TREAT for 7 days, followed by a 14-day washout period, followed by the alternate diet. Fecal microbiome and metabolome were assessed before and after each diet. HLA-B7 and HLA-B27 transgenic rats with gut inflammation received EEN, CD-TREAT, or standard chow for 4 weeks. Fecal, luminal, and tissue microbiome, fecal metabolites, and gut inflammation were assessed. Five children with active CD activity received CD-TREAT and their clinical activity and calprotectin were evaluated after 8 weeks of treatment. RESULTS: For healthy adults, CD-TREAT was easier to comply with and more acceptable than EEN. CD-TREAT induced similar effects to EEN (EEN vs CD-TREAT) on fecal microbiome composition, metabolome, mean total sulfide (increase 133.0 ± 80.5 vs 54.3 ± 47.0 nmol/g), pH (increase 1.3 ± 0.5 vs 0.9 ± 0.6), and the short-chain fatty acids (µmol/g) acetate (decrease 27.4 ± 22.6 vs 21.6 ± 20.4), propionate (decrease 5.7 ± 7.8 vs 5.2 ± 7.9), and butyrate (decrease 7.0 ± 7.4 vs 10.2 ± 8.5). In the rat model, CD-TREAT and EEN produced similar changes in bacterial load (decrease 0.3 ± 0.3 log10 16S rRNA gene copies per gram), short-chain fatty acids, microbiome, and ileitis severity (mean histopathology score decreases of 1.25 for EEN [P = .015] and 1.0 for CD-TREAT [P = .044] vs chow). In children receiving CD-TREAT, 4 (80%) had a clinical response and 3 (60%) entered remission, with significant concurrent decreases in fecal calprotectin (mean decrease 918 ± 555 mg/kg; P = .002). CONCLUSION: CD-TREAT replicates EEN changes in the microbiome, decreases gut inflammation, is well tolerated, and is potentially effective in patients with active CD. ClinicalTrials.gov, numbers NCT02426567 and NCT03171246.

Role of Gut Inflammation in Altering the Monocyte Compartment and Its Osteoclastogenic Potential in HLA-B27-Transgenic Rats.

OBJECTIVE: To investigate the relationship between intestinal inflammation and the central and peripheral innate immune system in the pathogenesis of HLA-B27-associated spondyloarthritis using an HLA-B27-transgenic (B27-Tg) rat model. METHODS: The myeloid compartment of the blood and bone marrow (BM) of B27-Tg rats, as well as HLA-B7-Tg and non-Tg rats as controls, was evaluated by flow cytometry. Plasma from rats was assessed by enzyme-linked immunosorbent assay for levels of CCL2 and interleukin-1α (IL-1α). Rats were treated with antibiotics for 4 weeks, and the myeloid compartment of the blood and BM was evaluated by flow cytometry. The osteoclastogenic potential of BM-derived cells from antibiotic-treated rats, in the presence or absence of tumor necrosis factor (TNF), was evaluated in vitro. RESULTS: B27-Tg rats had substantially higher numbers of circulating Lin-CD172a+CD43low monocytes as compared to control animals, and this was significantly correlated with higher levels of plasma CCL2. Antibiotic treatment of B27-Tg rats markedly reduced the severity of ileitis, plasma levels of CCL2 and IL-1α, and number of BM and blood Lin-CD172a+CD43low monocytes, a cell subset shown in the present study to have the greatest in vitro osteoclastogenic potential. Antibiotic treatment also prevented the TNF-dependent enhancement of osteoclastogenesis in B27-Tg rats. CONCLUSION: Microbiota-dependent intestinal inflammation in B27-Tg rats directly drives the systemic inflammatory and bone-erosive potential of the monocyte compartment.