Identification of genes regulating TRAIL-induced apoptosis in rheumatoid arthritis fibroblasts-like synoviocytes.

We previously described that sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis varied in rheumatoid arthritis fibroblasts-like synoviocytes (RAFLS) from one patient to another and was correlated with disease severity. Therefore, we screened for genes differentially expressed in RAFLS sensitive and resistant to TRAIL-induced apoptosis. The sensitivity of RAFLS was defined based on the percentage of TRAIL-induced apoptosis: 0-10% for resistant cells and >25% for sensitive RAFLS. We performed transcriptomic comparison between RAFLS-S (n=6) and RAFLS-R (n=6) and then examined the implication of identified candidates in the regulation of apoptosis using small interference RNA (siRNA). Microarray analysis revealed 10 functional genes differentially expressed according to TRAIL sensitivity. These factors are implicated in different functions, such as the respiratory chain (ND3), the transport of lipids (OSBP2, PLTP), the regulation of signaling linked to extracellular factors (SULF2, GALNT1, SIAE) or the regulation of gene expression (TET2 and LARP6). We confirmed differential expression for GALNT1 and LARP6 by quantitative reverse transcriptase-PCR. Using siRNA extinction, we demonstrated the implication of GALNT1, SULF2 and LARP6 in the control of TRAIL-induced responses. These results are of particular interest as GALNT1 and LARP6 have been implicated in the regulation of cell death and may represent interesting targets to induce apoptosis of RAFLS.

Gut-derived acetate promotes B10 cells with antiinflammatory effects.

Autoimmune diseases are characterized by a breakdown of immune tolerance partly due to environmental factors. The short-chain fatty acid acetate, derived mostly from gut microbial fermentation of dietary fiber, promotes antiinflammatory Tregs and protects mice from type 1 diabetes, colitis, and allergies. Here, we show that the effects of acetate extend to another important immune subset involved in tolerance, the IL-10-producing regulatory B cells (B10 cells). Acetate directly promoted B10 cell differentiation from mouse B1a cells both in vivo and in vitro. These effects were linked to metabolic changes through the increased production of acetyl-coenzyme A, which fueled the TCA cycle and promoted posttranslational lysine acetylation. Acetate also promoted B10 cells from human blood cells through similar mechanisms. Finally, we identified that dietary fiber supplementation in healthy individuals was associated with increased blood-derived B10 cells. Direct delivery of acetate or indirect delivery via diets or bacteria that produce acetate might be a promising approach to restore B10 cells in noncommunicable diseases.

The pleiotropic effect of TRAIL on tumor-like synovial fibroblasts from rheumatoid arthritis patients is mediated by caspases.

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has gained much attention as a possible therapeutic reagent for the treatment of tumors, as TRAIL was originally described to induce apoptosis specifically in cancer cells, but not in normal cells. Fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) patients exhibit tumor-like features and we have described earlier that TRAIL induces apoptosis only in a subset of RA FLS, but an induction of proliferation in the surviving cells. This observation corresponds to the pleiotropic effects of TRAIL observed on primary human tumor cells. Here, we describe that the PI3 kinase/Akt-signaling pathway, but not that of the MAP kinases ERK and p38, protects RA FLS from TRAIL-induced apoptosis by modulating the expression of the cell survival regulators p21, XIAP, Mcl-1 and RIP. Moreover, we found that not only TRAIL-induced apoptosis, but also TRAIL-triggered proliferation in RA FLS is mediated by caspases with a crucial role for caspase 8. TRAIL was found to induce degradation of p21 and p27 that was caspase-dependent, but independent of the ERK, p38 and PI3 kinase/Akt-signaling pathways. The finding that TRAIL-triggered proliferation and apoptosis share intracellular routes has to be taken in consideration in defining therapeutic strategies on the basis of the administration of TRAIL.