Increased IL-6 expression on THP-1 by IL-34 stimulation up-regulated rheumatoid arthritis Th17 cells

Abstract

IL-34 is a pleiotropic cytokine, which is a key regulator of monocytes/macrophages and might participate in the pathogenesis of RA. In this study, we aimed to explore the effect of IL-34 on the monocyte-like cell line THP-1 and the quantitative variation of Th17 cells in THP-1 and RA CD4T cells coculture system. CD4T cells were purified from RA PBMC using immunomagnetic beads. THP-1 were cultured with RA CD4T cells. The frequency of Th17 cells was determined by FACS. Fluorscence indensity and expression of ROS were detected by FACS and cell staining, respectively. The expression of IL-6, IL-23, IL-21, TNF-α and IL-1β in the coculture supernatants were detected by ELISA. We found that CSF-1R was constitutively expressed on peripheral monocytes as well as THP-1, but not on the T/B cells. IL-34-CSF-1R binding could activate THP-1 to secret IL-6. IL-34 could up-regulate the numbers of Th17 cells in coculture system, which was possibly via the production of IL-6. We further observed ROS levels were increased in the coculture system. The percentage of Th17 cells was reduced when ROS production was inhibited by NAC, a specific inhibitor of ROS production. In addition, TNFRII antagonist but not IL-1βR antagonist could restrict the production of ROS, expression of IL-6 and generation of Th17 cells. In conclusion, IL-34-stimulated THP-1 can produce higher levels of ROS, which promoted IL-6 secretion and up-regulated Th17 cells. Our study suggests a novel mechanistic insight into how the interaction of IL-34-stimulated monocytes and CD4T cells participates in the RA pathogenesis.

Interleukin-34, a comprehensive review

“…Since IL‐34 is expressed at mRNA level in various tissues, this expression is expected to be changed under pathological conditions. Indeed, several studies have confirmed the enhancement of IL‐34 expression at mRNA and protein levels in the context of various diseases including autoimmune disorders, inflammation, infections, metabolic diseases, neurological disorders, and cancer . At the cellular level, IL‐34‐producing cells include synovial fibroblasts, immune cells, epithelial cells, endothelial cells, adipocytes, and cancer cells.…”

“…Pro‐inflammatory cytokines are fundamental to the pathophysiology of RA. Numerous studies have unveiled the pathologic role of IL‐34 in RA as a downstream effector of pro‐inflammatory cytokines, contributing importantly to inflammation and bone erosion . Elevated levels of IL‐34 can be detected in the blood, synovial fluids, and synovial tissues of RA patients.…”

“…Evidence from in vitro experiments has shown that pro‐inflammatory cytokines, including TNF‐α, IL‐1β, IL‐6, and IL‐17, can induce the expression of IL‐34 in osteoblasts and synovial fibroblasts via JNK‐ and NF‐κB‐mediated mechanisms . Functionally, IL‐34 contributes to the pathophysiology of RA via multiple molecular and cellular mechanisms: (1) IL‐34 mediates a positive feedback loop that results in an enhanced expression of pro‐inflammatory cytokines such as IL‐6 and IL‐17, (2) promotes migration of PBMCs that showed enhanced expression of IL‐17, (3) enhances proliferation and differentiation of M ϕ s, which serve as a predominant infiltrating cell type in the inflamed synovia that promotes inflammation by enriching the environment with pro‐inflammatory factors, and (4) supports RANKL‐induced osteoclastogenesis resulting in bone erosions . Additionally, IL‐34 induces STAT3 activation and miRNA‐21 increment in synovial fibroblast, resulting in increased resistance of fibroblast to apoptosis and enhanced IL‐6 expression, which in turns contribute to Th17 production .…”

“…as a potential therapeutic strategy in kidney injuries . In autoimmune diseases, neutralizing IL‐34 is similarly expected to have multiple therapeutic effects in autoimmune diseases such as RA, including (1) blocking of the inflammatory circle caused by cytokine storm such as IL‐6 and IL‐17, (2) reduction of pathogenic immune cell subsets such as Th17 cell, sensitizing synovial fibroblasts to apoptosis, and (3) controlling bone erosion and cartilage destruction caused by excessive osteoclastogenesis . In Sjogren's syndrome, targeting of IL‐34 was suggested as promising immunotherapy that may help to suppress the expansion of pro‐inflammatory CD14 bright CD16 + monocytes in the inflamed salivary glands …”

Immunomodulation of Interleukin-34 and its Potential Significance as a Disease Biomarker and Therapeutic Target

“…IL-34 can induce the differentiation, proliferation, and infiltration of macrophages in the inflamed synovia, which are the central immune cells in RA pathogenesis 31,32,36. It also stimulates IL-17-producing Th17 cells, which are the crucial drivers of autoimmune tissue injury in RA 38-40. Furthermore, overexpression of IL-17 is implicated in RA etiology.…”