Immunogenomics and Inflammation Research Unit EA 4130, Department of Clinical Immunology and Rheumatology, Edouard Herriot Hospital, University of Lyon 1 , Lyon , France.
Front Immunol. 2014 Sep 2;5:425. doi: 10.3389/fimmu.2014.00425. eCollection 2014.
Rheumatoid arthritis (RA) is characterized by defective bone repair and excessive destruction and ankylosing spondylitis (AS) by increased ectopic bone formation with syndesmophytes. Since TNF-α and IL-17A are involved in both diseases, this study investigated their effects on the osteogenic differentiation of isolated human bone marrow-derived mesenchymal stem cells (hMSCs).
Differentiation of hMSCs into osteoblasts was induced in the presence or absence of IL-17A and/or TNF-α. Matrix mineralization (MM) was evaluated by alizarin red staining and alkaline phosphatase (ALP) activity. mRNA expression was measured by qRT-PCR for bone morphogenetic protein (BMP)-2 and Runx2, genes associated with osteogenesis, DKK-1, a negative regulator of osteogenesis, Schnurri-3 and receptor activator of nuclear factor kappa B ligand (RANKL), associated with the cross talk with osteoclasts, and TNF-α receptor type I and TNF-α receptor type II (TNFRII).
TNF-α alone increased both MM and ALP activity. IL-17A alone increased ALP but not MM. Their combination was more potent. TNF-α alone increased BMP2 mRNA expression at 6 and 12 h. These levels decreased in combination with IL-17A at 6 h only. DKK-1 mRNA expression was inhibited by TNF-α and IL-17A either alone or combined. Supporting an imbalance toward osteoblastogenesis, RANKL expression was inhibited by TNF-α and IL-17A. However, TNF-α but not IL-17 alone decreased Runx2 mRNA expression at 6 h. In parallel, TNF-α but not IL-17 alone increased Schnurri-3 expression with a synergistic effect with their combination. This may be related to an increase of TNFRII overexpression.
IL-17 increased the effects of TNF-α on bone matrix formation by hMSCs. However, IL-17 decreased the TNF-α-induced BMP2 inhibition. Synergistic interactions between TNF-α and IL-17 were seen for RANKL inhibition and Schnurri-3 induction. Such increase of Schnurri-3 may in turn activate osteoclasts leading to bone destruction as in RA. Conversely, in the absence of osteoclasts, this could promote ectopic bone formation as in AS.
类风湿关节炎（RA）的特征是骨修复缺陷和过度破坏，强直性脊柱炎（AS）则表现为骨形成增加和骨桥形成。由于 TNF-α 和 IL-17A 均参与这两种疾病，因此本研究旨在探讨它们对分离的人骨髓间充质干细胞（hMSC）成骨分化的影响。
在存在或不存在 IL-17A 和/或 TNF-α 的情况下，诱导 hMSC 向成骨细胞分化。通过茜素红染色和碱性磷酸酶（ALP）活性评估基质矿化（MM）。通过 qRT-PCR 测量骨形态发生蛋白（BMP）-2 和 Runt 相关转录因子 2（Runx2）的 mRNA 表达，这两种基因与成骨有关，Dickkopf 相关蛋白 1（DKK-1）是成骨的负调节剂，Schnurri-3 和核因子 κB 受体激活剂配体（RANKL）与破骨细胞的相互作用有关，以及 TNF-α 受体 I 和 TNF-α 受体 II（TNFRII）。
TNF-α 单独增加 MM 和 ALP 活性。IL-17A 单独增加 ALP，但不增加 MM。两者的组合更有效。TNF-α 单独在 6 和 12 小时增加 BMP2 mRNA 表达。仅在与 IL-17A 联合使用时，6 小时后这些水平降低。TNF-α 和 IL-17A 单独或联合抑制 DKK-1 mRNA 表达。支持向成骨细胞分化的失衡，RANKL 表达受 TNF-α 和 IL-17A 抑制。然而，TNF-α 而不是单独的 IL-17 在 6 小时时降低 Runx2 mRNA 表达。平行地，TNF-α 而不是单独的 IL-17 增加 Schnurri-3 表达，与两者的组合具有协同作用。这可能与 TNFRII 过表达的增加有关。
IL-17 增加了 TNF-α 对 hMSC 骨基质形成的作用。然而，IL-17 降低了 TNF-α 诱导的 BMP2 抑制作用。TNF-α 和 IL-17 之间存在协同相互作用，可抑制 RANKL 并诱导 Schnurri-3。Schnurri-3 的这种增加反过来可能激活破骨细胞，导致 RA 中出现骨破坏。相反，在没有破骨细胞的情况下，这可能会促进 AS 中异位骨形成。
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