Mesenchymal cell targeting by TNF as a common pathogenic principle in chronic inflammatory joint and intestinal diseases

Abstract

Tumor necrosis factor (TNF) is key to the pathogenesis of various arthritic diseases and inflammatory bowel disease (IBD). Anti-TNF therapies have proved successful in the clinical treatment of these diseases, but a mechanistic understanding of TNF function is still lacking. We have investigated early cellular mechanisms of TNF function in these diseases using an established TNF transgenic model, which develops a spondyloarthritis-like disease characterized by peripheral joint arthritis, sacroiliitis, enthesitis, and Crohn's-like IBD. Bone marrow grafting experiments demonstrated that development of arthritis requires TNF receptor I (TNFRI) expression in the radiation-resistant compartment, which is also known to be a sufficient target of TNF in the development of Crohn's-like IBD in the same model. Early activation of synovial fibroblasts and intestinal myofibroblasts could also be demonstrated by perturbed expression of matrix metalloproteases and their inhibitors. Notably, selective Cre/loxP-mediated TNFRI expression in mesenchymal cells resulted in a fully arthritic-spondyloarthritic and intestinal phenotype, indicating that mesenchymal cells are primary and sufficient targets of TNF in these pathologies. Our results offer a novel mechanistic perspective for TNF function in gut and joint pathologies and indicate early common cellular pathways that may also explain the often observed synovial-gut axis in human disease.

Figure 1.

Bilateral inflammation in sacroiliac joints of Tnf^ΔARE mice. (A–C) Sacroiliac joint from a healthy C57BL/6 control. The lower two thirds of the joint consists of fibrocartilagenous tissue, and it is well defined and separated from the periost of the iliac bone. (D–F) Sacroiliac joint from a Tnf^ΔARE/+ mouse on the C57BL/6 background. The presence of a mononuclear infiltrate within the sacroiliac joint with an increased number of blood vessels is shown. The fibrocartilagenous portion of the joint is invaded by mononuclear cells that protrude from the periost of the iliac bone into the BM. Paraffin sections are stained with hematoxylin and eosin. The boxes in B and E indicate the high-magnification areas shown in C and F, respectively. Bars: (A and D) 500 μm; (B and E) 200 μm; (C and F) 50 μm.

Figure 2.

Mesenchymal cells from Tnf^ΔARE mice are activated before disease onset. (A) Representative gelatin zymogram showing MMP9 and MMP2 secretion either from SFs (left) or IMFs (right) derived from WT and Tnf^ΔARE/+ 4-wk-old mice. (B) Representative semiquantitative RT-PCR for MMP3 and TIMP1 expression in SFs (left) or IMFs (right) derived from WT and Tnf^ΔARE/+ 4-wk-old mice. WT cells treated with TNF were used as a positive control in A and B.

Figure 3.

TNFRI-expressing mesenchymal cells are sufficient targets of pathogenic TNF. (A–D) Histological examination of joint (8-wk-old) and ileal (16-wk-old) sections from ColVI-Cre Tnf^ΔARE/+ TnfRI^{flxneo/flxneo} (A and C) and Tnf^ΔARE/+ TnfRI^{flxneo/flxneo} mice (B and D). (E and F) Histological examination of sacroiliac joint sections from 10-mo-old ColVI-Cre Tnf^ΔARE/+ TnfRI^{flxneo/flxneo} (E) and Tnf^ΔARE/+ TnfRI^{flxneo/flxneo} mice (F). (G and H) Histological examination of joint sections from 7-wk-old ColVI-Cre Tg197 TnfRI^{flxneo/flxneo} (G) and Tg197 TnfRI^{flxneo/flxneo} mice (H). Paraffin sections were stained with hematoxylin and eosin. Bars: (A, B, G, and H) 600 μm; (C–F) 100 μm. (I) Southern blot analysis of BamHI-digested tissue DNA from ColVI-Cre TnfRI^{flxneo/flxneo} mice for detection of the recombined loxP TnfRI allele. (J) Flow cytometric analysis or the detection of TNFRI expression in ColVI-Cre Tnf^ΔARE/+ TnfRI^{flxneo/flxneo} SFs derived from the cultures of individual mice. White lines indicate that intervening lanes have been spliced out.