Tumor necrosis factor (TNF) α increases collagen accumulation and proliferation in intestinal myofibroblasts via TNF receptor 2

Intestinal fibrosis is an incurable complication of Crohn's disease involving increased numbers of collagen-producing myofibroblasts. Tumor necrosis factor (TNF) alpha has defined proinflammatory roles in Crohn's disease but its role in fibrosis is unclear. We tested the hypothesis that TNF alpha increases collagen accumulation and proliferation in intestinal myofibroblasts and has additive effects in combination with insulin-like growth factor (IGF) I. The mechanisms, TNF receptor isoform, and downstream signaling pathways were examined. Intestinal myofibroblasts from wild-type (WT) mice or mice homozygous for disruption of genes encoding TNFR1 ( TNFR1(-/-)), TNFR2 ( TNFR2(-/-)), or both (TNFR1/2(-/-)), were treated with TNF alpha, IGF-I, or both. In WT cells, TNF alpha and IGF- I stimulated type I collagen accumulation and DNA synthesis in an additive manner. IGF- I, but not TNF alpha, stimulated type I collagen gene activation. TNF alpha, but not IGF- I, induced tissue inhibitor of metalloproteinase-1 (TIMP-1) expression and reduced matrix metalloproteinases-2 activity and collagen degradation. TNF alpha also activated ERK1/2. These responses to TNF alpha were absent in TNFR2(-/-) and TNFR1/2(-/-) myofibroblasts, whereas TNFR1(-/-) cells showed similar responses to WT. Inhibition of ERK1/2 diminished TNF alpha-induced DNA synthesis in WT and TNFR1(-/-) cells. Differences in TNF alpha-induced STAT3/DNA binding activity and not NF kappa B and AP-1 transcriptional activation correlated with impaired collagen accumulation/TIMP-1 induction in TNFR2(-/-) cells. Constitutively active STAT3 rescued TIMP-1 expression in TNFR2(-/-) cells. We conclude that TNF alpha and IGF- I may additively contribute to fibrosis during intestinal inflammation. TNFR2 is a primary mediator of fibrogenic actions of TNF alpha acting through ERK1/2 to stimulate proliferation and through STAT3 to stimulate TIMP-1 and inhibit collagen degradation.