TGF-β1 and IGF-1 Production and Recurrence of Crohn's Disease After Ileo-Colonic Resection

Background

Recurrence after surgery is a major problem in the treatment of Crohn's disease (CD). Alteration of healing processes may play a role in this phenomenon. Transforming growth factor beta (TGF-β) and insulin-like growth factor (IGF-1) have pro-fibrogenic properties and are involved in wound-healing mechanisms. The aim of this study was to assess their role in the CD recurrence after ileo-colonic resection.

Patients and methods

Twenty patients with CD, who underwent ileo-colonic resection in the period between 1999 and 2005, were enrolled in this study. Tissue samples were obtained from macroscopically diseased and healthy ileum. The TGF-β1 and IGF-1 mRNAs were quantified by real-time polymerase chain reaction using glyceraldehyde 3-phosphate dehydrogenase as the housekeeping gene. Histological severity of the disease was assessed to quantify the ileal inflammation. Patients' follow-up was investigated. Comparisons and correlations were carried out with nonparametric tests and survival analysis was performed.

Results

Histological inflammation was moderately severe in the diseased bowel, while it was absent in healthy segments (P < 0.01). TGF-β1 production in healthy bowels showed a direct correlation with clinical CD recurrence (τ = 0.43, P = 0.04) and survival analysis showed that patients who expressed high TGF-β1 mRNA transcripts in healthy intestines had higher cumulative recurrence rates than those who expressed low TGF-β1 mRNA levels (P = 0.02).

Conclusion

Our study suggests that the high levels of TGF-β1 in healthy bowels of patients who undergo ileo-colonic resection for CD are associated with early clinical disease recurrence, while there seems to be no association between IGF-1 and CD recurrence.

Introduction

One of the most common problems connected to the surgical treatment of Crohn's disease (CD) is the high frequency of recurrence after bowel resection [1, 2]. Several factors have been investigated but only abolishing smoking, prophylactic treatment with a full dose of 5ASA after resection, or side-to-side stapled anastomosis seem to reduce the recurrence rate after surgery [3].

CD is characterized by transmural, granulomatous inflammation and by a thickening of the bowel wall due to an overgrowth of muscularis layers and to fibrosis that contributes to strictures development, which are the major cause of bowel resection. Acute injury may cause normal mesenchymal cells (myofibroblasts) to convert to the fibrogenic phenotype but this process is usually not maintained during normal healing and would lead to fibrosis when inappropriately sustained [4]. Proliferation of normal or fibrogenic mesenchymal cells may lead to muscularis overgrowth associated with fibrosis. The presence of an increased number of vimentine-positive cells within fibrotic, hypertrophied muscularis in CD suggests that changes in the mesenchymal phenotype and quantity may indeed be associated with fibrosis [5, 6, 7]. Intestinal fibroblasts in CD possess an enhanced potential for collagen reorganization and a contractile capacity in vitro, which might be responsible for stricture formation in CD [8].

Transforming growth factor beta (TGF-β) belongs to a family of multifunctional 12-kDa polypeptide dimers produced by a wide variety of lymphoid and nonlymphoid cells appearing to be universally involved in organ fibrosis [9]. The 3 mature isoforms, TGF-β1, TGF-β2, and TGF-β3, bind to specific transmembrane receptors, TGF-β receptor Type 1 and 2, and to target genes via the Smad family of signal transducing proteins [10]. TGF-β functions as a healing mediator as well as an inhibitor of T- and B-cell proliferation and cytokine production [11, 12]. TGF-β1 mediates the suppression of T-helper cell type 1 response through interleukin (IL)-10 induction and IL-12 receptor β2 chain down-regulation [13].

TGF-β expression has been demonstrated to be increased in the diseased intestinal mucosa and in the serum in active CD [14, 15], and to be localized for the most part in the lamina propria with the highest concentration in inflammatory cells closest to the luminal surface [14]. It would seem to be produced by the greater proportion of memory T-cells from CD patients than from healthy persons [16] and it significantly increases collagen type 3 synthesis in intestinal lamina propria fibroblasts isolated from CD patients. The effect of TGF-β1 on Type 3 collagen synthesis in fibroblasts from strictures in these patients was significantly higher than that in fibroblasts from inflamed specimens [17].

Insulin-like growth factor 1 (IGF-1) is the main local effector of GH stimulation on target cells in the liver and other target tissues including the intestine [18]. It is a potent enterotrophic factor in the healthy intestine, playing a relevant role in chronic inflammation and the wound-healing process in CD because of its pro-fibrogenic actions [18, 19]. In the intestinal tract, IGF-1 stimulates proliferation of fibroblasts, myofibroblasts, and smooth muscle cells, all implicated as cellular mediators of fibrosis in CD. It also stimulates collagen synthesis in intestinal fibroblasts and myofibroblasts and in intestinal smooth muscle cells [20]. TGF-β seems to enhance the effects of IGF-1 on cell proliferation and differentiation and both IGF-1 and TGF-β seem to act synergistically to stimulate collagen synthesis by intestinal cells [7, 21]. Intestinal resection significantly increases IGF-1 mRNA local expression, suggesting an up-regulation of the IGF-1 system in the residual bowel [22].

The aim of this study was to assess the role of TGF-β1 and IGF-1 in connection to the intestinal inflammation/repair mechanisms that may lead to CD recurrence after ileo-colonic resection. Local TGF-β1 and IGF-1 expression levels as well as systemic and local inflammatory parameters were thus investigated as predictors of early postoperative bowel inflammation and of CD recurrence.