Lack of TNFRI signaling enhances annexin A1 biological activity in intestinal inflammation

Abstract

We evaluated whether the lack of TNF-α signaling increases mucosal levels of annexin A1 (AnxA1); the hypothesis stems from previous findings showing that TNF-α neutralization in Crohn’s disease patients up-regulates systemic AnxA1 expression. Biopsies from healthy volunteers and patients under anti-TNF-α therapy with remittent ulcerative colitis (UC) showed higher AnxA1 expression than those with active disease. We also evaluated dextran sulfate sodium (DSS)-acute colitis in TNF-α receptor 1 KO (TNFR1−/−) strain with impaired TNF-α signaling and C57BL/6 (WT) mice. Although both strains developed colitis, TNFR1−/− mice showed early clinical recovery, lower myeloperoxidase (MPO) activity and milder histopathological alterations. Colonic epithelium from control and DSS-treated TNFR1−/− mice showed intense AnxA1 expression and AnxA1+ CD4+ and CD8+ T cells were more frequent in TNFR1−/− animals, suggesting an extra supply of AnxA1. The pan antagonist of AnxA1 receptors exacerbated the colitis outcome in TNFR1−/− mice, supporting the pivotal role of AnxA1 in the early recovery. Our findings demonstrate that the TNF-α signaling reduction favors the expression and biological activity of AnxA1 in inflamed intestinal mucosa.

Introduction

Annexin A1 (AnxA1) is a phospholipid binding protein able to inhibit leukocyte transmigration and activation. Originally described as a glucocorticoid (GC)-induced factor with anti-phospholipase activity, later on AnxA1 has been implicated in prevention of inflammation in several disease models, such as peritonitis, air-pouch edema, myocardium infarct, respiratory tract allergy, endotoxemia, kidney ischemia/reperfusion, uveitis, arthritis and others [1], [2], [3], [4], [5], [6], [7], [8], [9]. AnxA1 binds to formyl peptide receptors (FPR) [10] and supports the resolution of inflammation and the wound healing suggesting a protective role on the intestinal epithelium damage [11], [12], [13], [14].

Inflammatory bowel diseases (IBD) are chronic gut illnesses. Between them, ulcerative colitis (UC) is a prevailing entity with continuous superficial colonic inflammation, abdominal pain and recurrent diarrhea [15]. The proposed mechanism for UC development is the breakdown of the interaction between environmental stimuli and gut microbiota that results in mucosal inflammation [16]. This change may include disruption of the barrier function and alteration in the regulation of acute and adaptive immune responses [17].

The pro-inflammatory cytokine TNF-α plays a pivotal role in the signaling cascade that causes chronic intestinal inflammation in IBD [18]. Biologic agents such as anti-TNF-α antibodies Infliximab (IFX) and Adalimumab (ADA) attenuate the inflammatory process and have been approved for the treatment of moderate-to-severe UC that is refractory to conventional therapy [19]. These antibodies are well tolerated, induce and maintain clinical remission and mucosal healing, and permit the tapering of corticosteroids while allow remission [19], [20]. Interestingly, the anti-TNF-α therapy produces early changes in the gene expression profiles of intestinal epithelial cells that could be predictive of clinical responses [21], [22]. The availability of predictive correlates of clinical response is highly relevant as could enable to determine the benefits or risks of enduring biologic therapies on individual basis. In agreement, in a longitudinal assessment of peripheral blood samples from IBD patients recently we showed that systemic mononuclear cell transcripts as well as plasma levels of the anti-inflammatory biomarker AnxA1 are affected by initial and continuous IFX therapy [23]. Surprisingly, the response correlated with lower C-reactive protein and better quality of life of these patients.

We hypothesized that the absence or reduction of TNF-α signaling could amplify mucosal levels of the protein AnxA1. Herein, biopsies from patients under anti-TNF-α therapy during UC remission showed an increase in mucosal AnxA1 expression. We also used mice lacking TNFR1 (transmembrane and soluble receptor of TNF-α) to mimic the activity of anti TNF-α antibody, and we examined the expression and anti-inflammatory activity of AnxA1 in the colon mucosa in the well characterized animal model of dextran sulfate sodium (DSS) induced colitis. We found that the blockade of the TNF-α pathway upregulated the AnxA1 expression in the epithelium and colon mucosa and simultaneously accelerated the resolution process of the colitis.