Contrasting roles for CXCR2 during experimental colitis

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Abstract

Neutrophil recruitment into the colon is believed to play a crucial pathogenic role in the progression of clinical and experimental inflammatory bowel diseases (IBDs). The chemokine receptor CXCR2 is highly expressed on neutrophils, and promotes neutrophil recruitment in several inflammatory diseases. The present study determined the biological role of CXCR2 during trinitrobenzene sulfonic acid (TNBS)-induced colitis in the rat by assessing effects of CXCR2 antibody neutralization on neutrophil accumulation during the early (8 h) and late phase (day 7) of TNBS-induced colitis. CXCR2 expression was elevated (>3-fold above control) within 8 h and remained elevated to day 7 of colitis induction, in parallel with significant increases in neutrophil infiltration. Treatment of colitic rats with a single dose of CXCR2 neutralizing antibody significantly reduced colonic neutrophil accumulation during the early (8 h) phase of TNBS-induced colitis. However, chronic administration of CXCR2 antibody did not reduce colonic neutrophil accumulation during the late phase (day 7) of TNBS-induced colitis. In summary, the present findings suggest a functional role for CXCR2 in initiating neutrophil recruitment during the early phase of TNBS-induced acute colitis, and demonstrate that: early colonic neutrophil accumulation is CXCR2 dependent and the late phase colonic neutrophil accumulation is CXCR2 independent.

Introduction

There is ample evidence from the clinical and experimental setting supporting a crucial role for neutrophils in tissue ulceration and inflammation during inflammatory bowel disease (IBD) including Crohn's disease and ulcerative colitis Anezaki et al., 1998, Daig et al., 1996, Izzo et al., 1992, Keshavarzian et al., 1999. As a result, in recent years, much effort has been focused on characterizing further the role played by endogenous mediators in promoting neutrophil recruitment during active IBD. There is now a growing realization that chemokines may facilitate neutrophil recruitment during acute colitis Anezaki et al., 1998, Daig et al., 1996, Izzo et al., 1992, Keshavarzian et al., 1999.

Chemokines constitute a family of small (∼8–15 kDa) structurally related proteins that are widely regarded as one of the most important regulators of leukocyte trafficking and activation during the inflammatory process (Luster, 1998). The notion that chemokines could contribute to the pathogenesis of IBD stems from a series of clinical studies published a decade ago, in which rectal biopsies of patients with active ulcerative colitis or Crohn's disease were observed to produce high levels of the human chemokine CXCL8/IL-8 Anezaki et al., 1998, Izzo et al., 1992, Keshavarzian et al., 1999. Subsequent studies by Mazzucchelli et al. (1994) and Daig et al. (1996) showed that the expression of CXCL8/IL-8 correlated with the severity of inflammation and notably, this chemokine accounted for the majority of the leukocyte chemotactic activity that could be extracted from the inflamed colon Anezaki et al., 1998, Izzo et al., 1992, Keshavarzian et al., 1999.

The CXC chemokine CXCL1/KC (the murine analogue of CXCL8/IL-8; Boisvert et al., 1998, Luster, 1998, Terkeltaub et al., 1998) is a potent neutrophil chemoattractant in vivo Belperio et al., 2002, Bhatia et al., 2000, Boisvert et al., 1998, Podolin et al., 2002, Schuh et al., 2002a, and increases in the expression of this chemokine are associated with the progression of inflammatory diseases including hepatic injury (Campbell et al., 2003) and pancreatitis (Bhatia et al., 2000). CXCR2 is the sole receptor through which CXCL1/KC mediates its biological effects Belperio et al., 2002, Boisvert et al., 1998, Podolin et al., 2002, Schuh et al., 2002a, and a major mediator of neutrophil influx during an inflammatory response as reported in disease models of arthritis (Podolin et al., 2002) as well as allergic (Schuh et al., 2002a) and respiratory diseases (Belperio et al., 2002).

The present study assessed the biological role of CXCR2 during trinitrobenzene sulfonic (TNBS) acid-induced colitis.

Section snippets

Animals

Male Wistar rats (175 ± 20 g) were purchased from Charles River Breeding Farms Limited (Montreal, Canada). The animals were fed a standard chow pellet diet, had free access to water and were maintained on a 12-h light/dark cycle. All procedures were approved by the Animal Care Committee of the University of Calgary and were performed in compliance with the guidelines of the Canadian Council on Animal Care.

Induction of colitis

Rats were lightly anesthetized with Halothane and the hapten TNBS (60 mg/ml in 0.5 ml of

Neutrophil accumulation during TNBS-induced colitis

As previously documented Ajuebor et al., 2000, Ajuebor et al., 2001, Galvez et al., 2000, intracolonic administration of TNBS caused a time-dependent increase in neutrophil accumulation in the colon with significant increases within 8 h of colitis induction and remained elevated to day 7 of colitis induction (see MPO activity; Fig. 1).

CXCL1/KC and CXCR2 expression during TNBS-induced colitis

The finding of increased neutrophil accumulation in the colon led us to hypothesize that neutrophil chemoattractants such as the CXC chemokine CXCL1/KC, and its

Discussion

Over the past decade, a wealth of evidence has been generated to support a crucial role for neutrophils in the pathogenesis of colitis. Evidence that colonic neutrophil infiltrates contribute to the progression of colitis stems from a series of clinical studies in which increased neutrophil accumulation is observed in rectal biopsies of patients with active IBD relative to healthy controls Ajuebor and Swain, 2002, Anezaki et al., 1998, Daig et al., 1996, Izzo et al., 1992, Keshavarzian et al.,

Acknowledgements

This work was supported by a grant from the Canadian Institute of Health and Research (CIHR). Maureen N. Ajuebor is supported by a Canadian Association of Gastroenterology/Schering/CIHR post-doctoral fellowship.

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