Insulin-like growth factor-I reduces stress-induced gastric mucosal injury by inhibiting neutrophil activation in mice

https://doi.org/10.1016/j.ghir.2008.08.003Get rights and content

Abstract

Objective

We previously reported that activated neutrophils are critically involved in the development of stress-induced gastric mucosal injury in mice. Caspase activation plays an important role in the pathogenesis of tissue injury by activating neutrophils through an increase in the expression of endothelial monocyte-activating polypeptide-II (EMAP-II), a chemoattractant for neutrophils. Since insulin-like growth factor-I (IGF-I) inhibits caspase activation, it is possible that IGF-I reduces gastric mucosal injury by inhibiting neutrophil activation. In the present study, we examined this possibility in mice subjected to water-immersion restraint stress (WIR).

Design

Mice were intraperitoneally administered with IGF-I or vehicle before being subjected to WIR. Gastric mucosal injury, gastric myeloperoxidase (MPO) activity, the immunofluorescence intensity of MPO, caspase-3 activity, number of apoptotic cells, EMAP-II expression and activation of Akt and glycogen synthase kinase-3β (GSK-3β) in gastric mucosa were determined in mice subjected to WIR. Neutropenia was induced by administration of methotrexate (MTX).

Results

Administration of IGF-I at dosages higher than 200 μg/kg significantly reduced gastric mucosal injury and inhibited increases in gastric MPO activities after 8 h of WIR. Administration of MTX also reduced the gastric mucosal injury as well as inhibiting increases in both gastric mucosal MPO activities and circulating neutrophil number. IGF-I (500 μg/kg) inhibited the increases in both gastric MPO activity and the immunofluorescence intensity of MPO observed in the gastric mucosa, but had no effect on the increase in circulating neutrophil number after 8 h of WIR. It also markedly blunted WIR-induced increases in caspase-3 activities and the number of apoptotic cells in the gastric mucosa after 8 h of WIR. Gastric expression of EMAP-II was markedly increased at 8 h after starting WIR and this increase was inhibited by IGF-I administration. Administration of IGF-I enhanced WIR-induced phosphorylation of Akt and GSK-3β in the gastric mucosa.

Conclusion

These observations indicate that IGF-I reduces stress-induced gastric mucosal injury by inhibiting gastric accumulation of neutrophils through inhibition of caspase-3-mediated EMAP-II activation. Furthermore, IGF-I might inhibit caspase-3 activation through Akt/GSK-3β signaling.

Introduction

Neutrophils play an important role in the development of tissue injury by releasing a variety of inflammatory mediators [1]. We previously showed that neutrophils appear to be critically involved in the pathogenesis of gastric mucosal injury induced by shock [2], stress [3] and indomethacin [4].

Insulin-like growth factor-I (IGF-I), a basic peptide consisting of 70 amino acids, exerts various important biological actions including promotion of the differentiation of various cell types, a potent anti-apoptotic activity, and an anabolic effect [5]. IGF-I has been shown to reduce tissue injury through prevention of cell death in animal models of renal ischemia/reperfusion (I/R) [6], burns [7], irradiation [8] and sepsis [9], [10]. Among the various activities of IGF-I, its anti-apoptotic activity has been shown to play an important role in the reduction of I/R-induced tissue injury by attenuating inflammatory responses [6], [11].

The gastrointestinal tract has been identified as one of the most sensitive target tissues for IGF-I [12]. Transduction of signals through the IGF-I receptor triggers multiple series of intracellular phosphorylation events as well as those activating several signaling pathways which prevent cell death [5]. Apoptosis is normally observed in the gastrointestinal tract and plays an important role in the maintenance of normal gastrointestinal homeostasis and mucosal integrity [13], [14]. Recent studies have demonstrated that apoptosis is critically involved in gastric ulceration [15], [16].

Caspases are normally present in intact cells as inactive precursors [17]. However, all known stimuli inducing apoptosis initiate events that culminate in caspase activation [17]. Endothelial monocyte-activating polypeptide-II (EMAP-II) is a pro-inflammatory cytokine that is capable of increasing the tissue accumulation of neutrophils [18]. Caspase activation has been shown to increase renal neutrophil infiltration after renal I/R in the kidney by converting proEMAP-II into EMAP-II [6]. These observations suggest that caspase activation might not only induce apoptosis, but also initiate inflammation by increasing neutrophil infiltration through activation of EMAP-II, thereby contributing to the development of I/R-induced tissue injury.

The PI3K/Akt pathway predominantly activated by IGF-I is a strong cell survival cascade. A downstream target of IGF-I/Akt signaling is glycogen synthase kinase-3β (GSK-3β), which is phosphorylated and thereby inhibited by activated Akt [19]. GSK-3β has been shown to play an important role in activation of caspase-3 [20]. These observations indicate that IGF-I inhibits caspase-3 activation by inactivating GSK-3β through PI3K/Akt signaling.

Taken together, these observations raise the possibility that IGF-I reduces WIR-induced gastric mucosal injury by inhibiting neutrophil accumulation through inhibition of EMAP-II expression in the stomach. In the present study, we examined this possibility in mice subjected to WIR.

Section snippets

Reagents and animals

Human recombinant IGF-I was kindly supplied by Astellas Pharmaceutical Co. (Tokyo, Japan). Other chemicals and reagents were of analytical grade.

Administration of IGF-I

IGF-I was dissolved in sterile distilled water and injected intraperitoneally 30 min before WIR at doses ranging from 50 to 500 μg/kg.

Water-immersion restraint stress (WIR)-induced gastric mucosal lesion formation in mice

All experiments were carried out on male C57BL/6 mice (7–12 weeks old; Nihon SLC, Hamamatsu, Japan), weighing 19–24 g. The care and handling of the animals were in accordance with the National Institutes of Health

Effect of IGF-I on gastric mucosal injury, gastric MPO activities and the number of circulating neutrophils in mice subjected to WIR

In the evaluation of WIR-induced gastric mucosal injury in mice, the total area of lesions in the stomach was expressed as the morphological index of gastric injury (Fig. 1A). In contrast to the normal appearance of the gastric mucosa in control mice, numerous hemorrhagic lesions were observed in the stomachs of mice subjected to 8 h WIR; the gastric lesion index was 11.2 ± 2.49 mm (Fig. 1A). IGF-I administered intraperitoneally (i.p.) reduced WIR-induced gastric mucosal injury in a dose-dependent

Discussion

As shown in the present study, IGF-I administration significantly reduced gastric mucosal injury and inhibited neutrophil accumulation in the gastric mucosa of mice subjected to WIR. We previously demonstrated that neutrophils play a causative role in the development of WIR-induced gastric mucosal injury in rats by decreasing endothelial production of prostacyclin, an important gastric cytoprotective substance, through release of neutrophil elastase [28]. Observations in the present study

References (35)

  • D.P. Brazil et al.

    PKB binding proteins. Getting in on the Akt

    Cell

    (2002)
  • N. Harada et al.

    Administration of capsaicin and isoflavone promotes hair growth by increasing insulin-like growth factor-I production in mice and in humans with alopecia

    Growth Horm. IGF Res.

    (2007)
  • J.M. Harlan et al.

    Mechanisms and consequences of leukocyte–endothelial interaction

    Western J. Med.

    (1991)
  • S. Kushimoto et al.

    Role of granulocyte elastase in the formation of hemorrhagic shock-induced gastric mucosal lesions in the rat

    Crit. Care Med.

    (1996)
  • M.A. Daemen et al.

    Inhibition of apoptosis induced by ischemia-reperfusion prevents inflammation

    J. Clin. Invest.

    (1999)
  • M.G. Jeschke et al.

    Gut mucosal homeostasis and cellular mediators after severe thermal trauma and the effect of insulin-like growth factor-I in combination with insulin-like growth factor binding protein-3

    Endocrinology

    (2007)
  • G.S. Howarth et al.

    Effects of insulin-like growth factor-I administration on radiation enteritis in rats

    Scand. J. Gastroenterol.

    (1997)
  • Cited by (0)

    View full text