SHIP-Deficient Mice Develop Spontaneous Intestinal Inflammation and Arginase-Dependent Fibrosis

Abstract

Intestinal fibrosis is a serious complication of Crohn's disease (CD) that can lead to stricture formation, which requires surgery. Mechanisms underlying intestinal fibrosis remain elusive because of a lack of suitable mouse models. Herein, we describe a spontaneous mouse model of intestinal inflammation with fibrosis and the profibrotic role of arginase I. The Src homology 2 domain-containing inositol polyphosphate 5'-phosphatase-deficient (SHIP(-/-)) mice developed spontaneous discontinuous intestinal inflammation restricted to the distal ileum starting at the age of 4 weeks. Mice developed several key features resembling CD, including inflammation and fibrosis. Inflammation was characterized by abundant infiltrating Gr-1-positive immune cells, granuloma-like immune cell aggregates that contained multinucleated giant cells, and a mixed type 2 and type 17 helper T-cell cytokine profile. Fibrosis was characterized by a thickened ileal muscle layer, collagen deposition, and increased fibroblasts at the sites of collagen deposition. SHIP(-/-) ilea had increased arginase activity and arginase I expression that was inversely proportional to nitrotyrosine staining. SHIP(-/-) mice were treated with the arginase inhibitor S-(2-boronoethyl)-l-cysteine, and changes in the disease phenotype were measured. Arginase inhibition did not affect the number of immune cell infiltrates in the SHIP(-/-) mouse ilea; rather, it reduced collagen deposition and muscle hyperplasia. These findings suggest that arginase activity is a potential target to limit intestinal fibrosis in patients with CD.

Phosphatase regulation of macrophage activation

“…The SHIP deficient mouse macrophage activation and lung phenotype are also recapitulated in C57BL/6 mice doubly deficient in Src family kinases Lyn and Hck, which are deficient in SHIP signalling, and can be rescued by transfection with membrane bound SHIP [31]. SHIP deficient mice on a 129Sv × C57BL/6 background or on a C57BL/6 background also develop spontaneous Crohn's disease-like intestinal inflammation, which is almost completely restricted to the distal ileum [32,33]. Disease is characterized by high levels of IL-4 and IL-13 in full thickness tissue homogenates from the site of inflammation and all infiltrating immune cells, primarily granulocytes and macrophages, are arginase 1 positive [32].…”

“…SHIP deficient mice on a 129Sv × C57BL/6 background or on a C57BL/6 background also develop spontaneous Crohn's disease-like intestinal inflammation, which is almost completely restricted to the distal ileum [32,33]. Disease is characterized by high levels of IL-4 and IL-13 in full thickness tissue homogenates from the site of inflammation and all infiltrating immune cells, primarily granulocytes and macrophages, are arginase 1 positive [32]. Arginase 1 activity leads to the production of l-proline, which is abundantly required for collagen biosynthesis.…”

“…Arginase 1 activity leads to the production of l-proline, which is abundantly required for collagen biosynthesis. Ileal pathology in the SHIP deficient mouse is accompanied by elevated collagen deposition, which is dependent on arginase 1 activity [32]. While the role of M(IL-4) in fibrosis remains controversial, the profound M(IL-4)-like activation in in vivo-differentiated SHIP deficient macrophages is clearly associated with increased susceptibility to fibrosis [34].…”

Signaling Mechanisms Regulating Innate Immune Responses

“…SHIP −/− mice develop ileitis starting at four weeks of age, which subsequently progresses to fibrosis (Kerr et al, 2011). Interestingly, arginase I expression is elevated in the ilea of these mice, and pharmacologic inhibition of arginase I reduces the ileal collagen deposition and muscle hyperplasia (McLarren et al, 2011). SHIP −/− mice exhibit increased macrophage infiltration in the bone marrow and spleen, which ultimately decreases survival (Helgason et al, 1998).…”

The Crohn’s disease-associated polymorphism in ATG16L1 (rs2241880) reduces SHIP gene expression and activity in human subjects

“…SHIP antagonizes class I PI3K signaling by dephosphorylating the 5′ position of class I PI3K-generated phosphatidylinositol 3,4,5 trisphosphate (PI(3,4,5)P 3 ). Class I PI3K is critical in many cellular processes including immune activation, thus, SHIPdeficient mice are hyperresponsive to immune stimuli, [23][24][25][26] including increased IL-1β production in response to innate immune activation. 24 We, and others, have reported that SHIPdeficient mice develop spontaneous CD-like intestinal inflammation that is primarily restricted to the distal ileum.…”