Resistin-like molecule α enhances myeloid cell activation and promotes colitis

Expression of Relm-α in DSS-induced colitis. Wild-type mice were treated with DSS for up to 8 days. Representative immunofluorescence microphotographs of Relm-α expression in the colons of wild-type control mice (A) and DSS-treated wild-type mice (B-F) are shown. Frozen sections were stained with anti–Relm-α (red; Fig 1, A-F), DAPI (blue; Fig 1, A-F), and either anti–Mac-3 (green; Fig 1, A, E, and F) or anti-MBP (green; Fig 1, B and C). A high-resolution image of double-stained MBP⁺/Relm-α⁺ cells is shown (Fig 1, C). Arrows indicate Relm-α⁺ cells (Fig 1, B-E).

Generation of Retnla^−/− mice. The Retnla gene was replaced by a reporter-selection cassette, which consists of β-galactosidase and a neomycin resistance gene. The diagram shows the wild-type murine Retnla gene locus and the gene-targeted locus. The construct deletes all 4 exons of the Retnla gene (A). The mice were identified as heterozygotes and homozygotes by means of the Taqman assay with probes for LacZ genes and the Retnla loss-of-allele probes. Each lane represents a separate animal (B). Sera of wild-type, Retnla^−/−, and Retnlb^−/− mice were subjected to ELISA (C). ^∗∗∗P < .001 when comparing with Retnla^−/− mice (n = 8-10 mice). Validation of anti–Relm-α antibody specificity and Retnla deficiency was obtained by means of immunofluorescent staining of a DSS-treated colon sections of Retnla^−/− mice (D). mRelm-α, Murine Relm-α.

The effects of Relm-α on DSS-induced colitis. Wild-type (WT) and Retnla^−/− mice were exposed to DSS for the indicated time points and analyzed for the clinical disease features diarrhea (A), rectal bleeding (B), and weight loss (C). The colon length of wild-type and Retnla^−/− mice after DSS treatment was assessed (D). Mice were also monitored for survival after 3.5% DSS treatment (E). In Fig 3, A and B, the numbers in parentheses represent the actual number of mice that displayed clinical symptoms of disease development. Data are for a representative experiment of 4 (6-8 mice per experimental group). ^∗P < .05, ^∗∗P < .01, ^∗∗∗P < .001. Ctrl, Control.

The effects of Relm-α on DSS-induced colitis. Wild-type (WT) and Retnla^−/− mice were subjected to 2.5% DSS in drinking water for up to 8 days. At day 7, colons were excised, fixed, paraffin embedded, and stained with hematoxylin and eosin. A representative microphotograph of control (Ctrl) and DSS-treated colons is shown. Arrows indicate sites of epithelial erosion (A, left and middle). In addition, high-resolution images of the DSS-treated colons of wild-type and Retnla^−/− mice are shown (Fig 4, A; right column; magnification ×10, left and middle panels; magnification ×40, right panel). Digital morphometric analysis of the histologic score is shown. B, Data represent n = 4 (6-8 mice per experimental group). ^∗∗∗P < .001. Representative immunofluorescent photomicrographs of Relm-β expression in the colons of control (C, upper panels) and DSS-treated (Fig 4, C; lower panels) wild-type (Fig 4, C; left panels) or Retnla^−/− (Fig 4, C; right panels) mice is shown. Frozen sections were stained with anti–Relm-β (red) and DAPI (blue; Fig 4, C). A high-resolution image (magnification ×40) is shown.

Relm-α induces LPS- and DSS-induced IL-6 and TNF-α expression and inhibits IL-10 expression. Bone marrow–derived macrophages were obtained from wild-type (WT) or Retnla^−/− mice and stimulated with LPS, Relm-α, or both at the indicated concentrations for 24 hours (A-C). IL-6 (Fig 5, A), TNF-α (Fig 5, B), and IL-10 (Fig 5, C) concentrations in the cell supernatant were assessed by using a commercially available ELISA (n = 3). ^∗∗P < .01; ^∗∗∗P < .001. The concentrations of IL-6 (D) and IL-10 (E) in the culture supernatants of colon biopsy specimens taken from the distal part of control and DSS-treated wild-type and Retnla^−/− mice are shown (Fig 5, D and E; n = 6). ^∗∗P < .01.

The proinflammatory effects of Relm-α. Frozen sections of DSS-treated wild-type (WT) and Retnla^−/− mice were stained with anti-pJNK and DAPI (A and B). A representative photomicrograph of pJNK⁺ cells in the proximal colon is shown (Fig 6, A). Computerized morphometric analysis and quantitation of pJNK⁺ cells per high-power field is shown (Fig 6, B; n = 6-8). ^∗∗P < .01. The indicated concentrations of Relm-α (C; bottom left) were injected intraperitoneally to wild-type mice. Thereafter, peritoneal lavage followed by differential cell analysis was performed (Fig 6, C; n = 4). ^∗∗P < .01. ns, Nonsignificant. Chemotaxis of CD2-IL5Tg eosinophils was assessed toward Relm-α and eotaxin (D). The numbers in parentheses indicate the average fold increase (n = 3). ^∗P < .05, ^∗∗P < .01, ^∗∗∗P < .001. A schematic model for Relm-α activity in colonic inflammation is shown (E). The colonic luminal content, including bacteria and LPS, triggers an inflammatory response (1) involving recruitment of Relm-α⁺ myeloid cells, mainly eosinophils, as well as induction of Relm-α expression by epithelial cells (2 and 3). On its release, Relm-α synergizes with LPS-induced signaling to amplify a proinflammatory response characterized by increased colonic IL-6 and TNF-α and decreased IL-10 production from macrophages (4). In addition, Relm-α can promote further eosinophil accumulation, acting in an autocrine fashion. Ctrl, Control.

Macrophage accumulationin the colon and arginase-1 and YM1 expression after DSS treatment. Wild-type mice were treated with DSS for up to 8 days. At the indicated time points (days 0, 3, and 5), the colon was excised and either frozen for slide and protein lysate preparation (A, B, and D) or enzymatically digested for differential cell analysis (C). Representative microphotographs of anti-CD68–stained slides are shown (Fig E1, A). Anti-CD68⁺ cells were quantified by using digital morphometric analysis (Fig E1, B). Single-cell suspensions were stained with anti-CD11b and anti-F4/80 and analyzed by means of FlowJo software (Tree Star, Inc, Ashland, Ore) for CD11b⁺/F4/80⁺ cells in the colon (Fig E1, C). Total protein lysates of whole colon specimens were subjected to Western blot analysis and probed with anti-arginase, anti-YM1, and anti-actin as loading control. A representative Western blot is shown in which each lane represents the colon from 1 mouse (n = 4; Fig E1, D).