Enhanced Production of Early Lineages of Monocytic and Granulocytic Cells in Mice with Colitis
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Enhanced production of early lineages of monocytic and granulocytic cells in mice with colitis Mark D. Trottiera,1, Regina Irwinb, Yihang Lia,2, Laura R. McCabeb, and Pamela J. Frakera,3 Departments of aBiochemistry and Molecular Biology and bPhysiology, Michigan State University, East Lansing, MI 48824 Contributed by Pamela J. Fraker, August 28, 2012 (sent for review April 26, 2012) The bone marrow (BM) is a large, highly active, and responsive numbers in the stools, being used in the past as one method for tissue. Interestingly, little is known about the impact of colitis on determining the pathology of the various forms of IBD (12). hematopoietic functions. Using dextran sodium sulfate (DSS) to Therefore, understanding how forms of IBD affect the production induce colitis in mice, we identified significant changes in the BM. of these cells in the marrow was also important to understanding Specifically, cells of the monocytic and granulocytic lineages in- the etiology of this disease. creased nearly 60% and 80%, respectively. This change would sup- Although CD and UC are categorized as autoimmune diseases, port and promote the large infiltration of the gut with neutrophils it is known that modifying the epithelial barrier, for example and monocytes that are the primary cause of inflammation and tis- through modulation of β-catenin, causes a Crohn’s-like colitis (13). sue damage during colitis. Conversely, the early lineages of B and T Studies in senescence accelerated mouse P-1 (SAMP) mice, which cells declined in the marrow and thymus with particularly large los- display ileitis similar to Crohn’s disease, also suggest that defects in ses observed among pre-B and pre-T cells with heightened levels of epithelial permeability may be the primary source of ileitis sus- + + apoptosis noted among CD4 CD8 thymocytes from DSS-treated ceptibility in these mice and that inflammatory responses occur mice. Also noteworthy was the 40% decline in cells of the erythro- as a consequence of this initial barrier break (14). Therefore, to cytic lineages in the marrow of colitis mice, which undoubtedly con- carefully assess how changes in barrier function impact hemato- tributed to the anemia observed in these mice. The peripheral blood poiesis, we used a DSS mouse model of colitis. DSS treatment reflected the marrow changes as demonstrated by a 2.6-fold increase induces colitis by increasing gut epithelial barrier permeabil- in neutrophils, a 60% increase in monocytes, and a decline in the ity, which is thought to allow gut bacteria to activate immune lymphocyte population. Thus, colitis changed the BM in profound responses and promote colitis. The data will show that colitis IMMUNOLOGY ways that parallel the general outcomes of colitis including infiltra- made substantial changes in lymphopoiesis in both the marrow tion of the gut with monocytes and neutrophils, inflammation, and and the thymus with major losses in pre-T and pre-B cells within anemia. The data provide important understandings of the full im- 15 d. Likewise, there were substantial reductions in erythrocytic pact of colitis that may lead to unique treatments and therapies. lineages that would contribute to and extend the anemia in DSS- treated mice. Conversely, cells of the monocytic and granulocytic granulopoiesis | lymphopoiesis | inflammatory bowel disease lineages increased significantly in the marrow and peripheral blood of mice with colitis, which could promote or sustain in- lcerative colitis (UC) and Crohn’s disease (CD) are chronic flammation and tissue damage in the gut. These important find- Uinflammatory bowel diseases (IBD) that affect more than 1.4 ings clearly show that colitis significantly alters hematopoietic million Americans (1). Both genetic and environmental factors processes. contribute to the hyperactivity and dysregulation of the immune system associated with colitis. IBD is characterized by recurrent Results bouts of illness associated with symptoms of weight loss, diarrhea, Confirmation of Disease in Mice. Mice, 6 wk of age, were separated anemia, rectal bleeding, and abdominal pain (1, 2). Past studies into two weight-matched groups (22.4 ± 1.4 g for controls and demonstrate that gut infiltration with neutrophils, monocytes, and 22.6 ± 1.6 g for colitis mice). The colitis group received 1% DSS macrophages is a major contributor to the gastrointestinal tissue in drinking water, whereas controls received regular drinking injury and inflammation noted in IBD (3–7). water. After 15 d, DSS-treated mice lost 1.8 ± 1.8 g (4.7%) of Although many facets of immune function in the IBD patient body weight, whereas controls gained 1.1 ± 0.9 g (8.0%), and in animal models have been investigated, almost nothing was resulting in an 11.1% lower body weight for DSS-treated mice known of the impact of IBD on the bone marrow (BM). In par- compared with controls (Fig. S1A). By 8 d, the majority of DSS- ticular, it was not known whether the ability of marrow to produce treated mice showed signs of rectal bleeding and soft fecal pel- fi new leukocytes or red blood cells each day was altered by UC or lets. DSS-treated mice displayed signi cant histologic changes in B CD. This question was of interest because the marrow is a large, cecums (Fig. S1 ) including structural changes marked by longer ± active tissue that produces billions of new cells each day and is and distorted crypt structure (scored at 4 1.3 compared with ± often impacted by changes in nutriture, stress, and disease (8–10). 1.2 1.0 for control mice), hyperchromasia, and few goblet cells Indeed, it was known that UC changed the rate of maturation of marrow osteoblasts, which contributed to the thinning of bones (11). Thus, the purpose of the research reported herein was to Author contributions: M.D.T., R.I., L.R.M., and P.J.F. designed research; M.D.T., R.I., Y.L., L.R.M., and P.J.F. performed research; M.D.T., R.I., and L.R.M. contributed new reagents/ determine the impact of dextran sodium sulfate (DSS)-induced analytic tools; M.D.T., R.I., Y.L., L.R.M., and P.J.F. analyzed data; and M.D.T., R.I., Y.L., L.R.M., colitis on hematopoietic function, with a focus on erythropoiesis, and P.J.F. wrote the paper. lymphopoiesis, and myelopoiesis (the production of neutrophils The authors declare no conflict of interest. and monocytes). Freely available online through the PNAS open access option. Myelopoietic processes in the marrow were of particular interest 1 fi Present address: College of Human Medicine, Michigan State University, Grand Rapids, because neutrophils are among the rst cells to be found in mucosa MI 49503. – of the gut, especially in the case of UC (3 5, 7). They secrete large 2Present address: Geriatric Research, Education and Clinical Center, VA Palo Alto Health amounts of chemokines that subsequently cause increasing num- Care System, Palo Alto, CA 94304. bers of monocytes/macrophages to enter these areas, creating 3To whom correspondence should be addressed. E-mail: [email protected]. fl – sustained injury and in ammation (3 5, 7). Indeed, cells of the This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. myeloid lineages become so prevalent that they are found in large 1073/pnas.1213854109/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1213854109 PNAS Early Edition | 1of6 Downloaded by guest on September 26, 2021 with colitis or enhanced elimination of lymphocytes from marrow via cell death and/or egress to peripheral sites (see Fig. S2 for typical flow cytometry plots; refs. 8 and 15). The erythrocyte compartment was reduced from 16.3% to 9.8% (down 40%) of nucleated cells. These data are particularly noteworthy given that anemia often accompanies colitis, and DSS treatment of rodents is known to cause anemia (16–19). Indeed, in blood of DSS-treated mice, significantly fewer red blood cells, reduced hemoglobin, and a lower hematocrit was observed, indicative of the beginnings of anemia (Table S1). Of note, colitis did not change the total number of nucleated cells within the marrow [38.0 ± 6.1 vs. 37.0 ± 5.0 (×106) in control versus colitis mice, respectively]. Thus, the deficits in cells of the lymphoid and erythroid lineages represented absolute declines in cell numbers, not just changes in the proportion of cells present. Conversely, increases in the number and proportion of cells of the myeloid lineages (monocytes, granulocytes) were noted in colitis mice. Monocytes increased more than 58%, from 9.8% of nucleated marrow cells in controls to 15.5% of cells in DSS mice. Likewise, granulocytes in marrow increased from 34% to 60% in DSS mice, an almost 80% increase (Fig. 1). These increases in cells of the myeloid lineages represent significant changes in the composition of the marrow and, therefore, its activity. These increases are also an important facet in the etiology of colitis that has been overlooked. It should be noted that the mixed pro- genitor population also declined nearly 40% in DSS-treated mice (Fig. 1). Because the composition of this group was not de- termined here, its potential impact if any is unknown. Because of the large decline in the lymphocyte compartment, the BM B-cell subpopulations were further examined. This dis- covery is important because in adults the majority of developing lymphocytes in the marrow are of the B lineage. We found that the B-cell population as a whole declined 70% in mice with colitis, representing a substantial decline in lymphopoiesis. Much of the decline in the marrow B-cell population was due to the loss of the pre–B-cell subset, which showed decreases in both Fig.