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. 2012;7(6):e38368.
doi: 10.1371/journal.pone.0038368. Epub 2012 Jun 6.

Cellular basis of tissue regeneration by omentum

Shivanee Shah  1 , Erin Lowery, Rudolf K Braun, Alicia Martin, Nick Huang, Melissa Medina, Periannan Sethupathi, Yoichi Seki, Mariko Takami, Kathryn Byrne, Christopher Wigfield, Robert B Love, Makio Iwashima
Affiliations

Cellular basis of tissue regeneration by omentum

Shivanee Shah et al. PLoS One. 2012.

Abstract

The omentum is a sheet-like tissue attached to the greater curvature of the stomach and contains secondary lymphoid organs called milky spots. The omentum has been used for its healing potential for over 100 years by transposing the omental pedicle to injured organs (omental transposition), but the mechanism by which omentum helps the healing process of damaged tissues is not well understood. Omental transposition promotes expansion of pancreatic islets, hepatocytes, embryonic kidney, and neurons. Omental cells (OCs) can be activated by foreign bodies in vivo. Once activated, they become a rich source for growth factors and express pluripotent stem cell markers. Moreover, OCs become engrafted in injured tissues suggesting that they might function as stem cells.Omentum consists of a variety of phenotypically and functionally distinctive cells. To understand the mechanism of tissue repair support by the omentum in more detail, we analyzed the cell subsets derived from the omentum on immune and inflammatory responses. Our data demonstrate that the omentum contains at least two groups of cells that support tissue repair, immunomodulatory myeloid derived suppressor cells and omnipotent stem cells that are indistinguishable from mesenchymal stem cells. Based on these data, we propose that the omentum is a designated organ for tissue repair and healing in response to foreign invasion and tissue damage.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Effect of omentum cells on inflammation in the bleomycin induced mouse lung injury model.
Saline or bleomycin was given intra-tracheally to C57BL/6 mice. 4 hours later, mice received i.p. injections of omentum cells (1×106 cells) or saline alone. (a) H&E staining of lung sections from mice sacrificed 7 days after bleomycin injury. Upper panels (×10), Lower panels (×20). (b) Quantification of inflammation by a volume density of lesion analysis. (c, d) Total cell numbers and percentages of T cell subsets in the bronchoalveolar lavage fluid (BAL) 7 days after bleomycin instillation. (e, f) Cytokine analysis on BAL samples 3 days after bleomycin instillation. * denotes for p<0.05.
Figure 2
Figure 2. Dose- and cell-cell contact-dependent suppression of T cell proliferation by omentum cells.
(a) CFSE labeled splenocytes were cultured with omentum cells at different ratios of omentum cells with or without 1 µg/ml anti-CD3. Cells were labeled with anti-CD4 or anti-CD8 and analyzed by flow cytometry. Omentum cells were added at different ratios to splenocytes (1∶1, 1∶3, or 1∶10) as indicated in the figure. (b) CFSE labeled splenocytes were cultured with omentum cells or lung cells in a 1∶1 ratio and surface labeled as in (a). (c) CFSE labeled splenocytes were cultured in the transwell with or without anti-CD3 across a semi-permeable membrane containing omentum cells and CFSE labeled splenocytes.
Figure 3
Figure 3. Effect of omentum cells on ex vivo T cell proliferation.
(a) CFSE labeled splenocytes were cultured with or without omentum cells in a 1∶1 ratio for 3 days. T cells were either left unstimulated (grey solid) or stimulated with 1 µg/ml anti-CD3 (dark lines). Cells were labeled with anti-CD4 and analyzed by flow cytometry. (b) Surface phenotypic analysis of cells derived from naïve and day 7 omentum by flow cytometry. (c) Omentum cells were sorted into CD45− and CD45+ cells before culturing with CFSE labeled splenocytes with 1 µg/ml anti-CD3 (solid lines) or left unstimulated (dotted lines). Cells were harvested and surface labeled with anti-CD4. (d) Surface antigen expression by CD45+ omentum cells: Activated omentum cells were stained and analyzed for the expression of antigens indicated. (e) iNOS expression was determined in total omentum cells, CD45+ omentum cells, or CD45− omentum cells upon IFNγ stimulation for 24 hrs by western blotting. (f) Omentum cells were sorted into Gr1+/Gr1− cells and tested as in (c) for the effect on T cell proliferation.
Figure 4
Figure 4. Suppression of effector but not regulatory T cells by omentum cells.
(a) Immunosuppressive functions of omentum cells on effector T cells. Naïve CD4+ T cells were induced to differentiate into Th1, Th2, Th17, or iTregs. 5 days after induction, omentum cells were added to each group of cells. T cells were maintained further with the same culture medium for 2 days, harvested, and were stimulated with PMA and ionomycin for 4 hours to induce cytokine production. (b) Cells were cultured with (+) or without (−) omentum cells and treated as in (a). Cell numbers that are expressing IFNγ, IL-4, IL-17, or Foxp3 were determined after intracellular cytokine stain. For nTregs, CD4+CD25+ from spleen were expanded prior to co-culture for 2 weeks, then cultured with omentum cells for 2 days. (c) Effect of iNOS inhibitor on Th1 and Th17 inhibition by omentum cells. Differentiated Th1 or Th17 cells were cultured with omentum cells in the presence/absence of an iNOS inhibitor for 2 days as in (a). (d) Omentum cells were sorted into CD45− and CD45+ cells, then co-cultured with CD4+T cell differentiated into Th1 (upper panels) or Th17 (lower panels) cells for 5 days. After 2 days of co-culture, cells were harvested and cytokine profiles were determined as in (a).
Figure 5
Figure 5. Differentiation of omentum cells into lung epithelium or osteoblasts.
Omentum cells were cultured in the medium conditioned to induce (a, b, d) lung epithelium or (c) osteoblast. (a) After 5 weeks of culture, cells were stained for expression of CCSP. (×10) (b) Cells cultured as in (a) were used to determine the expression of ccsp mRNA by semi-quantitative RT-PCR. gapdh mRNA level was examined to determine the amount of mRNA in each sample. (c) Omentum cells cultured in the basal (lower panels) or medium conditioned for osteoblast induction (upper panels) for 2 weeks. Cells were stained by DAPI (middle) or with anti-osteopontin antibody. (d) Omentum cells were separated into CD45+, CD45−CD34+, or CD45−CD34− cells, and were cultured in the medium conditioned for lung epithelium cell induction. Only CD45−CD34+ cells survived and expanded to the analyzable level in the conditioned medium and are shown.
Figure 6
Figure 6. Survival and expansion of omentum cell subsets ex vivo.
Omentum cells were separated into CD45+, CD45−CD34+, and CD45−CD34− subsets and cultured in the conditioned medium for lung epithelium differentiation (upper panel) or in the basal medium. Cell numbers for each group were counted on days as indicated in triplicate.
Figure 7
Figure 7. Presence of omentum-derived cells in the bleomycin-injured mouse lung.
Omentum cells from transgenic mice that express GFP in non-hematopoietic cells or PBS (Bleo only) were injected into mice that underwent bleomycin-induced lung injury. 1 week after cell injection, mice were analyzed for the presence of GFP+ cells (green cells). (×10).
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