Spaceflight Influences both Mucosal and Peripheral Cytokine Production in PTN-Tg and Wild Type Mice

et al. (2013) Spaceflight Influences both Mucosal and Peripheral Cytokine Production in PTN-Tg and Wild Type Mice. PLoS ONE 8(7): e68961. doi:10.1371/journal.pone.0068961 Spaceflight Influences both Mucosal and Peripheral Cytokine Production in PTN-Tg and Wild Type Mice Justin L. McCarville 0 Sandra T. Clarke 0 Padmaja Shastri 0 Yi Liu 0 Martin Kalmokoff 0 Stephen P. J. Brooks 0 Julia M. Green-Johnson 0 Sudha Agarwal, Ohio State University, United States of America 0 1 Applied Bioscience Graduate Program and Faculty of Science, University of Ontario Institute of Technology , Oshawa, Ontario , Canada , 2 Universita` degil Studi di Genova, Dipartimento di Oncologia, Biologia e Genetica , Genova, Italy, 3 Istituo Nazionale per la Ricerca sul Cancro, Genova , Italy , 4 Atlantic Food and Horticulture Research Center, Agriculture and Agri-Food Canada , Kentville, Nova Scotia , Canada , 5 Bureau of Nutritional Sciences, Health Canada , Ottawa, Ontario , Canada Spaceflight is associated with several health issues including diminished immune efficiency. Effects of long-term spaceflight on selected immune parameters of wild type (Wt) and transgenic mice over-expressing pleiotrophin under the human bone-specific osteocalcin promoter (PTN-Tg) were examined using the novel Mouse Drawer System (MDS) aboard the International Space Station (ISS) over a 91 day period. Effects of this long duration flight on PTN-Tg and Wt mice were determined in comparison to ground controls and vivarium-housed PTN-Tg and Wt mice. Levels of interleukin-2 (IL-2) and transforming growth factor-beta1 (TGF-b1) were measured in mucosal and systemic tissues of Wt and PTN-Tg mice. Colonic contents were also analyzed to assess potential effects on the gut microbiota, although no firm conclusions could be made due to constraints imposed by the MDS payload and the time of sampling. Spaceflight-associated differences were observed in colonic tissue and systemic lymph node levels of IL-2 and TGF-b1 relative to ground controls. Total colonic TGFb1 levels were lower in Wt and PTN-Tg flight mice in comparison to ground controls. The Wt flight mouse had lower levels of IL-2 and TGF-b1 compared to the Wt ground control in both the inguinal and brachial lymph nodes, however this pattern was not consistently observed in PTN-Tg mice. Vivarium-housed Wt controls had higher levels of active TGF-b1 and IL-2 in inguinal lymph nodes relative to PTN-Tg mice. The results of this study suggest compartmentalized effects of spaceflight and on immune parameters in mice. - . These authors contributed equally to this work. Copyright: 2013 McCarville et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Multiple studies have demonstrated that spaceflight has both short and long term physiological effects, in human and animal subjects. These effects include bone loss, cardiovascular alteration (cardiac atrophy and change in heart rhythm), muscle loss, and immune dysfunction, among others [1]. Specifically, it has been reported that spaceflight modifies the immune system by altering cytokine production [2] and lymphocyte numbers, specifically T cells [3]. Although the effects of spaceflight on the immune system have been the focus of several studies, there is currently a lack of knowledge with respect to how the gut microbiota is altered in spaceflight and under microgravity conditions, and the consequent impact on the immune system. Therefore, colonic contents were analyzed to determine whether effects on the gut microbiota could also be detected. The gut microbiota is known to affect both mucosal and systemic immunity, including IgA-secreting plasma cells, CD4+ T cell populations and antimicrobial peptide secretion, as well as altering intestinal epithelial cell cytokine expression [4,5,6,7]. Therefore, changes in the gut microbiota during spaceflight and under microgravity conditions may also affect the immune system. Transgenic mice over-expressing pleiotrophin under the human bone specific osteocalcin promoter (PTN-Tg) and wild type (Wt) mice were also used for this study [8], allowing for additional insight into effects of this transgene on the immune system under both flown and ground control conditions. PTN is part of the midkine family of heparin-binding growth factors, and is involved in osteogenesis and bone formation, as well as neurogenesis, cell proliferation and inflammation [9,10]. Decreased bone density and bone mass are issues associated with space flight [8]. The PTN-Tg mouse model was selected for the leading study in the MDS mission flown aboard the ISS, in order to determine whether PTN over-expression would provide protection from bone loss due to microgravity [8,11]. The aim of present study was to examine effects of long-term space flight on immune parameters and the gut microbiota, through participation in a tissue-sharing program [11]. However, as little is currently known about the effects of PTN overexpression on immune parameters, the use of both wild type and PTN-Tg mice in the MDS system also provided a novel opportunity to examine effects of PTN overexpression and of long-duration space flight on the immune system. While numerous effects of spaceflight on the immune system have been reported, the potential contribution of spaceflightassociated effects on the gut microbiota to such changes has received little attention to date. Increasing evidence points to numerous interactions of the gut microbiota with the immune system [12], and determining effects of spaceflight on the gut microbiota, and the subsequent outcomes for immune activity will be valuable for optimizing long-term space flight conditions. To gain insight into these interactions utilizing a limited quantity and range of tissues, our focus was on cytokines previously reported to be affected by spaceflight, important for immune regulatory or effector activity, and responsive to gut microbiota changes: TGFb1 and IL-2 [13,14]. TGF-b1 is a multifunctional cytokine that plays an integral role in adaptive immunity, mucosal immunoregulation as well as bone formation, osteoblast proliferation and differentiation, and is influenced by the gut microbiota [13,15,16,17,18]. TGF-b1 is often considered a regulatory cytokine, involved in intestinal immune homeostasis and control of T cell activity and differentiation [19]. Previous studies have demonstrated that TGF-b1 is down-regulated in certain tissues under microgravity conditions, including reduced TGF-b1 mRNA levels in bone and in osteoblasts, as well as decreased osteoblast TGF-b1 production [17,20,21,22]. While little is currently known about interactions between PTN-Tg and TGF-b1, concurrent upregulation of PTN and TGF-b1 has been reported in chlorhexidine gluconate (CG)induced fibrosis [9]. Given the role (...truncated)