| Microgravity/simulated microgravity can induce systemic organ damages, such as bone loss, muscle loss and atrophy, and cardiovascular disorders. However, until now, there is not any research report about digestive system dysfunction after simulated microgravity, mainly in the inhibition of gastrointestinal peristalsis and intestinal flora imbalance. The countermeasures of microgravity/simulated microgravity mainly focus on physical exercises, in recent years several Chinese drugs taken by the host under simulated weightlessness was developed as a countermeasures. Thus, this study investigated the effects of simulated weightlessness on liver and pancreas enzymes, intestinal morphology, intestinal mucosal barrier and intestinal mucosal immunity by using four-week rat-tail suspension model, and intestine injury improvement by rat-tail suspension with acupuncture point stimulus and running training model, separately. Methods used in the study include serum biochemistry, histochemical pathology, immunohistochemical staining, and Western blot. From the experiments, the following results were acquired:1The effects of simulated microgravity on rat liver and pancreas morphology After four-week tail suspension, the levels serum ALT and AST in TS group rats did not change, whereas, significant reduction of SOD activity and significantly increased of MDA content were noted in TS liver (p<0.05), indicating the decline of liver antioxidant capacity. Meanwhile, significant reduction of glycogen levels, and significantly higher expression of Bax, Bcl-2and Caspase3were observed in TS liver (p<0.05), significantly increased number of apoptotic hepatocytes by TUNEL staining suggesting that simulated microgravity may induce hepatccyte apoptosis. Besides, the levels of serum INS and IGF-1decreased significantly (p<0.05), suggesting dysfunction of the pancreas. PAS staining showed that the glycogen levels decreased significantly in TS pancreas (p<0.05), further confirmed that the abnormal function of the pancreas.2The effects of simulated microgravity on rat intestinal morphology and intestinal mucosal barrier Compared to control group, the morphology of intestinal mucosa in TS rats showed a certain degree of pathological changes, including epithelial cells proliferation, significantly decreased of duodenum and jejunum villi length, width and crypt depth (p<0.05), significantly increased of goblet cell number (p<0.05). Furthermore, the expressions of protein involved in intestinal mucosal mechanical barrier were also detected by IHC and Western Blot, the results showed that the down-regulation of ZO-1and Claudinl, the tight junction proteins between epithelial cells, were noted. Meanwhile, the level of Mcu2in TS intestine, involved in intestinal mucosal mucous barrier, was markedly reduced. Besides, the level of Numb protein significantly decreased in TS group (p<0.05), while the expression of Hesl protein was elevated significantly (p<0.05). The alterations of above intestinal mucosal barrier related proteins demonstrated that four-week simulated microgravity could induce injury of intestinal mucosal barrier.3The effects of simulated microgravity on rat intestinal immuno-barrier function After four-week tail suspension, compared to control group, the numbers of intestinal intraepithelial lymphocytes cells, Paneth cells, and mast cells increased significantly. At the same time, intestinal mucosal immunity related molecular were detected by IHC and Western Blot, the results showed that the expressions of SIgA, IL-1β, IL-6, NF-κB, and CD23elevated significantly (p<0.05), otherwise, the level of substance p was significantly reduced (p<0.05). The alterations of immune cells and immunity related molecular demonstrated that four-week simulated microgravity could simulate rat intestinal immuno-barrier function.4Protective effects of acupuncture point stimulus on intestinal mucosa of simulated microgravity rat Acupoint stimulation were used in the rats of TS+ACU group during rat-tail suspension, as consequences, significantly increased SOD activity and decreased MDA content were noted in TS+ACU liver compared to TS group (p<0.05), moreover, the levels of serum INS and IGF-1were significantly higher in in TS+ACU group compared to TS group (p<0.05), indicating that acupoint stimulation may improve rat liver and pancreas function under imulated microgravity. Furthermore, milder morphological changes were observed in the intestines of TS+ACU rats and the levels of ZO-1, Claudinl, Mcu2, and Numb were significantly higher (p<0.05) companied by down-regulation expression of Hesl in TS+ACU group compared to TS group, indicating that acupoint stimulation could improve the damage of intestinal mucosal mechanical barrier induced by simulated microgravity. On other hand, significant reductions of the numbers of intestine intraepithelial lymphocytes, Paneth cells, and mast cells were observed in TS+ACU small intestines (p<0.05). Besides, the expression levels of mucosal immunity related molecular SIgA, IL-1β,1L-6, NF-κB, and CD23were significantly lowered in the intestines of TS+ACU rats (p<0.05), and the expression of substance p increased significantly (p<0.05), indicating that acupoint stimulation plays a protective role on the mucosal immune injury caused by simulated weightlessness.5Protective effects of running training on intestinal mucosa of simulated microgravity rats After running training exercise, compared with TS group, there were no significant changes of the levels of liver SOD, MDA and serum INS, IGF1in TS+RT group rats. However, improved morphology of intestinal mucosa was observed in TS+RT group, including significantly increased of duodenum villus length, width, crypt depth, and number of goblet cells. In addition, the levels of ZO-1, Claudinl, Numb, and Muc2elevated obviously, showing that running exercise had some protection on rat intestinal mucosal mechanical barrier against4-weeks simulated weightlessness. Furthermore, duodenum immune cells and the levels of proteins associated intestinal mucosal immune were decreased significantly in TS+RT group compared with TS group, whereas intestinal immuno-barrier function of jejunum and ileum showed slight changes between TS and TS+RT group, demonstrating that the protection of running exercise on intestinal mucosal immune hyperfunction was more likely limited in duodenum.In conclusions,4-week simulated weightlessness could induce the pathological changes of the intestinal mucosa, injury of intestinal mucosa barrier, and stimulate intestinal mucosal immune-barrier function of rats. Acupoint stimulation could effectively improve the damage of intestinal mucous barrier of simulated weightlessness rats. Running exercise accompanied by simulated weightlessness also has certain degree of protective effect on intestinal mucosa barrier. The study of the acupuncture point stimulus opens a new research branch for countermeasures of microgravity. |
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