Molecular Mechanism Of Intestine In Response To Simulated Microgravity In Caenorhabditis Elegans

Microgravity is an important factor affecting the health of astronauts in space flight.As a classic model animal,Caenorhabditis elegans is an important model for molecular toxicology research.Till date,the analysis model of simulated microgravity has been established in C.elegans,and the related toxicity evaluation has also been carried out.The intestine is an important target organ of C.elegans in response to environmental stress or environmental toxins.However,the effect of simulated microgravity on functional state of intestinal barrier in C.elegans is still largely unclear,and the intestinal molecular mechanism of C.elegans in response to simulated microgravity stress remains largely unclear.Therefore,using C.elegans as an animal model,this thesis will focus on analyzing the molecular mechanism of intestine in response to simulated microgravity.Three parts of work have been carried out in this thesis:1 Molecular basis for simulated microgravity-induced damage on functional state of intestinal barrierSimulated microgravity treatment resulted in the intestinal damage,including both the deficit in intestinal development and especially the enhancement in intestinal permeability.Simulated microgravity dysregulated genes required for control of oxidative stress,including mev-1,sod-2,sod-3,and sod-4.Meanwhile,intestinal overexpression of SOD-2 prevented the increase in intestinal permeability caused by simulated microgravity and induced a resistance to toxicity of simulated microgravity,suggesting the crucial role of oxidative stress in inducing the damage on functional state of intestinal barrier in simulated microgravity treated nematodes.Furthermore,simulated microgravity treatment could significantly reduce transcriptional expression of genes(acs-22,erm-1,and hmp-2)required for maintenance of functional state of intestinal barrier.Intestinal RNAi knockdown of acs-22,erm-1,or hmp-2 caused the deficit in functional state of intestinal barrier,and induced a susceptibility to toxicity of simulated microgravity.These observations further indicated that the dysregulation of expression of genes(such as acs-22,erm-1,and hmp-2)required for maintenance of intestinal barrier was also associated with simulated microgravity-induced damage on functional state of intestinal barrier in nematodes.2 Molecular basis for intestinal lipid metabolic sensors in response to simulated microgravitySimulated microgravity could significantly increase the transcriptional expression of genes encoding lipid metabolism sensors,including mdt-15 and sbp-1.MDT-15 and SBP-1 acted in the intestine to regulate the response to simulated microgravity.Intestine-specific RNAi knocked down of mdt-15 and sbp-1 induced a susceptibility to toxicity of simulated microgravity.SBP-1 further acted downstream of MDT-15 in the intestine to regulate the response to simulated microgravity.Moreoer,intestinal SBP-1 acted upstream of FAT-6,a fatty acyl Co A desaturase,to regulate the response to simulated microgravity.Meanwhile,simulated microgravity obviously enhanced fat storage in nematodes by increasing expressions of fat-5 and fat-6.Therefore,the intestinal signaling cascade of MDT-15-SBP-1-FAT-6 was involved in regulating the response to simulated microgravity.In addition,C.elegans possibly showed adaptive response to simulated microgravity by moderately increasing fat storage.3 Molecular basis of Notch receptor GLP-1 in response to simulated microgravitySimulated microgravity could significantly decrease the transcriptional expression of glp-1encoding a Notch receptor.GLP-1 acted in the germline to regulate response to simulated microgravity stress.Germline-specific RNAi knocked down of glp-1 induced a resistance to toxicity of simulated microgravity.In simulated microgravity treated worms,glp-1 RNAi knockdown in germline cells increased expression of daf-16 and decreased daf-2,age-1,and akt-1 expressions.Moreover,DAF-16 acted downstream of GLP-1 to regulate the response to simulated microgravity.Furthermore,germline GLP-1 acted upstream of INS-8/INS 39/DAF-28 to control the response to simulated microgravity stress.In simulated microgravity treated worms,glp-1,daf-28,ins-39,or ins-8 RNAi knockdown further noticeably increased percentage of worms with DAF-16:GFP nucleus localization.Therefore,germline GLP-1 acted upstream of INS-8/INS 39/DAF-28 to activate the intestinal signaling cascade of DAF-2-AGE-1-AKT-1-DAF-16 so as to mediate a germline-intestine communication in controlling the simulated microgravity stress.In conclusion,the evidence presented in this study demonstrated that the induction of oxidative stress and the dysregulation of expression of genes required for intestinal barrier maintenance play crucial roles in inducing intestinal damage in simulated microgravity treated nematodes.In addition,intestinal lipid metabolism related signaling cascade of MDT-15-SBP-1-FAT-6 and germline-intestine communication related signaling cascade of GLP-1-INS-8/INS-39/DAF-28-DAF-2-AGE-1-AKT-1-DAF-16 provided important molecular basis for induction of protective response to simulated microgravity in nematodes.Our study will be helpful for deeply understanding important functions and molecular mechanisms of intestinal barrier in response to microgravity stress in organisms.