Abstract
BackgroundLong-term space travel simulation experiments enabled to discover different aspects of human metabolism such as the complexity of NaCl salt balance. Detailed proteomics data were collected during the Mars105 isolation experiment enabling a deeper insight into the molecular processes involved.ResultsWe studied the abundance of about two thousand proteins extracted from urine samples of six volunteers collected weekly during a 105-day isolation experiment under controlled dietary conditions including progressive reduction of salt consumption. Machine learning using Self Organizing maps (SOM) in combination with different analysis tools was applied to describe the time trajectories of protein abundance in urine. The method enables a personalized and intuitive view on the physiological state of the volunteers. The abundance of more than one half of the proteins measured clearly changes in the course of the experiment. The trajectory splits roughly into three time ranges, an early (week 1-6), an intermediate (week 7-11) and a late one (week 12-15). Regulatory modes associated with distinct biological processes were identified using previous knowledge by applying enrichment and pathway flow analysis. Early protein activation modes can be related to immune response and inflammatory processes, activation at intermediate times to developmental and proliferative processes and late activations to stress and responses to chemicals.ConclusionsThe protein abundance profiles support previous results about alternative mechanisms of salt storage in an osmotically inactive form. We hypothesize that reduced NaCl consumption of about 6 g/day presumably will reduce or even prevent the activation of inflammatory processes observed in the early time range of isolation. SOM machine learning in combination with analysis methods of class discovery and functional annotation enable the straightforward analysis of complex proteomics data sets generated by means of mass spectrometry.
Highlights
The physiological impact of human space flights missions exceeding several weeks poses problems such as radiation exposure, immunological depression and stress
Each landscape ‘portrays’ the proteomics phenotype of the about 2,000 protein species identified by mass spectrometry in the urine samples (IPI items)
The spot patterns clearly change in the course of the experiment reflecting alterations in the proteomics phenotypes potentially caused by isolation, modifications of salt (NaCl) consumption and presumably other factors
Summary
The physiological impact of human space flights missions exceeding several weeks poses problems such as radiation exposure, immunological depression and stress. Volunteers were confined to an enclosed, restricted environment where they obtained diets with defined amounts of salt (NaCl) and micro elements content and performed different activity programs. These studies were remarkable for their sustained duration and tight control of environmental variables. This groundbased space station model experiment enabled a novel, profound and extended trip to our ‘inner space’ to discover new aspects of human metabolism [1]. Long-term space travel simulation experiments enabled to discover different aspects of human metabolism such as the complexity of NaCl salt balance. Detailed proteomics data were collected during the Mars105 isolation experiment enabling a deeper insight into the molecular processes involved
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