Alterations to mouse skin in space
Microgravity as experienced in the International Space Station (ISS) caused a thinning of the skin, an alteration of hair follicles cycling and of collagen accumulation in mice that spent 91 days in space. Even more significant, transcriptomic analyses shed a new light on the theory that muscles that are subjected to microgravity become atrophied only due to a lack of body burden since, in these mice, a non-load bearing muscle undergoes similar types of changes. The results of this study carried out by the Laboratory of Connective Tissues Biology (LCTB) at the University of Liege have been published in the journal npj Microgravity. Reaping the rewards of good collaborationThe Laboratory of Connective Tissues Biology (LCTB), directed by Dr Alain Colige in GIGA-R, is specialized in the study of supporting tissues, such as skin, bones and tendons, in which cells are embedded within an extracellular matrix. “The connective tissues are involved in a large number of biological processes and implicated in various diseases such as arthritis, osteoporosis, cardiovascular diseases and even cancer.”, explains Dr Colige. Another particularly interesting aspect to be investigated is the reaction of connective tissues to different types of mechanical forces. “For example, a decalcification of bones can be observed in individuals remaining in lying position for prolonged periods due to a lack of mechanical stimulation of the osseous tissues”. Gravitational field on Earth is one of the permanent mechanical forces to which our tissues are subjected. “Hence the interest in studying the behavior of connective tissues in a microgravity environment”, he continues. By placing cells or organisms in a situation where gravity is virtually non-existent, the researchers can observe the effect on the regulation of the biological processes driving the connective tissues homeostasis, and from this, to deduce the influence of gravity on these same processes. “An exceptional experience”Some years later, a research proposal was submitted by the Italian team from Genoa in collaboration with the Italian space agency (ASI) and with the help of the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). “This program originally aimed at studying bone remodeling in mice kept for three months in the ISS. We proposed to study the skin of the mice that they planned to send into space for a spell aboard the ISS and our project was accepted allowing us to participate to this exceptional experiment”, continues Charles Lambert. “Mice spent 91 days on the International Space Station and a similar experiment was performed in the same housing on ground as control. We were able to begin our skin analyses in 2011”. Upon their return to Earth, the different organs and tissues of the rodents were dispatched to specialized laboratories all over the world. Charles Lambert and his team were tasked with analyzing the effects that time spent in microgravity had on the skin of these mice. He explains, “We conducted three types of experiments: histochemical analyses carried out by microscopy completed bybiochemical and transcriptomic analyses”. The first tests were aimed at examining the effect of microgravity on the structure of the skin and its appendages such as hair follicles. The second tests were mainly concerned with collagen accumulation measurements in the dermis thanks to a technique that can distinguish newly-synthesized collagen from older collagen. “Collagen is the main protein of the dermis which ensures the mechanical quality of the skin and which is renewed along all life”, he continues. Finally, transcriptomic analyses allowed to quantify the messenger RNAs present in the skin samples. “This enabled us to analyze the entire transcriptome of the skin mice without a priori hypothesis, to identify genes expressed in the samples and their level of expression and to compare these results with those of the skin from the mice kept on ground”.
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