Surprising skin modifications

The results of this study, published in the journal npj Microgravity of the Nature publishing group (1), astonished the scientists. “We did not expect to observe such histological changes in the dermis and hair follicles of the mice”, says Charles Lambert. And yet…the analyses clearly showed that the mice that spent 3 months in space had a much thinner skin (15% thinner) than the control group. “The thinning of the skin of these little rodents is comparable to that associated with ageing”, explains the scientist.

Microgravity also affects hair follicles.  “During normal development, hair follicles cycle from an anagen phase (hair growth) to a catagen phase (growth arrest and involution) and finally to a telogen phase (hair loss)”, explains Charles Lambert. “In mice subjected to a microgravity environment, a large number of follicles are in anagen phase as opposed to a resting pattern in control mice”. “This is very surprising! And these results have been confirmed by transcriptomic analyses which have shown the existence of more messenger RNAs typical of hair follicles in anagen phase”.

From a biochemical point of view, the observations concerning the collagen present in the dermis of the mice also surprised the researchers. “Given that the skin of the mice was thinner on their return from the ISS, it was logical to postulate that the dermal collagen was either less synthetized or more degraded by specific enzymes” indicates Charles Lambert. The results of this study revealed the contrary, that in fact collagen synthesis was actually increased in the dermis of the mice sent to space. But transcriptomic analyses showed that the enzymes that ensure fabrication of good-quality collagen were less abundant!! “One hypothesis is that newly-synthesized collagen is not matured correctly and is eliminated before its accumulation in tissues, similarly to what happens in vitamin C deficiency. The balance would therefore tends toward a reduction of the collagen deposition in the dermis of these mice”, explains the scientist. This hypothesis remains however to be firmly proven.

The skin, an organ that has not been studied enough among astronauts

Finally, the transcriptomic analyses have scrutinized the expression of 22,000 genes among which 11,000 have been seen to be “active”. “The results show that around 400 of these genes are differentially expressed as compared to the control mice”, explains Charles Lambert. The scientists mainly investigated three families of genes: those related to the components of the extracellular matrix (notably to collagen synthesis), those participating to the development of hair follicles and those which code for the muscular proteins. “The mice possess a muscle in the dermis that has disappeared in humans during evolution”, points out the researcher. “And we noticed changes in this muscle similar to those observed in the other so-called “load-bearing” muscles in the mice that spent time in space”, he continues.  These results call into question the theory that muscles subjected to microgravity are altered due to a lack of body burden since a non-load bearing muscle shows the same type of alterations.  

The discoveries made in the context of this study show that the skin of mice is clearly affected by microgravity. What about the skin of astronauts who spend months or, in the future, years in space during missions? “The skin of astronauts has hardly ever been studied to date”, explains Charles Lambert. “And yet this is a very important organ playing a critical role as a barrier towards organism water loss and deleterious environmental factors (UV, radiations, pathogens,…).  Moreover astronauts often complain of skin problems such as itching or chapping during missions”. The scientists hope that the observations made on the skin of these mice will encourage decision-makers to initiate research on the impact of space flights on astronaut’s skin.

(1)  Thibaut Neutelings, Betty V Nusgens, Yi Liu, Sara Tavella, Alessandra Ruggiu, Ranieri Cancedda, Maude Gabriel, Alain Colige & Charles Lambert. Skin physiology in microgravity: a 3-month stay aboard ISS induces dermal atrophy and affects cutaneous muscle and hair follicles cycling in mice. Npj Microgravity, online 27/05/2015, doi 10.1038/npjmgrav.2015.2