Bone density in space linked to microbiome

One downside of being one of the few lucky scientists sent to space is that, when you return to earth, you might be left with the skeleton of a 70 year old. The natural remodelling our bones go through gets disrupted when our bodies are exposed to microgravity, and you can lose 1-2% density for every month you’re up there. Why this happens, scientists are not entirely sure, but they think it has something to do with changes in our microbiome - the trillions of bacteria living inside us. To help get to the bottom of things, UCLA’s Joe Bedree studied the simultaneous changes to the microbiome and bone density of mice sent up to the International Space Station. He hopes that his research, as well as helping astronauts, might also help the millions around the world suffering with bone conditions like osteoporosis.

Joe - What's really cool is NASA has this device called the rodent habitat. It almost looks like a giant computer case where the mice can kind of live and has sophisticated sensors and other kinds of cameras and things along those lines. However, since you're in microgravity, the fecal matter that we analyzed wasn't able to be actively sampled. And so at the end of the experiment, we had to acquire those samples and then did a kind of time point analysis there.

James - And can you sum up, well, your findings, the change in the microbiomes of these mice that you'd sent into space?

Joe - The microbiomes were relatively similar between flight and ground, except for a handful of species. And two species in particular, Lactobacillus and Dorea were elevated in the flight group, which was really interesting. We see these changes in microbes. We see their ability to potentially contribute to some of these metabolites that we detected. And then we saw that the bone homeostasis was changing. And so we thought perhaps this is just the host responding to microgravity and bone loss, or perhaps it could be an active compensation. But further studies are needed to really validate those hypotheses.

James - And you've kind of preempted my question there, Joe, about how you separated cause and affect here. Whether it was the changes in the microbiome that affected the body of the mice, or whether it was the changes in the bone density of the mice that changed the microbiome.

Joe - As much as I do love microbiology and the microbiome, I think my kind of scientific hunch, although I don't have evidence to prove this right now, is that it's probably the body that's influencing the microbiome and it could be a response. So one other piece of information that I think is really important is that mice participate in this behavioral called coprophagy, in which they ingest their own feces, which in microgravity they're not able to do.

James - Lovely.

Joe - I know it's quite an interesting process, but it's another way where they can kind of reintroduce microorganisms from the environment. And so while that is an aberration from normal behavior, it also offered a really unique opportunity, a kind of almost a selection event, in this unique environmental exposure. So again, we'll need to see if we can evaluate whether these microorganisms could actually mitigate bone loss.

James - Just so I have understood, correct me if I've got this wrong, you saw the microbiome increase in diversity of the mice you sent into space, and usually you'd associate that with health benefits, if anything. But is it kind of unique that you've seen actually have a detriment to health in this case?

Joe - Yeah, you're asking all of the great questions and I think this is a really great moment to kind of take a step back because this is a unique environment and you really literally have gravitational forces that are affecting all of these different cellular processes. Given that context, you know, really at the end of the day, this is just a selection pressure on the microbes. And so whether the diversity increases in this case doesn't necessarily mean that it's going to kind of confer a particular health benefit or health loss, but the microbes are responding to this environment and then there's a multitude of different biological processes that are changing.