Tip:
Highlight text to annotate it
X
>> Thank you very much for the opportunity
to talk about this subject.
I am going to specifically focus on vertebrates in space
and human studies and astronaut responses
to spaceflight environment, absolutely in form
and our motivation for these studies I am going to leave most
of that discussion to Dr. Charles.
Next slide please.
So, I am going to give you an overview.
I will be talking about fundamental questions
in the context of vertebrates and some general comments
about what occurs when the gravity vector changes
in a multi-cellular complex organism, such as vertebrate,
what those early consequences are and subsequent.
I will be discussing the complexities
because I thought one of--
an important component of this talk would be
to help define what we have been able to learn
and over the past few decades from animal studies and how
to use that in our experimental design potentially
for the station.
I will make a few comments about integrated physiology
and the development of a ground based model that helps inform.
And as a final comment through the talk,
you will see some asterisks.
Those refer to-- I have a list of publications
that very specifically addresses some of the points here
and they are very quite selected.
I think it is difficult in first entering this field
to identify really the key references that are
in a peer review available formats, so you will be able
to do that through emailing me next slide please.
So, the fundamental questions and some of these are going
to look remarkably familiar because they arise directly
from some of the issues that the basic physics and biology
that occurs at the cellular level.
And the first question is what are the organism's response
to microgravity at the tissue level.
And unfortunately, what scientists,
biomedical scientists, and basic cell biologists have discovered
is that sometimes responses that we observed in cultured cells,
we may identify a specific molecule
that plays a key role in specific process.
Sometimes when you go to the organism and disrupt
that pathway, you find that there is a delibrate redundancy
and there may be no effect, whereas,
in cultured there may be large effect.
So, it becomes very important to look in the context
of a more complex system at the tissue level.
In the same issue is what are the molecular and cellular,
as well as physiological mechanisms that account
for the observed responses, just because we measure a difference,
it doesn't mean that difference is important
and what the mechanism--
identifying the mechanism allows us
to do is it lends a great deal of predictive power
and for other responses under regular circumstances.
The mechanism also informs countermeasures,
way to interfere with that.
The third is we don't-- the third item is directly lifted
from Neil's talk, what is the gravity threshold
or the G-doses dependence needed.
We both know virtually nothing about that at this time
in the context
of the multi-cellular organism vertebrate.
How does the microgravity modify the organism's response
to other space-like factors such as radiation and that is an area
of research now, active research.
And finally, what motivates the work with animals and that is
to use those studies to understand what the implications
that microgravity responses are for human health
and the development of the countermeasures.
This is relevant both to space and on earth.
Next slide please.
So, upon entry into space, two things happen immediately,
very acutely, that is there is a headward,
shift in the body fluids
and there are rapid compensatory changes that take place
in the circulatory system.
Also, the one attribute we think about most often is
that we are exposed to weightlessness.
So, from the 1g environment that we have all evolved in,
we enter an environment in which we no longer experience
mechanical loading in a negative form.
We think of that most often in terms
of musculoskeletal system atrophy that occurs with muscle
and the bone loss that occurs,
but in fact all cells may be affected to some extent
and more work is needed to define that, and finally,
an immediate disorientation that results from these changes.
Now, these are acute and acute changes don't necessarily lead
to long-term changes, but in fact of course we know they do.
Next slide please.
This slide is basically to communicate a couple of points.
One is that after this acute phase,
our bodies have this amazing ability to adapt to changes
and as we all know now, we survive quite nicely in space
for quite a long period of time and we adapt quite well.
But in order to understand the underlying mechanisms and how
to go in and disrupt that process, it is important
to understand what are the underlying structural
and in characteristics.
By structural I mean both the composition
and the anatomy of a given change.
That is very important because once
in a given tissue the response to that acute change,
once there is a structural change, then that then return
to earth, it is maybe profoundly affected
and it may trigger subsequent changes.
The next point I would like to make about this is
that this physiological responses, we,
as scientists we all tend to study them in a specific system,
but in fact they are all quite interrelated.
And finally, and this has repercussions
for analyzing flight data once it is obtained is
that these responses are time dependent
and different for each system.
Typically, in flight experiments we get a snapshot of one
or several time points after flight and so
that we may not appreciate some of the changes
that are occurring acutely elsewhere, but in terms
of human health, it is important to start to see
that as an integrated whole.
Next slide please.
So, in terms of practical aspects, there are complexities
to the space environment.
I am only going to mention a few because of the impact
on interpretation of previous results and thinking
about experimental design for future experiments.
There are some variables in space and independent variables,
many of which tend to be rather poorly controlled
or at least we wish they were better controlled.
Each has a potential, each of these variables has a potential
to profoundly affect the function
of a multi-cellular organism and yet, we don't know how important
that is until it is tested or looked at in the context
of these other studies.
The other aspect of these poorly controlled variables is
that it can complicate between
and within experiment comparisons.
So, it is very-- we have
to interpret previous results with great care.
The first studies that were done with animals, extensive studies
that were done with animals
with U.S. investigators were have done on the Cosmos missions
and the launch and landing profiles were quite dramatically
different and housing conditions were quite
dramatically different.
And so, all of the results that obtained
in one study may not be obtained in the other study, but in fact,
there is value to this and that together when we see this,
we are encouraged that this a physiologically
and biologically significant change.
I just want to mention quickly a couple aspects,
the unique aspects of housing.
Some of these things we don't think about on earth,
rodents in particular
as an example are exquisitely sensitive to housing density.
We probably all remember from high school learning
about putting too many rats in a cage.
In fact, what happen in space is now the two dimensions
of the floor space thrown into three dimensions
and we don't have a lot of, we don't have a database in which
to know how to interpret that change, but it needs
to inform how these cages are designed.
Next slide please.
So, what are the differences that arise specifically
in the course of the experiment?
Launching, landing, these are, there are trangent acceleration
and vibration forces that have the potential to influence.
And I want to mention one important study
in terms of landing.
Most of the vertebrate studies have been done on samples
that have been recovered after animals have been exposed
to spaceflight and then returned to earth.
And there is a whole suite of changes that occurs
in skeletal muscle in response to flight, atrophy,
which you are probably familiar with,
but also there was evidence of edema, accumulation of fluid
within the tissue and some lesions in the sarcomeres.
And what they found through studies
that allowed the facilitated in-flight to sections
of sample collection was that the changes,
the damage to the muscle arose due to landing.
Atrophy itself was a unique consequence
of the weightless environment of space
and then other issues of course of timing.
Now fortunately, many of these factors and variables
that I have been talking about can be tested and are tested
in control experiments and that really necessitates for PIs
to have a pretty robust ground based research program
that support those, all those control studies, next.
So, NASA has flown a wide variety of vertebrates
at different stages from embryonic to juvenile or adult.
The vast majority have been rodents, mostly rats initially
and now more and more mice which have the advantage of being able
to manipulate them genetically.
Some of the factors that have come up, two other factors
that are important to consider is stress and age of the animal.
Our astronaut population is adult,
but many of the earlier studies were done with growing animals.
Nonetheless, if one of our goals in terms of the basic science
in understanding what is going to happen in the future
with exploration, if one of our goal is to understand cradle to,
cradle to cradle development in a microgravity environment,
we need to understand these other developmental consequences
of being in space.
Next slide please.
So, as in any scientific investigation,
what is key is selection of controls and I want
to just briefly mention the different kinds of controls
that you can think about in terms of trying
to define the influence of microgravity and vertebrates.
So typically, in flight experiments, I will talk mostly
about rodents from now on, in flight experiments,
there are typically two kinds of cage controls,
one that are typical standard cages that we use
in our ground based studies
and the other is the flight hard-wire cages because animals
and in particular mice are exquisitely sensitive to changes
and things like position, position of loop bars and wire
versus flat cages, so it is important to have it
in the course of the experiment those appropriate controls.
Now, the second item listed under that top bullet
on board centrifuge, there have been very limited opportunities
for that.
There wasn't a Cosmos mission and on-board centrifuge
that was used in an effort
to understand what might be the effects of microgravity on rats,
not-- and those animals having been exposed
to all the other stressors and changes in spaceflight.
And those studies provided some initial evidence
that the bone changes and some of these changes did not occur
if an animal was exposed to 1g, but on the centrifuge,
but much more work needs to be done in that area.
The second way this is done
in a practical level is time-delay of controls.
So, the ground controls can be euthanized
or samples collected two days later or three days later
so that you can match all the precisely the conditions
of flight.
The other that I want to comment on because this is a question
that comes up often is well, if you take an animal,
a rodent to the space, how much of that response is due
to stress and how much is actually due
to microgravity or the fluid shifts.
And so, spaceflight experiments subsequent
to the initial studies where you define the effect are useful
because you can address that.
So, one of the ways that was addressed in the past
with rats is that the stress hormone, corticosterone
which we have the analog is called cortisol,
which we produce when we are stressed, they were,
these animals when manipulated
to maintain constant stress hormone levels in space
and to prevent any rise that would occur with stress
and in those animals, they still had bone loss.
So, we knew from that that the bone loss is independent
of the stress response.
We know less about-- those kinds of studies need
to be done also in other species.
But with physiology and when that's been done
in the past despite the limited number of flights we have,
it is held up pretty well,
the molecular gene expression changes overall have pretty well
reflected some of the catabolic changes
in the musculoskeletal system.
Now, the other way you can accomplish integrated approach
much greater than any single investigator alone is how the
spaceflight, animal spaceflight experiments are
conducted themselves.
Next slide please.
That is done with basically with the tissue sharing approach
and I am going to show you another couple
of examples of that.
So, SLS1 and SLS2 were flight experiments
and there is extensive tissue sharing.
I am just showing you a few of the areas,
so by having other investigators analyze samples we are able
to get a bigger picture.
Next slide.
The Neurolab studies are an example where a flight was--
the studies were dedicated to a single system,
the neurological system and also
in this study there was in-flight dissections.
So, as we all know our opportunities are extremely few
and far between and are limited by payload size
and many other variables, and so, to make progress
in understanding the underlying processes,
physiological processes that occur, we need to be able
to do basically iterative experiments.
Learn from one study and then turn around, repeat that result
and modify the experiments so we gain new insights
and that is how we make rapid progress,
that is how drugs are discovered on earth.
But that is quite limited in space,
so next slide please about--
next slide, about 30 plus years ago,
a ground based model was developed to facilitate that.
That is the hindlimb unloading model.
This is where rats or mice can be unloaded in special cages
that allow them free movement.
And what we find in these animals is
that there is a head-ward fluid shift as we see
in the astronauts and also,
there is also selective unloading of the hind quarters.
This model has enabled over the years an extensive analysis not
only of how this disuse affect specific systems,
but how recovery occurs and how might we accelerate
recovery post-flight.
And also, it is an excellent model in terms of animal model
for clinically relevant conditions
such as prolonged bed rest and inactivity.
Now, in rats we found many of the changes we see that occur
in astronauts and in animals in space,
also occurring rats with this model.
Not all, so it is important to be critically evaluate them,
but they are entirely consistent.
In mice, there is also consistency in the responses.
They have been studied less in space as I mentioned,
but one of the, some of the data suggests that stress maybe,
play in a more important role in the mouse than the rat.
Next slide please.
So, for concluding comments, our animal experiments
that have been done over the last 30 years
and in space have first defined some of the main effects
of microgravity on the vertebrates and also just begun
to define mechanisms and counter measures,
but all of these studies have been done really
in short-term flights.
We find ourselves in a really unique situation.
That is where humans have been in space for as long
as two years, for very prolonged periods of time.
Our experimental animals that on earth we used to ensure safety
of drugs and long-term consequences
of a given treatment, those animals have only been,
vertebrates have only been in space up to 19 days
on the shuttle in terms of results obtained so far.
And so, I see the ISS
as a really unique opportunity potentially
to do both the basic cell biology
and translational research
that will help move this field forward.
Thank you.
[ Applause ]
>> Yes?
[ Inaudible audience question ]
>> There have been an extensive-- oh, I am sorry.
The question is, have there been studies in immune system
and the immune response either animals or astronauts
and the answer to that question is there have been extensive
studies and it is a very active area of research.
The studies in astronauts previously have shown
that if you take the blood cells, the immune cells
out of the astronaut and challenge them,
there is a defective response.
And in fact when investigators have looked at the immune system
in rats and in mice after exposure to space,
there are a complex series of changes that occur.
And the question is whether those are stress or unloading
and I think the answer to that question will depend
on who you ask, which investigator.
Some of the changes are very-- seem to be very clearly related
to stress, but there is a good solid and brand new evidence
that should come out soon that the results obtained
in cell culture in terms of astronauts,
blood actually have an influence at the whole vertebrate level,
the whole system level.
[ Inaudible audience question ]
>> Anecdotally, there has always been reports
of more impaired wound healing, skin lesions,
and also activation of latent viruses and infections,
upper respiratory infections.
So, this is a really important area of research especially
in light of the newer evidence that there is greater virulence.
Yes sir?
[ Inaudible audience question ]
>> Right. Right and oh, the question is,
are satellite cells able to repair the damage
in skeletal muscle that occurs,
is there damage repair, is that-- ?
Or does a muscle fiber repair itself?
I believe that both play a role.
I think that some of the work in terms of replacement
by satellite cells is relatively new work that is being done,
but there are definitely repair processes that occur.
Much like in bone after flight in animals,
the repair processes are not complete especially
in those animals that have experienced damaged
with landing.
Yes?
[ Inaudible audience question ]
>>Could you define what you mean by ramping of fluid?
[ Inaudible audience question ]
>> On the station versus--
I am going to leave that to Dr. Charles to address.
It is to-- it helps to address the changes in the,
compensatory changes
in the circulatory system before the gravity transition,
but I don't know in terms of differences
between the station and the shuttle.
So, we want address that.
[ Inaudible audience question ]
>> Alright?
[ Applause ]