A Conversation with
Luis de Lecea
Roger Bingham: We are in Seattle at Sleep 2009 with Luis de
Lecea who is in the department of psychiatry and biobehavioral sciences at Stanford University. What’s happened
since we last spoke? Just to fill you in, I’ve been talking
to a lot of the colleagues that we had from the previous
meeting and I would like to get some sense of your part of
the picture, now, which was largely involving hypocretin.
In fact, let’s start with an important paper that you’ve
done in the interim. Let me read the title for you from
Nature, Neural Substrates of Awakening, I understand that,
the brain underpinning awakening, Probed with optogenetic
control of hypocretin in neurons. That part needs to be
unpacked for a general audience, I think, could you do that
for me?
Luis de Lecea: Sure. Well, we’ve been fortunate at Stanford
to team up with Karl Deisseroth to develop this new
technology called optogenetics and what optogenetics means
is a new method that allows you to put a new channel, a
light activated channel in specific groups of neurons and
you can activate the channel and the neurons using light.
So we’ve been able to do that using channelrhodopsin,
that’s that channel that is light sensitive. We’ve been
putting channelrhodopsin neurons, specifically, in mice,
and then we can activate those neurons en vivo using an
optical fiber that is inserted into the brain.
Bingham: Now explain, just remind us why hypocretin neurons
are important.
De Lecea: Hypocretins were discovered about a decade ago by
our group and another group and they’ve been shown to be
responsible for stability of wakefulness. For instance,
narcoleptics, they fall asleep all the time and they have
this cataplexy, which is sudden loss of muscle tone. They
have disrupted sleep architecture. Narcolepsy has been used
for many years to study sleep because it is one of these
diseases that tell you exactly what is about the
coordination of sleep states. It turns out that hypocretin
is deficient. Narcoleptic patients have dysfunction of the
hypocretin system, specifically. Narcoleptics have
selective neural degeneration of these neurons that produce
hypocretin.
Bingham: So this is a genetic component related to having
an efficient hypocretin system?
De Lecea: Well, narcolepsy is supposed to caused by an
autoimmune attack to hypocretin neurons. There might be a
genetic susceptibility but it’s an essence an autoimmune
disorder. But you can make any animal narcoleptic if you
remove hypocretin so there’s a causal relationship between
hypocretin activity and narcolepsy. So that’s why there was
this hypothesis that hypocretins were actually essential to
maintain wakefulness. What we’ve done with the optogenetic
technology has been to manipulate hypocretin neurons
remotely and determine what is exactly the role of these
neurons in the transitions between sleep states and that
was something that couldn’t be done using pharmacology or
other methods.
Bingham: This was a point that came up in a previous
conversation with Chiara Cirelli, which was, I said to her,
what’s the problem here? It’s something we do, everybody
does it everyday. Goes to sleep. Why don’t we understand
it? And she was making the point that, yes, it’s slightly
embarrassing but the lack of technology up to this point,
so it’s sort of a new era in sleep medicine.
De Lecea: Absolutely. This new technology that we are
talking about such as optogenetics allows us to deconstruct
neural circuits and unprecedented cellular specificity and
temporal resolution, millisecond temporal resolution. That
technology has become available only in the last couple of
years. We’ve been fortunate enough to be at the right place
at the right time to use these technologies to uncover the
underpinnings of sleep and wakefulness.
Bingham: Hard to separate sleep and wakefulness from diet,
nutrition, metabolism, aging, these are all so intimately
bound together. How does your piece fit into that larger
picture?
De Lecea: Absolutely. The hypocretins, neurons that make
hypocretin, this neurotransmitter that is essential for
sleep and arousal stability, these neurons happen to be
very, very sensitive to metabolism and we believe that
these neurons are the sensors that dictate the metabolic
status of the organism. So those are the integrators of
physiological functions of how alert you are, how hungry
you are, how stressed you are and the output of this small
group of neurons is responsible for triggering a cascade of
events that results in wakefulness. So there are many
different mechanisms involving in the regulation of hyper
neuron activity and we’re now at a position of manipulating
the activity of these neurons as we wish and therefore we
can determine exactly when, for instance, we diet, what
kind of effect that will have on hyper neuron activity and
the activity of all other neural circuits that have to do
with sleep and wakefulness. And stress, it’s pretty much
the same thing, we know can manipulate brain circuits that
are activated by stress and monitor the role of stress on
sleep and wakefulness.
Bingham: So how does this system, hypocretin system, fit
into issues like exercise, learning, I’m thinking like
practical applications.
De Lecea: Sure. Of course not everything is related to
hypocretin but we’re trying to connect those thoughts by
manipulating the transitions between sleep states. And of
course hypocretin is one way that we can manipulate
transitions between sleep and wakefulness and REM sleep.
Indeed the exercise has a prominent effect on transmitters
that have to do with monoamines, serotonin and dopamine and
so on and so forth. And these transmitters have a very,
very important role in regulating hypocretin function and
sleep and wakefulness by other mechanisms. So we are indeed
at the point that we can selectively manipulate dopamine
activity or neuralgic activity, exercise and monitor what
is the interaction between these transmitter systems and
other physical functions, exercise, appetite, and so on and
so forth. So we are really at a very exciting moment
because we can now do that in living, freely moving animals
en vivo and that allows us to generate hypothesis about
the, again, the relationship between exercise, diet,
stress, and transitions between sleep states.
Bingham: That will lead to some practical suggestions.
De Lecea: Absolutely.
Bingham: So, optogenetics. Again, what kind of equipment
are you talking about?
De Lecea: In essence, we are introducing this light
activated channel using molecular biology methods, using
either viruses or transgenic animals to introduce these
light activated channels in the neurons that we want and
with a specific promoter and that is the [unintelligible]
gene promoter but we are doing this in other cell types as
well and that is, like I said, with molecular biology
methods. Then, once we know that the channel has been
introduced in the right cells, we assess the activity of
the channel using electrophysiology methods and then we use
optical methods, like I said, laser, with a laser source,
we deliver that light into the brain then we monitor brain
activity on an electro sonogram. The opto of the
optogenetic comes from the light activated channel and
genetic is genetically encoded light activity channels.
That’s sort of a newly coined term in the Deisseroth lab.
Bingham: I’m not sure people will know what channel meant
in this particular example.
De Lecea: A protein that is inserted into the membrane that
allows the flow of ions into the neuron and that is
basically a normal signaling. The way neurons communicate
with each other and transmit electrical signal. In essence,
we are bypassing the natural communication between neurons
by entering light when we want, where we want.
Bingham: Does this kind of technology, would it help
resolve some of these issues that are covered in articles
like Why Sleep? What are we sleeping for? Is it
restorative? Is it pruning? What’s going on?
De Lecea: there’s still a very interesting debate going on
as to what’s the function of sleep and we hope to be able
to answer those questions in the midterm by addressing
specifically what’s the posticity, how the specific
circuits of neurons react to sleep deprivation and insults
to sleep physiology. And by doing that we are hoping to
address, specifically, what’s sleep for? What is the
function of sleep? We, particularly right now, we are using
this optogenetic technology to manipulate sleep so that we
can introduce a normal sleep, we can introduce what we call
noise or micro arousals. Those are one second awakenings
that don’t interfere with a normal amount of sleep but they
interfere with sleep architecture. So we can address the
issue what is the role of intact sleep architecture on
memory function, cognition, performance in general.
Bingham: To you, sleep architecture means what? The
transitions from different stages of sleep?
De Lecea: That’s right. Natural sleep occurs in different
cycles and there’s, in human sleep there’re ninety minute
sleep cycles, from slow wave to REM sleep, back to non REM
sleep and in rodents that’s not consolidated so the cycles
are not as defined but the debate is still there as to
whether we need sleep for memory consolidation or brain
plasticity or we need the exact sequence of events that
occur during sleep. In other words, do we need stage one,
stage two, stage three or can we mess it all up,
maintaining the amount of sleep and basically assessing
cognitive functions after these disruptions.
Bingham: So you actually put a sort of a very quick kink in
the system and see what happens.
De Lecea: That’s right.
Bingham: And the results so far?
De Lecea: Well, the results are still unpolished but we can
pretty much conclude that the sequence of events during
sleep is essential to consolidate memory and that’s an
important aspect of sleep. We need an intact sleep
architecture in order to function well.
Bingham: How does that work with things like napping or
micro naps?
De Lecea: That’s a great question, of course, we don’t know
yet and that is something we would like to explore. Of
course, in rodents, there’s not an available model of
napping in rodents because they nap all the time but we are
hoping to assess those particular questions in different
animal models and obviously humans are not yet available to
optogenetic methods but we are hoping to address that in
the near future.
Bingham: Do you have any children?
De Lecea: Yes.
Bingham: So you have to be concerned about their sleep
hygiene. Do you take anything from the lab that gives you
suggestions on what you should do? Information, I mean, not
products.
De Lecea: No, the quick answer is no. Of course, there is a
lot of common sense to maintain their sleep hygiene, of
course regular exercise activity and sensible diet. That’s
what’s known to be the best and my children have not had
any sleep problems so far. So I think, set aside the
genetic component, people who have a propensity for
insomnia and of course narcolepsy. Other people within the
normal phenotype in sleep will need an architecture and
will need to use common sense to maintain those sleeping
routine.
Bingham: What led you into this field in the first place?
De Lecea: Coincidence and serendipity. I was initially
interested in looking for molecules that were specifically
expressed in different, various, restricted brain nuclei
and the first gene we isolated was a neuropeptide that was
expressed in the cortex in rodents and in order to identify
the function of this gene we asked the collaborator to
inject the peptide into the brain and look at cortical
activity which is where the gene was expressed. Our
collaborators recorded an EEG and that’s how I became
equated with the technology and the sleep field. The second
gene that we pulled out was hypocretin, which was also, of
course, involved with sleep as we later learned. Since
then, I’ve been mostly involved.
Bingham: Have you always wanted to go into science?
De Lecea: Yes. Pretty much, yeah, from, I would say,
elementary school. I had an uncle who was a mathematician
and I was fascinated by his passion for science and I
wanted to follow that pathway.
Bingham: The point I was making early, though, about the
practical applications, I wasn’t sort of forcing
connections, I think it was just our perspective, here,
that the intersection between experimental science, bench
science and social policy is one that has to be
acknowledged especially if you are talking about issues
such as sleep and learning, education. This kind of work
has a bearing on it.
De Lecea: Of course, this is basic science. We just want to
learn about the basic mechanisms underlying sleep and by
learning more about how sleep works, we hope to, not only,
of course, learn about the intellectual challenge, but we
hope to generate drugs that may help people sleep better,
more and better and also treat sleep disorders, which are
disabling in some cases. For example, narcolepsy, we can
theoretically, now, cure narcolepsy. We have a good orexin
receptor selective agonist that’s possibly going to come
out in the next ten years or so and that, of course is very
rewarding to our field.
Bingham: The relationship between narcolepsy and hypocretin
neurons is, if you don’t have hypocretin neurons you’re a
narcoleptic. So, what would the remedy be in that
situation?
De Lecea: A molecule would bind in the T Cell receptors and
that would essentially wipe out narcolepsy. Cure narcolepsy
for good.
Bingham: Do you know how prevalent that is?
De Lecea: It’s about one in two thousand people. Those are
the estimates and another estimate is about one in five
thousand. That’s the ballpark.
Bingham: You would obviously know the work of Emmanuel
Mignot and the notion of, as you said, the idea that
narcolepsy is an autoimmune response. Could you just
elaborate that a bit?
De Lecea: Well, it’s probably too early to tell. There’s
very recent data from the Mignot lab suggesting there’s
some genetic susceptibility in a segment of the population
that have a variant of the T Cell receptor and that
suggests that indeed narcolepsy might be autoimmune since a
particular combination of that T Cell receptor and MHE
complex which is the molecule that binds to the T Cell
receptor would probably generate this, sort of, autoimmune
attack specific to hypocretin cells but the mechanisms are
still unknown and it is still unknown whether it’s
autoimmunity or molecule mimicry, bio infection.
Bingham: Specifically, specially, affected populations?
De Lecea: Right, so the critical population that is
affected in narcolepsy is the set of neurons that produce
hypocretin.
Bingham: Is there an evolutionary story here? No
geographical distribution.
De Lecea: Within the brain? Oh, you mean, no, no, no. And I
think in terms of ethnicity there’s some variance between
Asians and Caucasians and African Americans but that has
not been resolved yet, actually.
Bingham: Do you sometimes feel it’s hard sometimes to get
this balance feeling how, explaining to the general public
explaining what you do, sounding reductionistic,
mechanistic, and where there’s experience of being an
integrated, functioning individual. Do you see the
disconnect sometimes there?
De Lecea: Absolutely. I think during this conversation it
also became quite clear that, of course we are doing basic
science to understand the basic circuitry, the mechanisms
of how those transitions between sleep states might work,
how does this translate into a drug, or how does this
translate into someone sleeping better? Well, the answer
is, of course, we can’t make these connections yet, but, we
are making very good progress towards identifying the
actual culprits of sleep disorders and that’s extremely
challenging and I think during the next few years we are
going to see more of that and obviously, that’s exciting.
Bingham: I was thinking back to Francis Crick’s remark in
his book The Astonishing Hypothesis, which is science in
the search for the soul, you’re nothing but a pack of
neurons. That’s a very hard. . .
De Lecea: Thing to swallow? Well, as Terry Sejnowski would
tell us, the bandwidth of our brain is equivalent to ten
Internets, which is just a pack of neurons, very well
connected. And the connectivity is what makes us who we
are. I think those, I would say, simplistic views of sleep
as you need sleep to recover, you need sleep to make the
neurons better. Those are, again, very simplistic, very
reductionistic views of how a very, very complex,
interconnected machine works and to me, it’s all about
circuitry and the more circuits we can tease apart, the
more we learn about how, actually, the brain works and
sleep is only one of the many functions of the brain and
these regulated connectivities.
Bingham: I’m not trying to romanticize this here, but, you
know in talking to people that sleep is intimately
connected with dreams, the whole consciousness thing,
what’s conscious, what’s not conscious, what’s awake,
what’s not awake, what’s sleep, what’s not. All those
things are, sort of, such an ill defined state of
exploration at some point. We still have this old folk
psychological sense of what’s going on. This is why I asked
the question about here you are getting right down into
specific neurons that are implicated in a specific disease,
narcolepsy. And I was just making the point that at some
point do you think it’s all going to go that way? We will
know the function of pretty much all the circuits you are
talking about.
De Lecea: Well, maybe not but it’s a first step and it’s an
essential first step to understand what the circuitry is
all about. And I think there’s going to be another level of
analysis, which will be the whole connector or how the
circuits are connected between each other, which will tell
us more about the functions, the higher cognitive
functions, but those are the next steps in the next decade
or so we will start to learn about those functions that we
cannot understand yet.
Bingham: Yeah, but if you were at a cocktail party and you
say what you do for a living and you said sleep, don’t
people start asking you about dreams and stuff like that
all that all the time?
De Lecea: Sure, but I disconnect that all the time and say,
well, I’m only studying the very basics of sleep and things
are far ahead from us so time will connect dreams with
circuitry that we talked about.
Bingham: So that’s in your dreams?
De Lecea: That’s in my dreams. Correct.
Bingham: Luis de Lecea, thank you very much.
De Lecea: Thank you.