cc >> Tom Zinnen: Welcome,
everybody, to Wednesday Nite at the Lab.
I'm Tom Zinnen. I work here and the University
of Wisconsin Madison Biotechnology Center and for UW
Extension Cooperative Extension, and on behalf of our other
sponsors, Wisconsin Public Television and the Wisconsin
Alumni Association, thanks again for coming to Wednesday Nite
at the Lab. We do this every Wednesday
night, 50 times a year. Tonight I'm delighted
to introduce to you Hilary Gerstein.
She's currently in the neuroscience training program
here at UW Madison. Her interests focus on using
rodent models to explore how cellular and molecular changes
in the brain relate to behavior. Hilary has done past work with
transgenic mouse models of Alzheimer's disease and also
studied the effect of pharmacological manipulations on
maternal behaviors and histology in mice.
Currently as a graduate student she's studying the function of
certain genes expressed in the hippocampus that have previously
been implicated in learning and memory.
In the Berger lab they use recombinant adeno-associated
virus, otherwise known as rAAV, as a gene delivery system to
over-express or knock down function of these candidate
genes in specific regions of the brain.
Hilary will then examine the resulting phenotypes with a
variety of behavioral tests and anatomical techniques.
Whoa, I like that.
Hilary gave this talk at PLATO Frontiers in Life Sciences
last fall. I think you're really going to
enjoy it. Please join me in welcoming
Hilary to Wednesday Nite at the Lab.
[APPLAUSE]
Hilary Gerstein: Is this on? Yes? Okay.
It's really impossible to tell from here.
Okay, so one of the nice things about the introduction that Tom
gave is it wasn't just what am I doing now but it's what did I do
in the past as well, because there's only going to be a
little bit of what am I doing now.
There's going to be several sections of this talk.
I hope everyone got a chance to look at the cartoon because
cartoons are awesome. There will be more cartoons.
So this is where we're going today.
First we're going to talk about memory, and it's kind of what I
like to think of as information everyone should know about
memory and how the brains works. Just basic overview.
And then when we talk about that, you'll be prepared to talk
about happens in the brain, what changes occur with aging and how
does that relate to learning and memory.
And once we have that down then we can look at some different
ways in which aging can affect learning and memory.
And we'll first start off with some theories about how
Alzheimer's disease works. That is perhaps the most famous
example of a disease involving aged individuals and learning
memory deficits. And then lastly we'll look at
some of the research I'm doing now in my graduate career in
terms of what changes are going on in the brains of normal
individuals as they age that causes their memory to change or
not be quite as good. So it's a little bit of
everything, but I think those are the best kind of public
talks so you get a little bit of everything and not just too much
detail on any one thing. And you can raise your hands and
ask questions as you like. Okay, so the first thing is that
memory is not all just one thing.
There's different types of memory, and that's actually
really functionally important to know the difference between the
different types of memory. So first we have short-term
memory or working memory. And this is if someone tells you
on the telephone, oh, you need to call this number, you need to
call the restaurant to make a reservation, let me tell you the
number. And then you look around for a
pen, and you can't see a pen so you start repeating the number
to yourself as you walk around your home looking for a pen so
you can write it down. That's a type of working memory,
short-term memory. It could also be if you sit down
or are cramming for something very last minute and then right
it all down within a few short hours.
Long-term memory is, as it states, long term.
And there's two major types of long-term memory.
First is conscious memory or declarative memory.
And this is facts. So people, places, events, what
year William the Conqueror invaded Normandy, D-Day, what
your grandmother looks like, what your birthday is, any of
these things are facts. That's conscious or declarative
memory. Unconscious or procedural memory
is different. That's something like riding a
bicycle, for example. Once you have learned or
acquired the task of riding a bicycle, when you get on a
bicycle you don't think okay I'm going to move my legs like this
and I need to stand up straight and balance, it just sort of
happens. It's unconscious.
And these, as you'll see in a bit, are the important in terms
of how they are different. So interestingly, both
short-term or working memory and conscious and declarative memory
show a gradual decline or aren't quite as good in individuals
that are aged. And that's just a normal event.
That doesn't mean there's anything wrong with the
individual. It is something that happens
pretty much across the board. But what's even more interesting
is that specifically the conscious or declarative memory
is greatly impaired in certain forms of dementia and also in
also Alzheimer's disease. So this is the type of memory
we're going to be looking at today.
We're going to be looking at long-term memory for facts,
people, places, events, things. Okay, so something I always like
to start off with is we're going to talk for a while about how
your memory is going to get worse but first let's talk about
how your memory can be improved. So memory palaces, this is
actually very fortuitous because there is a book coming out, I
think it comes out this week by Jonathan Foer and it's called, I
have it written down on the next slide I think, Moonwalking With
Einstein. It's about how he trained
himself using this exact method I'm going to explain to you
right now to become a national memory champion.
And he started investigating this because he wanted to write
a newspaper article about it. And then he got sucked into the
competitive world of memory games and became a national
memory champion himself not having any previous experience
with it. So it does work.
It can work. Let's explain.
This is a tool by the ancient Greeks.
Not everything was always written down.
It was very expensive to have scribes.
So it was very common for important people in the learning
community to memorize works of literature or science.
And the way, one way you can memorize something very large
like a string of numbers or an entire book is to your spatial
memory. So they developed this thing
called a memory palace, and you think about a building that you
know incredibly well. I like to use the house I grew
up in. My husband likes to use the
Metropolitan Museum of Art in New York because he grew up near
there as a child. Something that you know very
well, you can imagine yourself walking through it in
three-dimensions in your mind's eye.
And as you go through the palace in your mind's eye, you deposit
the little items that you need to remember.
So if I'm trying to remember a long string of numbers I'm going
to think about walking in the front door of my parent's house
where I grew up, and what do I do next?
I would take out my keys and put them down on the little bowl
where we have the keys, and that's where I would leave the
first number in the string I was remembering.
Then I probably take off my shoes, and so I look down and,
look, I would put the number in my mind's eye, number two, on
top of where my shoes are right inside the door.
Then I would probably walk to go let the dog out of his crate, on
top of the crate I would leave the third digit.
And you can actually leave a trail of the numbers or the
objects that you were trying to remember throughout this entire
palace, and all you need to do to retrieve them is take the
same path through your memory palace.
And you can train yourself to be very effective at this.
And, in fact, one of the most famous world memory champions
has used this method repeatedly for eight national championships
or eight world championships. And he can use this exact method
to memorize 1,000 random numbers at over 300 locations, and he
can commit them all to memory in half an hour.
That's pretty extreme but I've personally used memory palaces
to remember, like, eight numbers, and that works pretty
well for me so I was excited about that.
[LAUGHTER] Starting small.
They do that only with numbers?
So, you can do it with anything, but the common tasks
that you have to complete to become a world memory
championship are often things that don't have a lot of meaning
so they're difficult to remember.
So strings of random numbers or the order of a deck of cards are
common things that they use. Things that are very emotionally
salient like JFK being shot, like where you were when you
found out about the buildings falling in 9/11, those are not
things you have to struggle to remember, they are very
emotionally salient. So to really test these people's
memories they want to use something that is not
emotionally salient at all. So the memory champions are
using an interesting piece of information about the brain is
that they're using the hippocampus.
And the hippocampus is important for this because it is required
for both the conscious declarative memory that I just
mentioned that's important for facts, places, long strings of
numbers. It's also required for spatial
memory. So when you are navigating in
space such as in a house, even if you're not physically in the
house just walking through the house in your mind's eye, or if
you're trying to remember facts, strings of numbers in both cases
you're using your hippocampus. So it makes sense that the
memory palace would work because it's sort of a combination of
conscious declarative memory for facts and memory for a space.
Additionally your hippocampus is important for taking short-term
memories and changing them into long-term memories.
And if you have your hippocampus removed for some reason, then
you no longer have the ability to make new long-term memories.
And you'll talk about that more in a minute.
So where is the hippocampus? It's the sort of blue C-shaped
guy right there. It's in your temporal lobe.
And so if you were to put your hands right about here just
underneath your skull in your temporal lobes on either side of
your brain. And it's, as you can see, quite
small. It is not a large part of your
brain at all, but it's very important.
So the discovery of this role for the hippocampus in
declarative memory owes a great debt to an individual who used
to be known as patient HM, but he died a few years ago so now
we can use his full name which is Henry Molaison.
And Henry had a childhood head injury and also a deep family
history of epilepsy, and this led to common blackouts and more
than one major or grand mal seizure per week in his late
20s. That's a lot of seizures, and
that made his life very difficult for him.
So as was common at the time and still occurs, they treated these
seizures by removing the part of the brain where the seizures
emerge from. And for him, that was the medial
temporal lobe which included the hippocampus.
So they removed the entire medial temporal lobe and both
hippocampi from Henry Molaison. And, as you can imagine, they
didn't know this at the time but when testing him afterwards when
he came out of surgery and was recovering weeks later they
discovered that there has been one striking and totally
unexpected behavior result: a grave loss of recent memory.
And I don't mean that he couldn't remember his childhood,
I mean that he couldn't make new long-term memories.
So after the surgery, anyone he met he would be able to talk
with them for a brief period of time, if they got up and left
the room for more than a minute and came back in, he would
introduce himself to them all over again.
And he had no ability to maintain memories for more than
a few minutes, at most maybe half an hour.
So if anyone has seen the movie Memento or 50 First Dates,
that's actually somewhat accurate in terms of the type of
memory loss this individual went through.
And as you can imagine it's pretty devastating.
So to look at exactly what they removed from HM you can see here
the red sections where they've removed a good half of the
hippocampus, the medial or the inner part.
It's actually quite a significant amount of tissue
they removed. So most of the really
interesting work performed on patient HM was done by a
researcher named Brenda Milner at the McGill University, and
this was back in the '60s when they were first starting to
understand the role of the hippocampus in learning and
memory. And something that she really
ingeniously figured out is that patient HM didn't have a loss of
all memory. He only had a loss of conscious
or declarative memory, that memory for facts, places,
people, events. His unconscious or procedural
memory was still in intact. And the way she discovered it
was this is she had a task which was pretty common in
neurological testing called a mirror tracing task.
And as you can see on the screen there's a star and what the
individual has to do is their hand is placed into a box and
they look forward into a mirror and they can only see their hand
in the mirror and based on the image of their hand in the
mirror they have to trace the star.
So if you've ever done this, it's incredibly difficult
because you move your hand this way but the image moves that
way. And it's really disconcerting,
it's very difficult to control. And if you practice it enough
over multiple times, you get good at it like any other motor
task you need to learn, like riding a bicycle, like writing
in cursive. If you get used to it, you get
good at it. In HM's case, over the course of
several days she would present this task to him and have him do
it. And each time they would ask
him, do you remember having done this before, have you ever done
a similar test before? And he would say no I've never
done this before. Even on the third day when he
sat down and did it perfectly, expertly, he said, I've never
done this before, I guess I must just be good at it.
So he had no memory of performing the task, of the fact
of performing the task, of the event of performing the task,
but he had learned it his procedural or unconscious
memory. So the hippocampus is this area
that we're talking about right now, and I want to show you a
little bit more about it. So if we zoom into the blue
C-shaped item over there, and then we take a cross section
through it, what you see is this big image right here.
And you can see it's not just a mish-mash of cells.
There are parts of the brain that don't have a lot of
structure to them, that just look like a big blob, but this
is not one of them. It's a highly structured part of
the brain, and it has specific layers of cells that are
arranged in a very specific pattern.
And the neurons in one part of the hippocampus can project to
and make connections with neurons in other parts of the
hippocampus. And this way they form a complex
or an intricate circuitry. And that circuitry is thought to
be responsible for how we encode memories.
So how do the cells communicate with each other?
How do the neurons in the hippocampus communicate?
So first we have a sending neuron, and it's going to be
sending an electric signal which we call an action potential.
So it's sending its electric signal down the long part of it,
which we call the axon, and this is kind of the long telephone
wire that reaches out and connects to the next neuron in
the chain. And at the end of the axon it
gets close to the receiving neuron that's going to receive
its signal, but it doesn't actually touch the receiving
neuron. The space between the sending
neuron and the receiving neuron is called the synapse.
And when the electric signal reaches the bottom of the axon
in this sort of large area called the terminal, it will
trigger chemicals to be released from that sending neuron.
And these chemicals are called neurotransmitters because they
transmit a neurological signal. These chemicals can then flow
across the gap and bind to special receptors on the surface
of the receiving neuron. The receiving neuron can then
take that signal and use it to do a whole host of things inside
the cell including its own electric signal down its own
axon and continuing the sort of whisper down the lane effect.
Okay, so how does this relate to memory?
Well it's thought that new memories are encoded by changing
the pattern of synapses. So how much neurotransmitter is
released by each electrical signal can change.
You can have some synapses that are very strong that will
release lots of neurotransmitter.
You can have some synapses that are very weak and don't, and
this pattern of which synapses release neurotransmitter when
and how much is what we think encodes memory.
So, again, how does this relate to aging?
Well, there is evidence of shrinkage of the hippocampus in
certain old people. Not all elderly persons have a
shrunken hippocampus, but those that do been found to perform
less well on certain memory tasks, especially memory tasks
that involve spatial memory. So when I was a technician at
the lab I'm going to show you the research for in a minute,
one of the graduate students would visits individuals in the
Alzheimer's ward, and she would take them on a specific route
around the hospital and then show them pictures of landmarks
from that route and ask them to explain where they saw it.
And individuals with smaller hippocampi are impaired at this
task compared to older individuals with larger
hippocampi. So that's one clue as to how the
hippocampus could relate to memory and aging.
Another one is that there seems to be evidence for changes in
the number of synapses, in the strength of synapses and what
molecules go into make up synapses in elderly people.
So it's been found that age-related changes in the
expression of certain genes and those genes encode certain
proteins that make up the synapse could be important for
learning and memory. And that's the research I'll
show you at the end. But in the meantime, I'm going
to first show you some theories of Alzheimer's disease now that
we have a sort of good overview of what the different types of
memory are, why the hippocampus is important for the type of
memory that is often deficient in older populations.
And now we're going to talk about the hippocampus and its
role in the most famous example, in my opinion most famous
example, of an aging related memory problem.
Okay, so some people, unfortunately, are not diagnosed
with Alzheimer's disease as early as would be useful in
order to start treating them right away because the early
behavioral symptoms are kind of vague.
Forgetfulness, irritability, depression, confusion.
That could come from a whole host of different causes, and in
the later stages of Alzheimer's we get changes in personality
and most famously the inability to encode new information.
So those are the behavioral problems, but what are the
physiological symptoms? So the physiological symptoms
include neuronal death, and that neuronal death usually starts at
the hippocampus which explains some of the memory problems that
we'll discuss in a minute. But if you can see this picture,
we have a nice healthy brain on the left-hand side, nice and
full, and on the right-hand side with an advanced Alzheimer's
individual there's a shrunken-ness of the cerebral
cortex which is all the dead neurons being sloughed off.
And as you can see where the hippocampus that I've circled in
blue is on the healthy individual, there's just nothing
there on the Alzheimer's individual.
So you can see how that would affect learning and memory.
Okay, so there's many, many theories as to the cause of
Alzheimer's disease, but these are two of the most highly
researched theories. So I thought I would explain a
little bit about them and how they might relate to each other.
So the first theory is called the A beta theory.
And it goes like this: so there's a large protein on the
cell membrane in neurons called APP, and it's very large.
And in order for its parts to go off and do their jobs in the
cell, they need to be cut down into smaller pieces.
And one of those smaller pieces is called A beta, and you can
see it in purple. Now if you have a lot of APP
that needs to get cut down, the enzyme that cuts isn't quite as
accurate. I mean, if you're being rushed
and you are have a lot of work to do, you might not be as
accurate either. So in this case there's so much
APP that it's not cut very accurately, and the APP that
does end up being cut is too long, and this long abnormal
A beta is toxic. And it aggregates or just forms
into clumps that we know of as plaques.
So what do plaques look like? So here on the left we have a
slice of healthy brain tissue from a human being, and the
little purple dots are cell bodies and they look nice and
healthy. And on the right we have the
similar cell bodies in purple, but we also have these large
brown plaques and a lot of them. So that is what tissue looks
like with A beta plaques. Now the Tau theory is a little
bit different. Tau is a very important protein
that allows neurons to communicate.
First we should go over the parts of the neuron.
So we have the cell body which is the large part of the neuron.
Like any cell it has a nucleus. And the dendrites are the areas
where the cell will receive information from other neurons.
Then we have that long axon, that long protruding axon I
mentioned previously, and that's where the outgoing information
will go from our cell here to the next cell.
So Tau is very important because it holds together the axon, the
physical structure of the axon, it holds it together the way
railroad ties hold together a train track.
And if you've ever, you know, seen an old movie where a train
is going to go off the tracks because someone has sabotaged
the railway and ripped the ties off, it's kind of like that.
So if Tau is not there to do its job, the axon will literally
break apart. And as is common with many cell
types, if the cell can't do its job, if it can't communicate, it
will die. So this is an image right here
of axons, and if there's two many phosphate groups, if the
Tau becomes hyperphosphorylated, then it can no longer hold on to
the axon and it falls off. Without this structural Tau
holding the axon together, it just falls apart, it spreads out
and it dissociates and then we have neuronal death.
Additionally, those hyperphosphorylated Tau proteins
cluster together or aggregate into tangles.
And so we can also see this visually just by inspecting the
brains of individuals of a certain age.
So on the left we have healthy brain tissue.
It looks lovely. And on the right we can see that
in the stain that is staining for axons or axonal proteins, we
can see that there's a lot of business there which is the Tau
tangles. So I've just explained a little
bit about the A beta theory, and I've explained a little bit
about the Tau theory, so the question is which one is it?
So let me show you some evidence for each.
So the gene that encodes the protein APP is found on human
chromosome 21, and many of you may realize or already know that
Down syndrome occurs if an individual has three copies of
chromosome 21. So those individuals with Down
syndrome, besides having Down syndrome, also have 50% more APP
than a normal individual, and people with Down syndrome almost
across the board develop Alzheimer's disease by the time
they are 40. So this is some evidence for
A beta and APP being very important in causing
Alzheimer's. Additionally, they've looked at
the brains of elderly people, some elderly people that were
starting to get forgetful but they died, some elderly people
that were really just mentally sharp until the day they died,
and they saw differences in the number of Tau tangles in these
individuals. The individuals that were very,
very sharp had very few Tau tangles and they had a young
looking brain, according to researchers.
Whereas individuals that were getting more forgetful, maybe a
little bit of a dementia, had many Tau tangles.
So this is some evidence for Tau.
So which one is it? If you perform histology, if you
look at the brains of individuals with Alzheimer's
disease, you'll actually see both forms of pathology.
So it's thought that both may play a role but many, especially
10 years ago, many researchers who investigate Alzheimer's
disease tend to favor one over the other, tend to concentrate
their lab looking at either Tau or looking at APP.
And this brings me to my cardinal rule of science number
one, which is when some scientists say that something is
caused by A and other scientists say that something is caused by
B, it's pretty likely that both might be involved because
scientists are smart people and they probably both have evidence
in both cases. So let's consider both of them
together. But especially a number of years
ago this was a delicate matter. People would fight about this
and squabble. So the lab I was in before I
started graduate school where I was a research technician wanted
to prove just that, that both of these proteins I just explained
to you might play a role in Alzheimer's disease.
So this is the title of the paper, but what you need to know
is that we looked at special mice with Alzheimer's disease.
However, mice don't get Alzheimer's disease.
So we have to give them the human APP gene so that they can
then have Alzheimer's. This is a very common model that
we use for Alzheimer's, and these mice show the same
behavioral symptoms and they also show this same
physiological symptoms in their brain as humans with Alzheimer's
do. So we gave the human APP gene to
certain mice, and, happily for us, all mice expressed the Tau
protein. So that was already there.
So the question is, oh, so we also, to make things
interesting, knocked out the Tau gene from some mice.
So we have mice that have APP but no Tau, mice that have Tau
but no APP, and mice that have both.
So the question is, do mice with APP and Tau have worse or better
memory than mice with just APP or mice with just Tau?
How do these two proteins work together to affect the memory in
these animals? So what we did in order to
investigate this is we used the Morris water maze.
And the Morris water maze is a great task because it's very
dependent on the hippocampus, and it uses that spatial memory
I was talking about that is one of the main roles of the
hippocampus. So what the animal does, so rats
and mice are both very good swimmers.
They don't like being wet, especially if the water is a
little cold, but they're very good at it.
They can do it very well. And so we put the animals in
this tank of water, and we have a hidden platform somewhere, and
when I said hidden I mean that the platform is just under the
surface of the water so they can't see it.
They have to just swim around and find it.
The first day or two that we're testing them, that we're
training them on this task, there's a large flag or
something really visually obvious sticking out the top of
the platform saying here it is. So they can just swim directly
to that nice visual cue, get on to the platform.
Their feet are still wet but they don't have to be swimming,
they're not soaked in the cold water anymore.
And they like that, that's a reward for them.
So they learn to do that. They learn to swim to the visual
cue, and then we take the visual cue away.
And now they have to use visual and spatial cues around the
room. We tend to hang up a lot of
things on the walls to try to make it easier for them.
They have to use their spatial memory to remember where that
platform is, and we can drop them at different places around
the edge of the pool. And by the end they will learn
where the platform is and swim directly to it no matter where
we drop them because the platform is always in the same
place. Okay, a graph.
I know, I will take you through it.
So on the left we have escape latency.
So what we're learning or what we're measuring here is how long
did the mouse swim. How long did it take this mouse
to find the platform and escape from the water.
So that's what we're looking at in seconds on the left.
And then on the bottom it's just what day of training are we on.
We have five days of training. So this is time.
And if you can sort of see the colors, I don't know if you can,
but there are six different groups, and there's three groups
that are red, and they're sort of at the top, and there's three
groups that are black, and they're at the bottom.
The groups that are black don't have any APP.
They don't have Alzheimer's. The groups that are red at the
top have APP. And for each of those having APP
or not having APP we have having two copies of the Tau gene, one
from the mother, one from the father, one copy of the Tau gene
or zero copies of the Tau gene. This is a Tau knockout.
And so what we see is that all three groups in black, if they
have two copies of the Tau gene, one copy of the Tau gene or zero
copies of the Tau gene and no APP, they all learn well, and by
learn well I mean their escape latency or how long it takes
them to find the platform goes down every day, and by the last
fifth day it's quite low, it's 10 seconds or under which is
quite good. However, when we look at the
animals that are expressing APP, that do have Alzheimer's, we can
see a difference that's caused by the amount of Tau they have.
So at the top we have animals that have APP and two copies of
the Tau gene, and they're at the top with the red boxes and the
solid line. And then performing a little bit
better than them are the animals with APP and Alzheimer's
disease, and they only have one copy of the Tau gene.
And then performing at the last day almost as well as the
animals with no APP are the animals with APP and no Tau.
So this is very interesting. It seems that the more Tau the
animals have, if they have APP, the worse they do.
So after the last day of training, we do something really
sneaky with the water maze, and we take the platform out.
So now there's no way to solve the maze, and it's really mean
but it's important. So the mouse needs to swim
around for the entire minute, the entire 60 seconds and we
track what path he swims. So on the left we have an animal
with no APP and two copies of the Tau gene.
So this is a very normal mouse. And a normal mouse by the end of
the fifth day you drop him in the upper left-hand corner and
he'll swim straight to the quadrant that has the platform,
and he'll just swim around, swim around, I know it's here
somewhere, I know it. And he'll keep doing that very
religiously. However, an animal that has the
APP gene and a full amount of Tau, both copies of Tau, we'll
place him in and he kind of swims haphazardly around the
entire pool. You can see he would have
eventually found the platform, his little path crosses the
little platform box at one point, but he's not very
confident of his answer there. He's swimming everywhere.
And then if we look in an animal that has this same APP but no
Tau, we can see that he's performing quite well.
He's really sticking to right near where that platform was,
very similarly to the animal that had no APP.
So, what did we learn here? So lowering the amount of Tau or
knocking out Tau completely from animals with APP who are a mouse
model of Alzheimer's disease seems to make them smarter.
So this is interesting. But I just said that lowering
the Tau expression in mice with APP makes them smarter, but it
doesn't change the way their brains look at all, which is
weird. If you saw behavioral changes,
you want to see structural changes in the brain to go with
it, but you don't in this case. So if you look at, if you can
see the top and the bottom, at the top row of three pictures we
have a picture of the cross-section of the hippocampus
similar to the one I showed you before, but now glowing green
are all those little plaques that we talked about before, all
those clusters of APP. And the same thing is in B, it's
just that it's not green, they're brown.
I don't really see much of a difference between the animals
with APP expressing lots of Tau who were very stupid and the
animals with APP expressing no Tau who were smarter.
There's not really any difference.
They both have a lot of plaques, and that's a lot of plaques
especially compared to a normal wild type animal in the lower
left-hand corner that doesn't have any plaques.
So what's going on? Let's review.
So mice that express the APP gene get Alzheimer's disease.
Okay? Mice that express the APP gene
but do not express the Tau gene, have had the Tau gene knocked
out, do a lot better on memory tasks.
Okay, that's cool. And mice with APP always get
plaques even if their memory isn't so bad and regardless of
how much Tau they have, which is very interesting.
So what does this mean? So it mean that is both APP and
Tau need to be present to have both types of Alzheimer's
symptoms. They need to both be there in
order to have the plaques and in order to have the memory
problems. Yeah?
Is there a possibility to move the Tau and the plaque
response are a reaction to a different level of perhaps a low
level inflammation of the brain, and somehow the plaque and the
Tau just simply respond to that? The reason I'm saying this is on
the way over here I heard on the news that seniors who take a low
level dose of ibuprofen had a significantly lower level,
40%, of developing Parkinson's disease.
And ibuprofen, of course, is an anti-inflammatory.
So is there any relationship between the inflammatory
response in the brain system in the development of Alzheimer's?
So that's really spot on and very interesting.
So it's totally possible that both of these events might be
caused by a third item that doesn't have a obvious thing to
look at. Like plaques, I see them,
they're right there, let's find what causes them, that's
probably what causes it. Inflammation is generally
thought to result from the A beta.
There's been some experiments that show even before the plaque
formation that just the higher levels of APP and A beta result
in inflammation which, of course, can change how the brain
is and make it more susceptible to further insults as well.
So it's kind of this beautiful vicious cycle in a lot of ways.
And, yes, inflammation in general can make the brain
susceptible to a lot of diseases, but then the diseases
can also make the brain more inflamed.
Okay, but so yes so this feeds right into what I was saying.
So what does this mean? A beta plaques are correlated
with Alzheimer's disease, but they may not be causing the
disease on their own. And this is fairly new.
Like 15 years ago no one was really thinking that.
So one of the other things I was working on in that lab was to
test a new plaque busting drug, and these plaque busting drugs
were shown to go in and just blast apart those plaques which
everyone thought would be great because there's these big ugly
plaques in the brain, let's just get rid of them.
But actually we found that this made the mice even more stupid.
This made them worse. And that wasn't really expected,
and it depended on how long after the drugs you tested them,
how long a course of the drugs they had, what dose of the drugs
they had, but we found that it was thought that breaking those
plaques apart released the toxic A beta so it was free to float
around in the brain. And so there's a new theory
which is that collecting the toxic A beta protein into these
plaques is kind of the brain's way of gathering up all the mess
and just kind of making dust piles as it sweeps around, like
trying to condense the areas of damage.
And so just spreading someone's dust piles all over the house is
just going to make everything dirty all over again and
actually be worse. So the take-home message from
this is my cardinal rule of science number two is that
correlation is not causation and that even scientists jump to
conclusions sometimes. Dr. Alzheimer's met a woman with
severe memory problems, and when she died he looked at her brain
and it was full of plaques. And so scientists have been
assuming for many, many years after that that these plaques
must have caused the memory problems, but it may not be
direct causal relationship. And so this is one of my
favorite comics on that topic. So it's important to remember
that just because something is correlated, it might not be the
cause. And everyone loses track of that
sometimes, but it's important to keep it in mind.
Okay, so the last thing that we're going to talk about now
that we've talked about general ideas of what memory is, we've
talked about how aging can affect memory, and we've talked
about one very clear example of disease in terms of aging and
memory. We're going to talk more now
about normal changes in memory that might occur during the
course of aging. So here's a little spiel about
what might be happening in normal aging in terms of gene
expression. So by gene expression I mean DNA
that is being read into RNA and then being made into protein.
And the protein is the tool of the cell.
It can go around and perform lots of jobs.
So in babies and teenagers and young individuals different
genes are expressed in their brains than an adults.
And the same is true for the elderly.
Different genes are expressed in their brains than in adults,
which is very interesting. So we found that certain genes
are expressed more in adults than in the elderly and certain
genes are expressed less in adults than in the elderly.
What's also interesting for us is that this phenomena of genes
being expressed differently in the elderly is not just in
humans. It's also true in many mammals,
for example, rats and mice. There are old rats that are just
very, very old but they still learn and remember just as well
as young animals. And that's great.
And there's some old rats that are incredibly demented, and
they don't have any one particular disease or problem,
they're just really not with it anymore.
And that's kind of similar to humans.
Some individuals age incredibly well in terms of their ability
to learn and remember and some don't.
And so we're interested in what genes are responsible for that.
So my lab previously performed a gene expression study to look at
what genes in the rat are changing or have changed in
elderly individuals, and we can use that to get a good idea of
what might be changing in old humans because humans and rats
are actually fairly similar. So the gene that I personally
work on is called Homer 1, and there's different forms
of Homer 1. There's Homer 1B and Homer 1C
and Homer 1A. And they're found all over the
brain, but since we're talking about learning and memory we're
just going to talk about the hippocampus today and keep it
simple. So we found that after a
learning task or a memory task such as the Morris water maze I
just showed you, animals, old rats, had an increase in their
Homer 1C levels if they were smart.
So we took all the animals that were old that learned the task
really well and looked at their brains and their brains had more
Homer 1C in them. And we took all the animals that
didn't do terribly well on the task, that didn't remember very
well, and their brains did not have very much more levels of
Homer 1C. They had fairly low levels of
Homer 1C. So maybe these old rats were
learning impaired because they didn't have enough Homer 1C.
Okay, so we were not the first individuals to think to look at
the behavioral effects of the Homer 1 gene.
Actually another lab knocked this gene completely out of a
strain of mice. And they found that these mice
had a whole host of symptoms including small body size,
they're really tiny. They have poor motor
coordination. They have an enhanced social
drive. They are also really anxious and
kind of crazy, very twitchy. But most important for us, they
feature significant learning deficits.
And another group took some healthy rats, just totally
normal rats, and injected the Homer 1C gene into the
hippocampus. And they tested those rats
against normal rats, and the rats with the more Homer 1C did
better. So imagine if I could take you
and crack open your skull and inject something into your
hippocampus and then you'd be smarter.
That's what they did. That doesn't happen a lot.
That's really cool. So this raises the question if
we restore specifically the Homer 1C form to the hippocampus
of these knockout mice, will it help their problems that our
hippocampus based, and we know that the hippocampus is
important for declarative memory and spatial memory.
So would it fix their problems in spatial memory?
So that's what we're finding out.
So in this experiment since we're using mice we did not use
the Morris water maze which was developed with rats in mind, we
used the radial arm water mace which is very similar in that
the animal is in a pool of water.
There is a platform that they need to swim to.
The platform is always in the same place.
First the animals are trained to swim to a platform with a large
visible cue sticking out the top.
And then we take the visible cue away, and they have to use
spatial cues around the room to remember where the platform is.
However in this case there's sort of arms, it's not just a
big open circle, there's arms or lanes it can swim down.
And this makes it a little bit easier for the mouse, and it's
easier for us to record their behavior because now we're
looking at the number of errors they make and each error is any
time they swim down an arm that does not have the platform.
So if he swam into three arms that didn't have the platform
and then swam down the arm with the platform and found the
platform, that'd be three errors.
So let's look at some of the data.
So on the left-hand side we have the number of errors they made
or the wrong arms they entered. And on the bottom again we have
the trials that we performed or time.
So the two groups that I'm showing here are both Homer 1
knockout mice. However, the red ones at the top
have had Homer 1C injected back into their hippocampi.
And we used a viral vector as Tom mentioned in the
introduction. We use rAAV as a viral vector to
deliver our little gene package into the brain because viruses
are very good are going in and injecting DNA into cells so we
said, hey, you want to do that for us?
And they did. So we have animals that, so
these are both Homer 1 knockout animals, and in red we have
Homer 1 knockout animals that we added Homer 1C back in the
hippocampus. And in green we have Homer 1
knockout animals that we've added green fluorescent protein
to their hippocampi. Now you might ask, why did we do
that? That's not going to help them
learn, it's just going to make their brains green.
And that's true, but it's very important to have proper
controls. So we wanted to make sure that
there was a group of animals that were treated the same as
our animals injected with Homer 1C that were genetically
identical, they're also Homer 1 knockouts and they've undergone
the exact same brain surgery and the exact same recovery period
and the exact same experience of having a virus in their
hippocampus, but the gene that is expressing is just green and
it's not a gene that's going to change how their synapses work
which is Homer 1C. So this is a great control.
And if we look at how these animals perform, we can see when
there's a visible platform, which is the first four dots,
both of these animals are decreasing the number of errors
they make each time. So they're maker fewer and fewer
errors. They're getting better and
better at the task. However, when we move to the
hidden platform, so we take away the visible cue, both of the
animals have an uptake in the number of errors they make
because I just changed everything on them, that's kind
of sneaky, but the animals expressing the GFP just kind of
flat line. They're not really getting
better very much anymore. Whereas by the end, the Homer 1
knockout animals that have had Homer 1C put back into their
hippocampus are performing significantly better than the
animals without Homer 1C. And this difference is
significant which is awesome. And if you want to see what this
looks like compared to a normal animal, we took the litter mates
or the brothers and sisters of our Homer 1 knockouts that are
genetically normal, and we ran them as well.
And you can see that they have a similar learning curve on the
visible platform, they're not thrown off as much by the change
in the paradigm. And by the end you can see that
Homer 1 knockout animals where we've added the Homer 1C back to
the hippocampus, they're performing almost as well as
their wild type brothers and sisters, which is super cool.
So to sort of review what I just showed you, we have these Homer
1 knockout animals where we've added Homer 1C back to their
hippocampus. These mice perform significantly
better on a task of spatial memory, which we know to involve
the hippocampus, than the Homer 1 knockout animals that were
just expressing GFP, they were just green.
So basically injecting Homer 1C into Homer 1 knockout mice fixed
their memory deficits. And you might say, well of
course, they were lacking it and you gave it back to them, of
course that would fix it. No, not of course.
Not of course at all. In fact it is very, very
difficult and rare to be able to fix a knockout animal by giving
them back the gene later in life because if you think about it,
their entire embryological development, their entire
childhood and in most of their adulthood they've lacked this
gene. Their brain has come up with
other methods for doing what needs to get done.
And then you're adding this tool, this protein back in, and
the brain hasn't ever seen that before.
It may not integrate, it may not have a use for it anymore.
So being able to do this kind of gene therapy in animals in a
knockout animal and get it to fix the deficits is really cool
and not all that common. So what we can say here is that
if there is a lack of Homer 1C, we added it back to the
hippocampus and it made the animal have a better memory.
So how does this relate back to aging, which we had been talking
about for the entire rest of the talk and then I started talking
about young animals. So this experiment took younger
animals in mid-adulthood that were lacking the Homer 1 gene
and it added the specific Homer 1C form back to the hippocampus.
And this helped the hippocampus recover its ability to make
memories. So previous research in our lab
showed that learning impaired older animals had very low
levels of Homer 1C. So the next question we wanted
to know is can we add Homer 1C to the hippocampus of these old
learning impaired animals and will it help them too?
Or maybe it's too late for it to have an effect.
We don't know. So stay tuned because I'm going
to be starting that experiment next month.
[LAUGHTER] And that's the end.
This is a picture of me and Brenda Milner who did all of
that really seminal work on HM, and I've been to rock concerts
where there have been fewer people swarming the main event
afterwards. She had body guards, and there
were at least 5,000 people swarming this 90-year-old woman
who had just stood and given an hour lecture on her feet
in her nice high heels. And she's awesome.
So a round of applause for her. [APPLAUSE]