Stem Cell Universe with Stephen Hawking Page #3

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with a donated organ...

Which she then turns

into a ghostly corpse.

What we're looking at here

are rat hearts

going through

the decellularization process.

And you can see here

we have a heart

that's still red and muscular.

You can see one here

that's part way through

the process.

And then here,

you can see a heart

that's lost all of its muscle.

If we sliced the heart in half,

the valves would be there,

the blood Vessels

would be there,

all the rough inside lining

of the heart would be there,

but without cells.

Doris' goal

is to transform

heart transplants.

She wants to seed

a ghost heart from a donor

with a recipient's stem cells

and then restore it to life.

If we can use

your stem cells

to build you an organ,

then you're not trading

one disease for another

like you do today.

Today, you may get a heart,

but you have to take

anti-rejection drugs

for the rest of your life.

We'd love to be able to build

an organ that matches you,

is available for you.

And that wasn't even fathomable

10 years ago, 15 years ago.

But rebuilding in a dish

what it takes our bodies

nine months to create

in the womb

is an enormous challenge.

To build a heart,

you've got to bring together

the extracellular matrix,

or ghost heart,

different kinds of stem cells,

and a beat.

So, we have this flash mob and it

looked like it came out of nowhere,

but as you can see,

there were actually cues.

The extracellular matrix

Scaffold...

The people in white coats...

who are showing the cells

where to go.

The different kinds of cells...

You see blue, green,

orange, yellow...

They're organized

like they would be in the heart,

and they're beating.

Doris and her team

have to coax stem cells

to turn into all the different

cell types that exist in a heart

and get them to precisely

where they need to go.

They're distributed differently

all throughout the heart.

What's in the valve is different

than what's

in the left ventricle

is different than

what's in the right ventricle.

The ghost heart

turns out to play

an unexpected and vital role

in this complex

cell choreography.

Doris discovered its pale flesh

is laced with chemical clues.

Its different anatomical areas,

like valves or ventricles,

are tagged

with different proteins.

These proteins trigger

the reorganization of DNA

in the patient's stem cells

and turn them into the right

heart cell type for each area.

And we can begin

to put cells back in

and the cells not only seem

to know where to go,

they seem to know

how to organize.

And they can start distributing

in ways that say,

"hey, I'm a heart muscle cell,"

"hey, I'm a blood Vessel cell."

Then we hook up a pacemaker,

and we teach them

to beat together.

And over time, they develop

contraction like a normal heart.

Now, we're not there yet,

but we've made

significant progress

and gotten to the point

that we can get to about 25%

of a normal heart contraction.

In just a few years,

custom-made

replacement body parts

built from a patient's own

stem cells will be a reality.

But these two men want

to push stem cell technology

even further.

If they succeed,

it would be

a profound achievement,

one that would mean

a great deal to me personally.

Can stem cells cure paralysis?

Our bodies

rebuild themselves every day.

We create

millions of new skin cells.

We regenerate our muscle fibers.

Slowly,

we are beginning to understand

these natural repair mechanisms

and to manipulate them.

But some parts of the body

don't seem to have

any ability to repair.

The nerves in my spine

have been slowly degrading

since I was in my 20s.

No one has yet found a way

to regenerate them.

But Paul Liu

and Mark Tuszynski believe

stem cells

will help them succeed

where all others have failed.

Mark, I found one.

Oh, let's see.

Okay.

All right.

Let's give it a go.

Okay. Let's go.

16 years ago,

I had a terrible car accident.

It broke my spine,

and I was desperate looking

for medical research

to cure the spinal cord injury.

And that's how I found

Dr. Mark Tuszynski.

I write him a letter to request

if I can work in his lab.

So, we met, and I was

really struck by his dignity,

his intelligence, his potential.

And so, Paul joined the team.

Reconnecting

a severed spinal cord

is like rebuilding

the electrical system

of a wrecked car...

Only a million times

more complex.

So, this is our cut spinal cord.

And see, we have

about 30 cut wires here.

But in reality, the spinal cord

has about a million.

We have to connect

each one of those

from the right spot

where we've done the cut

to the right target

a long distance away.

Fixing a car's electrical

harness is straightforward.

Solder the cut wires

back together,

and the electricity

will move along them again.

But in a severed spinal cord,

every nerve below the cut

has to be regrown from scratch.

In the real spinal cord,

you have to do this

a million times

from one right one going

to the other right one.

But all these wires go away.

You have to put in cells here

that will grow new wires

and link them up

to the right targets.

This is an enormously

challenging task.

Paul thought injecting

stem cells into the injury site

could automate

this intricate rewiring process.

But Mark was skeptical.

And I said,

"hmm, you know, Paul,

"people have been

working on that for 100 years

and, you know,

it just hasn't gone very far."

And so, Paul basically went off

and did some experiments

and brought back some results,

and they were absolutely

astonishing.

The cells that Paul

had implanted, few survived.

But the few that did

sent their wires, their axons,

for remarkable distances

through the spinal cord.

And this was, in a sense,

the holy grail

of spinal cord injury research

to be able to grow axons

for long distances.

But both Mark and Paul knew

that getting stem cells

to change into nerve cells

and then grow long axons

was only half the battle.

For a spinal cord especially,

for severe spinal cord,

it's a big lesion cavity.

The key step then,

at that point,

was to fill the injury site...

not have a few cells survive

at the edges of the injury,

but to fill the lesion sites

so that more cells survive

and can send out more axons.

Paul and Mark decided

to use a protein called fibrin,

which forms a mesh

over the injured area.

They hoped it would create

a foothold

for the stem cells

to latch on to.

Then this amazing phenomenon

happened.

Almost all our graphed

stem cells survived.

I took a look

into the microscope.

I backed away my chair.

I turned to him and I said,

"congratulations.

I have never seen anything

like this."

The injury site was full.

It was glowing green

with surviving cells

that completely filled

the injury.

And yet, more astonishing,

there were now

tens of thousands of axons

streaming out of the injury site

for very long distances.

And this in the most severe type

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