00:01
Let's get it down
inside the cell there.
00:03
So there we talked about things that
are kind of at the tissue level.
00:06
Atrophy, hypertrophy,
hyperplasia, metaplasia,
talked about the mechanisms,
but I'm talk more specifically
about what things can happen
at the subcellular level in
response to various injury.
00:17
So we've already talked about
one, that's autophagy.
00:20
I stress a cell cut
off its nutrient supply
and it will start to eat itself.
00:25
It will undergo autophagy.
00:28
I can also dumped on,
say for example, I give the liver
a lot of phenobarbital,
for whatever reason, it's a sedative,
and the patient is taking more..
00:40
Taking a certain level of that.
00:42
With time, the patient
becomes relatively refractory
to the effect of that
dose of phenobarbital
and that's because
the drug is inducing
more and more production of
smooth endoplasmic reticulum
to metabolize that drug.
00:56
So I've gotten
hypertrophy, more smooth ER
that's occurring
because of the drug
that increased
amount of smooth ER
means there's more
cytochrome p450
means there's more degradation,
which means that the longer
I take phenobarbital,
the less sensitive I am to it.
01:14
So that's a subset of response
to a particular injury.
01:19
You can also have
cytoskeletal changes.
01:20
This is just an example of
something that's fairly common
with heavy alcohol ingestion.
01:27
This is now a cross-linking and an
abnormal form of intracellular keratin.
01:32
So those intermediate filaments,
and in alcoholics and other
patients who have injury,
where we are now cross-linking
the proteins we get
cytoskeletal aberrations.
01:45
This is called Mallory's
alcoholic hyaline.
01:47
It's that bright pink material and
it's cross-linked cytoskeleton.
01:52
It's cross-linked
intermediate filaments,
so you can get cytoskeletal changes
and clearly when I'm doing that
a cytoskeleton is not
working appropriately
but it is a response to
injury subcellularly,
and then finally,
we're going to spend the next couple
slides talking about heat shock proteins.
02:11
So heat shock proteins,
they are called
heat shock proteins
because they were first seen
in fruit flies of all things.
02:18
When they raise the temperature
just 5 degrees centigrade,
the response of the flies
to that raise in temperature
made a whole bunch
of new proteins
and it turns out that there are
homologs to those proteins in all of us,
and they've actually
fundamentally do a very
important job in protein folding.
02:38
So we'll talk about that.
02:39
So heat shock proteins.
02:40
That's why they're called
heat shock proteins.
02:42
So let's look.
02:44
We have new peptide synthesis.
So we have our messenger RNA.
02:47
We've got a ribosome sitting there
and we have a new peptide coming off.
02:50
Well, how does it know how to fold
into exactly the right configuration?
And actually it may be that
you don't want it to fold
until the very end until the
entire thing is synthesized.
03:01
So what we do is as
we are synthesizing
this new nascent chain of
polypeptide and it's growing,
we interact with chaperones.
03:10
Cytosol like proteins that can hold a
protein in a particular configuration.
03:17
And then when the time comes,
they can fold it appropriately.
03:21
So some chaperones,
are used to move proteins that
are synthesized in the cytosol
into other organelles,
for example, the mitochondria.
03:30
Remember that only about
13 of the electron transport
chain proteins involved
in ATP synthesis are actually
made by the mitochondria
and the other thousand and seventy
five or so are made in the nucleus
or are transcribed
to messenger RNA in the nucleus
and synthesized in the cytosol.
03:47
We got to get them in somehow.
03:49
We have mitochondrial
chaperones that are able to take
an unfolded protein,
not yet folded,
squirrel it across through
pours into the mitochondria
and then we had can have
mitochondrial chaperones
that fold it to the
appropriate file configuration.
04:06
So we can have a
mitochondrial chaperone.
04:08
We can have things chaperones
that help a protein become
its final mature
folded configuration.
04:16
And we can have things that
are somewhere in between
that sit on and unfolded protein
and keep it unfolded
until the very end.
04:27
So we have various chaperones.
04:29
There are several different
members of this particular family
that can do all these kind of
wonderful things making sure
that we get proteins to
the right configuration
in to the right place.
04:40
Okay, so that's kind of one job.
That's their day job.
04:43
There's a night job.
04:44
Because proteins are
constantly being denatured,
because of
ultraviolet light or heat
or free radical injury,
all those things that we've talked
about in terms of forms of injury,
and we take a nicely
folded protein
and it may become
partially unfolded.
05:00
Well, we can do a couple
things at that point.
05:02
We can just give up
the ghost and say..
05:05
I have too many
unfolded proteins.
05:06
I guess I'll die.
05:08
Well, that's fine and that can happen
if we exceed the capacity to do repair
but in most cases,
when it's low level,
we have chaperones that
take that denature protein
unfold it, refold it and get the
right configuration at the end.
05:22
Magical.
05:23
Again, if we think about
this at a molecular level,
how does it know that it's
misfolded to begin with
and how does it know
what is the right configuration?
Those are many steps that we
haven't yet worked out but
interesting projects to work on.
05:37
The other thing is well, okay, I wasn't
able to get it refolded correctly.
05:42
Oh well, but I don't want
that thing lying around either
because that's that's
not a good thing.
05:47
I need to degrade it.
05:49
So, it turns out ubiquitin is in
fact a form of a heat shock protein
and you have a little
green balls there
on a denatured misfolded protein
and we just say,
let's degrade it.
06:01
Ubiquitin targets it for
degradation in the proteasome.
06:04
We get peptides back out
turning into amino acids.
06:07
And we can start
over from scratch.
06:09
So chaperones,
fold things appropriately
the first time
but also help to do repair
if we've had injury,
after we've already
synthesized the protein.
06:21
So, heat shock proteins,
go up when their stress,
so in fruit flies,
it went up when we heated them up,
but it also happens
with any kind of injury
to a cell, we will see
increased heat shock proteins.
06:35
So if we see a lot
of denature proteins
and we mechanisms
to recognize that,
we will increase
the production of those proteins and
see if we can't rectify the damage.
06:46
So, in that very
short period of time,
we've talked about the ways,
kind of the really cool ways
that cells can adapt to
injury without dying.