00:01
Welcome.
00:02
So we're just about through
making a scar in tissues
that cannot regenerate.
00:07
The final stages.
00:09
Now that we've laid down
new blood vessels
is to deposit and remodel
the extracellular matrix.
00:18
Here's where we are
on our overall roadmap.
00:21
Remember, we've talked about
moderating acute inflammation,
recruiting and activating
macrophages,
regenerating the parenchyma,
if we can.
00:29
And now these last two topics
is our when we cannot
completely regenerate.
00:36
So we have to have
angiogenesis granulation tissue.
00:39
And now we're going to
deposit and remodel the matrix.
00:42
So let's get going.
00:45
Here we are
on our sequential curves.
00:49
And really at the peak of the
chronic inflammatory response,
where the macrophages are peaking
at three to five days
after the original injury,
read the green arrow.
01:00
And at that point,
we are starting to lay down
granulation tissue,
And at that's going to peak
at somewhere between
seven and 10 days.
01:08
And even with the very earliest
stages of new vessel formation,
we're also starting
to lay down the matrix
that's going to be a scar.
01:18
We may also have some
degree of regeneration,
Remember, the macrophages are
still cranking out growth factors.
01:25
But when we're
going to have scar,
it's going to be
mostly that fibrosis.
01:30
Okay, let's get going.
01:33
This is a transverse section
of an animal preparation of a heart
where the heart
in the upper left hand side
has had a myocardial infarct
induced by tying a suture
around the coronary artery.
01:51
This is a five to 10 days.
01:53
And the special stain here
is a trichrome stain,
where blue is collagen.
02:00
And we can see
in the area of the infarct
on the upper left hand side
that we do have some blue,
but it's pretty, it's pretty loose,
and it's not well developed.
02:10
Okay, that's it five to 10 days
when we're at the peak
of granulation tissue.
02:15
If we wait four weeks, wow, we have
quite a bit of dark peacock blue.
02:21
And that blueness there represents
the deposition of collagen.
02:26
That's where we're going to go
for the next few slides.
02:29
We are over the course
of four weeks
on that provisional matrix
of the newly formed blood vessels,
the granulation tissue,
we're going to lay down
extracellular matrix,
and then we're going
to remodel it.
02:40
So, Factor 5.
02:42
We've had
"Factor 1" Interferon gamma.
02:44
Factor 2: Interleukin-1 / TNF.
02:47
Factor 3: Epidermal Growth Factor
Factor 4: The angiogenic Factors,
basic FGF, and VEGF.
02:53
"Factor 5" in quotes, remember is
Transforming Growth Factor-Beta
This is actually a pretty important
one, and worth remembering,
because it really does drive
the final stages of scarring.
03:06
So it's important for causing
fibroblasts migration chemotaxis
and to drive them
to synthesize matrix.
03:17
It also will cause
the reduced expression
of matrix metalloproteinases.
03:24
So there are various ways
that we can degrade matrix.
03:26
Matrix metalloproteinases
are a major pathway.
03:29
There is several of the
matrix metalloproteinases
in excess of 20.
03:33
And when they are chewing away,
they're degrading matrix.
03:36
But if we turn them off,
if we turn off their synthesis,
then we can get more
matrix accumulate.
03:43
So this is happening also
because of TGF-beta.
03:47
An important brake
on the entire process,
Everything up to this point
has been kind of
go go, go, go, go, go.
03:53
Well, at some point,
we have to turn it off
and go back to just being
whatever it was to begin with.
03:59
And TGF-beta
inhibits the inflammation.
04:02
It's going to be a very important
anti-inflammatory break
on the entire process.
04:08
TGF-beta is synthesized
in an inactive form
by activated macrophages
and T cells.
04:13
As well as smooth muscle cells
and endothelial cells.
04:17
Its importance,
they're in an inactive form.
04:19
It's actually secreted
into the provisional stroma.
04:23
And it's sitting there,
and it doesn't do its thing
until we have proteolysis,
until we have enzymes proteases
elaborated that will digest it.
04:32
So that's a fairly nuanced
way to have regulation
of this particular activity.
04:40
It's going to be
an important mechanism
by which we shut off inflammation,
and promote scarring.
04:46
So that's what you need to remember
that TGF-beta does.
04:53
After we'd lay down the scar,
we just don't leave it there.
04:56
But in fact, we remodeled that.
04:58
So let's look at our
M1 macrophage again,
it's providing a whole bunch
of M1 macrophage cytokines
such as epidermal growth factor,
interleukin1,
tumor necrosis factor.
05:09
Those will actually drive
fibroblasts to make precursors
procollagenases, prostromelysins
that when activated by
plasmin and other activators
that will create
matrix metalloproteinases
that degrade the matrix.
05:26
That's part of the original
cleaning up the debris
is to break down all that
degenerated extracellular matrix.
05:34
And that's what
M1 macrophages do.
05:36
Degrading the matrix.
05:40
M2, mainly through the effects
of TGF-beta
turn off that process.
05:45
So we don't make those
matrix metalloproteinases.
05:48
This will allow us
to accumulate extra matrix.
05:52
So part of what TGF-beta is doing,
besides turning off the inflammation
is inhibiting
the breakdown of matrix.
05:59
And that's going to allow us
to synthesize more.
06:04
M2 macrophages also make tissue
inhibitors of metalloproteinases.
06:09
So, this is getting again
into alphabet soup.
06:12
But TIMPs are molecules
that inhibit
any activated
matrix metalloproteinase.
06:20
So not only do M2 macrophages
through TGF-beta turn off
fibroblasts synthesis
of things that would be
MMPs that are active.
06:29
Matrix metalloproteinases
that are active to cleave matrix.
06:33
There are also banking inhibitors
that will turn off any residual MMPs
that might be out there.
06:41
Okay.
06:43
Steroids.
06:44
And I mentioning this as a sidelight
because steroids
are frequently given
by plastic surgeons and other people
to limit scarring.
06:51
How is that happening?
Well, steroids, in fact, inhibit
both M1 and M2 macrophages
to some extent,
that's part of what makes them
so potent
in terms of
anti-inflammatory agents.
07:05
But they turns out,
they inhibit M2 macrophages
much, much more.
07:10
So they're more effective on that.
07:12
So there is a relative decrease
in the amount of TGF-beta.
07:16
So there'll be a relative increase
in the amount of
matrix metalloproteinases,
and a relative increase in
the degradation of the matrix,
because we are having more
of an effect on M2.
07:29
So all things considered
if we give steroids,
we get less scarring,
because there's reduced fibrosis
because of less activation of M2.
07:37
And that's why we give that.
07:39
On the other hand, if we really want
good scarring to occur,
we have a big surgical incision, and
we want it to heal up really nicely,
we don't want to give steroids.
07:49
And patients who are on steroids
for autoimmune disease
need to be very
carefully monitored,
and the steroids adjusted so
that we don't have this effect.
07:59
Okay.