Okay, so one of the points I wanted to start out making is,
as Americans, we're all eating way too much sugar.
The average American is eating about 140 pounds
of sugar annually, that equates to about 57 gallons of soda.
100 years ago or so we ate about 10 pounds, so
it's gone up enormously.
This is mostly in the form of sucrose, table sugar, glucose,
and fructose.
And fructose is particularly bad because sugar is not sugar, as
you've heard the corn companies say, it's simply not the case.
Fructose is metabolized quite a bit differently than glucose.
And in fact high fructose corn syrup is now very cheap compared
to sucrose, for example.
But it's ubiquitous,
it's in virtually every processed food you look.
And I encourage you,
when you go to the grocery store, usually the first or
second ingredient in things like ketchup and almost anything.
In fact, this weekend I was trying to find chocolate milk
for my granddaughter, and I had trouble finding chocolate milk
where the second ingredient wasn't high fructose corn syrup.
And I think this is really bad, because fructose, unlike glucose
and table sugar, sucrose has both glucose and fructose in it.
And so glucose is actually stimulates insulin signaling and
is regulated.
However, when you eat large quantities of fructose,
almost all of it goes to the liver and is metabolized as fat,
and it doesn't turn on insulin signaling to regulate.
And it also, eating a lot of sugar makes you hungry.
It actually inhibits the signals in your brain that tell you to
stop eating.
And so if you think about diabetes, and
I'm struck by the fact, and my own family is this way, if
people are diagnosed with cancer or heart disease or something
else, they really get upset and they take it seriously.
A lot of people when they get diabetes don't
think it's any big deal.
It's a very big deal.
The number of people that die from diabetes every year is on
the order of 70,000 directly and
250,000 indirectly a year In the United States.
And why is that?
Well, you have hyperglycemia, or high blood sugar for
prolonged times, what happens
is you develop particularly the symptoms shown on this slide.
So, for example, your kidney quits working properly, so
you have nephropathy.
It's a major cause of blindness, you get retinopathies.
A lot of people that have diabetes, something like 74%
of them, have neuropathies of the feet in particular.
It's a major cause of amputations.
Cardiovascular disease,
a lot of it is, in fact, indirectly caused by diabetes.
The beta cells, when they're exposed to high glucose for
a long amount of time lose the ability to even make insulin,
and that contributes to the later stages of the disease.
And of course your liver and skeletal muscle and
adipose become resistant to insulin the more it's exposed to
high glucose.
So why is prolonged blood sugar so toxic?
If you think about this as a chemist,
these sugars are not toxic molecules at all.
They're not chemically reactive all that much.
So why are they so toxic?
Ugh.
So it turns, this, I'm not so a big fan of this thing.
So it turns out that several years ago my laboratory
discovered a modification of proteins that involves
the direct attachment of sugar to practically every regulatory
protein in the cell, in the nucleus and the cytoplasm.
What this sugar is is a molecule of glucose that has
a nitrogen and a so-called N-acetyl group attached to it.
It's an enzymatic modification and
it's very much analogous to what you've heard about in signaling,
about phosphorylation.
It acts like a switch that turns proteins on and off much
the same way phosphorylation does, but it's a sugar.
It's an extremely abundant modification.
So far, about 4,000 proteins have been identified.
But, you can get a feel for it in that gel up there,
in the corner, is a 2D gel, just giving you an idea of how many
proteins are in the nucleus or cytoplasm
of most cells that have this sugar attached to them.
It's most abundant, as it turns out,
in the pancreas, the brain, and lowest in the liver, but
it turns out the liver has the highest dynamic range
of this modification.
And this sugar cycles on and off proteins during their lifetime
and it turns out it's a nutrient sensor.
It's the way your cells in your body
regulate what their proteins do in response to nutrients.
And it's a perfect nutrient sensor because the donor of
the sugar is a molecule called UDP-GlcNAc are UDP
anti-glucosamine and the biosynthesis of this molecule is
directly tied to glucose, amino acid, fatty acid and
nucleotide metabolism.
So the metabolic pathways in your cell raise and
lower the levels of UDP-GlcNAc, which in turn help determine
the amount of this sugar that's attached to your proteins.
And it turns out that the site on the molecules where this
sugar is attached in many cases are the same sites that
are often phosphorylated in signaling transduction pathways.
And so signaling you can think of as microcircuitry that
controls the protein's functions in metabolism much the same way
switches do and
it turns out that the O-GlcNAc sugar is like a rheostat
that modifies the signaling in response to nutrients.
And because it has this complex relationship with
phosphorylation it's involved in virtually everything the cell
does including gene expression by transcription,
nutrient sensing, it's involved in numerous diseases.
So this is an example of how sensitive, if you take a cell,
this one happened to be a lymphocyte.
And you expose it to increased levels of glucose,
you can see from the top panel, that's normal glucose.
And if you expose it to diabetic levels of glucose,
the number of proteins and the amount of proteins that have
this sugar attached to them goes up dramatically.
And, so, we now, and others, now think that
this is one of the major molecular mechanism of why so
much goes wrong when you have prolonged hyperglycemia, or
too much glucose, surrounding cells.
And, so, how might this work?
Well it turns out that, as I said, signaling molecules,
the switches that regulate metabolism, are regulated
by this nutrient sensor, this sugar attachment to proteins.
And so there's a balance between phosphorylation and
the addition of this sugar that gets out of whack when sugar
stays up too high.
It turns out that virtually every protein that's involved in
regulating the expression of genes is modified by this sugar,
and we're just beginning to learn how this sugar plays
a role in whether genes get activated or not activated.
And also it turns out that mitochondria, we've known for
a long time that in diabetes, when glucose gets high,
the mitochondria quit working right.
We never had understood the relationship.
How does high glucose cause a mitochondria to not work right?
And when the mitochondria doesn't work right,
it makes these reactive oxygen species
that do further damage to the cell.
So what I wanna do now is just go through one example or so
of each one of these kinds of processes and
how they're important to toxicity of glucose.
So one of the things that happens in both adipocyte and
muscle is, we know about the insulin signaling pathway, so
insulin binds to its receptor and
then through a complex cascade of signalling.
It causes GLUT-4 vesicals to go to the surface and
bring in glucose and this helps lower the glucose in the blood
stream and it's very important in skeletal muscle and.
Well it turns out that when the sugar levels get high, O-GlcNAc,
this sugar I'm talking about goes up and
it actually stops insulin signaling at all the steps
that are shown there with a star.
So it's a molecular mechanism of what we call insulin resistance.
The second thing is we now know that virtually half and
maybe more of the kinases that regulate these signalling
cascades are themselves modified by this sugar.
And I have a list of ones that have recently shown how they're
regulated by it.
And an interesting example of this, from a collaboration we
did with Don Bers at UC Davis talks about Cam Kinase II.
Calcium–calmodulin kinase II.
This is the kinase that regulates your heartbeat.
It's very important in regulating calcium flux in
your heart.
And it turns out in diabetes, this GlcNAc sugar,
which normally is not there,
attached to it at the position shown here in the molecule,
and it causes this enzyme to become constitutively active.
And so therefore it contributes greatly to arrhythmias in
the heart with individuals that have diabetes.
Another example from work in our lab by post doc
named Sherket Peterson, we were looking at the expression.
So she's really interested in diabetic nephropathy, or
the kidney function.
And there's two proteins in the kidney called nephron and
potassan.
In this cartoon, they're the filtration apparatus that
make the kidney filter out large molecules and
let the rest of the urine pass through.
What happens when O-GlcNAc is high, as it is in diabetes,
you can see the levels in this label TMG,
which is an inhibitor of the enzyme that removes the sugar,
the addition of this sugar gets very high.
It turns out that when the addition of this sugar is high
on the proteins that regulate gene expression,
called transcription factors.
As you can see on this bar graph, the black and
the grey bar going down on both nephron and
potassan these genes are no longer transcribed.
And basically the filtration apparatus of the kidney begins
to fall apart,
because the proteins that make it are not being made properly.
And you can reverse this,
even in high glucose, if you add an inhibitor of the enzyme that
adds this sugar to proteins, you can see in the checkered bar
that the transcription of these proteins is restored.
Now, coming back to the mitochondria, so
why does the mitochondria quit working when glucose is high?
It didn't really make a whole lot of sense biochemically.
Well, it turns out there's about 88 proteins in the mitochondria
in the electron transport chain.
And this is the portion of the cell that makes ATP from glucose
and other molecules and makes energy that drives your cells.
And 88 proteins involved in that have this sugar attached
to them.
And it turns out that in normal mitochondria, when the levels of
this sugar goes up, it actually makes the mitochondria work
better to make more, as it would If the nutrients are around.
But if you look at diabetes, it turns out that the enzyme that
adds this sugar, by mechanisms we don't yet
understand, becomes mislocalised.
Normally it's located in a protein complex called complex
IV in the complexes that make ATP.
But in diabetic animals a lot of it moves to complex III, and
as a consequence of that, a whole different set of
proteins become modified with this sugar that normally
would not be modified to this extent in the mitochondria.
And this actually results in the mitochondria not working
properly.
So there now is a direct link to having hyperglycemia,
or high glucose, and the misfunction of the mitochondria.
And the last thing I wanna talk about is appetite control.
So we've already heard that there's a reason in your brain,
called the para-ventricular nucleus
in the hypothalamus that, where lepton signals and
other things and it's involved an appetite control.
And together with Rick Huganir's lab in Neurosciences at
Johns Hopkins, a graduate student Olof Lagerlof decided to
knock out the enzyme that adds this sugar in adult
mice in that region of the brain and ask what happens.
Well it turns out within two to three weeks you get a morbidly
obese mouse.
This mouse cannot stop eating.
And it's a little bit like the lepton mouse you heard,
about except in this case, what this is telling us is not only
is this sugar a nutrient sensor in every cell in your body,
but it is also a nutrient sensor in your brain.
It tells your brain how much glucose is there and
it's one of the mechanisms in controlling appetite.
And so what I have told you about is a sugar modification
that's really quite ubiquitous in biology.
All plants and animals.
It's actually required for
life, even at the single cell level in mammals and plants.
It has this cross-talk with other molecules in signaling
like phosphorylation.
It's very important in gene regulation.
And we know very little bit how it works in regulating whether
genes get transcribed or not in response to nutrients.
But the bottom line of what I'm telling you here is that
this is a mechanism that probably underlies
why having too much sugar in your bloodstream and
surrounding your cells causes all of the range of problems
that exist and contributes to the disease we call diabetes.
And the future for this, if we have a drug that could lower
the extent of this GlcNAcylation globally,
you'd have to not lower it too much or it would be bad.
But the real of drug power is in the future.
It turns out this enzyme is regulated by specific
targeting proteins, and if you could make small molecules that
stopped it from being targeted to specific substrates,
then you could have a useful drug for diabetes.
And so I just wanted to thank the people in the lab and
collaborators that helped us do this work and thank you.