Title: Secrets of the lac operon: A unified mechanism for aging, diabetes, and obesity
1Secrets of the lac operonA unified mechanism
for aging, diabetes, and obesity
2Lac operon Substrates induce their own
metabolism, and exhibit hysteresis
3The Metabolic Mystery Aging and Disease
- Obesity increases with age
- Obesity pre-disposes to age-related diseases
(metabolic syndrome) - Caloric restriction extends lifespan
WHY??
4WHY??
- Does obesity increase with age?
- Does protein oxidation increase with age?
- Does glycolysis increase with age?
- Does protein turnover decrease with age?
- Are effects of aging progressive and apparently
irreversible? - Are effects of diabetes progressive and
apparently irreversible? - Are effects of aging and diabetes really
irreversible?
5Caloric (glucose?) restriction
Nutrient sensors (transcription factors?)
And then a miracle occurs
Increased lifespan
6 How do (glucose) calories kill?Focus on brain
gene expression
- Diabetic complications mainly in
insulin-insensitive tissues - Neurons implicated in many models of aging
- Neurons regulate metabolism
7Dietary restriction alters characteristics of
glucose fuel use.Masoro, EJ, McCarter, RJ, Katz,
MS, and McMahan, C AJ. Gerontology (1992)
47(6)B202-B208
8Molecular hysteresis residual effects of
hormones and glucose on genes during aging.C.V.
MobbsNeurobiology of Aging (1994) 15523-534
9Glucose hysteresis
Glucose resistance
SIP down
VMH neurons glucose resistant
Inducedgenes
Inhibitedgenes
YoungThin
Old Fat
Many meals(glucoseexcursions)
10But is it glucose??
- Reducing glucose increases lifespan in yeast
- DR (including methionine) reduces glucose
- Every-other day feeding does not reduce calories,
but reduces glucose and extends lifespan - Elevated glucose causes toxicity (diabetic
complications)
11What does glucose do?
12BUT- Low glucose blocks glycolysis
- Phosphofructokinase DOWN
- Transaldolase DOWN
- Ketohexokinase DOWN
- Moncarboxylate transporter 1 Down
- Pyruvate dehydrogenase kinase 4 UP
13AND- low glucose blocks NADH glycerol shuttle
- Mitochondrial glycerolphosphate dehydrogenase
DOWN - Cytoplasmic glycerolphosphate dehydrogenase
UP
14Low glucose stimulates pentose pathway (makes
NADPH)
- Glucose-6-phosphate dehydrogenase UP
- Linked to aging and stress resistance
15Low glucose stimulates TCA cycle and
mitochondrial NADPH
- Isocitrate dehydrogenase 2 UP
- Linked to aging and stress resistance
16Low glucose activates hypothalamic mitochondrial
lipid oxidation
- Carnitine palmitoyl transferase UP
- Fatty acid transport protein UP
- Mitochondrial Acyl-CoA thioesterase UP
17AND- Low glucose activates peroxisomal fatty acid
oxidation
- Peroxisome membrane protein UP
- Peroxysomal Acyl-CoA peroxidase Up
- Peroxisomal integral membrane protein UP
- Peroxisome membrane protein UP
- Peroxisomal integral membrane protein UP
- Peroxisomal biogenesis factor UP
18AND- Low glucose activates protein and amino acid
degradation
- Multi-ubiquitin chain binding protein UP
- Ubiquitin fusion degradation protein 1 Up
- Proteasome delta subunit UP
- Proteasome (prosome) subunit UP
- Proteasome alpha subunit UP
19AND- Low glucose activates protein synthesis
- Ribosomal protein S7 UP
- Translation initiation factor eIF2 gamma Up
- Ribosomal protein S5 UP
20Low glucose induces the highly anti-oxidant
glucose switch profile of gene expression
- Glycolysis down (blocks NADH complex I)
- Complex I produces free radicals
- Pentose pathway up
- Makes antioxidant NADPH
- Lipid oxidation up (favors FADH2 complex II)
- Complex II does not produce free radicals
- Amino acid oxidation up
- Eliminates oxidatively damaged proteins
- Favors NAD
- Induces protective effects (e.g., SIR1)
21The glucose switch ATP-neutral substrate
repartitioning
Glucose Transport
GLUT1
Pentose Shunt
Cytoplasm
Glycolysis
PFK
Glucose-6-Phosphate DH
NADPH
Fatty Acid Oxidation
Glucose to Krebs
PDHK4
CPT1 PPaR?
NAD
Krebs Cycle
NADH
Complex I
Complex II
FADH2
Isocitrate DH2
NADPH
Mitochondria/Peroxisome
Respiratory Chain Shift to Complex II
22Conversely, high glucose blocks the glucose
switch profile, leading to an oxidative profile
- Glycolysis up (favors NADH complex I)
- Complex I produces free radicals
- Reduced Complex I, III, IV, and V increase
lifespan - Pentose pathway down
- Reducing antioxidant NADPH
- Lipid oxidation down (inhibits FADH2 complex II)
- Complex II does not produce free radicals
- Impaired Complex II reduces lifespan
- Amino acid oxidation down
- Allows accumulation of oxidatively damaged
proteins - Favors NAD
- Inhibits protective mechanisms (e.g., SIR1)
23Mechanistic studies Evidence that NADH mediates
toxic effects of glucose
a
a
a
a
cells alive (CCK)
100
b
50
b
0
5 15 0 15 0 15
Glucose Lactate Pyruvate 5 mM
Glucose
24High-throughput screen discovers drugs protective
against glucose toxicity
25High-throughput screen discovers drugs protective
against glucose toxicity
26 OK, high glucose can cause oxidative damage
acutely, but what accounts for the progressive
and (apparently) irreversible nature of
age-related impairments?
27Hypothalamic glucose sensor similarities to and
differences from pancreatic beta-cell
mechanisms.Yang, Kow, Funabashi, MobbsDiabetes
1999 Sep48(9)1763-72
The pancreatic, but not hepatic, form of
glucokinase was expressed in the VMH..These data
suggest that glucose-responsive neurons sense
glucose through glycolysis, specifically the
production of NADH, not ATP.
28Implication of glucose switch
- Glucose activates its own metabolism (esp. NADH)
- Cytoplasmic NADH is the unique signature of
glucose, thus particularly suited as a signal - This implies a self-perpetuating, cumulative
sensitization or priming effect HYSTERESIS! - Could this be reversed?
29Multistability in the lactose utilization network
of Escherichia coliOzbudak et al.Nature (2004)
Feb 427737-740
The phase diagram of the wild-type network shows
that lac induction always takes place
hysteretically, with cells increasing their
expression levels discontinuously as a switching
threshold is reached.
30Molecular hysteresis in metabolic gene expression
31 Implication Aging is reversible
32Mechanistic studies Evidence that NADH mediates
toxic effects of glucose
a
a
cells alive (CCK)
100
b
50
b
0
0 10 0 10
Glucose (mM)
33Obesity What is the question?
34How much variability in genetically identical
laboratory mice? About the same as in humans!
.
20
.
.
.
Body Wt Gain (gm)
15
.
.
10
.
5
0
Coefficent of variation 47!
35Variability in caloric intake is much less than
variability in weight gain
.
.
.
.
.
.
Caloric intake (kCal)
500
0
Coefficent of variation 8!
3620 of retired breeder C57Bl/6J mice dont gain
weight on a high-fat diet but eat each just as
much
37Diet-induced obesity (independent of food intake)
depends on genotype
25
20
Body weight Gain on HF Diet (grams)
15
10
5
A/J C57
38Hypothalamus
According to glucostatic hypothesis A/J mice are
resistant to diet-induced obesity because they
have increased hypothalamic sensitivity to
glucose.
- This hypothesis implies that induction of genes
by hypoglycemia will be less robust in
(glucose-sensitive?) A/J mice than in
(glucose-insensitive?)
39GLUT 1
40Ubp41
41CITED-1
42NPY and AGRP
43AGRP (in vitro)
44Liver and Cortex
- Evidence of a hypothalamic defect
45Liver Glut1
46Cortex Glut1
47Humanized monoclonal antibody reverses genetic
obesity
48Anti-obesity effect of FGF antibody is at least
partially independent of feeding