Utilization of mouse models in

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Utilization of mouse models in the
study of diabetes
Maureen Gannon, Ph.D.
April 2, 2003
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Diabetes disease of decreased b cell function
and/or decreased responsiveness to insulin
signaling
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Glucose stimulated insulin secretion in b cells
K channel closed
Glucose uptake
g
Glucokinase
p
g
Ca
Glycolysis,
GLUT2
TCA
ATP
Ca
Nucleus
Insulin release
4
Insulin acts to suppress glucose production by
the liver and to promote glucose uptake in liver,
muscle, and fat
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Response of peripheral tissues to insulin
signaling
liver, muscle, fat
i
i
i
i
Activation of PI3 and MAP kinase pathways
IRS
p
g
p
IR
AKT
g
GLUT4
g
Nucleus
g
g
g
g
g
g
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(No Transcript)
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Known mutations in Type I diabetes
1. major histocompatibility complex HLA class II
region
45 of genetic susceptibility
presentation of antigens to T cells
2. iNOS (inducible nitric oxide synthase)
synthesizes NO in response to cytokines
NO triggers apoptosis
mutation in autoinhibitory domain may result in
constitutive activity
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Mouse models of Type I diabetes
1. NOD (non-obese diabetic) mouse
spontaneously arising, unique MHC class II region
islet inflammation at 3-5 weeks of age
- increased TNF-a, increased NO, activated cell
death pathway
diabetes at 12-15 weeks
etiology may differ between mice and humans, but
subsequent pathogenesis is very similar
2. iNOS over-expressing transgenic mice
over-expressed in b cells
b cell death
no inflammation
3. Streptozotocin treatment
cytotoxic to b cells
islet inflammation by 2-3 weeks
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Type II diabetes
Maturity onset diabetes of the young (MODY)
monogenic, dominant
decreased insulin gene transcription
decrease in insulin secretion
diabetes
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Type II diabetes
Maturity onset diabetes of the young (MODY)
monogenic, dominant
decreased insulin gene transcription
decrease in insulin secretion
diabetes
What kinds of genes might be involved in this
pathology?
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Glucose stimulated insulin secretion in b cells
K channel closed
Glucose uptake
g
Glucokinase
p
g
Ca
Glycolysis,
GLUT2
TCA
ATP
Ca
Nucleus
Insulin release
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Known mutations leading to MODY in humans
transcription factors
glucose metabolism
HNF1?
(MODY5)
HNF6
ngn3
Beta2/NeuroD1
(MODY6)
HNF4
glucokinase
(MODY1)
HNF3?
(MODY2)
HNF1?
insulin
pdx1
(MODY3)
(MODY4)
GLUT2
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GK, pdx1 heterozygotes have defects in glucose
homeostasis
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To elucidate mechanism of action of MODY
mutations
For example
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Other mouse models with MODY phenotype
1. GLUT2 null mutants
lack glucose transporter
greatly reduced b cell glucose metabolism
greatly reduced insulin secretion
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Glucose stimulated insulin secretion in b cells
K channel closed
Glucose uptake
g
Glucokinase
p
g
Ca
Glycolysis,
GLUT2
TCA
ATP
Ca
Nucleus
Insulin release
17
Other mouse models with MODY phenotype
1. GLUT2 null mutants
lack glucose transporter
greatly reduced b cell glucose metabolism
greatly reduced insulin secretion
2. HNF6 over-expressing transgenic mice
mis-express HNF6 in mature islets
decreased GLUT2 expression
greatly reduced insulin secretion
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Known mutations leading to MODY in humans
transcription factors
glucose metabolism
HNF1?
(MODY5)
HNF6
ngn3
Beta2/NeuroD1
(MODY6)
HNF4
glucokinase
(MODY1)
HNF3?
(MODY2)
HNF1?
insulin
pdx1
(MODY3)
(MODY4)
GLUT2
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(No Transcript)
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Response of peripheral tissues to insulin
signaling
liver, muscle, fat
i
i
i
i
Activation of PI3 and MAP kinase pathways
IRS
p
g
p
IR
AKT
g
GLUT4
g
Nucleus
g
g
g
g
g
g
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Known mutations in Type II diabetes
1. pdx1
b cell transcription factor
heterozygosity leads to glucose intolerance
in situations of insulin resistance may
contribute to b cell failure
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Mouse models of Type II diabetes
Spontaneously arising
1. ob/ob
lacking in leptin production (made in adipose
tissue)
obesity, hyperphagia
peripheral insulin resistance
islet hyperplasia
2. db/db
mutation in leptin receptor (expressed highly in
brain)
obesity, hyperphagia
peripheral insulin resistance
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Mouse models of Type II diabetes
Genetically engineered
1. pdx1 KO
heterozygotes are glucose intolerant
deletion specifically from b cells results in
diabetes
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Response of peripheral tissues to insulin
signaling
liver, muscle, fat
i
i
i
i
Activation of PI3 and MAP kinase pathways
IRS
p
g
p
IR
AKT
g
GLUT4
g
Nucleus
g
g
g
g
g
g
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Overall conclusions
1. diabetes is a heterogeneous group of diseases
2. 95 of diabetes is polygenic (either Type I
or Type II)
3. monogenic forms of diabetes are very rare
(MODY)
4. mouse models do not always recapitulate human
mutations
5. engineering mice to contain mutations
identified in humans may elucidate the
mechanisms resulting in diabetes
6. mutations leading to diabetes can occur in
insulin gene transcription factors
insulin secretory pathway
insulin receptor signaling pathway
immune system
b cell survival factors