characterizing the skeletal phenotype of db/db mice
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Characterizing the Skeletal Phenotype of db/db Mice. Student: Bailey Lindenmaier Mentors: Dr. Russell Turner & Dr. Urszula Iwaniec Skeletal Biology Lab. Introduction. Age related Osteoporosis- Porous bone - PowerPoint PPT PresentationTRANSCRIPT
Characterizing the Skeletal Phenotype of db/db Mice
Student: Bailey LindenmaierMentors: Dr. Russell Turner & Dr. Urszula IwaniecSkeletal Biology Lab
Introduction
• Age related Osteoporosis- Porous bone
• 1 in 3 women and 1 in 5 men over the age of 50 worldwide are estimated to have osteoporosis
• In 2005, osteoporosis-related fractures were responsible for an estimated $19 billion in costs.
• Health risks▫ Increases individuals risk of fractures ▫ Following peak bone mass, lost bone mass is
difficult to restore
Leptin• Product of the OB gene
• Primarily produced by adipose tissue.
• Pleiotropic hormone▫ Appetite control▫ Energy regulation▫ Immune response▫ Cardiovascular and renal function
• Essential for achieving optimal peak bone mass.
Identifying the Mechanism of Leptin on Bone Remodeling
• Leptin is a key hormone in regulating and maintaining healthy bones.
• Early work suggests that s.c. leptin injection reduced bone loss following ovx.
• Current data proposes that leptin functions via the CNS.
• Osteoblast express leptin receptor. Possible peripheral affect?
• Answers may lead to a generation of drugs to treat osteoporosis.
Proposed Pathways of Leptin’s Effects on the Skeleton
Leptin
ObRb Receptor
db/db mice
• Loss of function in the leptin receptor
• Mosaic skeletal type▫ Overall reduced bone mass▫ High cancellous bone mass
of vertebrae.▫ Low bone mass in femur.▫ Decreased length of femoral
bones.
• Obese, hypogonadic, hyperinsulemic, hypercortisolic
db/db Wild Type
Goal
Characterize skeletal growth of WT and leptin-deficient
db/db mice.
Study Design • A group of 10 WT and db/db
mice sacrificed at 8 weeks for baseline.
• A group of 7 WT and db/db mice sacrificed at 17 weeks.
• Fed ad libitum, 12h light/dark cycle
• Both femurs and LV 5 were excised at necropsy
B6.BKS(D)-Leprdb
µ CT Analysis•Micro - Computed
Tomography
•Fires an x-ray beam at a rotating specimen
•Produces 3D images for structural measurements
Femoral cortex
Femur Metaphysis (trabecular bone)
Bones Analyzed
Vertebral Cancellous Bone
WT ob/ob WT ob/ob10
11
12
13
14
15
16
Fem
ur L
engt
h (m
m)
Femur Length
8 weeks 17 weeks
WT db/db WT db/db10
11
12
13
14
15
16
17
18
19
Fem
ur B
one
Vol
ume
(mm
3)
Total Femur Bone Volume
8 weeks 17 weeks
db/dbdb/db
Results
0 0
ANOVA EffectsGenotype: p<.001Age: p<.002Genotype x Age: p<.004
ANOVA EffectsGenotype: p<.001Age: p<.001Genotype x Age: p<.002
WT ob/ob WT ob/ob100
110
120
130
140
150
160
170
180
190
200
210
Fem
ur C
ortic
al T
hick
ness
(µm
)
Femur Cortical Thickness
8 weeks 17 weeksdb/dbdb/db
Results
0
Diaphysis-Cortical Bone
ANOVA EffectsGenotype: p<.001Age: p<.001Genotype x Age: p<.001
WT ob/ob WT ob/ob0
1
2
3
4
5
6
7
8
9
10
11
12
Fem
ur M
etap
hysi
s B
V/T
V (%
)
Metaphysis Bone Volume/Tissue Volume
8 weeks 17 weeks
db/dbdb/db
Results
ANOVA EffectsGenotype: N.SAge: p<.001Genotype x Age: p<.038
WT ob/ob WT ob/ob12
13
14
15
16
17
18
19
20
21
22
23
24
25
Lum
bar V
erte
brae
5 B
V/T
V (%
)
Lumbar Vertebrae 5 Bone Volume/Tissue
Volume
8 weeks 17 weeksdb/dbdb/db
Results
0
ANOVA EffectsGenotype: p<.001Age: p<.026Genotype x Age: p<.007
WT db/db WT db/db0
1
2
3
4
5
6
7
8
9
Lum
bar V
erte
brae
5 T
rabe
cula
r Num
ber
WT db/db WT db/db35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Lum
bar V
erte
brae
5 T
rabe
cula
r Thi
ckne
ss (µ
m))
Lumbar Vertebrae 5 Trabecular Thickness
8 weeks 17 weeks 8 weeks 17 weeks
Lumbar Vertebrae 5 Trabecular Number
Results
0
ANOVA EffectsGenotype: p<.001Age: p<.001Genotype x Age: p<.004
ANOVA EffectsGenotype: N.SAge: p<.001Genotype x Age: N.S
Conclusions
•Aging db/db mice have high bone mass in their lumbar vertebrae▫Maintain trabecular number▫Increase in trabecular thickness
•Aging db/db mice have low bone mass in their femur.▫Low cortical thickness ▫Reduced femoral length
On the Horizon
•Histomorphometric analysis of bone.
•Bone marrow transplantation following irradiation to determine if leptin has a direct effect on bone remodeling.
Acknowledgements
•Dr. Russell Turner•Urszula Iwaniec•Dawn Olson •Kenneth Philbrick•Kevin Ahern•Howard Hughes Medical Institute