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