asbmr ptn 2008 082008
TRANSCRIPT
Anabolic Response to Skeletal Loading in Mice with Targeted Disruption of
Pleiotrophin Gene
C. Kesavan and S. Mohan
JLP VA Medical Center, Loma Linda Univ
Loma Linda, CA, 92357
ASBMR 2008
Acknowledgements
• US Army Research
• Veterans administration
The authors have no conflict of interest
Load
Load
Good Responder
Poor Responder
Skeletal Response to Loading Differs in Different Individuals
Variation in skeletal response to loading is genetically determined
0.00
5.00
10.00
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20.00
6 7 8 9Load (N)
% In
cre
as
e in
vB
MD
v
s u
nlo
ad
ed b
on
e
Four point bending device
C57BL/6J
C3H/HeJ
Four point bending IncreasesBMD in C57BL but not in C3H mice
P<0.001
Kesavan et al., 2005
P<0.01
ML increases pleiotrophin (PTN) expression-Whole
genome microarray analysis
PTN signals through β-catenin and PI3K
0
400,000
800,000
1,200,000
Unloaded Loaded
PT
N e
xp
ress
ion
lev
el
(
arb
itra
ry u
nit
s)
p<0.0001
Xing et al., 2005
PTN/HB-GAM/OSF
SyndecanRprpζ
β-catenin PI3K
Proliferation/survival/Migration
Time course changes in PTN expression in the loaded bones of C57BL Mice
Ap<0.05 vs. 2- and 4- days of loading (One-way ANOVA)
0
3
6
9
0 2 4 6 8 10 12 14
p<0.05
p<0.001
p<0.0001
Days (Duration)
Fo
ld i
ncr
ease
in
PT
N
v
s. u
nlo
aded
bo
nes
A
024
68
10
C57BL C3H
Greater PTN expression in response to ML in good responder C57BL versus poor
responder C3H mice
Fo
ld i
ncr
ease
in
PT
N
vs.
un
load
ed b
on
es
P<0.0001
P<0.05
P<0.05
Mean ± SD; N = 6
Hypothesis
PTN plays a role in mediating anabolic effects of mechanical
loading on bone formation
9N load produces equivalent amount of strain in the tibia of PTN KO and
littermate control mice
• CSA (mm2) 4.69 ± 0.21 4.56 ± 0.24
• BMD (mg/cm3) 838 ± 40 881 ± 51
• Strain (µe) 6351 ± 414 6310 ± 726
at 9N load
Control PTN KO
Mean ± SD, N = 7
Skeletal changes in response to loading in PTN KO and control mice
*p<0.05 vs. unloaded bones, N = 7
Pe
rce
nt
inc
rea
se
vs
.
un
loa
de
d b
on
es
0
10
20
30
BMC PC BMD
Control KO* *
* ** *
Micro-CT analysis of skeletal response to loading
Control
PTN KO
Unloaded Loaded
Mean ± SD, N = 7
BV/TV (%) 3.88 ± 2.6Tb.N (1/mm) 1.56 ± 0.76Tb.Th (mm) 0.037 ± 0.0.01Tb.S (mm) 0.76 ± 0.28
BV/TV (%) 2.81 ± 1.5Tb.N (1/mm) 1.61 ± 0.36Tb.Th (mm) 0.036 ± 0.0.01Tb.S (mm) 0.57 ± 0.21
Greater midkine expression in response to ML in PTN KO and Control mice
0
2
4
6
8
Control PTN KO
Fo
ld i
ncr
ease
vs.
u
nlo
aded
bo
nes
P<0.05
P<0.05
P<0.001
N=6
Summary
• PTN expression is increased in response to ML but decreased during osteoblast differentiation
• Lack of PTN does not influence peak bone mass
• PTN disruption in mice although caused a small decrease in the amount of new bone formed in response to ML, this difference was not statistically significant
• Disruption of PTN gene in mice caused significant increase in midkine, member of PTN family that shares similar functional properties
Conclusions
1) Disruption of PTN alone is not sufficient to impair skeletal anabolic response to external loading in mice
2) Disruption of both PTN and midkine may be necessary to fully evaluate the role of heparin binding growth associated molecules in mediating anabolic effects of mechanical loading in bone.
Thank you
Skeletal Un loadingSkeletal Loading