Role of Leptin in the

Pathophysiology of Osteoarthritis

Mohamed Aoulad Aissa, Aline Delalandre

Daniel Lajeunesse Centre Hospitalier de l’Université de Montréal, Hôpital Notre-Dame,

Introduction

•Osteoarthritis (OA ) is characterized by: - Progressive articular cartilage loss - Bone sclerosis of the subchondral trabeculae and growth plate - formation of osteophytes

• OA risk factors: - Age (1/3 over 65 ) - Sex ( > women over 50) - Heredity - Obesity

• Adipocytes share a common mesenchymal stem cell precursor with osteoblasts, chondrocytes, tenocytes, and myoblasts, all affected by OA.

OA bone: Bone sclerosis: increased osteoid tissueIncreased trabecular thickness (Tb.Th)Decreased trabecular space (Tb. Sp.)

Hence: Altered mecanical properties Increased tissue rigidity

Decreased shock absorbing capacities

Caracteristics of osteoarthritic subchondral bone

Normal OA

Role of Leptin in Joint Tissues Metabolism

• Leptin has dual effects, both central and local, depending on bone tissue, skeletal maturity and/or signaling.

• Leptin plays a role in endochondral ossification possibly via its influence on angiogenesis due to enhanced MMP-2 activity.

• Leptin acts as a growth factor for chondrocytes in young individuals yet its role on mature chondrocytes is unclear.

• Leptin enhances the metabolic markers of osteoblasts i.e. ALPase, osteocalcin, Coll1, IGF-1 and TGF-, all of which are elevated in OA osteoblasts.

HYPOTHESIS

The local increase in leptin production and/or leptin

signaling in OA Ob leads to the abnormal osteoblast cell function

observed in OA and possibly abnormal bone remodeling in this

pathology. This also facilitates cartilage deterioration and loss.

Phenotypic characteristics of normal and OASubchcondral osteoblasts

Normal OA0

200

400

600

800

1000

1200

1400

Normal OA0

100

200

300

400

500

Alk

alin

e ph

osph

atas

e(n

mol

/mg

prot

ein/

30 m

in

Ost

eoca

lcin

(ng

/mg

prot

ein/

48 h p<0.01p<0.02

Leptin expression by OA osteoblasts, chondrocytes andSynoviocytes by Real-time PCR

Osteoblasts Chondrocytes Synoviocytes0.000e+0

1.000e-4

2.000e-4

3.000e-4

4.000e-4

Lep1

Lep2

Lepti

n/G

APD

H r

ati

o

Normal OA0.00

0.05

0.10

0.15

0.20

0.25Le

pti

n/G

APD

H (

rela

tive v

alu

e)

Leptin release by normal and OA Osteoblasts by Real-time PCR

Leptin release by normal and OA Osteoblasts

Normal OA0

20

40

60

80

100

Lep

tin

(p

g/m

g p

rote

in/4

8 h

) p<0.025

Regulation of Leptin Expression in OA OsteoblastsMeasured by Real-time PCR

Basal HGF TGF D3 D3 + HGF0

2

4

6

8

10

12Le

pti

n e

xpre

ssio

n (

rela

tive v

alu

e)

p<0.01

p<0.01

p<0.01

Basal + anti OB-RL0

100

200

300

400O

steoca

lcin

(ng/m

g p

rote

in/4

8 h

p<0.05

Effect of anti leptin receptor (OB-RL) antibodies onosteocalcin secretion by OA osteoblasts

Effect of anti leptin receptor (OB-RL) antibodies onalkaline phosphatase activity in OA osteoblasts

Basal + anti OB-RL

A

lkalin

e p

hosp

hata

se (

nm

ol/m

g p

rote

in/3

0 m

in)

0

200

400

600

800

1000

1200p<0.05

Basal D3 D3 + leptin D3 +anti leptin

0

200

400

600

800

1000

1200

1400

A

lkalin

e p

hosp

hata

se(n

mol/m

g p

rote

in/3

0 m

in)

Effect of leptin on alkaline phosphatase activityin OA osteoblasts

85

6050

Ctr

1,25

(OH

) 2D 3

Lep

Exo

TG

FH

GF

M

Induction of Leptin Receptor (OB-RB) in human osteoblasts treated with leptin, D3, TGF, or HGF. Leptin Receptors were detected with a monoclonal anti-OB-RB

antibody.

Regulation of Leptin Receptor Production in OA OsteoblastsMeasured by Western blot

DISCUSSION

Leptin expression was restricted to subchondral Ob whereaswe could not detect significant expression in chondrocytesnor synoviocytes. This would suggest that leptin found inarticular cartilage must be due to this production by Ob.

OA Ob produced more leptin than normal Ob. Enhancedleptin production by OA subchondral bone tissue maycontribute to both abnormal expression of cellular markersby Ob and inflammation, leading to loss of cartilage.

The interaction between TGF-, HGF, 1,25(OH)2D3 and leptin that exist in OA bone tissue needs to be studied further.

Osteoblasts Osteoclast

IL-6IGF-1TGF-PGE2

Tidemark

Micro-fractureuPA, IGF-1

IL-1 IL-6 IGF-1 TNF

TGF-bFGF

LeptinHGF

CollagenasesGelatinasesStromelysin

NO, free radicals

HGF/NK2

Trabecular bone

Subchondralbone

Cartilage

OsteoblastsOsteoclast

IL-6IGF-1TGF-PGE2

Tidemark

Micro-fractureuPA, IGF-1

IL-1 IL-6IGF-1 TNFTGF-bFGF

Leptin

CollagenasesGelatinasesStromelysin

NO, free radicals

Trabecular bone

Subchondralbone

Cartilage

?

?

Inflammation

IL-1/IFN

Acknowledgments

Daniel Lajeunesse

Aline Delalandre

Denis Couchourel