Obesity and osteoarthritis: more complex than predicted!
- 1Faculté de Médecine, UMR CNRS-UHP 7561, Vandoeuvre les Nancy, France
- 2Service de Rhumatologie, Hôpital Saint-Antoine, Paris, France
- Correspondence to:
Faculté de Médecine, UMR CNRS-UHP 7561, Avenue de la foret de Haye, BP 184, 54505 Vandoeuvre les Nancy, France;
- Accepted 30 August 2006
Dysregulation of lipid homeostasis is one of the mechanisms leading to osteoarthritis
Osteoarthritis is usually considered to be a joint disorder the central pathological feature of which is cartilage destruction. However, this concept has evolved, and today osteoarthritis is generally regarded as a disease that may affect the whole joint (bone, muscles, ligaments and synovium). Although the aetiology of osteoarthritis is not established, the main risk factors are well known and commonly include mechanical, biochemical and genetic factors. Of these risk factors, obesity is beyond doubt considered a prominent one.
MECHANOBIOLOGY IN OBESITY-INDUCED OSTEOARTHRITIS
The overload effect on joint cartilage may explain part of the increased risk of osteoarthritis, at least for osteoarthritis of the knee, in overweight people. A recent discovery in the discipline of cartilage biology is the presence of mechanoreceptors at the surface of chondrocytes, which are sensitive to pressure and link extracellular environment to intracellular signalling cascades. Three types of mechanoreceptors have been described on chondrocytes: the stretch-activated channels, the α-5β1 integrin and CD44. Compression and stretch stimulate integrins and stretch-activated channels leading to the activation of signalling pathways (mitogen-activated protein kinase, NF-κB), as well as the release of second messengers (calcium, Inositol triphosphate and Adenosine monophosphate cyclic). 1 After mechanoreceptor activation, cytokines, growth factors and metalloproteinases may be expressed, and mediators such as prostaglandins or nitric oxide may be produced.2 As experimental studies have shown that under specific conditions overload may trigger both inhibition of matrix synthesis and cartilage degradation, we can speculate that obesity may induce cartilage damage through activation of these mechanoreceptors. In the same manner, the mechanoreceptors expressed on osteoblasts3,4 may also be involved in the impaired response of chondrocytes to the obesity-induced overload.
ADIPOKINES: THE METABOLIC LINK BETWEEN OBESITY AND OSTEOARTHRITIS?
Even if it is usually accepted that mechanical loading contributes to joint cartilage destruction in overweight patients, recent advances …