Adipokine actions on cartilage homeostasis

Epidemiological studies have shown an intriguing correlation between obesity and articular cartilage disease. An increase in mechanical forces across weight-bearing joints has long been considered the primary factor leading to joint degeneration. However, emerging data suggest that additional soluble factors such as the adipocyte-derived molecules "adipokines" may also play an important role in the onset and progression of weight-associated cartilage degradative process. Adipokines are pleiotropic secretory molecules mainly produced by white adipose tissue. Adipokines exert their actions through endocrine, paracrine, autocrine, or juxtacrine cross talk in a wide variety of physiological or pathophysiological processes. In particular, they are mainly involved in the regulation of food intake and energy metabolism, in both health and disease states, and in the inflammatory response. Recent observations have shown that, among adipokines, leptin, adiponectin, resistin, visfatin, and apelin may also participate to the complex mechanisms that regulate skeleton biology, both at bone and cartilage level. Herein, we review the present knowledge about the role of these adipokines in cartilage function as well as in inflammatory and degenerative joint diseases. Moreover, we describe some methodological approaches which can be utilized in the measurement of these adipokines in different biological matrices, like plasma and synovial fluid (SF), and may be helpful to better clarify the involvement of these molecules in cartilage disease.