TRPV4 channels activity in bovine articular chondrocytes: regulation by obesity-associated mediators.

Turnover of the cartilage extracellular matrix depends exclusively on chondrocytes and varies in response to load and osmolarity fluctuations. Obesity can affect chondrocyte physiology; adipokines, insulin and proinflammatory cytokines levels are all altered in the obese and are related to matrix turnover impairments and thus to osteoarthritis. TRPV4, a mechanosensitive cation channel, is responsible for reacting to hypotonic variations. In this study, the presence and activity of TRPV4 channels in bovine chondrocytes were evaluated using the whole-cell patch-clamp technique and fluorescence measurements to perform characterisations of these channels and to determine intracellular calcium responses. The expression of TRPV4 was determined by RT-PCR. The TRPV4 regulation by hypotonic shock, insulin and adipokines were analysed. Hypoosmolarity induced a Gd(3+)-, ruthenium red-, and HC-067047-sensitive current, predominantly inward, an intracellular Ca(2+) concentration increase and a membrane depolarisation. The current had a reversal potential of +28±4mV and exhibited preferential permeability to Ca(2+); 4αPDD, a specific TRPV4 agonist, evoked the same response. TNFα, IL-1β, insulin, and, to a lesser degree, leptin and resistin attenuated the TRPV4-mediated effects; in contrast, adiponectin did not affect them. These results confirm the function of TRPV4 in bovine articular chondrocytes and its regulation by obesity-associated mediators.