Transient receptor potential vanilloid 4: The sixth sense of the musculoskeletal system?

The critical discovery in the past two decades of the transient receptor potential (TRP) superfamily of ion channels has revealed the potential mechanisms by which cells sense diverse stimuli beyond the prototypical "five senses," identifying ion channels that are gated by heat, cold, mechanical loading, osmolarity, and other physical and chemical stimuli. TRP vanilloid 4 (TRPV4) is a Ca(2+)-permeable nonselective cation channel that appears to play a mechanosensory or osmosensory role in several musculoskeletal tissues. In articular cartilage, TRPV4 exhibits osmotic sensitivity, controlling cellular volume recovery, and other physiologic responses to osmotic stress. TRPV4 is expressed in both osteoblasts and osteoclasts, and the absence of TRPV4 prevents disuse-induced bone loss. TRPV4 activation promotes chondrogenesis by inducing SOX9 transcription, whereas a TRPV4 gain-of-function mutation leads to a developmental skeletal dysplasia, suggesting a critical role for TRPV4 in skeletal development. These studies provide mounting evidence for a regulatory role for the sensory channel TRPV4 in control of musculoskeletal tissues.