Hypotonic stimuli promote osteocyte dendrite formation by modulating actin dynamics via the TRPV4-CDC42 signaling...

Osteocytes are the primary mechanosensory cells in bone and play a vital role in maintaining bone homeostasis. The distinct star-shaped morphology of osteocytes, marked by their numerous dendrites, is integral to their mechanosensory function. However, the mechanisms underlying osteocyte dendrite formation remain poorly understood. In this study, we cultured osteocytes in a 3D matrix of type I collagen hydrogel and demonstrated that mechanical factors are essential for dendrite formation. We further showed that osmotic stimuli, which can occur during normal physiological activities, significantly influence dendrite formation; hypotonic conditions promote dendrite growth, while hypertonic stimuli inhibit it. Using local delivery assays, we confirmed that hypotonic stimuli initiate dendrite formation and drive their elongation by regulating actin dynamics. Furthermore, we identified the transient receptor potential vanilloid 4 (TRPV4) channel as a critical mediator of hypotonic stimuli-triggered dendrite formation. Upon exposure to hypotonic shock, increased intracellular pressure activates the TRPV4 channel, which, in turn, activates the small GTPase Cdc42 to regulate dendrite formation. Our findings uncover a mechanical pathway that governs osteocyte dendrite development, providing valuable insights into bone homeostasis and implications for bone tissue engineering.