Figure 6. Conceptual model detailing osmolarity-dependent NC to sNPC differentiation.

Under normal conditions, cells can maintain a healthy cell volume by adjusting expression (number of channels) and activation (how long channel is open) of ion and water channels. TRPV4 adjusts intracellular Ca²⁺ while Aqp 1 and 3 adjusts intracellular water/osmolytes to maintain cell volume in response to osmotic gradients. Under long-term static hyperosmolarity conditions, resulted in differentiation of NCs to sNPCs with increased extracellular matrix GAG accumulation. During this transition of NCs to sNPCs, Aqp3 expression was increased, while Aqp 1 and TRPV4 remained constant. Under all osmolarity conditions, all NP cells expressed sustained expression of notochordal markers CK8, Ck19 and Shh, suggesting the transition of NCs to sNPCs was a differentiation process. Also shown are the changes in the NP mechanotransduction proteins with NP cell differentiation with NCs having greater expression of N-cad and sNPC having greater expression of Cx-43.