Abstract
Introduction
The intervertebral disc (IVD) is a highly hydrated and hyperosmotic tissue, water and salt content fluctuate daily due to mechanical loading. Resident IVD cells must adapt to this ever-changing osmotic environment, to maintain normal behaviour. However, during IVD degeneration the disc becomes permanently dehydrated and cells can no longer perform their correct function. Here, we investigated how human nucleus pulposus (NP) cells respond to altered osmolality with regards to cell size and the rate of water permeability, along with the potential involvement of aquaporins (AQPs) and transient receptor potential vanilloid (TRPV) membrane channels.
Methods
Water permeability of NP cells exposed to altered osmolality (225–525mOsm/kg) in the presence or absence of AQP and TRPV channel inhibitors was investigated with the cell-permeable calcein-AM fluorescent dye, and cell size determined using microscopy and flow cytometry.
Results
Human NP cells modulate their size and water permeability in response to altered osmolality. Inhibiting channel proteins, specifically AQP4, modified NP cell responses to altered osmolality.
Conclusion
IVD cells must regulate their size in order to survive and function within an osmotically challenging environment. Here, we demonstrated that NP cells alter their size and permeability in response to altered osmolality which enables them to adapt to their environment. Furthermore these processes were shown to be dependent at least in part by AQP4 expression, which we have previously shown to be decreased during disc degeneration. This potentially highlights novel ways to restore NP cell and overall IVD function by modulating AQPs in the disc.
No conflicts of interest
Funded by BMRC, Sheffield Hallam University
