Stratification of nucleus pulposus cell sub-populations during intervertebral disc development, ageing and degeneration

Back pain is a leading cause of disability in the UK and intervertebral disc (IVD) degeneration has been identified as the cause in a high proportion of patients. As current therapies for chronic back pain demonstrate poor long-term efficacy, there is an urgent clinical need for advanced cell-based regenerative therapies. However, an essential step in development of such therapies is a detailed understanding of native cell biology and how this changes with development, ageing and degeneration. The central nucleus pulposus (NP) region of the IVD is formed from the embryonic notochord as it segments during foetal development, while the surrounding ligamentous annulus fibrosus (AF) region is formed from the sclerotome/mesoderm. At birth, the NP is populated by morphologically distinct, large vacuolated notochordal cells (NCs), but these cells gradually disappear during skeletal maturation eventually becoming undetectable and replaced by a population of smaller round cells - i.e. the NP cells. This change in cell population correlates with initiation of degenerate changes within the matrix suggesting that loss of NC cells may be responsible for degeneration and ultimately back pain. However, it is currently unclear whether there is persistence of NCs or other progenitor cells in the adult human IVD, or how the cellular composition of the NP changes with development, ageing and degeneration. Elucidation of such changes will allow identification of anabolic cell sub-populations which may be critical to IVD homeostasis and as such may have potential in regenerative therapies.

The lab has recently undertaken phenotypic profiling of both human foetal NCs and adult NP cells, which have identified potential markers of NC and NP populations and have preliminary evidence that subpopulations of cells exist with the adult IVD. They have also identified changes in phenotype of adult NP cells during degeneration, including evidence of cellular senescence and adoption of a catabolic phenotype. The overall aims of this study are: (i) to use a panel of novel phenotypic markers to identify and isolate cell sub-populations from the human IVD during different stages of foetal development, adolescent skeletal maturation, and ageing/degeneration; and (ii) to compare the phenotype and function of isolated sub-populations to establish whether a population exists which has regenerative potential. These aims will be achieved through a range of state-of-the-art techniques, including CyTOF mass cytometry, RNAseq transcriptomic profiling and functional in vitro human cell studies to elucidate the phenotype and behaviour of human NP cells across development, skeletal maturation, ageing and degeneration.