Research projects

Inflammation and Repair - Regenerative Medicine - IVD regeneration - current projects (projects)

The role of notochordal cells in the intervertebral disc through ageing and degeneration: implications for tissue engineering

Duration of the project

October 2011 - September 2014

Funding body

Programme for Advanced Medical Education

Members of the project

Ricardo Rodrigues PintoPhD student
Professor Judith HoylandSupervisor
Dr Stephen RichardsonSupervisor

Low back pain is a condition that affects up to 85% of people at some time during their lives resulting in substantial economical and financial burden to individuals and their families and also to health-care systems. It is estimated that £11 billion was spent in direct and indirect expenditures related to this condition in the year 2000. Significantly both the severity and incidence of back pain increase as people age and with the increased ageing of the world population, the burden this condition imposes to society will certainly increase in future years. Degenerative Disc Disease (DDD) is the leading cause of low back pain and leads to the clinical conditions associated with it (isolated spinal discopathy, disc herniation, spinal stenosis without spondylolisthesis, spinal stenosis with degenerative spondylolisthesis and degenerative scoliosis). Current treatments aim mostly at relieving symptoms and fail to address the genesis of the problem. One of the predominant reasons for this is an incomplete understanding of the cellular population of the immature and mature disc and how the degenerative process occurs.

 The nucleus pulposus (NP) - the inner core of the intervertebral disc - derives from the embryonic notochord. At birth, the human NP is populated by notochordal cells. During the first decade of life, however, these morphologically distinct cells are reported to disappear to be replaced mature NP cells (MNPC); this process correlates with the beginning of the degenerative process. To date, however, it is not clear if the cells that populate the mature NP are de-differentiated notochordal cells, or if the original notochordal cells die and are replaced by cells migrating from adjacent tissues or if it is a mixed population of the above two. For this reason, much attention has been given to the identification of the NP phenotype and to understand the role of notochordal cells in the mature NP.  The phenotype change seen during this early period of life, correlates with the acquisition of the upright posture and the abrupt anatomical changes in the intervertebral disc (IVD) during the first years of life. This phenomenon exposes the NP to increased stresses. Hydrostatic pressure, hypoxia, low glucose levels and low pH are among these stresses and have been implicated both in the phenotype change and in triggering the processes driving degeneration.

 In recent years notochordal cells have been proposed as the ideal population of cells to aid regeneration of degenerated discs as they have been shown to synthesize a more hydrated and proteoglycan rich extracellular matrix, and can act as supporter cells for resident NP cells.   However, in order to utilize thse cells, or factors they produce,   distinct notochordal markers need to be identified in order to isolate and purify appropriate NC populations.

 

The hypotheses for this project are that:

  1. NC differentiate into MNPC during ageing
  2. The phenotype change is the result of the hostile conditions experienced by the NC cells and correlates with degeneration.
  3. A clear understanding of the young NP phenotype is essential for tissue engineering a biologic treatment for DDD

 

To address this hypothesis the specific aims will be:

  1. Compare NC microarray gene expression with healthy adult MNPC in bovine NP isolated by laser micro-dissection.

(Proof of principle: validate laser micro-dissection as a technique to isolate a pure cell population from NP)

  1. Confirm previously identified bovine NP markers
  2. Identify new notochordal cell (young NP) markers
  3. Unveil mechanisms/ genes involved in the phenotype change. These genes may be the target of future therapeutic approaches
  4. Search for the identified specific NC markers in human samples. Can they be used as human markers? If so, is the population in the adult NP all notochordal-derived?
  5. Expose NC to different combinations of known NP stresses (load, hypoxia, low pH and low glucose)
    1. Induce NC differentiation into NP cells (morphology and gene expression analysis)
    2. Identify factors sufficient / necessary for the phenotype change