Thesis: Chemical and physical factors to regenerate the nucleus pulposus
Promotoren: prof.dr. F.C.Öner, prof.dr. M.T.Tryfonidou
Copromotor: dr. L.B.Creemers
Defense date: 22 January 2019
Intervertebral disc (IVD) degeneration leading to chronic low back pain is a major problem in developed countries. Regeneration of the IVD can prevent pain and costs related to health care expenditure and work absenteeism, and improve quality of life.
The IVD is the flexible structure between our vertebral bodies that allows for movement of our spinal column. Degeneration is thought to start in the nucleus pulposus (NP), the gelatinous core of the IVD. The osmotic value of a disc decreases during degeneration due to the characteristic loss of proteoglycans. NP cells were cultured with medium of different osmolalities, adjusted with different osmolytes. Raising osmolality during expansion can enhance matrix production, but raising osmolality during regeneration has no regenerative effect
Hydrogels are employed as NP cell carriers and can facilitate regeneration, either for clinical application or research into mechanisms of regeneration. We compared six different hydrogels based on natural polymers: alginate, agarose, fibrin, type II collagen, gelatin methacryloyl (gelMA), and hyaluronic acid–poly(ethylene glycol), and investigated the role of serum in the medium and of osmolarity during expansion or redifferentiation of NP cells. Agarose hydrogels seem to be the best option for in vitro culture of human NP cells, but for clinical application, type II collagen hydrogels may be better because they are more biocompatible.
One way hydrogels can influence regeneration is by their biomechanical properties. Stiffness sensing through the cell’s focal adhesions is believed to direct chondrogenesis, but the mechanisms involved are largely unknown. We compared focal adhesion formation and proteoglycan deposition by NP cells in a range of hydrogels. We demonstrated that focal adhesions are present in 3D cultures of NP cells and influence the response to integrin-containing hydrogels
NP cells can also be stimulated to regenerate by addition of growth factors or mesenchymal stromal cells (MSCs). Bone morphogenetic proteins (BMPs) are among the most promising growth factors for NP regeneration. Our results indicate that BMP4 might have the highest potential for regeneration of the intervertebral disc and can be applied together with MSCs.
The results, alone or in combination, can be used in research that will lead to successful therapies for intervertebral disc regeneration.