Defended by Mathilde PADRONA
Thesis director: Esther POTIER and Hervé PETITE
Abstract
Back pain, leading cause of years lived with disability, represents a major public health problem, affecting approximately 80% of the worldwide population at least once in their lifetime. Although multifactorial, one of the main causes of back pain is the intervertebral disc (IVD) degeneration. The IVD is composed of three components: the nucleus pulposus, the gelatinous, water-rich core of the disc, surrounded by the annulus fibrosus, a fibrous and elastic ring, both sandwiched by the cartilaginous endplates present on the vertebrae. The IVDs ensure the mobility and stability of the spine and are the largest avascular structure in the human body. As a result, nutrient supply and metabolic waste removal are solely relying on diffusion through the cartilaginous endplates, resulting in low oxygen and glucose concentrations and a low pH in the nucleus pulposus.
Disc degeneration starts in the nucleus pulposus and is characterized by cell loss, change in surviving cell phenotype, extracellular matrix degradation, and release of inflammatory mediators. Although the etiology of disc degeneration still remains unclear, one of the causes suspected to play a major role and studied here is nutrient depletion. The already modest nutrient supply of the disc is, indeed, disrupted during disc degeneration, with a decrease in blood flow at IVD periphery and occlusion of the cartilaginous endplates.
Thus, nutrient depletion may play a crucial part in nucleus pulposus cell survival and functionality, which are essential for maintaining extracellular matrix hydration and related IVD functions. While oxygen depletion only exhibited little or no effect, studies on glucose depletion, mostly done on nucleus pulposus cells isolated from their environment, revealed contradictory effects. Those studies, however, did not preserve the extracellular matrix, known to modulate cell survival, proliferation and functionality.
In order to study the effect of glucose depletion in a physiologically relevant environment, the first objective of this work is therefore the establishment of a 3D model of bovine nucleus pulposus explant cultured under conditions representative of the disc environment.
The second (and main) part of this work aims at characterizing the impact of glucose depletion on the nucleus pulposus homeostasis. Using the explant model previously developed, I have shown that a glucose concentration such as found during disc degeneration leads to a significant decrease in the viability and to a phenotypic alteration of the nucleus pulposus cells, although it does not affect senescence, matrix catabolism or inflammation, other typical features of disc degeneration.
This study showed the major implication of glucose depletion in nucleus pulposus homeostasis but also suggested that other micro-environmental factor(s) may be at play during disc degeneration.
Based on these results, the last part of this work aims at developing a hydrogel capable of delivering glucose in order to restore glucose concentration to a healthy level and thus promote the survival and functionality of nucleus pulposus cells in a degenerated disc environment.
Overall, this work contributes to a better understanding of the players involved in disc degeneration. It also suggests that glucose supplementation, used alone or in combination with other regenerative therapies, may help repair IVD.