Photo C Denoeud

Soutenue par Cyprien DENOEUD le 30-09-2019

Directeurs de thèse: Hervé PETITE, Esther POTIER

Abstract

Mesenchymal stem cells (MSCs) appear to be ideal candidates for tissue engineering. More and more clinical trials are now using these cells to repair damaged tissues or organs in order to restore their functions. Once implemented, however, MSCs die quickly and massively, significantly reducing the success of this therapeutical approach. Although this massive death is multifactorial, the ischemic environment (characterized by, among other things, oxygen and nutrient depletion) at which cells are confronted once implanted, seems to be the main cause. Surprisingly, the limiting factor for cell survival in this avascular environment is not the depletion in oxygen, but the one in glucose.

The metabolic pathways used by MSCs to convert glucose into energy after implantation  are, to date, poorly understood. Moreover, no strategy based on continuous glucose supply to implanted cells has been established so far to improve cell survival, and therefore the functionality of MSCs after implantation.

The first study of this doctoral project aimed to better understand the energy metabolism used by glucose within the MSCs after implantation.

We have demonstrated that the in vitro quasi-anoxic conditions (0.1% pO2) associated with the absence of glucose and serum best reflect the in vivo implantation microenvironment . Within this environment, MSCs produce their energy as ATP exclusively via anaerobic glycolysis and from a single substrate (glucose). Glucose, however, is lacking in the ischemic environment and MSCs have very limited glycolytic reserves which they consume within 24 hours, resulting in ATP reserve shortage within 3 days, leading to a massive and rapid cell death.

The second (and main) study consisted of developing and evaluating a strategy based on continuous glucose delivery to improve the survival and functionality of MSCs after implantation.

We have, for the first time, provided a proof of concept that a nutritive hydrogel, composed of a glucose polymer (starch) and an enzyme (amyloglucosidase), previously patented (EP 14306700), improved MSC survival for 14 days, both in an in vitro quasi-anoxic model and in in vivo ectopic model. In addition, this innovative device improves the paracrine functions of the MSCs, as shown by an increased neovascularization up to 21 days after implantation.

By increasing the survival and functionality of MSCs after implantation through continuous glucose delivery, nutritive hydrogels composed of starch and amyloglucosidase appear as a strategy of interest to improve the therapeutic outcomes of MSC-based products in tissue engineering.