Investigation of spontaneous differentiation of neural stem cells on synthetic scaffolds

Abstract

Despite the increasing incidents of brain injuries and neurodegenerative diseases, a definitive clinical therapy for these conditions has not been found yet. Nervous system injuries result in loss of neural cells, causing loss of function in the neural circuitry. As mature neurons do not divide, it is not possible to tolerate the loss of neurons by the production of new ones. In the central nervous system, even though neural stem cells are present, their number and regenerative capacity are very low. In addition, inhibitory molecules are released at the degeneration site which hinders reconnection of the remaining cells. As the damage is due to the loss of neurons, cell therapy is considered as a promising option. Neural stem cells are capable of differentiating into the three major cell types in the central nervous system: neurons, astrocytes, and oligodendrocytes. However, due to low rate of survival of the transplanted cells, there is still a need for a cell vehicle system to promote their survival, adhesion, migration, and differentiation. On the other hand, use of biological molecules such as growth factors or extracellular matrix proteins as vehicle systems should be minimized due to the immunological risks. Nanotechnological approaches serve as a great opportunity to mimic the native environment of the cells. Peptide amphiphiles (PAs) are self-assembling molecules that provide precise control over their secondary structure and the amino acid sequence, which can mimic proteins and show hydrogel properties. In this thesis, self-assembling PA scaffolds that mimic laminin, heparan sulfate and cadherin, which are key players in nervous system regeneration, have been investigated as cell delivery vehicles. Neurospheres are great models for studying the behavior of neural stem cells within a heterogeneous 3-dimensional cell population. Migration and differentiation behavior of neurospheres were investigated on laminin (LN), heparan sulfate (GAG), and cadherin-mimetic (HAV) PA nanofiber scaffolds. The results indicated that LN and GAG mimicking PA scaffolds cooperatively enhanced the migration of neurospheres, whereas cadherin mimetic PA scaffolds were individually sufficient to promote their migration. Also, a fine neural network was observed to be established on HAV-PA. These scaffolds hold high potential to be used as cell delivery vehicles.