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Bioactive scaffolds for redirecting endogenous neural stem cell migration to repair the injured brain
thesis
posted on 2017-02-14, 23:01 authored by Sepideh MotamedThe number of
individuals affected by neurological disorders rises rapidly world-wide,
however, there is no clinical treatment to restore lost functions. The brain’s
attempt at regeneration happens through the re-direction of neural stem cells
residing in the stem cell niches towards the injured zones. However,
insufficient numbers of migrating cells and an inhibitory environment limits
endogenous regeneration after severe damage. The design and synthesis of new
biomaterials to provide a defined pathway for neuroblast migration from the
subventricular zone (SVZ) towards the lesion site of the brain is essential as
a promising therapy for brain repair. This dissertation introduces the design
and functionalization of a new class of self-assembling peptide hydrogel to enhance
neurogenesis in the injured adult brain. A novel aspect of this work is the
design of self-assembling peptide hydrogels solely composed of β-amino acids as
a proteolytically stable material.
Amongst the proposed biomaterials for brain tissue engineering, hydrogels based on peptide self-assembly have received the most attention due to their similarity to brain tissue. However, they can degrade rapidly by proteolytic enzymes in vivo, which limits their application to provide long term physical guidance for cellular migration. To address the rapid degradation, peptide hydrogels have been synthesized through a novel self-assembly approach consisting of only β3-amino acids which are inherently stable against proteolytic enzymes. An alkyl chain was laterally attached to the N-acetylated tripeptide to induce self-assembly in physiological conditions and eventually form a stable hydrogel (C14-peptide). The hydrogel showed similar mechanical properties to brain tissue and proved non-toxic to neuronal cells, however, a deposition of serum proteins was essential for cell attachment to the hydrogel. To induce cell attachment, fibronectin-derived RGD was laterally attached to the side chain of the peptide through the incorporation of a novel alloc-protected β-amino acid (RGD-peptide). The bioactive signalling for fibroblast cell attachment and similar stiffness to brain tissue was optimised by mixing the two aforementioned peptides (RGD-peptide: C14-peptide; 5%:95%).
To investigate the feasibility of the synthesized peptide hydrogels to induce neural stem cell migration through the newly defined pathway, the optimum hydrogel consisting of 10% RGD-peptide and 90% C14-peptide was implanted into the brain to disrupt the SVZ. The inflammatory response was minimal and the scaffold integrated with the parenchyma, proving the biocompatibility of the synthesized hydrogel. Most importantly, it was shown that the scaffold was capable of migrating cells along defined pathways to distant regions in the brain. The effect of brain-derived neurotrophic factor (BDNF) on the rate of migrating cells and their survival has also been investigated. By releasing BDNF, the scaffold provides a suitable migratory stream for neuroblasts to migrate in larger numbers. This study represents a promising therapy for the treatment of the injured brain.
Amongst the proposed biomaterials for brain tissue engineering, hydrogels based on peptide self-assembly have received the most attention due to their similarity to brain tissue. However, they can degrade rapidly by proteolytic enzymes in vivo, which limits their application to provide long term physical guidance for cellular migration. To address the rapid degradation, peptide hydrogels have been synthesized through a novel self-assembly approach consisting of only β3-amino acids which are inherently stable against proteolytic enzymes. An alkyl chain was laterally attached to the N-acetylated tripeptide to induce self-assembly in physiological conditions and eventually form a stable hydrogel (C14-peptide). The hydrogel showed similar mechanical properties to brain tissue and proved non-toxic to neuronal cells, however, a deposition of serum proteins was essential for cell attachment to the hydrogel. To induce cell attachment, fibronectin-derived RGD was laterally attached to the side chain of the peptide through the incorporation of a novel alloc-protected β-amino acid (RGD-peptide). The bioactive signalling for fibroblast cell attachment and similar stiffness to brain tissue was optimised by mixing the two aforementioned peptides (RGD-peptide: C14-peptide; 5%:95%).
To investigate the feasibility of the synthesized peptide hydrogels to induce neural stem cell migration through the newly defined pathway, the optimum hydrogel consisting of 10% RGD-peptide and 90% C14-peptide was implanted into the brain to disrupt the SVZ. The inflammatory response was minimal and the scaffold integrated with the parenchyma, proving the biocompatibility of the synthesized hydrogel. Most importantly, it was shown that the scaffold was capable of migrating cells along defined pathways to distant regions in the brain. The effect of brain-derived neurotrophic factor (BDNF) on the rate of migrating cells and their survival has also been investigated. By releasing BDNF, the scaffold provides a suitable migratory stream for neuroblasts to migrate in larger numbers. This study represents a promising therapy for the treatment of the injured brain.
