Ph.D Thesis


Ph.D StudentGuo Shaowei
SubjectEngineered Constructs to Promote Regeneration in Rats with
Complete Spinal Cord Transection
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Shulamit Levenberg


Abstract

The regeneration of injured spinal cord is hampered by the lack of vascular supply, neurotrophic support, and limited intrinsic regenerative capacity. This work focuses on two aspects aiming to improve functional recovery in rats with complete spinal cord injury (SCI): 1). Prevascularized stem-cell embedded scaffolds. Here, we engineered 3D prevascularized scaffolds embedded with human dental pulp stem cells (DPSCs) which possess paracrine-mediated angiogenic and neuroregenerative potentials. More rapid and mature vascular networks were formed on scaffolds, when endothelial cells were supported by DPSCs, as compared to human adipose-derived mesenchymal stem cells or fibroblasts. Additionally, DPSCs secreted neurotrophic factors, capable of inducing the differentiation of pheochromocytoma (PC12) cells to neuron-like cells. More importantly, in rat complete SCI model, the implantation of those scaffolds to the injured spinal cords could also promote revascularization, as well as axon regeneration, myelin deposition, and sensory recovery. Furthermore, 3D microCT imaging and novel morphometric analysis on the vasculature of the remodeled spinal cord tissue revealed the importance of prevascularization in enhancing SCI repair. 2). Exosome-based therapy. Phosphatase and tensin homolog (PTEN) is highly re-regulated in SCI, profoundly inhibiting the downstream mTOR pathway for axonal growth. Exosomes have emerged as promising natural drug delivery vehicles to target CNS disorders. Here, we show that intranasal administrations of mesenchymal stem cells-derived exosomes could penetrate the blood brain barrier, home selectively to the spinal cord lesion, and showed affinity to neurons within the lesion. When these exosomes were loaded with PTEN small interfering RNA, termed ExoPTEN, they migrated from the nose and silenced PTEN expression in the lesion. Furthermore, the loaded exosomes promoted robust axonal regeneration and angiogenesis, accompanied with decreased astrogliosis and microgliosis. Moreover, the intranasal ExoPTEN treatment partially restored electrophysiological and structural integrity, and most importantly, enabled significant functional recovery. This rapid, non-invasive approach, using cell-free nano-vesicles carrying molecules to target pathophysiological mechanisms, suggests potential clinical translation to treat SCI.