ABSTRACT
Numerous signaling molecules are altered following nerve injury, serving as a blueprint for drug delivery approaches that promote nerve repair. However, challenges with achieving the appropriate temporal duration of recombinant protein delivery have limited the therapeutic success of this approach. Genetic engineering of mesenchymal stem cells (MSCs) to enhance the secretion of proangiogenic molecules such as vascular endothelial growth factor (VEGF) may provide an alternative. We hypothesized that the administration of VEGF-expressing human MSCs would stimulate neurite outgrowth and proliferation of cell-types involved in neural repair. When cultured with dorsal root ganglion (DRG) explants in vitro, control and VEGF-expressing MSCs (VEGF-MSCs) increased neurite extension and proliferation of Schwann cells (SCs) and endothelial cells, while VEGF-MSCs stimulated significantly greater proliferation of endothelial cells. When embedded within a 3D fibrin matrix, VEGF-MSCs maintained overexpression and expressed detectable levels over 21 days. After transplantation into a murine sciatic nerve injury model, VEGF-MSCs maintained high VEGF levels for 2 weeks. This study provides new insight into the role of VEGF on peripheral nerve injury and the viability of transplanted genetically engineered MSCs. The study aims to provide a framework for future studies with the ultimate goal of developing an improved therapy for nerve repair.
ABSTRACT
Approximately 2% of the human genome is reported to be occupied by genes. Various forms of repetitive elements (REs), both characterized and uncharacterized, are presumed to make up the vast majority of the rest of the genomes of human and other species. In conjunction with a comprehensive annotation of genes, information regarding components of genome biology, such as gene polymorphisms, non-coding RNAs, and certain REs, is found in human genome databases. However, the genome-wide profile of unique RE arrangements formed by different groups of REs has not been fully characterized yet. In this study, the entire human genome was subjected to an unbiased RE survey to establish a whole-genome profile of REs and their arrangements. Due to the limitation in query size within the bl2seq alignment program (National Center for Biotechnology Information [NCBI]) utilized for the RE survey, the entire NCBI reference human genome was fragmented into 6206 units of 0.5M nucleotides. A number of RE arrangements with varying complexities and patterns were identified throughout the genome. Each chromosome had unique profiles of RE arrangements and density, and high levels of RE density were measured near the centromere regions. Subsequently, 175 complex RE arrangements, which were selected throughout the genome, were subjected to a comparison analysis using five different human genome sequences. Interestingly, three of the five human genome databases shared the exactly same arrangement patterns and sequences for all 175 RE arrangement regions (a total of 12,765,625 nucleotides). The findings from this study demonstrate that a substantial fraction of REs in the human genome are clustered into various forms of ordered structures. Further investigations are needed to examine whether some of these ordered RE arrangements contribute to the human pathobiology as a functional genome unit.
