EphB Receptors Coordinate Migration and Proliferation in the Intestinal Stem Cell Niche

SummaryMore than 1010 cells are generated every day in the human intestine. Wnt proteins are key regulators of proliferation and are known endogenous mitogens for intestinal progenitor cells. The positioning of cells within the stem cell niche in the intestinal epithelium is controlled by B subclass ephrins through their interaction with EphB receptors. We report that EphB receptors, in addition to directing cell migration, regulate proliferation in the intestine. EphB signaling promotes cell-cycle reentry of progenitor cells and accounts for approximately 50% of the mitogenic activity in the adult mouse small intestine and colon. These data establish EphB receptors as key coordinators of migration and proliferation in the intestinal stem cell niche

Vascular Endothelial Growth Factor (VEGF) and Peripheral Nerve Regeneration

This thesis concerns vascular endothelial growth factor (VEGF) and its possible role as a neurotrophic factor. I have investigated the effect of VEGF on neurons in culture but also in vivo, following a crush lesion of the sciatic nerve, and following nerve repair. Attempts were also made to unravel the mechanism by which VEGF affects neurons and Schwann cells, using a pharmacological approach in combination with techniques like tissue culture, BrdU-labelling, in situ hybridization, immunocytochemistry, image analysis, SDS-PAGE and Western blotting. I found that VEGF stimulates axonal outgrowth from dorsal root (DRG)- and superior cervical ganglia (SCG) through activation of the flk-1 receptor and the MAPK pathway, and that activation of the same receptor on Schwann cells results in a proliferative response. VEGF also promotes survival of neurons and satellite cells. We suggest that VEGF acts both by auto- and paracrine mechanisms in the peripheral nervous system, considering the expression of VEGF and flk-1 in cells of DRG, SCG and the sciatic nerve. My second approach was to develop a cell-free nerve graft which could be used for nerve repair. The idea was that by removing the cells from the graft but maintaining the basal lamina the rejection process could be suppressed while regeneration was enhanced. I could show that nerve grafts made acellular by chemical extraction supported regeneration of nerve fibers when transplanted into a defect in the sciatic nerve of recipient rats of a different rat strain. In this system VEGF treatment promoted both vascularization and migration of Schwann cells in the graft, suggesting that for nerve repair VEGF treatment could be beneficial since it stimulates two important aspects of the regeneration process i.e. Schwann cell invasion and neovascularization. Taken together my work lend strong support to our hypothesis that VEGF is a neurotrophic factor, a finding which can have implications for our understanding of nerve injuries

Regeneration in, and properties of, extracted peripheral nerve allografts and xenografts.

Abstract When not enough conventional autologous nerve grafts are available, alternatives are needed to bridge nerve defects. Our aim was to study regeneration of nerves in chemically-extracted acellular nerve grafts from frogs, mice, humans (fresh and stored sural nerve), pigs and rats when defects in rat sciatic nerves were bridged. Secondly, we compared two different extraction procedures (techniques described by Sondell et al. and Hudson et al.) with respect to how efficiently they supported axonal outgrowth, and remaining laminin and myelin basic protein (MBP), after extraction. Isografts (rat) and xenografts (mouse) were transplanted into defects in rat sciatic nerves. Acellular nerve allografts from rats, extracted by the Sondell et al's technique, had an appreciably longer axonal outgrowth based on immunohistochemical staining of neurofilaments, than acellular nerve xenografts except those from the pig. Among acellular xenografts there was considerably longer axonal outgrowth in the grafts from pigs compared with those from humans (fresh), but there were no other differences among the xenografts with respect to axonal outgrowth. Axonal outgrowth in acellular nerve xenografts from mice, extracted by the method described by Sondell et al. was longer than in those extracted by Hudson et al's method, while there was no difference in outgrowth between extracted nerve isografts from rats. Electrophoretic analysis of extracted acellular nerve grafts showed remaining laminin, but not MBP, after both extraction procedures. These preserved laminin and removed MBP in acellular nerve grafts. Such grafts can be used to reconstruct short defects in nerves irrespective of their origin. However, selecting and matching a suitable combination of graft and host species may improve axonal outgrowth

Axonal outgrowth in muscle grafts made acellular by chemical extraction

Purpose: To compare nerve regeneration in autologous detergent extracted and freeze-thawed muscle grafts and to electrophoretically characterize the grafts. Methods: Autologous acellular muscle grafts were created either by freeze/thawing or by detergent extraction and then used to bridge a 10 mm gap in rat sciatic nerve. The autologous grafts were compared with respect to protein content, using electrophoresis preimplantation, and axonal outgrowth, Schwann cell and macrophage content, using immunocytochemistry (neurofilaments, S-100 protein, ED 1 macrophages) at 5-20 days postimplantation. Results: The extracted muscle grafts were elastic, but the amount of several proteins was reduced and laminin was still present at a position of basal laminae of the muscle fibers. The freeze/thawed grafts were brittle and lacked elasticity, but resulted in minor changes in major proteins. The axons regenerated through both types of grafts (initial delay 6 days and rate 0.7-0.8 mm/day), which shrunk in length by 25 %. There were no apparent differences with respect to Schwann cells and macrophages. Conclusions: The results suggest that detergent extracted mucle tissue, in which some basal lamina proteins remain but cells are removed, could present a new favourable option for nerve grafting

Development of fibrous biodegradable polymer conduits for guided nerve regeneration

10.1007/s10856-005-0637-6Journal of Materials Science: Materials in Medicine164367-375JSMM