Neuroectodermal Stem Cells Grafted into the Injured Spinal Cord Induce Both Axonal Regeneration and Morphological Restoration via Multiple Mechanisms

Abstract

Spinal cord contusion injury leads to severe loss of gray and white matter and subsequent deficit of motor and sensory functions below the lesion. In this study, we investigated whether application of murine clonal embryonic neuroectodermal stem cells can prevent the spinal cord secondary damage and induce functional recovery. Stem cells (NE-GFP-4C cell line) were grafted intraspinally or intravenously immediately or one week after thoracic spinal cord contusion injury. Control animals received cell culture medium or fibrin intraspinally one week after injury. Functional tests (Basso, Beattie, Bresnahan, CatWalk®) and detailed morphological analysis were performed to evaluate the effects of grafted cells. Stem cells applied either locally or intravenously induced significantly improved functional recovery compared with their controls. Morphologically, stem cell grafting prevented the formation of secondary injury and promoted sparing of the gray and white matters. The transplanted cells integrated into the host tissue and differentiated into neurons, astrocytes, and oligodendrocytes. In intraspinally grafted animals, the corticospinal tract axons regenerated along the ventral border of the cavity and have grown several millimeters, even beyond the caudal end of the lesion. The extent of regeneration and functional improvement was inversely related to the amounts of chondroitin sulphate and ephrin-B2 molecules around the cavity and to the microglial and astrocytic reactions in the injured segment early after injury. The grafts produced glial cell derived neurotrophic factor, macrophage inflammatory protein-1a, interleukin (IL)-6 and IL-10 in a paracrine fashion for at least one week. Treating the grafted cords with neutralizing antibodies against these four factors through the use of osmotic pumps nearly completely abolished the effect of the graft. The non-significant functional improvement after function blocking is likely because the stem cell derivatives settled in the injured cord. These data suggest that grafted neuroectodermal stem cells are able to prevent the secondary spinal cord damage and induce significant regeneration via multiple mechanisms.

Grafted human induced pluripotent stem cells improve the outcome of spinal cord injury: modulation of the lesion microenvironment

“…Similarly to other studies, the intravenously administered cells did not settle in the organs due to the rapid cell clearance 27 , 37 . It could be argued that this controversy between the morphological and functional data may be partly due to the poor survival of human cells in immune-competent animals or a higher dose of hiPSCs is required to improve the tissue-sparing after SCI.…”

“…Moreover, IL-10 treatment reportedly induces functional improvement following SCI, promotes neuronal survival and increases axon sparing 57 , 66 . The exact role of MIP1-alpha is not fully understood in the injured CNS, however, results from our laboratory earlier suggested that it may have a modulatory effect after SCI 26 , 27 .…”

“…Our earlier study has shown that neuroectodermal cells grafted into the injured spinal cord were able to induce functional recovery due to a secretion mechanism by the transplanted cells 25 , 27 , 28 . The effect was exerted by the undifferentiated stem cells soon after grafting in a narrow time window of a few days.…”

“…Previous studies have shown that intravenous cell treatment is a promising strategy to induce both morphological and functional recovery following subacute SCI 27 , 36 – 38 . Intravenous infusion of stem cells for SCI had a protective effect on blood vessels, reduced the area of spinal cord cavitation and promoted the restoration of motor function 27 , 37 , 39 – 41 . In this study, the intravenous application of hiPSCs was also able to reduce the microglia/macrophage reactions and deposition of chondroitin-sulphate, but no significant tissue sparing was observed in the affected segment.…”

Application of fibrin-based hydrogels for nerve protection and regeneration after spinal cord injury

“…The combined application resulted in inflammation aggravation, macrophages cell infiltration, and chondroitin sulfate proteoglycans (CSPGs) increase at the transplant site, which reduced the transplanted cells’ survival rate [ 119 ]. In the experiment of Pajer et al, after implanting the human fibrin hydrogels carrying stem cells (NE-GFP-4C cell line), the disintegrated fibrin matrix induced stem cells’ death, which failed to improve the motor function and reduce the formation of glial [ 141 ]. Besides, the undesirable consequences of cell transplantation are noteworthy, such as allodynia caused by abnormal astrocyte differentiation [ 142 ], pain and spasm caused by the inappropriate functional connection of regenerative axons [ 143 ], tumors caused by excessive hyperplasia [ 133 ], abnormal activities and tissue compression caused by ectopic colonies [ 144 ], and others.…”