PURPOSE: Injury to the adult optic nerve, caused mechanically or by diseases, is still not reparable because the retinal ganglion cells (RGCs) are not allowed to regrow their axons and die retrogradely, although they possess the intrinsic propensity to regenerate axons in experimental conditions. METHODS: In vitro propagated embryonic stem cells derived from the early chicken neural tube (NTSCs) were used to examine whether transplanted NTSCs produce growth-promoting factors and pave the microenvironment, thus facilitating axonal regeneration within the rat optic nerve. RESULTS: NTSCs survived within the site where the optic nerve had been cut and continued to be nestin-positive, thus preserving their undifferentiated cell phenotype. Transplanted NTSCs activated the matrix metalloproteases (MMP)-2 and -14 in glial fibrillary acidic protein (GFAP)-positive optic nerve astrocytes. MMP2 production correlated with immunohistochemically visible degradation of inhibitory chondroitin sulfate proteoglycans (CSPGs). In addition, NTSCs produced a panoply of neurite-promoting factors including oncomodulin, ciliary neurotrophic factor, brain-derived neurotrophic factor and crystallins beta and gamma. Cut axons intermingled with NTSCs and passed through the zone of injury to enter the distal optic nerve over long distances, arriving at the thalamus and midbrain. CONCLUSIONS: This study showed evidence that paving of the distal optic nerve microenvironment with proteolytically active MMPs and providing stem-cell-derived growth factors is a suitable method for facilitating regenerative repair of the optic nerve. Understanding the molecular mechanisms of this repair has fundamental implications for development of NTSC-based subsidiary therapy after neural injuries.
PURPOSE: Injury to the adult optic nerve, caused mechanically or by diseases, is still not reparable because the retinal ganglion cells (RGCs) are not allowed to regrow their axons and die retrogradely, although they possess the intrinsic propensity to regenerate axons in experimental conditions. METHODS: In vitro propagated embryonic stem cells derived from the early chicken neural tube (NTSCs) were used to examine whether transplanted NTSCs produce growth-promoting factors and pave the microenvironment, thus facilitating axonal regeneration within the rat optic nerve. RESULTS: NTSCs survived within the site where the optic nerve had been cut and continued to be nestin-positive, thus preserving their undifferentiated cell phenotype. Transplanted NTSCs activated the matrix metalloproteases (MMP)-2 and -14 in glial fibrillary acidic protein (GFAP)-positive optic nerve astrocytes. MMP2 production correlated with immunohistochemically visible degradation of inhibitory chondroitin sulfate proteoglycans (CSPGs). In addition, NTSCs produced a panoply of neurite-promoting factors including oncomodulin, ciliary neurotrophic factor, brain-derived neurotrophic factor and crystallins beta and gamma. Cut axons intermingled with NTSCs and passed through the zone of injury to enter the distal optic nerve over long distances, arriving at the thalamus and midbrain. CONCLUSIONS: This study showed evidence that paving of the distal optic nerve microenvironment with proteolytically active MMPs and providing stem-cell-derived growth factors is a suitable method for facilitating regenerative repair of the optic nerve. Understanding the molecular mechanisms of this repair has fundamental implications for development of NTSC-based subsidiary therapy after neural injuries.