Fluororuby as a marker for detection of acute axonal injury in rat spinal cord

Neuroprotection, Recovery of Function and Endogenous Neurogenesis in Traumatic Spinal Cord Injury Following Transplantation of Activated Adipose Tissue

Spinal cord injury (SCI) is a devastating disease, which leads to paralysis and is associated to substantially high costs for the individual and society. At present, no effective therapies are available. Here, the use of mechanically-activated lipoaspirate adipose tissue (MALS) in a murine experimental model of SCI is presented. Our results show that, following acute intraspinal MALS transplantation, there is an engraftment at injury site with the acute powerful inhibition of the posttraumatic inflammatory response, followed by a significant progressive improvement in recovery of function. This is accompanied by spinal cord tissue preservation at the lesion site with the promotion of endogenous neurogenesis as indicated by the significant increase of Nestin-positive cells in perilesional areas. Cells originated from MALS infiltrate profoundly the recipient cord, while the extra-dural fat transplant is gradually impoverished in stromal cells. Altogether, these novel results suggest the potential of MALS application in the promotion of recovery in SCI.

EPO-releasing neural precursor cells promote axonal regeneration and recovery of function in spinal cord traumatic injury

Background:

Spinal cord injury (SCI) is a debilitating condition characterized by a complex of neurological dysfunctions ranging from loss of sensation to partial or complete limb paralysis. Recently, we reported that intravenous administration of neural precursors physiologically releasing erythropoietin (namely Er-NPCs) enhances functional recovery in animals following contusive spinal cord injury through the counteraction of secondary degeneration. Er-NPCs reached and accumulated at the lesion edges, where they survived throughout the prolonged period of observation and differentiated mostly into cholinergic neuron-like cells.

Objective:

The aim of this study was to investigate the potential reparative and regenerative properties of Er-NPCs in a mouse experimental model of traumatic spinal cord injury.

Methods and Results:

We report that Er-NPCs favoured the preservation of axonal myelin and strongly promoted the regrowth across the lesion site of monoaminergic and chatecolaminergic fibers that reached the distal portions of the injured cord. The use of an anterograde tracer transported by the regenerating axons allowed us to assess the extent of such a process. We show that axonal fluoro-ruby labelling was practically absent in saline-treated mice, while it resulted very significant in Er-NPCs transplanted animals.

Conclusion:

Our study shows that Er-NPCs promoted recovery of function after spinal cord injury, and that this is accompanied by preservation of myelination and strong re-innervation of the distal cord. Thus, regenerated axons may have contributed to the enhanced recovery of function after SCI.

Fluoro-Ruby as a reliable marker for regenerating fiber tracts

Axon visualization techniques are important in assessing the efficacy of interventional approaches to stimulate neural regeneration. Whereas the labeling of descending tracts in the spinal cord has been well established using the intracortical injection of biotin dextran amine (BDA), the labeling of ascending sensory fibers of the dorsal funiculus is more problematic. Fluoro-Ruby (FR; dextran tetramethylrhodamine; MW 10,000) is a bidirectional permanent tracer, but the retrograde tracing of fibers is particularly prominent, and FR is a highly sensitive tracer that can be applied in discrete injection sites. In the present report, we used FR to efficiently label ascending fibers in the dorsal columns of the rat spinal cord. After transplantation of olfactory ensheathing cells into the transected dorsal funiculus, the application of FR was able to detect regenerating ascending fibers in the spinal cord. Regenerated fibers crossing the injury site were labeled and easily identified. It is likely that the tracer was taken up by damaged fibers. As additional advantages, the labeling is resistant to photobleaching and no additional tissue processing is necessary for visualization. It can be used for in vivo as well as in vitro injections. The findings indicate that FR can be used as a reliable fluorescent marker to study ascending regenerated fibers in the spinal cord axonal regeneration.

Sciatic nerve conditioning lesion increases macrophage response but it does not promote the regeneration of injured optic nerves

Injured optic nerves in the matured central nervous system (CNS), alike injured neurons in other CNS regions, fail to regenerate. Interestingly, activation of inflammatory cells (macrophages) following optic lens injury or implantation of peripheral nerve fragments into the vitreous body, have been previously reported to stimulate retinal ganglion cells (RGCs) to regenerate axons across the injury site and into the distal optic nerve. In addition, the beneficial role of macrophage cells has also been demonstrated in the regeneration of lesioned spinal neurons following sciatic nerve injury. However, it is not known whether these locally activated macrophage cells also contribute to the regeneration of remotely injured neurons within the CNS. Adult Sprague Dawley rats received a conditioning sciatic nerve injury followed by an optic nerve crush (ONC). Retrograde and anterograde tracing results revealed that injured optic axons did not regenerate after peripheral dorsal root ganglion (DRG) lesion, as the beneficial effects of this injury extended only locally. However, a greater inflammatory infiltration/activation was found in injury-combined animals compared to controls, although this was not sufficient to trigger a systemic regenerative response. Proximity of cell body response to injury, accompanied by a timely macrophage activation are critical factors for regeneration of injured CNS neurons to occur. Immune cell surveillance into the CNS compartment was enhanced following peripheral nerve injury.

SCOPE

nervous system development, regeneration and aging.

FK1706, a novel non-immunosuppressant neurophilin ligand, ameliorates motor dysfunction following spinal cord injury through its neuroregenerative action

Injured spinal cord axons fail to regenerate in part due to a lack of trophic support. While various methods for replacing neurotrophins have been pursued, clinical uses of these methods face significant barriers. FK1706, a non-immunosuppressant neurophilin ligand, potentiates nerve growth factor signaling, suggesting therapeutic potential for functional deficits following spinal cord injury. Here, we demonstrate that FK1706 significantly improves behavioral outcomes in animal models of spinal cord hemisection and contusion injuries in rats. Furthermore, we show that FK1706 is effective even if administration is delayed until 1 week after injury, suggesting that FK1706 has a reasonable therapeutic time-window. Morphological analysis of injured axons in the dorsal corticospinal tract showed an increase in the radius and perimeter of stained axons, which were reduced by FK1706 treatment, suggesting that axonal swelling and retraction balls observed in injured spinal cord were improved by the neurotrophic effect of FK1706. Taken together, FK1706 improves both behavioral motor function and the underlying morphological changes, suggesting that FK1706 may have therapeutic potential in meeting the significant unmet needs in spinal cord injury.

Transplantation of Fibroblasts that Overexpress Matrix Metalloproteinase-3 into the Site of Spinal Cord Injury in Rats

Growth-inhibitory chondroitin sulfate proteoglycans (CSPGs) are upregulated during glial scar formation at the site of spinal cord injury (SCI) in adult mammals. This CSPG-containing glial scar inhibits axonal regeneration. Matrix metalloproteinases (MMPs) can degrade CSPGs and other inhibitory proteins to promote neurite outgrowth. Increased MMP synthesis and secretion are observed in fibroblasts adjacent to tumor cells that express the protein EMMPRIN (Extracellular Matrix MetalloPRoteinase INducer). EMMPRIN transduction of cells provides an avenue to deliver increased levels of MMPs to the site of SCI in a sustained, localized, and moderate fashion. We explored the use of EMMPRIN-transduced cells as a mechanism to degrade CSPGs, facilitate axonal growth and improve recovery after SCI. Human dermal fibroblasts infected with a recombinant EMMPRIN adenovirus significantly increased secretion of MMP-3 compared to fibroblasts infected with a control adenovirus. Decreased CSPG immunoreactivity was observed in injured spinal cord sections when they were incubated with media from EMMPRIN-transduced fibroblasts. Conditioned media from EMMPRIN-transduced fibroblasts increased the length of neurites that were grown on a CSPG substrate. Rats that received contusive SCI and EMMPRIN-transduced fibroblast transplants demonstrated improved locomotor recovery compared to rats that received control fibroblasts, but not compared to other control groups. EMMPRIN-transplanted rats showed a significant increase in the number of retrogradely labeled cell bodies within brainstem nuclei and an increase in serotonergic fibers distal to the site of injury. EMMPRIN, and consequently MMP, delivery to the injured spinal cord may prove to be beneficial in reducing some of the physical barriers to axonal growth after SCI.

Studies on the development and behavior of the dystrophic growth cone, the hallmark of regeneration failure, in an in vitro model of the glial scar and after spinal cord injury

We have developed a novel in vitro model of the glial scar that mimics the gradient of proteoglycan found in vivo after spinal cord injury. In this model, regenerated axons from adult sensory neurons that extended deeply into the gradient developed bulbous, vacuolated endings that looked remarkably similar to dystrophic endings formed in vivo. We demonstrate that despite their highly abnormal appearance and stalled forward progress, dystrophic endings are extremely dynamic both in vitro and in vivo after spinal cord injury. Time-lapse movies demonstrated that dystrophic endings continually send out membrane veils and endocytose large membrane vesicles at the leading edge, which were then retrogradely transported to the rear of the "growth cone." This direction of movement is contrary to membrane dynamics that occur during normal neurite outgrowth. As further evidence of this motility, dystrophic endings endocytosed large amounts of dextran both in vitro and in vivo. We now have an in vitro model of the glial scar that may serve as a potent tool for developing and screening potential treatments to help promote regeneration past the lesion in vivo.