Axonal sprouting into the denervated spinal cord and synaptic and postsynaptic protein expression in the spinal cord after transplantation of bone marrow stromal cell in stroke rats

Marrow stromal cell transplantation in stroke and traumatic brain injury

There is a paucity of therapies for most central nervous system (CNS) disorders. Bone marrow stromal cells (MSCs) are a mixed cell population, including stem and progenitor cells, and are currently a strong candidate for cell-based therapy in "brain attack", including stroke, and traumatic brain injury (TBI), since they are easily isolated and can be expanded in culture from patients without ethical and technical problems. Although it has been suggested that trans-differentiation of MSCs into cells of neural lineage may occur in vitro, no one has yet observed that MSCs give rise to fully differentiated and functional neurons in vivo. The overwhelming body of data indicate that bioactive factors secreted by MSCs in response to the local environment underlie the tissue restorative effects of MSCs. The MSCs that are employed in this therapy are not necessarily stem cells, but progenitor and differentiated cells that escape immune system surveillance and survive in the CNS even for transplantation of allogeneic or xenogeneic MSCs. The injured CNS is stimulated by the MSCs to amplify its intrinsic restorative processes. Treatment of damaged brain with MSCs promotes functional recovery, and facilitates CNS endogenous plasticity and remodeling. The current mini-review is mainly based on our data and focuses on possible cellular and molecular mechanisms of interaction of MSCs with glia, neurons and vessels after brain attack. The transplantation of MSCs opens up new avenues of cell therapy and may provide an effective treatment for various CNS diseases.

Mechanisms underlying improved recovery of neurological function after stroke in the rodent after treatment with neurorestorative cell-based therapies

We discuss the mechanisms of action underlying the beneficial effects of treating ischemic stroke in the rodent with exogenously administered cells. The essential hypothesis proposed is that the administered cells enhance recovery of neurological function by stimulating the production of restorative factors by parenchymal cells. These activated endogenous brain cells evoke white matter remodeling in the brain and the spinal cord and generate microenvironments within the injured brain that amplify brain plasticity and lead to improvement in neurological function poststroke.

Down-regulation of neurocan expression in reactive astrocytes promotes axonal regeneration and facilitates the neurorestorative effects of bone marrow stromal cells in the ischemic rat brain

The glial scar, a primarily astrocytic structure bordering the infarct tissue inhibits axonal regeneration after stroke. Neurocan, an axonal extension inhibitory molecule, is up-regulated in the scar region after stroke. Bone marrow stromal cells (BMSCs) reduce the thickness of glial scar wall and facilitate axonal remodeling in the ischemic boundary zone. To further clarify the role of BMSCs in axonal regeneration and its underlying mechanism, the current study focused on the effect of BMSCs on neurocan expression in the ischemic brain. Thirty-one adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 x 10(6) rat BMSCs (n = 16) or phosphate-buffered saline (n = 15) into the tail vein 24 h later. Animals were sacrificed at 8 days after stroke. Immunostaining analysis showed that reactive astrocytes were the primary source of neurocan, and BMSC-treated animals had significantly lower neurocan and higher growth associated protein 43 expression in the penumbral region compared with control rats, which was confirmed by Western blot analysis of the brain tissue. To further investigate the effects of BMSCs on astrocyte neurocan expression, single reactive astrocytes were collected from the ischemic boundary zone using laser capture microdissection. Neurocan gene expression was significantly down-regulated in rats receiving BMSC transplantation (n = 4/group). Primary cultured astrocytes showed similar alterations; BMSC coculture during reoxygenation abolished the up-regulation of neurocan gene in astrocytes undergoing oxygen-glucose deprivation (n = 3/group). Our data suggest that BMSCs promote axonal regeneration by reducing neurocan expression in peri-infarct astrocytes.

Axon sprouting in adult mouse spinal cord after motor cortex stroke

Functional reorganization of brain cortical areas occurs following stroke in humans, and many instances of this plasticity are associated with recovery of function. Rodent studies have shown that following a cortical stroke, neurons in uninjured areas of the brain are capable of sprouting new axons into areas previously innervated by injured cortex. The pattern and extent of structural plasticity depend on the species, experimental model, and lesion localization. In this study, we examined the pattern of axon sprouting in spinal cord after a localized lesion which selectively targeted the primary motor cortex in adult mice. We subjected mice to a stereotaxic-guided photothrombotic stroke of the left motor cortex, followed 2 weeks later by an injection of the neuronal tracer biotinylated dextran amine (BDA) into the uninjured right motor cortex. BDA-positive axons originating from the uninjured motor cortex were increased in the gray matter of the right cervical spinal cord in stroke mice, compared to sham control mice. These results show that axon sprouting can occur in the spinal cord of adult wild-type mice after a localized stroke in motor cortex.

Contralesional axonal remodeling of the corticospinal system in adult rats after stroke and bone marrow stromal cell treatment

BACKGROUND AND PURPOSE

Motor recovery after stroke is associated with neuronal reorganization in bilateral hemispheres. We investigated contralesional corticospinal tract remodeling in the brain and spinal cord in rats after stroke and treatment of bone marrow stromal cells.

METHODS

Adult male Wistar rats were subjected to permanent right middle cerebral artery occlusion. Phosphate-buffered saline or bone marrow stromal cells were injected into a tail vein 1 day postischemia. An adhesive removal test was performed weekly to monitor functional recovery. Threshold currents of intracortical microstimulation on the left motor cortex for evoking bilateral forelimb movements were measured 6 weeks after stroke. When intracortical microstimulation was completed, biotinylated dextran amine was injected into the left motor cortex to anterogradely label the corticospinal tract. At 4 days before euthanization, pseudorabies virus-152-EGFP and 614-mRFP were injected into left or right forelimb extensor muscles, respectively. All animals were euthanized 8 weeks after stroke.

RESULTS

In normal rats (n=5), the corticospinal tract showed a unilateral innervation pattern. In middle cerebral artery occlusion rats (n=8), our data demonstrated that: 1) stroke reduced the stimulation threshold evoking ipsilateral forelimb movement; 2) EGFP-positive pyramidal neurons were increased in the left intact cortex, which were labeled from the left stroke-impaired forelimb; and 3) biotinylated dextran amine-labeled contralesional axons sprouted into the denervated spinal cord. Bone marrow stromal cells significantly enhanced all 3 responses (n=8, P<0.05).

CONCLUSIONS

Our data demonstrated that corticospinal tract fibers originating from the contralesional motor cortex sprout into the denervated spinal cord after stroke and bone marrow stromal cells treatment, which may contribute to functional recovery.

TSP-1 secreted by bone marrow stromal cells contributes to retinal ganglion cell neurite outgrowth and survival

Background

Bone marrow stromal cells (BMSCs) are pluripotent and thereby a potential candidate for cell replacement therapy for central nervous system degenerative disorders and traumatic injury. However, the mechanism of their differentiation and effect on neural tissues has not been fully elucidated. This study evaluates the effect of BMSCs on neural cell growth and survival in a retinal ganglion cell (RGCs) model by assessing the effect of changes in the expression of a BMSC-secreted protein, thrombospondin-1 (TSP-1), as a putative mechanistic agent acting on RGCs.

Methods and Findings

The effect of co-culturing BMSCs and RGCs in vitro was evaluated by measuring the following parameters: neurite outgrowth, RGC survival, BMSC neural-like differentiation, and the effect of TSP-1 on both cell lines under basal secretion conditions and when TSP-1 expression was inhibited. Our data show that BMSCs improved RGC survival and neurite outgrowth. Synaptophysin, MAP-2, and TGF-β expression are up-regulated in RGCs co-cultured with BMSCs. Interestingly, the BMSCs progressively displayed neural-like morphology over the seven-day study period. Restriction display polymerase chain reaction (RD-PCR) was performed to screen for differentially expressed genes in BMSCs cultured alone or co-cultured with RGCs. TSP-1, a multifactorial extracellular matrix protein, is critically important in the formation of neural connections during development, so its function in our co-culture model was investigated by small interfering RNA (siRNA) transfection. When TSP-1 expression was decreased with siRNA silencing, BMSCs had no impact on RGC survival, but reduced neurite outgrowth and decreased expression of synaptophysin, MAP-2 and TGF-β in RGCs. Furthermore, the number of BMSCs with neural-like characteristics was significantly decreased by more than two-fold using siRNA silencing.

Conclusions

Our data suggest that the TSP-1 signaling pathway might have an important role in neural-like differentiation in BMSCs and neurite outgrowth in RGCs. This study provides new insights into the potential reparative mechanisms of neural cell repair.

Human adult bone marrow-derived somatic cell therapy results in functional recovery and axonal plasticity following stroke in the rat

Stroke is the leading cause of adult disability in the United States. To date there is no satisfactory treatment for stroke once neuronal damage has occurred. Human adult bone marrow-derived somatic cells (hABM-SC) represent a homogenous population of CD49c/CD90 co-positive, non-hematopoietic cells that have been shown to secrete therapeutically relevant trophic factors and to support axonal growth in a rodent model of spinal cord injury. Here we demonstrate that treatment with hABM-SC after ischemic stroke in adult rats results in recovery of forelimb function on a skilled motor test, and that this recovery is positively correlated with increased axonal outgrowth of the intact, uninjured corticorubral tract. While the complete mechanism of repair is still unclear, we conclude that enhancement of structural neuroplasticity from uninjured brain areas is one mechanism by which hABM-SC treatment after stroke leads to functional recovery.