Soheila Karimi-Abdolrezaee

Delayed Transplantation of Adult Neural Precursor Cells Promotes Remyelination and Functional Neurological Recovery after Spinal Cord Injury

Spinal cord injury (SCI) results in loss of oligodendrocytes demyelination of surviving axons and severe functional impairment. Spontaneous remyelination is limited. Thus, cell replacement therapy is an attractive approach for myelin repair. In this study, we transplanted adult brain-derived neural precursor cells (NPCs) isolated from yellow fluorescent protein-expressing transgenic mice into the injured spinal cord of adult rats at 2 and 8 weeks after injury, which represents the subacute and chronic phases of SCI. A combination of growth factors, the anti-inflammatory drug minocycline, and cyclosporine A immunosuppression was used to enhance the survival of transplanted adult NPCs. Our results show the presence of a substantial number of surviving NPCs in the injured spinal cord up to 10 weeks after transplantation at the subacute stage of SCI. In contrast, cell survival was poor after transplantation into chronic lesions. After subacute transplantation, grafted cells migrated >5 mm rostrally and caudally. The surviving NPCs integrated principally along white-matter tracts and displayed close contact with the host axons and glial cells. Approximately 50% of grafted cells formed either oligodendroglial precursor cells or mature oligodendrocytes. NPC-derived oligodendrocytes expressed myelin basic protein and ensheathed the axons. We also observed that injured rats receiving NPC transplants had improved functional recovery as assessed by the Basso, Beattie, and Bresnahan Locomotor Rating Scale and grid-walk and footprint analyses. Our data provide strong evidence in support of the feasibility of adult NPCs for cell-based remyelination after SCI.

Synergistic effects of transplanted adult neural stem/progenitor cells, chondroitinase, and growth factors promote functional repair and plasticity of the chronically injured spinal cord.

The transplantation of neural stem/progenitor cells (NPCs) is a promising therapeutic strategy for spinal cord injury (SCI). However, to date NPC transplantation has exhibited only limited success in the treatment of chronic SCI. Here, we show that chondroitin sulfate proteoglycans (CSPGs) in the glial scar around the site of chronic SCI negatively influence the long-term survival and integration of transplanted NPCs and their therapeutic potential for promoting functional repair and plasticity. We targeted CSPGs in the chronically injured spinal cord by sustained infusion of chondroitinase ABC (ChABC). One week later, the same rats were treated with transplants of NPCs and transient infusion of growth factors, EGF, bFGF, and PDGF-AA. We demonstrate that perturbing CSPGs dramatically optimizes NPC transplantation in chronic SCI. Engrafted NPCs successfully integrate and extensively migrate within the host spinal cord and principally differentiate into oligodendrocytes. Furthermore, this combined strategy promoted the axonal integrity and plasticity of the corticospinal tract and enhanced the plasticity of descending serotonergic pathways. These neuroanatomical changes were also associated with significantly improved neurobehavioral recovery after chronic SCI. Importantly, this strategy did not enhance the aberrant synaptic connectivity of pain afferents, nor did it exacerbate posttraumatic neuropathic pain. For the first time, we demonstrate key biological and functional benefits for the combined use of ChABC, growth factors, and NPCs to repair the chronically injured spinal cord. These findings could potentially bring us closer to the application of NPCs for patients suffering from chronic SCI or other conditions characterized by the formation of a glial scar.

Reactive Astrogliosis after Spinal Cord Injury—Beneficial and Detrimental Effects

Reactive astrogliosis is a pathologic hallmark of spinal cord injury (SCI). It is characterised by profound morphological, molecular, and functional changes in astrocytes that occur within hours of SCI and evolves as time elapses after injury. Astrogliosis is a defense mechanism to minimize and repair the initial damage but eventually leads to some detrimental effects. Reactive astrocytes secrete a plethora of both growth promoting and inhibitory factors after SCI. However, the production of inhibitory components surpasses the growth stimulating factors, thus, causing inhibitory effects. In severe cases of injury, astrogliosis results in the formation of irreversible glial scarring that acts as regeneration barrier due to the expression of inhibitory components such as chondroitin sulfate proteoglycans. Scar formation was therefore recognized from a negative perspective for many years. Accumulating evidence from pharmacological and genetic studies now signifies the importance of astrogliosis and its timing for spinal cord repair. These studies have advanced our knowledge regarding signaling pathways and molecular mediators, which trigger and modulate reactive astrocytes and scar formation. In this review, we discuss the recent advances in this field. We also review therapeutic strategies that have been developed to target astrocytes reactivity and glial scaring in the environment of SCI. Astrocytes play pivotal roles in governing SCI mechanisms, and it is therefore crucial to understand how their activities can be targeted efficiently to harness their potential for repair and regeneration after SCI.

Modulation of the proteoglycan receptor PTPσ promotes recovery after spinal cord injury.

Contusive spinal cord injury leads to a variety of disabilities owing to limited neuronal regeneration and functional plasticity. It is well established that an upregulation of glial-derived chondroitin sulphate proteoglycans (CSPGs) within the glial scar and perineuronal net creates a barrier to axonal regrowth and sprouting. Protein tyrosine phosphatase σ (PTPσ), along with its sister phosphatase leukocyte common antigen-related (LAR) and the nogo receptors 1 and 3 (NgR), have recently been identified as receptors for the inhibitory glycosylated side chains of CSPGs. Here we find in rats that PTPσ has a critical role in converting growth cones into a dystrophic state by tightly stabilizing them within CSPG-rich substrates. We generated a membrane-permeable peptide mimetic of the PTPσ wedge domain that binds to PTPσ and relieves CSPG-mediated inhibition. Systemic delivery of this peptide over weeks restored substantial serotonergic innervation to the spinal cord below the level of injury and facilitated functional recovery of both locomotor and urinary systems. Our results add a new layer of understanding to the critical role of PTPσ in mediating the growth-inhibited state of neurons due to CSPGs within the injured adult spinal cord.

Current status of experimental cell replacement approaches to spinal cord injury

✓ Despite advances in medical and surgical care, the current clinical therapies for spinal cord injury (SCI) are largely ineffective. During the last 2 decades, the search for new therapies has been revolutionized by the discovery of stem cells, which has inspired scientists and clinicians to search for a stem cell–based reparative approaches to many diseases, including neurotrauma. In the present study, the authors briefly summarize current knowledge related to the pathophysiology of SCI, including the concepts of primary and secondary injury and the importance of posttraumatic demyelination. Key inhibitory obstacles that impede axonal regeneration include the glial scar and a number of myelin inhibitory molecules including Nogo. Recent advancements in cell replacement therapy as a therapeutic strategy for SCI are summarized. The strategies include the use of pluripotent human stem cells, embryonic stem cells, and a number of adult-derived stem and progenitor cells such as mesenchymal stem cells, Schwann...Despite advances in medical and surgical care, the current clinical therapies for spinal cord injury (SCI) are largely ineffective. During the last 2 decades, the search for new therapies has been revolutionized by the discovery of stem cells, which has inspired scientists and clinicians to search for a stem cell-based reparative approaches to many diseases, including neurotrauma. In the present study, the authors briefly summarize current knowledge related to the pathophysiology of SCI, including the concepts of primary and secondary injury and the importance of posttraumatic demyelination. Key inhibitory obstacles that impede axonal regeneration include the glial scar and a number of myelin inhibitory molecules including Nogo. Recent advancements in cell replacement therapy as a therapeutic strategy for SCI are summarized. The strategies include the use of pluripotent human stem cells, embryonic stem cells, and a number of adult-derived stem and progenitor cells such as mesenchymal stem cells, Schwann cells, olfactory ensheathing cells, and adult-derived neural precursor cells. Although current strategies to repair the subacutely injured cord appear promising, many obstacles continue to render the treatment of chronic injuries challenging. Nonetheless, the future for stem cell-based reparative strategies for treating SCI appears bright.

Myelination of Congenitally Dysmyelinated Spinal Cord Axons by Adult Neural Precursor Cells Results in Formation of Nodes of Ranvier and Improved Axonal Conduction

Emerging evidence suggests that cell-based remyelination strategies may be a feasible therapeutic approach for CNS diseases characterized by myelin deficiency as a result of trauma, congenital anomalies, or diseases. Although experimental demyelination models targeted at the transient elimination of oligodendrocytes have suggested that transplantation-based remyelination can partially restore axonal molecular structure and function, it is not clear whether such therapeutic approaches can be used to achieve functional remyelination in models associated with long-term, irreversible myelin deficiency. In this study, we transplanted adult neural precursor cells (aNPCs) from the brain of adult transgenic mice into the spinal cords of adult Shiverer (shi/shi) mice, which lack compact CNS myelin. Six weeks after transplantation, the transplanted aNPCs expressed oligodendrocyte markers, including MBP, migrated extensively along the white matter tracts of the spinal cord, and formed compact myelin. Conventional and three-dimensional confocal and electron microscopy revealed axonal ensheathment, establishment of paranodal junctional complexes leading to de novo formation of nodes of Ranvier, and partial reconstruction of the juxtaparanodal and paranodal molecular regions of axons based on Kv1.2 and Caspr (contactin-associated protein) expression by the transplanted aNPCs. Electrophysiological recordings revealed improved axonal conduction along the transplanted segments of spinal cords. We conclude that myelination of congenitally dysmyelinated adult CNS axons by grafted aNPCs results in the formation of compact myelin, reconstruction of nodes of Ranvier, and enhanced axonal conduction. These data suggest the therapeutic potential of aNPCs to promote functionally significant myelination in CNS disorders characterized by longstanding myelin deficiency.

Chondroitinase and Growth Factors Enhance Activation and Oligodendrocyte Differentiation of Endogenous Neural Precursor Cells after Spinal Cord Injury

The adult spinal cord harbours a population of multipotent neural precursor cells (NPCs) with the ability to replace oligodendrocytes. However, despite this capacity, proliferation and endogenous remyelination is severely limited after spinal cord injury (SCI). In the post-traumatic microenvironment following SCI, endogenous spinal NPCs mainly differentiate into astrocytes which could contribute to astrogliosis that exacerbate the outcomes of SCI. These findings emphasize a key role for the post-SCI niche in modulating the behaviour of spinal NPCs after SCI. We recently reported that chondroitin sulphate proteoglycans (CSPGs) in the glial scar restrict the outcomes of NPC transplantation in SCI by reducing the survival, migration and integration of engrafted NPCs within the injured spinal cord. These inhibitory effects were attenuated by administration of chondroitinase (ChABC) prior to NPC transplantation. Here, in a rat model of compressive SCI, we show that perturbing CSPGs by ChABC in combination with sustained infusion of growth factors (EGF, bFGF and PDGF-AA) optimize the activation and oligodendroglial differentiation of spinal NPCs after injury. Four days following SCI, we intrathecally delivered ChABC and/or GFs for seven days. We performed BrdU incorporation to label proliferating cells during the treatment period after SCI. This strategy increased the proliferation of spinal NPCs, reduced the generation of new astrocytes and promoted their differentiation along an oligodendroglial lineage, a prerequisite for remyelination. Furthermore, ChABC and GF treatments enhanced the response of non-neural cells by increasing the generation of new vascular endothelial cells and decreasing the number of proliferating macrophages/microglia after SCI. In conclusions, our data strongly suggest that optimization of the behaviour of endogenous spinal NPCs after SCI is critical not only to promote endogenous oligodendrocyte replacement, but also to reverse the otherwise detrimental effects of their activation into astrocytes which could negatively influence the repair process after SCI.

Temporal and spatial patterns of Kv1.1 and Kv1.2 protein and gene expression in spinal cord white matter after acute and chronic spinal cord injury in rats: implications for axonal pathophysiology after neurotrauma

After spinal cord injury (SCI), surviving white matter axons display axonal dysfunction associated with demyelination and altered K+ channel activity. To clarify the molecular basis of posttraumatic axonal pathophysiology after SCI, we investigated the changes in expression and distribution of the axonal K+ channel subunits Kv1.1 and Kv1.2 in spinal cord white matter after in vivo SCI in the rat. Using Western blot analysis, we found an increased expression of Kv1.1 and Kv1.2 at 2 and 6 weeks after SCI. By real‐time PCR we observed an increase in Kv1.1 and Kv1.2 mRNA levels 1 day after SCI, which persisted until 6 weeks. Confocal immunohistochemistry showed a markedly dispersed labelling of Kv1.1 and Kv1.2 along the injured axons, in contrast to the tight localization of these channels to the juxtaparanodes of noninjured axons. This redistribution of Kv1.1 and Kv1.2 occurred as early as 1 h postinjury along some injured axons, and persisted at 6 weeks postinjury. In parallel with the redistribution of Kv1.1 and 1.2, contactin‐associated protein (Caspr), which is normally confined to a paranodal location, also displayed a more diffuse distribution along the injured spinal cord axons. Our results suggest that the increased expression of Kv1.1 and Kv1.2 proteins is transcriptionally regulated. In contrast, the redistribution of the axonal K+ channel subunits occurs very early postinjury and probably reflects a disruption of the juxtaparanodal axonal region due to physical trauma, as shown by altered localization of Caspr.

Myelin damage and repair in pathologic CNS: challenges and prospects

Injury to the central nervous system (CNS) results in oligodendrocyte cell death and progressive demyelination. Demyelinated axons undergo considerable physiological changes and molecular reorganizations that collectively result in axonal dysfunction, degeneration and loss of sensory and motor functions. Endogenous adult oligodendrocyte precursor cells and neural stem/progenitor cells contribute to the replacement of oligodendrocytes, however, the extent and quality of endogenous remyelination is suboptimal. Emerging evidence indicates that optimal remyelination is restricted by multiple factors including (i) low levels of factors that promote oligodendrogenesis; (ii) cell death among newly generated oligodendrocytes, (iii) inhibitory factors in the post-injury milieu that impede remyelination, and (iv) deficient expression of key growth factors essential for proper re-construction of a highly organized myelin sheath. Considering these challenges, over the past several years, a number of cell-based strategies have been developed to optimize remyelination therapeutically. Outcomes of these basic and preclinical discoveries are promising and signify the importance of remyelination as a mechanism for improving functions in CNS injuries. In this review, we provide an overview on: (1) the precise organization of myelinated axons and the reciprocal axo-myelin interactions that warrant properly balanced physiological activities within the CNS; (2) underlying cause of demyelination and the structural and functional consequences of demyelination in axons following injury and disease; (3) the endogenous mechanisms of oligodendrocyte replacement; (4) the modulatory role of reactive astrocytes and inflammatory cells in remyelination; and (5) the current status of cell-based therapies for promoting remyelination. Careful elucidation of the cellular and molecular mechanisms of demyelination in the pathologic CNS is a key to better understanding the impact of remyelination for CNS repair.

Chondroitin sulfate proteoglycans: Key modulators in the developing and pathologic central nervous system

Chondroitin Sulfate Proteoglycans (CSPGs) are a major component of the extracellular matrix in the central nervous system (CNS) and play critical role in the development and pathophysiology of the brain and spinal cord. Developmentally, CSPGs provide guidance cues for growth cones and contribute to the formation of neuronal boundaries in the developing CNS. Their presence in perineuronal nets plays a crucial role in the maturation of synapses and closure of critical periods by limiting synaptic plasticity. Following injury to the CNS, CSPGs are dramatically upregulated by reactive glia which form a glial scar around the lesion site. Increased level of CSPGs is a hallmark of all CNS injuries and has been shown to limit axonal plasticity, regeneration, remyelination, and conduction after injury. Additionally, CSPGs create a non-permissive milieu for cell replacement activities by limiting cell migration, survival and differentiation. Mounting evidence is currently shedding light on the potential benefits of manipulating CSPGs in combination with other therapeutic strategies to promote spinal cord repair and regeneration. Moreover, the recent discovery of multiple receptors for CSPGs provides new therapeutic targets for targeted interventions in blocking the inhibitory properties of CSPGs following injury. Here, we will provide an in depth discussion on the impact of CSPGs in normal and pathological CNS. We will also review the recent preclinical therapies that have been developed to target CSPGs in the injured CNS.