Strategic Approaches to Regeneration of a Damaged Central Nervous System

Unravelling the Parkinson's puzzle, from medications and surgery to stem cells and genes: a comprehensive review of current and future management strategies

Parkinson's disease (PD) is a neurodegenerative disorder, prevalent in the elderly population. Neuropathological hallmarks of PD include loss of dopaminergic cells in the nigro-striatal pathway and deposition of alpha-synuclein protein in the neurons and synaptic terminals, which lead to a complex presentation of motor and non-motor symptoms. This review focuses on various aspects of PD, from clinical diagnosis to currently accepted treatment options, such as pharmacological management through dopamine replacement and surgical techniques such as deep brain stimulation (DBS). The review discusses in detail the potential of emerging stem cell-based therapies and gene therapies to be adopted as a cure, in contrast to the present symptomatic treatment in PD. The potential sources of stem cells for autologous and allogeneic stem cell therapy have been discussed, along with the progress evaluation of pre-clinical and clinical trials. Even though recent techniques hold great potential to improve the lives of PD patients, we present the importance of addressing the safety, efficacy, ethical, cost, and regulatory concerns before scaling them to clinical use.

Mini-review: "Enteric glia functions in nervous tissue repair: Therapeutic target or tool?"

In the body, nerve tissue is not only present in the central nervous system, but also in the periphery. The enteric nervous system (ENS) is a highly organized intrinsic network of neurons and glial cells grouped to form interconnected ganglia. Glial cells in the ENS are a fascinating cell population: their neurotrophic role is well established, as well as their plasticity in specific circumstances. Gene expression profiling studies indicate that ENS glia retain neurogenic potential. The identification of neurogenic glial subtype(s) and the molecular basis of glia-derived neurogenesis may have profound biological and clinical implications. In this review, we discuss the potential of using gene-editing for ENS glia and cell transplantation as therapies for enteric neuropathies. Glia in the ENS: target or tool for nerve tissue repair?

Central nervous system regeneration: the roles of glial cells in the potential molecular mechanism underlying remyelination

Glial cells play crucial roles in brain homeostasis and pathogenesis of central nervous system (CNS) injuries and diseases. However, the roles of these cells and the molecular mechanisms toward regeneration in the CNS have not been fully understood, especially the capacity of them toward demyelinating diseases. Therefore, there are still very limited therapeutic strategies to restore the function of adult CNS in diseases such as multiple sclerosis (MS). Remyelination, a spontaneous regeneration process in the CNS, requires the involvement of multiple cellular and extracellular components. Promoting remyelination by therapeutic interventions is a promising novel approach to restore the CNS function. Herein, we review the role of glial cells in CNS diseases and injuries. Particularly, we discuss the roles of glia and their functional interactions and regulatory mechanisms in remyelination, as well as the current therapeutic strategies for MS.

Current progress of rehabilitative strategies in stem cell therapy for spinal cord injury: a review

Stem cell-based regenerative therapy has opened an avenue for functional recovery of patients with spinal cord injury (SCI). Regenerative rehabilitation is attracting wide attention owing to its synergistic effects, feasibility, non-invasiveness, and diverse and systemic properties. In this review article, we summarize the features of rehabilitation, describe the mechanism of combinatorial treatment, and discuss regenerative rehabilitation in the context of SCI. Although conventional rehabilitative methods have commonly been implemented alone, especially in studies of acute-to-subacute SCI, the combinatorial effects of intensive and advanced methods, including various neurorehabilitative approaches, have also been reported. Separating the concept of combined rehabilitation from regenerative rehabilitation, we suggest that the main roles of regenerative rehabilitation can be categorized as conditioning/reconditioning, functional training, and physical exercise, all of which are indispensable for enhancing functional recovery achieved using stem cell therapies.

Conductive Biomaterials as Substrates for Neural Stem Cells Differentiation towards Neuronal Lineage Cells

The injuries and defects in the central nervous system are the causes of disability and death of an affected person. As of now, there are no clinically available methods to enhance neural structural regeneration and functional recovery of nerve injuries. Recently, some experimental studies claimed that the injuries in brain can be repaired by progenitor or neural stem cells located in the neurogenic sites of adult mammalian brain. Various attempts have been made to construct biomimetic physiological microenvironment for neural stem cells to control their ultimate fate. Conductive materials have been considered as one the best choices for nerve regeneration due to the capacity to mimic the microenvironment of stem cells and regulate the alignment, growth, and differentiation of neural stem cells. The review highlights the use of conductive biomaterials, e.g., polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), multi-walled carbon nanotubes, single-wall carbon nanotubes, graphene, and graphite oxide, for controlling the neural stem cells activities in terms of proliferation and neuronal differentiation. The effects of conductive biomaterials in axon elongation and synapse formation for optimal repair of central nervous system injuries are also discussed.

Apolipoprotein E Affects In Vitro Axonal Growth and Regeneration via the MAPK Signaling Pathway

Following central nervous system injury in mammals, failed axonal regeneration is closely related to dysneuria. Previous studies have shown that the obvious effects of apolipoprotein E (ApoE) on traumatic brain injury (TBI) were associated with an axonal mechanism. However, little information on the actions of ApoE and its isoforms on axonal regeneration following TBI was provided. In our study, the cerebral cortices of ApoE-deficient (ApoE^-/-) and wild-type (ApoE^+/+) mice were cultured in vitro, and an axonal transection model was established. Interventions included the conditioned medium of astrocytes, human recombinant ApoE2/3/4 isoforms and inhibitors of the JNK/ERK/p38 pathway. Axonal growth and regeneration were evaluated by measuring the maximum distance and area of the axons. The expression levels of β-tubulin III, MAP2, ApoE, p-JNK, p-ERK and p-p38 were detected by immunofluorescence and western blotting. The results showed that ApoE mRNA and protein were expressed in intact axons and regenerated axons. Axonal growth and regeneration were attenuated in ApoE^-/- mice but recovered by exogenous ApoE. Human recombinant ApoE3 positively influenced axonal growth and regeneration; these effects were mediated by the JNK/ERK/p38 pathway. These results suggest ApoE and its isoforms may have influenced axonal growth and regeneration via the MAPK signaling pathway in vitro.

Fractalkine promotes chemotaxis of bone marrow-derived mesenchymal stem cells towards ischemic brain lesions through Jak2 signaling and cytoskeletal reorganization

The fractalkine (FKN)-CX3CR1 (FKN receptor) axis reportedly plays an important role in the progression of many neural pathologies. However, its role in the recruitment of bone marrow-derived progenitor cells for neurogenesis remains elusive. The chemokine-based mechanism underlying the migration of bone marrow-derived mesenchymal stem cells (BMSCs) was investigated in a double-chamber transmigration model with recombinant FKN and endogenous FKN extract, and the results confirmed the involvement of FKN in migration. This chemotactic response was CX3CR1-dependent and FKN-sensitive. Western blotting, immunoprecipitation and transmigration assays revealed that the Janus kinase (Jak)2-signal transducer and activator of transcription (Stat)5α-extracellular signal-related kinase (ERK)1/2 pathway was activated by FKN. Confocal laser scanning microscopy was used to demonstrate cytoskeletal reorganization caused by remodeling of the surface receptor integrin α5β1, intracellular phosphorylation of Fak and Pax, and upregulation of intercellular adhesion molecule-1 during BMSC migration. Moreover, significant inhibition of signaling and migration was detected after treatment of cells with Jak2-interfering RNA or the antagonist AG490. In addition, the results of a fluorescence immunohistochemical analysis of an in vivo chemotactic model, developed via transplantation of BMSCs into transient middle cerebral artery-occluded rats, were consistent with the in vitro results. These findings suggest that FKN activates Jak2-Stat5α-ERK1/2 signaling through CX3CR1, thereby triggering integrin-dependent machinery reorganization to allow chemotactic migration of BMSCs towards an ischemic cerebral lesion.