Glial restricted precursors maintain their permissive properties after long-term expansion but not following exposure to pro-inflammatory factors

Age-related loss of axonal regeneration is reflected by the level of local translation

Regeneration capacity is reduced as CNS axons mature. Using laser-mediated axotomy, proteomics and puromycin-based tagging of newly-synthesized proteins in a human embryonic stem cell-derived neuron culture system that allows isolation of axons from cell bodies, we show here that efficient regeneration in younger axons (d45 in culture) is associated with local axonal protein synthesis (local translation). Enhanced regeneration, promoted by co-culture with human glial precursor cells, is associated with increased axonal synthesis of proteins, including those constituting the translation machinery itself. Reduced regeneration, as occurs with the maturation of these axons by d65 in culture, correlates with reduced levels of axonal proteins involved in translation and an inability to respond by increased translation of regeneration promoting axonal mRNAs released from stress granules. Together, our results provide evidence that, as in development and in the PNS, local translation contributes to CNS axon regeneration.

Glial restricted precursor delivery of dendrimer N-acetylcysteine promotes migration and differentiation following transplant in mouse white matter injury model

Oligodendrocyte replacement using glial restricted precursors (GRPs) is a promising avenue for the treatment of acquired or genetic white matter disorders; however, limited long-term survival of these cells post-transplant may impede maximal recovery. Nanotherapeutic approaches can facilitate stem cell delivery while simultaneously delivering factors aimed at enhancing and nourishing stem cells en route to, and at, the target site. Hydroxyl polyamidoamine (PAMAM) dendrimer nanoparticles have been used in a variety of models to deliver therapeutics in a targeted manner to injury sites at low doses. Here, survival and migration of GRPs was assessed in a mouse model of neonatal white matter injury with different methods of dendrimer nanoparticle support. Our findings demonstrate the ability of GRPs to take up nanoparticle-drug conjugates and for these conjugates to act beyond the injury site in vivo. Compared to GRPs alone, mice receiving dendrimer-drug in parallel to GRPs, or via GRPs as the delivery vector, showed improved migration and differentiation of cells 8 weeks post-transplant. These studies demonstrate that drug-conjugated nanoparticles can enhance transplanted progenitor cell survival and migration, and suggest that combination therapies may allow engraftment without overt immunosuppression.

Immunological Characteristics and Properties of Glial Restricted Progenitors of Mice, Canine Primary Culture Suspensions, and Human QSV40 Immortalized Cell Lines for Prospective Therapies of Neurodegenerative Disorders

Neurodegeneration can be defined as a process in which neuronal structures and functions undergo changes leading to reduced neuronal survival and increased cell death in the central nervous system (CNS). Neuronal degeneration in specific regions of the CNS is a hallmark of many neurodegenerative disorders, and there is reliable proof that neural stem cells bring therapeutic benefits in treatment of neurological lesions. However, effective therapy with neural stem cells is associated with their biological properties. The assessment of immunological properties and comprehensive studies on the biology of glial restricted progenitors (GRP) are necessary prior to the application of these cells in humans. This study provides an in vitro characterization of the QSV40 glial human cell line, as well as murine and canine primary culture suspensions of GRPs and their mature, astrocytic forms using flow cytometry and immunohistochemical staining. Cytokines and chemokines released by GRPs were assessed by Multiplex ELISA. Some immunological differences observed among species suggest the necessity of reconsidering the pre-clinical model, and that careful testing of immunomodulatory strategies is required before cell transplantation into the CNS can be undertaken.

Neural Progenitor Cells Promote Axonal Growth and Alter Axonal mRNA Localization in Adult Neurons

The inhibitory environment of the spinal cord and the intrinsic properties of neurons prevent regeneration of axons following CNS injury. However, both ascending and descending axons of the injured spinal cord have been shown to regenerate into grafts of embryonic neural progenitor cells (NPCs). Previous studies have shown that grafts composed of glial-restricted progenitors (GRPs) and neural-restricted progenitors (NRPs) can provide a permissive microenvironment for axon growth. We have used cocultures of adult rat dorsal root ganglion (DRG) neurons together with NPCs, which have shown significant enhancement of axon growth by embryonic rat GRP and GRPs/NRPs, both in coculture conditions and when DRGs are exposed to conditioned medium from the NPC cultures. This growth-promoting effect of NPC-conditioned medium was also seen in injury-conditioned neurons. DRGs cocultured with GRPs/NRPs showed altered expression of regeneration-associated genes at transcriptional and post-transcriptional levels. We found that levels of GAP-43 mRNA increased in DRG cell bodies and axons. However, hepcidin antimicrobial peptide (HAMP) mRNA decreased in the cell bodies of DRGs cocultured with GRPs/NRPs, which is distinct from the increase in cell body HAMP mRNA levels seen in DRGs after injury conditioning. Endogenous GAP-43 and β-actin mRNAs as well as reporter RNAs carrying axonally localizing 3'UTRs of these transcripts showed significantly increased levels in distal axons in the DRGs cocultured with GRPs/NRPs. These results indicate that axon growth promoted by NPCs is associated not only with enhanced transcription of growth-associated genes but also can increase localization of some mRNAs into growing axons.

Examining the properties and therapeutic potential of glial restricted precursors in spinal cord injury

In the aftermath of spinal cord injury, glial restricted precursors (GRPs) and immature astrocytes offer the potential to modulate the inflammatory environment of the injured spinal cord and promote host axon regeneration. Nevertheless clinical application of cellular therapy for the repair of spinal cord injury requires strict quality-assured protocols for large-scale production and preservation that necessitates long-term in vitro expansion. Importantly, such processes have the potential to alter the phenotypic and functional properties and thus therapeutic potential of these cells. Furthermore, clinical use of cellular therapies may be limited by the inflammatory microenvironment of the injured spinal cord, altering the phenotypic and functional properties of grafted cells. This report simulates the process of large-scale GRP production and demonstrates the permissive properties of GRP following long-term in vitro culture. Furthermore, we defined the phenotypic and functional properties of GRP in the presence of inflammatory factors, and call attention to the importance of the microenvironment of grafted cells, underscoring the importance of modulating the environment of the injured spinal cord.