Polysialic acid (PSA) is a cell-surface glycan with an enormous hydrated volume that serves to modulate the distance between cells. This regulation has direct effects on several cellular mechanisms ...that underlie the formation of the vertebrate nervous system, most conspicuously in the migration and differentiation of progenitor cells and the growth and targeting of axons. PSA is also involved in a number of plasticity-related responses in the adult CNS, including changes in circadian and hormonal patterns, adaptations to pain and stress, and aspects of learning and memory. The ability of PSA to increase the plasticity of neural cells is being exploited to improve the repair of adult CNS tissue.
Parkinson’s disease is characterized by the loss of dopaminergic neurons in the substantia nigra leading to disabling deficits. Dopamine neuron grafts may provide a significant therapeutic advance ...over current therapies. We have generated midbrain dopamine neurons from human embryonic stem cells and manufactured large-scale cryopreserved dopamine progenitors for clinical use. After optimizing cell survival and phenotypes in short-term studies, the cell product, MSK-DA01, was subjected to an extensive set of biodistribution, toxicity, and tumorigenicity assessments in mice under GLP conditions. A large-scale efficacy study was also performed in rats with the same lot of cells intended for potential human use and demonstrated survival of the grafted cells and behavioral amelioration in 6-hydroxydopamine lesioned rats. There were no adverse effects attributable to the grafted cells, no obvious distribution outside the brain, and no cell overgrowth or tumor formation, thus paving the way for a future clinical trial.
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•Derivation from human ESCs of a cryopreserved dopamine progenitor cell product, MSK-DA01•MSK-DA01 cells rescue motor deficits in Parkinsonian rats•MSK-DA01 had no adverse effects in biodistribution, toxicology, and tumorigenicity studies•MSK-DA01 cells differentiate predominately into dopamine neurons in the host striatum
Tabar et al. report the development of an hESC-derived dopamine neuron product for clinical applications.
Embryonic stem cells (ESCs) represent a promising source of midbrain dopaminergic (DA) neurons for applications in Parkinson disease. However, ESC-based transplantation paradigms carry a risk of ...introducing inappropriate or tumorigenic cells. Cell purification before transplantation may alleviate these concerns and enable identification of the specific DA neuron stage most suitable for cell therapy. Here, we used 3 transgenic mouse ESC reporter lines to mark DA neurons at 3 stages of differentiation (early, middle, and late) following induction of differentiation using Hes5::GFP, Nurr1::GFP, and Pitx3::YFP transgenes, respectively. Transplantation of FACS-purified cells from each line resulted in DA neuron engraftment, with the mid-stage and late-stage neuron grafts being composed almost exclusively of midbrain DA neurons. Mid-stage neuron cell grafts had the greatest amount of DA neuron survival and robustly induced recovery of motor deficits in hemiparkinsonian mice. Our data suggest that the Nurr1+ stage (middle stage) of neuronal differentiation is particularly suitable for grafting ESC-derived DA neurons. Moreover, global transcriptome analysis of progeny from each of the ESC reporter lines revealed expression of known midbrain DA neuron genes and also uncovered previously uncharacterized midbrain genes. These data demonstrate remarkable fate specificity of ESC-derived DA neurons and outline a sequential stage-specific ESC reporter line paradigm for in vivo gene discovery.
Polysialic acid (PSA), a large cell-surface carbohydrate that regulates cell interactions, is used during vertebrate development to promote precursor cell migration and axon path-finding. The ...induction of PSA expression in damaged adult CNS tissues could help them to rebuild by creating conditions permissive for architectural remodeling. This possibility has been explored in two contexts, the regeneration of axons and the recruitment of endogenous neural precursors to a lesion. Glial scars that form at CNS injury sites block axon regeneration. It has been found that transfection of scar astrocytes by a viral vector encoding polysialyltransferase leads to sustained expression of high levels of PSA. With this treatment, a substantial portion of severed corticospinal tract axon processes were able to grow through a spinal injury site. In the studies of precursor cell migration to a cortical lesion, it was found that induced PSA expression in a path extending from the subventricular zone to a lesion near the cortical surface increased recruitment of BrdU/nestin-positive cells along the path and into the injury site. These displaced precursors were able to differentiate in a regionally appropriate manner. These findings suggest that induced PSA expression can be used as a strategy for promoting tissue repair involving both replacement of cells and rebuilding of neural connections.
Molecular force measurements quantified the impact of polysialylation on the adhesive properties both of membrane-bound neural cell adhesion molecule (NCAM) and of other proteins on the same ...membrane. These results show quantitatively that NCAM polysialylation increases the range and magnitude of intermembrane repulsion. The repulsion is sufficient to overwhelm both homophilic NCAM and cadherin attraction at physiological ionic strength, and it abrogates the protein-mediated intermembrane adhesion. The steric repulsion is ionic strength dependent and decreases substantially at high monovalent salt concentrations with a concomitant increase in the intermembrane attraction. The magnitude of the repulsion also depends on the amount of polysialic acid (PSA) on the membranes, and the PSA-dependent attenuation of cadherin adhesion increases with increasing PSA-NCAM:cadherin ratios. These findings agree qualitatively with independent reports based on cell adhesion studies and reveal the likely molecular mechanism by which NCAM polysialylation regulates cell adhesion and intermembrane space.
Calcium-permeable neurotransmitter receptors are concentrated into structurally and biochemically isolated cellular compartments to localize calcium-mediated events during neurotransmission. The ...cytoplasmic membrane contains lipid microdomains called lipid rafts, which can gather into microscopically visible clusters, and thus the association of a particular protein with lipid rafts can result in its redistribution on the cell surface. The present study asks whether lipid rafts participate in the formation and maintenance of the calcium-permeable α7-subunit nicotinic acetylcholine receptor (α7nAChR) clusters found in somatic spines of ciliary neurons. Lipid rafts and α7nAChR become progressively colocalized within somatic spines during synaptogenesis. To determine whether these rafts are required for the maintenance of α7nAChR aggregates, cholesterol was extracted from dissociated ciliary neurons by treatment with methyl-β-cyclodextrin. This treatment caused the dispersion of lipid rafts and the redistribution of α7nAChR into small clusters over the cell surface, suggesting that the integrity of lipid rafts is required to maintain the receptor clustering. However, lipid raft dispersion also caused the depolymerization of the F-actin cytoskeleton, which can also tether the receptor at specific sites. To assess whether interaction between rafts and α7nAChR is independent of F-actin filaments, the lipid raft patches were stabilized with a combination of the cholera toxin B subunit (CTX), which specifically binds to the raft component ganglioside GM1, and an antibody against CTX. The stabilized rafts were then treated with latrunculin-A to depolymerize F-actin. Under these conditions, large patches of CTX persisted and were colocalized with α7nAChR, indicating that the aggregates of receptors can be maintained independently of the underlying F-actin cytoskeleton. Moreover, it was found that the α7nAChR is resistant to detergent extraction at 4°C and floats with the caveolin-containing lipid-rich fraction during density gradient centrifugation, properties that are consistent with a direct association between the receptor and the membrane microdomains.
Principal neurons in the adult cerebral cortex undergo synaptic, dendritic, and spine remodeling in response to different stimuli, and several reports have demonstrated that the polysialylated form ...of the neural cell adhesion molecule (PSA-NCAM) participates in these plastic processes. However, there is only limited information on the expression of this molecule on interneurons and on its role in the structural plasticity of these cells. We have found that PSA-NCAM is expressed in mature interneurons widely distributed in all the extension of the cerebral cortex and have excluded the expression of this molecule in most principal cells. Although PSA-NCAM expression is generally considered a marker of immature neurons, birth-dating analyses reveal that these interneurons do not have an adult or perinatal origin and that they are generated during embryonic development. PSA-NCAM expressing interneurons show reduced density of perisomatic and peridendritic puncta expressing different synaptic markers and receive less perisomatic synapses, when compared with interneurons lacking this molecule. Moreover, they have reduced dendritic arborization and spine density. These data indicate that PSA-NCAM expression is important for the connectivity of interneurons in the adult cerebral cortex and that its regulation may play an important role in the structural plasticity of inhibitory networks.
It is well established that peripheral nerves regenerate after injury. Therefore, incomplete functional recovery usually results from misguided axons rather than a lack of regeneration per se. ...Despite this knowledge very little is known about the molecular mechanisms regulating axon guidance during regeneration. In the developing neuromuscular system the neural cell adhesion molecule (NCAM) and its polysialic acid (PSA) moiety are essential for proper motor axon guidance. In this study we used a well established model of nerve transection and repair to examine whether NCAM and/or PSA promotes selective regeneration of femoral motor nerves in wild-type and NCAM (-/-) mice. We found that regenerating axons innervating the muscle pathway and, to a lesser extent, cutaneous axons in the sensory pathway reexpress high levels of PSA during the time when the cut axons are crossing the lesion site. Second, we found that motor neurons in wild-type mice preferentially reinnervated muscle pathways, whereas motor neurons in NCAM (-/-) mice reinnervated muscle and cutaneous pathways with equal preference. Preferential regeneration was not observed in wild-type mice when PSA was removed enzymatically from the regenerating nerve, indicating that this form of selective motor axon targeting requires PSA. Finally, transgenic mice were used to show that the number of collateral sprouts, their field of arborization, and the withdrawal of misprojected axons were all attenuated significantly in mice lacking PSA. These results indicate that regenerating motor axons must express polysialylated NCAM, which reduces axon-axon adhesion and enables motor neurons to reinnervate their appropriate muscle targets selectively.
The mossy fiber axons of both the developing and adult dentate gyrus express the highly polysialylated form of neural cell adhesion molecule (NCAM) as they innervate the proximal apical dendrites of ...pyramidal cells in the CA3 region of the hippocampus. The present study used polysialic acid (PSA)-deficient and NCAM mutant mice to evaluate the role of PSA in mossy fiber development. The results indicate that removal of PSA by either specific enzymatic degradation or mutation of the NCAM-180 isoform that carries PSA in the brain causes an aberrant and persistent innervation of the pyramidal cell layer by mossy fibers, including excessive collateral sprouting and/or defasciculation of these processes, as well as formation of ectopic mossy fiber synaptic boutons. These results are considered in terms of two possible effects of PSA removal: an increase in the number of mossy fibers that can grow into the pyramidal cell layer and an inhibition of process retraction by formation of stable junctions including synapses. As these defects on granule cells in the adult animal and PSA-positive granule cells continue to be produced in the mature brain, the present findings may be relevant to previous studies suggesting that PSA-NCAM function is required for long-term potentiation, long-term depression, and learning behaviors associated with hippocampus.
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