Cortical overexpression of neuronal calcium sensor-1 induces functional plasticity in spinal cord following unilateral pyramidal tract injury in rat

Corticospinal tract transduction: a comparison of seven adeno-associated viral vector serotypes and a non-integrating lentiviral vector

The corticospinal tract (CST) is extensively used as a model system for assessing potential therapies to enhance neuronal regeneration and functional recovery following spinal cord injury (SCI). However, efficient transduction of the CST is challenging and remains to be optimised. Recombinant adeno-associated viral (AAV) vectors and integration-deficient lentiviral vectors are promising therapeutic delivery systems for gene therapy to the central nervous system (CNS). In the present study the cellular tropism and transduction efficiency of seven AAV vector serotypes (AAV1, 2, 3, 4, 5, 6, 8) and an integration-deficient lentiviral vector were assessed for their ability to transduce corticospinal neurons (CSNs) following intracortical injection. AAV1 was identified as the optimal serotype for transducing cortical and CSNs with green fluorescent protein (GFP) expression detectable in fibres projecting through the dorsal CST (dCST) of the cervical spinal cord. In contrast, AAV3 and AAV4 demonstrated a low efficacy for transducing CNS cells and AAV8 presented a potential tropism for oligodendrocytes. Furthermore, it was shown that neither AAV nor lentiviral vectors generate a significant microglial response. The identification of AAV1 as the optimal serotype for transducing CSNs should facilitate the design of future gene therapy strategies targeting the CST for the treatment of SCI.

Gene therapy approaches to enhancing plasticity and regeneration after spinal cord injury

During the past decades, new insights into mechanisms that limit plasticity and functional recovery after spinal cord injury have spurred the development of novel approaches to enhance axonal regeneration and rearrangement of spared circuitry. Gene therapy may provide one means to address mechanisms that underlie the insufficient regenerative response of injured neurons and can also be used to identify factors important for axonal growth. Several genetic approaches aimed to modulate the environment of injured axons, for example by localized expression of growth factors, to enhance axonal sprouting and regeneration and to guide regenerating axons towards their target have been described. In addition, genetic modification of injured neurons via intraparenchymal injection, or via retrograde transport of viral vectors has been used to manipulate the intrinsic growth capacity of injured neurons. In this review we will summarize some of the progress and limitations of cell transplantation and gene therapy to enhance axonal bridging and regeneration across a lesion site, and to maximize the function, collateral sprouting and connectivity of spared axonal systems.

Neuronal calcium sensor-1 regulation of calcium channels, secretion, and neuronal outgrowth

Calcium (Ca(2+)) is an important intracellular messenger underlying cell physiology. Ca(2+) channels are the main entry route for Ca(2+) into excitable cells, and regulate processes such as neurotransmitter release and neuronal outgrowth. Neuronal Calcium Sensor-1 (NCS-1) is a member of the Calmodulin superfamily of EF-hand Ca(2+) sensing proteins residing in the subfamily of NCS proteins. NCS-1 was originally discovered in Drosophila as an overexpression mutant (Frequenin), having an increased frequency of Ca(2+)-evoked neurotransmission. NCS-1 is N-terminally myristoylated, can bind intracellular membranes, and has a Ca(2+) affinity of 0.3 μM. Over 10 years ago it was discovered that NCS-1 overexpression enhances Ca(2+)-evoked secretion in bovine adrenal chromaffin cells. The mechanism was unclear, but there was no apparent direct effect on the exocytotic machinery. It was revealed, again in chromaffin cells, that NCS-1 regulates voltage-gated Ca(2+) channels (Cavs) in G-Protein Coupled Receptor (GPCR) signaling pathways. This work in chromaffin cells highlighted NCS-1 as an important modulator of neurotransmission. NCS-1 has since been shown to regulate and/or directly interact with many proteins including Cavs (P/Q, N, and L), TRPC1/5 channels, GPCRs, IP3R, and PI4 kinase type IIIβ. NCS-1 also affects neuronal outgrowth having roles in learning and memory affecting both short- and long-term synaptic plasticity. It is not known if NCS-1 affects neurotransmission and synaptic plasticity via its effect on PIP2 levels, and/or via a direct interaction with Ca(2+) channels or their signaling complexes. This review gives a historical account of NCS-1 function, examining contributions from chromaffin cells, PC12 cells and other models, to describe how NCS-1's regulation of Ca(2+) channels allows it to exert its physiological effects.

The human G93A-SOD1 mutation in a pre-symptomatic rat model of amyotrophic lateral sclerosis increases the vulnerability to a mild spinal cord compression

Background

Traumatic injuries can undermine neurological functions and act as risk factors for the development of irreversible and fatal neurodegenerative disorders like amyotrophic lateral sclerosis (ALS). In this study, we have investigated how a mutation of the superoxide dismutase 1 (SOD1) gene, linked to the development of ALS, modifies the acute response to a gentle mechanical compression of the spinal cord. In a 7-day post-injury time period, we have performed a comparative ontological analysis of the gene expression profiles of injured spinal cords obtained from pre-symptomatic rats over-expressing the G93A-SOD1 gene mutation and from wild type (WT) littermates.

Results

The steady post-injury functional recovery observed in WT rats was accompanied by the early activation at the epicenter of injury of several growth-promoting signals and by the down-regulation of intermediate neurofilaments and of genes involved in the regulation of ion currents at the 7 day post-injury time point. The poor functional recovery observed in G93A-SOD1 transgenic animals was accompanied by the induction of fewer pro-survival signals, by an early activation of inflammatory markers, of several pro-apoptotic genes involved in cytochrome-C release and by the persistent up-regulation of the heavy neurofilament subunits and of genes involved in membrane excitability. These molecular changes occurred along with a pronounced atrophy of spinal cord motor neurones in the G93A-SOD1 rats compared to WT littermates after compression injury.

Conclusions

In an experimental paradigm of mild mechanical trauma which causes no major tissue damage, the G93A-SOD1 gene mutation alters the balance between pro-apoptotic and pro-survival molecular signals in the spinal cord tissue from the pre-symptomatic rat, leading to a premature activation of molecular pathways implicated in the natural development of ALS.

Acute adaptive responses of central sensorimotor neurons after spinal cord injury

Spinal cord injury (SCI) can be a lifelong, devastating condition for both the patient and the caregiver, with a daunting incidence rate. Still, there are only limited available therapies and the effectiveness of precise regeneration within the central nervous system is minimal throughout postnatal life. Recently, improved regeneration after SCI was seen by manipulating a pathway in sensorimotor neocortices that is involved in phosphorylation of an RNA binding protein (RBP) required for mRNA translation, the Eukaryotic translation initiation factor 4E (eIF4E). Our data identifies rapid molecular alterations of eIF4E in the sensorimotor neocortices 1 and 3 days after a lateral hemisection SCI, used as a model for Brown-Séquard syndrome. The function of an RBP depends on both its distribution sites within the cell and its phosphorylation states. Indeed, we found both to be affected after SCI. There was a distinct subcellular redistribution of eIF4E and phosphorylated-eIF4E was reduced, indicating that the eIF4E’s translation was disrupted. Upon identification and analysis of the mRNA cargo of eIF4E in uninjured sensorimotor neocortices, we found that eIF4E binds both Importin-13 (Ipo13) and Parvalbumin (Pv) mRNAs, indicating a role in their translation. Remarkably, eIF4E’s interaction with both Ipo13 and Pv mRNAs was disrupted 1 and 3 days after SCI, despite preservation of total Ipo13 and Pv mRNA levels. Finally, we detected a selective loss of expression of both IPO13 and PV proteins in projection neurons of sensorimotor neocortices, as well as their disrupted dendritic polarity. Since IPO13 is predominantly expressed in neocortical projection neurons and PV in a subset of neocortical interneurons, these data suggest a strong acute effect of SCI on neocortical microcircuitry. Taken together, these data indicate that neocortical eIF4E and a subset of mRNAs may be rapidly recruited to translational machinery after SCI to promote adaptive regeneration response of sensorimotor neurons.