Lentiviral-mediated silencing of glial fibrillary acidic protein and vimentin promotes anatomical plasticity and functional recovery after spinal cord injury.

In spinal cord injury (SCI), absence of functional recovery and lack of spontaneous axonal regeneration are attributed, among other factors, to the formation of a glial scar that forms both physical and chemical barriers. The glial scar is composed mainly of reactive astrocytes that overexpress two intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin (VIM). To promote regeneration and sprouting of spared axons after spinal cord trauma and with the objective of translation to clinics, we designed an original in vivo gene transfer strategy to reduce glial scar formation after SCI, based on the RNA interference (RNAi)-mediated inhibition of GFAP and VIM. We first show that direct injection of lentiviral vectors expressing short hairpin RNA (shRNA) against GFAP and VIM in a mouse model of SCI allows efficient and specific targeting of astrocytes. We then demonstrate that the lentiviral-mediated and stable expression of shGFAP and shVIM leads to a strong reduction of astrogliosis, improves functional motor recovery, and promotes axonal regrowth and sprouting of spared axons. This study thus examplifies how the nonneuronal environment might be a major target within the lesioned central nervous system to promote axonal regeneration (and sprouting) and validates the use of lentiviral-mediated RNAi in SCI.

Development of NMDAR antagonists with reduced neurotoxic side effects: a study on GK11.

The NMDAR glutamate receptor subtype mediates various vital physiological neuronal functions. However, its excessive activation contributes to neuronal damage in a large variety of acute and chronic neurological disorders. NMDAR antagonists thus represent promising therapeutic tools that can counteract NMDARs' overactivation. Channel blockers are of special interest since they are use-dependent, thus being more potent at continuously activated NMDARs, as may be the case in pathological conditions. Nevertheless, it has been established that NMDAR antagonists, such as MK801, also have unacceptable neurotoxic effects. Presently only Memantine is considered a safe NMDAR antagonist and is used clinically. It has recently been speculated that antagonists that preferentially target extrasynaptic NMDARs would be less toxic. We previously demonstrated that the phencyclidine derivative GK11 preferentially inhibits extrasynaptic NMDARs. We thus anticipated that this compound would be safer than other known NMDAR antagonists. In this study we used whole-genome profiling of the rat cingulate cortex, a brain area that is particularly sensitive to NMDAR antagonists, to compare the potential adverse effects of GK11 and MK801. Our results showed that in contrast to GK11, the transcriptional profile of MK801 is characterized by a significant upregulation of inflammatory and stress-response genes, consistent with its high neurotoxicity. In addition, behavioural and immunohistochemical analyses confirmed marked inflammatory reactions (including astrogliosis and microglial activation) in MK801-treated, but not GK11-treated rats. Interestingly, we also showed that GK11 elicited less inflammation and neuronal damage, even when compared to Memantine, which like GK11, preferentially inhibits extrasynaptic NMDAR. As a whole, our study suggests that GK11 may be a more attractive therapeutic alternative in the treatment of CNS disorders characterized by the overactivation of glutamate receptors.