Functional applications of novel Semliki Forest virus vectors are limited by vector toxicity in cultures of primary neurons in vitro and in the substantia nigra in vivo

Corpus callosum: a favorable target for rSFV-mediated gene transfer to rat brain with broad and efficient expression

Recombinant Semliki Forest virus (rSFV), as a new kind of neurotropic vector system, has great potential of gene therapy for stroke. However, very little is known about its transduction characteristics in cerebral cortex or corpus callosum (CC) in vivo, which are common targets for gene transfer in experimental stroke therapy. Here, we investigate and compare rSFV-mediated gene expression at above two brain regions in rat; 2.0 x 10(7) IU of rSFV encoding green fluorescent protein (rSFV-GFP) was locally injected into CC or cerebral cortex in two groups. At 36 h following injection, the number of GFP-positive cells, GFP distribution volume, and GFP expression level were examined in the rat brain of each group using continuous frozen sections and enzyme-linked immunosorbent assay. rSFV vector displayed noticeably different transduction patterns in CC and cerebral cortex in vivo. CC injection of vector increased GFP-positive cell number by 802%, GFP transduction volume by 958%, and GFP expression level by 508% compared with cortical injection (all P < 0.01). We concluded that rSFV CC delivery significantly enhances transduction efficiency in rat brain with its ability to achieve transgene extensive transduction and abundant expression, and CC may be a favorable target for improving rSFV-based gene delivery efficiency to brain.

beta-amyloid precursor protein can be transported independent of any sorting signal to the axonal and dendritic compartment

In neurons, amyloid precursor protein (APP) is localized to the dendritic and axonal compartment. Changes in subcellular localization affect secretase cleavage of APP, altering the generation of Abeta, and presumably also its pathogenic features. It was reported that APP is sorted initially to the axon and transcytosed subsequently to the somatodendritic compartment. This may be carried out by a recessive dendritic sorting signal in the cytoplasmic C-terminus, possibly the tyrosine based basolateral sorting signal (BaSS), and an axonal sorting motif within the extracellular juxtamembraneous domain. We investigated whether the C- or N-terminal domain of APP contains an independent dendritic or axonal sorting signal. We generated different APP deletion mutants, and produced chimeric proteins of APP and a non-related Type I transmembrane protein. Quantitative immunocytochemical analyses of transfected primary neurons showed that similar amounts of all APP mutants, lacking either the N- or C-terminus, were transported to the axonal and dendritic compartment. Investigations of the chimeric proteins showed that neither the N- nor the C-terminus of APP functions as independent sorting signal, whereas another tyrosine based dendritic sorting signal was sufficient to prevent axonal entry of APP. This data shows that, under steady state conditions, Heterologously expressed APP is transported equally to axons and dendrites irrespective of any putative sorting signal in its N- or C-terminus. This shows that APP can enter the axon in absence of the initial axonal sorting motif, indicating the existence of an alternative pathway allowing axonal entry of APP.

Membrane-permeable Bcl-xL prevents MPTP-induced dopaminergic neuronal loss in the substantia nigra

The anti-apoptotic Bcl-xL is a promising agent to prevent neurodegeneration in Parkinson's disease, which is characterized by a demise of dopaminergic neurons. We linked Bcl-xL to a peptide that allows its delivery across biological membranes and the blood-brain barrier. We tested the fusion protein in two models of Parkinson's Disease. Cell-permeable Bcl-xL protected neuroblastoma cells from the selective neurotoxin 1-methyl-4-phenylpyridinium. Furthermore, its systemic application in aged mice protected dopaminergic neurons following administration of MPTP as revealed by counting of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra pars compacta. Hence, we present that a cell-permeable form of an anti-apoptotic protein can be delivered to CNS neurons through its systemic application, and we provide the proof that the delivery of this protein to the CNS neurons effectively prevents neuronal cell death in models of chronic neurodegenerative diseases.

Evaluation of epitope tags for protein detection after in vivo CNS gene transfer

Functional characterization of disease-related proteins, their splice variants and dominant negative mutants in the context of complex CNS tissues such as brain and retina is frequently assessed by in vivo gene transfer. For correct interpretation of results it is imperative that the protein under investigation is unambiguously detected in the transduced cell types and can be distinguished from any endogenously expressed physiological variants. Therefore the first systematic evaluation of epitope tags used to trace ectopically expressed proteins in the central nervous system is presented here. Substantial differences in the performances of various epitope tag-antibody combinations with respect to sensitivity, specificity and influence of the epitope tag on the fusion protein are elucidated. Epitope tags already established for protein detection in vitro and to some extent in vivo (c-Myc, HA and FLAG tags) were immunohistochemically detected with high sensitivity. However, detection of these tags revealed problems with background staining and we also document structural and functional influence of the tags on the fusion protein. In order to prevent such unwanted side-effects, epitope tags which have not yet been used for in vivo applications (IRS, EE and AU1 tags) were characterized in brain, retina and cultured neurons. While use of the IRS and EE tags was hindered by low sensitivity or specificity, optimal results were obtained with the AU1 epitope, which may develop into a standard tool for detection of ectopic protein expression in the central nervous system.

CNS gene therapy applications of the Semliki Forest virus 1 vector are limited by neurotoxicity

The Semliki Forest virus (SFV) 1 vector system is highly efficient at gene transduction in a broad range of host cells, including neurons. To determine the potential of SFV1-based vectors to mediate gene expression in substantia nigra neurons, we inoculated d1EGFP-expressing SFV virus-like particles stereotaxically into the mouse brain. This system selectively and extensively mediated gene expression in dopaminergic neurons of the substantia nigra. Continual reporter gene expression was evident in neuronal cell bodies for up to 3 weeks postinoculation and d1EGFP-positive neuronal processes were apparent for 12 weeks. There was no evidence of an apoptotic response to infection, but with time cell degeneration and an axonopathy, indicative of neuronal loss, were increasingly apparent. This system has potential for experimental studies requiring efficient transient gene transduction of mouse CNS neurons. The current SFV1 vector system is, however, limited in its potential for CNS gene therapy by neurotoxicity.