Versatile somatic gene transfer for modeling neurodegenerative diseases

Abstract

A growing variety of technical approaches allow control over the expression of selected genes in living organisms. The ability to deliver functional exogenous genes involved in neurodegenerative diseases has opened pathological processes to experimental analysis and targeted therapeutic development in rodent and primate preclinical models. Biological adaptability, economic animal use, and reduced model development costs complement improved control over spatial and temporal gene expression compared with conventional transgenic models. A review of viral vector studies, typically adeno-associated virus or lentivirus, for expression of three proteins that are central to major neurodegenerative diseases, will illustrate how this approach has powered new advances and opportunities in CNS disease research.

Fig. 1

AAV is a icosahedral capsid containing either a (+) or (−)-sense single-stranded DNA. Binding to cell-surface receptors (1) triggers endocytosis (2) and passage through acidic endosomes (3) where capsid proteins are hydrolyzed. Genomic DNA escapes (4) and enters the nucleus (5) where synthesis of the complementary strand (6) permits transcription of mRNA (7) that enters the cytoplasm (8) for translation (9)

Fig. 2

Electron microscopy for tau or alpha-synuclein in the rat, 4 months after gene transfer with either tau (a, b) or alpha-synuclein (ASN; c, d) AAV vectors. Tau filaments in the basal forebrain (a) or substantia nigra (b), labeled with 10 nm gold particles and an antibody specific for hyperphosphorylated tau, found only in cases of tau vector injections. c, d ASN filaments in a myelinated axon in the midbrain labeled with 10 nm gold particles and a human-specific ASN antibody, found only in cases of ASN vector injections. M, mitochondria. Reprinted from Klein et al. (2004, with permission

Fig. 3

Widespread expression of recombinant green fluorescent protein (GFP) in the rat hippocampus via adeno-associated virus (AAV) vector gene transfer. a, b GFP expressed from AAV9 on the ipsilateral, injected side and the contralateral, uninjected side. Contralateral GFP is largely due to projections from neurons on the injected side. The scarcity of GFP+ somata contralateral to injection argues against transduction subsequent to retrograde transport of vector. c GFP from AAV8 vector. Native GFP fluorescence in a–c, i.e., no immunofluorescent enhancement. d Hippocampal GFP visualized in whole AAV-GFP-injected brains (2 per vector group). Spread and intensity of gene transfer efficiency can be rapidly quantified with the technique. Bars: a, b = 540 μm; c = 104 μm. Reprinted from Klein et al. (2008) with permission