Abstract
We report the pattern of transgene expression across brain regions after intrathecal delivery of adeno-associated virus serotype 5 (AAV5). Labeling in hindbrain appeared to be primarily neuronal, and was detected in sensory nuclei of medulla, pontine nuclei, and all layers of cerebellar cortex. Expression in midbrain was minimal, and generally limited to isolated neurons and astrocytes in the cerebral peduncles. GFP immunoreactivity (-ir) in thalamus was most prominent in medial geniculate nucleus, and otherwise limited to posterior nuclei of the dorsal and lateral margins. Labeling was also observed in neurons and astrocytes of the hippocampal formation and amygdaloid complex. In the hippocampal formation, GFP-ir was found in neuronal cell bodies of the rostral ventral portion, but was largely restricted to fiber-like staining in the molecular layer of dentate gyrus and stratum lacunosum-moleculare of the rostral dorsal region. GFP-ir was seen in neurons and astroglia throughout caudal cortex, whereas in rostral regions of neocortex it was limited to isolated neurons and non-neuronal cells. Labeling was also present in olfactory bulb. These results demonstrate that intrathecal delivery of AAV5 vector leads to transgene expression in discrete CNS regions throughout the rostro-caudal extent of the neuraxis. A caudal-to-rostral gradient of decreasing GFP-ir was present in choroid plexus and Purkinje cells, suggesting that spread of virus through cerebrospinal fluid plays a role in the resulting transduction pattern. Other factors contributing to the observed expression pattern likely include variations in cell-surface receptors and inter-parenchymal space.
Highlights
In recent years a growing body of evidence has indicated that adeno-associated virus (AAV) is a useful vector for delivery of therapeutic genes to the central nervous system (CNS)
Six weeks after intrathecal administration of associated virus serotype 5 (AAV5), GFP expression was observed in discrete areas of the central nervous system (CNS), while intravenous delivery of an equivalent total dose of vector resulted in no detectable expression in the CNS
To address the immune status of the brains of AAV treated animals we performed labeling for the microglial marker CD68, and found no qualitative difference in CD68 labeling between naïve and AAV5 treated animals
Summary
In recent years a growing body of evidence has indicated that adeno-associated virus (AAV) is a useful vector for delivery of therapeutic genes to the central nervous system (CNS). Direct injection of AAV vectors into a specific CNS nucleus can result in a high level of gene expression in that nucleus, as well as physically adjacent and functionally connected areas (Fu et al, 2002; Ciesielska et al, 2011; White et al, 2011). This method carries the drawback of tissue damage that is potentially both detrimental and irreparable. Methods to improve vector distribution upon cisternal administration, such as pretreatment with mannitol delivered intravenously or removal of some CSF followed by a large injection volume, have shown the potential for an enhanced pattern of gene expression spanning several CNS regions (Fu et al, 2003; Iwamoto et al, 2009)
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