Mapping the Structural Determinants Required for AAVrh.10 Transport across the Blood-Brain Barrier

Blake H. Albright, Claire M. Storey, Giridhar Murlidharan, Ruth M. Castellanos Rivera, Garrett E. Berry, Victoria J. Madigan, Aravind Asokan; Molecular Therapy, Volume 26, Issue 2, p510–523, 7 February 2018 DOI: 10.1016/j.ymthe.2017.10.017

Effective gene delivery to the CNS by intravenously administered adeno-associated virus (AAV) vectors requires crossing the blood-brain barrier (BBB). To achieve therapeutic CNS transgene expression, high systemic vector doses are often required, which poses challenges such as scale-up costs and dose-dependent hepatotoxicity. To improve the specificity and efficiency of CNS gene transfer, a better understanding of the structural features that enable AAV transit across the BBB is needed. We generated a combinatorial domain swap library using AAV1, a serotype that does not traverse the vasculature, and AAVrh.10, which crosses the BBB in mice. We then screened individual variants by phylogenetic and structural analyses and subsequently conducted systemic characterization in mice. Using this approach, we identified key clusters of residues on the AAVrh.10 capsid that enabled transport across the brain vasculature and widespread neuronal transduction in mice. Through rational design, we mapped a minimal footprint from AAVrh.10, which, when grafted onto AAV1, confers the aforementioned CNS phenotype while diminishing vascular and hepatic transduction through an unknown mechanism. Functional mapping of this capsid surface footprint provides a roadmap for engineering synthetic AAV capsids for efficient CNS gene transfer with an improved safety profile.

Hepcidin, an emerging and important player in brain iron homeostasis

Driton Vela. Journal of Translational Medicine 201816:25 doi:10.1186/s12967-018-1399-5

Iron dysregulation has been observed consistently in different organs in Friedreich ataxia (FA). This disease affects CNS by causing neurodegenerative damages in dentate nuclei of the cerebellum, dorsal root ganglia, but also in cerebrum, thalamus and other structures. FA is caused by a defective frataxin, which main functions include involvement in iron-sulfur cluster formation and in iron delivery to ferrochelatase. Although some observations did find iron accumulation in dentate nuclei in FA patients, other studies have revealed a pattern of iron redistribution, rather than iron accumulation in FA. Studies suggest that iron dysregulation in FA is not needed for neurodegeneration to occur, while animal models reveal tissue-specific damages due to frataxin deficiency. These differences are related with levels of frataxin expression, where most of the damage is observed in tissues with higher expression of frataxin, such as the heart and dorsal root ganglia. In the heart, inflammatory infiltrate produces hepcidin and has been proposed as one of the pathogenic mechanisms of heart damage in FA. Frataxin deficiency in animal models can cause a strong inflammatory reaction in Schwann cells, which are known to enwrap neurons of dorsal root ganglia. These neurons are frequently affected in FA and are characterized with iron dysregulation and inappropriate myelination. But, hepcidin expression in these cells has not been studied in models of FA, therefore it is not known what role, if any, does hepcidin have in the pathophysiology of neurodegeneration in FA.