Abstract
Loss of the maternal UBE3A allele causes Angelman syndrome (AS), a debilitating neurodevelopmental disorder. Here, we devised an AS treatment strategy based on reinstating dual-isoform expression of human UBE3A (hUBE3A) in the developing brain. Kozak sequence engineering of our codon-optimized vector (hUBE3Aopt) enabled translation of both short and long hUBE3A protein isoforms at a near-endogenous 3:1 (short/long) ratio, a feature that could help to support optimal therapeutic outcomes. To model widespread brain delivery and early postnatal onset of hUBE3A expression, we packaged the hUBE3Aopt vector into PHP.B capsids and performed intracerebroventricular injections in neonates. This treatment significantly improved motor learning and innate behaviors in AS mice, and it rendered them resilient to epileptogenesis and associated hippocampal neuropathologies induced by seizure kindling. hUBE3A overexpression occurred frequently in the hippocampus but was uncommon in the neocortex and other major brain structures; furthermore, it did not correlate with behavioral performance. Our results demonstrate the feasibility, tolerability, and therapeutic potential for dual-isoform hUBE3A gene transfer in the treatment of AS.
Highlights
Angelman syndrome (AS) is a neurodevelopmental disorder characterized by severe developmental delay, motor dysfunction, absence of speech, and highly penetrant epilepsy [1, 2]
We revealed 3 remarkably well-conserved UBE3A expression features across species: (a) highly consistent ratios of short to long isoform expression during brain development; (b) dynamic subcellular localization in neurons, whereby UBE3A becomes increasingly nuclear as maturation progresses; and (c) ubiquitous neuronal expression with early developmental onset
These parameters guided our design of a potentially novel dual-isoform hUBE3Aopt vector, in which we manipulated Kozak sequence strengths to bias expression in favor of short UBE3A, successfully recapitulating ~3:1 short/long protein isoform representation. human UBE3A (hUBE3A) gene transfer shares with paternal UBE3A unsilencing approaches [15,16,17] the capacity to match nuanced aspects of endogenous isoform expression, which may be necessary to reinstate the full repertoire of neuronal UBE3A functions resident to specific subcellular compartments
Summary
Angelman syndrome (AS) is a neurodevelopmental disorder characterized by severe developmental delay, motor dysfunction, absence of speech, and highly penetrant epilepsy [1, 2] While symptoms such as epilepsy can be managed, albeit with considerable difficulty [3], specific treatments for AS are lacking. Rendered devoid of critical UBE3A functions, both neurons derived from patients with AS and neurons in AS model mice exhibit severe deficits in morphology, electrophysiology, and synaptic function and plasticity [11, 12]. These deficits are compounded over the course of neurodevelopment, across neural circuits, to yield the neurological phenotypes that typify AS
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