A cross-species discovery and validation study of microRNA dysregulation in Angelman syndrome

Thesis

Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by the lack of functional UBE3A protein in neurons. Several therapeutic approaches are now in preclinical and clinical development, with three antisense oligonucleotides targeting the UBE3A-antisense transcript (UBE3A-ATS) currently advancing to phase III trials. AS is thus emerging as a leading example for drug development of disease-modifying treatments in other neurodevelopmental disorders.

To support clinical trial readiness, I designed, set up, and led the operational management of the Oxford AS Natural History Study (NHS). This study aimed to develop ‘fit-for-purpose’ clinical outcome assessments (COAs). It included novel COAs, such as the Observer-Reported Communication Ability (ORCA), specifically developed for AS, and the wearable-derived digital stride velocity 95th centile (SV95C). Through protocol sharing, the Liège AS NHS was also established, enabling data pooling. The combined dataset was used to model trajectories across various COAs and to estimate minimal clinically important differences (MCIDs) using an FDA-adherent, anchor-based method.

The plasma samples collected in the Oxford AS NHS are a valuable resource for identifying potential readily available biomarkers. MicroRNAs (miRNAs) are particularly promising due to their ability, or that of their carriers, to cross the blood-brain barrier. I employed plasma samples from the Oxford AS NHS cohort and brain tissue from a validated AS rat model, as well as next-generation sequencing, to investigate miRNA dysregulation in AS. Notably, miR-143-3p and miR-143-5p were both significantly upregulated across patient genotype-based subgroups, and their levels correlated with phenotypic severity, supporting their potential use as biomarkers.

Additionally, miR-92a-3p was consistently upregulated in both human plasma and animal brain tissue samples. Using immortalised cell lines and patient iPSC-derived neurons, I observed that miR-92a-3p can modulate UBE3A expression by regulating the levels of UBE3A-ATS but not of other upstream portions of the small nucleolar RNA host gene 14 (SNHG14). I hypothesized a feedback loop in which miR-92a-3p, via a non-canonical miRNA function, may act as a molecular ‘brake’ on UBE3A-ATS under physiological conditions and may serve as a compensatory mechanism which increases UBE3A expression in AS.

Authors: Markati, T

• DOI: 10.5287/ora-j2yzqeoxk
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Angelman syndrome; microRNA; UBE3A; UBE3A-ATS; biomarker discovery; natural history study; clinical outcome assessments; iPSC-derived neurons
• Subjects: Genetics; Neurosciences; RNA