Authors :
Presenting Author: Christian Wolff, PhD – UCB
Jérôme Clasadonte, PhD – UCB
Yana Van den herrewegen, PhD – UCB
Catherine Thyssen, BS – UCB
Colette Chaussee, Technician – UCB
Marie Tripoli, BS – UCB
Brice Mullier, BS – UCB
Ana Rita Gomez, PhD – UCB
Catherine Vandenplas, BS – UCB
Amandine Cornil, PhD – UCB
Geroges Mairet-Coello, PhD – UCB
Maryia Semkova, PhD – UCB
Marcella Widya, PhD – UCB
Hazel Poyntz-Farminer, PhD – UCB
Denis Goosen, PhD – UCB
Rocio Lledo-Garcia, PhD – UCB
Peter Hall, PhD – UCB
Miranda Cornet, PhD – UCB
Doug Blanton, PhD – UCB
Onur Kas, PhD – UCB
Brittany Vallette, PhD – UCB
Natalia Rodriguez, PhD – UCB
Rationale:
STXBP1 disorders are linked to a loss of function of the syntaxin-binding-protein-1 (STXBP1) and are associated with severe neuronal development delay, intellectual disability and seizures. There are currently not efficacious treatments for the disease and we explored the potential of a gene therapy (GT) approach to modulate STXBP1 haploinsufficiency in a relevant mouse model. Multiple splice variants have been reported for STXBP1, including a long and a short isoform generated by the splicing of the last exon. These splice variants show regional brain tissue distribution and cellular specificity but the functional roles of these variants have not yet been elucidated. In this study we compared the overexpression of the long and short splice variants of STXBP1 and evaluated their impact on disease symptoms.
Methods:
STXBP1 heterozygous (HET) KO mice have been licensed from the University of Amsterdam. AAV9 constructs encode the long and short hSTXBP1-HA tag gene under the control of a neuronal promoter. Animals have been injected at post-natal day 1 (PND1) using intra cerebroventricular administration (ICV) with either vehicle or AAV treatment. EEG recordings were performed in group housing video-EEG wireless telemetry platform (24 hours/day). A battery of behavioral tests was performed to evaluate motor and cognitive performances. Biochemical analysis of transgene expression was performed in prefrontal cortex tissue using qPCR, Western Blot and LC-MS. Immunohistochemistry analysis using HA-tag antibodies was performed on fixed sagittal brain slices.Results:
STXBP1 HET mice have reduced mSTXBP1 protein levels and present a robust disease phenotype with reduced body weight, frequent absence seizures, motor and cognitive deficits. AAV GT administered at PND1 by ICV translates into increased levels of total STXBP1 in the prefrontal cortex and to a large brain distribution of the HA-STXBP1 protein. GT does not affect basal mSTXBP1 expression and both isoforms are efficiently overexpressed up to 6 months and leading to a significant reduction of ~75% of spike wave discharges. No convulsive seizures are observed during that period in treated mice. Both variants produce a significant reduction in hindlimb clasping and “moonwalking” but only the long variant was able to rescue body weight, fear conditioning, hyperactivity in the open field test and the latency to fall in the wire hanging test. The short isoform showed an opposite effect in the open field with a reduced locomotor activity compared to WT mice.
Conclusions:
An AAV GT approach using the ICV administration of the long hSTXBP1 construct at post natal day 1 leads to a wide brain distribution of the transgene protein and to a global rescue of the disease symptoms. The overexpression of the short STXBP1 isoform shows a rescue of the total STXBP1 protein levels but with lower efficacy across disease symptoms and with a potential for reduced locomotor activity in STXBP1 KO mice.
Funding: UCB sponsored study