New drugs that stabilise motor axons (UK Spinal Muscular Atrophy Consortium)

The primary cause of spinal muscular atrophy (SMA) is a lack of functional SMN protein, which, in turn influences the splicing and expression levels of several dozen downstream genes. Recent therapeutic approaches to enhance the amount of SMN have been successful in improving development and health of young patients with the most severe form of SMA, SMA Type 1. However, it is clear that additional therapies may be needed to preserve life-long health of motor neurons and other organs affected by SMN. Here, we aim to identify and develope novel targets for SMA therapy through drug screening in zebrafish models

We aim to find small molecule drugs that rescue fish motor axon defects caused by SMN downstream gene chondrolectin (chodl) to provide leads for mammalian testing of potential therapeutics for use in conjunction with SMN1 read-through approaches. Our hypothesis is that the phenotypes observed in fish are an indicator of motor axon stability and hence, their health.

Chodl is mis-spliced downstream of SMN1 loss and chodl over-expression partially rescues SMN deficiency in in zebrafish (Sleigh, 2014). Knock down of chodl in zebrafish leads to a highly penetrant shortening of axons (Zhong, 2012). Drugs that rescue axon length would substitute chodl function and will be taken into mammalian models (iPS cells and mouse SMA models with Talbot and Gillingwater respectively). We have generated a CRISPR/cas9 Chodl mutant, leading to a phenotype (axons shorter than in controls) with 95% penetrance (Hannah Smith). Mutant embryos will be arrayed into 96 well plates, loaded with candidate drugs and automatically scanned in the new VAST zebrafish screening setup (National Zebrafish Screening Facility, funded by BBSRC). Axon growth in embryos will be quantified as % axons of wild type length for 8 motor roots/embryo. Using 10 and 25 µM in duplicate to take into account variability and concentration dependence, as well as the speed of development of the zebrafish allows us to test roughly 45 drugs per day. Hits will be further tested in mutant mice, before being assessed for use in potential clinical trials.