Two of the p38 inhibitors were successful. Many of the 74 compounds identified from the worm screen were then tested for their ability to improve the movement of zebrafish that lacked a gene called ryr1b that encodes one of the ryanodine receptors: these mutants are normally poor swimmers ( Hirata et al., 2007). Again the mutant worms reached adulthood, confirming that the results were likely due to p38 being inhibited and not due to off-target effects. used RNAi to knock-down orthologs of p38 in worms. To explore if off-target effects might be responsible for their results, Volpatti et al. Compounds that inhibited a protein kinase called p38 were over-represented in this sample. Initially, the screen revealed 278 compounds, but this number dropped to 74 after additional testing. The researchers screened 3700 compounds to identify those that permitted mutant worms that had been exposed to nemadipine-A to reach adulthood.
exposed the mutant animals to a DHP inhibitor called nemadipine-A that induces larval growth arrest in mutant animals but not in wild-type animals. To make the phenotype more robust, Volpatti et al. elegans has just one type of ryanodine receptor (humans have three) and mutants that lack unc-68, the gene for this receptor, move much less than wild-type worms ( Maryon et al., 1996). elegans, the zebrafish and mouse cells (see Figure 1B). The pipeline involved three species: the worm C. Now, in eLife, James Dowling (Hospital for Sick Children and the University of Toronto) and colleagues – including Jonathan Volpatti as first author – report how they have used a 'multi-species discovery pipeline' to identify two compounds that might be effective in treating these patients ( Volpatti et al., 2020). There are currently no effective therapies for any of these conditions. Mutations in this gene cause malignant hyperthermia (a rare severe reaction that can occur during anesthesia), central core disease and a range of other myopathies that can result in severe disabilities and early mortality. Both compounds were known to be inhibitors of a protein kinase called p38, and both were found to induce the release of calcium ions in mutant mouse muscle cells.Ĭongenital muscle diseases in humans can result from mutations in at least 20 genes, but mutations in the gene for ryanodine receptor 1 (RyR1) are the most common cause of such myopathies ( Jungbluth et al., 2018 Robinson et al., 2006).
Testing many of these 74 compounds on zebrafish revealed two compounds that improved the swimming performance of the mutant animals. elegans identified 74 compounds that enabled the mutants to grow. elegans (top), zebrafish (middle), and mouse myotubes (bottom). ( B) Drug screening was performed sequentially using null mutants in C. The DHP receptor is activated by action potentials (red spikes) travelling along a structure called a T-tubule (blue). The calcium ions cause structures on the thick filaments called myosin heads (not shown) to bind to the thin filaments and pull them so that the muscle contracts. Muscle tissue contains thick filaments (blue) and thin filaments (orange) arranged in units called sarcomeres. ( A) Ryanodine receptor 1 (RyR1 blue) is a channel protein that releases calcium ions (yellow) from the sarcoplasmic reticulum (SR) when activated by a dihydropyridine receptor (DHP green).
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