Heterozygous MH knock-in mice model Human MH susceptibility

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The long-term goal of Project 1 is to define the mechanisms responsible for the ryanodine receptor (RyR1) myopathies, malignant hyperthermia and central core disease (MH/CCD). Our immediate objectives are to create suitable models for human disease in mice and use them to study how mutations of RyR1 alter intracellular Ca2+ homeostasis and to create a noninvasive diagnostic test for MH that has a high degree of specificity and sensitivity. HYPOTHESIS I: Heterozygous MH "knock-in" mice model Human MH susceptibility. A 1.1. To create a "hot-spot" region 2 MH 'knock in' mouse line (RyR1 G2434R). In addition to our recently created R163C (region 1) and T4826I (region 3) RyR1 MHS mice. A 1.2.To determine the relationship between the clinical MH phenotype and myoplasmic resting free calcium ([Ca2+],) in vivo, with contracture properties in vitro for each heterozygous MH/CCD mouse. A1.3 To determine the relationship between IVCT and myoplasmic resting [Ca2+] in myotubes from human biopsy samples. A1.4 To determine if genetic background can rescue the birth lethal phenotype seen in homozygous MH/CCD mice. A1.5 To determine if genetic background will lower or raise [Ca2+]i or sensitivity to halothane in heterozygous MH/CCD mice. HYPOTHESIS II: Mutations responsible for human MH/CCD increase passive RyR1 "leak" and alter the dynamics of EC coupling by enhancing ECCE and SOCE. A 2.1 To analyze heterozygous and homozygous MH/CCD myotubes for abnormalities in EC coupling and two forms of Ca2+ entry, ECCE and SOCE. A 2.2 To establish how halothane and dantrolene enhance and diminish aberrant Ca2+ signaling in MH/CCD myotubes. A 2.3 To validate murine MH/CCD myotube model results with myotubes obtained from humans with an analogous mutation. Hypothesis III: The "Funnel" approach can be used to create a non-invasive screening test for MH that has both a high degree of specificity and a high degree of sensitivity. A 3.1. We will analyze whole blood transcriptional profiles from patients with known MHS RyR1 mutations and use the Funnel approach to select a set of predictive markers to be used for future MHS screening.