The R249Q hypertrophic cardiomyopathy myosin mutation decreases contractility in Drosophila by impeding force production

Abstract

Key pointsr Hypertrophic cardiomyopathy (HCM) is a genetic disease that causes thickening of the heart's ventricular walls and is a leading cause of sudden cardiac death. r HCM is caused by missense mutations in muscle proteins including myosin, but how these mutations alter muscle mechanical performance in largely unknown.r We investigated the disease mechanism for HCM myosin mutation R249Q by expressing it in the indirect flight muscle of Drosophila melanogaster and measuring alterations to muscle and flight performance.r Muscle mechanical analysis revealed R249Q decreased muscle power production due to slower muscle kinetics and decreased force production; force production was reduced because fewer mutant myosin cross-bridges were bound simultaneously to actin.r This work does not support the commonly proposed hypothesis that myosin HCM mutations increase muscle contractility, or causes a gain in function; instead, it suggests that for some myosin HCM mutations, hypertrophy is a compensation for decreased contractility.Abstract Hypertrophic cardiomyopathy (HCM) is an inherited disease that causes thickening of the heart's ventricular walls. A generally accepted hypothesis for this phenotype is that myosin heavy chain HCM mutations increase muscle contractility. To test this hypothesis, we expressed an HCM myosin mutation, R249Q, in Drosophila indirect flight muscle (IFM) and assessed myofibril structure, skinned fibre mechanical properties, and flight ability. Mechanics experiments were performed on fibres dissected from 2-h-old adult flies, prior to degradation of IFM myofilament structure, which started at 2 days old and increased with age. Homozygous and heterozygous R249Q fibres showed decreased maximum power generation by 67% and 44%, respectively. Kaylyn Bell received her Bachelor's Degree in Biochemistry and Biophysics at Rensselaer Polytechnic Institute. She is continuing her research in biophysics at RPI with Dr. Douglas Swank for her PhD. Her work uses the Drosophila model system to characterize the muscle mechanical properties of myosin mutations that cause the heart disease hypertrophic cardiomyopathy, and the skeletal muscle disease Freeman-Sheldon Syndrome. She is also investigating a possible myosin based mechanism behind the muscle phenomenon known as stretch activation. K. M. Bell and W. A. Kronert contributed equally to this work. J Physiol 597.9 Decreases in force and work and slower overall muscle kinetics caused homozygous fibres to produce less power. While heterozygous fibres showed no overall slowing of muscle kinetics, active force and work production dropped by 68% and 47%, respectively, which hindered power production. The muscle apparent rate constant 2πb decreased 33% for homozygous but increased for heterozygous fibres. The apparent rate constant 2πc was greater for homozygous fibres. This indicates that R249Q myosin is slowing attachment while speeding up detachment from actin, resulting in less time bound. Decreased IFM power output caused 43% and 33% decreases in Drosophila ...

Myosin motor domains carrying mutations implicated in early or late onset hypertrophic cardiomyopathy have similar properties

“…Curiously, 1 of the mutations examined here shares these properties; the early onset P710R, suggesting some overlap between the groupings. Intersection of molecular phenotypes among different cardiomyopathies has been observed in studies of thin filament mutations and experiments performed in Drosophila (31,32).…”

Drosophila Heart as a Model for Cardiac Development and Diseases

“…The Drosophila model has helped to identify novel genes and pathways involved in arrhythmias [47], atrial fibrillation [80], and channelopathies [81]. It has also been applied to modeling cardiac aging [51], and cardiomyopathies including dilated [82][83][84][85][86][87], hypertrophic [88][89][90], and restrictive cardiomyopathy [82,91,92], in which heart failure could occur [43]. Finally, the developed Drosophila models of muscular diseases with cardiac symptoms such as DM1 have been instrumental in dissecting the gene deregulations underlying heart defects and in identifying new therapeutic strategies.…”

The R369 Myosin Residue within Loop 4 Is Critical for Actin Binding and Muscle Function in Drosophila

“…Mutant and control females were maintained at 25 °C, acclimated to 22–23 °C for 1 h, and tested for flight ability at 22–23 °C as previously reported [ 11 , 12 , 33 , 40 ]. Each fly was released individually into a Plexiglas box illuminated at the top, and scored for its flight trajectory toward a light source, where upward flight (U) = 6, horizontal flight (H) = 4, downward flight (D) = 2, or no flight (N) = 0 [ 41 ].…”