Genetic Variation Results in Differing Age-Related Drosophila Myocardial Stiffness

Abstract

Rapid aging of Drosophila melanogaster makes it suitable for studying age-related mechanical changes such as impaired heart function. The Drosophila heart consists of a cardiomyocyte tube bonded to a thin ventral muscle layer. It has previously been observed that there is a decrease in the diastolic heart tube diameter with age (>20%) in the control fly strain yellow-white (yw), which we hypothesized was due to an increase in passive tension due to myocardial stiffening. We sought to investigate this through nanoindentation in both yw and other control lines. Using a modified Hertzian analysis method, we probed the stiffness of juvenile and geriatric female yw flies and found age-related stiffening, a finding consistent with myocyte stiffening in other cardiac systems over time. Stiffness at the cardiac cell-cell junctions was 1.8± 0.1 vs. 3.8 ± 0.3 kPa in 1 week old flies which increased to 3.8 ± 0.3 kPa in 5 week flies. In contrast, white (w1118) flies were found to have no age-related stiffening. Consistently, w1118 also have a less significant decrease in diastolic diameter with age (<10%). Moreover, our analysis method is capable of detecting mechanical separation of the muscle layers, which was found to occur more frequently in w1118 than yw (0.41± 0.04 vs. 0.00 ± 0.02 μm separation, respectively, 1 week flies). Detection of mechanical separation between muscle layers via nanoindentation was modeled and verified in a microfabricated polydimethylsiloxane system. This first in situ mechanical analysis of a living myocardium revealed differences in cardiac mechanics due to age and suggest that aspects of the mechanical properties of the aging phenotype differ between Drosophila strains. We investigation on other laboratory Drosophila wildtype strains to assess the impact of diverse genetic backgrounds or mutations on age-related myocardial stiffening and cardiomyopathy.