Abstract 179: Mechanical Assessment of the Drosophila Heart Reveals Conservation of Human Heart Failure Mechanisms

Abstract

Rationale: Current models for investigating the mechanisms of heart failure are limited by low throughput or genetic intractability. Therefore, we have developed a nanoindentation method to measure the intrinsic stiffness of the intact, living Drosophila heart tube to assess mechanical function in this rapidly aging, genetically malleable system which has been shown to experience age-related decline in cardiac function. Objective: Fruit fly strains universally experience decline in fractional shortening with age due to decreased diastolic diameter, though severity varies between strains. We compared a strain with significant decline in diameter with age and one without to examine the hypothesis that diastolic decline is the consequence of increase passive tension due to myocardial stiffening with age. Quantitative PCR was employed targeted towards mechanosensitive molecules known to be overexpressed in failing human hearts. Methods and Results: Female yw flies experience ∼18% reduction in diastolic diameter with age (59.3 at 1 week to 48.4 µm at 5 weeks of age, p < 10-3) as calculated from m-mode kymographs of beating heart tube. Nanoindentation reveals 111% increase in stiffness (1.82 to 3.85 kPa, p < 10-10) proximal to the cardiac cell-cell junctions. In contrast, w1118 flies experience ∼6% decline in diastolic diameter (74.1 to 69.5 µm, p = 0.049) and do not stiffen with age (p = 0.1923). qPCR reveals increased expression of cell-cell adhesion molecules in yw, such as vinculin and cadherin. Expression levels remain steady or decline in w1118. Further analysis reveals that w1118 experiences separation between juxtaposed muscle layers (410 nm at 1wk, 448 nm at 5wks) indicating matrix adhesion defects not observed in yw (0 nm, p < 10-7 compared to 1wk w1118; 0 nm, p < 10-8 compared to 5wk w1118). Conclusion: These data indicate structural changes in the fly are a consequence of adherens-junction-mediated mechanical remodeling similar to that which is observed in the failing human heart. Matrix defects and the lack of remodeling in w1118 suggest a link between costamere and adherens signaling during aging. Cardiac matrix content and adhesion signatures likely direct cardiac remodeling and function.