The Larval Requirement for Matrix Metalloproteinase-Mediated Remodelling of the Cardiac Extracellular Matrix in Drosophila melanogaster

Abstract

The Drosophila heart is a tubular vessel surrounded by a dynamic scaffold of extracellular matrix (ECM) proteins. Heart development and function rely upon protease-mediated remodelling and turnover of the ECM, and changes in ECM composition correlate with age and cardiac disease. Previous research has shown that a family of proteases called matrix metalloproteinases (MMPs), and their inhibitors (TIMPs), are necessary for normal cardiac cell migration and lumenogenesis. The Drosophila heart expands considerably throughout growth, but the role of MMP activity has not been elucidated at this time. I examine the role of the two Drosophila MMPs, MMP1 and MMP2, as well as TIMP, in defining larval heart structure and ECM protein distribution. I observe heart phenotypes via immunofluorescence labelling and confocal microscopy using loss-of-function mutants, gene over-expression, and gene knock-down techniques. Reduced MMP1 function during embryogenesis correlates with myofibrillar disorganisation, whereas reduced MMP2 function or TIMP over-expression both result in cardia bifida as well as increased density and ectopic localisation of Collagen-IV and Pericardin. Post-embryonic MMP reduction compromises cardiac structural integrity but does not affect Pericardin localisation. Live imaging of the larval heart with optical coherence tomography (OCT) and light microscopy reveals that reduced MMP2 function correlates with decreased heart rate but not impaired dilation or contraction. These data suggest that MMP2 activity during embryogenesis is critical for larval heart development. In contrast, post-embryonic protease function appears to have a less pronounced effect on ECM protein distribution throughout larval development.