In Vivo Characterization of Endogenous Cardiovascular Extracellular Vesicles in Larval and Adult Zebrafish: Endogenous cardiovascular extracellular vesicles

Objective: Extracellular vesicles (EVs) facilitate molecular transport across extracellular space, allowing local and systemic signalling during homeostasis and in disease. Extensive studies have described functional roles for EV populations, including during cardiovascular disease, but the in vivo characterisation of endogenously produced EVs is still in its infancy. Due to their genetic tractability and live imaging amenability, zebrafish represent an ideal but under-used model to investigate endogenous EVs. We aimed to establish a transgenic zebrafish model to allow the in vivo identification, tracking and extraction of endogenous EVs produced by different cell types.

Approach and Results: Using a membrane-tethered fluorophore reporter system, we show that EVs can be fluorescently labelled in larval and adult zebrafish and demonstrate that multiple cell types including endothelial cells and cardiomyocytes actively produce EVs in vivo. Cell-type specific EVs can be tracked by high spatiotemporal resolution light-sheet live imaging and modified flow cytometry methods allow these EVs to be further evaluated. Additionally, cryo-EM reveals the full morphological diversity of larval and adult EVs. Importantly, we demonstrate the utility of this model by showing that different cell types exchange EVs in the adult heart and that ischaemic injury models dynamically alter EV production.

Conclusions: We describe a powerful in vivo zebrafish model for the investigation of endogenous EVs in all aspects of cardiovascular biology and pathology. A cell membrane fluorophore labelling approach allows cell type-specific tracing of EV origin without bias towards the expression of individual protein markers and will allow detailed future examination of their function.