Thomas Juan – Blood flow mechanosensation during cardiovascular development

Microscope image of zebrafish hearts where the blood vessels are visualised in green, red and yellow.

My laboratory aims to understand how blood flow forces shape the development and function of the cardiovascular system. We generate genetic tools to control cardiac contractions and modulate the function of mechanosensor proteins in cardiovascular subpopulations.

Hemodynamic forces generated by the blood flow are an essential regulator of cardiovascular development and function. Vascular morphogenesis, cardiac differentiation, and organogenesis as such, are steered through the forces from blood flow. Understanding how these forces shape the cardiovascular system is critical to the development of treatments for cardiovascular disease, the leading cause of death worldwide, claiming 18 million lives every year globally.

Blood flow mechanosensation in endothelial cells

Multiple types of cardiovascular cell respond to blood flow, such as the vascular smooth muscle cells that wrap around the blood vessels, the pericytes that are associated with small blood vessels, and the cardiomyocytes that allow cardiac contractions. We focus on endothelial cells, the inner lining of the vasculature, which are in direct contact with blood flow, and are the first line of response to hemodynamic forces. Despite the identification of several endothelial mechanosensitive proteins, which transduce mechanical signals into cellular responses, the precise mechanotransduction mechanisms responsible for these responses remain largely unknown.

Microscope imaging of wild-type and pkd1a mutant hearts, showing that the flow between the chambers is affected in the mutant.

Confocal imaging of wild-type (A) and pkd1a mutant (B) hearts. The rightmost image in each pair shows a magnification of the atrioventricular valve region (Juan et al. 2023)

Zebrafish and cardiovascular development

The zebrafish can survive severe cardiac injury and zebrafish larvae can grow without a functional cardiovascular system during the first week of development. Although the zebrafish heart is only two-chambered, zebrafish genetic models recapitulate all cardiovascular diseases. The transparency of the zebrafish during development facilitates the use of optical methods, such as light sheet, confocal, and spinning disc microscopy, enabling high-resolution fast imaging of cardiovascular cell dynamics and cellular trajectories in vivo. These features make zebrafish the best model to study the effects of mechanical forces on cardiovascular development and to dissect the underlying genetic pathways.

Microscope image of a zebrafish where the blood flow and heart contractions are visualised in orange.

Brightfield imaging of a zebrafish embryo; coloring highlights blood flow motion and heart contractions (Juan et al. 2024).

Genetic tools to interrogate cardiovascular gene function

Genetic dissection of cardiovascular phenotypes typically involves mutants that recapitulate human disease. Recently, CRISPR-mediated genome editing has enabled the high-throughput generation of floxed alleles to interrogate gene function conditionally. However, this approach is limited by compensation responses and the stability of target proteins and mRNA. To address these issues, we generate conditional knockdown genetic tools that can bypass these mechanisms. Combined with high-resolution live imaging techniques, these tools allow blood flow control and the systemic identification of mechanosensors.

Confocal imaging of a wild-type zebrafish heart that glows in green and a Tnnt2a-depleted heart that is much less green due to the lack of the TNNT2 protein.

Confocal imaging of a wild-type zebrafish heart (left) and a heart that has been depleted of the Tnnt2a protein (right).

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