Three-Dimensional Imaging of Aortic Tissues in Atherosclerosis.

Recent research has advanced the understanding of atherosclerosis as a transmural chronic inflammatory disease involving all three layers of the arterial wall, including the intima plaque, the media, and the adventitia, which forms the outer connective tissue coat of arteries. Our recent studies have suggested that the adventitia is used by the peripheral nervous system as a conduit for reaching all tissue cells. We also found that the peripheral nervous system, that is, the sensory and sympathetic nervous system, undergoes major remodeling processes involving the neogenesis of axon networks adjacent to atherosclerotic plaques. In this context, understanding the structure of the neural network and its interactions with vascular components of diseased arteries holds major promises for a better understanding of cardiovascular disease pathogenesis. To achieve these objectives, methods to visualize the subcellular architecture of the intact healthy and diseased arteries together with their surrounding perivascular compartments are needed. Tissue clearing allows intact deep-tissue imaging of larger tissue compartments that are otherwise inaccessible. It allows volumetric imaging of intact arteries through the integration of labeling, clearing, advanced microscopic imaging, and image processing tools. Here, we describe two distinct but complementary passive tissue clearing approaches, that is, aqueous-based 2, 2-thiodiethanol (TDE) clearing and solvent-based immunolabeling-enabled three-dimensional imaging of solvent-cleared organ (iDISCO) clearing to image isolated aortic segments or whole aorta in-situ in the whole mouse.