Visualization of Monocytic Cells in Regressing Atherosclerotic Plaques by Intravital 2-Photon and Positron Emission Tomography–Based Imaging—Brief Report

Abstract

Cervical transplantation of atherosclerotic mouse aortic arches represents a novel experimental tool to investigate cellular mechanisms that contribute to the remodeling of atherosclerotic plaques.

Limited Macrophage Positional Dynamics in Progressing or Regressing Murine Atherosclerotic Plaques—Brief Report

“…Intravital imaging of atherosclerotic plaques is challenging, not least because of the need to confront motion associated with breathing and heart rhythm in the arterial tree. However, using different approaches, these hurdles are being overcome in different groups, largely either with the use of software that collects images in rhythm with the heart beat 7 or with physical stabilization of arterial tissue to reduce motion 6, 11 . We developed a preparation capable of direct imaging of established plaque in the carotid artery.…”

“…We developed a preparation capable of direct imaging of established plaque in the carotid artery. To our knowledge, our preparation is the first to image high fat-diet induced established plaques native to the animal being evaluated, as compared with injury-induced plaques 6 , transplanted vessels 11 , or monocyte interactions with the vessel wall prior to plaque progression 8 . Having developed a stable and high resolution imaging approach, we found that macrophages piled in clusters within the plaque were highly sessile, displaying minimal net displacement.…”

“…To address the issue of defining macrophage dynamics in plaque, we undertook a two-pronged approach modeled after that used by Egen et al 5 , first employing intravital imaging to examine macrophage behavior in the living mouse and then adding a second approach to track cells over a much longer period of time than is possible with intravital imaging. Intravital two-photon microscopy has advanced our understanding of immune responses during steady state and in a wide variety of disease models, and some recent advances have been made in imaging atherosclerotic disease using this technique 6–11 . Here, we have applied a stable and high resolution imaging approach to visualize native atherosclerotic plaques in the carotid artery to allow for short-term observation of macrophage motility within the developing plaque.…”

Novel Positron Emission Tomography Tracers for Imaging Vascular Inflammation

“…PET tracers targeted at C-C chemokine receptor type 5 (CCR5), type 2 (CCR2), and other immune cell chemokine surface receptors have been evaluated in animal models of vascular injury and atherosclerosis [29][30][31][32]. In one study, the feasibility of imaging 8 chemokine receptors simultaneously was tested using targeted nanoparticles [33].…”

Intravital imaging of leukocyte behavior in atherosclerosis

“…In this model, a murine heart is transplanted into the neck of a recipient and the graft is stabilized, which enables intravital imaging for several hours. Appreciating the work done by Chevre and colleagues [7], where intravital two-photon imaging was applied to carotid artery atherosclerotic lesions, we developed a method of cervical aortic arch transplantation [8]. By transplanting plaque-bearing aortic arches from apoE-deficient mice into the neck of CX 3 CR1 GFP-reporter mice, we were able to stabilize the grafts and visualize the recruitment of CX 3 CR1 + monocytes into atherosclerotic plaques in real time, where they display only little motility and progressively decrease in number as the lesions regress.…”