Characterization of Atherosclerotic Mice Reveals a Sex-Dependent Susceptibility to Plaque Calcification but No Major Changes in the Lymphatics in the Arterial Wall.

Lymphatics participate in reverse cholesterol transport, and their presence in the arterial wall of the great vessels and prior experimental results suggest their possible role in the development of atherosclerosis. The aim of this study was to characterize the lymphatic vasculature of the arterial wall in atherosclerosis. Tissue sections and tissue-cleared aortas of wild-type mice unveiled significant differences in the density of the arterial lymphatic network throughout the arterial tree. Male and female Ldlr-/- and ApoE-/- mice on a Western diet showed sex-dependent differences in plaque formation and calcification. Female mice on a Western diet developed more calcification of atherosclerotic plaques than males. The lymphatic vessels within the aortic wall of these mice showed no major changes regarding the number of lymphatic junctions and end points or the lymphatic area. However, female mice on a Western diet showed moderate dilation of lymphatic vessels in the abdominal aorta and exhibited indications of increased peripheral lymphatic function, findings that require further studies to understand the role of lymphatics in the arterial wall during the development of atherosclerosis.

CCBE1 regulates the development and prevents the age-dependent regression of meningeal lymphatics.

Recent studies have described the importance of lymphatics in numerous organ-specific physiological and pathological processes. The role of meningeal lymphatics in various neurological and cerebrovascular diseases has been suggested. It has also been shown that these structures develop postnatally and are altered by aging and that the vascular endothelial growth factor C (VEGFC)/ vascular endothelial growth factor receptor 3 (VEGFR3) signaling plays an essential role in the development and maintenance of them. However, the molecular mechanisms governing the development and maintenance of meningeal lymphatics are still poorly characterized. Recent in vitro cell culture-based experiments, and in vivo studies in zebrafish and mouse skin suggest that collagen and calcium binding EGF domains 1 (CCBE1) is involved in the processing of VEGFC. However, the organ-specific role of CCBE1 in developmental lymphangiogenesis and maintenance of lymphatics remains unclear. Here, we aimed to investigate the organ-specific functions of CCBE1 in developmental lymphangiogenesis and maintenance of meningeal lymphatics during aging. We demonstrate that inducible deletion of CCBE1 leads to impaired postnatal development of the meningeal lymphatics and decreased macromolecule drainage to deep cervical lymph nodes. The structural integrity and density of meningeal lymphatics are gradually altered during aging. Furthermore, the meningeal lymphatic structures in adults showed regression after inducible CCBE1 deletion. Collectively, our results indicate the importance of CCBE1-dependent mechanisms not only in the development, but also in the prevention of the age-related regression of meningeal lymphatics. Therefore, targeting CCBE1 may be a good therapeutic strategy to prevent age-related degeneration of meningeal lymphatics.

Visualization of Organ-Specific Lymphatic Growth: An Efficient Approach to Labeling Molecular Markers in Cleared Tissues.

Organ-specific lymphatics are essential for the maintenance of healthy organ function and lymphatic dysfunction can lead to the development of various diseases. However, the precise role of those lymphatic structures remains unknown, mainly due to inefficient visualization techniques. Here, we present an efficient approach to visualizing organ-specific lymphatic growth. We used a modified CUBIC protocol to clear mouse organs and combined it with whole-mount immunostaining to visualize lymphatic structures. We acquired images using upright, stereo and confocal microscopy and quantified them with AngioTool, a tool for the quantification of vascular networks. Using our approach, we then characterized the organ-specific lymphatic vasculature of the Flt4kd/+ mouse model, showing symptoms of lymphatic dysfunction. Our approach enabled us to visualize the lymphatic vasculature of organs and to analyze and quantify structural changes. We detected morphologically altered lymphatic vessels in all investigated organs of Flt4kd/+ mice, including the lungs, small intestine, heart and uterus, but no lymphatic structures in the skin. Quantifications showed that these mice have fewer and dilated lymphatic vessels in the small intestine and the lungs. Our results demonstrate that our approach can be used to investigate the importance of organ-specific lymphatics under both physiological and pathophysiological conditions.