Role of endothelial permeability hotspots and endothelial mitosis in determining age-related patterns of macromolecule uptake by the rabbit aortic wall near branch points

Abstract

Background and aimsTransport of macromolecules between plasma and the arterial wall plays a key role in atherogenesis. Scattered hotspots of elevated endothelial permeability to macromolecules occur in the aorta; a fraction of them are associated with dividing cells. Hotspots occur particularly frequently downstream of branch points, where lesions develop in young rabbits and children. However, the pattern of lesions varies with age, and can be explained by similar variation in the pattern of macromolecule uptake. We investigated whether patterns of hotspots and mitosis also change with age.MethodsEvans’ Blue dye-labeled albumin was injected intravenously into immature or mature rabbits and its subsequent distribution in the aortic wall around intercostal branch ostia examined by confocal microscopy and automated image analysis. Mitosis was detected by immunofluorescence after adding 5-bromo-2-deoxiuridine to drinking water.ResultsHotspots were most frequent downstream of branches in immature rabbits, but a novel distribution was observed in mature rabbits. Neither pattern was explained by mitosis. Hotspot uptake correlated spatially with the much greater non-hotspot uptake (p < 0.05), and the same pattern was seen when only the largest hotspots were considered.ConclusionsThe pattern of hotspots changes with age. The data are consistent with there being a continuum of local permeabilities rather than two distinct mechanisms. The distribution of the dye, which binds to elastin and collagen, was similar to that of non-binding tracers and to lesions apart from a paucity at the lateral margins of branches that can be explained by lower levels of fibrous proteins in those regions.

NO Synthesis but Not Apoptosis, Mitosis or Inflammation Can Explain Correlations between Flow Directionality and Paracellular Permeability of Cultured Endothelium

“…What is missing from such studies is an estimate of the fraction of the total uptake caused by apoptotic and mitotic cells. We recently addressed that issue using en face confocal microscopy to detect uptake of rhodamine-labelled albumin in the vicinity of aortic branches and found that uptake in hotspots was an order of magnitude lower than the total uptake [ 38 ]. That is consistent with the present study where proliferating, mitotic and apoptotic cells together accounted for less than 10% of the total uptake under shear.…”

Haemodynamic Wall Shear Stress, Endothelial Permeability and Atherosclerosis—A Triad of Controversy

“…However, the cell turnover leaky junction hypothesis of Weinbaum et al (1985) proposes that the width of intercellular junctions temporarily increases when endothelial cells divide or die, and that large particles might then cross by this route. Consistent with this hypothesis, "hotspots" of high permeability have been observed for a range of macromolecular tracers (reviewed by Chooi et al, 2016). They are associated with enhanced entry of LDL and often, although not exclusively, with mitosis or apoptosis (Stemerman et al, 1986;Lin et al, 1988;Lin et al, 1989;Lin et al, 1990;Truskey et al, 1992;Malinauskas et al, 1995); in rabbits weighing <3 kg, they occur at high frequency downstream of aortic side branches (Barakat et al, 1992;Herrmann et al, 1994).…”

“…One study ( Chooi et al, 2016 ) has investigated whether the pattern of hotspots and mitosis changes with age around rabbit intercostal branch ostia. EBD pre-mixed with albumin was used as the tracer; it was allowed to circulate for only 10 min in order to limit any inhibition of the NO pathway.…”