Abstract-Mice with inactivated genes are increasingly used as models of human atherosclerosis. The aim of the present study was to determine whether the characteristic age-related distributions of lipid deposition seen around human arterial branches are replicated in such mice. Lesions occur downstream of branch ostia in immature human aortas, but these regions are spared in adult vessels, with lesions occurring more frequently at the sides or upstream of the branches. We determined the pattern of lipid staining around 102 intercostal branch ostia from apolipoprotein E/low density lipoprotein receptor double-knockout mice aged 9 to 20 weeks by using en face microscopy and a frequency-mapping technique. Lesion prevalence was high in the ostium and the region immediately surrounding it. Frequencies were 2.12Ϯ0.30 (meanϮSEM, nϭ11) times higher upstream than downstream (PϽ0.01), but the pattern did not resemble the adult human pattern: there were no peaks in frequency at the sides or upstream of the branch, and there was no sparing downstream. Furthermore, a patch of sparing upstream of the branch was seen, which has not been reported for human vessels, and there was no trend toward a more upstream pattern with age. We conclude that knockout mice may not be a suitable model in which to investigate localizing factors. Key Words: apolipoprotein E Ⅲ LDL receptor Ⅲ knockout mice Ⅲ atherosclerosis Ⅲ distribution M any recent studies have used mice with inactivated genes as models of human atherosclerosis. Inducing disease in normal mice, even of susceptible strains, requires prolonged administration of high-cholesterol diets with toxic additives, and the resulting lesions tend to be restricted to fatty streaks in the aortic root. [1][2][3][4] The genetically modified mice, in contrast, develop more advanced, more widely distributed lesions on Western or normal mouse diets while retaining the advantages of small size and fast breeding. Furthermore, they allow investigation of the effects of single gene products on lesion development.The true value of the new models, however, depends on the extent to which their disease resembles that occurring in human arteries. The present study addresses this similarity; more specifically, it is concerned with the nonuniform distribution of disease within the vasculature. The patchy occurrence of human atherosclerosis has attracted considerable attention because it demonstrates the existence of significant local risk factors. The determination of lesion distributions in models is an important test of the similarity to human disease and also indicates whether the models can be used to investigate localizing factors. The issue is particularly important for knockout mouse models because of their widespread and increasing use and because they could be used for investigating local risk factors at the single gene level.The distribution of lesions has previously been studied in apoE knockout [5][6][7] and LDL receptor (LDLR) knockout 8 mice.In both models, disease preferentially affects the fo...

SummaryMeasurements of the transport of circulating sulphorhodamine B-labelled albumin into the arterial wall, made by applying digital imaging fluorescence microscopy to sections of arteries fixed in situ, are limited in sensitivity by the low levels of tracer fluorescence and high levels of autofluorescence emitted from the tissue. Three attempts to improve these ratios are described. In the first, spectra of the tracer in solution and of arterial autofluorescence were used to design novel microscope filters for rhodamine-like dyes. By exciting with the rarely used yellow lines of the mercury arc lamp and detecting a narrow band of emission with Stokes shifts as small as 15 nm, the ratio of tracer fluorescence to autofluorescence was tripled. In the second, effects of different fixatives were investigated. Using a model system, it was confirmed that Karnovsky's fixative gives good tracer immobilization but elevates autofluorescence, whereas fixative-free buffer solutions give low autofluorescence but do not retain the tracer. It was further found that simple formaldehyde-based fixatives, hitherto considered to be poor fixatives of albumin, immobilized the tracer as well as the glutaraldehyde-based fixative, whilst giving autofluorescence levels comparable to those seen with buffer alone; they therefore give excellent tracer fluorescence to autofluorescence ratios. In the third, lowering specimen temperature by 50 8C was found to increase the intensity of tracer fluorescence by 30% whilst autofluorescence was unaffected. These data may have relevance to microscopical studies using other tissues and fluorescent tracers.