Increased atherosclerosis in myeloperoxidase-deficient mice
Marie-Luise Brennan, Melissa M. Anderson, Diana M. Shih, Xiao-Dan Qu, Xuping Wang, Asha C. Mehta, Lesley L. Lim, Weibin Shi, Stanley L. Hazen, Jason S. Jacob, Jan R. Crowley, Jay W. Heinecke, Aldons J. Lusis
Marie-Luise Brennan, Melissa M. Anderson, Diana M. Shih, Xiao-Dan Qu, Xuping Wang, Asha C. Mehta, Lesley L. Lim, Weibin Shi, Stanley L. Hazen, Jason S. Jacob, Jan R. Crowley, Jay W. Heinecke, Aldons J. Lusis
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Article

Increased atherosclerosis in myeloperoxidase-deficient mice

Abstract

Myeloperoxidase (MPO), a heme enzyme secreted by activated phagocytes, generates an array of oxidants proposed to play critical roles in host defense and local tissue damage. Both MPO and its reaction products are present in human atherosclerotic plaque, and it has been proposed that MPO oxidatively modifies targets in the artery wall. We have now generated MPO-deficient mice, and show here that neutrophils from homozygous mutants lack peroxidase and chlorination activity in vitro and fail to generate chlorotyrosine or to kill Candida albicans in vivo. To examine the potential role of MPO in atherosclerosis, we subjected LDL receptor–deficient mice to lethal irradiation, repopulated their marrow with MPO-deficient or wild-type cells, and provided them a high-fat, high-cholesterol diet for 14 weeks. White cell counts and plasma lipoprotein profiles were similar between the two groups at sacrifice. Cross-sectional analysis of the aorta indicated that lesions in MPO-deficient mice were about 50% larger than controls. Similar results were obtained in a genetic cross with LDL receptor–deficient mice. In contrast to advanced human atherosclerotic lesions, the chlorotyrosine content of aortic lesions from wild-type as well as MPO-deficient mice was essentially undetectable. These data suggest an unexpected, protective role for MPO-generated reactive intermediates in murine atherosclerosis. They also identify an important distinction between murine and human atherosclerosis with regard to the potential involvement of MPO in protein oxidation.

Authors

Marie-Luise Brennan, Melissa M. Anderson, Diana M. Shih, Xiao-Dan Qu, Xuping Wang, Asha C. Mehta, Lesley L. Lim, Weibin Shi, Stanley L. Hazen, Jason S. Jacob, Jan R. Crowley, Jay W. Heinecke, Aldons J. Lusis

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Figure 1

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Targeted disruption of the mouse MPO gene. (a) The targeting vector, wil...
Targeted disruption of the mouse MPO gene. (a) The targeting vector, wild-type MPO locus (including exons 1–9), and targeted MPO gene are shown. Exon 7 was disrupted by insertion of positive-selection marker PGK-Neo (Neo) at a BssHII (S) site. HSV-thymidine kinase (TK) served for negative selection. BglII (B) digestion sites, lengths of diagnostic BglII fragments, and external probe (checkered box) used for Southern blot analysis are indicated. (b) DNA isolated from progeny of chimeric founder male mated with C57BL/6J female was subjected to BglII digestion and Southern blot analysis. Lanes 1 and 2 contained the wild-type controls 129/SvJ DNA (lane 1) and C57BL/6J DNA (lane 2). Note the difference in band size between the two strains, indicative of a restriction fragment length variant. Strain 129/SvJ has BglII restriction enzyme sites at nucleotides 189 and 8075, yielding a 7.9-kb product, whereas C57BL/6J is lacking one of these sites, and the fragment generated represents digestion at a more distal BglII site. Restriction variants, such as this one, are due to naturally occurring nucleic acid sequence differences between inbred strains. Lanes 3 and 4 are from progeny. The larger band in both lanes is inherited from the C57BL/6J mother, and the lower band, inherited from the chimeric father, is either wild-type (lane 3) or targeted (lane 4). (c) RNA samples isolated from bone marrow from wild-type (lanes 1 and 2) and mutant (lanes 3 and 4) mice were subjected to Northern blot analysis with a human cDNA probe.