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Papers In Press, published online ahead of print August 25, 2007
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Cardiovascular Biology, Meharry Medical College, Nashiville, TN 37208
Corresponding Author: zguo{at}mmc.edu
Apolipoprotein (Apo) E deficiency has been suggested to induce foam cell formation. Using lipoproteins obtained from wild-type mice and ApoE-deficient mice expressing ApoB48 but not B100, this report studied ApoE-deficient lipoprotein-induced changes in lipoprotein catabolism and protein expression in mouse peritoneal macrophages (MPMs). Our data demonstrated that incubation of MPMs with ApoE-deficient lipoproteins induced intracellular lipoprotein, cholesterol ester and triglyceride accumulation, which was associated with a time-related decline in ApoE-deficient lipoprotein degradation in MPMs. Confocal microscopy analysis indicated that the accumulated lipids were localized in lysosomes. ApoE-deficient lipoproteins reduced the protein levels of lysosomal acid lipase, cathepsin B, and cation-dependent mannose 6 phosphate receptor (MPR46). Exogenous ApoE reduced ApoE-deficient lipoprotein-induced lipid accumulation, and attenuated the suppressive effect of ApoE-deficient lipoproteins on lysosomal hydrolase and MPR46 expression. Although oxidized lipoproteins also increased lipid contents in MPMs, exogenous ApoE could not attenuate oxidized lipoprotein-induced lipid accumulation. Our in vivo studies also showed that feeding ApoE-deficient mice a high-fat diet resulted in cholesterol ester and triglyceride accumulation, and reduced lysosomal hydrolase expression in MPMs. These data suggest that ApoE-deficient lipoproteins elevate cellular lipid contents through pathway(s) different from those activated by oxidized lipoproteins, and that reducing lysosomal hydrolases in macrophages might be a mechanism by which ApoE-deficient lipoproteins result in intralysosomal lipoprotein accumulation, thereby inducing foam cell formation.
Revised on August 2, 2007
Accepted on August 24, 2007
Apolipoprotein E-deficient lipoproteins induce foam cell formation by downregulation of lysosomal hydrolases in macrophages
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