Enzymatically modified LDL induces cathepsin H in human monocytes: potential relevance in early atherogenesis.

OBJECTIVE Modification with proteases and cholesterylesterase transforms LDL to a moiety that resembles lipoproteins isolated from atherosclerotic lesions and possesses atherogenic properties. To identify changes in monocyte-derived foam cells laden with enzymatically modified LDL (E-LDL), we compared patterns of the most abundant transcripts in these cells after incubation with LDL or E-LDL. METHODS AND RESULTS Serial analyses of gene expression (SAGE) libraries were constructed from human monocytes after treatment with LDL or E-LDL. Several tags were differentially expressed in LDL-treated versus E-LDL-treated cells, whereby marked selective induction by E-LDL of cathepsin H was conspicuous. We show that cathepsin H is expressed in atherosclerotic lesions in colocalization with E-LDL. Furthermore, we demonstrate that LDL modified with cathepsin H and cholesterylesterase can confer onto LDL the capacity to induce macrophage foam cell formation and to induce cathepsin H. CONCLUSIONS Cathepsin H could contribute to the transformation of LDL to an atherogenic moiety; the process might involve a self-sustaining amplifying circle.