Caspase-Dependent Apoptosis in THP-1 Cells Exposed to Oxidized Low-Density Lipoproteins

Oxidized low-density lipoproteins (oxLDL) play a critical role in atherogenesis. We investigated the apoptotic process in human monocytic THP-1 cell line, exposed to oxLDL generated by treatment of native LDL either with hypochlorous acid (HOCl), mainly affecting the protein moiety, or with copper sulfate (CuSO4), mainly affecting the lipid moiety. After incubation with both types of oxLDL, we observed: (i) microscopy signs of apoptosis in THP-1 cells, (ii) a significant increase of apoptotic cells proportional to LDL protein concentration, either by annexin V or by cell cycle phase analysis with propodium iodide flow cytometry, (iii) a reduction of THP-1 cell apoptosis in presence of the caspase inhibitor Z-VAD.fmk, (iv) the resistance of THP-1 cells apoptosis after PMA-elicited differentiation. In conclusion, HOCl-oxLDL are as potent as Cu-oxLDL to induce high rates of apoptosis in monocytes through a caspase-dependent pathway. Moreover, the resistance of differentiated THP-1 cells to oxLDL-induced apoptosis is compatible with the hypothesis that mature macrophages have prolonged survival and thereby enhance the atherogenic process.