Changes in vimentin in human macrophages during apoptosis induced by oxidised low density lipoprotein.

Macrophage apoptosis contributes to the development of human atherosclerotic lesions. Oxidised LDL may be involved in macrophage death in vivo. We examined morphological and biochemical changes to the vimentin filament network during apoptosis of human macrophages. Only oxidised LDL, but not native or acetylated LDL, induced apoptosis, wherein vimentin was cleaved into fragments of 48-50, 46, 29 and 26 kDa. The use of caspase inhibitors suggested that caspase-6 mediates the formation of the 26 and 46 kDa fragments of vimentin. We were unable to demonstrate any significant involvement of caspase-3 in vimentin cleavage. However, caspase-3 was clearly activated during apoptosis whilst caspase-6 expression in macrophages was minimal. Vimentin filament breakdown occurred early during apoptosis and vimentin immunoreactivity was present in apoptotic bodies. However, the application of caspase inhibitors had no effect on the morphology of the vimentin network in apoptotic cells, suggesting that filament breakdown is not mediated by caspase proteolysis. Similar changes in vimentin were also seen in gliotoxin-induced apoptosis.