Influence of oxidatively modified LDL on monocyte-macrophage differentiation

Transendothelial migration of peripheral blood mononuclear cells (PBMCs) and their subsequent interaction with the subendothelial matrix lead to their differentiation to macrophages (mphis). To study whether preexposure of monocytes in circulation to modified proteins influences their differentiation to mphis, an in vitro model system using isolated PBMC in culture was used. The effect of modified proteins such as oxidatively modified LDL (ox-LDL), acetylated and non-enzymatically glycated-BSA (NEG-BSA) on the differentiation process was studied by monitoring the upregulation of mphi specific functions such as endocytosis, production of matrix metalloproteinases (MMPs), expression of surface antigen, activity of beta-glucuronidase and down regulation of monocyte specific myeloperoxidase activity. Rate of endocytosis, production of MMPs and beta-glucuronidase activity were significantly greater in cells treated with modified proteins irrespective of the nature of modification. Both CuSO4 ox-LDL and HOCl ox-LDL increased the rate of expression of the mphi specific functions. FACS analysis showed that the rate of upregulation of mphi specific CD71 and down regulation of monocyte specific CD14 were high in cells supplemented with modified proteins. Studies using PPARgamma antagonist and agonist suggest its involvement in CuSO4 ox-LDL induced monocyte-macrophage (mo-mphi) differentiation whereas the expression of macrophage specific functions in cells exposed to other modified proteins was independent of PPARgamma. PBMC isolated from hypercholesterolemic rabbits in culture expressed mphi specific functions at a faster rate compared to normal controls indicating that these observations are relevant in vivo. These results indicate that preexposure of monocytes to modified proteins promote their differentiation to mphis and may serve as a feed forward type control for clearing modified proteins.