Increased expression of the DNA-binding cytokine HMGB1 in human atherosclerotic lesions - Role of activated macrophages and cytokines

Objective - Atherosclerosis is a chronic inflammatory response of the arterial wall to injury. High-mobility group box 1 (HMGB1) is a DNA-binding protein, which on release from cells exhibits potent inflammatory actions. We examined its expression in atherosclerotic lesions and regulation by cytokines. Methods and Results - In atherosclerotic lesions, HMGB1 protein is expressed by endothelial cells, some intimal smooth muscle cells, and macrophages. As atherosclerosis develops and progresses from fatty streaks to fibrofatty lesion, the number of HMGB1-producing macrophages increases markedly. Studies using the THP-1 cell line indicated that HMGB1 mRNA expression could be markedly upregulated by inflammatory cytokines, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and also transforming growth factor (TGF)-beta. IFN-gamma, TNF-alpha, TWEAK, and TGF-beta induced an intracellular redistribution of HMGB1 and stimulated secretion by THP-1 cells and human blood monocytes. Inhibitors of MEK1/MEK2, protein kinase C, and PI-3/Akt, which inhibit lysosomal degranulation and mRNA translation, attenuated cytokine-induced HMGB1 secretion. Conclusions - Macrophage is the major cell type responsible for HMGB1 production in human atherosclerotic lesions. Inflammatory cytokines and TGF-beta increase HMGB1 expression and secretion by monocyte/macrophages. HMGB1 appears to be a common mediator of inflammation induced by inflammatory cytokines and is likely to contribute to lesion progression and chronic inflammation.