Macrophage receptor-mediated processing and regulation of advanced glycosylation endproduct (AGE)-modified proteins: role in diabetes and aging.

Tissue and cell surface proteins modified nonenzymatically by glucose are shown to be removed by macrophages through a recently characterized high affinity receptor. Insulin appears to be a potent suppressor of this macrophage AGE removal activity, while TNF acts as a stimulant. Coupling of AGE-proteins to their AGE-receptor results in TNF and IL-1 synthesis and secretion. This suggests that AGE may act as a signal for growth-promoting factor secretion in a coordinated replacement process during tissue remodeling. A greater than 2-fold decrease in receptor number and binding capacity found in cells from aged mice as compared to young suggests that aging may adversely affect the AGE-receptor-efficiency and by impeding crosslinked AGE-protein removal add to ongoing aging tissue damage.