Role of macrophage-specific calpain in diabetic atherosclerosis (DRC Pilot Project)

Atherosclerotic vascular disease is the leading cause of death in patients with diabetes. Macrophages are the most abundant inflammatory cells accumulating in the sub-endothelial space in atherosclerotic lesions. Recently, the direct effect of diabetes on macrophages in atherosclerotic lesion has gained an increased attention in accelerating atherosclerosis. While searching for a mechanism of diabetes-accelerated atherosclerosis, recently I have discovered that calpains, calcium-dependent cysteine proteases are activated at increased levels in macrophages stimulated with high glucose, and that immunoreactive calpains are abundant in atherosclerotic lesions that co-localized with macrophages. Human atherosclerosis is associated with prolonged activation of calpains, however, surprisingly few cellular substrates of calpain have been identified in atherosclerosis. Recently, I have provided novel evidence that pharmacolgical inhibition of calpains attenuates angiotensin II-induced atherosclerosis in LDLr-/- mice. The two major isoforms, calpain-1 and -2, are ubiquitously expressed whereas others are tissue specific. Using calpain-1 deficient mice, I have determined that calpain-2 compensates the loss of calpain-1 and both isoforms are involved in atherosclerosis. Therefore, the role of calpain-1 and -2 in atherosclerosis development is presently unknown. My recent preliminary studies demonstrate that in addition to lipid loading, elevated glucose levels lead to an increased expression of calpains in macrophages, suggesting a close connection between the dyslipidemia and calpain in macrophages, under states of hyperglycemia. Understanding the physiological function of calpains in diabetic atherosclerosis and identifying their substrate proteins would yield a novel insight into atherosclerotic mechanisms. Based on this, the proposal will test the central hypothesis that calpain deficiency in macrophages will attenuate diabetes-accelerated atherosclerosis by suppressing macrophage foam cell formation and NF-kB mediated inflammation. To test this hypothesis, the following aims are proposed. 1. Determine the role of calpain in macrophage foam cell formation and inflammation. 2. Determine the contribution of macrophage specific-calpain to diabetic atherosclerosis.