Tribbles Homolog 3 Promotes Foam Cell Formation Associated with Decreased Proinflammatory Cytokine Production in Macrophages: Evidence for Reciprocal Regulation of Cholesterol Uptake and Inflammation.

BACKGROUND: Insulin resistance is central in the pathophysiology of cardiometabolic disease; however, common mechanisms that explain the parallel development of both type 2 diabetes and atherosclerosis have not been elucidated. We have previously shown that tribbles homolog 3 (TRB3) can exert a chronic pathophysiological role in promoting insulin resistance and also has an acute physiological role to alternatively regulate glucose uptake in fat and muscle during short-term fasting and nutrient excess. Since TRB3 is expressed in human atherosclerotic plaques, we explored its role in foam cell formation to assess its potential contribution to atherogenesis.
METHODS: We have used human THP-1 monocytes, which transition to lipid-laden macrophage foam cells when exposed to oxidized low-density lipoprotein (ox-LDL).
RESULTS: We first observed that TRB3 was upregulated by more than twofold (P < 0.01) within 24 hr of treatment with ox-LDL. To determine whether TRB3 actively participated in foam cell formation, we overexpressed TRB3 in THP-1 monocytes and found that this led to a 1.5-fold increase in cholesterol accumulation after 48 hr (P < 0.01), compared with controls. At the same time, TRB3 overexpression suppressed inflammation in macrophages as evidenced by reduced expression and secretion of tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) (both P < 0.01).
CONCLUSIONS: (1) TRB3 is upregulated in macrophages upon treatment with ox-LDL; (2) TRB3 promotes lipid accumulation and suppresses cytokine expression; and (3) inflammation and foam cell formation can be reciprocally regulated, and TRB3 orients the macrophage to assume a more primary role for lipid accumulation while maintaining a secondary role as an inflammatory immune cell.