Atherogenic lipids and lipoproteins trigger CD36-TLR2-dependent apoptosis in macrophages undergoing endoplasmic reticulum stress.

Macrophage apoptosis in advanced atheromata, a key process in plaque necrosis, involves the combination of ER stress with other proapoptotic stimuli. We show here that oxidized phospholipids, oxidized LDL, saturated fatty acids (SFAs), and lipoprotein(a) trigger apoptosis in ER-stressed macrophages through a mechanism requiring both CD36 and Toll-like receptor 2 (TLR2). In vivo, macrophage apoptosis was induced in SFA-fed, ER-stressed wild-type but not Cd36⁻(/)⁻ or Tlr2⁻(/)⁻ mice. For atherosclerosis, we combined TLR2 deficiency with that of TLR4, which can also promote apoptosis in ER-stressed macrophages. Advanced lesions of fat-fed Ldlr⁻(/)⁻ mice transplanted with Tlr4⁻(/)⁻Tlr2⁻(/)⁻ bone marrow were markedly protected from macrophage apoptosis and plaque necrosis compared with WT →Ldlr⁻(/)⁻ lesions. These findings provide insight into how atherogenic lipoproteins trigger macrophage apoptosis in the setting of ER stress and how TLR activation might promote macrophage apoptosis and plaque necrosis in advanced atherosclerosis.