Disruption of Mammalian Target of Rapamycin Complex 1 in Macrophages Decreases Chemokine Gene Expression and Atherosclerosis

Abstract

Rationale: The mammalian target of rapamycin complex 1 inhibitor, rapamycin, has been shown to decrease atherosclerosis, even while increasing plasma low-density lipoprotein levels. This suggests an antiatherogenic effect possibly mediated by the modulation of inflammatory responses in atherosclerotic plaques. Objective: Our aim was to assess the role of macrophage mammalian target of rapamycin complex 1 in atherogenesis. Methods and Results: We transplanted bone marrow from mice in which a key mammalian target of rapamycin complex 1 adaptor, regulatory-associated protein of mTOR, was deleted in macrophages by Cre/loxP recombination ( Mac-Rap KO mice) into Ldlr −/− mice and then fed them the Western-type diet. Atherosclerotic lesions from Mac-Rap KO mice showed decreased infiltration of macrophages, lesion size, and chemokine gene expression compared with control mice. Treatment of macrophages with minimally modified low-density lipoprotein resulted in increased levels of chemokine mRNAs and signal transducer and activator of transcription (STAT) 3 phosphorylation; these effects were reduced in Mac-Rap KO macrophages. Although wild-type and Mac-Rap KO macrophages showed similar STAT3 phosphorylation on Tyr705, Mac-Rap KO macrophages showed decreased STAT3Ser727 phosphorylation in response to minimally modified low-density lipoprotein treatment and decreased Ccl2 promoter binding of STAT3. Conclusions: The results demonstrate cross-talk between nutritionally induced mammalian target of rapamycin complex 1 signaling and minimally modified low-density lipoprotein–mediated inflammatory signaling via combinatorial phosphorylation of STAT3 in macrophages, leading to increased STAT3 activity on the chemokine (C-C motif) ligand 2 (monocyte chemoattractant protein 1) promoter with proatherogenic consequences.