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 (mTORC1) inhibitor, rapamycin, has been shown to decrease atherosclerosis, even while increasing plasma LDL levels. This suggests an anti-atherogenic effect possibly mediated by modulation of inflammatory responses in atherosclerotic plaques. Objective To assess the role of macrophage mTORC1 in atherogenesis. Methods and Results We transplanted bone marrow from mice in which a key mTORC1 adaptor, Raptor, was deleted in macrophages by Cre/loxP recombination (Mac-RapKO mice) into Ldlr-/- mice and then fed them the Western-type diet (WTD). Atherosclerotic lesions from Mac-RapKO mice showed decreased infiltration of macrophages, lesion size and chemokine gene expression compared with control mice. Treatment of macrophages with minimally modified LDL (mmLDL) resulted in increased levels of chemokine mRNAs and STAT3 phosphorylation; these effects were reduced in Mac-RapKO macrophages. While wild-type and Mac-RapKO macrophages showed similar STAT3 phosphorylation on Tyr705, Mac-RapKO macrophages showed decreased STAT3 Ser727 phosphorylation in response to mmLDL treatment and decreased Ccl2 promoter binding of STAT3. Conclusions The results demonstrate cross-talk between nutritionally-induced mTORC1 signaling and mmLDL-mediated inflammatory signaling via combinatorial phosphorylation of STAT3 in macrophages, leading to increased STAT3 activity on the CCL2 (MCP-1)promoter with pro-atherogenic consequences.

Tsc1 is a Critical Regulator of Macrophage Survival and Function

“…The results revealed that Tsc1-deficient macrophages showed increased expression of chemokines including CCL2, CCL3, CCL4, CCL5, CCL7, CCL8 on both mTORC1-dependent and independent pathways. These data were consistent with a previous study showing that disruption of mTORC1 in macrophages decreased the expression of CCL2, CCL6, CCL3 [30]. It was also reported that G-protein-coupled bile acid receptor 1 (TGR5) reduces macrophage migration and chemokines expression via mTORC1-dependent pathway [31].…”

Macrophage Activation and Polarization: Nomenclature and Experimental Guidelines

“…Other mutations in the mTOR pathway have produced disparate results. However, systematic investigation of mTOR pathway mutants using the principles described here will likely resolve why rapamycin treated macrophages and macrophages from Raptor, Rictor and TSC1 mutants have diverse phenotypes (Ai et al, 2014; Byles et al, 2013; Festuccia et al, 2014; Weichhart et al, 2008). Some of these mutants are summarized in Figure 1C.…”

Blood–brain barrier breakdown promotes macrophage infiltration and cognitive impairment in leptin receptor-deficient mice

“…4,5,30,31 Acute slices were cut on a Vibratome (Leica, Buffalo Grove, IL, USA) into a bath of oxygenated artificial cerebrospinal fluid (ACSF). After 1 h recovery at 37 C, extracellular recordings were performed in ACSF in the presence of 50 mM picrotoxin (SigmaAldrich, St. Louis, MO, USA). For some experiments, Enzastaurin (1 mM) 32 was bath-applied for 30 min before and during the recordings.…”