Metabolic Reprogramming Of Macrophages Research Articles

Macrophage metabolic reprogramming aggravates aortic dissection through the HIF1α-ADAM17 pathway✰.

BackgroundAortic dissection is a severe inflammatory vascular disease with high mortality and limited therapeutic options. The hallmarks of aortic dissection comprise aortic inflammatory cell infiltration and elastic fiber disruption, highlighting the involvement of macrophage. Here a role for macrophage hypoxia-inducible factor 1-alpha (HIF-1α) in aortic dissection was uncovered.MethodsImmunochemistry, immunofluorescence, western blot and qPCR were performed to test the change of macrophage HIF-1α in two kinds of aortic dissection models and human tissues. Metabolomics and Seahorse extracellular flux analysis were used to detect the metabolic state of macrophages involved in the development of aortic dissection. Chromatin Immunoprecipitation (ChIP), enzyme-linked immunosorbent assay (ELISA) and cytometric bead array (CBA) were employed for mechanistic studies.FindingsMacrophages involved underwent distinct metabolic reprogramming, especially fumarate accumulation, thus inducing HIF-1α activation in the development of aortic dissection in human and mouse models. Mechanistic studies revealed that macrophage HIF-1α activation triggered vascular inflammation, extracellular matrix degradation and elastic plate breakage through increased a disintegrin and metallopeptidase domain 17 (ADAM17), identified as a novel target gene of HIF-1α. A HIF-1α specific inhibitor acriflavine elicited protective effects on aortic dissection dependent on macrophage HIF-1α.InterpretationThis study reveals that macrophage metabolic reprogramming activates HIF-1α and subsequently promotes aortic dissection progression, suggesting that macrophage HIF-1α inhibition might be a potential therapeutic target for treating aortic dissection.

Metabolic Programming of Macrophages: Implications in the Pathogenesis of Granulomatous Disease.

Metabolic reprogramming is rapidly gaining appreciation in the etiology of immune cell dysfunction in a variety of diseases. Tuberculosis, schistosomiasis, and sarcoidosis represent an important class of diseases characterized by the formation of granulomas, where macrophages are causatively implicated in disease pathogenesis. Recent studies support the incidence of macrophage metabolic reprogramming in granulomas of both infectious and non-infectious origin. These publications identify the mechanistic target of rapamycin (mTOR), as well as the major regulators of lipid metabolism and cellular energy balance, peroxisome proliferator receptor gamma (PPAR-γ) and adenosine monophosphate-activated protein kinase (AMPK), respectively, as key players in the pathological progression of granulomas. In this review, we present a comprehensive breakdown of emerging research on the link between macrophage cell metabolism and granulomas of different etiology, and how parallels can be drawn between different forms of granulomatous disease. In particular, we discuss the role of PPAR-γ signaling and lipid metabolism, which are currently the best-represented metabolic pathways in this context, and we highlight dysregulated lipid metabolism as a common denominator in granulomatous disease progression. This review therefore aims to highlight metabolic mechanisms of granuloma immune cell fate and open up research questions for the identification of potential therapeutic targets in the future.

Two-stage metabolic remodelling in macrophages in response to lipopolysaccharide and interferon-γ stimulation.

In response to signals associated with infection or tissue damage, macrophages undergo a series of dynamic phenotypic changes. Here we show that during the response to LPS and interferon-γ stimulation, metabolic reprogramming in macrophages is also highly dynamic. Specifically, the TCA cycle undergoes a two-stage remodeling: the early stage is characterized by a transient accumulation of intermediates including succinate and itaconate, while the late stage is marked by the subsidence of these metabolites. The metabolic transition into the late stage is largely driven by the inhibition of pyruvate dehydrogenase complex (PDHC) and oxoglutarate dehydrogenase complex (OGDC), which is controlled by the dynamic changes in lipoylation state of both PDHC and OGDC E2 subunits and phosphorylation of PDHC E1 subunit. This dynamic metabolic reprogramming results in a transient metabolic state that strongly favors HIF-1α stabilization during the early stage, which subsides by the late stage; consistently, HIF-1α levels follow this trend. This study elucidates a dynamic and mechanistic picture of metabolic reprogramming in LPS and interferon-γ stimulated macrophages, and provides insights into how changing metabolism can regulate the functional transitions in macrophages over a course of immune response.

Metabolic reprogramming of macrophages during infections and cancer.

In response to different microenvironmental stimuli, macrophages are polarized into two populations, M1 macrophages which are classically activated by interferon (IFN)-γ with lipopolysaccharides (LPSs) and M2 macrophages which are alternatively activated by interleukin-4 (IL-4), to perform specific roles in innate immune responses. Accordingly, macrophages occupy distinct metabolic profiles, regulated by orchestrated factors and signaling pathways, including the PI3K-AKT, HIF, c-Myc, AMPK, and PPARs pathways. These factors and pathways play pivotal roles not only in metabolic regulation but also in macrophage polarization. After activation, classically activated M1 macrophages and alternatively activated M2 macrophages display distinct patterns in glucose, lipid, amino acid and iron metabolism. Here, we summarized recently discovered metabolism-related inflammatory signaling factors, along with reprogrammed metabolism, after the activation of macrophages under conditions related to immunity and cancer. Additionally, macrophage regulatory roles in infectious diseases, cancer progression and anti-cancer immunotherapy are discussed in terms of metabolic profiles, providing insight into the prevention and treatment of immune-associated diseases.

Macrophage Origin, Metabolic Reprogramming and IL-1 Signaling: Promises and Pitfalls in Lung Cancer.

Macrophages are tissue-resident cells that act as immune sentinels to maintain tissue integrity, preserve self-tolerance and protect against invading pathogens. Lung macrophages within the distal airways face around 8000–9000 L of air every day and for that reason are continuously exposed to a variety of inhaled particles, allergens or airborne microbes. Chronic exposure to irritant particles can prime macrophages to mediate a smoldering inflammatory response creating a mutagenic environment and favoring cancer initiation. Tumor-associated macrophages (TAMs) represent the majority of the tumor stroma and maintain intricate interactions with malignant cells within the tumor microenvironment (TME) largely influencing the outcome of cancer growth and metastasis. A number of macrophage-centered approaches have been investigated as potential cancer therapy and include strategies to limit their infiltration or exploit their antitumor effector functions. Recently, strategies aimed at targeting IL-1β signaling pathway using a blocking antibody have unexpectedly shown great promise on incident lung cancer. Here, we review the current understanding of the bridge between TAM metabolism, IL-1β signaling, and effector functions in lung adenocarcinoma and address the challenges to successfully incorporating these pathways into current anticancer regimens.

20 - PKM2 S-glutathionylation promotes the reprogramming of macrophage metabolism and activation states

Introduction Pyruvate Kinase Isoform M2 (PKM2) regulates glycolysis in monocytes and macrophages and is induced and S-glutathionylated in response to diet-induced metabolic stress. We hypothesized that PKM2 S-glutathionylation promotes PKM2 tetramer dissociation into glycolytically-inactive dimers and that nuclear translocation of these dimers activates HIF1a-dependent gene expression, inducing both glycolytic enzymes as well and pro-inflammatory proteins, reprogramming macrophages to a hyper-inflammatory phenotype. Methods Bone marrow derived macrophages (BMDM) overexpressing glutaredoxin-1-EGFP (Grx1) or EGFP only were exposed for 36 h to metabolic stress (high glucose plus native human LDL). PKM2 expression and phosphorylation state (Tyr105) were assessed in cell lysates by Western blot analysis. PKM2 S-glutathionylation was quantified using the Biotin-switch assay. PKM2 oligomerization state was measured by non-reducing SDS-PAGE and Western blot analysis. To confirm the role of PKM2 S-glutathionylation on metabolic reprogramming of monocytes in vivo, we conducted lentiviral gene transfer experiments in mice using CD68 promoter-driven Grx1 and EGFP expression. Mice were fed a HFD for 10 week to induce monocyte priming. We purified blood monocytes from EGFPMactg and Grx1Mactg mice and determined by single-cell Western blot PKM2 induction and phosphorylation, GLUT1, 14-3-3z and IL-1b expression. Results PKM2 induction, -glutathionylation, and phosphorylation were all enhanced in metabolically stressed BMDMs but prevented in Grx1-overexpressing BMDMs. The dimer/tetramer ratio was increased in response to metabolic stress as was HIF1a-dependent expression of GLUT1 and IL-1b. Compared to monocytes isolated from HFD-fed mice, monocyte from Grx1Mactg mice showed reduced priming, reduced expression of PKM2, GLUT1 and IL-1b and diminished PKM2 phosphorylation. Conclusion Metabolic stress-induced PKM2 S-glutathionylation promotes PKM2 tetramer dissociation, phosphorylation and subsequent nuclear translocation, which, via HIF1a-dependent expression of glycolytic enzymes and inflammatory cytokines, reprograms monocyte-derived macrophages into a hyper-inflammatory phenotype. This mechanism may contribute to chronic inflammatory diseases associated with metabolic disorders.

Dicer in Macrophages Prevents Atherosclerosis by Promoting Mitochondrial Oxidative Metabolism.

Alternative macrophage activation, which relies on mitochondrial oxidative metabolism, plays a central role in the resolution of inflammation and prevents atherosclerosis. Moreover, macrophages handle large amounts of cholesterol and triglycerides derived from the engulfed modified lipoproteins during atherosclerosis. Although several microRNAs regulate macrophage polarization, the role of the microRNA-generating enzyme Dicer in macrophage activation during atherosclerosis is unknown. To evaluate the role of Dicer in atherosclerosis, Apoe-/- mice with or without macrophage-specific Dicer deletion were fed a high-fat diet for 12 weeks. Anti-argonaute 2 RNA immunoprecipitation chip and RNA deep sequencing combined with microRNA functional screening were performed in the Dicer wild-type and knockout bone marrow-derived macrophages to identify the individual microRNAs and the mRNA targets mediating the phenotypic effects of Dicer. The role of the identified individual microRNA and its target in atherosclerosis was determined by tail vein injection of the target site blockers in atherosclerotic Apoe-/- mice. We show that Dicer deletion in macrophages accelerated atherosclerosis in mice, along with enhanced inflammatory response and increased lipid accumulation in lesional macrophages. In vitro, alternative activation was limited whereas lipid-filled foam cell formation was exacerbated in Dicer-deficient macrophages as a result of impaired mitochondrial fatty acid oxidative metabolism. Rescue of microRNA (miR)-10a, let-7b, and miR-195a expression restored the oxidative metabolism in alternatively activated Dicer-deficient macrophages. Suppression of ligand-dependent nuclear receptor corepressor by miR-10a promoted fatty acid oxidation, which mediated the lipolytic and anti-inflammatory effect of Dicer. miR-10a expression was negatively correlated to the progression of atherosclerosis in humans. Blocking the interaction between ligand-dependent nuclear receptor corepressor and miR-10a by target site blockers aggravated atherosclerosis development in mice. Dicer plays an atheroprotective role by coordinately regulating the inflammatory response and lipid metabolism in macrophages through enhancing fatty acid-fueled mitochondrial respiration, suggesting that promoting Dicer/miR-10a-dependent metabolic reprogramming in macrophages has potential therapeutic implications to prevent atherosclerosis.

Mycobacterium tuberculosis carrying a rifampicin drug resistance mutation reprograms macrophage metabolism through cell wall lipid changes.

Tuberculosis is a significant global health threat, with one-third of the world's population infected with its causative agent Mycobacterium tuberculosis (Mtb). The emergence of multidrug-resistant (MDR) Mtb that is resistant to the frontline anti-tubercular drugs rifampicin and isoniazid forces treatment with toxic second-line drugs. Currently, ~4% of new and ~21% of previously treated tuberculosis cases are either rifampicin-drug-resistant or MDR Mtb infections1. The specific molecular host-pathogen interactions mediating the rapid worldwide spread of MDR Mtb strains remain poorly understood. W-Beijing Mtb strains are highly prevalent throughout the world and associated with increased drug resistance2. In the early 1990s, closely related MDR W-Beijing Mtb strains (W strains) were identified in large institutional outbreaks in New York City and caused high mortality rates3. The production of interleukin-1β (IL-1β) by macrophages coincides with the shift towards aerobic glycolysis, a metabolic process that mediates protection against drug-susceptible Mtb4. Here, using a collection of MDR W-Mtb strains, we demonstrate that the overexpression of Mtb cell wall lipids, phthiocerol dimycocerosates, bypasses the interleukin 1 receptor, type I (IL-1R1) signalling pathway, instead driving the induction of interferon-β (IFN-β) to reprogram macrophage metabolism. Importantly, Mtb carrying a drug resistance-conferring single nucleotide polymorphism in rpoB (H445Y)5 can modulate host macrophage metabolic reprogramming. These findings transform our mechanistic understanding of how emerging MDR Mtb strains may acquire drug resistance single nucleotide polymorphisms, thereby altering Mtb surface lipid expression and modulating host macrophage metabolic reprogramming.

The TLR4 Agonist Monophosphoryl Lipid A Drives Broad Resistance to Infection via Dynamic Reprogramming of Macrophage Metabolism.

Monophosphoryl lipid A (MPLA) is a clinically used TLR4 agonist that has been found to drive nonspecific resistance to infection for up to 2 wk. However, the molecular mechanisms conferring protection are not well understood. In this study, we found that MPLA prompts resistance to infection, in part, by inducing a sustained and dynamic metabolic program in macrophages that supports improved pathogen clearance. Mice treated with MPLA had enhanced resistance to infection with Staphylococcus aureus and Candida albicans that was associated with augmented microbial clearance and organ protection. Tissue macrophages, which exhibited augmented phagocytosis and respiratory burst after MPLA treatment, were required for the beneficial effects of MPLA. Further analysis of the macrophage phenotype revealed that early TLR4-driven aerobic glycolysis was later coupled with mitochondrial biogenesis, enhanced malate shuttling, and increased mitochondrial ATP production. This metabolic program was initiated by overlapping and redundant contributions of MyD88- and TRIF-dependent signaling pathways as well as downstream mTOR activation. Blockade of mTOR signaling inhibited the development of the metabolic and functional macrophage phenotype and ablated MPLA-induced resistance to infection in vivo. Our findings reveal that MPLA drives macrophage metabolic reprogramming that evolves over a period of days to support a macrophage phenotype highly effective at mediating microbe clearance and that this results in nonspecific resistance to infection.

In This Issue

Abstract Getting to the Heart of Inflammation See article p. 3697 NSAIDs Impact Listeria Immunity See article p. 3729 TLR4 Drives Macrophage Metabolic Reprogramming See article p. 3777 Plunging into the Depths of Chemokine Receptor Interaction Sites See article p. 3825

Regulation of Immune Cell Functions by Metabolic Reprogramming.

Recent findings show that the metabolic status of immune cells can determine immune responses. Metabolic reprogramming between aerobic glycolysis and oxidative phosphorylation, previously speculated as exclusively observable in cancer cells, exists in various types of immune and stromal cells in many different pathological conditions other than cancer. The microenvironments of cancer, obese adipose, and wound-repairing tissues share common features of inflammatory reactions. In addition, the metabolic changes in macrophages and T cells are now regarded as crucial for the functional plasticity of the immune cells and responsible for the progression and regression of many pathological processes, notably cancer. It is possible that metabolic changes in the microenvironment induced by other cellular components are responsible for the functional plasticity of immune cells. This review explores the molecular mechanisms responsible for metabolic reprogramming in macrophages and T cells and also provides a summary of recent updates with regard to the functional modulation of the immune cells by metabolic changes in the microenvironment, notably the tumor microenvironment.

Papers of note in Science 356 (6337)

This week’s articles address the role of macrophage metabolic reprogramming in resolving inflammation and an epidermal pattern formation system that is self-organizing and can adjust to fit the size of the tissue.

Anti-inflammatory effect of IL-10 mediated by metabolic reprogramming of macrophages.

Interleukin 10 (IL-10) is an anti-inflammatory cytokine that plays a critical role in the control of immune responses. However, its mechanisms of action remain poorly understood. Here, we show that IL-10 opposes the switch to the metabolic program induced by inflammatory stimuli in macrophages. Specifically, we show that IL-10 inhibits lipopolysaccharide-induced glucose uptake and glycolysis and promotes oxidative phosphorylation. Furthermore, IL-10 suppresses mammalian target of rapamycin (mTOR) activity through the induction of an mTOR inhibitor, DDIT4. Consequently, IL-10 promotes mitophagy that eliminates dysfunctional mitochondria characterized by low membrane potential and a high level of reactive oxygen species. In the absence of IL-10 signaling, macrophages accumulate damaged mitochondria in a mouse model of colitis and inflammatory bowel disease patients, and this results in dysregulated activation of the NLRP3 inflammasome and production of IL-1β.

Macrophage Metabolism As Therapeutic Target for Cancer, Atherosclerosis, and Obesity

Macrophages are not only essential components of innate immunity that contribute to host defense against infections, but also tumor growth and the maintenance of tissue homeostasis. An important feature of macrophages is their plasticity and ability to adopt diverse activation states in response to their microenvironment and in line with their functional requirements. Recent immunometabolism studies have shown that alterations in the metabolic profile of macrophages shape their activation state and function. For instance, to fulfill their respective functions lipopolysaccharides-induced pro-inflammatory macrophages and interleukin-4 activated anti-inflammatory macrophages adopt a different metabolism. Thus, metabolic reprogramming of macrophages could become a therapeutic approach to treat diseases that have a high macrophage involvement, such as cancer. In the first part of this review, we will focus on the metabolic pathways altered in differentially activated macrophages and link their metabolic aspects to their pro- and anti-inflammatory phenotype. In the second part, we will discuss how macrophage metabolism is a promising target for therapeutic intervention in inflammatory diseases and cancer.

Metabolic reprogramming through fatty acid transport protein 1 (FATP1) regulates macrophage inflammatory potential and adipose inflammation.

ObjectiveA novel approach to regulate obesity-associated adipose inflammation may be through metabolic reprogramming of macrophages (MΦs). Broadly speaking, MΦs dependent on glucose are pro-inflammatory, classically activated MΦs (CAM), which contribute to adipose inflammation and insulin resistance. In contrast, MΦs that primarily metabolize fatty acids are alternatively activated MΦs (AAM) and maintain tissue insulin sensitivity. In actuality, there is much flexibility and overlap in the CAM-AAM spectrum in vivo dependent upon various stimuli in the microenvironment. We hypothesized that specific lipid trafficking proteins, e.g. fatty acid transport protein 1 (FATP1), would direct MΦ fatty acid transport and metabolism to limit inflammation and contribute to the maintenance of adipose tissue homeostasis.MethodsBone marrow derived MΦs (BMDMs) from Fatp1−/− and Fatp1+/+ mice were used to investigate FATP1-dependent substrate metabolism, bioenergetics, metabolomics, and inflammatory responses. We also generated C57BL/6J chimeric mice by bone marrow transplant specifically lacking hematopoetic FATP1 (Fatp1B−/−) and controls Fatp1B+/+. Mice were challenged by high fat diet (HFD) or low fat diet (LFD) and analyses including MRI, glucose and insulin tolerance tests, flow cytometric, histologic, and protein quantification assays were conducted. Finally, an FATP1-overexpressing RAW 264.7 MΦ cell line (FATP1-OE) and empty vector control (FATP1-EV) were developed as a gain of function model to test effects on substrate metabolism, bioenergetics, metabolomics, and inflammatory responses.ResultsFatp1 is downregulated with pro-inflammatory stimulation of MΦs. Fatp1−/− BMDMs and FATP1-OE RAW 264.7 MΦs demonstrated that FATP1 reciprocally controled metabolic flexibility, i.e. lipid and glucose metabolism, which was associated with inflammatory response. Supporting our previous work demonstrating the positive relationship between glucose metabolism and inflammation, loss of FATP1 enhanced glucose metabolism and exaggerated the pro-inflammatory CAM phenotype. Fatp1B−/− chimeras fed a HFD gained more epididymal white adipose mass, which was inflamed and oxidatively stressed, compared to HFD-fed Fatp1B+/+ controls. Adipose tissue macrophages displayed a CAM-like phenotype in the absence of Fatp1. Conversely, functional overexpression of FATP1 decreased many aspects of glucose metabolism and diminished CAM-stimulated inflammation in vitro. FATP1 displayed acyl-CoA synthetase activity for long chain fatty acids in MΦs and modulated lipid mediator metabolism in MΦs.ConclusionOur findings provide evidence that FATP1 is a novel regulator of MΦ activation through control of substrate metabolism. Absence of FATP1 exacerbated pro-inflammatory activation in vitro and increased local and systemic components of the metabolic syndrome in HFD-fed Fatp1B−/− mice. In contrast, gain of FATP1 activity in MΦs suggested that Fatp1-mediated activation of fatty acids, substrate switch to glucose, oxidative stress, and lipid mediator synthesis are potential mechanisms. We demonstrate for the first time that FATP1 provides a unique mechanism by which the inflammatory tone of adipose and systemic metabolism may be regulated.

Maintenance of Macrophage Redox Status by ChREBP Limits Inflammation and Apoptosis and Protects against Advanced Atherosclerotic Lesion Formation.

Enhanced glucose utilization can be visualized in atherosclerotic lesions and may reflect a high glycolytic rate in lesional macrophages, but its causative role in plaque progression remains unclear. We observe that the activity of the carbohydrate-responsive element binding protein ChREBP is rapidly downregulated upon TLR4 activation in macrophages. ChREBP inactivation refocuses cellular metabolism to a high redox state favoring enhanced inflammatory responses after TLR4 activation and increased cell death after TLR4 activation or oxidized LDL loading. Targeted deletion of ChREBP in bone marrow cells resulted in accelerated atherosclerosis progression in Ldlr(-/-) mice with increased monocytosis, lesional macrophage accumulation, and plaque necrosis. Thus, ChREBP-dependent macrophage metabolic reprogramming hinders plaque progression and establishes a causative role for leukocyte glucose metabolism in atherosclerosis.

Orphan Nuclear Receptor ERRα Controls Macrophage Metabolic Signaling and A20 Expression to Negatively Regulate TLR-Induced Inflammation

The orphan nuclear receptor estrogen-related receptor α (ERRα; NR3B1) is a key metabolic regulator, but its function in regulating inflammation remains largely unknown. Here, we demonstrate that ERRα negatively regulates Toll-like receptor (TLR)-induced inflammation by promoting Tnfaip3 transcription and fine-tuning of metabolic reprogramming in macrophages. ERRα-deficient (Esrra(-/-)) mice showed increased susceptibility to endotoxin-induced septic shock, leading to more severe pro-inflammatory responses than control mice. ERRα regulated macrophage inflammatory responses by directly binding the promoter region of Tnfaip3, a deubiquitinating enzyme in TLR signaling. In addition, Esrra(-/-) macrophages showed an increased glycolysis, but impaired mitochondrial respiratory function and biogenesis. Further, ERRα was required for the regulation of NF-κB signaling by controlling p65 acetylation via maintenance of NAD(+) levels and sirtuin 1 activation. These findings unravel a previously unappreciated role for ERRα as a negative regulator of TLR-induced inflammatory responses through inducing Tnfaip3 transcription and controlling the metabolic reprogramming.

Metabolic reprogramming in macrophages and dendritic cells in innate immunity.

Activation of macrophages and dendritic cells (DCs) by pro-inflammatory stimuli causes them to undergo a metabolic switch towards glycolysis and away from oxidative phosphorylation (OXPHOS), similar to the Warburg effect in tumors. However, it is only recently that the mechanisms responsible for this metabolic reprogramming have been elucidated in more detail. The transcription factor hypoxia-inducible factor-1α (HIF-1α) plays an important role under conditions of both hypoxia and normoxia. The withdrawal of citrate from the tricarboxylic acid (TCA) cycle has been shown to be critical for lipid biosynthesis in both macrophages and DCs. Interference with this process actually abolishes the ability of DCs to activate T cells. Another TCA cycle intermediate, succinate, activates HIF-1α and promotes inflammatory gene expression. These new insights are providing us with a deeper understanding of the role of metabolic reprogramming in innate immunity.

Abstract 175: Lack of Macrophage GLUT1-Mediated Glucose Metabolism Increases Atherosclerotic Lesion Instability

Macrophages play a key role in the pathogenesis of atherosclerosis. Metabolic programs powered by glucose or lipid enable macrophages to elicit pro- or anti-inflammatory responses, respectively. Although the chronic inflammatory feature of atherosclerosis has been well-established, the role of macrophage substrate metabolism in atherogenesis remains unclear. We previously demonstrated that macrophages with elevated GLUT1-mediated glucose metabolism have an increased inflammatory response. Therefore, we created a novel macrophage GLUT1-deficient murine model by crossing GLUT1 floxed to LysM-Cre mice. Recent work suggests that lack of GLUT1 reduces the pro-inflammatory response and the ability for GLUT1-/- macrophages to polarize to the classically activated state in vitro. Therefore, the objective of this study was to examine how macrophage metabolic reprogramming affects the development of atherosclerosis. We hypothesized that macrophages with restricted glucose metabolism due to lack of glucose transporter GLUT1 will have reduced pro-inflammatory activation during atherogenesis. We transplanted bone marrow from Glut1MΦfl/fl or Glut1MΦ-/- mice into Ldlr-/- mice and fed mice a Western diet for 12 weeks. Glut1MΦfl/fl Ldlr-/- or Glut1MΦ-/- Ldlr-/- chimeric mice did not exhibit significant differences in body weight, body composition, blood pressure, fasting blood glucose, or triacylglycerol and LDL and HDL cholesterol. Digital histology analysis of Oil Red O stained slides indicated that deleting macrophage GLUT1 did not affect total lesion area in aortic root; however, mice with blunted glucose metabolism displayed more and larger necrotic cores. Ongoing studies are investigating apoptosis and phagocytic capacity of macrophages with and without GLUT1 to elucidate the roles of macrophage glucose metabolism on the morphology of atherosclerotic lesion. In summary, we observed that mice lacking macrophage GLUT1 developed increased necrotic cores in lesions of the aorta root relative to mice with wild type macrophage GLUT1 which suggests that maintenance of atherosclerotic lesion stability may be regulated by glucose-dependent mechanisms.

Commentary

A novel approach to regulate obesity-associated adipose inflammation may be through metabolic reprogramming of macrophages (MΦs). Broadly speaking, MΦs dependent on glucose are pro-inflammatory, classically activated MΦs (CAM), which contribute to adipose inflammation and insulin resistance. In contrast, MΦs that primarily metabolize fatty acids are alternatively activated MΦs (AAM) and maintain tissue insulin sensitivity. In actuality, there is much flexibility and overlap in the CAM-AAM spectrum in vivo dependent upon various stimuli in the microenvironment. We hypothesized that specific lipid trafficking proteins, e.g. fatty acid transport protein 1 (FATP1), would direct MΦ fatty acid transport and metabolism to limit inflammation and contribute to the maintenance of adipose tissue homeostasis.Bone marrow derived MΦs (BMDMs) from Fatp1−/− and Fatp1+/+ mice were used to investigate FATP1-dependent substrate metabolism, bioenergetics, metabolomics, and inflammatory responses. We also generated C57BL/6J chimeric mice by bone marrow transplant specifically lacking hematopoetic FATP1 (Fatp1B−/−) and controls Fatp1B+/+. Mice were challenged by high fat diet (HFD) or low fat diet (LFD) and analyses including MRI, glucose and insulin tolerance tests, flow cytometric, histologic, and protein quantification assays were conducted. Finally, an FATP1-overexpressing RAW 264.7 MΦ cell line (FATP1-OE) and empty vector control (FATP1-EV) were developed as a gain of function model to test effects on substrate metabolism, bioenergetics, metabolomics, and inflammatory responses.Fatp1 is downregulated with pro-inflammatory stimulation of MΦs. Fatp1−/− BMDMs and FATP1-OE RAW 264.7 MΦs demonstrated that FATP1 reciprocally controled metabolic flexibility, i.e. lipid and glucose metabolism, which was associated with inflammatory response. Supporting our previous work demonstrating the positive relationship between glucose metabolism and inflammation, loss of FATP1 enhanced glucose metabolism and exaggerated the pro-inflammatory CAM phenotype. Fatp1B−/− chimeras fed a HFD gained more epididymal white adipose mass, which was inflamed and oxidatively stressed, compared to HFD-fed Fatp1B+/+ controls. Adipose tissue macrophages displayed a CAM-like phenotype in the absence of Fatp1. Conversely, functional overexpression of FATP1 decreased many aspects of glucose metabolism and diminished CAM-stimulated inflammation in vitro. FATP1 displayed acyl-CoA synthetase activity for long chain fatty acids in MΦs and modulated lipid mediator metabolism in MΦs.Our findings provide evidence that FATP1 is a novel regulator of MΦ activation through control of substrate metabolism. Absence of FATP1 exacerbated pro-inflammatory activation in vitro and increased local and systemic components of the metabolic syndrome in HFD-fed Fatp1B−/− mice. In contrast, gain of FATP1 activity in MΦs suggested that Fatp1-mediated activation of fatty acids, substrate switch to glucose, oxidative stress, and lipid mediator synthesis are potential mechanisms. We demonstrate for the first time that FATP1 provides a unique mechanism by which the inflammatory tone of adipose and systemic metabolism may be regulated.