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

Abstract

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 pote...

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“…While most work has focused on the former characteristics, little work has been conducted on understanding the metabolic phenotype of MΦs, or how MΦ metabolic phenotype influences disease progression, until recent years [6, 7]. In general, in vitro studies have shown that pro-inflammatory classically activated MΦs (LPS and IFNγ- stimulated, CAM or M1-like) are highly glycolytic while immunoregulatory alternatively activated MΦs (IL4-stimulated, AAM or M2-like) primarily oxidize fatty acids [8, 9]. However, in vivo MΦ phenotype is highly dynamic, with mixed inflammatory and metabolic phenotypes [7, 10–13].…”

“…Fatty acid transport protein 1 (FATP1, Slc27a1 ) is an acyl-CoA synthetase wherein expression within hematopoietic populations is limited to MΦs and plasmacytoid dendritic cells [14], but not other cells that may contribute to inflammation in atherosclerosis, including monocytes, microglia, B cells, T cells, neutrophils and eosinophils [9]. We have recently reported through loss and gain of function models that FATP1 is necessary to maintain the immunoregulatory AAM phenotype in vivo and ex vivo .…”

“…We have recently reported through loss and gain of function models that FATP1 is necessary to maintain the immunoregulatory AAM phenotype in vivo and ex vivo . Fatp1 is downregulated with pro-inflammatory stimulation of bone marrow derived MΦs [9]. Chimeric mice lacking Fatp1 through bone marrow transplantation and fed high fat diet gained more weight and had impaired glucose tolerance on high fat diet, along with greater white adipose mass, MΦ infiltration, and crown-like structures formation.…”

“…Consequently, in white adipose tissue of Fatp1 −/− transplanted mice, inflammation was elevated with evidence of oxidative stress. Fatp1 −/− adipose tissue MΦs (ATMs) isolated from white adipose were more CAM-like compared to ATMs isolated from Fatp1 +/+ transplanted mice fed a high fat diet [9]. In vitro studies additionally demonstrated that MΦs lacking Fatp1 displayed a hyper-inflammatory response to CAM stimuli, with elevations in iNOS ( Nos2 ), among others, and reductions in immunoregulatory AAM marker arginase 1 ( Arg1 ).…”

“…In vitro studies additionally demonstrated that MΦs lacking Fatp1 displayed a hyper-inflammatory response to CAM stimuli, with elevations in iNOS ( Nos2 ), among others, and reductions in immunoregulatory AAM marker arginase 1 ( Arg1 ). Furthermore, absence of Fatp1 led to a metabolic shift from fatty acid uptake and oxidative metabolism to increased glucose transporter GLUT1 expression, glycolysis, and metabolic intermediates associated with oxidative stress and pentose phosphate pathway [9]. Conversely, an in vitro gain of function model was utilized by over-expressing Fatp1 in the RAW264.7 CAM-like MΦ cell line.…”