Role of IL-18 in adipose tissue remodeling and metabolic dysfunction.

BACKGROUND/OBJECTIVES: Proinflammatory cytokines are increased in obese adipose tissue, including inflammasome key masters. Conversely, IL-18 protects against obesity and metabolic dysfunction. We focused on the IL-18 effect in controlling adipose tissue remodeling and metabolism. MATERIALS/SUBJECTS AND METHODS: We used C57BL/6 wild-type (WT) and interleukine-18 deficient (IL-18-/-) male mice fed a chow diet and samples from bariatric surgery patients. RESULTS: IL-18-/- mice showed increased adiposity and proinflammatory cytokine levels in adipose tissue, leading to glucose intolerance. IL-18 was widely secreted by stromal vascular fraction but not adipocytes from mice's fatty tissue. Chimeric model experiments indicated that IL-18 controls adipose tissue expansion through its presence in tissues other than bone marrow. However, IL-18 maintains glucose homeostasis when present in bone marrow cells. In humans with obesity, IL-18 expression in omental tissue was not correlated with BMI or body fat mass but negatively correlated with IRS1, GLUT-4, adiponectin, and PPARy expression. Also, the IL-18RAP receptor was negatively correlated with IL-18 expression. CONCLUSIONS: IL-18 signaling may control adipose tissue expansion and glucose metabolism, as its absence leads to spontaneous obesity and glucose intolerance in mice. We suggest that resistance to IL-18 signaling may be linked with worse glucose metabolism in humans with obesity.

Splenic monocytes drive pathogenic subretinal inflammation in age-related macular degeneration.

Age-related macular degeneration (AMD) is invariably associated with the chronic accumulation of activated mononuclear phagocytes in the subretinal space. The mononuclear phagocytes are composed of microglial cells but also of monocyte-derived cells, which promote photoreceptor degeneration and choroidal neovascularization. Infiltrating blood monocytes can originate directly from bone marrow, but also from a splenic reservoir, where bone marrow monocytes develop into angiotensin II receptor (ATR1)+ splenic monocytes. The involvement of splenic monocytes in neurodegenerative diseases such as AMD is not well understood. Using acute inflammatory and well-phenotyped AMD models, we demonstrate that angiotensin II mobilizes ATR1+ splenic monocytes, which we show are defined by a transcriptional signature using single-cell RNA sequencing and differ functionally from bone marrow monocytes. Splenic monocytes participate in the chorio-retinal infiltration and their inhibition by ATR1 antagonist and splenectomy reduces the subretinal mononuclear phagocyte accumulation and pathological choroidal neovascularization formation. In aged AMD-risk ApoE2-expressing mice, a chronic AMD model, ATR1 antagonist and splenectomy also inhibit the chronic retinal inflammation and associated cone degeneration that characterizes these mice. Our observation of elevated levels of plasma angiotensin II in AMD patients, suggests that similar events take place in clinical disease and argue for the therapeutic potential of ATR1 antagonists to inhibit splenic monocytes for the treatment of blinding AMD.

FLT3L-dependent dendritic cells control tumor immunity by modulating Treg and NK cell homeostasis.

FLT3-L-dependent classical dendritic cells (cDCs) recruit anti-tumor and tumor-protecting lymphocytes. We evaluate cancer growth in mice with low, normal, or high levels of cDCs. Paradoxically, both low or high numbers of cDCs improve survival in mice with melanoma. In low cDC context, tumors are restrained by the adaptive immune system through influx of effector T cells and depletion of Tregs and NK cells. High cDC numbers favor the innate anti-tumor response, with massive recruitment of activated NK cells, despite high Treg infiltration. Anti CTLA-4 but not anti PD-1 therapy synergizes with FLT3-L therapy in the cDCHi but not in the cDCLo context. A combination of cDC boost and Treg depletion dramatically improves survival of tumor-bearing mice. Transcriptomic data confirm the paradoxical effect of cDC levels on survival in several human tumor types. cDCHi-TregLo state in such patients predicts best survival. Modulating cDC numbers via FLT3 signaling may have therapeutic potential in human cancer.

Cholesterol efflux pathways hinder KRAS-driven lung tumor progenitor cell expansion.

Cholesterol efflux pathways could be exploited in tumor biology to unravel cancer vulnerabilities. A mouse model of lung-tumor-bearing KRASG12D mutation with specific disruption of cholesterol efflux pathways in epithelial progenitor cells promoted tumor growth. Defective cholesterol efflux in epithelial progenitor cells governed their transcriptional landscape to support their expansion and create a pro-tolerogenic tumor microenvironment (TME). Overexpression of the apolipoprotein A-I, to raise HDL levels, protected these mice from tumor development and dire pathologic consequences. Mechanistically, HDL blunted a positive feedback loop between growth factor signaling pathways and cholesterol efflux pathways that cancer cells hijack to expand. Cholesterol removal therapy with cyclodextrin reduced tumor burden in progressing tumor by suppressing the proliferation and expansion of epithelial progenitor cells of tumor origin. Local and systemic perturbations of cholesterol efflux pathways were confirmed in human lung adenocarcinoma (LUAD). Our results position cholesterol removal therapy as a putative metabolic target in lung cancer progenitor cells.

Neural crest-related NXPH1/α-NRXN signaling opposes neuroblastoma malignancy by inhibiting organotropic metastasis.

Neuroblastoma is a pediatric cancer that can present as low- or high-risk tumors (LR-NBs and HR-NBs), the latter group showing poor prognosis due to metastasis and strong resistance to current therapy. Whether LR-NBs and HR-NBs differ in the way they exploit the transcriptional program underlying their neural crest, sympatho-adrenal origin remains unclear. Here, we identified the transcriptional signature distinguishing LR-NBs from HR-NBs, which consists mainly of genes that belong to the core sympatho-adrenal developmental program and are associated with favorable patient prognosis and with diminished disease progression. Gain- and loss-of-function experiments revealed that the top candidate gene of this signature, Neurexophilin-1 (NXPH1), has a dual impact on NB cell behavior in vivo: whereas NXPH1 and its receptor α-NRXN1 promote NB tumor growth by stimulating cell proliferation, they conversely inhibit organotropic colonization and metastasis. As suggested by RNA-seq analyses, these effects might result from the ability of NXPH1/α-NRXN signalling to restrain the conversion of NB cells from an adrenergic state to a mesenchymal one. Our findings thus uncover a transcriptional module of the sympatho-adrenal program that opposes neuroblastoma malignancy by impeding metastasis, and pinpoint NXPH1/α-NRXN signaling as a promising target to treat HR-NBs.

Network analysis of large-scale ImmGen and Tabula Muris datasets highlights metabolic diversity of tissue mononuclear phagocytes.

The diversity of mononuclear phagocyte (MNP) subpopulations across tissues is one of the key physiological characteristics of the immune system. Here, we focus on understanding the metabolic variability of MNPs through metabolic network analysis applied to three large-scale transcriptional datasets: we introduce (1) an ImmGen MNP open-source dataset of 337 samples across 26 tissues; (2) a myeloid subset of ImmGen Phase I dataset (202 MNP samples); and (3) a myeloid mouse single-cell RNA sequencing (scRNA-seq) dataset (51,364 cells) assembled based on Tabula Muris Senis. To analyze such large-scale datasets, we develop a network-based computational approach, genes and metabolites (GAM) clustering, for unbiased identification of the key metabolic subnetworks based on transcriptional profiles. We define 9 metabolic subnetworks that encapsulate the metabolic differences within MNP from 38 different tissues. Obtained modules reveal that cholesterol synthesis appears particularly active within the migratory dendritic cells, while glutathione synthesis is essential for cysteinyl leukotriene production by peritoneal and lung macrophages.

Phosphatidylserine enhances anti-inflammatory effects of reconstituted HDL in macrophages via distinct intracellular pathways.

Phosphatidylserine (PS) is a minor phospholipid constituent of high-density lipoprotein (HDL) that exhibits potent anti-inflammatory activity. It remains indeterminate whether PS incorporation can enhance anti-inflammatory effects of reconstituted HDL (rHDL). Human macrophages were treated with rHDL containing phosphatidylcholine alone (PC-rHDL) or PC and PS (PC/PS-rHDL). Interleukin (IL)-6 secretion and expression was more strongly inhibited by PC/PS-rHDL than PC-rHDL in both tumor necrosis factor (TNF)-α- and lipopolysaccharide (LPS)-stimulated macrophages. siRNA experiments revealed that the enhanced anti-inflammatory effects of PC/PS-rHDL required scavenger receptor class B type I (SR-BI). Furthermore, PC/PS-rHDL induced a greater increase in Akt1/2/3 phosphorylation than PC-rHDL. In addition, PC/PS but not PC-rHDL decreased the abundance of plasma membrane lipid rafts and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation. Finally, when these rHDL formulations were administered to dyslipidemic low-density lipoprotein (LDL)-receptor knockout mice fed a high-cholesterol diet, circulating IL-6 levels were significantly reduced only in PC/PS-rHDL-treated mice. In parallel, enhanced Akt1/2/3 phosphorylation by PC/PS-rHDL was observed in the mouse aortic tissue using immunohistochemistry. We concluded that the incorporation of PS into rHDLs enhanced their anti-inflammatory activity by modulating Akt1/2/3- and p38 MAPK-mediated signaling through SR-BI in stimulated macrophages. These data identify PS as a potent anti-inflammatory component capable of enhancing therapeutic potential of rHDL-based therapy.

Immune cell-mediated features of non-alcoholic steatohepatitis.

Non-alcoholic fatty liver disease (NAFLD) includes a range of hepatic manifestations, starting with liver steatosis and potentially evolving towards non-alcoholic steatohepatitis (NASH), cirrhosis or even hepatocellular carcinoma. NAFLD is a major health burden, and its incidence is increasing worldwide. Although it is primarily a disease of disturbed metabolism, NAFLD involves several immune cell-mediated inflammatory processes, particularly when reaching the stage of NASH, at which point inflammation becomes integral to the progression of the disease. The hepatic immune cell landscape is diverse at steady state and it further evolves during NASH with direct consequences for disease severity. In this Review, we discuss current concepts related to the role of immune cells in the onset and progression of NASH. A better understanding of the mechanisms by which immune cells contribute to NASH pathogenesis should aid the design of innovative drugs to target NASH, for which current therapeutic options are limited.

Adipose Tissue Fibrosis in Obesity: Etiology and Challenges.

Obesity is a chronic and progressive process affecting whole-body energy balance and is associated with comorbidity development. In addition to increased fat mass, obesity induces white adipose tissue (WAT) inflammation and fibrosis, leading to local and systemic metabolic dysfunctions, such as insulin resistance (IR). Accordingly, limiting inflammation or fibrosis deposition may improve IR and glucose homeostasis. Although no targeted therapy yet exists to slow or reverse adipose tissue fibrosis, a number of findings have clarified the underlying cellular and molecular mechanisms. In this review, we highlight adipose tissue remodeling events shown to be associated with fibrosis deposition, with a focus on adipose progenitors involved in obesity-induced healthy as well as unhealthy WAT expansion.

Non-canonical glutamine transamination sustains efferocytosis by coupling redox buffering to oxidative phosphorylation.

Macrophages rely on tightly integrated metabolic rewiring to clear dying neighboring cells by efferocytosis during homeostasis and disease. Here we reveal that glutaminase-1-mediated glutaminolysis is critical to promote apoptotic cell clearance by macrophages during homeostasis in mice. In addition, impaired macrophage glutaminolysis exacerbates atherosclerosis, a condition during which, efficient apoptotic cell debris clearance is critical to limit disease progression. Glutaminase-1 expression strongly correlates with atherosclerotic plaque necrosis in patients with cardiovascular diseases. High-throughput transcriptional and metabolic profiling reveals that macrophage efferocytic capacity relies on a non-canonical transaminase pathway, independent from the traditional requirement of glutamate dehydrogenase to fuel ɑ-ketoglutarate-dependent immunometabolism. This pathway is necessary to meet the unique requirements of efferocytosis for cellular detoxification and high-energy cytoskeletal rearrangements. Thus, we uncover a role for non-canonical glutamine metabolism for efficient clearance of dying cells and maintenance of tissue homeostasis during health and disease in mouse and humans.

Macrophage ontogeny and functional diversity in cardiometabolic diseases.

Macrophages are the dominant immune cell types in the adipose tissue, the liver or the aortic wall and they were originally believed to mainly derived from monocytes to fuel tissue inflammation in cardiometabolic diseases. However, over the last decade the identification of tissue resident macrophages (trMacs) from embryonic origin in these metabolic tissues has provided a breakthrough in the field forcing to better comprehend macrophage diversity during pathological states. Infiltrated monocyte-derived macrophages (moMacs), similar to trMacs, adapt to the local metabolic environment that eventually shapes their functions. In this review, we will summarize the emerging versatility of macrophages in cardiometabolic diseases with a focus in the control of adipose tissue, liver and large vessels homeostasis.

SHP2 drives inflammation-triggered insulin resistance by reshaping tissue macrophage populations.

Insulin resistance is a key event in type 2 diabetes onset and a major comorbidity of obesity. It results from a combination of fat excess-triggered defects, including lipotoxicity and metaflammation, but the causal mechanisms remain difficult to identify. Here, we report that hyperactivation of the tyrosine phosphatase SHP2 found in Noonan syndrome (NS) led to an unsuspected insulin resistance profile uncoupled from altered lipid management (for example, obesity or ectopic lipid deposits) in both patients and mice. Functional exploration of an NS mouse model revealed this insulin resistance phenotype correlated with constitutive inflammation of tissues involved in the regulation of glucose metabolism. Bone marrow transplantation and macrophage depletion improved glucose homeostasis and decreased metaflammation in the mice, highlighting a key role of macrophages. In-depth analysis of bone marrow-derived macrophages in vitro and liver macrophages showed that hyperactive SHP2 promoted a proinflammatory phenotype, modified resident macrophage homeostasis, and triggered monocyte infiltration. Consistent with a role of SHP2 in promoting inflammation-driven insulin resistance, pharmaceutical SHP2 inhibition in obese diabetic mice improved insulin sensitivity even better than conventional antidiabetic molecules by specifically reducing metaflammation and alleviating macrophage activation. Together, these results reveal that SHP2 hyperactivation leads to inflammation-triggered metabolic impairments and highlight the therapeutical potential of SHP2 inhibition to ameliorate insulin resistance.

Lysosomal Acid Lipase Drives Adipocyte Cholesterol Homeostasis and Modulates Lipid Storage in Obesity, Independent of Autophagy.

Besides cytoplasmic lipase-dependent adipocyte fat mobilization, the metabolic role of lysosomal acid lipase (LAL), highly expressed in adipocytes, is unclear. We show that the isolated adipocyte fraction, but not the total undigested adipose tissue (ATs), from obese patients has decreased LAL expression compared with that from nonobese people. Lentiviral-mediated LAL knockdown in the 3T3L1 mouse cell line to mimic the obese adipocytes condition did not affect lysosome density or autophagic flux, but it did increase triglyceride storage and disrupt endoplasmic reticulum cholesterol, as indicated by activated SREBP. Conversely, mice with adipose-specific LAL overexpression (Adpn-rtTA x TetO-hLAL) gained less weight and body fat than did control mice fed a high-fat diet, resulting in ameliorated glucose tolerance. Blood cholesterol level in the former was lower than that of control mice, although triglyceridemia in the two groups of mice was similar. The adipose-specific LAL-overexpressing mouse phenotype depends on the housing temperature and develops only under mild hypothermic stress (e.g., room temperature) but not at thermoneutrality (30°C), demonstrating the prominent contribution of brown AT (BAT) thermogenesis. LAL overexpression increased levels of BAT free cholesterol, decreased SREBP targets, and induced the expression of genes involved in initial steps of mitochondrial steroidogenesis, suggesting conversion of lysosome-derived cholesterol to pregnenolone. In conclusion, our study demonstrates that adipose LAL drives tissue-cholesterol homeostasis and affects BAT metabolism, suggesting beneficial LAL activation in anti-obesity approaches aimed at reactivating thermogenic energy expenditure.

Impaired Kupffer Cell Self-Renewal Alters the Liver Response to Lipid Overload during Non-alcoholic Steatohepatitis.

Kupffer cells (KCs) are liver-resident macrophages that self-renew by proliferation in the adult independently from monocytes. However, how they are maintained during non-alcoholic steatohepatitis (NASH) remains ill defined. We found that a fraction of KCs derived from Ly-6C+ monocytes during NASH, underlying impaired KC self-renewal. Monocyte-derived KCs (MoKCs) gradually seeded the KC pool as disease progressed in a response to embryo-derived KC (EmKC) death. Those MoKCs were partly immature and exhibited a pro-inflammatory status compared to EmKCs. Yet, they engrafted the KC pool for the long term as they remained following disease regression while acquiring mature EmKC markers. While KCs as a whole favored hepatic triglyceride storage during NASH, EmKCs promoted it more efficiently than MoKCs, and the latter exacerbated liver damage, highlighting functional differences among KCs with different origins. Overall, our data reveal that KC homeostasis is impaired during NASH, altering the liver response to lipids, as well as KC ontogeny.

Autophagy inhibition blunts PDGFRA adipose progenitors' cell-autonomous fibrogenic response to high-fat diet.

Adipose tissue (AT) fibrosis in obesity compromises adipocyte functions and responses to intervention-induced weight loss. It is driven by AT progenitors with dual fibro/adipogenic potential, but pro-fibrogenic pathways activated in obesity remain to be deciphered. To investigate the role of macroautophagy/autophagy in AT fibrogenesis, we used Pdgfra-CreErt2 transgenic mice to create conditional deletion of Atg7 alleles in AT progenitor cells (atg7 cKO) and examined sex-dependent, depot-specific AT remodeling in high-fat diet (HFD)-fed mice. Mice with atg7 cKO had markedly decreased extracellular matrix (ECM) gene expression in visceral, subcutaneous, and epicardial adipose depots compared to Atg7lox/lox littermates. ECM gene program regulation by autophagy inhibition occurred independently of changes in the mass of fat tissues or adipocyte numbers of specific depots, and cultured preadipocytes treated with pharmacological or siRNA-mediated autophagy disruptors could mimic these effects. We found that autophagy inhibition promotes global cell-autonomous remodeling of the paracrine TGF-BMP family landscape, whereas ECM gene modulation was independent of the autophagic regulation of GTF2IRD1. The progenitor-specific mouse model of ATG7 inhibition confirms the requirement of autophagy for white/beige adipocyte turnover, and combined to in vitro experiments, reveal progenitor autophagy dependence for AT fibrogenic response to HFD, through the paracrine remodeling of TGF-BMP factors balance. Abbreviations: CQ: chloroquine; ECM: extracellular matrix; EpiAT: epididymal adipose tissue; GTF2IRD1: general transcription factor II I repeat domain-containing 1; HFD: high-fat diet; KO: knockout; OvAT: ovarian adipose tissue; PDGFR: platelet derived growth factor receptor; ScAT: subcutaneous adipose tissue; TGF-BMP: transforming growth factor-bone morphogenic protein.

Targeted invalidation of SR-B1 in macrophages reduces macrophage apoptosis and accelerates atherosclerosis.

AIMS: SR-B1 is a cholesterol transporter that exerts anti-atherogenic properties in liver and peripheral tissues in mice. Bone marrow (BM) transfer studies suggested an atheroprotective role in cells of haematopoietic origin. Here, we addressed the specific contribution of SR-B1 in the monocyte/macrophage. METHODS AND RESULTS: We generated mice deficient for SR-B1 in monocytes/macrophages (Lysm-Cre × SR-B1f/f) and transplanted their BM into Ldlr-/- mice. Fed a cholesterol-rich diet, these mice displayed accelerated aortic atherosclerosis characterized by larger macrophage-rich areas and decreased macrophage apoptosis compared with SR-B1f/f transplanted controls. These findings were reproduced in BM transfer studies using another atherogenic mouse recipient (SR-B1 KOliver × Cholesteryl Ester Transfer Protein). Haematopoietic reconstitution with SR-B1-/- BM conducted in parallel generated similar results to those obtained with Lysm-Cre × SR-B1f/f BM; thus suggesting that among haematopoietic-derived cells, SR-B1 exerts its atheroprotective role primarily in monocytes/macrophages. Consistent with our in vivo data, free cholesterol (FC)-induced apoptosis of macrophages was diminished in the absence of SR-B1. This effect could not be attributed to differential cellular cholesterol loading. However, we observed that expression of apoptosis inhibitor of macrophage (AIM) was induced in SR-B1-deficient macrophages, and notably upon FC-loading. Furthermore, we demonstrated that macrophages were protected from FC-induced apoptosis by AIM. Finally, AIM protein was found more present within the macrophage-rich area of the atherosclerotic lesions of SR-B1-deficient macrophages than controls. CONCLUSION: Our findings suggest that macrophage SR-B1 plays a role in plaque growth by controlling macrophage apoptosis in an AIM-dependent manner.

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-1 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-1 signaling, and effector functions in lung adenocarcinoma and address the challenges to successfully incorporating these pathways into current anticancer regimens.

Lysosomal Cholesterol Hydrolysis Couples Efferocytosis to Anti-Inflammatory Oxysterol Production.

RATIONALE: Macrophages face a substantial amount of cholesterol after the ingestion of apoptotic cells, and the LIPA (lysosomal acid lipase) has a major role in hydrolyzing cholesteryl esters in the endocytic compartment. OBJECTIVE: Here, we directly investigated the role of LIPA-mediated clearance of apoptotic cells both in vitro and in vivo. METHODS AND RESULTS: We show that LIPA inhibition causes a defective efferocytic response because of impaired generation of 25-hydroxycholesterol and 27-hydroxycholesterol. Reduced synthesis of 25-hydroxycholesterol after LIPA inhibition contributed to defective mitochondria-associated membrane leading to mitochondrial oxidative stress-induced NLRP3 (NOD-like receptor family, pyrin domain containing) inflammasome activation and caspase-1-dependent Rac1 (Ras-related C3 botulinum toxin substrate 1) degradation. A secondary event consisting of failure to appropriately activate liver X receptor-mediated pathways led to mitigation of cholesterol efflux and apoptotic cell clearance. In mice, LIPA inhibition caused defective clearance of apoptotic lymphocytes and stressed erythrocytes by hepatic and splenic macrophages, culminating in splenomegaly and splenic iron accumulation under hypercholesterolemia. CONCLUSIONS: Our findings position lysosomal cholesterol hydrolysis as a critical process that prevents metabolic inflammation by enabling efficient macrophage apoptotic cell clearance.