A palmitate-rich metastatic niche enables metastasis growth via p65 acetylation resulting in pro-metastatic NF-κB signaling.

Metabolic rewiring is often considered an adaptive pressure limiting metastasis formation; however, some nutrients available at distant organs may inherently promote metastatic growth. We find that the lung and liver are lipid-rich environments. Moreover, we observe that pre-metastatic niche formation increases palmitate availability only in the lung, whereas a high-fat diet increases it in both organs. In line with this, targeting palmitate processing inhibits breast cancer-derived lung metastasis formation. Mechanistically, breast cancer cells use palmitate to synthesize acetyl-CoA in a carnitine palmitoyltransferase 1a-dependent manner. Concomitantly, lysine acetyltransferase 2a expression is promoted by palmitate, linking the available acetyl-CoA to the acetylation of the nuclear factor-kappaB subunit p65. Deletion of lysine acetyltransferase 2a or carnitine palmitoyltransferase 1a reduces metastasis formation in lean and high-fat diet mice, and lung and liver metastases from patients with breast cancer show coexpression of both proteins. In conclusion, palmitate-rich environments foster metastases growth by increasing p65 acetylation, resulting in a pro-metastatic nuclear factor-kappaB signaling.

CD8+ T cell metabolic rewiring defined by scRNA-seq identifies a critical role of ASNS expression dynamics in T cell differentiation.

T cells dynamically rewire their metabolism during an immune response. We applied single-cell RNA sequencing to CD8+ T cells activated and differentiated in vitro in physiological medium to resolve these metabolic dynamics. We identify a differential time-dependent reliance of activating T cells on the synthesis versus uptake of various non-essential amino acids, which we corroborate with functional assays. We also identify metabolic genes that potentially dictate the outcome of T cell differentiation, by ranking them based on their expression dynamics. Among them, we find asparagine synthetase (Asns), whose expression peaks for effector T cells and decays toward memory formation. Disrupting these expression dynamics by ASNS overexpression promotes an effector phenotype, enhancing the anti-tumor response of adoptively transferred CD8+ T cells in a mouse melanoma model. We thus provide a resource of dynamic expression changes during CD8+ T cell activation and differentiation, and identify ASNS expression dynamics as a modulator of CD8+ T cell differentiation.

PHGDH heterogeneity potentiates cancer cell dissemination and metastasis.

Cancer metastasis requires the transient activation of cellular programs enabling dissemination and seeding in distant organs1. Genetic, transcriptional and translational heterogeneity contributes to this dynamic process2,3. Metabolic heterogeneity has also been observed4, yet its role in cancer progression is less explored. Here we find that the loss of phosphoglycerate dehydrogenase (PHGDH) potentiates metastatic dissemination. Specifically, we find that heterogeneous or low PHGDH expression in primary tumours of patients with breast cancer is associated with decreased metastasis-free survival time. In mice, circulating tumour cells and early metastatic lesions are enriched with Phgdhlow cancer cells, and silencing Phgdh in primary tumours increases metastasis formation. Mechanistically, Phgdh interacts with the glycolytic enzyme phosphofructokinase, and the loss of this interaction activates the hexosamine-sialic acid pathway, which provides precursors for protein glycosylation. As a consequence, aberrant protein glycosylation occurs, including increased sialylation of integrin αvß3, which potentiates cell migration and invasion. Inhibition of sialylation counteracts the metastatic ability of Phgdhlow cancer cells. In conclusion, although the catalytic activity of PHGDH supports cancer cell proliferation, low PHGDH protein expression non-catalytically potentiates cancer dissemination and metastasis formation. Thus, the presence of PHDGH heterogeneity in primary tumours could be considered a sign of tumour aggressiveness.

Altered propionate metabolism contributes to tumour progression and aggressiveness.

The alteration of metabolic pathways is a critical strategy for cancer cells to attain the traits necessary for metastasis in disease progression. Here, we find that dysregulation of propionate metabolism produces a pro-aggressive signature in breast and lung cancer cells, increasing their metastatic potential. This occurs through the downregulation of methylmalonyl coenzyme A epimerase (MCEE), mediated by an extracellular signal-regulated kinase 2-driven transcription factor Sp1/early growth response protein 1 transcriptional switch driven by metastatic signalling at its promoter level. The loss of MCEE results in reduced propionate-driven anaplerotic flux and intracellular and intratumoral accumulation of methylmalonic acid, a by-product of propionate metabolism that promotes cancer cell invasiveness. Altogether, we present a previously uncharacterized dysregulation of propionate metabolism as an important contributor to cancer and a valuable potential target in the therapeutic treatment of metastatic carcinomas.

Macrophages are metabolically heterogeneous within the tumor microenvironment.

Macrophages are often prominently present in the tumor microenvironment, where distinct macrophage populations can differentially affect tumor progression. Although metabolism influences macrophage function, studies on the metabolic characteristics of ex vivo tumor-associated macrophage (TAM) subsets are rather limited. Using transcriptomic and metabolic analyses, we now reveal that pro-inflammatory major histocompatibility complex (MHC)-IIhi TAMs display a hampered tricarboxylic acid (TCA) cycle, while reparative MHC-IIlo TAMs show higher oxidative and glycolytic metabolism. Although both TAM subsets rapidly exchange lactate in high-lactate conditions, only MHC-IIlo TAMs use lactate as an additional carbon source. Accordingly, lactate supports the oxidative metabolism in MHC-IIlo TAMs, while it decreases the metabolic activity of MHC-IIhi TAMs. Lactate subtly affects the transcriptome of MHC-IIlo TAMs, increases L-arginine metabolism, and enhances the T cell suppressive capacity of these TAMs. Overall, our data uncover the metabolic intricacies of distinct TAM subsets and identify lactate as a carbon source and metabolic and functional regulator of TAMs.

Fat Induces Glucose Metabolism in Nontransformed Liver Cells and Promotes Liver Tumorigenesis.

Hepatic fat accumulation is associated with diabetes and hepatocellular carcinoma (HCC). Here, we characterize the metabolic response that high-fat availability elicits in livers before disease development. After a short term on a high-fat diet (HFD), otherwise healthy mice showed elevated hepatic glucose uptake and increased glucose contribution to serine and pyruvate carboxylase activity compared with control diet (CD) mice. This glucose phenotype occurred independently from transcriptional or proteomic programming, which identifies increased peroxisomal and lipid metabolism pathways. HFD-fed mice exhibited increased lactate production when challenged with glucose. Consistently, administration of an oral glucose bolus to healthy individuals revealed a correlation between waist circumference and lactate secretion in a human cohort. In vitro, palmitate exposure stimulated production of reactive oxygen species and subsequent glucose uptake and lactate secretion in hepatocytes and liver cancer cells. Furthermore, HFD enhanced the formation of HCC compared with CD in mice exposed to a hepatic carcinogen. Regardless of the dietary background, all murine tumors showed similar alterations in glucose metabolism to those identified in fat exposed nontransformed mouse livers, however, particular lipid species were elevated in HFD tumor and nontumor-bearing HFD liver tissue. These findings suggest that fat can induce glucose-mediated metabolic changes in nontransformed liver cells similar to those found in HCC. SIGNIFICANCE: With obesity-induced hepatocellular carcinoma on a rising trend, this study shows in normal, nontransformed livers that fat induces glucose metabolism similar to an oncogenic transformation.

In Vivo Evidence for Serine Biosynthesis-Defined Sensitivity of Lung Metastasis, but Not of Primary Breast Tumors, to mTORC1 Inhibition.

In tumors, nutrient availability and metabolism are known to be important modulators of growth signaling. However, it remains elusive whether cancer cells that are growing out in the metastatic niche rely on the same nutrients and metabolic pathways to activate growth signaling as cancer cells within the primary tumor. We discovered that breast-cancer-derived lung metastases, but not the corresponding primary breast tumors, use the serine biosynthesis pathway to support mTORC1 growth signaling. Mechanistically, pyruvate uptake through Mct2 supported mTORC1 signaling by fueling serine biosynthesis-derived α-ketoglutarate production in breast-cancer-derived lung metastases. Consequently, expression of the serine biosynthesis enzyme PHGDH was required for sensitivity to the mTORC1 inhibitor rapamycin in breast-cancer-derived lung tumors, but not in primary breast tumors. In summary, we provide in vivo evidence that the metabolic and nutrient requirements to activate growth signaling differ between the lung metastatic niche and the primary breast cancer site.

Age-induced accumulation of methylmalonic acid promotes tumour progression.

The risk of cancer and associated mortality increases substantially in humans from the age of 65 years onwards1-6. Nonetheless, our understanding of the complex relationship between age and cancer is still in its infancy2,3,7,8. For decades, this link has largely been attributed to increased exposure time to mutagens in older individuals. However, this view does not account for the established role of diet, exercise and small molecules that target the pace of metabolic ageing9-12. Here we show that metabolic alterations that occur with age can produce a systemic environment that favours the progression and aggressiveness of tumours. Specifically, we show that methylmalonic acid (MMA), a by-product of propionate metabolism, is upregulated in the serum of older people and functions as a mediator of tumour progression. We traced this to the ability of MMA to induce SOX4 expression and consequently to elicit transcriptional reprogramming that can endow cancer cells with aggressive properties. Thus, the accumulation of MMA represents a link between ageing and cancer progression, suggesting that MMA is a promising therapeutic target for advanced carcinomas.

mTOR Signaling and SREBP Activity Increase FADS2 Expression and Can Activate Sapienate Biosynthesis.

Cancer cells display an increased plasticity in their lipid metabolism, which includes the conversion of palmitate to sapienate via the enzyme fatty acid desaturase 2 (FADS2). We find that FADS2 expression correlates with mammalian target of rapamycin (mTOR) signaling and sterol regulatory element-binding protein 1 (SREBP-1) activity across multiple cancer types and is prognostic in some cancer types. Accordingly, activating mTOR signaling by deleting tuberous sclerosis complex 2 (Tsc2) or overexpression of SREBP-1/2 is sufficient to increase FADS2 mRNA expression and sapienate metabolism in mouse embryonic fibroblasts (MEFs) and U87 glioblastoma cells, respectively. Conversely, inhibiting mTOR signaling decreases FADS2 expression and sapienate biosynthesis in MEFs with Tsc2 deletion, HUH7 hepatocellular carcinoma cells, and orthotopic HUH7 liver xenografts. In conclusion, we show that mTOR signaling and SREBP activity are sufficient to activate sapienate metabolism by increasing FADS2 expression. Consequently, targeting mTOR signaling can reduce sapienate metabolism in vivo.

Analyzing the Metabolism of Metastases in Mice.

Metastasis formation is the leading cause of death in cancer patients. It has recently emerged that cancer cells adapt their metabolism to successfully transition through the metastatic cascade. Consequently, measuring and analyzing the in vivo metabolism of metastases has the potential to reveal novel treatment strategies to prevent metastasis formation. Here, we describe two different metastasis mouse models and how their metabolism can be analyzed with metabolomics and 13C tracer analysis.

Breast cancer cells rely on environmental pyruvate to shape the metastatic niche.

The extracellular matrix is a major component of the local environment-that is, the niche-that determines cell behaviour1. During metastatic growth, cancer cells shape the extracellular matrix of the metastatic niche by hydroxylating collagen to promote their own metastatic growth2,3. However, only particular nutrients might support the ability of cancer cells to hydroxylate collagen, because nutrients dictate which enzymatic reactions are active in cancer cells4,5. Here we show that breast cancer cells rely on the nutrient pyruvate to drive collagen-based remodelling of the extracellular matrix in the lung metastatic niche. Specifically, we discovered that pyruvate uptake induces the production of α-ketoglutarate. This metabolite in turn activates collagen hydroxylation by increasing the activity of the enzyme collagen prolyl-4-hydroxylase (P4HA). Inhibition of pyruvate metabolism was sufficient to impair collagen hydroxylation and consequently the growth of breast-cancer-derived lung metastases in different mouse models. In summary, we provide a mechanistic understanding of the link between collagen remodelling and the nutrient environment in the metastatic niche.

Evidence for an alternative fatty acid desaturation pathway increasing cancer plasticity.

Most tumours have an aberrantly activated lipid metabolism1,2 that enables them to synthesize, elongate and desaturate fatty acids to support proliferation. However, only particular subsets of cancer cells are sensitive to approaches that target fatty acid metabolism and, in particular, fatty acid desaturation3. This suggests that many cancer cells contain an unexplored plasticity in their fatty acid metabolism. Here we show that some cancer cells can exploit an alternative fatty acid desaturation pathway. We identify various cancer cell lines, mouse hepatocellular carcinomas, and primary human liver and lung carcinomas that desaturate palmitate to the unusual fatty acid sapienate to support membrane biosynthesis during proliferation. Accordingly, we found that sapienate biosynthesis enables cancer cells to bypass the known fatty acid desaturation pathway that is dependent on stearoyl-CoA desaturase. Thus, only by targeting both desaturation pathways is the in vitro and in vivo proliferation of cancer cells that synthesize sapienate impaired. Our discovery explains metabolic plasticity in fatty acid desaturation and constitutes an unexplored metabolic rewiring in cancers.

Measuring In Vivo Tissue Metabolism Using 13C Glucose Infusions in Mice.

Metabolic alterations are a hallmark of cancer. While determining metabolic changes in vitro has delivered valuable insight into the metabolism of cancer cells, it emerges that determining the in vivo metabolism adds an additional layer of information. Here, we therefore describe how to measure the in vivo metabolism of cancer tissue using 13C glucose infusions in mice.

Proline metabolism supports metastasis formation and could be inhibited to selectively target metastasizing cancer cells.

Metastases are the leading cause of mortality in patients with cancer. Metastasis formation requires cancer cells to adapt their cellular phenotype. However, how metabolism supports this adaptation of cancer cells is poorly defined. We use 2D versus 3D cultivation to induce a shift in the cellular phenotype of breast cancer cells. We discover that proline catabolism via proline dehydrogenase (Prodh) supports growth of breast cancer cells in 3D culture. Subsequently, we link proline catabolism to in vivo metastasis formation. In particular, we find that PRODH expression and proline catabolism is increased in metastases compared to primary breast cancers of patients and mice. Moreover, inhibiting Prodh is sufficient to impair formation of lung metastases in the orthotopic 4T1 and EMT6.5 mouse models, without adverse effects on healthy tissue and organ function. In conclusion, we discover that Prodh is a potential drug target for inhibiting metastasis formation.

Multipotent adult progenitor cells improve the hematopoietic function in myelodysplasia.

BACKGROUND AIMS: Myelodysplastic syndromes (MDS) are a group of clonal stem cell disorders affecting the normal hematopoietic differentiation process and leading to abnormal maturation and differentiation of all blood cell lineages. Treatment options are limited, and there is an unmet medical need for effective therapies for patients with severe cytopenias. METHODS: We demonstrate that multipotent adult progenitor cells (MAPC) improve the function of hematopoietic progenitors derived from human MDS bone marrow (BM) by significantly increasing the frequency of primitive progenitors as well as the number of myeloid colonies. RESULTS: This effect was more pronounced in a non-contact culture, indicating the importance of soluble factors produced by the MAPC cells. Moreover, the cells did not stimulate the growth of the abnormal MDS clone, as shown by fluorescent in situ hybridization analysis on BM cells from patients with a known genetic abnormality. We also demonstrate that MAPC cells can provide stromal support for patient-derived hematopoietic cells. When MAPC cells were intravenously injected into a mouse model of MDS, they migrated to the site of injury and increased the hematopoietic function in diseased mice. DISCUSSION: The preclinical studies undertaken here indicate an initial proof of concept for the use of MAPC cell therapy in patients with MDS-related severe and symptomatic cytopenias and should pave the way for further investigation in clinical trials.

Breast Cancer-Derived Lung Metastases Show Increased Pyruvate Carboxylase-Dependent Anaplerosis.

Cellular proliferation depends on refilling the tricarboxylic acid (TCA) cycle to support biomass production (anaplerosis). The two major anaplerotic pathways in cells are pyruvate conversion to oxaloacetate via pyruvate carboxylase (PC) and glutamine conversion to α-ketoglutarate. Cancers often show an organ-specific reliance on either pathway. However, it remains unknown whether they adapt their mode of anaplerosis when metastasizing to a distant organ. We measured PC-dependent anaplerosis in breast-cancer-derived lung metastases compared to their primary cancers using in vivo 13C tracer analysis. We discovered that lung metastases have higher PC-dependent anaplerosis compared to primary breast cancers. Based on in vitro analysis and a mathematical model for the determination of compartment-specific metabolite concentrations, we found that mitochondrial pyruvate concentrations can promote PC-dependent anaplerosis via enzyme kinetics. In conclusion, we show that breast cancer cells proliferating as lung metastases activate PC-dependent anaplerosis in response to the lung microenvironment.

Deletion or Inhibition of the Oxygen Sensor PHD1 Protects against Ischemic Stroke via Reprogramming of Neuronal Metabolism.

The oxygen-sensing prolyl hydroxylase domain proteins (PHDs) regulate cellular metabolism, but their role in neuronal metabolism during stroke is unknown. Here we report that PHD1 deficiency provides neuroprotection in a murine model of permanent brain ischemia. This was not due to an increased collateral vessel network. Instead, PHD1(-/-) neurons were protected against oxygen-nutrient deprivation by reprogramming glucose metabolism. Indeed, PHD1(-/-) neurons enhanced glucose flux through the oxidative pentose phosphate pathway by diverting glucose away from glycolysis. As a result, PHD1(-/-) neurons increased their redox buffering capacity to scavenge oxygen radicals in ischemia. Intracerebroventricular injection of PHD1-antisense oligonucleotides reduced the cerebral infarct size and neurological deficits following stroke. These data identify PHD1 as a regulator of neuronal metabolism and a potential therapeutic target in ischemic stroke.

Highly proliferative primitive fetal liver hematopoietic stem cells are fueled by oxidative metabolic pathways.

Hematopoietic stem cells (HSCs) in the fetal liver (FL) unlike adult bone marrow (BM) proliferate extensively, posing different metabolic demands. However, metabolic pathways responsible for the production of energy and cellular building blocks in FL HSCs have not been described. Here, we report that FL HSCs use oxygen dependent energy generating pathways significantly more than their BM counterparts. RNA-Seq analysis of E14.5 FL versus BM derived HSCs identified increased expression levels of genes involved in oxidative phosphorylation (OxPhos) and the citric acid cycle (TCA). We demonstrated that FL HSCs contain more mitochondria than BM HSCs, which resulted in increased levels of oxygen consumption and reactive oxygen species (ROS) production. Higher levels of DNA repair and antioxidant pathway gene expression may prevent ROS-mediated (geno)toxicity in FL HSCs. Thus, we here for the first time highlight the underestimated importance of oxygen dependent pathways for generating energy and building blocks in FL HSCs.

Alternative Routes to Induce Naïve Pluripotency in Human Embryonic Stem Cells.

Human embryonic stem cells (hESCs) closely resemble mouse epiblast stem cells exhibiting primed pluripotency unlike mouse ESCs (mESCs), which acquire a naïve pluripotent state. Efforts have been made to trigger naïve pluripotency in hESCs for subsequent unbiased lineage-specific differentiation, a common conundrum faced by primed pluripotent hESCs due to heterogeneity in gene expression existing within and between hESC lines. This required either ectopic expression of naïve genes such as NANOG and KLF2 or inclusion of multiple pluripotency-associated factors. We report here a novel combination of small molecules and growth factors in culture medium (2i/LIF/basic fibroblast growth factor + Ascorbic Acid + Forskolin) facilitating rapid induction of transgene-free naïve pluripotency in hESCs, as well as in mESCs, which has not been shown earlier. The converted naïve hESCs survived long-term single-cell passaging, maintained a normal karyotype, upregulated naïve pluripotency genes, and exhibited dependence on signaling pathways similar to naïve mESCs. Moreover, they undergo global DNA demethylation and show a distinctive long noncoding RNA profile. We propose that in our medium, the FGF signaling pathway via PI3K/AKT/mTORC induced the conversion of primed hESCs toward naïve pluripotency. Collectively, we demonstrate an alternate route to capture naïve pluripotency in hESCs that is fast, reproducible, supports naïve mESC derivation, and allows efficient differentiation.