Articles in 2019

In this issue, Diehl et al. report that exogenous serine is essential for the cellular redox state and cancer nucleotide production, despite the ability of cancer cells to synthesize serine de novo in vitro.

Obesity is the result of an imbalance between caloric intake from the diet and energy expenditure. A new study provides evidence that alterations in calcium transport efficiency in muscle lead to an increased metabolic rate and protect mice against diet-induced obesity.

The liver is a heterogeneous organ organized in lobules that are radially polarized. The use of single-cell spatial transcriptomics has revealed that half of hepatic genes are differentially expressed across the lobule. Ben-Moshe et al. show how a multi-omics approach, which consists of transcriptomics, micro RNA profiling and proteomics, allows for characterization of liver heterogeneity with higher resolution.

Cancer cells increase serine synthesis; however, exogenous serine is required for maximal proliferation. Here the authors show that the demand for oxidized NAD⁺ constrains serine synthesis, which is needed for purine production to support cell proliferation.

Tajima and colleagues identify mitochondrial lipoylation as a post-transcriptional molecular signature of aged brown adipose tissue (BAT) in mice. Reduced mitochondrial lipoylation is tightly coupled with the age-associated decline in BAT function, whereas enhanced lipoylation restores BAT activity in aged mice.

The role of skeletal muscle in non-shivering thermogenesis is not fully elucidated. Here the authors show that, in muscle, phospholipids can influence whole-body metabolic rate and counteract obesity by altering calcium signalling and inducing energy expenditure.

Asano et al. dissect the functional difference between the soluble and membrane-bound forms of RANKL. Membrane-bound RANKL is sufficient for most physiological RANKL functions, whereas soluble RANKL promotes bone metastases by stimulating tumour cell migration to bone, without affecting tumour cell growth or osteoclast differentiation.

Systemic accumulation of branched-chain amino acids (BCAAs) is a major metabolic hallmark and contributor to insulin resistance associated with obesity. A recent report identifies SLC25A44 as the BCAA transporter in mitochondrial membranes and shows that BCAA catabolism in brown adipose tissue significantly affects thermogenic activity, systemic BCAA clearance, energy expenditure and overall metabolic health.

Dopamine is an important neurotransmitter with essential roles in movement control and salience, and implications in addiction as well as weight loss, decreased food intake and a reduced motivational drive to eat. Folgueira et al. now demonstrate that dopamine causes weight loss and increases brown adipose tissue temperature via activation of the dopamine receptor D2R in hypothalamic GABA-expressing neurons in mice, and treatment with the dopamine agonist cabergoline causes weight loss in humans.

Cells contributing to atherosclerotic disease are highly plastic and can shift their phenotype in a changing microenvironment. A study in Nature Metabolism now reveals that transforming growth factor-β (TGF-β) can transform endothelial cells into pro-inflammatory cells and that inhibition of TGF-β-receptor signalling in the endothelium can reverse atherosclerosis in mice.

Chen et al. report that TGF-β signalling, although largely considered anti-inflammatory, has proinflammatory effects on endothelial cells. Inhibition of endothelial TGF-β signalling decreases atherosclerosis in mice and reverts established plaques, in part by decreasing endothelial-to-mesenchymal transitions.

The gene encoding the RagC GTPase (RRAGC), an activator of a nutrient-sensing pathway that drives cellular anabolism, is mutated in 15% of follicular lymphoma cases. A new study provides evidence that RRAGC mutations promote lymphomagenesis by distorting the nutrient-dependent control of paracrine signals from the microenvironment, thus enhancing B-cell activation.

A recent study by Esteghamat et al., published in Nature Genetics, has reported that CELA2A, encoding a pancreatic enzyme, is a novel genetic cause of metabolic syndrome and atherosclerosis.

Some follicular B cell lymphomas harbour activating mutations in RRAGC, activator of the nutrient sensor mTORC1. Here the authors show that these mutations confer insensitivity to nutrient deprivation and synergize with paracrine cues from the supportive T cell microenvironment to accelerate lymphomagenesis, but impose vulnerability to inhibition of mTORC1.

Folgueira et al. show that dopamine signalling in the lateral hypothalamic area and the zona incerta reduces body weight and increases energy expenditure by increasing brown adipose tissue thermogenesis in rodents. Weight loss and increased energy expenditure were also observed in patients treated with a dopamine receptor 2 agonist.

Brown adipose tissue (BAT) has high thermogenic potential and is considered a promising target to counteract obesity. Here de Jong et al. demonstrate that human BAT is more similar to classical brown than to beige adipose tissue from mice kept at thermoneutrality and challenged with a high-fat diet.

Although germline removal normally extends Caenorhabditis elegans lifespan, Lee et al. show that low temperature does not extend lifespan in germline-lacking mutant worms. Cold temperatures (10 °C, 15 °C) delay germline stem cell exhaustion, releasing prostaglandin E2 hormone, which induces cbs-1 in the intestine to produce hydrogen sulfide and prolong lifespan.

Jeffrey Friedman reviews the biology and evolutionary role of leptin as a regulator of behaviour and metabolism. He goes on to propose the existence of two states of obesity, distinguished by hyposecretion or hypersecretion of leptin, referred to as ‘Type 1 obesity’ and ‘Type 2 obesity’, respectively.

Mammalian cell culture represents a cornerstone of modern biomedical research. There is growing appreciation that the media conditions in which cells are cultured can profoundly influence the observed biology and reproducibility. Here, we consider a key but often ignored variable, oxygen, and review why being mindful of this environmental parameter is so important in the design and interpretation of cell culture studies.