Tumors consist of a wide variety of cells, including immune cells, that affect tumor progression. Macrophages are abundant innate immune cells in the tumor microenvironment (TME) and are crucial in regulating tumorigenicity. Specific metabolic conditions in the TME can alter the phenotype of tumor-associated macrophages (TAMs) in a direction that supports their pro-tumor functions. One of these conditions is the accumulation of metabolites, also known as oncometabolites. Interactions of oncometabolites with TAMs can promote a pro-tumorigenic phenotype, thereby sustaining cancer cell growth and decreasing the chance of eradication. This review focuses on the metabolic cancer-macrophage crosstalk in the TME. We discuss how cancer cell metabolism and oncometabolites affect macrophage phenotype and function, and conversely how macrophage metabolism can impact tumor progression. Lastly, we propose tumor-secreted exosome-mediated metabolic signaling as a potential factor in tumorigenesis. Insight in these processes may contribute to the development of novel cancer therapies.

Dilated cardiomyopathy amongst children (pediatric cardiomyopathy, pediatric CM) is associated with a high morbidity and mortality. Because little is known about the pathophysiology of pediatric CM, treatment is largely based on adult heart failure therapy. The reason for high morbidity and mortality is largely unknown as well as data on cellular pathomechanisms is limited. Here, we assessed cardiomyocyte contractility and protein expression to define cellular pathomechanisms in pediatric CM. Explanted heart tissue of 11 pediatric CM patients and 18 controls was studied. Contractility was measured in single membrane-permeabilized cardiomyocytes and protein expression was assessed with gel electrophoresis and western blot analysis. We observed increased Ca2+-sensitivity of myofilaments which was due to hypophosphorylation of cardiac troponin I, a feature commonly observed in adult DCM. We also found a significantly reduced maximal force generating capacity of pediatric CM cardiomyocytes, as well as a reduced passive force development over a range of sarcomere lengths. Myofibril density was reduced in pediatric CM compared to controls. Correction of maximal force and passive force for myofibril density normalized forces in pediatric CM cardiomyocytes to control values. This implies that the hypocontractility was caused by the reduction in myofibril density. Unlike in adult DCM we did not find an increase in compliant titin isoform expression in end-stage pediatric CM. The limited ability of pediatric CM patients to maintain myofibril density might have contributed to their early disease onset and severity.

Chronic low-grade inflammation, also called metaflammation, is associated with prevalent non-communicable diseases, such as atherosclerosis. Anti-inflammatory therapy provides a clinical benefit in patients, but the triggers that incite metaflammation remain largely unknown. To uncover non-genetic inflammatory factors influencing atherosclerosis severity, we performed an unbiased in vivo screen measuring thousands of host- and microbe-derived molecules in a mouse model of atherosclerosis. Machine learning-supported analyses identified, next to known pro- and anti-atherogenic factors, the medium fatty acid-chain sphingomyelin d18:1/14:0 (S14) as highly positively associated with atherogenesis. S14 activated macrophage innate immune signalling, immune-metabolic reprogramming and pro-inflammatory gene transcription. The inflammatory activity of S14 was TLR4- and MD-2-dependent, consistent with biochemical and molecular dynamics simulation analyses showing that S14 promoted the formation of active TLR4/MD-2 dimers. Human interventional and observational trials demonstrated that dietary changes altered concentrations of S14 and that increased circulating S14 was associated with carotid plaque development in obese individuals. Collectively, these findings identify an inducible endogenous ligand for TLR4 that drives metaflammation, providing the rationale for preventative approaches and pharmacological interventions that may curb detrimental inflammation secondary to Western-type lifestyle habits.