Spatially resolved characterization of tissue metabolic compartments in fasted and high-fat diet livers.

Cells adapt their metabolism to physiological stimuli, and metabolic heterogeneity exists between cell types, within tissues, and subcellular compartments. The liver plays an essential role in maintaining whole-body metabolic homeostasis and is structurally defined by metabolic zones. These zones are well-understood on the transcriptomic level, but have not been comprehensively characterized on the metabolomic level. Mass spectrometry imaging (MSI) can be used to map hundreds of metabolites directly from a tissue section, offering an important advance to investigate metabolic heterogeneity in tissues compared to extraction-based metabolomics methods that analyze tissue metabolite profiles in bulk. We established a workflow for the preparation of tissue specimens for matrix-assisted laser desorption/ionization (MALDI) MSI that can be implemented to achieve broad coverage of central carbon, nucleotide, and lipid metabolism pathways. Herein, we used this approach to visualize the effect of nutrient stress and excess on liver metabolism. Our data revealed a highly organized metabolic tissue compartmentalization in livers, which becomes disrupted under high fat diet. Fasting caused changes in the abundance of several metabolites, including increased levels of fatty acids and TCA intermediates while fatty livers had higher levels of purine and pentose phosphate-related metabolites, which generate reducing equivalents to counteract oxidative stress. This spatially conserved approach allowed the visualization of liver metabolic compartmentalization at 30 µm pixel resolution and can be applied more broadly to yield new insights into metabolic heterogeneity in vivo.

Metabolomic and transcriptomic signatures of chemogenetic heart failure.

The failing heart is characterized by elevated levels of reactive oxygen species. We have developed an animal model of heart failure induced by chemogenetic production of oxidative stress in the heart using a recombinant adeno-associated virus (AAV9) expressing yeast d-amino acid oxidase (DAAO) targeted to cardiac myocytes. When DAAO-infected animals are fed the DAAO substrate d-alanine, the enzyme generates hydrogen peroxide (H2O2) in the cardiac myocytes, leading to dilated cardiomyopathy. However, the underlying mechanisms of oxidative stress-induced heart failure remain incompletely understood. Therefore, we investigated the effects of chronic oxidative stress on the cardiac transcriptome and metabolome. Rats infected with recombinant cardiotropic AAV9 expressing DAAO or control AAV9 were treated for 7 wk with d-alanine to stimulate chemogenetic H2O2 production by DAAO and generate dilated cardiomyopathy. After hemodynamic assessment, left and right ventricular tissues were processed for RNA sequencing and metabolomic profiling. DAAO-induced dilated cardiomyopathy was characterized by marked changes in the cardiac transcriptome and metabolome both in the left and right ventricle. Downregulated transcripts are related to energy metabolism and mitochondrial function, accompanied by striking alterations in metabolites involved in cardiac energetics, redox homeostasis, and amino acid metabolism. Upregulated transcripts are involved in cytoskeletal organization and extracellular matrix. Finally, we noted increased metabolite levels of antioxidants glutathione and ascorbate. These findings provide evidence that chemogenetic generation of oxidative stress leads to a robust heart failure model with distinct transcriptomic and metabolomic signatures and set the basis for understanding the underlying pathophysiology of chronic oxidative stress in the heart.NEW & NOTEWORTHY We have developed a "chemogenetic" heart failure animal model that recapitulates a central feature of human heart failure: increased cardiac redox stress. We used a recombinant DAAO enzyme to generate H2O2 in cardiomyocytes, leading to cardiomyopathy. Here we report striking changes in the cardiac metabolome and transcriptome following chemogenetic heart failure, similar to changes observed in human heart failure. Our findings help validate chemogenetic approaches for the discovery of novel therapeutic targets in heart failure.

Mitochondria: Their relevance during oocyte ageing.

The oocyte is recognised as the largest cell in mammalian species and other multicellular organisms. Mitochondria represent a high proportion of the cytoplasm in oocytes and mitochondrial architecture is different in oocytes than in somatic cells, characterised by a rounder appearance and fragmented network. Although the number of mitochondria per oocyte is higher than in any other mammalian cell, their number and activity decrease with advancing age. Mitochondria integrate numerous processes essential for cellular function, such as metabolic processes related to energy production, biosynthesis, and waste removal, as well as Ca2+ signalling and reactive oxygen species (ROS) homeostasis. Further, mitochondria are responsible for the cellular adaptation to different types of stressors such as oxidative stress or DNA damage. When these stressors outstrip the adaptive capacity of mitochondria to restore homeostasis, it leads to mitochondrial dysfunction. Decades of studies indicate that mitochondrial function is multifaceted, which is reflected in the oocyte, where mitochondria support numerous processes during oocyte maturation, fertilization, and early embryonic development. Dysregulation of mitochondrial processes has been consistently reported in ageing and age-related diseases. In this review, we describe the functions of mitochondria as bioenergetic powerhouses and signal transducers in oocytes, how dysfunction of mitochondrial processes contributes to reproductive ageing, and whether mitochondria could be targeted to promote oocyte rejuvenation.

Proteome-wide analysis of cysteine oxidation reveals metabolic sensitivity to redox stress.

Reactive oxygen species (ROS) are increasingly recognised as important signalling molecules through oxidation of protein cysteine residues. Comprehensive identification of redox-regulated proteins and pathways is crucial to understand ROS-mediated events. Here, we present stable isotope cysteine labelling with iodoacetamide (SICyLIA), a mass spectrometry-based workflow to assess proteome-scale cysteine oxidation. SICyLIA does not require enrichment steps and achieves unbiased proteome-wide sensitivity. Applying SICyLIA to diverse cellular models and primary tissues provides detailed insights into thiol oxidation proteomes. Our results demonstrate that acute and chronic oxidative stress causes oxidation of distinct metabolic proteins, indicating that cysteine oxidation plays a key role in the metabolic adaptation to redox stress. Analysis of mouse kidneys identifies oxidation of proteins circulating in biofluids, through which cellular redox stress can affect whole-body physiology. Obtaining accurate peptide oxidation profiles from complex organs using SICyLIA holds promise for future analysis of patient-derived samples to study human pathologies.

Anti-cancer effects of vitamin C revisited.

Vitamin C was first suggested to have cancer-fighting properties in the 1930s and has been the subject of controversy ever since. Despite repeated reports of selective cancer cell toxicity induced by high-dose vitamin C treatment in vitro and in mouse models, the mechanism of action has remained elusive.