Dynamic regulation of subcellular mitochondrial position for localized metabolite levels

Mitochondria are not passive bystanders aimlessly floating throughout our cell's cytoplasm. Instead, mitochondria actively move, anchor, divide, fuse, self-destruct and transfer between cells in a coordinated fashion, all to ensure proper structure and position supporting cell function. The existence of the mitochondria in our cells has long been appreciated, but their dynamic nature and interaction with other subcellular compartments has only recently been fully realized with the advancement of high-resolution live-cell microscopy and improved fractionization techniques. The how and why that dictates positioning of mitochondria to specific subcellular sites is an ever-expanding research area. Furthermore, the advent of new and improved functional probes, sensitive to changes in subcellular metabolite levels has increased our understanding of local mitochondrial populations. In this review, we will address the evidence for intentional mitochondrial positioning in supporting subcellular mitochondrial metabolite levels, including calcium, adenosine triphosphate and reactive oxygen species and the role mitochondrial metabolites play in dictating cell outcomes.

Restricted exchange microenvironments for cell culture

Metabolite diffusion in tissues produces gradients and heterogeneous microenvironments that are not captured in standard 2D cell culture models. Here we describe restricted exchange environment chambers (REECs) in which diffusive gradients are formed and manipulated on length scales approximating those found in vivo. In REECs, cells are grown in 2D in an asymmetric chamber (<50 μL) formed between a coverglass and a glass bottom cell culture dish separated by a thin (~100 μm) gasket. Diffusive metabolite exchange between the chamber and bulk media occurs through one or more openings micromachined into the coverglass. Cell-generated concentration gradients form radially in REECs with a single round opening (~200 μm diameter). At steady state only cells within several hundred micrometers of the opening experience metabolite concentrations that permit survival which is analogous to diffusive exchange near a capillary in tissue. The chamber dimensions, the openings' shape, size, and number, and the cellular density and metabolic activity define the gradient structure. For example, two parallel slots above confluent cells produce the 1D equivalent of a spheroid. Using REECs, we found that fibroblasts align along the axis of diffusion while MDCK cells do not. MDCK cells do, however, exhibit significant morphological variations along the diffusive gradient.

Trans-right ventricle metabolite gradients in obesity highlight multiple metabolic pathways

Obesity and metabolic dysfunction are associated with pulmonary vascular remodeling, yet molecular mechanisms remain poorly understood. We sought to study trans-right ventricular (RV) metabolite gradients to elucidate potential molecular pathways operant among individuals with obesity and pulmonary hypertension. In this study, 38 individuals with obesity (mean age 58 years, 68% women, average BMI 36.6 kg/m2) underwent invasive right heart catheterization. Multi-site blood sampling from the superior vena cava and pulmonary artery was performed to assess trans-RV gradients, with targeted metabolite profiling using liquid chromatography-mass spectrometry. We found 56 metabolites with significant trans-RV gradients (FDR q < 0.05), including intermediates of fatty acid oxidation, the tricarboxylic acid cycle, and nucleotide metabolism. Further, trans-RV gradients in lipid and purine metabolism were associated with BMI and related cardiometabolic traits, such as waist circumference, insulin resistance, and serum lipids. Finally, differential levels of bile acids, intermediates of lipid peroxidation, and nucleotide metabolism across the RV were associated with pulmonary hypertension. In conclusion, trans-RV metabolite gradients among individuals with obesity reveal alterations in metabolites representative of molecular pathways such as fatty acid oxidation, and others correlated with cardiometabolic traits and/or pulmonary hypertension, including orotic acid, bile acids, and acylcarnitines.