Metabolism plays a role in virtually all cellular processes. Understanding how nutrients, metabolites, and byproducts flow through intracellular pathways (i.e., metabolic flux) is invaluable for elucidating disease mechanisms and designing new therapies. To quantitatively visualize pathway activity we employ stable isotope-labeled metabolic tracers and detect isotope enrichment in metabolites using chromatography coupled to mass spectrometry. The amount of isotope-labeled atoms that are incorporated into biomass or other pathways tells us about how our tracer was metabolized. Finally, to account for the interconnected nature of metabolic networks we apply systems-level analyses of these data, since flux through one reaction is affected by many other pathways.
Oncogenes and tumor suppressor proteins induce profound changes in cell behavior to drive tumor progression. Defects in the function of metabolic enzymes or regulatory molecules can promote cancer in this manner. By correlating cancer cell genetics (mutations, deletions, etc.) with metabolic reprogramming we can better understand how metabolic pathways function in patient tumors. Ultimately we hope to use this information to design therapies that target the metabolic enzymes and pathways on which tumors rely most.
Stem cells in the body maintain tissue homeostasis through regeneration and differentiation. Pluripotent stem cells can differentiate to diverse cell types (each of the three embryonic germ layers) while serving as model systems for development, drug testing, or genetic diseases. Metabolic processes are important for stem cell maintenance, growth, and differentiation and must be controlled appropriately. Upon differentiation to specific lineages such as cardiomyocytes, cells must perform specific functions that often involve significant metabolic reprogramming. We are applying MFA to understand how metabolism operates in stem cells and changes during lineage specification. These findings may provide better means of controlling pluripotent cell proliferation and differentiation while enhancing the performance of stem cell derivatives.
Type 2 diabetes and obesity are emerging as epidemics in the Western world. These disorders involve dysregulation of metabolic homeostasis, particularly in metabolically active cells in the liver (hepatocytes), adipose tissue (adipocytes), or muscle. These cells must constantly assess the extracellular microenvironment and respond to changes in nutrient availability by reprogramming metabolic pathways. When these responses go awry disease ensues. For example, oxygen is critical to maintain normal cell function, and limitations in tissue oxygen (hypoxia) occur in numerous pathologies. Changes in oxygen availability have profound effects on metabolism. By applying metabolic flux analysis (MFA) to cells and animals we hope to discover how changes in carbohydrate, protein, amino acid, and lipid metabolism contribute to obesity and metabolic syndrome.
We are developing new methods to probe metabolic pathways in greater detail. These include tools to study pathways involved in redox control and within individual cellular compartments. Additional approaches involve the application of discovery-based methods to probe metabolism in a non-targeted manner. As these techniques are validated and applied to in vitro and in vivo systems they will improve our ability to study the diverse metabolic pathways involved in cancer progression and metabolic disease.