Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, NJ, USA.
Department of Chemistry, Princeton University, Princeton, NJ, USA.
Nat Methods. 2022 Feb;19(2):223-230. doi: 10.1038/s41592-021-01378-y. Epub 2022 Feb 7.
Isotope tracing has helped to determine the metabolic activities of organs. Methods to probe metabolic heterogeneity within organs are less developed. We couple stable-isotope-labeled nutrient infusion to matrix-assisted laser desorption ionization imaging mass spectrometry (iso-imaging) to quantitate metabolic activity in mammalian tissues in a spatially resolved manner. In the kidney, we visualize gluconeogenic flux and glycolytic flux in the cortex and medulla, respectively. Tricarboxylic acid cycle substrate usage differs across kidney regions; glutamine and citrate are used preferentially in the cortex and fatty acids are used in the medulla. In the brain, we observe spatial gradations in carbon inputs to the tricarboxylic acid cycle and glutamate under a ketogenic diet. In a carbohydrate-rich diet, glucose predominates throughout but in a ketogenic diet, 3-hydroxybutyrate contributes most strongly in the hippocampus and least in the midbrain. Brain nitrogen sources also vary spatially; branched-chain amino acids contribute most in the midbrain, whereas ammonia contributes in the thalamus. Thus, iso-imaging can reveal the spatial organization of metabolic activity.
同位素示踪法有助于确定器官的代谢活动。探测器官内代谢异质性的方法还不够发达。我们将稳定同位素标记的营养物输注与基质辅助激光解吸电离成像质谱联用（iso-imaging），以空间分辨的方式定量哺乳动物组织中的代谢活性。在肾脏中，我们分别可视化皮质和髓质中的糖异生通量和糖酵解通量。三羧酸循环底物在肾脏区域的使用存在差异；皮质中优先使用谷氨酰胺和柠檬酸，而髓质中则使用脂肪酸。在大脑中，我们观察到生酮饮食下三羧酸循环和谷氨酸的碳输入存在空间梯度。在富含碳水化合物的饮食中，葡萄糖在整个大脑中占主导地位，但在生酮饮食中，3-羟基丁酸在海马体中贡献最大，在中脑中贡献最小。大脑的氮源也存在空间差异；支链氨基酸在中脑中贡献最大，而氨在丘脑中有贡献。因此，iso-imaging 可以揭示代谢活性的空间组织。
