In order to be well prepared for any situation, one should always expect the unexpected. This even holds true in the complex realm of biochemistry. Schoors et al. embodied this quite well in their paper entitled “Fatty acid carbon is essential for dNTP synthesis in endothelial cells” (doi: 10.1038/nature14362). The research team embarked with the goal of better understanding how metabolism of endothelial cells affect the production and migration of blood vessels. Their method was to deactivate the crucial shuttling enzyme carnitine palmitoyltransferase 1 (CPT1), the focal point of fatty acid oxidation (FAO), and investigate the consequences of this action. They were able to predict some of the expected results, but unpredictable observations sprouted into the picture.
The authors cleverly use subheadings to strategically guide the progression of their article. They start off by discussing the effects of knocking out the CPT1 gene. This mutation diminishes the proliferation of endothelial cells, but leaves these the migration and motility of these cells untouched. Rather than the mechanisms of endothelial cellular proliferation and migration being one in the same, the data suggests the two are monitored differently. By eliminating a separate FAO gene, similar results are seen. Coupling this experimental data with over-expression of CPT1 promoting endothelial cell proliferation, it is supported that FAO regulates proliferation and not migration.
With FAO becoming the main focus of regulating proliferation, the hunt continues for what exact mechanism is responsible for the deficiency caused. ATP production and redox homeostasis is the first to be examined. The CPT1 mutation does not trigger an ATP depletion and is quickly ruled out as a potential cause. Though reactive oxygen species (ROS) are noted to be higher than the wildtype specimen, lowering the ROS levels does not restore the proliferation caused by the CTP1 mutation. With two of the main hypotheses coming up bare, new innovative thoughts can be explored. By utilizing isotopic labeling, fatty acids are seen to be incorporated in de novo DNA synthesis. The labelling also shows that CPT1 knockout diminishes the amount of aspartate levels, which is a necessary precursor to DNA synthesis, and depletes the pools of dNTP available. Administering supplemental acetate to CTP1 mutant endothelial cells restores the aspartate and dNTPs, which reaffirms DNA synthesis reliance on FAO. This finding is groundbreaking due to the fact that, apart from fibroblasts, no other cells utilize fatty acids as building blocks for DNA synthesis.
With better understanding of FAO inhibition, new clinical applications can be developed to combat pathogenic angiogenesis. Extomoxir is one instance of pharmaceutically blocking CPT1 to curb FAO and in turn impact endothelial cell proliferation. Investigations such Schoor et al. not only gains further insight biological systems, but also help generate information than can be utilized for the greater good. Sometimes further inquiry of an unclear subject matter, unforeseen advancements are waited to be brought into the light.