The 2025 Sir David Cuthbertson Lecture: Energy metabolism: Beyond calories, feeding the mitochondria

In this article, I explore how energy metabolism depends on proper mitochondrial function. Adenosine triphosphate (ATP), the main source of energy for cells, is mainly produced in the mitochondria as a result of the fusion of hydrogen produced by the breakdown of nutrients with oxygen. This reaction allows protons to be pumped across the inner mitochondrial membrane, creating a gradient that powers ATP synthesis. However, ATP production is not perfectly efficient. Some oxygen is consumed without generating ATP due to proton leaks or other processes that utilize the gradient. Diet, hormones, and cellular signals can alter mitochondrial efficiency: for example, hyperthyroidism and polyunsaturated fatty acid deficiency cause uncoupling, while hypothyroidism and nitric oxide increase coupling but reduce maximum ATP production. I also point out that the use of ATP depends on its thermodynamic value, which is reflected in the Adenosine triphosphate/Adenosine diphosphate ratio ([ATP]/[ADP] ratio). A decrease in this ratio can selectively reduce certain ATP-consuming processes, as shown in studies on metformin and imeglimin. In cases of stress or nutritional deficiency, cells can consume ATP without performing useful work, leading to inefficiency or even cell death when the [ATP]/[ADP] ratio collapses. Knowing that these concepts are quite complex, I have simplified them to make clear that mitochondria are more than just passive "powerhouses of cells".