The first period of the fellowship was used to establish all necessary methods for the measurement of mitochondrial function on cells in which a mitochondrial malfunction was induced. This included the state of the art high resolution respirometry for measurement of mitochondrial oxygen consumption. For inducing a dysfunction in mitochondria, both a pharmacologic approach applying a chemotherapeutic agent and a genetic approach (downregulation of the Nnt enzyme) were used. When using the chemotherapeutic agent, we found that, although NAD levels declined in the cells treated with this agent and cells died subsequently, the cells did not survive better if supplemented with NAD. This resulted in a collaboration of the fellow with researchers from Leipzig University, Germany, where the fellow is now working and continuing the collaboration.
In the second part, two different mouse strains were challenged with a high fat diet to induce metabolic stress, obesity and fat deposition in the liver. These mice either received NAD supplementation or not. In this experiment the method of supplementation of NAD via drinking water was established in the host lab which will be used in subsequent studies. We examined metabolic responses such as expended energy, preferred usage of nutrients, glucose tolerance - referred to as metabolic phenotyping - and mitochondrial function of different tissues. We could show that NAD supplementation induced slight effects on energy metabolism, that were different in the two mouse models. Mitochondrial oxygen usage of cardiac muscle fibres as a measure for mitochondrial function was increased upon NAD supplementation in one, but not the other mouse strain. Using NAD metabolomics as a method which is currently being established in the host lab for quantitating the exact amounts of NAD and NAD intermediates in different tissues, we will find out how much of the supplemented NAD precursor has arrived in what tissue. This is part of an ongoing collaboration between the fellow and host.
