A team of researchers from OHSU has developed a new biosensor for a molecule critical for healthy cellular function, nicotinamide adenine dinucleotide (NAD⁺). NAD+ is a coenzyme found in every cell, helping  to drive glucose metabolism. It is known to decline with advancing age, and this decline is thought to play a role in age-related diseases such as cancer, cardiovascular disease, and neurodegeneration. While NAD+ was discovered about 100 years ago, we still don’t know much about how it is regulated in cells or tissues. Most cellular NAD⁺ is found within mitochondria, but other pools are found in the cytoplasm and nucleus, where they regulate enzymes that serve many different functions. To date, no one has been able to determine how much free NAD⁺ was available in specific cellular compartments, whether these levels were appropriate to regulate the various NAD⁺-related enzymes, or even how NAD⁺ gets into mitochondria. Now, OHSU authors Xiaolu A. Cambronne, Melissa L. Stewart, DongHo Kim, Amber M. Jones-Brunette, Rory K. Morgan, David L. Farrens, Michael S. Cohen, and Richard H. Goodman describe a new fluorescent biosensor that allows direct measurement of free NAD+ concentrations in live cells—in essence, opening an entirely new field. Their work, “Biosensor reveals multiple sources for mitochondrial NAD+,” was published in Science on June 17.

The biosensor is genetically encoded, utilizing a form of fluorescent protein and a bipartite NAD⁺-binding domain. Using this tool, Cambronne and colleagues found that NAD+ is distinctly regulated in different cell types and subcellular pools and that its local concentrations can regulate resident enzymes. This work builds on long-standing work—including earlier work carried out at the Vollum. It confirms previous estimates of NAD⁺ concentrations that were based on fluorescence lifetime measurements, details how the different cellular compartments of NAD⁺ relate to one another, and suggests how NAD⁺ gets into the mitochondria, where it can participate in metabolic processes. This discovery is important because it lays the groundwork for determining exactly how NAD+ contributes to health and disease. For example, the biosensor could provide insight into some forms of neurodegeneration, such as those caused by axon injury.

Cambronne, Stewart, Kim, and Goodman are from the Vollum Institute; Jones-Brunette and Farrens are from the Department of Biochemistry and Molecular Biology in the School of Medicine; and Morgan and Cohen are from the Department of Physiology and Pharmacology in the School of Medicine.