Decreased oxidative phosphorylation leads to ATP deficiency, accumulation of reactive oxygen species and depletion of neuronal NAD+, one of the most critical molecules for bioenergetic conversions and signalling in human cells. Modulation of mitochondrial bioenergetics may be an effective therapeutic strategy to counteract neurodegeneration, and drugs boosting mitochondrial biogenesis and function have indeed been associated with decreased incidence of Parkinson’s disease and dementia in various independent studies. Based on these findings, the group propose that therapies promoting mitochondrial function via replenishing the NAD+ pool can shield neurons against the neurodegenerative processes and delay disease progression. Nicotinamide riboside (NR) is a well-established precursor which effectively elevates NAD+ synthesis and is non-toxic in animals and humans. It is fully approved for human use, has good oral bioavailability, crosses the blood-brain barrier and has been shown to extend lifespan in yeast and to have strong neuroprotective effects in animals. Therefore, the group believes that NR is an excellent candidate for correcting NAD+ deficiency and rectifying the metabolic impairment in neurodegeneration.
Using various cell systems and state-of-the-art metabolomics approaches, the group is studying the impact of NAD+ deficiency on major cellular bioenergetics and signalling systems. Previously, they have been able to set up the analytical technologies to measure the NAD+ metabolome and its dynamics in biological samples. They have established cellular NAD+ turnover rates in human cell lines and identified metabolic adjustments evoked by chronic NAD+ deficiency. These measurements require the use of stable isotope-labeled NAD+ precursors and highresolution mass spectrometry. In turn, the group needed to develop suitable algorithms enabling appropriate correction for naturally occurring isotopes. This has been achieved in a way applicable to a wide
range of biomolecules (preprint Dietze et al., https://doi.org/10.1101/2020.10.31.361725).
In cellular model systems, the group has mimicked age-dependent decline of NAD levels using genetic engineering to introduce NAD consuming enzyme activities into various subcellular compartments. Phenotypic and mechanistic studies revealed a tight regulation of total cellular NAD turnover, independent of the organelle targeted and the actual total cellular NAD concentration. Based on cell biological analyses, fluxomics and mathematical modelling, they propose that mitochondria serve as cellular NAD buffer. This function requires a mitochondrial NAD carrier as well as a mitochondrial enzyme which reversibly converts NAD to NMN and ATP (preprint vanLinden et al., doi. org/10.21203/rs.3.rs-116850/v1). A key contribution to develop this hypothesis was the discovery of a mitochondrial NAD carrier to which the group made major contributions (Luongo et al.).
The group will now extend their efforts and use the developed methodology to analyze the potential metabolic effect of NR supplementation in patients with Parkinson’s disease as part of the NAD-PARK and NOPARK clinical studies.
Selected Key Publications
1. Chiarugi, A., Dölle, C., Felici, R., and Ziegler, M. (2012) The NAD metabolome – a key determinant of cancer cell biology. Nat Rev Cancer 12, 741-752
2. VanLinden MR, Dölle C, Pettersen IK, Kulikova VA, Niere M, Agrimi G, Dyrstad SE, Palmieri F, Nikiforov AA, Tronstad KJ, Ziegler M. (2015) Subcellular Distribution of NAD+ between Cytosol and Mitochondria Determines the Metabolic Profile of Human Cells. J Biol Chem. Nov 290, 27644-27659
3. Love NR, Pollak N, Dölle C, Niere M, Chen Y, Oliveri P, Amaya E, Patel S, Ziegler M. (2015) NAD kinase controls animal NADP biosynthesis and is modulated via evolutionarily divergent calmodulin-dependent mechanisms. Proc Natl Acad Sci U S A. 112, 1386-1391
4. Buonvicino D, Mazzola F, Zamporlini F, Resta F, Ranieri G, Camaioni E, Muzzi M, Zecchi R, Pieraccini G, Dölle C, Calamante M, Bartolucci G, Ziegler M, Stecca B, Raffaelli N, Chiarugi A. (2018) Identification of the Nicotinamide Salvage Pathway as a New Toxification Route for Antimetabolites. Cell Chem Biol. 25, 471-482
5. Bockwoldt M, Houry D, Niere M, Gossmann TI, Reinartz I, Schug A, Ziegler M, Heiland I. (2019) Identification of evolutionary and kinetic drivers of NAD-dependent signaling. Proc Natl Acad Sci U S A. 116, 15957-15966
6. Ziegler M, Nikiforov, AA (2020) NAD on the rise again. Nat Metabolism 2, 291-292
7. Luongo TS, Eller JM, Lu MJ, Niere M, Raith F, Perry C, Bornstein MR, Oliphint P, Wang L, McReynolds MR, Migaud ME, Rabinowitz JD, Johnson FB, Johnsson K, Ziegler M, Cambronne XA, Baur JA. (2020) SLC25A51 is a mammalian mitochondrial NAD+ transporter. Nature 588, 174-179.