Høyland Lena E, VanLinden Magali R, Niere Marc, Strømland Øyvind, Sharma Suraj, Dietze Jörn, Tolås Ingvill, Lucena Eva, Bifulco Ersilia, Sverkeli Lars J, Cimadamore-Werthein Camila, Ashrafi Hanan, Haukanes Kjellfrid F, van der Hoeven Barbara, Dölle Christian, Davidsen Cédric, Pettersen Ina K N, Tronstad Karl J, Mjøs Svein A, Hayat Faisal, Makarov Mikhail V, Migaud Marie E, Heiland Ines, Ziegler Mathias
Department of Biomedicine, University of Bergen, Bergen, Norway.
Neuro-SysMed Center, Department of Neurology, Haukeland University Hospital, Bergen, Norway.
Nat Metab. 2024 Dec;6(12):2319-2337. doi: 10.1038/s42255-024-01174-w. Epub 2024 Dec 13.
The coenzyme NAD is consumed by signalling enzymes, including poly-ADP-ribosyltransferases (PARPs) and sirtuins. Ageing is associated with a decrease in cellular NAD levels, but how cells cope with persistently decreased NAD concentrations is unclear. Here, we show that subcellular NAD pools are interconnected, with mitochondria acting as a rheostat to maintain NAD levels upon excessive consumption. To evoke chronic, compartment-specific overconsumption of NAD, we engineered cell lines stably expressing PARP activity in mitochondria, the cytosol, endoplasmic reticulum or peroxisomes, resulting in a decline of cellular NAD concentrations by up to 50%. Isotope-tracer flux measurements and mathematical modelling show that the lowered NAD concentration kinetically restricts NAD consumption to maintain a balance with the NAD biosynthesis rate, which remains unchanged. Chronic NAD deficiency is well tolerated unless mitochondria are directly targeted. Mitochondria maintain NAD by import through SLC25A51 and reversibly cleave NAD to nicotinamide mononucleotide and ATP when NMNAT3 is present. Thus, these organelles can maintain an additional, virtual NAD pool. Our results are consistent with a well-tolerated ageing-related NAD decline as long as the vulnerable mitochondrial pool is not directly affected.
辅酶NAD会被包括多聚ADP核糖基转移酶（PARP）和去乙酰化酶在内的信号酶消耗。衰老与细胞内NAD水平的降低有关，但细胞如何应对持续降低的NAD浓度尚不清楚。在这里，我们表明亚细胞NAD池是相互连接的，线粒体起着变阻器的作用，在NAD过度消耗时维持其水平。为了引发NAD在特定区室的慢性过度消耗，我们构建了在 mitochondria、细胞质、内质网或过氧化物酶体中稳定表达PARP活性的细胞系，导致细胞NAD浓度下降高达50%。同位素示踪通量测量和数学模型表明，降低的NAD浓度在动力学上限制了NAD的消耗，以维持与保持不变的NAD生物合成速率的平衡。慢性NAD缺乏症耐受性良好，除非线粒体直接受到影响。线粒体通过SLC25A51进行导入来维持NAD，并且当存在NMNAT3时，将NAD可逆地裂解为烟酰胺单核苷酸和ATP。因此，这些细胞器可以维持一个额外的虚拟NAD池。我们的结果与只要脆弱的线粒体池不直接受到影响，衰老相关的NAD下降就具有良好耐受性这一观点一致。
