Spatial Dynamics of SIRT1 Relates to Metabolic Transitions in the Cell Nucleus

Abstract

SIRT1 is a NAD+ -dependent deacetylase functioning as metabolic sensor of cellular energy and it adapts different biochemical pathways to the changes in the environment. SIRT1 substrates include histones and proteins related to enhancement of mitochondrial and antioxidant protection. Fluctuations in intracellular NAD+ levels regulate SIRT1 activity, yet the exact pathway SIRT1 enzymatic activity impacts NAD+ levels and its intracellular distribution remains unclear. Here, we demonstrate that SIRT1 determines the nuclear organization of protein bound NADH. Using multiphoton microscopy in live cells, we show that free and bound NADH are compartmentalized inside of the nucleus, and its subnuclear distribution depends on SIRT1. Importantly, SIRT6, a chromatin-bound deacetylase of the same class does not influence NADH nuclear localization. In addition, using fluorescence fluctuation spectroscopy, especially phasorFCS in single living cells, we reveal that NAD+ metabolism in the nucleus is linked to subnuclear dynamics of active SIRT1. SIRT1 diffuses faster on the periphery of nucleus and the diffusion is slower in the center. Comparison of results from phasorFCS and autofluorescence FLIM divulge a relationship between NAD+ metabolism, NADH distribution and SIRT1 activity in the nucleus of live cells, and leads off to decipher links between nuclear organization and metabolism.