Spatial Dynamics of SIRT1 Dictate Metabolic Transitions in the Cell Nucleus

Abstract

Sirtuins are a highly conserved family of NAD+-dependent deacylases that function as metabolic sensors by detecting the cellular energy state to modulate biochemical pathways to allow the cell to adapt to the environment. SIRT1, one of the seven mammalian sirtuins, has been widely studied. Previous reports have implicated that SIRT1 activity can be regulated by fluctuations in intracellular NAD+ concentrations. However the direct impact of SIRT1 on the regulation of the metabolism of its own cofactor, NAD+, remains unclear. Here, we demonstrate the nuclear organization of NAD+/NADH states are determined by SIRT1. Phasor approach to two photon autofluorescence lifetime microscopy in live cells shows that the redox state is compartmentalized inside of the nucleus, and that the subnuclear distribution as well as the redox ratio itself depends on SIRT1. Moreover, this effect seems specific for SIRT1, as the other nuclear sirtuin SIRT6, doesn't play a major role. Fluorescence fluctuation spectroscopy studies, RICS and phasor FCS in single living cells, reveal that NAD+ metabolism in the nucleus impacts subnuclear dynamics of active SIRT1 enzyme. These results provide direct evidence of an intimate crosstalk between NAD+ states and SIRT1 activity in the nucleus of live cells, and open the path to study connections between nuclear organization and metabolism.Grants: NIH- DA036408, AG041504, P41-GM103540 and P50-GM076516