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Biosensor reveals multiple sources for mitochondrial NAD+

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Science  17 Jun 2016:
Vol. 352, Issue 6292, pp. 1474-1477
DOI: 10.1126/science.aad5168

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  1. Fig. 1 Characterization of a NAD+ biosensor.

    (A) The NAD+ biosensor comprises cpVenus (cpV) and a bipartite NAD+-binding domain (blue). The unbound species fluoresces after excitation at 488 nm; NAD+ binding causes a loss of fluorescence. (B) Excitation (Ex, dashed lines) and emission (Em, solid lines) scans of purified sensor with either 0 (black) or 500 μM (red) NAD+. Excitation was monitored at 530 nm, and emission was monitored after excitation at 488 nm (F, fluorescence; AU, arbitrary units). (C) Fluorescence emission and excitation scans at indicated NAD+ concentrations (solid lines) or with buffer-only control (dashed line). The inset shows fluorescence from excitation at 405 nm. (D) Maxima from 488-nm emission peaks of sensor (S) and cpVenus (250 nM) at indicated NAD+ concentrations (F0, 0 μM NAD+). (E) Fluorescence excitation and emission of sensor incubated with 0 (black solid lines) or 500 μM (red solid lines) NAD+. NAD+ was washed out and fluorescence was reevaluated in each sample (dashed lines). (F) GAPDH (red) increases sensor fluorescence (monitored at 520 nm after excitation at 488 nm). (G) Excitation and emission profiles (left) and maxima from 488-nm emission with indicated substrates (right). NADH, reduced NAD+; NADP+, nicotinamide adenine dinucleotide phosphate; NADPH, reduced NADP+; Nam, nicotinamide; ATP, adenosine triphosphate; AMP, adenosine monophosphate. In (D), (F), and the right panel of (G), data are shown as means ± SD (n = 3).

  2. Fig. 2 Free intracellular NAD+ measurements.

    (A) HEK293T cells stably expressing nuclear, cytoplasmic, or mitochondrial sensors (nuclear marker Draq5, blue; mitochondrial marker Mitotracker CMXRos, red; sensor, green). (B) The cytoplasmic sensor was calibrated for NAD+-dependent fluorescence changes in digitonin-permeabilized HEK293T cells. The fluorescence ratios (488 nm/405 nm) measured with flow cytometry were normalized to cpVenus and fit with a variable slope model (dotted lines, 95% confidence interval; error bars, SD). (C) Representative images from adherent HeLa cells permeabilized with saponin in the presence of indicated NAD+ concentrations (left), as monitored by PI internalization (excitation at 561 nm, emission monitored with a 670/30-nm filter) (right). Live images were captured every 2.5 min. Fluorescence intensity from 488-nm excitation is normalized to the scale bar.

  3. Fig. 3 NAD+ fluctuations in cells.

    (A) Free NAD+ concentrations in HEK293T cells after treatment with FK866 (10 nM). Sensor/cpVenus (488 nm/405 nm) fluorescence ratios were measured by flow cytometry, and the fold change compared with untreated controls was interpolated onto an in vitro standard curve. (B) Cytoplasmic free NAD+ was decreased by NAMPT depletion (siNAMPT) and partially restored by NR (100 μM) treatment. Imaging measurements are from excitation at 488 nm. Shown are means ± SEM (n = 3) from residual maximum likelihood (REML) analysis. ***P < 0.001; *P < 0.05. (C) Effect of free NAD+ on PARP activation (poly-ADPR). siScramble, scrambled RNA control; αGAPDH, anti-GAPDH antibody.

  4. Fig. 4 Multiple sources for mitochondrial NAD+.

    (A) Representative images are shown on the left of the mitochondrial NAD+ sensor after depletion of either NMNAT2 (siNMNAT2) or NMNAT3 (siNMNAT3) in HEK293T cells. Scale bar, 25 μm. Excitation at 488 nm. Fluorescence intensities were normalized to scramble RNA (siScramble) and mitochondrial cpVenus (cpV) controls. Plotted are means ± SEM (n = 3) from REML analysis. *P = 0.03; **P < 0.005. (B) Effect of NR treatment (250 μM, 24 hours) on NAD+ concentration in the mitochondria of HeLa cells depleted of NMNAT2 (siNMNAT2). Representative images are shown on the left (scale bar, 25 μm). Fluorescence intensities were normalized to scramble RNA (siScramble) and mitochondrial cpVenus (cpV) controls. Plotted are means ± SEM (n = 3) from REML analysis. **P < 0.01.

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