Hydrogen peroxide (H 2 O 2 ) produced by cell-surface NADPH Oxidase (Nox) enzymes is emerging as an important signaling molecule for growth, differentiation, and migration processes. However, how cells spatially regulate H 2 O 2 to achieve physiological redox signaling over nonspecific oxidative stress pathways is insufficiently understood. Here we report that the water channel Aquaporin-3 (AQP3) can facilitate the uptake of H 2 O 2 into mammalian cells and mediate downstream intracellular signaling. Molecular imaging with Peroxy Yellow 1 Methyl-Ester (PY1-ME), a new chemoselective fluorescent indicator for H 2 O 2 , directly demonstrates that aquaporin isoforms AQP3 and AQP8, but not AQP1, can promote uptake of H 2 O 2 specifically through membranes in mammalian cells. Moreover, we show that intracellular H 2 O 2 accumulation can be modulated up or down based on endogenous AQP3 expression, which in turn can influence downstream cell signaling cascades. Finally, we establish that AQP3 is required for Noxderived H 2 O 2 signaling upon growth factor stimulation. Taken together, our findings demonstrate that the downstream intracellular effects of H 2 O 2 can be regulated across biological barriers, a discovery that has broad implications for the controlled use of this potentially toxic small molecule for beneficial physiological functions.growth factor signaling | redox biology | reactive oxygen species | fluorescent sensor | membrane regulation H ydrogen peroxide (H 2 O 2 ) is garnering increased attention as a molecule involved not only in immune response and oxidative stress, but also as a physiological effector in essential cellular processes (1-5). Seminal contributions have elucidated ligand stimulants (6-10) and enzymatic sources (11-13) for cellular H 2 O 2 production as well as putative downstream targets (14-24), but principles of how this reactive oxygen species (ROS) is spatially and temporally regulated to promote redox signaling over oxidative stress pathways remain insufficiently understood. Because many of the signaling functions of H 2 O 2 rely on its generation by nonphagocytic forms of NADPH (Nox) proteins on the extracellular side of cell membranes, understanding how cells funnel H 2 O 2 toward beneficial pathways in these locales is of significant interest. Despite its reactive nature, H 2 O 2 has been long thought to be freely diffusible across biological membranes in a manner akin to the related canonical small-molecule signal nitric oxide (NO) (25). More recent studies implicate the role of AQP water channels, a class of membrane-spanning proteins that facilitate the diffusion of water and other substrates with varying specificity (26-28), in mediating H 2 O 2 passage across the plasma membrane of reconstituted yeast (29) and plant (30) cells. However, given that the experiments described in these reports utilized nonspecific chemical reagents for determination of the redox signal that was passed into the cell, direct evidence that aquaporins influence the cellular uptake of H 2 O 2 in a na...

We present the synthesis, properties, and biological applications of Coppersensor-1 (CS1), a new water-soluble, turn-on fluorescent sensor for intracellular imaging of copper in living biological samples. CS1 utilizes a BODIPY reporter and thioether-rich receptor to provide high selectivity and sensitivity for Cu+ over other biologically relevant metal ions, including Cu2+, in aqueous solution. This BODIPY-based probe is the first Cu+-responsive sensor with visible excitation and emission profiles and gives a 10-fold turn-on response for detecting this ion. Confocal microscopy experiments further establish that CS1 is membrane-permeable and can successfully monitor intracellular Cu+ levels within living cells.

The syntheses, properties, and biological applications of the Peroxysensor family, a new class of fluorescent probes for hydrogen peroxide, are presented. These reagents utilize a boronate deprotection mechanism to provide high selectivity and optical dynamic range for detecting H 2 O 2 in aqueous solution over similar reactive oxygen species (ROS) including superoxide, nitric oxide, tert-butyl hydroperoxide, hypochlorite, singlet oxygen, ozone, and hydroxyl radical. Peroxyresorufin-1 (PR1), Peroxyfluor-1 (PF1), and Peroxyxanthone-1 (PX1) are first-generation probes that respond to H 2 O 2 by an increase in red, green, and blue fluorescence, respectively. The boronate dyes are cell-permeable and can detect micromolar changes in H 2 O 2 concentrations in living cells, including hippocampal neurons, using confocal microscopy and two-photon microscopy. The unique combination of ROS selectivity, membrane permeability, and a range of available excitation/ emission colors establishes the potential value of PR1, PF1, PX1, and related probes for interrogating the physiology and pathology of cellular H 2 O 2 .

Fluorescence imaging is an attractive method for monitoring neuronal activity. A key challenge for optically monitoring voltage is development of sensors that can give large and fast responses to changes in transmembrane potential. We now present fluorescent sensors that detect voltage changes in neurons by modulation of photo-induced electron transfer (PeT) from an electron donor through a synthetic molecular wire to a fluorophore. These dyes give bigger responses to voltage than electrochromic dyes, yet have much faster kinetics and much less added capacitance than existing sensors based on hydrophobic anions or voltagesensitive ion channels. These features enable single-trial detection of synaptic and action potentials in cultured hippocampal neurons and intact leech ganglia. Voltage-dependent PeT should be amenable to much further optimization, but the existing probes are already valuable indicators of neuronal activity. F luorescence imaging can map the electrical activity and communication of multiple spatially resolved neurons and thus complements traditional electrophysiological measurements (1, 2). Ca 2+ imaging is the most popular of such techniques, because the indicators are well-developed (3-6), highly sensitive (5, 6), and genetically encodable (7-13), enabling investigation of the spatial distribution of Ca 2+ dynamics in structures as small as dendritic spines and as large as functional circuits. However, because neurons translate depolarizations into Ca 2+ signals via a complex series of pumps, channels, and buffers, fluorescence imaging of Ca 2+ transients cannot provide a complete picture of electrical activity in neurons. Observed Ca 2+ spikes are temporally low-pass filtered from the initial depolarization and provide limited information regarding hyperpolarizations and subthreshold events. Direct measurement of transmembrane potential with fluorescent indicators would provide a more accurate account of the timing and location of neuronal activity. Despite the promise of fluorescent voltage-sensitive dyes (VSDs), previous classes of VSDs have each been hampered by some combination of insensitivity, slow kinetics (14-16), heavy capacitative loading (17-21), lack of genetic targetability, or phototoxicity. Two of the more widely used classes of VSDs, electrochromic and FRET dyes, illustrate the problems associated with developing fast and sensitive fluorescent VSDs.Electrochromic dyes respond to voltage through a direct interaction between the chromophore and the electric field (Scheme 1A). This Stark effect leads to small wavelength shifts in the absorption and emission spectrum. Because the electric field directly modulates the energy levels of the chromophore, the kinetics of voltage sensing occur on a timescale commensurate with absorption and emission, resulting in ultrafast (fs to ps) hypso-or bathochromic shifts many orders-of-magnitude faster than required to resolve fast spiking events and action potentials in neurons. This small wavelength shift dictates that the fluorescence signal ...

Hydrogen peroxide (H2O2) is emerging as a newly recognized messenger in cellular signal transduction. However, a substantial challenge in elucidating its diverse roles in complex biological environments is the lack of methods for probing this reactive oxygen metabolite in living systems with molecular specificity. Here we report the synthesis and application of Peroxy Green 1 (PG1) and Peroxy Crimson 1 (PC1), two new fluorescent probes that show high selectivity for H2O2 and are capable of visualizing endogenous H2O2 produced in living cells by growth factor stimulation, including the first direct imaging of peroxide produced for brain cell signaling. The combined features of reactive oxygen species selectivity, sensitivity to signaling levels of H2O2, and live-cell compatibility presage many new opportunities for PG1, PC1 and related synthetic reagents for exploring the physiological roles of H2O2 in living systems with molecular imaging.