Multiparametric optical analysis of mitochondrial redox signals during neuronal physiology and pathology in vivo

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Abstract

Mitochondrial redox signals have a central role in neuronal physiology and disease. Here we describe a new optical approach to measure fast redox signals with single-organelle resolution in living mice that express genetically encoded redox biosensors in their neuronal mitochondria. Moreover, we demonstrate how parallel measurements with several biosensors can integrate these redox signals into a comprehensive characterization of mitochondrial function. This approach revealed that axonal mitochondria undergo spontaneous 'contractions' that are accompanied by reversible redox changes. These contractions are amplified by neuronal activity and acute or chronic neuronal insults. Multiparametric imaging reveals that contractions constitute respiratory chain-dependent episodes of depolarization coinciding with matrix alkalinization, followed by uncoupling. In contrast, permanent mitochondrial damage after spinal cord injury depends on calcium influx and mitochondrial permeability transition. Thus, our approach allows us to identify heterogeneity among physiological and pathological redox signals, correlate such signals to functional and structural organelle dynamics and dissect the underlying mechanisms.

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Most cited references 26

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ROS as signalling molecules: mechanisms that generate specificity in ROS homeostasis.

Benoit D'Autréaux, Michel B. Toledano (2007)

Reactive oxygen species (ROS) have been shown to be toxic but also function as signalling molecules. This biological paradox underlies mechanisms that are important for the integrity and fitness of living organisms and their ageing. The pathways that regulate ROS homeostasis are crucial for mitigating the toxicity of ROS and provide strong evidence about specificity in ROS signalling. By taking advantage of the chemistry of ROS, highly specific mechanisms have evolved that form the basis of oxidant scavenging and ROS signalling systems.

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A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish

Philipp Niethammer, Clemens Grabher, A. Thomas Look … (2009)

Barrier structures (e.g. epithelia around tissues, plasma membranes around cells) are required for internal homeostasis and protection from pathogens. Wound detection and healing represent a dormant morphogenetic program that can be rapidly executed to restore barrier integrity and tissue homeostasis. In animals, initial steps include recruitment of leukocytes to the site of injury across distances of hundreds of micrometers within minutes of wounding. The spatial signals that direct this immediate tissue response are unknown. Due to their fast diffusion and versatile biological activities, reactive oxygen species (ROS), including hydrogen peroxide (H2O2), are interesting candidates for wound-to-leukocyte signalling. We probed the role of H2O2 during the early events of wound responses in zebrafish larvae expressing a genetically encoded H2O2 sensor1. This reporter revealed a sustained rise in H2O2 concentration at the wound margin, starting ∼3 min after wounding and peaking at ∼20 min, which extended ∼100−200 μm into the tail fin epithelium as a decreasing concentration gradient. Using pharmacological and genetic inhibition, we show that this gradient is created by Dual oxidase (Duox), and that it is required for rapid recruitment of leukocytes to the wound. This is the first observation of a tissue-scale H2O2 pattern, and the first evidence that H2O2 signals to leukocytes in tissues, in addition to its known antiseptic role.

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Improving the photostability of bright monomeric orange and red fluorescent proteins.

Nathan Shaner, Michael Lin, Michael R. McKeown … (2008)

All organic fluorophores undergo irreversible photobleaching during prolonged illumination. Although fluorescent proteins typically bleach at a substantially slower rate than many small-molecule dyes, in many cases the lack of sufficient photostability remains an important limiting factor for experiments requiring large numbers of images of single cells. Screening methods focusing solely on brightness or wavelength are highly effective in optimizing both properties, but the absence of selective pressure for photostability in such screens leads to unpredictable photobleaching behavior in the resulting fluorescent proteins. Here we describe an assay for screening libraries of fluorescent proteins for enhanced photostability. With this assay, we developed highly photostable variants of mOrange (a wavelength-shifted monomeric derivative of DsRed from Discosoma sp.) and TagRFP (a monomeric derivative of eqFP578 from Entacmaea quadricolor) that maintain most of the beneficial qualities of the original proteins and perform as reliably as Aequorea victoria GFP derivatives in fusion constructs.