ROS are evolutionary conserved cell-to-cell stress signals

Abstract

Cell-to-cell communication is fundamental to multicellular organisms and unicellular organisms living in a microbiome. It is thought to have evolved as a stress- or quorum-sensing mechanism in unicellular organisms. A unique cell-to-cell communication mechanism that uses reactive oxygen species (ROS) as a signal (termed the “ROS wave”) was identified in flowering plants. This process is essential for systemic signaling and plant acclimation to stress and can spread from a small group of cells to the entire plant within minutes. Whether a similar signaling process is found in other organisms is however unknown. Here, we report that the ROS wave can be found in unicellular algae, amoeba, ferns, mosses, mammalian cells, and isolated hearts. We further show that this process can be triggered in unicellular and multicellular organisms by a local stress or H 2 O 2 treatment and blocked by the application of catalase or NADPH oxidase inhibitors and that in unicellular algae it communicates important stress–response signals between cells. Taken together, our findings suggest that an active process of cell-to-cell ROS signaling, like the ROS wave, evolved before unicellular and multicellular organisms diverged. This mechanism could have communicated an environmental stress signal between cells and coordinated the acclimation response of many different cells living in a community. The finding of a signaling process, like the ROS wave, in mammalian cells further contributes to our understanding of different diseases and could impact the development of drugs that target for example cancer or heart disease.

Propagation of a rapid cell-to-cell H2O2signal over long distances in a monolayer of cardiomyocyte cells

“…H 2 O 2 -mediated cell-to-cell signaling in monolayers of H9c2 cells was previously shown to be blocked by catalase application, as well as a mixture of the NOX inhibitors APX115 and Setanaxib (but not each of these inhibitors applied individually) 20 . However, the role of superoxide in this signaling pathway was not substantiated.…”

“…A . Monolayers of rat cardiomyocytes (H9c2) grown in culture were wounded with a heated metal rod to induce injury 20 and O 2 · - accumulation was imaged using DHE in the presence or absence of a mixture of Carbenoxolone (CBX; 600 μM) and β-glycyrrhetinic acid (βGA; 180 μM), added 60 min prior to wounding. Representative time-lapse images of whole plate O 2 · - accumulation in treated and untreated plates are shown alongside bar graphs of combined data from all plates used for the analysis at the 0- and 30-min time points (local and systemic; Background levels of O 2 · - measured at time 0, were subtracted from all other time points).…”

“…The mechanism that was proposed to drive this ‘long-distance’ H 2 O 2 signal was termed the reactive oxygen species wave (‘ROS wave’) and it is based on the enhanced production of H 2 O 2 by each cell along the path of the signal. An initiating cell would therefore produce H 2 O 2 that is sensed by a neighboring cell and cause it to actively generate H 2 O 2 , triggering a cascade of cell-to-cell ‘enhanced H 2 O 2 production’ state 18,20-25 . In this respect, it is important to note that it is not H 2 O 2 that diffuses over long distances, rater, it is a state of ‘enhanced H 2 O 2 production’ that is propagating in a cell-to-cell fashion from the initiating cell(s) through the tissue, sometimes in a directional manner, with a rate of 0.15-0.4 cm/min 18,20-25 .…”

“…This limitation is mainly attributed to the H 2 O 2 scavenging activity of the extracellular matrix/neighboring cells, that generates a gradient from the producing cells, all the way up to the point H 2 O 2 levels drop to normal levels at the tissue(s) they are generated at 15-17,19 . Recent studies in plant and mammalian cells have, however, challenged this concept showing that H 2 O 2 signals can propagate within minutes over long distances (measured in centimeters) in different plant tissues, as well as in monolayers of human MDA-MB-231 breast cancer and rat H9c2 cardiomyocyte cells, and isolated mice hearts 18,20-25 . The mechanism that was proposed to drive this ‘long-distance’ H 2 O 2 signal was termed the reactive oxygen species wave (‘ROS wave’) and it is based on the enhanced production of H 2 O 2 by each cell along the path of the signal.…”

“…An initiating cell would therefore produce H 2 O 2 that is sensed by a neighboring cell and cause it to actively generate H 2 O 2 , triggering a cascade of cell-to-cell ‘enhanced H 2 O 2 production’ state 18,20-25 . In this respect, it is important to note that it is not H 2 O 2 that diffuses over long distances, rater, it is a state of ‘enhanced H 2 O 2 production’ that is propagating in a cell-to-cell fashion from the initiating cell(s) through the tissue, sometimes in a directional manner, with a rate of 0.15-0.4 cm/min 18,20-25 . Although H 2 O 2 does not diffuse over long distances per se in this cell-to-cell signaling mechanism, it is nonetheless required for the signal to propagate, as external application of catalase, NOX inhibitors, or the introduction of a loss-of-function NOX mutation into cells, block it 18,20-25 .…”