Transient and Sustained Ganglion Cell Light Responses Are Differentially Modulated by Intrinsically Produced Reactive Oxygen Species Acting upon Specific Voltage-Gated Na⁺Channel Isoforms

Abstract

Increasing spike rates drive greater neuronal energy demand. In turn, mitochondrial ATP production leads to the generation of reactive oxygen species (ROS) that can modulate ion channel gating. Does ROS production autoregulate a neuron’s excitability? We investigated the links between retinal ganglion cell (RGC) excitability and spike activity-driven ROS production in male and female mice. Changes to the light- and current-evoked spike patterns of functionally identified αRGC subtypes, along with their NaVchannel gating properties, were recorded during experimentally induced decreases and increases of intracellular ROS. During periods of highest spike rates, e.g., following light onset in ON sustained RGCs and light offset in OFF sustained RGCs, these αRGC subtypes responded toreductionsof ROS (induced by catalase or glutathione monoethyl ester) with higher spike rates.Increases inROS (induced by mercaptosuccinate, antimycin-A or H2O2) lowered spike rates. In ON and OFF transient RGCs, there were no changes in spike rate during ROS decreases but increased ROS increased spiking. This suggests endogenous ROS are intrinsic neuromodulators in RGCs having high metabolic demands but not in RGCs with lower energy needs. We identified ROS-induced shifts in the voltage-dependent gating of specific isoforms of NaVchannels that account for the modulation of ON and OFF sustained RGC spike frequency by ROS-mediated feedback. ROS-induced changes to NaVchannel gating, affecting activation and inactivation kinetics, are consistent with the differing spike pattern alterations observed in RGC subtypes. Cell autonomous generation of ROS during spiking contributes to tuning the spike patterns of RGCs.Significance StatementEnergy production within retinal ganglion cells (RGCs) is accompanied by metabolic by-products harmful to cellular function. How these by-products modulate the excitability of RGCs bears heavily on visual function and the etiology of optic neuropathies. A novel hypothesis of how RGC metabolism can produce automodulation of electrical signaling was tested by identifying the characteristics and biophysical origins of changes to the excitability of RGCs caused by oxidizing by-products in the retina. This impacts our understanding of the pathophysiology of RGC dysfunction, supporting an emerging model in which increases in oxidizing chemical species during energy production, but not necessarily bioenergetic failure, lead to preferential degeneration of specific subtypes of RGCs, yielding loss of different aspects of visual capacity.

Spike desensitisation as a mechanism for high-contrast selectivity in retinal ganglion cells

“…For example, in suppressed-by-contrast RGCs, a depolarization block, resulting from a low VGSC conductance, short axonal initial segment (AIS), and selective expression of Na v isoforms (see below), defines the cells’ response ( Wienbar and Schwartz, 2022 ). Another example would be direct (neuro)modulation of Na v function by reactive oxygen species (ROS), as it was recently shown for sustained RGCs ( Smith et al, 2023 ). In complement, our study suggests that the functional properties of VGSCs expressed in tOn-small cells are one of the key mechanisms that shape these cells’ responses.…”

Piezo1 and Piezo2 channels in retinal ganglion cells and the impact of Piezo1 stimulation on light-dependent neural activity

“…To our knowledge, this is the first study to identify both baseline and scotopic response changes with Piezo1 activation in the retina, using MEA recording. Increases in excitability drive greater energy demand and can lead to a greater accumulation of metabolic by-products, including reactive oxygen species, from mitochondrial ATP production trying to mitigate the energy imbalance of the RGCs, which in turn may lead to RGC dysfunction 70 . Similar emergence of spontaneous hyperactivity in RGCs has also been detected in animal models of retinal degeneration as the disease progress 71–74 .…”

Inhibition of high-voltage-activated calcium currents by acute hypoxia in cultured retinal ganglion cells

“…Acidosis can also trigger a chain of intracellular processes, such as increasing the production of reactive oxygen species (ROS) by mitochondria (Riemann et al, 2011 ). It has been shown that ROS produced by RGCs' mitochondria modulate ion channel gating and excitability (Smith et al, 2023 ). It is also important to remember that RGCs can directly sense pH changes with TWIK-related acid-sensitive K+ (TASK) channels (Zhong et al, 2013 ; Wen et al, 2022 ) and to consider this in planning the research and interpretation of the results.…”