Uncovering a possible role of reactive oxygen species in magnetogenetics

Abstract

Recent reports have shown that intracellular, (super)paramagnetic ferritin nanoparticles can gate TRPV1, a non-selective cation channel, in a magnetic field. Here, we report the effects of differing field strength and frequency as well as chemical inhibitors on channel gating using a Ca 2+-sensitive promoter to express a secreted embryonic alkaline phosphatase (SEAP) reporter. Exposure of TRPV1ferritin-expressing HEK-293T cells at 30 °C to an alternating magnetic field of 501 kHz and 27.1 mT significantly increased SEAP secretion by ~ 82% relative to control cells, with lesser effects at other field strengths and frequencies. Between 30-32 °C, SEAP production was strongly potentiated 3.3-fold by the addition of the TRPV1 agonist capsaicin. This potentiation was eliminated by the competitive antagonist AMG-21629, the NADPH oxidase assembly inhibitor apocynin, and the reactive oxygen species (RoS) scavenger N-acetylcysteine, suggesting that ROS contributes to magnetogenetic TRPV1 activation. These results provide a rational basis to address the heretofore unknown mechanism of magnetogenetics. New approaches have been advanced for controlling signal transduction 1 , cell activity, and protein expression 2 with temporal precision, contributing to advances in on-demand biomanufacturing of protein biologics 3 , developing new tools for drug discovery 4 , in vitro expansion and differentiation of stem cells for regenerative medicine 5 , and regulating the activity of neurons and other cell types in vivo 5. One example is optogenetics, which uses precise wavelengths of light to stimulate light sensitive channels 6,7. Alternatively, gold nanorods (AuNRs) can be actuated by near-infrared (NIR) wavelengths to confer light-sensitivity to light-insensitive, heat-sensitive targets. Specifically, antibody-coated AuNRs targeted to transient receptor potential (TRP) vanilloid 1 (TRPV1) cation channels and integrins generated plasmonic heating when stimulated with select wavelengths of NIR light and gated Ca 2+ flux into cells to control cellular functions 8. In each optical technique, the low penetration depth of visible and NIR light into cellular systems limits application either in vitro or in vivo 9. Another example is chemogenetics, in which drug ligands can gate mutated ion channels 10 or G-protein coupled receptors 11. Chemogenetics does not require an implant but is limited by a slow onset of action that is dictated by the pharmacokinetics of the drug actuator in vivo and the addition of a chemical inducer to in vitro cell-based reactors 12. Still other approaches for activating signal transduction have been developed including the use of size-controlled microbubbles targeted to Piezo1 ion channels to gate Ca 2+ flux by ultrasound stimulation 13 and magnetic activation of engineered ion channels 14-18. The use of magnetic fields to gate TRPV1 and related ion channels has been shown in multiple studies. Pralle and co-workers used megahertz radio frequency (RF) alternating magnetic fields (AMFs) to gate TRPV1 when external ...

Evaluating Methods and Protocols of Ferritin-Based Magnetogenetics

“…1C). The influence of the cellular iron import on ferritin iron load was corroborated by a recent study that reported that the ferritin iron core size depends on the presence of fetal bovine serum, ferric citrate and holotransferrin (Brier et al, 2020). Thus, the use of ferritin-based magnetogenetic tools in in vitro studies can be optimized by increasing the cellular iron import via holotransferrin supplementation or as reported recently, by a combination of holotransferrin and ferric citrate (Brier et al, 2020).…”

“…It has been reported that RF fields at high kHz frequencies activate a ferritin-tagged TRPV1 (Brier et al, 2020; Stanley et al, 2015, 2016). Thus, we also estimated the E field amplitude for a 465 kHz RF stimulus of 31 μT which resulted in about 0.1 V/m (Figure S2A, B).…”

“…Although several independent studies have reported the magnetic control of TRPV1 and TRPV4 (Brier et al, 2020;Duret et al, 2019;Hernández-Morales et al, 2020;Hutson et al, 2017;Stanley et al, 2015Stanley et al, , 2016Wheeler et al, 2016), magnetogenetics has generated controversies about its underlying mechanisms. Some theoretical studies have suggested that the interaction between magnetic fields and ferritin could produce heat and mechanical stimuli to activate the ferritin-tagged TRPV (Barbic, 2019;Duret et al, 2019), but there is no experimental data to support those hypotheses yet.…”

“…Some theoretical studies have suggested that the interaction between magnetic fields and ferritin could produce heat and mechanical stimuli to activate the ferritin-tagged TRPV (Barbic, 2019;Duret et al, 2019), but there is no experimental data to support those hypotheses yet. On the other hand, recent studies have postulated that a biochemical mechanism is responsible for the RF-induced activation of ferritin tagged-TRPV (Brier et al, 2020;Hernández-Morales et al, 2020). Besides this controversy, the efficacy of some ferritin-based magnetogenetics has been questioned (Kole et al, 2019;Wang et al, 2019;Wheeler et al, 2016;Xu et al, 2019).…”

“…These differences have contributed to the confusion and debates regarding the biophysical mechanisms and experimental reproducibility. In one class of magnetogenetic techniques, static, low frequency or radio frequency (RF) alternating magnetic fields have been applied to activate transient receptor potential vanilloid channels (TRPV) coupled to ferritin (Brier et al, 2020; Duret et al, 2019; Hernández-Morales et al, 2020; Hutson et al, 2017; Stanley et al, 2016). The biophysical mechanisms responsible for magnetic activation of the channels are still being worked out.…”