Reply to: Magneto is ineffective in controlling electrical properties of cerebellar Purkinje cells, Assessing the utility of Magneto to control neuronal excitability in the somatosensory cortex and Revaluation of magnetic properties of Magneto

Evaluating methods and protocols of ferritin-based magnetogenetics

FeRIC (Ferritin iron Redistribution to Ion Channels) is a magnetogenetic technique that uses radiofrequency (RF) alternating magnetic fields to activate the transient receptor potential channels, TRPV1 and TRPV4, coupled to cellular ferritins. In cells expressing ferritin-tagged TRPV, RF stimulation increases the cytosolic Ca²⁺ levels via a biochemical pathway. The interaction between RF and ferritin increases the free cytosolic iron levels that, in turn, trigger chemical reactions producing reactive oxygen species and oxidized lipids that activate the ferritin-tagged TRPV. In this pathway, it is expected that experimental factors that disturb the ferritin expression, the ferritin iron load, the TRPV functional expression, or the cellular redox state will impact the efficiency of RF in activating ferritin-tagged TRPV. Here, we examined several experimental factors that either enhance or abolish the RF control of ferritin-tagged TRPV. The findings may help optimize and establish reproducible magnetogenetic protocols.

Nanotransducers for Wireless Neuromodulation

Understanding the signal transmission and processing within the central nervous system (CNS) is a grand challenge in neuroscience. The past decade has witnessed significant advances in the development of new tools to address this challenge. Development of these new tools draws diverse expertise from genetics, materials science, electrical engineering, photonics and other disciplines. Among these tools, nanomaterials have emerged as a unique class of neural interfaces due to their small size, remote coupling and conversion of different energy modalities, various delivery methods, and mitigated chronic immune responses. In this review, we will discuss recent advances in nanotransducers to modulate and interface with the neural system without physical wires. Nanotransducers work collectively to modulate brain activity through optogenetic, mechanical, thermal, electrical and chemical modalities. We will compare important parameters among these techniques including the invasiveness, spatiotemporal precision, cell-type specificity, brain penetration, and translation to large animals and humans. Important areas for future research include a better understanding of the nanomaterials-brain interface, integration of sensing capability for bidirectional closed-loop neuromodulation, and genetically engineered functional materials for cell-type specific neuromodulation.

Lipid Oxidation Induced by RF Waves and Mediated by Ferritin Iron Causes Activation of Ferritin-Tagged Ion Channels

One approach to magnetogenetics uses radiofrequency (RF) waves to activate transient receptor potential channels (TRPV1 and TRPV4) that are coupled to cellular ferritins. The mechanisms underlying this effect are unclear and controversial. Theoretical calculations suggest that the heat produced by RF fields is likely orders of magnitude weaker than needed for channel activation. Using the FeRIC (Ferritin iron Redistribution to Ion Channels) system, we have uncovered a mechanism of activation of ferritin-tagged channels via a biochemical pathway initiated by RF disturbance of ferritin and mediated by ferritin-associated iron. We show that, in cells expressing TRPV^FeRIC channels, RF increases the levels of the labile iron pool in a ferritin-dependent manner. Free iron participates in chemical reactions, producing reactive oxygen species and oxidized lipids that ultimately activate the TRPV^FeRIC channels. This biochemical pathway predicts a similar RF-induced activation of other lipid-sensitive TRP channels and may guide future magnetogenetic designs.

Uncovering a possible role of reactive oxygen species in magnetogenetics

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 Ca2+-sensitive promoter to express a secreted embryonic alkaline phosphatase (SEAP) reporter. Exposure of TRPV1-ferritin-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.