Engineering Cortical Neuron Polarity with Nanomagnets on a Chip

Abstract

Intra- and extracellular signaling play critical roles in cell polarity, ultimately leading to the development of functional cell-cell connections, tissues, and organs. In the brain, pathologically oriented neurons are often the cause for disordered circuits, severely impacting motor function, perception, and memory. Aside from control through gene expression and signaling pathways, it is known that nervous system development can be manipulated by mechanical stimuli (e.g., outgrowth of axons through externally applied forces). The inverse is true as well: intracellular molecular signals can be converted into forces to yield axonal outgrowth. The complete role played by mechanical signals in mediating single-cell polarity, however, remains currently unclear. Here we employ highly parallelized nanomagnets on a chip to exert local mechanical stimuli on cortical neurons, independently of the amount of superparamagnetic nanoparticles taken up by the cells. The chip-based approach was utilized to quantify the effect of nanoparticle-mediated forces on the intracellular cytoskeleton as visualized by the distribution of the microtubule-associated protein tau. While single cortical neurons prefer to assemble tau proteins following poly-L-lysine surface cues, an optimal force range of 4.5-70 pN by the nanomagnets initiated a tau distribution opposed to the pattern cue. In larger cell clusters (groups comprising six or more cells), nanoparticle-mediated forces induced tau repositioning in an observed range of 190-270 pN, and initiation of magnetic field-directed cell displacement was observed at forces above 300 pN. Our findings lay the groundwork for high-resolution mechanical encoding of neural networks in vitro, mechanically driven cell polarization in brain tissues, and neurotherapeutic approaches using functionalized superparamagnetic nanoparticles to potentially restore disordered neural circuits.

Acute and Chronic Neural Stimulation via Mechano-Sensitive Ion Channels

“…Although high amplitude Ca 2+ influxes were observed in the latter case, 154 and intracellular distribution of proteins 54,155 and suggest the use of wireless magnetic forces to remotely modulate neural network activity.…”

“…53 It has been shown that internalized MNPs can influence the protein tau distribution which affects the polarization of neurites for axon formation. 54 Calcium is an important second messenger that is implicated in various signaling pathways that regulate gene expression. 55 In order to act as a specific second messenger, cytoplasmic calcium 9 concentration is maintained at a much lower concentration (100-300 nM) compared to extracellular spaces (1-3 mM) and endoplasmic reticulum (10-100 µM).…”

“…By monitoring the movements of microparticles, the magnetic field strength 1 µm above the magnetic elements is ~0.73*Bmax (applied magnetic field). 54 Fabrication of the magnetic chips is based on previously described protocol 54 . Briefly, …”

“…54 A particle with a magnetic dipole within a magnetic flux density gradient, referred as magnetic gradient in the main text ( ), experiences magnetic forces (eq. 1) due to its magnetic moment (m).…”

Modulating motility of intracellular vesicles in cortical neurons with nanomagnetic forces on-chip

“…Thus, through engineering Tau concentrations in neurons we may prevent neurons from degenerating their networks, especially, when no other growth cues are available. In this context, we have shown previously that a nanomagnetic force stimulus 5 – 70 pN, applied over 24 hours, locally modulated Tau distribution in cortical neurons 34 While the translocation of Tau was related to the nanomagnetic force strength, how vesicle transport gets impacted under the application of nanomagnetic forces remains an open question.…”