Regulation of Neurite Outgrowth by Intermittent Irradiation of Visible Light

Physical Stimulation Methods Developed for In Vitro Neuronal Differentiation Studies of PC12 Cells: A Comprehensive Review

PC12 cells, which are derived from rat adrenal pheochromocytoma cells, are widely used for the study of neuronal differentiation. NGF induces neuronal differentiation in PC12 cells by activating intracellular pathways via the TrkA receptor, which results in elongated neurites and neuron-like characteristics. Moreover, the differentiation requires both the ERK1/2 and p38 MAPK pathways. In addition to NGF, BMPs can also induce neuronal differentiation in PC12 cells. BMPs are part of the TGF-β cytokine superfamily and activate signaling pathways such as p38 MAPK and Smad. However, the brief lifespan of NGF and BMPs may limit their effectiveness in living organisms. Although PC12 cells are used to study the effects of various physical stimuli on neuronal differentiation, the development of new methods and an understanding of the molecular mechanisms are ongoing. In this comprehensive review, we discuss the induction of neuronal differentiation in PC12 cells without relying on NGF, which is already established for electrical, electromagnetic, and thermal stimulation but poses a challenge for mechanical, ultrasound, and light stimulation. Furthermore, the mechanisms underlying neuronal differentiation induced by physical stimuli remain largely unknown. Elucidating these mechanisms holds promise for developing new methods for neural regeneration and advancing neuroregenerative medical technologies using neural stem cells.

Wireless near-infrared electrical stimulation of neurite outgrowth

Herein, through using electropolymerized pyrrole (PPy) to coat near-infrared upconversion nanoparticles (UCNPs) on an indium tin oxide (ITO) electrode, the as-prepared PPy/UCNPs photoelectrode could generate an interfacial electric field, release rare earth ions and induce reactive oxygen species (ROS) in PC12 cells under NIR irradiation, which could realize wireless neurite development and outgrowth.

Comparison of visible and UVA phototoxicity in neural culture systems micropatterned with digital projection photolithography

Photopolymerization provides a favorable method for hydrogel formation due to its simplicity, convenience, and versatility. However, the light exposure required to initiate photopolymerization is known to have a cytotoxic effect on encapsulated cells. Here, a 3D in vitro model of the nervous system microenvironment, micropatterned through the use of digital projection photolithography using a single hydrogel formulation that cross-links similarly under ultraviolet A (UVA, 315-400 nm) and visible light (400-700 nm) exposure, is presented. This setup allowed for the investigation of neuronal responses to different light wavelengths and exposure times during photoencapsulation, while ruling out effects due to the hydrogel formulation or photoinitiators used. Cellular studies-including neurite viability, DNA fragmentation, and neurite outgrowth for both UVA and visible light irradiation, the most common spectra used in biological photomicropatterning applications-were performed to assess the effect of light source on neuronal cultures. These studies indicated that while cell death occurs after exposure to either spectrum, visible light was less phototoxic than UVA, when using comparable levels of irradiation, and interestingly, glial cells were more susceptible to phototoxicity than neuronal cells. Thus, while utilizing visible light for micropatterning and cell encapsulation for nervous system applications is beneficial, it is helpful to keep the light exposure low to ensure optimal neuronal survival and growth. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 134-144, 2019.

Optical fiber light source directs neurite growth

Guiding the growth of a neurite by directing ~800 nm laser light to the leading edge of the neurite's growing region can be accomplished by controlling the position and direction in three dimensional space of a tapered optical fiber through which the light is projected. We control the position, angle and power of the laser beam to direct the growth of actin accumulations in neurites which affects their mobility.

Analysis of laser-induced heating in optical neuronal guidance

Recently, it has been shown that it is possible to control the growth direction of neuronal growth cones by stimulation with weak laser light; an effect dubbed optical neuronal guidance. The effect exists for a broad range of laser wavelengths, spot sizes, spot intensities, optical intensity profiles and beam modulations, but it is unknown which biophysical mechanisms govern it. Based on thermodynamic modeling and simulation using published experimental parameters as input, we argue that the guidance is linked to heating. Until now, temperature effects due to laser-induced heating of the guided neuron have been neglected in the optical neuronal guidance literature. The results of our finite-element-method simulations show the relevance of the temperature field in optical guidance experiments and are consistent with published experimental results and modeling in the field of optical traps. Furthermore, we propose two experiments designed to test this hypotheses experimentally. For one of these experiments, we have designed a microfluidic platform, to be made using standard microfabrication techniques, for incubation of neurons in temperature gradients on micrometer lengthscales.

Measurements of movement and diffusion coefficients of single cells on polymeric surface from image analysis

Time-lapse digital images were taken every 30 s of PC12 cells cultured on polystyrene dishes, collagen-coated dishes and poly(L-lysine)-coated dishes in high-serum medium, low-serum medium and neurite outgrowth factor (NGF)-containing medium to investigate their diffusion coefficients (i.e., self-diffusion coefficients), D and specific movement (i.e., specific frequent movement) using image analysis and Fast Fourier Transform (FFT) analysis. D for these cells was found to fluctuate as a function of time, D varying between 0 and 0.08 microm(2)/s. The trend observed upon examination of average D values was: D in high-serum medium > or = D in low-serum medium > or = D in NGF-containing medium. Image analysis and FFT analysis of single cells cultured on polymeric dishes in these three media did not have any specific frequency of cell movement between 0 and 0.0167 Hz. The high diffusion coefficient and high amplitude of power spectra of PC12 cells in high-serum medium might be attributed to the high energy necessary for their continual suppression of the mitogen-activated protein kinase (MAPK) cascade and for them to maintain their undifferentiated state.

Low infra red laser light irradiation on cultured neural cells: effects on mitochondria and cell viability after oxidative stress

Background

Considerable interest has been aroused in recent years by the well-known notion that biological systems are sensitive to visible light. With clinical applications of visible radiation in the far-red to near-infrared region of the spectrum in mind, we explored the effect of coherent red light irradiation with extremely low energy transfer on a neural cell line derived from rat pheochromocytoma. We focused on the effect of pulsed light laser irradiation vis-à-vis two distinct biological effects: neurite elongation under NGF stimulus on laminin-collagen substrate and cell viability during oxidative stress.

Methods

We used a 670 nm laser, with extremely low peak power output (3 mW/cm²) and at an extremely low dose (0.45 mJ/cm²). Neurite elongation was measured over three days in culture. The effect of coherent red light irradiation on cell reaction to oxidative stress was evaluated through live-recording of mitochondria membrane potential (MMP) using JC1 vital dye and laser-confocal microscopy, in the absence (photo bleaching) and in the presence (oxidative stress) of H₂O₂, and by means of the MTT cell viability assay.

Results

We found that laser irradiation stimulates NGF-induced neurite elongation on a laminin-collagen coated substrate and protects PC12 cells against oxidative stress.

Conclusion

These data suggest that red light radiation protects the viability of cell culture in case of oxidative stress, as indicated by MMP measurement and MTT assay. It also stimulates neurite outgrowth, and this effect could also have positive implications for axonal protection.

Electrical pulsed stimulation of surfaces homogeneously coated with gold nanoparticles to induce neurite outgrowth of PC12 cells

In this study, the potential of gold nanoparticles (20 nm) to deliver electrical stimulation to nerve cell cultures in vitro to induce nerve regeneration was evaluated. In order to use these biomaterials to deliver an electrical stimulus, we devised a novel method for the fabrication of a nanostructured 2D substrate comprising gold nanoparticles attached to the surface of a cover glass via an adsorption system. In this strategy, gold nanoparticles are created and then coated onto a positively charged cover glass that has been pretreated with polyethyleneimine (PEI). Scanning electron microscopy (SEM) revealed that the PC 12 cells extended neurites well on the gold nanoparticles in the presence of electrical stimulation. In addition, the neurite outgrowth of PC12 cells in response to pulsed and constant electrical stimulation was evaluated by live/dead cell determination, by reverse transcriptase polymerase chain reaction (RT-PCR) analysis, as well as by beta-tubulin and NF-200 expression. By electrical stimulation (250 mV for 1 h), PC12 cells with their neurite outgrowth length were highly increased, with a mean diameter of 98.5 microm. However, the neurite outgrowth length without electrical stimulation was approximately 10 approximately 20 microm. Moreover, the alternating current stimulation also showed good viability (<90%), while a high amount of cell death (more than 30%) was observed with constant current stimulation. Thus, the gold nanoparticles with pulsed current stimulation may provide suitable tools for the nerve regeneration using neuronal cells.

Visible light regulates neurite outgrowth of nerve cells

The neurite outgrowth of PC12 cells on collagen-coated glass plates under light emitting diode (LED) irradiation at several wavelengths (i.e., 455, 470, 525, 600, 630, 880 and 945 nm) was investigated. No neurite outgrowth was observed during cultivation under irradiation from the lamp of an inverted light microscope through filters (yielding mixed light at ca. 525 nm and more than 800 nm), whereas neurite outgrowth was observed during cultivation in the dark. When these cells were irradiated with monochromatic LED light, neurite outgrowth was slightly, but not completely, suppressed at 455, 525, 600, 630, 880 and 945 nm, as was observed in the case of mixed light. Long connected neuronal outgrowths (e.g., 3 mm length) were observed with LED light at 470 nm and 1.8 mW/cm(2) intensity. No such outgrowths were observed at other LED light wavelengths (i.e., 455, 525, 600, 630, 880 and 945 nm). Irradiation at 470 nm may have caused specific responses to transductional signals in these cells that led to the connection of neuronal outgrowths between cells. Not only suppressed neurite outgrowth but also long connected neurite outgrowths were observed when PC12 cells were cultured under several different wavelengths of light.