Transcriptional Regulation of Neuronal Genes and Its Effect on Neural Functions: Gene Expression in Response to Static Magnetism in Cultured Rat Hippocampal Neurons

Static Magnetic Field Exposure In Vivo Enhances the Generation of New Doublecortin-expressing Cells in the Sub-ventricular Zone and Neocortex of Adult Rats

Static magnetic field (SMF) is gaining interest as a potential technique for modulating CNS neuronal activity. Previous studies have shown a pro-neurogenic effect of short periods of extremely low frequency pulsatile magnetic fields (PMF) in vivo and pro-survival effect of low intensity SMF in cultured neurons in vitro, but little is known about the in vivo effects of low to moderate intensity SMF on brain functions. We investigated the effect of continuously-applied SMF on subventricular zone (SVZ) neurogenesis and immature doublecortin (DCX)-expressing cells in the neocortex of young adult rats and in primary cultures of cortical neurons in vitro. A small (3 mm diameter) magnetic disc was implanted on the skull of rats at bregma, producing an average field strength of 4.3 mT at SVZ and 12.9 mT at inner neocortex. Levels of proliferation of SVZ stem cells were determined by 5-ethynyl-2'-deoxyuridine (EdU) labelling, and early neuronal phenotype development was determined by expression of doublecortin (DCX). To determine the effect of SMF on neurogenesis in vitro, permanent magnets were placed beneath the culture dishes. We found that low intensity SMF exposure enhances cell proliferation in SVZ and new DCX-expressing cells in neocortical regions of young adult rats. In primary cortical neuronal cultures, SMF exposure increased the expression of newly generated cells co-labelled with EdU and DCX or the mature neuronal marker NeuN, while activating a set of pro neuronal bHLH genes. SMF exposure has potential for treatment of neurodegenerative disease and conditions such as CNS trauma and affective disorders in which increased neurogenesis is desirable.

Neuroprotective effect of weak static magnetic fields in primary neuronal cultures

Low intensity static magnetic fields (SMFs) interact with various biological tissues including the CNS, thereby affecting key biological processes such as gene expression, cell proliferation and differentiation, as well as apoptosis. Previous studies describing the effect of SMFs on apoptotic cell death in several non-neuronal cell lines, emphasize the importance of such a potential modulation in the case of neurodegenerative disorders, where apoptosis constitutes a major route via which neurons degenerate and die. In this study, we examine the effect of SMFs on neuronal survival in primary cortical and hippocampal neurons that constitute a suitable experimental system for modeling the neurodegenerative state in vitro. We show that weak SMF exposure interferes with the apoptotic programing in rat primary cortical and hippocampal neurons, thereby providing protection against etoposide-induced apoptosis in a dose- and time-dependent manner. Primary cortical neurons exposed to SMF (50G) for 7days exhibited a 57.1±6.3% decrease in the percentage of cells undergoing apoptosis induced by etoposide (12μM), accompanied by a marked decrease in the expression of the pro-apoptotic markers: cleaved poly ADP ribose polymerase-1, cleaved caspase-3, active caspase-9 and the phospho-histone H2A variant (Ser139) by 41.0±5.0%, 81.2±5.0%, 72.9±6.4%, 42.75±2.9%, respectively, and by a 57.2±1.0% decrease in the extent of mitochondrial membrane potential collapse. Using the L-type voltage-gated Ca(2+) channel inhibitor nifedipine, which is selective to Ca(2+) influx through Cav1.2, we found that the anti-apoptotic effect of SMFs was mediated by Ca(2+) influx through these channels. Our findings demonstrating altered Ca(2+)-influx in response to thapsigargin stimulation in SMF-exposed cortical neurons, along with enhanced inhibition of KCl-induced Ca(2+)-influx through Cav1.2 channels and enhanced expression of Cav1.2 and Cav1.3 channels, allude to the involvement of voltage- and store-operated Ca(2+) channels in various aspects of the protective effect exerted by SMFs. These findings show the potential susceptibility of the CNS to weak SMF exposure and have implications for the design of novel strategies for the treatment and/or prevention of neurodegenerative diseases.

Gene expression profile in cultured human umbilical vein endothelial cells exposed to a 300 mT static magnetic field

In a previous investigation we reported that exposure to a moderate (300 mT) static magnetic field (SMF) causes transient DNA damage and promotes mitochondrial biogenesis in human umbilical vein endothelial cells (HUVECs). To better understand the response of HUVECs to the 300 mT SMF, a high-quality subtracted cDNA library representative of genes induced in cells after 4 h of static magnetic exposure was constructed. The global gene expression profile showed that several genes were induced after the SMF exposure. The characterized clones are involved in cell metabolism, energy, cell growth/division, transcription, protein synthesis, destination and storage, membrane injury, DNA damage/repair, and oxidative stress response. Quantitative real-time polymerase chain reaction (qRT-PCR) experiments were performed at 4 and 24 h on four selected genes. Their expression profiles suggest that HUVEC's response to SMF exposure is transient. Furthermore, compared to control cells, an up-regulation of several genes involved in cell growth and division was observed. This up-regulation is likely to be the cause of the slight, but significant, increase in cell proliferation at 12 h post-treatment. These results provide additional support to the notion that SMFs may be harmless to human health, and could support the rationale for their possible use in medical treatments.

Biocompatibility and Delivery of NGF by Hematite Nanotubes for Differentiation of PC12 Cells

This report discusses the compatibility of hematite nanotubes with PC12 cells and the use of these hematite nanotubes to deliver nerve growth factor (NGF) for the differentiation and growth of PC12 cells. The hematite nanotubes used in this work were synthesized using template-assisted thermal decomposition method, followed by dissolving the template. The synthesized hematite nanotubes have a diameter around 200 nm and an average length of about 10 μm, and they have a low coercivity (about 10 Oe) at room temperature. To study the biocompatibility of hematite nanotubes, PC12 cells were cultured in the presence of hematite nanotubes. Neurite (axon and dendrite) outgrowth, formation of morphological connections, and close contacts between PC12 cells and hematite nanotubes unequivocally confirmed the biocompatibility of hematite nanotubes. The efficiency of hematite nanotubes to bind with NGF and the ability of the NGF-incorporated hematite nanotubes to release the bound NGF were also investigated. It is found that NGF-incorporated hematite nanotubes enabled the differentiation of PC12 cells into neurons, and the filopodia extending from growth cones were in close proximity to the NGF-incorporated hematite nanotubes, at times appearing to extend toward or into them. These observations indicate that hematite nanotubes can be used as a vehicle for NGF delivery. This research paves the way toward developing potential treatments using magnetic nanotubes with incorporated growth factors for neurodegenerative disorders and injuries to the nervous system in the future.

Mechanisms of geomagnetic field influence on gene expression using influenza as a model system: basics of physical epidemiology

Recent studies demonstrate distinct changes in gene expression in cells exposed to a weak magnetic field (MF). Mechanisms of this phenomenon are not understood yet. We propose that proteins of the Cryptochrome family (CRY) are "epigenetic sensors" of the MF fluctuations, i.e., magnetic field-sensitive part of the epigenetic controlling mechanism. It was shown that CRY represses activity of the major circadian transcriptional complex CLOCK/BMAL1. At the same time, function of CRY, is apparently highly responsive to weak MF because of radical pairs that periodically arise in the functionally active site of CRY and mediate the radical pair mechanism of magnetoreception. It is known that the circadian complex influences function of every organ and tissue, including modulation of both NF-kappaB- and glucocorticoids- dependent signaling pathways. Thus, MFs and solar cycles-dependent geomagnetic field fluctuations are capable of altering expression of genes related to function of NF-kappaB, hormones and other biological regulators. Notably, NF-kappaB, along with its significant role in immune response, also participates in differential regulation of influenza virus RNA synthesis. Presented data suggests that in the case of global application (example-geomagnetic field), MF-mediated regulation may have epidemiological and other consequences.