Effects of static magnetic fields on eukaryotic cytoskeleton

Abstract

The cytoskeleton includes microtubules, actin filaments (also called microfilaments) and intermediate filaments, which play vital roles in maintaining cell morphology, intracellular transport and cell migration. They are involved in several physiological and pathological processes, such as the development and oncogenesis. Here in this review, we focus on summarizing the known effects of static magnetic fields on eukaryotic cytoskeleton, including microtubules, actin filaments and intermediate filaments. Since 1970s and 1980s, a series of progresses about the effects of static magnetic fields on eukaryotic cytoskeleton have been made both theoretically and experimentally. Theoretically, researchers have calculated the diamagnetic anisotropy of peptide bonds, which is relatively weak but could be amplified by highly ordered and organized structures, such as alpha helix and beta sheet in proteins. The diamagnetic anisotropy can be further amplified by highly ordered polymer structures such as microtubules. Experimentally, the orientation of purified microtubule and microfilament, as well as the cellular microtubule and microfilament changes that were induced by static magnetic fields has all been reported by multiple studies. For microtubules, it was shown that a 0.02 T static magnetic field was able to align the purified microtubule polymers in parallel with the magnetic field direction. The degree of purified microtubule polymer orientation changes is directly correlated with the magnetic field intensity. Moreover, there were also studies about the microtubule related cellular structures, such as mitotic spindles, sperm tails and Paramecium cilia. The mitotic spindle orientation of human nasopharyngeal carcinoma cell CNE-2Z, human retinal pigment epithelial cell RPE1 and frog eggs could all be affected by high static magnetic fields in a magnetic field intensity dependent manner. However, the magnetic field-induced orientation changes in these cells are also determined by chromosome alignment as well as the spindle morphology. Moreover, the orientation and swimming behaviors of Paramecium were both affected by high static magnetic fields. For actin and actin polymers, it has been shown that 10 T static magnetic field could affect the self-assembly process of G-actin in vitro. Moreover, static magnetic fields of various intensities could also cause the microfilament distribution changes or actin alteration in some cells. For example, 80 mT static magnetic field increased the accumulation of actin and myosin and promoted the formation of large multinucleated myotubes. There were also a few studies about static magnetic fields and intermediate filaments, but the evidences are much less than that of microtubules or microfilaments. Overall, the progresses about magnetic field effects on human and animal cytoskeleton are promising but still at an initial stage. The direct effect of magnetic fields on cytoskeleton dynamics has not been investigated due to the microscopy technology limitations under magnetic conditions. More importantly, the organism complexity and the different magnetic field parameters (such as homogeneous or gradient magnetic fields, magnetic fields with different intensities, etc.) make the investigation complicated. It is very important to further explore the static magnetic fields of different parameters for their effects on various cytoskeleton, which will be critical to understand the static magnetic field effects on some physiological and pathological conditions, as well as to explore the potentials of static magnetic fields in applications such as cancer therapy.