Static magnetic field accelerates aging and development in nematode

Abstract

Electro-magnetic fields are everywhere in our life. The strength and duration of human exposure is proportional to the degree of industrialization. The possible health hazard has been investigated for decades. C. elegans (nematode) has been a sensitive tool to study aging and development. The current study investigated the possible effects of static magnetic fields (SMFs) on the developmental and aging processes of C. elegans. Nematodes were grown in the presence of SMFs of strengths varying from 0 to 200 mT. Treatment with a 200 mT SMF reduced the development times from L2 to young adult by approximately 20%. After SMF treatment, the average lifespan was reduced from 31 days to 25 days for wild-type nematodes. The up-regulation of genes associated with development and aging was verified by quantitative real-time RT-PCR. Nematodes carrying mutation in these genes also exhibited resistance to the SMFs treatment. Apparently, induction of gene expression is selective and dose-dependent. SMFs accelerate nematode development and shorten nematode lifespan through pathways associated with let-7, clk-1, unc-3, and age-1.

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We live on a big magnet; the terrestrial magnetism is about 30∼60 µT.1 The magnetic force around our life can be more than 1,000 times stronger than the Earth's natural magnetic field. And the magnet is applied to our life, clinical practice, soil contamination detection, and so on. The magnetic strength of the instruments for medical treatment, like magnetic resonance imaging (MRI) and magnetic nanoparticles, is higher than 3 T. And the strength becomes stronger for higher resolution application. The hazardous effects associated with SMF on human health have become conspicuous. The increase of human exposure to magnetic fields (including static magnetic fields, pulsed electromagnetic fields and alternating electromagnetic fields), due to the use of electrical appliances such as microwave oven, cellular phone or increasingly powerful medical instrument, has prompted investigations into the effects of magnetic fields on living organisms.

The safety of static magnetic fields (SMFs) has been discussed for decades.2 Various studies have examined the effects of SMFs, but their results were often inconclusive.3 SMFs alone do not have a lethal effect on the basic properties of cell growth and survival under normal culture conditions.4,5 Early studies did not show any effect of the exposure to SMFs on the organogenesis, fetal development or cortical development of mice.6–9 However, SMFs may cause minor effects at the cellular level that then accumulate and eventually cause distinct symptoms.

Until recently, the International Agency for Research on Cancer (IARC) proposed that SMFs might affect embryonic development in amphibians.10 Morphological analyses indicated that SMFs could induce modifications in cell shape, the cell surface and the cytoskeleton.11–18 SMFs have been reported to be toxic to rat embryos,19 and have been reported to cause significant time and dose-dependent increases in the frequency of micronuclei in mice20 and in the rates of germination and early growth in Cicer arietinum L.21 The abnormal growth and increased incidence of malformations in embryos exposed to a static field of 1 T have been observed.22,23

Static Magnetic Field Accelerates Aging Process in Nematodes

C. elegans has been a powerful tool to study current interests in aging and development. Decline in lifespan and physiological processes24–28 are important index of aging. Under the laboratory condition, SMF at strength of 200 mT is sufficient to accelerate developmental process of nematodes. Time required from larva to adult is shortened by approximately 20 to 30%. SMF also shortens the lifespan of nematode by ∼20%.

The advantage of nematode as genetic model is the large number of mutants available in the library upon request. It is of particular interest that some mutant nematodes are resistant to the SMF treatment, such as clk-1, lim-7, daf-2 and age-1 genes which are associated with development and aging; however, these genes belong to distinct pathways within the development and aging processes. The upregulation of clk-1, lim-7, daf-2, unc-3 and age-1 after SMF treatment was verified by quantitative real-time RT-PCR. Lifespan analyses revealed that the let-7, unc-3 and age-1 mutants were not affected by SMF treatment. Apparently, induction of gene expression by SMFs is selective and dose-dependent. The genetic analysis of mutant nematode indicates that the effect of SMF is very likely global.

Is the decline of physiological processes in nematode analogous to aging processes in human? For an averaged lifespan of 80 years, 20% reduction could mean in 16 years shorter than normal lifespan under the influence of 200 mT field strength. Under laboratory condition, nematodes live constantly under the magnetic field. For human, this may not be true. However, the abnormality in gene expression indicated that this hazardous effect might be accumulative. Since long-term survey in public health could not provide conclusive evidence, further study applying nematode may shed a light on the revealing of molecular mechanism involved in the SMF-induced health hazard and possible cure to this situation.