Study On The Effect And Mechanism Of Medium-strength Static Magnetic Field On Breast Cancer Cells

Static magnetic field(SMF)extensively exist in environments related with human lives,including natural geomagnetic field(GMF,?40 ?T)and artificial magnetic field which is generated by magnetic materials or tools.Magnetic fields with different intensities play an important role in the diagnosis and treatment of diseases,among which the medium intensity SMF(1 mT?1 T)is widely applied to the replacement and supplementary treatment of various diseases.For example,the traditional Chinese medicine CiShi can be taken orally to subdue yang and receive qi,calm fright and tranquilize mind.Magnetic therapeutic apparatus for external use can be used for the treatment of all kinds of acute or chronic pain to reduce swelling,relieve pain and stop bleeding.Recent researches found SMF can inhibit the growth of many types of cancer cells and it has the potential as a treatment for cancers.However,the analysis about changes in the nature and metastasis of cancer cells and corresponding mechanisms under the magnetic field still need to be done.A more comprehensive and in-depth understanding about the influence and mechanism of SMF is essential for its clinical application.Breast cancer is the malignant tumor with the highest incidence in women.The high mortality rate of breast cancer results from the primary or secondary drug resistance and distant metastasis of tumours.Breast cancer cell is the common model for tumor cell metastasis analysis.Studies have shown that moderate static magnetic field can increase the inhibitory effect of some chemotherapy drugs such as paclitaxel and 5-fluorouracil on breast cancer cells.In the early stage of this study,we also found that treatment with hypomagnetic field(HMF,?1 ? T)can inhibit the migration of human neuroblastoma cells.It is suggested that SMF may be used not only for inhibition of tumor growth but also for intervention of tumor metastasis.Therefore,in this study,we take 4T1 as the research object and GMF as the control to further explore the effect and mechanism of static magnetic field(?254 mT)with moderate intensity on the proliferation,migration,apoptosis and other properties of 4T1 cells.The results of cell count,cell viability and CFSE staining showed that SMF treatment could accelerate the proliferation of 4T1 cells,but the cell viability decreased significantly.Wound healing assay and trans-well assay showed that SMF treatment could significantly inhibit the migration of 4T1 cells.In order to further explore the common way that static magnetic fields with different intensity work on cells,we used HMF,GMF and SMF three different intensity of magnetic field environments to intervene 4T1 cells;the second generation high-throughput sequencing technology to sequence the transcriptome,and a variety of gene screening strategies and bioinformatics methods to analyze the sequencing results.The results indicate that the mitochondrial and telomere regions may respond to the continuous changes of magnetic field intensity,which is one of the targets of the static magnetic field.In order to verify the effect of SMF on mitochondria,we examined the structure and function of mitochondria.The results observed by transmission electron microscopy showed after SMF treatment the morphology of mitochondria in 4T1 cells did not change significantly,but the width of mitochondria decreased significantly.According to seahorse energy metabolism analyzer,the oxygen consumption rate of mitochondria after SMF treatment decreased significantly,the extracellular acidification rate increased significantly,the ATP production and the intracellular ROS content decreased significantly;further analysis indicated that SMF could decrease the activity of antioxidant enzymes such as catalase and GSH reductase,increase the content of lactate in cell culture medium,and significantly increase the expression of myc and pdk 1,the key genes of glycolysis pathway.The results above turned out that SMF reduced the function of mitochondria,inhibited the oxidative phosphorylation process,and promoted the increase of glycolysis metabolism.At the same time,we observed that the membrane potential of mitochondria treated with SMF increased,which was different from the general statement about mitochondria treated with SMF.By analyzing the data of seahorse energy metabolism analyzer,we thought that SMF may have some influence on ATP synthase in mitochondrial respiratory chain,which results in the decrease of mitochondrial ATP synthesis and the increase of membrane potential.Through further study,we found that SMF can significantly inhibit the activity of ATP synthase.After Western-blot and fluorescence co-localization detection,we found that after the treatment of SMF,the content of ATP synthase did not have significant change,but the position of ATP synthase and the outer mitochondrial membrane became further apart.At the same time,we detected the telomere and telomere status of cells after SMF treatment.The results showed that under the SMF condition the telomerase activity of 4T1 cells decreased and the length of telomeres shortened also the q-PCR indicated the expression of telomerase reverse transcriptase(tert)turned down.Tert not only related to the infinite proliferation of cells,but also to the migration of cells.In order to further confirm whether the magnetic field inhibited cell migration by tert,siRNA was used to knock down the tert of 4T1 cells.It is found that when tert was knocked down,the inhibition of SMF treatment to migration disappeared.These results proved that SMF treatment could reduce the expression and activity of telomerase in 4T1 cells,shorten the length of telomeres,and the tert may be one of the direct targets of SMF treatment.In conclusion,it is reasonable to believe that mitochondria and telomerase can respond to changes of the steady magnetic field.SMF treatment reduces the mitochondrial function of mouse breast tumor cells,which may be accomplished through the magnetic field acting on ATP synthase.In view of the fact that most of the chemotherapy drugs work based on the rapid division of tumor cells to inhibit tumor proliferation,the static magnetic field with moderate intensity can accelerate the proliferation of mouse breast tumor cells,which provides a new idea for the drug combination of tumor treatment in the future.More importantly,the static magnetic field with moderate intensity can inhibit the migration of tumor cells at the same time,which indicates the potential applied value of magnetic field for the treatment of breast cancer and provides a new direction for the combination of magnetic field and chemotherapy drugs to treat breast cancer.