We show that both supplemental and ambient magnetic fields modulate myogenesis. A lone 10 min exposure of myoblasts to 1.5 mT amplitude supplemental pulsed magnetic fields (PEMFs) accentuated in vitro myogenesis by stimulating transient receptor potential (TRP)‐C1‐mediated calcium entry and downstream nuclear factor of activated T cells (NFAT)‐transcriptional and P300/CBP‐associated factor (PCAF)‐epigenetic cascades, whereas depriving myoblasts of ambient magnetic fields slowed myogenesis, reduced TRPC1 expression, and silenced NFAT‐transcriptional and PCAF‐epigenetic cascades. The expression levels of peroxisome proliferatoractivated receptor g coactivator 1α, the master regulator of mitochondriogenesis, was also enhanced by brief PEMF exposure. Accordingly, mitochondriogenesis and respiratory capacity were both enhanced with PEMF exposure, paralleling TRPC1 expression and pharmacological sensitivity. Clustered regularly interspaced short palindromic repeats‐Cas9 knockdown of TRPC1 precluded proliferative and mitochondrial responses to supplemental PEMFs, whereas small interfering RNA gene silencing of TRPM7 did not, coinciding with data that magnetoreception did not coincide with the expression or function of other TRP channels. The aminoglycoside antibiotics antagonized and down‐regulated TRPC1 expression and, when applied concomitantly with PEMF exposure, attenuated PEMF‐stimulated calcium entry, mitochondrial respiration, proliferation, differentiation, and epigenetic directive in myoblasts, elucidating why the developmental potential of magnetic fields may have previously escaped detection. Mitochondrial‐based survival adaptations were also activated upon PEMF stimulation. Magnetism thus deploys an authentic myogenic directive that relies on an interplay between mitochondria and TRPC1 to reach fruition.—Yap, J. L. Y., Tai, Y. K., Fröhlich, J., Fong, C. H. H., Yin, J. N., Foo, Z. L., Ramanan, S., Beyer, C., Toh, S. J., Casarosa, M., Bharathy, N., Kala, M. P., Egli, M., Taneja, R., Lee, C. N., Franco‐Obregón, A. Ambient and supplemental magnetic fields promote myogenesis via a TRPC1‐mitochondrial axis: evidence of a magnetic mitohormetic mechanism. FASEB J. 33, 12853–12872 (2019). http://www.fasebj.org

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No abstract

Pulsed electromagnetic fields (PEMFs) are capable of specifically activating a TRPC1‐mitochondrial axis underlying cell expansion and mitohormetic survival adaptations. This study characterizes cell‐derived vesicles (CDVs) generated from C2C12 murine myoblasts and shows that they are equipped with the sufficient molecular machinery to confer mitochondrial respiratory capacity and associated proliferative responses upon their fusion with recipient cells. CDVs derived from wild type C2C12 myoblasts include the cation‐permeable transient receptor potential (TRP) channels, TRPC1 and TRPA1, and directly respond to PEMF exposure with TRPC1‐mediated calcium entry. By contrast, CDVs derived from C2C12 muscle cells in which TRPC1 has been genetically knocked‐down using CRISPR/Cas9 genome editing, do not. Wild type C2C12‐derived CDVs are also capable of restoring PEMF‐induced proliferative and mitochondrial activation in two C2C12‐derived TRPC1 knockdown clonal cell lines in accordance to their endogenous degree of TRPC1 suppression. C2C12 wild type CDVs respond to menthol with calcium entry and accumulation, likewise verifying TRPA1 functional gating and further corroborating compartmental integrity. Proteomic and lipidomic analyses confirm the surface membrane origin of the CDVs providing an initial indication of the minimal cellular machinery required to recover mitochondrial function. CDVs hence possess the potential of restoring respiratory and proliferative capacities to senescent cells and tissues.

Chemotherapy is the mainstream treatment modality for invasive breast cancer. Unfortunately, chemotherapy-associated adverse events can result in early termination of treatment. Paradoxical effects of chemotherapy are also sometimes observed, whereby prolonged exposure to high doses of chemotherapeutic agents results in malignant states resistant to chemotherapy. In this study, potential synergism between doxorubicin (DOX) and pulsed electromagnetic field (PEMF) therapy was investigated in: 1) MCF-7 and MDA-MB-231 cells in vitro; 2) MCF-7 tumors implanted onto a chicken chorioallantoic membrane (CAM) and; 3) human patient-derived and MCF-7 and MDA-MB-231 breast cancer xenografts implanted into NOD-SCID gamma (NSG) mice. In vivo, synergism was observed in patient-derived and breast cancer cell line xenograft mouse models, wherein PEMF exposure and DOX administration individually reduced tumor size and increased apoptosis and could be augmented by combined treatments. In the CAM xenograft model, DOX and PEMF exposure also synergistically reduced tumor size as well as reduced Transient Receptor Potential Canonical 1 (TRPC1) channel expression. In vitro, PEMF exposure alone impaired the survival of MCF-7 and MDA-MB-231 cells, but not that of non-malignant MCF10A breast cells; the selective vulnerability of breast cancer cells to PEMF exposure was corroborated in human tumor biopsy samples. Stable overexpression of TRPC1 enhanced the vulnerability of MCF-7 cells to both DOX and PEMF exposure and promoted proliferation, whereas TRPC1 genetic silencing reduced sensitivity to both DOX and PEMF treatments and mitigated proliferation. Chronic exposure to DOX depressed TRPC1 expression, proliferation, and responses to both PEMF exposure and DOX in a manner that was reversible upon removal of DOX. TRPC1 channel overexpression and silencing positively correlated with markers of epithelial-mesenchymal transition (EMT), including SLUG, SNAIL, VIMENTIN, and E-CADHERIN, indicating increased and decreased EMT, respectively. Finally, PEMF exposure was shown to attenuate the invasiveness of MCF-7 cells in correlation with TRPC1 expression. We thus demonstrate that the expression levels of TRPC1 consistently predicted breast cancer sensitivity to DOX and PEMF interventions and positively correlated to EMT status, providing an initial rationale for the use of PEMF-based therapies as an adjuvant to DOX chemotherapy for the treatment of breast cancers characterized by elevated TRPC1 expression levels.

Pulsed electromagnetic fields (PEMFs) are capable of specifically activating a TRPC1mitochondrial axis underlying cell expansion and mitohormetic survival adaptations. This study characterizes cell-derived vesicles (CDVs) generated from C2C12 murine myoblasts and shows that they are equipped with the sufficient molecular machinery to confer mitochondrial respiratory capacity and associated proliferative responses upon their fusion with recipient cells.CDVs derived from wild type C2C12 myoblasts include the cation-permeable transient receptor potential (TRP) channels, TRPC1 and TRPA1, and directly respond to PEMF exposure with TRPC1-mediated calcium entry. By contrast, CDVs derived from C2C12 muscle cells in which TRPC1 had been genetically knocked-down using CRISPR/Cas9 genome editing, do not. Wild type C2C12-derived CDVs are also capable of restoring PEMF-induced proliferative and mitochondrial activation in two C2C12-derived TRPC1 knockdown clonal cell lines in accordance to their endogenous degree of TRPC1 suppression. C2C12 wild type CDVs respond to menthol with calcium entry and accumulation, likewise verifying TRPA1 functional gating and further corroborating compartmental integrity. Proteomic and lipidomic analyses confirm the surface membrane origin of the CDVs providing an initial indication of the minimal cellular machinery required to recover mitochondrial function. CDVs hence possess the potential of restoring respiratory and proliferative capacities to senescent cells and tissues.

Mitochondrial function is central to human health and has been recently shown to be modulated by magnetic field‐induced TRPC1 (red) activation. In article number 2000146, Petra S. Dittrich, Alfredo Franco‐Obregón, and co‐workers show that cell‐derived vesicles from wild type muscle are capable of reinstating lost mitochondrial sensitivity to magnetic fields in muscle cells in which TRPC1 had been genetically silenced.

In the original article, there was a nonconsequential error in Figure 1 as published. A file concatenation error occurred within the FACS analysis software that implicated the scatter dotplots shown in Figure 1C. The corrected Figure 1 appears below.