TRPC1 and PEMF

TRPC1, a calcium channel with broad tissue expression data in the featured image came from ProteinAtlas.com, a site operated by Atlas Antibodies. Atlas Antibodies compiles messenger RNA data that tell us how much a gene is transcribed and protein expression as measured by staining intensity of Atlas antibodies using tissue sections from human donors. How does extremely low frequency electromagnetic radiation interact with TRPC1 channels? What are the down stream effects of this interaction?

Gating of TRPC1 Ca²⁺ currents [1]

Is it plausible that This Ca²⁺ channel can respond to electromagnetic fields of PEMF? These channels are gated by different means than voltage gated ion channels that respond to the transmembrane electrical potential charge difference. The Chen 2020 review covers many of the means that TRPC Ca²⁺/Na⁺ channel family members are gated. UniProt has a nice summary of TRPC1 Gene Onthology terms.

TrpC1 and PI-3 kinase [2]

These authors started of with the following points in their introduction:

Points from the introduction

1. Insulin-like growth factors (IGFs) bind to a receptor tyrosine kinase on myoblasts and muscle that results in signaling needed for regeneration after an injury.
2. Ligand binding leads to recruitment of the phosphotyrosine-binding domain of insulin receptor substrates (IRS) and results in IRS phosphorylation on specific tyrosine residues.
3. Activated IRS recruits and sequesters the p85 subunit of PI3K, liberating the p110 catalytic subunit.
4. The active p110 subunit generates 3′-phosphorylated phosphoinositides which bind the pleckstrin homology domain of phosphoinositide-dependent kinase 1 and Akt inducing their membrane targeting.
5. Phosphoinositide-dependent kinase 1phosphorylates Akt, which phosphorylates the mammalian target of rapamycin mTOR, which in turn, phosphorylates p70S6K and activates protein synthesis.

Extracellular Ca²⁺ also is known to play an important role in muscle development. These authors had shown in previous studies that knock down of the TRPC1 channels are responsible for the increased Ca²⁺ influx observed at the onset of myoblast differentiation.

studies in Trpc1^−/− knockout mice

To investigate the role of Trpc1 channels during skeletal muscle regeneration in vivo, the authors used a model of cardiotoxin-induced muscle injury and compared muscle regeneration in adult Trpc1^+/+ and Trpc1^−/− mice. Trpc1^−/− mice presented a delayed regeneration

• smaller fibers
• higher proportion of central nuclei
• delayed and diminished expression of myogenic transcription

Lack of a functional TrpC1 inhibited Akt phosphorylation and delayed muscle cell differentiation. They hypothesized that the entry of Ca²⁺ through Trpc1 channels enhances the activity of PI3K/Akt/mTOR/p70S6K pathway and accelerates muscle regeneration.

in cell culture

Cultured primary myoblasts derived from Trpc1^−/− muscles had less expression of the muscle protein gene specific transcription factor MyoD and cell cycle arrest p27, aka cyclin dependent protein kinase inhibitor. The study concluded that Trpc1 channels play a role in skeletal muscle development in vivo and in vitro by modulating the PI3K/Akt/mTOR/p70S6K pathway. The question arises as to if TRPC1 is activated by cell-cell contact.

Detecting magnetic fields [3]

The Franco-Obregón review attributed sensing of magnetic fields via the Radical Pair Mechansim (RPM). In this model Photo activation facilitates the reduction of the flavin by a neighboring protein moiety, commonly a cryptochrome, to form a coherent radical pair between the two molecules. The reduced flavo enzyme may also undertake an electron transfer to molecular oxygen (O₂) to produce super oxide (O₂^•−) The Franco-Obregón review also provided evidence that the Fe-S center of mitochondria complex I could sense magnetic fields and produce super oxide (O₂^•−).

Radical Pair Mechanisms is attractive because CRY2 also has near ubiquitous expression like TRPC1. Immuno histochemistry from Protein Atlas also suggests membrane localization where it could be close to TRPC1.

A look at cysteines in and domains of TRPC1 [4]

Domains and post translational modification of TRPC family have been discussed extensively in an excellent review. [4] The UniPort sequence of human TRPC1 was searched for cysteine that could be oxidized by super oxide from Cry2 exposed to magnetic fields… or other sources.

It is very speculative, but the potential exists that cysteine ainimo acid side chains in the regulatory domains of TRPC1 could become modified.

Myoblasts in culture [5]

This story also comes out of the Franco-Obregón Lab. This group used a device that produces spatially homogeneous, time-varying magnetic fields, consisting of 20 × 150 μs pulses for 6 ms repeated at a frequency of 15 Hz. The magnetic field amplitudes were between 0.5 and 3 mT. See the text for details. Exposure was for 10 min. All PEMF-treated samples were compared with time-matched control samples (0 mT)

1. Calcium entry was known to enhance to proliferation of myoblasts. This study proved that myoblast proliferation was enhanced by 10 min exposure to PEMF. Proliferation could be prevented by both CsA (calcineurin/NFAT inhibitor) and 2-APB (TRPC inhibitor)
2. 15 Hz pulsed of 7kHzPEMF @ 1.5 mT increased intracellular Ca²⁺ in the myoblasts in a manner that was blocked by TRPC1 blocker 2-ABP that worked at earlier time points but not later time points.
3. PEMF increases myoblast proliferation in a manner that is blocked by 2-ABP
4. A more TRPC1 specific drug, SKF-96365 (50 µM), blocked the PEMF increase in proliferation. TRPM7 inhibitor Mg²⁺ and TRPM4 inhibitor ruthenium red were without effect. PEMF TRPC1 atagonism by aminoglycoside antibiotics, 1% penicillin/streptomycin, also inhibited PEMF proliferation.
5. (NFAT)-transcriptional and P300/CBP-associated factor (PCAF).a histone
   acetyltransferase. PCAF, myogenin, and transcription activator MyoD were enhanced by PEMF exposure at 24 hours but not 48 hours. MyoD expression also increased after 24 hour exposure. Activation of calcineurin/calcium dependent NFAT was implicated.
6. 1.5 mT PEMF almost doubled ATP production as well as H₂O₂ production. PS and SK both diminished PEMF ROS production. Basal respiration, spare capacity, and ATP production were all generally increased in a manner that depended on cell density. Knock down of TRPC1 blocked significant increases in mitochondrial activity in response to PEMF.
7. In terms of cell cycle promoting cyclin D1, TRPC1 silencing precludes sensitivity to PEMF.
8. Mitochondria respiration in response to PEMF tracks expression of TRPC1.
9. Mitochondrial gene transcripts were examined. Cytochrome C oxidase subunit CoxII was increased by PEMF.
10. Shielding the cells against ambient magnetic fields decreased the TRPC1/NFAT/PCAF myogenic cascade that was reversed by supplementary PEMFs. Mechanical vibrations similar to those produced by PEMF did not replicate the response.

Continued thoughts [6,7] on the Franco-Obregón report [5]

Cry2 was cited as a possible source of H₂O₂ to activate TRPC1. [5] Willschko have a good review on how blue and other wavelengths of visible light contribute to magnetic field perception by cryptochromes in birds. [6]

Figure 10 cryptochrome ion radical pairs in birds [6]

The link to figure 10 is provided in order to avoid copyright issues. The redox cycle of flavinFADox, oxidized flavin; FADH^●, photo-reduced neutral radical form; FADH⁻, fully reduced form. Nt, nitrogen-terminus; Ct, carboxy-terminus of the Cry1a, with the antiserum-binding epitope in red. In parentheses, radical pairs, black arrows indicate light-independent reactions.

Scheme 2 theories explaining the bio effects of electromagnetic radiation [7]

• (A) Ion cyclotron resonance model applied to PEMF to voltage gated calcium channel signaling.
• (B) Energy diagram of electronic spin states (S, T₀, T₊, and T₋) of a radical pair in a magnetic field B. The vector representation… This one is extremely complicated. See above link to the text.
• (C) Reaction scheme for a radical pair reaction with magnetic field-dependent reaction products. The radical pair is generated by an electron transfer from a donor molecule 
• (D) Radical pair reaction of Cry. A flavin adenine dinucleotide (FAD) bounded with cryptochrome (Cry) is excited by a photon (FAD→FAD∗) and then protonated (FAD∗→(FADH⁺)∗). Three electron transfers occur sequentially:
• (E) Magnetosensitive radical pair reactions involving radical pairs of enzyme-bound neutral flavin FADH and superoxide …

Some of the abbreviated bullet points from the summary figure should give the casual reader a good feel for how deeply biophysical this magnetic field sensing is.

References

1. Chen X, Sooch G, Demaree IS, White FA, Obukhov AG. Transient Receptor Potential Canonical (TRPC) Channels: Then and Now. Cells. 2020 Aug 28;9(9):1983 PMC free paper
2. Zanou N, Schakman O, Louis P, Ruegg UT, Dietrich A, Birnbaumer L, Gailly P. Trpc1 ion channel modulates phosphatidylinositol 3-kinase/Akt pathway during myoblast differentiation and muscle regeneration. J Biol Chem. 2012 Apr 27;287(18):14524-34. PMC free article
3. Franco-Obregón A. Harmonizing Magnetic Mitohormetic Regenerative Strategies: Developmental Implications of a Calcium-Mitochondrial Axis Invoked by Magnetic Field Exposure. Bioengineering (Basel). 2023 Oct 10;10(10):1176. PMC free article
4. Liu X, Yao X, Tsang SY. Post-Translational Modification and Natural Mutation of TRPC Channels. Cells. 2020 Jan 7;9(1):135 PMC free article
5. Yap JLY, Tai YK, Fröhlich J, Fong CHH, Yin JN, Foo ZL, Ramanan S, Beyer C, Toh SJ, Casarosa M, Bharathy N, Kala MP, Egli M, Taneja R, Lee CN, Franco-Obregón A. Ambient and supplemental magnetic fields promote myogenesis via a TRPC1-mitochondrial axis: evidence of a magnetic mitohormetic mechanism. FASEB J. 2019 Nov;33(11):12853-12872.PMC free article
6. Wiltschko R, Wiltschko W. Sensing magnetic directions in birds: radical pair processes involving cryptochrome. Biosensors (Basel). 2014 Jul 24;4(3):221-42. PMC free article
7. Liu L, Huang B, Lu Y, Zhao Y, Tang X, Shi Y. Interactions between electromagnetic radiation and biological systems. iScience. 2024 Feb 10;27(3):109201. doi: 10.1016/j.isci.2024.109201. PMC free paper