Mechanisms and Mitochondrial Redox Signaling in Photobiomodulation

Abstract

Photobiomodulation (PBM) involves the use of red or near-infrared light at low power densities to produce a beneficial effect on cells or tissues. PBM therapy is used to reduce pain, inflammation, edema, and to regenerate damaged tissues such as wounds, bones, and tendons. The primary site of light absorption in mammalian cells has been identified as the mitochondria and, more specifically, cytochrome c oxidase (CCO). It is hypothesized that inhibitory nitric oxide can be dissociated from CCO, thus restoring electron transport and increasing mitochondrial membrane potential. Another mechanism involves activation of light or heat-gated ion channels. This review will cover the redox signaling that occurs in PBM and examine the difference between healthy and stressed cells, where PBM can have apparently opposite effects. PBM has a marked effect on stem cells, and this is proposed to operate via mitochondrial redox signaling. PBM can act as a preconditioning regimen and can interact with exercise on muscles.

Figure 1. Proposed photodissociation of NO from cytochrome c oxidase (CCO)

CCO is a multi-subunit enzyme containing two heme co-factors and two copper centers that oxidizes four reduced cytochrome c molecules, while at the same time reducing oxygen to water and producing four protons that go on to form ATP via ATP synthase. Nitric oxide can inhibit this process by binding to Cu_B and it is proposed that red or NIR light can dissociate this non-covalently bound NO increasing the rate of respiration and ATP production.

Figure 2. Proposed activation of TRP (transient receptor potential) ion channels by blue/green light or 980 nm NIR

It is proposed that blue light (in the region of 420 nm) or green light in the region of 540 nm can activate opsins such as melanopsin (OPN5) by a cis-trans retinal isomerization. Activation of OPN5 can in turn, open TRPV calcium ion channels via Gα_Q, phospholipase C and phosphoinositide signaling. Alternatively, NIR light in the region of 980 nm may directly perturb the conformational structure of TRPV channels via absorption by nanostructured water.

Figure 3. Activation of NF-kB (nuclear factor kappaB) in mouse embryonic fibroblasts

Cells were isolated from NF-kB luciferase reporter mice. (A) Biphasic dose response of NF-kB activation (0.003 to 30 J/cm² of 810 nm laser) measured by bioluminescence signal production at 1, 6, 10 and 24 hours post-PBM. (B) Western blot showing phosphorylation of NF-kB with different doses and times. Adapted from data contained in (45).

Figure 4. Dose response of PBM in primary cultured cortical neurons

Primary cultured mouse cortical neurons were treated with a wide range of doses of 810 nm laser from 0.03 to 30 J/cm². (A) Mitochondrial membrane potential measured by red/green ratio of fluorescence from JC1 probe. (B) Intracellular calcium measured by fluorescence from fluo-4 calcium probe. (C) Intracellular ROS mesured by fluorescence from mitosox red probe. Adapted from data contained in (53).

Figure 5. Effects of PBM on cells under oxidative stress

Primary cortical neurons were treated with one of three different agents (cobalt chloride, hydrogen peroxide, rotenone) each of which produced oxidative stress. They were treated either with no PBM or with 3 J/cm² of 810 nm laser. (A) Intracellular ROS (measured by CellRox red fluorescent probe) were modestly increased in control cells, but significantly reduced in all three types of oxidative stress. (B) In every case the mitochondrial membrane potential (measured by tetramethyl-rhodamine methyl ester fluorescent probe, TMRM) was significantly increased. Adapted from data contained in (54).

Figure 6. Activation of transcription factors and signaling pathways after PBM

Akt, protein kinase B; AMPK, 5′ adenosine monophosphate-activated protein kinase; AP1, activator protein 1; ATP, adenosine triphosphate; camp, cyclic adenosine monophosphate; CBP, CREB-binding protein; cyclin D1, cyclin-rependent kinase co-regulator; EPO, erythropoietin; ERK, extracellular regulated kinase; FoxM1, forkhead box protein M1; GSK3β, glycogen synthase kinase 3 beta; HIF1α, hypoxia-inducible factor 1alpha; mTOR, mechanistic target of rapamycin; osterix, osteoblast-specific transcription factor; p300, CBP co-activator; PPARγ, peroxisome proliferator-activated receptor gamma; ROS, reactive oxygen species; RUNX2, runt-related transcription factor 2; VEGF, vascular endothelial growth factor.

Figure 7. Effect of PBM with four different wavelengths on human adipose-derived stem cells (hADSC)

hADSCs in prolioferation medium (PM) were exposed to 3 J/cm² of 415, 540, 660, or 810 nm light. (A) ATP measured 3 h post PBM for luciferase assay. (B) MMP measured by TMRM 1 h post PBM. (C) intracellular ROS measured by CM-H2DCFDA fluorescence probe 30 min post-PBM. (D) Expression of RUNX2 and (E) expression of osterix (OSX), both measured by RT-PCR after cells were cultured in osteogenic differentiation medium and received PBM as above every 2 days for 3 weeks. Both 415 nm and 540 nm gave significant increases in osteogenic markers that could be blocked by TRP ion channel inhibitors capsazepine, CPZ and SKF96365. 660 nm and 810 nm were less effective at osteogenic differentiation and ion channel blockers had no effect (data not shown). Partly adapted from data contained in (67).

Figure 8. Chemical structures of TRP ion channel inhibitors

Capsazepine (CPZ) and broad-spectrum ion channel blocker, SKF96365.

Figure 9. Future directions. Similarities between PBM and exercise and synergistic combinations

AICAR, aminoimidazole carboxamide ribonucleotide; PCG-1α, peroxisome proliferator activated receptor γ coactivator 1α; AMPK, adenosine monophosphate (AMP)-activated kinase; DNMT1, DNA methyltransferase 1; RBBP7, RB binding protein 7; HAT1, histone deacetylase 1; TRPV1, transient receptor potential vanilloid 1; Tfam, mitochondrial transcription factor A; Drp1, dynamin-related protein; Fis1, mitochondrial fission 1 protein; Mff, mitochondrial fission factor.