Long-Term Photobiomodulation of Cellular and Mitochondrial Activities in IMR-32 Cells Using an 810 nm Light-Emitting Diode

In photobiomodulation (PBM), biological tissues are stimulated using low-energy light. Mitochondria are thought to be integral to the process, and PBM effects vary with light parameters. Biphasic curves are commonly used to describe the dose response of PBM but do not fit in some cases. Dose-dependent PBM effects, especially mitochondrial responses, must be understood to optimize clinical therapies. However, most previous studies have reported short-term mitochondrial activity changes, neglecting long-term effects or dose-dependent changes in whole transcriptomes. We studied the effects of 3-day PBM with an 810 nm circular LED beam on human neuroblastoma IMR-32 cells. Two light doses with opposite effects on mitochondrial DNA copy number were chosen to analyze total RNA, protein content and function of mitochondrial respiratory complexes, and mitochondrial morphology. Daily 15-minute 810 nm light treatment enhanced drug resistance to the mitochondrial inhibitors and uncoupling agent via two distinct mechanisms: 1.40 mW/cm
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light increased cell proliferation and the proportion of cells in the cell cycle S phase; 1.95 mW/cm
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light enhanced oxidative phosphorylation at the RNA, protein, and functional levels and the proportion of network-like mitochondria. Our findings reveal the complexity of PBM dose responses and provide insights into light-cell interactions.