Effect of 670 nm Photobiomodulation on Retinal Function and Energy Metabolism in Aging Mice

Metabolic dysfunction is a common hallmark of aging and recent studies have established the metabolic footprint of aging in the mouse which report disruption of mitochondrial function and redox homeostasis genes in liver and muscle tissue in aged animals. Photobiomodulation (PBM) also known as low-level level laser therapy is the use of red and near-infrared light to stimulate healing, relieve pain, and reduce inflammation. Mechanistically, PBM stimulates cytochrome c oxidase, a primary chromophore and key component in mitochondrial respiration. Downstream effects include increased production of ATP, alterations in oxidative stress, modulation of transcription leading to improved cell survival, increased proliferation and migration, and new protein synthesis. In mice, 670nm light has improved age-related changes within 12-month-old mouse retina including improved ATP production and reduced oxidative stress resulting in improved retinal function. Thus, we hypothesized that a brief course of light treatment would improve the metabolic footprint of aging in C57/BL mice compared to aged mice who did not receive light treatment (sham). We tested this hypothesis by treating 11-month-old, female mice with 670nm light at 4.5J/cm2 (25mW/cm2 for 180 sec), 5 times per week for 4 weeks. Control mice were not treated with light but were handled similarly to those treated with light. Following the four weeks of light treatment, we assessed retinal function through full flash scotopic electroretinogram recordings. In addition, we harvested liver, heart, and brain tissues for qPCR analysis of targets important to aging and mitochondrial health including cytochrome c oxidase (CoxIV), carnitine palmitoyl transferase 1b (Cpt1b), uncoupling protein 3 (Ucp3), transcription factor A (Tfam), and mitofusin 2 (mfn2). In aged animals, we predict that expression of each of these targets will be higher amongst those treated with 670nm light compared to sham controls implicating an important role for light treatment in metabolic health