Exposure to long wavelength light that improves aged mitochondrial function shifts acute cytokine expression in serum and the retina

PLOS ONE RESEARCH ARTICLE Exposure to long wavelength light that improves aged mitochondrial function shifts acute cytokine expression in serum and the retina Harpreet Shinhmar, Chris Hogg, Glen Jeffery ID* Institute of Ophthalmology, University College London, London, United Kingdom * a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Shinhmar H, Hogg C, Jeffery G (2023) Exposure to long wavelength light that improves aged mitochondrial function shifts acute cytokine expression in serum and the retina. PLoS ONE 18(7): e0284172. https://doi.org/10.1371/journal. pone.0284172 Editor: Alfred S. Lewin, University of Florida, UNITED STATES Received: October 12, 2022 Abstract Aged mitochondrial function can be improved with long wavelength light exposure. This reduces cellular markers of inflammation and can improve system function from fly through to human. We have previously shown that with age there are increases in cytokine expression in mouse serum. Here, we ask what impact 670nm light has on this expression using a 40 cytokine array in blood serum and retina in C57Bl6 mice. 670nm exposure was delivered daily for a week in 12 month old mice. This shifted patterns of cytokine expression in both serum and retina inducing a selective increase. In serum examples of significant increases were found in IL (interleukins) 1α, IL-7, 10, 16, 17 along with TNF-α and CXCL (chemokines) 9 and 10. In retina the increases were again mainly in some IL’s and CXCL’s. A few cytokines were reduced by light exposure. Changes in serum cytokines implies that long wavelengths impact systemically even to unexposed tissues deep in the body. In the context of wider literature, increased cytokine expression may be protective. However, their upregulation by light merits further analysis as cytokines upregulation can also be negative and there are probably complex patterns of interaction in the dynamics of their expression. Accepted: March 8, 2023 Published: July 21, 2023 Copyright: © 2023 Shinhmar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript and its Supporting Information files. Funding: This study was funded by the Biotechnology and Biological Sciences Research Council (Grant No. BB/N000250/1) awarded to GJ). Competing interests: The authors have declared that no competing interests exist. Introduction Mitochondria regulate metabolism and the pace of ageing. When their membrane potential declines adenosine triphosphate (ATP) production is compromised reducing available cellular energy. This is often associated with progressive increases in reactive oxygen species (ROS) that further undermines cell function [1]. However, long wavelength light (650-900nm) can reverse many of these features in ageing and disease, particularly in the CNS with its high metabolic demand and mitochondrial dependence [2]. Exposure to longer wavelengths has been widely shown to have therapeutic value in the CNS. In invertebrates it extends lifespan and improves aged motor skills, cognition and visual function [3–6]. In mammals it has similar impact and also reduces cellular markers of PLOS ONE | https://doi.org/10.1371/journal.pone.0284172 July 21, 2023 1 / 10 PLOS ONE Red light shifts cytokines inflammation and the pace of age related cell loss [7–9]. Its application is now extended to humans where aged visual function is significantly improved [10]. There is limited evidence that longer wavelength exposure also impacts on immunity [11– 13]. However, this remains relatively unexplored. A key question here relates to whether changes in immunity induced by longer wavelengths can also be found in serum. If this were the case, then it may imply that the impact of such lights can act systemically. There has been evidence for this when longer wavelengths have been targeted at distal regions of the body and have had positive impacts on the retina [13]. But the mechanism for this has not been revealed. The absence of data on the interactions between immunity and longer wavelengths is problematic for the development of therapies based on their use. We have previously shown in mouse serum that ageing is associated with a general increase in cytokine expression [14]. Here we expose aged mice to a commonly used long wavelength, 670nm, and assess its impact on the cytokine expression in blood serum and retina. The hypothesis is that consistent with improved mitochondrial function, there will be a decline in the patterns of cytokine expression following 670nm light exposure. This proved not to be the case. Methods Animals Investigations were performed under a UK Home Office Project License (PPL 94/5839) in accordance with UK and EU regulation and approved by the UCL Animal Welfare and Ethical Review Body. All methods were carried out in compliance with ARRIVE guidelines. A total of 12 old male C57Bl6 mice at 12 months of age were used. The investigation consisted of an age-matched control group housed under identical conditions, and an experimental group who were exposed to long-wavelength light at 670nm (40mW/cm2, CH Electronics UK) daily at 10am for 15 minutes lasting 1 week. Mice were exposed to light within their cages [15], and free to roam thereby reducing the amount of stress to the animals. Samples of blood serum and retina from individual mice in both control (N = 6) and 670nm light exposed (N = 6) groups were analysed to allow for statistical analysis. All mice were killed by cervical dislocation. Eyes were rapidly removed, and the retina extracted on ice and processed as tissue lysates as below. Bloods were taken via cardiac puncture prior to cervical dislocation. Blood serum collection To avoid false cytokine readings and minimize stress all animals were acclimatized to the room and person for at least 1 hour prior to time of death. Mice were deeply anaesthetized to allow for open chest cardiac puncture. The amount of blood collected with very little needle movement as possible to avoid hemolysis of samples was limited to 0.5ml per animal, as this would commonly yield *0.2ml of serum. Blood was rapidly harvested into tubes and allowed to coagulate on ice for approximately 20 minutes. After the blood had coagulated for 20 minutes the tubes were then centrifuged at 2000 x g for 15 minutes and the serum that was creamy white was transferred to a new tube. Protein concentration was calculated using a BCA Assay kit (Thermo Scientific). As advised by the manufacturer’s protocol (Proteome Profiler, R&D Systems, Minneapolis, USA), 150μl of serum per group was added to each cytokine array membrane from both pooled samples and individual mouse samples. PLOS ONE | https://doi.org/10.1371/journal.pone.0284172 July 21, 2023 (...truncated)