Novel imaging biomarkers for mapping the impact of mild mitochondrial uncoupling in the outer retina in vivo

• Published in: PloS one 2020-01, Vol.15 (1), p.e0226840-e0226840
• Main Authors: Berkowitz, Bruce A, Olds, Hailey K, Richards, Collin, Joy, Joydip, Rosales, Tilman, Podolsky, Robert H, Childers, Karen Lins, Hubbard, W Brad, Sullivan, Patrick G, Gao, Shasha, Li, Yichao, Qian, Haohua, Roberts, Robin
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - radiation effects; Animals; Biology and Life Sciences; Biomarkers; Biomarkers - metabolism; Dark adaptation; Darkness; Drug dosages; Energy consumption; Epithelium; Evaluation; Free radicals; In vivo methods and tests; Injection; Laboratory animals; Magnetic Resonance Imaging; Male; Mapping; Medicine; Medicine and Health Sciences; Metabolism; Mice; Mice, Inbred C57BL; Mitochondria; Mitochondria - metabolism; Neurosciences; Oxygen; pH effects; Photoreceptors; Physical Sciences; Relaxation time; Research and Analysis Methods; Retina; Retina - cytology; Retina - diagnostic imaging; Retina - physiology; Retina - radiation effects; Retinal pigment epithelium; Spinal cord; Thickness; Thinning; Tomography, Optical Coherence; Traumatic brain injury; Water treatment
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0226840

To test the hypothesis that imaging biomarkers are useful for evaluating in vivo rod photoreceptor cell responses to a mitochondrial protonophore. Intraperitoneal injections of either the mitochondrial uncoupler 2,4 dinitrophenol (DNP) or saline were given to mice with either higher [129S6/eVTac (S6)] or lower [C57BL/6J (B6)] mitochondrial reserve capacities and were studied in dark or light. We measured: (i) the external limiting membrane-retinal pigment epithelium region thickness (ELM-RPE; OCT), which decreases substantially with upregulation of a pH-sensitive water removal co-transporter on the apical portion of the RPE, and (ii) the outer retina R1 (= 1/(spin lattice relaxation time (T1), an MRI parameter proportional to oxygen / free radical content. In darkness, baseline rod energy production and consumption are relatively high compared to that in light, and additional metabolic stimulation with DNP provoked thinning of the ELM-RPE region compared to saline injection in S6 mice; ELM-RPE thickness was unresponsive to DNP in B6 mice. Also, dark-adapted S6 mice given DNP showed a decrease in outer retina R1 values compared to saline injection in the inferior retina. In dark-adapted B6 mice, transretinal R1 values were unresponsive to DNP in superior and inferior regions. In light, with its relatively lower basal rod energy production and consumption, DNP caused ELM-RPE thinning in both S6 and B6 mice. The present results raise the possibility of non-invasively evaluating the mouse rod mitochondrial energy ecosystem using new DNP-assisted OCT and MRI in vivo assays.