The Surviving, Not Thriving, Photoreceptors in Patients with Stargardt Disease.

Stargardt disease (STGD1), associated with biallelic variants in the gene, is the most common heritable macular dystrophy and is currently untreatable. To identify potential treatment targets, we characterized surviving STGD1 photoreceptors. We used clinical data to identify macular regions with surviving STGD1 photoreceptors.

Daily Light Onset and Plasma Membrane Tethers Regulate Mitochondria Redistribution within the Retinal Pigment Epithelium.

The retinal pigment epithelium (RPE) is an essential component of the retina that plays multiple roles required to support visual function. These include light onset- and circadian rhythm-dependent tasks, such as daily phagocytosis of photoreceptor outer segments. Mitochondria provide energy to the highly specialized and energy-dependent RPE.

Biomarker evidence of early vision and rod energy-linked pathophysiology benefits from very low dose DMSO in 5xFAD mice.

Here, we test whether early visual and OCT rod energy-linked biomarkers indicating pathophysiology in nicotinamide nucleotide transhydrogenase (Nnt)-null 5xFAD mice also occur in Nnt-intact 5xFAD mice and whether these biomarkers can be pharmacologically treated. Four-month-old wild-type or 5xFAD C57BL/6 substrains with either a null (B6J) Nnt or intact Nnt gene (B6NTac) and 5xFAD B6J mice treated for one month with either R-carvedilol + vehicle or only vehicle (0.01% DMSO) were studied.

Acetazolamide Challenge Changes Outer Retina Bioenergy-Linked and Anatomical OCT Biomarkers Depending on Mouse Strain.

Purpose: The purpose of this study was to test the hypothesis that optical coherence tomography (OCT) bioenergy-linked and anatomical biomarkers are responsive to an acetazolamide (ACZ) provocation.

Methods: C57BL/6J mice (B6J, a strain with relatively inefficient mitochondria) and 129S6/ev mice (S6, a strain with relatively efficient mitochondria) were given a single IP injection of ACZ (carbonic anhydrase inhibitor) or vehicle. In each mouse, the Mitochondrial Configuration within Photoreceptors based on the profile shape Aspect Ratio (MCP/AR) index was determined from the hyper-reflective band immediately posterior to the external limiting membrane (ELM).

Do multiple physiological OCT biomarkers indicate age-related decline in rod mitochondrial function in C57BL/6J mice?

Purpose: To test the hypothesis that rod photoreceptor mitochondria function progressively declines over time.

Methods: 2, 12, and 24 month-old dark- and light-adapted C57BL/6J (B6J) mice were examined by OCT. We measured (i) an index of mitochondrial configuration within photoreceptors measured from the profile shape aspect ratio (MCP/AR) of the hyperreflective band posterior to the external limiting membrane (ELM), (ii) a proxy for energy-dependent pH-triggered water removal, the thickness of the ELM-retinal pigment epithelium (ELM-RPE), and its correlate (iii) the hyporeflective band (HB) signal intensity at the photoreceptor tips.

Blockade of IL-6R prevents preterm birth and adverse neonatal outcomes.

Background: Preterm birth preceded by spontaneous preterm labour often occurs in the clinical setting of sterile intra-amniotic inflammation (SIAI), a condition that currently lacks treatment.

Methods: Proteomic and scRNA-seq human data were analysed to evaluate the role of IL-6 and IL-1α in SIAI. A C57BL/6 murine model of SIAI-induced preterm birth was developed by the ultrasound-guided intra-amniotic injection of IL-1α.

Multiple Bioenergy-Linked OCT Biomarkers Suggest Greater-Than-Normal Rod Mitochondria Activity Early in Experimental Alzheimer's Disease.

Purpose: In Alzheimer's disease, central brain neurons show evidence for early hyperactivity. It is unclear if this occurs in the retina, another disease target. Here, we tested for imaging biomarker manifestation of prodromal hyperactivity in rod mitochondria in vivo in experimental Alzheimer's disease.

Transducin-Deficient Rod Photoreceptors Evaluated With Optical Coherence Tomography and Oxygen Consumption Rate Energy Biomarkers.

Purpose: To test the hypothesis that rod energy biomarkers in light and dark are similar in mice without functional rod transducin (Gnat1rd17).

Methods: Gnat1rd17 and wildtype (WT) mice were studied in canonically low energy demand (light) and high energy demand (dark) conditions. We measured rod inner segment ellipsoid zone (ISez) profile shape, external limiting membrane-retinal pigment epithelium (ELM-RPE) thickness, and magnitude of a hyporeflective band (HB) intensity dip located between photoreceptor tips and apical RPE; antioxidants were given in a subset of mice.

Fast and slow light-induced changes in murine outer retina optical coherence tomography: complementary high spatial resolution functional biomarkers.

Fast (seconds) and slow (minutes to hours) optical coherence tomography (OCT) responses to light stimulation have been developed to probe outer retinal function with higher spatial resolution than the classical full-field electroretinogram (ERG). However, the relationships between functional information revealed by OCT and ERG are largely unexplored. In this study, we directly compared the fast and slow OCT responses with the ERG.

Functional Changes Within the Rod Inner Segment Ellipsoid in Wildtype Mice: An Optical Coherence Tomography and Electron Microscopy Study.

Purpose: To test the hypothesis that changing energy needs alter mitochondria distribution within the rod inner segment ellipsoid.

Methods: In mice with relatively smaller (C57BL/6J [B6J]) or greater (129S6/ev [S6]) retina mitochondria maximum reserve capacity, the profile shape of the rod inner segment ellipsoid zone (ISez) was measured with optical coherence tomography (OCT) under higher (dark) or lower (light) energy demand conditions. ISez profile shape was characterized using an unbiased ellipse descriptor (minor/major aspect ratio).

Clinically relevant mitochondrial-targeted therapy improves chronic outcomes after traumatic brain injury.

Pioglitazone, an FDA-approved compound, has been shown to target the novel mitochondrial protein mitoNEET and produce short-term neuroprotection and functional benefits following traumatic brain injury. To expand on these findings, we now investigate the dose- and time-dependent effects of pioglitazone administration on mitochondrial function after experimental traumatic brain injury. We then hypothesize that optimal pioglitazone dosing will lead to ongoing neuroprotection and cognitive benefits that are dependent on pioglitazone-mitoNEET signalling pathways.

Photoreceptor Cell Calcium Dysregulation and Calpain Activation Promote Pathogenic Photoreceptor Oxidative Stress and Inflammation in Prodromal Diabetic Retinopathy.

This study tested the hypothesis that diabetes promotes a greater than normal cytosolic calcium level in rod cells that activates a Ca-sensitive protease, calpain, resulting in oxidative stress and inflammation, two pathogenic factors of early diabetic retinopathy. Nondiabetic and 2-month diabetic C57Bl/6J and calpain1 knockout (Capn1) mice were studied; subgroups were treated with a calpain inhibitor (CI). Ca content was measured in photoreceptors using Fura-2.

Correcting QUEST Magnetic Resonance Imaging-Sensitive Free Radical Production in the Outer Retina In Vivo Does Not Correct Reduced Visual Performance in 24-Month-Old C57BL/6J Mice.

Purpose: To test the hypothesis that acutely correcting a sustained presence of outer retina free radicals measured in vivo in 24-month-old mice corrects their reduced visual performance.

Methods: Male C57BL/6J mice two and 24 months old were noninvasively evaluated for unremitted production of paramagnetic free radicals based on whether 1/T1 in retinal laminae are reduced after acute antioxidant administration (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]). Superoxide production was measured in freshly excised retina (lucigenin assay).

OCT imaging of rod mitochondrial respiration .

There remains a need for high spatial resolution imaging indices of mitochondrial respiration in the outer retina that probe normal physiology and measure pathogenic and reversible conditions underlying loss of vision. Mitochondria are involved in a critical, but somewhat underappreciated, support system that maintains the health of the outer retina involving stimulus-evoked changes in subretinal space hydration. The subretinal space hydration light-dark response is important because it controls the distribution of vision-critical interphotoreceptor matrix components, including anti-oxidants, pro-survival factors, ions, and metabolites.

Functional regulation of an outer retina hyporeflective band on optical coherence tomography images.

Human and animal retinal optical coherence tomography (OCT) images show a hyporeflective band (HB) between the photoreceptor tip and retinal pigment epithelium layers whose mechanisms are unclear. In mice, HB magnitude and the external limiting membrane-retinal pigment epithelium (ELM-RPE) thickness appear to be dependent on light exposure, which is known to alter photoreceptor mitochondria respiration. Here, we test the hypothesis that these two OCT biomarkers are linked to metabolic activity of the retina.

Superoxide free radical spin-lattice relaxivity: A quench-assisted MR study.

Purpose: QuEnch-assiSTed (QUEST) MRI provides a unique biomarker of excessive production of paramagnetic free radicals (oxidative stress) in vivo. The contribution from superoxide, a common upstream species found in oxidative stress-based disease, to the QUEST metric is unclear. Here, we begin to address this question by measuring superoxide spin-lattice relaxivity (r1) in phantoms.

Sildenafil-evoked photoreceptor oxidative stress in vivo is unrelated to impaired visual performance in mice.

Purpose: The phosphodiesterase inhibitor sildenafil is a promising treatment for neurodegenerative disease, but it can cause oxidative stress in photoreceptors ex vivo and degrade visual performance in humans. Here, we test the hypotheses that in wildtype mice sildenafil causes i) wide-spread photoreceptor oxidative stress in vivo that is linked with ii) impaired vision.

Methods: In dark or light-adapted C57BL/6 mice ± sildenafil treatment, the presence of oxidative stress was evaluated in retina laminae in vivo by QUEnch-assiSTed (QUEST) magnetic resonance imaging, in the subretinal space in vivo by QUEST optical coherence tomography, and in freshly excised retina by a dichlorofluorescein assay.

Rod Photoreceptor Neuroprotection in Dark-Reared Pde6brd10 Mice.

Purpose: The purpose of this study was to test the hypothesis that anti-oxidant and / or anti-inflammation drugs that suppress rod death in cyclic light-reared Pde6brd10 mice are also effective in dark-reared Pde6brd10 mice.

Methods: In untreated dark-reared Pde6brd10 mice at post-natal (P) days 23 to 24, we measured the outer nuclear layer (ONL) thickness (histology) and dark-light thickness difference in external limiting membrane-retinal pigment epithelium (ELM-RPE) (optical coherence tomography [OCT]), retina layer oxidative stress (QUEnch-assiSTed [QUEST] magnetic resonance imaging [MRI]); and microglia/macrophage-driven inflammation (immunohistology). In dark-reared P50 Pde6brd10 mice, ONL thickness was measured (OCT) in groups given normal chow or chow admixed with methylene blue (MB) + Norgestrel (anti-oxidant, anti-inflammatory), or MB or Norgestrel separately.

Preventing diabetic retinopathy by mitigating subretinal space oxidative stress .

Patients with diabetes continue to suffer from impaired visual performance before the appearance of overt damage to the retinal microvasculature and later sight-threatening complications. This diabetic retinopathy (DR) has long been thought to start with endothelial cell oxidative stress. Yet newer data surprisingly finds that the avascular outer retina is the primary site of oxidative stress before microvascular histopathology in experimental DR.

Age-related murine hippocampal CA1 laminae oxidative stress measured in vivo by QUEnch-assiSTed (QUEST) MRI: impact of isoflurane anesthesia.

Age-related impairments in spatial learning and memory often precede non-familial neurodegenerative disease. Ex vivo studies suggest that physiologic age-related oxidative stress in hippocampus area CA1 may contribute to prodromal spatial disorientation and to morbidity. Yet, conventional blood or cerebrospinal fluid assays appear insufficient for early detection or management of oxidative stress within CA1 sub-regions in vivo.

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

Purpose: To test the hypothesis that imaging biomarkers are useful for evaluating in vivo rod photoreceptor cell responses to a mitochondrial protonophore.

Methods: 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.

Publisher Correction: Novel QUEST MRI In Vivo Measurement of Noise-induced Oxidative Stress in the Cochlea.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Novel QUEST MRI In Vivo Measurement of Noise-induced Oxidative Stress in the Cochlea.

Effective personalized therapeutic treatment for hearing loss is currently not available. Cochlear oxidative stress is commonly identified in the pathogenesis of hearing loss based upon findings from excised tissue, thus suggesting a promising druggable etiology. However, the timing and site(s) to target for anti-oxidant treatment in vivo are not clear.

QUEST MRI assessment of fetal brain oxidative stress in utero.

Purpose: To achieve sufficient precision of R1 (=1/T1) maps of the fetal brain in utero to perform QUEnch-assiSTed (QUEST) MRI in which a significant anti-oxidant-induced reduction in R1 indicates oxidative stress.

Methods: C57BL/6 mouse fetuses in utero were gently and non-surgically isolated and secured using a homemade 3D printed clip. Using a commercial receive-only surface coil, brain maps of R1, an index sensitive to excessive and continuous free radical production, were collected using either a conventional Cartesian or a non-Cartesian (periodically rotated overlapping parallel lines with enhanced reconstruction) progressive saturation sequence.