Retinal function and structure in Ant1-deficient mice

A visually guided swim assay for mouse models of human retinal disease recapitulates the multi-luminance mobility test in humans

PURPOSE

The purpose of this study was to develop a visually guided swim assay (VGSA) for measuring vision in mouse retinal disease models comparable to the multi-luminance mobility test (MLMT) utilized in human clinical trials.

METHODS

Three mouse retinal disease models were studied: Bardet-Biedl syndrome type 1 (Bbs1M390R/M390R), n = 5; Bardet-Biedl syndrome type 10 (Bbs10-/-), n = 11; and X linked retinoschisis (retinoschisin knockout; Rs1-KO), n = 5. Controls were normally-sighted mice, n = 10. Eyeless Pax6Sey-Dey mice, n = 4, were used to determine the performance of animals without vision in VGSA.

RESULTS

Eyeless Pax6Sey-Dey mice had a VGSA time-to-platform (TTP) 7X longer than normally-sighted controls (P < 0.0001). Controls demonstrated no difference in their TTP in both lighting conditions; the same was true for Pax6Sey-Dey. At 4-6 M, Rs1-KO and Bbs10-/- had longer TTP in the dark than controls (P = 0.0156 and P = 1.23 × 10-8, respectively). At 9-11 M, both BBS models had longer TTP than controls in light and dark with times similar to Pax6Sey-Dey (P < 0.0001), demonstrating progressive vision loss in BBS models, but not in controls nor in Rs1-KO. At 1 M, Bbs10-/- ERG light-adapted (cone) amplitudes were nonrecordable, resulting in a floor effect. VGSA did not reach a floor until 9-11 M. ERG combined rod/cone b-wave amplitudes were nonrecordable in all three mutant groups at 9-11 M, but VGSA still showed differences in visual function. ERG values correlate non-linearly with VGSA, and VGSA measured the continual decline of vision.

CONCLUSION

ERG is no longer a useful endpoint once the nonrecordable level is reached. VGSA differentiates between different levels of vision, different ages, and different disease models even after ERG is nonrecordable, similar to the MLMT in humans.

Using Micro-Electrode-Array Recordings and Retinal Disease Models to Elucidate Visual Functions: Simultaneous Recording of Local Electroretinograms and Ganglion Cell Action Potentials Reveals the Origin of Retinal Oscillatory Potentials

BACKGROUND

The electroretinogram (ERG) is an essential diagnostic tool for visual function, both in clinical and research settings. Here, we establish an advanced in vitro approach to assess cell-type-specific ERG signal components.

METHODS

Retinal explant cultures, maintained under entirely controlled conditions, were derived from wild-type mice and rd10 rod- and cpfl1 cone-degeneration mouse models. Local micro-ERG (µERG) and simultaneous ganglion cell (GC) recordings were obtained from the retinal explants using multi-electrode arrays. Band-pass filtering was employed to distinguish photoreceptor, bipolar cell, amacrine cell (AC), and GC responses.

RESULTS

Scotopic and photopic stimulation discriminated between rod and cone responses in wild-type and mutant retina. The 25 kHz sampling rate allowed the visualization of oscillatory potentials (OPs) in extraordinary detail, revealing temporal correlations between OPs and GC responses. Pharmacological isolation of different retinal circuits found that OPs are generated by inner retinal AC electrical synapses. Importantly, this AC activity helped synchronise GC activity.

CONCLUSION

Our µERG protocol simultaneously records the light-dependent activities of the first-, second-, and third-order neurons within the native neuronal circuitry, providing unprecedented insights into retinal physiology and pathophysiology. This method now also enables complete in vitro retinal function testing of therapeutic interventions, providing critical guidance for later in vivo investigations.

G-Protein-Coupled Receptors Mediate Modulations of Cell Viability and Drug Sensitivity by Aberrantly Expressed Recoverin 3 within A549 Cells

To elucidate the currently unknown molecular mechanisms responsible for the aberrant expression of recoverin (Rec) within cancerous cells, we examined two-dimensional (2D) and three-dimensional (3D) cultures of Rec-negative lung adenocarcinoma A549 cells which had been transfected with a plasmid containing human recoverin cDNA (A549 Rec) or an empty plasmid as a mock control (A549 MOCK). Using these cells, we measured cytotoxicity by several anti-tumor agents (2D), cellular metabolism including mitochondrial and glycolytic functions by a Seahorse bio-analyzer (2D), the physical properties, size and stiffness of the 3D spheroids, trypsin sensitivities (2D and 3D), and RNA sequencing analysis (2D). Compared with the A549 MOCK, the A549 Rec cells showed (1) more sensitivity toward anti-tumor agents (2D) and a 0.25% solution of trypsin (3D); (2) a metabolic shift from glycolysis to oxidative phosphorylation; and (3) the formation of larger and stiffer 3D spheroids. RNA sequencing analysis and bioinformatic analyses of the differentially expressed genes (DEGs) using Gene Ontology (GO) enrichment analysis suggested that aberrantly expressed Rec is most likely associated with several canonical pathways including G-protein-coupled receptor (GPCR)-mediated signaling and signaling by the cAMP response element binding protein (CREB). The findings reported here indicate that the aberrantly expressed Rec-induced modulation of the cell viability and drug sensitivity may be GPCR mediated.

Paeonol attenuates retinopathy in streptozotocin-induced diabetes in rats by regulating the oxidative stress and polyol pathway

The current research work was planned to study the effects of paeonol in the management of diabetic retinopathy. Diabetes was induced in male Sprague Dawley rats using Streptozotocin (55 mg/kg, i.p.). After 4 weeks, the diabetic animals were treated with paeonol at a dose of 50, 100, and 200 mg/kg body weight daily for the next 4 weeks. At the end of treatment, retinal physiology was studied by recording an electroretinogram (ERG); biochemical parameters and oxidative stress were estimated. The histopathology of the retina was also carried out at the end of the study. The ERG of paeonol-treated animals showed a significant improvement in a-wave amplitude, b-wave amplitude, a-wave latency, and b-wave latency (p < 0.001) at 15 cd s/m² when compared with the diabetic control animals. The paeonol treatment (200 mg/kg) in diabetic animals showed a significant decrease in the plasma glucose level (p < 0.001) when compared to the animals in diabetic control group. Paeonol also significantly decreased the lactate dehydrogenase, aldose reductase, and sorbitol dehydrogenase levels when compared with the diabetic control animals. The oxidative stress in the eye was significantly reduced after the paeonol treatment in the diabetic rats. The histopathology showed a significant reduction (p < 0.05) in the retinal thickness after the paeonol treatment. The results of the study indicate that paeonol can be considered an effective management option for diabetic retinopathy.

Alterations in Retinal Signaling Across Age and Sex in 3xTg Alzheimer’s Disease Mice

Background:

Visual disturbances often precede cognitive dysfunction in patients with Alzheimer’s disease (AD) and may coincide with early accumulation of amyloid-β (Aβ) protein in the retina. These findings have inspired critical research on in vivo ophthalmic Aβ imaging for disease biomarker detection but have not fully answered mechanistic questions on how retinal pathology affects visual signaling between the eye and brain.

Objective:

The goal of this study was to provide a functional and structural assessment of eye-brain communication between retinal ganglion cells (RGCs) and their primary projection target, the superior colliculus, in female and male 3xTg-AD mice across disease stages.

Methods:

Retinal electrophysiology, axonal transport, and immunofluorescence were used to determine RGC projection integrity, and retinal and collicular Aβ levels were assessed with advanced protein quantitation techniques.

Results:

3xTg mice exhibited nuanced deficits in RGC electrical signaling, axonal transport, and synaptic integrity that exceeded normal age-related decrements in RGC function in age- and sex-matched healthy control mice. These deficits presented in sex-specific patterns among 3xTg mice, differing in the timing and severity of changes.

Conclusion:

These data support the premise that retinal Aβ is not just a benign biomarker in the eye, but may contribute to subtle, nuanced visual processing deficits. Such disruptions might enhance the biomarker potential of ocular amyloid and differentiate patients with incipient AD from patients experiencing normal age-related decrements in visual function.

Ablation of Mto1 in zebrafish exhibited hypertrophic cardiomyopathy manifested by mitochondrion RNA maturation deficiency

Deficient maturations of mitochondrial transcripts are linked to clinical abnormalities but their pathophysiology remains elusive. Previous investigations showed that pathogenic variants in MTO1 for the biosynthesis of τm⁵U of tRNA^Glu, tRNA^Gln, tRNA^Lys, tRNA^Trp and tRNA^Leu(UUR) were associated with hypertrophic cardiomyopathy (HCM). Using mto1 knock-out(KO) zebrafish generated by CRISPR/Cas9 system, we demonstrated the pleiotropic effects of Mto1 deficiency on mitochondrial RNA maturations. The perturbed structure and stability of tRNAs caused by mto1 deletion were evidenced by conformation changes and sensitivity to S1-mediated digestion of tRNA^Gln, tRNA^Lys, tRNA^Trp and tRNA^Leu(UUR). Notably, mto1^KO zebrafish exhibited the global decreases in the aminoacylation of mitochondrial tRNAs with the taurine modification. Strikingly, ablated mto1 mediated the expression of MTPAP and caused the altered polyadenylation of cox1, cox3, and nd1 mRNAs. Immunoprecipitation assay indicated the interaction of MTO1 with MTPAP related to mRNA polyadenylation. These alterations impaired mitochondrial translation and reduced activities of oxidative phosphorylation complexes. These mitochondria dysfunctions caused heart development defects and hypertrophy of cardiomyocytes and myocardial fiber disarray in ventricles. These cardiac defects in the mto1^KO zebrafish recapitulated the clinical phenotypes in HCM patients carrying the MTO1 mutation(s). Our findings highlighted the critical role of MTO1 in mitochondrial transcript maturation and their pathological consequences in hypertrophic cardiomyopathy.

An animal model for mitochondrial tyrosyl-tRNA synthetase deficiency reveals links between oxidative phosphorylation and retinal function

Mitochondria maintain a distinct pool of ribosomal machinery, including tRNAs and tRNAs activating enzymes, such as mitochondrial tyrosyl-tRNA synthetase (YARS2). Mutations in YARS2, which typically lead to the impairment of mitochondrial protein synthesis, have been linked to an array of human diseases including optic neuropathy. However, the lack of YARS2 mutation animal model makes us difficult to elucidate the pathophysiology underlying YARS2 deficiency. To explore this system, we generated YARS2 knockout (KO) HeLa cells and zebrafish using CRISPR/Cas9 technology. We observed the aberrant tRNA^Tyr aminoacylation overall and reductions in the levels in mitochondrion- and nucleus-encoding subunits of oxidative phosphorylation system (OXPHOS), which were especially pronounced effects in the subunits of complex I and complex IV. These deficiencies manifested the decreased levels of intact supercomplexes overall. Immunoprecipitation assays showed that YARS2 bound to specific subunits of complex I and complex IV, suggesting the posttranslational stabilization of OXPHOS. Furthermore, YARS2 ablation caused defects in the stability and activities of OXPHOS complexes. These biochemical defects could be rescued by the overexpression of YARS2 cDNA in the YARS2^KO cells. In zebrafish, the yars2^KO larva conferred deficient COX activities in the retina, abnormal mitochondrial morphology, and numbers in the photoreceptor and retinal ganglion cells. The zebrafish further exhibited the retinal defects affecting both rods and cones. Vision defects in yars2^KO zebrafish recapitulated the clinical phenotypes in the optic neuropathy patients carrying the YARS2 mutations. Our findings highlighted the critical role of YARS2 in the stability and activity of OXPHOS and its pathological consequence in vision impairments.

ROCK inhibition reduces morphological and functional damage to rod synapses after retinal injury

Retinal detachment (RD) causes damage, including disjunction, of the rod photoreceptor-bipolar synapse, which disrupts vision and may contribute to the poor visual recovery observed after retinal reattachment surgery. We created a model of iatrogenic RD in adult female pigs to study damage to the rod-bipolar synapse after injury and the ability of a highly specific Rho-kinase (ROCK) inhibitor to preserve synaptic structure and function. This model mimics procedures used in humans when viral vectors or cells are injected subretinally for treatment of retinal disease. Synaptic disjunction by retraction of rod spherules, quantified by image analysis of confocal sections, was present 2 h after detachment and remained 2 days later even though the retina had spontaneously reattached by then. Moreover, spherule retraction occurred in attached retina 1-2 cms from detached retina. Synaptic damage was significantly reduced by ROCK inhibition in detached retina whether injected subretinally or intravitreally. Dark-adapted full-field electroretinograms were recorded in reattached retinas to assess rod-specific function. Reduction in synaptic injury correlated with increases in rod-driven responses in drug-treated eyes. Thus, ROCK inhibition helps prevent synaptic damage and improves functional outcomes after retinal injury and may be a useful adjunctive treatment in iatrogenic RD and other retinal degenerative diseases.

Deletion of Gtpbp3 in zebrafish revealed the hypertrophic cardiomyopathy manifested by aberrant mitochondrial tRNA metabolism

GTPBP3 is a highly conserved tRNA modifying enzyme for the biosynthesis of τm⁵U at the wobble position of mitochondrial tRNA^Glu, tRNA^Gln, tRNA^Lys, tRNA^Trp and tRNA^Leu(UUR). The previous investigations showed that GTPBP3 mutations were associated with hypertrophic cardiomyopathy (HCM). However, the pathophysiology of GTPBP3 deficiency remains elusively. Using the gtpbp3 knockout zebrafish generated by CRISPR/Cas9 system, we demonstrated the aberrant mitochondrial tRNA metabolism in gtpbp3 knock-out zebrafish. The deletion of gtpbp3 may alter functional folding of tRNA, indicated by conformation changes and sensitivity to S1-mediated digestion of tRNA^Glu, tRNA^Lys, tRNA^Trp and tRNA^Leu(UUR). Strikingly, gtpbp3 knock-out zebrafish displayed the global increases in the aminoacylated efficiencies of mitochondrial tRNAs. The aberrant mitochondrial tRNA metabolisms impaired mitochondrial translation, produced proteostasis stress and altered activities of respiratory chain complexes. These mitochondria dysfunctions caused the alterations in the embryonic heart development and reduced fractional shortening of ventricles in mutant zebrafish. Notably, the gtpbp3 knock-out zebrafish exhibited hypertrophy of cardiomyocytes and myocardial fiber disarray in ventricles. These cardiac defects in the gtpbp3 knock-out zebrafish recapitulated the clinical phenotypes in HCM patients carrying the GTPBP3 mutation(s). Our findings highlight the fundamental role of defective nucleotide modifications of tRNAs in mitochondrial biogenesis and their pathological consequences in hypertrophic cardiomyopathy.

Deletion of Mtu1 (Trmu) in zebrafish revealed the essential role of tRNA modification in mitochondrial biogenesis and hearing function

Mtu1(Trmu) is a highly conserved tRNA modifying enzyme responsible for the biosynthesis of τm5s2U at the wobble position of tRNAGln, tRNAGlu and tRNALys. Our previous investigations showed that MTU1 mutation modulated the phenotypic manifestation of deafness-associated mitochondrial 12S rRNA mutation. However, the pathophysiology of MTU1 deficiency remains poorly understood. Using the mtu1 knock-out zebrafish generated by CRISPR/Cas9 system, we demonstrated the abolished 2-thiouridine modification of U34 of mitochondrial tRNALys, tRNAGlu and tRNAGln in the mtu1 knock-out zebrafish. The elimination of this post-transcriptional modification mediated mitochondrial tRNA metabolisms, causing the global decreases in the levels of mitochondrial tRNAs. The aberrant mitochondrial tRNA metabolisms led to the impairment of mitochondrial translation, respiratory deficiencies and reductions of mitochondrial ATP production. These mitochondria dysfunctions caused the defects in hearing organs. Strikingly, mtu1-/- mutant zebrafish displayed the abnormal startle response and swimming behaviors, significant decreases in the sizes of saccular otolith and numbers of hair cells in the auditory and vestibular organs. Furthermore, mtu1-/- mutant zebrafish exhibited the significant reductions in the hair bundle densities in utricle, saccule and lagena. Therefore, our findings may provide new insights into the pathophysiology of deafness, which was manifested by the deficient modifications at wobble position of mitochondrial tRNAs.

Long-Term Functional and Structural Consequences of Primary Blast Overpressure to the Eye

Acoustic blast overpressure (ABO) injury in military personnel and civilians is often accompanied by delayed visual deficits. However, most animal model studies dealing with blast-induced visual defects have focused on short-term (≤1 month) changes. Here, we evaluated long-term (≤8 months) retinal structure and function deficits in rats with ABO injury. Adult male Long-Evans rats were subjected to ABO from a single blast (approximately 190 dB SPL, ∼63 kPa, @80 psi), generated by a shock tube device. Retinal function (electroretinography; ERG), visual function (optomotor response), retinal thickness (spectral domain-optical coherence tomography; SD-OCT), and spatial cognition/exploratory motor behavior (Y-maze) were measured at 2, 4, 6, and 8 months post-blast. Immunohistochemical analysis of glial fibrillary acidic protein (GFAP) in retinal sections was performed at 8 months post-blast. Electroretinogram a- and b-waves, oscillatory potentials, and flicker responses showed greater amplitudes with delayed implicit times in both eyes of blast-exposed animals, relative to controls. Contrast sensitivity (CS) was reduced in both eyes of blast-exposed animals, whereas spatial frequency (SF) was decreased only in ipsilateral eyes, relative to controls. Total retinal thickness was greater in both eyes of blast-exposed animals, relative to controls, due to increased thickness of several retinal layers. Age, but not blast exposure, altered Y-maze outcomes. GFAP was greatly increased in blast-exposed retinas. ABO exposure resulted in visual and retinal changes that persisted up to 8 months post-blast, mimicking some of the visual deficits observed in human blast-exposed patients, thereby making this a useful model to study mechanisms of injury and potential treatments.

Morphological and functional changes in the rat retina associated with 2 months of intermittent moderate intraocular pressure elevation

Morphological and functional changes in the rat retina and optic nerve head (ONH), associated with 8 weeks of intermittent moderately elevated intraocular pressure (IOP) were measured with a combined ultrahigh resolution optical coherence tomography (UHR-OCT) and electroretinography (ERG) system. The IOP of male Sprague-Dawley rats was raised in one eye to ~35 mmHg for 1 hour/day on 6 days each week using vascular loops. Single-flash ERG traces and volumetric UHR-OCT images of the ONH were acquired from both eyes before, during and after IOP elevations at weeks 1, 5 and 9 of the study. The UHR-OCT images showed depression of the posterior eye around the ONH during the IOP elevations, the magnitude of which increased significantly from week 1 to week 9 (p = 0.01). The ERG a-wave and b-wave amplitudes increased temporarily during IOP elevations and returned to normal ~30 minutes after loop removal. Recurrent intermittent IOP spikes caused > 30% decrease in the ERG a-wave and b-wave amplitudes measured during the IOP elevations over the course of 2 months. This study suggests that recurrent, relatively short-duration IOP spikes for extended period of time are associated with peri-ONH tissue hypercompliance and reduced retinal functional response to visual stimulation during acute IOP elevation.

Structural, functional and blood perfusion changes in the rat retina associated with elevated intraocular pressure, measured simultaneously with a combined OCT+ERG system

Acute elevation of intraocular pressure (IOP) to ischemic and non-ischemic levels can cause temporary or permanent changes in the retinal morphology, function and blood flow/blood perfusion. Previously, such changes in the retina were assessed separately with different methods in clinical studies and animal models. In this study, we used a combined OCT+ ERG system in combination with Doppler OCT and OCT angiography (OCTA) imaging protocols, in order to evaluate simultaneously and correlate changes in the retinal morphology, the retinal functional response to visual stimulation, and the retinal blood flow/blood perfusion, associated with IOP elevation to ischemic and non-ischemic levels in rats. Results from this study suggest that the inner retina responds faster to IOP elevation to levels greater than 30 mmHg with significant reduction of the total retinal blood flow (TRBF), decrease of the capillaries’ perfusion and reduction of the ON bipolar cells contribution to the ERG traces. Furthermore, this study showed that ischemic levels of IOP elevation cause an additional significant decrease in the ERG photoreceptor response in the posterior retina. Thirty minutes after IOP normalization, retinal morphology, blood flow and blood perfusion recovered to baseline values, while retinal function did not recover completely.

Identification of an Epitope from Adenine Nucleotide Translocator 1 That Induces Inflammation in Heart in A/J Mice

Heart failure, a leading cause of death in humans, can emanate from myocarditis. Although most individuals with myocarditis recover spontaneously, some develop chronic dilated cardiomyopathy. Myocarditis may result from both infectious and noninfectious causes, including autoimmune responses to cardiac antigens. In support of this notion, intracellular cardiac antigens, like cardiac myosin heavy chain-α, cardiac troponin-I, and adenine nucleotide translocator 1 (ANT₁), have been identified as autoantigens in cardiac autoimmunity. Herein, we demonstrate that ANT₁ can induce autoimmune myocarditis in A/J mice by generating autoreactive T cells. We show that ANT₁ encompasses multiple immunodominant epitopes (namely, ANT₁ 21-40, ANT₁ 31-50, ANT₁ 171-190, and ANT₁ 181-200). Although all four peptides induce comparable T-cell responses, only ANT₁ 21-40 was found to be a major myocarditogenic epitope in immunized animals. The myocarditis-inducing ability of ANT₁ 21-40 was associated with the generation of T cells producing predominantly IL-17A, and the antigen-sensitized T cells could transfer the disease to naïve recipients. These data indicate that cardiac mitochondrial proteins can be target autoantigens in myocarditis, supporting the notion that the antigens released as a result of primary damage may contribute to the persistence of chronic inflammation through autoimmunity.

Protective effect of resveratrol against light-induced retinal degeneration in aged SAMP8 mice

Purpose

The purpose of this study was to determine the protective effects of Resveratrol (RESV) on acute bright light-induced retinal degeneration in aged senescence accelerated mouse strain.

Methods

Ten three-month-old male SAMP8 mice (prone to aging) were randomly assigned to two experimental dietary groups: one untreated group and one RESV treatment group (n=20 eyes for each group). After 30 days of treatment, mice were exposed to intense bright light. Ten male SAMR1 mice (resistant to aging) served as control (n=20 eyes). The protective effects of RESV administration on light-induced retinal degeneration in SAMP8 strain as well as the effect of bright light damage in the retinas of SAMP8 mice were analyzed by electroretinography (ERG), retinal histology, mRNA, protein and lipid profile.

Results

68%-85% of a-wave amplitude and 72%-92% of b-wave amplitude were persevered by RESV in SAMP8 mice that were exposed to light damage. Also, RESV preserved their photoreceptor nuclei. mRNA expression of neuroprotective factors leukemia inhibitory factor (LIF), brain derived neurotrophic factor (BDNF), oncostatin M (OSM), cardiotrophin 1(CT-1) and cardiotrophin-like cytokine (CLC) were up-regulated 28, 8, 7, 5 and 9-fold in SAMP8 mice after RESV treatment. In addition, RESV could suppress the NF-κB pathway by down-regulating the expression of pIκB. Light damage led to increase of saturated FA, monoenoic FA, n6 PUFA and n6/n3 ratio and decrease of Docosahexaenoic acid (DHA). There was no significant difference on DHA and the ratio of n6/n3-FA between the untreated and RESV treated SAMP8 mice.

Conclusions

Collectively, our study provides evidence that RESV prevents light-induced retinal damage associated with aging.

Mitochondrial dysfunction underlying outer retinal diseases

Dysfunction of photoreceptors, retinal pigment epithelium (RPE) or both contribute to the initiation and progression of several outer retinal disorders. Disrupted Müller glia function might additionally subsidize to these diseases. Mitochondrial malfunctioning is importantly associated with outer retina pathologies, which can be classified as primary and secondary mitochondrial disorders. This review highlights the importance of oxidative stress and mitochondrial DNA damage, underlying outer retinal disorders. Indeed, the metabolically active photoreceptors/RPE are highly prone to these hallmarks of mitochondrial dysfunction, indicating that mitochondria represent a weak link in the antioxidant defenses of outer retinal cells.

Assessment of Murine Retinal Function by Electroretinography

The electroretinogram (ERG) is a sensitive and noninvasive method for testing retinal function. In this protocol, we describe a method for performing ERGs in mice. Contact lenses on the mouse cornea measure the electrical response to a light stimulus of photoreceptors and downstream retinal cells, and the collected data are analyzed to evaluate retinal function.

Short-Term Moderately Elevated Intraocular Pressure Is Associated With Elevated Scotopic Electroretinogram Responses

Purpose

Moderately elevated intraocular pressure (IOP) is a risk factor for open-angle glaucoma. Some patients suffer glaucoma despite clinically measured normal IOPs. Fluctuations in IOP may have a significant role since IOPs are higher during sleep and inversion activities. Controlled transient elevations of IOPs in rats over time lead to optic nerve structural changes that are similar to the early changes observed in constant chronic models of glaucoma. Because early intervention decreases glaucoma progression, this study was done to determine if early physiological changes to the retina could be detected with noninvasive electrophysiological and optical imaging tests during moderately elevated IOP.

Methods

Intraocular pressures were raised to moderately high levels (35 mm Hg) in one eye of Sprague-Dawley rats while the other (control) eye was untreated. One group of rats underwent scotopic threshold response (STR) and electroretinogram (ERG) testing, while another 3 groups underwent optical coherence tomography (OCT) imaging, Western blot, or histologic evaluation.

Results

The amplitudes of the STR and ERG responses in eyes with moderately elevated IOPs were enhanced compared to the values before IOP elevation, and compared to untreated contralateral eyes. Structural changes to the optic nerve also occurred during IOP elevation.

Conclusions

Although ischemic IOP elevations are well-known to globally reduce components of the scotopic ERG, acute elevation in rats to levels often observed in untreated glaucoma patients caused an increase in these parameters. Further exploration of these phenomena may be helpful in better understanding the mechanisms mediating early retinal changes during fluctuating or chronically elevated IOP.

Mitochondrial Diseases Part II: Mouse models of OXPHOS deficiencies caused by defects in regulatory factors and other components required for mitochondrial function

Mitochondrial disorders are defined as defects that affect the oxidative phosphorylation system (OXPHOS). They are characterized by a heterogeneous array of clinical presentations due in part to a wide variety of factors required for proper function of the components of the OXPHOS system. There is no cure for these disorders owing to our poor knowledge of the pathogenic mechanisms of disease. To understand the mechanisms of human disease numerous mouse models have been developed in recent years. Here we summarize the features of several mouse models of mitochondrial diseases directly related to those factors affecting mtDNA maintenance, replication, transcription, translation as well as other proteins that are involved in mitochondrial dynamics and quality control which affect mitochondrial OXPHOS function without being intrinsic components of the system. We discuss how these models have contributed to our understanding of mitochondrial diseases and their pathogenic mechanisms.

Phenotypic rescue of a Drosophila model of mitochondrial ANT1 disease

A point mutation in the Drosophila gene that codes for the major adult isoform of adenine nuclear translocase (ANT) represents a model for human diseases that are associated with ANT insufficiency [stress-sensitive B¹ (sesB¹)]. We characterized the organismal, bioenergetic and molecular phenotype of sesB¹ flies then tested strategies to compensate the mutant phenotype. In addition to developmental delay and mechanical-stress-induced seizures, sesB¹ flies have an impaired response to sound, defective male courtship, female sterility and curtailed lifespan. These phenotypes, excluding the latter two, are shared with the mitoribosomal protein S12 mutant, tko^25t. Mitochondria from sesB¹ adults showed a decreased respiratory control ratio and downregulation of cytochrome oxidase. sesB¹ adults exhibited ATP depletion, lactate accumulation and changes in gene expression that were consistent with a metabolic shift towards glycolysis, characterized by activation of lactate dehydrogenase and anaplerotic pathways. Females also showed downregulation of many genes that are required for oogenesis, and their eggs, although fertilized, failed to develop to the larval stages. The sesB¹ phenotypes of developmental delay and mechanical-stress-induced seizures were alleviated by an altered mitochondrial DNA background. Female sterility was substantially rescued by somatic expression of alternative oxidase (AOX) from the sea squirt Ciona intestinalis, whereas AOX did not alleviate developmental delay. Our findings illustrate the potential of different therapeutic strategies for ANT-linked diseases, based on alleviating metabolic stress.