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Importance: Retinal ganglion cells endure significant metabolic stress with ageing and glaucoma-related stressors. Injured cells require increased energy for repair but maintain capacity to recover function despite periods of functional loss. Nicotinamide, a precursor of redox co-factor and metabolite, NAD + , is low in serum of patients with primary open-angle glaucoma and its supplementation provides robust protection of retinal ganglion cells by targeting mitochondrial health in glaucoma models. However, the potential of nicotinamide to improve retinal ganglion cell function in humans with glaucoma is yet unknown. Objective: To determine whether nicotinamide supplementation taken in conjunction with conventional IOP-lowering therapy leads to early improvement in retinal ganglion cell function in people with glaucoma. Design: Crossover, double-masked, randomized clinical trial conducted between October 2017 to January 2019. Setting: Study participants recruited from two tertiary care centers in Melbourne, Australia. Participants: Adults diagnosed and treated for primary glaucoma. Ninety-four participants assessed for study eligibility. Intervention: Participants randomized to first receive oral placebo or nicotinamide and reviewed six-weekly. Accelerated dosing method utilized; participants commenced 6-week course of 1.5 grams/day followed by 6 weeks of 3.0 grams/day. After 12 weeks, participants crossed over to other intervention for 12 weeks without washout. At each visit, visual function measured using full-field flash electroretinography and white-on-white perimetry. Main outcome measures: Primary endpoint was change in inner retinal function determined a-priori as change in photopic negative response (PhNR) parameters: saturated PhNR amplitude (Vmax), ratio of PhNR/b-wave amplitude (Vmax ratio). Results: Fifty-seven participants (65.5±10.0 years, 39% female) enrolled. PhNR Vmax improved beyond 95% coefficient of repeatability (COR) in 23% of participants following 12 weeks of nicotinamide versus 9% on placebo. Conversely, PhNR Vmax deteriorated in 9% on placebo and 7% on nicotinamide. Overall, Vmax improved by 14.8% [95% CI: 2.8%, 26.9%], (p=0.02) on nicotinamide and 5.2% [-4.2%, 14.6%], (p=0.27) on placebo. Vmax ratio improved on average by 12.6% [5.0%, 20.2%], (p=0.002) following nicotinamide and 3.6% [-3.4%, 10.5%], (p=0.30) on placebo. A concomitant trend for improved visual field mean deviation was observed with 27% improving ≥1dB on nicotinamide and fewer deteriorating ≥1dB (4%) compared to placebo (p=0.02). Moderate correlation was observed between PhNR and visual field change with treatment. Participants demonstrated excellent treatment adherence rates (>94%) and nicotinamide was well tolerated with minimal side effects. Conclusions and Relevance: Nicotinamide supplementation can improve inner retinal function in patients receiving concurrent IOP-lowering glaucoma therapy. Further studies are underway to elucidate the effects of long-term nicotinamide supplementation on glaucoma progression.

Mitochondrial complex I dysfunction is the most common respiratory chain defect in human disorders and a hotspot for neurodegenerative diseases. Amyloid precursor protein (APP) and its non-amyloidogenic processing products, in particular soluble APP α (sAPPα), have been shown to provide neuroprotection in models of neuronal injury; however, APP-mediated protection from acute mitochondrial injury has not been previously reported. Here, we use the plant-derived pesticide rotenone, a potent complex I-specific mitochondrial inhibitor, to discover neuroprotective effects of APP and sAPPα in vitro, in neuronal cell lines over-expressing APP, and in vivo, in a retinal neuronal rotenone toxicity mouse model. Our results show that APP over-expression is protective against rotenone toxicity in neurons via sAPPα through an autocrine/paracrine mechanism that involves the Pi3K/Akt pro-survival pathway. APP−/− mice exhibit greater susceptibility to retinal rotenone toxicity, while intravitreal delivery of sAPPα reduces inner retinal neuronal death in wild-type mice following rotenone challenge. We also show a significant decrease in human retinal expression of APP with age. These findings provide insights into the therapeutic potential of non-amyloidogenic processing of APP in complex I-related neurodegeneration. Electronic supplementary material The online version of this article (10.1007/s12035-018-1460-7) contains supplementary material, which is available to authorized users.

Despite clear evidence of a neuroprotective physiological role of amyloid precursor protein (APP) and its non-amyloidogenic processing products, APP has been investigated mainly in animal and cellular models of amyloid pathology in the context of Alzheimer's disease. The rare familial mutations in APP and presenilin-1/2, which sometimes drive increased amyloid β (Aβ) production, may have unduly influenced Alzheimer's disease research. APP and its cleavage products play important roles in cellular and mitochondrial metabolism, but many studies focus solely on Aβ. Mitochondrial bioenergetic metabolism is essential for neuronal function, maintenance and survival, and multiple reports indicate mitochondrial abnormalities in patients with Alzheimer's disease. In this review, we focus on mitochondrial abnormalities reported in sporadic Alzheimer's disease patients and the role of full-length APP and its non-amyloidogenic fragments, particularly soluble APPα, on mitochondrial bioenergetic metabolism. We do not review the plethora of animal and in vitro studies using mutant APP/presenilin constructs or experiments using exogenous Aβ. In doing so, we aim to invigorate research and discussion around non-amyloidogenic APP processing products and the mechanisms linking mitochondria and complex neurodegenerative disorders such as sporadic Alzheimer's disease. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

The lack of effective treatments for mitochondrial disease has seen the development of new approaches, including those that aim to stimulate mitochondrial biogenesis to boost ATP generation above a critical disease threshold. Here, we examine the effects of the peroxisome proliferator-activated receptor γ (PPARγ) activator pioglitazone (PioG), in combination with deoxyribonucleosides (dNs), on mitochondrial biogenesis in cybrid cells containing >90% of the m.3243A>G mutation associated with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). PioG + dNs combination treatment increased mtDNA copy number and mitochondrial mass in both control (CON) and m.3243A>G (MUT) cybrids, with no adverse effects on cell proliferation. PioG + dNs also increased mtDNA-encoded transcripts in CON cybrids, but had the opposite effect in MUT cybrids, reducing the already elevated transcript levels. Steady-state levels of mature oxidative phosphorylation (OXPHOS) protein complexes were increased by PioG + dNs treatment in CON cybrids, but were unchanged in MUT cybrids. However, treatment was able to significantly increase maximal mitochondrial oxygen consumption rates and cell respiratory control ratios in both CON and MUT cybrids. Overall, these findings highlight the ability of PioG + dNs to improve mitochondrial respiratory function in cybrid cells containing the m.3243A>G MELAS mutation, as well as their potential for development into novel therapies to treat mitochondrial disease.

Leber hereditary optic neuropathy (LHON) is one of the most common primary mitochondrial diseases. It is caused by point mutations in mitochondrial DNA (mtDNA) genes and in some cases, it can result in irreversible vision loss, primarily in young men. It is currently unknown why LHON mutations affect only some carriers and whether bioenergetic compensation enables unaffected carriers to overcome mitochondrial impairment and preserve cellular function. Here, we conducted bioenergetic metabolic assays and RNA sequencing to address this question using male-only, age-matched, m.11778G > A lymphoblasts and primary fibroblasts from both unaffected carriers and affected individuals. Our work indicates that OXPHOS bioenergetic compensation in LHON peripheral cells does not explain disease phenotype. We show that complex I impairment is similar in cells from unaffected carrier and affected patients, despite a transcriptional downregulation of metabolic pathways including glycolysis in affected cells relative to carriers detected by RNA sequencing. Although we did not detect OXPHOS bioenergetic compensation in carrier cells under basal conditions, our results indicate that cells from affected patients suffer a growth impairment under metabolic challenge compared to carrier cells, which were unaffected by metabolic challenge. If recapitulated in retinal ganglion cells, decreased susceptibility to metabolic challenge in unaffected carriers may help preserve metabolic homeostasis in the face of the mitochondrial complex I bioenergetic defect.

Die Tatsache einer moglichen Visus- und Gesichtsfelderholung beim Glaukom ist ein bekanntes, wenn auch bisher wenig erforschtes Phanomen. Unser Ziel ist es, einen Einblick in die funktionelle Regeneration retinaler Ganglienzellen (RGZ) besonders nach einem zugefugten Schaden zu gewahren. Dabei mochten wir ein besonderes Augenmerk auf die Entwicklung therapeutischer Ansatze in diesem Bereich richten. Verwendet wurde ein Mausmodell zur Untersuchung der funktionellen Regeneration der RGZ nach einem durch kurzzeitige Augeninnendruck (IOP)-Erhohung gesetzten Schaden. Trotz prolongierten RGZ-Schadens, der durch eine akute IOP-Erhohung induziert wurde, zeigte sich eine fast vollstandige funktionelle Erholung der zunachst dysfunktionalen RGZ. Dabei wurde deutlich, dass ein fortgeschrittenes Alter der Mause sowie eine fettreiche Kost die Regeneration der RGZ negativ beeinflussten, wohingegen korperliche Aktivitat die Regeneration der RGZ verbesserte. Es konnte bei alten, korperlich aktiven Mausen eine ahnlich ausgepragte RGZ-Regeneration nachgewiesen werden, wie sie in jungen untrainierten Mausen zu finden war. Geschadigte RGZ besitzen auch nach langerer Zeit die Kapazitat zu regenerieren. Therapeutische Interventionen, die speziell geschadigte RGZ identifizieren und ihre Regeneration fordern, konnten einen vielversprechenden neuen Ansatz in der Glaukomtherapie darstellen.

Cybrid technology was used to replace Leber hereditary optic neuropathy (LHON) causing mitochondrial DNA (mtDNA) mutations from patient-specific fibroblasts with wildtype mtDNA, and mutation-free induced pluripotent stem cells (iPSCs) were generated subsequently. Retinal ganglion cell (RGC) differentiation demonstrates increased cell death in LHON-RGCs and can be rescued in cybrid corrected RGCs.

Summary Retinal ganglion cells (RGCs) become increasingly vulnerable to injury with advancing age. We recently showed that this vulnerability can be strongly modified in mice by exercise. However, the characteristics and underlying mechanisms of retinal protection with exercise remain unknown. Hence, the aim of this study was to investigate cellular changes associated with exercise‐induced protection of aging retinal cells and the role of local and peripheral trophic signalling in mediating these effects. We focussed on two molecules that are thought to play key roles in mediating beneficial effects of exercise: brain‐derived neurotrophic factor (BDNF) and AMP‐activated protein kinase (AMPK). In middle‐aged (12 months old) C57BL/6J mice, we found that exercise protected RGCs against dysfunction and cell loss after an acute injury induced by elevation of intra‐ocular pressure. This was associated with preservation of inner retinal synapses and reduced synaptic complement deposition. Retinal expression of BDNF was not upregulated in response to exercise alone. Rather, exercise maintained BDNF levels in the retina, which were decreased postinjury in nonexercised animals. Confirming a critical role for BDNF, we found that blocking BDNF signalling during exercise by pharmacological means or genetic knock‐down suppressed the functional protection of RGCs afforded by exercise. Protection of RGCs with exercise was independent of activation of AMPK in either retina or skeletal muscle. Our data support a previously unidentified mechanism in which exercise prevents loss of BDNF in the retina after injury and preserves neuronal function and survival by preventing complement‐mediated elimination of synapses.

Reprogramming of somatic cells into a pluripotent state is known to be accompanied by extensive restructuring of mitochondria and switch in metabolic requirements. Here we utilized Leber's hereditary optic neuropathy (LHON) as a mitochondrial disease model to study the effects of homoplasmic mtDNA mutations and subsequent oxidative phosphorylation (OXPHOS) defects in reprogramming. We obtained fibroblasts from a total of 6 LHON patients and control subjects, and showed a significant defect in complex I respiration in LHON fibroblasts by high-resolution respiratory analysis. Using episomal vector reprogramming, our results indicated that human induced pluripotent stem cell (hiPSC) generation is feasible in LHON fibroblasts. In particular, LHON-specific OXPHOS defects in fibroblasts only caused a mild reduction and did not significantly affect reprogramming efficiency, suggesting that hiPSC reprogramming can tolerate a certain degree of OXPHOS defects. Our results highlighted the induction of genes involved in mitochondrial biogenesis (TFAM, NRF1), mitochondrial fusion (MFN1, MFN2) and glycine production (GCAT) during reprogramming. However, LHON-associated OXPHOS defects did not alter the kinetics or expression levels of these genes during reprogramming. Together, our study provides new insights into the effects of mtDNA mutation and OXPHOS defects in reprogramming and genes associated with various aspects of mitochondrial biology.

Oxidative phosphorylation (OXPHOS) drives ATP production by mitochondria, which are dynamic organelles, constantly fusing and dividing to maintain kidney homoeostasis. In diabetic kidney disease (DKD), mitochondria appear dysfunctional, but the temporal development of diabetes-induced adaptations in mitochondrial structure and bioenergetics have not been previously documented. In the present study, we map the changes in mitochondrial dynamics and function in rat kidney mitochondria at 4, 8, 16 and 32 weeks of diabetes. Our data reveal that changes in mitochondrial bioenergetics and dynamics precede the development of albuminuria and renal histological changes. Specifically, in early diabetes (4 weeks), a decrease in ATP content and mitochondrial fragmentation within proximal tubule epithelial cells (PTECs) of diabetic kidneys were clearly apparent, but no changes in urinary albumin excretion or glomerular morphology were evident at this time. By 8 weeks of diabetes, there was increased capacity for mitochondrial permeability transition (mPT) by pore opening, which persisted over time and correlated with mitochondrial hydrogen peroxide (H2O2) generation and glomerular damage. Late in diabetes, by week 16, tubular damage was evident with increased urinary kidney injury molecule-1 (KIM-1) excretion, where an increase in the Complex I-linked oxygen consumption rate (OCR), in the context of a decrease in kidney ATP, indicated mitochondrial uncoupling. Taken together, these data show that changes in mitochondrial bioenergetics and dynamics may precede the development of the renal lesion in diabetes, and this supports the hypothesis that mitochondrial dysfunction is a primary cause of DKD.

The maternally inherited mitochondrial genome (mtDNA) is present in multimeric form within cells and harbors sequence variants (heteroplasmy). While a single mtDNA variant at high load can cause disease, naturally occurring variants likely persist at low levels across generations of healthy populations. To determine how naturally occurring variants are segregated and transmitted, we generated a mini-pig model, which originates from the same maternal ancestor. Following next-generation sequencing, we identified a series of low-level mtDNA variants in blood samples from the female founder and her daughters. Four variants, ranging from 3% to 20%, were selected for validation by high-resolution melting analysis in 12 tissues from 31 animals across three generations. All four variants were maintained in the offspring, but variant load fluctuated significantly across the generations in several tissues, with sex-specific differences in heart and liver. Moreover, variant load was persistently reduced in high-respiratory organs (heart, brain, diaphragm, and muscle), which correlated significantly with higher mtDNA copy number. However, oocytes showed increased heterogeneity in variant load, which correlated with increased mtDNA copy number during in vitro maturation. Altogether, these outcomes show that naturally occurring mtDNA variants segregate and are maintained in a tissue-specific manner across generations. This segregation likely involves the maintenance of selective mtDNA variants during organogenesis, which can be differentially regulated in oocytes and preimplantation embryos during maturation.

We assessed structural elements of the retina in individuals with Friedreich ataxia (FRDA) and in mouse models of FRDA, as well as functions of the retinal pigment epithelium (RPE) in FRDA using induced pluripotent stem cells (iPSCs). We analyzed the retina of the FRDA mouse models YG22R and YG8R containing a human FRATAXIN (FXN) transgene by histology. We complemented this work with post-mortem evaluation of eyes from FRDA patients. Finally, we derived RPE cells from patient FRDA-iPSCs to assess oxidative phosphorylation (OXPHOS) and phagocytosis. We showed that whilst the YG22R and YG8R mouse models display elements of retinal degeneration, they do not recapitulate the loss of retinal ganglion cells (RGCs) found in the human disease. Further, RPE cells differentiated from human FRDA-iPSCs showed normal OXPHOS and we did not observe functional impairment of the RPE in Humans., Highlights • We examined the retinal pigment epithelium in Friedreich ataxia. • We used mouse models, human postmortem eyes and human induced pluripotent stem cell-derived retinal pigment epithelium cells. • We did not find evidence of retinal pigment epithelium impairment in humans. • We described elements of degeneration in YG22R and YG8R mouse retina and human eyes.

Accumulating evidence from experimental and clinical studies suggest that retinal ganglion cells at least in the earlier stages of glaucoma have the capacity to recover function following periods of functional loss. The capacity for recovery may be negatively impacted by advancing age but can be boosted by interventions such as diet restriction and exercise.

Amyloid precursor protein (APP) and its extracellular domain, soluble APP alpha (sAPPα) play important physiological and neuroprotective roles. However, rare forms of familial Alzheimer’s disease are associated with mutations in APP that increase toxic amyloidogenic cleavage of APP and produce amyloid beta (Aβ) at the expense of sAPPα and other non-amyloidogenic fragments. Although mitochondrial dysfunction has become an established hallmark of neurotoxicity, the link between Aβ and mitochondrial function is unclear. In this study we investigated the effects of increased levels of neuronal APP or Aβ on mitochondrial metabolism and gene expression, in human SH-SY5Y neuroblastoma cells. Increased non-amyloidogenic processing of APP, but not Aβ, profoundly decreased respiration and enhanced glycolysis, while mitochondrial DNA (mtDNA) transcripts were decreased, without detrimental effects to cell growth. These effects cannot be ascribed to Aβ toxicity, since higher levels of endogenous Aβ in our models do not cause oxidative phosphorylation (OXPHOS) perturbations. Similarly, chemical inhibition of β-secretase decreased mitochondrial respiration, suggesting that non-amyloidogenic processing of APP may be responsible for mitochondrial changes. Our results have two important implications, the need for caution in the interpretation of mitochondrial perturbations in models where APP is overexpressed, and a potential role of sAPPα or other non-amyloid APP fragments as acute modulators of mitochondrial metabolism.

Mitochondrial DNA copy number is strictly regulated during development as naive cells differentiate into mature cells to ensure that specific cell types have sufficient copies of mitochondrial DNA to perform their specialised functions. Mitochondrial DNA haplotypes are defined as specific regions of mitochondrial DNA that cluster with other mitochondrial sequences to show the phylogenetic origins of maternal lineages. Mitochondrial DNA haplotypes are associated with a range of phenotypes and disease. To understand how mitochondrial DNA haplotypes induce these characteristics, we used four embryonic stem cell lines that have the same set of chromosomes but possess different mitochondrial DNA haplotypes. We show that mitochondrial DNA haplotypes influence changes in chromosomal gene expression and affinity for nuclear-encoded mitochondrial DNA replication factors to modulate mitochondrial DNA copy number, two events that act synchronously during differentiation. Global DNA methylation analysis showed that each haplotype induces distinct DNA methylation patterns, which, when modulated by DNA demethylation agents, resulted in skewed gene expression patterns that highlight the effectiveness of the new DNA methylation patterns established by each haplotype. The haplotypes differentially regulate α-ketoglutarate, a metabolite from the TCA cycle that modulates the TET family of proteins, which catalyse the transition from 5-methylcytosine, indicative of DNA methylation, to 5-hydroxymethylcytosine, indicative of DNA demethylation. Our outcomes show that mitochondrial DNA haplotypes differentially modulate chromosomal gene expression patterns of naive and differentiating cells by establishing mitochondrial DNA haplotype-specific DNA methylation patterns.

We sought to identify the impacts of Friedreich's ataxia (FRDA) on cardiomyocytes. FRDA is an autosomal recessive degenerative condition with neuronal and non-neuronal manifestations, the latter including progressive cardiomyopathy of the left ventricle, the leading cause of death in FRDA. Little is known about the cellular pathogenesis of FRDA in cardiomyocytes. Induced pluripotent stem cells (iPSCs) were derived from three FRDA individuals with characterized GAA repeats. The cells were differentiated into cardiomyocytes to assess phenotypes. FRDA iPSC- cardiomyocytes retained low levels of FRATAXIN (FXN) mRNA and protein. Electrophysiology revealed an increased variation of FRDA- cardiomyocyte beating rates which was prevented by addition of nifedipine, suggestive of a calcium handling deficiency. Finally, calcium imaging was performed and we identified small amplitude, diastolic and systolic calcium transients confirming a deficiency in calcium handling. We defined a robust FRDA cardiac-specific electrophysiological profile in patient-derived iPSCs which could be used for high throughput compound screening. This cell-specific signature will contribute to the identification and screening of novel treatments for this life-threatening disease.

Cybrid technology was used to replace Leber hereditary optic neuropathy (LHON) causing mitochondrial DNA (mtDNA) mutations from patient-specific fibroblasts with wildtype mtDNA, and mutation-free induced pluripotent stem cells (iPSCs) were generated subsequently. Retinal ganglion cell (RGC) differentiation demonstrates increased cell death in LHON-RGCs and can be rescued in cybrid corrected RGCs.

We have previously shown that the optic nerve of mice becomes increasingly vulnerable to injury with advancing age. Here, we investigated whether regular exercise can modify this age-related vulnerability and improve optic nerve recovery after injury. Aged (12-month-old) C57BL/6J mice were exercised by swimming for 60 min/d, 5 d/wk for 6 weeks. After 5 weeks, injury to the optic nerve was induced by short-term elevation of intraocular pressure. Retinal function was recorded using the electroretinogram and the cellular and biochemical changes induced by injury were assessed using immunohistochemistry and quantitative polymerase chain reaction. We found that exercise almost completely reversed age-related vulnerability of the optic nerve to injury such that exercised aged mice had a similar functional response to injury as non-exercised young (3-month-old) mice. Exercise also abrogated injury-induced astrocytic gliosis and macrophage activation in the aged retina. These data suggest that the known benefits of exercise also extend to the visual system and support further investigation of physical activity as a means of protecting against injury, dysfunction, and degeneration in the aging eye.

The original version of this article unfortunately contained a mistake in the author name. The family name of Dr. Vanessa A. Johannsen should be written as "Johanssen."

Mitochondria play an integral role in cell death signaling, yet how mitochondrial defects disrupt this important function is not well understood. We have used a mouse L-cell fibroblast model harboring Rattus norvegicus mtDNA (Rn xenocybrids) to examine the effects of multiple oxidative phosphorylation (OXPHOS) defects on reactive oxygen species (ROS) generation and cell death signaling. Blue native-PAGE analyses of Rn xenocybrids revealed defects in OXPHOS complex biogenesis with reduced steady-state levels of complexes I, III and IV. Isolated Rn xenocybrid mitochondria exhibited deficiencies in complex II+III and III activities, with CIII-stimulated ROS generation 66% higher than in control mitochondria. Rn xenocybrid cells were resistant to staurosporine-induced cell death, but exhibited a four-fold increase in sensitivity to ceramide-induced cell death that was caspase-3 independent and did not induce chromosomal DNA degradation. Furthermore, ceramide directly inhibited Rn xenocybrid complex II+III activity by 97%, although this inhibition could be completely abolished by exogenous decylubiquinone. Ceramide also induced a further increase in ROS output from Rn xenocybrid complex III by 42%. These results suggest that the interaction of ceramide with OXPHOS complex III is significantly enhanced by the presence of the xenotypic Rattus cytochrome b in complex III, likely due to the increased affinity for ceramide at the ubiquinone binding site. We propose a novel mechanism of altered mitochondrial cell death signaling due to mtDNA mutations whereby ceramide directly induces OXPHOS complex ROS generation to initiate cell death pathways.

Mitochondrial DNA haplotypes are associated with various phenotypes, such as altered susceptibility to disease, environmental adaptations, and aging. Accumulating evidence suggests that mitochondrial DNA is essential for cell differentiation and the cell phenotype. However, the effects of different mitochondrial DNA haplotypes on differentiation and development remain to be determined. Using embryonic stem cell lines possessing the same Mus musculus chromosomes but harboring one of Mus musculus, Mus spretus, or Mus terricolor mitochondrial DNA haplotypes, we have determined the effects of different mitochondrial DNA haplotypes on chromosomal gene expression, differentiation, and mitochondrial metabolism. In undifferentiated and differentiating embryonic stem cells, we observed mitochondrial DNA haplotype-specific expression of genes involved in pluripotency, differentiation, mitochondrial energy metabolism, and DNA methylation. These mitochondrial DNA haplotypes also influenced the potential of embryonic stem cells to produce spontaneously beating cardiomyocytes. The differences in gene expression patterns and cardiomyocyte production were independent of ATP content, oxygen consumption, and respiratory capacity, which until now have been considered to be the primary roles of mitochondrial DNA. Differentiation of embryonic stem cells harboring the different mitochondrial DNA haplotypes in a 3D environment significantly increased chromosomal gene expression for all haplotypes during differentiation. However, haplotype-specific differences in gene expression patterns were maintained in this environment. Taken together, these results provide significant insight into the phenotypic consequences of mitochondrial DNA haplotypes and demonstrate their influence on differentiation and development. We propose that mitochondrial DNA haplotypes play a pivotal role in the process of differentiation and mediate the fate of the cell.

Mitochondrial dysfunction increases reactive oxygen species (ROS) production and when this overwhelms the cellular antioxidant defences, oxidative stress ensues. Oxidative stress is recognized as a common pathologic pathway in many neurodegenerative diseases. Recent reports have also demonstrated oxidative stress in ocular tissues derived from experimental glaucoma models and clinical samples. There is also accumulating evidence pointing to mitochondrial dysfunction being present in some glaucoma patients. Thus oxidative stress from mitochondrial dysfunction may also play a causal role in glaucoma. The mechanisms by which oxidative stress may induce retinal ganglion cell loss in glaucoma are not fully understood but could include direct neurotoxic effects from ROS or indirect damage from oxidative stress-induced dysfunction of glial cells. This review will consider the evidence for the presence of oxidative stress in glaucoma; the mechanisms by which oxidative stress may contribute to disease pathogenesis; and also consider therapeutic approaches that target oxidative stress as a means of protecting against optic nerve degeneration.

Obesity is associated with chronic low-grade inflammation that contributes to defects in energy metabolism and insulin resistance. Suppressor of cytokine signaling (SOCS)-3 expression is increased in skeletal muscle of obese humans. SOCS3 inhibits leptin signaling in the hypothalamus and insulin signal transduction in adipose tissue and the liver. Skeletal muscle is an important tissue for controlling energy expenditure and whole-body insulin sensitivity; however, the physiological importance of SOCS3 in this tissue has not been examined. Therefore, we generated mice that had SOCS3 specifically deleted in skeletal muscle (SOCS MKO). The SOCS3 MKO mice had normal muscle development, body mass, adiposity, appetite, and energy expenditure compared with wild-type (WT) littermates. Despite similar degrees of obesity when fed a high-fat diet, SOCS3 MKO mice were protected against the development of hyperinsulinemia and insulin resistance because of enhanced skeletal muscle insulin receptor substrate 1 (IRS1) and Akt phosphorylation that resulted in increased skeletal muscle glucose uptake. These data indicate that skeletal muscle SOCS3 does not play a critical role in regulating muscle development or energy expenditure, but it is an important contributing factor for inhibiting insulin sensitivity in obesity. Therapies aimed at inhibiting SOCS3 in skeletal muscle may be effective in reversing obesity-related glucose intolerance and insulin resistance.

The unique features of the mitochondrial genome, such as its high copy number and lack of defined mechanisms of recombination, have hampered efforts to manipulate its sequence to create specific mutations in mouse mtDNA. As such, the generation of in vivo mouse models of mtDNA disease has proved technically challenging. This chapter describes a unique approach to create mitochondrial oxidative phosphorylation (OXPHOS) defects in mouse ES cells by transferring mtDNA from different murid species into Mus musculus domesticus ES cells using cytoplasmic hybrid ("cybrid") fusion. The resulting "xenocybrid" ES cells carry OXPHOS defects of varying severity, and can be utilized to generate live mouse models of mtDNA disease.

DNA methylation is an essential mechanism controlling gene expression during differentiation and development. We investigated the epigenetic regulation of the nuclear-encoded, mitochondrial DNA (mtDNA) polymerase γ catalytic subunit (PolgA) by examining the methylation status of a CpG island within exon 2 of PolgA. Bisulphite sequencing identified low methylation levels (40%). In contrast, induced pluripotent stem (iPS) cells and somatic nuclear transfer ESCs were hypermethylated (>20%), indicating abnormal epigenetic reprogramming. Real time PCR analysis of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) immunoprecipitated DNA suggests active DNA methylation and demethylation within exon 2 of PolgA. Moreover, neural differentiation of ESCs promoted de novo methylation and demethylation at the exon 2 locus. Regression analysis demonstrates that cell-specific PolgA expression levels were negatively correlated with DNA methylation within exon 2 and mtDNA copy number. Finally, using chromatin immunoprecipitation (ChIP) against RNA polymerase II (RNApII) phosphorylated on serine 2, we show increased DNA methylation levels are associated with reduced RNApII transcriptional elongation. This is the first study linking nuclear DNA epigenetic regulation with mtDNA regulation during differentiation and cell specialization.

Advancing age predisposes us to a number of neurodegenerative diseases, yet the underlying mechanisms are poorly understood. With some 70 million individuals affected, glaucoma is the world's leading cause of irreversible blindness. Glaucoma is characterized by the selective loss of retinal ganglion cells that convey visual messages from the photoreceptive retina to the brain. Age is a major risk factor for glaucoma, with disease incidence increasing near exponentially with increasing age. Treatments that specifically target retinal ganglion cells or the effects of aging on glaucoma susceptibility are currently lacking. On page 756 of this issue, Williams et al. ( 1 ) report substantial advances toward filling these gaps by identifying nicotinamide adenine dinucleotide (NAD+) decline as a key age-dependent risk factor and showing that restoration with long-term dietary supplementation or gene therapy robustly protects against neuronal degeneration.

Radiolabeled diacetylbis(4-methylthiosemicarbazonato)copper II [Cu II (atsm)] is an effective positron-emission tomography imaging agent for myocardial ischemia, hypoxic tumors, and brain disorders with regionalized oxidative stress, such as mitochondrial myopathy, encephalopathy, and lactic acidosis with stroke-like episodes (MELAS) and Parkinson’s disease. An excessively elevated reductive state is common to these conditions and has been proposed as an important mechanism affecting cellular retention of Cu from Cu II (atsm). However, data from whole-cell models to demonstrate this mechanism have not yet been provided. The present study used a unique cell culture model, mitochondrial xenocybrids, to provide whole-cell mechanistic data on cellular retention of Cu from Cu II (atsm). Genetic incompatibility between nuclear and mitochondrial encoded subunits of the mitochondrial electron transport chain (ETC) in xenocybrid cells compromises normal function of the ETC. As a consequence of this impairment to the ETC we show xenocybrid cells upregulate glycolytic ATP production and accumulate NADH. Compared to control cells the xenocybrid cells retained more Cu after being treated with Cu II (atsm). By transfecting the cells with a metal-responsive element reporter construct the increase in Cu retention was shown to involve a Cu II (atsm)-induced increase in intracellular bioavailable Cu specifically within the xenocybrid cells. Parallel experiments using cells grown under hypoxic conditions confirmed that a compromised ETC and elevated NADH levels contribute to increased cellular retention of Cu from Cu II (atsm). Using these cell culture models our data demonstrate that compromised ETC function, due to the absence of O 2 as the terminal electron acceptor or dysfunction of individual components of the ETC, is an important determinant in driving the intracellular dissociation of Cu II (atsm) that increases cellular retention of the Cu.

© 2011 The Authors. Aging Cell © 2011 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland

Purpose: To determine whether mitochondrial DNA haplogroups or rare variants associate with primary open-angle glaucoma in subjects of European descent. Methods: A case-control comparison of age- and sex-matched cohorts of 90 primary open-angle glaucoma patients and 95 population controls. Full mitochondrial DNA sequences from peripheral blood were generated by next-generation sequencing and compared to the revised Cambridge Reference Sequence to define mitochondrial haplogroups and variants. Results: Most subjects were of the major European haplogroups H, J, K, U, and T. Logistic regression analysis showed haplogroup U to be significantly underrepresented in male primary open-angle glaucoma subjects (odds ratio 0.25; 95% confidence interval [CI] 0.09-0.67; P = 0.007; Bonferroni multiple testing P = 0.022). Variants in the mitochondrial DNA gene MT-ND2 were overrepresented in the control group (P = 0.005; Bonferroni multiple testing correction P = 0.015). Conclusions: Mitochondrial DNA ancestral lineages modulate the risk for primary open-angle glaucoma in populations of European descent. Haplogroup U and rare variants in the mitochondrial DNA-encoded MT-ND2 gene may be protective against primary open-angle glaucoma. Larger studies are warranted to explore haplogroup associations with disease risk in different ethnic groups and define biomarkers of primary open-angle glaucoma endophenotypes to target therapeutic strategies.

Aging is the greatest risk factor for glaucoma, implying that intrinsic age-related changes to retinal ganglion cells, their supporting tissue or both make retinal ganglion cells susceptible to injury. Changes to the ocular vasculature, connective tissue of the optic nerve head and mitochondria, which have been documented with advancing age and shown to be exacerbated in glaucoma, may predispose to glaucomatous injury. When considering such age-related changes, it is difficult to separate pathological change from physiological change, and cause from consequence. The insults that predispose aged retinal ganglion cells to injury are likely to be varied and multiple; therefore, it may be more relevant to identify and treat common mechanisms that predispose to retinal ganglion cell failure and/or death. We suggest that mitochondrial dysfunction, as either a cause or consequence of injury, renders retinal ganglion cells sensitive to degeneration. Therapeutic approaches that target mitochondria and promote energy production may provide a general means of protecting aged retinal ganglion cells from degeneration, regardless of the etiology.

Corticosterone induces neuroanatomical and neurochemical changes in the hippocampus that are associated with cognitive impairments. In the present study corticosterone induced cell death in primary hippocampal neurons cultured in Neurobasal + B27 medium. Insulin prevents neuronal cell death induced in a concentration dependent manner. The neuroprotective effect of insulin was reversed by LY294002, a phosphatidylinositol 3′-kinase (PI3 kinase) inhibitor, whereas the mitogen-activated protein kinase (MAPK) inhibitor PD98059, an upstream blocker of MAPK had no effect. Western blot analyses showed that insulin induced the activation of protein kinase B (Akt). These results suggest that insulin can prevent neuronal cell death induced by corticosterone in hippocampal neurons by modulating the activity of the PI3 kinase/Akt pathway.

Optic neuropathies are an important cause of blindness worldwide. The study of the most common inherited mitochondrial optic neuropathies, Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA) has highlighted a fundamental role for mitochondrial function in the survival of the affected neuron-the retinal ganglion cell. A picture is now emerging that links mitochondrial dysfunction to optic nerve disease and other neurodegenerative processes. Insights gained from the peculiar susceptibility of retinal ganglion cells to mitochondrial dysfunction are likely to inform therapeutic development for glaucoma and other common neurodegenerative diseases of aging. Despite it being a fast-evolving field of research, a lack of access to human ocular tissues and limited animal models of mitochondrial disease have prevented direct retinal ganglion cell experimentation and delayed the development of efficient therapeutic strategies to prevent vision loss. Currently, there are no approved treatments for mitochondrial disease, including optic neuropathies caused by primary or secondary mitochondrial dysfunction. Recent advances in eye research have provided important insights into the molecular mechanisms that mediate pathogenesis, and new therapeutic strategies including gene correction approaches are currently being investigated. Here, we review the general principles of mitochondrial biology relevant to retinal ganglion cell function and provide an overview of the major optic neuropathies with mitochondrial involvement, LHON and ADOA, whilst highlighting the emerging link between mitochondrial dysfunction and glaucoma. The pharmacological strategies currently being trialed to improve mitochondrial dysfunction in these optic neuropathies are discussed in addition to emerging therapeutic approaches to preserve retinal ganglion cell function.

The unique features of the mitochondrial genome, such as its high copy number and lack of defined mechanisms of recombination, have hampered efforts to manipulate its sequence to create specific mutations in mouse mtDNA. As such, the generation of in vivo mouse models of mtDNA disease has proved technically challenging. This chapter describes a unique approach to create mitochondrial oxidative phosphorylation (OXPHOS) defects in mouse ES cells by transferring mtDNA from different murid species into Mus musculus domesticus ES cells using cytoplasmic hybrid ("cybrid") fusion. The resulting "xenocybrid" ES cells carry OXPHOS defects of varying severity, and can be utilized to generate live mouse models of mtDNA disease.

Mitochondrial complex I (NADH:ubiquinone oxidoreductase) must be assembled precisely from 45 protein subunits for it to function correctly. One of its mitochondrial DNA (mtDNA) encoded subunits, ND1, is incorporated during the early stages of complex I assembly. However, little is known about how mutations in ND1 affect this assembly process. We found that in human 143B cybrid cells carrying a homoplasmic MT-ND1 mutation, ND1 protein could not be translated. As a result, the early stages of complex I assembly were disrupted, with mature complex I undetectable and complex I-linked respiration severely reduced to 2.0% of control levels. Interestingly, complex IV (ferrocytochrome c:oxygen oxidoreductase) steady-state levels were also reduced to 40.3%, possibly due to its diminished stability in the absence of respiratory supercomplex formation. This was in comparison with 143B cybrid controls (that contained wild-type mtDNA on the same nuclear background), which exhibited normal complex I, complex IV, and supercomplex assembly. We conclude that the loss of ND1 stalls complex I assembly during the early stages of its biogenesis, which not only results in the loss of mature complex I but also disrupts the stability of complex IV and the respiratory supercomplex to cause mitochondrial dysfunction.-Lim, S. C., Hroudova, J., Van Bergen, N. J., Lopez Sanchez, M. I. G., Trounce, I. A., McKenzie, M. Loss of mitochondrial DNA-encoded protein ND1 results in disruption of complex I biogenesis during early stages of assembly.

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein with dual roles in redox signaling and programmed cell death. Deficiency in AIF is known to result in defective oxidative phosphorylation (OXPHOS), via loss of complex I activity and assembly in other tissues. Because the kidney relies on OXPHOS for metabolic homeostasis, we hypothesized that a decrease in AIF would result in chronic kidney disease (CKD). Here, we report that partial knockdown of Aif in mice recapitulates many features of CKD, in association with a compensatory increase in the mitochondrial ATP pool via a shift toward mitochondrial fusion, excess mitochondrial reactive oxygen species production, and Nox4 upregulation. However, despite a 50% lower AIF protein content in the kidney cortex, there was no loss of complex I activity or assembly. When diabetes was superimposed onto Aif knockdown, there were extensive changes in mitochondrial function and networking, which augmented the renal lesion. Studies in patients with diabetic nephropathy showed a decrease in AIF within the renal tubular compartment and lower AIFM1 renal cortical gene expression, which correlated with declining glomerular filtration rate. Lentiviral overexpression of Aif1m rescued glucose-induced disruption of mitochondrial respiration in human primary proximal tubule cells. These studies demonstrate that AIF deficiency is a risk factor for the development of diabetic kidney disease.

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most prevalent neurodegenerative diseases of the central nervous system. These two diseases share a common feature in that a normally soluble peptide (amyloid-beta) or protein (alpha-synuclein) aggregates into an ordered fibrillar structure. As well as structural similarities observed between fibrillar aggregates related to these diseases, common pathological processes of increased oxidative injury, excitotoxicity and altered cell cycle are also evident. It was the aim of this study to identify novel interacting proteins to the amyloid-like motif and therefore identify common potential pathways between neurodegenerative diseases that share biophysical properties common to classical amyloid fibrils. Optimal ageing of recombinant proteins to form amyloid-like fibrils was determined by electron microscopy, Congo red birefringement and photo-induced cross-linking. Using pull-down assays the strongest detected interacting protein to the amyloid-like motifs of amyloid-beta, alpha-synuclein and lysozyme was identified as histone H1. The interaction with the amyloid-like motif was confirmed by techniques including surface plasmon resonance and immunohistochemistry. Histone H1 is known to be an integral part of chromatin within the nucleus, with a primary role of binding DNA that enters and exits from the nucleosome, and facilitating the shift in equilibrium of chromatin towards a more condensed form. However, phosphorylated histone H1 is predominantly present in the cytoplasm and as yet the functional significance of this translocation is unknown. This study also found that histone H1 is localised within the cytoplasm of neurons and astrocytes from areas affected by disease as well as amyloid plaques, supporting the hypothesis that histone H1 favoured binding to an ordered fibrillar motif. We conclude that the binding of histone H1 to a general amyloid-like motif indicates that histone H1 may play an important common role in diseases associated with amyloid-like fibrils.

We describe a model of acute intraocular pressure (IOP) elevation in the mouse eye that induces reversible loss of inner retinal function associated with oxidative stress, glial cell activation and minimal loss of retinal ganglion cell (RGC) number. Young healthy mouse eyes recover inner retinal function within 7-days but more persistent functional loss is seen in older mice. Manipulation of diet and exercise further modify RGC recovery demonstrating the utility of this injury model for investigating lifestyle and therapeutic interventions. We believe that systematic investigation into the characteristics and determinants of RGC recovery following an IOP challenge will shed light on processes that govern RGC vulnerability in the early stages of glaucoma.

In studies of Alzheimer's disease pathogenesis there is an increasing focus on mechanisms of intracellular amyloid-β (Aβ) generation and toxicity. Here we investigated the inhibitory potential of the 42 amino acid Aβ peptide (Aβ1-42) on activity of electron transport chain enzyme complexes in human mitochondria. We found that synthetic Aβ1-42specifically inhibited the terminal complex cytochromecoxidase (COX) in a dose-dependent manner that was dependent on the presence of Cu2+and specific “aging” of the Aβ1-42solution. Maximal COX inhibition occurred when using Aβ1-42solutions aged for 3-6 h at 30°C. The level of Aβ1-42-mediated COX inhibition increased with aging time up to ∼6 h and then declined progressively with continued aging to 48 h. Photo-induced cross-linking of unmodified proteins followed by SDS-PAGE analysis revealed dimeric Aβ as the only Aβ species to provide significant temporal correlation with the observed COX inhibition. Analysis of brain and liver from an Alzheimer's model mouse (Tg2576) revealed abundant Aβ immunoreactivity within the brain mitochondria fraction. Our data indicate that endogenous Aβ is associated with brain mitochondria and that Aβ1-42, possibly in its dimeric conformation, is a potent inhibitor of COX, but only when in the presence of Cu2+. We conclude that Cu2+-dependent Aβ-mediated inhibition of COX may be an important contributor to the neurodegeneration process in Alzheimer's disease.

The characterization of mitochondrial diseases has proceeded rapidly since the first descriptions of mitochondrial DNA (mtDNA)-linked disease mutations appeared in the late 1980s. To elucidate mechanisms of a variety of mitochondrial disorders and disease, both in vitro and in vivo modeling systems have been exploited. To produce these models, numerous approaches have been undertaken due to the difficulty associated with targeted mutagenesis and directed modification of the mitochondrial genome. Currently available models of mitochondrial disease are discussed in this paper, including our xenomitochondrial mice. In this model, mitochondria from one donor species are transferred to another. By doing so, cells and animals were generated with varying levels of heteroplasmy (or homoplasmy) for the introduced mitochondrial genomes. This caused graded variations in electron transport chain (ETC) dysfunction which were dependent upon the evolutionary divergence between donor and recipient. The protocol in generating these models involved the utilization of rhodamine-6G (R6G) to remove or eliminate endogenous mtDNA from the recipient cells. This paper will highlight the process and the implications of R6G treatment of mouse embryonic stem (ES) cells to create transmitochondrial cybrids. We summarize the history and mechanism of action of R6G as well as the future prospects for xenomitochondrial models toward increasing our understanding of mitochondrial biology and the dynamic interplay in signaling between mitochondria and the nucleus.

Xenomitochondrial mice harboring trans-species mitochondria on a Mus musculus domesticus (MD) nuclear background were produced. We created xenomitochondrial ES cell cybrids by fusing Mus spretus (MS), Mus caroli (MC), Mus dunni (Mdu), or Mus pahari (MP) mitochondrial donor cytoplasts and rhodamine 6-G treated CC9.3.1 or PC4 ES cells. The selected donor backgrounds reflected increasing evolutionary divergence from MD mice and the resultant mitochondrial-nuclear mismatch targeted a graded respiratory chain defect. Homoplasmic (MS, MC, Mdu, and MP) and heteroplasmic (MC) cell lines were injected into MD ova, and liveborn chimeric mice were obtained (MS/MD 18 of 87, MC/MD 6 of 46, Mdu/MD 31 of 140, and MP/MD l of 9 founder chimeras, respectively). Seven MS/MD, 1 MC/MD, and 11 Mdu/MD chimeric founder females were mated with wild-type MD males, and 18 of 19 (95%) were fertile. Of fertile females, only one chimeric MS/MD (1% coat color chimerism) and four chimeric Mdu/MD females (80-90% coat color chimerism) produced homoplasmic offspring with low efficiency (7 of 135; 5%). Four male and three female offspring were homoplasmic for the introduced mitochondrial backgrounds. Three male and one female offspring proved viable. Generation of mouse lines using additional female ES cell lineages is underway. We hypothesize that these mice, when crossbred with neurodegenerative-disease mouse models, will show accelerated age-related neuronal loss, because of their suboptimal capacity for oxidative phosphorylation and putatively increased oxidative stress.

The large number of extant Muridae species provides the opportunity of investigating functional limits of nuclear/ mitochondrial respiratory chain (RC) subunit interactions by introducing mitochondrial genomes from progressively more divergent species into Mus musculus domesticus mtDNA-less (ρ 0 ) cells. We created a panel of such xenomitochondrial cybrids, using as mitochondrial donors cells from six murid species with divergence from M. m. domesticus estimated at 2 to 12 Myr before present. Species used were Mus spretus, Mus caroli, Mus dunni, Mus pahari, Otomys irroratus, and Rattus norvegicus. Parsimony analysis of partial mtDNA sequences showed agreement with previous molecular phylogenies, with the exception that Otomys did not nest within the murinae as suggested by some recent nuclear gene analyses. Cellular production of lactate, a sensitive indicator of decreased respiratory chain ATP production, correlated with divergence. Functional characterization of the chimeric RC complexes in isolated mitochondria using enzymological analyses demonstrated varying decreases in activities of complexes I, III, and IV, which have subunits encoded in both mitochondrial and nuclear genomes. Complex III showed a striking decline in electron transfer function in the most divergent xenocybrids, being greatly reduced in the Rattus xenocybrid and virtually absent in the Otomys xenocybrid. This suggests that nuclear subunits interacting with cytochrome b face the greatest constraints in the coevolution of murid RC subunits. We sequenced the cytochrome b gene from the species used to identify potential amino acid substitutions involved in such interactions. The greater sensitivity of complex III to xenocybrid dysfunction may result from the encoding of redox center apoproteins in both nuclear and mitochondrial genomes, a unique feature of this RC complex.

We have developed a flow cytometric assay to measure the oxidative capacity of cultured lymphoblasts as a possible screening test for patients suspected of having a defect of the mitochondrial respiratory chain. Cells were incubated overnight in serum free media, followed by incubation with dihydroethidium with and without rotenone, and then analysed using flow cytometry to measure fluorescence. Inhibition with rotenone gave an increase in fluorescence compared to uninhibited cells. The change in fluorescence was significantly lower in four of the six patient cell lines, with a correlation between the activity of complex I and change in fluorescence. This method may be applicable to cell lines with defects in other complexes of the respiratory chain.