Complex I deficiencies in neurological disorders

Role of Mitochondrial Dysfunctions in Neurodegenerative Disorders: Advances in Mitochondrial Biology

Mitochondria, essential organelles responsible for cellular energy production, emerge as a key factor in the pathogenesis of neurodegenerative disorders. This review explores advancements in mitochondrial biology studies that highlight the pivotal connection between mitochondrial dysfunctions and neurological conditions such as Alzheimer's, Parkinson's, Huntington's, ischemic stroke, and vascular dementia. Mitochondrial DNA mutations, impaired dynamics, and disruptions in the ETC contribute to compromised energy production and heightened oxidative stress. These factors, in turn, lead to neuronal damage and cell death. Recent research has unveiled potential therapeutic strategies targeting mitochondrial dysfunction, including mitochondria targeted therapies and antioxidants. Furthermore, the identification of reliable biomarkers for assessing mitochondrial dysfunction opens new avenues for early diagnosis and monitoring of disease progression. By delving into these advancements, this review underscores the significance of understanding mitochondrial biology in unraveling the mechanisms underlying neurodegenerative disorders. It lays the groundwork for developing targeted treatments to combat these devastating neurological conditions.

Dietary Marine Hydrolysate Improves Memory Performance and Social Behavior through Gut Microbiota Remodeling during Aging

Aging is characterized by a decline in social behavior and cognitive functions leading to a decrease in life quality. In a previous study, we show that a fish hydrolysate supplementation prevents age-related decline in spatial short-term memory and long-term memory and anxiety-like behavior and improves the stress response in aged mice. The aim of this study was to determine the effects of a fish hydrolysate enriched with EPA/DHA or not on the cognitive ability and social interaction during aging and the biological mechanisms involved. We showed for the first time that a fish hydrolysate enriched with EPA/DHA or not improved memory performance and preference for social novelty that were diminished by aging. These changes were associated with the modulation of the gut microbiota, normalization of corticosterone, and modulation of the expression of genes involved in the mitochondrial respiratory chain, circadian clock, neuroprotection, and antioxidant activity. Thus, these changes may contribute to the observed improvements in social behavior and memory and reinforced the innovative character of fish hydrolysate in the prevention of age-related impairments.

Targeting Mitochondrial Oxidative Stress as a Strategy to Treat Aging and Age-Related Diseases

Mitochondria are one of the organelles undergoing rapid alteration during the senescence process. Senescent cells show an increase in mitochondrial size, which is attributed to the accumulation of defective mitochondria, which causes mitochondrial oxidative stress. Defective mitochondria are also targets of mitochondrial oxidative stress, and the vicious cycle between defective mitochondria and mitochondrial oxidative stress contributes to the onset and development of aging and age-related diseases. Based on the findings, strategies to reduce mitochondrial oxidative stress have been suggested for the effective treatment of aging and age-related diseases. In this article, we discuss mitochondrial alterations and the consequent increase in mitochondrial oxidative stress. Then, the causal role of mitochondrial oxidative stress on aging is investigated by examining how aging and age-related diseases are exacerbated by induced stress. Furthermore, we assess the importance of targeting mitochondrial oxidative stress for the regulation of aging and suggest different therapeutic strategies to reduce mitochondrial oxidative stress. Therefore, this review will not only shed light on a new perspective on the role of mitochondrial oxidative stress in aging but also provide effective therapeutic strategies for the treatment of aging and age-related diseases through the regulation of mitochondrial oxidative stress.

Fish Models for Exploring Mitochondrial Dysfunction Affecting Neurodegenerative Disorders

Neurodegenerative disorders are characterized by the progressive loss of neuronal structure or function, resulting in memory loss and movement disorders. Although the detailed pathogenic mechanism has not been elucidated, it is thought to be related to the loss of mitochondrial function in the process of aging. Animal models that mimic the pathology of a disease are essential for understanding human diseases. In recent years, small fish have become ideal vertebrate models for human disease due to their high genetic and histological homology to humans, ease of in vivo imaging, and ease of genetic manipulation. In this review, we first outline the impact of mitochondrial dysfunction on the progression of neurodegenerative diseases. Then, we highlight the advantages of small fish as model organisms, and present examples of previous studies regarding mitochondria-related neuronal disorders. Lastly, we discuss the applicability of the turquoise killifish, a unique model for aging research, as a model for neurodegenerative diseases. Small fish models are expected to advance our understanding of the mitochondrial function in vivo, the pathogenesis of neurodegenerative diseases, and be important tools for developing therapies to treat diseases.

Single-cell analysis reveals changes in BCG vaccine-injected mice modeling tuberculous meningitis brain infection

Tuberculous meningitis (TBM) is the most severe and deadly manifestation of tuberculosis. Neurological complications are observed in up to 50% of patients affected. Here, attenuated Mycobacterium bovis are injected into the cerebellum of mice, and histopathological images and cultured colonies confirm successful brain infection. Then, whole-brain tissue is dissected for 10X Genomics single-cell sequencing, and we acquire 15 cell types. Transcriptional changes of inflammation processes are found in multiple cell types. Specifically, Stat1 and IRF1 are shown to mediate inflammation in macrophages and microglia. For neurons, decreased oxidative phosphorylation activity in neurons is observed, which corresponds to TBM clinical symptoms of neurodegeneration. Finally, ependymal cells present prominent transcriptional changes, and decreased FERM domain containing 4A (Frmd4a) may contribute to TBM clinical symptoms of hydrocephalus and neurodegeneration. This study shows a single-cell transcriptome of M. bovis infection in mice and improves the understanding of brain infection and neurological complications in TBM.

Mitochondrial Complex I, a Possible Sensible Site of cAMP Pathway in Aging

In mammals during aging, reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, cause oxidative damage of macromolecules leading to respiratory chain dysfunction, which in turn increases ROS mitochondrial production. Many efforts have been made to understand the role of oxidative stress in aging and age-related diseases. The complex I of the mitochondrial respiratory chain is the major source of ROS production and its dysfunctions have been associated with several forms of neurodegeneration, other common human diseases and aging. Complex I-ROS production and complex I content have been proposed as the major determinants for longevity. The cAMP signal has a role in the regulation of complex I activity and the decrease of ROS production. In the last years, an increasing number of studies have attempted to activate cAMP signaling to treat age-related diseases associated with mitochondrial dysfunctions and ROS production. This idea comes from a long-line of studies showing a main role of cAMP signal in the memory consolidation mechanism and in the regulation of mitochondrial functions. Here, we discuss several evidences on the possible connection between complex I and cAMP pathway in the aging process.

Traditional and Innovative Anti-seizure Medications Targeting Key Physiopathological Mechanisms: Focus on Neurodevelopment and Neurodegeneration

Despite the wide range of compounds currently available to treat epilepsy, there is still no drug that directly tackles the physiopathological mechanisms underlying its development. Indeed, antiseizure medications attempt to prevent seizures but are inefficacious in counteracting or rescuing the physiopathological phenomena that underlie their onset and recurrence, and hence do not cure epilepsy. Classically, the altered excitation/inhibition balance is postulated as the mechanism underlying epileptogenesis and seizure generation. This oversimplification, however, does not account for deficits in homeostatic plasticity resulting from either insufficient or excessive compensatory mechanisms in response to a change in network activity. In this respect, both neurodevelopmental epilepsies and those associated with neurodegeneration may share common underlying mechanisms that still need to be fully elucidated. The understanding of these molecular mechanisms shed light on the identification of new classes of drugs able not only to suppress seizures, but also to present potential antiepileptogenic effects or "disease-modifying" properties.

The c-Abl/p73 pathway induces neurodegeneration in a Parkinson's disease model

Parkinson's disease is the second most common neurodegenerative disorder. Although it is clear that dopaminergic neurons degenerate, the underlying molecular mechanisms are still unknown, and thus, successful treatment is still elusive. One pro-apoptotic pathway associated with several neurodegenerative diseases is the tyrosine kinase c-Abl and its target p73. Here, we evaluated the contribution of c-Abl and p73 in the degeneration of dopaminergic neurons induced by the neurotoxin 6-hydroxydopamine as a model for Parkinson's disease. First, we found that in SH-SY5Y cells treated with 6-hydroxydopamine, c-Abl and p73 phosphorylation levels were up-regulated. Also, we found that the pro-apoptotic p73 isoform TAp73 was up-regulated. Then, to evaluate whether c-Abl tyrosine kinase activity is necessary for 6-hydroxydopamine-induced apoptosis, we co-treated SH-SY5Y cells with 6-hydroxydopamine and Imatinib, a c-Abl specific inhibitor, observing that Imatinib prevented p73 phosphorylation, TAp73 up-regulation, and protected SH-SY5Y cells treated with 6-hydroxydopamine from apoptosis. Interestingly, this observation was confirmed in the c-Abl conditional null mice, where 6-hydroxydopamine stereotaxic injections induced a lesser reduction of dopaminergic neurons than in the wild-type mice significantly. Finally, we found that the intraperitoneal administration of Imatinib prevented the death of dopaminergic neurons induced by injecting 6-hydroxydopamine stereotaxically in the mice striatum. Thus, our findings support the idea that the c-Abl/p73 pathway is involved in 6-hydroxydopamine degeneration and suggest that inhibition of its kinase activity might be used as a therapeutical drug in Parkinson's disease.

Mitochondrial protein dysfunction in pathogenesis of neurological diseases

Mitochondria are essential organelles for neuronal function and cell survival. Besides the well-known bioenergetics, additional mitochondrial roles in calcium signaling, lipid biogenesis, regulation of reactive oxygen species, and apoptosis are pivotal in diverse cellular processes. The mitochondrial proteome encompasses about 1,500 proteins encoded by both the nuclear DNA and the maternally inherited mitochondrial DNA. Mutations in the nuclear or mitochondrial genome, or combinations of both, can result in mitochondrial protein deficiencies and mitochondrial malfunction. Therefore, mitochondrial quality control by proteins involved in various surveillance mechanisms is critical for neuronal integrity and viability. Abnormal proteins involved in mitochondrial bioenergetics, dynamics, mitophagy, import machinery, ion channels, and mitochondrial DNA maintenance have been linked to the pathogenesis of a number of neurological diseases. The goal of this review is to give an overview of these pathways and to summarize the interconnections between mitochondrial protein dysfunction and neurological diseases.

Mitochondria-lysosome crosstalk in GBA1-associated Parkinson's disease

Organelle crosstalk is significant in regulating their respective functions and subsequent cell fate. Mitochondria and lysosomes are amongst the essential organelles in maintaining cellular homeostasis. Mitochondria-lysosome connections, which may develop dynamically in the human neurons, have been identified as sites of bidirectional communication. Aberrancies are often associated with neurodegenerative disorders like Parkinson's disease (PD), suggesting the physical and functional link between these two organelles. PD is often linked with genetic mutations of several mutations discovered in the familial forms of the disease; some are considered risk factors. Many of these genes are either associated with mitochondrial function or belong to endo-lysosomal pathways. The recent investigations have indicated that neurons with mutant glucosylceramidase beta (GBA1) exhibit extended mitochondria-lysosome connections in individuals with PD. This may be due to impaired control of the untethering protein, which aids in the hydrolysis of Rab7 GTP required for contact untethering. A GCase modulator may be used to augment the reduced GBA1 lysosomal enzyme activity in the neurons of PD patients. This review focuses on how GBA1 mutation in PD is interlinked with mitochondria-lysosome (ML) crosstalk, exploring the pathways governing these interactions and mechanistically comprehending the mitochondrial and lysosomal miscommunication in the pathophysiology of PD. This review is based on the limited literature available on the topic and hence may be subject to bias in its views. Our estimates may be conservative and limited due to the lack of studies under the said discipline due to its inherent complex nature. The current association of GBA1 to PD pathogenesis is based on the limited scope of study and further research is necessary to explore the risk factors further and identify the relationship with more detail.

cAMP/PKA Signaling Modulates Mitochondrial Supercomplex Organization

The oxidative phosphorylation (OXPHOS) system couples the transfer of electrons to oxygen with pumping of protons across the inner mitochondrial membrane, ensuring the ATP production. Evidence suggests that respiratory chain complexes may also assemble into supramolecular structures, called supercomplexes (SCs). The SCs appear to increase the efficiency/capacity of OXPHOS and reduce the reactive oxygen species (ROS) production, especially that which is produced by complex I. Studies suggest a mutual regulation between complex I and SCs, while SCs organization is important for complex I assembly/stability, complex I is involved in the supercomplex formation. Complex I is a pacemaker of the OXPHOS system, and it has been shown that the PKA-dependent phosphorylation of some of its subunits increases the activity of the complex, reducing the ROS production. In this work, using in ex vivo and in vitro models, we show that the activation of cAMP/PKA cascade resulted in an increase in SCs formation associated with an enhanced capacity of electron flux and ATP production rate. This is also associated with the phosphorylation of the NDUFS4 subunit of complex I. This aspect highlights the key role of complex I in cellular energy production.

5-Methoxy-1-methyl-2-{[4-(2-hydroxyphenyl)piperazin-1-yl]methyl}-1Hindole (KAD22) with Antioxidant Activity

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Compound KAD22 (5-methoxy-1-methyl-2-[4-(2-hydroxyphenyl)piperazin-1-yl]methyl-1H-indole) was designed as a potential dopamine D2 receptor agonist with antioxidant activity for possible treatment of Parkinson’s disease. The compound was obtained from 5-methoxy-1-methyl-1H-indole-2-carbaldehyde and 2-(piperazin-1-yl)phenol. KAD22 showed no affinity to dopamine D2 receptor but it is a potent antioxidant. Experimental and computational structural studies (conformational analysis, HOMO and LUMO orbitals, electrostatic potential map, non-covalent interaction plot, spectral properties, ligand-receptor interactions) of KAD22 were performed to address its biological activity.

Sex-specific genetic regulation of adipose mitochondria and metabolic syndrome by Ndufv2

We have previously suggested a central role for mitochondria in the observed sex differences in metabolic traits. However, the mechanisms by which sex differences affect adipose mitochondrial function and metabolic syndrome are unclear. Here we show that in both mice and humans, adipose mitochondrial functions are elevated in females and are strongly associated with adiposity, insulin resistance and plasma lipids. Using a panel of diverse inbred strains of mice, we identify a genetic locus on mouse chromosome 17 that controls mitochondrial mass and function in adipose tissue in a sex- and tissue-specific manner. This locus contains Ndufv2 and regulates the expression of at least 89 mitochondrial genes in females, including oxidative phosphorylation genes and those related to mitochondrial DNA content. Overexpression studies indicate that Ndufv2 mediates these effects by regulating supercomplex assembly and elevating mitochondrial reactive oxygen species production, which generates a signal that increases mitochondrial biogenesis.

The allosteric protein interactions in the proton-motive function of mammalian redox enzymes of the respiratory chain

Insight into mammalian respiratory complexes defines the role of allosteric protein interactions in their proton-motive activity. In cytochrome c oxidase (CxIV) conformational change of subunit I, caused by O₂ binding to heme a₃²⁺-Cu_B⁺ and reduction, and stereochemical transitions coupled to oxidation/reduction of heme a and Cu_A, combined with electrostatic effects, determine the proton pumping activity. In ubiquinone-cytochrome c oxidoreductase (CxIII) conformational movement of Fe-S protein between cytochromes b and c₁ is the key element of the proton-motive activity. In NADH-ubiquinone oxidoreductase (CxI) ubiquinone binding and reduction result in conformational changes of subunits in the quinone reaction structure which initiate proton pumping.

Neuroprotective effect of the somatostatin receptor 5 agonist L-817,818 on retinal ganglion cells in experimental glaucoma

Somatostatin plays important roles in modulating neuronal functions by activating the five specific G-protein coupled receptors (sst1-sst5). Previous studies have demonstrated that sst5 were expressed in retinal ganglion cells (RGCs) and sst5 agonist attenuated the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid-induced retinal neurotoxicity. In this study, we investigated effects and underlying mechanisms of the sst5 agonist L-817,818 on RGC injury induced by elevated intraocular pressure (COH) in experimental glaucoma. Our results showed that intraperitoneal administration of L-817,818 significantly reduced RGC loss and decreased the number of terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling (TUNEL)-positive RGCs in COH retinas, suggesting that L-817,818 may attenuate RGC apoptosis. Consistently, in COH retinas with L-817,818 administration, both the down-regulated mRNA and protein levels of anti-apoptotic Bcl-2 and the up-regulated mRNA and protein levels of pro-apoptotic Bax were partially reversed. L-817,818 administration downregulated the expression of apoptosis-related proteins caspase-9 and caspase-3 in COH retinas. In addition, L-817,818 administration reduced the concentrations of reactive oxygen species/reactive nitrogen species and malondialdehyde, and ameliorated the functions of mitochondrial respiratory chain complex (MRCC). Our results imply that administration of the sst5 agonist L-817,818 reduces RGC loss in COH rats through decreasing RGC apoptosis, which is mediated by regulating Bcl-2/Bax balance, reducing oxidative stress and rescuing activities of MRCC. Activation of sst5 may provide neuroprotective roles for RGCs in glaucoma.

Novel PET Biomarkers to Disentangle Molecular Pathways across Age-Related Neurodegenerative Diseases

There is a need to disentangle the etiological puzzle of age-related neurodegenerative diseases, whose clinical phenotypes arise from known, and as yet unknown, pathways that can act distinctly or in concert. Enhanced sub-phenotyping and the identification of in vivo biomarker-driven signature profiles could improve the stratification of patients into clinical trials and, potentially, help to drive the treatment landscape towards the precision medicine paradigm. The rapidly growing field of neuroimaging offers valuable tools to investigate disease pathophysiology and molecular pathways in humans, with the potential to capture the whole disease course starting from preclinical stages. Positron emission tomography (PET) combines the advantages of a versatile imaging technique with the ability to quantify, to nanomolar sensitivity, molecular targets in vivo. This review will discuss current research and available imaging biomarkers evaluating dysregulation of the main molecular pathways across age-related neurodegenerative diseases. The molecular pathways focused on in this review involve mitochondrial dysfunction and energy dysregulation; neuroinflammation; protein misfolding; aggregation and the concepts of pathobiology, synaptic dysfunction, neurotransmitter dysregulation and dysfunction of the glymphatic system. The use of PET imaging to dissect these molecular pathways and the potential to aid sub-phenotyping will be discussed, with a focus on novel PET biomarkers.

Genetic perspective on the synergistic connection between vesicular transport, lysosomal and mitochondrial pathways associated with Parkinson's disease pathogenesis

Parkinson's disease (PD) and atypical parkinsonian syndromes (APS) are symptomatically characterized by parkinsonism, with the latter presenting additionally a distinctive range of atypical features. Although the majority of patients with PD and APS appear to be sporadic, genetic causes of several rare monogenic disease variants were identified. The knowledge acquired from these genetic factors indicated that defects in vesicular transport pathways, endo-lysosomal dysfunction, impaired autophagy-lysosomal protein and organelle degradation pathways, α-synuclein aggregation and mitochondrial dysfunction play key roles in PD pathogenesis. Moreover, membrane dynamics are increasingly recognized as a key player in the disease pathogenesis due lipid homeostasis alterations, associated with lysosomal dysfunction, caused by mutations in several PD and APS genes. The importance of lysosomal dysfunction and lipid homeostasis is strengthened by both genetic discoveries and clinical epidemiology of the association between parkinsonism and lysosomal storage disorders (LSDs), caused by the disruption of lysosomal biogenesis or function. A synergistic coordination between vesicular trafficking, lysosomal and mitochondria defects exist whereby mutations in PD and APS genes encoding proteins primarily involved one PD pathway are frequently associated with defects in other PD pathways as a secondary effect. Moreover, accumulating clinical and genetic observations suggest more complex inheritance patters of familial PD exist, including oligogenic and polygenic inheritance of genes in the same or interconnected PD pathways, further strengthening their synergistic connection.Here, we provide a comprehensive overview of PD and APS genes with functions in vesicular transport, lysosomal and mitochondrial pathways, and highlight functional and genetic evidence of the synergistic connection between these PD associated pathways.

Mitochondrial Complex 1, Sigma 1, and Synaptic Vesicle 2A in Early Drug-Naive Parkinson's Disease

BACKGROUND

Dysfunction of mitochondrial energy generation may contribute to neurodegeneration, leading to synaptic loss in Parkinson's disease (PD). The objective of this study was to find cross-sectional and longitudinal changes in PET markers of synaptic vesicle protein 2A, sigma 1 receptor, and mitochondrial complex 1 in drug-naive PD patients.

METHODS

Twelve early drug-naive PD patients and 16 healthy controls underwent a 3-Tesla MRI and PET imaging to quantify volume of distribution of [¹¹ C]UCB-J, [¹¹ C]SA-4503, and [¹⁸ F]BCPP-EF for synaptic vesicle protein 2A, sigma 1 receptor, and mitochondrial complex 1, respectively. Nine PD patients completed approximately 1-year follow-up assessments.

RESULTS

Reduced [¹¹ C]UCB-J volume of distribution in the caudate, putamen, thalamus, brain stem, and dorsal raphe and across cortical regions was observed in drug-naive PD patients compared with healthy controls. [¹¹ C]UCB-J volume of distribution was reduced in the locus coeruleus and substantia nigra but did not reach statistical significance. No significant differences were found in [¹¹ C]SA-4503 and [¹⁸ F]BCPP-EF volume of distribution in PD compared with healthy controls. Lower brain stem [¹¹ C]UCB-J volume of distribution correlated with Movement Disorder Society Unified Parkinson's Disease Rating Scale part III and total scores. No significant longitudinal changes were identified in PD patients at follow-up compared with baseline.

CONCLUSIONS

Our findings represent the first in vivo evidence of mitochondrial, endoplasmic reticulum, and synaptic dysfunction in drug-naive PD patients. Synaptic dysfunction likely occurs early in disease pathophysiology and has relevance to symptomatology. Mitochondrial complex 1 and sigma 1 receptor pathology warrants further investigations in PD. Studies in larger cohorts with longer follow-up will determine the validity of these PET markers to track disease progression. © 2020 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Mitochondrial Supercomplexes: Physiological Organization and Dysregulation in Age-Related Neurodegenerative Disorders

Several studies suggest that the assembly of mitochondrial respiratory complexes into structures known as supercomplexes (SCs) may increase the efficiency of the electron transport chain, reducing the rate of production of reactive oxygen species. Therefore, the study of the (dis)assembly of SCs may be relevant for the understanding of mitochondrial dysfunction reported in brain aging and major neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Here we briefly reviewed the biogenesis and structural properties of SCs, the impact of mtDNA mutations and mitochondrial dynamics on SCs assembly, the role of lipids on stabilization of SCs and the methodological limitations for the study of SCs. More specifically, we summarized what is known about mitochondrial dysfunction and SCs organization and activity in aging, AD and PD. We focused on the critical variables to take into account when postmortem tissues are used to study the (dis)assembly of SCs. Since few works have been performed to study SCs in AD and PD, the impact of SCs dysfunction on the alteration of brain energetics in these diseases remains poorly understood. The convergence of future progress in the study of SCs structure at high resolution and the refinement of animal models of AD and PD, as well as the use of iPSC-based and somatic cell-derived neurons, will be critical in understanding the biological relevance of the structural remodeling of SCs.

Modulation of key enzymes linked to Parkinsonism and neurologic disorders by Antiaris africana in rotenone-toxified rats

Background The physiopathologies of many neurologic diseases are characterized by related biochemical dysfunctions that could be explored as drug targets. This study evaluated the effect of a methanol leaf extract of Antiaris africana (MEA) on critical bioindices of Parkinsonism and related neurologic dysfunctions in rats with rotenone-induced neurotoxicity. Methods Animals were administered 50 or 100 mg/kg MEA for 14 consecutive days. Rotenone (1.5 mg/kg) was administered three times per day on days 13 and 14. Coenzyme Q10 (5 mg/kg) was the reference drug. Complex I activity, dopamine level, activities of acetylcholinesterase, myeloperoxidase, Na+/K+ ATPase and glutamine synthetase, as well as oxidative stress indices were evaluated at the end of the period of treatment. Results Rotenone-intoxicated group showed disruption of complex 1 activity, dopamine level, and glutamine synthetase activity with negative alterations to activities of acetylcholinesterase, myeloperoxidase, and Na+/K+ ATPase as well as heightened cerebral oxidative stress. MEA restored brain mitochondria functionality, mitigated altered neurochemical integrity, and ameliorated cerebral oxidative stress occasioned by rotenone neurotoxicity. The activity of A. Africana was comparable with that of 5 mg/kg coenzyme Q10. Conclusions These results indicated that A. africana displayed therapeutic potential against Parkinsonism and related neurologic dysfunctions and support its ethnobotanical use for the treatment of neurologic disorders.

Synergistic Effect of Mitochondrial and Lysosomal Dysfunction in Parkinson's Disease

Crosstalk between lysosomes and mitochondria plays a central role in Parkinson’s Disease (PD). Lysosomal function may be influenced by mitochondrial quality control, dynamics and/or respiration, but whether dysfunction of endocytic or autophagic pathway is associated with mitochondrial impairment determining accumulation of defective mitochondria, is not yet understood. Here, we performed live imaging, western blotting analysis, sequencing of mitochondrial DNA (mtDNA) and senescence-associated beta-galactosidase activity assay on primary fibroblasts from a young patient affected by PD, her mother and a healthy control to analyze the occurrence of mtDNA mutations, lysosomal abundance, acidification and function, mitochondrial biogenesis activation and senescence. We showed synergistic alterations in lysosomal functions and mitochondrial biogenesis, likely associated with a mitochondrial genetic defect, with a consequent block of mitochondrial turnover and occurrence of premature cellular senescence in PARK2-PD fibroblasts, suggesting that these alterations represent potential mechanisms contributing to the loss of dopaminergic neurons.

Differential Effects of Yeast NADH Dehydrogenase (Ndi1) Expression on Mitochondrial Function and Inclusion Formation in a Cell Culture Model of Sporadic Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that exhibits aberrant protein aggregation and mitochondrial dysfunction. Ndi1, the yeast mitochondrial NADH dehydrogenase (complex I) enzyme, is a single subunit, internal matrix-facing protein. Previous studies have shown that Ndi1 expression leads to improved mitochondrial function in models of complex I-mediated mitochondrial dysfunction. The trans-mitochondrial cybrid cell model of PD was created by fusing mitochondrial DNA-depleted SH-SY5Y cells with platelets from a sporadic PD patient. PD cybrid cells reproduce the mitochondrial dysfunction observed in a patient's brain and periphery and form intracellular, cybrid Lewy bodies comparable to Lewy bodies in PD brain. To improve mitochondrial function and alter the formation of protein aggregates, Ndi1 was expressed in PD cybrid cells and parent SH-SY5Y cells. We observed a dramatic increase in mitochondrial respiration, increased mitochondrial gene expression, and increased PGC-1α gene expression in PD cybrid cells expressing Ndi1. Total cellular aggregated protein content was decreased but Ndi1 expression was insufficient to prevent cybrid Lewy body formation. Ndi1 expression leads to improved mitochondrial function and biogenesis signaling, both processes that could improve neuron survival during disease. However, other aspects of PD pathology such as cybrid Lewy body formation were not reduced. Consequently, resolution of mitochondrial dysfunction alone may not be sufficient to overcome other aspects of PD-related cellular pathology.

Prohibitins: A Critical Role in Mitochondrial Functions and Implication in Diseases

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are ubiquitously expressed, and are present in the nucleus, cytosol, and mitochondria. Depending on the cellular localization, PHB1 and PHB2 have distinctive functions, but more evidence suggests a critical role within mitochondria. In fact, PHB proteins are highly expressed in cells that heavily depend on mitochondrial function. In mitochondria, these two proteins assemble at the inner membrane to form a supra-macromolecular structure, which works as a scaffold for proteins and lipids regulating mitochondrial metabolism, including bioenergetics, biogenesis, and dynamics in order to determine the cell fate, death, or life. PHB alterations have been found in aging and cancer, as well as neurodegenerative, cardiac, and kidney diseases, in which significant mitochondrial impairments have been observed. The molecular mechanisms by which prohibitins regulate mitochondrial function and their role in pathology are reviewed and discussed herein.

Subclinical Leber's hereditary optic neuropathy with pediatric acute spinal cord onset: more than meets the eye

Background

Leber’s hereditary optic neuropathy (LHON) is a mitochondrial disease characterized by visual loss consequent to optic nerve atrophy. In some cases, LHON is associated with heterogeneous neurological extraocular manifestations and is referred to as “Leber plus disease”; rarely it is associated with a multiple sclerosis (MS)-like syndrome known as Harding disease, but no pediatric extraocular acute spinal onset is reported.

Case presentation

We describe the case of a 5-year-old girl carrying the G3460A mtDNA mutation who was referred to clinical examination for bilateral upper and lower limb weakness with no sign of optic neuropathy. Spinal cord MRI showed hyperintense signal alterations in T2-weighted and restricted diffusion in DWI sequences in the anterior portion of the cervical and dorsal spinal cord resembling a spinal cord vascular injury. No association between this mutation and pediatric spinal cord lesions has previously been reported. Alternative diagnostic hypotheses, including infective, ischemic and inflammatory disorders, were not substantiated by clinical and instrumental investigations.

Conclusions

Our case reports a novel pediatric clinical manifestation associated with the m.3460G > A mtDNA mutation, broadening the clinical spectrum of this disease. Early identification of new cases and monitoring of carriers beginning in childhood is important to prevent neurological deterioration and preserve long-term function.

Impact of atypical mitochondrial cyclic-AMP level in nephropathic cystinosis

Nephropathic cystinosis (NC) is a rare disease caused by mutations in the CTNS gene encoding for cystinosin, a lysosomal transmembrane cystine/H+ symporter, which promotes the efflux of cystine from lysosomes to cytosol. NC is the most frequent cause of Fanconi syndrome (FS) in young children, the molecular basis of which is not well established. Proximal tubular cells have very high metabolic rate due to the active transport of many solutes. Not surprisingly, mitochondrial disorders are often characterized by FS. A similar mechanism may also apply to NC. Because cAMP has regulatory properties on mitochondrial function, we have analyzed cAMP levels and mitochondrial targets in CTNS-/- conditionally immortalized proximal tubular epithelial cells (ciPTEC) carrying the classical homozygous 57-kb deletion (delCTNS-/-) or with compound heterozygous loss-of-function mutations (mutCTNS-/-). Compared to wild-type cells, cystinotic cells had significantly lower mitochondrial cAMP levels (delCTNS-/- ciPTEC by 56% ± 10.5, P < 0.0001; mutCTNS-/- by 26% ± 4.3, P < 0.001), complex I and V activities, mitochondrial membrane potential, and SIRT3 protein levels, which were associated with increased mitochondrial fragmentation. Reduction of complex I and V activities was associated with lower expression of part of their subunits. Treatment with the non-hydrolysable cAMP analog 8-Br-cAMP restored mitochondrial potential and corrected mitochondria morphology. Treatment with cysteamine, which reduces the intra-lysosomal cystine, was able to restore mitochondrial cAMP levels, as well as most other abnormal mitochondrial findings. These observations were validated in CTNS-silenced HK-2 cells, indicating a pivotal role of mitochondrial cAMP in the proximal tubular dysfunction observed in NC.

Trilobatin Protects Against Oxidative Injury in Neuronal PC12 Cells Through Regulating Mitochondrial ROS Homeostasis Mediated by AMPK/Nrf2/Sirt3 Signaling Pathway

Oxidative stress-induced neuronal cell damage is a crucial factor in the pathogenesis of mitochondria-associated neurological diseases. Therefore, elimination of overproduction of mitochondrial reactive oxygen species (mtROS) may be a potential strategy for prevention and treatment of neurological diseases. In the present study, the neuroprotective effects of trilobatin (TLB), a novel small molecule monomer derived from Lithocarpus polystachyus Rehd, and its underlying mechanisms were investigated in vitro using hydrogen peroxide (H₂O₂)-induced oxidative stress model in a neuron-like PC12 cell. The findings revealed that pre-treatment with TLB dramatically concentration-dependently suppressed H₂O₂-induced PC12 cells damage by enhancing cell viability, repressed reduction of mitochondrial membrane potential (MMP) and decreased mtROS overgeneration, thereby deferring cell apoptosis. Further study demonstrated that TLB not only increased the enzymatic activities of glutathione peroxidase (GPx), isocitrate dehydrogenase 2 (IDH2),superoxide dismutase 2 (SOD2) and deacetylation of SOD2, but also activated silent mating-type information regulation 2 homolog 3 (Sirt3) within the mitochondria and thereby upregulating forkheadboxO3a (FoxO3a), which regulated mitochondrial DNA genes, then led to improving complex I activity and adenosine triphosphate (ATP) synthesis. What’s more, TLB up-regulated p-adenosine monophosphate-activated protein kinase (AMPK) level, the expression of peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α), and ERRα. Intriguingly, TLB failed to mitigate H₂O₂-induced PC12 injury in the presence of the AMPK inhibitor (Compound C), indicating that the beneficial effects of TLB on the regulation of mtROS homeostasis were reliance on AMPK -Sirt3 signaling pathway. Moreover, TLB also facilitated nuclear factor erythroid 2-related factor 2 (Nrf2) and promoted antioxidant gene expression in turn, and knockdown of Nrf2 by siRNA dramatically reduced the neuroprotective effects of TLB. Notably, AMPK inhibitor abolished the activation of Nrf2 and Sirt3, whereas, knockdown of Nrf2 blocked the upregulation of Sirt3, but it did not affect p-AMPK level. In conclusion, our findings demonstrate that TLB protects against oxidative injury in neuronal PC12 cells through regulating mtROS homeostasis in the first time, which is, at least partly, mediated through the AMPK/Nrf2/Sirt3 signaling pathway.

Mitochondrial alterations in Parkinson's disease human samples and cellular models

Mitochondrial impairment is one of the most important hallmarks of Parkinson's disease (PD) pathogenesis. In this work, we wanted to verify the molecular basis of altered mitochondrial dynamics and disposal in Substantia nigra specimens of sporadic PD patients, by the comparison with two cellular models of PD. Indeed, SH-SY5Y cells were treated with either dopamine or 1-methyl-4-phenylpyridinium (MPP⁺) in order to highlight the effect of altered dopamine homeostasis and of complex I inhibition, respectively. As a result, we found that fusion impairment of the inner mitochondrial membrane is a common feature of both PD human samples and cellular models. However, the effects of dopamine and MPP⁺ treatments resulted to be different in terms of the mitochondrial damage induced. Opposite changes in the levels of two mitochondrial protein markers (voltage-dependent anion channels (VDACs) and cytochrome c oxidase subunit 5β (COX5β)) were observed. In this case, dopamine treatment better recapitulated the molecular picture of patients' samples. Moreover, the accumulation of PTEN-induced putative kinase 1 (PINK1), a mitophagy marker, was not observed in both PD patients samples and cellular models. Eventually, in transmission electron microscopy images, small electron dense deposits were observed in mitochondria of PD subjects, which are uniquely reproduced in dopamine-treated cells. In conclusion, our study suggests that the mitochondrial molecular landscape of Substantia nigra specimens of PD patients can be mirrored by the impaired dopamine homeostasis cellular model, thus supporting the hypothesis that alterations in this process could be a crucial pathogenetic event in PD.

Neuroprotective effect of 5ɑ-androst-3β,5,6β-triol on retinal ganglion cells in a rat chronic ocular hypertension model

Previous studies have demonstrated that 5ɑ-androst-3β,5,6β-triol (Triol), a synthesized steroid compound, showed notable neuroprotective effect in cultured cortical neurons. In the present study, we explored whether and how Triol have neuroprotective effect on retinal ganglion cells (RGCs) in a chronic ocular hypertension (COH) rat model. COH model was produced by injecting superparamagnetic iron oxide micro-beads into the anterior chamber, and Triol was administrated (4.8μg/100g, i.p., once daily for 4 weeks). Immunohistochemistry experiments showed that in whole flat-mounted COH retinas, the number of CTB-labeled survival RGCs was progressively reduced, while TUNEL-positive signals were significantly increased from 1 to 4 weeks after the micro-bead injection. Triol administration significantly attenuated the reduction in the number of CTB-labeled RGCs, and partially reduced the increased number of TUNEL-positive signals in COH retinas. Furthermore, Triol administration partially reduced the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), and significantly rescued the activities of mitochondrial respiratory chain complex (MRCC) I/II/III in COH retinas. Our results suggest that Triol prevents RGCs from apoptotic death in COH retinas by reducing the lipid peroxidation and enhancing the activities of MRCCs.

Redox-based therapeutics in neurodegenerative disease

This review describes recent developments in the search for effective therapeutic agents that target redox homeostasis in neurodegenerative disease. The disruption to thiol redox homeostasis in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis is discussed, together with the experimental strategies that are aimed at preventing, or at least minimizing, oxidative damage in these diseases. Particular attention is given to the potential of increasing antioxidant capacity by targeting the Nrf2 pathway, the development of inhibitors of NADPH oxidases that are likely candidates for clinical use, together with strategies to reduce nitrosative stress and mitochondrial dysfunction. We describe the shortcomings of compounds that hinder their progression to the clinic and evaluate likely avenues for future research.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

The mechanism of neuroprotective action of natural compounds

Disturbance of cerebral redox homeostasis is the primary cause of human neurodegenerative disorders, such as Parkinson's disease or Alzheimer's disease. Well known experimental research demonstrates that oxidative stress is a main cause of cell death. A high concentration of reactive oxygen and nitrogen species leads to damage of a lot of proteins, lipids and also DNA. Synthetic compounds used for the treatment in the neurodegenerative diseases failed to meet the hopes they had raised and often exhibit a number of side effects. Therefore, in recent years interest in natural compounds derived from plants appears to be on the rise. This review describes a few natural compounds (1MeTIQ, resveratrol, curcumin, vitamin C and Gingko biloba) which revealed neuroprotective potential both in experimental studies and clinical trials. 1MeTIQ has a privileged position because, as opposed to the remaining compounds, it is an endogenous amine synthesized in human and animal brain. Based on evidence from research, it seems that a common protective mechanism for all the above-mentioned natural compounds relies on their ability to inhibit or even scavenge the excess of free radicals generated in oxidative and neurotoxin-induced processes in nerve cells of the brain. However, it was demonstrated that further different molecular processes connected with neurotoxicity (e.g. the inhibition of mitochondrial complex I, activation of caspase-3, apoptosis) follow later and are initiated by the reactive oxygen species. What is more, these natural compounds are able to inhibit further stages of apoptosis triggered by neurotoxins in the brain.

Mitochondrial cAMP signaling

Cyclic adenosine 3, 5'-monophosphate (cAMP) is a ubiquitous second messenger regulating many biological processes, such as cell migration, differentiation, proliferation and apoptosis. cAMP signaling functions not only on the plasma membrane, but also in the nucleus and in organelles such as mitochondria. Mitochondrial cAMP signaling is an indispensable part of the cytoplasm-mitochondrion crosstalk that maintains mitochondrial homeostasis, regulates mitochondrial dynamics, and modulates cellular stress responses and other signaling pathways. Recently, the compartmentalization of mitochondrial cAMP signaling has attracted great attentions. This new input should be carefully taken into account when we interpret the findings of mitochondrial cAMP signaling. In this review, we summarize previous and recent progress in our understanding of mitochondrial cAMP signaling, including the components of the signaling cascade, and the function and regulation of this signaling pathway in different mitochondrial compartments.

Accessory subunit NUYM (NDUFS4) is required for stability of the electron input module and activity of mitochondrial complex I

Mitochondrial complex I is an intricate 1MDa membrane protein complex with a central role in aerobic energy metabolism. The minimal form of complex I consists of fourteen central subunits that are conserved from bacteria to man. In addition, eukaryotic complex I comprises some 30 accessory subunits of largely unknown function. The gene for the accessory NDUFS4 subunit of human complex I is a hot spot for fatal pathogenic mutations in humans. We have deleted the gene for the orthologous NUYM subunit in the aerobic yeast Yarrowia lipolytica, an established model system to study eukaryotic complex I and complex I linked diseases. We observed assembly of complex I which lacked only subunit NUYM and retained weak interaction with assembly factor N7BML (human NDUFAF2). Absence of NUYM caused distortion of iron sulfur clusters of the electron input domain leading to decreased complex I activity and increased release of reactive oxygen species. We conclude that NUYM has an important stabilizing function for the electron input module of complex I and is essential for proper complex I function.

Micropatterning Facilitates the Long-Term Growth and Analysis of iPSC-Derived Individual Human Neurons and Neuronal Networks

The discovery of induced pluripotent stem cells (iPSCs) and their application to patient-specific disease models offers new opportunities for studying the pathophysiology of neurological disorders. However, current methods for culturing iPSC-derived neuronal cells result in clustering of neurons, which precludes the analysis of individual neurons and defined neuronal networks. To address this challenge, cultures of human neurons on micropatterned surfaces are developed that promote neuronal survival over extended periods of time. This approach facilitates studies of neuronal development, cellular trafficking, and related mechanisms that require assessment of individual neurons and specific network connections. Importantly, micropatterns support the long-term stability of cultured neurons, which enables time-dependent analysis of cellular processes in living neurons. The approach described in this paper allows mechanistic studies of human neurons, both in terms of normal neuronal development and function, as well as time-dependent pathological processes, and provides a platform for testing of new therapeutics in neuropsychiatric disorders.

Mitochondrial Oxidative Phosphorylation System (OXPHOS) Deficits in Schizophrenia: Possible Interactions with Cellular Processes

Mitochondria are key players in the generation and regulation of cellular bioenergetics, producing the majority of adenosine triphosphate molecules by the oxidative phosphorylation system (OXPHOS). Linked to numerous signaling pathways and cellular functions, mitochondria, and OXPHOS in particular, are involved in neuronal development, connectivity, plasticity, and differentiation. Impairments in a variety of mitochondrial functions have been described in different general and psychiatric disorders, including schizophrenia (SCZ), a severe, chronic, debilitating illness that heavily affects the lives of patients and their families. This article reviews findings emphasizing the role of OXPHOS in the pathophysiology of SCZ. Evidence accumulated during the past few decades from imaging, transcriptomic, proteomic, and metabolomic studies points at OXPHOS deficit involvement in SCZ. Abnormalities have been reported in high-energy phosphates generated by the OXPHOS, in the activity of its complexes and gene expression, primarily of complex I (CoI). In addition, cellular signaling such as cAMP/protein kinase A (PKA) and Ca(+2), neuronal development, connectivity, and plasticity have been linked to OXPHOS function and are reported to be impaired in SCZ. Finally, CoI has been shown as a site of interaction for both dopamine (DA) and antipsychotic drugs, further substantiating its role in the pathology of SCZ. Understanding the role of mitochondria and the OXPHOS in particular may encourage new insights into the pathophysiology and etiology of this debilitating disorder.

Resveratrol attenuates oxidative stress in mitochondrial Complex I deficiency: Involvement of SIRT3

The pathophysiological mechanisms underlying Complex I (CI) deficiencies are understood only partially which severely limits the treatment of this common, devastating, mitochondrial disorder. Recently, we have shown that resveratrol (RSV), a natural polyphenol, has beneficial effects on CI deficiency of nuclear origin. Here, we demonstrate that RSV is able to correct the biochemical defect in oxygen consumption in five of thirteen CI-deficient patient cell lines. Other beneficial effects of RSV include a decrease of total intracellular ROS and the up-regulation of the expression of mitochondrial superoxide dismutase (SOD2) protein, a key antioxidant defense enzyme. The molecular mechanisms leading to the up-regulation of SOD2 protein expression by RSV require the estrogen receptor (ER) and the estrogen-related receptor alpha (ERRα). Although RSV increases the level of SOD2 protein in patients' fibroblasts, the enzyme activity is not increased, in contrast to normal fibroblasts. This led us to hypothesize that SOD2 enzyme activity is regulated post-translationally. This regulation involves SIRT3, a mitochondrial NAD(+)-dependent deacetylase and is critically dependent on NAD(+) levels. Taken together, our data show that the metabolic effects of RSV combined with its antioxidant capacities makes RSV particularly interesting as a candidate molecule for the therapy of CI deficiencies.

ROS and ROS-Mediated Cellular Signaling

It has long been recognized that an increase of reactive oxygen species (ROS) can modify the cell-signaling proteins and have functional consequences, which successively mediate pathological processes such as atherosclerosis, diabetes, unchecked growth, neurodegeneration, inflammation, and aging. While numerous articles have demonstrated the impacts of ROS on various signaling pathways and clarify the mechanism of action of cell-signaling proteins, their influence on the level of intracellular ROS, and their complex interactions among multiple ROS associated signaling pathways, the systemic summary is necessary. In this review paper, we particularly focus on the pattern of the generation and homeostasis of intracellular ROS, the mechanisms and targets of ROS impacting on cell-signaling proteins (NF-κB, MAPKs, Keap1-Nrf2-ARE, and PI3K-Akt), ion channels and transporters (Ca(2+) and mPTP), and modifying protein kinase and Ubiquitination/Proteasome System.

cAMP regulates the functional activity, coupling efficiency and structural organization of mammalian FOF1 ATP synthase

The present study shows that in isolated mitochondria and myoblast cultures depletion of cAMP, induced by sAC inhibition, depresses both ATP synthesis and hydrolysis by the FOF1 ATP synthase (complex V) of the oxidative phosphorylation system (OXPHOS). These effects are accompanied by the decrease of the respiratory membrane potential, decreased level of FOF1 connecting subunits and depressed oligomerization of the complex. All these effects of sAC inhibition are prevented by the addition of the membrane-permeant 8-Br-cAMP. These results show, for the first time, that cAMP promotes ATP production by complex V and prevents, at the same time, its detour to a mitochondrial membrane leak conductance, which is involved in cell death.

Saxagliptin: a novel antiparkinsonian approach

The emergence of glucagon-like peptide-1 as a crucial contender in modifying neurodegenerative diseases in the preclinical studies has instigated interest in investigating the antiparkinsonian effect of dipeptidyl peptidase (DPP)-4 inhibition. Notably, saxagliptin (SAX), the DPP-4 inhibitor, recently showed efficacy in ameliorating streptozotocin-induced Alzheimer's disease; however, its effect on Parkinson's disease (PD) has not yet been elucidated. In a rat rotenone (ROT) model, SAX prominently improved motor performance as well as muscle coordination and corrected akinesia. Moreover, SAX preserved substantia nigra pars compacta tyrosine hydroxylase (TH) immunoreactivity while halting the reduction in the striatal TH, dopamine (DA) and complex I. Meanwhile, SAX prevented the ROT-induced increment of striatal DPP-4 and the decline in cAMP, ATP/ADP and brain-derived neurotropic factor levels. Improvement in striatal energy level was associated with partial hindrance of ROT-induced body weight reduction. In addition, through its anti-inflammatory potential, SAX decreased the ROT-induced nuclear factor-κΒ, inducible nitric oxide synthase, tumor necrosis factor-α, intracellular adhesion molecule-1 and myeloperoxidase. The antiapoptotic marker B-cell lymphoma-2 was enhanced by SAX, versus reduction in caspase-3 and its intrinsic apoptotic activator cytochrome C. Furthermore, SAX amended alterations induced by ROT in the thiobarbituric acid reactive substances and the transcriptional factor Nrf-2 level. In conclusion, SAX can be introduced as a novel approach for the management of PD based on the remarkable improvement in motor functions denoting antiparkinsonian efficacy via antioxidant, anti-inflammatory, antiapoptotic, neuroprotective and neurorestorative mechanisms. These effects were linked to DPP-4 inhibition, reduced neurodegeneration and enhanced DA synthesis.

Mitochondrial free radical overproduction due to respiratory chain impairment in the brain of a mouse model of Rett syndrome: protective effect of CNF1

Rett syndrome (RTT) is a pervasive neurodevelopmental disorder mainly caused by mutations in the X-linked MECP2 gene associated with severe intellectual disability, movement disorders, and autistic-like behaviors. Its pathogenesis remains mostly not understood and no effective therapy is available. High circulating levels of oxidative stress markers in patients and the occurrence of oxidative brain damage in MeCP2-deficient mouse models suggest the involvement of oxidative stress in RTT pathogenesis. However, the molecular mechanism and the origin of the oxidative stress have not been elucidated. Here we demonstrate that a redox imbalance arises from aberrant mitochondrial functionality in the brain of MeCP2-308 heterozygous female mice, a condition that more closely recapitulates that of RTT patients. The marked increase in the rate of hydrogen peroxide generation in the brain of RTT mice seems mainly produced by the dysfunctional complex II of the mitochondrial respiratory chain. In addition, both membrane potential generation and mitochondrial ATP synthesis are decreased in RTT mouse brains when succinate, the complex II respiratory substrate, is used as an energy source. Respiratory chain impairment is brain area specific, owing to a decrease in either cAMP-dependent phosphorylation or protein levels of specific complex subunits. Further, we investigated whether the treatment of RTT mice with the bacterial protein CNF1, previously reported to ameliorate the neurobehavioral phenotype and brain bioenergetic markers in an RTT mouse model, exerts specific effects on brain mitochondrial function and consequently on hydrogen peroxide production. In RTT brains treated with CNF1, we observed the reactivation of respiratory chain complexes, the rescue of mitochondrial functionality, and the prevention of brain hydrogen peroxide overproduction. These results provide definitive evidence of mitochondrial reactive oxygen species overproduction in RTT mouse brain and highlight CNF1 efficacy in counteracting RTT-related mitochondrial defects.

Rabies virus phosphoprotein interacts with mitochondrial Complex I and induces mitochondrial dysfunction and oxidative stress

Our previous studies in an experimental model of rabies showed neuronal process degeneration in association with severe clinical disease. Cultured adult rodent dorsal root ganglion neurons infected with challenge virus standard (CVS)-11 strain of rabies virus (RABV) showed axonal swellings and reduced axonal growth with evidence of oxidative stress. We have shown that CVS infection alters a variety of mitochondrial parameters and increases reactive oxygen species (ROS) production and mitochondrial Complex I activity vs. mock infection. We have hypothesized that a RABV protein targets mitochondria and triggers dysfunction. Mitochondrial extracts of mouse neuroblastoma cells were analyzed with a proteomics approach. We have identified peptides belonging to the RABV nucleocapsid protein (N), phosphoprotein (P), and glycoprotein (G), and our data indicate that the extract was most highly enriched with P. P was also detected by immunoblotting in RABV-infected purified mitochondrial extracts and also in Complex I immunoprecipitates from the extracts but not in mock-infected extracts. A plasmid expressing P in cells increased Complex I activity and increased ROS generation, whereas expression of other RABV proteins did not. We have analyzed recombinant plasmids encoding various P gene segments. Expression of a peptide from amino acid 139-172 increased Complex I activity and ROS generation similar to expression of the entire P protein, whereas peptides that did not contain this region did not increase Complex I activity or induce ROS generation. These results indicate that a region of the RABV P interacts with Complex I in mitochondria causing mitochondrial dysfunction, increased generation of ROS, and oxidative stress.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

Intramitochondrial adenylyl cyclase controls the turnover of nuclear-encoded subunits and activity of mammalian complex I of the respiratory chain

In mammalian cells the nuclear-encoded subunits of complex I are imported into mitochondria, where they are assembled with mt-DNA encoded subunits in the complex, or exchanged with pre-existing copies in the complex. The present work shows that in fibroblast cultures inhibition by KH7 of cAMP production in the mitochondrial matrix by soluble adenylyl cyclase (sAC) results in decreased amounts of free non-incorporated nuclear-encoded NDUFS4, NDUFV2 and NDUFA9 subunits of the catalytic moiety and inhibition of the activity of complex I. Addition of permeant 8-Br-cAMP prevents this effect of KH7. KH7 inhibits accumulation in isolated rat-liver mitochondria and incorporation in complex I of "in vitro" produced, radiolabeled NDUFS4 and NDUFV2 subunits. 8-Br-cAMP prevents also this effect of KH7. Use of protease inhibitors shows that intramitochondrial cAMP exerts this positive effect on complex I by preventing digestion of nuclear-encoded subunits by mitochondrial protease(s), whose activity is promoted by KH7 and H89, an inhibitor of PKA.

Whole-mitochondrial genome sequencing in primary open-angle glaucoma using massively parallel sequencing identifies novel and known pathogenic variants

PURPOSE

The aim of this study was to determine whether mutations in mitochondrial DNA play a role in high-pressure primary open-angle glaucoma (OMIM 137760) by analyzing new data from massively parallel sequencing of mitochondrial DNA.

METHODS

Glaucoma patients with high-tension primary open-angle glaucoma and ethnically matched and age-matched control subjects without glaucoma were recruited. The entire human mitochondrial genome was amplified in two overlapping fragments by long-range polymerase chain reaction and used as a template for massively parallel sequencing on an Ion Torrent Personal Genome Machine. All variants were confirmed by conventional Sanger sequencing.

RESULTS

Whole-mitochondrial genome sequencing was performed in 32 patients with primary open-angle glaucoma from India (n = 16) and Ireland (n = 16). In 16 of the 32 patients with primary open-angle glaucoma (50% of cases), there were 22 mitochondrial DNA mutations consisting of 7 novel mutations and 8 previously reported disease-associated sequence variants. Eight of 22 (36.4%) of the mitochondrial DNA mutations were in complex I mitochondrial genes.

CONCLUSION

Massively parallel sequencing using the Ion Torrent Personal Genome Machine with confirmation by Sanger sequencing detected a pathogenic mitochondrial DNA mutation in 50% of the primary open-angle glaucoma cohort. Our findings support the emerging concept that mitochondrial dysfunction results in the development of glaucoma and, more specifically, that complex I defects play a significant role in primary open-angle glaucoma pathogenesis.