A cybrid cell model for the assessment of the link between mitochondrial deficits and sporadic Parkinson's disease

Synucleinopathies: Intrinsic and Extrinsic Factors

α-Synucleinopathies are a group of neurodegenerative disorders characterized by alterations in α-synuclein (α-syn), a protein associated with membrane phospholipids, whose precise function in normal cells is still unknown. These kinds of diseases are caused by multiple factors, but the regulation of the α-syn gene is believed to play a central role in the pathology of these disorders; therefore, the α-syn gene is one of the most studied genes. α-Synucleinopathies are complex disorders that derive from the interaction between genetic and environmental factors. Here, we offer an update on the landscape of the epigenetic regulation of α-syn gene expression that has been linked with α-synucleinopathies. We also delve into the reciprocal influence between epigenetic modifications and other factors related to these disorders, such as posttranslational modifications, microbiota participation, interactions with lipids, neuroinflammation and oxidative stress, to promote α-syn aggregation by acting on the transcription and/or translation of the α-syn gene.

A blood-based marker of mitochondrial DNA damage in Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, and neuroprotective or disease-modifying interventions remain elusive. High-throughput markers aimed at stratifying patients on the basis of shared etiology are required to ensure the success of disease-modifying therapies in clinical trials. Mitochondrial dysfunction plays a prominent role in the pathogenesis of PD. Previously, we found brain region-specific accumulation of mitochondrial DNA (mtDNA) damage in PD neuronal culture and animal models, as well as in human PD postmortem brain tissue. To investigate mtDNA damage as a potential blood-based marker for PD, we describe herein a PCR-based assay (Mito DNADX) that allows for the accurate real-time quantification of mtDNA damage in a scalable platform. We found that mtDNA damage was increased in peripheral blood mononuclear cells derived from patients with idiopathic PD and those harboring the PD-associated leucine-rich repeat kinase 2 (LRRK2) G2019S mutation in comparison with age-matched controls. In addition, mtDNA damage was elevated in non-disease-manifesting LRRK2 mutation carriers, demonstrating that mtDNA damage can occur irrespective of a PD diagnosis. We further established that Lrrk2 G2019S knock-in mice displayed increased mtDNA damage, whereas Lrrk2 knockout mice showed fewer mtDNA lesions in the ventral midbrain, compared with wild-type control mice. Furthermore, a small-molecule kinase inhibitor of LRRK2 mitigated mtDNA damage in a rotenone PD rat midbrain neuron model and in idiopathic PD patient-derived lymphoblastoid cell lines. Quantifying mtDNA damage using the Mito DNADX assay may have utility as a candidate marker of PD and for measuring the pharmacodynamic response to LRRK2 kinase inhibitors.

Cell type and sex specific mitochondrial phenotypes in iPSC derived models of Alzheimer's disease

Introduction

Mitochondrial dysfunction is observed in Alzheimer's disease (AD). Altered mitochondrial respiration, cytochrome oxidase (COX) Vmax, and mitophagy are observed in human subjects and animal models of AD. Models derived from induced pluripotent stem cells (iPSCs) may not recapitulate these phenotypes after reprogramming from differentiated adult cells.

Methods

We examined mitochondrial function across iPSC derived models including cerebral organoids, forebrain neurons, and astrocytes. iPSCs were reprogrammed from fibroblasts either from the University of Kansas Alzheimer's Disease Research Center (KU ADRC) cohort or purchased from WiCell. A total of four non-demented and four sporadic AD iPSC lines were examined. Models were subjected to mitochondrial respiration analysis using Seahorse XF technology, spectrophotometric cytochrome oxidase (COX) Vmax assays, fluorescent assays to determine mitochondrial mass, mitochondrial membrane potential, calcium, mitochondrial dynamics, and mitophagy levels. AD pathological hallmarks were also measured.

Results

iPSC derived neurons and cerebral organoids showed reduced COX Vmax in AD subjects with more profound defects in the female cohort. These results were not observed in astrocytes. iPSC derived neurons and astrocytes from AD subjects had reduced mitochondrial respiration parameters with increased glycolytic flux. iPSC derived neurons and astrocytes from AD subjects showed sex dependent effects on mitochondrial membrane potential, mitochondrial superoxide production, and mitochondrial calcium. iPSC derived neurons from AD subjects had reduced mitochondrial localization in lysosomes with sex dependent effects on mitochondrial mass, while iPSC derived astrocytes from female AD subjects had increased mitochondrial localization to lysosomes. Both iPSC derived neurons and astrocytes from AD subjects showed altered mitochondrial dynamics. iPSC derived neurons had increased secreted Aβ, and sex dependent effects on total APP protein expression. iPSC derived astrocytes showed sex dependent changes in GFAP expression in AD derived cells.

Conclusion

Overall, iPSC derived models from AD subjects show mitochondrial phenotypes and AD pathological hallmarks in a cell type and sex dependent manner. These results highlight the importance of sex as a biological variable in cell culture studies.

Mitochondrial dysfunction in cognitive neurodevelopmental disorders: Cause or effect?

Mitochondria have a crucial role in brain development and neurogenesis, both in embryonic and adult brains. Since the brain is the highest energy consuming organ, it is highly vulnerable to mitochondrial dysfunction. This has been implicated in a range of brain disorders including, neurodevelopmental conditions, psychiatric illnesses, and neurodegenerative diseases. Genetic variations in mitochondrial DNA (mtDNA), and nuclear DNA encoding mitochondrial proteins, have been associated with several cognitive disorders. However, it is not yet clear whether mitochondrial dysfunction is a primary cause of these conditions or a secondary effect. Our review article deals with this topic, and brings out recent advances in mitochondria-oriented therapies. Mitochondrial dysfunction could be involved in the pathogenesis of a subset of disorders involving cognitive impairment. In these patients, mitochondrial dysfunction could be the cause of the condition, rather than the consequence. There are vast areas in this topic that remains to be explored and elucidated.

Studying the effect of alpha-synuclein and Parkinson's disease linked mutants on inter pathway connectivities

Parkinson's disease is a common neurodegenerative disease. The differential expression of alpha-synuclein within Lewy Bodies leads to this disease. Some missense mutations of alpha-synuclein may resultant in functional aberrations. In this study, our objective is to verify the functional adaptation due to early and late-onset mutation which can trigger or control the rate of alpha-synuclein aggregation. In this regard, we have proposed a computational model to study the difference and similarities among the Wild type alpha-synuclein and mutants i.e., A30P, A53T, G51D, E46K, and H50Q. Evolutionary sequence space analysis is also performed in this experiment. Subsequently, a comparative study has been performed between structural information and sequence space outcomes. The study shows the structural variability among the selected subtypes. This information assists inter pathway modeling due to mutational aberrations. Based on the structural variability, we have identified the protein-protein interaction partners for each protein that helps to increase the robustness of the inter-pathway connectivity. Finally, few pathways have been identified from 12 semantic networks based on their association with mitochondrial dysfunction and dopaminergic pathways.

The Role of Mitochondrial Dysfunction in Vascular Disease, Tumorigenesis, and Diabetes

Mitochondrial dysfunction is known to be associated with a wide range of human pathologies, such as cancer, metabolic, and cardiovascular diseases. One of the possible ways of mitochondrial involvement in the cellular damage is excessive production of reactive oxygen and nitrogen species (ROS and RNS) that cannot be effectively neutralized by existing antioxidant systems. In mitochondria, ROS and RNS can contribute to protein and mitochondrial DNA (mtDNA) damage causing failure of enzymatic chains and mutations that can impair mitochondrial function. These processes further lead to abnormal cell signaling, premature cell senescence, initiation of inflammation, and apoptosis. Recent studies have identified numerous mtDNA mutations associated with different human pathologies. Some of them result in imbalanced oxidative phosphorylation, while others affect mitochondrial protein synthesis. In this review, we discuss the role of mtDNA mutations in cancer, diabetes, cardiovascular diseases, and atherosclerosis. We provide a list of currently described mtDNA mutations associated with each pathology and discuss the possible future perspective of the research.

Mitophagy and the Brain

Stress mechanisms have long been associated with neuronal loss and neurodegenerative diseases. The origin of cell stress and neuronal loss likely stems from multiple pathways. These include (but are not limited to) bioenergetic failure, neuroinflammation, and loss of proteostasis. Cells have adapted compensatory mechanisms to overcome stress and circumvent death. One mechanism is mitophagy. Mitophagy is a form of macroautophagy, were mitochondria and their contents are ubiquitinated, engulfed, and removed through lysosome degradation. Recent studies have implicated mitophagy dysregulation in several neurodegenerative diseases and clinical trials are underway which target mitophagy pathways. Here we review mitophagy pathways, the role of mitophagy in neurodegeneration, potential therapeutics, and the need for further study.

Mitochondrial Dysfunction in Parkinson's Disease: Focus on Mitochondrial DNA

Mitochondria, the energy stations of the cell, are the only extranuclear organelles, containing their own (mitochondrial) DNA (mtDNA) and the protein synthesizing machinery. The location of mtDNA in close proximity to the oxidative phosphorylation system of the inner mitochondrial membrane, the main source of reactive oxygen species (ROS), is an important factor responsible for its much higher mutation rate than nuclear DNA. Being more vulnerable to damage than nuclear DNA, mtDNA accumulates mutations, crucial for the development of mitochondrial dysfunction playing a key role in the pathogenesis of various diseases. Good evidence exists that some mtDNA mutations are associated with increased risk of Parkinson’s disease (PD), the movement disorder resulted from the degenerative loss of dopaminergic neurons of substantia nigra. Although their direct impact on mitochondrial function/dysfunction needs further investigation, results of various studies performed using cells isolated from PD patients or their mitochondria (cybrids) suggest their functional importance. Studies involving mtDNA mutator mice also demonstrated the importance of mtDNA deletions, which could also originate from abnormalities induced by mutations in nuclear encoded proteins needed for mtDNA replication (e.g., polymerase γ). However, proteomic studies revealed only a few mitochondrial proteins encoded by mtDNA which were downregulated in various PD models. This suggests nuclear suppression of the mitochondrial defects, which obviously involve cross-talk between nuclear and mitochondrial genomes for maintenance of mitochondrial functioning.

Platelets in Neurodegenerative Conditions-Friend or Foe?

It is now apparent that platelet function is more diverse than originally thought, shifting the view of platelets from blood cells involved in hemostasis and wound healing to major contributors to numerous regulatory processes across different tissues. Given their intriguing ability to store, produce and release distinct subsets of bioactive molecules, including intercellular signaling molecules and neurotransmitters, platelets may play an important role in orchestrating healthy brain function. Conversely, a number of neurodegenerative conditions have recently been associated with platelet dysfunction, further highlighting the tissue-independent role of these cells. In this review we summarize the requirements for platelet-neural cell communication with a focus on neurodegenerative diseases, and discuss the therapeutic potential of healthy platelets and the proteins which they release to counteract these conditions.

The oligosaccharide portion of ganglioside GM1 regulates mitochondrial function in neuroblastoma cells

The crucial role of ganglioside GM1 in the regulation of neural homeostasis has been assessed by several studies. Recently we shed new light on the molecular basis underlying GM1 effects demonstrating that GM1 oligosaccharide directly binds TrkA receptor and triggers MAPK pathway activation leading to neuronal differentiation and protection. Following its exogenous administration, proteomic analysis revealed an increased expression of proteins involved in several biochemical mechanisms, including mitochondrial bioenergetics. Based on these data, we investigated the possible effect of GM1 oligosaccharide administration on mitochondrial function. We show that wild-type Neuro2a cells exposed to GM1 oligosaccharide displayed an increased mitochondrial density and an enhanced mitochondrial activity together with reduced reactive oxygen species levels. Interestingly, using a Neuro2a model of mitochondrial dysfunction, we found an increased mitochondrial oxygen consumption rate as well as increased complex I and II activities upon GM1 oligosaccharide administration. Taken together, our data identify GM1 oligosaccharide as a mitochondrial regulator that by acting at the plasma membrane level triggers biochemical signaling pathway inducing mitochondriogenesis and increasing mitochondrial activity. Although further studies are necessary, the capability to enhance the function of impaired mitochondria points to the therapeutic potential of the GM1 oligosaccharide for the treatment of pathologies where these organelles are compromised, including Parkinson's disease.

Patient-specific neural progenitor cells derived from induced pluripotent stem cells offer a promise of good models for mitochondrial disease

Mitochondria are the primary generators of ATP in eukaryotic cells through the process of oxidative phosphorylation. Mitochondria are also involved in several other important cellular functions including regulation of intracellular Ca²⁺, cell signaling and apoptosis. Mitochondrial dysfunction causes disease and since it is not possible to perform repeated studies in humans, models are essential to enable us to investigate the mechanisms involved. Recently, the discovery of induced pluripotent stem cells (iPSCs), made by reprogramming adult somatic cells (Takahashi and Yamanaka 2006; Yamanaka and Blau 2010), has provided a unique opportunity for studying aspects of disease mechanisms in patient-specific cells and tissues. Reprogramming cells to neuronal lineage such as neural progenitor cells (NPCs) generated from the neural induction of reprogrammed iPSCs can thus provide a useful model for investigating neurological disease mechanisms including those caused by mitochondrial dysfunction. In addition, NPCs display a huge clinical potential in drug screening and therapeutics.

Lipid-based nanodelivery approaches for dopamine-replacement therapies in Parkinson's disease: From preclinical to translational studies

The incidence of Parkinson's disease (PD), the second most common neurodegenerative disorder, has increased exponentially as the global population continues to age. Although the etiological factors contributing to PD remain uncertain, its average incidence rate is reported to be 1% of the global population older than 60 years. PD is primarily characterized by the progressive loss of dopaminergic (DAergic) neurons and/or associated neuronal networks and the subsequent depletion of dopamine (DA) levels in the brain. Thus, DA or levodopa (l-dopa), a precursor of DA, represent cardinal targets for both idiopathic and symptomatic PD therapeutics. While several therapeutic strategies have been investigated over the past decade for their abilities to curb the progression of PD, an effective cure for PD is currently unavailable. Even DA replacement therapy, an effective PD therapeutic strategy that provides an exogenous supply of DA or l-dopa, has been hindered by severe challenges, such as a poor capacity to bypass the blood-brain barrier and inadequate bioavailability. Nevertheless, with recent advances in nanotechnology, several drug delivery systems have been developed to bypass the barriers associated with central nervous system therapeutics. In here, we sought to describe the adapted lipid-based nanodrug delivery systems used in the field of PD therapeutics and their recent advances, with a particular focus placed on DA replacement therapies. This work initially explores the background of PD; offers descriptions of the most recent molecular targets; currently available clinical medications/limitations; an overview of several lipid-based PD nanotherapeutics, functionalized nanoparticles, and technical aspects in brain delivery; and, finally, presents future perspectives to enhance the use of nanotherapeutics in PD treatment.

Creation of Cybrid Cultures Containing mtDNA Mutations m.12315G>A and m.1555G>A, Associated with Atherosclerosis

In the present work, a pilot creation of four cybrid cultures with high heteroplasmy level was performed using mitochondrial genome mutations m.12315G>A and m.1555G>A. According to data of our preliminary studies, the threshold heteroplasmy level of mutation m.12315G>A is associated with atherosclerosis. At the same time, for a mutation m.1555G>A, such a heteroplasmy level is associated with the absence of atherosclerosis. Cybrid cultures were created by fusion of rho0-cells and mitochondria from platelets with a high heteroplasmy level of the investigated mutations. To create rho0-cells, THP-1 culture of monocytic origin was taken. According to the results of the study, two cybrid cell lines containing mutation m.12315G>A with the heteroplasmy level above the threshold value (25% and 44%, respectively) were obtained. In addition, two cybrid cell lines containing mutation m.1555G>A with a high heteroplasmy level (24%) were obtained. Cybrid cultures with mtDNA mutation m.12315G>A can be used to model both the occurrence and development of atherosclerosis in cells and the titration of drug therapy for patients with atherosclerosis. With the help of cybrid cultures containing single nucleotide replacement of mitochondrial genome m.1555G>A, it is possible to develop approaches to the gene therapy of atherosclerosis.

Mitochondrial dysfunction increases fatty acid β-oxidation and translates into impaired neuroblast maturation

The metabolic transition from anaerobic glycolysis and fatty acid β-oxidation to glycolysis coupled to oxidative phosphorylation is a key process for the transition of quiescent neural stem cells to proliferative neural progenitor cells. However, a full characterization of the metabolic shift and the involvement of mitochondria during the last step of neurogenesis, from neuroblasts to neuron maturation, is still elusive. Here, we describe a model of neuroblasts, Neuro2a cells, with impaired differentiation capacity due to mitochondrial dysfunction. Using a detailed biochemical characterization consisting of steady-state metabolomics and metabolic flux analysis, we find increased fatty acid β-oxidation as a peculiar feature of neuroblasts with altered mitochondria. The consequent metabolic switch favors neuroblast proliferation at the expense of neuron maturation.

Mitochondria, OxPhos, and neurodegeneration: cells are not just running out of gas

Mitochondrial respiratory deficiencies have been observed in numerous neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. For decades, these reductions in oxidative phosphorylation (OxPhos) have been presumed to trigger an overall bioenergetic crisis in the neuron, resulting in cell death. While the connection between respiratory defects and neuronal death has never been proven, this hypothesis has been supported by the detection of nonspecific mitochondrial DNA mutations in these disorders. These findings led to the notion that mitochondrial respiratory defects could be initiators of these common neurodegenerative disorders, instead of being consequences of a prior insult, a theory we believe to be misconstrued. Herein, we review the roots of this mitochondrial hypothesis and offer a new perspective wherein mitochondria are analyzed not only from the OxPhos point of view, but also as a complex organelle residing at the epicenter of many metabolic pathways.

Complex spatio-temporal distribution and genomic ancestry of mitochondrial DNA haplogroups in 24,216 Danes

Mitochondrial DNA (mtDNA) haplogroups (hgs) are evolutionarily conserved sets of mtDNA SNP-haplotypes with characteristic geographical distribution. Associations of hgs with disease and physiological characteristics have been reported, but have frequently not been reproducible. Using 418 mtDNA SNPs on the PsychChip (Illumina), we assessed the spatio-temporal distribution of mtDNA hgs in Denmark from DNA isolated from 24,642 geographically un-biased dried blood spots (DBS), collected from 1981 to 2005 through the Danish National Neonatal Screening program. ADMIXTURE was used to establish the genomic ancestry of all samples using a reference of 100K+ autosomal SNPs in 2,248 individuals from nine populations. Median-joining analysis determined that the hgs were highly variable, despite being typically Northern European in origin, suggesting multiple founder events. Furthermore, considerable heterogeneity and variation in nuclear genomic ancestry was observed. Thus, individuals with hg H exhibited 95%, and U hgs 38.2% - 92.5%, Danish ancestry. Significant clines between geographical regions and rural and metropolitan populations were found. Over 25 years, macro-hg L increased from 0.2% to 1.2% (p = 1.1*E-10), and M from 1% to 2.4% (p = 3.7*E-8). Hg U increased among the R macro-hg from 14.1% to 16.5% (p = 1.9*E-3). Genomic ancestry, geographical skewedness, and sub-hg distribution suggested that the L, M and U increases are due to immigration. The complex spatio-temporal dynamics and genomic ancestry of mtDNA in the Danish population reflect repeated migratory events and, in later years, net immigration. Such complexity may explain the often contradictory and population-specific reports of mito-genomic association with disease.

Schizophrenia-associated mt-DNA SNPs exhibit highly variable haplogroup affiliation and nuclear ancestry: Bi-genomic dependence raises major concerns for link to disease

Mitochondria play a significant role in human diseases. However, disease associations with mitochondrial DNA (mtDNA) SNPs have proven difficult to replicate. An analysis of eight schizophrenia-associated mtDNA SNPs, in 23,743 Danes without a psychiatric diagnosis and 2,538 schizophrenia patients, revealed marked inter-allelic differences in mitochondrial haplogroup affiliation and nuclear ancestry. This bi-genomic dependence could entail population stratification. Only two mitochondrial SNPs, m.15043A and m.15218G, were significantly associated with schizophrenia. However, these associations disappeared when corrected for haplogroup affiliation and nuclear ancestry. The extensive bi-genomic dependence documented here is a major concern when interpreting historic, as well as designing future, mtDNA association studies.

Cybrid Models of Pathological Cell Processes in Different Diseases

Modelling of pathological processes in cells is one of the most sought-after technologies of the 21st century. Using models of such processes may help to study the pathogenetic mechanisms of various diseases. The aim of the present study was to analyse the literature, dedicated to obtaining and investigating cybrid models. Besides, the possibility of modeling pathological processes in cells and treatment of different diseases using the models was evaluated. Methods of obtaining Rho0 cell cultures showed that, during their creation, mainly a standard technique, based on the use of mtDNA replication inhibitors (ethidium bromide), was applied. Cybrid lines were usually obtained by PEG fusion. Most frequently, platelets acted as donors of mitochondria. According to the analysis of the literature data, cybrid cell cultures can be modeled to study the dysfunction of the mitochondrial genome and molecular cellular pathological processes. Such models can be very promising for the development of therapeutic approaches to the treatment of various human diseases.

Impairment of mitochondria dynamics by human A53T α-synuclein and rescue by NAP (davunetide) in a cell model for Parkinson's disease

The formation of oligomers and aggregates of overexpressed or mutant α-synuclein play a role in the degeneration of dopaminergic neurons in Parkinson's disease by causing dysfunction of mitochondria, reflected in their disturbed mobility and production of ROS. The mode of action and mechanisms underlying this mitochondrial impairment is still unclear. We have induced stable expression of wild-type, A30P or A53T α-synuclein in neuronally differentiated SH-SY5Y neuroblastoma cells and studied anterograde and retrograde mitochondrial trafficking in this cell model for Parkinson's disease. In contrast to wild-type and A30P, A53T α-synuclein significantly inhibited mitochondrial trafficking, at first retrogradely and in a later stage anterogradely. Accordingly, A53T α-synuclein also caused the highest increase in ROS production in the dysmobilized mitochondria in comparison to wild-type or A30P α-synuclein. Treatment with NAP, the eight amino acid peptide identified as the active component of activity-dependent neuroprotective protein (ADNP), completely annihilated the adverse effects of A53T on mitochondrial dynamics. Our results reveal that A53T α-synuclein (oligomers or aggregates) leads to the inhibition of mitochondrial trafficking, which can be rescued by NAP, suggesting the involvement of microtubule disruption in the pathophysiology of Parkinson's disease.

Mitochondria in Multiple Sclerosis: Molecular Mechanisms of Pathogenesis

Mitochondria, the organelles that function as the powerhouse of the cell, have been increasingly linked to the pathogenesis of many neurological disorders, including multiple sclerosis (MS). MS is a chronic inflammatory demyelinating disease of the central nervous system (CNS) and a leading cause of neurological disability in young adults in the western world. Its etiology remains unknown, and while the inflammatory component of MS has been heavily investigated and targeted for therapeutic intervention, the failure of remyelination and the process of axonal degeneration are still poorly understood. Recent studies suggest a role of mitochondrial dysfunction in the neurodegenerative aspects of MS. This review is focused on mitochondrial functions under physiological conditions and the consequences of mitochondrial alterations in various CNS disorders. Moreover, we summarize recent findings linking mitochondrial dysfunction to MS and discuss novel therapeutic strategies targeting mitochondria-related pathways as well as emerging experimental approaches for modeling mitochondrial disease.