Mitochondrial therapeutics in Alzheimer's disease and Parkinson's disease

Sirtuins, a key regulator of ageing and age-related neurodegenerative diseases

Sirtuins are Nicotinamide Adenine Dinucleotide (NAD+) dependent class ІΙΙ histone deacetylases enzymes (HDACs) present from lower to higher organisms such as bacteria (Sulfolobus solfataricus L. major), yeasts (Saccharomyces cerevisiae), nematodes (Caenorhabditis elegans), fruit flies (Drosophila melanogaster), humans (Homo sapiens sapiens), even in plants such as rice (Oryza sativa), thale cress (Arabidopsis thaliana), vine (Vitis vinifera L.) tomato (Solanum lycopersicum). Sirtuins play an important role in the regulation of various vital cellular functions during metabolism and ageing. It also plays a neuroprotective role by modulating several biological pathways such as apoptosis, DNA repair, protein aggregation, and inflammatory processes associated with ageing and neurodegenerative diseases. In this review, we have presented an updated Sirtuins and its role in ageing and age-related neurodegenerative diseases (NDDs). Further, this review also describes the therapeutic potential of Sirtuins and the use of Sirtuins inhibitor/activator for altering the NDDs disease pathology.

Mitochondrial Medicine: A Promising Therapeutic Option Against Various Neurodegenerative Disorders

Abnormal mitochondrial morphology and metabolic dysfunction have been observed in many neurodegenerative disorders (NDDs). Mitochondrial dysfunction can be caused by aberrant mitochondrial DNA, mutant nuclear proteins that interact with mitochondria directly or indirectly, or for unknown reasons. Since mitochondria play a significant role in neurodegeneration, mitochondriatargeted therapies represent a prosperous direction for the development of novel drug compounds that can be used to treat NDDs. This review gives a brief description of how mitochondrial abnormalities lead to various NDDs such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. We further explore the promising therapeutic effectiveness of mitochondria- directed antioxidants, MitoQ, MitoVitE, MitoPBN, and dimebon. We have also discussed the possibility of mitochondrial gene therapy as a therapeutic option for these NDDs.

Differential expression of skeletal muscle mitochondrial proteins in yak, dzo, and cattle: a proteomics-based study

Changes in yak mitochondria by natural selection in a hypoxic environment could be utilized to understand adaptation to low-oxygen conditions. Therefore, the differences in proteome profile of skeletal muscle mitochondria from yak, dzo, and cattle were analyzed by mass spectrometry, which were then classified into 3 groups, comparing between yak and dzo, yak and cattle, and dzo and cattle. 376 unique mitochondrial proteins were identified, including 192, 191, and 281 proteins in the yak-dzo, yak-cattle, and dzo-cattle groups, respectively. NRDP1 and COQ8A were expressed at higher levels in yak and dzo compared to those in cattle, indicating higher endurance capacity of yak and dzo in a low-oxygen environment. Gene Ontology (GO) terms of biological processes were significantly enriched in oxidation-reduction process, and that of molecular functions and cellular component were enriched in oxidoreductase activity and the mitochondrion, respectively. The most significantly affected pathways in Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were Parkinson’s disease, Huntington’s disease, and oxidative phosphorylation between the yak-cattle and dzo-cattle groups; while metabolic pathways, citrate cycle, and carbon metabolism were significantly affected pathways in the yak-dzo group. ATP synthases, MTHFD1, MDH2, and SDHB were the most enriched hub proteins in the protein-protein interaction (PPI) network. These results indicated that mammals living at high altitudes could possibly possess better bioenergy metabolism than those living in the plains. The key proteins identified in the present study may be exploited as candidate proteins for understanding and fine-tuning mammalian adaptation to high altitudes.

High-Resolution Respirometry in Assessment of Mitochondrial Function in Neuroblastoma SH-SY5Y Intact Cells

Mitochondria are organelles with significant cellular functions, especially cellular bioenergetics and apoptosis. They are structural and functional elements of cell respiration with the electron transport system (ETS), whose role is to provide adenosine triphosphate (ATP), used as a source of chemical energy. The Krebs cycle and fatty acid oxidation take place within mitochondria. Other metabolic pathways and cycles include some steps inside and outside the mitochondria (e.g., the urea cycle, steroid biosynthesis, heme biosynthesis, and cardiolipin synthesis). Dysfunction of mitochondria plays a critical role in the pathophysiology of a variety of diseases including degenerative diseases, aging, and cancer, etc. Nowadays the interest of the mitochondrial respiratory function is still increasing due to their importance in the physiology and pathophysiology of an organism. Neuroblastoma cell line SH-SY5Y is widely used as an in vitro model in neurodegenerative diseases, where mitochondrial dysfunction is considered as a key mechanism in pathophysiology of neurodegenerative disorders. This paper gives first insight into the mitochondrial respiration and characterization of SH-SY5Y cells, with basic information of respiration in different coupling control states including ROUTINE, LEAK, and maximal electron transport (ET) capacity.

Modulation of Mitochondrial Dynamics in Neurodegenerative Diseases: An Insight Into Prion Diseases

Mitochondrial dysfunction is a common and prominent feature of prion diseases and other neurodegenerative disorders. Mitochondria are dynamic organelles that constantly fuse with one another and subsequently break apart. Defective or superfluous mitochondria are usually eliminated by a form of autophagy, referred to as mitophagy, to maintain mitochondrial homeostasis. Mitochondrial dynamics are tightly regulated by processes including fusion and fission. Dysfunction of mitochondrial dynamics can lead to the accumulation of abnormal mitochondria and contribute to cellular damage. Neurons are among the cell types that consume the most energy, have a highly complex morphology, and are particularly dependent on mitochondrial functions and dynamics. In this review article, we summarize the molecular mechanisms underlying the mitochondrial dynamics and the regulation of mitophagy and discuss the dysfunction of these processes in the progression of prion diseases and other neurodegenerative disorders. We have also provided an overview of mitochondrial dynamics as a therapeutic target for neurodegenerative diseases.

Abnormal Glucose Metabolism in Alzheimer's Disease: Relation to Autophagy/Mitophagy and Therapeutic Approaches

Diminished glucose metabolism accompanies many neurodegenerative diseases including Alzheimer's disease. An understanding of the relation of these metabolic changes to the disease will enable development of novel therapeutic strategies. Following a metabolic challenge, cells generally conserve energy to preserve viability. This requires activation of many cellular repair/regenerative processes such as mitophagy/autophagy and fusion/fission. These responses may diminish cell function in the long term. Prolonged fission induces mitophagy/autophagy which promotes repair but if prolonged progresses to mitochondrial degradation. Abnormal glucose metabolism alters protein signaling including the release of proteins from the mitochondria or migration of proteins from the cytosol to the mitochondria or nucleus. This overview provides an insight into the different mechanisms of autophagy/mitophagy and mitochondrial dynamics in response to the diminished metabolism that occurs with diseases, especially neurodegenerative diseases such as Alzheimer's disease. The review discusses multiple aspects of mitochondrial responses including different signaling proteins and pathways of mitophagy and mitochondrial biogenesis. Improving cellular bioenergetics and mitochondrial dynamics will alter protein signaling and improve cellular/mitochondrial repair and regeneration. An understanding of these changes will suggest new therapeutic strategies.

Role of SCOX in determination of Drosophila melanogaster lifespan

In man, COX (cytochrome c oxidase) deficiency is reported to be related to mutation of the SCO2 (synthesis of cytochrome c oxidase 2) gene, which encodes one of the copper-donor chaperones involved in the assembly of mitochondrial cytochrome c oxidase. Such COX deficiency due to the genetic condition leads to heart disease and the Leigh syndrome and is frequently fatal in childhood. Synthesis of cytochrome c oxidase X (SCOX) is a Drosophila orthologue of human SCO2. Here, we generated SCOX-knockdown flies and the full length SCOX transgenic flies to investigate the in vivo roles of SCOX. Our results demonstrated knockdown of SCOX gene in all cells and tissues to be associated with lethality at larval or pupal stages and this correlated with a decrease in ATP level. In contrast, the full length SCOX transgenic flies showed a longer lifespan than wild type flies and control flies carrying Act5C-GAL4 alone and this correlated with an increase in ATP level. Finally, when cultured on paraquat-added medium, full length SCOX transgenic flies also exhibited an elongated lifespan. Therefore, we hypothesized that SCOX plays an important role in ATP production and consumption, which helps to prevent production of mitochondrial reactive oxygen species and/or impairment of mitochondrial activity under oxidative stress.

Insulin action in brain regulates systemic metabolism and brain function

Insulin receptors, as well as IGF-1 receptors and their postreceptor signaling partners, are distributed throughout the brain. Insulin acts on these receptors to modulate peripheral metabolism, including regulation of appetite, reproductive function, body temperature, white fat mass, hepatic glucose output, and response to hypoglycemia. Insulin signaling also modulates neurotransmitter channel activity, brain cholesterol synthesis, and mitochondrial function. Disruption of insulin action in the brain leads to impairment of neuronal function and synaptogenesis. In addition, insulin signaling modulates phosphorylation of tau protein, an early component in the development of Alzheimer disease. Thus, alterations in insulin action in the brain can contribute to metabolic syndrome, and the development of mood disorders and neurodegenerative diseases.

The impact of reactive oxygen species and genetic mitochondrial mutations in Parkinson's disease

The exact pathogenesis of Parkinson's disease (PD) is still unknown and proper mechanisms that correspond to the disease remain unidentified. It is understood that PD is age-related; as age increases, the chance of onset responds accordingly. Although there are no current means of curing PD, the understanding of reactive oxygen species (ROS) provides significant insight to possible treatments. Complex I deficiencies of the respiratory chain account for the majority of unfavorable neural apoptosis generation in PD. Dopaminergic neurons are severely damaged as a result of the deficiency. Symptoms such as inhibited cognitive ability and loss of smooth motor function are the results of such impairment. The genetic mutations of Parkinson's related proteins such as PINK1 and LRRK2 contribute to mitochondrial dysfunction which precedes ROS formation. Various pathways are inhibited by these mutations, and inevitably causing neural cell damage. Antioxidants are known to negate the damaging effects of free radical overexpression. This paper expands on the specific impact of mitochondrial genetic change and production of free radicals as well as its correlation to the neurodegeneration in Parkinson's disease.

Mitochondrial dysfunction in psychiatric and neurological diseases: cause(s), consequence(s), and implications of antioxidant therapy

Mitochondrial dysfunction is at the base of development and progression of several psychiatric and neurologic diseases with different etiologies. MtDNA/nDNA mutational damage, failure of endogenous antioxidant defenses, hormonal malfunction, altered membrane permeability, metabolic dysregulation, disruption of calcium buffering capacity and ageing have been found to be the root causes of mitochondrial dysfunction in psychatric and neurodegenerative diseases. However, the overall consequences of mitochondrial dysfunction are only limited to increase in oxidative/nitrosative stress and cellular energy crises. Thus far, extensive efforts have been made to improve mitochondrial function through specific cause-dependent antioxidant therapy. However, owing to complex genetic and interlinked causes of mitochondrial dysfunction, it has not been possible to achieve any common, unique supportive antioxidant therapeutic strategy for the treatment of psychiatric and neurologic diseases. Hence, we propose an antioxidant therapeutic strategy for management of consequences of mitochondrial dysfunction in psychiatric and neurologic diseases. It is expected that this will not only reduces oxidative stress, but also promote anaerobic energy production.

Mitochondrial fusion and fission after spinal sacord injury in rats

Responsible for orchestrating cellular energy production, mitochondria are central to the maintenance of life and the gatekeepers of cell death. Its morphology is dynamic and controlled by continual and balanced fission and fusion events. In this study, we analyzed the mitochondrial dynamics and functions after spinal cord injury in rats and further to discuss the mechanisms of the mitochondria regulated cell injury during SCI. Using adult rat spinal cord injury model, it was found that the absolute number of mitochondria per area was significantly less and the individual mitochondrial cross-sectional area was significantly greater in the neurons of rats in SCI group than in the sham-operated group at 3h and 6h after SCI, and the reverse pattern at 12h and 24h after SCI. The results from Western blot and RT-PCR assays showed that the protein and mRNA levels of mitochondrial fusion-related genes (Mfn1 and Mfn2) decreased and fission-related genes (Drp1 and Fis1) increased at 3h and 6h after SCI. At 12h and 24h after SCI the reverse pattern of Mfn1, Mfn2, Drp1 and Fis1 expression was found. Taken together the results of the present study showed the mitochondrial tendency of elongation and fusion in the injured spinal cord at 3h and 6h after SCI, and the tendency of mitochondrial fission at 12h and 24h after SCI in our SCI models of rat. These findings have important implications for our understanding of the mechanisms of mitochondrial dynamics and functions after SCI injury. And mitochondrial fusion may potentially be used as a target for improving spinal cord function in the first 6h after SCI. Mitochondrial fusion may be inhibited at 12-24h after SCI for improving functional outcomes following SCI.

Hypothalamic inflammation: a double-edged sword to nutritional diseases

The hypothalamus is one of the master regulators of various physiological processes, including energy balance and nutrient metabolism. These regulatory functions are mediated by discrete hypothalamic regions that integrate metabolic sensing with neuroendocrine and neural controls of systemic physiology. Neurons and nonneuronal cells in these hypothalamic regions act supportively to execute metabolic regulations. Under conditions of brain and hypothalamic inflammation, which may result from overnutrition-induced intracellular stresses or disease-associated systemic inflammatory factors, extracellular and intracellular environments of hypothalamic cells are disrupted, leading to central metabolic dysregulations and various diseases. Recent research has begun to elucidate the effects of hypothalamic inflammation in causing diverse components of metabolic syndrome leading to diabetes and cardiovascular disease. These new understandings have provocatively expanded previous knowledge on the cachectic roles of brain inflammatory response in diseases, such as infections and cancers. This review describes the molecular and cellular characteristics of hypothalamic inflammation in metabolic syndrome and related diseases as opposed to cachectic diseases, and also discusses concepts and potential applications of inhibiting central/hypothalamic inflammation to treat nutritional diseases.