In aging, the vulnerability of rat brain mitochondria is enhanced due to reduced level of 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNP) and subsequently increased permeability transition in brain mitochondria in old animals

Targeting Mitochondria to Control Ageing and Senescence

Ageing is accompanied by a progressive impairment of cellular function and a systemic deterioration of tissues and organs, resulting in increased vulnerability to multiple diseases. Here, we review the interplay between two hallmarks of ageing, namely, mitochondrial dysfunction and cellular senescence. The targeting of specific mitochondrial features in senescent cells has the potential of delaying or even reverting the ageing process. A deeper and more comprehensive understanding of mitochondrial biology in senescent cells is necessary to effectively face this challenge. Here, we discuss the main alterations in mitochondrial functions and structure in both ageing and cellular senescence, highlighting the differences and similarities between the two processes. Moreover, we describe the treatments available to target these pathways and speculate on possible future directions of anti-ageing and anti-senescence therapies targeting mitochondria.

The Improvement of Functional State of Brain Mitochondria with Astaxanthin in Rats after Heart Failure

The relationship between neurological damage and cardiovascular disease is often observed. This type of damage is both a cause and an effect of cardiovascular disease. Mitochondria are the key organelles of the cell and are primarily subject to oxidative stress. Mitochondrial dysfunctions are involved in the etiology of various diseases. A decrease in the efficiency of the heart muscle can lead to impaired blood flow and decreased oxygen supply to the brain. Astaxanthin (AST), a marine-derived xanthophyll carotenoid, has multiple functions and its effects have been shown in both experimental and clinical studies. We investigated the effects of AST on the functional state of brain mitochondria in rats after heart failure. Isoproterenol (ISO) was used to cause heart failure. In the present study, we found that ISO impaired the functional state of rat brain mitochondria (RBM), while the administration of AST resulted in an improvement in mitochondrial efficiency. The respiratory control index (RCI) in RBM decreased with the use of ISO, while AST administration led to an increase in this parameter. Ca²⁺ retention capacity (CRC) decreased in RBM isolated from rat brain after ISO injection, and AST enhanced CRC in RBM after heart failure. The study of changes in the content of regulatory proteins such as adenine nucleotide translocase 1 and 2 (ANT1/2), voltage dependent anion channel (VDAC), and cyclophilin D (CyP-D) of mitochondrial permeability transition pore (mPTP) showed that ISO reduced their level, while AST restored the content of these proteins almost to the control value. In general, AST improves the functional state of mitochondria and can be considered as a prophylactic drug in various therapeutic approaches.

Molecular and cellular mechanisms leading to catatonia: an integrative approach from clinical and preclinical evidence

This review aims to describe the clinical spectrum of catatonia, in order to carefully assess the involvement of astrocytes, neurons, oligodendrocytes, and microglia, and articulate the available preclinical and clinical evidence to achieve a translational understanding of the cellular and molecular mechanisms behind this disorder. Catatonia is highly common in psychiatric and acutely ill patients, with prevalence ranging from 7.6% to 38%. It is usually present in different psychiatric conditions such as mood and psychotic disorders; it is also a consequence of folate deficiency, autoimmunity, paraneoplastic disorders, and even autistic spectrum disorders. Few therapeutic options are available due to its complexity and poorly understood physiopathology. We briefly revisit the traditional treatments used in catatonia, such as antipsychotics, electroconvulsive therapy, and benzodiazepines, before assessing novel therapeutics which aim to modulate molecular pathways through different mechanisms, including NMDA antagonism and its allosteric modulation, and anti-inflammatory drugs to modulate microglia reaction and mitigate oxidative stress, such as lithium, vitamin B12, and NMDAr positive allosteric modulators.

The inhibitory effects of Dulaglutide on cellular senescence against high glucose in human retinal endothelial cells

Diabetic nephropathy is one of the most important chronic microvascular complications of diabetes, and its main feature is diabetic glomerulosclerosis. Endothelial sirtuin 1 (SIRT1) expression is related to aging, and reducing SIRT1 expression promotes endothelial cell aging. Plasminogen activator inhibitor-1 (PAI-1) can be synthesized in a variety of cells, such as endothelial cells. Dulaglutide is a glucagon-like peptide-1 (GLP-1) drug, and it can activate the GLP-1 receptor and promote the conversion of intracellular adenosine triphosphate to adenylate cyclase, thereby activating phosphokinase A, and regulating blood glucose levels effectively in the body. We analyzed the effects of Dulaglutide on inhibiting cell senescence by studying the effects of its different concentrations on telomerase activity and senescence-related gene expression. Our results suggest that Dulaglutide can alleviate high-glucose-induced oxidative stress in human retinal endothelial cells by restoring the expressions of SIRT1 and endothelial nitric oxide synthase (eNOS), thereby inhibiting the expression of PAI-1, and restoring telomerase activity. This suggests that the activity of retinal endothelial cells can be controlled by regulating the expression of SIRT1, so as to achieve the effect of treating diabetic retinopathy.

Alcohol-Induced Neuroinflammatory Response and Mitochondrial Dysfunction on Aging and Alzheimer's Disease

Mitochondria are essential organelles central to various cellular functions such as energy production, metabolic pathways, signaling transduction, lipid biogenesis, and apoptosis. In the central nervous system, neurons depend on mitochondria for energy homeostasis to maintain optimal synaptic transmission and integrity. Deficiencies in mitochondrial function, including perturbations in energy homeostasis and mitochondrial dynamics, contribute to aging, and Alzheimer's disease. Chronic and heavy alcohol use is associated with accelerated brain aging, and increased risk for dementia, especially Alzheimer's disease. Furthermore, through neuroimmune responses, including pro-inflammatory cytokines, excessive alcohol use induces mitochondrial dysfunction. The direct and indirect alcohol-induced neuroimmune responses, including pro-inflammatory cytokines, are critical for the relationship between alcohol-induced mitochondrial dysfunction. In the brain, alcohol activates microglia and increases inflammatory mediators that can impair mitochondrial energy production, dynamics, and initiate cell death pathways. Also, alcohol-induced cytokines in the peripheral organs indirectly, but synergistically exacerbate alcohol's effects on brain function. This review will provide recent and advanced findings focusing on how alcohol alters the aging process and aggravates Alzheimer's disease with a focus on mitochondrial function. Finally, we will contextualize these findings to inform clinical and therapeutic approaches towards Alzheimer's disease.

NAD(H) Regulates the Permeability Transition Pore in Mitochondria through an External Site

The opening of the permeability transition pore (mPTP) in mitochondria initiates cell death in numerous diseases. The regulation of mPTP by NAD(H) in the mitochondrial matrix is well established; however, the role of extramitochondrial (cytosolic) NAD(H) is still unclear. We studied the effect of added NADH and NAD⁺ on: (1) the Ca²⁺-retention capacity (CRC) of isolated rat liver, heart, and brain mitochondria; (2) the Ca²⁺-dependent mitochondrial swelling in media whose particles can (KCl) or cannot (sucrose) be extruded from the matrix by mitochondrial carriers; (3) the Ca²⁺-dependent mitochondrial depolarization and the release of entrapped calcein from mitochondria of permeabilized hepatocytes; and (4) the Ca²⁺-dependent mitochondrial depolarization and subsequent repolarization. NADH and NAD⁺ increased the CRC of liver, heart, and brain mitochondria 1.5-2.5 times, insignificantly affecting the rate of Ca²⁺-uptake and the free Ca²⁺ concentration in the medium. NAD(H) suppressed the Ca²⁺-dependent mitochondrial swelling both in KCl- and sucrose-based media but did not induce the contraction and repolarization of swollen mitochondria. By contrast, EGTA caused mitochondrial repolarization in both media and the contraction in KCl-based medium only. NAD(H) delayed the Ca²⁺-dependent depolarization and the release of calcein from individual mitochondria in hepatocytes. These data unambiguously demonstrate the existence of an external NAD(H)-dependent site of mPTP regulation.

Sirt3 increases CNPase enzymatic activity through deacetylation and facilitating substrate accessibility

Myocardial 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) metabolizes a nucleoside 2',3'-cyclic phosphate to a nucleoside 2'-phosphate. Recently, the roles of CNPase in the pathophysiological processes of heart failure have emerged. The mitochondrial acylome subjected to SIRT3 regulation give us comprehensive understanding of acylation modifications to a vast array of protein targets, and the list of acetylated mitochondrial proteins is still growing. However, it remains elusive whether CNPase is subjected to the regulation of acetylation and deacetylation, and the effects of which on CNPase enzymatic activity are still unknown. In this study, the mitochondrial distribution of CNPase was identified by immunofluorescence and cytosol/mitochondria fractioning. The immunofluorescence staining pattern of CNPase and Sirt3 overlapped on the same focal plane. Moreover, Sirt3 associates directly with CNPase, and the CNPase enzymatic activity was subjected to Sirt3 activity. Then biochemical methods using acetic anhydride was employed to acetylate the CNPase proteins, the enzymatic activity of CNPase decreased. Furthermore, co-immunoprecipitation coupled mass spectrometry identifies K196, K379, K128 as the main acetylation sites. Molecular dynamic simulation shows that acetylation modification suppressed the CNPase enzymatic activity through decreasing the opening probability of the binding pocket and restricting substrate accessibility. Together with these findings, this study reveals a molecular mechanism underlying Sirt3 regulating CNPase enzymatic activity, and suggests that targeting CNPase's post-translational modifications represents a promising therapeutic strategy.

Genes associated with amyloid-beta-induced inflammasome-mediated neuronal death identified using functional gene trap mutagenesis approach

Alzheimer's disease is an irreversible neurodegenerative disease, which accounts for most dementia cases. Neuroinflammation is increasingly recognised for its roles in Alzheimer's disease pathogenesis which, in part, links amyloid-beta to neuronal death. Neuroinflammatory signalling can be exhibited by neurons themselves, potentially leading to widespread neuronal cell death, although neuroinflammation is commonly associated with glial cells. The presence of the inflammasomes such as nucleotide-binding leucine-rich repeat receptors protein 1 in neurons accelerates amyloid-beta -induced neuroinflammation and has been shown to trigger neuronal pyroptosis in murine Alzheimer's disease models. However, the pathways involved in amyloid-beta activation of inflammasomes have yet to be elucidated. In this study, a gene trap mutagenesis approach was utilised to resolve the genes functionally involved in inflammasome signalling within neurons, and the mechanism behind amyloid-beta-induced neuronal death. The results indicate that amyloid-beta significantly accelerated neuroinflammatory cell death in the presence of a primed inflammasome (the NLR family pyrin domain-containing 1). The mutagenesis screen discovered the atypical mitochondrial Ras homolog family member T1 as a significant contributor to amyloid-beta-induced inflammasome -mediated neuronal death. The mutagenesis screen also identified two genes involved in transforming growth factor beta signalling, namely Transforming Growth Factor Beta Receptor 1 and SNW domain containing 1. Additionally, a gene associated with cytoskeletal reorganisation, SLIT-ROBO Rho GTPase Activating Protein 3 was found to be neuroprotective. In conclusion, these genes could play important roles in inflammasome signalling in neurons, which makes them promising therapeutic targets for future drug development against neuroinflammation in Alzheimer's disease.

Melatonin as a Potential Multitherapeutic Agent

Melatonin (N-acetyl-5-methoxytryptamine, MEL) is a hormone produced by the pineal gland that was discovered many years ago. The physiological roles of this hormone in the body are varied. The beneficial effects of MEL administration may be related to its influence on mitochondrial physiology. Mitochondrial dysfunction is considered an important factor in various physiological and pathological processes, such as the development of neurodegenerative and cardiovascular diseases, diabetes, various forms of liver disease, skeletal muscle disorders, and aging. Mitochondrial dysfunction induces an increase in the permeability of the inner membrane, which leads to the formation of a permeability transition pore (mPTP) in the mitochondria. The long-term administration of MEL has been shown to improve the functional state of mitochondria and inhibit the opening of the mPTP during aging. It is known that MEL is able to suppress the initiation, progression, angiogenesis, and metastasis of cancer as well as the sensitization of malignant cells to conventional chemotherapy and radiation therapy. This review summarizes the studies carried out by our group on the combined effect of MEL with chemotherapeutic agents (retinoic acid, cytarabine, and navitoclax) on the HL-60 cells used as a model of acute promyelocytic leukemia. Data on the effects of MEL on oxidative stress, aging, and heart failure are also reported.

Mitochondrial Permeability Transition: A Pore Intertwines Brain Aging and Alzheimer's Disease

Advanced age is the greatest risk factor for aging-related brain disorders including Alzheimer's disease (AD). However, the detailed mechanisms that mechanistically link aging and AD remain elusive. In recent years, a mitochondrial hypothesis of brain aging and AD has been accentuated. Mitochondrial permeability transition pore (mPTP) is a mitochondrial response to intramitochondrial and intracellular stresses. mPTP overactivation has been implicated in mitochondrial dysfunction in aging and AD brains. This review summarizes the up-to-date progress in the study of mPTP in aging and AD and attempts to establish a link between brain aging and AD from a perspective of mPTP-mediated mitochondrial dysfunction.

Changing Functional Signatures of Microglia along the Axis of Brain Aging

Microglia, the innate immune cells of the brain, are commonly perceived as resident macrophages of the central nervous system (CNS). This definition, however, requires further specification, as under healthy homeostatic conditions, neither morphological nor functional properties of microglia mirror those of classical macrophages. Indeed, microglia adapt exceptionally well to their microenvironment, becoming a legitimate member of the cellular brain architecture. The ramified or surveillant microglia in the young adult brain are characterized by specific morphology (small cell body and long, thin motile processes) and physiology (a unique pattern of Ca²⁺ signaling, responsiveness to various neurotransmitters and hormones, in addition to classic “immune” stimuli). Their numerous physiological functions far exceed and complement their immune capabilities. As the brain ages, the respective changes in the microglial microenvironment impact the functional properties of microglia, triggering further rounds of adaptation. In this review, we discuss the recent data showing how functional properties of microglia adapt to age-related changes in brain parenchyma in a sex-specific manner, with a specific focus on early changes occurring at middle age as well as some strategies counteracting the aging of microglia.

Comparison of Effects of Metformin, Phenformin, and Inhibitors of Mitochondrial Complex I on Mitochondrial Permeability Transition and Ischemic Brain Injury

Damage to cerebral mitochondria, particularly opening of mitochondrial permeability transition pore (MPTP), is a key mechanism of ischemic brain injury, therefore, modulation of MPTP may be a potential target for a neuroprotective strategy in ischemic brain pathologies. The aim of this study was to investigate whether biguanides-metformin and phenformin as well as other inhibitors of Complex I of the mitochondrial electron transfer system may protect against ischemia-induced cell death in brain slice cultures by suppressing MPTP, and whether the effects of these inhibitors depend on the age of animals. Experiments were performed on brain slice cultures prepared from 5-7-day (premature) and 2-3-month old (adult) rat brains. In premature brain slice cultures, simulated ischemia (hypoxia plus deoxyglucose) induced necrosis whereas in adult rat brain slice cultures necrosis was induced by hypoxia alone and was suppressed by deoxyglucose. Phenformin prevented necrosis induced by simulated ischemia in premature and hypoxia-induced-in adult brain slices, whereas metformin was protective in adult brain slices cultures. In premature brain slices, necrosis was also prevented by Complex I inhibitors rotenone and amobarbital and by MPTP inhibitor cyclosporine A. The latter two inhibitors were protective in adult brain slices as well. Short-term exposure of cultured neurons to phenformin, metformin and rotenone prevented ionomycin-induced MPTP opening in intact cells. The data suggest that, depending on the age, phenformin and metformin may protect the brain against ischemic damage possibly by suppressing MPTP via inhibition of mitochondrial Complex I.

The Effects of PK11195 and Protoporphyrin IX Can Modulate Chronic Alcohol Intoxication in Rat Liver Mitochondria under the Opening of the Mitochondrial Permeability Transition Pore

Decades of active research have shown that mitochondrial dysfunction, the associated oxidative stress, impaired anti-stress defense mechanisms, and the activation of the proapoptotic signaling pathways underlie pathological changes in organs and tissues. Pathologies caused by alcohol primarily affect the liver. Alcohol abuse is the cause of many liver diseases, such as steatosis, alcoholic steatohepatitis, fibrosis, cirrhosis, and, potentially, hepatocellular cancer. In this study, the effect of chronic alcohol exposure on rat liver mitochondria was investigated. We observed an ethanol-induced increase in sensitivity to calcium, changes in the level of protein kinase Akt and GSK-3β phosphorylation, an induction of the mitochondrial permeability transition pore (mPTP), and strong alterations in the expression of mPTP regulators. Moreover, we also showed an enhanced effect of PK11195 and PPIX, on the parameters of the mPTP opening in rat liver mitochondria (RLM) isolated from ethanol-treated rats compared to the RLM from control rats. We suggest that the results of this study could help elucidate the mechanisms of chronic ethanol action on the mitochondria and contribute to the development of new therapeutic strategies for treating the effects of ethanol-related diseases.

The Functions of Mitochondrial 2',3'-Cyclic Nucleotide-3'-Phosphodiesterase and Prospects for Its Future

2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNPase) is a myelin-associated enzyme that catalyzes the phosphodiester hydrolysis of 2’,3’-cyclic nucleotides to 2’-nucleotides. However, its presence is also found in unmyelinated cells and other cellular structures. Understanding of its specific physiological functions, particularly in unmyelinated cells, is still incomplete. This review concentrates on the role of mitochondrial CNPase (mtCNPase), independent of myelin. mtCNPase is able to regulate the functioning of the mitochondrial permeability transition pore (mPTP), and thus is involved in the mechanisms of cell death, both apoptosis and necrosis. Its participation in the development of various diseases and pathological conditions, such as aging, heart disease and alcohol dependence, is also reviewed. As such, mtCNPase can be considered as a potential target for the development of therapeutic strategies in the treatment of mitochondria-related diseases.

The need to incorporate aged animals into the preclinical modeling of neurological conditions

Neurological conditions such as traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease are serious clinical problems that affect millions of people worldwide. The majority of clinical trials for these common conditions have failed, and there is a critical need to understand why treatments in preclinical animal models do not translate to patients. Many patients with these conditions are middle-aged or older, however, the majority of preclinical studies have used only young-adult animals. Considering that aging involves biological changes that are relevant to the pathobiology of neurological diseases, the lack of aged subjects in preclinical research could contribute to translational failures. This paper details how aging affects biological processes involved in neurological conditions, and reviews aging research in the context of traumatic brain injury, stroke, Parkinson's disease, epilepsy, multiple sclerosis, and Alzheimer's disease. We conclude that aging is an important, but often overlooked, factor that influences biology and outcomes in neurological conditions, and provide suggestions to improve our understanding and treatment of these diseases in aged patients.

The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process

The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca²⁺-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca²⁺ increased in both PMCA-deficient lines affecting the expression of several Ca²⁺-associated proteins, i.e., sarco/endoplasmic Ca²⁺-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP₃Rs, and certain types of voltage-gated Ca²⁺ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.

Candesartan Neuroprotection in Rat Primary Neurons Negatively Correlates with Aging and Senescence: a Transcriptomic Analysis

Preclinical experiments and clinical trials demonstrated that angiotensin II AT₁ receptor overactivity associates with aging and cellular senescence and that AT₁ receptor blockers (ARBs) protect from age-related brain disorders. In a primary neuronal culture submitted to glutamate excitotoxicity, gene set enrichment analysis (GSEA) revealed expression of several hundred genes altered by glutamate and normalized by candesartan correlated with changes in expression in Alzheimer's patient's hippocampus. To further establish whether our data correlated with gene expression alterations associated with aging and senescence, we compared our global transcriptional data with additional published datasets, including alterations in gene expression in the neocortex and cerebellum of old mice, human frontal cortex after age of 40, gene alterations in the Werner syndrome, rodent caloric restriction, Ras and oncogene-induced senescence in fibroblasts, and to tissues besides the brain such as the muscle and kidney. The most significant and enriched pathways associated with aging and senescence were positively correlated with alterations in gene expression in glutamate-injured neurons and, conversely, negatively correlated when the injured neurons were treated with candesartan. Our results involve multiple genes and pathways, including CAV1, CCND1, CDKN1A, CHEK1, ICAM1, IL-1B, IL-6, MAPK14, PTGS2, SERPINE1, and TP53, encoding proteins associated with aging and senescence hallmarks, such as inflammation, oxidative stress, cell cycle and mitochondrial function alterations, insulin resistance, genomic instability including telomere shortening and DNA damage, and the senescent-associated secretory phenotype. Our results demonstrate that AT₁ receptor blockade ameliorates central mechanisms of aging and senescence. Using ARBs for prevention and treatment of age-related disorders has important translational value.

Simultaneous alterations of oligodendrocyte-specific CNP, astrocyte-specific AQP4 and neuronal NF-L demarcate ischemic tissue after experimental stroke in mice

Ischemic stroke not only affects neurons, but also glial and vascular elements. The development of novel neuroprotective strategies thus requires an improved pathophysiological understanding of ischemia-affected cell types that comprise the 'neurovascular unit' (NVU). To explore spatiotemporal alterations of oligodendrocytes, astrocytes and neurons after experimental ischemic stroke, we applied a permanent middle cerebral artery occlusion model in mice for 4 and 24 h. Using fluorescence microscopy, the oligodendrocyte marker 2',3'-cyclic nucleotide phosphodiesterase (CNP), the neuronal neurofilament light chain (NF-L) and the astroglial aquaporin-4 (AQP4) were analyzed in regional relation to one another. Immunofluorescence intensities of CNP and NF-L were simultaneously increased in the ischemic neocortex and striatum. AQP4 immunoreactivity was decreased in the ischemic striatum, which represents the initial and potentially strongest affected site of infarction. The more distant ischemic neocortex and infarct border zones exhibited areas with alternately increased or decreased AQP4 immunoreactivity, leading to an increase of fluorescence intensity in total. Further, deformed CNP-immunopositive processes were found around axonal spheroids, indicating a combined affection of oligodendrocytes and neurons due to ischemia. Importantly, altered AQP4 immunosignals were not limited to the ischemic core, but were also detectable in penumbral areas. This applies for CNP and NF-L also, since altered immunosignals of all three markers coincided regionally at both time points. In conclusion, the present study provides evidence for a simultaneous affection of oligodendrocytes, astrocytes and neurons after experimental focal cerebral ischemia. Consequently, CNP, AQP4 and NF-L immunofluorescence alterations can be utilized to identify ischemia-affected tissue. The simultaneity of the described alterations further strengthens the concept of interdependent NVU components and distinguishes NF-L, CNP and AQP4 as highly ischemia-sensitive elements. Consequently, future therapeutic approaches might influence stroke evolution via strategies simultaneously addressing both neuronal and glial functions.

Proteomic Analysis of Mouse Brain Subjected to Spaceflight

There is evidence that spaceflight poses acute and late risks to the central nervous system. To explore possible mechanisms, the proteomic changes following spaceflight in mouse brain were characterized. Space Shuttle Atlantis (STS-135) was launched from the Kennedy Space Center (KSC) on a 13-day mission. Within 3–5 h after landing, brain tissue was collected to evaluate protein expression profiles using quantitative proteomic analysis. Our results showed that there were 26 proteins that were significantly altered after spaceflight in the gray and/or white matter. While there was no overlap between the white and gray matter in terms of individual proteins, there was overlap in terms of function, synaptic plasticity, vesical activity, protein/organelle transport, and metabolism. Our data demonstrate that exposure to the spaceflight environment induces significant changes in protein expression related to neuronal structure and metabolic function. This might lead to a significant impact on brain structural and functional integrity that could affect the outcome of space missions.

Possible Involvement of 2',3'-Cyclic Nucleotide-3'-Phosphodiesterase in the Protein Phosphorylation-Mediated Regulation of the Permeability Transition Pore

Calcium as a secondary messenger regulates the phosphorylation of several membrane-bound proteins in brain and liver mitochondria. Regulation of the activity of different protein kinases and phosphatases by Ca²⁺ occurs through its binding with calmodulin. The protein phosphorylation is strongly dependent on the Ca²⁺-induced mitochondrial permeability transition pore (mPTP) opening. 2′,3′-Cyclic nucleotide-3′-phosphodiesterase (CNPase) was phosphorylated by protein kinases A and C. CNPase and melatonin (MEL) might interact with calmodulin. The effects of the calmodulin antagonist calmidazolium and the inhibitor of protein kinase A H89 on mPTP opening in rat brain mitochondria of male Wistar rats were investigated. In addition, the role of CNPase, serine/threonine kinases, and MEL in the mPTP opening was examined. The anti-CNPase antibody added to rat brain mitochondria (RBM) reduced the content of CNPase in mitochondria. The threshold [Ca²⁺] decreased, and mitochondrial swelling was accelerated in the presence of the anti-CNPase antibody. H89 enhanced the effect of anti-CNPase antibody and accelerated the swelling of mitochondria, while CmZ abolished the effect of anti-CNPase antibody under mPTP opening. The levels of phospho-Akt and phospho-GSK3β increased, while the MEL content did not change. It can be assumed that CNPase may be involved in the regulation of these kinases, which in turn plays an important role in mPTP functioning.

Mitochondria and aging: A role for the mitochondrial transition pore?

The cellular mechanisms responsible for aging are poorly understood. Aging is considered as a degenerative process induced by the accumulation of cellular lesions leading progressively to organ dysfunction and death. The free radical theory of aging has long been considered the most relevant to explain the mechanisms of aging. As the mitochondrion is an important source of reactive oxygen species (ROS), this organelle is regarded as a key intracellular player in this process and a large amount of data supports the role of mitochondrial ROS production during aging. Thus, mitochondrial ROS, oxidative damage, aging, and aging-dependent diseases are strongly connected. However, other features of mitochondrial physiology and dysfunction have been recently implicated in the development of the aging process. Here, we examine the potential role of the mitochondrial permeability transition pore (mPTP) in normal aging and in aging-associated diseases.

Effect of Melatonin on Rat Heart Mitochondria in Acute Heart Failure in Aged Rats

Excessive generation of reactive oxygen species (ROS) in mitochondria and the opening of the nonselective mitochondrial permeability transition pore are important factors that promote cardiac pathologies and dysfunction. The hormone melatonin (MEL) is known to improve the functional state of mitochondria via an antioxidant effect. Here, the effect of MEL administration on heart mitochondria from aged rats with acute cardiac failure caused by isoprenaline hydrochloride (ISO) was studied. A histological analysis revealed that chronic intake of MEL diminished the age-dependent changes in the structure of muscle fibers of the left ventricle, muscle fiber swelling, and injury zones characteristic of acute cardiac failure caused by ISO. In acute heart failure, the respiratory control index (RCI) and the Ca²⁺ retention capacity in isolated rat heart mitochondria (RHM) were reduced by 30% and 40%, respectively, and mitochondrial swelling increased by 34%. MEL administration abolished the effect of ISO. MEL partially prevented ISO-induced changes at the subunit level of respiratory complexes III and V and drastically decreased the expression of complex I subunit NDUFB8 both in control RHM and in RHM treated with ISO, which led to the inhibition of ROS production. MEL prevents the mitochondrial dysfunction associated with heart failure caused by ISO. It was shown that the level of 2′,3′-cyclicnucleotide-3′-phosphodiasterase (CNPase), which is capable of protecting cells in aging, increased in acute heart failure. MEL also retained the CNPase content in RHM both in control experiments and after ISO-induced heart damage. We concluded that an increase in the CNPase level promotes cardioprotection.

Mitochondria as pharmacological targets in Down syndrome

Mitochondria play a pivotal role in cellular energy-generating processes and are considered master regulators of cell life and death fate. Mitochondrial function integrates signalling networks in several metabolic pathways controlling neurogenesis and neuroplasticity. Indeed, dysfunctional mitochondria and mitochondrial-dependent activation of intracellular stress cascades are critical initiating events in many human neurodegenerative or neurodevelopmental diseases including Down syndrome (DS). It is well established that trisomy of human chromosome 21 can cause DS. DS is associated with neurodevelopmental delay, intellectual disability and early neurodegeneration. Recently, molecular mechanisms responsible for mitochondrial damage and energy deficits have been identified and characterized in several DS-derived human cells and animal models of DS. Therefore, therapeutic strategies targeting mitochondria could have great potential for new treatment regimens in DS. The purpose of this review is to highlight recent studies concerning mitochondrial impairment in DS, focusing on alterations of the molecular pathways controlling mitochondrial function. We will also discuss the effects and molecular mechanisms of naturally occurring and chemically synthetized drugs that exert neuroprotective effects through modulation of mitochondrial function and attenuation of oxidative stress. These compounds might represent novel therapeutic tools for the modulation of energy deficits in DS.

Multiscale network modeling of oligodendrocytes reveals molecular components of myelin dysregulation in Alzheimer's disease

BACKGROUND

Oligodendrocytes (OLs) and myelin are critical for normal brain function and have been implicated in neurodegeneration. Several lines of evidence including neuroimaging and neuropathological data suggest that Alzheimer's disease (AD) may be associated with dysmyelination and a breakdown of OL-axon communication.

METHODS

In order to understand this phenomenon on a molecular level, we systematically interrogated OL-enriched gene networks constructed from large-scale genomic, transcriptomic and proteomic data obtained from human AD postmortem brain samples. We then validated these networks using gene expression datasets generated from mice with ablation of major gene expression nodes identified in our AD-dysregulated networks.

RESULTS

The robust OL gene coexpression networks that we identified were highly enriched for genes associated with AD risk variants, such as BIN1 and demonstrated strong dysregulation in AD. We further corroborated the structure of the corresponding gene causal networks using datasets generated from the brain of mice with ablation of key network drivers, such as UGT8, CNP and PLP1, which were identified from human AD brain data. Further, we found that mice with genetic ablations of Cnp mimicked aspects of myelin and mitochondrial gene expression dysregulation seen in brain samples from patients with AD, including decreased protein expression of BIN1 and GOT2.

CONCLUSIONS

This study provides a molecular blueprint of the dysregulation of gene expression networks of OL in AD and identifies key OL- and myelination-related genes and networks that are highly associated with AD.

Brain aging and neurodegeneration: from a mitochondrial point of view

Aging is defined as a progressive time-related accumulation of changes responsible for or at least involved in the increased susceptibility to disease and death. The brain seems to be particularly sensitive to the aging process since the appearance of neurodegenerative diseases, including Alzheimer's disease, is exponential with the increasing age. Mitochondria were placed at the center of the 'free-radical theory of aging', because these paramount organelles are not only the main producers of energy in the cells, but also to main source of reactive oxygen species. Thus, in this review, we aim to look at brain aging processes from a mitochondrial point of view by asking: (i) What happens to brain mitochondrial bioenergetics and dynamics during aging? (ii) Why is the brain so sensitive to the age-related mitochondrial impairments? (iii) Is there a sex difference in the age-induced mitochondrial dysfunction? Understanding mitochondrial physiology in the context of brain aging may help identify therapeutic targets against neurodegeneration. This article is part of a series "Beyond Amyloid".

The path from mitochondrial ROS to aging runs through the mitochondrial permeability transition pore

Excessive production of mitochondrial reactive oxygen species (mROS) is strongly associated with mitochondrial and cellular oxidative damage, aging, and degenerative diseases. However, mROS also induces pathways of protection of mitochondria that slow aging, inhibit cell death, and increase lifespan. Recent studies show that the activation of the mitochondrial permeability transition pore (mPTP), which is triggered by mROS and mitochondrial calcium overloading, is enhanced in aged animals and humans and in aging-related degenerative diseases. mPTP opening initiates further production and release of mROS that damage both mitochondrial and nuclear DNA, proteins, and phospholipids, and also releases matrix NAD that is hydrolyzed in the intermembrane space, thus contributing to the depletion of cellular NAD that accelerates aging. Oxidative damage to calcium transporters leads to calcium overload and more frequent opening of mPTP. Because aging enhances the opening of the mPTP and mPTP opening accelerates aging, we suggest that mPTP opening drives the progression of aging. Activation of the mPTP is regulated, directly and indirectly, not only by the mitochondrial protection pathways that are induced by mROS, but also by pro-apoptotic signals that are induced by DNA damage. We suggest that the integration of these contrasting signals by the mPTP largely determines the rate of cell aging and the initiation of cell death, and thus animal lifespan. The suggestion that the control of mPTP activation is critical for the progression of aging can explain the conflicting and confusing evidence regarding the beneficial and deleterious effects of mROS on health and lifespan.

Mitochondrial Function and Mitophagy in the Elderly: Effects of Exercise

Aging is a natural, multifactorial and multiorganic phenomenon wherein there are gradual physiological and pathological changes over time. Aging has been associated with a decrease of autophagy capacity and mitochondrial functions, such as biogenesis, dynamics, and mitophagy. These processes are essential for the maintenance of mitochondrial structural integrity and, therefore, for cell life, since mitochondrial dysfunction leads to an impairment of energy metabolism and increased production of reactive oxygen species, which consequently trigger mechanisms of cellular senescence and apoptotic cell death. Moreover, reduced mitochondrial function can contribute to age-associated disease phenotypes in model organisms and humans. Literature data show beneficial effects of exercise on the impairment of mitochondrial biogenesis and dynamics and on the decrease in the mitophagic capacity associated to aging. Thus, exercise could have effects on the major cell signaling pathways that are involved in the mitochondria quality and quantity control in the elderly. Although it is known that several exercise protocols are able to modify the activity and turnover of mitochondria, further studies are necessary in order to better identify the mechanisms of interaction between mitochondrial functions, aging, and physical activity, as well as to analyze possible factors influencing these processes.

2',3'-Cyclic nucleotide 3'-phosphodiesterase as a messenger of protection of the mitochondrial function during melatonin treatment in aging

The process of aging is considered to be tightly related to mitochondrial dysfunction. One of the causes of aging is an increased sensitivity to the induction of mitochondrial permeability transition pore (mPTP) opening in the inner membrane of mitochondria. Melatonin, a natural antioxidant, is a hormone produced by the pineal gland. The role of melatonin whose level decreases with aging is well understood. In the present study, we demonstrated that long-term treatment of aged rats with melatonin improved the functional state of mitochondria; thus, the Ca²⁺ capacity was enhanced and mitochondrial swelling was deaccelerated in mitochondria. Melatonin prevented mPTP and impaired the release of cytochrome c and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) from mitochondria of both young and aged rats. Our data suggest that melatonin retains СNPase inside mitochondria, thereby providing the protection of the protein against deleterious effects of 2',3'-cAMP in aging.

Identification of Four Kinds of 2',3'-cNMPs in Escherichia coli and a Method for Their Preparation

Four kinds of 2',3'-cNMPs have been identified in animals and plants, and their physiological roles are also suggested. However, in prokaryotes, while 2',3'-cCMP and 2',3'-cUMP are reported, 2',3'-cGMP or 2',3'-cAMP have never been identified from bacteria or archaea. In addition, there has been no biological method to prepare these cyclic nucleotides. During the study of a novel gene LfliZ from deep-sea bacterium Pseudoalteromonas sp. SM9913, we found that the recombinant LfliZ oligomers contained endogenous substrates, which were then identified to be 2',3'-cCMP, 2',3'-cUMP, 2',3'-cGMP, and 2',3'-cAMP, showing the first evidence for the biological existence of four kinds of 2',3'-cNMPs in prokaryotes. In addition, we further developed a biological method to simultaneously prepare four kinds of 2',3'-cNMPs from Escherichia coli through expressing LfliZ.

Temporal lobe in human aging: A quantitative protein profiling study of samples from Chinese Human Brain Bank

The temporal lobe is a portion of the cerebral cortex with critical functionality. The age-related protein profile changes in the human temporal lobe have not been previously studied. This 4-plex tandem mass tag labeled proteomic study was performed on samples of temporal lobe from Chinese donors. Tissue samples were assigned to four age groups: Group A (the young, age: 34±13 years); Group B (the elderly, 62±5 years); Group C (the aged, 84±4 years) and Group D (the old, 95±1 years). Pooled samples from the different groups were subjected to proteomics and bioinformatics analysis to identify age-related changes in protein expression and associated pathways. We isolated 5072 proteins, and found that 67 proteins were downregulated and 109 proteins were upregulated in one or more groups during the aging process. Western blotting assays were performed to verify the proteomic results. Bioinformatic analysis identified proteins involved in neuronal degeneration, including proteins involved in neuronal firing, myelin sheath damage, and cell structure stability. We also observed the accumulation of extracellular matrix and lysosomal proteins which imply the occurrence of fibrosis and autophagy. Our results suggest a series of changes across a wide range of proteins in the human temporal lobe that may relate to aging and age-related neurodegenerative disorders.

Structural and functional evolution of 2',3'-cyclic nucleotide 3'-phosphodiesterase

2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) is an abundant membrane-associated enzyme within the vertebrate myelin sheath. While the physiological function of CNPase still remains to be characterized in detail, it is known - in addition to its in vitro enzymatic activity - to interact with other proteins, small molecules, and membrane surfaces. From an evolutionary point of view, it can be deduced that CNPase is not restricted to myelin-forming cells or vertebrate tissues. Its evolution has involved gene fusion, addition of other small segments with distinct functions, such as membrane attachment, and possibly loss of function at the polynucleotide kinase-like domain. Currently, it is unclear whether the enzymatic function of the conserved phosphodiesterase domain in vertebrate myelin has a physiological role, or if CNPase could actually function - like many other classical myelin proteins - in a more structural role. This article is part of a Special Issue entitled SI: Myelin Evolution.

Mitochondrial 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNP) interacts with mPTP modulators and functional complexes (I-V) coupled with release of apoptotic factors

We previously reported that 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) is present in rat brain and liver mitochondria, in the outer membrane and mitoplasts. Substrates of CNP, 2',3'-cAMP and 2',3'-cNADP, were found to accelerate opening of mitochondrial permeability transition pore (mPTP). In purified non-synaptic mitochondria, CNP was observed to co-immunoprecipitate with main modulators of mPTP, i.e. VDAC, ANT, and cyclophilin D, as well as with tubulin and COX IV. Using Blue Native Electrophoresis, with following Western blot, CNP was revealed to associate with functional inner membrane mitochondrial complexes I-V. In Ca(2+) -overloaded mitochondria, association of CNP with complexes I-V was decreased. Cyclosporine A increased the association of CNP with complexes I and III, supporting the idea of the involvement of these complexes in mPTP function. 2',3'-cAMP enhanced CNP dissociation from complexes I, III, IV and V in Ca(2+)-overloaded mitochondria (i.e. when pore is opened). Association of CNP with complexes I, III, IV, and V was shown in mitochondria isolated from brain, liver and heart. Stimulation of the opening of the non-selective pore in mitochondria correlated with CNP release from mitochondria in parallel with release of cytochrome c, AIF and Endo G. In Ca(2+)-overloaded mitochondria, 2',3'-cAMP further accelerated the release of AIF, Endo G and CNP, but did not alter cytochrome c release. These results provide strong evidence that CNP, one of the possible regulators of mPTP complex, might be involved in the control of respiration and energy production in mitochondria. This reveals a new function of CNP outside the myelin structure.