Cyclophilin D deficiency attenuates mitochondrial and neuronal perturbation and ameliorates learning and memory in Alzheimer's disease. Nat Med. 2008;14:1097-1105. [PMID: 18806802 DOI: 10.1038/nm.1868]

The Toxicity and Polymorphism of β-Amyloid Oligomers

It is widely accepted that β-amyloid oligomers (Aβos) play a key role in the progression of Alzheimer's disease (AD) by inducing neuron damage and cognitive impairment, but Aβos are highly heterogeneous in their size, structure and cytotoxicity, making the corresponding studies tough to carry out. Nevertheless, a number of studies have recently made remarkable progress in the describing the characteristics and pathogenicity of Aβos. We here review the mechanisms by which Aβos exert their neuropathogenesis for AD progression, including receptor binding, cell membrane destruction, mitochondrial damage, Ca2+ homeostasis dysregulation and tau pathological induction. We also summarize the characteristics and pathogenicity such as the size, morphology and cytotoxicity of dimers, trimers, Aβ*56 and spherical oligomers, and suggest that Aβos may play a different role at different phases of AD pathogenesis, resulting in differential consequences on neuronal synaptotoxicity and survival. It is warranted to investigate the temporal sequence of Aβos in AD human brain and examine the relationship between different Aβos and cognitive impairment.

Revisiting the role of brain and peripheral Aβ in the pathogenesis of Alzheimer's disease

Amyloid beta (Aβ) is an intricate molecule that interacts with several biomolecules and/or produces insoluble assemblies and eventually the nonphysiological depositions of its alternate with normal neuronal conditions leading to Alzheimer's disease (AD). Aβ is formed through the proteolytic cleavage of the amyloid precursor protein (APP). Significant efforts are being made to explore the exact role of Aβ in AD pathogenesis. It is believed that the deposition of Aβ in the brain takes place from Aβ components which are derived from the brain itself. However, recent evidence suggests that Aβ derived also from the periphery and hence the Aβ circulating in the blood is capable of penetrating the blood-brain barrier (BBB) and the role of Aβ derived from the periphery is largely unknown so far. Therefore, Aβ origin determination and the underlying mechanisms of its pathological effects are of considerable interest in exploring effective therapeutic strategies. The purpose of this review is to provide a novel insight into AD pathogenesis based on Aβ in both the brain and periphery and highlight new therapeutic avenues to combat AD pathogenesis.

Central and Peripheral Metabolic Defects Contribute to the Pathogenesis of Alzheimer's Disease: Targeting Mitochondria for Diagnosis and Prevention

Significance: Epidemiological studies indicate that metabolic disorders are associated with an increased risk for Alzheimer's disease (AD). Metabolic remodeling occurs in the central nervous system (CNS) and periphery, even in the early stages of AD. Mitochondrial dysfunction has been widely accepted as a molecular mechanism underlying metabolic disorders. Therefore, focusing on early metabolic changes, especially from the perspective of mitochondria, could be of interest for early AD diagnosis and intervention. Recent Advances: We and others have identified that the levels of several metabolites are fluctuated in the periphery before their accumulation in the CNS, which plays an important role in the pathogenesis of AD. Mitochondrial remodeling is likely one of the earliest signs of AD, linking nutritional imbalance to cognitive deficits. Notably, by improving mitochondrial function, mitochondrial nutrients efficiently rescue cellular metabolic dysfunction in the CNS and periphery in individuals with AD. Critical Issues: Peripheral metabolic disorders should be intensively explored and evaluated for the early diagnosis of AD. The circulating metabolites derived from mitochondrial remodeling represent novel potential diagnostic biomarkers for AD that are more readily detected than CNS-oriented biomarkers. Moreover, mitochondrial nutrients provide a promising approach to preventing and delaying AD progression. Future Directions: Abnormal mitochondrial metabolism in the CNS and periphery is involved in AD pathogenesis. More clinical studies provide evidence for the suitability and reliability of circulating metabolites and cytokines for the early diagnosis of AD. Targeting mitochondria to rewire cellular metabolism is a promising approach to preventing AD and ameliorating AD-related metabolic disorders.

Omega-3 Fatty Acid-Type Docosahexaenoic Acid Protects against Aβ-Mediated Mitochondrial Deficits and Pathomechanisms in Alzheimer's Disease-Related Animal Model

It has been reported that damage to the mitochondria affects the progression of Alzheimer's disease (AD), and that mitochondrial dysfunction is improved by omega-3. However, no animal or cell model studies have confirmed whether omega-3 inhibits AD pathology related to mitochondria deficits. In this study, we aimed to (1) identify mitigating effects of endogenous omega-3 on mitochondrial deficits and AD pathology induced by amyloid beta (Aβ) in fat-1 mice, a transgenic omega-3 polyunsaturated fatty acids (PUFAs)-producing animal; (2) identify if docosahexaenoic acid (DHA) improves mitochondrial deficits induced by Aβ in HT22 cells; and (3) verify improvement effects of DHA administration on mitochondrial deficits and AD pathology in B6SJL-Tg(APPSwFlLon,PSEN1*M146L*L286V)6799Vas/Mmjax (5XFAD), a transgenic Aβ-overexpressing model. We found that omega-3 PUFAs significantly improved Aβ-induced mitochondrial pathology in fat-1 mice. In addition, our in vitro and in vivo findings demonstrate that DHA attenuated AD-associated pathologies, such as mitochondrial impairment, Aβ accumulation, neuroinflammation, neuronal loss, and impairment of adult hippocampal neurogenesis.

The Role of Mitochondria in Neurodegenerative Diseases: the Lesson from Alzheimer's Disease and Parkinson's Disease

Although the pathogenesis of neurodegenerative diseases is still widely unclear, various mechanisms have been proposed and several pieces of evidence are supportive for an important role of mitochondrial dysfunction. The present review provides a comprehensive and up-to-date overview about the role of mitochondria in the two most common neurodegenerative disorders: Alzheimer's disease (AD) and Parkinson's disease (PD). Mitochondrial involvement in AD is supported by clinical features like reduced glucose and oxygen brain metabolism and by numerous microscopic and molecular findings, including altered mitochondrial morphology, impaired respiratory chain function, and altered mitochondrial DNA. Furthermore, amyloid pathology and mitochondrial dysfunction seem to be bi-directionally correlated. Mitochondria have an even more remarkable role in PD. Several hints show that respiratory chain activity, in particular complex I, is impaired in the disease. Mitochondrial DNA alterations, involving deletions, point mutations, depletion, and altered maintenance, have been described. Mutations in genes directly implicated in mitochondrial functioning (like Parkin and PINK1) are responsible for rare genetic forms of the disease. A close connection between alpha-synuclein accumulation and mitochondrial dysfunction has been observed. Finally, mitochondria are involved also in atypical parkinsonisms, in particular multiple system atrophy. The available knowledge is still not sufficient to clearly state whether mitochondrial dysfunction plays a primary role in the very initial stages of these diseases or is secondary to other phenomena. However, the presented data strongly support the hypothesis that whatever the initial cause of neurodegeneration is, mitochondrial impairment has a critical role in maintaining and fostering the neurodegenerative process.

Constitutive cyclophilin-D ablation in mice increases exercise and cognitive-behavioral performance under normoxic and hypoxic conditions

We recently reported that constitutive ablation of cyclophilin-D (Cyp-D) in mice reduces oxygen consumption (VO2) while paradoxically increasing exercise endurance, thereby demonstrating increased O2 utilization efficiency. This response was associated with augmented glucose uptake and glucose utilization, in part mediated through adenosine monophosphate-activated kinase signaling. We now hypothesized that Cyp-D knock-out (KO) mice might also exhibit improved cognitive-behavioral performance and that these favorable adaptive responses may persist under hypoxic conditions. We therefore assessed under normoxic (20.9% O2, simulating ground O2 levels) and hypoxic (8% O2, simulating 7600 m altitude O2 levels) conditions exercise capacity and cognitive-behavioral performance. We used a treadmill test to assess exercise capacity, a pole-test to assess agility, an elevated-plus-maze test to assess anti-anxiety, and a passive avoidance test to assess learning and memory retention. Compared to wild type, Cyp-D KO mice showed comparable treadmill work under normoxia (48 ± 12 vs 47 ± 9 Joules) but increased treadmill work (12 ± 1 vs 8 ± 1 Joules; p = 0.02) under hypoxia. Cyp-D KO mice displayed increased pole-descending time (17 ± 3 vs 8 ± 2 s; p ≤ 0.05) under normoxia but shorter pole-descending time (21 ± 3 vs 37 ± 4 s; p ≤ 0.01) under hypoxia. In addition, the Cyp-D KO mice demonstrated increased elevated plus-maze open arm time (91 ± 31 vs 23 ± 12 s; p ≤ 0.05) under hypoxia and increased latency to enter dark chamber (261 ± 23 vs 185 ± 42 s; p ≤ 0.05) under normoxia. Thus, our experiments showed that under normoxia Cyp-D KO mice displayed anti-anxiety behavior and improved learning and memory retention. Under hypoxia, Cyp-D KO mice displayed increased exercise capacity, increased agility, and increased anti-anxiety consistent with our previously reported findings of increased O2 utilization efficiency. Identifying interventions to elicit these effects could be beneficial in a myriad of physiological and clinical conditions in which increasing O2 utilization efficiency would be advantageous.

Peptidyl-Prolyl Cis/Trans Isomerase Pin1 and Alzheimer's Disease

Alzheimer’s disease (AD) is the most common cause of dementia with cognitive decline. The neuropathology of AD is characterized by intracellular aggregation of neurofibrillary tangles consisting of hyperphosphorylated tau and extracellular deposition of senile plaques composed of beta-amyloid peptides derived from amyloid precursor protein (APP). The peptidyl-prolyl cis/trans isomerase Pin1 binds to phosphorylated serine or threonine residues preceding proline and regulates the biological functions of its substrates. Although Pin1 is tightly regulated under physiological conditions, Pin1 deregulation in the brain contributes to the development of neurodegenerative diseases, including AD. In this review, we discuss the expression and regulatory mechanisms of Pin1 in AD. We also focus on the molecular mechanisms by which Pin1 controls two major proteins, tau and APP, after phosphorylation and their signaling cascades. Moreover, the major impact of Pin1 deregulation on the progression of AD in animal models is discussed. This information will lead to a better understanding of Pin1 signaling pathways in the brain and may provide therapeutic options for the treatment of AD.

Mitochondrial dysfunction and Alzheimer's disease: prospects for therapeutic intervention

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease and has become a major socioeconomic issue in many developed countries. Currently available therapeutic agents for AD provide only symptomatic treatments, mainly because the complete mechanism of the AD pathogenesis is still unclear. Although several different hypotheses have been proposed, mitochondrial dysfunction has gathered interest because of its profound effect on brain bioenergetics and neuronal survival in the pathophysiology of AD. Various therapeutic agents targeting the mitochondrial pathways associated with AD have been developed over the past decade. Although most of these agents are still early in the clinical development process, they are used to restore mitochondrial function, which provides an alternative therapeutic strategy that is likely to slow the progression of the disease. In this mini review, we will survey the AD-related mitochondrial pathways and their small-molecule modulators that have therapeutic potential. We will focus on recently reported examples, and also overview the current challenges and future perspectives of ongoing research.

MCL-1Matrix maintains neuronal survival by enhancing mitochondrial integrity and bioenergetic capacity under stress conditions

Mitochondria play a crucial role in neuronal survival through efficient energy metabolism. In pathological conditions, mitochondrial stress leads to neuronal death, which is regulated by the anti-apoptotic BCL-2 family of proteins. MCL-1 is an anti-apoptotic BCL-2 protein localized to mitochondria either in the outer membrane (OM) or inner membrane (Matrix), which have distinct roles in inhibiting apoptosis and promoting bioenergetics, respectively. While the anti-apoptotic role for Mcl1 is well characterized, the protective function of MCL-1 ^Matrix remains poorly understood. Here, we show MCL-1^OM and MCL-1^Matrix prevent neuronal death through distinct mechanisms. We report that MCL-1^Matrix functions to preserve mitochondrial energy transduction and improves respiratory chain capacity by modulating mitochondrial oxygen consumption in response to mitochondrial stress. We show that MCL-1^Matrix protects neurons from stress by enhancing respiratory function, and by inhibiting mitochondrial permeability transition pore opening. Taken together, our results provide novel insight into how MCL-1^Matrix may confer neuroprotection under stress conditions involving loss of mitochondrial function.

CypD deficiency confers neuroprotection against mitochondrial abnormality caused by lead in SH-SY5Y cell

Mitochondrial permeability transition (MPT), which is mainly regulated by cyclophilin D (CypD) encoded by ppif gene, is an early event that occurs during mitochondrial stimuli exposure. Lead (Pb) induces MPT and subsequently causes mitochondrial abnormality, followed by events, including oxidative stress and cell death. Here, we generated a ppif-/- SH-SY5Y cell line to determine the role of CypD in Pb-induced mitochondrial abnormality. CypD deficiency significantly blocked mitochondrial permeability transition pore (MPTP) opening and inhibited mitochondrial membrane potential (MMP) collapse, as well as mitochondrial structure damage and fragmentation caused by Pb. Mitochondria fragmentation and MMP collapse, accompanying with Pb-induced downregulation of Glut1 and Glut3 and inactivation of AMPK signaling pathway, could impair the energy supply in wildtype cells. Meanwhile, ppif knockout can alleviate these impairments and maintain the energy supply. In addition, reactive oxygen species accumulation and cell death caused by Pb can also be attenuated by ppif knockout, thereby promoting cell survival. Our study tends to identify CypD as an important contributor to Pb-induced mitochondrial abnormality and provides a potential strategy to inhibit Pb neurotoxicity.

Increased mitochondrial calcium levels associated with neuronal death in a mouse model of Alzheimer's disease

Mitochondria contribute to shape intraneuronal Ca2+ signals. Excessive Ca2+ taken up by mitochondria could lead to cell death. Amyloid beta (Aβ) causes cytosolic Ca2+ overload, but the effects of Aβ on mitochondrial Ca2+ levels in Alzheimer's disease (AD) remain unclear. Using a ratiometric Ca2+ indicator targeted to neuronal mitochondria and intravital multiphoton microscopy, we find increased mitochondrial Ca2+ levels associated with plaque deposition and neuronal death in a transgenic mouse model of cerebral β-amyloidosis. Naturally secreted soluble Aβ applied onto the healthy brain increases Ca2+ concentration in mitochondria, which is prevented by blockage of the mitochondrial calcium uniporter. RNA-sequencing from post-mortem AD human brains shows downregulation in the expression of mitochondrial influx Ca2+ transporter genes, but upregulation in the genes related to mitochondrial Ca2+ efflux pathways, suggesting a counteracting effect to avoid Ca2+ overload. We propose lowering neuronal mitochondrial Ca2+ by inhibiting the mitochondrial Ca2+ uniporter as a novel potential therapeutic target against AD.

Fibroblast growth factor 21 and autophagy: A complex interplay in Parkinson disease

Parkinson disease (PD) is the second common neurodegenerative disorder after Alzheimer's disease (AD). The predominant pathological hallmark is progressive loss of dopaminergic (DA) neurones in the substantia nigra (SN) complicated by aggregation of misfolded forms of alpha-synuclein (α-syn). α-syn is a cytosolic synaptic protein localized in the presynaptic neuron under normal circumstances. What drives misfolding of this protein is largely unknown. However, recent studies suggest that autophagy might be an important risk factor for contributing towards PD. Autophagy is an evolutionarily conserved mechanism that causes the clearance or degradation of misfolded, mutated and damaged proteins, organelles etc. However, in an aging individual this process might deteriorate which could possibly lead to the accumulation of damaged proteins. Hence, autophagy modulation might provide some interesting cues for the treatment of PD. Additionally, Fibroblast growth factor 21 (FGF21) which is known for its role as a potent regulator of glucose and energy metabolism has also proved to be neuroprotective in various neurodegenerative conditions possibly via mediation of autophagy.

Going the Extra (Synaptic) Mile: Excitotoxicity as the Road Toward Neurodegenerative Diseases

Excitotoxicity is a phenomenon that describes the toxic actions of excitatory neurotransmitters, primarily glutamate, where the exacerbated or prolonged activation of glutamate receptors starts a cascade of neurotoxicity that ultimately leads to the loss of neuronal function and cell death. In this process, the shift between normal physiological function and excitotoxicity is largely controlled by astrocytes since they can control the levels of glutamate on the synaptic cleft. This control is achieved through glutamate clearance from the synaptic cleft and its underlying recycling through the glutamate-glutamine cycle. The molecular mechanism that triggers excitotoxicity involves alterations in glutamate and calcium metabolism, dysfunction of glutamate transporters, and malfunction of glutamate receptors, particularly N-methyl-D-aspartic acid receptors (NMDAR). On the other hand, excitotoxicity can be regarded as a consequence of other cellular phenomena, such as mitochondrial dysfunction, physical neuronal damage, and oxidative stress. Regardless, it is known that the excessive activation of NMDAR results in the sustained influx of calcium into neurons and leads to several deleterious consequences, including mitochondrial dysfunction, reactive oxygen species (ROS) overproduction, impairment of calcium buffering, the release of pro-apoptotic factors, among others, that inevitably contribute to neuronal loss. A large body of evidence implicates NMDAR-mediated excitotoxicity as a central mechanism in the pathogenesis of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and epilepsy. In this review article, we explore different causes and consequences of excitotoxicity, discuss the involvement of NMDAR-mediated excitotoxicity and its downstream effects on several neurodegenerative disorders, and identify possible strategies to study new aspects of these diseases that may lead to the discovery of new therapeutic approaches. With the understanding that excitotoxicity is a common denominator in neurodegenerative diseases and other disorders, a new perspective on therapy can be considered, where the targets are not specific symptoms, but the underlying cellular phenomena of the disease.

The role of cell type-specific mitochondrial dysfunction in the pathogenesis of Alzheimer's disease

The decrease of metabolism in the brain has been observed as the important lesions of Alzheimer’s disease (AD) from the early stages of diagnosis. The cumulative evidence has reported that the failure of mitochondria, an organelle involved in diverse biological processes as well as energy production, maybe the cause or effect of the pathogenesis of AD. Both amyloid and tau pathologies have an impact upon mitochondria through physical interaction or indirect signaling pathways, resulting in the disruption of mitochondrial function and dynamics which can trigger AD. In addition, mitochondria are involved in different biological processes depending on the specific functions of each cell type in the brain. Thus, it is necessary to understand mitochondrial dysfunction as part of the pathological phenotypes of AD according to each cell type. In this review, we summarize that 1) the effects of AD pathology inducing mitochondrial dysfunction and 2) the contribution of mitochondrial dysfunction in each cell type to AD pathogenesis.

Tumor Necrosis Factor Receptor-Associated Protein 1 Protects against Mitochondrial Injury by Preventing High Glucose-Induced mPTP Opening in Diabetes

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease worldwide. Renal tubular epithelial cell apoptosis and tubular atrophy have been recognized as indicators of the severity and progression of DKD, while the mechanism remains elusive. Tumor necrosis factor receptor-associated protein 1 (TRAP1) plays critical roles in apoptosis. The aim of this study was to investigate the protective role TRAP1 plays in DKD and to study the potential underlying mechanisms. TRAP1 expression was decreased, and mitochondria were injured in NRK-52e cells under high-glucose (HG) conditions. The overexpression of TRAP1 ameliorated HG-induced apoptosis, increased cell viability, maintained mitochondrial morphology, adenosine triphosphate (ATP) levels, and mitochondrial membrane potential (MMP), and buffered oxidative stress, whereas TRAP1 knockdown aggravated these effects. The protective effects of TRAP1 may be exerted via the inhibition of mitochondrial permeability transition pore (mPTP) opening, and the damage caused by TRAP1 knockdown can be partially reversed by treatment with the mPTP opening inhibitor cyclosporin A (CsA). In vivo, TRAP1 expression upregulation by AAV2/9 injection prevented renal dysfunction, ameliorated histopathological changes, maintained mitochondrial morphology and function, and reduced apoptosis and reactive oxygen species (ROS) in STZ-treated DKD rats. Thus, our results suggest that TRAP1 ameliorates diabetes-induced renal injury by preventing abnormal mPTP opening and maintaining mitochondrial structure and function, which may be treated as a potential target for DKD treatment.

Keap1-targeting microRNA-941 protects endometrial cells from oxygen and glucose deprivation-re-oxygenation via activation of Nrf2 signaling

BACKGROUND

Mimicking ischemia-reperfusion injury, oxygen and glucose deprivation (OGD)-re-oxygenation (OGDR) applied to endometrial cells produces significant oxidative stress and programmed necrosis, which can be inhibited by nuclear-factor-E2-related factor 2 (Nrf2) signaling. MicroRNA (miRNA)-induced repression of Keap1, a Nrf2 suppressor protein that facilitates Nrf2 degradation, is novel strategy to activate Nrf2 cascade.

METHODS

MicroRNA-941 (miR-941) was exogenously expressed in HESC and primary human endometrial cells, and the Nrf2 pathway examined by Western blotting and real-time quantitative PCR analysis. The endometrial cells were treated with OGDR, cell programmed necrosis and apoptosis were tested.

RESULTS

MiR-941 is a novel Keap1-targeting miRNA that regulates Nrf2 activity. In T-HESC cells and primary human endometrial cells, ectopic overexpression of miR-941 suppressed Keap1 3'-UTR (untranslated region) expression and downregulated its mRNA/protein expression, leading to activation of the Nrf2 cascade. Conversely, inhibition of miR-941 elevated Keap1 expression and activity in endometrial cells, resulting in suppression of Nrf2 activation. MiR-941 overexpression in endometrial cells attenuated OGDR-induced oxidative stress and programmed necrosis, whereas miR-941 inhibition enhanced oxidative stress and programmed necrosis. MiR-941 overexpression and inhibition were completely ineffective in Keap1-/Nrf2-KO T-HESC cells (using CRISPR/Cas9 strategy). Restoring Keap1 expression, using an UTR-depleted Keap1 construct, abolished miR-941-induced anti-OGDR activity in T-HESC cells. Thus Keap1-Nrf2 cascade activation is required for miR-941-induced endometrial cell protection.

CONCLUSIONS

Targeting Keap1 by miR-941 activates Nrf2 cascade to protect human endometrial cells from OGDR-induced oxidative stress and programmed necrosis. Video Abstract.

Cyclophilin D Contributes to Anesthesia Neurotoxicity in the Developing Brain

Anesthetic sevoflurane induces mitochondrial dysfunction, impairment of neurogenesis, and cognitive impairment in young mice, but the underlying mechanism remains to be determined. Cyclophilin D (CypD) is a modulatory factor for the mitochondrial permeability transition pore (mPTP). We, therefore, set out to evaluate the role of CypD in these sevoflurane-induced changes in vitro and in young mice. Wild-type (WT) and CypD knockout (KO) young (postnatal day 6, 7, and 8) mice received 3% sevoflurane 2 h daily and the neural progenitor cells (NPCs) harvested from the WT or CypD KO mice received 4.1% sevoflurane. We used immunohistochemistry and immunocytochemistry imaging, flow cytometry, Western blot, RT-PCR, co-immunoprecipitation, and Morris Water Maze to assess the interaction of sevoflurane and CypD on mitochondria function, neurogenesis, and cognition in vitro and in WT or CypD KO mice. We demonstrated that the sevoflurane anesthesia induced accumulation of CypD, mitochondrial dysfunction, impairment of neurogenesis, and cognitive impairment in WT mice or NPCs harvested from WT mice, but not in CypD KO mice or NPCs harvested from CypD KO mice. Furthermore, the sevoflurane anesthesia reduced the binding of CypD with Adenine nucleotide translocator, the other component of mPTP. These data suggest that the sevoflurane anesthesia might induce a CypD-dependent mitochondria dysfunction, impairment of neurogenesis, and cognitive impairment in young mice and NPCs.

Misconnecting the dots: altered mitochondrial protein-protein interactions and their role in neurodegenerative disorders

Introduction: Mitochondria (mt) are protein-protein interaction (PPI) hubs in the cell where mt-localized and associated proteins interact in a fashion critical for cell fitness. Altered mtPPIs are linked to neurodegenerative disorders (NDs) and drivers of pathological associations to mediate ND progression. Mapping altered mtPPIs will reveal how mt dysfunction is linked to NDs.Areas covered: This review discusses how database sources reflect on the number of mt protein or interaction predictions, and serves as an update on mtPPIs in mt dynamics and homeostasis. Emphasis is given to mRNA expression profiles for mt proteins in human tissues, cellular models relevant to NDs, and altered mtPPIs in NDs such as Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD).Expert opinion: We highlight the scarcity of biomarkers to improve diagnostic accuracy and tracking of ND progression, obstacles in recapitulating NDs using human cellular models to underpin the pathophysiological mechanisms of disease, and the shortage of mt protein interactome reference database(s) of neuronal cells. These bottlenecks are addressed by improvements in induced pluripotent stem cell creation and culturing, patient-derived 3D brain organoids to recapitulate structural arrangements of the brain, and cell sorting to elucidate mt proteome disparities between cell types.

Mitophagy in Alzheimer's Disease and Other Age-Related Neurodegenerative Diseases

Mitochondrial dysfunction is a central aspect of aging and neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Mitochondria are the main cellular energy powerhouses, supplying most of ATP by oxidative phosphorylation, which is required to fuel essential neuronal functions. Efficient removal of aged and dysfunctional mitochondria through mitophagy, a cargo-selective autophagy, is crucial for mitochondrial maintenance and neuronal health. Mechanistic studies into mitophagy have highlighted an integrated and elaborate cellular network that can regulate mitochondrial turnover. In this review, we provide an updated overview of the recent discoveries and advancements on the mitophagy pathways and discuss the molecular mechanisms underlying mitophagy defects in Alzheimer's disease and other age-related neurodegenerative diseases, as well as the therapeutic potential of mitophagy-enhancing strategies to combat these disorders.

Thyroid Stimulating Hormone Triggers Hepatic Mitochondrial Stress through Cyclophilin D Acetylation

BACKGROUND & AIMS

Oxidative stress-related liver diseases were shown to be associated with elevated serum thyroid stimulating hormone (TSH) levels. Mitochondria are the main source of cellular reactive oxygen species. However, the relationship between TSH and hepatic mitochondrial stress/dysfunction and the underlying mechanisms are largely unknown. Here, we focused on exploring the effects and mechanism of TSH on hepatic mitochondrial stress.

METHODS

As the function of TSH is mediated through the TSH receptor (TSHR), Tshr -/- mice and liver-specific Tshr -/- mice and liver-specific Tshr -/- mice and liver-specific.

RESULTS

A relatively lower degree of mitochondrial stress was observed in the livers of Tshr -/- mice and liver-specific in vitro. Microarray and RT-PCR analyses showed that Tshr -/- mice and liver-specific.

CONCLUSIONS

TSH stimulates hepatic CypD acetylation through the lncRNA-AK044604/SIRT1/SIRT3 signaling pathway, indicating an essential role for TSH in mitochondrial stress in the liver.

Stem Cell Therapy for Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease caused by eventually aggregated amyloid β (Aβ) plaques in degenerating neurons of the aging brain. These aggregated protein plaques mainly consist of Aβ fibrils and neurofibrillary tangles (NFTs) of phosphorylated tau protein. Even though some cholinesterase inhibitors, NMDA receptor antagonist, and monoclonal antibodies were developed to inhibit neurodegeneration or activate neural regeneration or clear off the Aβ deposits, none of the treatment is effective in improving the cognitive and memory dysfunctions of the AD patients. Thus, stem cell therapy represents a powerful tool for the treatment of AD. In addition to discussing the advents in molecular pathogenesis and animal models of this disease and the treatment approaches using small molecules and immunoglobulins against AD, we will focus on the stem cell sources for AD using neural stem cells (NSCs); embryonic stem cells (ESCs); and mesenchymal stem cells (MSCs) from bone marrow, umbilical cord, and umbilical cord blood. In particular, patient-specific-induced pluripotent stem cells (iPS cells) are proposed as a future prospective and the challenges for the treatment of AD.

Orexin-A aggravates cytotoxicity and mitochondrial impairment in SH-SY5Y cells transfected with APPswe via p38 MAPK pathway

Background

Alzheimer's disease (AD) is one of the common neurodegenerative diseases and is characterized by the accumulation of amyloid-β (Aβ). Orexin-A is a neuropeptide produced in the hypothalamus and thought to be involved in the pathogenesis of AD. However, its underlying mechanism and signaling pathway remains unclear. The aim of this work was to investigate the effect of Orexin-A on AD, and to explore its potential mechanism and signaling pathway.

Methods

SH-SY5Y cells that were stably transfected with the Swedish mutant amyloid precursor protein (APPswe), a cell model of AD with excessive Aβ production, were used in this study. Cells were treated with Orexin-A, and with or without SB203580, an inhibitor of the p38 mitogen-activated protein kinase (MAPK) pathway, one of the key MAPK pathways associated with cell death. Following treatment, cells were collected and analyzed by western blotting, ELISA, electron microscopy, real-time PCR, fluorescence microscopy, and other biochemical assays.

Results

Orexin-A increased the level of Aβ_1-40 and Aβ_1-42 in the cell medium, and activated the p38 MAPK pathway. As evidenced by the CCK-8 and ELISA BrdU assays, Orexin-A decreased cell viability and cell proliferation. Electron microscopic analysis used to observe the morphology of mitochondria, showed that Orexin-A increased the percentage of abnormal mitochondria. Further, decreased activity of cytochrome c oxidase (CCO), level of ATP, and mitochondrial DNA (mtDNA) copy number following Orexin-A treatment showed that Orexin-A exacerbated mitochondrial dysfunction. The level of intracellular reactive oxygen species (ROS), which is mainly generated in mitochondria and reflects mitochondrial dysfunction, was also increased by Orexin-A. SB203580 blocked the cytotoxicity and mitochondrial impairment aggravated by Orexin-A.

Conclusions

These findings demonstrate that Orexin-A aggravates cytotoxicity and mitochondrial impairment in SH-SY5Y cells transfected with APPswe through the p38 MAPK pathway, and suggest that Orexin-A participates in the pathogenesis of AD, which may provide a new treatment target in the future.

Mitochondrial dysfunction and Alzheimer's disease: prospects for therapeutic intervention

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease and has become a major socioeconomic issue in many developed countries. Currently available therapeutic agents for AD provide only symptomatic treatments, mainly because the complete mechanism of the AD pathogenesis is still unclear. Although several different hypotheses have been proposed, mitochondrial dysfunction has gathered interest because of its profound effect on brain bioenergetics and neuronal survival in the pathophysiology of AD. Various therapeutic agents targeting the mitochondrial pathways associated with AD have been developed over the past decade. Although most of these agents are still early in the clinical development process, they are used to restore mitochondrial function, which provides an alternative therapeutic strategy that is likely to slow the progression of the disease. In this mini review, we will survey the AD-related mitochondrial pathways and their small-molecule modulators that have therapeutic potential. We will focus on recently reported examples, and also overview the current challenges and future perspectives of ongoing research. [BMB Reports 2020; 53(1): 47-55].

Coniferaldehyde attenuates Alzheimer's pathology via activation of Nrf2 and its targets

Background: Alzheimer's disease (AD) currently lacks a cure. Because substantial neuronal damage usually occurs before AD is advanced enough for diagnosis, the best hope for disease-modifying AD therapies likely relies on early intervention or even prevention, and targeting multiple pathways implicated in early AD pathogenesis rather than focusing exclusively on excessive production of β-amyloid (Aβ) species.

Methods: Coniferaldehyde (CFA), a food flavoring and agonist of NF-E2-related factor 2 (Nrf2), was selected by multimodal in vitro screening, followed by investigation of several downstream effects potentially involved. Furthermore, in the APP/PS1 AD mouse model, the therapeutic effects of CFA (0.2 mmol kg^-1d^-1) were tested beginning at 3 months of age. Behavioral phenotypes related to learning and memory capacity, brain pathology and biochemistry, including Aβ transport, were assessed at different time intervals.

Results: CFA promoted neuron viability and showed potent neuroprotective effects, especially on mitochondrial structure and functions. In addition, CFA greatly enhanced the brain clearance of Aβ in both free and extracellular vesicle (EV)-contained Aβ forms. In the APP/PS1 mouse model, CFA effectively abolished brain Aβ deposits and reduced the level of toxic soluble Aβ peptides, thus eliminating AD-like pathological changes in the hippocampus and cerebral cortex and preserving learning and memory capacity of the mice.

Conclusion: The experimental evidence overall indicated that Nrf2 activation may contribute to the potent anti-AD effects of CFA. With an excellent safety profile, further clinical investigation of coniferaldehyde might bring hope for AD prevention/therapy.

The Role of Mitochondrial Impairment in Alzheimer´s Disease Neurodegeneration: The Tau Connection

Accumulative evidence has shown that mitochondrial dysfunction plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). Mitochondrial impairment actively contributes to the synaptic and cognitive failure that characterizes AD. The presence of soluble pathological forms of tau like hyperphosphorylated at Ser396 and Ser404 and cleaved at Asp421 by caspase 3, negatively impacts mitochondrial bioenergetics, transport, and morphology in neurons. These adverse effects against mitochondria health will contribute to the synaptic impairment and cognitive decline in AD. Current studies suggest that mitochondrial failure induced by pathological tau forms is likely the result of the opening of the mitochondrial permeability transition pore (mPTP). mPTP is a mitochondrial mega-channel that is activated by increases in calcium and is associated with mitochondrial stress and apoptosis. This structure is composed of different proteins, where Ciclophilin D (CypD) is considered to be the primary mediator of mPTP activation. Also, new studies suggest that mPTP contributes to Aβ pathology and oxidative stress in AD. Further, inhibition of mPTP through the reduction of CypD expression prevents cognitive and synaptic impairment in AD mouse models. More importantly, tau protein contributes to the physiological regulation of mitochondria through the opening/interaction with mPTP in hippocampal neurons. Therefore, in this paper, we will discuss evidence that suggests an important role of pathological forms of tau against mitochondrial health. Also, we will discuss the possible role of mPTP in the mitochondrial impairment produced by the presence of tau pathology and its impact on synaptic function present in AD.

Targeting cyclophilin-D by miR-1281 protects human macrophages from Mycobacterium tuberculosis-induced programmed necrosis and apoptosis

Mycobacterium tuberculosis (MTB) infection induces cytotoxicity to host human macrophages. The underlying signaling mechanisms are largely unknown. Here we discovered that MTB infection induced programmed necrosis in human macrophages, causing mitochondrial cyclophilin-D (CypD)-p53-adenine nucleotide translocator type 1 association, mitochondrial depolarization and lactate dehydrogenase medium release. In human macrophages MTB infection-induced programmed necrosis and apoptosis were largely attenuated by CypD inhibition (by cyclosporin A), silencing and knockout, but intensified with ectopic CypD overexpression. Further studies identified microRNA-1281 as a CypD-targeting miRNA. Ectopic overexpression of microRNA-1281 decreased CypD 3'-untranslated region activity and its expression, protecting human macrophages from MTB-induced programmed necrosis and apoptosis. Conversely, microRNA-1281 inhibition in human macrophages, by the anti-sense sequence, increased CypD expression and potentiated MTB-induced cytotoxicity. Importantly, in CypD-KO macrophages miR-1281 overexpression or inhibition was ineffective against MTB infection. Restoring CypD expression, by an untranslated region-depleted CypD construct, reversed miR-1281-induced cytoprotection against MTB in human macrophages. Collectively, these results show that targeting CypD by miR-1281 protects human macrophages from MTB-induced programmed necrosis and apoptosis.

The application of patient-derived induced pluripotent stem cells for modeling and treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is the most prevalent age-related neurodegenerative disease which is mainly caused by aggregated protein plaques in degenerating neurons of the brain. These aggregated protein plaques are mainly consisting of amyloid β (Aβ) fibrils and neurofibrillary tangles (NFTs) of phosphorylated tau protein. Even though the transgenic murine models can recapitulate some of the AD phenotypes, they are not the human cell models of AD. Recent breakthrough in somatic cell reprogramming made it available to use induced pluripotent stem cells (iPSCs) for patientspecific disease modeling and autologous transplantation therapy. Human iPSCs provide alternative ways to obtain specific human brain cells of AD patients to study the molecular mechanisms and therapeutic approaches for familial and sporadic forms of AD. After differentiation into neuronal cells, iPSCs have enabled the investigation of the complex aetiology and timescale over which AD develops in human brain. Here, we first go over the pathological process of and transgenic models of AD. Then we discuss the application of iPSC for disease model and cell transplantation. At last the challenges and future applications of iPSCs for AD will be summarized to propose cell-based approaches for the treatment of this devastating disorder.

Early administration of galantamine from preplaque phase suppresses oxidative stress and improves cognitive behavior in APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease that progressively impairs memory and cognition. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark of AD. Oxidative stress induced by generation of reactive oxygen species (ROS) is a prominent phenomenon in AD and known to occur early in the course of AD. Several reports suggest a relationship between change in redox status and AD pathology including progressive Aβ deposition, glial cell activation, and inflammation. Galantamine is an acetylcholinesterase inhibitor and has been reported to have an oxidative stress inhibitory function. In the present study, galantamine was administered orally to AD model mice from before the appearance of Aβ plaques (preplaque phase), and in vivo change in redox status of the brain was measured using electron paramagnetic resonance (EPR) imaging. Administration of galantamine from the preplaque phase ameliorated memory decline in Morris water maze test and novel object recognition test. Monitoring of the redox status of the brain using EPR imaging showed that galantamine treatment improved the unbalanced redox state. Additionally, galantamine administration enhanced microglial function to promote Aβ clearance, reducing the Aβ-positive area in the cortex and amount of insoluble Aβ in the brain. In contrast, galantamine treatment from the preplaque phase suppressed the production of proinflammatory cytokines through neurotoxic microglial activity. Therefore, galantamine administration from the preplaque phase may have the potential of clinical application for the prevention of AD. In addition, our results demonstrate the usefulness of EPR imaging for speedy and quantitative evaluation of the efficacy of disease-modifying drugs for AD.

Parkin Regulates Programmed Necrosis and Myocardial Ischemia/Reperfusion Injury by Targeting Cyclophilin-D

Aims: Cardiomyocyte death critically contributes to the pathogenesis of cardiac disorders, such as myocardial infarction, heart failure, and cardiac ischemia/reperfusion (I/R) injury. As one of the main forms of cardiac cell death, necrosis plays a critical role in heart diseases. Multiple signaling pathways of necrosis have been demonstrated, in which death receptors, receptor-interacting serine/threonine-protein 1 and 3 kinases, and cyclophilin-D (CypD) have been deeply implicated. However, the fundamental mechanism underlying myocardial necroptosis, especially the mitochondrial permeability transition pore (mPTP)-CypD-dependent death pathway, is poorly understood. Parkin functions as an E3 ubiquitin protein ligase that mainly mediates mitophagy cascades. As yet, it is not clear whether Parkin participates in regulating necrosis and myocardial I/R injury. Results: Here, our results showed that Parkin mediated mitophagy and inhibited necrosis under oxidative stress. In further exploring the underlying mechanisms, we found that Parkin suppressed mPTP opening by catalyzing the ubiquitination of CypD in necrotic cascades, which were not involved in Parkin-regulated mitophagy. Parkin inhibited necrosis, reduced myocardial I/R injury, and improved cardiac function. Innovation: Our present work reveals a highlighted connection between the mitochondrial matrix-localized Parkin and the mPTP-CypD-dependent necrotic signaling pathway in cardiac injury. Conclusion: Our results revealed a novel myocardial necrotic regulating model composed of Parkin, CypD, and mPTP, which may provide potential therapeutic targets and strategies to modulate the levels of these molecules.

The Interplay between Ca2+ Signaling Pathways and Neurodegeneration

Calcium (Ca²⁺) homeostasis is essential for cell maintenance since this ion participates in many physiological processes. For example, the spatial and temporal organization of Ca²⁺ signaling in the central nervous system is fundamental for neurotransmission, where local changes in cytosolic Ca²⁺ concentration are needed to transmit information from neuron to neuron, between neurons and glia, and even regulating local blood flow according to the required activity. However, under pathological conditions, Ca²⁺ homeostasis is altered, with increased cytoplasmic Ca²⁺ concentrations leading to the activation of proteases, lipases, and nucleases. This review aimed to highlight the role of Ca²⁺ signaling in neurodegenerative disease-related apoptosis, where the regulation of intracellular Ca²⁺ homeostasis depends on coordinated interactions between the endoplasmic reticulum, mitochondria, and lysosomes, as well as specific transport mechanisms. In neurodegenerative diseases, alterations-increased oxidative stress, energy metabolism alterations, and protein aggregation have been identified. The aggregation of α-synuclein, β-amyloid peptide (Aβ), and huntingtin all adversely affect Ca²⁺ homeostasis. Due to the mounting evidence for the relevance of Ca²⁺ signaling in neuroprotection, we would focus on the expression and function of Ca²⁺ signaling-related proteins, in terms of the effects on autophagy regulation and the onset and progression of neurodegenerative diseases.

Brain activity regulates loose coupling between mitochondrial and cytosolic Ca2+ transients

Mitochondrial calcium ([Ca²⁺]_mito) dynamics plays vital roles in regulating fundamental cellular and organellar functions including bioenergetics. However, neuronal [Ca²⁺]_mito dynamics in vivo and its regulation by brain activity are largely unknown. By performing two-photon Ca²⁺ imaging in the primary motor (M1) and visual cortexes (V1) of awake behaving mice, we find that discrete [Ca²⁺]_mito transients occur synchronously over somatic and dendritic mitochondrial network, and couple with cytosolic calcium ([Ca²⁺]_cyto) transients in a probabilistic, rather than deterministic manner. The amplitude, duration, and frequency of [Ca²⁺]_cyto transients constitute important determinants of the coupling, and the coupling fidelity is greatly increased during treadmill running (in M1 neurons) and visual stimulation (in V1 neurons). Moreover, Ca²⁺/calmodulin kinase II is mechanistically involved in modulating the dynamic coupling process. Thus, activity-dependent dynamic [Ca²⁺]_mito-to-[Ca²⁺]_cyto coupling affords an important mechanism whereby [Ca²⁺]_mito decodes brain activity for the regulation of mitochondrial bioenergetics to meet fluctuating neuronal energy demands as well as for neuronal information processing.

Dysfunctional Mitochondria and Mitophagy as Drivers of Alzheimer's Disease Pathogenesis

Neurons are highly specialized post-mitotic cells that are inherently dependent on mitochondria owing to their high bioenergetic demand. Mitochondrial dysfunction is therefore associated with various age-related neurodegenerative disorders such as Alzheimer's disease (AD), wherein accumulation of damaged and dysfunctional mitochondria has been reported as an early symptom further contributing to disease progression. In AD, impairment of mitochondrial function causes bioenergetic deficiency, intracellular calcium imbalance and oxidative stress, thereby aggravating the effect of Aβ and tau pathologies, leading to synaptic dysfunction, cognitive impairment and memory loss. Although there are reports suggesting intricate parallelism between mitochondrial dysfunction and AD pathologies such as Aβ aggregation and hyperphosphorylated tau accumulation, the factors that drive the pathogenesis of either are unclear. In addition, emerging evidence suggest that mitochondrial quality control (QC) mechanisms such as mitophagy are impaired in AD. As an important mitochondrial QC mechanism, mitophagy plays a critical role in maintaining neuronal health and function. Studies show that various proteins involved in mitophagy, mitochondrial dynamics, and mitochondrial biogenesis are affected in AD. Compromised mitophagy may also be attributed to impairment in autophagosome-lysosome fusion and defects in lysosomal acidification. Therapeutic interventions aiming to restore mitophagy functions can be used as a strategy for ameliorating AD pathogenesis. Recent evidence implicates the role of microglial activation via mitophagy induction in reducing amyloid plaque load. This review summarizes the current developments in the field of mitophagy and mitochondrial dysfunction in AD.

In vitro study of interaction of 17β-hydroxysteroid dehydrogenase type 10 and cyclophilin D and its potential implications for Alzheimer's disease

In early stages of Alzheimer's disease (AD), amyloid-β (Aβ) accumulates in neuronal mitochondria where it interacts with a number of biomolecules including 17beta-hydroxysteroide dehydrogenase 10 (17β-HSD10) and cyclophilin D (cypD). It has been hypothesized that 17β-HSD10 interacts with cypD preventing it from opening mitochondrial permeability transition pores and that its regulation during AD may be affected by the accumulation of Aβ. In this work, we demonstrate for the first time that 17β-HSD10 and cypD form a stable complex in vitro. Furthermore, we show that factors, such as pH, ionic environment and the presence of Aβ, affect the ability of 17β-HSD10 to bind cypD. We demonstrate that K+ and Mg2+ ions present at low levels may facilitate this binding. We also show that different fragments of Aβ (Aβ1-40 and Aβ1-42) affect the interaction between 17β-HSD10 and cypD differently and that Aβ1-42 (in contrast to Aβ1-40) is capable of simultaneously binding both 17β-HSD10 and cypD in a tri-complex.

OSCP subunit of mitochondrial ATP synthase: role in regulation of enzyme function and of its transition to a pore

The permeability transition pore (PTP) is a latent, high-conductance channel of the inner mitochondrial membrane. When activated, it plays a key role in cell death and therefore in several diseases. The investigation of the PTP took an unexpected turn after the discovery that cyclophilin D (the target of the PTP inhibitory effect of cyclosporin A) binds to FO F1 (F)-ATP synthase, thus inhibiting its catalytic activity by about 30%. This observation was followed by the demonstration that binding occurs at a particular subunit of the enzyme, the oligomycin sensitivity conferral protein (OSCP), and that F-ATP synthase can form Ca2+ -activated, high-conductance channels with features matching those of the PTP, suggesting that the latter originates from a conformational change in F-ATP synthase. This review is specifically focused on the OSCP subunit of F-ATP synthase, whose unique features make it a potential pharmacological target both for modulation of F-ATP synthase and its transition to a pore. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Nanoparticle-mediated approaches for Alzheimer's disease pathogenesis, diagnosis, and therapeutics

Alzheimer's disease (AD) is an irreversible and progressive neurodegenerative disorder manifested by memory loss and cognitive impairment. Deposition of the amyloid β plaques has been identified as the most common AD pathology; however, the excessive accumulation of phosphorylated or total tau proteins, reactive oxygen species, and higher acetylcholinesterase activity are also strongly associated with Alzheimer's dementia. Several therapeutic approaches targeting these pathogenic mechanisms have failed in clinical or preclinical trials, partly due to the limited bioavailability, poor cell, and blood-brain barrier penetration, and low drug half-life of current regimens. The nanoparticles (NPs)-mediated drug delivery systems improve drug solubility and bioavailability, thus renders as superior alternatives. Moreover, NPs-mediated approaches facilitate multiple drug loading and targeted drug delivery, thereby increasing drug efficacy. However, certain NPs can cause acute toxicity damaging cellular and tissue architecture, therefore, NP material should be carefully selected. In this review, we summarize the recent NPs-mediated studies that exploit various pathologic mechanisms of AD by labeling, identifying, and treating the affected brain pathologies. The disadvantages of the select NP-based deliveries and the future aspects will also be discussed.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Mitochondrial dysfunction in Alzheimer's disease: Role in pathogenesis and novel therapeutic opportunities

Dysfunction of cell bioenergetics is a common feature of neurodegenerative diseases, the most common of which is Alzheimer's disease (AD). Disrupted energy utilization implicates mitochondria at its nexus. This review summarizes some of the evidence that points to faulty mitochondrial function in AD and highlights past and current therapeutic development efforts. Classical neuropathological hallmarks of disease (β-amyloid and τ) and sporadic AD risk genes (APOE) may trigger mitochondrial disturbance, yet mitochondrial dysfunction may incite pathology. Preclinical and clinical efforts have overwhelmingly centred on the amyloid pathway, but clinical trials have yet to reveal clear-cut benefits. AD therapies aimed at mitochondrial dysfunction are few and concentrate on reversing oxidative stress and cell death pathways. Novel research efforts aimed at boosting mitochondrial and bioenergetic function offer an alternative treatment strategy. Enhancing cell bioenergetics in preclinical models may yield widespread favourable effects that could benefit persons with AD. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Impaired mitochondrial calcium efflux contributes to disease progression in models of Alzheimer's disease

Impairments in neuronal intracellular calcium (_iCa²⁺) handling may contribute to Alzheimer’s disease (AD) development. Metabolic dysfunction and progressive neuronal loss are associated with AD progression, and mitochondrial calcium (_mCa²⁺) signaling is a key regulator of both of these processes. Here, we report remodeling of the _mCa²⁺ exchange machinery in the prefrontal cortex of individuals with AD. In the 3xTg-AD mouse model impaired _mCa²⁺ efflux capacity precedes neuropathology. Neuronal deletion of the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX, Slc8b1 gene) accelerated memory decline and increased amyloidosis and tau pathology. Further, genetic rescue of neuronal NCLX in 3xTg-AD mice is sufficient to impede AD-associated pathology and memory loss. We show that _mCa²⁺ overload contributes to AD progression by promoting superoxide generation, metabolic dysfunction and neuronal cell death. These results provide a link between the calcium dysregulation and metabolic dysfunction hypotheses of AD and suggest _mCa²⁺ exchange as potential therapeutic target in AD.

Dysregulation of intracellular calcium is reported in Alzheimer’s disease. Here the authors show that loss of the mitochondrial Na⁺ /Ca²⁺ exchanger, NCLX – primary route of mitochondrial calcium efflux, precedes neuronal pathology in experimental models and contributes to Alzheimer’s disease progression.

Role of PGC-1α in Mitochondrial Quality Control in Neurodegenerative Diseases

As one of the major cell organelles responsible for ATP production, it is important that neurons maintain mitochondria with structural and functional integrity; this is especially true for neurons with high metabolic requirements. When mitochondrial damage occurs, mitochondria are able to maintain a steady state of functioning through molecular and organellar quality control, thus ensuring neuronal function. And when mitochondrial quality control (MQC) fails, mitochondria mediate apoptosis. An apparently key molecule in MQC is the transcriptional coactivator peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α). Recent findings have demonstrated that upregulation of PGC-1α expression in neurons can modulate MQC to prevent mitochondrial dysfunction in certain in vivo and in vitro aging or neurodegenerative encephalopathy models, such as Huntington's disease, Alzheimer's disease, and Parkinson's disease. Because mitochondrial function and quality control disorders are the basis of pathogenesis in almost all neurodegenerative diseases (NDDs), the role of PGC-1α may make it a viable entry point for the treatment of such diseases. This review focuses on multi-level MQC in neurons, as well as the regulation of MQC by PGC-1α in these major NDDs.

Mitochondria at the neuronal presynapse in health and disease

Synapses enable neurons to communicate with each other and are therefore a prerequisite for normal brain function. Presynaptically, this communication requires energy and generates large fluctuations in calcium concentrations. Mitochondria are optimized for supplying energy and buffering calcium, and they are actively recruited to presynapses. However, not all presynapses contain mitochondria; thus, how might synapses with and without mitochondria differ? Mitochondria are also increasingly recognized to serve additional functions at the presynapse. Here, we discuss the importance of presynaptic mitochondria in maintaining neuronal homeostasis and how dysfunctional presynaptic mitochondria might contribute to the development of disease.

microRNA-7 inhibition protects human osteoblasts from dexamethasone via activation of epidermal growth factor receptor signaling

Sustained dexamethasone (Dex) treatment could induce secondary osteoporosis, osteonecrosis, or even bone fractures. Dex can induce potent cytotoxicity in cultured human osteoblasts. The aim of this study was to test the potential role of microRNA-7 (miR-7), which targets the epidermal growth factor receptor (EGFR), in Dex-treated human osteoblasts. In OB-6, hFOB1.19, and primary human osteoblasts, miR-7 depletion by a lentiviral antagomiR-7 construct (LV-antagomiR-7) increased EGFR expression and downstream Akt activation, protecting cells from Dex-induced viability reduction, cell death, and apoptosis. In contrast, forced overexpression of miR-7 by a lentiviral miR-7 construct (LV-miR-7) inhibited EGFR expression and Akt activation, potentiating Dex-induced cytotoxicity in OB-6, hFOB1.19, and primary human osteoblasts. EGFR is the primary target of miR-7 in human osteoblasts. Luciferase activity of the EGFR 3-untranslated region was enhanced by LV-antagomiR-7, but decreased by LV-miR-7 in OB-6 cells. Further, LV-antagomiR-7-induced osteoblast cytoprotection against Dex was abolished by the EGFR inhibitors AG1478 and PD153035. Moreover, neither LV-antagomiR-7 nor LV-miR-7 was functional in EGFR-KO OB-6 cells. We also show that miR-7 is upregulated in the necrotic femoral head tissues of Dex-administered patients, correlating with EGFR downregulation. Together, we conclude that miR-7 inhibition protects human osteoblasts from Dex via activation of EGFR signaling.

Mangiferin: A multipotent natural product preventing neurodegeneration in Alzheimer's and Parkinson's disease models

Alzheimer's disease (AD) and Parkinson's disease (PD) are recognized as the universal neurodegenerative diseases, with the involvement of misfolded proteins pathology, leading to oxidative stress, glial cells activation, neuroinflammation, mitochondrial dysfunction, and cellular apoptosis. Several discoveries indicate that accumulation of pathogenic proteins, i.e. amyloid β (Aβ), the microtubule-binding protein tau, and α-synuclein, are parallel with oxidative stress, neuroinflammation, and mitochondrial dysfunction. Whether the causative factors are misfolded proteins or these pathophysiological changes, leading to neurodegeneration still remain ambiguous. Importantly, directing pharmacological researches towards the prevention of AD and PD seem a promising approach to detect these complicating mechanisms, and provide new insight into therapy for AD and PD patients. Mangiferin (MGF, 2-C-β-D-glucopyranosyl-1, 3, 6, 7-tetrahydroxyxanthone), well-known as a natural product, is detached from multiple plants, including Mangifera indica L. With the structure of C-glycosyl and phenolic moiety, MGF possesses multipotent properties starting from anti-oxidant effects, to the alleviation of mitochondrial dysfunction, neuroinflammation, and cellular apoptosis. In particular, MGF can cross the blood-brain barrier to exert neuronal protection. Different researches implicate that MGF is able to protect the central nervous system from oxidative stress, mitochondrial dysfunction, neuroinflammation, and apoptosis under in vitro and in vivo models. Additional facts support that MGF plays a role in improving the declined memory and cognition of rat models. Taken together, the neuroprotective capacity of MGF may stand out as an agent candidate for AD and PD therapy.

Mitochondrial Function, Dynamics, and Permeability Transition: A Complex Love Triangle as A Possible Target for the Treatment of Brain Aging and Alzheimer's Disease

Because of the failure of all amyloid-β directed treatment strategies for Alzheimer's disease (AD), the concept of mitochondrial dysfunction as a major pathomechanism of the cognitive decline in aging and AD has received substantial support. Accordingly, improving mitochondrial function as an alternative strategy for new drug development became of increasing interest and many different compounds have been identified which improve mitochondrial function in preclinical in vitro and in vivo experiments. However, very few if any have been investigated in clinical trials, representing a major drawback of the mitochondria directed drug development. To overcome these problems, we used a top-down approach by investigating several older antidementia drugs with clinical evidence of therapeutic efficacy. These include EGb761® (standardized ginkgo biloba extract), piracetam, and Dimebon. All improve experimentally many aspects of mitochondrial dysfunction including mitochondrial dynamics and also improve cognition and impaired neuronal plasticity, the functionally most relevant consequences of mitochondrial dysfunction. All partially inhibit opening events of the mitochondrial permeability transition pore (mPTP) which previously has mainly been discussed as a mechanism relevant for the induction of apoptosis. However, as more recent work suggests the mPTP as a master regulator of many mitochondrial functions, our data suggest the mPTP as a possible relevant drug target within the love triangle between mPTP regulation, mitochondrial dynamics, and mitochondrial function including regulation of neuronal plasticity. Drugs interfering with mPTP function will improve not only mitochondrial impairment in aging and AD but also will have beneficial effects on impaired neuronal plasticity, the pathomechanism which correlates best with functional deficits (cognition, behavior) in aging and AD.

Modelling mitochondrial dysfunction in Alzheimer’s disease using human induced pluripotent stem cells

Alzheimer’s disease (AD) is the most common form of dementia. To date, only five pharmacological agents have been approved by the Food and Drug Administration for clinical use in AD, all of which target the symptoms of the disease rather than the cause. Increasing our understanding of the underlying pathophysiology of AD will facilitate the development of new therapeutic strategies. Over the years, the major hypotheses of AD etiology have focused on deposition of amyloid beta and mitochondrial dysfunction. In this review we highlight the potential of experimental model systems based on human induced pluripotent stem cells (iPSCs) to provide novel insights into the cellular pathophysiology underlying neurodegeneration in AD. Whilst Down syndrome and familial AD iPSC models faithfully reproduce features of AD such as accumulation of Aβ and tau, oxidative stress and mitochondrial dysfunction, sporadic AD is much more difficult to model in this way due to its complex etiology. Nevertheless, iPSC-based modelling of AD has provided invaluable insights into the underlying pathophysiology of the disease, and has a huge potential for use as a platform for drug discovery.

Amyloid Beta and Phosphorylated Tau-Induced Defective Autophagy and Mitophagy in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by memory loss and multiple cognitive impairments. Several decades of intense research have revealed that multiple cellular changes are implicated in the development and progression of AD, including mitochondrial damage, synaptic dysfunction, amyloid beta (Aβ) formation and accumulation, hyperphosphorylated tau (P-Tau) formation and accumulation, deregulated microRNAs, synaptic damage, and neuronal loss in patients with AD. Among these, mitochondrial dysfunction and synaptic damage are early events in the disease process. Recent research also revealed that Aβ and P-Tau-induced defective autophagy and mitophagy are prominent events in AD pathogenesis. Age-dependent increased levels of Aβ and P-Tau reduced levels of several autophagy and mitophagy proteins. In addition, abnormal interactions between (1) Aβ and mitochondrial fission protein Drp1; (2) P-Tau and Drp1; and (3) Aβ and PINK1/parkin lead to an inability to clear damaged mitochondria and other cellular debris from neurons. These events occur selectively in affected AD neurons. The purpose of our article is to highlight recent developments of a Aβ and P-Tau-induced defective autophagy and mitophagy in AD. This article also summarizes several aspects of mitochondrial dysfunction, including abnormal mitochondrial dynamics (increased fission and reduced fusion), defective mitochondrial biogenesis, reduced ATP, increased free radicals and lipid peroxidation, and decreased cytochrome c oxidase (COX) activity and calcium dyshomeostasis in AD pathogenesis. Our article also discusses how reduced levels of Drp1, Aβ, and P-Tau can enhance the clearance of damaged mitochondria and other cellular debris by autophagy and mitophagy mechanisms.

Mitochondria and Mitochondrial Cascades in Alzheimer's Disease

Decades of research indicate mitochondria from Alzheimer's disease (AD) patients differ from those of non-AD individuals. Initial studies revealed structural differences, and subsequent studies showed functional deficits. Observations of structure and function changes prompted investigators to consider the consequences, significance, and causes of AD-related mitochondrial dysfunction. Currently, extensive research argues mitochondria may mediate, drive, or contribute to a variety of AD pathologies. The perceived significance of these mitochondrial changes continues to grow, and many currently believe AD mitochondrial dysfunction represents a reasonable therapeutic target. Debate continues over the origin of AD mitochondrial changes. Some argue amyloid-β (Aβ) induces AD mitochondrial dysfunction, a view that does not challenge the amyloid cascade hypothesis and that may in fact help explain that hypothesis. Alternatively, data indicate mitochondrial dysfunction exists independent of Aβ, potentially lies upstream of Aβ deposition, and suggest a primary mitochondrial cascade hypothesis that assumes mitochondrial pathology hierarchically supersedes Aβ pathology. Mitochondria, therefore, appear at least to mediate or possibly even initiate pathologic molecular cascades in AD. This review considers studies and data that inform this area of AD research.