The Mitochondrion: A Potential Therapeutic Target for Alzheimer's Disease

Chronic Traumatic Encephalopathy as the Course of Alzheimer's Disease

This editorial investigates chronic traumatic encephalopathy (CTE) as a course of Alzheimer's disease (AD). CTE is a debilitating neurodegenerative disease that is the result of repeated mild traumatic brain injury (TBI). Many epidemiological studies show that experiencing a TBI in early or middle life is associated with an increased risk of dementia later in life. Chronic traumatic encephalopathy (CTE) and Alzheimer's disease (AD) present a series of similar neuropathological features that were investigated in this work like recombinant tau into filaments or the accumulation and aggregation of Aβ protein. However, these two conditions differ from each other in brain-blood barrier damage. The purpose of this review was to evaluate information about CTE and AD from various articles, focusing especially on new therapeutic possibilities for the improvement in cognitive skills.

Clarity on the blazing trail: clearing the way for amyloid-removing therapies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a complex pathogenesis. Senile plaques composed of the amyloid-β (Aβ) peptide in the brain are the core hallmarks of AD and a promising target for the development of disease-modifying therapies. However, over the past 20 years, the failures of clinical trials directed at Aβ clearance have fueled a debate as to whether Aβ is the principal pathogenic factor in AD and a valid therapeutic target. The success of the recent phase 3 trials of lecanemab (Clarity AD) and donanemab (Trailblazer Alz2), and lessons from previous Aβ clearance trials provide critical evidence to support the role of Aβ in AD pathogenesis and suggest that targeting Aβ clearance is heading in the right direction for AD treatment. Here, we analyze key questions relating to the efficacy of Aβ targeting therapies, and provide perspectives on early intervention, adequate Aβ removal, sufficient treatment period, and combinatory therapeutics, which may be required to achieve the best cognitive benefits in future trials in the real world.

Mitochondrial Modulators: The Defender

Mitochondria are widely considered the "power hub" of the cell because of their pivotal roles in energy metabolism and oxidative phosphorylation. However, beyond the production of ATP, which is the major source of chemical energy supply in eukaryotes, mitochondria are also central to calcium homeostasis, reactive oxygen species (ROS) balance, and cell apoptosis. The mitochondria also perform crucial multifaceted roles in biosynthetic pathways, serving as an important source of building blocks for the biosynthesis of fatty acid, cholesterol, amino acid, glucose, and heme. Since mitochondria play multiple vital roles in the cell, it is not surprising that disruption of mitochondrial function has been linked to a myriad of diseases, including neurodegenerative diseases, cancer, and metabolic disorders. In this review, we discuss the key physiological and pathological functions of mitochondria and present bioactive compounds with protective effects on the mitochondria and their mechanisms of action. We highlight promising compounds and existing difficulties limiting the therapeutic use of these compounds and potential solutions. We also provide insights and perspectives into future research windows on mitochondrial modulators.

Prospective Evaluation of an Amide-Based Zinc Scaffold as an Anti-Alzheimer Agent: In Vitro, In Vivo, and Computational Studies

Alzheimer's disease is the most common progressive neurodegenerative mental disorder associated with loss of memory, decline in cognitive function, and dysfunction of language. The prominent pathogenic causes of this disease involve deposition of amyloid-β plaques, acetylcholine neurotransmitter deficiency, and accumulation of neurofibrillary tangles. There are multiple pathways that have been targeted to treat this disease. The inhibition of the intracellular cyclic AMP regulator phosphodiesterase IV causes the increase in CAMP levels that play an important role in the memory formation process. Organometallic chemistry works in a different way in treating pharmacological disorders. In the field of medicinal chemistry and pharmaceuticals, zinc-based amide carboxylates have been shown to be a preferred pharmacophore. The purpose of this research work was to investigate the potential of zinc amide carboxylates in inhibition of phosphodiesterase IV for the Alzheimer's disease management. Swiss Albino mice under controlled conditions were divided into seven groups with 10 mice each. Group I was injected with carboxymethylcellulose (CMC) at 1 mL/100 g dose, group II was injected with Streptozotocin (STZ) at 3 mg/kg dose, group III was injected with Piracetam acting as a standard drug at 200 mg/kg dosage, while groups IV-VII were injected with a zinc scaffold at the dose regimen of 10, 20, 40, and 80 mg/kg through intraperitoneal injection. All groups except group I were injected with Streptozotocin on the first day and third day of treatment at the dose of 3 mg/kg through an intracerebroventricular route to induce Alzheimer's disease. Afterward, respective treatment was continued for all groups for 23 days. In between the treatment regimen, groups were analyzed for memory and learning improvement through various behavioral tests such as open field, elevated plus maze, Morris water maze, and passive avoidance tests. At the end of the study, different biochemical markers in the brain were estimated like neurotransmitters (dopamine, serotonin and adrenaline), oxidative stress markers (superoxide dismutase, glutathione, and catalase), acetylcholinesterase (AchE), tau proteins, and amyloid-β levels. A PCR study was also performed. Results showed that the LD₅₀ of the zinc scaffold is greater than 2000 mg/kg. Research indicated that the zinc scaffold has the potential to improve the memory impairment and learning behavior in Alzheimer's disease animal models in a dose-dependent manner. At the dose of 80 mg/kg, a maximum response was observed for the zinc scaffold. Maximum reduction in the acetylcholinesterase enzyme was observed at 80 mg/kg dose, which was further strengthened and verified by the PCR study. Oxidative stress was restored by the zinc scaffold due to the significant activation of the endogenous antioxidant enzymes. This research ended up with the conclusion that the zinc-based amide carboxylate scaffold has the potential to improve behavioral disturbances and vary the biochemical markers in the brain.

A new hope: Mitochondria, a critical factor in the war against prions

Prion diseases encompass a group of incurable neurodegenerative disorders that occur due to the misfolding and aggregation of infectious proteins. The most well-known prion diseases are Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (also known as mad cow disease), and kuru. It is estimated that around 1-2 persons per million worldwide are affected annually by prion disorders. Infectious prion proteins propagate in the brain, clustering in the cells and rapidly inducing tissue degeneration and death. Prion disease alters cell metabolism and energy production damaging mitochondrial function and dynamics leading to a fast accumulation of damage. Dysfunction of mitochondria could be considered as an early precursor and central element in the pathogenesis of prion diseases such as in sporadic CJD. Preserving mitochondria function may help to resist the rapid spread and damage of prion proteins and even clearance. In the war against prions and other degenerative diseases, studying how to preserve the function of mitochondria by using antioxidants and even replacing them with artificial mitochondrial transfer/transplant (AMT/T) may bring a new hope and lead to an increase in patients' survival. In this perspective review, we provide key insights about the relationship between the progression of prion disease and mitochondria, in which understanding how protecting mitochondria function and viability by using antioxidants or AMT/T may help to develop novel therapeutic interventions.

The war against Alzheimer, the mitochondrion strikes back!

Alzheimer's disease (AD) is a leading neurodegenerative pathology associated with aging worldwide. It is estimated that AD prevalence will increase from 5.8 million people today to 13.8 million by 2050 in the United States alone. AD effects in the brain are well known; however, there is still a lack of knowledge about the cellular mechanisms behind the origin of AD. It is known that AD induces cellular stress affecting the energy metabolism in brain cells. During the pathophysiological advancement of AD, damaged mitochondria enter a vicious cycle, producing reactive oxygen species (ROS), harming mitochondrial DNA and proteins, leading to more ROS and cellular death. Additionally, mitochondria are interconnected with the plaques formed by amyloid-β in AD and have underlying roles in the progression of the disease and severity. For years, the biomedical field struggled to develop new therapeutic options for AD without a significant advancement. However, mitochondria are striking back existing outside cells in a new mechanism of intercellular communication. Extracellular mitochondria are exchanged from healthy to damaged cells to rescue those with a perturbed metabolism in a process that could be applied as a new therapeutic option to repair those brain cells affected by AD. In this review we highlight key aspects of mitochondria's role in CNS' physiology and neurodegenerative disorders, focusing on AD. We also suggest how mitochondria strikes back as a therapeutic target and as a potential agent to be transplanted to repair neurons affected by AD.

Fighting Parkinson's disease: the return of the mitochondria

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, worldwide. PD neuro-energetically affects the extrapyramidal system, by the progressive loss of striatal dopaminergic neurons in the substantia nigra pars compacta, leading to motor impairment. During the progression of PD, there will be an increase in mitochondrial dysfunction, reactive oxygen species (ROS), stress and accumulation of α-synuclein in neurons. This results in mitochondrial mutations altering their function and fission-fusion mechanisms and central nervous system (CNS) degeneration. Intracellular mitochondrial dysfunction has been studied for a long time in PD due to the decline of mitochondrial dynamics inside neurons. Mitochondrial damage-associated molecular patterns (DAMPs) have been known to contribute to several CNS pathologies especially PD pathogenesis. New and exciting evidence regarding the exchange of mitochondria between healthy to damaged cells in the central nervous system (CNS) and the therapeutic use of the artificial mitochondrial transfer/transplant (AMT) marked a return of this organelle to develop innovative therapeutic procedures for PD. The focus of this review aims to shed light on the role of mitochondria, both intra and extracellularly in PD, and how AMT could be used to generate new potential therapies in the fight against PD. Moreover, we suggest that mitochondrial therapy could work as a preventative measure, motivating the field to move towards this goal.

Adaptation of mitochondrial network dynamics and velocity of mitochondrial movement to chronic stress present in fibroblasts derived from patients with sporadic form of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Only 10% of all cases are familial form, the remaining 90% are sporadic form with unknown genetic background. The etiology of sporadic AD is still not fully understood. Pathogenesis and pathobiology of this disease are limited due to the limited number of experimental models. We used primary culture of fibroblasts derived from patients diagnosed with sporadic form of AD for investigation of dynamic properties of mitochondria, including fission-fusion process and localization of mitochondria within the cell. We observed differences in mitochondrial network organization with decreased mitochondrial transport velocity, and a drop in the frequency of fusion-fission events. These studies show how mitochondrial dynamics adapt to the conditions of long-term mitochondrial stress that prevails in cells of sporadic form of AD.

Transplantation of GABAergic Interneuron Progenitor Attenuates Cognitive Deficits of Alzheimer's Disease Model Mice

Excitatory (E) and inhibitory (I) balance of neural network activity is essential for normal brain function and of particular importance to memory. Disturbance of E/I balance contributes to various neurological disorders. The appearance of neural hyperexcitability in Alzheimer's disease (AD) is even suggested as one of predictors of accelerated cognitive decline. In this study, we found that GAD67+, Parvalbumin+, Calretinin+, and Neuropeptide Y+ interneurons were progressively lost in the brain of APP/PS1 mice. Transplanted embryonic medial ganglionic eminence derived interneuron progenitors (IPs) survived, migrated, and differentiated into GABAergic interneuron subtypes successfully at 2 months after transplantation. Transplantation of IPs hippocampally rescued impaired synaptic plasticity and cognitive deficits of APP/PS1 transgenic mice, concomitant with a suppression of neural hyperexcitability, whereas transplantation of IPs failed to attenuate amyloid-β accumulation, neuroinflammation, and synaptic loss of APP/PS1 transgenic mice. These observations indicate that transplantation of IPs improves learning and memory of APP/PS1 transgenic mice via suppressing neural hyperexcitability. This study highlights a causal contribution of GABAergic dysfunction to AD pathogenesis and the potentiality of IP transplantation in AD therapy.

Vitamin K2 protects against Aβ42-induced neurotoxicity by activating autophagy and improving mitochondrial function in Drosophila

OBJECTIVE

Alzheimer disease is characterized by progressive decline in cognitive function due to neurodegeneration induced by accumulation of Aβ and hyperphosphorylated tau protein. This study was conducted to explore the protective effect of vitamin K2 against Aβ42-induced neurotoxicity.

METHODS

Alzheimer disease transgenic Drosophila model used in this study was amyloid beta with the arctic mutation expressed in neurons. Alzheimer disease flies were treated with vitamin K2 for 28 days after eclosion. Aβ42 level in brain was detected by ELISA. Autophagy-related genes and NDUFS3, the core subunit of mitochondrial complex I, were examined using real-Time PCR (RT-PCR) and western blot analysis.

RESULTS

Vitamin K2 improved climbing ability (P = 0.0105), prolonged lifespan (P < 0.0001) and decreased Aβ42 levels (P = 0.0267), upregulated the expression of LC3 and Beclin1(P = 0.0012 and P = 0.0175, respectively), increased the conversion of LC3I to LC3II (P = 0.0206) and decreased p62 level (P =0.0115) in Alzheimer disease flies. In addition, vitamin K2 upregulated the expression of NDUFS3 (P = 0.001) and increased ATP production (P = 0.0033) in Alzheimer disease flies.

CONCLUSION

It seems that vitamin K2 protect against Aβ42-induced neurotoxicity by activation of autophagy and rescue mitochondrial dysfunction, which suggests that it may be a potential valuable therapeutic approach for Alzheimer disease.

Tau Accumulation via Reduced Autophagy Mediates GGGGCC Repeat Expansion-Induced Neurodegeneration in Drosophila Model of ALS

Expansions of trinucleotide or hexanucleotide repeats lead to several neurodegenerative disorders, including Huntington disease [caused by expanded CAG repeats (CAGr) in the HTT gene], and amyotrophic lateral sclerosis [ALS, possibly caused by expanded GGGGCC repeats (G4C2r) in the C9ORF72 gene], of which the molecular mechanisms remain unclear. Here, we demonstrated that lowering the Drosophila homologue of tau protein (dtau) significantly rescued in vivo neurodegeneration, motor performance impairments, and the shortened life-span in Drosophila expressing expanded CAGr or expanded G4C2r. Expression of human tau (htau4R) restored the disease-related phenotypes that had been mitigated by the loss of dtau, suggesting an evolutionarily-conserved role of tau in neurodegeneration. We further revealed that G4C2r expression increased tau accumulation by inhibiting autophagosome-lysosome fusion, possibly due to lowering the level of BAG3, a regulator of autophagy and tau. Taken together, our results reveal a novel mechanism by which expanded G4C2r causes neurodegeneration via an evolutionarily-conserved mechanism. Our findings provide novel autophagy-related mechanistic insights into C9ORF72-ALS and possible entry points to disease treatment.

Functional prediction and characterization of Dip2 gene in mice

Disconnected interacting protein 2 (DIP2) is a highly conserved protein family among invertebrates and vertebrates, but its function remains unclear. In this paper, we summarized the conservation of gene sequences and protein domains of DIP2 family members and predicted that they may have a similar functional role in acetyl-coenzyme A (acetyl-CoA) synthesis. We then used the most characterized member, disconnected interacting protein 2 homolog A (DIP2A), for further study. DIP2A is a cytoplasmic protein that is preferentially localized to mitochondria, and its acetyl-CoA synthetase activity has been demonstrated in vitro. Furthermore, the level of acetyl-CoA in HEK293 cells overexpressing DIP2A was increased, which is consistent with its metabolically related function. Together, these data enrich the evolutionary and functional characterization of dip2 genes and provide significant insights into the identification and application of other homologs of DIP2.

Mitochondrial Dysfunction in Neural Injury

Mitochondria are the double membrane organelles providing most of the energy for cells. In addition, mitochondria also play essential roles in various cellular biological processes such as calcium signaling, apoptosis, ROS generation, cell growth, and cell cycle. Mitochondrial dysfunction is observed in various neurological disorders which harbor acute and chronic neural injury such as neurodegenerative diseases and ischemia, hypoxia-induced brain injury. In this review, we describe how mitochondrial dysfunction contributes to the pathogenesis of neurological disorders which manifest chronic or acute neural injury.