Mitochondrial Disruption by Amyloid Beta 42 Identified by Proteomics and Pathway Mapping

Poration of mitochondrial membranes by amyloidogenic peptides and other biological toxins

Mitochondria are essential organelles known to serve broad functions, including in cellular metabolism, calcium buffering, signaling pathways and the regulation of apoptotic cell death. Maintaining the integrity of the outer (OMM) and inner mitochondrial membranes (IMM) is vital for mitochondrial health. Cardiolipin (CL), a unique dimeric glycerophospholipid, is the signature lipid of energy-converting membranes. It plays a significant role in maintaining mitochondrial architecture and function, stabilizing protein complexes and facilitating efficient oxidative phosphorylation (OXPHOS) whilst regulating cytochrome c release from mitochondria. CL is especially enriched in the IMM and at sites of contact between the OMM and IMM. Disorders of protein misfolding, such as Alzheimer's and Parkinson's diseases, involve amyloidogenic peptides like amyloid-β, tau and α-synuclein, which form metastable toxic oligomeric species that interact with biological membranes. Electrophysiological studies have shown that these oligomers form ion-conducting nanopores in membranes mimicking the IMM's phospholipid composition. Poration of mitochondrial membranes disrupts the ionic balance, causing osmotic swelling, loss of the voltage potential across the IMM, release of pro-apoptogenic factors, and leads to cell death. The interaction between CL and amyloid oligomers appears to favour their membrane insertion and pore formation, directly implicating CL in amyloid toxicity. Additionally, pore formation in mitochondrial membranes is not limited to amyloid proteins and peptides; other biological peptides, as diverse as the pro-apoptotic Bcl-2 family members, gasdermin proteins, cobra venom cardiotoxins and bacterial pathogenic toxins, have all been described to punch holes in mitochondria, contributing to cell death processes. Collectively, these findings underscore the vulnerability of mitochondria and the involvement of CL in various pathogenic mechanisms, emphasizing the need for further research on targeting CL-amyloid interactions to mitigate mitochondrial dysfunction.

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

Rotenone Induces a Neuropathological Phenotype in Cholinergic-like Neurons Resembling Parkinson's Disease Dementia (PDD)

Parkinson's disease with dementia (PDD) is a neurological disorder that clinically and neuropathologically overlaps with Parkinson's disease (PD) and Alzheimer's disease (AD). Although it is assumed that alpha-synuclein ( α -Syn), amyloid beta (A β ), and the protein Tau might synergistically induce cholinergic neuronal degeneration, presently the pathological mechanism of PDD remains unclear. Therefore, it is essential to delve into the cellular and molecular aspects of this neurological entity to identify potential targets for prevention and treatment strategies. Cholinergic-like neurons (ChLNs) were exposed to rotenone (ROT, 10 μ M) for 24 h. ROT provokes loss of Δ Ψ m , generation of reactive oxygen species (ROS), phosphorylation of leucine-rich repeated kinase 2 (LRRK2 at Ser935) concomitantly with phosphorylation of α -synuclein ( α -Syn, Ser129), induces accumulation of intracellular A β (iA β ), oxidized DJ-1 (Cys106), as well as phosphorylation of TAU (Ser202/Thr205), increases the phosphorylation of c-JUN (Ser63/Ser73), and increases expression of proapoptotic proteins TP53, PUMA, and cleaved caspase 3 (CC3) in ChLNs. These neuropathological features resemble those reproduced in presenilin 1 (PSEN1) E280A ChLNs. Interestingly, anti-oxidant and anti-amyloid cannabidiol (CBD), JNK inhibitor SP600125 (SP), TP53 inhibitor pifithrin- α (PFT), and LRRK2 kinase inhibitor PF-06447475 (PF475) significantly diminish ROT-induced oxidative stress (OS), proteinaceous, and cell death markers in ChLNs compared to naïve ChLNs. In conclusion, ROT induces p- α -Syn, iA β , p-Tau, and cell death in ChLNs, recapitulating the neuropathology findings in PDD. Our report provides an excellent in vitro model to test for potential therapeutic strategies against PDD. Our data suggest that ROT induces a neuropathologic phenotype in ChLNs similar to that caused by the mutation PSEN1 E280A.

Mitochondria-sequestered Aβ renders synaptic mitochondria vulnerable in the elderly with a risk of Alzheimer disease

Mitochondria are critical for neurophysiology, and mitochondrial dysfunction constitutes a characteristic pathology in both brain aging and Alzheimer disease (AD). Whether mitochondrial deficiency in brain aging and AD is mechanistically linked, however, remains controversial. We report a correlation between intrasynaptosomal amyloid β 42 (Aβ42) and synaptic mitochondrial bioenergetics inefficiency in both aging and amnestic mild cognitive impairment, a transitional stage between normal aging and AD. Experiments using a mouse model expressing nonmutant humanized Aβ (humanized Aβ-knockin [hAβ-KI] mice) confirmed the association of increased intramitochondrial sequestration of Aβ42 with exacerbated synaptic mitochondrial dysfunction in an aging factor- and AD risk-bearing context. Also, in comparison with global cerebral Aβ, intramitochondrial Aβ was relatively preserved from activated microglial phagocytosis in aged hAβ-KI mice. The most parsimonious interpretation of our results is that aging-related mitochondrial Aβ sequestration renders synaptic mitochondrial dysfunction in the transitional stage between normal aging and AD. Mitochondrial dysfunction in both brain aging and the prodromal stage of AD may follow a continuous transition in response to escalated intraneuronal, especially intramitochondrial Aβ, accumulation. Moreover, our findings further implicate a pivotal role of mitochondria in harboring early amyloidosis during the conversion from normal to pathological aging.

Mitochondrial Proteomes in Neural Cells: A Systematic Review

Mitochondria are ancient endosymbiotic double membrane organelles that support a wide range of eukaryotic cell functions through energy, metabolism, and cellular control. There are over 1000 known proteins that either reside within the mitochondria or are transiently associated with it. These mitochondrial proteins represent a functional subcellular protein network (mtProteome) that is encoded by mitochondrial and nuclear genomes and significantly varies between cell types and conditions. In neurons, the high metabolic demand and differential energy requirements at the synapses are met by specific modifications to the mtProteome, resulting in alterations in the expression and functional properties of the proteins involved in energy production and quality control, including fission and fusion. The composition of mtProteomes also impacts the localization of mitochondria in axons and dendrites with a growing number of neurodegenerative diseases associated with changes in mitochondrial proteins. This review summarizes the findings on the composition and properties of mtProteomes important for mitochondrial energy production, calcium and lipid signaling, and quality control in neural cells. We highlight strategies in mass spectrometry (MS) proteomic analysis of mtProteomes from cultured cells and tissue. The research into mtProteome composition and function provides opportunities in biomarker discovery and drug development for the treatment of metabolic and neurodegenerative disease.

The many "Neurofaces" of Prohibitins 1 and 2: Crucial for the healthy brain, dysregulated in numerous brain disorders

Prohibitin 1 (PHB1) and prohibitin 2 (PHB2) are proteins that are nearly ubiquitously expressed. They are localized in mitochondria, cytosol and cell nuclei. In the healthy CNS, they occur in neurons and non-neuronal cells (oligodendrocytes, astrocytes, microglia, and endothelial cells) and fulfill pivotal functions in brain development and aging, the regulation of brain metabolism, maintenance of structural integrity, synapse formation, aminoacidergic neurotransmission and, probably, regulation of brain action of certain hypothalamic-pituitary hormones.With regard to the diseased brain there is increasing evidence that prohibitins are prominently involved in numerous major diseases of the CNS, which are summarized and discussed in the present review (brain tumors, neurotropic viruses, Alzheimer disease, Down syndrome, Fronto-temporal and vascular dementia, dementia with Lewy bodies, Parkinson disease, Huntington disease, Multiple sclerosis, Amyotrophic lateral sclerosis, stroke, alcohol use disorder, schizophrenia and autism). Unfortunately, there is no PHB-targeted therapy available for any of these diseases.

Potential benefits of medium chain fatty acids in aging and neurodegenerative disease

Neurodegenerative diseases are a large class of neurological disorders characterized by progressive dysfunction and death of neurones. Examples include Alzheimer's disease, Parkinson's disease, frontotemporal dementia, and amyotrophic lateral sclerosis. Aging is the primary risk factor for neurodegeneration; individuals over 65 are more likely to suffer from a neurodegenerative disease, with prevalence increasing with age. As the population ages, the social and economic burden caused by these diseases will increase. Therefore, new therapies that address both aging and neurodegeneration are imperative. Ketogenic diets (KDs) are low carbohydrate, high-fat diets developed initially as an alternative treatment for epilepsy. The classic ketogenic diet provides energy via long-chain fatty acids (LCFAs); naturally occurring medium chain fatty acids (MCFAs), on the other hand, are the main components of the medium-chain triglyceride (MCT) ketogenic diet. MCT-based diets are more efficient at generating the ketone bodies that are used as a secondary energy source for neurones and astrocytes. However, ketone levels alone do not closely correlate with improved clinical symptoms. Recent findings suggest an alternative mode of action for the MCFAs, e.g., via improving mitochondrial biogenesis and glutamate receptor inhibition. MCFAs have been linked to the treatment of both aging and neurodegenerative disease via their effects on metabolism. Through action on multiple disease-related pathways, MCFAs are emerging as compounds with notable potential to promote healthy aging and ameliorate neurodegeneration. MCFAs have been shown to stimulate autophagy and restore mitochondrial function, which are found to be disrupted in aging and neurodegeneration. This review aims to provide insight into the metabolic benefits of MCFAs in neurodegenerative disease and healthy aging. We will discuss the use of MCFAs to combat dysregulation of autophagy and mitochondrial function in the context of "normal" aging, Parkinson's disease, amyotrophic lateral sclerosis and Alzheimer's disease.

Proteomic responses in the human dopaminergic LUHMES cell line to imidacloprid and its metabolites imidacloprid-olefin and desnitro-imidacloprid

Neonicotinoids (neonics) are amongst the most commonly used class of pesticides globally. In the United States, imidacloprid (IMI) is extensively used for agriculture and in other common applications such as house-hold pest control. Regular exposure to IMI, and several of its known metabolites including IMI-olefin and desnitro-imidacloprid (DN-IMI), has been shown to be harmful to many organisms including mammals, birds, and fish. Studies show that neonics bind human nicotinicacetylcholine receptors (nAChRs) and cause cellular toxicity. In the dopaminergic Lund human mesencephalic (LUHMES) cell line, IMI and other neonics (10-100 μM) have been recently shown to activate intracellular calcium signaling through nAChRs. Thus, we examined proteomic responses of LUHMES cells to a 48-h treatment with 50 μM IMI, IMI-olefin, or DN-IMI. Our findings show differential effects of these neonics on cellular protein expression. Bioinformatic analysis of significantly altered proteins indicates an effect of IMI, IMI-olefin, and DN-IMI on protein synthesis and ribosomal function. These findings suggest a role for protein synthesis and transcriptional regulation in neonic-mediated dopaminergic neurotoxicity.

The human acetylcholinesterase C-terminal T30 peptide activates neuronal growth through alpha 7 nicotinic acetylcholine receptors and the mTOR pathway

Acetylcholinesterase (AChE) is a highly conserved enzyme responsible for the regulation of acetylcholine signaling within the brain and periphery. AChE has also been shown to participate in non-enzymatic activity and contribute to cellular development and aging. In particular, enzymatic cleavage of the synaptic AChE isoform, AChE-T, is shown to generate a bioactive T30 peptide that binds to the ⍺7 nicotinic acetylcholine receptor (nAChR) at synapses. Here, we explore intracellular mechanisms of T30 signaling within the human cholinergic neural cell line SH-SY5Y using high performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS/MS). Proteomic analysis of cells exposed to (100 nM) T30 for 3-days reveals significant changes within proteins important for cell growth. Specifically, bioinformatic analysis identifies proteins that converge onto the mammalian target of rapamycin (mTOR) pathway signaling. Functional experiments confirm that T30 regulates neural cell growth via mTOR signaling and ⍺7 nAChR activation. T30 was found promote mTORC1 pro-growth signaling through an increase in phosphorylated elF4E and S6K1, and a decrease in the autophagy LC3B-II protein. These findings are corroborated in hippocampal neurons and show that T30 promotes dendritic arborization. Taken together, our findings define mTOR as a novel pathway activated by T30 interaction with the nAChR and suggest a role for this process in human disease.

PSEN1 E280A Cholinergic-like Neurons and Cerebral Spheroids Derived from Mesenchymal Stromal Cells and from Induced Pluripotent Stem Cells Are Neuropathologically Equivalent

Alzheimer's disease (AD) is a chronic neurological condition characterized by the severe loss of cholinergic neurons. Currently, the incomplete understanding of the loss of neurons has prevented curative treatments for familial AD (FAD). Therefore, modeling FAD in vitro is essential for studying cholinergic vulnerability. Moreover, to expedite the discovery of disease-modifying therapies that delay the onset and slow the progression of AD, we depend on trustworthy disease models. Although highly informative, induced pluripotent stem cell (iPSCs)-derived cholinergic neurons (ChNs) are time-consuming, not cost-effective, and labor-intensive. Other sources for AD modeling are urgently needed. Wild-type and presenilin (PSEN)1 p.E280A fibroblast-derived iPSCs, menstrual blood-derived menstrual stromal cells (MenSCs), and umbilical cord-derived Wharton Jelly's mesenchymal stromal cells (WJ-MSCs) were cultured in Cholinergic-N-Run and Fast-N-Spheres V2 medium to obtain WT and PSEN 1 E280A cholinergic-like neurons (ChLNs, 2D) and cerebroid spheroids (CSs, 3D), respectively, and to evaluate whether ChLNs/CSs can reproduce FAD pathology. We found that irrespective of tissue source, ChLNs/CSs successfully recapitulated the AD phenotype. PSEN 1 E280A ChLNs/CSs show accumulation of iAPPβ fragments, produce eAβ42, present TAU phosphorylation, display OS markers (e.g., oxDJ-1, p-JUN), show loss of ΔΨm, exhibit cell death markers (e.g., TP53, PUMA, CASP3), and demonstrate dysfunctional Ca2+ influx response to ACh stimuli. However, PSEN 1 E280A 2D and 3D cells derived from MenSCs and WJ-MSCs can reproduce FAD neuropathology more efficiently and faster (11 days) than ChLNs derived from mutant iPSCs (35 days). Mechanistically, MenSCs and WJ-MSCs are equivalent cell types to iPSCs for reproducing FAD in vitro.

Myelin in Alzheimer's disease: culprit or bystander?

Alzheimer's disease (AD) is a neurodegenerative disorder with neuronal and synaptic losses due to the accumulation of toxic amyloid β (Αβ) peptide oligomers, plaques, and tangles containing tau (tubulin-associated unit) protein. While familial AD is caused by specific mutations, the sporadic disease is more common and appears to result from a complex chronic brain neuroinflammation with mitochondriopathies, inducing free radicals' accumulation. In aged brain, mutations in DNA and several unfolded proteins participate in a chronic amyloidosis response with a toxic effect on myelin sheath and axons, leading to cognitive deficits and dementia. Αβ peptides are the most frequent form of toxic amyloid oligomers. Accumulations of misfolded proteins during several years alters different metabolic mechanisms, induce chronic inflammatory and immune responses with toxic consequences on neuronal cells. Myelin composition and architecture may appear to be an early target for the toxic activity of Aβ peptides and others hydrophobic misfolded proteins. In this work, we describe the possible role of early myelin alterations in the genesis of neuronal alterations and the onset of symptomatology. We propose that some pathophysiological and clinical forms of the disease may arise from structural and metabolic disorders in the processes of myelination/demyelination of brain regions where the accumulation of non-functional toxic proteins is important. In these forms, the primacy of the deleterious role of amyloid peptides would be a matter of questioning and the initiating role of neuropathology would be primarily the fact of dysmyelination.

Prohibitins in neurodegeneration and mitochondrial homeostasis

The incidence of age-related neurodegenerative disorders has risen with the increase of life expectancy. Unfortunately, the diagnosis of such disorders is in most cases only possible when the neurodegeneration status is already advanced, and symptoms are evident. Although age-related neurodegeneration is a common phenomenon in living animals, the cellular and molecular mechanisms behind remain poorly understood. Pathways leading to neurodegeneration usually diverge from a common starting point, mitochondrial stress, which can serve as a potential target for early diagnosis and treatments. Interestingly, the evolutionarily conserved mitochondrial prohibitin (PHB) complex is a key regulator of ageing and metabolism that has been associated with neurodegenerative diseases. However, its role in neurodegeneration is still not well characterized. The PHB complex shows protective or toxic effects in different genetic and physiological contexts, while mitochondrial and cellular stress promote both up and downregulation of PHB expression. With this review we aim to shed light into the complex world of PHB’s function in neurodegeneration by putting together the latest advances in neurodegeneration and mitochondrial homeostasis associated with PHB. A better understanding of the role of PHB in neurodegeneration will add knowledge to neuron deterioration during ageing and help to identify early molecular markers of mitochondrial stress. This review will deepen our understanding of age-related neurodegeneration and provide questions to be addressed, relevant to human health and to improve the life quality of the elderly.

Nicotinic receptor components of amyloid beta 42 proteome regulation in human neural cells

Alzheimer’s disease (AD) is associated with chronic neurodegeneration often accompanied by elevated levels of the neurotoxic peptide amyloid-beta 1–42 (Aβ₄₂) in the brain. Studies show that extracellular Aβ₄₂ binds to various cell surface receptors including the human α7 nicotinic acetylcholine receptor (nAChR) and activates pathways of neurotoxicity leading to cell death. The α7 nAChR is thus considered a promising drug target for therapy against neurodegenerative disease such as AD. In this study, we use mass spectrometry-based label-free precursor ion quantification to identify proteins and pathways that are changed by a 72-hour treatment with Aβ₄₂ or Aβ₄₂ in the presence of the α7 nAChR blocker, α-bungarotoxin (Bgtx) in the human neuroblastoma SH-SY5Y cell line. Bioinformatic gene ontology enrichment analysis was used to identify and characterize proteins and pathways altered by Aβ₄₂ presentation. The results support evidence on the involvement of mitochondrial proteins in Aβ₄₂ responses and define potential mechanisms of α7 nAChR mediated amyloid toxicity. These findings can inform pharmacological strategies for drug design and treatment against amyloid disease.