Small Hexokinase 1 Peptide against Toxic SOD1 G93A Mitochondrial Accumulation in ALS Rescues the ATP-Related Respiration

VDAC1-Targeted NHK1 Peptide Recovers Mitochondrial Dysfunction Counteracting Amyloid-β Oligomers Toxicity in Alzheimer's Disease

Mitochondrial dysfunction has been implicated in a broad range of age-related pathologies and has been proposed as a causative factor in Alzheimer's disease (AD). Analysis of post-mortem brains from AD patients showed increased levels of Voltage-dependent anion-selective channel 1 (VDAC1) in the dystrophic neurites surrounding amyloid-β (Aβ) deposits, suggesting a direct association between VDAC1 and mitochondrial toxicity. VDAC1 is the most abundant pore-forming protein of the outer mitochondrial membrane and, as a channel, it plays a pivotal role in regulating cellular bioenergetics, allowing the continuous exchange of ions and metabolites (ATP/ADP, Krebs cycle intermediates) between cytosol and mitochondria. In light of this evidence, we looked into the effects of Aβ oligomers on VDAC1 functions through electrophysiological and respirometric techniques. Our findings indicate that Aβ oligomers significantly modify the conductance, voltage dependency, and kinetic features of VDAC1, as well as its slight selectivity for anions, leading to a marked preference for cations. Given that VDAC1 is mainly involved in the trafficking of charged molecules in and out of mitochondria, a general reduction of cell viability and mitochondrial respiration was detected in neuroblastoma cells and primary cortical neurons exposed to Aβ oligomers. Interestingly, the toxic effect mediated by Aβ oligomers was counteracted by the use of NHK1, a small synthetic, cell-penetrating peptide that binds and modulates VDAC1. On these results, VDAC1 emerges as a crucial molecule in mitochondrial dysfunction in AD and as a promising pharmacological target for the development of new therapeutic avenues for this devastating neurodegenerative disease still without a cure.

Glucose Metabolic Reprogramming in Microglia: Implications for Neurodegenerative Diseases and Targeted Therapy

As intrinsic immune cells in the central nervous system, microglia play a crucial role in maintaining brain homeostasis. Microglia can transition from homeostasis to various responsive states in reaction to different external stimuli, undergoing corresponding alterations in glucose metabolism. In neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS), microglial glucose metabolic reprogramming is widespread. This reprogramming leads to changes in microglial function, exacerbating neuroinflammation and the accumulation of pathological products, thereby driving the progression of neurodegeneration. This review summarizes the specific alterations in glucose metabolism within microglia in AD, PD, ALS, and MS, as well as the corresponding treatments aimed at reprogramming glucose metabolism. Compounds that inhibit key glycolytic enzymes like hexokinase 2 (HK2) and pyruvate kinase M2 (PKM2), or activate regulators of energy metabolism such as AMP-activated protein kinase (AMPK), have shown significant potential in the treatment of various neurodegenerative diseases. However, current research faces numerous challenges, including side effects and blood-brain barrier (BBB) penetration of compounds. Screening relevant drugs from natural products, especially flavonoids, is a reliable approach. On the one hand, longtime herbal medical practices provide a certain degree of assurance regarding clinical safety, and their chemical properties contribute to effective BBB permeability. On the other hand, the concurrent anti-tumor and anti-neuroinflammatory activities of flavonoids suggest that regulation of glucose metabolism reprogramming might be a potential common mechanism of action. Notably, considering the dynamic nature of microglial metabolism, there is an urgent need to develop technologies for real-time monitoring of glucose metabolism processes, which would significantly advance research in this field.

Hexokinase-I directly binds to a charged membrane-buried glutamate of mitochondrial VDAC1 and VDAC2

Binding of hexokinase HKI to mitochondrial voltage-dependent anion channels (VDACs) has far-reaching physiological implications. However, the structural basis of this interaction is unclear. Combining computer simulations with experiments in cells, we here show that complex assembly relies on intimate contacts between the N-terminal α-helix of HKI and a charged membrane-buried glutamate on the outer wall of VDAC1 and VDAC2. Protonation of this residue blocks complex formation in silico while acidification of the cytosol causes a reversable release of HKI from mitochondria. Membrane insertion of HKI occurs adjacent to the bilayer-facing glutamate where a pair of polar channel residues mediates a marked thinning of the cytosolic leaflet. Disrupting the membrane thinning capacity of VDAC1 dramatically impairs its ability to bind HKI in silico and in cells. Our data reveal key topological and mechanistic insights into HKI-VDAC complex assembly that may benefit the development of therapeutics to counter pathogenic imbalances in this process.

VDAC1: A Key Player in the Mitochondrial Landscape of Neurodegeneration

Voltage-Dependent Anion Channel 1 (VDAC1) is a mitochondrial outer membrane protein that plays a crucial role in regulating cellular energy metabolism and apoptosis by mediating the exchange of ions and metabolites between mitochondria and the cytosol. Mitochondrial dysfunction and oxidative stress are central features of neurodegenerative diseases. The pivotal functions of VDAC1 in controlling mitochondrial membrane permeability, regulating calcium balance, and facilitating programmed cell death pathways, position it as a key determinant in the delicate balance between neuronal viability and degeneration. Accordingly, increasing evidence suggests that VDAC1 is implicated in the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and others. This review summarizes the current findings on the contribution of VDAC1 to neurodegeneration, focusing on its interactions with disease-specific proteins, such as amyloid-β, α-synuclein, and mutant SOD1. By unraveling the complex involvement of VDAC1 in neurodegenerative processes, this review highlights potential avenues for future research and drug development aimed at alleviating mitochondrial-related neurodegeneration.

Recent Advances in Expression Screening and Sample Evaluation for Structural Studies of Membrane Proteins

Membrane proteins are involved in numerous biological processes and represent more than half of all drug targets; thus, structural information on these proteins is invaluable. However, the low expression level of membrane proteins, as well as their poor stability in solution and tendency to precipitate and aggregate, are major bottlenecks in the preparation of purified membrane proteins for structural studies. Traditionally, the evaluation of membrane protein constructs for structural studies has been quite time consuming and expensive since it is necessary to express and purify the proteins on a large scale, particularly for X-ray crystallography. The emergence of fluorescence detection size exclusion chromatography (FSEC) has drastically changed this situation, as this method can be used to rapidly evaluate the expression and behavior of membrane proteins on a small scale without the need for purification. FSEC has become the most widely used method for the screening of expression conditions and sample evaluation for membrane proteins, leading to the successful determination of numerous structures. Even in the era of cryo-EM, FSEC and the new generation of FSEC derivative methods are being widely used in various manners to facilitate structural analysis. In addition, the application of FSEC is not limited to structural analysis; this method is also widely used for functional analysis of membrane proteins, including for analysis of oligomerization state, screening of antibodies and ligands, and affinity profiling. This review presents the latest advances and applications in membrane protein expression screening and sample evaluation, with a particular focus on FSEC methods.

Current potential pathogenic mechanisms of copper-zinc superoxide dismutase 1 (SOD1) in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurodegenerative disease which damages upper and lower motor neurons (UMN and LMN) innervating the muscles of the trunk, extremities, head, neck and face in cerebrum, brain stem and spinal cord, which results in the progressive weakness, atrophy and fasciculation of muscle innervated by the related UMN and LMN, accompanying with the pathological signs leaded by the cortical spinal lateral tract lesion. The pathogenesis about ALS is not fully understood, and no specific drugs are available to cure and prevent the progression of this disease at present. In this review, we reviewed the structure and associated functions of copper-zinc superoxide dismutase 1 (SOD1), discuss why SOD1 is crucial to the pathogenesis of ALS, and outline the pathogenic mechanisms of SOD1 in ALS that have been identified at recent years, including glutamate-related excitotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, oxidative stress, axonal transport disruption, prion-like propagation, and the non-cytologic toxicity of glial cells. This review will help us to deeply understand the current progression in this field of SOD1 pathogenic mechanisms in ALS.

Ezetimibe Lowers Risk of Alzheimer's and Related Dementias over Sevenfold, Reducing Aggregation in Model Systems by Inhibiting 14-3-3G::Hexokinase Interaction

Numerous factors predispose to progression of cognitive impairment to Alzheimer's disease and related dementias (ADRD), most notably age, APOE(ε4) alleles, traumatic brain injury, heart disease, hypertension, obesity/diabetes, and Down's syndrome. Protein aggregation is diagnostic for neurodegenerative diseases, and may be causal through promotion of chronic neuroinflammation. We isolated aggregates from postmortem hippocampi of ADRD patients, heart-disease patients, and age-matched controls. Aggregates, characterized by high-resolution proteomics (with or without crosslinking), were significantly elevated in heart-disease and ADRD hippocampi. Hexokinase-1 (HK1) and 14-3-3G/γ proteins, previously implicated in neuronal signaling and neurodegeneration, are especially enriched in ADRD and heart-disease aggregates vs. controls (each P<0.008), and their interaction was implied by extensive crosslinking in both disease groups. Screening the hexokinase-1::14-3-3G interface with FDA-approved drug structures predicted strong affinity for ezetimibe, a benign cholesterol-lowering medication. Diverse cultured human-cell and whole-nematode models of ADRD aggregation showed that this drug potently disrupts HK1::14-3-3G adhesion, reduces disease-associated aggregation, and activates autophagy. Mining clinical databases supports drug reduction of ADRD risk, decreasing it to 0.14 overall (P<0.0001; 95% C.I. 0.06-0.34), and <0.12 in high-risk heart-disease subjects (P<0.006). These results suggest that drug disruption of the 14-3-3G::HK1 interface blocks an early "lynchpin" adhesion, prospectively reducing aggregate accrual and progression of ADRD.

VDAC1-interacting molecules promote cell death in cancer organoids through mitochondrial-dependent metabolic interference

The voltage-dependent anion-selective channel isoform 1 (VDAC1) is a pivotal component in cellular metabolism and apoptosis with a prominent role in many cancer types, offering a unique therapeutic intervention point. Through an in-silico-to-in-vitro approach we identified a set of VA molecules (VDAC Antagonists) that selectively bind to VDAC1 and display specificity toward cancer cells. Biochemical characterization showed that VA molecules can directly interact with VDAC1 with micromolar affinity by competing with the endogenous ligand NADH for a partially shared binding site. NADH displacement results in mitochondrial distress and reduced cell proliferation, especially when compared to non-cancerous cells. Experiments performed on organoids derived from intrahepatic cholangiocarcinoma patients demonstrated a dose-dependent reduction in cell viability upon treatment with VA molecules with lower impact on healthy cells than conventional treatments like gemcitabine. VA molecules are chemical entities representing promising candidates for further optimization and development as cancer therapy strategies through precise metabolic interventions.

AAV-mediated upregulation of VDAC1 rescues the mitochondrial respiration and sirtuins expression in a SOD1 mouse model of inherited ALS

Mitochondrial dysfunction represents one of the most common molecular hallmarks of both sporadic and familial forms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder caused by the selective degeneration and death of motor neurons. The accumulation of misfolded proteins on and within mitochondria, as observed for SOD1 G93A mutant, correlates with a drastic reduction of mitochondrial respiration and the inhibition of metabolites exchanges, including ADP/ATP and NAD+/NADH, across the Voltage-Dependent Anion-selective Channel 1 (VDAC1), the most abundant channel protein of the outer mitochondrial membrane. Here, we show that the AAV-mediated upregulation of VDAC1 in the spinal cord of transgenic mice expressing SOD1 G93A completely rescues the mitochondrial respiratory profile. This correlates with the increased activity and levels of key regulators of mitochondrial functions and maintenance, namely the respiratory chain Complex I and the sirtuins (Sirt), especially Sirt3. Furthermore, the selective increase of these mitochondrial proteins is associated with an increase in Tom20 levels, the receptor subunit of the TOM complex. Overall, our results indicate that the overexpression of VDAC1 has beneficial effects on ALS-affected tissue by stabilizing the Complex I-Sirt3 axis.

Disturb mitochondrial associated proteostasis: Neurodegeneration and imperfect ageing

The disturbance in mitochondrial functions and homeostasis are the major features of neuron degenerative conditions, like Parkinson’s disease, Amyotrophic Lateral Sclerosis, and Alzheimer’s disease, along with protein misfolding. The aberrantly folded proteins are known to link with impaired mitochondrial pathways, further contributing to disease pathogenesis. Despite their central significance, the implications of mitochondrial homeostasis disruption on other organelles and cellular processes remain insufficiently explored. Here, we have reviewed the dysfunction in mitochondrial physiology, under neuron degenerating conditions. The disease misfolded proteins impact quality control mechanisms of mitochondria, such as fission, fusion, mitophagy, and proteasomal clearance, to the detriment of neuron. The adversely affected mitochondrial functional roles, like oxidative phosphorylation, calcium homeostasis, and biomolecule synthesis as well as its axes and contacts with endoplasmic reticulum and lysosomes are also discussed. Mitochondria sense and respond to multiple cytotoxic stress to make cell adapt and survive, though chronic dysfunction leads to cell death. Mitochondria and their proteins can be candidates for biomarkers and therapeutic targets. Investigation of internetworking between mitochondria and neurodegeneration proteins can enhance our holistic understanding of such conditions and help in designing more targeted therapies.

ERK1/2-dependent TSPO overactivation associates with the loss of mitophagy and mitochondrial respiration in ALS

Mitochondrial dysfunction and the loss of mitophagy, aimed at recycling irreversibly damaged organelles, contribute to the onset of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease affecting spinal cord motor neurons. In this work, we showed that the reduction of mitochondrial respiration, exactly oxygen flows linked to ATP production and maximal capacity, correlates with the appearance of the most common ALS motor symptoms in a transgenic mouse model expressing SOD1 G93A mutant. This is the result of the equal inhibition in the respiration linked to complex I and II of the electron transport chain, but not their protein levels. Since the overall mitochondrial mass was unvaried, we investigated the expression of the Translocator Protein (TSPO), a small mitochondrial protein whose overexpression was recently linked to the loss of mitophagy in a model of Parkinson's disease. Here we clearly showed that levels of TSPO are significantly increased in ALS mice. Mechanistically, this increase is linked to the overactivation of ERK1/2 pathway and correlates with a decrease in the expression of the mitophagy-related marker Atg12, indicating the occurrence of impairments in the activation of mitophagy. Overall, our work sets out TSPO as a key regulator of mitochondrial homeostasis in ALS.

VDAC1 Knockout Affects Mitochondrial Oxygen Consumption Triggering a Rearrangement of ETC by Impacting on Complex I Activity

Voltage-Dependent Anion-selective Channel isoform 1 (VDAC1) is the most abundant isoform of the outer mitochondrial membrane (OMM) porins and the principal gate for ions and metabolites to and from the organelle. VDAC1 is also involved in a number of additional functions, such as the regulation of apoptosis. Although the protein is not directly involved in mitochondrial respiration, its deletion in yeast triggers a complete rewiring of the whole cell metabolism, with the inactivation of the main mitochondrial functions. In this work, we analyzed in detail the impact of VDAC1 knockout on mitochondrial respiration in the near-haploid human cell line HAP1. Results indicate that, despite the presence of other VDAC isoforms in the cell, the inactivation of VDAC1 correlates with a dramatic impairment in oxygen consumption and a re-organization of the relative contributions of the electron transport chain (ETC) enzymes. Precisely, in VDAC1 knockout HAP1 cells, the complex I-linked respiration (N-pathway) is increased by drawing resources from respiratory reserves. Overall, the data reported here strengthen the key role of VDAC1 as a general regulator of mitochondrial metabolism.

Mapping the N-Terminal Hexokinase-I Binding Site onto Voltage-Dependent Anion Channel-1 To Block Peripheral Nerve Demyelination

The voltage-dependent anion channel (VDAC), the most abundant protein on the outer mitochondrial membrane, is implicated in ATP, ion and metabolite exchange with cell compartments. In particular, the VDAC participates in cytoplasmic and mitochondrial Ca²⁺ homeostasis. Notably, the Ca²⁺ efflux out of Schwann cell mitochondria is involved in peripheral nerve demyelination that underlies most peripheral neuropathies. Hexokinase (HK) isoforms I and II, the main ligands of the VDAC, possess a hydrophobic N-terminal structured in α-helix (NHKI) that is necessary for the binding to the VDAC. To gain further insight into the molecular basis of HK binding to the VDAC, we developed and optimized peptides based on the NHKI sequence. These modifications lead to an increase of the peptide hydrophobicity and helical content that enhanced their ability to prevent peripheral nerve demyelination. Our results provide new insights into the molecular basis of VDAC/HK interaction that could lead to the development of therapeutic compounds for demyelinating peripheral neuropathies.

α-Synuclein A53T Promotes Mitochondrial Proton Gradient Dissipation and Depletion of the Organelle Respiratory Reserve in a Neuroblastoma Cell Line

α-synuclein (αSyn) is a small neuronal protein whose accumulation correlates with Parkinson’s disease. αSyn A53T mutant impairs mitochondrial functions by affecting substrate import within the organelle, activity of complex I and the maximal respiratory capacity. However, the precise mechanism initiating the bioenergetic dysfunction is not clearly understood yet. By overexpressing αSyn A53T in SH-SY5Y cells, we investigated the specific changes in the mitochondrial respiratory profile using High-Resolution Respirometry. We found that αSyn A53T increases dissipative fluxes across the intermembrane mitochondrial space: this does not compromise the oxygen flows devoted to ATP production while it reduces the bioenergetic excess capacity of mitochondria, providing a possible explanation of the increased cell susceptibility observed in the presence of further stress stimuli.

Mechanistic Insights of Mitochondrial Dysfunction in Amyotrophic Lateral Sclerosis: An Update on a Lasting Relationship

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive loss of the upper and lower motor neurons. Despite the increasing effort in understanding the etiopathology of ALS, it still remains an obscure disease, and no therapies are currently available to halt its progression. Following the discovery of the first gene associated with familial forms of ALS, Cu–Zn superoxide dismutase, it appeared evident that mitochondria were key elements in the onset of the pathology. However, as more and more ALS-related genes were discovered, the attention shifted from mitochondria impairment to other biological functions such as protein aggregation and RNA metabolism. In recent years, mitochondria have again earned central, mechanistic roles in the pathology, due to accumulating evidence of their derangement in ALS animal models and patients, often resulting in the dysregulation of the energetic metabolism. In this review, we first provide an update of the last lustrum on the molecular mechanisms by which the most well-known ALS-related proteins affect mitochondrial functions and cellular bioenergetics. Next, we focus on evidence gathered from human specimens and advance the concept of a cellular-specific mitochondrial “metabolic threshold”, which may appear pivotal in ALS pathogenesis.

Voltage Dependent Anion Channel 3 (VDAC3) protects mitochondria from oxidative stress

Unraveling the role of VDAC3 within living cells is challenging and still requires a definitive answer. Unlike VDAC1 and VDAC2, the outer mitochondrial membrane porin 3 exhibits unique biophysical features that suggest unknown cellular functions. Electrophysiological studies on VDAC3 carrying selective cysteine mutations and mass spectrometry data about the redox state of such sulfur containing amino acids are consistent with a putative involvement of isoform 3 in mitochondrial ROS homeostasis. Here, we thoroughly examined this issue and provided for the first time direct evidence of the role of VDAC3 in cellular response to oxidative stress. Depletion of isoform 3 but not isoform 1 significantly exacerbated the cytotoxicity of redox cyclers such as menadione and paraquat, and respiratory complex I inhibitors like rotenone, promoting uncontrolled accumulation of mitochondrial free radicals. High-resolution respirometry of transiently transfected HAP1-ΔVDAC3 cells expressing the wild type or the cysteine-null mutant VDAC3 protein, unequivocally confirmed that VDAC3 cysteines are indispensable for protein ability to counteract ROS-induced oxidative stress.