bims-axbals 2025-12-14 papers

bims-axbals

Biomed News

on Axonal biology and ALS

Issue of 2025–12–14
eighteen papers selected by
TJ Krzystek

The TDP-43I383V heterozygous mutation results in increased TDP-43 expression and altered neuronal activity in ALS patient-derived iPSC motor neurons.
Ubiquitin Proteasome System Components, RAD23A and USP13, Modulate TDP-43 Solubility and Neuronal Toxicity.
LRRK2 G2019S mutation contributes to mitochondrial transfer dysfunction in a Drp1-STX17-dependent manner.
Adaptations of the axon initial segment in fast-spiking interneurons of the human neocortex support low action potential thresholds.
Depletion of BLOC1S1 with splice-switching oligonucleotides in ALS motor neurons improves mitochondrial respiration and rescues disease phenotypes.
Chronic Overexpression of Neuronal NRG1-III in Mice Causes Long-Term Detrimental Changes in Lower Motor Neurons, Neuromuscular Synapses and Motor Behaviour.
NEDD8, stress granules, and amyotrophic lateral sclerosis: unveiling the therapeutic potential of the NEDP1 protease.
Molecular mechanisms underlying p62-dependent secretion of the Alzheimer-associated ubiquitin variant UBB+1.
Axon initial segment damage and hyperexcitability in a mutant mouse with increased calpain-dependent cleavage of αII-Spectrin.
The profiling of extracellular vesicle subtypes in Huntington's disease brains identifies Alix as a novel marker of neuropathology.
A metabolic cell death program downstream of SARM1 couples NAD+ depletion to BAX activation and APAF1 degradation.
Spatial and morphological organization of mitochondria in neurons across a connectome.
Differential effects of overexpression of mutant huntingtin and TDP-43 in agouti-related protein neurons in the arcuate nucleus of the hypothalamus in mice.
Quantifying multimodal longitudinal brain changes in presymptomatic C9orf72 disease.
Novel and rare variants in amyotrophic lateral sclerosis genes identified in Malaysian patients.
Spatiotemporal Ca2+ nanodomain remodeling at MERCS regulates mitochondrial proteostasis.
Autophagy-NAD+ axis: emerging insights into neuronal homeostasis and neurodegenerative diseases.
Human PSC-derived organoids model sympathetic ganglion development and its functional crosstalk with the heart.

Neurosci Res. 2025 Dec 04. pii: S0168-0102(25)00186-5. [Epub ahead of print] 105003

The TDP-43I383V heterozygous mutation results in increased TDP-43 expression and altered neuronal activity in ALS patient-derived iPSC motor neurons.

Ryo Chikuchi, Yuta Kato, Aya Tomatsu, Shuto Nishisaki, Yu Kawakami, Takashi Yoshimura, Jiayi Li, Yohei Iguchi, Kazunari Onodera, Rina Hashimoto, Ikuko Aiba, Ryoichi Nakamura, Genki Tohnai, Naoki Atsuta, Gen Sobue, Yohei Okada, Masahisa Katsuno, Satoshi Yokoi.

  TAR-binding protein 43 (TDP-43) is a pathogenic RNA-binding protein associated with amyotrophic lateral sclerosis (ALS). To elucidate the pathogenesis of ALS, we generated induced pluripotent stem cells (iPSCs) from lymphoblastoid cell line (LCL) cells of an ALS patient with the TDP-43I383V heterozygous mutation. Furthermore, we generated isogenic wild-type iPSCs from wild-type LCL cells using scarless genome editing with CRISPR/Cas9. A modified iPSC-derived motor neuron culture method utilizing BrainPhys neuronal medium and rat astrocyte co-culture effectively promoted and maintained neuronal activity. Under these conditions, the TDP-43I383V heterozygous mutation resulted in increased TDP-43 protein expression through prolonged stabilization. Moreover, mutant iPSC-derived motor neurons showed increased numbers of pre-synapses and altered neuronal activity. These results suggest that the modified motor neuron culture method can help elucidate abnormalities in TDP-43 expression, synapse formation, and neuronal activity caused by the heterozygous TDP-43I383V mutation. The model developed in this study has the potential to facilitate the analysis of the early pathological phenotype of ALS.

Keywords:  Neurodegenerative disorder; RNA-binding protein; TDP-43; calcium imaging; iPSC-derived motor neuron; synapse

DOI:  https://doi.org/10.1016/j.neures.2025.105003
J Neurosci. 2025 Dec 10. pii: e0906252025. [Epub ahead of print]

Ubiquitin Proteasome System Components, RAD23A and USP13, Modulate TDP-43 Solubility and Neuronal Toxicity.

Casey Dalton, Jelena Mojsilovic-Petrovic, Nathaniel Safren, Carley Snoznik, Kamil K Gebis, Yi-Zhi Wang, Alexandra B Sutter, Todd Lamitina, Jeffrey N Savas, Robert G Kalb.

At autopsy, >95% of ALS cases display a redistribution of the essential RNA binding protein TDP-43 from the nucleus into cytoplasmic aggregates. The mislocalization and aggregation of TDP-43 is believed to be a key pathological driver in ALS. Due to its vital role in basic cellular mechanisms, direct depletion of TDP-43 is unlikely to lead to a promising therapy. Therefore, we have explored the utility of identifying genes that modify its mislocalization or aggregation. We have previously shown that loss of rad-23 improves locomotor deficits in TDP-43 C. elegans models of disease and increases the degradation rate of TDP-43 in cellular models. To understand the mechanism through which these protective effects occur, we generated an inducible mutant TDP-43 HEK293 cell line. We find that knockdown of RAD23A reduces insoluble TDP-43 levels in this model and primary rat cortical neurons expressing human TDP-43A315T Utilizing a discovery-based proteomics approach, we then explored how loss of RAD23A remodels the proteome. Through this proteomic screen, we identified USP13, a deubiquitinase, as a new potent modifier of TDP-43 induced aggregation and cytotoxicity. We find that knockdown of USP13 reduces the abundance of sarkosyl insoluble mTDP-43 in both our HEK293 model and primary rat neurons, reduces cell death in primary rat motor neurons, and improves locomotor deficits in C. elegans ALS models.Significance Statement Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease (NDD) with no effective therapies. The mislocalization and aggregation of TAR DNA binding protein 43 (TDP-43) is a key pathological marker of ALS and other NDDs. Due to its vital functions, targeted therapeutic reduction of TDP-43 could be problematic. Here, we have explored the utility of targeting modifier genes. We find that knockdown of two members of the ubiquitin proteasome system, RAD23A and USP13, enhance TDP-43 solubility and decrease TDP-43 induced neurotoxicity.

DOI: https://doi.org/10.1523/JNEUROSCI.0906-25.2025
Transl Neurodegener. 2025 Dec 08. 14(1): 64

LRRK2 G2019S mutation contributes to mitochondrial transfer dysfunction in a Drp1-STX17-dependent manner.

Mei Ding, Fen Wang, Lan-Lan Jiang, Chao Ma, Yu-Wan Qi, Jun-Yi Liu, Juan Li, Mei-Xia Wang, Hong Jin, Jin-Ru Zhang, Cheng-Jie Mao, Xiao-Kang Li, Chun-Feng Liu, Xiao-Yu Cheng.

   BACKGROUND: Previous studies have shown that astrocytes can transfer healthy mitochondria to dopaminergic (DA) neurons, which may serve as an intrinsic neuroprotective mechanism in Parkinson's disease (PD). LRRK2 G2019S is the most common pathogenic mutation associated with PD. In this study, we explored whether mitochondrial transfer is influenced by genetic and environmental factors and whether dysfunction in this process is one of the mechanisms of the pathogenic LRRK2 G2019S mutation.
METHODS: DA neurons and astrocytes were differentiated from induced pluripotent stem cells generated from the peripheral blood of a healthy individual and a PD patient carrying the LRRK2 G2019S mutation. A coculture system of astrocytes and DA neurons was established to explore the pathogenic mechanisms of LRRK2 G2019S.
RESULTS: Exposure to the environmental toxin rotenone impaired mitochondrial transfer from astrocytes to DA neurons. Compared with the co-culture system from the healthy participant, the co-culture system harboring the LRRK2 G2019S mutation experienced more pronounced damage. Specifically, STX17 was colocalized with the mitochondrial outer membrane marker TOM20, and its knockdown caused damage to mitochondrial transfer. Drp1 interacted with STX17. LRRK2 G2019S-mutant astrocytes exhibited markedly increased phosphorylation of Drp1 at Ser616 upon rotenone exposure. Moreover, the degree of colocalization of STX17 with TOM20 decreased. The Drp1 phosphorylation inhibitor DUSP6 restored the colocalization of STX17 and TOM20, as well as the mitochondrial transfer efficiency and neuronal survival.
CONCLUSIONS: The impairment of mitochondrial transfer is a potential pathogenic mechanism associated with LRRK2 G2019S mutation. The molecular mechanisms of mitochondrial transfer were observed to occur through a Drp1-STX17-dependent pathway. Notably, inhibitors for Drp1 Ser616 phosphorylation may offer neuroprotection through mitigating mitochondrial transfer impairments. This study provides novel insights into the pathogenesis of PD and the development of new therapeutic targets.

Keywords:   LRRK2 G2019S mutation; Astrocyte; Dopaminergic neuron; Induced pluripotent stem cell; Membrane fusion-related protein STX17; Mitochondrial transfer; Parkinson’s disease

DOI:  https://doi.org/10.1186/s40035-025-00525-1
PLoS Biol. 2025 Dec 10. 23(12): e3003549

Adaptations of the axon initial segment in fast-spiking interneurons of the human neocortex support low action potential thresholds.

Emoke Bakos, Ádám Tiszlavicz, Viktor Szegedi, Abdennour Douida, Szabina Furdan, Daphne K Welter, Jonathan M Landry, Balazs Bende, Gabor Hutoczki, Pal Barzo, Gabor Tamas, Vladimir Benes, Attila Szucs, Karri Lamsa.

The mammalian brain exhibits notable interspecies variation. Microanatomical and molecular differences in homologous neurons, those with similar locations and developmental origins across species, are best characterized in the neocortical mantle, the center of complex brain functions; however, the purpose of these differences remains unclear. We performed whole-cell microelectrode recordings along with microanatomical and molecular analyses of human fast-spiking parvalbumin (pvalb)-expressing interneurons in neocortical tissue resected during brain surgery, comparing them with similar data obtained from the mouse neocortex. The action potential (AP) firing threshold was lower in human neurons than in mouse neurons. This was due to a deficiency in low-voltage-activated inhibitory Kv1.1 and Kv1.2 potassium channels in the axon initial segment (AIS), a specialized axonal region that determines AP threshold and initiation, in human cells. In contrast, Kv1 ion channels were prominent in mouse neurons. The AIS was also moderately elongated in humans. Computational simulations of fast-spiking interneurons revealed that the human-type AIS lowers the AP threshold and shortens the time lag for AP initiation. We found that the low membrane AP firing threshold in pvalb neurons is closely linked to slow membrane potential kinetics in the soma. Thus, the human AIS supports fast in-fast out circuit function in human pvalb neurons, compensating for electrically slow somatic membrane responses. When formulating therapeutic strategies that involve fast-spiking neurons, it is crucial to take into account the molecular and functional species differences.

DOI: https://doi.org/10.1371/journal.pbio.3003549
Mol Ther. 2025 Dec 11. pii: S1525-0016(25)01049-4. [Epub ahead of print]

Depletion of BLOC1S1 with splice-switching oligonucleotides in ALS motor neurons improves mitochondrial respiration and rescues disease phenotypes.

Jin-Hui Hor, Jin Rong Ow, Winanto Ng, Boominathan Ramasamy, Tommaso Tabaglio, Kimberly Ngee Hui Lim, Muhammad Ikhsan Bin Muzakar, Valerie Jing Wen Lim, Rajasekhar Reddy Gurrampati, Ravisankar Rajarethinam, Shyuan T Ngo, Venkataramanan Ramadass, Shuo-Chien Ling, Manikandan Lakshmanan, Keng Boon Wee, Shi-Yan Ng.

Amyotrophic Lateral Sclerosis (ALS) is a rapidly progressing and debilitating neurodegenerative disease, yet the mechanisms underlying disease onset and progression remain poorly understood, particularly in sporadic ALS. Emerging evidence suggests that mitochondrial dysfunction and metabolic dysregulation are central to ALS pathophysiology. A key feature of ALS motor neurons (MNs) is hyper-acetylation of mitochondrial proteins, which disrupt mitochondrial respiration and energy homeostasis. In this study, we identify BLOC1S1 (also known as GCN5L1) as a novel regulator of mitochondrial acetylation in ALS. We demonstrate that BLOC1S1 is significantly upregulated in ALS patient-derived MNs, post-mortem motor cortices, and spinal cords of ALS mouse models. Functional studies in induced pluripotent stem cell (iPSC)-derived MNs reveal that BLOC1S1 depletion rescues key disease phenotypes. Therefore, we develop an efficacious splice-switching antisense oligonucleotide (SSO) that induces nonsense-mediated decay of BLOC1S1 transcripts as a potential therapeutic candidate. Besides mitigating ALS-relevant cellular deficits in MN cultures from diverse genetic backgrounds, it was validated to extend disease-free and overall survival that is associated with improved rotarod performance in an ALS mouse model. These findings establish BLOC1S1 as a critical modifier of disease progression in ALS and highlight its potential as a novel therapeutic target.

DOI: https://doi.org/10.1016/j.ymthe.2025.12.026
Int J Mol Sci. 2025 Nov 26. pii: 11421. [Epub ahead of print]26(23):

Chronic Overexpression of Neuronal NRG1-III in Mice Causes Long-Term Detrimental Changes in Lower Motor Neurons, Neuromuscular Synapses and Motor Behaviour.

Sara Salvany, Sara Hernández, Anna Casanovas, Sílvia Gras, Lídia Piedrafita, Mar Bosch-Queralt, Markus H Schwab, Jordi Calderó, Josep E Esquerda, Olga Tarabal.

  Neuregulins (NRGs) are ligands of tyrosine kinase receptors from the ErbB family and play multiple developmental roles. NRG1-ErbB signaling regulates myelination and has been associated with amyotrophic lateral sclerosis (ALS) pathology. Given the potential therapeutic relevance of this pathway for motor neuron (MN) diseases, we employed a transgenic (TG) mouse with persistent neuronal overexpression of neuregulin type III (NRG1-III) to investigate its impact on the neuromuscular system. We performed an analysis of phenotypic changes in this TG model, including motor behavior, neuropathological evaluation by immunocytochemistry and ultrastructural examination of the spinal cord, peripheral nerves, and neuromuscular junctions (NMJs). Calcium dynamics in cultured MNs were also examined. We found that cholinergic C-boutons on TG MNs, where NRG1-III typically accumulates, exhibited upregulation of C-bouton-associated proteins and expansion of the subsynaptic cistern (SSC)-associated endoplasmic reticulum. Calcium imaging revealed altered homeostasis in TG MNs, accompanied by the upregulation of molecules linked to axonal plasticity. At NMJs, regressive changes involving autophagic dysregulation were observed. These alterations were accompanied by increased motor activity in behavioral tests. Overall, our findings indicate that persistently elevated NRG1-III signaling compromises MN connectivity and long-term health, a factor to consider when developing therapeutic strategies for neurodegenerative diseases such as ALS.

Keywords:  Neuregulin 1 (NRG1); degeneration; motor neuron (MN); muscle; neuromuscular junction (NMJ); plasticity; spinal cord; synapse

DOI:  https://doi.org/10.3390/ijms262311421
Essays Biochem. 2025 Dec 12. pii: EBC20253036. [Epub ahead of print]

NEDD8, stress granules, and amyotrophic lateral sclerosis: unveiling the therapeutic potential of the NEDP1 protease.

Dimitra Mitsiadou, Dimitris P Xirodimas, Jolanta Polanowska.

  Protein quality control (PQC) systems are crucial for maintaining cellular proteostasis, particularly under stress that promotes misfolded protein accumulation. A central component of this response is the assembly of stress granules (SGs), cytoplasmic condensates of RNA and proteins that temporarily stall translation. Aberrant SG dynamics, often linked to mutations in SG proteins, contribute to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), where persistent protein aggregates are hallmarks. This review examines the emerging role of the ubiquitin-like modifier NEDD8 and its deconjugating enzyme NEDP1 in regulating SG homeostasis. Recent studies identify NEDP1 as a critical factor controlling SG clearance. Inhibition of NEDP1 enhances SG turnover, prevents pathological solidification, and promotes the disassembly of toxic aggregates through hyper-NEDDylation of PARP1, a DNA repair enzyme that also governs SG dynamics. Unlike broad-spectrum PARP1 inhibitors, which can impair DNA repair and cause cytotoxicity, NEDP1 inhibition offers a stress-specific approach that preserves normal cellular functions. Encouragingly, NEDP1 inhibition effectively causes aggregate elimination in ALS patient-derived fibroblasts and restores motility in Caenorhabditis elegans disease models. Altogether, these findings highlight NEDP1 as a key regulator of SG regulation and a promising therapeutic target for ALS and related neurodegenerative disorders.

Keywords:  NEDD8; NEDP1/SENP8; PARP1; amyotrophic lateral sclerosis; stress granules

DOI:  https://doi.org/10.1042/EBC20253036
Proc Natl Acad Sci U S A. 2025 Dec 16. 122(50): e2504528122

Molecular mechanisms underlying p62-dependent secretion of the Alzheimer-associated ubiquitin variant UBB+1.

Ajay R Wagh, Michael H Glickman.

  UBB+1, a ubiquitin variant protein resulting from a frameshift in the ubiquitin-B gene, is a pathological hallmark of Alzheimer disease (AD). At the cellular level, UBB+1 disrupts the ubiquitin-proteasome system while inducing autophagy. Notably, UBB+1 itself is secreted via autophagosome-like vesicles. Here, we demonstrate that UBB+1 can be removed from the cell by degradative and secretory autophagy. Sequestosome 1 (SQSTM1)/p62 functions as a pivotal ubiquitin receptor for UBB+1, recognizing its ubiquitin domain and facilitating loading into autophagosomes. Oligomerization of SQSTM1/p62 was critical to isolate UBB+1 in bodies preventing its aggregation. Intriguingly, both gain- and loss-of-function SQSTM1/p62 suppressed UBB+1 secretion, causing intracellular retention: SQSTM1/p62 knockout led to UBB+1 accumulation in insoluble aggregates, while its overexpression promoted the formation of p62-UBB+1 bodies. We further identified distinct roles for SNARE-mediated membrane fusion in secretory autophagy of UBB+1. Specifically, the R-SNARE SEC22B and the Q-SNAREs Syntaxin-4 and SNAP23 participated in UBB+1 exocytosis. Disruption of SEC22B impaired the fusion of UBB+1-containing autophagosomes with the plasma membrane, reducing UBB+1 secretion without affecting its intracellular turnover. Inhibition of lysosomes partially stabilized UBB+1 indicating that degradation and secretion are complementary processes that determine the fate of UBB+1. This study elucidates the dual roles of autophagy in managing neurotoxic proteins, highlighting SQSTM1/p62 as a key mediator of UBB+1 trafficking and secretion. Although ubiquitin typically acts as a degradation signal, our findings reveal a rare instance of a ubiquitin-related protein driving secretory autophagy. These findings advance our understanding of cellular mechanisms underlying the clearance of misfolded proteins in neurodegenerative diseases.

Keywords:  Alzheimer’s disease; autophagy; p62; trafficking; ubiquitin

DOI:  https://doi.org/10.1073/pnas.2504528122
Neurobiol Dis. 2025 Dec;pii: S0969-9961(25)00373-0. [Epub ahead of print]217 107156

Axon initial segment damage and hyperexcitability in a mutant mouse with increased calpain-dependent cleavage of αII-Spectrin.

Ryan L Hobbib, Gelareh Vakilzadeh, Daniel Fonseca Barriendos, Yasmin Cruz Del Angel, Marco I González.

  The cytoskeleton is essential for maintaining the structural integrity of axons and the axon initial segment (AIS), a specialized domain located at the axon shaft that plays a critical role in regulating neuronal excitability. Among cytoskeletal components, spectrins are key structural proteins that help to maintain the integrity of axons. Mutations in SPTAN1, the gene coding for αII-spectrin, are linked to a group of neurodevelopmental disorders known as SPTAN1 encephalopathies. These disorders are characterized by developmental and epileptic encephalopathies, with clinical features including brain atrophy, hypomyelination, developmental delay, intellectual disability, infantile spasms, and seizures. However, a clear genotype-phenotype relationship remains elusive. In this study, we investigated a novel mouse model carrying the R1098Q point mutation within the tenth triple-helical repeat of αII-spectrin. This mutation destabilizes the protein's structure and increases its sensitivity to calpain-dependent degradation. Similar mutations in humans are believed to disrupt electrostatic interactions necessary for proper αII-spectrin folding, contributing to disease pathogenesis. The primary goal of this study was to determine how the R1098Q mutation affects AIS integrity and contributes to brain hyperexcitability and seizure susceptibility. Our results show that R1098Q mutant mice display abnormal electroencephalographic activity, increased neuronal excitability, and heightened sensitivity to a chemoconvulsant. Morphological analysis revealed fewer AIS structures, along with structural defects such as shortening and thinning of these segments. Overall, this study provides new insight into how specific SPTAN1 mutations may lead to neurodevelopmental disorders. The R1098Q mouse model provides a valuable tool to dissect the cellular mechanisms underlying SPTAN1 encephalopathies and could support the development of targeted therapies. However, further structural and functional analyses of R1098Q mutant mice are essential to fully elucidate the diverse pathological consequences of αII-spectrin dysfunction and to better define the spectrum of αII-spectrinopathies.

Keywords:  AIS; Spectrin; Sptan1; hyperexcitability; seizures

DOI:  https://doi.org/10.1016/j.nbd.2025.107156
Acta Neuropathol Commun. 2025 Dec 08.

The profiling of extracellular vesicle subtypes in Huntington's disease brains identifies Alix as a novel marker of neuropathology.

Rocío Pérez-González, Anna Vázquez-Oliver, Nil Salvat-Rovira, Saül Martínez-Horta, Elisa Rivas-Asensio, Eva Borràs, Samanta Ortuño-Miquel, María Sánchez-Carcelén, Marta Garcia-Forn, Frederic Sampedro, Jesús Pérez-Pérez, Eduard Sabidó, Esther Pérez-Navarro, Jaime Kulisevsky.

   BACKGROUND: Huntington's disease (HD) is the most frequent autosomal dominant neurodegenerative disorder, which is caused by a CAG repeat expansion in the HTT gene. Despite its well-defined genetic origin, there is currently no cure, and reliable biomarkers for disease progression and pathophysiology remain limited. Mutant huntingtin protein accumulates in endosomal compartments, disrupting endosomal trafficking and potentially affecting the biogenesis, release, and cargo of exosomes-extracellular vesicles (EVs) derived from the endosomal pathway. However, the role of exosomes in HD pathogenesis and their potential as biomarkers has been underexplored. In this work, we investigated whether the levels and content of small EV subpopulations, including exosomes, are altered in the brains of HD patients.
METHODS: We analyzed two distinct subpopulations of small EVs from the striatum and cortex of postmortem HD brains at early and advanced neuropathological stages, as well as from age-matched controls. EVs were isolated by differential ultracentrifugation and high-resolution iodixanol density gradient centrifugation, and analyzed by Western blotting, electron microscopy, NTA, and proteomics using mass spectrometry. EV secretion was also analyzed in primary fibroblasts derived from HD patients and healthy controls.
RESULTS: Mass spectrometry data revealed HD-associated alterations in EV protein content, particularly proteins related to the endosomal system. Our data also indicate that the level of ectosomes increased in the HD cortex, whereas exosomes were reduced in both the HD striatum and cortex compared to controls. In terms of EV content, EVs from HD brains showed increased levels of Annexin A2 and decreased levels of Alix, a key component of the endosomal sorting complex required for transport (ESCRT). Alix depletion in EVs mirrored a progressive reduction of Alix in brain tissue, correlating with disease severity based on Vonsattel staging. In vitro, HD fibroblasts secreted EVs with reduced Alix content, despite no significant difference in cellular Alix levels compared to controls.
CONCLUSIONS: These findings highlight disease-specific changes in EV populations and cargo in HD, and identify Alix as a potential neuropathological marker. This study advances our understanding of the role of brain-derived EVs in HD and underscores their potential utility in biomarker discovery.

Keywords:  Alix; Annexin A2; Ectosomes; Exosomes; Huntington’s disease; Neurodegeneration

DOI:  https://doi.org/10.1186/s40478-025-02187-6
Proc Natl Acad Sci U S A. 2025 Dec 16. 122(50): e2522444122

A metabolic cell death program downstream of SARM1 couples NAD+ depletion to BAX activation and APAF1 degradation.

Weilong Pan, Dejia Guo, Daiyuan Liu, Xiaodong Wang.

  SARM1 is a neuronal Nicotinamide adenine dinucleotide (NAD+) hydrolase that drives axonal degeneration and neuronal death by depleting NAD+, yet how NAD+ loss triggers axon loss and cell death has remained unclear. Here, we define a nonapoptotic death program downstream of endogenous SARM1 activation and NAD+ loss using a genetically tractable nonneuronal eHAP cell model. Upon NAD+ depletion, BAX is activated but caspase activation is suppressed due to APAF1 degradation via the E3 ligase HERC4, effectively uncoupling mitochondrial outer membrane permeabilization from apoptosome formation. Mechanistically, NAD+ depletion inhibits mTOR/AKT signaling, destabilizing MCL1 and relieving BAX from repression. We further identified Neurofibromatosis type II, NF2, as a regulator that promotes SARM1 transcription through the Hippo-YAP/TAZ pathway. The SARM1-dependent BAX activation and the role of NF2 in axon degradation were validated in neuronal models of axon degeneration. Together, these findings reveal how SARM1-driven metabolic collapse rewires cell death execution, positioning BAX, MCL1, APAF1, NF2, and HERC4 as core effectors in a nonapoptotic degenerative pathway linking metabolic stress to neurodegeneration.

Keywords:  APAF1; Apoptosis; BAX; NAD+; SARM1

DOI:  https://doi.org/10.1073/pnas.2522444122
Science. 2025 Dec 11. eads6674

Spatial and morphological organization of mitochondria in neurons across a connectome.

Garrett Sager, Paul Pfeiffer, Heng Wu, Fabian Pallasdies, Robert Gowers, Snusha Ravikumar, Elizabeth Wu, Daniel Colón-Ramos, Susanne Schreiber, Damon A Clark.

Neuronal function depends on mitochondria, but little is known about their organization across neurons. Using an electron microscopy Drosophila connectome, we uncovered quantitative rules governing the morphology and positioning of hundreds of thousands of mitochondria across thousands of neurons. We discover that mitochondrial morphological features are specific to cell and neurotransmitter type, providing fingerprints to identify neurons. Mitochondria are positioned with 2-3 μm precision relative to synaptic and structural features, with systematic differences across neuron types and compartments. Mitochondrial localization correlates with regional activity and postsynaptic targets. Analysis of a mouse visual cortex connectome confirms cell-type specific morphology and identifies partially divergent positioning rules. These results establish mitochondria as circuit-embedded organelles whose distribution links subcellular architecture to brain connectivity.

DOI: https://doi.org/10.1126/science.ads6674
Acta Neuropathol Commun. 2025 Dec 07.

Differential effects of overexpression of mutant huntingtin and TDP-43 in agouti-related protein neurons in the arcuate nucleus of the hypothalamus in mice.

Jennifer Oraha, Ronja Wagner, Sofia Bergh, Nicola J Lee, Deniz Kirik, Åsa Petersén.

  The spectrum of frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS) and Huntington disease (HD) are fatal neurodegenerative disorders with no major disease-modifying therapies. Recent work has shown that the hallmark pathological proteins TAR DNA binding protein of 43 kDa (TDP-43) in FTD/ALS and mutant huntingtin (mHTT) in HD may be interlinked. Furthermore, these disorders share early features of altered metabolism and psychiatric symptoms that have been suggested to arise from pathology in the hypothalamus, an important brain region involved in the regulation of metabolism and emotions. Agouti-related protein (AgRP)-expressing neurons localised exclusively to the arcuate nucleus (ARC) of the hypothalamus are key modulators of body weight regulation and food seeking behaviour, and they have recently been implicated in anxiety- and anhedonic-like processes. The aim of this study was to investigate the effects of overexpression of TDP-43 or mHTT in AgRP-expressing neurons on metabolic, behavioral and neuropathological features in mice. Flex-switch adeno associated viral vectors expressing human wild-type TDP-43, mHTT or green fluorescent protein to serve as a control, were injected into male and female AgRP-Cre mice to target the ARC using stereotactic surgery. We demonstrate targeted overexpression of transgenes including formation of mHTT inclusions in the ARC of the hypothalamus. Overexpression of mHTT led to a significant reduction in AgRP fibres in the hypothalamus 21 weeks post-injection, as well as higher food consumption in female mice. Overexpression of TDP-43 did not lead to the development of any metabolic or behavioral phenotypes in the mice. Our data suggest that AgRP neurons in the ARC are protected from the toxic effects resulting from overexpression of TDP-43 whereas they display some sensitivity to mHTT overexpression resulting in mHTT inclusion formation, reduction in AgRP fibers and sex-specific effects on food consumption. Taken together, other hypothalamic neuronal populations may be more important for the development of non-motor features resulting from overexpression of TDP-43 and mHTT in the hypothalamus.

Keywords:  Agouti-related protein; Amyotrophic lateral sclerosis; Arcuate nucleus; Behavioural features; Frontotemporal dementia; Huntington disease; Hypothalamus; Metabolism; Neurodegeneration

DOI:  https://doi.org/10.1186/s40478-025-02201-x
Alzheimers Dement. 2025 Dec;21(12): e70902

Quantifying multimodal longitudinal brain changes in presymptomatic C9orf72 disease.

PREV‐DEMALS and STRATALS study groups

   INTRODUCTION: The presymptomatic phase of frontotemporal dementia and amyotrophic lateral sclerosis associated with C9orf72 repeat expansion features widespread structural brain changes. We aimed at fulfilling the unmet need of quantitative magnetic resonance imaging (MRI)-derived measures suitable for disease tracking.
METHODS: We compared the profile of longitudinal gray (GM) and white matter (WM) changes in 66 presymptomatic carriers and 52 controls over 3-year follow-up and appraised their annualized rate of change (ARC).
RESULTS: Both putamen (p < 0.01) and left insula (p = 0.005) volumes declined the most in carriers over 40, with an ARC up to four-fold higher than in controls. Increases in mean diffusivity occurred first in the left uncinate fasciculus, followed by thalamo-cortical bundles (p < 0.05), associated with higher neurofilament levels.
DISCUSSION: Our study highlighted the GM and WM structures showing the greatest longitudinal decline during the preclinical stage, whose ARC may serve as an MRI-derived biomarker for longitudinal surveillance and therapeutic outcome.
CLINICAL TRIAL REGISTRATION: NCT02590276 and NCT05358431.
HIGHLIGHTS: We studied longitudinal multimodal MRI changes in presymptomatic C9orf72 disease. Carriers displayed faster atrophy in putamen, insula and cerebellar regions. Mean diffusivity increased mainly in uncinate and thalamo-cortical tracts. These differences were even more significant in older (> 40) participants. We proposed targeted annualized rate of change as a quantitative biomarker.

Keywords:  C9orf72; amyotrophic lateral sclerosis (ALS); basal ganglia; biomarker; clinical trials; diffusion tensor imaging (DTI); frontotemporal dementia (FTD); frontotemporal lobar degeneration (FTLD); genetic; longitudinal; magnetic resonance imaging (MRI); neurofilaments; neuroimaging; presymptomatic; voxel‐based morphometry

DOI:  https://doi.org/10.1002/alz.70902
Amyotroph Lateral Scler Frontotemporal Degener. 2025 Dec 08. 1-10

Novel and rare variants in amyotrophic lateral sclerosis genes identified in Malaysian patients.

Nurul Angelyn Zulhairy-Liong, Suzanna Edgar, Melina Ellis, Danqing Zhu, Kaitao Lai, David Paul Capelle, Sakinah Sabirin, Eu Way Pek, Prasana Nair, Chui Munn Ang, Marina L Kennerson, Nortina Shahrizaila, Azlina Ahmad-Annuar.

  There is limited information on the genetic architecture of amyotrophic lateral sclerosis (ALS) in Southeast Asian populations. To address this knowledge gap, we performed 1) SOD1 (exon 1-4), FUS (exon 13-15), TARDBP (exon 6) and ATXN2 repeat expansion screening in 201 multi-ethnic Malaysian (Malay, Chinese, Indian and others) ALS patients, 2) C9orf72 repeat expansion testing in 179 subset patients, and 3) a panel of 61 ALS-associated genes screening in 112 subset cases using either whole genome (n = 21) or exome (n = 91) sequencing datasets. Among the patients, the observed mutational frequencies in key ALS genes were: SOD1 3.0% (6/201), C9orf72 2.2% (4/179), ATXN2 2.0% (4/201), FUS 1.5% (3/201), and TARDBP 1.5% (3/201). Of the 112 cases that underwent WGS/WES, 6.3% (7/112) comprised of pathogenic and likely pathogenic variants in FIG4 (p.Lys657Serfs*2), FUS (p.Arg485Profs*32), TARDBP (p.Ile383del), NEK1 (p.Ile633Asnfs*28), GRN (c.599-1G > C), CYP27A1 (p.Met1Thr) and SPAST (p.Glu449Gly). Additionally, 42.9% (48/112) had at least one variant of uncertain significance (VUS) in 34 genes. Notably, in the 24 genes classified as 'definitive' by the ClinGen ALS Spectrum Disorders Gene Curation Expert Panel, five patients (4.5%, 5/112) harbored more than one likely pathogenic variant and/or VUS. However, burden analysis revealed no significant differences in clinical characteristics between patients with varying numbers of variants. Our findings highlight the utility of next-generation sequencing in elucidating the genetic basis of ALS in Malaysian and Southeast Asian ethnic groups, including the identification of several novel variants of clinical interest as well as increasing diagnostic yield up to 47.7%.

Keywords:  Amyotrophic lateral sclerosis; Malaysia; genetic screening; whole exome sequencing; whole genome sequencing

DOI:  https://doi.org/10.1080/21678421.2025.2582832
Protein Cell. 2025 Dec 08. pii: pwaf109. [Epub ahead of print]

Spatiotemporal Ca2+ nanodomain remodeling at MERCS regulates mitochondrial proteostasis.

Yanan Lv, Xuejing Zhao, Di Li, Zhaoqi Hao, Yue Zhao, Yuhang Zhou, Yujing Zhang, Han Chen, Zhongbing Lu, Dong Li, Yuting Guo.

  Mitochondrial calcium fluxes serve as pivotal regulators of optimal organellar function and cellular viability, yet the spatiotemporal regulation of nanodomain Ca2+ transients at mitochondria-ER contact sites (MERCS) and their integration into adaptive mitochondrial stress signaling remain unresolved. In this study, we employed custom-built high temporal-spatial resolution GI/3D-SIM imaging techniques to achieve nanoscale resolution of calcium transients. We identify that MERCS-localized calcium oscillations gate retrograde stress signaling. Mechanistically, we demonstrate that augmented mitochondria-associated ER membrane (MAMs) connectivity unexpectedly attenuated global mitochondrial Ca2+ efflux, which triggering ATF5 shuttling-mediated transcriptional licensing and calcium-sensitive epigenetic reprogramming that synergistically activating stress-resilience programs. Quantitative protein expression and transcriptome analyses confirm that CsA-mediated calcium retention mimics MAMs induction preserves mitochondrial integrity and protecting cells from apoptosis in Aβ1-42-challenged neurons through synchronized UPRmt activation. Our findings reveal a novel mechanism by which MERCS decode proteotoxic stress into transcriptional and epigenetic adaptations, offering therapeutic potential for neurodegenerative diseases.

Keywords:  Alzheimer’s disease; Mito-ER interaction; calcium transients; mitochondrial stress response; super-resolution microscopy

DOI:  https://doi.org/10.1093/procel/pwaf109
Front Mol Biosci. 2025 ;12 1695486

Autophagy-NAD+ axis: emerging insights into neuronal homeostasis and neurodegenerative diseases.

Gamze Kocak, Mylla M Dimas, Luiz F S E Silva, Danyelle Silva-Amaral, Congxin Sun, Sophie Cruddas, Timothy Barrett, Daniel Martins-de-Souza, Edecio Cunha-Neto, Patricia S Brocardo, Tetsushi Kataura, Viktor I Korolchuk, Sovan Sarkar.

  Autophagy is an evolutionarily conserved catabolic process that plays a central role in maintaining cellular homeostasis by degrading and recycling damaged or surplus proteins, organelles, and other cellular macromolecules and components. A growing body of evidence highlights a bidirectional relationship between autophagy and nicotinamide adenine dinucleotide (NAD+), a vital metabolic cofactor involved in numerous cellular processes, including energy metabolism, genomic maintenance, stress resistance, and cell survival. Autophagy supports NAD+ homeostasis by recycling metabolic precursors, while NAD+-dependent enzymes such as sirtuins and PARPs regulate autophagy initiation and lysosomal function. Disruption of this autophagy-NAD+ axis has emerged as a common feature in several neurodegenerative diseases, where impaired cellular clearance and metabolic dysfunction contribute to neuronal vulnerability. In this review, we summarize the advances of the molecular links between autophagy and NAD+ metabolism, with a particular focus on their roles in mitochondrial quality control, bioenergetic regulation, and cellular resilience. We also discuss the therapeutic potential of targeting the autophagy-NAD+ axis to promote neuroprotection in neurodegenerative disease.

Keywords:  NAD+; NAD+ precursor; NAD+ supplementation; NAD+-dependent enzyme; autophagy; autophagy inducer; neuronal cell death; neuroprotection

DOI:  https://doi.org/10.3389/fmolb.2025.1695486
Cell Stem Cell. 2025 Dec 11. pii: S1934-5909(25)00410-2. [Epub ahead of print]

Human PSC-derived organoids model sympathetic ganglion development and its functional crosstalk with the heart.

Yantong Liu, Jinkui Zhu, Xiaoxiang Lu, Xuran Zhuang, Jianfeng Wei, Linlin Jiang, Wei Zhou, Wei Pang, Yao Yin, Ziling Chen, Yajing Cao, Qinzhi Zhang, Sisi Chen, Siyuan Chu, Xinrui Zhang, Yangfei Xiang.

  The sympathetic ganglia are essential components of the nervous system that regulate various aspects of involuntary body functions. Recapitulating sympathetic ganglion development with three-dimensional (3D) organoids is challenging and has not been achieved. Here, we report a method to differentiate human pluripotent stem cells into 3D neural organoids that resemble peripheral sympathetic ganglia, producing both neurons and glial cells of the ganglia in a self-organized manner. We developed an organoid system to construct functional connections between the sympathetic ganglia and one of their peripheral targets, the heart, by fusing human sympathetic ganglion organoids (hSGOs) and heart-forming organoids. Notably, this system enables the evaluation of signaling controls (i.e., nerve growth factor [NGF] signaling) on human sympathetic-to-cardiac innervation and reveals the reciprocal impacts between the sympathetic and cardiac lineages during their co-development. Our study provides a physiologically relevant platform for understanding the development of human sympathetic ganglia, their crosstalk with peripheral targets, and related diseases.

Keywords:  assembloids; hPSCs; heart; organoids; sympathetic ganglion

DOI:  https://doi.org/10.1016/j.stem.2025.11.003