Biology subjects

Sasaki, Y.

Publications and source records attributed to Sasaki, Y..

At least 19 recordsLinked to original sources

bioRxiv2026

Genetic ablation of Sarm1 attenuates axonal degeneration in a mouse model of CMT2J

Charcot-Marie-Tooth (CMT) disease is the most common inherited neuropathy, affecting approximately 1 in 2,500 individuals, and comprises a clinically and genetically heterogeneous group of disorders involving more than 100 genes. Mutations in myelin protein zero (MPZ) typically cause the demyelinating form CMT1B, whereas the T124M substitution gives rise to CMT2J, a late-onset, predominantly axonal neuropathy with minimal myelin involvement. We previously generated a MpzT124M mouse model that recapitulates key features of the human disease, including progressive axonal degeneration and fibre loss in peripheral nerves. Because SARM1 (sterile and TIR motif-containing protein 1) is a central executioner of programmed axonal degeneration, we crossed MpzT124M mice with Sarm1-null animals and assessed electrophysiological, morphological, and molecular parameters in both heterozygous and homozygous mutants. Sarm1 deletion did not rescue electrophysiological deficits in either genotype. However, in 12-month-old homozygous MpzT124M/T124M mice, Sarm1 ablation partially reduced axonal degeneration in peripheral nerves and lowered plasma neurofilament light chain, a biomarker of neurodegeneration. In heterozygous MpzT124M/+ mice, where axonal degeneration develops more slowly, Sarm1 deletion was associated with improved motor performance and reduced morphological signs of disease by 18 months of age. Together, these findings indicate that SARM1 contributes to axonal degeneration in CMT2J and that its ablation confers partial protection, although it is insufficient to fully prevent disease progression, supporting SARM1 as a therapeutically relevant target in MPZ-associated axonal neuropathy despite incomplete disease rescue.

neuroscience↗

bioRxiv2026

Mitochondrial NAD+ import gates neuronal resilience to active SARM1

SARM1 is an inducible NADase that executes pathological axon degeneration, but how NAD+ destruction causes neuronal failure remains unclear. Because SARM1 is predicted to act outside the mitochondrial matrix, cytosolic NAD+ loss has been viewed as the critical lethal lesion. We show that SARM1 activation rapidly depletes cytosolic and mitochondrial NAD+ and collapses ATP in both compartments, revealing early, coupled metabolic failure. Enhancing mitochondrial NAD+ import through SLC25A51, the mitochondrial NAD+ transporter, preserves mitochondrial NAD+, maintains mitochondrial function, and delays axon degeneration and neuronal death despite ongoing SARM1 activity. Unexpectedly, SLC25A51 restores cytosolic NAD+-dependent metabolism, reversing a glycolytic block and increasing NAD+ synthesis during stress. Glycolytic inhibition attenuates protection, identifying cytosolic metabolic recovery as an important component of neuronal resilience. AAV-SLC25A51 improves function in a chronic SARM1-dependent neuropathy model. Thus, mitochondrial NAD+ import gates SARM1-driven degeneration by limiting coupled mitochondrial-cytosolic metabolic failure, presenting a downstream intervention point for axon preservation.

neuroscience↗

bioRxiv2026

Fragile X syndrome-linked mutations impair FMRP accumulation in neuronal transport granules

RNA granules are biomolecular condensates that are reversibly formed through multivalent interactions among mRNAs and RNA-binding proteins (RBPs). RNA granules include stress granules and neuronal transport granules, which share common components and functions in translational regulation. Fragile X messenger ribonucleoprotein (FMRP) is an RBP encoded by FMR1, whose loss of function causes fragile X syndrome (FXS), a neurodevelopmental disorder. FMRP is a component of both stress granules and neuronal transport granules. Although several FXS-associated missense mutations in FMRP have been identified, it remains unclear whether these mutations affect the assembly of FMRP into RNA granules. Here, we found that the KH1 domain mutation G266E markedly reduced the accumulation of FMRP in stress granules in HEK293T cells, whereas the KH2 domain mutation I304N had little effect. In addition, both G266E and I304N reduced the accumulation of FMRP within neuronal transport granules in FMRP-deficient mouse cortical neurons. Because G266E and I304N have been reported to impair the RNA-binding and/or RNA-associated functions of FMRP, our findings suggest that the KH1 and KH2 domains are important for the assembly of FMRP into RNA granules. These findings further raise the possibility that impaired RNA granule assembly may contribute to the pathogenesis of FXS and other neurodevelopmental disorders.

neuroscience↗

bioRxiv2026

Reward evokes value-independent arousal and value-dependent reinforcement processing as dissociable physiological consequences

Reward is traditionally thought to drive value-dependent reinforcement processing, whereas recent work suggests reward may instead raise arousal that mimics reinforcement. Because reinforcement and arousal depend on partly distinct neuromodulatory systems yet are co-triggered by reward, they have been widely treated as closely linked, though rarely tested directly, leaving reward's physiological consequences difficult to interpret. We manipulated the value of a primary reward by varying thirst while independently inducing arousal with sound, and measured pupil diameter and electroencephalographic activity. High- and low-value rewards produced comparable pupil dilation, indicating value-independent arousal. In contrast, only high-value reward increased alpha-band power, progressing from anterior to posterior regions, whereas low-value reward and sound produced similar alpha suppression without regional progression. Thus, reward evokes two dissociable consequences: value-independent arousal and value-dependent reinforcement. Rather than a single coupled process, these arise through separable mechanisms, providing a physiological framework for distinguishing each mechanism's contribution to reward processing.

neuroscience↗

bioRxiv2025

Selective PPAR-α activation with pemafibrate attenuates macrophage-mediated progression of calcific aortic valve disease

BACKGROUNDCalcific aortic valve disease (CAVD) compromises valve compliance and cardiac hemodynamics leading to aortic stenosis (AS) and cardiovascular dysfunction. With treatment for severe AS limited to valve replacement and no effective pharmacotherapies, new interventions are urgently needed for patients. This study evaluated pemafibrate, a selective peroxisome proliferator-activated receptor alpha (PPAR) activator as a novel therapeutic for CAVD and AS. METHODS AND RESULTSIn an aortic valve wire injury (AVWI) model of AS in Ldlr-/- mice, pemafibrate administration (0.2 mg/kg/day) for 15 weeks improved aortic valve function and reduced valvular calcification by 39% (p<0.001), accompanied by reduced leaflet inflammation and CD68 macrophage infiltration. These effects were independent of changes in plasma triglyceride levels. In vitro, pemafibrate suppressed inflammation-mediated calcification of primary human valvular interstitial cells (VICs) by modulating macrophage-derived secreted factors, identifying macrophage-VIC crosstalk as a key disease mechanism. Direct treatment of macrophages with pemafibrate, or exposure to serum from pemafibrate-treated participants in the PROMINENT randomized controlled trial, shifted macrophages toward a less inflammatory and less chemotactic phenotype. Proteomic analyses of patient serum substantiated these findings by reflecting a systemic reduction in inflammatory parameters and monocyte activation. Network integration of the in vitro derived pemafibrate-responsive proteome with human calcified AV tissue proteomes identified aberrant protein translation (GNB2L1, GSPT1) and disrupted bioenergetics (MYDGF, PDIA4) as potential clinically relevant pemafibrate-responsive pathways and effector proteins relevant to AS progression. CONCLUSIONSPemafibrate slows experimental AS progression and valve calcification through modulation of macrophage-VIC crosstalk, independent of lipid lowering. These findings support further evaluation of pemafibrate as a potential pharmacological approach for CAVD and support further testing in randomized clinical trials.

pharmacology and toxicology↗

bioRxiv2025

Dysregulated lactate metabolism synergizes with ALS genetic risk factors to accelerate motor decline

Neurons rely on glial lactate shuttling for metabolic support, which declines with aging and in neurodegenerative disease. Full disruption of lactate shuttling in peripheral nerves causes progressive axon degeneration, but we were interested to understand how partial disruption, a scenario more relevant to aging and disease, contributes to neurodegeneration risk. Pyruvate and lactate are interconverted by lactate dehydrogenases (LDHA and LDHB) in both lactate producing and consuming cells. We therefore began by investigating Ldhb knockout mice (loss of LDHA, the dominant LDH in liver and muscle, caused embryonic lethality), and discovered that they develop progressive neuromuscular junction atrophy and functional decline without axon degeneration. Because even Ldhb+/- heterozygosity significantly affects motor behavior, we also wondered about a potential link to congenital disease and pursued this by identifying rare loss-of-function LDHB variants among ALS patients. Next, to better understand how LDHB loss leads to motor decline, we selectively deleted it in defined cell types. SC-specific deletion caused robust motor defects, whereas motor neuron-specific deletion has little effect. Reasoning that neuronal LDHB deficiency could model age-associated decline in lactate metabolism, we asked whether it would interact with ALS genetic risk. Indeed, motor-neuron LDHB deficiency synergizes with relatively mild ALS risk variants-- TDP43Q331Kand Sod1D83G knock-in alleles--to produce early motor neuropathy, indicating that LDHB loss enhances disease risk. These findings establish lactate metabolism as a modifier of motor system vulnerability and highlight it as a therapeutic target in peripheral as well as central neurodegeneration.

neuroscience↗

bioRxiv2025

Unconscious switching of dorsal and medial pathways for plasticity and stability during NREM and REM sleep

While visual perceptual learning improves during non-REM sleep and stabilizes during REM sleep via excitatory-inhibitory neurotransmitter (E/I) balance in early visual areas (EVA), the role of prefrontal regions remains unclear. Here, we show that contributions of the dorsolateral prefrontal cortex (DLPFC) and medial prefrontal cortex (mPFC) differ by sleep stage in human adults. During non-REM sleep, plasticity increased in DLPFC--indexed by elevated E/I balance measured with magnetic resonance spectroscopy and polysomnography--in correlation with performance gains. During REM sleep, stability increased in mPFC--indexed by reduced E/I balance--in correlation with resilience to retrograde interference from new learning. E/I balance changes and their effects on learning paralleled those in EVA. Connectivity weights between EVA and DLPFC, and between EVA and mPFC, switched with sleep stage. These findings suggest the presence of dorsal and medial pathways that unconsciously alternate between non-REM sleep and REM sleep to improve and stabilize learning.

neuroscience↗

bioRxiv2025

MAESTRO uncovers tandem paralog dynamics as a core driver of fungal stress adaptation

Understanding how fungi adapt to diverse stresses is critical for mitigating emerging drug resistance and harnessing their robustness for biotechnology. Pichia kudriavzevii is a stress-tolerant and intrinsically drug-resistant yeast, with dual industrial and clinical importance. We analyzed 170 strains using MAESTRO, a machine-learning-assisted GWAS pipeline optimized for small cohorts. MAESTRO identified biologically meaningful features and revealed that copy number variation (CNV) of tandem paralogs (TPs) is a core mechanism of multi-stress adaptation. TPs were recurrently linked to tolerance of industrial inhibitors (HMF, phenolics, heat) and antifungal drugs (fluconazole, azoles), and deletion of the TP pair gene4260/gene4261 confirmed pleiotropic effects across stresses. These findings support a TP CNV model where recombination-driven TP CNVs and gene fusions enable rapid stress adaptation. Importantly, our results suggest that antifungal resistance can arise through co-option of mechanisms originally evolved for environmental stressors, raising a One Health concern about the environmental origins of drug-resistant pathogens.

genomics↗

bioRxiv2025

Carbon and nitrogen stable isotopic profiling of chimpanzees and other primate hairs in Kalinzu Forest Reserve, Uganda

Stable isotope analysis is a widely used tool in primate ecology for investigating diet and environment, with numerous studies focusing on chimpanzees. However, few studies have explored the dietary niche of chimpanzees in comparison to other primates or examined intra-individual dietary variability. This limitation hinders the understanding of the comparability of isotopic data with the wealth of behavioral observational data in primate ecology. In this study, we report the carbon and nitrogen stable isotope ratios of hairs from wild chimpanzees and four other primate species in the Kalinzu Forest Reserve, Uganda. Bulk analysis revealed that both plant foods and chimpanzees in Kalinzu exhibited lower carbon isotope ratios than expected for the regions rainfall. Additionally, preliminary compound-specific nitrogen isotope analysis of amino acids was conducted, revealing that chimpanzees in Kalinzu have a lower degree of faunivory than the sympatric Cercopithecus primates. Furthermore, ultra-fine sectioning of a hair sample was conducted to investigate dietary variation over daily to weekly timescales. In one adult male chimpanzee, carbon and nitrogen isotope ratios fluctuated by more than 1{per thousand} within approximately 10 days. These findings highlight the importance of recognizing uncontrolled ecological variability and hidden intra-individual dietary changes when interpreting stable isotope data in relation to behavior and environmental traits.

ecology↗

bioRxiv2025

SARM1 is an essential component of neuronal Parthanatos

The NAD+ hydrolase SARM1 is the central executioner of pathological axon degeneration. SARM1 is allosterically activated by an increased NMN/NAD+ ratio resulting from depletion of NAD+ or accumulation of its precursor, NMN, typically due to loss of the labile NAD+ synthetase NMNAT2 following axon injury. Another NAD+ hydrolase, PARP1, is hyperactivated by DNA damage, triggering the Parthanatos cell death pathway. We demonstrate that multiple mechanistically-distinct DNA-damaging agents lead to SARM1 activation and axon degeneration following PARP1 activation. Remarkably, SARM1 is required for key steps downstream of PARP1 activation by DNA damage that are pathognomonic of Parthanatos, including mitochondrial depolarization, nuclear translocation of AIF (apoptosis-inducing factor), and cell death. Moreover, SARM1 mediates glutamate excitotoxicity, a clinically significant pathomechanism attributed to Parthanatos. The identification of SARM1 as an essential component of neuronal Parthanatos, a major contributor to cell death in neurodegenerative disease, greatly expands the potential clinical utility of SARM1 inhibitors.

neuroscience↗

bioRxiv2025

Sleep is associated with reduction of excitatory signaling in medial prefrontal cortex

Although many sleep medications enhance inhibitory signaling, it remains unclear whether inhibitory or excitatory neurotransmitters contribute to the natural transition from wakefulness to sleep in humans. Here, we show that changes in excitatory, rather than inhibitory, neurotransmitter levels are associated with this transition. Young, healthy participants underwent two nap sessions with polysomnography, during which glutamate and GABA concentrations in the medial prefrontal cortex were measured using magnetic resonance spectroscopy. Glutamate gradually decreased during deeper sleep stages compared to wakefulness in the second session, with better sleep quality. No such change occurred in the first session with poorer sleep, likely due to the first-night effect. Furthermore, reduced glutamate significantly mediated sleep-onset latency in both sessions. Conversely, GABA concentration did not change from wakefulness to sleep in either session. These findings provide the first evidence that reduced excitatory signaling is a key feature of natural good sleep onset in the human brain.

neuroscience↗

bioRxiv2025

Concurrent multimodal measurement of excitation and inhibition shows that EEG-based estimates are linked to the ratio of glutamate to GABA

Neural excitation/inhibition (E/I) ratio is dynamically regulated on multiple timescales. Adaptive changes in E/I ratio can support healthy development, learning, and cognition, while disordered E/I ratio has been implicated in neurodevelopmental disorders, neurodegenerative disorders, and states of impaired vigilance. There has been growing interest in inferring E/I ratio from efficient and noninvasive measurements such as electroencephalography (EEG), and several algorithms have been proposed to estimate E/I ratio from EEG. Despite promising results, there has been a lack of validation studies testing the underlying neurochemical changes leading to increased or decreased EEG-based E/I ratio. Here, using concurrent EEG and magnetic resonance spectroscopy (MRS) for over an hour, we assessed which algorithm of EEG-based E/I ratio best matched with MRS-based E/I ratio in humans of both sexes. The MRS-based E/I ratio was obtained by the ratio of glutamate concentration to GABA concentration. We applied 10 candidate indices of EEG-based E/I ratio using four approaches in several spontaneous frequency bands. Uniquely, we quantified the associations between the EEG-based E/I ratio and MRS-based E/I ratio separately for between-subjects and within-subjects variations. We found that each EEG-based E/I algorithm showed reliable and positive associations with MRS-based E/I, and especially EEG-based E/I ratio in alpha band with a criticality theory based approach showed the best association to the MRS-based E/I ratio. While these associations were evident for between-subjects comparisons, they were quite weak for within-subjects comparisons. These results suggest that EEG-based E/I algorithms are likely to reflect, at least in part, relative concentrations of glutamate and GABA.

neuroscience↗

bioRxiv2025

Quantification of SARM1 activity in human peripheral blood mononuclear cells

SARM1 (sterile and TIR motif-containing protein-1) is an NADase enzyme that has been identified as the central executioner of Wallerian axon degeneration. Given this, SARM1 is of high interest as a candidate therapeutic target and SARM1 inhibitors are currently in clinical trials for prevention and treatment of neurodegeneration. Beyond neuroscience, emerging studies reveal that SARM1 activation may also drive aspects of bone fragility, liver pathology, adipose tissue expansion, and insulin resistance in settings of metabolic disease. However, we lack methods to quantify SARM1 activation in humans using clinical isolates to better define patients at high risk of SARM1-mediated tissue damage, informing the future clinical application of SARM1 inhibitors. Unlike neurons, peripheral blood mononuclear cells (PBMCs) represent an easily accessible population of cells for clinical screening. We hypothesized that by pairing activators and inhibitors of SARM1 with analysis of downstream changes in cellular metabolites, we could quantify both the basal SARM1 activity and the SARM1 activation potential of human PBMCs. Our results reveal that SARM1 agonist pyrinuron, also known as Vacor, activates a dose-dependent increase in cAPDR and the cADPR:ADPR ratio that is arrested when paired with SARM1 inhibitor DSRM-3716. Various changes in secondary metabolites were also characterized and reported herein. Overall, these findings demonstrate that human PBMCs have detectable SARM1 activation potential and could be leveraged as a clinical readout of SARM1 expression and activity across diverse disease contexts.

cell biology↗

bioRxiv2024

Unsupervised learning as a computational principle works in visual learning of natural scenes, but not of artificial stimuli

Unsupervised learning--learning through repeated exposure without instruction or reward--is central to both machine learning and human cognition, including language acquisition and statistical learning. However, its role in visual perceptual learning (VPL) remains debated, as previous studies have not shown VPL for task-irrelevant but visible features, particularly in artificial stimuli. Here, we show that task-irrelevant exposure to natural scene images induces robust VPL, while artificial images that lack complex structure characteristics of natural scene images, known as higher-order statistics, do not. Behavioral and fMRI results suggest that although unsupervised learning underlies VPL, it can be suppressed by top-down attention. Higher-order statistics may evade this suppression, possibly because their slower processing reaches visual areas beyond V1 outside the optimal temporal window for attentional suppression. These findings suggest that unsupervised learning underlies VPL, but its occurrence depends on both higher-order stimulus structure and the brains attentional gating mechanisms.

neuroscience↗

bioRxiv2024

Suppressing phagocyte activation by overexpressing the phosphatidylserine lipase ABHD12 preserves sarmopathic nerves

Programmed axon degeneration (AxD) is a key feature of many neurodegenerative diseases. In healthy axons, the axon survival factor NMNAT2 inhibits SARM1, the central executioner of AxD, preventing it from initiating the rapid local NAD+ depletion and metabolic catastrophe that precipitates axon destruction. Because these components of the AxD pathway act within neurons, it was also assumed that the timetable of AxD was set strictly by a cell-intrinsic mechanism independent of neuron-extrinsic processes later activated by axon fragmentation. However, using a rare human disease model of neuropathy caused by hypomorphic NMNAT2 mutations and chronic SARM1 activation (sarmopathy), we demonstrated that neuronal SARM1 can initiate macrophage-mediated axon elimination long before stressed-but-viable axons would otherwise succumb to cell-intrinsic metabolic failure. Investigating potential SARM1-dependent signals that mediate macrophage recognition and/or engulfment of stressed-but-viable axons, we found that chronic SARM1 activation triggers axonal blebbing and dysregulation of phosphatidylserine (PS), a potent phagocyte immunomodulatory molecule. Neuronal expression of the phosphatidylserine lipase ABDH12 suppresses nerve macrophage activation, preserves motor axon integrity, and rescues motor function in this chronic sarmopathy model. We conclude that PS dysregulation is an early SARM1-dependent axonal stress signal, and that blockade of phagocytic recognition and engulfment of stressed-but-viable axons could be an attractive therapeutic target for management of neurological disorders involving SARM1 activation.

neuroscience↗

bioRxiv2024

Glutathione supersulphide regulates T-cell receptor signalling

Immunometabolism regulates functions and fates of immune cells including T cells. Supersulphides, which are universal metabolites containing catenated sulphur atoms, have various physiological functions based on their unique redox properties. Here we found that activation of T-cell receptor (TCR) signalling was accompanied by supersulphide decrease, which suggests a regulatory contribution of sulphur metabolism to immune function. Consistently, inhibiting supersulphide synthesis facilitated TCR activation and exacerbated allergen-induced type 2 inflammation in mice. Supplementation with glutathione trisulphide (GSSSG), a major endogenous supersulphide, suppressed TCR signalling in naive CD4+ T cells and their differentiation and effectively alleviated the inflammation. Docking simulation revealed interaction of GSSSG with CD3{varepsilon} chain in the TCR/CD3 complex, which was supported by mass spectrometry detection of persulphidated glutathionylation at a functionally important CXXC motif of CD3{varepsilon} chain. This study identified a new post-translational modification with supersulfides and demonstrated a critical contribution of sulphur metabolism to TCR signalling regulation.

biochemistry↗

bioRxiv2024

First-night effect reduces the beneficial effects of sleep on visual plasticity and modifies the underlying neurochemical processes

Individuals experience difficulty falling asleep in a new environment, termed the first night effect (FNE). However, the impact of the FNE on sleep-induced brain plasticity remains unclear. Here, using a within-subject design, we found that the FNE significantly reduces visual plasticity during sleep in young adults. Sleep-onset latency (SOL), an indicator of the FNE, was significantly longer during the first sleep session than the second session, confirming the FNE. We assessed performance gains in visual perceptual learning after sleep and increases in the excitatory-to-inhibitory neurotransmitter (E/I) ratio in early visual areas during sleep using magnetic resonance spectroscopy and polysomnography. These parameters were significantly smaller in sleep with the FNE than in sleep without the FNE; however, these parameters were not correlated with SOL. These results suggest that while the neural mechanisms of the FNE and brain plasticity are independent, sleep disturbances temporarily block the neurochemical process fundamental for brain plasticity.

neuroscience↗

bioRxiv2023

Learning of the same task subserved by substantially different mechanisms between patients with Body Dysmorphic Disorder and healthy individuals

It is generally believed that learning of a perceptual task involving low-level neuronal mechanisms is similar between individuals. However, it is unclear whether this assumption also applies to individuals with psychiatric disorders that are known to have altered brain activation during visual processing. We investigated this question in patients with body dysmorphic disorder (BDD), a psychiatric disorder characterized by distressing or impairing preoccupation with nonexistent or slight defects in ones physical appearance, and in healthy controls. Participants completed six training sessions on separate days on a visual detection task for human faces with low spatial frequency (LSF) components. Brain activation during task performance was measured with functional magnetic resonance imaging (fMRI) on separate days prior to and after training. The behavioral results showed that both groups of participants improved on the visual detection task to a similar extent through training. Despite this similarity in behavioral improvement, neuronal changes in the Fusiform Face Area (FFA), a core cortical region involved in face processing, with training were substantially different between groups. First, activation in the right FFA for LSF faces relative to High Spatial Frequency (HSF) faces that were used as an untrained control increased after training in BDD patients but decreased in controls. Second, resting state functional connectivity between left and right FFAs decreased after training in BDD patients but increased in controls. Contrary to the assumption that learning of a perceptual task is subserved by the same neuronal mechanisms across individuals, our results indicate that the neuronal mechanisms involved in learning of a face detection task differ fundamentally between patients with BDD and healthy individuals. The involvement of different neuronal mechanisms for learning of even simple perceptual tasks in patients with BDD might reflect the brains adaptations to altered functions imposed by the psychiatric disorder.

neuroscience↗