SARM1 activation triggers axon degeneration locally via NAD⁺ destruction

Neuronal guidance signaling in neurodegenerative diseases: Key regulators that function at neuron-glia and neuroimmune interfaces

The nervous system processes a vast amount of information, performing computations that underlie perception, cognition, and behavior. During development, neuronal guidance genes, which encode extracellular cues, their receptors, and downstream signal transducers, organize neural wiring to generate the complex architecture of the nervous system. It is now evident that many of these neuroguidance cues and their receptors are active during development and are also expressed in the adult nervous system. This suggests that neuronal guidance pathways are critical not only for neural wiring but also for ongoing function and maintenance of the mature nervous system. Supporting this view, these pathways continue to regulate synaptic connectivity, plasticity, and remodeling, and overall brain homeostasis throughout adulthood. Genetic and transcriptomic analyses have further revealed many neuronal guidance genes to be associated with a wide range of neurodegenerative and neuropsychiatric disorders. Although the precise mechanisms by which aberrant neuronal guidance signaling drives the pathogenesis of these diseases remain to be clarified, emerging evidence points to several common themes, including dysfunction in neurons, microglia, astrocytes, and endothelial cells, along with dysregulation of neuron-microglia-astrocyte, neuroimmune, and neurovascular interactions. In this review, we explore recent advances in understanding the molecular and cellular mechanisms by which aberrant neuronal guidance signaling contributes to disease pathogenesis through altered cell-cell interactions. For instance, recent studies have unveiled two distinct semaphorin-plexin signaling pathways that affect microglial activation and neuroinflammation. We discuss the challenges ahead, along with the therapeutic potentials of targeting neuronal guidance pathways for treating neurodegenerative diseases. Particular focus is placed on how neuronal guidance mechanisms control neuron-glia and neuroimmune interactions and modulate microglial function under physiological and pathological conditions. Specifically, we examine the crosstalk between neuronal guidance signaling and TREM2, a master regulator of microglial function, in the context of pathogenic protein aggregates. It is well-established that age is a major risk factor for neurodegeneration. Future research should address how aging and neuronal guidance signaling interact to influence an individual's susceptibility to various late-onset neurological diseases and how the progression of these diseases could be therapeutically blocked by targeting neuronal guidance pathways.

Diverse cell types establish a pathogenic immune environment in peripheral neuropathy

Neuroinflammation plays a complex and context-dependent role in many neurodegenerative diseases. We identified a key pathogenic function of macrophages in a mouse model of a rare human congenital neuropathy in which SARM1, the central executioner of axon degeneration, is activated by hypomorphic mutations in the axon survival factor NMNAT2. Macrophage depletion blocked and reversed neuropathic phenotypes in this sarmopathy model, revealing SARM1-dependent neuroimmune mechanisms as key drivers of disease pathogenesis. In this study, we investigated the impact of chronic subacute SARM1 activation on the peripheral nerve milieu using single cell/nucleus RNA-sequencing (sc/snRNA-seq). Our analyses reveal an expansion of immune cells (macrophages and T lymphocytes) and repair Schwann cells, as well as significant transcriptional alterations to a wide range of nerve-resident cell types. Notably, endoneurial fibroblasts show increased expression of chemokines (Ccl9, Cxcl5) and complement components (C3, C4b, C6) in response to chronic SARM1 activation, indicating enhanced immune cell recruitment and immune response regulation by non-immune nerve-resident cells. Analysis of CD45+ immune cells in sciatic nerves revealed an expansion of an Il1b+ macrophage subpopulation with increased expression of markers associated with phagocytosis and T cell activation/proliferation. We also found a significant increase in T cells in sarmopathic nerves. Remarkably, T cell depletion rescued motor phenotypes in the sarmopathy model. These findings delineate the significant changes chronic SARM1 activation induces in peripheral nerves and highlights the potential of immunomodulatory therapies for SARM1-dependent peripheral neurodegenerative disease.

Evolutionarily ancient functions of enzymatic TIR proteins in innate immunity

Proteins with a Toll/interleukin-1 receptor/resistance (TIR) domain are among the most ancient immune regulators and include well-known pattern recognition receptors (PRRs). A specialized subset of TIR domain proteins are enzymes that predominantly use nicotinamide adenine dinucleotide (NAD+) to generate second messenger metabolites. These enzymatic TIR proteins have essential roles in bacteria, plant, and animal immunity. The mechanism of activation of these TIR proteins, conserved across Kingdoms, involves oligomerization into higher-ordered structures, which activates their intrinsic enzymatic activity. Here, we review the functions of enzymatic TIR proteins in innate immunity in bacteria, plants, and animals. This work offers insights into the evolutionary origins of immunity itself and defines fundamental principles of immune surveillance across the Tree of Life.

Nicotinamide N-Methyltransferase (NNMT) and Liver Cancer: From Metabolic Networks to Therapeutic Targets

Hepatocellular carcinoma (HCC), the predominant form of primary liver cancer, remains a global health challenge with limited therapeutic options and high mortality rates. Despite advances in understanding its molecular pathogenesis, the role of metabolic reprogramming in HCC progression and therapy resistance demands further exploration. Nicotinamide N-methyltransferase (NNMT), a metabolic enzyme central to NAD+ and methionine cycles, has emerged as a critical regulator of tumorigenesis across cancers. However, its tissue-specific mechanisms in HCC-particularly in the context of viral hepatitis and methionine cycle dependency-remain understudied. This review systematically synthesizes current evidence on NNMT's dual role in HCC: (1) driving NAD+ depletion and homocysteine (Hcy) accumulation via metabolic dysregulation, (2) promoting malignant phenotypes (proliferation, invasion, metastasis, and drug resistance), and (3) serving as a prognostic biomarker and therapeutic target. We highlight how NNMT intersects with epigenetic modifications, immune evasion, and metabolic vulnerabilities unique to HCC. Additionally, we critically evaluate NNMT inhibitors, RNA-based therapies, and non-pharmacological strategies (e.g., exercise) as novel interventions. By bridging gaps between NNMT's molecular mechanisms and clinical relevance, this review provides a roadmap for advancing NNMT-targeted therapies and underscores the urgency of addressing challenges in biomarker validation, inhibitor specificity, and translational efficacy. Our work positions NNMT not only as a metabolic linchpin in HCC but also as a promising candidate for precision oncology.

SARM1: a key multifaceted component in immunoregulation, inflammation and neurodegeneration

The downstream signaling pathways of TLR activation involve a family of adaptor proteins, including MYD88, TIRAP, TRIF, TRAM, and SARM1. The first four proteins stimulate inflammatory and antiviral responses, playing crucial roles in innate immunity against various pathogens. In contrast, SARM1 promotes immunity to microorganisms in invertebrate animals independently of TLRs, and negatively regulates inflammatory responses in metazoan organisms. SARM1 inhibits TRIF, reduces the activation of various inflammasomes, and induces mitochondrial damage and cell death to eliminate hyperactivated cells. This regulation is essential to ensure timely control of immune responses and to prevent excessive inflammation. Recently, it was discovered that SARM1 can hydrolyze NAD, a critical component of cellular metabolism. The reduction of NAD levels by SARM1 is linked to the progression of Wallerian degeneration following neuronal injury and may also play a role in the immunoregulation of lymphoid and myeloid cells. Since SARM1 can be pharmacologically modulated, it presents promising opportunities for developing treatments for inflammatory and neurodegenerative diseases.

SARM1 deletion inhibits astrogliosis and BBB damage through Jagged-1/Notch-1/NF-κB signaling to improve neurological function after ischemic stroke

Reactive astrogliosis is a critical process in the development of ischemic stroke. However, the precise mechanism by which reactive astrogliosis changes the pathogenesis of ischemic stroke remains elusive. Sterile alpha and TIR motif-containing 1 protein (SARM1) plays a key role in axonal degeneration and is involved in different cell death programs that regulate neuronal survival. The present study investigated the role of SARM1 in regulating reactive astrogliosis and neurological function after stroke in whole-body SARM1 knockout (SARM1-/-) mice. SARM1-/- mice showed significantly smaller infarction, slighter apoptosis, and fewer neurological function deficits 1-7 days after ischemic injury. Immunohistochemistry, western blot, and real-time PCR analyses revealed that compared with the wild-type (WT) mice, SARM1-/- mice exhibited reduced astrocytic proliferation, increased anti-inflammatory astrocytes, decreased glial scar formation in the infarct zone on day 7 after ischemic injury. SARM1 deletion also suppressed cerebral microvascular damage and blood-brain barrier (BBB) injury in ischemic brains. Mechanistically, SARM1 deletion inhibited the stroke-triggered activation of NF-κB signaling and decreased the expression of Jagged-1 and NICD in astrocytes. Overall, these findings provide the first line of evidence for a causative role of SARM1 protein in ischemia-induced reactive astrogliosis and ischemic neurovascular damage.

Klebsiella pneumoniae emerging anti-immunology paradigms: from stealth to evasion

Klebsiella pneumoniae (KP) is a global threat to human health due to the isolation of multidrug-resistant strains. Despite advancements in understanding KP's population structure, antibiotic resistance mechanisms, and transmission patterns, a gap remains in how KP evades defenses, allowing the pathogen to flourish in tissues despite an activated immune system. KP infection biology has been shaped by the notion that the pathogen has evolved to shield from defenses more than actively suppress them. This review describes new paradigms of how KP exploits the coevolution with the innate immune system to hijack immune effectors and receptors to ablate signaling pathways and to counteract cell-intrinsic immunity, making apparent that KP can no longer be considered only as a stealth pathogen.

TIR domains produce histidine-ADPR as an immune signal in bacteria

Toll/interleukin-1 receptor (TIR) domains are central components of pattern recognition immune proteins across all domains of life1,2. In bacteria and plants, TIR-domain proteins recognize pathogen invasion and then produce immune signalling molecules exclusively comprising nucleotide moieties2-5. Here we show that the TIR-domain protein of the type II Thoeris defence system in bacteria produces a unique signalling molecule comprising the amino acid histidine conjugated to ADP-ribose (His-ADPR). His-ADPR is generated in response to phage infection and activates the cognate Thoeris effector by binding a Macro domain located at the C terminus of the effector protein. By determining the crystal structure of a ligand-bound Macro domain, we describe the structural basis for His-ADPR and its recognition and show its role by biochemical and mutational analyses. Our analyses furthermore reveal a family of phage proteins that bind and sequester His-ADPR signalling molecules, enabling phages to evade TIR-mediated immunity. These data demonstrate diversity in bacterial TIR signalling and reveal a new class of TIR-derived immune signalling molecules that combine nucleotide and amino acid moieties.

Patterns of pathogenesis in innate immunity: insights from C. elegans

The cells in barrier tissues can distinguish pathogenic from commensal bacteria and target inflammatory responses only in the context of infection. As such, these cells must be able to identify pathogen infection specifically and not just the presence of an infectious organism, because many innocuous bacteria express the ligands that activate innate immunity in other contexts. Unravelling the mechanisms that underly this specificity, however, is challenging. Free-living nematodes, such as Caenorhabditis elegans, are faced with a similar dilemma, as they live in microorganism-rich habitats and eat bacteria as their source of nutrition. Nematodes lost canonical mechanisms of pattern recognition during their evolution and have instead evolved mechanisms to identify specific ligands or symptoms in the host that indicate active infection with an infectious microorganism. Here we review how C. elegans surveys for these patterns of pathogenesis to activate innate immune defences. Collectively, this work demonstrates that using C. elegans as an experimental platform to study host-pathogen interactions at barrier surfaces reveals primordial and fundamentally important principles of innate immune sensing in the animal branch of the tree of life.

Pyruvate kinase deficiency links metabolic perturbations to neurodegeneration and axonal protection

Neurons rely on tightly regulated metabolic networks to sustain their high-energy demands, particularly through the coupling of glycolysis and oxidative phosphorylation. Here, we investigate the role of pyruvate kinase (PyK), a key glycolytic enzyme, in maintaining axonal and synaptic integrity in the Drosophila melanogaster neuromuscular system. Using genetic deficiencies in PyK, we show that disrupting glycolysis induces progressive synaptic and axonal degeneration and severe locomotor deficits. These effects require the conserved dual leucine zipper kinase (DLK), Jun N-terminal kinase (JNK), and activator protein 1 (AP-1) Fos transcription factor axonal damage signaling pathway and the SARM1 NADase enzyme, a key driver of axonal degeneration. As both DLK and SARM1 regulate degeneration of injured axons (Wallerian degeneration), we probed the effect of PyK loss on this process. Consistent with the idea that metabolic shifts may influence neuronal resilience in context-dependent ways, we find that pyk knockdown delays Wallerian degeneration following nerve injury, suggesting that reducing glycolytic flux can promote axon survival under stress conditions. This protective effect is partially blocked by DLK knockdown and fully abolished by SARM1 overexpression. Together, our findings help bridge metabolism and neurodegenerative signaling by demonstrating that glycolytic perturbations causally activate stress response pathways that dictate the balance between protection and degeneration depending on the system's state. These results provide a mechanistic framework for understanding metabolic contributions to neurodegeneration and highlight the potential of metabolism as a target for therapeutic strategies.

Abstract Figure

Macrophages protect against sensory axon loss in peripheral neuropathy

Peripheral neuropathy is a common complication of type 2 diabetes, which is strongly associated with obesity1, causing sensory loss and, in some patients, neuropathic pain2,3. Although the onset and progression of diabetic peripheral neuropathy is linked with dyslipidaemia and hyperglycaemia4, the contribution of inflammation to peripheral neuropathy pathogenesis has not been investigated. Here we used a high-fat, high-fructose diet (HFHFD), which induces obesity and prediabetic metabolic changes, to study the onset of peripheral neuropathy. Mice fed the HFHFD developed persistent heat hypoalgesia after 3 months, but a reduction in epidermal skin nerve fibre density manifested only at 6 months. Using single-cell sequencing, we found that CCR2+ macrophages infiltrate the sciatic nerves of HFHFD-fed mice well before axonal degeneration is detectable. These infiltrating macrophages share gene expression similarities with nerve-crush-induced macrophages5 and express neurodegeneration-associated microglial marker genes6, although there is no axon loss or demyelination. Inhibiting the macrophage recruitment by genetically or pharmacologically blocking CCR2 signalling resulted in more severe heat hypoalgesia and accelerated skin denervation, as did deletion of Lgals3, a gene expressed in recruited macrophages. Recruitment of macrophages into the peripheral nerves of obese prediabetic mice is, therefore, neuroprotective, delaying terminal sensory axon degeneration by means of galectin 3. Potentiating and sustaining early neuroprotective immune responses in patients could slow or prevent peripheral neuropathy.

Inhibition of SARM1 Reduces Neuropathic Pain in a Spared Nerve Injury Rodent Model

INTRODUCTION/AIMS

The function of the sterile alpha and toll/interleukin receptor motif-containing protein 1 (SARM1) in neuropathic pain development has not yet been established. This protein has a central role in regulating axon degeneration and its depletion delays this process. This study aims to demonstrate the effects of SARM1 deletion on the development of neuropathic pain.

METHODS

Thirty-two wild-type (WT) or SARM1 knockout (KO) rats underwent spared nerve injury (SNI) or sham surgery. Mechanical allodynia was assessed by electronic Von Frey and cold hyperalgesia by the acetone test. Nociception was evaluated at the baseline, Day-1, Day-2, Week-1, Week-2, Week-3, and Week-4 time points. Nerve sections were examined by immunohistochemistry (IHC).

RESULTS

WT Injury rats were more sensitive to pain than WT Sham at all postoperative time points, validating the pain model. Injured SARM1 KO rats only demonstrated a difference in mechanical or cold nociception from KO Sham at Week 3. Injured KO rats demonstrated a clear trend of decreased sensitivity compared to WT Injury nociception, reaching significance at Week 4 (p = 0.044). Injured KO rats showed attenuated sensitivity to cold allodynia relative to WT at Week 2 (p = 0.019). IHC revealed decreased macrophages in spared sural nerves of injured KO animals at 2 and 4 weeks, and the proximal portion of tibial/peroneal nerves at Week 2.

DISCUSSION

This study demonstrates that SARM1 KO rats are less sensitive to mechanical and cold nociception than WT rats in an SNI model with decreased inflammatory response. Given these results, inhibition of SARM1 should be further investigated in the treatment of neuropathic pain.

A phage-encoded counter-defense inhibits an NAD-degrading anti-phage defense system

Bacteria contain a diverse array of genes that provide defense against predation by phages. Anti-phage defense genes are frequently located on mobile genetic elements and spread through horizontal gene transfer. Despite the many anti-phage defense systems that have been identified, less is known about how phages overcome the defenses employed by bacteria. The integrative and conjugative element ICEBs1 in Bacillus subtilis contains a gene, spbK, that confers defense against the temperate phage SPβ through an abortive infection mechanism. Using genetic and biochemical analyses, we found that SpbK is an NADase that is activated by binding to the SPβ phage portal protein YonE. The presence of YonE stimulates NADase activity of the TIR domain of SpbK and causes cell death. We also found that the SPβ-like phage Φ3T has a counter-defense gene that prevents SpbK-mediated abortive infection and enables the phage to produce viable progeny, even in cells expressing spbK. We made SPβ-Φ3T hybrid phages that were resistant to SpbK-mediated defense and identified a single gene in Φ3T (phi3T_120, now called nip for NADase inhibitor from phage) that was both necessary and sufficient to block SpbK-mediated anti-phage defense. We found that Nip binds to the TIR (NADase) domain of SpbK and inhibits NADase activity. Our results provide insight into how phages overcome bacterial immunity by inhibiting enzymatic activity of an anti-phage defense protein.

Subcellular proteomics and iPSC modeling uncover reversible mechanisms of axonal pathology in Alzheimer's disease

Dystrophic neurites (also termed axonal spheroids) are found around amyloid deposits in Alzheimer's disease (AD), where they impair axonal electrical conduction, disrupt neural circuits and correlate with AD severity. Despite their importance, the mechanisms underlying spheroid formation remain incompletely understood. To address this, we developed a proximity labeling approach to uncover the proteome of spheroids in human postmortem and mouse brains. Additionally, we established a human induced pluripotent stem cell (iPSC)-derived AD model enabling mechanistic investigation and optical electrophysiology. These complementary approaches revealed the subcellular molecular architecture of spheroids and identified abnormalities in key biological processes, including protein turnover, cytoskeleton dynamics and lipid transport. Notably, the PI3K/AKT/mTOR pathway, which regulates these processes, was activated in spheroids. Furthermore, phosphorylated mTOR levels in spheroids correlated with AD severity in humans. Notably, mTOR inhibition in iPSC-derived neurons and mice ameliorated spheroid pathology. Altogether, our study provides a multidisciplinary toolkit for investigating mechanisms and therapeutic targets for axonal pathology in neurodegeneration.

Stepwise activation of SARM1 for cell death and axon degeneration revealed by a biosynthetic NMN mimic

Axon degeneration, driven by the NAD+ hydrolyzing enzyme SARM1, is an early pathological hallmark of numerous neurodegenerative diseases. SARM1 exists in an inactive form and is activated following nerve injury. However, the precise molecular mechanism underlying SARM1 activation remains to be fully elucidated. In this study, we report the identification of a potent proactivator of SARM1, G10, which is converted into a direct activator (M1) by the enzyme nicotinamide phosphoribosyltransferase. Cryoelectron microscopy structures of SARM1 bound to M1, as well as to M1 and a nonhydrolyzable NAD+ analog (1AD), captured two intermediate activation states and the fully active state, revealing a stepwise mechanism of SARM1 activation. Further, introducing a disulfide bond to prevent conformational transitions between the two intermediate states mediated by M1 stabilized SARM1 in its inactive form and blocked M1-induced cell death. Together, these findings propose a sequential, stepwise activation model for SARM1 and offer a framework for developing potential SARM1 inhibitors for the treatment of neurodegenerative diseases.

Quantification of SARM1 activity in human peripheral blood mononuclear cells

SARM1 (sterile α 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.

Emerging interactions between mitochondria and NAD+ metabolism in cardiometabolic diseases

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme for redox reactions and regulates cellular catabolic pathways. An intertwined relationship exists between NAD+ and mitochondria, with consequences for mitochondrial function. Dysregulation in NAD+ homeostasis can lead to impaired energetics and increased oxidative stress, contributing to the pathogenesis of cardiometabolic diseases. In this review, we explore how disruptions in NAD+ homeostasis impact mitochondrial function in various cardiometabolic diseases. We discuss emerging studies demonstrating that enhancing NAD+ synthesis or inhibiting its consumption can ameliorate complications of this family of pathological conditions. Additionally, we highlight the potential role and therapeutic promise of mitochondrial NAD+ transporters in regulating cellular and mitochondrial NAD+ homeostasis.

Hypoxia-inducible factor 1 protects neurons from Sarm1-mediated neurodegeneration

The Sarm1 NAD + hydrolase drives neurodegeneration in many contexts, but how Sarm1 activity is regulated remains poorly defined. Using CRISPR/Cas9 screening, we found loss of VHL suppressed Sarm1-mediated cellular degeneration. VHL normally promotes O 2 -dependent constitutive ubiquitination and degradation of hypoxia-inducible factor 1 (HIF-1), but during hypoxia, HIF-1 is stabilized and regulates gene expression. We observed neuroprotection after depletion of VHL or other factors required for HIF-1 degradation, and expression of a non-ubiquitinated HIF-1 variant led to even stronger blockade of axon degeneration in mammals and Drosophila . Neuroprotection required HIF-1 DNA binding, prolonged expression, and resulted in broad gene expression changes. Unexpectedly, stabilized HIF-1 prevented the precipitous NAD + loss driven by Sarm1 activation in neurons, despite NAD + hydrolase activity being intrinsic to the Sarm1 TIR domain. Our work argues hypoxia inhibits Sarm1 activity through HIF-1 driven transcriptional changes, rendering neurons less sensitive to Sarm1-mediated neurodegeneration when in a hypoxic state.

Competing interests

Marc Freeman is co-founder of Nura Bio, a biotech startup pursuing novel neuroprotective therapies including SARM1 inhibition. The remaining authors declare no competing interests.

Programmed neurite degeneration in human central nervous system neurons driven by changes in NAD+ metabolism

Neurite degeneration (ND) precedes cell death in many neurodegenerative diseases. However, it remains unclear how this compartmentalized cell death process is orchestrated in the central nervous system (CNS). The establishment of a CNS axotomy model (using modified 3D LUHMES cultures) allowed us to study metabolic control of ND in human midbrain-derived neurons without the use of toxicants or other direct disturbance of cellular metabolism. Axotomy lead to a loss of the NAD+ synthesis enzyme NMNAT2 within 2 h and a depletion of NAD+ within 4-6 h. This process appeared specific, as isolated neurites maintained ATP levels and a coupled mitochondrial respiration for at least 6 h. In the peripheral nervous system (PNS) many studies observed that NAD+ metabolism, in particular by the NADase SARM1, plays a major role in the ND occurring after axotomy. Since neither ferroptosis nor necroptosis, nor caspase-dependent apoptosis seemed to be involved in neurite loss, we investigated SARM1 as potential executioner (or controller). Knock-down or expression of a dominant-negative isoform of SARM1 indeed drastically delayed ND. Various modifications of NAD+ metabolism known to modulate SARM1 activity showed the corresponding effects on ND. Moreover, supplementation with NAD+ attenuated ND. As a third approach to investigate the role of altered NAD+ metabolism, we made use of the WLD(s) protein, which has been found in a mutant mouse to inhibit Wallerian degeneration of axons. This protein, which has a stable NMNAT activity, and thus can buffer the loss of NMNAT2, protected the neurites by stabilizing neurite NAD+ levels. Thus CNS-type ND was tightly linked to neurite metabolism in multiple experimental setups. Based on this knowledge, several new strategies for treating neurodegenerative diseases can be envisaged.

Local translatome sustains synaptic function in impaired Wallerian degeneration

After injury, severed axons separated from their somas activate programmed axon degeneration, a conserved pathway to initiate their degeneration within a day. Conversely, severed projections deficient in programmed axon degeneration remain morphologically preserved with functional synapses for weeks to months after axotomy. How this synaptic function is sustained remains currently unknown. Here, we show that dNmnat overexpression attenuates programmed axon degeneration in distinct neuronal populations. Severed projections remain morphologically preserved for weeks. When evoked, they elicit a postsynaptic behavior, a readout for preserved synaptic function. We used ribosomal pulldown to isolate the translatome from these projections 1 week after axotomy. Translatome candidates of enriched biological classes identified by transcriptional profiling are validated in a screen using a novel automated system to detect evoked antennal grooming as a proxy for preserved synaptic function. RNAi-mediated knockdown reveals that transcripts of the mTORC1 pathway, a mediator of protein synthesis, and of candidate genes involved in protein ubiquitination and Ca2+ homeostasis are required for preserved synaptic function. Our translatome dataset also uncovers several uncharacterized Drosophila genes associated with human disease. It may offer insights into novel avenues for therapeutic treatments.

A Role for SARM1 in Photoreceptor Cell Death

Photoreceptor cell death is a common feature of many retinal degenerative diseases, leading to incurable vision loss. While there is evidence to support the involvement of cell death pathways such as apoptosis and necroptosis in the degeneration of photoreceptors, the inhibition of these pathways has not been sufficient to rescue photoreceptors and preserve vision in a number of models of disease. Therefore, there is a need to identify other pathways involved in photoreceptor cell death. SARM1 is a TLR adaptor protein with a novel role in the induction of axonal degeneration and neuronal cell death. Our lab and others have demonstrated a role for SARM1 in the induction of photoreceptor cell death in models of retinal degenerative disease. Here, we summarize the current knowledge on SARM1 function and its role in photoreceptor cell death.

DLK-dependent axonal mitochondrial fission drives degeneration after axotomy

Currently there are no effective treatments for an array of neurodegenerative disorders to a large part because cell-based models fail to recapitulate disease. Here we develop a reproducible human iPSC-based model where laser axotomy causes retrograde axon degeneration leading to neuronal cell death. Time-lapse confocal imaging revealed that damage triggers an apoptotic wave of mitochondrial fission proceeding from the site of injury to the soma. We demonstrate that this apoptotic wave is locally initiated in the axon by dual leucine zipper kinase (DLK). We find that mitochondrial fission and resultant cell death are entirely dependent on phosphorylation of dynamin related protein 1 (DRP1) downstream of DLK, revealing a mechanism by which DLK can drive apoptosis. Importantly, we show that CRISPR mediated Drp1 depletion protects mouse retinal ganglion neurons from degeneration after optic nerve crush. Our results provide a platform for studying degeneration of human neurons, pinpoint key early events in damage related neural death and provide potential focus for therapeutic intervention.

Pathobiochemistry of Aging and Neurodegeneration: Deregulation of NAD+ Metabolism in Brain Cells

NAD+ plays a pivotal role in energy metabolism and adaptation to external stimuli and stressful conditions. A significant reduction in intracellular NAD+ levels is associated with aging and contributes to the development of chronic cardiovascular, neurodegenerative, and metabolic diseases. It is of particular importance to maintain optimal levels of NAD+ in cells with high energy consumption, particularly in the brain. Maintaining the tissue level of NAD+ with pharmacological tools has the potential to slow down the aging process, to prevent the development of age-related diseases. This review covers key aspects of NAD+ metabolism in terms of brain metabolic plasticity, including NAD+ biosynthesis and degradation in different types of brain cells, as well as its contribution to the development of neurodegeneration and aging, and highlights up-to-date approaches to modulate NAD+ levels in brain cells.

SARM1 in the pathogenesis of immune-related disease

Background

Sterile alpha and toll interleukin receptor motif-containing protein 1 (SARM1) are primarily expressed in the mammalian nervous system, with their presence in neurons being associated with mitochondrial aggregation. SARM1 functions as a mediator of cell death and morphological changes, while also regulating Waller degeneration in nerve fibers and influencing glial cell formation.

Purpose

Recent reports demonstrate SARM1 serves as a connector in the Toll-like receptor (TLR) pathway and plays a role in regulating inflammation during periods of stress such as infection, trauma, and hypoxia. These findings offer new insights into pathogenesis research and the prevention and treatment of neurodegenerative diseases and pathogen infections.

Methods

This review synthesizes recent findings on the immune-related mechanisms of SARM1, emphasizing its roles in inflammation and its functional impact on the nervous system and other bodily systems.

Conclusions

Understanding the multifaceted roles of SARM1 in immune regulation and neuronal health provides novel insights into its involvement in disease pathogenesis. These insights hold promise for advancing research into the prevention and treatment of neurodegenerative diseases and pathogen-induced conditions.

An Ionic Sensor acts in Parallel to dSarm to Promote Neurodegeneration

How neurons to sense when they are terminally dysfunctional and activate neurodegeneration remains poorly defined. The pro-degenerative NAD + hydrolase dSarm/SARM1 can act as a metabolic sensor by detecting pathological changes in NAD + /NMN and subsequently induce catastrophic axon degeneration. Here we show Drosophila with-no-lysine kinase (dWnk), which can directly sense Cl - , K + and osmotic pressure, is required for neurodegeneration induced by depletion of the NAD + biosynthetic enzyme dNmnat. dWnk functions in parallel to dSarm and acts through the downstream kinase Frayed to promote axon degeneration and neuronal cell death. dWnk and dSarm ultimately converge on the BTB-Back domain molecule Axundead (Axed) to execute neurodegeneration. Our work argues that neurons use direct sensors of both metabolism (dSarm/SARM1) and ionic/osmotic status (dWnk) to evaluate cellular health and, when dysfunctional, promote neurodegeneration though a common axon death signaling molecule, Axundead.

NAD+ enhancers as therapeutic agents in the cardiorenal axis

Cardiorenal diseases represent a complex interplay between heart failure and renal dysfunction, being clinically classified as cardiorenal syndromes (CRS). Recently, the contributions of altered nicotinamide adenine dinucleotide (NAD+) metabolism, through deficient NAD+ synthesis and/or elevated consumption, have proved to be decisive in the onset and progress of cardiorenal disease. NAD+ is a pivotal coenzyme in cellular metabolism, being significant in various signaling pathways, such as energy metabolism, DNA damage repair, gene expression, and stress response. Convincing evidence suggests that strategies designed to boost cellular NAD+ levels are a promising therapeutic option to address cardiovascular and renal disorders. Here, we review and discuss the implications of NAD+ metabolism in cardiorenal diseases, focusing on the propitious NAD+ boosting therapeutic strategies, based on the use of NAD+ precursors, poly(ADP-ribose) polymerase inhibitors, sirtuin activators, and other alternative approaches, such as CD38 blockade, nicotinamide phosphoribosyltransferase activation and combined interventions.

Downregulation of SARM1 Protects Retinal Ganglion Cell Axonal and Somal Degeneration Via JNK Activation in a Glaucomatous Model of Ocular Hypertension

Purpose

This study aimed to assess the expression of sterile alpha and TIR motif containing protein 1 (SARM1) in both chronic and acute glaucomatous animal models and investigate the underlying SARM1-JNK signaling mechanism responsible for the protective effects of SARM1 downregulation on retinal ganglion cell (RGC) soma and axons in a chronic intraocular hypertension (COH) model.

Methods

The COH model was induced by injecting magnetic microbeads into the anterior chamber, whereas the acute model was created through ischemia-reperfusion (I/R) injury. Immunohistochemistry and Western blot were used to assess SARM1 expression and JNK phosphorylation in the retina and optic nerve. SARM1 downregulation was achieved through the intravitreal injection of adeno-associated virus (AAV)2-shRNA. Quantitative analysis of RGC survival was performed by the counting of Brn3A-positive RGCs, and surviving axons were assessed through optic nerve toluidine blue stain.

Results

The expression of SARM1 increased 1 week after microbead injection in the optic nerve, whereas the retinal SARM1 expression decreased at 3 days post-injection in the COH model. After 24 hours of reperfusion, SARM1 expression increased in both the optic nerves and the retinas in the I/R injury model. SARM1 downregulation led to increased survival of RGC soma and axons in the COH model. In this model, JNK phosphorylation was significantly reduced concomitant with decreased SARM1 expression.

Conclusions

Elevated SARM1 expression was observed in the optic nerves in both the COH and I/R injury models. Downregulation of SARM1 exhibited a protective effect on RGC soma and axons in the COH model, with JNK identified as a downstream regulator of SARM1 in this context.

Molecular mechanisms of neuropathic pain

Peripheral neuropathic pain, which occurs after a lesion or disease affecting the peripheral somatosensory nervous system, is a complex and challenging condition to treat. This chapter will cover molecular mechanisms underlying the pathophysiology of peripheral neuropathic pain, focusing on (1) sensitization of nociceptors, (2) neuro-immune crosstalk, and (3) axonal degeneration and regeneration. The chapter will also emphasize the importance of identifying novel therapeutic targets in non-neuronal cells. A comprehensive understanding of how changes at both neuronal and non-neuronal levels contribute to peripheral neuropathic pain may significantly improve pain management and treatment options, expanding to topical application that bypass the side effects associated with systemic administration.

Exploring clinical markers of Axon degeneration processes in Chemotherapy-induced peripheral neuropathy among young adults receiving vincristine or paclitaxel

BACKGROUND

Approximately 70% of patients receiving neurotoxic chemotherapy (e.g., paclitaxel or vincristine) will develop chemotherapy-induced peripheral neuropathy. Despite the known negative effects of CIPN on physical functioning and chemotherapy dosing, little is known about how to prevent CIPN. The development of efficacious CIPN prevention interventions is hindered by the lack of knowledge surrounding CIPN mechanisms. Nicotinamide adenine dinucleotide (NAD+) and cyclic-adenosine diphosphate ribose (cADPR) are potential markers of axon degeneration following neurotoxic chemotherapy, however, such markers have been exclusively measured in preclinical models of chemotherapy-induced peripheral neuropathy (CIPN). The overall objective of this longitudinal, observational study was to determine the association between plasma NAD+, cADPR, and ADPR with CIPN severity in young adults receiving vincristine or paclitaxel.

METHODS

Young adults (18-39 years old) beginning vincristine or paclitaxel were recruited from Dana-Farber Cancer Institute. Young adults completed the QLQ-CIPN20 sensory and motor subscales and provided a blood sample prior to starting chemotherapy (T1) and at increasing cumulative vincristine (T2: 3-5 mg, T3: 7-9 mg) and paclitaxel (T2: 300-500 mg/m2, T3: 700-900 mg/m2) dosages. NAD+, cADPR, and ADPR were quantified from plasma using mass spectrometry. Metabolite levels and QLQ-CIPN20 scores over time were compared using mixed-effects linear regression models and/or paired two-sample tests.

RESULTS

Participants (N = 50) were mainly female (88%), white (80%), and receiving paclitaxel (78%). Sensory and motor CIPN severity increased from T1-T3 (p < 0.001). NAD+ (p = 0.28), cADPR (p = 0.62), and ADPR (p = 0.005) values decreased, while cADPR/NAD+ ratio increased from T1-T3 (p = 0.50). There were no statistically significant associations between NAD + and QLQ-CIPN20 scores over time.

CONCLUSIONS

To our knowledge, this is the first study to measure plasma NAD+, cADPR, and ADPR among patients receiving neurotoxic chemotherapy. Although, no meaningful changes in NAD+, cADPR, or cADPR/NAD+ were observed among young adults receiving paclitaxel or vincristine. Future research in an adequately powered sample is needed to explore the clinical utility of biomarkers of axon degeneration among patients receiving neurotoxic chemotherapy to guide mechanistic research and novel CIPN treatments.

Lysosome-related organelle integrity suppresses TIR-1 aggregation to restrain toxic propagation of p38 innate immunity

Innate immunity in bacteria, plants, and animals requires the specialized subset of Toll/interleukin-1/resistance gene (TIR) domain proteins that are nicotinamide adenine dinucleotide (NAD+) hydrolases. Aggregation of these TIR proteins engages their enzymatic activity, but it is unknown how this protein multimerization is regulated. Here, we discover that TIR oligomerization is controlled to prevent immune toxicity. We find that p38 propagates its own activation in a positive feedback loop, which promotes the aggregation of the lone enzymatic TIR protein in the nematode C. elegans (TIR-1, homologous to human sterile alpha and TIR motif-containing 1 [SARM1]). We perform a forward genetic screen to determine how the p38 positive feedback loop is regulated. We discover that the integrity of the specific lysosomal subcompartment that expresses TIR-1 is actively maintained to limit inappropriate TIR-1 aggregation on the membranes of these organelles, which restrains toxic propagation of p38 innate immunity. Thus, innate immunity in C. elegans intestinal epithelial cells is regulated by specific control of TIR-1 multimerization.

Mechanisms of the NAD+ salvage pathway in enhancing skeletal muscle function

Nicotinamide adenine dinucleotide (NAD+) is crucial for cellular energy production, serving as a coenzyme in oxidation-reduction reactions. It also supports enzymes involved in processes such as DNA repair, aging, and immune responses. Lower NAD+ levels have been associated with various diseases, highlighting the importance of replenishing NAD+. Nicotinamide phosphoribosyltransferase (NAMPT) plays a critical role in the NAD+ salvage pathway, which helps sustain NAD+ levels, particularly in high-energy tissues like skeletal muscle.This review explores how the NAMPT-driven NAD+ salvage pathway influences skeletal muscle health and functionality in aging, type 2 diabetes mellitus (T2DM), and skeletal muscle injury. The review offers insights into enhancing the salvage pathway through exercise and NAD+ boosters as strategies to improve muscle performance. The findings suggest significant potential for using this pathway in the diagnosis, monitoring, and treatment of skeletal muscle conditions.

Microglial cGAS-STING signaling underlies glaucoma pathogenesis

Characterized by progressive degeneration of retinal ganglion cells (RGCs) and vision loss, glaucoma is the primary cause of irreversible blindness, incurable and affecting over 78 million patients. However, pathogenic mechanisms leading to glaucoma-induced RGC loss are incompletely understood. Unexpectedly, we found that cGAS-STING (2'3'-cyclic GMP-AMP-stimulator of interferon genes) signaling, which surveils displaced double-stranded DNA (dsDNA) in the cytosol and initiates innate immune responses, was robustly activated during glaucoma in retinal microglia in distinct murine models. Global or microglial deletion of STING markedly relieved glaucoma symptoms and protected RGC degeneration and vision loss, while mice bearing genetic cGAS-STING supersensitivity aggravated retinal neuroinflammation and RGC loss. Mechanistically, dsDNA from tissue injury activated microglial cGAS-STING signaling, causing deleterious macroglia reactivity in retinas by cytokine-mediated microglia-macroglia interactions, progressively driving apoptotic death of RGCs. Remarkably, preclinical investigations of targeting cGAS-STING signaling by intraocular injection of TBK1i or anti-IFNAR1 antibody prevented glaucoma-induced losses of RGCs and vision. Therefore, we unravel an essential role of cGAS-STING signaling underlying glaucoma pathogenesis and suggest promising therapeutic strategies for treating this devastating disease.

Histone deacetylase inhibition expands cellular proteostasis repertoires to enhance neuronal stress resilience

Neurons are long-lived, terminally differentiated cells with limited regenerative capacity. Cellular stressors such as endoplasmic reticulum (ER) protein folding stress and membrane trafficking stress accumulate as neurons age and accompany age-dependent neurodegeneration. Current strategies to improve neuronal resilience are focused on using factors to reprogram neurons or targeting specific proteostasis pathways. We discovered a different approach. In an unbiased screen for modifiers of neuronal membrane trafficking defects, we unexpectedly identified a role for histone deacetylases (HDACs) in limiting cellular flexibility in choosing cellular pathways to respond to diverse types of stress. Genetic or pharmacological inactivation of HDACs resulted in improved neuronal health in response to ER protein folding stress and endosomal membrane trafficking stress in C. elegans and mammalian neurons. Surprisingly, HDAC inhibition enabled neurons to activate latent proteostasis pathways tailored to the nature of the individual stress, instead of generalized transcriptional upregulation. These findings shape our understanding of neuronal stress responses and suggest new therapeutic strategies to enhance neuronal resilience.

Pyridine-based small molecule inhibitors of SARM1 alleviate cell death caused by NADase activity

Our investigation has unveiled a series of pyridine-based SARM1 inhibitors, with the lead compound TH-408 exhibiting remarkable potency, achieving an IC50 value of 0.46 μM. This exceptional inhibitory effect significantly curtailed SARM1-mediated cell death across diverse biological models. This finding highlights the promising therapeutic potential for neurodegenerative disorders by disrupting SARM1 activation and advances our understanding of molecular interventions in these complex disorders, including the regulation of NAD+ metabolism.

How does Nogo-A signalling influence mitochondrial function during multiple sclerosis pathogenesis?

Multiple sclerosis (MS) is a severe neurological disorder that involves inflammation in the brain, spinal cord and optic nerve with key disabling neuropathological outcomes being axonal damage and demyelination. When degeneration of the axo-glial union occurs, a consequence of inflammatory damage to central nervous system (CNS) myelin, dystrophy and death can lead to large membranous structures from dead oligodendrocytes and degenerative myelin deposited in the extracellular milieu. For the first time, this review covers mitochondrial mechanisms that may be operative during MS-related neurodegenerative changes directly activated during accumulating extracellular deposits of myelin associated inhibitory factors (MAIFs), that include the potent inhibitor of neurite outgrowth, Nogo-A. Axonal damage may occur when Nogo-A binds to and signals through its cognate receptor, NgR1, a multimeric complex, to initially stall axonal transport and limit the delivery of important growth-dependent cargo and subcellular organelles such as mitochondria for metabolic efficiency at sites of axo-glial disintegration as a consequence of inflammation. Metabolic efficiency in axons fails during active demyelination and progressive neurodegeneration, preceded by stalled transport of functional mitochondria to fuel axo-glial integrity.

SARM1-Dependent Axon Degeneration: Nucleotide Signaling, Neurodegenerative Disorders, Toxicity, and Therapeutic Opportunities

Axons are an essential component of the nervous system, and axon degeneration is an early feature of many neurodegenerative disorders. The NAD+ metabolome plays an essential role in regulating axonal integrity. Axonal levels of NAD+ and its precursor NMN are controlled in large part by the NAD+ synthesizing survival factor NMNAT2 and the pro-neurodegenerative NADase SARM1, whose activation triggers axon destruction. SARM1 has emerged as a promising axon-specific target for therapeutic intervention, and its function, regulation, structure, and role in neurodegenerative diseases have been extensively characterized in recent years. In this review, we first introduce the key molecular players involved in the SARM1-dependent axon degeneration program. Next, we summarize recent major advances in our understanding of how SARM1 is kept inactive in healthy neurons and how it becomes activated in injured or diseased neurons, which has involved important insights from structural biology. Finally, we discuss the role of SARM1 in neurodegenerative disorders and environmental neurotoxicity and its potential as a therapeutic target.

Peripheral blood mononuclear cell respiratory function is associated with progressive glaucomatous vision loss

Intraocular pressure (IOP) is currently the only modifiable risk factor for glaucoma and all licensed treatments lower IOP. However, many patients continue to lose vision despite IOP-lowering treatment. Identifying biomarkers for progressive vision loss would have considerable clinical utility. We demonstrate that lower peripheral blood mononuclear cell (PBMC) oxygen consumption rate (OCR) is strongly associated with faster visual field (VF) progression in patients treated by lowering IOP (P < 0.001, 229 eyes of 139 participants), explaining 13% of variance in the rate of progression. In a separate reference cohort of untreated patients with glaucoma (213 eyes of 213 participants), IOP explained 16% of VF progression variance. OCR is lower in patients with glaucoma (n = 168) than in controls (n = 50; P < 0.001) and is lower in patients with low baseline IOP (n = 99) than those with high baseline IOP (n = 69; P < 0.01). PBMC nicotinamide adenine dinucleotide (NAD) levels are lower in patients with glaucoma (n = 29) compared to controls (n = 25; P < 0.001) and strongly associated with OCR (P < 0.001). Our results support PBMC OCR and NAD levels as new biomarkers for progressive glaucoma.

Characterization of the Structural Requirements for the NADase Activity of Bacterial Toll/IL-1R domains in a Course-based Undergraduate Research Experience

TLRs initiate innate immune signaling pathways via Toll/IL-1R (TIR) domains on their cytoplasmic tails. Various bacterial species also express TIR domain-containing proteins that contribute to bacterial evasion of the innate immune system. Bacterial TIR domains, along with the mammalian sterile α and TIR motif-containing protein 1 and TIRs from plants, also have been found to exhibit NADase activity. Initial X-ray crystallographic studies of the bacterial TIR from Acinetobacter baumannii provided insight into bacterial TIR structure but were unsuccessful in cocrystallization with the NAD+ ligand, leading to further questions about the TIR NAD binding site. In this study, we designed a Course-Based Undergraduate Research Experience (CURE) involving 16-20 students per year to identify amino acids crucial for NADase activity of A. baumannii TIR domain protein and the TIR from Escherichia coli (TIR domain-containing protein C). Students used structural data to identify amino acids that they hypothesized would play a role in TIR NADase activity, and created plasmids to express mutated TIRs through site-directed mutagenesis. Mutant TIRs were expressed, purified, and tested for NADase activity. The results from these studies provide evidence for a conformational change upon NAD binding, as was predicted by recent cryogenic electron microscopy and hydrogen-deuterium exchange mass spectrometry studies. Along with corroborating recent characterization of TIR NADases that could contribute to drug development for diseases associated with dysregulated TIR activity, this work also highlights the value of CURE-based projects for inclusion of a diverse group of students in authentic research experiences.

NMNAT2 is a druggable target to drive neuronal NAD production

Maintenance of NAD pools is critical for neuronal survival. The capacity to maintain NAD pools declines in neurodegenerative disease. We identify that low NMNAT2, the critical neuronal NAD producing enzyme, drives retinal susceptibility to neurodegenerative insults. As proof of concept, gene therapy over-expressing full length human NMNAT2 is neuroprotective. To pharmacologically target NMNAT2, we identify that epigallocatechin gallate (EGCG) can drive NAD production in neurons through an NMNAT2 and NMN dependent mechanism. We confirm this by pharmacological and genetic inhibition of the NAD-salvage pathway. EGCG is neuroprotective in rodent (mixed sex) and human models of retinal neurodegeneration. As EGCG has poor drug-like qualities, we use it as a tool compound to generate novel small molecules which drive neuronal NAD production and provide neuroprotection. This class of NMNAT2 targeted small molecules could have an important therapeutic impact for neurodegenerative disease following further drug development.

Advances in the Synthesis and Physiological Metabolic Regulation of Nicotinamide Mononucleotide

Nicotinamide mononucleotide (NMN), the direct precursor of nicotinamide adenine dinucleotide (NAD+), is involved in the regulation of many physiological and metabolic reactions in the body. NMN can indirectly affect cellular metabolic pathways, DNA repair, and senescence, while also being essential for maintaining tissues and dynamic metabolic equilibria, promoting healthy aging. Therefore, NMN has found many applications in the food, pharmaceutical, and cosmetics industries. At present, NMN synthesis strategies mainly include chemical synthesis and biosynthesis. Despite its potential benefits, the commercial production of NMN by organic chemistry approaches faces environmental and safety problems. With the rapid development of synthetic biology, it has become possible to construct microbial cell factories to produce NMN in a cost-effective way. In this review, we summarize the chemical and biosynthetic strategies of NMN, offering an overview of the recent research progress on host selection, chassis cell optimization, mining of key enzymes, metabolic engineering, and adaptive fermentation strategies. In addition, we also review the advances in the role of NMN in aging, metabolic diseases, and neural function. This review provides comprehensive technical guidance for the efficient biosynthesis of NMN as well as a theoretical basis for its application in the fields of food, medicine, and cosmetics.

Assessment of corneal nerve regeneration after axotomy in a compartmentalized microfluidic chip model with automated 3D high resolution live-imaging

Introduction

Damage to the corneal nerves can result in discomfort and chronic pain, profoundly impacting the quality of life of patients. Development of novel in vitro method is crucial to better understand corneal nerve regeneration and to find new treatments for the patients. Existing in vitro models often overlook the physiology of primary sensory neurons, for which the soma is separated from the nerve endings.

Methods

To overcome this limitation, our novel model combines a compartmentalized microfluidic culture of trigeminal ganglion neurons from adult mice with live-imaging and automated 3D image analysis offering robust way to assess axonal regrowth after axotomy.

Results

Physical axotomy performed by a two-second aspiration led to a reproducible 70% axonal loss and altered the phenotype of the neurons, increasing the number of substance P-positive neurons 72 h post-axotomy. To validate our new model, we investigated axonal regeneration after exposure to pharmacological compounds. We selected various targets known to enhance or inhibit axonal regrowth and analyzed their basal expression in trigeminal ganglion cells by scRNAseq. NGF/GDNF, insulin, and Dooku-1 (Piezo1 antagonist) enhanced regrowth by 81, 74 and 157%, respectively, while Yoda-1 (Piezo1 agonist) had no effect. Furthermore, SARM1-IN-2 (Sarm1 inhibitor) inhibited axonal regrowth, leading to only 6% regrowth after 72 h of exposure (versus 34% regrowth without any compound).

Discussion

Combining compartmentalized trigeminal neuronal culture with advanced imaging and analysis allowed a thorough evaluation of the extent of the axotomy and subsequent axonal regrowth. This innovative approach holds great promise for advancing our understanding of corneal nerve injuries and regeneration and ultimately improving the quality of life for patients suffering from sensory abnormalities, and related conditions.

Age-dependent small fiber neuropathy: Mechanistic insights from animal models

Small fiber neuropathy (SFN) is a common and debilitating disease in which the terminals of small diameter sensory axons degenerate, producing sensory loss, and in many patients neuropathic pain. While a substantial number of cases are attributable to diabetes, almost 50% are idiopathic. An underappreciated aspect of the disease is its late onset in most patients. Animal models of human genetic mutations that produce SFN also display age-dependent phenotypes suggesting that aging is an important contributor to the risk of development of the disease. In this review we define how particular sensory neurons are affected in SFN and discuss how aging may drive the disease. We also evaluate how animal models of SFN can define disease mechanisms that will provide insight into early risk detection and suggest novel therapeutic interventions.

A comprehensive review of soybean RNL and TIR domain proteins

Both prokaryotic and eukaryotic organisms use the nucleotide-binding domain/leucine-rich repeat (NBD/LRR)-triggered immunity (NLR-triggered immunity) signaling pathway to defend against pathogens. Plant NLRs are intracellular immune receptors that can bind to effector proteins secreted by pathogens. Dicotyledonous plants express a type of NLR known as TIR domain-containing NLRs (TNLs). TIR domains are enzymes that catalyze the production of small molecules that are essential for immune signaling and lead to plant cell death. The activation of downstream TNL signaling components, such as enhanced disease susceptibility 1 (EDS1), phytoalexin deficient 4 (PAD4), and senescence-associated gene 101 (SAG101), is facilitated by these small molecules. Helper NLRs (hNLRs) and the EDS1-PAD4/SAG101 complex associate after activation, causing the hNLRs to oligomerize, translocate to the plasma membrane (PM), and produce cation-selective channels. According to a recent theory, cations enter cells through pores created by oligomeric hNLRs and trigger cell death. Occasionally, TNLs can self-associate to create higher-order oligomers. Here, we categorized soybean TNLs based on the protein domains that they possess. We believe that TNLs may help soybean plants effectively fight pathogens by acting as a source of genetic resistance. In summary, the purpose of this review is to elucidate the range of TNLs that are expressed in soybean.

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.

NAD metabolism-related genes provide prognostic value and potential therapeutic insights for acute myeloid leukemia

Introduction

Acute myeloid leukemia (AML) is an aggressive blood cancer with high heterogeneity and poor prognosis. Although the metabolic reprogramming of nicotinamide adenine dinucleotide (NAD) has been reported to play a pivotal role in the pathogenesis of acute myeloid leukemia (AML), the prognostic value of NAD metabolism and its correlation with the immune microenvironment in AML remains unclear.

Methods

We utilized our large-scale RNA-seq data on 655 patients with AML and the NAD metabolism-related genes to establish a prognostic NAD metabolism score based on the sparse regression analysis. The signature was validated across three independent datasets including a total of 1,215 AML patients. ssGSEA and ESTIMATE algorithms were employed to dissect the tumor immune microenvironment. Ex vivo drug screening and in vitro experimental validation were performed to identify potential therapeutic approaches for the high-risk patients. In vitro knockdown and functional experiments were employed to investigate the role of SLC25A51, a mitochondrial NAD+ transporter gene implicated in the signature.

Results

An 8-gene NAD metabolism signature (NADM8) was generated and demonstrated a robust prognostic value in more than 1,800 patients with AML. High NADM8 score could efficiently discriminate AML patients with adverse clinical characteristics and genetic lesions and serve as an independent factor predicting a poor prognosis. Immune microenvironment analysis revealed significant enrichment of distinct tumor-infiltrating immune cells and activation of immune checkpoints in patients with high NADM8 scores, acting as a potential biomarker for immune response evaluation in AML. Furthermore, ex vivo drug screening and in vitro experimental validation in a panel of 9 AML cell lines demonstrated that the patients with high NADM8 scores were more sensitive to the PI3K inhibitor, GDC-0914. Finally, functional experiments also substantiated the critical pathogenic role of the SLC25A51 in AML, which could be a promising therapeutic target.

Conclusion

Our study demonstrated that NAD metabolism-related signature can facilitate risk stratification and prognosis prediction in AML and guide therapeutic decisions including both immunotherapy and targeted therapies.

Nicotinamide N-Methyltransferase (NNMT): A New Hope for Treating Aging and Age-Related Conditions

The complex process of aging leads to a gradual deterioration in the function of cells, tissues, and the entire organism, thereby increasing the risk of disease and death. Nicotinamide N-methyltransferase (NNMT) has attracted attention as a potential target for combating aging and its related pathologies. Studies have shown that NNMT activity increases over time, which is closely associated with the onset and progression of age-related diseases. NNMT uses S-adenosylmethionine (SAM) as a methyl donor to facilitate the methylation of nicotinamide (NAM), converting NAM into S-adenosyl-L-homocysteine (SAH) and methylnicotinamide (MNA). This enzymatic action depletes NAM, a precursor of nicotinamide adenine dinucleotide (NAD+), and generates SAH, a precursor of homocysteine (Hcy). The reduction in the NAD+ levels and the increase in the Hcy levels are considered important factors in the aging process and age-related diseases. The efficacy of RNA interference (RNAi) therapies and small-molecule inhibitors targeting NNMT demonstrates the potential of NNMT as a therapeutic target. Despite these advances, the exact mechanisms by which NNMT influences aging and age-related diseases remain unclear, and there is a lack of clinical trials involving NNMT inhibitors and RNAi drugs. Therefore, more in-depth research is needed to elucidate the precise functions of NNMT in aging and promote the development of targeted pharmaceutical interventions. This paper aims to explore the specific role of NNMT in aging, and to evaluate its potential as a therapeutic target.

Inhibiting the SARM1-NAD+ axis reduces oxidative stress-induced damage to retinal and nerve cells

Retinal neurodegenerative diseases are a category of refractory blinding eye conditions closely associated with oxidative stress induced by mitochondrial dysfunction in retinal cells. SARM1, a core driver molecule leading to axonal degeneration, possesses NAD+ enzyme (NADase) activity. However, the role of the SARM1-NAD+ axis in oxidative stress-induced retinal cell death remains unclear. Here, we employed the SARM1 NADase inhibitor DSRM-3716 and established a glucose oxidase (GOx)-induced oxidative stress cell model. We found that compared to the GOx group, the DSRM-3716 pre-treated group reduced the hydrolysis of NAD+, inhibited the elevation of oxidative stress markers induced by GOx, decreased mitochondrial dysfunction, lowered the phosphorylation level of JNK, and attenuated the occurrence of pyroptosis in retinal and nerve cells, thereby providing protection for neurite growth. Further utilization of the JNK activator Anisomycin activated JNK, revealed that the JNK/c-Jun pathway down-regulated NMNAT2 expression. Consequently, it reduced cellular NAD+ synthesis, exacerbated mitochondrial dysfunction and cell pyroptosis, and reversed the protective effect of DSRM-3716 on cells. In summary, the inhibition of SARM1 NADase activity substantially mitigates oxidative damage to retinal cells and mitochondrial damage. Additionally, JNK simultaneously serves as both an upstream and downstream regulator in the SARM1-NAD+ axis, regulating retinal cell pyroptosis and neurite injury. Thus, this study provides new insights into the pathological processes of retinal cell oxidative stress and identifies potential therapeutic targets for retinal neurodegenerative diseases.

Context-Specific Stress Causes Compartmentalized SARM1 Activation and Local Degeneration in Cortical Neurons

Sterile alpha and TIR motif containing 1 (SARM1) is an inducible NADase that localizes to mitochondria throughout neurons and senses metabolic changes that occur after injury. Minimal proteomic changes are observed upon either SARM1 depletion or activation, suggesting that SARM1 does not exert broad effects on neuronal protein homeostasis. However, whether SARM1 activation occurs throughout the neuron in response to injury and cell stress remains largely unknown. Using a semiautomated imaging pipeline and a custom-built deep learning scoring algorithm, we studied degeneration in both mixed-sex mouse primary cortical neurons and male human-induced pluripotent stem cell-derived cortical neurons in response to a number of different stressors. We show that SARM1 activation is differentially restricted to specific neuronal compartments depending on the stressor. Cortical neurons undergo SARM1-dependent axon degeneration after mechanical transection, and SARM1 activation is limited to the axonal compartment distal to the injury site. However, global SARM1 activation following vacor treatment causes both cell body and axon degeneration. Context-specific stressors, such as microtubule dysfunction and mitochondrial stress, induce axonal SARM1 activation leading to SARM1-dependent axon degeneration and SARM1-independent cell body death. Our data reveal that compartment-specific SARM1-mediated death signaling is dependent on the type of injury and cellular stressor.

DLK-dependent axonal mitochondrial fission drives degeneration following axotomy

Currently there are no effective treatments for an array of neurodegenerative disorders to a large part because cell-based models fail to recapitulate disease. Here we developed a reproducible human iPSC-based model where laser axotomy causes retrograde axon degeneration leading to neuronal cell death. Time-lapse confocal imaging revealed that damage triggers an apoptotic wave of mitochondrial fission proceeding from the site of injury to the soma. We demonstrated that this apoptotic wave is locally initiated in the axon by dual leucine zipper kinase (DLK). We found that mitochondrial fission and resultant cell death are entirely dependent on phosphorylation of dynamin related protein 1 (DRP1) downstream of DLK, revealing a new mechanism by which DLK can drive apoptosis. Importantly, we show that CRISPR mediated Drp1 depletion protected mouse retinal ganglion neurons from degeneration after optic nerve crush. Our results provide a powerful platform for studying degeneration of human neurons, pinpoint key early events in damage related neural death and new focus for therapeutic intervention.

IL1A enhances TNF-induced retinal ganglion cell death

Glaucoma is a neurodegenerative disease that leads to the death of retinal ganglion cells (RGCs). A growing body of literature suggests a role for neuroinflammation in RGC death after glaucoma-relevant insults. For instance, it was shown that deficiency of three proinflammatory cytokines, complement component 1, subcomponent q ( C1q ), interleukin 1 alpha ( Il1a ), and tumor necrosis factor ( Tnf ), resulted in near complete protection of RGCs after two glaucoma-relevant insults, optic nerve injury and ocular hypertension. While TNF and C1Q have been extensively investigated in glaucoma-relevant model systems, the role of IL1A in RGC is not as well defined. Thus, we investigated the direct neurotoxicity of IL1A on RGCs in vivo. Intravitreal injection of IL1A did not result in RGC death at either 14 days or 12 weeks after insult. Consistent with previous studies, TNF injection did not result in significant RGC loss at 14 days but did after 12 weeks. Interestingly, IL1A+TNF resulted in a relatively rapid RGC death, driving significant RGC loss two weeks after injection. JUN activation and SARM1 have been implicated in RGC death in glaucoma and after cytokine insult. Using mice deficient in JUN or SARM1, we show RGC loss after IL1A+TNF insult is JUN-independent and SARM1-dependent. Furthermore, RNA-seq analysis showed that RGC death by SARM1 deficiency does not stop the neuroinflammatory response to IL1A+TNF. These findings indicate that IL1A can potentiate TNF-induced RGC death after combined insult is likely driven by a SARM1-dependent RGC intrinsic signaling pathway.