Peripheral nerve injuries, particularly those involving the sciatic nerve, remain a major clinical challenge due to incomplete functional recovery and the limited translation of preclinical advances into effective therapies. This review synthesizes current evidence on the phase-specific evaluation of sciatic nerve regeneration in preclinical models, integrating behavioral, sensory, electrophysiological, and morphological approaches across the acute, subacute (Wallerian degeneration), early regenerative, and late regenerative phases. By mapping functional readouts onto the underlying biological events of each phase, we highlight how tools such as the Sciatic Functional Index, Beam Walk test, Rotarod test, nerve conduction studies, and nociceptive assays provide complementary and often non-interchangeable information about motor, sensory, and neuromuscular recovery. We further examine emerging therapeutic strategies, including intraoperative electrical stimulation, immunomodulation, platelet-rich plasma, bioengineered scaffolds, conductive and piezoelectric conduits, exosome-based hydrogels, tacrolimus delivery systems, and small molecules, emphasizing the importance of aligning their mechanisms of action with the dynamic microenvironment of peripheral nerve repair. Despite substantial advancements in experimental models, an analysis of publication trends and registries reveals a persistent translational gap, with remarkably few clinical trials relative to the high volume of preclinical studies. To illustrate how mechanistic insights can be complemented by molecular-level characterization, we also present a targeted computational analysis of alpha-lipoic acid (ALA,) including frontier orbital energies, physicochemical descriptors, and docking interactions with IL-6, TGF-β, and a growth-factor receptor-performed solely for this molecule due to its documented structural availability and relevance. By presenting an integrated, phase-specific framework for functional assessment and therapeutic evaluation, this review underscores the need for standardized, biologically aligned methodologies to improve the rigor, comparability, and clinical relevance of future studies in sciatic nerve regeneration.

Peripheral nerve injuries occur due to accidents and in manufacturing every day. Unlike the central nervous system, injured peripheral nerves can self‑regenerate after injury. The study explored changes in gene expression and related biological processes after peripheral nerve injury and regeneration. Male Sprague‑Dawley rats were divided into six groups and underwent sciatic nerve resection followed by recovery for 0, 3, 6, 10, 15, and 20 days; distal sciatic nerve segments were collected for sequencing, real‑time quantitative polymerase chain reaction (RT‑qPCR), and Western blotting. According to DNA microarray analysis, approximately 5,000 genes were differentially expressed, and six biological processes were identified at different time points after nerve transection, with expression mainly observed in the mid and latter stages after injury. Four genes (UDP glycosyltransferase 8 [Ugt8], C‑C motif chemokine ligand 2 [Ccl2], neuregulin 1 [Nrg1], and heme oxygenase‑1 [Hmox1]) with nerve regeneration‑specific function were selected for further verification using RT‑qPCR and Western blot. The results demonstrated that genes such as Ugt8 decreased initially and then peaked at 20 days, whereas Ccl2 and Hmox1 both exhibited two peaks at three and 20 days. Nrg1 showed a gradual increase, peaking around 15 days. The study identified differential gene expression in distal nerve segments during Wallerian degeneration and analyzed the associated dynamic biological changes. The findings provide insights into research on peripheral nerve injury and regeneration, and further studies will involve screening key genes and more detailed investigations.

Sarm1 is enriched at presynaptic dystrophies and correlated with Aβ.Genetic deletion of Sarm1 prevents synapse degeneration in AD.Sarm1 depletion is sufficient to reverse synaptic dysfunction and memory loss.Sarm1 depletion reduces Aβ burden and neuroinflammationC1q--MERTK axis acts downstream of synaptic Sarm1 activation.

The central nervous system is characterized by its limited regenerative potential, yet striking examples of functional recovery after injury in animal models and humans highlight its capacity for repair. Little is known about repair of pathways/circuits after traumatic brain injury (TBI), which results in disruption of connectivity. Here we utilize a mouse model of diffuse traumatic axonal injury (Impact-acceleration TBI) in order to explore, for the first time, the evolution of structural and functional changes in the terminal fields of the injured visual system. Retinal ganglion cell (RGC) axons and synapses were genetically labeled via AAV transduction, while anterograde and transsynaptic tracers were used to mark terminals and postsynaptic cells. Functional connectivity and visual integrity were assessed by monitoring c-Fos expression following light stimulation and pattern-reversal visual evoked potentials (pVEPs). Our findings demonstrate that, although TAI results in approximately a 50% loss of RGC axons and terminals, surviving RGCs undergo collateral sprouting, a form of compensatory branching of surviving axons, that restores terminal density to pre-injury levels. Transsynaptic tracing and c-Fos mapping confirmed the reestablishment of connectivity, which was also associated with significant improvements in visual function as measured by pVEPs. Interestingly, the recovery process exhibited sexual dimorphism, with female mice showing delayed or incomplete repair. Moreover, collateral sprouting proceeded normally in Sarm1 knockout mice, evidence of some independence from Wallerian degeneration. Our findings show that collateral sprouting may be an important mechanism of circuit repair in TAI and may represent a promising target for therapeutic interventions.Significance Statement Homotypic collateral sprouting -the process by which uninjured axons from the same neuronal source extend new branches to reinnervate targets deprived of their original connections- is a fundamental yet understudied mechanism for CNS repair following injury. Unlike heterotypic sprouting, involving sprouting from unrelated pathways, homotypic sprouting offers potential to restore circuit architecture after partial lesions. Here, we employed a model of diffuse axonal injury in the mouse visual system to examine this mechanism. Our research demonstrates surviving retinal ganglion cell axons can re-establish terminal fields, achieving structural and functional connectivity. Importantly, we discovered significant sex differences: female mice showed delayed/incomplete recovery compared to males. These findings provide evidence of repair of brain circuits perturbed by TBI and the role of homotypic sprouting.

Sterile Alpha and TIR Motif Containing 1 (SARM1) is the central executioner of Wallerian degeneration (WD) following axonal injury, with its inhibition having been shown to delay WD. However, little is known about its effect on functional recovery after nerve transection and repair. This study aimed to evaluate whether recovery after nerve transection and delayed repair is enhanced in an SARM1 knockout (KO) model. A total of 16 SARM1 KO and 16 wild-type (WT) Lewis rats underwent sciatic nerve transection, followed by repair at 4 days with functional analysis at either 2 or 6 weeks. Primary outcome measures included muscle tetanic force, compound nerve action potential (CNAP) amplitude and latency, and sciatic function index (SFI). Both SARM1 KO and WT groups were compared using independent t tests with a priori level of significance of P ≤ .05. The SARM1 KO rats displayed significantly lower tibialis anterior (1.43 ± 0.98 N vs 2.56 ± 1.43 N, P = .016) and gastrocnemius (2.35 ± 0.64 N vs 4.48 ± 1.32 N, P = .002) muscle strength at 6 weeks. There were no differences in CNAP amplitudes or latencies at 2 or 6 weeks after delayed repair compared with WT. There was no difference in SFI between SARM1 KO and WT groups at 2 or 6 weeks after repair. The SARM1 KO impeded recovery of muscle strength after nerve transection and delayed repair. Knockout rodents also appeared to have increased scarring, reflective of poor axonal regeneration. Further work should aim to better understand the inhibitory effects of SARM1 deletion and its role in nerve regeneration.

ObjectivesThis study aimed to determine the preferred timing and measurement sites for electroneuronography (ENoG) to predict early recovery from acute peripheral facial paralysis.MethodsWe retrospectively evaluated 42 patients with acute peripheral facial paralysis who received standard treatment with oral corticosteroids. The severity of facial paralysis was assessed at the initial visit and after 1 month using the House–Brackmann grading system. Patients were classified into recovery and non-recovery groups according to changes in the grade. ENoG was performed at the initial visit and after 2 weeks. ENoG amplitudes of four facial muscles (frontalis, nasalis, orbicularis oculi, and orbicularis oris) at the initial visit and after 2 weeks, as well as age, sex, affected side, and diagnosis, were compared between the two groups.ResultsNo differences were observed in degeneration ratios across all subsites in the initial ENoG, which can be explained by the fact that Wallerian degeneration is not yet complete at this early stage. However, the second ENoG, performed after degeneration had progressed, showed significant differences across all subsites. Binary logistic regression analysis revealed that the degeneration ratio of the orbicularis oris muscle was the best predictor of early recovery (odds ratio, 0.961; p = 0.014). Receiver operating characteristic curve analysis also revealed that the degeneration ratios of all subsites measured in the second ENoG were useful in predicting early recovery, with the highest possibility at the orbicularis oris muscle (area under the curve = 0.789). When the degeneration ratio exceeded 60% in all subsites in the second ENoG, a favorable prognosis was not expected.ConclusionThis study provides the preferred testing time and measurement sites for ENoG to predict early recovery from facial paralysis. Given the personal and social impact of facial paralysis, predicting early recovery is crucial for reassuring patients, providing better treatment, and encouraging early reintegration into society.

ABSTRACTAimsTo characterize white matter geometric pathology in cerebellar subtype of multiple system atrophy (MSA‐C) using director field analysis (DFA) and identify stage‐specific biomarkers.MethodsWe analyzed single‐shell diffusion MRI (b = 1000) in 31 MSA‐C patients (15 early‐, 16 late‐stage) and 33 controls. DFA quantified axonal geometry (splay/bend/twist), complemented by fixel‐based analysis (FBA) and brainstem volumetry. Group comparisons used threshold free cluster enhancement (TFCE) (p < 0.05 FWE‐corrected). DFA‐altered regions were correlated with clinical scores. AutoGluon evaluated classification performance using different feature sets.ResultsMSA‐C exhibited distinct geometric degeneration patterns: cerebellar pathways showed reduced splay, bend, and twist (reflecting Wallerian degeneration), whereas brainstem tracts demonstrated dissociated geometry (increased splay/bend but decreased twist). Brainstem twist reduction strongly differentiated early‐ and late‐stage MSA‐C (AUC = 0.95). Clinically, middle cerebellar peduncle bend correlated with motor progression (UMSARS‐II: r = 0.48), while cerebellar splay reduction predicted ataxia severity (SARA: r = −0.43).ConclusionDFA captures circuit‐specific white matter pathology in MSA‐C, with brainstem twist emerging as a novel biomarker associated with disease stage. The integration of geometric metrics with automated machine learning provides a robust framework for early diagnosis and disease staging, highlighting distinct neurodegenerative mechanisms in cerebellar versus brainstem pathways.

Liposomal bupivacaine (LB) provides prolonged analgesia, but it remains unclear whether it prevents rebound pain or merely delays its onset. This study investigated the effect of LB on rebound pain in a mouse model of peripheral nerve block to determine whether its resolution results in a pain response exceeding that of unblocked controls. Methylene blue staining was employed to compare the success rate of nerve stimulator-guided versus anatomical landmark-based techniques for combined sciatic and femoral nerve blockade.Postoperative rebound pain following liposomal bupivacaine administration under nerve stimulator guidance was assessed at multiple time points using von Frey and Hargreaves tests. Histological analyses of perineural inflammation and Wallerian degeneration were conducted on postoperative days 2 and 28. Nerve stimulator-guided blocks had high success rates (sciatic: 93.3%, P=0.035; femoral: 73.3%,P=0.030).LB extended thermal (24h,P<0.05) and mechanical (36h,P<0.05) analgesia. Transient thermal rebound pain occurred at 48h (P=0.003), but no mechanical rebound was observed. LB group showed significantly more severe Wallerian degeneration and Neural inflammation in both the sciatic and femoral nerves compared to the S group at day 2 (P<0.05). Liposomal bupivacaine did not prevent rebound pain but merely delayed its onset in a mouse model of combined sciatic and femoral nerve block.

Glioblastoma (GBM) is the most aggressive and devastating primary brain cancer in adults. Most GBMs are diagnosed at an advanced stage with therapy resistance, posing a major obstacle to understanding the tumor microenvironment (TME) at the earliest stages of disease development. A precise characterization of early-stage GBM and its TME could provide critical insights into tumor progression and inform new therapeutic strategies. In a recent issue of Nature, Clements and colleagues demonstrated that white matter (WM) injury, induced by early tumor cells, constitutes a key TME factor driving GBM progression. Using somatic mouse models, patient-derived xenografts, and human tissues, they showed that early glioma cells preferentially infiltrate WM tracts, inducing sterile alpha and TIR motif-containing 1-mediated Wallerian degeneration that propagates into distal WM regions. Remarkably, WM injury induced by axonal transection significantly accelerated GBM progression at distal sites, whereas this effect was abolished by Sarm1 knockout, confirming that axonal injury followed by Wallerian degeneration drives distal tumor progression. Collectively, these findings reveal a previously unrecognized evolutionary process in GBM development and highlight potential targets for therapeutic intervention.

Chronic low back pain (CLBP) is a common condition that can be treated with radiofrequency ablation (RFA). However, RFA can be destructive to tissue surrounding the targeted nerves. Cryoneurolysis is an alternative to RFA that applies cold temperatures to disrupt nerve conduction pathways via Wallerian degeneration, allowing for nerve regrowth. To compare the safety and efficacy of cryoneurolysis to RFA for treatment for CLBP. A randomized pilot study (NCT06016127) that received institutional review board approval from Advarra, Inc. (Pro00062787). A single center in the United States. Eligible patients with facet-mediated CLBP underwent lumbar RFA or cryoneurolysis of the lumbar medial branch nerve. The patients were originally followed for 180 days after treatment, with an optional study extension to 360 days. Study outcomes included pain scores on the numeric rating scale (NRS), functional disability status on the Oswestry Disability Index (ODI), Patient Global Impression of Change (PGIC) score, and safety. Analyses were adjusted for baseline NRS score, gender, and tobacco use. Age, body mass index, low back pain duration, and baseline ODI scores were similarly distributed between the cryoneurolysis and RFA groups (n = 15 each). At Days 180 and 360, cryoneurolysis was associated with significantly lower NRS pain scores vs. RFA (Day 180: least squares mean [LSM; 95% confidence interval (CI)], 3.1 [2.1-4.1] vs. 5.4 [4.3-6.4]; LSM difference [95% CI], -2.1 [-3.6, -0.5]; P = 0.01; Day 360: LSM [95% CI], 3.0 [1.4-4.7] vs. 6.1 [4.5-7.7]; LSM difference [95% CI], -2.7 [-4.7, -0.7]; P = 0.01). ODI scores were numerically lower in the cryoneurolysis group than in the RFA group at Day 180 (LSM [95% CI], 13.3 [8.9-17.7] vs. 18.1 [13.6-22.6]; LSM difference [95% CI], -4.8 [-11.4, 1.9]; P = 0.15) and significantly lower at Day 360 (LSM [95% CI], 10.1 [6.0-14.3] vs. 20.6 [16.5-24.7]; LSM difference [95% CI], -10.5 [-16.6, -4.3]; P = 0.002). The mean percent decrease in ODI score from the baseline was greatest at Day 360 in the cryoneurolysis group than in the RFA group (-21.7% vs. -4.0%; P = 0.42). More cryoneurolysis-treated patients than RFA-treated patients had "no disability" or "mild disability" at Day 360 (6/11 vs. 5/12). Cryoneurolysis was associated with lower PGIC scores vs. RFA at Day 180 (LSM [95% CI], 2.6 [1.6-3.7] vs. 3.6 [2.6-4.7]; LSM difference [95% CI], -0.98 [-2.5, 0.6]; P = 0.2) and Day 360 (LSM [95% CI], 1.7 [0.7-2.8] vs. 4.4 [3.3-5.4]; LSM difference [95% CI], -2.6 [-4.2, -1.1]; P = 0.002). After Day 180, 45.5% of patients (5/11) who underwent cryoneurolysis and 75% (9/12) who underwent RFA required more than one additional spinal injection. No serious adverse events were observed. One mild adverse event considered unrelated to study treatment was reported (a compression fracture in the cryoneurolysis group). The study was not blinded, and the short tip of the cryoneurolysis device restricted its use to patients with low body mass indexes. Longer device tips are in development. At 12 months after treatment for CLBP, cryoneurolysis had a favorable safety profile and led to more significant improvements in pain and functional disability than did RFA. A large multicenter trial is warranted to further investigate the effects of cryoneurolysis on CLBP.

BackgroundTraumatic amputations have increased worldwide over the past two decades and are expected to increase by 72% by 2050. Surgical replantation provides superior functional recovery and patient satisfaction but is limited to specialized centers and restricted by short ischemia times, due to life-over-limb prioritization in patient care. To overcome these limitations, we developed an ex vivo limb perfusion system (EVEP) to extend limb viability and, for the first time, investigate its impact on peripheral nerve regeneration, a key prerequisite for functional recovery following replantation.MethodsHind limbs of 6 healthy pigs were amputated, and after 2 h of warm ischemia, limbs were either perfused normothermally for 6 h with PerfadexPlus® ± medication using in-house developed EVEP or stored statically (4 °C vs. room temperature). Perfusion parameters, blood gas analysis, serum markers, cytokine levels, thermal imaging, colloid oncotic pressure, weight gain, joint mobility, peripheral nerve histomorphometric and stereological analyses were performed.ResultsData confirm a valid and reliable EVEP with an optimized perfusion protocol. Comparison of perfusion groups revealed lower serum injury markers in the medication group, which included methylprednisolone treatment. Additionally, the medication group exhibited reduced weight gain and preserved unrestricted joint mobility, but concurrently led to a significant decrease in pro-regenerative cytokine levels associated with Wallerian degeneration (WD).ConclusionsIn general, EVEP mitigates ischemia-related damage and facilitates ex vivo induction of WD, a critical prerequisite for nerve regeneration, functional recovery, and prevention of neuroma formation with subsequent phantom pain, by establishing the pro-regenerative environment for WD, which is further amplified by omitting the anti-inflammatory methylprednisolone.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40779-025-00656-6.

The occurrence and extent of central nervous system (CNS) fiber tract inflammation in chronic-phase intracerebral hemorrhage (ICH) patients are not well understood due to the heterogeneity of Wallerian degeneration (WD). This study aims to investigate the presence of CNS fiber tract inflammation in chronic-phase ICH patients and to characterize any inflammatory cells in the fiber tract. An in vivo translocator protein (TSPO)-PET study was undertaken in 22 ICH patients over 6 months after stroke who were admitted to the First Affiliated Hospital of Fujian Medical University or Tianjin Medical University General Hospital from April 2017 to June 2020. Twenty-three healthy controls or participants with various CNS diseases were included. Cerebral peduncle (CP) TSPO uptake was calculated as the average standardized uptake value ratio (SUVr). To aid interpretation of the TSPO uptake results at the CNS fiber tract level, spatial transcriptome sequencing was used to identify fiber tract inflammation in an ICH mouse model at 4wks post-onset and to characterize the cells present in the inflamed fiber tract. PET imaging showed that CP TSPO SUVr values in patients over 6 months since ICH were higher than in healthy controls (mean CP SUVr ± SD; ICH: 1.19 ± 0.11; control: 1.02 ± 0.08; P < 0.0001), and there was an obvious negative correlation between CP TSPO uptake and CP volume, which means that the CNS fiber tract inflammation persists and is still active in chronic-phase ICH patients, which may worsen their prognosis. Spatial transcriptome sequencing of the CNS fiber tract in ICH model mice identified a population of peripheral-derived pro-inflammatory macrophages contributing to the increased TSPO uptake. CP uptake was associated with frontal bone marrow uptake according to association analyses, indicating the cells possibly extending from the skull bone marrow into CNS in the chronic phase.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40478-025-02139-0.

After peripheral nerve lesion, the role of reactive oxygen species (ROS) has not been clarified during Wallerian degeneration. The present study examined the participation of oxidant stress after rat sciatic nerve injury induced by two experimental models (crush and transection). Here, biochemical parameters indicative of oxidant stress, nitric oxide (NO) metabolism, cell proliferation, apoptosis, and bioenergetics were determined in injured and contralateral sciatic nerves and caudofemoralis muscle. After crushing, we found two peaks of increased lipid peroxidation (LP) by-products and carbonylation of proteins in crushed nerves. In transected nerves, increases in LP showed similar patterns in both proximal and distal nerve. In both models, NO production was decreased and accompanied by an early increase in cell proliferation. Moreover, caspase-3 activity increased later only in crushed nerves. NAD availability and mitochondrial cytochrome oxidase activity were increased in transected but not in crushed nerves. The contralateral nerves also had changes in these parameters, but in a differential manner depending on the type of nerve lesion. In conclusion, present data suggest that changes in the patterns of LP may play a regulatory role in cell damage and death, somehow exerting a control in the progression of Wallerian degeneration.

IntroductionBiological aging and sex interact to shape systemic metabolism, yet their role in chronic pain resolution remains unexplored. We hypothesized that metabolic resilience—the ability to flexibly switch fuel sources and maintain energy homeostasis—rules successful recovery from nerve injury in a sex-dependent manner during aging.MethodsIn 12-month-old male and female mice, corresponding to the perimenopausal phase in females and the onset of hormonal decline in both sexes, we induced sciatic nerve chronic constriction injury and performed multi-omics profiling during Wallerian degeneration, a phase known to trigger long-term neurobiological remodeling.ResultsAging females exhibited early activation of fatty acid oxidation, increased resting energy expenditure, upregulation of mitochondrial redox enzymes and circulating progesterone and corticosterone. Proteomic and metabolomic analysis revealed pentose phosphate pathway enrichment and gluconeogenesis, supporting redox balance and metabolic flexibility. Conversely, males displayed persistent glycolytic reliance, long-chain acylcarnitine accumulation, suppression of adiponectin and PPARγ, indicating metabolic inflexibility. Longitudinal behavioral analysis revealed that aging females recovered earlier and more fully than aging males, reversing the pattern previously shown in our adult mouse study, where females developed persistent pain and males recovered rapidly.DiscussionThese patterns highlight a non-linear, sex-specific interaction between biological aging and injury response, where hormonal decline reprograms the metabolic trajectory and reshapes pain outcomes. Metabolic resilience governs sex-specific recovery following nerve injury by directing early systemic adaptations that precede and predict long-term pain trajectories. These results define mechanistically anchored, sex- and age-specific biomarkers, and propose preclinical targets for timely, personalized interventions in age-associated neuropathic pain.

Upon injury to the mammalian peripheral nervous system (PNS), severed axons undergo rapid SARM1-dependent programmed axon death (Wallerian degeneration), but a potential role for Sarm1 in PNS regeneration remains unclear. We show that in mouse dorsal root ganglia with their axons cut, Sarm1 delayed the activation of injury-induced transcriptional programs associated with axon outgrowth and immune function. After sciatic nerve crush in Sarm1-/- mice, axons rapidly extended through the nerve injury site, but growth stalled more distally. Slow axon regeneration in the distal nerve was accompanied by delayed induction of the nerve repair response by Schwann cells and delayed clearance of disintegrating myelin. Nerve fibers did regenerate in Sarm1-/- mice, but regeneration was delayed, and axons exhibited reduced caliber and aberrant target innervation. Tibial nerve action potentials were weaker, and recovery of hind paw function was delayed but ultimately not impaired. Grafting of mouse Sarm1-/- nerves into wild-type mice and mouse wild-type nerves into Sarm1-/- mice revealed that the Sarm1-/- nerve microenvironment was hostile to wild-type axon regeneration and, conversely, that Sarm1-/- axons robustly grew into mouse wild-type nerve grafts. Ex vivo, the appearance of c-Jun-labeled Schwann cells in cultured mouse Sarm1-/- nerves was delayed but could be accelerated by pharmacological inhibition of ErbB kinase. Our study highlights the opposing functions of Sarm1 deficiency in dorsal root ganglia and distal nerves in mice, the consequence of which is delayed PNS regeneration.

The central nervous system is characterized by its limited regenerative potential, yet striking examples of functional recovery after injury in animal models and humans highlight its capacity for repair. Little is known about repair of pathways/circuits after traumatic brain injury (TBI), which results in disruption of connectivity. Here we utilize a mouse model of diffuse traumatic axonal injury (Impact-acceleration TBI) in order to explore, for the first time, the evolution of structural and functional changes in the terminal fields of the injured visual system. Retinal ganglion cell (RGC) axons and synapses were genetically labeled via AAV transduction, while anterograde and transsynaptic tracers were used to mark terminals and postsynaptic cells. Functional connectivity and visual integrity were assessed by monitoring c-Fos expression following light stimulation and pattern-reversal visual evoked potentials (pVEPs). Our findings demonstrate that, although TAI results in approximately a 50% loss of RGC axons and terminals, surviving RGCs undergo collateral sprouting, a form of compensatory branching of surviving axons, that restores terminal density to pre-injury levels. Transsynaptic tracing and c-Fos mapping confirmed the reestablishment of connectivity, which was also associated with significant improvements in visual function as measured by pVEPs. Interestingly, the recovery process exhibited sexual dimorphism, with female mice showing delayed or incomplete repair. Moreover, collateral sprouting proceeded normally in Sarm1 knockout mice, evidence of some independence from Wallerian degeneration. Our findings show that collateral sprouting may be an important mechanism of circuit repair in TAI and may represent a promising target for therapeutic interventions.

Abstract BACKGROUND Glioblastoma (GBM) is the commonest primary brain malignancy which, despite increasing understanding of advanced disease, remains incurable. A lack of relevant disease models has meant that the mechanisms driving earlier stages of GBM development and progression remain poorly understood. This is a key gap in knowledge as it opens new avenues for treatment and disease control of earlier grade disease. Somatic mouse models developed in our lab have now allowed us to explore the earliest phases of disease progression. Here, we explore what changes in the local tumour microenvironment (TME) drive gliomagenesis, and identify axonal injury as a key driver of GBM progression. We find that a programmed form of axonal injury is triggered by infiltrating tumour cells exerting mechanical strain on axons, triggering Sarm1-dependent axonal degeneration. We show that interference with this pathway leads to slowed disease progression, demonstrating the therapeutic potential of targeting axonal death in gliomagenesis. MATERIAL AND METHODS We combine a murine somatic GBM model with PDX models and patient tissue datasets. We use immunohistochemistry, spatial transcriptomics, single cell RNA sequencing and flow cytometry, as well as behavioural and survival studies to explore tumour development and progression in wild type (WT) and Sarm1-/- mice - which are resistant to Wallerian degeneration. RESULTS Time-course analysis of tumourigenesis showed that early GBM preferentially infiltrates the white matter. Spatial transcriptomics identified axonal loss as an early event which strongly correlates with the level of tumour cell infiltration and is accompanied by neuroinflammation. This was confirmed at the tissue level using immunohistochemistry and electron microscopy. Axonal injury was shown to drive tumour cell proliferation and neuroinflammation through injury experiments where a transection of corpus callosum axons accelerated tumourigenesis. Conversely, blocking Sarm1 dependent axonal degeneration using a Sarm1-/- mouse model led to a marked delay in GBM development. Consistently, terminal Sarm1-/- tumours were less dense, contained more immature tumour cells, and were marked as lower grade on histopathological assessment. Strikingly, Sarm1-/- mice had a significantly prolonged survival, and behavioural studies revealed that Sarm1-/- tumour-bearing mice experienced less neurological decline than WT mice. CONCLUSION Our work provides insights into GBM development, identifying axonal injury as a key tumour promoting event. This is elicited by early tumour infiltration into the white matter and orchestrated by Sarm1 dependent programmed axonal degeneration, a druggable pathway already in clinical trials for neurodegenerative diseases. Hence, this is a potential novel therapeutic target for GBM providing a clinical opportunity for disease control.

Charcot-Marie-Tooth (CMT) disease can be caused by mutations in over 100 different genes, most of which lead to demyelination (type 1) or degeneration (type 2) of peripheral motor and sensory axons. SARM1 is a protein involved in the active process of Wallerian degeneration after axonal injury. Inhibition of SARM1 protects against axon degeneration following injury or in cases such as chemotherapy-induced peripheral neuropathy. However, the effects of SARM1 inhibition on axon degeneration in genetic diseases such as CMT are less clear. Here we tested whether SARM1 inhibition may be of benefit in three different mouse models of axonal CMT: GarsETAQ/CTM2D, NeflN98S/CMT2E, and Ighmbp2Y918C/CMT2S. For these proof-of-concept studies, mice were treated as neonates with an AAV9 to deliver a dominant negative SARM1 construct (dnSARM1) to the nervous system by intracerebroventricular injection. At ages appropriate for each mouse model, animals were then evaluated with a combination of behavioral, neurophysiological, and histological outcomes. We reproduced the protective effects of the dnSARM1 construct in positive control experiments following sciatic nerve crush. However, we did not see a change in the phenotypes of any of the CMT mouse models examined. The neuropathy-related phenotypes neither worsened nor improved. Wild-type littermate controls treated with the AAV9 dnSARM1 had minor reductions in body weight and variable changes in motor performance compared to untreated controls, but no deficits by neurophysiology or histology. Inhibiting SARM1 using a virally delivered dominant negative construct was not efficacious in any of the three mouse models of CMT we tested. These mouse models were chosen for their relevance to the human disease and their prominent axon degeneration, and not for metabolic changes that would suggest SARM1 as a therapeutic target. SARM1 inhibition may remain an option for some forms of CMT, but a method for prescreening CMT subtypes to predict efficacy is needed.

Numerous large-scale epidemiological studies investigating the trajectory of cognitive recovery after ischemic stroke have presented data suggesting an immediate drop in cognition acutely post-stroke followed by persistent, accelerated decline over time when averaged as a group. We sought to further examine this trend, speculating that the average persistent decline may be a reflection of two subgroups with vastly different prognoses: 1) a minority experiencing decline secondary to neurodegenerative processes like vascular dementia and Alzheimer’s disease, and 2) a majority without marked progressive brain atrophy who typically see improvement. Our team thus investigated atrophy’s association with language recovery, hypothesizing that declining naming performance in the year after left hemisphere ischemic stroke would be correlated to atrophy of the contralesional hemisphere. We postulated that volume loss within the lesioned hemisphere would be less informative due to separate confounding processes related to the stroke itself like Wallerian degeneration and encephalomalacia.Participants (n=72; M[SD] age=60[11]) in a longitudinal cohort study of language following left hemisphere ischemic stroke were included if they completed an MRI both acutely and chronically (either 6- or 12-months post-stroke). Naming performance was assessed using the Boston Naming Test, stroke volumes were extracted from acute imaging, and atrophy was measured as the monthly percent change in hemispheric volume from baseline to chronic scan for each individual. Pearson’s correlations were calculated to determine the relationship between lesion volume and atrophy along with atrophy and change in Boston Naming Test score.Lesion volume was negatively correlated to the monthly percent change of volume in the left (ipsilesional) hemisphere (r=−0.48; p<0.0001) but was not correlated to rate of right (contralesional) hemisphere volume loss. While there was no clear relationship between atrophy of the left hemisphere and language recovery, we found that volume changes of greater negative magnitude within the right hemisphere (increased atrophy) were associated with worse functional recovery of language (r=0.38; p=0.0025).By showing that atrophy of the right hemisphere was not significantly impacted by left hemisphere lesion size, we suggest that accelerated volume loss in the non-lesioned hemisphere after stroke may be indicative of a separate pathology. We then go on to support this claim with behavioral data showing that greater rates of volume loss within the non-lesioned hemisphere were associated with poorer naming recovery. Together, these findings imply that contralesional atrophy after stroke may have negative implications for recovery and could serve as a useful imaging signature for separate neurodegenerative processes.

Posttraumatic painful mononeuropathy involves a permanent structural change in the affected nerve. Clinical and animal models have shown that exposure of nerves to specific cold temperatures for distinct time periods can induce: cessation of signal transduction, Wallerian degeneration, and predictable axonal regeneration. It is hypothesized that these processes may return a structurally altered painful nerve to a non-pathologic or normal state. We present four patients in which percutaneous cryoneurolysis was employed with the intent of inducing regeneration and repair. Primary outcomes included return of nerve function, pain relief, and peri/postprocedural adverse events. All patients demonstrated return of normal nerve function and significant pain reduction without major complications or adverse events. Whether or not structural abnormalities were repaired can only be inferred via interpretation of symptom improvement.