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Background: The number of mutations in nuclear encoded genes causing mitochondrial disease is ever increasing. Identification of these mutations is particularly important in the diagnosis of neuromuscular disorders as their presentation may mimic other acquired disorders.We present a novel heterozygous variant in mitochondrial fission factor (MFF) which mimics myasthenia gravis. Objective: To determine if the MFF c.937G>A, p.E313K variant causes a mild mitochondrial phenotype. Methods: We used whole exome sequencing (WES) to identify a novel heterozygous variant in MFF in a patient with ptosis, fatigue and muscle weakness. Using patient derived fibroblasts, we performed assays to evaluate mitochondrial and peroxisome dynamics. Results: We show that fibroblasts derived from this patient are defective in mitochondrial fission, despite normal recruitment of Drp1 to the mitochondria. Conclusions: The MFF c.937G>A, p.E313K variant leads to a mild mitochondrial phenotype and is associated with defective mitochondrial fission in patient-derived fibroblasts.

Neurodegeneration induced by inflammatory stress in multiple sclerosis (MS) leads to long-term neurological disabilities that are not amenable to current immunomodulatory therapies.Here, we report that neuronal downregulation of Splicing factor 3b subunit 2 (SF3B2), a component of U2 small nuclear ribonucleoprotein (snRNP), preserves retinal ganglion cell (RGC) survival and axonal integrity in experimental autoimmune encephalomyelitis (EAE)-induced mice. By employing an in vitro system recapitulating the inflammatory environment of MS lesion, we show that when SF3B2 levels are downregulated, cell viability and axon integrity are preserved in cortical neurons against inflammatory toxicity. Notably, knockdown of SF3B2 suppresses the expression of injury-response and necroptosis genes and prevents activation of Sterile Alpha and TIR Motif Containing 1 (Sarm1), a key enzyme that mediates programmed axon degeneration.Together, these findings suggest that the downregulation of SF3B2 is a novel potential therapeutic target to prevent secondary neurodegeneration in MS.

INTRODUCTION: Chemotherapy-induced peripheral neurotoxicity (CIPN) remains a significant toxicity in cancer survivors without preventative strategies or rehabilitation. Exercise and physical activity-based interventions have demonstrated promise in reducing existing CIPN symptoms and potentially preventing toxicity, however there is a significant gap in evidence due to the lack of quality clinical trials and appropriate outcome measures. AREAS COVERED: The authors systematically reviewed outcome measures in CIPN exercise and physical rehabilitation studies with expert panel consensus via the Peripheral Nerve Society Toxic Neuropathy Consortium to provide recommendations for future trials. Across 26 studies, 75 outcome measures were identified and grouped into 16 domains within three core areas - measures of manifestations of CIPN (e.g. symptoms/signs), measures of the impact of CIPN and other outcome measures. EXPERT OPINION: This article provides a conceptual framework for CIPN outcome measures and highlights the need for definition of a core outcome measures set. The authors provide recommendations for CIPN exercise and physical rehabilitation trial design and outcome measure selection. The development of a core outcome measure set will be critical in the search for neuroprotective and treatment approaches to support cancer survivors and to address the significant gap in the identification of effective rehabilitation and treatment options for CIPN.

After peripheral nerve injuries, successful axonal growth and functional recovery requires the reprogramming of Schwann cells into a reparative phenotype, a process dependent on the activation of the transcription factor c-Jun. Nevertheless, axonal regeneration is greatly impaired in aged organisms or after chronic denervation leading to important clinical problems. This regenerative failure has been associated to a diminished c-Jun expression by Schwann cells, but whether the inability of these cells to maintain a repair state is associated to the transition into a phenotype inhibitory for axonal growth, has not been evaluated so far. We find that repair Schwann cells transitions into a senescent phenotype, characterized by diminished c-Jun expression and secretion of factor inhibitory for axonal regeneration in both aging and chronic denervation. In both conditions, elimination of senescent Schwann cells by systemic senolytic drug treatment or genetic targeting improves nerve regeneration and functional recovery in aging and chronic denervation, associated with an upregulation of c-Jun expression and a decrease in nerve inflammation. This work provides the first characterization of senescent Schwann cells and their impact over axonal regeneration in aging and chronic denervation, opening new avenues for enhancing regeneration, and functional recovery after peripheral nerve injuries.

ObjectiveThe primary objective of this study was to evaluate the correlation of large mitochondrial DNA (mtDNA) deletions in skin samples of people with HIV (PWH) with measures of neuropathy and prior exposure to therapy. We hypothesized that deletions would be associated with neuropathy. As secondary objectives, we determined the correlation of deletion burden with demographic data and neuropathy measures.MethodsIn this retrospective cohort study, we measured the accumulation of large mtDNA deletions in skin biopsies from PWH recruited as part of the AIDS Clinical Trials Group (ACTG). Our cohort includes individuals with and without sensory neuropathy, as well as individuals with normal or abnormal skin biopsies. Skin biopsies, sural and peroneal nerve conduction studies, total neuropathy score, and deletion burden scores were measured, along with baseline demographic data such as age, CD4+ cell count, viral counts, and prior nucleoside reverse transcriptase inhibitor exposures.ResultsSixty-seven PWH were enrolled in the study. The mean age of the cohort (n = 67) was 44 years (SD 6.8, range 32–65 years), and 9 participants were female. The mean CD4+ T-cell count was 168 cells/mm3(SD 97 cells/mm3, range 1–416 cells/mm3) and mean viral load was 51,129 copies/mL (SD 114,586 copies/mL, range 147–657,775 copies/mL). We determined that there was a correlation between the total mtDNA deletion and intraepidermal nerve fiber density (IENFD) (r= −0.344,p= 0.04) and sural nerve amplitude (r= −0.359,p= 0.004).ConclusionsBoth IENFD and sural nerve amplitude statistically correlate with mitochondrial mutation burden in PWH, specifically in those with HIV-associated sensory neuropathy as assessed by skin biopsy.

Ethoxyquin (EQ), a quinolone-based antioxidant, has demonstrated neuroprotective properties against several neurotoxic drugs in a phenotypic screening and is shown to protect axons in animal models of chemotherapy-induced peripheral neuropathy. We assessed the effects of EQ on peripheral nerve function in the db/db mouse model of type II diabetes. After a 7 week treatment period, 12-week-old db/db-vehicle, db/+ -vehicle and db/db-EQ treated animals were evaluated by nerve conduction, paw withdrawal against a hotplate, and fiber density in hindlimb footpads. We found that the EQ group had shorter paw withdrawal latency compared to vehicle db/db group. The EQ group scored higher in nerve conduction studies, compared to vehicle-treated db/db group. Morphology studies yielded similar results. To investigate the potential role of mitochondrial DNA (mtDNA) deletions in the observed effects of EQ, we measured total mtDNA deletion burden in the distal sciatic nerve. We observed an increase in total mtDNA deletion burden in vehicle-treated db/db mice compared to db/+ mice that was partially prevented in db/db-EQ treated animals. These results suggest that EQ treatment may exert a neuroprotective effect in diabetic neuropathy. The prevention of diabetes-induced mtDNA deletions may be a potential mechanism of the neuroprotective effects of EQ in diabetic neuropathy.

ObjectiveTo present standardized diagnostic criteria for idiopathic distal sensory polyneuropathy (iDSP) and its subtypes: idiopathic mixed fiber sensory neuropathy (iMFN), idiopathic small fiber sensory neuropathy (iSFN), and idiopathic large fiber sensory neuropathy (iLFN) for use in research.MethodsThe Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities and Networks (ACTTION) public-private partnership with the Food and Drug Administration convened a meeting to develop consensus diagnostic criteria for iMFN, iSFN, and iLFN. After background presentations, a collaborative, iterative approach was used to develop expert consensus for new criteria.ResultsAn iDSP diagnosis requires at least 1 small fiber (SF) or large fiber (LF) symptom, at least 1 SF or LF sign, abnormalities in sensory nerve conduction studies (NCS) or distal intraepidermal nerve fiber density (IENFD), and exclusion of known etiologies. An iMFN diagnosis requires that at least 1 of the above clinical features is SF and 1 clinical feature is LF with abnormalities in sensory NCS or IENFD. Diagnostic criteria for iSFN require at least 1 SF symptom and at least 1 SF sign with abnormal IENFD, normal sensory NCS, and the absence of LF symptoms and signs. Diagnostic criteria for iLFN require at least 1 LF symptom and at least 1 LF sign with normal IENFD, abnormal sensory NCS, and absence of SF symptoms and signs.ConclusionAdoption of these standardized diagnostic criteria will advance research and clinical trials and spur development of novel therapies for iDSPs.

Activation of the NAD hydrolase domain of Sarm1 mediates axonal degeneration caused by chemotherapy drugs, but the downstream events are unknown. In this issue, Li and colleagues (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202106080) demonstrate that cADPR, a breakdown product of NAD, mediates paclitaxel-induced axonal degeneration by promoting influx of calcium into the axons.

Pharmacological strategies for chemotherapy-induced peripheral neurotoxicity (CIPN) are very limited. We systematically reviewed data on rehabilitation, exercise, physical therapy, and other physical non-pharmacological interventions and offered evidence-based recommendations for the prevention and treatment of CIPN. A literature search using PubMed, Web of Science and CINAHL was conducted from database inception until May 31st, 2021. 2791 records were title-abstract screened, 71 papers were full-text screened, 41 studies were included, 21 on prevention and 20 on treatment of CIPN. Treatment type, cancer type, chemotherapy compounds were heterogeneous, sample size was small (median: N = 34) and intention-to-treat analysis was lacking in 26/41 reports. Because of the methodological issues of included studies, the reviewed evidence should be considered as preliminary. Exercise, endurance, strength, balance, and sensorimotor training have been studied in low-to-moderate quality studies, while the evidence for other treatments is preliminary/inconclusive. We offer recommendation for the design of future trials on CIPN.

Normal nerve architecture is basic to a complete understanding of nerve pathology. Here, normal components of the nerve are illustrated, including myelinated and non-myelinated nerve fibres, stromal elements, and vascular components. These are relevant because the differential diagnosis of neuropathy depends on the pathological processes affecting axon, myelin, interstitial space, and blood vessels. Thus, we present a description of the general pathological characteristics for the diagnosis of peripheral nerve disorders.

Functional recovery following peripheral nerve injury is limited by progressive atrophy of denervated muscle and Schwann cells (SCs) that occurs during the long regenerative period prior to end-organ reinnervation. Insulin-like growth factor 1 (IGF-1) is a potent mitogen with well-described trophic and anti-apoptotic effects on neurons, myocytes, and SCs. Achieving sustained, targeted delivery of small protein therapeutics remains a challenge. We hypothesized that a novel nanoparticle (NP) delivery system can provide controlled release of bioactive IGF-1 targeted to denervated muscle and nerve tissue to achieve improved motor recovery through amelioration of denervation-induced muscle atrophy and SC senescence and enhanced axonal regeneration. Biodegradable NPs with encapsulated IGF-1/dextran sulfate polyelectrolyte complexes were formulated using a flash nanoprecipitation method to preserve IGF-1 bioactivity and maximize encapsulation efficiencies. Under optimized conditions, uniform PEG-b-PCL NPs were generated with an encapsulation efficiency of 88.4%, loading level of 14.2%, and a near-zero-order release of bioactive IGF-1 for more than 20 days in vitro. The effects of locally delivered IGF-1 NPs on denervated muscle and SCs were assessed in a rat median nerve transection-without- repair model. The effects of IGF-1 NPs on axonal regeneration, muscle atrophy, reinnervation, and recovery of motor function were assessed in a model in which chronic denervation is induced prior to nerve repair. IGF-1 NP treatment resulted in significantly greater recovery of forepaw grip strength, decreased denervation-induced muscle atrophy, decreased SC senescence, and improved neuromuscular reinnervation.

Purpose: Improved graft reinnervation and functional recovery would greatly enhance the utility of vascularized composite allotransplantation (VCA). Pre-implantation of nerve grafts in a limb transplant recipient prior to transplantation to increase the length of the severed nerves in the amputation stump offers a novel, readily translatable approach to this problem. At the time of transplantation a pre-implanted nerve graft (PING) would be elevated from its wound bed in the amputated stump and unfurled distally into the transplanted limb, allowing for a more distal nerve coaptation. Methods: We used a reversed sciatic-tibial nerve isograft coapted end-to-end to a median nerve in a rat to: (1) determine viability of distal axons after elevating PINGs; and (2) assess for ischemic injury to axons in the distal PING following elevation from the wound bed. For axonal viability, grafts of varying lengths (2cm,3cm,4cm, n≥5/group) were left to regenerate for 8 weeks. The distal ends were then biopsied prior to elevation, and again one week after elevation. For ischemia assessment, blood flow along 4cm long PINGs was measured with laser doppler at multiple timepoints: baseline (at time of grafting), 8 weeks after grafting (before elevation), immediately after elevation, and 3 and 7 days post-elevation (n=8/timepoint). Means were compared with t-tests and ANOVA. A pig forelimb model was used to assess the functional impact of PINGs. A 6cm long reversed ulnar-PING was coapted to the proximally transected ulnar nerve. After 12 weeks of regeneration, the distal PING was transferred end-to-end to the median nerve just proximal to the elbow. A control group underwent ulnar-to-median nerve transfer 6cm proximal to the elbow (n=4 limbs/group). Hoof flexion force was measured every three weeks. Results Axonal viability: after 8 weeks, axons had regenerated into the distal grafts in all lengths: mean myelinated axon counts (±SD): 7043 (±790), 6066 (±1838), 6491 (±983) in 2cm,3cm,4cm grafts, with no differences between graft lengths (p=0.48). One week after elevation and unfurling, the number of myelinated axons was significantly decreased in all groups (p

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and often dose-limiting side effect of many cancer drugs. Because the onset of neuronal injury is known, it is an ideal clinical target to develop neuroprotective strategies. Several years ago, we had identified ethoxyquin as a potent neuroprotective drug against CIPN through a phenotypic drug screening and demonstrated a novel mechanism of action, inhibition of chaperone domain of heat shock protein 90. To improve its drug-like properties we synthesized a novel analogue of ethoxyquin and named it EQ-6 (6-(5-amino)-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline hydrochloride). Here we show that EQ-6 prevents axon degeneration in primary dorsal root ganglion neurons in vitro, and this axon protection is associated with preserved levels of nicotinamide adenine dinucleotide, a key metabolite in programmed axon degeneration pathway. We also found that EQ-6 prevents loss of epidermal nerve fibers in a mouse model of CIPN induced by paclitaxel and that doses of EQ-6 that provide neuroprotection are associated with reduced tissue levels of SF3B2, a potential biomarker of target engagement. Furthermore, we show that EQ-6 is safe in vitro and in mice with daily administration for a month. We found that oral bioavailability is about 10%, partly due to rapid metabolism in liver, but EQ-6 appears to be concentrated in neural tissues. Given these findings, we propose EQ-6 as a first-in-class drug to prevent CIPN. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13311-021-01093-8.

Amyotrophic lateral sclerosis (ALS) is a progressive, neurodegenerative disease of the lower and upper motor neurons with sporadic or hereditary occurrence. Age of onset, pattern of motor neuron degeneration and disease progression vary widely among individuals with ALS. Various cellular processes may drive ALS pathomechanisms, but a monogenic direct metabolic disturbance has not been causally linked to ALS. Here we show SPTLC1 variants that result in unrestrained sphingoid base synthesis cause a monogenic form of ALS. We identified four specific, dominantly acting SPTLC1 variants in seven families manifesting as childhood-onset ALS. These variants disrupt the normal homeostatic regulation of serine palmitoyltransferase (SPT) by ORMDL proteins, resulting in unregulated SPT activity and elevated levels of canonical SPT products. Notably, this is in contrast with SPTLC1 variants that shift SPT amino acid usage from serine to alanine, result in elevated levels of deoxysphingolipids and manifest with the alternate phenotype of hereditary sensory and autonomic neuropathy. We custom designed small interfering RNAs that selectively target the SPTLC1 ALS allele for degradation, leave the normal allele intact and normalize sphingolipid levels in vitro. The role of primary metabolic disturbances in ALS has been elusive; this study defines excess sphingolipid biosynthesis as a fundamental metabolic mechanism for motor neuron disease.

Schwannomatosis is a multiple tumor syndrome in which patients develop benign tumors along peripheral nerves throughout the body. The first symptom with which schwannomatosis patients often present, prior to discovery of tumors, is pain. This pain can be debilitating and is often inadequately alleviated by pharmacological approaches. Schwannomatosis-associated pain can be localized to the area of a tumor, or widespread. Moreover, not all tumors are painful, and the occurrence of pain is often unrelated to tumor size or location. We speculate that some individual tumors, but not others, secrete factors that act on nearby nerves to augment nociception by producing neuronal sensitization or spontaneous neuronal firing. We created cell lines from human SWN tumors with varying degrees of pain. We have found that conditioned medium (CM) collected from painful SWN tumors, but not that from nonpainful SWN tumors, sensitized DRG neurons, causing increased sensitivity to depolarization by KCl, increased response to noxious TRPV1 and TRPA1 agonists and also upregulated the expression of pain-associated genes in DRG cultures. Multiple cytokines were also detected at higher levels in CM from painful tumors. Taken together our data demonstrate a differential ability of painful versus non-painful human schwannomatosis tumor cells to secrete factors that augment sensory neuron responsiveness, and thus identify a potential determinant of pain heterogeneity in schwannomatosis.