Sex-specific adipose tissue's dynamic role in metabolic and inflammatory response following peripheral nerve injury.

Epidemiological data and research highlight increased neuropathy and chronic pain prevalence among females, spanning metabolic and normometabolic contexts, including murine models. Prior findings demonstrated diverse immune and neuroimmune responses between genders in neuropathic pain (NeP), alongside distinct protein expression in sciatic nerves. This study unveils adipose tissue's (AT) role in sex-specific NeP responses after peripheral nerve injury. Metabolic assessments, metabolomics, energy expenditure evaluations, AT proteomic analyses, and adipokine mobilization depict distinct AT reactions to nerve damage. Females exhibit altered lipolysis, fatty acid oxidation, heightened energy expenditure, and augmented steroids secretion affecting glucose and insulin metabolism. Conversely, male neuropathy prompts glycolysis, reduced energy expenditure, and lowered unsaturated fatty acid levels. Males' AT promotes regenerative molecules, oxidative stress defense, and stimulates peroxisome proliferator-activated receptors (PPAR-γ) and adiponectin. This study underscores AT's pivotal role in regulating gender-specific inflammatory and metabolic responses to nerve injuries, shedding light on female NeP susceptibility determinants.

Wheel Running Adversely Affects Disease Onset and Neuromuscular Interplay in Amyotrophic Lateral Sclerosis Slow Progression Mouse Model.

BACKGROUND: Physical activity in Amyotrophic Lateral Sclerosis (ALS) plays a controversial role. In some epidemiological studies, both recreational or professional sport exercise has been associated to an increased risk for ALS but the mechanisms underlying the effects of exercise have not been fully elucidated in either patients or animal models. METHODS: To better reproduce the influence of this environmental factor in the pathogenesis of ALS, we exposed SOD1G93A low-copy male mice to multiple exercise sessions at asymptomatic and pre-symptomatic disease stages in an automated home-cage running-wheel system for about 3 months. RESULTS: Repeated voluntary running negatively influenced disease progression by anticipating disease onset, impairing neuromuscular transmission, worsening neuromuscular decline, and exacerbating muscle atrophy. Muscle fibers and neuromuscular junctions (NMJ) as well as key molecular players of the nerve-muscle circuit were similarly affected. CONCLUSION: It thus appears that excessive physical activity can be detrimental in predisposed individuals and these findings could model the increased risk of developing ALS in predisposed and specific professional athletes.

Xeomin®, a Commercial Formulation of Botulinum Neurotoxin Type A, Promotes Regeneration in a Preclinical Model of Spinal Cord Injury.

Xeomin® is a commercial formulation of botulinum neurotoxin type A (BoNT/A) clinically authorized for treating neurological disorders, such as blepharospasm, cervical dystonia, limb spasticity, and sialorrhea. We have previously demonstrated that spinal injection of laboratory purified 150 kDa BoNT/A in paraplegic mice, after undergoing traumatic spinal cord injury (SCI), was able to reduce excitotoxic phenomena, glial scar, inflammation, and the development of neuropathic pain and facilitate regeneration and motor recovery. In the present study, as proof of concept in view of a possible clinical application, we studied the efficacy of Xeomin® in the same preclinical SCI model in which we highlighted the positive effects of lab-purified BoNT/A. Data comparison shows that Xeomin® induces similar pharmacological and therapeutic effects, albeit with less efficacy, to lab-purified BoNT/A. This difference, which can be improved by adjusting the dose, can be attributable to the different formulation and pharmacodynamics. Although the mechanism by which Xeomin® and laboratory purified BoNT/A induce functional improvement in paraplegic mice is still far from being understood, these results open a possible new scenario in treatment of SCI and are a stimulus for further research.

Sex Differences in Neuropathy: The Paradigmatic Case of MetFormin.

As a widely prescribed anti-diabetic drug, metformin has been receiving novel attention for its analgesic potential. In the study of the complex etiology of neuropathic pain (NeP), male and female individuals exhibit quite different responses characterized by higher pain sensitivity and greater NeP incidence in women. This "gender gap" in our knowledge of sex differences in pain processing strongly limits the sex-oriented treatment of patients suffering from NeP. Besides, the current investigation of the analgesic potential of metformin has not addressed the "gender gap" problem. Hence, this study focuses on metformin and sex-dependent analgesia in a murine model of NeP induced by chronic constriction injury of the sciatic nerve. We investigated sexual dimorphism in signaling pathways involved by 7 days of metformin administration, such as changes in AMP-activated protein kinase and the positive regulation of autophagy machinery, discovering that metformin affected in a sexually dimorphic manner the immunological and inflammatory response to nerve lesion. These effects were complemented by morphological and adaptive changes occurring after peripheral nerve injury. Altogether these data can contribute to explaining a number of potential mechanisms responsible for the complete recovery from NeP found in male mice, as opposed to the failure of long-lasting recovery in female animals.

Sexually Dimorphic Immune and Neuroimmune Changes Following Peripheral Nerve Injury in Mice: Novel Insights for Gender Medicine.

Neuropathic pain (NeP) in humans is often a life-long condition with no effective therapy available. The higher incidence of female gender in NeP onset is worldwide reported, and although the cause is generally attributed to sex hormones, the actual mechanisms and the players involved are still unclear. Glial and immune cells take part in NeP development, and orchestrate the neuroimmune and inflammatory response, releasing pro-inflammatory factors with chemoattractant properties that activate resident immune cells and recruit immune cells from circulation. The neuro-immune crosstalk is a key contributor to pain hypersensitivity following peripheral nervous system injury. Our previous works showed that in spite of the fact that female mice had an earlier analgesic response than males following nerve lesion, the recovery from NeP was never complete, suggesting that this difference could occur in the very early stages after injury. To further investigate gender differences in immune and neuroimmune responses to NeP, we studied the main immune cells and mediators elicited both in plasma and sciatic nerves by peripheral nerve lesion. After injury, we found a different pattern of distribution of immune cell populations showing either a higher infiltration of T cells in nerves from females or a higher infiltration of macrophages in nerves from males. Moreover, in comparison to male mice, the levels of cytokines and chemokines were differently up- and down-regulated in blood and nerve lysates from female mice. Our study provides some novel insights for the understanding of gender-associated differences in the generation and perseveration of NeP as well as for the isolation of specific neurodegenerative mechanisms underlying NeP. The identification of gender-associated inflammatory profiles in neuropathy is of key importance for the development of differential biomarkers and gender-specific personalized medicine.

Corrigendum: Very Early Involvement of Innate Immunity in Peripheral Nerve Degeneration in SOD1-G93A Mice.

[This corrects the article DOI: 10.3389/fimmu.2020.575792.].

Very Early Involvement of Innate Immunity in Peripheral Nerve Degeneration in SOD1-G93A Mice.

Recent preclinical and clinical evidence suggest that immune system has a role in the progression and prognosis of Amyotrophic Lateral Sclerosis (ALS), but the identification of a clear mechanism and immune players remains to be elucidated. Here, we have investigated, in 30 and 60 days (presymptomatic) and 120 days (symptomatic) old SOD1-G93A mice, systemic, peripheral, and central innate and adaptive immune and inflammatory response, correlating it with the progression of the neurodegeneration in neuromuscular junction, sciatic nerves, and spinal cord. Surprisingly, we found a very initial (45-60 days) presence of IgG in sciatic nerves together with a gradual enhancement of A20/TNFAIP3 (protein controlling NF-κB signalling) and a concomitantly significant increase and activation of circulating mast cells (MCs) as well as MCs and macrophages in sciatic nerve and an enhancement of IL-6 and IL-10. This immunological frame coincided with a myelin aggregation. The 30-60 days old SOD1-G93A mice didn't show real elements of neuroinflammation and neurodegeneration in spinal cord. In 120 days old mice macrophages and monocytes are widely diffused in sciatic nerves, peripheral neurodegeneration reaches the tip, high circulating levels of TNFα and IL-2 were found and spinal cord exhibits clear signs of neural damage and infiltrating immune cells. Our results underpin a clear immunological disorder at the origin of ALS axonopathy, in which MCs are involved in the initiation and sustaining of inflammatory events. These data cannot be considered a mere epiphenomenon of motor neuron degeneration and reveal new potential selective immune targets in ALS therapy.

Revealing the Therapeutic Potential of Botulinum Neurotoxin Type A in Counteracting Paralysis and Neuropathic Pain in Spinally Injured Mice.

Botulinum neurotoxin type A (BoNT/A) is a major therapeutic agent that has been proven to be a successful treatment for different neurological disorders, with emerging novel therapeutic indications each year. BoNT/A exerts its action by blocking SNARE complex formation and vesicle release through the specific cleavage of SNAP-25 protein; the toxin is able to block the release of pro-inflammatory molecules for months after its administration. Here we demonstrate the extraordinary capacity of BoNT/A to neutralize the complete paralysis and pain insensitivity induced in a murine model of severe spinal cord injury (SCI). We show that the toxin, spinally administered within one hour from spinal trauma, exerts a long-lasting proteolytic action, up to 60 days after its administration, and induces a complete recovery of muscle and motor function. BoNT/A modulates SCI-induced neuroglia hyperreactivity, facilitating axonal restoration, and preventing secondary cells death and damage. Moreover, we demonstrate that BoNT/A affects SCI-induced neuropathic pain after moderate spinal contusion, confirming its anti-nociceptive action in this kind of pain, as well. Our results provide the intriguing and real possibility to identify in BoNT/A a therapeutic tool in counteracting SCI-induced detrimental effects. Because of the well-documented BoNT/A pharmacology, safety, and toxicity, these findings strongly encourage clinical translation.

Impact of caloric restriction on peripheral nerve injury-induced neuropathic pain during ageing in mice.

The incidence of peripheral neuropathy development and chronic pain is strongly associated with the arrival of senescence. The gradual physiological decline that begins after the mature stage produces myelin dysregulation and pathological changes in peripheral nervous system, attributed to reduction in myelin proteins expression and thinner myelin sheath. Moreover in elder subjects, when nerve damage occurs, the regenerative processes are seriously compromised and neuropathic pain (NeP) is maintained. We previously demonstrated that caloric restriction (CR) in adult (4 months) nerve-lesioned mice was able to facilitate remyelination and axons regeneration, to have anti-inflammatory action and to prevent NeP chronification. Here, we show CR therapeutic potential on nerve injury-induced neuropathy in mice at the beginning of the senescence (12 months). Long lasting decrease in hypersensitvity induced by peripheral nerve lesion and powerful reduction in proinflammatory circulating agents have been observed. Moreover, our results evidence that CR is able to counteract the ageing-related delay in axonal regeneration, enhancing Schwann cells proliferation and accelerating recovery processes. Differently from adults, it does not affect fibres myelination. In light of a continuous growth in elderly population and correlated health problems, including metabolic disorders, the prevalence of neuropathy is enhancing, generating a significant public cost and social concern. In this context energy depletion by dietary restriction can be a therapeutic option in NeP.

Publisher Correction: Innovative mouse model mimicking human-like features of spinal cord injury: efficacy of Docosahexaenoic acid on acute and chronic phases.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Innovative mouse model mimicking human-like features of spinal cord injury: efficacy of Docosahexaenoic acid on acute and chronic phases.

Traumatic spinal cord injury has dramatic consequences and a huge social impact. We propose a new mouse model of spinal trauma that induces a complete paralysis of hindlimbs, still observable 30 days after injury. The contusion, performed without laminectomy and deriving from the pressure exerted directly on the bone, mimics more closely many features of spinal injury in humans. Spinal cord was injured at thoracic level 10 (T10) in adult anesthetized female CD1 mice, mounted on stereotaxic apparatus and connected to a precision impactor device. Following severe injury, we evaluated motor and sensory functions, and histological/morphological features of spinal tissue at different time points. Moreover, we studied the effects of early and subchronic administration of Docosahexaenoic acid, investigating functional responses, structural changes proximal and distal to the lesion in primary and secondary injury phases, proteome modulation in injured spinal cord. Docosahexaenoic acid was able i) to restore behavioural responses and ii) to induce pro-regenerative effects and neuroprotective action against demyelination, apoptosis and neuroinflammation. Considering the urgent health challenge represented by spinal injury, this new and reliable mouse model together with the positive effects of docosahexaenoic acid provide important translational implications for promising therapeutic approaches for spinal cord injuries.

Effects of caloric restriction on neuropathic pain, peripheral nerve degeneration and inflammation in normometabolic and autophagy defective prediabetic Ambra1 mice.

There is a growing interest on the role of autophagy in diabetes pathophysiology, where development of neuropathy is one of the most frequent comorbidities. We have previously demonstrated that neuropathic pain after nerve damage is exacerbated in autophagy-defective heterozygous Ambra1 mice. Here, we show the existence of a prediabetic state in Ambra1 mice, characterized by hyperglycemia, intolerance to glucose and insulin resistance. Thus, we further investigate the hypothesis that prediabetes may account for the exacerbation of allodynia and chronic pain and that counteracting the autophagy deficit may relieve the neuropathic condition. We took advantage from caloric restriction (CR) able to exert a double action: a powerful increase of autophagy and a control on the metabolic status. We found that CR ameliorates neuropathy throughout anti-inflammatory and metabolic mechanisms both in Ambra1 and in WT animals subjected to nerve injury. Moreover, we discovered that nerve lesion represents, per se, a metabolic stressor and CR reinstates glucose homeostasis, insulin resistance, incomplete fatty acid oxidation and energy metabolism. As autophagy inducer, CR promotes and anticipates Schwann cell autophagy via AMP-activated protein kinase (AMPK) that facilitates remyelination in peripheral nerve. In summary, we provide new evidence for the role of autophagy in glucose metabolism and identify in energy depletion by dietary restriction a therapeutic approach in the fight against neuropathic pain.

Botulinum Toxin B Affects Neuropathic Pain but Not Functional Recovery after Peripheral Nerve Injury in a Mouse Model.

Clinical use of neurotoxins from Clostridium botulinum is well established and is continuously expanding, including in treatment of pain conditions. Background: The serotype A (BoNT/A) has been widely investigated, and current data demonstrate that it induces analgesia and modulates nociceptive processing initiated by inflammation or nerve injury. Given that data concerning the serotype B (BoNT/B) are limited, the aim of the present study was to verify if also BoNT/B is able not only to counteract neuropathic pain, but also to interfere with inflammatory and regenerative processes associated with the nerve injury. Methods: As model of neuropathic pain, chronic constriction injury (CCI) of the sciatic nerve was performed in CD1 male mice. Mice were intraplantarly injected with saline (control) or BoNT/B (5 or 7.5 pg/mouse) into the injured hindpaw. For comparison, another mouse group was injected with BoNT/A (15 pg/mouse). Mechanical allodynia and functional recovery of the injured paw was followed for 101 days. Spinal cords and sciatic nerves were collected at day 7 for immunohistochemistry. Results and Conclusions: The results of this study show that BoNT/B is a powerful biological molecule that, similarly to BoNT/A, can reduce neuropathic pain over a long period of time. However, the analgesic effects are not associated with an improvement in functional recovery, clearly highlighting an important difference between the two serotypes for the treatment of this chronic pain state.

Unbalance between Excitation and Inhibition in Phenylketonuria, a Genetic Metabolic Disease Associated with Autism.

Phenylketonuria (PKU) is the most common genetic metabolic disease with a well-documented association with autism spectrum disorders. It is characterized by the deficiency of the phenylalanine hydroxylase activity, causing plasmatic hyperphenylalaninemia and variable neurological and cognitive impairments. Among the potential pathophysiological mechanisms implicated in autism spectrum disorders is the excitation/inhibition (E/I) imbalance which might result from alterations in excitatory/inhibitory synapse development, synaptic transmission and plasticity, downstream signalling pathways, and intrinsic neuronal excitability. Here, we investigated functional and molecular alterations in the prefrontal cortex (pFC) of BTBR-Pahenu2 (ENU2) mice, the animal model of PKU. Our data show higher frequency of inhibitory transmissions and significant reduced frequency of excitatory transmissions in the PKU-affected mice in comparison to wild type. Moreover, in the pFC of ENU2 mice, we reported higher levels of the post-synaptic cell-adhesion proteins neuroligin1 and 2. Altogether, our data point toward an imbalance in the E/I neurotransmission favouring inhibition in the pFC of ENU2 mice, along with alterations of the molecular components involved in the organization of cortical synapse. In addition to being the first evidence of E/I imbalance within cortical areas of a mouse model of PKU, our study provides further evidence of E/I imbalance in animal models of pathology associated with autism spectrum disorders.

Synuclein expression in the lizard Anolis carolinensis.

The synuclein (syn) family comprises three proteins: α-, ß- and γ-syns. In humans, they are involved in neurodegenerative diseases such as Parkinson's disease and in tumors. Members of the syn family were sequenced in representative species of all vertebrates and the comparative analysis of amino acid sequences suggests that syns are evolutionarily conserved, but information about their expression in vertebrate lineages is still scarce and completely lacking in reptiles. In this study, the expression of genes coding for α-, ß- and γ-syns was analyzed in the green lizard Anolis carolinensis by semiquantitative RT-PCR and Western blot. Results demonstrate good expression levels of the three syns in the lizard nervous system, similarly to human syns. This, together with the high identity between lizard and human syns, suggests that these proteins fulfill evolutionarily conserved functions. However, differences between lizard and humans in the expression of syn variants (two different variants of γ-syn were detected in A. carolinensis) and differences in some amino acids in key positions for the regulation of protein conformation and affinity for lipid and metal ions also suggest that these proteins may have acquired different functional specializations in the two lineages.

Analgesic Effects Mediated by Muscarinic Receptors: Mechanisms and Pharmacological Approaches.

Chronic pain represents a research field on great clinical relevance and social impactful. It is associated to a variety of pathological events causing un altered excitability of peripheral nerves derived by tissue damage depending on physical, biological and chemical injury. In the last years much attention has been paid in the identification of novel molecules involved in mediating pain sensation useful as therapeutic tools for the development of new analgesic drugs. Muscarinic receptors are widely distributed both in the central and peripheral nervous system. It is known that muscarinic agonists cause analgesic effects via spinal and supraspinal mechanisms. Considering that the analgesia induced by cholinergic agonists is comparable to that observed with morphine, the identification of receptor subtypes involved and the identification of the muscarinic ligands capable of selectively activate these receptors, is of considerable interest for potential therapeutic application. In the present review we describe the role of muscarinic receptors in mediating central and peripheral pain and the mechanisms downstream these receptors responsible of the modulation of nociceptive stimuli. Moreover the therapeutic perspectives and the identification of potential drugs binding muscarinic receptors involved in pain modulation will also be discussed.

Nitric Oxide Synthase in the Central Nervous System and Peripheral Organs of Stramonita haemastoma: Protein Distribution and Gene Expression in Response to Thermal Stress.

Nitric oxide (NO) is generated via the oxidation of l-arginine by the enzyme NO synthase (NOS) both in vertebrates and invertebrates. Three NOS isoforms, nNOS, iNOS and eNOS, are known in vertebrates, whereas a single NOS isoform is usually expressed in invertebrates, sharing structural and functional characteristics with nNOS or iNOS depending on the species. The present paper is focused on the constitutive Ca(2+)/calmodulin-dependent nNOS recently sequenced by our group in the neogastropod Stramonita haemastoma (ShNOS). In this paper we provide new data on cellular distribution of ShNOS in the CNS (pedal ganglion) and peripheral organs (osphradium, tentacle, eye and foot) obtained by WB, IF, CM and NADPHd. Results demonstrated that NOS-like proteins are widely expressed in sensory receptor elements, neurons and epithelial cells. The detailed study of NOS distribution in peripheral and central neurons suggested that NOS is both intracellular and presynaptically located. Present findings confirm that NO may have a key role in the central neuronal circuits of gastropods and in sensory perception. The physiological relevance of NOS enzymes in the same organs was suggested by thermal stress experiments demonstrating that the constitutive expression of ShNOS is modulated in a time- and organ-dependent manner in response to environmental stressors.

Nicotinic receptor activation negatively modulates pro-inflammatory cytokine production in multiple sclerosis patients.

Acetylcholine (ACh) and its receptors of muscarinic and nicotinic types are involved in the modulation of immune and inflammatory responses. In present work we have characterized the nicotinic receptors expression in PBMC of RR-MS patients and healthy donors (HD) and their ability to modulate pro-inflammatory cytokines. Here we report that the IL-1ß e IL-17 levels are significantly increased in serum of RR-MS patients in respect to HD and that the PBMC stimulation with PHA caused a significant increase in pro-inflammatory cytokine levels both in RR-MS and HD subjects, with higher increase of protein release in RR-MS patients than in HD. The PBMC treatment with PHA plus nicotine produced a significant decrease of IL-1ß e IL-17 both as transcript and as protein, confirming that the PBMC of the patients respond to the cholinergic stimulation more than PBMC of HD. By real time PCR and western blot analysis we have also demonstrated that in particular α7 receptor subtype appeared expressed at comparable levels both in RR-MS patients and HD. The PHA stimulation results to inhibit the α7 subunit expression while the nicotine causes a significant increase in α7 transcripts but only in MS patients. The data obtained highlight the role of α7 receptor subtype in the modulation of anti-inflammatory cytokines also in MS. Moreover the ability of nicotine to up-regulate the expression of α7 receptor subtype in RR-MS patients, indicates that nicotinic receptor stimulation may contribute to down-modulate the inflammation occurred in MS by a positive feedback control of its expression.

Nicotine exposure during adolescence: cognitive performance and brain gene expression in adult heterozygous reeler mice.

RATIONALE: We have recently reported nicotine-induced stimulation of reelin and glutamic acid decarboxylase 67 (GAD67) mRNA expression levels in the brain of heterozygous reeler mice (HRM), a putative animal model for the study of symptoms relevant to major behavioral disorders. OBJECTIVES: We aimed to evaluate long-term behavioral effects and brain molecular changes as a result of adaptations to nicotine exposure in the developing HRM males. METHODS: Adolescent mice (pnd 37-42) were exposed to oral nicotine (10 mg/l) in a 6-day free-choice drinking schedule. As expected, no differences in total nicotine intake between WT (wild-type) mice and HRM were found. RESULTS: Long-term behavioral effects and brain molecular changes, as a consequence of nicotine exposure during adolescence, were only evidenced in HRM. Indeed, HRM perseverative exploratory behavior and poor cognitive performance were modulated to WT levels by subchronic exposure to nicotine during development. Furthermore, the expected reduction in the expression of mRNA of reelin and GAD67 in behaviorally relevant brain areas of HRM appeared persistently restored by nicotine. For brain-derived neurotrophic factor (BDNF) mRNA expression, no genotype-dependent changes appeared. However, expression levels were increased by previous nicotine in brains from both genotypes. The mRNA encoding for nicotine receptor subunits (α7, ß2 and α4) did not differ between genotypes and as a result of previous nicotine exposure. CONCLUSION: These findings support the hypothesis of pre-existing vulnerability (based on haploinsufficiency of reelin) to brain and behavioral disorders and regulative short- and long-term effects associated with nicotine modulation.

M2 receptors exert analgesic action on DRG sensory neurons by negatively modulating VR1 activity.

The peripheral application of the M2 cholinergic agonist arecaidine on sensory nerve endings shows anti-nociceptive properties. In this work, we analyze in vitro, the mechanisms downstream M2 receptor activation causing the analgesic effects, and in vivo the effects produced by M2 agonist arecaidine administration on nociceptive responses in a murine model of nerve growth factor (NGF)-induced pain. Cultured DRG neurons treated with arecaidine showed a decreased level of VR1 and SP transcripts. Conversely, we found an increased expression of VR1 and SP transcripts in DRG from M2/M4(-/-) mice compared to WT and M1(-/-) mice, confirming the inhibitory effect in particular of M2 receptors on SP and VR1 expression. Patch-clamp experiments in the whole-cell configuration showed that arecaidine treatment caused a reduction of the fraction of capsaicin-responsive cells, without altering the mean capsaicin-activated current in responsive cells. We also demonstrated that arecaidine prevents PKCϵ translocation to the plasma membrane after inflammatory agent stimulation, mainly in medium-small sensory neurons. Finally, in mice, we have observed that intraperitoneal injection of arecaidine reduces VR1 expression blocking hyperalgesia and allodynia caused by NGF intraplantar administration. In conclusion, our data demonstrate that in vivo M2 receptor activation induces desensitization to mechanical and heat stimuli by a down-regulation of VR1 expression and by the inhibition of PKCϵ activity hindering its translocation to the plasma membrane, as suggested by in vitro experiments.