The nociceptin receptor inhibits axonal regeneration and recovery from spinal cord injury

Fractional amplitude of low-frequency fluctuation alterations in patients with cervical spondylotic myelopathy: a resting-state fMRI study

PURPOSE

We sought to use the fractional amplitude of low-frequency fluctuation (fALFF) method to investigate the changes in spontaneous brain activity in CSM patients and their relationships with clinical features.

METHODS

We recruited 20 patients with CSM, and 20 healthy controls (HCs) matched for age, sex, and education status. The fALFF method was used to evaluate the altered spontaneous brain activities. The Pearson correlation analysis of fALFF and the clinical features were carried out.

RESULTS

Compared with HC, CSM group showed increased fALFF values in the left middle frontal gyrus, inferior parietal lobule, and right angular gyrus. Decreased fALFF values were found in the right lingual gyrus, cuneus (P < 0.05). Pearson correlation analysis shows that the fALFF values of all CSM were positively correlated with JOA score in the right angular gyrus (r = 0.518, P < 0.05).

CONCLUSION

CSM patients have abnormal fALFF distribution in multiple brain regions and might be an appealing alternative approach for further exploration of the pathological and neuropsychological states in CSM.

Artificially reprogrammed stem cells deliver transcytosable nanocomplexes for improved spinal cord repair

Stem cell transplantation holds great promise for restoring function after spinal cord injury (SCI), but its therapeutic efficacy heavily depends on the innate capabilities of the cells and the microenvironment at the lesion site. Herein, a potent cell therapeutic (NCs@SCs) is engineered by artificially reprogramming bone marrow mesenchymal stem cells (BMSCs) with oxidation-responsive transcytosable gene-delivery nanocomplexes (NCs), which endows cells with robust oxidative stress resistance and improved cytokine secretion. NCs@SCs can accumulate in the injured spinal cord after intravenous administration via chemotaxis and boost successive transcytosis to deliver NCs to neurons, augmenting ciliary neurotrophic factor (CNTF) production in both BMSCs and neurons in response to elevated ROS levels. Furthermore, NCs@SCs can actively sense and eliminate ROS and re-educate recruited M1-like macrophages into the anti-inflammatory M2 phenotype via a paracrine pathway, ultimately reshaping the inflammatory microenvironment. Synergistically, NCs@SCs exhibit durable survival and provide neuroprotection against secondary damage, enabling significant locomotor function recovery in SCI rats. Transcriptome analysis reveals that regulation of the ROS/MAPK signaling pathway is involved in SCI therapy by NCs@SCs. This study presents a nanomaterial-mediated cell-reprogramming approach for developing live cell therapeutics, showing significant potential in the treatment of SCI and other neuro-injury disorders.

Amino-terminal proteolytic fragment of the axon growth inhibitor Nogo-A (Rtn4A) is upregulated by injury and promotes axon regeneration

After adult mammalian central nervous system injury, axon regeneration is extremely limited or absent, resulting in persistent neurological deficits. Axon regeneration failure is due in part to the presence of inhibitory proteins, including NogoA (Rtn4A), from which two inhibitory domains have been defined. When these inhibitory domains are deleted, but an amino-terminal domain is still expressed in a gene trap line, mice show axon regeneration and enhanced recovery from injury. In contrast, when there is no amino-terminal Nogo-A fragment in the setting of inhibitory domain deletion, then axon regeneration and recovery are indistinguishable from WT. These data indicated that an amino-terminal Nogo-A fragment derived from the gene trap might promote axon regeneration, but this had not been tested directly and production of this fragment without gene targeting was unclear. Here, we describe posttranslation production of an amino-terminal fragment of Nogo-A from the intact gene product. This fragment is created by proteolysis near amino acid G214-N215 and levels are enhanced by axotomy. Furthermore, this fragment promotes axon regeneration in vitro and acts cell autonomously in neurons, in contrast to the inhibitory extracellular action of other Nogo-A domains.Proteins interacting with the amino-terminal Nogo-A fragment by immunoprecipitation include HSPA8 (HSC70, HSP7C). Suppression of HSPA8 expression by shRNA decreases axon regeneration from cerebral cortical neurons and overexpression increases axon regeneration. Moreover, the amino-terminal Nogo-A fragment increases HSPA8 chaperone activity. These data provide an explanation for varied results in different gene-targeted Nogo-A mice, as well as revealing an axon regeneration promoting domain of Nogo-A.

Whole cell response to receptor stimulation involves many deep and distributed subcellular biochemical processes

Neurite outgrowth is an integrated whole cell response triggered by the cannabinoid-1 receptor. We sought to identify the many different biochemical pathways that contribute to this whole cell response. To understand underlying mechanisms, we identified subcellular processes (SCPs) composed of one or more biochemical pathways and their interactions required for this response. Differentially expressed genes and proteins were obtained from bulk transcriptomics and proteomic analysis of extracts from cells stimulated with a cannabinoid-1 receptor agonist. We used these differentially expressed genes and proteins to build networks of interacting SCPs by combining the expression data with prior pathway knowledge. From these SCP networks, we identified additional genes that when ablated, experimentally validated the SCP involvement in neurite outgrowth. Our experiments and informatics modeling allowed us to identify diverse SCPs such as those involved in pyrimidine metabolism, lipid biosynthesis, and mRNA splicing and stability, along with more predictable SCPs such as membrane vesicle transport and microtubule dynamics. We find that SCPs required for neurite outgrowth are widely distributed among many biochemical pathways required for constitutive cellular functions, several of which are termed ‘deep’, since they are distal to signaling pathways and the key SCPs directly involved in extension of the neurite. In contrast, ‘proximal’ SCPs are involved in microtubule growth and membrane vesicle transport dynamics required for neurite outgrowth. From these bioinformatics and dynamical models based on experimental data, we conclude that receptor-mediated regulation of subcellular functions for neurite outgrowth is both distributed, that is, involves many different biochemical pathways, and deep.

Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a member of the opioid receptor superfamily with N/OFQ as its endogenous agonist. Wide expression of the NOP receptor and N/OFQ, both centrally and peripherally, and their ability to modulate several biological functions has led to development of NOP receptor modulators by pharmaceutical companies as therapeutics, based upon their efficacy in preclinical models of pain, anxiety, depression, Parkinson's disease, and substance abuse. Both posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are debilitating conditions that significantly affect the quality of life of millions of people around the world. PTSD is often a consequence of TBI, and, especially for those deployed to, working and/or living in a war zone or are first responders, they are comorbid. PTSD and TBI share common symptoms, and negatively influence outcomes as comorbidities of the other. Unfortunately, a lack of effective therapies or therapeutic agents limits the long term quality of life for either TBI or PTSD patients. Ours, and other groups, demonstrated that PTSD and TBI preclinical models elicit changes in the N/OFQ-NOP receptor system, and that administration of NOP receptor ligands alleviated some of the neurobiological and behavioral changes induced by brain injury and/or traumatic stress exposure. Here we review the past and most recent progress on understanding the role of the N/OFQ-NOP receptor system in PTSD and TBI neurological and behavioral sequelae. There is still more to understand about this neuropeptide system in both PTSD and TBI, but current findings warrant further examination of the potential utility of NOP modulators as therapeutics for these disorders and their co-morbidities. We advocate the development of standards for common data elements (CDE) reporting for preclinical PTSD studies, similar to current preclinical TBI CDEs. That would provide for more standardized data collection and reporting to improve reproducibility, interpretation and data sharing across studies.

Effects of methylprednisolone and treadmill training on spinal cord injury in experimental rats

Methylprednisolone (MP) is widely used to treat clinical spinal cord injury (SCI). Treadmill training is also considered an important treatment after SCI to improve motor function in patients, resulting in an evident improvement. Therefore, the present study was designed to evaluate and contrast the effects of MP and treadmill training administered in combination or alone after SCI in adult rats. A rat spinal cord T10 contusion model was induced in Sprague-Dawley rats using an impact device. A total of 40 rats were divided into four groups (n=10 rats/group): the MP, MP + treadmill training, SCI and sham group. At 30 min after injury, MP sodium succinate was injected into the rats of the MP and MP + treadmill training groups. Treadmill training began on the second week post-trauma and was performed for 8 weeks. The results showed that MP therapy combined with treadmill training significantly ameliorated several parameters of hind limb function compared with those by MP treatment alone (all P<0.05). A significantly reduced immunopositive area of Nogo receptor and chondroitin sulfate proteoglycans and reduced relative expression of these mRNAs were found in the MP + treadmill training group (P<0.05) compared with the findings in the MP group. In conclusion, the present study indicated that combined MP and treadmill training treatment improved the recovery of hind limb function in rats with SCI, thus potentially representing a promising strategy to cure SCI.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

β-Funaltrexamine Displayed Anti-inflammatory and Neuroprotective Effects in Cells and Rat Model of Stroke

Chronic treatment involving opioids exacerbates both the risk and severity of ischemic stroke. We have provided experimental evidence showing the anti-inflammatory and neuroprotective effects of the μ opioid receptor antagonist β-funaltrexamine for neurodegenerative diseases in rat neuron/glia cultures and a rat model of cerebral Ischemia/Reperfusion (I/R) injury. Independent of in vitro Lipopolysaccharide (LPS)/interferon (IFN-γ)-stimulated neuron/glia cultures and in vivo cerebral I/R injury in Sprague–Dawley rats, β-funaltrexamine downregulated neuroinflammation and ameliorated neuronal degeneration. Alterations in microglia polarization favoring the classical activation state occurred in LPS/IFN-γ-stimulated neuron/glia cultures and cerebral I/R-injured cortical brains. β-funaltrexamine shifted the polarization of microglia towards the anti-inflammatory phenotype, as evidenced by decreased nitric oxide, tumor necrosis factor-α, interleukin-1β, and prostaglandin E2, along with increased CD163 and arginase 1. Mechanistic studies showed that the suppression of microglia pro-inflammatory polarization by β-funaltrexamine was accompanied by the reduction of NF-κB, AP-1, cyclic AMP response element-binding protein, along with signal transducers and activators of transcription transcriptional activities and associated upstream activators. The effects of β-funaltrexamine are closely linked with its action on neuroinflammation by switching microglia polarization from pro-inflammatory towards anti-inflammatory phenotypes. These findings provide new insights into the anti-inflammatory and neuroprotective mechanisms of β-funaltrexamine in combating neurodegenerative diseases, such as stroke.

Injured adult neurons regress to an embryonic transcriptional growth state

Grafts of spinal-cord-derived neural progenitor cells (NPCs) enable the robust regeneration of corticospinal axons and restore forelimb function after spinal cord injury¹; however, the molecular mechanisms that underlie this regeneration are unknown. Here we perform translational profiling specifically of corticospinal tract (CST) motor neurons in mice, to identify their 'regenerative transcriptome' after spinal cord injury and NPC grafting. Notably, both injury alone and injury combined with NPC grafts elicit virtually identical early transcriptomic responses in host CST neurons. However, in mice with injury alone this regenerative transcriptome is downregulated after two weeks, whereas in NPC-grafted mice this transcriptome is sustained. The regenerative transcriptome represents a reversion to an embryonic transcriptional state of the CST neuron. The huntingtin gene (Htt) is a central hub in the regeneration transcriptome; deletion of Htt significantly attenuates regeneration, which shows that Htt has a key role in neural plasticity after injury.

Mechanisms of neurite repair

Upon receiving injury signals, neurons can activate various pathways to reduce harm, initiate neuroprotection, and repair damaged neurite without cell death. Here, we review recent progresses in the study of neurite repair focusing on neuronal cell-autonomous mechanisms, including new findings on ion channels that serve as key regulators to initiate neurite repair and intrinsic signaling pathways and transcriptional and post-transcriptional factors that facilitate neurite repair. We also touch upon reports on how dendrites may be affected upon axotomy and how the regeneration potential in injured neurites might be maximized.

Detailed In Vitro Pharmacological Characterization of the Clinically Viable Nociceptin/Orphanin FQ Peptide Receptor Antagonist BTRX-246040

The peptide nociceptin/orphanin FQ (N/OFQ) is the natural ligand of the N/OFQ receptor (NOP), which is widely expressed in the central and peripheral nervous system. Selective NOP antagonists are worthy of testing as innovative drugs to treat depression, Parkinson disease, and drug abuse. The aim of this study was to perform a detailed in vitro characterization of BTRX-246040 (also known as LY2940094, [2-[4-[(2-chloro-4,4-difluoro-spiro[5H-thieno[2,3-c]pyran-7,4'-piperidine]-1'-yl)methyl]-3-methyl-pyrazol-1-yl]-3-pyridyl]methanol), a novel NOP antagonist that has been already studied in humans. BTRX-246040 has been tested in vitro in the following assays: calcium mobilization in cells expressing NOP and classic opioid receptors and chimeric G proteins, bioluminescence resonance energy transfer assay measuring NOP interaction with G proteins and β-arrestins, the label-free dynamic mass redistribution assay, and the electrically stimulated mouse vas deferens. BTRX-246040 was systematically compared with the standard NOP antagonist SB-612111. In all assays, BTRX-246040 behaves as a pure and selective antagonist at human recombinant and murine native NOP receptors displaying 3-10-fold higher potency than the standard antagonist SB-612111. BTRX-246040 is an essential pharmacological tool to further investigate the therapeutic potential of NOP antagonists in preclinical and clinical studies. SIGNIFICANCE STATEMENT: NOP antagonists may be innovative antidepressant drugs. In this research, the novel clinically viable NOP antagonist BTRX-246040 has been deeply characterized in vitro in a panel of assays. BTRX-246040 resulted a pure, potent, and selective NOP antagonist.

A prevascularized nerve conduit based on a stem cell sheet effectively promotes the repair of transected spinal cord injury

Spinal cord injury (SCI) can result in severe loss of motor and sensory function caused by ischemia and hypoxia, which are the key limiting factors of SCI rehabilitation. Vascularization is considered an effective way to resolve the issues of ischemia and hypoxia. In this regard, we first fabricated prevascularized nerve conduits (PNC) based on the prevascularized stem cell sheet and evaluated their repair effects by implanting them into transected SCI rats. A better healing effect was presented in the PNC group than in the control group and the nonprevascularized nerve conduit (NPNC) group as shown in H&E staining and the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale assessment. In addition, the expression of β-III tubulin (Tuj-1) in the PNC group was higher than that in the control group and the NPNC group because of the introduction of MSCs. Conversely, the expression of the glial fibrillary acidic protein (GFAP) in both experimental groups was lower than that in the control group because of the inhibitory effect of MSCs on glial scar formation. Taken together, the introduction of prevascularization into the neuron conduit was an effective solution for improving the condition of ischemia and hypoxia, inhibiting glial scar formation, and promoting the healing of SCI, which implied that the PNC may be a potential alternative material to biomaterials for SCI rehabilitation. STATEMENT OF SIGNIFICANCE: 1. Prevascularized stem cell sheet was first used to repair spinal cord injury (SCI). 2. Prevascularized stem cell sheet use can effectively resolve the challenges faced during SCI, including ischemia and hypoxia and the limited regenerative ability of the remained neurons. 3. Prevascularized stem cell sheet was found to accelerate the healing of SCI as compared to those in the control group and the pure stem cell sheet group. 4. The introduction of stem cells can effectively inhibit the formation of a glial scar.

A proteolytic C-terminal fragment of Nogo-A (reticulon-4A) is released in exosomes and potently inhibits axon regeneration

Glial signals are known to inhibit axonal regeneration and functional recovery after mammalian central nervous system trauma, including spinal cord injury. Such signals include membrane-associated proteins of the oligodendrocyte plasma membrane and astrocyte-derived, matrix-associated proteins. Here, using cell lines and primary cortical neuron cultures, recombinant protein expression, immunoprecipitation and immunoblot assays, transmission EM of exosomes, and axon regeneration assays, we explored the secretion and activity of the myelin-associated neurite outgrowth inhibitor Nogo-A and observed exosomal release of a 24-kDa C-terminal Nogo-A fragment from cultured cells. We found that the cleavage site in this 1192-amino-acid-long fragment is located between amino acids 961-971. We also detected a Nogo-66 receptor (NgR1)-interacting Nogo-66 domain on the exosome surface. Enzyme inhibitor treatment and siRNA knockdown revealed that β-secretase 1 (BACE1) is the protease responsible for Nogo-A cleavage. Functionally, exosomes with the Nogo-66 domain on their surface potently inhibited axonal regeneration of mechanically injured cerebral cortex neurons from mice. Production of this fragment was observed in the exosomal fraction from neuronal tissue lysates after spinal cord crush injury of mice. We also noted that, relative to the exosomal marker Alix, a Nogo-immunoreactive, 24-kDa protein is enriched in exosomes 2-fold after injury. We conclude that membrane-associated Nogo-A produced in oligodendrocytes is processed proteolytically by BACE1, is released via exosomes, and is a potent diffusible inhibitor of regenerative growth in NgR1-expressing axons.

Plexina2 and CRMP2 Signaling Complex Is Activated by Nogo-A-Liganded Ngr1 to Restrict Corticospinal Axon Sprouting after Trauma

After brain or spinal cord trauma, interaction of Nogo-A with neuronal NgR1 limits regenerative axonal sprouting and functional recovery. Cellular signaling by lipid-anchored NgR1 requires a coreceptor but the relevant partner in vivo is not clear. Here, we examined proteins enriched in NgR1 immunoprecipitates by Nogo-A exposure, identifying CRMP2, a cytosolic protein implicated in axon growth inhibition by Semaphorin/Plexin complexes. The Nogo-A-induced association of NgR1 with CRMP2 requires PlexinA2 as a coreceptor. Non-neuronal cells expressing both NgR1 and PlexinA2, but not either protein alone, contract upon Nogo-A exposure. Inhibition of cortical axon regeneration by Nogo-A depends on a NgR1/PlexinA2 genetic interaction because double-heterozygous NgR1^+/-, PlexinA2^+/- neurons, but not single-heterozygote neurons, are rescued from Nogo-A inhibition. NgR1 and PlexinA2 also interact genetically in vivo to restrict corticospinal sprouting in mouse cervical spinal cord after unilateral pyramidotomy. Greater post-injury sprouting in NgR1^+/-, PlexinA2^+/- mice supports enhanced neurological recovery of a mixed female and male double-heterozygous cohort. Thus, a NgR1/PlexinA2/CRMP2 ternary complex limits neural repair after adult mammalian CNS trauma.SIGNIFICANCE STATEMENT Several decades of molecular research have suggested that developmental regulation of axon growth is distinct in most regards from titration of axonal regenerative growth after adult CNS trauma. Among adult CNS pathways, the oligodendrocyte Nogo-A inhibition of growth through NgR1 is thought to have little molecular relationship to axonal guidance mechanisms active embryonically. Here, biochemical analysis of NgR1 function uncovered a physical complex with CRMP cytoplasmic mediators, and this led to appreciation of a role for PlexinA2 in concert with NgR1 after adult trauma. The data extend molecular understanding of neural repair after CNS trauma and link it to developmental processes.

Axonal degeneration and demyelination following traumatic spinal cord injury: A systematic review and meta-analysis

The pathophysiology of spinal cord injury (SCI) related processes of axonal degeneration and demyelination are poorly understood. The present systematic review and meta-analysis were performed such to establish quantitative results of animal studies regarding the role of injury severity, SCI models and level of injury on the pathophysiology of axon and myelin sheath degeneration. 39 related articles were included in the analysis. The compiled data showed that the total number of axons, number of myelinated axons, myelin sheath thickness, axonal conduction velocity, and internode length steadily decreased as time elapsed from the injury (P_{for trend}<0.0001). The rate of axonal retrograde degeneration was affected by SCI model and severity of the injury. Axonal degeneration was higher in injuries of the thoracic region. The SCI model and the site of the injury also affected axonal retrograde degeneration. The number of myelinated axons in the caudal region of the injury was significantly higher than the lesion site and the rostral region. The findings of the present meta-analysis show that the pathophysiology of axons and myelin sheath differ in various phases of SCI and are affected by multiple factors related to the injury.

ERK and p38 contribute to the regulation of nociceptin and the nociceptin receptor in human peripheral blood leukocytes

Little is known about the mechanisms involved in the regulation of nociceptin and its receptor (nociceptin opioid peptide receptor, NOP) in response to inflammation and pain in humans. In this study, specific signaling pathways contributing to the regulation of nociceptin and NOP in human peripheral blood leukocytes were investigated. After approval by the ethics committee, peripheral blood obtained from healthy donors was cultured with or without phorbol-12-myristate-13-acetate (PMA). Prepronociceptin (ppNOC) and NOP mRNA were analyzed by real-time quantitative polymerase chain reaction, and nociceptin concentrations in culture supernatants by fluorescent enzyme immunoassay. Nociceptin and NOP protein levels in blood leukocyte subsets were determined using flow cytometry. To examine the contribution of signaling pathways to ppNOC and NOP regulation, blood was pre-treated with kinase inhibitors specific for ERK, JNK, p38, and NFκB pathways prior to culturing with or without PMA. PMA dose-dependently upregulated ppNOC mRNA but downregulated NOP mRNA in human peripheral blood leukocytes. PMA 10 ng/ml increased ppNOC after 6 h and suppressed NOP after 3 h compared to controls (both P <0.005). Nociceptin concentrations were increased in supernatants of PMA-induced blood samples after 24 h ( P <0.005), whereas expression of cell-membrane NOP was decreased by PMA in blood leukocyte subsets (all P <0.05). Blockade of ERK or p38 pathways partially prevented PMA effects on ppNOC and NOP mRNA (all P <0.05). The combination of ERK and p38 inhibitors completely reversed the effects of PMA ( P <0.05). ERK and p38 are two major signaling pathways regulating nociceptin and its receptor in human peripheral blood leukocytes under inflammatory conditions.

White-matter repair: Interaction between oligodendrocytes and the neurovascular unit

There are currently no adequate treatments for white-matter injury, which often follows central nervous system maladies and their accompanying neurodegenerative processes. Indeed, the white matter is compromised by the deterioration of the blood–brain barrier and the demyelination of neuronal axons. Key repairs to the white matter are mediated by oligodendrocyte lineage cells after damaging events. Oligodendrocytes are supported by other cells in the neurovascular unit and these cells collaborate in processes such as angiogenesis, neurogenesis, and oligodendrogenesis. Understanding the various interactions between these cells and oligodendrocytes will be imperative for developing reparative therapies for impaired white matter. This minireview will discuss how oligodendrocytes and oligodendrocyte lineage cells mend damage to the white matter and restore brain function ensuing neural injury.