Altered neuronatin expression in the rat dorsal root ganglion after sciatic nerve transection

Discovery and Preclinical Evaluation of a Novel Inhibitor of FABP5, ART26.12, Effective in Oxaliplatin-Induced Peripheral Neuropathy

Oxaliplatin-induced peripheral neuropathy (OIPN) is a dose-limiting toxicity characterised by mechanical allodynia and thermal hyperalgesia, without any licensed medications. ART26.12 is a fatty acid-binding protein (FABP) 5 inhibitor with antinociceptive properties, characterised here for the prevention and treatment of OIPN. ART26.12 binds selectively to FABP5 compared to FABP3, FABP4, and FABP7, with minimal off-target liabilities, high oral bioavailability, and a NOAEL of 1,000 mg/kg/day in rats and dogs. In an established preclinical OIPN model, acute oral dosing (25-100 mg/kg) showed a cannabinoid receptor type 1 (CB1)-dependent anti-allodynic effect lasting up to 8 hours (persisting longer than plasma exposure to ART26.12). Antagonists of cannabinoid receptor type 2 (CB2), peroxisome proliferator-activated receptor alpha, and transient receptor potential cation channel subfamily V member 1 (TRPV1) may have also been implicated. Twice daily oral dosing (25 mg/kg bis in die (BID) for 7 days) showed anti-allodynic effects in an established OIPN model without the development of tolerance. In a prevention paradigm, coadministration of ART26.12 (10 and 25 mg/kg BID for 15 days) with oxaliplatin prevented thermal hyperalgesia, mitigated mechanical allodynia, and attenuated OXA-induced weight loss. Multi-scale analyses revealed widespread lipid modulation, particularly among N-acyl amino acids in the spinal cord, including potential analgesic mediators. Additionally, ART26.12 administration led to upregulation of ion channels in the periaqueductal grey, and broad translational upregulation within the plasma proteome. These results show promise that ART26.12 is a safe and well-tolerated candidate for the treatment and prevention of OIPN through lipid modulation. PERSPECTIVE: Inhibition of fatty acid-binding protein 5 (FABP5) is a novel target for reducing pain associated with chemotherapy. ART26.12 is a safe and well-tolerated small molecule FABP5 inhibitor effective at preventing and reducing pain induced with oxaliplatin through lipid modulation and activation of cannabinoid receptors.

Cell-directed assembly of luminal nanofibril fillers in nerve conduits for peripheral nerve repair

Graphene and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), have attracted significant attention in the field of tissue engineering, particularly in nerve and muscle regeneration, owing to their excellent electrical conductivity. This paper reports the fabrication of cell-mixable rGO-decorated polycaprolactone (PCL) nanofibrils (NFs) to promote peripheral nerve repair with the assistant of electron transmission by rGO and cytokine paracrine by stem cells. Oxidized GO (GO-COOH) and branched polyethylenimine are layer-by-layer coated on hydrolyzed PCL NFs via electrostatic interaction, and the number of layering is manipulated to adjust the GO-COOH coating amount. The decorated GO-COOH is reduced in situ to rGO for electrical conductivity retrieval. PC12 cells cultivated with rGO-coated NF demonstrate spontaneous cell sheet assembly, and neurogenic differentiation is observed upon electrical stimulation. When transplant nerve guidance conduit containing the assembly of rGO-coated NF and adipose-derived stem cell to the site of neurotmesis injury of a sciatic nerve, animal movement is enhanced and autotomy is ameliorated for 8 weeks compared to transplanting the hollow conduit only. Histological analysis results reveal higher levels of muscle mass and lower levels of collagen deposition in the triceps surae muscle of the rGO-coated NF-treated legs. Therefore, the rGO-layered NF can be tailored to repair peripheral nerve injuries in combination with stem cell therapy.

Cancer aggravation due to persistent pain signals with the increased expression of pain-related mediators in sensory neurons of tumor-bearing mice

A growing body of evidence suggests that intractable pain reduces both the quality of life and survival in cancer patients. In the present study, we evaluated whether chronic pain stimuli could directly affect cancer pathology using tumor-bearing mice. For this purpose, we used two different models of chronic pain in mice, neuropathic pain and persistent postsurgical pain, with Lewis lung carcinoma (LLC) as tumor cells. We found that tumor growth was dramatically promoted in these pain models. As well as these pain models, tumor growth of LLC, severe osteosarcoma (AXT) and B16 melanoma cells was significantly promoted by concomitant activation of sensory neurons in AAV6-hM3Dq-injected mice treated with the designer drug clozapine-N-oxide (CNO). Significant increases in mRNA levels of vascular endothelial growth factor-A (Vegfa), tachykinin precursor 1 (Tac1) and calcitonin-related polypeptide alpha (Calca) in the ipsilateral side of dorsal root ganglion of AAV6-hM3Dq-injected mice were observed by concomitant activation of sensory neurons due to CNO administration. Moreover, in a model of bone cancer pain in which mice were implanted with AXT cells into the right femoral bone marrow cavity, the survival period was significantly prolonged by repeated inhibition of sensory neurons of AAV6-hM4Di-injected mice by CNO administration. These findings suggest that persistent pain signals may promote tumor growth by the increased expression of sensory-located peptides and growth factors, and controlling cancer pain may prolong cancer survival.

Association between overall dietary quality and constipation in American adults: a cross-sectional study

Background

Constipation seriously affects people’s life quality, and dietary adjustment has been one of the effective methods. Overall dietary quality has been reported to be associated with some diseases, while its association with constipation has not been reported. This study aims to explore the association between overall dietary quality and constipation.

Methods

A cross-sectional study was designed and data were extracted from National Health and Nutrition Examination Survey (NHANES). Overall dietary quality was assessed by healthy eating index-2015 (HEI-2015), and constipation was defined by either stool consistency or stool frequency. The association between overall dietary quality or components of HEI-2015 and constipation was assessed using logistic regression, with results expressed as odds ratio (OR) and 95% confidence intervals (95%CI). Subgroup analysis was conducted according to age and gender.

Results

A total of 13,945 participants were eligible, with 1,407 in constipation group and 12,538 in non-constipation group. Results showed that higher adherence to HEI-2015 was associated with reduced odds of constipation (OR: 0.98, 95%CI: 0.98–0.99) after adjusting potential confounders. Further, we found higher intake of total fruits, whole fruits, total vegetables, greens and beans, whole grains, total protein foods, seafood and plant proteins, and higher fatty acids ratio decreased the odds of constipation, while higher intake of sodium increased the odds (all P < 0.05). We also found negative association between HEI-2015 and constipation in participants with male sex, female sex, age ≥ 65 years, and age < 65 years (all P < 0.05).

Conclusion

We found higher adherence to HEI-2015 decreased the odds of constipation, suggesting that increasing HEI-2015 adherence may be one of effective methods to alleviate constipation.

Supplementary information

The online version contains supplementary material available at 10.1186/s12889-022-14360-w.

Transcriptomic Profiling in Mice With CB1 receptor Deletion in Primary Sensory Neurons Suggests New Analgesic Targets for Neuropathic Pain

Type 1 and type 2 cannabinoid receptors (CB1 and CB2, respectively) mediate cannabinoid-induced analgesia. Loss of endogenous CB1 is associated with hyperalgesia. However, the downstream targets affected by ablation of CB1 in primary sensory neurons remain unknown. In the present study, we hypothesized that conditional knockout of CB1 in primary sensory neurons (CB1cKO) alters downstream gene expression in the dorsal root ganglion (DRG) and that targeting these pathways alleviates neuropathic pain. We found that CB1cKO in primary sensory neurons induced by tamoxifen in adult Advillin-Cre:CB1-floxed mice showed persistent hyperalgesia. Transcriptome/RNA sequencing analysis of the DRG indicated that differentially expressed genes were enriched in energy regulation and complement and coagulation cascades at the early phase of CB1cKO, whereas pain regulation and nerve conduction pathways were affected at the late phase of CB1cKO. Chronic constriction injury in mice induced neuropathic pain and changed transcriptome expression in the DRG of CB1cKO mice, and differentially expressed genes were mainly associated with inflammatory and immune-related pathways. Nerve injury caused a much larger increase in CB2 expression in the DRG in CB1cKO than in wildtype mice. Interfering with downstream target genes of CB1, such as antagonizing CB2, inhibited activation of astrocytes, reduced neuroinflammation, and alleviated neuropathic pain. Our results demonstrate that CB1 in primary sensory neurons functions as an endogenous analgesic mediator. CB2 expression is regulated by CB1 and may be targeted for the treatment of neuropathic pain.

scRNA-sequencing reveals subtype-specific transcriptomic perturbations in DRG neurons of PirtEGFPf mice in neuropathic pain condition

Functionally distinct subtypes/clusters of dorsal root ganglion (DRG) neurons may play different roles in nerve regeneration and pain. However, details about their transcriptomic changes under neuropathic pain conditions remain unclear. Chronic constriction injury (CCI) of the sciatic nerve represents a well-established model of neuropathic pain, and we conducted single-cell RNA-sequencing (scRNA-seq) to characterize subtype-specific perturbations of transcriptomes in lumbar DRG neurons on day 7 post-CCI. By using Pirt^EGFPf mice that selectively express an enhanced green fluorescent protein in DRG neurons, we established a highly efficient purification process to enrich neurons for scRNA-seq. We observed the emergence of four prominent CCI-induced clusters and a loss of marker genes in injured neurons. Importantly, a portion of injured neurons from several clusters were spared from injury-induced identity loss, suggesting subtype-specific transcriptomic changes in injured neurons. Moreover, uninjured neurons, which are necessary for mediating the evoked pain, also demonstrated cell-type-specific transcriptomic perturbations in these clusters, but not in others. Notably, male and female mice showed differential transcriptomic changes in multiple neuronal clusters after CCI, suggesting transcriptomic sexual dimorphism in DRG neurons after nerve injury. Using Fgf3 as a proof-of-principle, RNAscope study provided further evidence of increased Fgf3 in injured neurons after CCI, supporting scRNA-seq analysis, and calcium imaging study unraveled a functional role of Fgf3 in neuronal excitability. These findings may contribute to the identification of new target genes and the development of DRG neuron cell-type-specific therapies for optimizing neuropathic pain treatment and nerve regeneration.

Comparing Gene Expression in the Parabrachial and Amygdala of Diestrus and Proestrus Female Rats after Orofacial Varicella Zoster Injection

The orofacial pain pathway projects to the parabrachial and amygdala, and sex steroids have been shown to affect neuronal activity in these regions. GABA positive cells in the amygdala are influenced by sex steroid metabolites to affect pain, and sex steroids have been shown to alter the expression of genes in the parabrachial, changing neuronal excitability. Mechanisms by which sex steroids affect amygdala and parabrachial signaling are unclear. The expression of genes in the parabrachial and amygdala in diestrus (low estradiol) and proestrus (high estradiol) female rats were evaluated in this study. First, varicella zoster virus was injected into the whisker pad of female rats to induce a pain response. Second, gene expression was quantitated using RNA-seq one week after injection. Genes that had the greatest change in expression and known to function in pain signaling were selected for the quantitation of protein content. Protein expression of four genes in the parabrachial and seven genes in the amygdala were quantitated by ELISA. In the parabrachial, neurexin 3 (Nrnx3) was elevated at proestrus. Nrnx3 has a role in AMPA receptor and GABA signaling. Neuronatin (Nnat) and protein phosphatase, Mg²⁺/Mn²⁺ dependent 1E (Ppm1e) were elevated in the parabrachial of diestrus animals both genes having a role in pain signaling. Epoxide hydroxylase (Ephx2) was elevated in the parabrachial at proestrus and the vitamin D receptor (Vdr) was elevated in the amygdala. Ephx2 antagonists and vitamin D have been used to treat neuropathic pain. In conclusion, sex steroids regulate genes in the parabrachial and amygdala that might result in the greater pain response observed during diestrus.

Signatures of Altered Gene Expression in Dorsal Root Ganglia of a Fabry Disease Mouse Model

Fabry disease is an X-linked lysosomal storage disorder with involvement of the nervous system. Accumulation of glycosphingolipids within peripheral nerves and/or dorsal root ganglia results in pain due to small-fiber neuropathy, which affects the majority of patients already in early childhood. The α-galactosidase A deficient mouse proved to be an adequate model for Fabry disease, as it shares many symptoms including altered temperature sensitivity and pain perception. To characterize the signatures of gene expression that might underlie Fabry disease-associated sensory deficits and pain, we performed one-color based hybridization microarray expression profiling of DRG explants from adult α-galactosidase A deficient mice and age-matched wildtype controls. Protein-protein interaction (PPI) and pathway analyses were performed for differentially regulated mRNAs. We found 812 differentially expressed genes between adult α-galactosidase A deficient mice and age-matched wildtype controls, 506 of them being upregulated, and 306 being downregulated. Among the enriched pathways and processes, the disease-specific pathways “lysosome” and “ceramide metabolic process” were identified, enhancing reliability of the current analysis. Novel pathways that we identified include “G-protein coupled receptor signaling” and “retrograde transport” for the upregulated genes. From the analysis of downregulated genes, immune-related pathways, autoimmune, and infection pathways emerged. The current analysis is the first to present a differential gene expression profile of DRGs from α-galactosidase A deficient mice, thereby providing knowledge on possible mechanisms underlying neuropathic pain related symptoms in Fabry patients. Therefore, the presented data provide new insights into the development of the pain phenotype and might lead to new treatment strategies.

Combination therapy with extracorporeal shock wave and melatonin markedly attenuated neuropathic pain in rat

This study tested the hypothesis that combination therapy using extracorporeal shock wave (ECSW)-melatonin (Mel) was superior to either alone at ameliorating neuropathic pain (NP). NP was induced by chronic constriction injury (CCI) to the left sciatic nerve in rats. Animals were categorized into sham control (group 1), CCI only (group 2), CCI-ECSW (group 3), CCI-Mel (group 4) and CCI-ECSW-Mel (group 5). By days 2 and 8 after CCI, the mechanical paw withdrawal threshold (MPWT)/thermal paw withdrawal latency (TPWL) were highest in group 2, lowest in group 1, significantly lower in group 5 than in groups 3 and 4 (all p<0.0001), and not significantly different between groups 3 and 4. The protein expressions of inflammatory (TNF-α/NF-κB/MMP-9/IL-1ß/GFAP/ox42), oxidative-stress (NOX-1/NOX-2/NOX-4/oxidized protein), DNA/mitochondrial-damaged (γ-H2AX/cytosolic mitochondria), apoptotic (cleaved capase-3/PARP), and MAPK family biomarkers (p-P38/p-JNK/p-ERK1/2) in dorsal root ganglia and spinal dorsal horn expressed a similar pattern of MPWT/TPWL among the five groups, except for significantly higher in group 4 than in group 3 (all p<0.0001). The protein expressions of Nav.1.3, Nav.1.8 and Nav.1.9 in sciatic nerve displayed an identical pattern to inflammation among the five groups (all p<0.001). Pain facilitated cellular expressions (p-P38+/peripherin+ cells, P38+/NF200+ cells) displayed an identical pattern to inflammation among the five groups (all p<0.0001). In conclusion, ECSW-Mel combination therapy markedly ameliorated NP induced by CCI.

Neuronatin gene: Imprinted and misfolded: Studies in Lafora disease, diabetes and cancer may implicate NNAT-aggregates as a common downstream participant in neuronal loss

Neuronatin (NNAT) is a ubiquitous and highly conserved mammalian gene involved in brain development. Its mRNA isoforms, chromosomal location, genomic DNA structure and regulation have been characterized. More recently there has been rapid progress in the understanding of its function in physiology and human disease. In particular there is fairly direct evidence implicating neuronatin in the causation of Lafora disease and diabetes. Neuronatin protein has a strong predisposition to misfold and form cellular aggregates that cause cell death by apoptosis. Aggregation of Neuronatin within cortical neurons and resulting cell death is the hallmark of Lafora disease, a progressive and fatal neurodegenerative disease. Under high glucose conditions simulating diabetes, neuronatin protein also accumulates and destroys pancreatic beta cells. The neuronatin gene is imprinted and only the paternal allele is normally expressed in the adult. However, changes in DNA methylation may cause the maternal allele to lose imprinting and trigger cell proliferation and metastasis. Neuronatin has also been shown to be translated peripherally within the dendrites of neurons, a finding of relevance in synaptic plasticity. The current understanding of the function of neuronatin raises the possibility that this gene may participate in the common downstream mechanisms associated with aberrant neuronal growth and death. A better understanding of these mechanisms may open new therapeutic targets to help modify the progression of devastating neurodegenerative conditions such as Alzheimer's and anterior horn cell disease.

Altered mitochondrial ATP synthase expression in the rat dorsal root ganglion after sciatic nerve injury and analgesic effects of intrathecal ATP

Mitochondrial ATP synthase has multiple interdependent biological functions in neurons. Among them, ATP generation and regulation are the most important. The present study investigated whether the expression of mitochondrial ATP synthase correlates with symptoms of neuropathic pain in adult rats after axotomy, and whether intrathecal ATP administration is therapeutic in these neuropathic rats. Male Sprague-Dawley rats received left sciatic nerve transection (axotomy) and were randomly designated to a control (sham-operated) group, a neuropathic pain group (axotomy), a neuropathic pain and intrathecal sterile saline group, and a neuropathic pain and intrathecal ATP group. The thermal and mechanical sensitivity tests were performed at 1, 3, 5, and 7 days after axotomy. Left L4-L5 dorsal root ganglions (DRGs) were harvested to assess mitochondrial ATP synthase by immunoblotting and immunohistochemistry. After nerve injury, the expression of mitochondrial ATP synthase was decreased in protein extracts and was found mainly in C-fiber and A-δ fiber neurons of the DRGs. The decreased expression of mitochondrial ATP synthase and its subcellular localization were related to thermal and mechanical hyperalgesia. Administration of intrathecal ATP significantly attenuated thermal and mechanical hypersensitivity throughout the experimental period, which suggests its potential role in the treatment of neuropathic pain.

Identification and functional analysis of novel micro-RNAs in rat dorsal root ganglia after sciatic nerve resection

Peripheral nerve injures are quite common in clinical practice, and many studies have tried to explore the underlying molecular mechanisms. This study focuses on the identification and functional analysis of novel miRNAs in rat dorsal root ganglia (DRGs) following sciatic nerve resection, which is a classic model for studying peripheral nerve injury and regeneration. By using Solexa sequencing, computational analysis, Q-PCR verification, and Dicer knockdown assay, 114 novel miRNAs in rats were identified, of which 51 novel miRNAs were first reported in rat DRGs, and 63 novel miRNAs were produced at days 1, 4, 7, and 14 following sciatic nerve resection. We further predicted target genes of these miRNAs and analyzed the biological processes in which they were involved. The identified biological processes were consistent with the time frame of peripheral nerve injury and regeneration, revealing that these miRNAs were genuine miRNAs related to nerve regeneration. Our data provide an important resource for the future study of function and regulation of these miRNAs and contribute to elucidation of tyhe molecular mechanisms responsible for peripheral nerve injury and regeneration.

Identification and functional annotation of novel microRNAs in the proximal sciatic nerve after sciatic nerve transection

The peripheral nervous system is able to regenerate after injury, and regeneration is associated with the expression of many genes and proteins. MicroRNAs are evolutionarily conserved, small, non-coding RNA molecules that regulate gene expression at the level of translation. In this paper, we focus on the identification and functional annotation of novel microRNAs in the proximal sciatic nerve after rat sciatic nerve transection. Using Solexa sequencing, computational analysis, and quantitative reverse transcription PCR verification, we identified 98 novel microRNAs expressed on days 0, 1, 4, 7, and 14 after nerve transection. Furthermore, we predicted the target genes of these microRNAs and analyzed the biological processes in which they were involved. The identified biological processes were consistent with the known time-frame of peripheral nerve injury and repair. Our data provide an important resource for further study of the role and regulation of microRNAs in peripheral nerve injury and regeneration.