Spinal glycinergic currents are reduced in a rat model of neuropathic pain following partial nerve ligation but not chronic constriction injury

Proteomic analysis of spinal dorsal horn in prior exercise protection against neuropathic pain

Neuropathic pain (NP) is a complex and prevalent chronic pain condition that affects millions of individuals worldwide. Previous studies have shown that prior exercise protects against NP caused by nerve injury. However, the underlying mechanisms of this protective effect remain to be uncovered. Therefore, the purpose of this study is to investigate how prior exercise affects protein expression in NP model rats and thus gain comprehensive insights into the molecular mechanisms involved. To achieve this objective, 6-week-old male Sprague-Dawley rats were randomly assigned into three groups, named as chronic constriction injury (CCI) of the sciatic nerve, CCI with prior 6-week swimming training (CCI_Ex), and sham operated (Sham). The CCI_Ex group underwent 6 weeks of swimming training before CCI surgery, while the CCI and sham groups had no intervention. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were used as the main observation indicators to evaluate the behavioral changes associated with pain. Tissues from the spinal dorsal horn of the rats in the three groups were collected at 4 weeks after operation. LC-MS/MS proteomic analysis based on the label-free approach was used to detect protein profiles, and volcano plots, Venn diagrams, and clustering heatmaps were used to identify differentially expressed proteins (DEPs). Gene Ontology (GO) annotations, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and protein-protein interaction networks were employed to explore the biological importance of DEPs. At 14, 21, and 28 days following CCI, CCI rats with prior exercise showed a significant increase in the MWT and TWL of the injured lateral hind paw compared with those without exercise. A total of 122 proteins with significant changes in abundance were detected after CCI surgery, and 55 proteins were detected in the comparison between the CCI_Ex and CCI groups. GO and KEGG enrichment analysis revealed that oxygen transport capacity and the complement and coagulation cascades may be the critical mechanism by which prior exercise protects against NP. Serpina1, DHX9, and Alb are the key proteins in this process and warrant further attention, as confirmed by the results of Western blot analysis. In conclusion, this study provides new evidence that active physical activity can accelerate the relief of hyperalgesia after NP. Proteomic analyses revealed the potential target proteins and pathways for this process, offering valuable data resources and new insights into the pathogenesis and therapeutic targets of NP.

miR-363-5p protects from neuropathic pain in chronic constriction injury (CCI) rat models and regulates Schwann cell injury via negatively modulating SERPING1

OBJECTIVES

Due to the complex and unclear pathogenesis of neuropathic pain, there is a lack of effective therapeutic strategy. miR-363-5p was considered of great potential in mediating the development of neuropathic pain, which has not been confirmed with direct evidence. This study evaluated the role of miR-363-5p in neuropathic pain with animal and cell models, aiming to reveal the potential of miR-363-5p in target therapy of neuropathic pain.

METHODS

Chronic constriction injury (CCI) rat models were established as the neuropathic pain model. The expression of miR-363-5p and its target was evaluated by PCR. The painology behaviors were evaluated to assess the function of miR-363-5p. Schwann cells were induced with LPS mimicking cell injury during neuropathic pain. Inflammation and cell growth were estimated by ELISA and CCK8 assays.

RESULTS

Significant downregulation of miR-363-5p and upregulation of SERPING1 were observed in CCI rats. miR-363-5p negatively regulated SERPING1 in CCI rats and LPS-induced Schwann cells. Overexpressing miR-363-5p could improve pain threshold and alleviate inflammation in CCI rats. It also a ttenuated LPS-induced inflammation and reduced proliferation in Schwann cells. The overexpression of SERPING1 could reverse the protective effect of miR-363-5p on CCI rats and LPS-induced Schwann cell injury.

CONCLUSION

miR-363-5p protected from neuropathic pain via alleviating Schwann cell injury by negatively modulating SERPING1.

Aged females unilaterally hypersensitize, lack descending inhibition, and overexpress alpha1D adrenergic receptors in a murine posttraumatic chronic pain model

ABSTRACT

Vulnerability to chronic pain is found to depend on age and sex. Most patients with chronic pain are elderly women, especially with posttraumatic pain after bone fracture that prevails beyond the usual recovery period and develops into a complex regional pain syndrome (CRPS). There, a distal bone fracture seems to initiate a pathophysiological process with unknown mechanism. To investigate whether sex, age, and alpha adrenergic receptors also contribute to a CRPS-like phenotype in animals, we performed experiments on tibia-fractured mice. Those mice commonly are resilient to the development of a CRPS-like phenotype. However, we found them to be vulnerable to long-lasting pain after distal bone fracture when they were of old age. These mice expressed mechanical and thermal hypersensitivity, as well as weight-bearing and autonomic impairment following bone trauma, which persisted over 3 months. Site-specific and body side-specific glycinergic and α1D-noradrenergic receptor expression in the spinal cord and the contralateral locus coeruleus were misbalanced. Aged female tibia-fractured mice lost descending noradrenergic inhibition and displayed enhanced spinal activity on peripheral pressure stimuli. Together, changes in the noradrenergic, hence, glycinergic system towards excitation in the pain pathway-ascending and descending-might contribute to the development or maintenance of long-lasting pain. Conclusively, changes in the noradrenergic system particularly occur in aged female mice after trauma and might contribute to the development of long-lasting pain. Our data support the hypothesis that some patients with chronic pain would benefit from lowering the adrenergic/sympathetic tone or antagonizing α1(D).

Neuropathic pain; what we know and what we should do about it

Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.