Aquaporin 4 knockout increases complete freund's adjuvant-induced spinal central sensitization

Inhibition of aquaporin-4 and its subcellular localization attenuates below-level central neuropathic pain by regulating astrocyte activation in a rat spinal cord injury model

The mechanisms of central neuropathic pain (CNP) caused by spinal cord injury have not been sufficiently studied. We have found that the upregulation of astrocytic aquaporin-4 (AQP4) aggravated peripheral neuropathic pain after spinal nerve ligation in rats. Using a T13 spinal cord hemisection model, we showed that spinal AQP4 was markedly upregulated after SCI and mainly expressed in astrocytes in the spinal dorsal horn (SDH). Inhibition of AQP4 with TGN020 suppressed astrocyte activation, attenuated the development and maintenance of below-level CNP and promoted motor function recovery in vivo. In primary astrocyte cultures, TGN020 also changed cell morphology, diminished cell proliferation and suppressed astrocyte activation. Moreover, T13 spinal cord hemisection induced cell-surface abundance of the AQP4 channel and perivascular localization in the SDH. Targeted inhibition of AQP4 subcellular localization with trifluoperazine effectively diminished astrocyte activation in vitro and further ablated astrocyte activation, attenuated the development and maintenance of below-level CNP, and accelerated functional recovery in vivo. Together, these results provide mechanistic insights into the roles of AQP4 in the development and maintenance of below-level CNP. Intervening with AQP4, including targeting AQP4 subcellular localization, might emerge as a promising agent to prevent chronic CNP after SCI.

AQP4 is an Emerging Regulator of Pathological Pain: A Narrative Review

Pathological pain presents significant challenges in clinical practice and research. Aquaporin-4 (AQP4), which is primarily found in astrocytes, is being considered as a prospective modulator of pathological pain. This review examines the association between AQP4 and pain-related diseases, including cancer pain, neuropathic pain, and inflammatory pain. In cancer pain, upregulated AQP4 expression in tumor cells is linked to increased pain severity, potentially through tumor-induced inflammation and edema. Targeting AQP4 may offer therapeutic strategies for managing cancer pain. AQP4 has also been found to play a role in nerve damage. Changes in AQP4 expression have been detected in pain-related regions of the brain and spinal cord; thus, modulating AQP4 expression or function may provide new avenues for treating neuropathic pain. Of note, AQP4-deficient mice exhibit reduced chronic pain responses, suggesting potential involvement of AQP4 in chronic pain modulation, and AQP4 is involved in pain modulation during inflammation, so understanding AQP4-mediated pain modulation may lead to novel anti-inflammatory and analgesic therapies. Recent advancements in magnetic resonance imaging (MRI) techniques enable assessment of AQP4 expression and localization, contributing to our understanding of its involvement in brain edema and clearance pathways related to pathological pain. Furthermore, targeting AQP4 through gene therapies and small-molecule modulators shows promise as a potential therapeutic intervention. Future research should focus on utilizing advanced MRI techniques to observe glymphatic system changes and the exchange of cerebrospinal fluid and interstitial fluid. Additionally, investigating the regulation of AQP4 by non-coding RNAs and exploring novel small-molecule medicines are important directions for future research. This review shed light on AQP4-based innovative therapeutic strategies for the treatment of pathological pain. Dark blue cells represent astrocytes, green cells represent microglia, and red ones represent brain microvasculature.

Involvement of Kir4.1 in pain insensitivity of the BTBR mouse model of autism spectrum disorder

Autism spectrum disorder (ASD) is a severe neurodevelopmental disorder. Abnormal pain sensation is a common clinical symptom of ASD that seriously affects the quality of life of patients with ASD and their families. However, the underlying mechanism is unclear. It is believed to be related to the excitability of neurons and the expression of ion channels. Herein, we confirmed that baseline pain and Complete Freund's adjuvant (CFA)-induced chronic inflammatory pain were impaired in the BTBR T+ Itpr3tf/J (BTBR) mouse model of ASD. RNA sequencing (RNA-seq) analyses of the dorsal root ganglia (DRG), which are closely related to pain in ASD model mice, revealed that high expression of KCNJ10 (encoding Kir4.1) might be an important factor in ASD pain sensation abnormalities. The levels of Kir4.1 were further verified by western blotting, RT-qPCR, and immunofluorescence. By inhibiting Kir4.1, the pain insensitivity of BTBR mice improved, confirming that a high expression level of Kir4.1 was highly correlated with decreased pain sensitivity in ASD. Meanwhile, we found that the anxiety behaviours and the social novelty recognition were changed after CFA induced inflammatory pain. And after inhibiting Kir4.1, the stereotyped behaviours and social novelty recognition of BTBR mice were also improved. Further, we found that the expression levels of glutamate transporters, excitatory amino acid transporter 1 (EAAT1), and excitatory amino acid transporter 2 (EAAT2) were increased in the DRG of BTBR mice but decreased after inhibiting Kir4.1. This suggests that Kir4.1 may play a key role in the improvement of pain insensitivity in ASD by regulating glutamate transporters. In conclusion, our findings revealed the possible mechanism and role of Kir4.1 in the pain insensitivity in ASD, using bioinformatics analyses and animal experiments, and provided a theoretical basis for clinically targeted intervention in ASD.

Effects of a novel probiotic mixture on the modulation of brain and intestine Aquaporin-4 gene expression in rats exposed to Cadmium

Cadmium (Cd) is a toxicant metal that risks human and animal health. Nowadays, the vital role of Aquaporin-4 (AQP-4) in brain and gut cell permeability has gathered too much attention to protecting against heavy metals. Studies have shown that heavy metals can harm the body due to oxidative stress. Probiotics are known for their health-beneficial effects and establish as dietary adjuncts mainly for their antioxidant properties. This study investigated the impact of a novel probiotic combination including Lactobacillus casei IBRC-M10783, Lactobacillus rhamnosus IBRC-M10782, and Lactobacillus helveticus TG-34 on the AQP-4 gene expression in CdCl2-induced Wistar rats. Rats were divided into three groups and received a specific dose of CdCl2 or probiotics. The AQP-4 expression level had estimated by Real-Time PCR in both the intestine and brain. These results showed a significant reduction in AQP-4 gene expression in the probiotic treatment group compared to the CdCl2 control group in the intestine and brain for the first time. Our research showed that consuming a probiotic mixture of L. casei, L. rhamnosus, and L. helveticus can reduce the expression of the aquaporin-4 gene in the brain and intestine of rats exposed to Cadmium, which can be promising in the field of aquaporin-4 regulation.

The role of astrocytes in neuropathic pain

Neuropathic pain, whose symptoms are characterized by spontaneous and irritation-induced painful sensations, is a condition that poses a global burden. Numerous neurotransmitters and other chemicals play a role in the emergence and maintenance of neuropathic pain, which is strongly correlated with common clinical challenges, such as chronic pain and depression. However, the mechanism underlying its occurrence and development has not yet been fully elucidated, thus rendering the use of traditional painkillers, such as non-steroidal anti-inflammatory medications and opioids, relatively ineffective in its treatment. Astrocytes, which are abundant and occupy the largest volume in the central nervous system, contribute to physiological and pathological situations. In recent years, an increasing number of researchers have claimed that astrocytes contribute indispensably to the occurrence and progression of neuropathic pain. The activation of reactive astrocytes involves a variety of signal transduction mechanisms and molecules. Signal molecules in cells, including intracellular kinases, channels, receptors, and transcription factors, tend to play a role in regulating post-injury pain once they exhibit pathological changes. In addition, astrocytes regulate neuropathic pain by releasing a series of mediators of different molecular weights, actively participating in the regulation of neurons and synapses, which are associated with the onset and general maintenance of neuropathic pain. This review summarizes the progress made in elucidating the mechanism underlying the involvement of astrocytes in neuropathic pain regulation.

Alum Pickering Emulsion as Effective Adjuvant to Improve Malaria Vaccine Efficacy

Malaria is a life-threatening global epidemic disease and has caused more than 400,000 deaths in 2019. To control and prevent malaria, the development of a vaccine is a potential method. An effective malaria vaccine should either combine antigens from all stages of the malaria parasite’s life cycle, or epitopes of multiple key antigens due to the complexity of the Plasmodium parasite. Malaria’s random constructed antigen-1 (M.RCAg-1) is one of the recombinant vaccines, which was selected from a DNA library containing thousands of diverse multi-epitope chimeric antigen genes. Moreover, besides selecting an antigen, using an adjuvant is another important procedure for most vaccine development procedures. Freund’s adjuvant is considered an effective vaccine adjuvant for malaria vaccine, but it cannot be used in clinical settings because of its serious side effects. Traditional adjuvants, such as alum adjuvant, are limited by their unsatisfactory immune effects in malaria vaccines, hence there is an urgent need to develop a novel, safe and efficient adjuvant. In recent years, Pickering emulsions have attracted increasing attention as novel adjuvant. In contrast to classical emulsions, Pickering emulsions are stabilized by solid particles instead of surfactant, having pliability and lateral mobility. In this study, we selected aluminum hydroxide gel (termed as “alum”) as a stabilizer to prepare alum-stabilized Pickering emulsions (ALPE) as a malaria vaccine adjuvant. In addition, monophosphoryl lipid A (MPLA) as an immunostimulant was incorporated into the Pickering emulsion (ALMPE) to further enhance the immune response. In vitro tests showed that, compared with alum, ALPE and ALMPE showed higher antigen load rates and could be effectively endocytosed by J774a.1 cells. In vivo studies indicated that ALMPE could induce as high antibody titers as Freund’s adjuvant. The biocompatibility study also proved ALMPE with excellent biocompatibility. These results suggest that ALMPE is a potential adjuvant for a malaria vaccine.

Variation in essential oil components and anti-inflammatory activity of Allophylus edulis leaves collected in central-western Brazil

ETHNOPHARMACOLOGICAL RELEVANCE

An infusion obtained from the leaves of "chal-chal" (Allophylus edulis Radlk.) is used for popular treatment of intestinal disorders and as an anti-inflammatory throat treatment. Because of the anti-inflammatory medicinal folk use, a previous work reported scientific research confirming the anti-inflammatory activity of A. edulis essential oil collected in Dourados, MS, Brazil, in March 2015.

AIM OF THE STUDY

The aim of this study was to evaluate the variation in the chemical profile of the essential oil of A. edulis plants collected in Dourados (EOAE-D) and Bonito (EOAE-B), two cities in Mato Grosso do Sul State, Brazil. Additionally, we evaluated the anti-inflammatory effects of the essential oil, as well as that of the major compounds (caryophyllene oxide and α-zingiberene), in experimental in vivo models of inflammation in mice.

MATERIALS AND METHODS

Leaves were collected from plants at both sites in July 2018. The composition of the essential oil (EOAE-D and EOAE-B) was determined by GC/MS, and major compounds (caryophyllene oxide and α-zingiberene) were isolated and identified by chromatographic methods and NMR spectroscopy. Anti-inflammatory capacities were assessed using two classical models of inflammatory models, carrageenan- and CFA-induced paw inflammation (mechanical and thermal hyperalgesia).

RESULTS

Both EOAE-D and EOAE-B showed sesquiterpenes as a major constituent, namely, caryophyllene oxide (29.5%) and α-zingiberene (45.0%), respectively. In tests, EOAE, caryophyllene oxide and α-zingiberene-induced antiedematogenic and antihyperalgesic effects were found in the different utilized models.

CONCLUSIONS

The results indicate that samples from the two cities differed in chemical composition but not in their anti-inflammatory and antihyperalgesic effects. This finding corroborates the use of A. edulis as a medicinal plant and indicates its potential in the therapy of inflammatory conditions.

MiRNA-107 contributes to inflammatory pain by down-regulating GLT-1 expression in rat spinal dorsal horn

BACKGROUND

Inflammatory pain is a severe clinical problem that affects the quality of life in patients. However, the currently available treatments for inflammatory pain have limited effect and even causes severe side effects. The aim of this study was to investigate the roles of miRNA-107 and glutamate transporter 1 (GLT-1) in the inflammatory pain of rats induced by complete Freund's adjuvant (CFA).

METHODS

Paw withdrawal threshold (PWT) of rats was measured by von Frey Filaments. The expressions of miRNA-107 and GLT-1 in the lumbar spinal dorsal horn (L4-L6) were measured with real-time quantitative PCR and western blotting analysis. Fluorescent in situ hybridization and fluorescent-immunohistochemistry were employed to detect the expression of miRNA-107, GLT-1 and co-location of miRNA-107 with GLT-1.

RESULTS

Injection of CFA significantly reduced PWT of rats. The miRNA-107 expression level was obviously up-regulated while the GLT-1 expression level was decreased in the spinal dorsal horn of CFA rats. miRNA-107 and GLT-1 were co-expressed in the same cells of the spinal dorsal horn in CFA rats. Ceftriaxone, a selective activator of GLT-1, obviously increased the PWT of CFA rats. Furthermore, antagomir of miRNA-107 reversed the down-regulation of GLT-1 and alleviated CFA-induced mechanical allodynia of CFA rats.

CONCLUSIONS

These results suggest that an increase of miR-107 contributes to inflammatory pain through downregulating GLT-1 expression, implying a promising strategy for pain therapy.

SIGNIFICANCE

The currently available treatments for inflammatory pain has limited effect even causes severe side effects. MiRNAs may have important diagnostic and therapeutic potential in inflammatory pain. In present study, we show a potential spinal mechanism of allodynia in rat inflammatory pain model induced by CFA. Increased miR-107 contribute to inflammatory pain by targeting and downregulating GLT-1 expression, implying a promising strategy for inflammatory pain.

Aquaporins in the nervous structures supplying the digestive organs – a review

Aquaporins (AQPs) are a family of integral membrane proteins which form pores in cell membranes and take part in the transport of water, contributing to the maintenance of water and electrolyte balance and are widely distributed in various tissues and organs. The high expression of AQPs has been described in the digestive system, where large-scale absorption and secretion of fluids occurs. AQPs are also present in the nervous system, but the majority of studies have involved the central nervous system. This paper is a review of the literature concerning relatively little-known issues, i.e. the distribution and functions of AQPs in nervous structures supplying the digestive organs.

Aquaporin 4 is involved in chronic pain but not acute pain

Accumulating evidence has revealed that spinal glia plays an important role in the processing of pain, particularly chronic pain. Aquaporin 4 (AQP4), the predominant water channel exists in astrocytes, has been proved to modulate astrocytic function and thus participate in many diseases of the central nervous system. However, there is still controversy over whether AQP4 is involved in pain modulation. In the present study, we investigated the effects of AQP4 on pain by examining chronic inflammatory pain, neuropathic pain, and thermal, chemical, and mechanical stimuli-induced acute pain in AQP4 knockout mice. In Complete Freund's adjuvant-induced chronic inflammatory pain and spared nerve injury-induced neuropathic pain models, AQP4^-/- mice attenuated pain-related behavioral responses compared with AQP4^+/+ mice, demonstrating that AQP4 deficiency relieved chronic inflammatory pain and neuropathic pain. In the tail-flick and hot-plate tests, two acute pain models of thermal stimuli, no differences in pain-related behaviors were detected between AQP4^+/+ and AQP4^-/- mice. In the formalin and capsaicin tests, two models of chemical stimuli-induced acute pain, no differences in the durations of licking the injected hindpaw were found between AQP4^+/+ and AQP4^-/- mice. In the von Frey hair test, a model of mechanical stimuli-induced acute pain, no significant differences in withdrawal thresholds were found between these two genotypes mice as well. These results indicated that AQP4 deficiency did not affect acute pain induced by thermal, chemical, and mechanical stimuli. Taken together, our findings suggested that AQP4 contributes to chronic pain, but not acute pain.