Correlation of TGN-020 with the analgesic effects via ERK pathway activation after chronic constriction injury

AQP4 is upregulated in schizophrenia and Its inhibition attenuates MK-801-induced schizophrenia-like behaviors in mice

BACKGROUND

The pathophysiology and molecular mechanisms of schizophrenia (SCZ) remain unclear, and the effective treatment resources are still limited. The goal of this study is to identify the expression of AQP4 in SCZ patients and explore whether AQP4 inhibition could ameliorate schizophrenia-like behaviors and its mechanisms.

METHODS

Microarray datasets of PFC compared with healthy control were searched in the Gene Expression Omnibus (GEO) database, and differentially expressed genes (DEGs) were analyzed with the GEO2R online tool. The Venny online tool and metascape online software were used to identify common abnormally expressed genes and conduct cell type signature enrichment analysis. SCZ mouse models were induced with MK-801, an NMDA receptor antagonist (intraperitoneal injection, 0.1 mg/kg/day for 7 days), and C6 cell models were treated with 100 μM MK-801. RT-qPCR, Western Blotting, and immunofluorescence were employed to determine the expression of AQP4, proinflammatory cytokines, and GFAP. Open field tests and social interaction tests were performed to evaluate the schizophrenia-like behaviors.

RESULTS

Bioinformatics analysis identified upregulation of AQP4 in the PFC of SCZ patients compared with healthy controls. Cell type signature enrichment analysis showed that all three DEGs lists were strongly enriched in the FAN EMBRYONIC CTX ASTROCYTE 2 category. Upregulation of AQP4 was also observed in MK-801-treated C6 cells and the PFC of MK-801-induced SCZ mouse model. Moreover, AQP4 inhibition with TGN-020 (an inhibitor of AQP4) improved anxiety-like behavior and social novelty preference defects in MK-801-treated mice. AQP4 inhibition also reduced the expression of IL-1β, IL-6, and TNF-α in MK-801-treated C6 cells and mouse model.

CONCLUSIONS

AQP4 is upregulated in the PFC of SCZ patients compared with healthy controls. AQP4 inhibition could alleviate the anxiety-like behavior and social novelty defects in MK-801-treated mice, this may be due to the role of AQP4 in the regulation of the expression of proinflammatory cytokines.

TGN-020 Alleviate Inflammation and Apoptosis After Cerebral Ischemia-Reperfusion Injury in Mice Through Glymphatic and ERK1/2 Signaling Pathway

Post-stroke acute inhibition of aquaporin 4 (AQP4) is known to exacerbate inflammation and apoptosis, yet the underlying mechanisms are not fully understood. The objective of this study was to investigate the specific mechanism of inflammation and apoptosis following cerebral ischemia-reperfusion (I/R) injury using the AQP4-specific inhibitor, N-(1,3,4-thiadiazol-2-yl) pyridine-3-carboxamide dihydrochloride (TGN-020). Ischemic stroke was induced in mice using the middle cerebral artery occlusion (MCAO) model. The C57/BL6 mice were randomly divided into three groups as follows: sham operation, I/R 48 h, and TGN-020 + I/R 48 h treatment. All mice were subjected to a series of procedures. These procedures encompassed 2,3,5-triphenyltetrazolium chloride (TTC) staining, neurological scoring, fluorescence tracing, western blotting, immunofluorescence staining, and RNA sequencing (RNA-seq). The glymphatic function in the cortex surrounding cerebral infarction was determined using tracer, glial fibrillary acid protein (GFAP), AQP4 co-staining, and beta-amyloid precursor protein (APP) staining; differential genes were detected using RNA-seq. The influence of TGN-020 on the extracellular signal-regulated kinase 1/2 (ERK) 1/2 pathway was confirmed using the ERK1/2 pathway agonists Ro 67-7467. Additionally, we examined the expression of inflammation associated with microglia and astrocytes after TGN-020 and Ro 67-7467 treatment. Compared with I/R group, TGN-020 alleviated glymphatic dysfunction by inhibiting astrocyte proliferation and reducing tracer accumulation in the peri-infarct area. RNA-seq showed that the differentially expressed genes were mainly involved in the activation of astrocytes and microglia and in the ERK1/2 pathway. Western blot and immunofluorescence further verified the expression of associated inflammation. The inflammation and cell apoptosis induced by I/R are mitigated by TGN-020. This mitigation occurs through the improvement of glymphatic function and the inhibition of the ERK1/2 pathway.

Aquaporin 4 beyond a water channel; participation in motor, sensory, cognitive and psychological performances, a comprehensive review

Aquaporin 4 (AQP4) is a protein highly expressed in the central nervous system (CNS) and peripheral nervous system (PNS) as well as various other organs, whose different sites of action indicate its importance in various functions. AQP4 has a variety of essential roles beyond water homeostasis. In this article, we have for the first time summarized different roles of AQP4 in motor and sensory functions, besides cognitive and psychological performances, and most importantly, possible physiological mechanisms by which AQP4 can exert its effects. Furthermore, we demonstrated that AQP4 participates in pathology of different neurological disorders, various effects depending on the disease type. Since neurological diseases involve a spectrum of dysfunctions and due to the difficulty of obtaining a treatment that can simultaneously affect these deficits, it is therefore suggested that future studies consider the role of this protein in different functional impairments related to neurological disorders simultaneously or separately by targeting AQP4 expression and/or polarity modulation.

Molecular Changes in the Dorsal Root Ganglion during the Late Phase of Peripheral Nerve Injury-induced Pain in Rodents: A Systematic Review

The dorsal root ganglion is widely recognized as a potential target to treat chronic pain. A fundamental understanding of quantitative molecular and genomic changes during the late phase of pain is therefore indispensable. The authors performed a systematic literature review on injury-induced pain in rodent dorsal root ganglions at minimally 3 weeks after injury. So far, slightly more than 300 molecules were quantified on the protein or messenger RNA level, of which about 60 were in more than one study. Only nine individual sequencing studies were performed in which the most up- or downregulated genes varied due to heterogeneity in study design. Neuropeptide Y and galanin were found to be consistently upregulated on both the gene and protein levels. The current knowledge regarding molecular changes in the dorsal root ganglion during the late phase of pain is limited. General conclusions are difficult to draw, making it hard to select specific molecules as a focus for treatment.

Inhibition of ERK1/2 phosphorylation attenuates spinal cord injury induced astrocyte activation and inflammation through negatively regulating aquaporin-4 in rats

The extracellular signal-regulated kinase (ERK) pathway has been reported to play a pivotal role in mediating spinal cord injury (SCI) progression. The present study aimed to investigate the effects of phosphorylated ERK1/2 (p-ERK1/2) inhibition on SCI-induced astrocyte activation and inflammation and its possible mechanism in rats. Here, female Sprague-Dawley rats were randomly assigned to four groups: (1) Sham group, (2) SCI group, (3) TGN-020 group (aquaporin-4, AQP4, blocking agent), (4) PD98059 group (ERK blocking agent). A well SCI model was established by compressing the thoracic vertebra 10 level (weight 35 g, time 5 min) in rats. Western blotting and immunofluorescence staining were used to measure the expression of associated proteins after SCI. HE staining and Nissl staining were performed to detect the morphological changes of spinal cords and the number of surviving neurons following SCI, respectively. The Basso-Beattie-Bresnahan open-field rating scale was used to evaluate functional locomotor recovery following SCI in rats. Our results demonstrated that SCI significantly induced the upregulation of aquaporin-4, p-ERK1/2, glial fibrillary acidic protein, proliferating cell nuclear antigen, and proinflammatory cytokines (tumor necrosis factor-α, interleukin-6 and interleukin-1β). However, treatment with TGN-020 or PD98059 could effectively inhibit astrocyte proliferation and proinflammatory cytokine release, preserve the number of surviving ventral horn neurons, and subsequently improve the locomotor function of rats after SCI. Interestingly, the SCI-induced elevation of AQP4 expression was downregulated by p-ERK1/2 inhibition, suggesting that blocking ERK1/2 phosphorylation could attenuate astrocyte activation and inflammatory processes through negative regulation of AQP4. Therefore, p-ERK1/2 blockade may be employed as a therapeutic target for SCI.

Astragalin Alleviates Neuropathic Pain by Suppressing P2X4-Mediated Signaling in the Dorsal Root Ganglia of Rats

Neurologic damage often leads to neuropathic pain, for which there are no effective treatments owing to its complex pathogenesis. The purinergic receptor P2X4 is closely associated with neuropathic pain. Astragalin (AST), a compound that is used in traditional Chinese medicine, has protective effects against allergic dermatitis and neuronal injury, but its mechanism of action is not well understood. The present study investigated whether AST can alleviate neuropathic pain in a rat model established by chronic constriction injury (CCI) to the sciatic nerve. The model rats exhibited pain behavior and showed increased expression of P2X4 and the activated satellite glial cell (SGC) marker glial fibrillary acidic protein in dorsal root ganglia (DRG). AST treatment partly abrogated the upregulation of P2X4, inhibited SGC activation, and alleviated pain behavior in CCI rats; it also suppressed ATP-activated currents in HEK293 cells overexpressing P2X4. These data demonstrate that AST relieves neuropathic pain by inhibiting P2X4 and SGC activation in DRG, highlighting its therapeutic potential for clinical pain management.

Differential effects of aquaporin-4 channel inhibition on BOLD fMRI and diffusion fMRI responses in mouse visual cortex

The contribution of astrocytes to the BOLD fMRI and DfMRI responses in visual cortex of mice following visual stimulation was investigated using TGN-020, an aquaporin 4 (AQP4) channel blocker, acting as an astrocyte function perturbator. Under TGN-020 injection the amplitude of the BOLD fMRI response became significantly higher. In contrast no significant changes in the DfMRI responses and the electrophysiological responses were observed. Those results further confirm the implications of astrocytes in the neurovascular coupling mechanism underlying BOLD fMRI, but not in the DfMRI responses which remained unsensitive to astrocyte function perturbation.

Crosstalk between Cdk5/p35 and ERK1/2 signalling mediates spinal astrocyte activity via the PPARγ pathway in a rat model of chronic constriction injury

The specific mechanisms underlying cyclin-dependent kinase 5 (Cdk5)-mediated neuropathic pain at the spinal cord level remain elusive. The aim of the present study was to explore the role of crosstalk between Cdk5/p35 and extracellular signal-regulated kinase 1/2 (ERK1/2) signalling in mediating spinal astrocyte activity via the PPARγ pathway in a rat model of chronic constriction injury (CCI). Here, we quantified pain behaviour after CCI; detected the localization of p35, Cdk5, phosphorylated ERK1/2 (pERK1/2), phosphorylated peroxisome proliferator-activated receptor γ (pPPARγ), neuronal nuclei (a neuronal marker), glial fibrillary acidic protein (GFAP, an activated astrocyte marker) and ionized calcium binding adaptor molecule 1 (a microglial marker) in the dorsal horn using immunofluorescence; measured the protein levels of Cdk5, p35, pERK1/2, pPPARγ and GFAP using western blot analysis; and gauged the enzyme activity of Cdk5/p35 kinase using a Cdk5/p35 kinase activity assay kit. Tumour necrosis factor-α, interleukin (IL)-1β and IL-6 levels were measured using enzyme-linked immunosorbent assay (ELISA). Ligation of the right sciatic nerve induced mechanical allodynia; thermal hyperalgesia; and the time-dependent upregulation of p35, pERK1/2 and GFAP and downregulation of pPPARγ. p35 colocalized with Cdk5, pERK1/2, pPPARγ, neurons and astrocytes but not microglia. Meanwhile, intrathecal injection of the Cdk5 inhibitor roscovitine, the mitogen-activated ERK kinase (MEK) inhibitor U0126 and the PPARγ agonist pioglitazone prevented or reversed behavioural allodynia, increased pPPARγ expression, inhibited astrocyte activation and alleviated proinflammatory cytokine (tumour necrosis factor-α, IL-1β, and IL-6) release from activated astrocytes. Furthermore, crosstalk between the Cdk5/p35 and ERK1/2 pathways was observed with CCI. Blockade of either Cdk5/p35 or ERK1/2 inhibited Cdk5 activity. These findings indicate that spinal crosstalk between the Cdk5/p35 and ERK1/2 pathways mediates astrocyte activity via the PPARγ pathway in CCI rats and that targeting this crosstalk could be an effective strategy to attenuate CCI and astrocyte-derived neuroinflammation.

TGN-020 alleviates edema and inhibits astrocyte activation and glial scar formation after spinal cord compression injury in rats

AIMS

Identifying drugs that inhibit edema and glial scar formation and increase neuronal survival is crucial to improving outcomes after spinal cord injury (SCI). Here, we used 2-(nicotinamide)-1,3,4-thiadiazole (TGN-020), a potent selective inhibitor of aquaporin 4 (AQP4), to investigate the effects of TGN-020 on SCI in Sprague-Dawley rats.

MAIN METHODS

We compressed the spinal cord at T10 using a sterile impounder (35 g, 5 min), to induce moderate injury. TGN-020 (100 mg/kg) or an equal volume of 10% dimethyl sulfoxide was then administered via intraperitoneal injection. Neurological function was evaluated using the Basso-Beattie-Bresnahan open-field locomotor scale 1, 3, 7, 14, 21, and 28 days after SCI. The degree of edema was assessed via determination of the precise spinal cord water content 3 days after SCI. Expression levels of AQP4, glial fibrillary acidic protein (GFAP), proliferating cell nuclear antigen (PCNA), and growth-associated protein-43 (GAP-43) were determined via western blotting and immunofluorescence staining 3 days after SCI and 4 weeks after SCI. Numbers of surviving neurons and glial scar sizes were determined using Nissl and hematoxylin-eosin staining, respectively.

KEY FINDINGS

Our results showed that TGN-020 promoted functional recovery at days 3, 7, 14, 21, and 28, as well as reduced the degree of edema and inhibited the expression of AQP4, GFAP, PCNA at days 3 after SCI. Furthermore, observations 4 weeks after SCI revealed that TGN-020 inhibited the glial scar formation and upregulated GAP-43 expression.

SIGNIFICANCE

TGN-020 can alleviate spinal cord edema, inhibit glial scar formation, and promote axonal regeneration, conferring beneficial effects on recovery in rats.