Regulation of aquaporin 4 expression by lipoxin A4 in astrocytes stimulated by lipopolysaccharide

Neuroprotective effect of triptolide on neuronal inflammation in rats with mild brain injury

Concussions sustained while playing sports are a prominent cause of mild traumatic brain injury (mTBI), which is prevalent among teenagers. The early and intermediate stages of mild traumatic brain injury (mTBI) can be characterized by inflammation, neurodegeneration, and brain tissue edema, which can lead to permanent brain damage. The present study investigated the therapeutic effects of triptolide in mTBI and brain damage recovery. After building mTBI model in male rat, triptolide administrated daily for 1 week in the treated group. On day 3 and day 7 of administration, hippocampus tissues were collected to evaluate inflammation and autophagy in the brain. The expressions of inflammatory factors interleukin (IL)-1β and tumor necrosis factor-alpha in serum were downregulated, while IL-10 expression was upregulated when compared with the mTBI group on day 3 and day 7. The expression of IL-10 on day 7 was higher than on day 3. Quantitative polymerase chain reaction (qPCR) analysis of inflammatory-related factors (i.e., Il-1β and nuclear factor-κB (Nf-κb), and western blot as well as immunofluorescence staining of autophagy-related proteins (i.e., LC3B) and aquaporin (AQP 4) showed lower expression on day 3 and day 7 in the triptolide-treated group. Moreover, NeuN immunostaining, and hematoxylin and eosin (HE) staining for hippocampus region revealed that the triptolide-treated group showed a decrease in damaged cells. Our findings emphasize the effectiveness of triptolide therapy after mild traumatic brain injury via modulating autophagy, attenuating inflammation and reduces edema by decreasing AQP 4 expression.

Leukemia-derived Exosomes Can Induce Responses Related to Tumorigenesis on Non-tumoral Astrocytes

Cancer is the second cause of disability and death worldwide. Identifying communication between cancer cells and normal cells can shed light on the underlying metastatic mechanisms. Among different suspected mechanisms, exosomes derived from cancer cells have been introduced as a main key player in metastatic processes. To this point, we evaluated the effects of exosomes derived from the leukemia nalm6 cell line on astrocytes behavior, such as proliferation and inflammatory pathways. To assess astrocyte responses, data were obtained by MTT, Annexin/PI to indicate proliferation and apoptosis. Further analyses were performed by Real-time PCR and western blot to assess the expression of IL6, IL1β, NFkβ, TNFα, and aquaporin-4 (AQP4). Our results demonstrated that the proliferation of astrocytes was significantly increased when treated with exosomes derived from Nalm6 cells. We also found that the expression of IL6, IL1β, NFkβ, and TNFα were significantly increased at the mRNA level when exposed to exosomes derived from Nalm6 cells. Finally, the mRNA and protein levels of AQP4 were profoundly increased after being treated by exosomes derived from Nalm6 cells. To sum up, our data indicated that the secretion of cancer cells could induce responses related to tumorigenesis. However, further studies on this topic are warranted to clarify exosomes' role in metastasis.

Lipoxins in the Nervous System: Brighter Prospects for Neuroprotection

Lipoxins (LXs) are generated from arachidonic acid and are involved in the resolution of inflammation and confer protection in a variety of pathological processes. In the nervous system, LXs exert an array of protective effects against neurological diseases, including ischemic or hemorrhagic stroke, neonatal hypoxia-ischemia encephalopathy, brain and spinal cord injury, Alzheimer's disease, multiple sclerosis, and neuropathic pain. Lipoxin administration is a potential therapeutic strategy in neurological diseases due to its notable efficiency and unique superiority regarding safety. Here, we provide an overview of LXs in terms of their synthesis, signaling pathways and neuroprotective evidence. Overall, we believe that, along with advances in lipoxin-related drug design, LXs will bring brighter prospects for neuroprotection.

The role of AQP4 in the pathogenesis of depression, and possible related mechanisms

Modulation of the aquaporin 4 (AQP4) water-regulatory channel or production of autoantibodies against this protein have been implicated in a variety of neuropsychiatric conditions, and possible mechanisms have been proposed. However, the nature of the interaction between AQP4 expression and its implications in depression remain elusive. To our knowledge, this is the first review summarising data for the involvement of AQP4 in the context of depression and related mechanisms across a wide range of experimental studies: pre-clinical (KO and wild-type), post-mortem, ex vivo, and clinical studies in depression. Overall, preclinical AQP4 wild-type studies showed that exposure to stress or inflammation, used as models of depression, decreased AQP4 protein and gene expression in various brain regions, including prefrontal cortex (PFC), choroid plexus and, especially, hippocampus. In preclinical AQP4 KO studies, AQP4 expression is necessary to prevent the effect of stress and inflammation on reduced neurogenesis and gliogenesis, and increased apoptosis and depressive-like behaviours. While in post-mortem and ex vivo studies of depression AQP4 expression was usually decreased in the hippocampus, prefrontal cortex and locus coeruleus, in clinical studies, where mRNA AQP4 expression or serum AQP4 autoantibodies were measured, there were no differences in depressed patients when compared with controls. In the future, studies should further investigate the mechanisms underlying the action of AQP4, and continue exploring if AQP4 autoantibodies are either contributing or underlying mechanisms of depression, or whether they are simply a mechanism underlying other autoimmune conditions where depression is present.

Time-Dependent Protective and Pro-Resolving Effects of FPR2 Agonists on Lipopolysaccharide-Exposed Microglia Cells Involve Inhibition of NF-κB and MAPKs Pathways

Prolonged or excessive microglial activation may lead to disturbances in the resolution of inflammation (RoI). The importance of specialized pro-resolving lipid mediators (SPMs) in RoI has been highlighted. Among them, lipoxins (LXA4) and aspirin-triggered lipoxin A4 (AT-LXA4) mediate beneficial responses through the activation of N-formyl peptide receptor-2 (FPR2). We aimed to shed more light on the time-dependent protective and anti-inflammatory impact of the endogenous SPMs, LXA4, and AT-LXA4, and of a new synthetic FPR2 agonist MR-39, in lipopolysaccharide (LPS)-exposed rat microglial cells. Our results showed that LXA4, AT-LXA4, and MR-39 exhibit a protective and pro-resolving potential in LPS-stimulated microglia, even if marked differences were apparent regarding the time dependency and efficacy of inhibiting particular biomarkers. The LXA4 action was found mainly after 3 h of LPS stimulation, and the AT-LXA4 effect was varied in time, while MR-39′s effect was mainly observed after 24 h of stimulation by endotoxin. MR-39 was the only FPR2 ligand that attenuated LPS-evoked changes in the mitochondrial membrane potential and diminished the ROS and NO release. Moreover, the LPS-induced alterations in the microglial phenotype were modulated by LXA4, AT-LXA4, and MR-39. The anti-inflammatory effect of MR-39 on the IL-1β release was mediated through FPR2. All tested ligands inhibited TNF-α production, while AT-LXA4 and MR-39 also diminished IL-6 levels in LPS-stimulated microglia. The favorable action of LXA4 and MR-39 was mediated through the inhibition of ERK1/2 phosphorylation. AT-LXA4 and MR39 diminished the phosphorylation of the transcription factor NF-κB, while AT-LXA4 also affected p38 kinase phosphorylation. Our results suggest that new pro-resolving synthetic mediators can represent an attractive treatment option for the enhancement of RoI, and that FPR2 can provide a perspective as a target in immune-related brain disorders.

Kir4.1 may represent a novel therapeutic target for diabetic retinopathy (Review)

As the major cause of irreversible loss of vision in adults, diabetic retinopathy (DR) is one of the most serious complications of diabetes. The imbalance of the retinal microenvironment and destruction of the blood-retinal barrier have a significant role in the progression of DR. Inward rectifying potassium channel 4.1 (Kir4.1) is located on Müller cells and is closely related to potassium homeostasis, water balance and glutamate clearance in the whole retina. The present review discusses the functions of Kir4.1 in regulating the retinal microenvironment and related biological mechanisms in DR. In the future, Kir4.1 may represent a novel alternative therapeutic target for DR through affecting the retinal microenvironment.

LncRNA NEAT1/miR-128-3p/AQP4 axis regulating spinal cord injury-induced neuropathic pain progression

BACKGROUND

Neuropathic pain (NP) is the comorbidity in spinal cord injury(SCI), which is the hardest to cure. Non-coding RNA dysregulations are related to the development of NP. NEAT1(nuclear paraspeckle assembly transcript 1) is a new type of lncRNA. This study explores the role and specific mechanism of NEAT1 in SCI-mediated NP.

METHODS

Firstly, the NEAT1 expression in SCI rats and the control group was detected with RT-PCR to analyze the relationship between NEAT13 and NP symptoms. Then, SCI rats were intrathecally injected with NEAT13 overexpressing and knocking down lentiviruses. Afterward, ELISA was utilized to assess the expression of IL-6, IL-1β and TNFα in rats. Subsequently, immunohistochemistry was adopted to verify the activation of microglial cells. After that, bioinformatics analysis was employed to further predict the downstream target genes of NEAT1, while RT-PCR and Western blot were conducted to determine the relative expression of miR-128-3p and aquaporin-4(AQP4). Meanwhile, a dual-luciferase reporter assay was performed to further study the targeting relationship between NEAT1 and miR-128-3p, and miR-128-3p and AQP4.

RESULTS

SCI rats showed distinctly higher NEAT1 expression compared with that of the control group. ELISA experiment confirmed that the over-expression of NEAT1 enhanced the expression of IL-6, IL-1β, and TNFα in SCI rats. Other related mechanism studies revealed that NEAT13 targeted and inhibited miR-128-3p as its competing endogenous RNA (ceRNA), and enhanced AQP4 expression, while miR-128-3p targeted AQP4 to regulate its expression.

SUMMARY

NEAT1 affects AQP4 signaling pathway to alleviate the spinal cord injury-induced NP via promoting miR-128-3p expression.

Astrocytes, HIV and the Glymphatic System: A Disease of Disrupted Waste Management?

The discovery of the glial-lymphatic or glymphatic fluid clearance pathway in the rodent brain led researchers to search for a parallel system in humans and to question the implications of this pathway in neurodegenerative diseases. Magnetic resonance imaging studies revealed that several features of the glymphatic system may be present in humans. In both rodents and humans, this pathway promotes the exchange of interstitial fluid (ISF) and cerebrospinal fluid (CSF) through the arterial perivascular spaces into the brain parenchyma. This process is facilitated in part by aquaporin-4 (AQP4) water channels located primarily on astrocytic end feet that abut cerebral endothelial cells of the blood brain barrier. Decreased expression or mislocalization of AQP4 from astrocytic end feet results in decreased interstitial flow, thereby, promoting accumulation of extracellular waste products like hyperphosphorylated Tau (pTau). Accumulation of pTau is a neuropathological hallmark in Alzheimer's disease (AD) and is accompanied by mislocalization of APQ4 from astrocyte end feet to the cell body. HIV infection shares many neuropathological characteristics with AD. Similar to AD, HIV infection of the CNS contributes to abnormal aging with altered AQP4 localization, accumulation of pTau and chronic neuroinflammation. Up to 30% of people with HIV (PWH) suffer from HIV-associated neurocognitive disorders (HAND), and changes in AQP4 may be clinically important as a contributor to cognitive disturbances. In this review, we provide an overview and discussion of the potential contributions of NeuroHIV to glymphatic system functions by focusing on astrocytes and AQP4. Although HAND encompasses a wide range of neurocognitive impairments and levels of neuroinflammation vary among and within PWH, the potential contribution of disruption in AQP4 may be clinically important in some cases. In this review we discuss implications for possible AQP4 disruption on NeuroHIV disease trajectory and how HIV may influence AQP4 function.