Background Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with high incidence in both advanced and developing countries. Children surviving from HIE often have severe long-term sequela including cerebral palsy, epilepsy, and cognitive disabilities. The severity of HIE in infants is tightly associated with increased IL-1β expression and astrocyte activation which was regulated by transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel in the TRP family. Methods Neonatal hypoxic ischemia (HI) and oxygen-glucose deprivation (OGD) were used to simulate HIE in vivo and in vitro. Primarily cultured astrocytes were used for investigating the expression of glial fibrillary acidic protein (GFAP), IL-1β, Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and activation of the nucleotide-binding, oligomerization domain (NOD)-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome by using Western blot, q-PCR, and immunofluorescence. Brain atrophy, infarct size, and neurobehavioral disorders were evaluated by Nissl staining, 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining and neurobehavioral tests (geotaxis reflex, cliff aversion reaction, and grip test) individually. Results Astrocytes were overactivated after neonatal HI and OGD challenge. The number of activated astrocytes, the expression level of IL-1β, brain atrophy, and shrinking infarct size were all downregulated in TRPV1 KO mice. TRPV1 deficiency in astrocytes attenuated the expression of GFAP and IL-1β by reducing phosphorylation of JAK2 and STAT3. Meanwhile, IL-1β release was significantly reduced in TRPV1 deficiency astrocytes by inhibiting activation of NLRP3 inflammasome. Additionally, neonatal HI-induced neurobehavioral disorders were significantly improved in the TRPV1 KO mice. Conclusions TRPV1 promotes activation of astrocytes and release of astrocyte-derived IL-1β mainly via JAK2-STAT3 signaling and activation of the NLRP3 inflammasome. Our findings provide mechanistic insights into TRPV1-mediated brain damage and neurobehavioral disorders caused by neonatal HI and potentially identify astrocytic TRPV1 as a novel therapeutic target for treating HIE in the subacute stages (24 h). Electronic supplementary material The online version of this article (10.1186/s12974-019-1487-3) contains supplementary material, which is available to authorized users.

BackgroundNeonatal hypoxic-ischemic brain damage (HIBD), a leading cause of neonatal mortality, has intractable sequela such as epilepsy that seriously affected the life quality of HIBD survivors. We have previously shown that ion channel dysfunction in the central nervous system played an important role in the process of HIBD-induced epilepsy. Therefore, we continued to validate the underlying mechanisms of TRPV1 as a potential target for epilepsy.MethodsNeonatal hypoxic ischemia and oxygen-glucose deprivation (OGD) were used to simulate HIBD in vivo and in vitro. Primarily cultured astrocytes were used to assess the expression of TRPV1, glial fibrillary acidic protein (GFAP), cytoskeletal rearrangement, and inflammatory cytokines by using Western blot, q-PCR, and immunofluorescence. Furthermore, brain electrical activity in freely moving mice was recorded by electroencephalography (EEG). TRPV1 current and neuronal excitability were detected by whole-cell patch clamp.ResultsAstrocytic TRPV1 translocated to the membrane after OGD. Mechanistically, astrocytic TRPV1 activation increased the inflow of Ca2+, which promoted G-actin polymerized to F-actin, thus promoted astrocyte migration after OGD. Moreover, astrocytic TRPV1 deficiency decreased the production and release of pro-inflammatory cytokines (TNF, IL-6, IL-1β, and iNOS) after OGD. It could also dramatically attenuate neuronal excitability after OGD and brain electrical activity in HIBD mice. Behavioral testing for seizures after HIBD revealed that TRPV1 knockout mice demonstrated prolonged onset latency, shortened duration, and decreased seizure severity when compared with wild-type mice.ConclusionsCollectively, TRPV1 promoted astrocyte migration thus helped the infiltration of pro-inflammatory cytokines (TNF, IL-1β, IL-6, and iNOS) from astrocytes into the vicinity of neurons to promote epilepsy. Our study provides a strong rationale for astrocytic TRPV1 to be a therapeutic target for anti-epileptogenesis after HIBD.

Epilepsy is a common brain disorder, repeated seizures of epilepsy may lead to a series of brain pathological changes such as neuronal or glial damage. However, whether circular RNAs are involved in neuronal injury during epilepsy is not fully understood.Here, we screened circIgf1r in the status epilepticus model through circRNA sequencing, and found that it was upregulated after the status epilepticus model through QPCR analysis. Astrocytes polarizing toward neurotoxic A1 phenotype and neurons loss were observed after status epilepticus. Through injecting circIgf1r siRNA into the lateral ventricle, it was found that knocking down circIgf1r in vivo would induce the polarization of astrocytes to phenotype A2 and reduce neuronal loss. The results in vitro further confirmed that inhibiting the expression of circIgf1r in astrocytes could protect neurons by converting reactive astrocytes from A1 to the protective A2. In addition, knocking down circIgf1r in astrocytes could functionally promote astrocyte autophagy and relieve the destruction of 4-AP-induced autophagy flux. In terms of mechanism, circIgf1r promoted the polarization of astrocytes to phenotype A1 by inhibiting autophagy. Taken together, our results reveal circIgf1r may serve as a potential target for the prevention and treatment of neuron damage after epilepsy.

Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with severe long-term sequelae such as cerebral palsy, epilepsy and cognitive disabilities. Na + -K + -2Cl − cotransporters 1 (NKCC1) is dramatically upregulated after hypoxia-ischemia (HI), which aggravates brain edema and brain damage. Clinically, an NKCC1-specific inhibitor, bumetanide, is used to treat diseases related to aberrant NKCC1 expression, but the underlying mechanism of aberrant NKCC1 expression has rarely been studied in HIE. In this study, the cooperative effect of hypoxia-inducible factor-1α (HIF-1α) and nuclear factor of activated T cells 5 (NFAT5) on NKCC1 expression was explored in hippocampal neurons under hypoxic conditions. HI increased HIF-1α nuclear localization and transcriptional activity, and pharmacological inhibition of the HIF-1α transcription activity or mutation of hypoxia responsive element (HRE) motifs recovered the hypoxiainduced aberrant expression and promoter activity of NKCC1. In contrast, oxygenglucose deprivation (OGD)-induced downregulation of NFAT5 expression was reversed by treating with hypertonic saline, which ameliorated aberrant NKCC1 expression. More importantly, knocking down NFAT5 or mutation of the tonicity enhancer element (TonE) stimulated NKCC1 expression and promoter activity under normal physiological conditions. The positive regulation of NKCC1 by HIF-1α and the negative regulation of NKCC1 by NFAT5 may serve to maintain NKCC1 expression levels, which may shed light on the transcription regulation of NKCC1 in hippocampal neurons after hypoxia.

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