Isoflurane Postconditioning Upregulates Phosphorylated Connexin 43 in the Middle Cerebral Artery Occlusion Model and Is Probably Associated with the TGF-β1/Smad2/3 Signaling Pathway

Astrocytes Modulate a Specific Paraventricular Thalamus→Prefrontal Cortex Projection to Enhance Consciousness Recovery from Anesthesia

Current anesthetic theory is mostly based on neurons and/or neuronal circuits. A role for astrocytes also has been shown in promoting recovery from volatile anesthesia, while the exact modulatory mechanism and/or the molecular target in astrocytes is still unknown. In this study by animal models in male mice and electrophysiological recordings in vivo and in vitro, we found that activating astrocytes of the paraventricular thalamus (PVT) and/or knocking down PVT astrocytic Kir4.1 promoted the consciousness recovery from sevoflurane anesthesia. Single-cell RNA sequencing of the PVT reveals two distinct cellular subtypes of glutamatergic neurons: PVT GRM and PVT ChAT neurons. Patch-clamp recording results proved astrocytic Kir4.1-mediated modulation of sevoflurane on the PVT mainly worked on PVT ChAT neurons, which projected mainly to the mPFC. In summary, our findings support the novel conception that there is a specific PVT→prefrontal cortex projection involved in consciousness recovery from sevoflurane anesthesia, which is mediated by the inhibition of sevoflurane on PVT astrocytic Kir4.1 conductance.

Isoflurane Enhances Autophagy by Activating AMPK/ULK1, Inhibits NLRP3, and Reduces Cognitive Impairment After Cerebral Ischemia-Reperfusion Injury in Rats

Cerebral ischemic stroke (CIS) has become the second leading cause of death worldwide, which is largely related to cerebral ischemia reperfusion injury (CIRI). Surgical intervention is a reliable treatment for CIS, which predictably causes cerebral reperfusion. Therefore, the choice of anesthetic drugs has important clinical significance. Isoflurane (ISO), one of the most used anesthetics, attenuates cognitive impairment and has brain protective effects. However, the role of isoflurane in regulating autophagy and its regulatory mechanism on inflammation in CIRI are still unclear. The middle cerebral artery occlusion (MCAO) method was used to establish a rat model of CIRI. After 24 h of reperfusion, all rats were evaluated by mNSS scoring and dark avoidance experiment. Western blotting and immunofluorescence were used to examine the expression of key proteins. Compared with the sham group, the MCAO group showed increased neurobehavioral scores and decreased cognitive memory function (P < 0.05). As for the ISO-treated MCAO rats, the neurobehavioral score was significantly decreased, the expression of AMPK, ULK1, Beclin1, and LC3B was significantly increased, and the cognitive and memory functions were also significantly improved (P < 0.05). After inhibition of autophagy pathway or key protein AMPK in autophagy, neurobehavioral scores and protein expression of NLRP3, IL-1β, and IL-18 were significantly increased (P < 0.05). Isoflurane post-treatment may enhance autophagy by activating the AMPK/ULK1 signaling pathway and further inhibit the release of inflammatory factors from NLRP3 inflammasomes, thereby ameliorating neurological function and cognitive impairment and exerting a protective effect on the brain in CIRI rats.

Smad7 in the hippocampus contributes to memory impairment in aged mice after anesthesia and surgery

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common neurological complication following anesthesia and surgery. Increasing evidence has demonstrated that neuroinflammation caused by systemic inflammatory responses during the perioperative period is a key factor in the occurrence of POCD. In addition, SMAD family member 7 (Smad7) has been confirmed to play vital roles in the pathogenesis and treatment of inflammatory diseases, such as inflammatory bowel disease. However, whether Smad7 participates in the regulatory process of neuroinflammation and apoptosis in the development of POCD is still unknown.

METHODS

In this study, a POCD mouse model was constructed by unilateral nephrectomy under anesthesia, and cognitive function was assessed using the fear conditioning test and open field test. The expression of Smad7 at the mRNA and protein levels in the hippocampus 3 days after surgery was examined by qRT-PCR, western blot and immunofluorescence assays. Furthermore, to identify whether the elevation of Smad7 in the hippocampus after unilateral nephrectomy contributes to cognitive impairment, the expression of Smad7 in the hippocampal CA1 region was downregulated by crossing Smad7fl/fl conditional mutant mice and CaMKIIα-Cre line T29-1 transgenic mice or stereotaxic injection of shRNA-Smad7. Inflammation and apoptosis in the hippocampus were assessed by measuring the mRNA levels of typical inflammatory cytokines, including TNF-α, IL-1β, IL-6, CCL2, CXCL1, and CXCL2, and the protein levels of apoptotic proteins, including Bax and Bcl2. In addition, apoptosis in the hippocampus postoperation was investigated by a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining assay. Finally, western blotting was used to explore how Smad7 mediates inflammation and apoptosis postoperation.

RESULTS

The results unequivocally revealed that elevated Smad7 in the hippocampal CA1 region significantly inhibited TGF-β signal transduction by blocking Smad2/3 phosphorylation, which enhanced neuroinflammation and apoptosis in the hippocampus and further led to learning and memory impairment after surgery.

CONCLUSIONS

Our results revealed that Smad7 contributes to cognitive impairment after surgery by enhancing neuroinflammation and apoptosis in the hippocampus and might serve as a promising therapeutic target for the treatment of memory impairment after anesthesia surgery.

Isoflurane Postconditioning Alleviates Ischemic Neuronal Injury Via MiR-384-5p Regulated Autophagy

The purpose of the study was to investigate the effect of isoflurane postconditioning on neuron injury in MCAO (middle cerebral artery occlusion) rats and its molecular mechanism of affecting autophagy through miR-384-5p/ATG5 (autophagy-related protein 5). HT22 cells (mouse hippocampal neuronal cell line) were exposed to 1.5% isoflurane for 30 min after OGD/R (oxygen-glucose deprivation/reoxygenation). Flow cytometry and CCK-8 kit were used to analyze changes in apoptosis and cell viability. The level of miR-384-5p was detected by qRT-PCR. Targetscan database prediction combined with dual luciferase reporter gene assay confirmed ATG5 as a target molecule downstream of miR-384-5p. In addition, western blot results confirmed that isoflurane postconditioning regulated miR-384-5p/ATG5 and significantly inhibited the expression of apoptosis-related proteins. Meanwhile, immunofluorescence staining for LC3II positivity combined with western blot results revealed that isoflurane postconditioning significantly inhibited autophagy. In vivo, MCAO induced neuronal injury for 90 min, followed by 24-h reperfusion. Isoflurane postconditioning (Iso) group underwent 1.5% isoflurane postconditioning for 60 min after reperfusion. Neurological scoring and TTC staining were used to evaluate the protective effect of isoflurane post-treatment on neurological injury, respectively. TUNEL staining and western blot results confirmed that isoflurane post-conditioning could regulate miR-384-5p and inhibit apoptosis. Immunofluorescence staining and western blot results confirmed that isoflurane post-conditioning inhibited autophagy in MCAO rats. Based on the above results, we speculated that the molecular mechanism of isoflurane post-conditioning to alleviate ischemic neuronal injury may be related to the regulation of miR-384-5p/ATG5-mediated autophagy.

Effects of Long Noncoding RNA H19 on Isoflurane-Induced Cognitive Dysregulation by Promoting Neuroinflammation

INTRODUCTION

Isoflurane (ISO) may cause neuronal apoptosis and synaptic disorder during development, and damage long-term learning and memory function. This observation aimed to study the function of H19 in vitro and in vivo tests and the further mechanism was identified.

METHODS

ISO cell models and rat models were established and reactive oxygen species (ROS) identified. The viability and apoptosis of HT22 cells were detected by the MTT and flow cytometer. Morris water maze test was conducted to analyze the neurotoxicity of ISO on spatial learning and memory ability. Quantitative PCR was the method to verify the expression of H19. The concentration of inflammatory indicators was identified by enzyme-linked immunosorbent assay.

RESULTS

1.5% and 2% ISO led to the neurotoxicity of HT22 cells and increased expression of H19. Silenced H19 meliorated these adverse impacts of ISO. Interference of H19 exerted neuroprotective roles by repressing modified neurological severity score, inhibiting escape latency, elevating distance and time of target area, and controlling ROS and inflammation. MiR-17-5p might be a promising competing endogenous RNA of H19. The expression of miR-17-5p was reduced in the ISO group and reversed by the absence of H19.

CONCLUSION

Our results of in vitro and in vivo assay indicated that the absence of HT22 is a neuroprotective regulator of cognition and inflammation by accumulating miR-17-5p.

Isoflurane post-conditioning attenuates cerebral ischemia/reperfusion injury by reducing apoptotic through activating the BMP7/SMAD signaling pathway in rats

The expressions of different temporal patterns of bone morphogenetic proteins (BMPs) have changed after ischemic strokes, and ischemic preconditioning-induced neuroprotection was attenuated when BMP7 was inhibited. In the previous study, the neuroprotection of isoflurane postconditioning (ISPOC) against cerebral ischemia-reperfusion (I/R) injury has been addressed, with particular relevance to the role of BMP7. Consequently, in the present study, we continued to explore the mechanisms involved in the BMP7 signal mediated the neuroprotection of ISPOC. A rat model of the middle cerebral artery occlusion was used in this study. Rats were administered 1.5 % isoflurane, 60 min after 90 min of ischemia, followed by a 24 h reperfusion period. The 1.5 % ISPOC significantly ameliorated the cerebral infarct volumes, neurologic deficit scores, damaged neurons, and apoptotic neurons. Moreover, ISPOC unregulated the expressions of BMP7, p-Smad1/5/9, and p-p38. Whereas, the neuroprotective effect was weakened by LDN-193189 and SB203580, respectively, a BMP7/Smad1/5/9 and p38MAPK signaling pathway inhibitor. Furthermore, LDN-193189 downregulated the expression of p-p38. The present results of this study indicated that the neuroprotection of 1.5 % isoflurane postconditioning to cerebral ischemia-reperfusion injury is related to the activating of BMP7/Smad1/5/9 and p38MAPK signal pathway.

MiR-21-5p but not miR-1-3p expression is modulated by preconditioning in a rat model of myocardial infarction

Isoflurane (Iso) preconditioning (PC) is known to be cardioprotective against ischemia/reperfusion (I/R) injury. It was previously shown that microRNA-21-5p (miR-21-5p) is regulated by Iso-PC. It is unclear, if expression of cardiac enriched miR-1-3p is also affected by Iso-PC, and associated with activation of HIF1α (hypoxia-inducible factor 1-alpha).  Male Wistar rats (n = 6–8) were randomly assigned to treatment with or without 1 MAC Iso for 30 min, followed by 25 min of regional myocardial ischemia, with 120 min reperfusion. At the end of reperfusion, myocardial expression of miR-1-3p, miR-21-5p and mRNAs of two HIF-1α-dependent genes, VEGF (vascular endothelial growth factor) and HO-1 (heme oxygenase-1), were determined by quantitative PCR. Protein expression of a miR-21 target gene, PDCD4 (programmed cell death protein 4), was assessed by western blot analysis. Infarct sizes were analyzed with triphenyltetrazoliumchloride staining. MiR-21-5p expression was increased by Iso, whereas expression of miR-1-3p was not altered. The expression of VEGF but not HO-1 was induced by Iso. Iso-PC reduced infarct sizes compared to untreated controls. No regulation of miRNA and mRNA expression was detected after I/R. PDCD4 protein expression was not affected after Iso exposure. Expression of miR-21-5p, in contrast to miR-1-3p, is altered during this early time point of Iso-PC. HIF1α signaling seems to be involved in miR-21-5p regulation.