Cyclin-dependent kinase 5/Collapsin response mediator protein 2 pathway may mediate sevoflurane-induced dendritic development abnormalities in rat cortical neurons

Unraveling the role and mechanism of mitochondria in postoperative cognitive dysfunction: a narrative review

Postoperative cognitive dysfunction (POCD) is a frequent neurological complication encountered during the perioperative period with unclear mechanisms and no effective treatments. Recent research into the pathogenesis of POCD has primarily focused on neuroinflammation, oxidative stress, changes in neural synaptic plasticity and neurotransmitter imbalances. Given the high-energy metabolism of neurons and their critical dependency on mitochondria, mitochondrial dysfunction directly affects neuronal function. Additionally, as the primary organelles generating reactive oxygen species, mitochondria are closely linked to the pathological processes of neuroinflammation. Surgery and anesthesia can induce mitochondrial dysfunction, increase mitochondrial oxidative stress, and disrupt mitochondrial quality-control mechanisms via various pathways, hence serving as key initiators of the POCD pathological process. We conducted a review on the role and potential mechanisms of mitochondria in postoperative cognitive dysfunction by consulting relevant literature from the PubMed and EMBASE databases spanning the past 25 years. Our findings indicate that surgery and anesthesia can inhibit mitochondrial respiration, thereby reducing ATP production, decreasing mitochondrial membrane potential, promoting mitochondrial fission, inducing mitochondrial calcium buffering abnormalities and iron accumulation, inhibiting mitophagy, and increasing mitochondrial oxidative stress. Mitochondrial dysfunction and damage can ultimately lead to impaired neuronal function, abnormal synaptic transmission, impaired synthesis and release of neurotransmitters, and even neuronal death, resulting in cognitive dysfunction. Targeted mitochondrial therapies have shown positive outcomes, holding promise as a novel treatment for POCD.

A Scoping Review of the Mechanisms Underlying Developmental Anesthetic Neurotoxicity

Although anesthesia makes painful or uncomfortable diagnostic and interventional health care procedures tolerable, it may also disrupt key cellular processes in neurons and glia, harm the developing brain, and thereby impair cognition and behavior in children. Many years of studies using in vitro, animal behavioral, retrospective database studies in humans, and several prospective clinical trials in humans have been invaluable in discerning the potential toxicity of anesthetics. The objective of this scoping review was to synthetize the evidence from preclinical studies for various mechanisms of toxicity across diverse experimental designs and relate their findings to those of recent clinical trials in real-world settings.

LncRNA SNHG3 Promotes Sevoflurane-Induced Neuronal Injury by Activating NLRP3 via NEK7

BACKGROUND

Early exposure to sevoflurane may cause brain tissue degeneration; however, the mechanism involved in this process has not been explored. In this study, we investigated the role of long non-coding RNA small nucleolar RNA host gene 3 (lncRNA SNHG3) in sevoflurane-induced neuronal injury.

METHODS

The injury models of HT22 and primary cultures of neurons were constructed using sevoflurane treatment. The WST-8 reduction was detected by CCK-8 assay, the level of inflammatory factors was detected by enzyme-linked immunosorbent assay (ELISA), and cell pyroptosis was detected by flow cytometry. The expression of genes and proteins was detected by qRT-PCR and Western blot, respectively. The level of β-tubulin III in primary cultures of hippocampal neurons was analyzed by immunofluorescence. The relationship among SNHG3, PTBP1 and NEK7 was confirmed by RIP assay.

RESULTS

The expression of SNHG3 and NEK7 were enhanced in sevoflurane-treated HT22 cells. Sevoflurane inhibited the WST-8 reduction in a concentration-dependent manner, promoted the pyroptosis, and increased pyroptosis-related protein expression. SNHG3 knockdown significantly inhibited sevoflurane-induced pyroptosis and inflammatory injury in HT22 cells and primary cultures of neurons. Furthermore, SNHG3 regulated NEK7 expression by binding to PTBP1. NEK7 knockdown reversed the decrease in WST-8 reduction, inhibited pyroptosis, and decreased the release of inflammatory factors and pyroptosis-related protein expression by inactivation of NLRP3 signaling in sevoflurane-induced HT22 cells. Moreover, NEK7 overexpression attenuated the effect of SNHG3 knockdown on neuronal pyroptosis and inflammation injury.

CONCLUSION

Downregulation of SNHG3 attenuates sevoflurane-induced neuronal inflammation and pyroptosis by mediating the NEK7/NLRP3 axis, suggesting that SNHG3 could be a potential target gene for neuronal injury.

Maternal sevoflurane exposure induces neurotoxicity in offspring rats via the CB1R/CDK5/p-tau pathway

Sevoflurane is widely used for maternal anesthesia during pregnancy. Sevoflurane exposure of rats at mid-gestation can cause abnormal development of the central nervous system in their offspring. Sevoflurane is known to increase the expression of cannabinoid 1 receptor (CB1R) in the hippocampus. However, the effect of cannabinoid 1 receptor on fetal and offspring rats after maternal anesthesia is still unclear. At gestational day 14, pregnant rats were subjected to 2-h exposure to 3.5% sevoflurane or air. Rats underwent intraperitoneal injection with saline or rimonabant (1 mg/kg) 30 min prior to sevoflurane or air exposure. cannabinoid 1 receptor, cyclin-dependent kinase 5 (CDK5), p35, p25, tau, and p-tau expression in fetal brains was measured at 6, 12, and 24 h post-sevoflurane/air exposure. Neurobehavioral and Morris water maze tests were performed postnatal days 3-33. The expression of cannabinoid 1 receptor/cyclin-dependent kinase 5/p-tau and histopathological staining of brain tissues in offspring rats was observed. We found that a single exposure to sevoflurane upregulated the activity of cyclin-dependent kinase 5 and the level of p-tau via cannabinoid 1 receptor. This was accompanied by the diminished number of neurons and dendritic spines in hippocampal CA1 regions. Finally, these effects induced lower scores and platform crossing times in behavioral tests. The present study suggests that a single exposure to 3.5% sevoflurane of rats at mid-gestation impairs neurobehavioral abilities and cognitive memory in offspring. cannabinoid 1 receptor is a possible target for the amelioration of postnatal neurobehavioral ability and cognitive memory impairments induced by maternal anesthesia.

Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases

It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.

Mechanistic insight into sevoflurane-associated developmental neurotoxicity

With the development of technology, more infants receive general anesthesia for surgery, other interventions, or clinical examination at an early stage after birth. However, whether general anesthetics can affect the function and structure of the developing infant brain remains an important, complex, and controversial issue. Sevoflurane is the most-used anesthetic in infants, but this drug is potentially neurotoxic. Short or single exposure to sevoflurane has a weak effect on cognitive function, while long or repeated exposure to general anesthetics may cause cognitive dysfunction. This review focuses on the mechanisms by which sevoflurane exposure during development may induce long-lasting undesirable effects on the brain. We review neural cell death, neural cell damage, impaired assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects as important mechanisms for sevoflurane-induced developmental neurotoxicity. More advanced technologies and methods should be applied to determine the underlying mechanism(s) and guide prevention and treatment of sevoflurane-induced neurotoxicity.

1. We discuss the mechanisms underlying sevoflurane-induced developmental neurotoxicity from five perspectives: neural cell death, neural cell damage, assembly and plasticity of neural circuits, tau phosphorylation, and neuroendocrine effects. 2. Tau phosphorylation, IL-6, and mitochondrial dysfunction could interact with each other to cause a nerve damage loop. 3. miRNAs and lncRNAs are associated with sevoflurane-induced neurotoxicity.

Inhibition of RhoA Activity Does Not Rescue Synaptic Development Abnormalities and Long-Term Cognitive Impairment After Sevoflurane Exposure

General anesthetics interfere with dendritic development and synaptogenesis, resulting in cognitive impairment in the developing animals. RhoA signal pathway plays important roles in dendritic development by regulating cytoskeleton protein such as tubulin and actin. However, it's not clear whether RhoA pathway is involved in inhaled general anesthetics sevoflurane-induced synaptic development abnormalities and long-term cognitive dysfunction. Rats at postnatal day 7 (PND7) were injected intraperitoneally with RhoA pathway inhibitor Y27632 or saline 20 min before exposed to 2.8% sevoflurane for 4 h. The apoptosis-related proteins and RhoA/CRMP2 pathway proteins in the hippocampus were measured 6 h after sevoflurane exposure. Cognitive functions were evaluated by the open field test on PND25 rats and contextual fear conditioning test on PND32-33 rats. The dendritic morphology and density of dendritic spines in the pyramidal neurons of hippocampus were determined by Golgi staining and the synaptic plasticity-related proteins were also measured on PND33 rats. Long term potentiation (LTP) from hippocampal slices was recorded on PND34-37 rats. Sevoflurane induced caspase-3 activation, decreased the ratio of Bcl-2/Bax and increased TUNEL-positive neurons in hippocampus of PND7 rats, which were attenuated by inhibition of RhoA. However, sevoflurane had no significant effects on activity of RhoA/CRMP2 pathway. Sevoflurane disturbed dendritic morphogenesis, reduced the number of dendritic spines, decreased proteins expression of PSD-95, drebrin and synaptophysin, inhibited LTP in hippocampal slices and impaired memory ability in the adolescent rats, while inhibition of RhoA activity did not rescue the changes above induced by sevoflurane. RhoA signal pathway did not participate in sevoflurane-induced dendritic and synaptic development abnormalities and cognitive dysfunction in developing rats.

Regulation of CRMP2 by Cdk5 and GSK-3β participates in sevoflurane-induced dendritic development abnormalities and cognitive dysfunction in developing rats

BACKGROUND

General anesthetics such as sevoflurane interfere with dendritic development and synaptogenesis, resulting in cognitive impairment. The collapsin response mediator protein2 (CRMP2) plays important roles in dendritic development and synaptic plasticity and its phosphorylation is regulated by cycline dependent kinase-5 (Cdk5) and glycogen synthase kinase-3β (GSK-3β). Here we investigated whether Cdk5/CRMP2 or GSK-3β/CRMP2 pathway is involved in sevoflurane-induced developmental neurotoxicity.

METHODS

Rats at postnatal day 7 (PND7) were i.p. injected with Cdk5 inhibitor roscovitine, GSK-3β inhibitor SB415286 or saline 20 min. before exposure to 2.8% sevoflurane for 4 h. Western-blotting was applied to measure the expression of Cdk5/CRMP2 and GSK-3β/CRMP2 pathway proteins in the hippocampus 6 h after the sevoflurane exposure. When rats grew to adolescence (from PND25), they were tested for open-field and contextual fear conditioning, and then long term potentiation (LTP) from hippocampal slices was recorded, and morphology of pyramidal neuron was examined by Golgi staining and synaptic plasticity-related proteins expression in hippocampus were measured by western-blotting. In another batch of experiment, siRNA-CRMP2 or vehicle control was injected into hippocampus on PND5.

RESULTS

Sevoflurane activated Cdk5/CRMP2 and GSK-3β/CRMP2 pathways in the hippocampus of neonatal rats, reduced dendritic length, branches and the density of dendritic spine in pyramidal neurons. It also reduced the expressions of PSD-95, drebrin and synaptophysin in hippocampus, impaired memory ability of rats and inhibited LTP in hippocampal slices. All the impairment effects by sevoflurane were attenuated by pretreatment with inhibitor of Cdk5 or GSK-3β. Furthermore, rat transfected with siRNA-CRMP2 eliminated the neuroprotective effects of Cdk5 or GSK-3β blocker in neurobehavioral and LTP tests.

CONCLUSION

Cdk5/CRMP2 and GSK-3β/CRMP2 pathways participate in sevoflurane-induced dendritic development abnormalities and cognitive dysfunction in developing rats.

Sevoflurane increases intracellular calcium to induce mitochondrial injury and neuroapoptosis

Sevoflurane is commonly used in clinical anesthesia. However, some reports indicated that Sevoflurane could induce mitochondrial injury and neuroapoptosis. Although the mechanism remains unclear, evidence points to the increase of intracellular calcium after administration of Sevoflurane. Herein, we sought whether the increment of intracellular Ca2+ caused by Sevoflurane administration could induce mitochondrial injury and apoptosis in primary neurons of the hippocampus. Fluo-4-acetoxymethyl ester Ca2+ probe was used for measuring intracellular Ca2+ concentrations. LDH assay, CCK-8 assay, and Western blotting were performed to confirm Sevoflurane-induced neuroapoptosis. ROS, mPTP, and ATP production were assayed to reveal mitochondrial injury. Our results indicated that Sevoflurane increased intracellular Ca2+ and neuronal death. Sevoflurane also elevated ROS and the opening of mPTP, and decreased ATP production in neurons. The expression of cytochrome c, cleaved caspase-9, cleaved caspase-3, and the ratio of Bax/Bcl-2 were also increased. By using calcium channel blocker Nimodipine, the increase of intracellular Ca2+ was attenuated, and the death rate of neurons, the ROS and opening of mPTP, decreased ATP production, the expressions of cytochrome c, cleaved caspase-9, cleaved caspase-3 and the ratio of Bax/Bcl-2 were alleviated. Our study suggested that Sevoflurane could increase intracellular Ca2+ to induce mitochondrial injury and mitochondria-mediated neuroapoptosis in neurons.

Downregulation of hippocampal SIRT6 activates AKT/CRMP2 signaling and ameliorates chronic stress-induced depression-like behavior in mice

Sirtuin 6 (SIRT6) has been reported to play a key role in cognitive function and mood regulation, yet its role in mood disorders is not completely understood. Here, we confirmed that knockdown of hippocampal SIRT6 alleviated depression-like behaviors induced by chronic unpredictable stress (CUS) in mice. Our in vitro data showed that SIRT6 negatively regulated protein kinase B (AKT) signaling by deacetylating histone 3 at Lys9 and Lys56. Knockdown of SIRT6 significantly increased AKT phosphorylation activity, while decreased collapsin response mediator protein 2 (CRMP2) phosphorylation activity. Furthermore, pharmacologic inhibition of SIRT6 by ferulic acid (FA) (40 or 80 mg· kg^-1 per day, i.g.) could activate AKT/CRMP2 pathway in vitro, which has been proved to exert an antidepressant-like effect on CUS-induced depressive models. In conclusion, our study suggested that hippocampal SIRT6 contributes to the performance of depression-like behaviors by suppressing AKT/CRMP2 signaling, and FA ameliorates CUS-induced depression-like behaviors in mice as a potential pharmacologic inhibitor of SIRT6.

Sevoflurane induces cognitive impairment in young mice via autophagy

Background

Anesthesia may induce neurotoxicity and neurocognitive impairment in young mice. However, the underlying mechanism remains largely to be determined. Meanwhile, autophagy is involved in brain development and contributes to neurodegenerative diseases. We, therefore, set out to determine the effects of sevoflurane on autophagy in the hippocampus of young mice and on cognitive function in the mice.

Methods

Six day-old mice received 3% sevoflurane, for two hours daily, on postnatal days (P) 6, 7 and 8. We then decapitated the mice and harvested the hippocampus of the young mice at P8. The level of LC3, the ratio of LC3-II to LC3-I, and SQSTM1/p62 level associated with the autophagy in the hippocampus of the mice were assessed by using Western blotting. We used different groups of mice for behavioral testing via the Morris Water Maze from P31 to P37.

Results

The anesthetic sevoflurane increased the level of LC3-II and ratio of LC3-II/LC3-I, decreased the p62 level in the hippocampus of the young mice, and induced cognitive impairment in the mice. 3-Methyladenine, the inhibitor of autophagy, attenuated the activation of autophagy and ameliorated the cognitive impairment induced by sevoflurane in the young mice.

Conclusion

These data showed that sevoflurane anesthesia might induce cognitive impairment in the young mice via activation of autophagy in the hippocampus of the young mice. These findings from the proof of concept studies have established a system and suggest the role of autophagy in anesthesia neurotoxicity and cognitive impairment in the young mice, pending further investigation.

Dexmedetomidine Ameliorates the Neurotoxicity of Sevoflurane on the Immature Brain Through the BMP/SMAD Signaling Pathway

Numerous studies have demonstrated that general anesthetics might damage the nervous system, thus, the effect of general anesthetics on the developing brain has attracted much attention. Dexmedetomidine (Dex) exhibits a certain neuroprotective effect, but the mechanism is obscure. In our study, pregnant rats on gestational day 20 (G20) were exposed to 3% sevoflurane for 2 h or 4 h, and the neuronal apoptosis in hippocampal CA1 region of the offspring rats was detected by quantification of TUNEL positive cells and cleaved-caspase3 (cl-caspase3). Different doses of Dex were intraperitoneally injected before sevoflurane anesthesia; then, the expression of apoptotic-related proteins including BCL-2, BAX and cl-caspase3 as well as amyloid precursor protein (APP, a marker of axonal injury), p-CRMP-2 and CRMP-2 were measured at postnatal days 0, 1and 3 (P0, P1, and P3, respectively). As an antagonist of the bone morphgenetic proteins (BMP) receptor, DMH1 was co-administered with sevoflurane plus Dex to investigate whether BMP/SMAD is associated with the neuroprotective effects of Dex. The results showed that prenatal sevoflurane anesthesia for 4 h activated apoptosis transiently, as manifested by the caspase3 activity peaked on P1 and disappeared on P3. In addition, the expressions of APP and p-CRMP-2/CRMP-2 in postnatal rat hippocampus were significantly increased, which revealed that prenatal sevoflurane anesthesia caused axonal injury of offspring. The long-term learning and memory ability of offspring rats was also impaired after prenatal sevoflurane anesthesia. These damaging effects of sevoflurane could be mitigated by Dex and DMH1 reversed the neuroprotective effect of Dex. Our results indicated that prenatal exposure to 3% sevoflurane for 4 h increased apoptosis and axonal injury, even caused long-term learning and memory dysfunction in the offspring rats. Dex dose-dependently reduced sevoflurane- anesthesia-induced the neurotoxicity by activating the BMP/SMAD signaling pathway.