Pharmacological inhibition of PTEN attenuates cognitive deficits caused by neonatal repeated exposures to isoflurane via inhibition of NR2B-mediated tau phosphorylation in rats

Luteolin protects mouse hippocampal neuronal cells against isoflurane-induced neurotoxicity through miR-214/PTEN/Akt pathway

Isoflurane is one of the most commonly used anaesthetic agents in surgery procedures. During the past decades, isoflurane has been found to cause impairment in neurological capabilities in new-borns and elderly patients. Luteolin is a flavonoid that has been documented to possess a neuroprotective effect. Here we investigated the putative neuroprotective effects of luteolin on isoflurane-induced neurotoxicity in mouse hippocampal neuronal HT22 cells and explored the potential mechanisms. We demonstrated that luteolin improved mitochondrial dysfunction and reduced oxidative stress and apoptosis in isoflurane-treated HT22 cells, and thus inhibiting the isoflurane-induced neuronal injury. Further investigations showed that isoflurane exposure caused miR-214 downregulation, which could be mitigated by treatment with luteolin. Knockdown of miR-214 attenuated the neuroprotection of luteolin on isoflurane-induced neuronal injury. More importantly, luteolin inhibited isoflurane-caused regulation of the PTEN/Akt pathway, while miR-214 knockdown altered the regulatory effect of luteolin on the PTEN/Akt pathway. Furthermore, the effects of miR-214 knockdown on the neuroprotection of luteolin could also be prevented by knockdown of PTEN, implying that the neuroprotective effect of luteolin was mediated by miR-214/PTEN/Akt signaling pathway. These findings provided evidence for the potential application of luteolin in preventing isoflurane-induced neurotoxicity.

A decrease in NR2B expression mediated by DNA hypermethylation induces perioperative neurocognitive disorder in aged mice

AIMS

This study was designed to investigate the role of NR2B and the contribution of DNA methylation to NR2B expression in the pathogenesis of PND.

METHODS

Eighteen-month-old C57BL/6J mice were subjected to experimental laparotomy under 1.4% isoflurane anesthesia. Hippocampus-dependent learning and memory were evaluated by using the Barnes maze and contextual fear conditioning tests. The protein and mRNA expression levels of NR2B were evaluated by western blotting and qRT-PCR respectively, and the methylation of the NR2B gene was examined by using targeted bisulfite sequencing. Long-term synaptic plasticity (LTP) was measured by electrophysiology.

RESULTS

Mice that underwent laparotomy exhibited hippocampus-dependent cognitive deficits accompanied by decreased NR2B expressions and LTP deficiency. The overexpression of NR2B in the dorsal hippocampus could improve learning and memory in mice subjected to laparotomy. In particular, the decreased NR2B expressions induced by laparotomy was attributed to the NR2B gene hypermethylation. Preoperative administration of S-adenosylmethionine (SAM) could hypomethylate the NR2B gene, upregulate NR2B expression and improve LTP, exerting a dose-dependent therapeutic effect against PND. Moreover, inhibiting NR2B abrogated the benefits of SAM pretreatment.

CONCLUSIONS

Laparotomy cause hippocampus-dependent cognitive decline by hypermethylating the NR2B gene, allowing us to understand the pathogenesis of PND in an epigenetic landscape.

Implications of Phosphoinositide 3-Kinase-Akt (PI3K-Akt) Pathway in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the foremost type of dementia that afflicts considerable morbidity and mortality in aged population. Several transcription molecules, pathways, and molecular mechanisms such as oxidative stress, inflammation, autophagy, and immune system interact in a multifaceted way that disrupt physiological processes (cell growth, differentiation, survival, lipid and energy metabolism, endocytosis) leading to apoptosis, tauopathy, β-amyloidopathy, neuron, and synapse loss, which play an important role in AD pathophysiology. Despite of stupendous advancements in pathogenic mechanisms, treatment of AD is still a nightmare in the field of medicine. There is compelling urgency to find not only symptomatic but effective disease-modifying therapies. Recently, phosphoinositide 3-kinase (PI3K) and Akt are identified as a pathway triggered by diverse stimuli, including insulin, growth factors, cytokines, and cellular stress, that link amyloid-β, neurofibrillary tangles, and brain atrophy. The present review aims to explore and analyze the role of PI3K-Akt pathway in AD and agents which may modulate Akt and have therapeutic prospects in AD. The literature was researched using keywords "PI3K-Akt" and "Alzheimer's disease" from PubMed, Web of Science, Bentham, Science Direct, Springer Nature, Scopus, and Google Scholar databases including books. Articles published from 1992 to 2021 were prioritized and analyzed for their strengths and limitations, and most appropriate ones were selected for the purpose of review. PI3K-Akt pathway regulates various biological processes such as cell proliferation, motility, growth, survival, and metabolic functions, and inhibits many neurotoxic mechanisms. Furthermore, experimental data indicate that PI3K-Akt signaling might be an important therapeutic target in treatment of AD.

Phosphatase and Tensin Homolog Deleted on Chromosome Ten Knockdown Attenuates Cognitive Deficits by Inhibiting Neuroinflammation in a Mouse Model of Perioperative Neurocognitive Disorder

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a crucial regulator of neuronal development, neuronal survival, axonal regeneration, and synaptic plasticity. In this study we examined the potential role of PTEN in cognitive function in a mouse model of perioperative neurocognitive disorder (PND). Adult male C57BL/6J mice received intracerebroventricular injections of small interfering RNA (siRNA) against PTEN or control siRNA 3 days prior to exploratory laparotomy (n = 8 per group). A group of healthy mice not undergoing surgery included as additional control. Barnes maze and fear conditioning tests were conducted 7 days after surgery. Mice were then sacrificed to examine the expression of PTEN, AMP-activated protein kinase (AMPK), ionized calcium binding adaptor molecule (Iba)-1, B-cell lymphoma (Bcl)-2, Bcl2-associated X protein (Bax), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α in the hippocampus. The microglial activation was examined by immunohistochemistry using Iba-1 as a microglia maker. Nissl and terminal transferase deoxyuridine triphosphate nick-end labeling (TUNEL) staining were used to measure cell death and apoptosis. In comparison to the healthy controls, surgically treated mice had longer latency to identify the target box in both training and testing sessions in the Barnes maze test and shorter freezing time in the fear conditioning test. Surgically treated mice had increased expression of PTEN, AMPK, Bax, IL-1β, and TNF-α, as well as increasing number of activated microglia and apoptosis neurons in the hippocampus. PTEN knockdown significantly attenuated the behavioral deficits in Barnes maze and fear conditioning tests, as well as over-expression of PTEN, AMPK, Bax, IL-1β, and TNF-α induced by surgery. PTEN knockdown could attenuate cognitive deficits induced by trauma, likely through inhibiting the activation of microglia.

Progranulin in neurodegenerative dementia

Long-term or severe lack of protective factors is important in the pathogenesis of neurodegenerative dementia. Progranulin (PGRN), a neurotrophic factor expressed mainly in neurons and microglia, has various neuroprotective effects such as anti-inflammatory effects, promoting neuron survival and neurite growth, and participating in normal lysosomal function. Mutations in the PGRN gene (GRN) have been found in several neurodegenerative dementias, including frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). Herein, PGRN deficiency and PGRN hydrolytic products (GRNs) in the pathological changes related to dementia, including aggregation of tau and TAR DNA-binding protein 43 (TDP-43), amyloid-β (Aβ) overproduction, neuroinflammation, lysosomal dysfunction, neuronal death, and synaptic deficit have been summarized. Furthermore, as some therapeutic strategies targeting PGRN have been developed in various models, we highlighted PGRN as a potential anti-neurodegeneration target in dementia.

Pten is a key intrinsic factor regulating raphe 5-HT neuronal plasticity and depressive behaviors in mice

Serotonin (5-HT)-based antidepressants, selective serotonin reuptake inhibitors (SSRIs) aim to enhance serotonergic activity by blocking its reuptake. We propose PTEN as a target for an alternative approach for regulating 5-HT neuron activity in the brain and depressive behaviors. We show that PTEN is elevated in central 5-HT neurons in the raphe nucleus by chronic stress in mice, and selective deletion of Pten in the 5-HT neurons induces its structural plasticity shown by increases of dendritic branching and density of PSD95-positive puncta in the dendrites. 5-HT levels are elevated and electrical stimulation of raphe neurons evokes more 5-HT release in the brain of condition knockout (cKO) mice with Pten-deficient 5-HT neurons. In addition, the 5-HT neurons remain normal electrophysiological properties but have increased excitatory synaptic inputs. Single-cell RNA sequencing revealed gene transcript alterations that may underlay morphological and functional changes in Pten-deficient 5-HT neurons. Finally, Pten cKO mice and wild-type mice treated with systemic application of PTEN inhibitor display reduced depression-like behaviors. Thus, PTEN is an intrinsic regulator of 5-HT neuron activity, representing a novel therapeutic strategy for producing antidepressant action.

Resveratrol Mitigates Hippocampal Tau Acetylation and Cognitive Deficit by Activation SIRT1 in Aged Rats following Anesthesia and Surgery

Postoperative cognitive dysfunction (POCD) is a sever postsurgical neurological complication in the elderly population. As the global acceleration of population ageing, POCD is proved to be a great challenge to the present labor market and healthcare system. In the present study, our findings showed that tau acetylation mediated by SIRT1 deficiency resulted in tau hyperphosphorylation in the hippocampus of the aged POCD model and consequently contributed to cognitive impairment. Interestingly, pretreatment with resveratrol almost restored the expression of SIRT1, reduced the levels of acetylated tau and hyperphosphorylated tau in the hippocampus, and improved the cognitive performance in the behavioral tests. What is more, we observed that microglia-derived neuroinflammation resulting from SIRT1 inhibition in microglia probably aggravated the tau acetylation in cultured neurons in vitro. Our findings supported the notion that activation SIRT1 provided dually beneficial effect in the aged POCD model. Taken together, our findings provided the initial evidence that tau acetylation was associated with cognitive impairment in the aged POCD model and paved a promising avenue to prevent POCD by inhibiting tau acetylation in a SIRT1-dependent manner.

NR2B receptor- and calpain-mediated KCC2 cleavage resulted in cognitive deficiency exposure to isoflurane

BACKGROUND

During brain development, volatile anesthetic can rapidly interfere with physiologic patterns of dendritic development and synaptogenesis and impair the formation of precise neuronal circuits. KCC2 plays vital roles in spine development and synaptogenesis through its Cl- transport function and structural interactions with the spine cytoskeleton protein 4.1 N. The aim of this study was to dissect the mechanism of volatile anesthetics, which impair dendritic development and synaptogenesis via mediation of KCC2 cleavage.

METHODS

Westernblotting was employed to assess the expression change of NR2B, NR2A, calpain-1, calpain-2, KCC2, and 4.1 N protein of rat (PND 5). Co-immunoprecipitation was applied to demonstrate the interaction between KCC2 and 4.1 N protein. Long-term cognitive deficiency was assessed by MWM. Lentivirus-calpain-2 was administered by hippocampus stereotaxic injection.

RESULTS

There was a significant increase in the level of NR2B instead of NR2A exposure to isoflurane. Calpain-2 was excessively activated via NR2B after 6 h of isoflurane exposure. The expression of plasmalemmal KCC2 and 4.1 N protein was significantly decreased treated with isoflurane. The isoflurane group showed longer traveled distance, prolonged escape latency, less time spent in the target quadrant, and decreased platform crossings. Pretreatment with ifenprodil and downregulated calpain-2 expression significantly alleviated these neurotoxicity responses and cognitive deficiency after isoflurane exposure.

CONCLUSIONS

A significant increase in NR2B, excessive activation of calpain-2 and increased cleavage of plasmalemmal KCC2, are involved in isoflurane-induced neurotoxicity and long-term cognitive deficiency. Blocking NR2B and calpain-2 activity significantly attenuated these responses. The KCC2 cleavage mediated by NR2B and calpain-2 is a major determinant of isoflurane-induced long-term cognitive deficiency.

Hemin treatment protects neonatal rats from sevoflurane-induced neurotoxicity via the phosphoinositide 3-kinase/Akt pathway

AIMS

Anaesthesia-related neurotoxicity in the developing brain is a controversial issue that has recently attracted much attention. Hemin plays a protective role in hypoxic and ischemic brain damage; however, its effects on sevoflurane-induced neurotoxicity remain unclear. Our aim was to investigate the mechanisms of sevoflurane neurotoxicity and potential neuroprotective roles of hemin upon sevoflurane exposure.

MAIN METHODS

Hippocampi were harvested 18 h after sevoflurane exposure. Haem oxygenase 1 (HMOX1), superoxide dismutase 2 (SOD2), discs large MAGUK scaffold protein 4 (DLG4), phosphorylated Akt, Akt, cleaved caspase 3, and neuroglobin were detected by western blotting. A water maze test was used to assess learning and memory ability in P30 rats.

KEY FINDINGS

Sevoflurane inhalation increased cleaved caspase 3 levels. Hemin treatment enhanced the antioxidant defence response, protecting rats from oxidative stress injury. Hemin plays its neuroprotective role via phosphoinositide 3-kinase (PI3K)/Akt signalling. A single inhalation of sevoflurane did not affect DLG4 expression, while hemin treatment did. Platform crossing increased in rats treated with hemin as well, which may be related to increased DLG4. Neuroglobin expression was not affected, suggesting that it may act upstream of PI3K/Akt signalling.

SIGNIFICANCE

Our study demonstrates that hemin plays a protective role in anaesthesia-induced neurotoxicity by both inhibiting apoptosis via the PI3K/Akt pathway and increasing the expression of antioxidant enzymes, reducing oxidative damage. The results provide mechanistic insight into the effects of sevoflurane anaesthesia on the developing brain and suggest that hemin could help avoid these effects.

The neuroprotective effect of bisperoxovandium (pyridin-2-squaramide) in intracerebral hemorrhage

Background: The authors have recently designed a new compound bisperoxovandium (pyridin-2-squaramide) [bpV(pis)] and verified that bpV(pis) confers neuroprotection through suppressing PTEN and activating ERK1/2, respectively. Intracerebral hemorrhage (ICH) is the second most common cause of stroke and has severe clinical outcome. In this study, we investigate the effect of bpV(pis) in ICH model both in vivo and in vitro.

Materials and methods: The novel drug bpV(pis) was synthesized in the Faculty of Pharmacy, Wuhan University School of Medicine. An ICH model was generated on both SD rats and cells. bpV(pis) was injected into intracerebroventricular or culture media. Western blotting was applied to test the signal pathway. To determine the effect of bpV(pis) on PTEN inhibition and ERK1/2 activation, we measured the phosphorylation level of AKT (a direct downstream target of PTEN that negatively regulates AKT) and ERK1/2. FJC, MTT, and LDH were applied to measure the cell viability. Neurobehavioral tests were performed to measure the effect of bpV(pis).

Results: The in vivo results showed that intracerebroventricular administration of bpV(pis) significantly alleviates hematoma, the damage of brain–blood barrier and brain edema. The in vitro results demonstrated that bpV(pis) treatment reduces ICH-induced neuronal injury. Western blotting results identified that bpV(pis) exerts a neuroprotective effect by significantly increasing the phosphorylation level of AKT and ERK1/2 after experimental ICH. Neurobehavioral tests indicate that bpV(pis) promotes functional recovery in ICH animals.

Conclusion: This study provides first and direct evidence for a potential role of bpV(pis) in ICH therapy.

PTEN Inhibition in Human Disease Therapy

The tumor suppressor PTEN is a major homeostatic regulator, by virtue of its lipid phosphatase activity against phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3], which downregulates the PI3K/AKT/mTOR prosurvival signaling, as well as by its protein phosphatase activity towards specific protein targets. PTEN catalytic activity is crucial to control cell growth under physiologic and pathologic situations, and it impacts not only in preventing tumor cell survival and proliferation, but also in restraining several cellular regeneration processes, such as those associated with nerve injury recovery, cardiac ischemia, or wound healing. In these conditions, inhibition of PTEN catalysis is being explored as a potentially beneficial therapeutic intervention. Here, an overview of human diseases and conditions in which PTEN inhibition could be beneficial is presented, together with an update on the current status of specific small molecule inhibitors of PTEN enzymatic activity, their use in experimental models, and their limitations as research or therapeutic drugs.

Podocyte-specific knockin of PTEN protects kidney from hyperglycemia

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) has proven to be downregulated in podocytes challenged with high glucose (HG), and knockout of PTEN in podocytes aggravated the progression of diabetic kidney disease (DKD). However, whether podocyte-specific knockin of PTEN protects the kidney against hyperglycemia in vivo remains unknown. The inducible podocyte-specific PTEN knockin (PPKI) mice were generated by crossing newly created transgenic loxP-stop- loxP-PTEN mice with podocin-iCreER^T2 mice. Diabetes mellitus was induced in mice by intraperitoneal injection of streptozotocin at a dose of 150 mg/kg. In vitro, small interfering RNA and adenovirus interference were used to observe the role of PTEN in HG-treated podocytes. Our data demonstrated that PTEN was markedly reduced in the podocytes of patients with DKD and focal segmental glomerulosclerosis, as well as in those of db/db mice. Interestingly, podocyte-specific knockin of PTEN significantly alleviated albuminuria, mesangial matrix expansion, effacement of podocyte foot processes, and incrassation of glomerular basement membrane in diabetic PPKI mice compared with wild-type diabetic mice, whereas no alteration was observed in the level of blood glucose. The potential renal protection of overexpressed PTEN in podocytes was partly attributed with an improvement in autophagy and motility and the inhibition of apoptosis. Our results showed that podocyte-specific knockin of PTEN protected the kidney against hyperglycemia in vivo , suggesting that targeting PTEN might be a novel and promising therapeutic strategy against DKD.

Profiling microRNA from Brain by Microarray in a Transgenic Mouse Model of Alzheimer's Disease

MicroRNAs (miRNAs) are small noncoding RNAs, which regulate numerous cell functions by targeting mRNA for cleavage or translational repression, and have been found to play an important role in Alzheimer's disease (AD). Our study aimed to identify differentially expressed miRNAs in AD brain as a reference of potential therapeutic miRNAs or biomarkers for this disease. We used amyloid precursor protein (APP) and presenilin 1 (PS1) double transgenic mice and age-matched wild-type (WT) littermates to determine the expression of miRNAs in the brain. MiRNAs were profiled by microarray, and differentially expressed miRNAs underwent target prediction and enrichment analysis. Microarray analysis revealed 56 differentially expressed miRNAs in AD mouse brain, which involved 39 miRNAs that were significantly upregulated and 19 that were downregulated at different ages. Among those miRNAs, a total of 11 miRNAs, including miR-342-3p, miR-342-5p, miR-376c-3p, and miR-301b-3p, were not only conserved in human but also predicted to have targets and signaling pathways closely related to the pathology of AD. In conclusion, in this study, differentially expressed miRNAs were identified in AD brain and proposed as biomarkers, which may have the potential to indicate AD progression. Despite being preliminary, these results may aid in investigating pathological hallmarks and identify effective therapeutic targets.

Vitamin B6 prevents isocarbophos-induced vascular dementia in rats through N-methyl-D-aspartate receptor signaling

BACKGROUND

We have previously reported that the long-term exposure of organophosphorus induces vascular dementia (VD) in rats. As a coenzyme, vitamin B6 is mainly involved in the regulation of metabolisms. Whether vitamin B6 improves VD remains unknown.

METHODS

The model of VD was induced by feeding rats with isocarbophos (0.5 mg/kg per two day, 12 weeks). The blood flow of the posterior cerebral artery (PCA) in rat was assessed by transcranial Doppler (TCD). The learning and memory were evaluated by the Morris Water Maze (MWM) test.

RESULTS

Administration of vitamin B6 increased the blood flow in the right and left posterior cerebral arteries and improved the functions of learning and memory in isocarbophos-treated rats. Vitamin B6 increased the protein levels of N-methyl-D-aspartate receptor (NMDAR) 2B, postsynaptic densities (PSDs) protein 95, and calmodulin-dependent protein kinase II (CaMK-II) in the hippocampus, which were decreased by isocarbophos in rats. Morphological analysis by light microscope and electronic microscope indicated disruptions of the hippocampus caused by isocarbophos were normalized by vitamin B6. Importantly, the antagonist of NMDAR signaling by eliprodil abolished these beneficial effects produced by vitamin B6 on PCA blood flow, learning, memory, and hippocampus structure in rats, as well as the protein expression of NMDAR 2B, PSDs protein 95, and CaMK-II in the hippocampus.

CONCLUSION

Vitamin B6 activates NMDAR signaling to prevent isocarbophos-induced VD in rats.