Intermittent hypoxia-induced protein phosphatase 2A activation reduces PC12 cell proliferation and differentiation

The study of the relationship between moderate to severe sleep obstructive apnea and cognitive impairment, anxiety, and depression

Objective

The present study endeavored to investigate the interconnection between obstructive sleep apnea (OSA) and cognitive function, alongside the manifestations of depression and anxiety. Simultaneously, an analysis was conducted to discern the factors exerting influence upon cognitive function.

Methods

A cohort of 102 patients, who had undergone polysomnography (PSG) at Binhu Hospital, Anhui Medical University, between January 2022 and June 2023, was encompassed in the study. Employing the PSG findings, these individuals were classified into two distinct categories: the grouping consisted of those with either negligible or mild OSA, and the other comprised individuals with moderate to severe OSA. Utilizing the Montreal Cognitive Assessment (MoCA-Beijing), Stroop Color and Word Test (SCWT), Digit Span Test (DST), Self-rating Depression Scale (SDS), and Self-rating Anxiety Scale (SAS), scores were recorded and analysed for each of the respective assessments. Additionally, discrepancies and associations between these groups were also scrutinized.

Results

The group exhibiting moderate to severe OSA demonstrated significantly elevated measurements in parameters such as neck circumference, BMI, completion times for SCWT-A, B, C, Sleep Inefficiency Index (SIE), SAS, and SDS, in comparison to the No or Mild OSA group. Furthermore, the moderate-severe OSA group manifested notably diminished MoCA scores in areas of visual-spatial and executive function, memory, language, abstraction, delayed recall, orientation, total MoCA score, lowest oxygen saturation (LSaO2), average oxygen saturation, Digit Span Test-backward(DST-b), and Digit Span Test-forward(DST-f), as contrasted with the no-mild OSA group. These inter-group disparities exhibited statistical significance (p < 0.05). The MoCA total score portrayed inverse correlations with age, Apnea-Hypopnea Index (AHI), BMI, SIE, SAS, SDS, CT90%, AHT90%, and Hypoxic Apnea Duration (HAD) (ranging from -0.380 to -0.481, p < 0.05). Conversely, it displayed positive correlations with DST-f, DST-b, LSaO2, and average oxygen saturation (ranging from 0.414 to 0.744, p < 0.05). Neck circumference, AHI, and SAS were autonomously linked to MoCA scores (OR = 1.401, 1.028, 1.070, p < 0.05), while AHI exhibited an independent correlation with SDS and SAS scores (OR = 1.001, p = 0.003).

Conclusion

Patients grappling with moderate to severe OSA frequently reveal cognitive impairment and concomitant emotional predicaments encompassing depression and anxiety. These manifestations share an intimate association with AHI, LSaO2, and average oxygen saturation. Notably, anxiety, when coupled with OSA, emerges as an autonomous influential element impinging upon cognitive impairment.

Harnessing the effects of hypoxia-like inhibition on homology-directed DNA repair

Hypoxia is a hallmark feature of the tumor microenvironment which can promote mutagenesis and instability. This increase in mutational burden occurs as a result of the downregulation of DNA repair systems. Deficits in the DNA damage response can be exploited to induce cytotoxicity and treat advanced stage cancers. With the advent of precision medicine, agents such as Poly (ADP-ribose) polymerase (PARP) inhibitors have been used to achieve synthetic lethality in homology directed repair (HDR) deficient cancers. However, most cancers lack these predictive biomarkers. Treatment for the HDR proficient population represents an important unmet clinical need. There has been interest in the use of anti-angiogenic agents to promote tumor hypoxia and induce deficiency in a HDR proficient background. For example, the use of cediranib to inhibit PDGFR and downregulate enzymes of the HDR pathway can be used synergistically with a PARP inhibitor. This combination can improve therapeutic responses in HDR proficient cancers. Preclinical results and Phase II and III clinical trial data support the mechanistic rationale for the efficacy of these agents in combination. Future investigations should explore the effectiveness of cediranib and other anti-angiogenic agents with a PARP inhibitor to elicit an antitumor response and sensitize cancers to immunotherapy.

Mechanism, prevention and treatment of cognitive impairment caused by high altitude exposure

Hypobaric hypoxia (HH) characteristics induce impaired cognitive function, reduced concentration, and memory. In recent years, an increasing number of people have migrated to high-altitude areas for work and study. Headache, sleep disturbance, and cognitive impairment from HH, severely challenges the physical and mental health and affects their quality of life and work efficiency. This review summarizes the manifestations, mechanisms, and preventive and therapeutic methods of HH environment affecting cognitive function and provides theoretical references for exploring and treating high altitude-induced cognitive impairment.

Dimethyloxalylglycine (DMOG), a Hypoxia Mimetic Agent, Does Not Replicate a Rat Pheochromocytoma (PC12) Cell Biological Response to Reduced Oxygen Culture

Cells respond to reduced oxygen availability predominately by activation of the hypoxia-inducible factor (HIF) pathway. HIF activation upregulates hundreds of genes that help cells survive in the reduced oxygen environment. The aim of this study is to determine whether chemical-induced HIF accumulation mimics all aspects of the hypoxic response of cells. We compared the effects of dimethyloxalylglycine (DMOG) (a HIF stabiliser) on PC12 cells cultured in air oxygen (20.9% O_2, AO) with those cultured in either intermittent 20.9% O₂ to 2% O₂ (IH) or constant 2% O₂ (CN). Cell viability, cell cycle, HIF accumulation, reactive oxygen species (ROS) formation, mitochondrial function and differentiation were used to characterise the PC12 cells and evaluate the impact of DMOG. IH and CN culture reduced the increase in cell numbers after 72 and 96 h and MTT activity after 48 h compared to AO culture. Further, DMOG supplementation in AO induced a dose-dependent reduction in the increase in PC12 cell numbers and MTT activity. IH-cultured PC12 cells displayed increased and sustained HIF-1 expression over 96 h. This was accompanied by increased ROS and mitochondrial burden. PC12 cells in CN displayed little changes in HIF-1 expression or ROS levels. DMOG (0.1 mM) supplementation resulted in an IH-like HIF-1 profile. The mitochondrial burden and action potential of DMOG-supplemented PC12 cells did not mirror those seen in other conditions. DMOG significantly increased S phase cell populations after 72 and 96 h. No significant effect on PC12 cell differentiation was noted with IH and CN culture without induction by nerve growth factor (NGF), while DMOG significantly increased PC12 cell differentiation with and without NGF. In conclusion, DMOG and reduced oxygen levels stabilise HIF and affect mitochondrial activity and cell behaviour. However, DMOG does not provide an accurate replication of the reduced oxygen environments.

Cognitive impairment caused by hypoxia: from clinical evidences to molecular mechanisms

Hypoxia is a state of reduced oxygen supply and excessive oxygen consumption. According to the duration of hypoxic period, it can be classified as acute and chronic hypoxia. Both acute and chronic hypoxia could induce abundant neurological deficits. Although there have been significant advances in the pathophysiological injuries, few studies have focused on the cognitive dysfunction. In this review, we focused on the clinical evidences and molecular mechanisms of cognitive impairment under acute and chronic hypoxia. Hypoxia can impair several cognitive domains such as attention, learning and memory, procession speed and executive function, which are similar in acute and chronic hypoxia. The severity of cognitive deficit correlates with the duration and degree of hypoxia. Recovery can be achieved after acute hypoxia, while sequelae or even dementia can be observed after chronic hypoxia, perhaps due to the different molecular mechanisms. Cardiopulmonary compensatory response, glycolysis, oxidative stress, calcium overload, adenosine, mitochondrial disruption, inflammation and excitotoxicity contribute to the molecular mechanisms of cognitive deficit after acute hypoxia. During the chronic stage of hypoxia, different adaptive responses, impaired neurovascular coupling, apoptosis, transcription factors-mediated inflammation, as well as Aβ accumulation and tau phosphorylation account for the neurocognitive deficit. Moreover, brain structural changes with hippocampus and cortex atrophy, ventricle enlargement, senile plaque and neurofibrillary tangle deposition can be observed under chronic hypoxia rather than acute hypoxia.

The protective effect of L-glutamine against acute Cantharidin-induced Cardiotoxicity in the mice

Background

Cantharidin (CTD) is a compound which have the potential to be exploited as an antitumor drug, and it has been demonstrated antitumor effects in a variety of cancers. However, the use is limited due to its severe toxicity. It has reported that it can induce fatal cardiac arrhythmias. Fortunately, we found that L-glutamine can alleviate cardiac toxicity caused by cantharidin in mice.

Methods

To investigate the protective effect of L-glutamine, we used a high dose of cantharidin in mice to create a model of cardiotoxicity. In the experimental mice, glutamine was given orally half an hour before they were administrated with cantharidin. The mice of control group were intraperitoneally injected with DMSO solution. The general state of all mice, cardiac mass index, electrocardiogram change and biological markers were determined. Hematoxylin-eosin staining (HE staining) of heart tissue was carried out in each group to reflect the protective effect of glutamine. To investigate the mechanisms underlying the injury and cardio-protection, multiple oxidative stress indexes were determined and succinate dehydrogenase activity was evaluated.

Result

The results showed that L-glutamine (Gln) pretreatment reduced weight loss and mortality. It also decreased the biological markers (p < 0.05), improved electrocardiogram and histological changes that CTD induced cardiotoxicity in mice. Subsequently, the group pretreated with L-glutamine before CTD treatment increases in MDA but decreases in SOD and GSH, in comparison to the group treated with CTD alone. Besides, succinate dehydrogenase activity also was improved when L-glutamine was administrated before cantharidin compared to cantharidin.

Conclusions

This study provided evidence that L-glutamine could protect cardiac cells against the acute cantharidin-induced cardiotoxicity and the protective mechanism of glutamine may be related to the myocardial cell membrane or the tricarboxylic acid cycle in the mitochondria.

Cediranib suppresses homology-directed DNA repair through down-regulation of BRCA1/2 and RAD51

Combining the anti-angiogenic agent cediranib with the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib improves progression-free survival compared to olaparib alone in ovarian cancer patients through an unknown mechanism. PARP inhibitors are used primarily in the treatment of patients with DNA repair-associated (BRCA1/2) mutated cancers because these mutations cause a deficit in homology-directed DNA repair (HDR) that confers sensitivity to these agents. However, the combination of cediranib and olaparib was effective in patients without BRCA1/2 mutations. We report here that cediranib confers sensitivity to olaparib by down-regulating HDR in tumor cells. This occurs partially as a result of cediranib inducing hypoxia, which suppresses expression of the HDR factors BRCA1/2 and RAD51 recombinase (RAD51). However, we also observed that cediranib has a direct effect on HDR independent of its ability to induce tumor hypoxia. This direct effect occurs through platelet-derived growth factor receptor (PDGFR) inhibition, activation of protein phosphatase 2A (PP2A), and E2F transcription factor 4 (E2F4)/RB transcriptional corepressor like 2 (RB2/p130)-mediated repression of BRCA1/2 and RAD51 gene expression. This down-regulation was seen in mouse tumor xenografts but not in mouse bone marrow, providing a therapeutic window for combining cediranib and olaparib in cancer therapy. Our work reveals a treatment strategy by which DNA repair can be manipulated in human tumors to induce synthetic lethality, broadening the potential therapeutic scope of cediranib based on its activity as a DNA repair inhibitor.

Protective effect of nitronyl nitroxide against hypoxia-induced damage in PC12 cells

Hypoxia induces cellular oxidative stress that is associated with neurodegenerative diseases. HPN (4'-hydroxyl-2-substituted phenyl nitronyl nitroxide), a stable nitronyl nitroxide, has excellent free radical scavenging properties. The purpose of this study was to investigate the protective effects of HPN on hypoxia-induced damage in PC12 cells. It was shown that HPN significantly attenuated hypoxia-induced loss of cell viability, release of lactate dehydrogenase (LDH), and morphological changes in PC12 cells. Moreover, hypoxic PC12 cells had increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), and expression of HIF-1α and VEGF, but had reduced levels of superoxide dismutase (SOD) and catalase (CAT), and HPN reversed these changes. HPN also inhibited hypoxia-induced cell apoptosis via suppressing the expression of Bax, cytochrome c, and caspase-3, and inducing the expression of Bcl-2. These results indicate that the protective effects of HPN on hypoxia-induced damage in PC12 cells is associated with the suppression of hypoxia-induced oxidative stress and cell apoptosis. HPN could be a promising candidate for the development of a novel neuroprotective agent.

Regulation of the phosphoprotein phosphatase 2A system and its modulation during oxidative stress: A potential therapeutic target?

Phosphoprotein phosphatases are of growing interest in the pathophysiology of many diseases and are often the neglected partner of protein kinases. One family member, PP2A, accounts for dephosphorylation of ~55-70% of all serine/threonine phosphosites. Interestingly, dysregulation of kinase signalling is a hallmark of many diseases in which an increase in oxidative stress is also noted. With this in mind, we assess the evidence to support oxidative stress-mediated regulation of the PP2A system In this article, we first present an overview of the PP2A system before providing an analysis of the regulation of PP2A by endogenous inhibitors, post translational modification, and miRNA. Next, a detailed critique of data implicating reactive oxygen species, ischaemia, ischaemia-reperfusion, and hypoxia in regulating the PP2A holoenzyme and associated regulators is presented. Finally, the pharmacological targeting of PP2A, its endogenous inhibitors, and enzymes responsible for its post-translational modification are covered. There is extensive evidence that oxidative stress modulates multiple components of the PP2A system, however, most of the data pertains to the catalytic subunit of PP2A. Irrespective of the underlying aetiology, free radical-mediated attenuation of PP2A activity is an emerging theme. However, in many instances, a dichotomy exists, which requires clarification and mechanistic insight. Nevertheless, this raises the possibility that pharmacological activation of PP2A, either through small molecule activators of PP2A or CIP2A/SET antagonists may be beneficial in modulating the cellular response to oxidative stress. A better understanding of which, will have wide ranging implications for cancer, heart disease and inflammatory conditions.

Radiofrequency radiation at 2.856 GHz does not affect key cellular endpoints in neuron-like PC12 cells

To investigate the potential cytotoxicity of radiofrequency (RF) radiation on central nervous system, rat pheochromocytoma (PC12) cells were exposed to 2.856 GHz RF radiation at a specific absorption rate (SAR) of 4 W/kg for 8 h a day for 2 days in 35 mm Petri dishes. During exposure, the real-time variation of the culture medium temperature was monitored in the first hour. Reactive oxygen species (ROS) production, intracellular Ca²⁺ concentration, and cell apoptosis rate were assessed immediately after exposure by flow cytometry. The results showed that the medium temperature raised about 0.93 °C, but no significant changes were observed in apoptosis, ROS levels or intracellular Ca²⁺ concentration after treatment. Although several studies suggested that RF radiation does indeed cause neurological effects, this study presented inconsistent results, indicating that 2.856 GHz RF radiation exposure at a SAR of 4 W/kg does not have a dramatic impact on PC12 cells, and suggests the need for further investigation on the key cellular endpoints of other nerve cells after exposure to RF radiation.

Brassinosteroids regulate root growth by controlling reactive oxygen species homeostasis and dual effect on ethylene synthesis in Arabidopsis

The brassinosteroids (BRs) represent a class of phytohormones, which regulate numerous aspects of growth and development. Here, a det2-9 mutant defective in BR synthesis was identified from an EMS mutant screening for defects in root length, and was used to investigate the role of BR in root development in Arabidopsis. The det2-9 mutant displays a short-root phenotype, which is result from the reduced cell number in root meristem and decreased cell size in root maturation zone. Ethylene synthesis is highly increased in the det2-9 mutant compared with the wild type, resulting in the hyper-accumulation of ethylene and the consequent inhibition of root growth. The short-root phenotype of det2-9 was partially recovered in the det2-9/acs9 double mutant and det2-9/ein3/eil1-1 triple mutant which have defects either in ethylene synthesis or ethylene signaling, respectively. Exogenous application of BR showed that BRs either positively or negatively regulate ethylene biosynthesis in a concentration-dependent manner. Different from the BR induced ethylene biosynthesis through stabilizing ACSs stability, we found that the BR signaling transcription factors BES1 and BZR1 directly interacted with the promoters of ACS7, ACS9 and ACS11 to repress their expression, indicating a native regulation mechanism under physiological levels of BR. In addition, the det2-9 mutant displayed over accumulated superoxide anions (O2-) compared with the wild-type control, and the increased O2- level was shown to contribute to the inhibition of root growth. The BR-modulated control over the accumulation of O2- acted via the peroxidase pathway rather than via the NADPH oxidase pathway. This study reveals an important mechanism by which the hormone cross-regulation between BRs and ethylene or/and ROS is involved in controlling root growth and development in Arabidopsis.

The Effect of Coatings and Nerve Growth Factor on Attachment and Differentiation of Pheochromocytoma Cells

Cellular attachment plays a vital role in the differentiation of pheochromocytoma (PC12) cells. PC12 cells are noradrenergic clonal cells isolated from the adrenal medulla of Rattus norvegicus and studied extensively as they have the ability to differentiate into sympathetic neuron-like cells. The effect of several experimental parameters including (i) the concentration of nerve growth factor (NGF); (ii) substratum coatings, such as poly-L-lysine (PLL), fibronectin (Fn), and laminin (Lam); and (iii) double coatings composed of PLL/Lam and PLL/Fn on the differentiation process of PC12 cells were studied. Cell morphology was visualised using brightfield phase contrast microscopy, cellular metabolism and proliferation were quantified using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, and the neurite outgrowth and axonal generation of the PC12 cells were evaluated using wide field fluorescence microscopy. It was found that double coatings of PLL/Lam and PLL/Fn supported robust adhesion and a two-fold enhanced neurite outgrowth of PC12 cells when treated with 100 ng/mL of NGF while exhibiting stable metabolic activity, leading to the accelerated generation of axons.

Phosphatases and solid tumors: focus on glioblastoma initiation, progression and recurrences

Phosphatases and cancer have been related for many years now, as these enzymes regulate key cellular functions, including cell survival, migration, differentiation and proliferation. Dysfunctions or mutations affecting these enzymes have been demonstrated to be key factors for oncogenesis. The aim of this review is to shed light on the role of four different phosphatases (PTEN, PP2A, CDC25 and DUSP1) in five different solid tumors (breast cancer, lung cancer, pancreatic cancer, prostate cancer and ovarian cancer), in order to better understand the most frequent and aggressive primary cancer of the central nervous system, glioblastoma.

Effect of different levels of intermittent hypoxia on autophagy of hippocampal neurons

PURPOSE

The current study was carried out to assess the effects of different levels of intermittent hypoxia (IH) on autophagy in hippocampal neurons, and explore the extent, frequency and duration of IH for researching on autophagy in hippocampal neurons.

METHODS

Hippocampal neurons were exposed to different levels of IH. To analyze the oxygen level of neuronal exposure environment, we detected the oxygen concentration in the chamber by O₂ analyzer, and monitored the oxygen partial pressure (PO₂), carbon dioxide partial pressure (PCO₂), and pH in the culture media by blood gas analyzer. After 4-, 8-, and 12-h IH, the morphology and quantity of neurons, as well as the expression of light chain 3 (LC3)-II positive dots were observed by immunofluorescence. The expression of apoptosis marker protein cleaved caspase-3 and autophagy marker protein LC3 were examined by western blotting.

RESULTS

The oxygen level in the chamber and the neuronal culture media both reached to the values set previously in three models. The level of cleaved caspase-3 and LC3 had no significant changes in IH-1 group. The morphology and quantity had no significant changes, while the levels of cleaved caspase-3 and LC3 were both increased in IH-2 group. The quantity of neurons was reduced significantly, and the chromatin condensed and nuclei fragmented in IH-3 group.

CONCLUSIONS

The effects of varying degrees of IH on autophagy in hippocampal neurons are different. The IH model, hypoxia phase (1.5% O₂, 5% CO₂, and balance N₂) for 5 min and reoxygenation phase (21% O₂, 5% CO₂, and balance N₂) for 10 min, may be the best condition for researching on autophagy in hippocampal neurons.

Altered Wnt Signaling Pathway in Cognitive Impairment Caused by Chronic Intermittent Hypoxia: Focus on Glycogen Synthase Kinase-3β and β-catenin

BACKGROUND

Cognitive impairment is a severe complication caused by obstructive sleep apnea (OSA). The mechanisms of causation are still unclear. The Wnt/β-catenin signaling pathway is involved in cognition, and abnormalities in it are implicated in neurological disorders. Here, we explored the Wnt/β-catenin signaling pathway abnormalities caused by chronic intermittent hypoxia (CIH), the most characteristic pathophysiological component of OSA.

METHODS

We divided 32 4-week-old male C57/BL mice into four groups of eight each: a CIH + normal saline (NS) group, CIH + LiCl group, sham CIH + NS group, and a sham CIH + LiCl group. The spatial learning performance of each group was assessed by using the Morris water maze (MWM). Protein expressions of glycogen synthase kinase-3β (GSK-3β) and β-catenin in the hippocampus were examined using the Western blotting test. EdU labeling and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining methods were used, respectively, to determine the proliferation and apoptosis of neurons in the hippocampal dentate gyrus region.

RESULTS

Mice exposed to CIH showed impaired spatial learning performance in the MWM, including increased mean escape latencies to reach the target platform, decreased mean times passing through the target platform and mean duration in the target quadrant. The GSK-3β activity increased, and expression of β-catenin decreased significantly in the hippocampus of the CIH-exposed mice. Besides, CIH significantly increased hippocampal neuronal apoptosis, with an elevated apoptosis index. Meanwhile, LiCl decreased the activity of GSK-3β and increased the expression of β-catenin and partially reversed the spatial memory deficits in MWM and the apoptosis caused by CIH.

CONCLUSIONS

Wnt/β-catenin signaling pathway abnormalities possibly play an important role in the development of cognitive deficits among mice exposed to CIH and that LiCl might attenuate CIH-induced cognitive impairment via Wnt/β-catenin signaling pathway.

Consequences of acclimation on the resistance to acute thermal stress: Proteomic focus on mussels from pristine site

Climate change constitutes an additional threat for intertidal species that already have to cope with a challenging environment. The present study focuses on the blue mussel Mytilus edulis and aims at investigating the importance of thermal acclimation in heat stress response. Microcosm exposures were performed with mussels submitted to an identical acute thermal stress following two thermal summer acclimations standing for present or future temperature conditions. Gill proteomes were analyzed by 2DE and 96 differentially expressed proteoforms were identified. Our results show that cell integrity appears to be maintained by the rise in molecular protective systems (i.e. Heat Shock Proteins), and by the reallocation of energy production via a switch to anaerobic metabolism and the setting up of alternative energy pathways. Finally, our results indicate that the response of mussels to acute thermal stress is conditioned by the acclimation temperature with an improved response in organisms acclimated to higher temperatures.

A Novel Chip for Cyclic Stretch and Intermittent Hypoxia Cell Exposures Mimicking Obstructive Sleep Apnea

Intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), plays a critical role in the pathogenesis of OSA-associated morbidities, especially in the cardiovascular and respiratory systems. Oxidative stress and inflammation induced by IH are suggested as main contributors of end-organ dysfunction in OSA patients and animal models. Since the molecular mechanisms underlying these in vivo pathological responses remain poorly understood, implementation of experimental in vitro cell-based systems capable of inducing high-frequency IH would be highly desirable. Here, we describe the design, fabrication, and validation of a versatile chip for subjecting cultured cells to fast changes in gas partial pressure and to cyclic stretch. The chip is fabricated with polydimethylsiloxane (PDMS) and consists of a cylindrical well-covered by a thin membrane. Cells cultured on top of the membrane can be subjected to fast changes in oxygen concentration (equilibrium time ~6 s). Moreover, cells can be subjected to cyclic stretch at cardiac or respiratory frequencies independently or simultaneously. Rat bone marrow-derived mesenchymal stem cells (MSCs) exposed to IH mimicking OSA and cyclic stretch at cardiac frequencies revealed that hypoxia-inducible factor 1α (HIF-1α) expression was increased in response to both stimuli. Thus, the chip provides a versatile tool for the study of cellular responses to cyclical hypoxia and stretch.