Brain-derived neurotrophic factor inhibits cell cycle reentry but not endoplasmic reticulum stress in cultured neurons following oxidative or excitotoxic stress

Uncovering Cell Cycle Dysregulations and Associated Mechanisms in Cancer and Neurodegenerative Disorders: A Glimpse of Hope for Repurposed Drugs

The cell cycle is the sequence of events orchestrated by a complex network of cell cycle proteins. Unlike normal cells, mature neurons subsist in a quiescent state of the cell cycle, and aberrant cell cycle activation triggers neuronal death accompanied by neurodegeneration. The periodicity of cell cycle events is choreographed by various mechanisms, including DNA damage repair, oxidative stress, neurotrophin activity, and ubiquitin-mediated degradation. Given the relevance of cell cycle processes in cancer and neurodegeneration, this review delineates the overlapping cell cycle events, signaling pathways, and mechanisms associated with cell cycle aberrations in cancer and the major neurodegenerative disorders. We suggest that dysregulation of some common fundamental signaling processes triggers anomalous cell cycle activation in cancer cells and neurons. We discussed the possible use of cell cycle inhibitors for neurodegenerative disorders and described the associated challenges. We propose that a greater understanding of the common mechanisms driving cell cycle aberrations in cancer and neurodegenerative disorders will open a new avenue for the development of repurposed drugs.

Oxidative Stress Biomarkers among Schizophrenia Inpatients

Background. Finding the associations between schizophrenia symptoms and the biomarkers of inflammation, oxidative stress and the kynurenine pathway may lead to the individualization of treatment and increase its effectiveness. Methods. The study group included 82 schizophrenia inpatients. The Positive and Negative Symptoms Scale (PANSS), the Brief Assessment of Cognition in Schizophrenia (BACS) and the Calgary Depression in Schizophrenia Scale were used for symptom evaluation. Biochemical analyses included oxidative stress parameters and brain-derived neurotrophic factor (BDNF). Results. Linear models revealed the following: (1) malondiadehyde (MDA), N-formylkynurenine (N-formKYN), advanced oxidation protein products (AOPP), advanced glycation end-products of proteins (AGE) and total oxidative status (TOS) levels are related to the PANSS-total score; (2) MDA, reduced glutathione (GSH) and BDNF levels are related to the PANSS-negative score; (3) TOS and kynurenine (KYN) levels are related to the PANSS-positive score; (4) levels of total antioxidant status (TAS) and AOPP along with the CDSS score are related to the BACS-total score; (5) TAS and N-formKYN levels are related to the BACS-working memory score. Conclusions. Oxidative stress biomarkers may be associated with the severity of schizophrenia symptoms in positive, negative and cognitive dimensions. The identification of biochemical markers associated with the specific symptom clusters may increase the understanding of biochemical profiles in schizophrenia patients.

Thymoquinone Attenuates Retinal Expression of Mediators and Markers of Neurodegeneration in a Diabetic Animal Model

BACKGROUND

Diabetic retinopathy (DR) is a slow eye disease that affects the retina due to a long-standing uncontrolled diabetes mellitus. Hyperglycemia-induced oxidative stress can lead to neuronal damage leading to DR.

OBJECTIVE

The aim of the current investigation is to assess the protective effects of thymoquinone (TQ) as a potential compound for the treatment and/or prevention of neurovascular complications of diabetes, including DR.

METHODS

Diabetes was induced in rats by the administration of streptozotocin (55 mg/kg intraperitoneally, i.p.). Subsequently, diabetic rats were treated with either TQ (2 mg/kg i.p.) or vehicle on alternate days for three weeks. A healthy control group was also run in parallel. At the end of the treatment period, animals were euthanized, and the retinas were collected and analyzed for the expression levels of brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), nerve growth factor receptor (NGFR), and caspase-3 using Western blotting techniques in the retina of diabetic rats and compared with the normal control rats. In addition, dichlorofluorescein (DCF) levels in the retina were assessed as a marker of reactive oxygen species (ROS), and blood-retinal barrier breakdown (BRB) was examined for vascular permeability. The systemic effects of TQ treatments on glycemic control, kidney and liver functions were also assessed in all groups.

RESULTS

Diabetic animals treated with TQ showed improvements in the liver and kidney functions compared with control diabetic rats. Normalization in the levels of neuroprotective factors, including BDNF, TH, and NGFR, was observed in the retina of diabetic rats treated with TQ. In addition, TQ ameliorated the levels of apoptosis regulatory protein caspase-3 in the retina of diabetic rats and reduced disruption of the blood-retinal barrier, possibly through a reduction in reactive oxygen species (ROS) generation.

CONCLUSION

These findings suggest that TQ harbors a significant potential to limit the neurodegeneration and retinal damage that can be provoked by hyperglycemia in vivo.

Regulatory mechanism of cyclins and cyclin-dependent kinases in post-mitotic neuronal cell division

Neurodegenerative diseases (NDDs) are the most common life-threatening disease of the central nervous system and it cause the progressive loss of neuronal cells. The exact mechanism of the disease's progression is not clear and thus line of treatment for NDDs is a baffling issue. During the progression of NDDs, oxidative stress and DNA damage play an important regulatory function, and ultimately induces neurodegeneration. Recently, aberrant cell cycle events have been demonstrated in the progression of different NDDs. However, the pertinent role of signaling mechanism, for instance, post-translational modifications, oxidative stress, DNA damage response pathway, JNK/p38 MAPK, MEK/ERK cascade, actively participated in the aberrant cell cycle reentry induced neuronal cell death. Mounting evidence has demonstrated that aberrant cell cycle re-entry is a major contributing factor in the pathogenesis of NDDs rather than a secondary phenomenon. In the brain of AD patients with mild cognitive impairment, post miotic cell division can be seen in the early stage of the disease. However, in the brain of PD patients, response to various neurotoxic signals, the cell cycle re-entry has been observed that causes neuronal apoptosis. On contrary, the contributing factors that leads to the induction of cell cycle events in mature neurons in HD and ALS brain pathology is remain unclear. Various pharmacological drugs have been developed to reduce the pathogenesis of NDDs, but they are still not helpful in eliminating the cause of these NDDs.

Cell Cycle Deficits in Neurodegenerative Disorders: Uncovering Molecular Mechanisms to Drive Innovative Therapeutic Development

Cell cycle dysregulation has been implicated in the pathogenesis of neurodegenerative disorders. Specialised function obligates neuronal cells to subsist in a quiescent state of cell cycle once differentiated and therefore the circumstances and mechanisms underlying aberrant cell cycle activation in post-mitotic neurons in physiological and disease conditions remains an intriguing area of research. There is a strict requirement of concurrence to cell cycle regulation for neurons to ensure intracellular biochemical conformity as well as interrelationship with other cells within neural tissues. This review deliberates on various mechanisms underlying cell cycle regulation in neuronal cells and underscores potential implications of their non-compliance in neural pathology. Recent research suggests that successful duplication of genetic material without subsequent induction of mitosis induces inherent molecular flaws that eventually assert as apoptotic changes. The consequences of anomalous cell cycle activation and subsequent apoptosis are demonstrated by the increased presence of molecular stress response and apoptotic markers. This review delineates cell cycle events under normal physiological conditions and deficits amalgamated by alterations in protein levels and signalling pathways associated with cell-division are analysed. Cell cycle regulators essentially, cyclins, CDKs, cip/kip family of inhibitors, caspases, bax and p53 have been identified to be involved in impaired cell cycle regulation and associated with neural pathology. The pharmacological modulators of cell cycle that are shown to impart protection in various animal models of neurological deficits are summarised. Greater understanding of the molecular mechanisms that are indispensable to cell cycle regulation in neurons in health and disease conditions will facilitate targeted drug development for neuroprotection.

The Role of Mitochondrial and Endoplasmic Reticulum Reactive Oxygen Species Production in Models of Perinatal Brain Injury

Significance: Perinatal brain injury is caused by hypoxia-ischemia (HI) in term neonates, perinatal arterial stroke, and infection/inflammation leading to devastating long-term neurodevelopmental deficits. Therapeutic hypothermia is the only currently available treatment but is not successful in more than 50% of term neonates suffering from hypoxic-ischemic encephalopathy. Thus, there is an urgent unmet need for alternative or adjunct therapies. Reactive oxygen species (ROS) are important for physiological signaling, however, their overproduction/accumulation from mitochondria and endoplasmic reticulum (ER) during HI aggravate cell death. Recent Advances and Critical Issues: Mechanisms underlying ER stress-associated ROS production have been primarily elucidated using either non-neuronal cells or adult neurodegenerative experimental models. Findings from mature brain cannot be simply transferred to the immature brain. Therefore, age-specific studies investigating ER stress modulators may help investigate ER stress-associated ROS pathways in the immature brain. New therapeutics such as mitochondrial site-specific ROS inhibitors that selectively inhibit superoxide (O2•-)/hydrogen peroxide (H2O2) production are currently being developed. Future Directions: Because ER stress and oxidative stress accentuate each other, a combinatorial therapy utilizing both antioxidants and ER stress inhibitors may prove to be more protective against perinatal brain injury. Moreover, multiple relevant targets need to be identified for targeting ROS before they are formed. The role of organelle-specific ROS in brain repair needs investigation. Antioxid. Redox Signal. 31, 643-663.

Postmortem Brain, Cerebrospinal Fluid, and Blood Neurotrophic Factor Levels in Alzheimer's Disease: A Systematic Review and Meta-Analysis

Accumulating evidence suggest that aberrations of neurotrophic factors are involved in the etiology and pathogenesis of Alzheimer's disease (AD), but clinical data were inconsistent. Therefore, a meta-analysis on neurotrophic factor levels in AD is necessary. We performed a systematic review of blood, CSF, and post-mortem brain neurotrophic factor levels in patients with AD compared with controls and quantitatively summarized the clinical data in blood and CSF with a meta-analytical technique. A systematic search of PubMed and Web of Science identified 98 articles in this study (with samples more than 9000). Random effects meta-analysis demonstrated that peripheral blood BDNF levels were significantly decreased in AD patients compared with controls. However, blood NGF, IGF, and VEGF did not show significant differences between cases and controls. In CSF, random effects meta-analysis showed significantly deceased BDNF and increased NGF levels in patients with AD, whereas IGF and VEGF did not show significant differences between the AD group and control group. In addition, 23 post-mortem studies were included in the systematic review. Although data from post-mortem brains were not always consistent across studies, most studies suggested decreased BDNF and increased (pro)NGF levels in hippocampus and neocortex of patients with AD. These results provide strong clinical evidence that AD is accompanied by an aberrant neurotrophin profile, and future investigations into neurotrophins as biomarkers (especially CSF BDNF and NGF) and therapeutic targets for AD may be warranted.

The effects of vitamin E on brain derived neurotrophic factor, tissues oxidative damage and learning and memory of juvenile hypothyroid rats

The effects of vitamin E (Vit E) on brain derived neurotrophic factor (BDNF) and brain tissues oxidative damage as well as on learning and memory impairments in juvenile hypothyroid rats were examined. The rats were grouped as: (1) Control; (2) Propylthiouracil (PTU); (3) PTU-Vit E and (4) Vit E. PTU was added to their drinking water (0.05%) during 6 weeks. Vit E (20 mg/kg) was daily injected (IP). Morris water maze (MWM) and passive avoidance (PA) were carried out. The animals were deeply anesthetized and the brain tissues were removed for biochemical measurements. PTU increased the escape latency and traveled path in MWM (P < 0.001). It also shortened the latency to enter the dark compartment of PA as well as the time spent in the target quadrant in probe trial of MWM (P < 0.01-P < 0.001). All the effects of PTU were reversed by Vit E (P < 0.01-P < 0.001). PTU administration attenuated thiol and BDNF content as well as the activities of superoxide dismutase (SOD) and catalase (CAT) in the brain tissues while increased molondialdehyde (MDA). Moreover, Vit E improved BDNF, thiol, SOD and CAT while diminished MDA. The results of the present study showed that Vit E improved BDNF and prevented from brain tissues oxidative damage as well as learning and memory impairments in juvenile hypothyroid rats.

Increased serum levels of mBDNF in women with minimal and mild endometriosis have no predictive power for the disease

The objective of our pilot clinical, prospective study was to determine the serum levels of mature brain-derived neurotrophic factor, in of women with endometriosis and controls and explore whether mature brain-derived neurotrophic factor is a potential biomarker for the disease. The patients were selected from the Endometriosis Marker Austria prospective cohort study conducted at the tertiary referral certified Endometriosis Center of the Medical University of Vienna. All women underwent laparoscopic surgery because there was a suspicion of endometriosis, or the women had pelvic pain, adnexal cysts, unexplained infertility, or uterine fibroids. Our main outcome parameter was total levels of mature brain-derived neurotrophic factor in serum, measured using ELISA. Our results show that serum levels of mature brain-derived neurotrophic factor are significantly higher in women with endometriosis compared to women without endometriosis. The mean serum protein levels are significantly higher in women with rAFS stage I and II endometriosis, whereas no difference was found in women with stage III and IV endometriosis and controls. Postoperative follow-up at 6-10 weeks revealed that surgical intervention leads to equilibration of the levels of secreted mature brain-derived neurotrophic factor between women with and without endometriosis. The difference between serum mature brain-derived neurotrophic factor levels of women with endometriosis compared to women without endometriosis is independent of menstrual cycle phase and overall self-reported pelvic pain. ROC-curve analysis showed that, the mature brain-derived neurotrophic factor is not a useful biomarker for endometriosis. In conclusion, although women with stage I and II endometriosis have increased levels of mature brain-derived neurotrophic factor in serum compared to controls, the difference is not predictive for the disease. Impact statement Endometriosis is a disease that can have a significant impact on the quality of life of affected women. The gold standard for diagnosis to this day remains visualization through laparoscopic surgery with histological verification. Current studies are attempting to find a biomarker with high sensitivity and specificity, which would bypass the surgery-associated risks and would significantly reduce costs. In an attempt to elucidate whether mature serum BDNF can serve as diagnostic marker for the disease, we compared the levels of the protein in women with endometriosis to endometriosis-free controls. While our results showed that serum concentrations of the mature protein were significantly higher in women with endometriosis, we did not find this marker to have the sensitivity or specificity needed in order to allow a reliable diagnosis.

Decreased peripheral brain-derived neurotrophic factor levels in Alzheimer's disease: a meta-analysis study (N=7277)

Studies suggest that dysfunction of brain-derived neurotrophic factor (BDNF) is a possible contributor to the pathology and symptoms of Alzheimer's disease (AD). Several studies report reduced peripheral blood levels of BDNF in AD, but findings are inconsistent. This study sought to quantitatively summarize the clinical BDNF data in patients with AD and mild cognitive impairment (MCI, a prodromal stage of AD) with a meta-analytical technique. A systematic search of Pubmed, PsycINFO and the Cochrane Library identified 29 articles for inclusion in the meta-analysis. Random-effects meta-analysis showed that patients with AD had significantly decreased baseline peripheral blood levels of BDNF compared with healthy control (HC) subjects (24 studies, Hedges' g=-0.339, 95% confidence interval (CI)=-0.572 to -0.106, P=0.004). MCI subjects showed a trend for decreased BDNF levels compared with HC subjects (14 studies, Hedges' g=-0.201, 95% CI=-0.413 to 0.010, P=0.062). No differences were found between AD and MCI subjects in BDNF levels (11 studies, Hedges' g=0.058, 95% CI=-0.120 to 0.236, P=0.522). Interestingly, the effective sizes and statistical significance improved after excluding studies with reported medication in patients (between AD and HC: 18 studies, Hedges' g=-0.492, P<0.001; between MCI and HC: 11 studies, Hedges' g=-0.339, P=0.003). These results strengthen the clinical evidence that AD or MCI is accompanied by reduced peripheral blood BDNF levels, supporting an association between the decreasing levels of BDNF and the progression of AD.

Downregulated Brain-Derived Neurotrophic Factor-Induced Oxidative Stress in the Pathophysiology of Diabetic Retinopathy

Brain-derived neurotrophic factor (BDNF), a member of neurotrophin growth factor family, physiologically mediates induction of neurogenesis and neuronal differentiation, promotes neuronal growth and survival and maintains synaptic plasticity and neuronal interconnections. Unlike the central nervous system, its secretion in the peripheral nervous system occurs in an activity-dependent manner. BDNF improves neuronal mortality, growth, differentiation and maintenance. It also provides neuroprotection against several noxious stimuli, thereby preventing neuronal damage during pathologic conditions. However, in diabetic retinopathy (a neuromicrovascular disorder involving immense neuronal degeneration), BDNF fails to provide enough neuroprotection against oxidative stress-induced retinal neuronal apoptosis. This review describes the prime reasons for the downregulation of BDNF-mediated neuroprotective actions during hyperglycemia, which renders retinal neurons vulnerable to damaging stimuli, leading to diabetic retinopathy.

Possible role of oxidative stress and brain derived neurotrophic factor in triazophos induced cognitive impairment in rats

Triazophos, O,O-diethyl-1-H-1,2,4-triazol-3-yl phosphorothioate, (TZ) is an organophosphate pesticide widely used as an insecticide in agriculture fields, however, its adverse effects on cognitive function remain unknown till date. The present study was designed to identify the effect of TZ on cognitive function in order to gain an insight into the molecular mechanism(s) probably involved in TZ induced toxicity. Wistar male albino rats were orally administered with TZ at 8.2 mg/kg bw daily for 30 days. Cognitive function was assessed by evaluating step down latency (SDL) in passive avoidance apparatus, transfer latency (TL) on elevated plus maze and escape latency (EL) using morris water maze. The biochemical changes, in terms of malondialdehyde (MDA), reduced glutathione (GSH) and brain derived neurotrophic factor (BDNF) levels were evaluated in hippocampi regions. Relative mRNA expression and protein expression of BDNF were also evaluated. The results demonstrated that rats treated with TZ showed significantly (p < 0.01) reduced SDL and prolonged TL and EL as compared to control group rats. Moreover, significantly low (p < 0.01) mRNA expression and protein levels (p < 0.001) of BDNF, increased MDA and reduced GSH levels were observed in TZ treated rats. The study concludes that chronic exposure to TZ significantly impairs the learning and memory which may be attributed to the significantly reduced mRNA and protein expression of BDNF in hippocampus. Moreover, BDNF is negatively correlated to MDA levels and positively correlated to GSH levels. Hence, it can be suggested that interplay between BDNF and oxidative stress plays an important role in mediating the toxic effects of TZ.

Intermittent hypoxia from obstructive sleep apnea may cause neuronal impairment and dysfunction in central nervous system: the potential roles played by microglia

Obstructive sleep apnea (OSA) is a common condition characterized by repetitive episodes of complete (apnea) or partial (hypopnea) obstruction of the upper airway during sleep, resulting in oxygen desaturation and arousal from sleep. Intermittent hypoxia (IH) resulting from OSA may cause structural neuron damage and dysfunction in the central nervous system (CNS). Clinically, it manifests as neurocognitive and behavioral deficits with oxidative stress and inflammatory impairment as its pathophysiological basis, which are mediated by microglia at the cellular level. Microglia are dominant proinflammatory cells in the CNS. They induce CNS oxidative stress and inflammation, mainly through mitochondria, reduced nicotinamide adenine dinucleotide phosphate oxidase, and the release of excitatory toxic neurotransmitters. The balance between neurotoxic versus protective and anti- versus proinflammatory microglial factors might determine the final roles of microglia after IH exposure from OSA. Microglia inflammatory impairments will continue and cascade persistently upon activation, ultimately resulting in clinically significant neuron damage and dysfunction in the CNS. In this review article, we summarize the mechanisms of structural neuron damage in the CNS and its concomitant dysfunction due to IH from OSA, and the potential roles played by microglia in this process.

Chronic intermittent hypoxia-induced deficits in synaptic plasticity and neurocognitive functions: a role for brain-derived neurotrophic factor

Obstructive sleep apnea (OSA) is well known for its metabolic as well as neurobehavioral consequences. Chronic intermittent hypoxia (IH) is a major component of OSA. In recent years, substantial advances have been made in elucidating the cellular and molecular mechanisms underlying the effect of chronic IH on neurocognitive functions, many of which are based on studies in animal models. A number of hypotheses have been put forward to explain chronic IH-induced neurological dysfunctions. Among these, the roles of oxidative stress and apoptosis-related neural injury are widely accepted. Here, focusing on results derived from animal studies, we highlight a possible role of reduced expression of brain-derived neurotrophic factor (BDNF) in causing impairment in long-term synaptic plasticity and neurocognitive functions during chronic IH. The possible relationship between BDNF and previous findings on this subject will be elucidated.

Differential effect of oxidative or excitotoxic stress on the transcriptional profile of amyotrophic lateral sclerosis-linked mutant SOD1 cultured neurons

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal, degenerative disorder of motor neurons. The causes of most cases of ALS are as yet undefined. In a previous study, it was shown that N-methyl-D-aspartate (NMDA) and H(2)O(2) stimuli reduce neuronal survival in cortical neurons in culture (Boutahar et al., 2008). To identify variations in gene expression in response to these neurotoxins in transgenic vs. control cortical neurons cultures, both microarray and RT-PCR analysis were performed. High-density oligonucleotide microarrays showed changes in the expression of about 600 genes involved in protein degradation, neurotrophic factors pathway, cell cycle, inflammation, cytoskeleton, cell adhesion, transcription, or signalling. The most up-regulated genes following H(2)O(2) treatment were involved in cytoskeletal organization and axonal transport, such as ARAP2, KIF17, and DKK2, or in trophic factors pathways, such as insulin-like growth factor-binding protein 4 (IGFBP4), FGF17, and serpin2. The most down-regulated genes were involved in ion transport, such as TRPV1. After NMDA treatment, the most up-regulated genes were involved in protein degradation, such as ubiquitin-conjugating enzyme E2I and cathepsin H, and the most down-regulated genes were involved in ion transport, such as SCN7A. We conclude that these neurotoxins act through different transcriptional inductions, and these changes may reflect an adaptative cellular response to the cellular stress induced by the neurotoxins involved in ALS in the presence of mutant human SOD1.

Protective Action of Neurotrophic Factors and Estrogen against Oxidative Stress-Mediated Neurodegeneration

Oxidative stress is involved in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. Low levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important for maintenance of neuronal function, though elevated levels lead to neuronal cell death. A complex series of events including excitotoxicity, Ca(2+) overload, and mitochondrial dysfunction contributes to oxidative stress-mediated neurodegeneration. As expected, many antioxidants like phytochemicals and vitamins are known to reduce oxidative toxicity. Additionally, growing evidence indicates that neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and estrogens significantly prevent neuronal damage caused by oxidative stress. Here, we review and discuss recent studies addressing the protective mechanisms of neurotrophic factors and estrogen within this system.