Cellular levels of TrkB and MAPK in the neuroprotective role of BDNF for embryonic rat cortical neurons against hypoxia in vitro

Cerebral Oxygen Delivery and Consumption in Brain-Injured Patients

Organism survival depends on oxygen delivery and utilization to maintain the balance of energy and toxic oxidants production. This regulation is crucial to the brain, especially after acute injuries. Secondary insults after brain damage may include impaired cerebral metabolism, ischemia, intracranial hypertension and oxygen concentration disturbances such as hypoxia or hyperoxia. Recent data highlight the important role of clinical protocols in improving oxygen delivery and resulting in lower mortality in brain-injured patients. Clinical protocols guide the rules for oxygen supplementation based on physiological processes such as elevation of oxygen supply (by mean arterial pressure (MAP) and intracranial pressure (ICP) modulation, cerebral vasoreactivity, oxygen capacity) and reduction of oxygen demand (by pharmacological sedation and coma or hypothermia). The aim of this review is to discuss oxygen metabolism in the brain under different conditions.

Aberration of the modulatory functions of intronic microRNA hsa-miR-933 on its host gene ATF2 results in type II diabetes mellitus and neurodegenerative disease development

BACKGROUND

MicroRNAs are ~ 22-nucleotide-long biological modifiers that act as the post-transcriptional modulator of gene expression. Some of them are identified to be embedded within the introns of protein-coding genes, these miRNAs are called the intronic miRNAs. Previous findings state that these intronic miRNAs are co-expressed with their host genes. This co-expression is necessary to maintain the robustness of the biological system. Till to date, only a few experiments are performed discretely to elucidate the functional relationship between few co-expressed intronic miRNAs and their associated host genes.

RESULTS

In this study, we have interpreted the underlying modulatory mechanisms of intronic miRNA hsa-miR-933 on its target host gene ATF2 and found that aberration can lead to several disease conditions. A protein-protein interaction network-based approach was adopted, and functional enrichment analysis was performed to elucidate the significantly over-represented biological functions and pathways of the common targets. Our approach delineated that hsa-miR-933 might control the hyperglycemic condition and hyperinsulinism by regulating ATF2 target genes MAP4K4, PRKCE, PEA15, BDNF, PRKACB, and GNAS which can otherwise lead to the development of type II diabetes mellitus. Moreover, we showed that hsa-miR-933 can regulate a target of ATF2, brain-derived neurotrophic factor (BDNF), to modulate the optimal expression of ATF2 in neuron cells to render neuroprotection for the inhibition of neurodegenerative diseases.

CONCLUSIONS

Our in silico model provides interesting resources for experimentations in a model organism or cell line for further validation. These findings may extend the common perception of gene expression analysis with new regulatory functionality.

Exploring the role of oxidative stress, fatty acids and neurotrophins in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) constitutes an unfavorable intrauterine environment for embryonic and feto-placental development. Women with GDM are at higher risk for materno-fetal complications and placental abnormalities. The placenta acts as an interface between the maternal and fetal circulations and also plays an important role in protecting the fetus from adverse effects of maternal metabolic conditions. One of the earliest abnormalities observed in GDM pregnancies is increased oxidative stress in the placenta which affects fetal development. Imbalances in maternal nutrition particularly long-chain polyunsaturated fatty acid (LCPUFA) intake and/or metabolism lead to increased oxidative stress. Reports indicate that oxidative stress and LCPUFA such as docosahexaenoic acid affect the levels of neurotrophins. The present review aims to provide insights into a mechanistic link between oxidative stress, LCPUFA and neurotrophin in the placenta in women with GDM and its implications for neurodevelopmental outcomes in children.

Sex differences in Hippocampal Memory and Learning following Neonatal Brain Injury: Is There a Role for Estrogen Receptor-α?

Neonatal encephalopathy due to hypoxia-ischemia (HI) leads to severe, life-long morbidities in thousands of neonates born in the USA and worldwide each year. Varying capacities of long-term episodic memory, verbal working memory, and learning can present without cerebral palsy and have been associated with the severity of neonatal encephalopathy sustained at birth. Among children who sustain a moderate degree of HI at birth, girls have larger hippocampal volumes compared to boys. Clinical studies indicate that female neonatal brains are more resistant to the effects of neonatal HI, resulting in better long-term cognitive outcomes compared to males with comparable brain injury. Our most recent mechanistic studies have addressed the origins and cellular basis of sex differences in hippocampal neuroprotection following neonatal HI-related brain injury and implicate estrogen receptor-α (ERα) in the neurotrophin receptor-mediated hippocampal neuroprotection in female mice. This review summarizes the recent findings on ERα-dependent, neurotrophin-mediated hippocampal neuroprotection and weighs the evidence that this mechanism plays an important role in preservation of long-term memory and learning following HI in females.

Thyroxin Protects White Matter from Hypoxic-Ischemic Insult in the Immature Sprague⁻Dawley Rat Brain by Regulating Periventricular White Matter and Cortex BDNF and CREB Pathways

Background: Periventricular white-matter (WM) injury is a prominent feature of brain injury in preterm infants. Thyroxin (T4) treatment reduces the severity of hypoxic-ischemic (HI)-mediated WM injury in the immature brain. This study aimed to delineate molecular events underlying T4 protection following periventricular WM injury in HI rats. Methods: Right common-carotid-artery ligation, followed by hypoxia, was performed on seven-day-old rat pups. The HI pups were injected with saline, or 0.2 or 1 mg/kg of T4 at 48–96 h postoperatively. Cortex and periventricular WM were dissected for real-time (RT)-quantitative polymerase chain reactions (PCRs), immunoblotting, and for immunofluorescence analysis of neurotrophins, myelin, oligodendrocyte precursors, and neointimal. Results: T4 significantly mitigated hypomyelination and oligodendrocyte death in HI pups, whereas angiogenesis of periventricular WM, observed using antiendothelium cell antibody (RECA-1) immunofluorescence and vascular endothelium growth factor (VEGF) immunoblotting, was not affected. T4 also increased the brain-derived neurotrophic factors (BDNFs), but not the nerve growth factor (NGF) expression of injured periventricular WM. However, phosphorylated extracellular signal regulated kinase (p-ERK) and phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB) concentrations, but not the BDNF downstream pathway kinases, p38, c-Jun amino-terminal kinase (c-JNK), or Akt, were reduced in periventricular WM with T4 treatment. Notably, T4 administration significantly increased BDNF and phosphorylated CREB in the overlying cortex of the HI-induced injured cortex. Conclusion: Our findings reveal that T4 reversed BNDF signaling to attenuate HI-induced WM injury by activating ERK and CREB pathways in the cortex, but not directly in periventricular WM. This study offers molecular insight into the neuroprotective actions of T4 in HI-mediated WM injury in the immature brain.

Mesenchymal Stem Cells Protect Against Hypoxia-Ischemia Brain Damage by Enhancing Autophagy Through Brain Derived Neurotrophic Factor/Mammalin Target of Rapamycin Signaling Pathway

Hypoxic-ischemic encephalopathy (HIE) is a serious disease for neonates. However, present therapeutic strategies are not effective enough for treating HIE. Previous study showed that mesenchymal stem cells (MSCs) can exert neuroprotective effects for brain damage, but its mechanism remains elusive. Using in vitro coculture of rat cortical primary neurons and MSCs in HI conditions, we demonstrated that MSCs help increase brain derived neurotrophic factor (BDNF) and autophagy markers (LC3II and Beclin1) in the cultures and decrease cells death (lactate dehydrogenase levels). We demonstrated a similar mechanism using an in vivo rat model of HI in combination with MSCs transplantation. Using a behavioral study, we further showed that MSCs transplantation into the rat brain after HI injury can attenuate behavioral deficits. Finally, we found that the increase in BDNF and autophagy related factors after HI injury combined with MSCs transplantation can be reversed by anti-BDNF treatment and strengthen the point that the protective effects of BDNF work through inhibition of the mammalin target of rapamycin (mTOR) pathway. Collectively, we proposed that coculture/transplantation of MSCs after HI injury leads to increased BDNF expression and a subsequent reduction in mTOR pathway activation that results in increased autophagy and neuroprotection. This finding gives a hint to explore new strategies for treating neonates with HIE. Stem Cells 2018;36:1109-1121.

Active forms of Akt and ERK are dominant in the cerebral cortex of newborn pigs that are unaffected by asphyxia

AIMS

Perinatal asphyxia (PA) often results in hypoxic-ischemic encephalopathy (HIE) in term neonates. Introduction of therapeutic hypothermia improved HIE outcome, but further neuroprotective therapies are still warranted. The present study sought to determine the feasibility of the activation of the cytoprotective PI-3-K/Akt and the MAPK/ERK signaling pathways in the subacute phase of HIE development in a translational newborn pig PA/HIE model.

MAIN METHODS

Phosphorylated and total levels of Akt and ERK were determined by Western blotting in brain samples obtained from untreated naive, time control, and PA/HIE animals at 24-48h survival (n=3-3-6,respectively). PA (20min) was induced in anesthetized piglets by ventilation with a hypoxic/hypercapnic (6%O₂20%CO₂) gas mixture. Furthermore, we studied the effect of topically administered specific Akt1/2 and MAPK/ERK kinase inhibitors on Akt and ERK phosphorylation (n=4-4) in the cerebral cortex under normoxic conditions.

KEY FINDINGS

PA resulted in significant neuronal injury shown by neuropathology assessment of haematoxylin/eosin stained sections. However, there were no significant differences among the groups in the high phosphorylation levels of both ERK and Akt in the cerebral cortex, hippocampus and subcortical structures. However, the Akt1/2 and MAPK/ERK kinase inhibitors significantly reduced cerebrocortical Akt and ERK phosphorylation within 30min.

SIGNIFICANCE

The major finding of the present study is that the PI-3-K/Akt and the MAPK/ERK signaling pathways appear to be constitutively active in the piglet brain, and this activation remains unaltered during HIE development. Thus, neuroprotective strategies aiming to activate these pathways to limit apoptotic neuronal death may offer limited efficacy in this translational model.

Comparative Response of Brain to Chronic Hypoxia and Hyperoxia

Two antithetic terms, hypoxia and hyperoxia, i.e., insufficient and excess oxygen availability with respect to needs, are thought to trigger opposite responses in cells and tissues. This review aims at summarizing the molecular and cellular mechanisms underlying hypoxia and hyperoxia in brain and cerebral tissue, a context that may prove to be useful for characterizing not only several clinically relevant aspects, but also aspects related to the evolution of oxygen transport and use by the tissues. While the response to acute hypoxia/hyperoxia presumably recruits only a minor portion of the potentially involved cell machinery, focusing into chronic conditions, instead, enables to take into consideration a wider range of potential responses to oxygen-linked stress, spanning from metabolic to genic. We will examine how various brain subsystems, including energetic metabolism, oxygen sensing, recruitment of pro-survival pathways as protein kinase B (Akt), mitogen-activated protein kinases (MAPK), neurotrophins (BDNF), erythropoietin (Epo) and its receptors (EpoR), neuroglobin (Ngb), nitric oxide (NO), carbon monoxide (CO), deal with chronic hypoxia and hyperoxia to end-up with the final outcomes, oxidative stress and brain damage. A more complex than expected pattern results, which emphasizes the delicate balance between the severity of the stress imposed by hypoxia and hyperoxia and the recruitment of molecular and cellular defense patterns. While for certain functions the expectation that hypoxia and hyperoxia should cause opposite responses is actually met, for others it is not, and both emerge as dangerous treatments.

High ω3-polyunsaturated fatty acids in fat-1 mice prevent streptozotocin-induced Purkinje cell degeneration through BDNF-mediated autophagy

Loss of Purkinje cells has been implicated in the development of diabetic neuropathy, and this degeneration is characterized by impairment of autophagic processes. We evaluated whether fat-1 transgenic mice, a well-established animal model that endogenously synthesizes ω3 polyunsaturated fatty acids (ω3-PUFA), are protected from Purkinje cell degeneration in streptozotocin (STZ)-treated model with fat-1 mice. STZ-treated fat-1 mice did not develop hyperglycemia, motor deficits, or Purkinje cell loss. The expression of LC3 I, II, Beclin-1 and p62 were increased in the cerebellum of STZ-treated wild-type mice, and these expressions were more increased in STZ-treated fat-1 mice, but not of p62. Moreover, cerebellar Rab7, Cathepsin D, and ATP6E were increased in STZ-treated fat-1 mice. There was also increased BDNF expression in Purkinje cells without any changes in TrkB, and phosphorylation of Akt and CREB in the cerebellums of fat-1 mice. Collectively, these findings indicate that STZ-treated fat-1 mice were protected from Purkinje cell loss and exhibited increased BDNF signaling, enhancing autophagic flux activity in cerebellar Purkinje neurons. These processes may underlie Purkinje cell survival and may be potential therapeutic targets for treatment of motor deficits related to diabetic neuropathy.

Neuroprotective effect of brain-derived neurotrophic factor mediated by autophagy through the PI3K/Akt/mTOR pathway

Brain‑derived neurotrophic factor (BDNF) has been demonstrated to be a potent growth factor that is beneficial in neuronal functions following hypoxia‑ischemia (HI). Mature BDNF triggers three enzymes, mitogen‑activated protein kinase (MAPK), phosphatidylinositol 3‑kinase (PI3K) and phosphoinositide phospholipase C-γ (PLCγ), which are its predominant downstream regulators. The PI3K‑Akt signaling pathway is upstream of the mammalian target of rapamycin (mTOR), which is important in the induction of autophagy. However, whether the neuroprotective effect of BDNF is mediated by autophagy through the PI3K/Akt/mTOR pathway remains to be elucidated. Cortical neurons were cultured following isolation from pregnant rats (gestational days 16‑18). The induction of autophagy following BDNF treatment was analyzed by microtubule‑associated protein light chain 3 (LC3) conversion and autophagosome formation. The phosphorylation of Akt, mTOR and ribosomal protein S6 kinase (p70S6K) was analyzed in cultured cells with or without BDNF treatment. Cell viability was determined by a Cell Counting Kit‑8 for estimating the protective effect of BDNF. Results demonstrated that autophagy was induced in cells with oxygen deprivation. BDNF promoted cell viability via the upregulation of autophagy. Moreover, LC3 upregulation was related to Akt/mTOR/p70S6K inhibition by BDNF. In conclusion, the results suggested that the neuroprotective effect of BDNF was mediated by autophagy through the PI3K/Akt/mTOR pathway.

BDNF protects retinal neurons from hyperglycemia through the TrkB/ERK/MAPK pathway

Diabetic retinopathy (DR) is one of the most common diabetic eye diseases and a leading cause of blindness. It is characterized by changes in the blood vessels of the retina. The pathogenesis of DR is complex and to date, the precise mechanisms involved remain unclear. Previous studies have reported that DR is associated with neurodegeneration and that apoptosis may occur in diabetic retinas. In the present study, retinal neurons under conditions of hyperglycemia were used as a model to study apoptosis in diabetic retinas. Retinal neurons exposed to hyperglycemia exhibited high levels of apoptosis. Brain‑derived neurotrophic factor (BDNF), a member of the neurotrophin family, was effective in protecting retinal neurons from hyperglycemia in vitro. BDNF promoted neuronal cell survival in a concentration‑dependent manner. In addition, BDNF was demonstrated to promote the expression of tropomyosin‑related kinase B (TrkB) and elevate the phosphorylation levels of TrkB and ERK in retinal neurons exposed to hyperglycemia. The results of the present study demonstrated that BDNF may protect retinal neurons from hyperglycemia via the TrkB/ERK/MAPK pathway and provides novel insights into the pathogenesis of DR.

The neuroprotective roles of BDNF in hypoxic ischemic brain injury

Hypoxia-ischemia (H/I) brain injury results in various degrees of damage to the body, and the immature brain is particularly fragile to oxygen deprivation. Hypothermia and erythropoietin (EPO) have long been known to be neuroprotective in ischemic brain injury. Brain-derived neurotrophic factor (BDNF) has recently been recognized as a potent modulator capable of regulating a wide repertoire of neuronal functions. This review was based on studies concerning the involvement of BDNF in the protection of H/I brain injury following a search in PubMed between 1995 and December, 2011. We initially examined the background of BDNF, and then focused on its neuroprotective mechanisms against ischemic brain injury, including its involvement in promoting neural regeneration/cognition/memory rehabilitation, angiogenesis within ischemic penumbra and the inhibition of the inflammatory process, neurotoxicity, epilepsy and apoptosis. We also provided a literature overview of experimental studies, discussing the safety and the potential clinical application of BDNF as a neuroprotective agent in the ischemic brain injury.

Edaravone protects cortical neurons from apoptosis by inhibiting the translocation of BAX and Increasing the interaction between 14-3-3 and p-BAD

Edaravone, a free radical scavenger, has shown neuroprotection properties in both animals and humans. To evaluate the mechanisms involved, we obtained a culture of almost pure neurons. The neurons, either untreated or prophylactically treated with edaravone, were exposed to 300 μM hydrogen peroxide. We examined alterations in mitochondria, the percent of apoptotic cells and the immunoblots of key regulatory proteins, and the protein-protein interactions and the cellular locations of cytochrome c. The levels of p-JNK (Thr183/Tyr185) and cytochrome c in cytosol and BAX in heavy membrane (HM), respectively, were increased at 0.5 h and reached the peak at 12 h after stimulation with hydrogen peroxide. The levels of p-BAD and BAX in the cytosol and the interaction between BAD and 14-3-3 were decreased in the untreated neurons. However, edaravone could prevent these changes. In addition, mitochondrial morphology was better preserved and the percentage of apoptosis was lower under the treatment with edaravone. In summary, the present study indicates that edaravone could protect neurons by inhibiting: (1) the activity of JNK, (2) the disassociation of BAD from 14-3-3, and (3) the translocation of BAX from cytosol to mitochondria.

Decreased neurotrophic response to birth hypoxia in the etiology of schizophrenia

BACKGROUND

Obstetric complications, particularly fetal hypoxia, are associated with increased risk for schizophrenia later in life. Such factors are also related to increased severity of certain neuropathological features of schizophrenia, including hippocampal and cortical gray matter reduction, among individuals with a genetic susceptibility to the disorder. However, the molecular mechanisms underlying these associations are unknown. Here, we sought to determine whether neurotrophic factors, which are stimulated as part of a neuroprotective response to fetal distress, are differentially expressed in cord blood samples at the time of birth following fetal hypoxia, maternal hypertension/small for gestational age status, and/or prematurity among individuals who developed schizophrenia as adults, as compared with control subjects.

METHODS

One hundred eleven cases with psychotic disorders (70 with schizophrenia) and 333 control subjects matched for gender, race, and date of birth were drawn from the Philadelphia cohort of the National Collaborative Perinatal Project in a nested case-control study. Brain-derived neurotrophic factor (BDNF) was assayed from cord and maternal blood samples taken at delivery and stored at -20 degrees C for 45 to 50 years.

RESULTS

Among control subjects, birth hypoxia was associated with a significant (10%) increase in BDNF in cord samples, while among cases, hypoxia was associated with a significant (20%) decrease in BDNF. This differential response to fetal hypoxia was specific to schizophrenia and was not explained by other obstetric complications or by the BDNF valine (val) to methionine (met) polymorphism at codon 66 (val66met).

CONCLUSIONS

These findings provide serologically based prospective evidence of disrupted neurotrophic signaling in response to birth hypoxia in the molecular pathogenesis of schizophrenia.