NKCC1 mediates traumatic brain injury-induced hippocampal neurogenesis through CREB phosphorylation and HIF-1α expression

Microglia-induced neuroinflammation in hippocampal neurogenesis following traumatic brain injury

Traumatic brain injury (TBI) is one of the most causes of death and disability among people, leading to a wide range of neurological deficits. The important process of neurogenesis in the hippocampus, which includes the production, maturation and integration of new neurons, is affected by TBI due to microglia activation and the inflammatory response. During brain development, microglia are involved in forming or removing synapses, regulating the number of neurons, and repairing damage. However, in response to injury, activated microglia release a variety of pro-inflammatory cytokines, chemokines and other neurotoxic mediators that exacerbate post-TBI injury. These microglia-related changes can negatively affect hippocampal neurogenesis and disrupt learning and memory processes. To date, the intracellular signaling pathways that trigger microglia activation following TBI, as well as the effects of microglia on hippocampal neurogenesis, are poorly understood. In this review article, we discuss the effects of microglia-induced neuroinflammation on hippocampal neurogenesis following TBI, as well as the intracellular signaling pathways of microglia activation.

Comparative analysis of early neurodegeneration signs in a mouse model of Alzheimer's disease-like pathology induced by two types of the central (Intracerebroventricular vs. Intrahippocampal) administration of Aβ25-35 oligomers

Animal models of Alzheimer's disease (AD) induced by intracerebroventricular (ICV) or intrahippocampal (IH) administration of amyloid-beta (Aβ) are widely used in current research. It remains unclear whether these models provide similar outcomes or mimic pathological mechanisms of AD equally. The aim of the work was to compare two models induced by ICV or IH administration of Aβ25-35 oligomers to C57BL/6 mice. Parameters characterizing cognitive function (passive avoidance test), protein expression (IBA1, Aβ, LC3-II) and expression of genes for neuroinflammation (Aif1, Lcn2, Nrf2), autophagy (Atg8, Becn1, Park2), or markers of neurodegeneration (Cst3, Insr, Vegfa) were analyzed. Сognitive deficits, amyloid accumulation, and neuroinflammatory response in the brain evaluated by the microglial activation were similar in both models. Thus, both ways of Aβ administration appear to be equally suitable for modelling AD-like pathology in mice. Our findings strongly support the key role of Aβ load and neuroinflammatory response in the hippocampus and frontal cortex for the progression of AD-like pathology and development of cognitive deficits. There were certain minor differences between the models in the mRNA level of genes involved in the processes of neuroinflammation, neurodegeneration, and autophagy. Modulating effects of the central administration of Aβ25-35 on the mRNA expression of Aif1, Lcn2, Park2, and Vegfa genes in different brain structures were revealed. The effects occurred to be more pronounced with the ICV method compared with the IH method. These findings give insight into the processes at initial stages of Aβ-induced pathology depending on a primary location of Aβ oligomers in the brain.

Myoglobin in Brown Adipose Tissue: A Multifaceted Player in Thermogenesis

Brown adipose tissue (BAT) plays an important role in energy homeostasis by generating heat from chemical energy via uncoupled oxidative phosphorylation. Besides its high mitochondrial content and its exclusive expression of the uncoupling protein 1, another key feature of BAT is the high expression of myoglobin (MB), a heme-containing protein that typically binds oxygen, thereby facilitating the diffusion of the gas from cell membranes to mitochondria of muscle cells. In addition, MB also modulates nitric oxide (NO•) pools and can bind C16 and C18 fatty acids, which indicates a role in lipid metabolism. Recent studies in humans and mice implicated MB present in BAT in the regulation of lipid droplet morphology and fatty acid shuttling and composition, as well as mitochondrial oxidative metabolism. These functions suggest that MB plays an essential role in BAT energy metabolism and thermogenesis. In this review, we will discuss in detail the possible physiological roles played by MB in BAT thermogenesis along with the potential underlying molecular mechanisms and focus on the question of how BAT-MB expression is regulated and, in turn, how this globin regulates mitochondrial, lipid, and NO• metabolism. Finally, we present potential MB-mediated approaches to augment energy metabolism, which ultimately could help tackle different metabolic disorders.

HIF-1α participates in secondary brain injury through regulating neuroinflammation

A deeper understanding of the underlying biological mechanisms of secondary brain injury induced by traumatic brain injury (TBI) will greatly advance the development of effective treatments for patients with TBI. Hypoxia-inducible factor-1 alpha (HIF-1α) is a central regulator of cellular response to hypoxia. In addition, growing evidence shows that HIF-1α plays the important role in TBI-induced changes in biological processes; however, detailed functional mechanisms are not completely known. The aim of the present work was to further explore HIF-1α-mediated events after TBI. To this end, next-generation sequencing, coupled with cellular and molecular analysis, was adopted to interrogate vulnerable events in a rat controlled cortical impact model of TBI. The results demonstrated that TBI induced accumulation of HIF-1α at the peri-injury site at 24 h post-injury, which was associated with neuronal loss. Moreover, gene set enrichment analysis unveiled that neuroinflammation, especially an innate inflammatory response, was significantly evoked by TBI, which could be attenuated by the inhibition of HIF-1α. Furthermore, the inhibition of HIF-1α could mitigate the activation of microglia and astrocytes. Taken together, all these data implied that HIF-1α might contribute to secondary brain injury through regulating neuroinflammation.

Insights into the role of pERK1/2 signaling in post-cerebral ischemia reperfusion sexual dysfunction in rats

The purpose of the present study was to investigate the effects of ERK1/2 inhibition on both the amygdala and hippocampal structures, and to investigate its role in regulating memory for sexual information. This study utilized a cerebral ischemia reperfusion (IR) model to produce a stressful brain condition that highlights the possible involvement of a hippocampal GC/pERK1/2/BDNF pathway in the resulting sexual consequences of this ailment. Male Wistar rats were divided into four groups: (1) sham; (2) IR: subjected to 45 min of ischemia followed by 48 h of reperfusion; (3) PD98059: received PD98059 at 0.3 mg/kg, i.p.; (4) IR + PD98059. This study provides new evidence for cerebral IR-induced amygdala injury and the sexual impairments that are associated with motor and cognitive deficits in rats. These findings were correlated with histopathological changes that are defined by extensive neuronal loss in both the hippocampus and the amygdala. The current study postulated that the ERK inhibitor PD98059 could reverse IR-induced injury in the amygdala as well as reversing IR-induced sexual impairments. This hypothesis is supported by the ability of PD98059 to: (1) restore luteinizing hormone and testosterone levels; (2) increase sexual arousal and copulatory performance (as evidenced by modulating mount, intromission, ejaculation latencies, and post-ejaculatory intervals); (3) improve the histological profile in the amygdala that is associated with reduced glutamate levels, c-Fos expression, and elevated gamma aminobutyric acid levels. In conclusion, the present findings introduce pERK1/2 inhibition as a possible strategy for enhancing sexual activity in survivors of IR.

A Novel Laser-Based Zebrafish Model for Studying Traumatic Brain Injury and Its Molecular Targets

Traumatic brain injury (TBI) is a major public health problem. Here, we developed a novel model of non-invasive TBI induced by laser irradiation in the telencephalon of adult zebrafish (Danio rerio) and assessed their behavior and neuromorphology to validate the model and evaluate potential targets for neuroreparative treatment. Overall, TBI induced hypolocomotion and anxiety-like behavior in the novel tank test, strikingly recapitulating responses in mammalian TBI models, hence supporting the face validity of our model. NeuN-positive cell staining was markedly reduced one day, but not seven days, after TBI, suggesting increased neuronal damage immediately after the injury, and its fast recovery. The brain-derived neurotrophic factor (Bdnf) level in the brain dropped immediately after the trauma, but fully recovered seven days later. A marker of microglial activation, Iba1, was elevated in the TBI brain, albeit decreasing from Day 3. The levels of hypoxia-inducible factor 1-alpha (Hif1a) increased 30 min after the injury, and recovered by Day 7, further supporting the construct validity of the model. Collectively, these findings suggest that our model of laser-induced brain injury in zebrafish reproduces mild TBI and can be a useful tool for TBI research and preclinical neuroprotective drug screening.

Upregulation of neuronal progranulin mediates the antinociceptive effect of trimetazidine in paclitaxel-induced peripheral neuropathy: Role of ERK1/2 signaling

Neuronal progranulin (PGRN) overexpression is an endogenous adaptive pain defense following nerve injury. It allows the survival of injured neurons to block enhanced nociceptive responses. Trimetazidine (TMZ) is widely used by cardiac patients as an anti-anginal drug, reflecting its anti-ischemic property. TMZ promotes axonal regeneration of sciatic nerves after crush injury. This study explored the interplay between PGRN and extracellular signal-regulated kinases (ERK1/2) to address mechanisms underlying neuropathic pain alleviation following paclitaxel (PTX) administration. Rats were given four injections of PTX (2 mg/kg, i.p.) every other day. Two days after the last dose, rats received TMZ (25 mg/kg) with or without the ERK inhibitor, PD98059, daily for 21 days. TMZ preserved the integrity of myelinated nerve fibers, as evidenced by an obvious reduction in axonal damage biomarkers. Accordingly, it alleviated PTX-evoked thermal, cold, and mechanical hyperalgesia/allodynia. TMZ also promoted ERK1/2 phosphorylation with a profound upsurge in PGRN content. These effects were associated with a substantial increase in Notch1 receptor gene expression and a prominent anti-inflammatory effect with a marked increase in mRNA expression of secretory leukocyte protease inhibitor. Further, TMZ decreased oxidative stress and caspase-3 activity in the sciatic nerve. Conversely, co-administration of PD98059 completely abolished these beneficial effects. Thus, the robust antinociceptive effect of TMZ is largely attributed to upregulating PGRN and Notch1 receptors via ERK1/2 activation.

Inosine attenuates 3-nitropropionic acid-induced Huntington's disease-like symptoms in rats via the activation of the A2AR/BDNF/TrKB/ERK/CREB signaling pathway

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disease characterized by involuntary bizarre movements, psychiatric symptoms, dementia, and early death. Several studies suggested neuroprotective activities of inosine; however its role in HD is yet to be elucidated. The current study aimed to demonstrate the neuroprotective effect of inosine in 3-nitropropionic acid (3-NP)-induced neurotoxicity in rats while investigating possible underlying mechanisms. Rats were randomly divided into five groups; group 1 received i.p. injections of 1% DMSO, whereas groups 2, 3, 4, and 5 received 3-NP (10 mg/kg, i.p.) for 14 days, concomitantly with inosine (200 mg/kg., i.p.) in groups 3, 4, and 5, SCH58261, a selective adenosine 2A receptor (A2AR) antagonist, (0.05 mg/kg, i.p.) in group 4, and PD98059, an extracellular signal-regulated kinase (ERK) inhibitor, (0.3 mg/kg, i.p.) in group 5. Treatment with inosine mitigated 3-NP-induced motor abnormalities and body weight loss. Moreover, inosine boosted the striatal brain-derived neurotrophic factor (BDNF) level, p-tropomyosin receptor kinase B (TrKB), p-ERK, and p-cAMP response element-binding protein (CREB) expression, which subsequently suppressed oxidative stress biomarkers (malondialdehyde and nitric oxide) and pro-inflammatory cytokines (tumor necrosis factor alpha and interleukin-1β) and replenished the glutathione content. Similarly, histopathological analyses revealed decreased striatal injury score, the expression of the glial fibrillary acidic protein, and neuronal loss after inosine treatment. These effects were attenuated by the pre-administration of SCH58261 or PD98059. In conclusion, inosine attenuated 3-NP-induced HD-like symptoms in rats, at least in part, via the activation of the A2AR/BDNF/TrKB/ERK/CREB signaling pathway.

On the potential role of globins in brown adipose tissue: a novel conceptual model and studies in myoglobin knockout mice

Myoglobin (Mb) regulates O₂ bioavailability in muscle and heart as the partial pressure of O₂ (Po₂) drops with increased tissue workload. Globin proteins also modulate cellular NO pools, "scavenging" NO at higher Po₂ and converting NO₂^- to NO as Po₂ falls. Myoglobin binding of fatty acids may also signal a role in fat metabolism. Interestingly, Mb is expressed in brown adipose tissue (BAT), but its function is unknown. Herein, we present a new conceptual model that proposes links between BAT thermogenic activation, concurrently reduced Po₂, and NO pools regulated by deoxy/oxy-globin toggling and xanthine oxidoreductase (XOR). We describe the effect of Mb knockout (Mb^-/-) on BAT phenotype [lipid droplets, mitochondrial markers uncoupling protein 1 (UCP1) and cytochrome C oxidase 4 (Cox4), transcriptomics] in male and female mice fed a high-fat diet (HFD, 45% of energy, ∼13 wk), and examine Mb expression during brown adipocyte differentiation. Interscapular BAT weights did not differ by genotype, but there was a higher prevalence of mid-large sized droplets in Mb^-/-. COX4 protein expression was significantly reduced in Mb^-/- BAT, and a suite of metabolic/NO/stress/hypoxia transcripts were lower. All of these Mb^-/--associated differences were most apparent in females. The new conceptual model, and results derived from Mb^-/- mice, suggest a role for Mb in BAT metabolic regulation, in part through sexually dimorphic systems and NO signaling. This possibility requires further validation in light of significant mouse-to-mouse variability of BAT Mb mRNA and protein abundances in wild-type mice and lower expression relative to muscle and heart.NEW & NOTEWORTHY Myoglobin confers the distinct red color to muscle and heart, serving as an oxygen-binding protein in oxidative fibers. Less attention has been paid to brown fat, a thermogenic tissue that also expresses myoglobin. In a mouse knockout model lacking myoglobin, brown fat had larger fat droplets and lower markers of mitochondrial oxidative metabolism, especially in females. Gene expression patterns suggest a role for myoglobin as an oxygen/nitric oxide-sensor that regulates cellular metabolic and signaling pathways.

Theacrine, a Potent Antidepressant Purine Alkaloid from a Special Chinese Tea, Promotes Adult Hippocampal Neurogenesis in Stressed Mice

Daily intake of tea has been known to relate to a low risk of depression. In this study, we report that a special variety of tea in China, Camellia assamica var. kucha (kucha), possesses antidepressant effects but with less adverse effects as compared to traditional tea Camellia sinensis. This action of kucha is related to its high amount of theacrine, a purine alkaloid structurally similar to caffeine. We investigated the antidepressant-like effects and mechanisms of theacrine in chronic water immersion restraint stress and chronic unpredictable mild stress mice models. PC12 cells and primary hippocampal neural stem cells were treated with stress hormone corticosterone (CORT) to reveal the potential antidepression mechanism of theacrine from the perspective of adult hippocampus neurogenesis. Results of behavioral and neurotransmitter analysis showed that intragastric administration of theacrine significantly counteracted chronic stress-induced depression-like disorders and abnormal 5-hydroxytryptamine (5-HT) metabolism with less central excitability. Further investigation from both in vivo and in vitro experiments indicated that the antidepressant mechanism of theacrine was associated with promoting adult hippocampal neurogenesis, via the modulation of the phosphodiesterase-4 (PDE4)/cyclic adenosine monophosphate (cAMP)/cAMP response-element binding (CREB)/brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) pathway. Collectively, our findings could promote the prevalence of kucha as a common beverage with uses for health care and contribute to the development of theacrine as a potential novel antidepressant medicine.

Regulation of Electrolyte Permeability by Herbal Monomers in Edematous Disorders

Edema is a gradual accumulation of fluid in the interstitial tissues or luminal cavities, which is regulated by ion transport pathways and reflects dysfunction of fluid and salt homeostasis. Increasing evidence suggests that some herbal monomers significantly reduce organ/tissue edema. In this review, we briefly summarized the electrolyte permeability involved in pathomechanisms of organ edema, and the benefits of herbal monomers on ionic transport machinery, including Na+-K+-ATPase, Na+ and Cl- channels, Na+-K+-2Cl- co-transporter, etc. Pharmaceutical relevance is implicated in developing advanced strategies to mitigate edematous disorders. In conclusion, the natural herbal monomers regulate electrolyte permeability in many edematous disorders, and further basic and clinical studies are needed.

The utilization of small non-mammals in traumatic brain injury research: A systematic review

Traumatic brain injury (TBI) is the leading cause of death and disability worldwide and has complicated underlying pathophysiology. Numerous TBI animal models have been developed over the past decade to effectively mimic the human TBI pathophysiology. These models are of mostly mammalian origin including rodents and non-human primates. However, the mammalian models demanded higher costs and have lower throughput often limiting the progress in TBI research. Thus, this systematic review aims to discuss the potential benefits of non-mammalian TBI models in terms of their face validity in resembling human TBI. Three databases were searched as follows: PubMed, Scopus, and Embase, for original articles relating to non-mammalian TBI models, published between January 2010 and December 2019. A total of 29 articles were selected based on PRISMA model for critical appraisal. Zebrafish, both larvae and adult, was found to be the most utilized non-mammalian TBI model in the current literature, followed by the fruit fly and roundworm. In conclusion, non-mammalian TBI models have advantages over mammalian models especially for rapid, cost-effective, and reproducible screening of effective treatment strategies and provide an opportunity to expedite the advancement of TBI research.

Effects of Selective Serotonin Reuptake Inhibitors on Depression-Like Behavior in a Laser-Induced Shock Wave Model

Primary blast injury can result in depression-like behavior in the long-term. However, the effects of the selective serotonin reuptake inhibitor (SSRI) on the depression induced by mild blast traumatic brain injury (bTBI) in the long-term remain unclear. We generated a mouse model of mild bTBI using laser-induced shock wave (LISW) and administered an SSRI to mice by oral gavage for 14 days after LISW exposure. This study aimed to investigate the mechanisms of SSRI-mediated alleviation of depression-like behavior induced by mild bTBI. Animals were divided into three groups: sham, LISW-Vehicle, and LISW-SSRI. LISW was applied to the head of anesthetized mice at 0.5 J/cm². Twenty-eight days after the LISW, mice in the LISW-SSRI group exhibited reduced depression-like behavior, a significant increase in the number of cells co-stained for 5-bromo-2'-deoxyuridine (Brd-U) and doublecortin (DCX) in the dentate gyrus (DG) as well as increased brain-derived neurotrophic factor (BDNF) and serotonin levels in the hippocampus compared to the sham and LISW-Vehicle groups. Additionally, levels of phosphorylated cAMP response element binding protein (pCREB) in the DG were significantly decreased in the LISW-Vehicle group compared to that in the sham group. Importantly, pCREB levels were not significantly different between LISW-SSRI and sham groups suggesting that SSRI treatment may limit the downregulation of pCREB induced by mild bTBI. In conclusion, recovery from depression-like behavior after mild bTBI may be mediated by hippocampal neurogenesis induced by increased BDNF and serotonin levels as well as the inhibition of pCREB downregulation in the hippocampus.

Targeting the WNK-SPAK/OSR1 Pathway and Cation-Chloride Cotransporters for the Therapy of Stroke

Stroke is one of the major culprits responsible for morbidity and mortality worldwide, and the currently available pharmacological strategies to combat this global disease are scanty. Cation-chloride cotransporters (CCCs) are expressed in several tissues (including neurons) and extensively contribute to the maintenance of numerous physiological functions including chloride homeostasis. Previous studies have implicated two CCCs, the Na+-K+-Cl- and K+-Cl- cotransporters (NKCCs and KCCs) in stroke episodes along with their upstream regulators, the with-no-lysine kinase (WNKs) family and STE20/SPS1-related proline/alanine rich kinase (SPAK) or oxidative stress response kinase (OSR1) via a signaling pathway. As the WNK-SPAK/OSR1 pathway reciprocally regulates NKCC and KCC, a growing body of evidence implicates over-activation and altered expression of NKCC1 in stroke pathology whilst stimulation of KCC3 during and even after a stroke event is neuroprotective. Both inhibition of NKCC1 and activation of KCC3 exert neuroprotection through reduction in intracellular chloride levels and thus could be a novel therapeutic strategy. Hence, this review summarizes the current understanding of functional regulations of the CCCs implicated in stroke with particular focus on NKCC1, KCC3, and WNK-SPAK/OSR1 signaling and discusses the current and potential pharmacological treatments for stroke.

Aldosterone up-regulates voltage-gated potassium currents and NKCC1 protein membrane fractions

Na+-K+-2Cl- Cotransporter (NKCC1) is a protein that aids in the active transport of sodium, potassium, and chloride ions across cell membranes. It has been shown that long-term systemic treatment with aldosterone (ALD) can enhance NKCC1 protein expression and activity in the aging cochlea resulting in improved hearing. In the present work, we used a cell line with confirmed NKCC1 expression to demonstrate that in vitro application of ALD increased outward voltage-gated potassium currents significantly, and simultaneously upregulated whole lysate and membrane portion NKCC1 protein expression. These ALD-induced changes were blocked by applying the mineralocorticoid receptor antagonist eplerenone. However, application of the NKCC1 inhibitor bumetanide or the potassium channel antagonist Tetraethyl ammonium had no effect. In addition, NKKC1 mRNA levels remained stable, indicating that ALD modulates NKCC1 protein expression via the activation of mineralocorticoid receptors and post-transcriptional modifications. Further, in vitro electrophysiology experiments, with ALD in the presence of NKCC1, K+ channel and mineralocorticoid receptor inhibitors, revealed interactions between NKCC1 and outward K+ channels, mediated by a mineralocorticoid receptor-ALD complex. These results provide evidence of the therapeutic potential of ALD for the prevention/treatment of inner ear disorders such as age-related hearing loss.

New insights into the effects of caffeine on adult hippocampal neurogenesis in stressed mice: Inhibition of CORT-induced microglia activation

Chronic stress-evoked depression has been implied to associate with the decline of adult hippocampal neurogenesis. Caffeine has been known to combat stress-evoked depression. Herein, we aim to investigate whether the protective effect of caffeine on depression is related with improving adult hippocampus neurogenesis and explore the mechanisms. Mouse chronic water immersion restraint stress (CWIRS) model, corticosterone (CORT)-established cell stress model, a coculture system containing CORT-treated BV-2 cells and hippocampal neural stem cells (NSCs) were utilized. Results showed that CWIRS caused obvious depressive-like disorders, abnormal 5-HT signaling, and elevated-plasma CORT levels. Notably, microglia activation-evoked brain inflammation and inhibited neurogenesis were also observed in the hippocampus of stressed mice. In comparison, intragastric administration of caffeine (10 and 20 mg/kg, 28 days) significantly reverted CWIRS-induced depressive behaviors, neurogenesis recession and microglia activation in the hippocampus. Further evidences from both in vivo and in vitro mechanistic experiments demonstrated that caffeine treatment significantly suppressed microglia activation via the A2AR/MEK/ERK/NF-κB signaling pathway. The results suggested that CORT-induced microglia activation contributes to stress-mediated neurogenesis recession. The antidepression effect of caffeine was associated with unlocking microglia activation-induced neurogenesis inhibition.

Relationship between HIF-1α and apoptosis in rats with traumatic brain injury and the influence of traditional Chinese medicine Sanqi

Objective To explore the expression of HIF-1α, neuronal apoptosis and the influence of traditional Chinese medicine Sanqi on hematoma after brain injury in rats. Methods Ninety SD rats were divided into 3 groups randomly: blank control group, traumatic brain injury (TBI) group and Sanqi intervention group, and they were decapitated after brain injury at different time points: 6 h, 1 d, 2 d, 3 d, 5 d, 7 d. The model of cerebral hemorrhage was made by autologous non-coagulation in stereotactic locator, the expression of HIF-1α and TUNEL-positive cells (apoptotic cells) in the perihematomal area was detected by immunohistochemistry. Results In blank control group, a small amount of HIF-1α was expressed and apoptotic cells were observed. The expression of HIF-1α was up-regulated in the brain injury group from 6 h, and the apoptotic cells increased in abundance. The peak of HIF-1α was reached at 3 d, then decreased, and remained at the high level on the 7 d. Compared with blank control group, the TBI group was statistically significant (P < 0.05). The Chinese medicine Sanqi intervention group significantly up-regulated HIF-1α'expression and decreased neuronal apoptosis, which was statistically significant (P < 0.05). Conclusion HIF-1α's expression was up-regulated around the hematoma after brain injury, and the apoptosis of nerve cells was obviously increased. The traditional Chinese medicine Sanqi can significantly increase the expression of HIF-1α, reduce the apoptosis around the hematoma, and thus play a neuroprotective role.

NFAT5 and HIF-1α Coordinate to Regulate NKCC1 Expression in Hippocampal Neurons After Hypoxia-Ischemia

Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with severe long-term sequelae such as cerebral palsy, epilepsy and cognitive disabilities. Na⁺-K⁺-2Cl^– cotransporters 1 (NKCC1) is dramatically upregulated after hypoxia-ischemia (HI), which aggravates brain edema and brain damage. Clinically, an NKCC1-specific inhibitor, bumetanide, is used to treat diseases related to aberrant NKCC1 expression, but the underlying mechanism of aberrant NKCC1 expression has rarely been studied in HIE. In this study, the cooperative effect of hypoxia-inducible factor-1α (HIF-1α) and nuclear factor of activated T cells 5 (NFAT5) on NKCC1 expression was explored in hippocampal neurons under hypoxic conditions. HI increased HIF-1α nuclear localization and transcriptional activity, and pharmacological inhibition of the HIF-1α transcription activity or mutation of hypoxia responsive element (HRE) motifs recovered the hypoxia-induced aberrant expression and promoter activity of NKCC1. In contrast, oxygen–glucose deprivation (OGD)-induced downregulation of NFAT5 expression was reversed by treating with hypertonic saline, which ameliorated aberrant NKCC1 expression. More importantly, knocking down NFAT5 or mutation of the tonicity enhancer element (TonE) stimulated NKCC1 expression and promoter activity under normal physiological conditions. The positive regulation of NKCC1 by HIF-1α and the negative regulation of NKCC1 by NFAT5 may serve to maintain NKCC1 expression levels, which may shed light on the transcription regulation of NKCC1 in hippocampal neurons after hypoxia.

Neuronal Transmembrane Chloride Transport Has a Time-Dependent Influence on Survival of Hippocampal Cultures to Oxygen-Glucose Deprivation

Neuronal ischemia results in chloride gradient alterations which impact the excitatory–inhibitory balance, volume regulation, and neuronal survival. Thus, the Na⁺/K⁺/Cl⁻ co-transporter (NKCC1), the K⁺/ Cl⁻ co-transporter (KCC2), and the gamma-aminobutyric acid A (GABA_A) receptor may represent therapeutic targets in stroke, but a time-dependent effect on neuronal viability could influence the outcome. We, therefore, successively blocked NKCC1, KCC2, and GABA_A (with bumetanide, DIOA, and gabazine, respectively) or activated GABA_A (with isoguvacine) either during or after oxygen-glucose deprivation (OGD). Primary hippocampal cultures were exposed to a 2-h OGD or sham normoxia treatment, and viability was determined using the resazurin assay. Neuronal viability was significantly reduced after OGD, and was further decreased by DIOA treatment applied during OGD (p < 0.01) and by gabazine applied after OGD (p < 0.05). Bumetanide treatment during OGD increased viability (p < 0.05), while isoguvacine applied either during or after OGD did not influence viability. Our data suggests that NKCC1 and KCC2 function has an important impact on neuronal viability during the acute ischemic episode, while the GABA_A receptor plays a role during the subsequent recovery period. These findings suggest that pharmacological modulation of transmembrane chloride transport could be a promising approach during stroke and highlight the importance of the timing of treatment application in relation to ischemia-reoxygenation.

Predator stress-induced depression is associated with inhibition of hippocampal neurogenesis in adult male mice

Stress has been suggested to disturb the 5-hydroxytryptamine system and decrease neurogenesis, which contribute to the development of depression. Few studies have investigated the effect of predator stress, a type of psychological stress, on depression and hippocampal neurogenesis in adult mice; we therefore investigated this in the present study. A total of 35 adult male Kunming mice were allocated to a cat stress group, cat odor stress group, cat stress + fluoxetine group, cat odor stress + fluoxetine group, or a control group (no stress/treatment). After 12 days of cat stress or cat odor stress, behavioral correlates of depression were measured using the open field test, elevated plus maze test, and dark-avoidance test. The concentrations of hippocampal 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were measured using high-performance liquid chromatography-electrochemical detection. Neurogenesis was also analyzed using a bromodeoxyuridine and doublecortin double-immunostaining method. Cat stress and cat odor stress induced depression-like behaviors; this effect was stronger in the cat stress model. Furthermore, compared with the control group, cat stress mice exhibited lower 5-hydroxytryptamine concentrations, higher 5-hydroxyindoleacetic acid concentrations, and significantly fewer bromodeoxyuridine⁺/doublecortin⁺-labeled cells in the dentate gyrus, which was indicative of less neurogenesis. The changes observed in the cat stress group were not seen in the cat stress + fluoxetine group, which suggests that the effects of predator stress on depression and neurogenesis were reversed by fluoxetine. Taken together, our results indicate that depression-like behaviors induced by predator stress are associated with the inhibition of hippocampal neurogenesis.

Kir6.2 Deficiency Promotes Mesencephalic Neural Precursor Cell Differentiation via Regulating miR-133b/GDNF in a Parkinson's Disease Mouse Model

The loss of dopaminergic (DA) neurons in the substantia nigra (SN) is a major feature in the pathology of Parkinson's disease (PD). Using neural stem or progenitor cells (NSC/NPCs), the prospect of replacing the missing or damaged DA neurons is very attractive for PD therapy. However, little is known about the endogenous mechanisms and molecular pathways regulating the NSC/NPC proliferation and differentiation in the development of PD. Herein, using Kir6.2 knockout (Kir6.2-/-) mice, we observed that genetic deficiency of Kir6.2 exacerbated the loss of SN DA neurons relatively early in a chronic MPTP/probenecid (MPTP/p) injection course, but rescued the damage of neurons 7 days after the last MPTP/p injection. Meanwhile, we found that Kir6.2 knockout predominantly increased the differentiation of nuclear receptor-related 1 (Nurr1+) precursors to DA neurons, indicating that Kir6.2 deficiency could activate an endogenous self-repair process. Furthermore, we demonstrated in vivo and in vitro that lack of Kir6.2 promoted neuronal differentiation via inhibiting the downregulation of glia cell line-derived neurotrophic factor (GDNF), which negatively related to the level of microRNA-133b. Notably, we revealed that Gdnf is a target gene of miR-133b and transfection of miR-133b could attenuate the enhancement of neural precursor differentiation induced by Kir6.2 deficiency. Collectively, we clarify for the first time that Kir6.2/K-ATP channel functions as a novel endogenous negative regulator of NPC differentiation, and provide a promising neuroprotective target for PD therapeutics.

Inhibition of NKCC1 Modulates Alveolar Fluid Clearance and Inflammation in Ischemia-Reperfusion Lung Injury via TRAF6-Mediated Pathways

Background: The expression of Na-K-2Cl cotransporter 1 (NKCC1) in the alveolar epithelium is responsible for fluid homeostasis in acute lung injury (ALI). Increasing evidence suggests that NKCC1 is associated with inflammation in ALI. We hypothesized that inhibiting NKCC1 would attenuate ALI after ischemia-reperfusion (IR) by modulating pathways that are mediated by tumor necrosis-associated factor 6 (TRAF6).

Methods: IR-ALI was induced by producing 30 min of ischemia followed by 90 min of reperfusion in situ in an isolated and perfused rat lung model. The rats were randomly allotted into four groups comprising two control groups and two IR groups with and without bumetanide. Alveolar fluid clearance (AFC) was measured for each group. Mouse alveolar MLE-12 cells were cultured in control and hypoxia-reoxygenation (HR) conditions with or without bumetanide. Flow cytometry and transwell monolayer permeability assay were carried out for each group.

Results: Bumetanide attenuated the activation of p-NKCC1 and lung edema after IR. In the HR model, bumetanide decreased the cellular volume and increased the transwell permeability. In contrast, bumetanide increased the expression of epithelial sodium channel (ENaC) via p38 mitogen-activated protein kinase (p38 MAPK), which attenuated the reduction of AFC after IR. Bumetanide also modulated lung inflammation via nuclear factor-κB (NF-κB). TRAF6, which is upstream of p38 MAPK and NF-κB, was attenuated by bumetanide after IR and HR.

Conclusions: Inhibition of NKCC1 by bumetanide reciprocally modulated epithelial p38 MAPK and NF-κB via TRAF6 in IR-ALI. This interaction attenuated the reduction of AFC via upregulating ENaC expression and reduced lung inflammation.

Chloride transporters and GABA polarity in developmental, neurological and psychiatric conditions

Neuronal chloride regulation is a determinant factor for the dynamic tuning of GABAergic inhibition during and beyond brain development. This regulation is mainly dependent on the two co-transporters K⁺/Cl^- co-transporter KCC2 and Na⁺/K⁺/Cl^- co-transporter NKCC1, whose activity can decrease or increase neuronal chloride concentrations respectively. Altered expression and/or activity of either of these co-transporters has been associated with a wide variety of brain disorders including developmental disorders, epilepsy, schizophrenia and stroke. Here, we review current knowledge on chloride transporter expression and activity regulation and highlight the intriguing potential for existing and future interventions to support chloride homeostasis across a wide range of mental disorders and neurological conditions.

Genetic Pathways of Neuroregeneration in a Novel Mild Traumatic Brain Injury Model in Adult Zebrafish

Mild traumatic brain injuries (mTBIs) are one of the most prevalent neurological disorders, and humans are severely limited in their ability to repair and regenerate central nervous system (CNS) tissue postinjury. However, zebrafish (Danio rerio) maintain the remarkable ability to undergo complete and functional neuroregeneration as an adult. We wish to extend knowledge of the known mechanisms of neuroregeneration by analyzing the differentially expressed genes (DEGs) in a novel adult zebrafish model of mTBI. In this study, a rodent weight drop model of mTBI was adapted to the adult zebrafish. A memory test showed significant deficits in spatial memory in the mTBI group. We identified DEGs at 3 and 21 days postinjury (dpi) through RNA-sequencing analysis. The resulting DEGs were categorized according to gene ontology (GO) categories. At 3 dpi, GO categories consisted of peak injury response pathways. Significantly, at 21 dpi, GO categories consisted of neuroregeneration pathways. Ultimately, these results validate a novel zebrafish model of mTBI and elucidate significant DEGs of interest in CNS injury and neuroregeneration.

Oncotic Cell Death in Stroke

Oncotic cell death or oncosis represents a major mechanism of cell death in ischaemic stroke, occurring in many central nervous system (CNS) cell types including neurons, glia and vascular endothelial cells. In stroke, energy depletion causes ionic pump failure and disrupts ionic homeostasis. Imbalance between the influx of Na⁺ and Cl^- ions and the efflux of K⁺ ions through various channel proteins and transporters creates a transmembrane osmotic gradient, with ensuing movement of water into the cells, resulting in cell swelling and oncosis. Oncosis is a key mediator of cerebral oedema in ischaemic stroke, contributing directly through cytotoxic oedema, and indirectly through vasogenic oedema by causing vascular endothelial cell death and disruption of the blood-brain barrier (BBB). Hence, inhibition of uncontrolled ionic flux represents a novel and powerful strategy in achieving neuroprotection in stroke. In this review, we provide an overview of oncotic cell death in the pathology of stroke. Importantly, we summarised the therapeutically significant pathways of water, Na⁺, Cl^- and K⁺ movement across cell membranes in the CNS and their respective roles in the pathobiology of stroke.

Transient receptor potential vanilloid type 4 channels mediate Na-K-Cl-co-transporter-induced brain edema after traumatic brain injury

Na⁺ -K⁺ -2Cl^- co-transporter (NKCC1) plays an important role in traumatic brain injury (TBI)-induced brain edema via the MAPK cascade. The transient receptor potential vanilloid type 4 (TRPV4) channel participates in neurogenic inflammation, pain transmission, and edema. In this study, we investigated the relationship between NKCC1 and TRPV4 and the related signaling pathways in TBI-induced brain edema and neuronal damage. TBI was induced by the calibrated weight-drop device. Adult male Wistar rats were randomly assigned into sham and experimental groups for time-course studies of TRPV4 expression after TBI. Hippocampal TRPV4, NKCC1, MAPK, and PI-3K cascades were analyzed by western blot, and brain edema was also evaluated among the different groups. Expression of hippocampal TRPV4 peaked at 8 h after TBI, and phosphorylation of the MAPK cascade and Akt was significantly elevated. Administration of either the TRPV4 antagonist, RN1734, or NKCC1 antagonist, bumetanide, significantly attenuated TBI-induced brain edema through decreasing the phosphorylation of MEK, ERK, and Akt proteins. Bumetanide injection inhibited TRPV4 expression, which suggests NKCC1 activation is critical to TRPV4 activation. Our results showed that hippocampal NKCC1 activation increased TRPV4 expression after TBI and then induced severe brain edema and neuronal damage through activation of the MAPK cascade and Akt-related signaling pathway.

Chloride co-transporters as possible therapeutic targets for stroke

Stroke is one of the major causes of death and disability worldwide. The major type of stroke is an ischaemic one, which is caused by a blockage that interrupts blood flow to the brain. There are currently very few pharmacological strategies to reduce the damage and social burden triggered by this pathology. The harm caused by the interruption of blood flow to the brain unfolds in the subsequent hours and days, so it is critical to identify new therapeutic targets that could reduce neuronal death associated with the spread of the damage. Here, we review some of the key molecular mechanisms involved in the progression of neuronal death, focusing on some new and promising studies. In particular, we focus on the potential of the chloride co-transporter (CCC) family of proteins, mediators of the GABAergic response, both during the early and later stages of stroke, to promote neuroprotection and recovery. Different studies of CCCs during the chronic and recovery phases post-stroke reveal the importance of timing when considering CCCs as potential neuroprotective and/or neuromodulator targets. The molecular regulatory mechanisms of the two main neuronal CCCs, NKCC1 and KCC2, are further discussed as an indirect approach for promoting neuroprotection and neurorehabilitation following an ischaemic insult. Finally, we mention the likely importance of combining different strategies in order to achieve more effective therapies.

Activation of Sphingosine 1-Phosphate Receptor 1 Enhances Hippocampus Neurogenesis in a Rat Model of Traumatic Brain Injury: An Involvement of MEK/Erk Signaling Pathway

Among sphingosine 1-phosphate receptors (S1PRs) family, S1PR1 has been shown to be the most highly expressed subtype in neural stem cells (NSCs) and plays a crucial role in the migratory property of NSCs. Recent studies suggested that S1PR1 was expressed abundantly in the hippocampus, a specific neurogenic region in rodent brain for endogenous neurogenesis throughout life. However, the potential association between S1PR1 and neurogenesis in hippocampus following traumatic brain injury (TBI) remains unknown. In this study, the changes of hippocampal S1PR1 expression after TBI and their effects on neurogenesis and neurocognitive function were investigated, focusing on particularly the extracellular signal-regulated kinase (Erk) signaling pathway which had been found to regulate multiple properties of NSCs. The results showed that a marked upregulation of S1PR1 occurred with a peak at 7 days after trauma, revealing an enhancement of proliferation and neuronal differentiation of NSCs in hippocampus due to S1PR1 activation. More importantly, it was suggested that mitogen-activated protein kinase-Erk kinase (MEK)/Erk cascade was required for S1PR1-meidated neurogenesis and neurocognitive recovery following TBI. This study lays a preliminary foundation for future research on promoting hippocampal neurogenesis and improving TBI outcome.

Traumatic brain injury: recent advances in plasticity and regeneration

PURPOSE OF REVIEW

There is an urgent need for effective therapies to restore neurologic function and decrease disability following traumatic brain injury (TBI). Here, emerging findings on the mechanisms of post-TBI neural repair and regeneration, as well as therapeutic implications, are selectively reviewed.

RECENT FINDINGS

Recent discoveries include the characterization of the inhibitory signaling systems within the injury site, postinjury stem cell niche activation, the role of serotonin signaling in repair, and environment enrichment. A potentially transformative finding has been the identification of exosomes, nano-sized extracellular vesicles which have key roles in cell signaling, and might serve as novel biomarkers and as vehicles for targeted delivery of repair-inducing molecules.

SUMMARY

In the experimental setting, post-TBI repair can be promoted by modulation of inhibitory signaling, neurotrophic factor administration, and amplified serotonin signaling; additional strategies include mobilization of endogenous stem cell populations, exogenous cell-based therapies, and environmental enhancement. Feasibility, safety, and efficacy of these approaches need further investigation in humans. Studies are also needed to evaluate biomarkers based on molecular traces of neural repair and regeneration, which could transform prognostic and predictive modeling of post-TBI recovery trajectories.

Scaffolding protein Homer1a protects against NMDA-induced neuronal injury

Excessive N-methyl-D-aspartate receptor (NMDAR) activation and the resulting activation of neuronal nitric oxide synthase (nNOS) cause neuronal injury. Homer1b/c facilitates NMDAR-PSD95-nNOS complex interactions, and Homer1a is a negative competitor of Homer1b/c. We report that Homer1a was both upregulated by and protected against NMDA-induced neuronal injury in vitro and in vivo. The neuroprotective activity of Homer1a was associated with NMDA-induced Ca²⁺ influx, oxidative stress and the resultant downstream signaling activation. Additionally, we found that Homer1a functionally regulated NMDAR channel properties in neurons, but did not regulate recombinant NR1/NR2B receptors in HEK293 cells. Furthermore, we found that Homer1a detached the physical links among NR2B, PSD95 and nNOS and reduced the membrane distribution of NMDAR. NMDA-induced neuronal injury was more severe in Homer1a homozygous knockout mice (KO, Homer1a^−/−) when compared with NMDA-induced neuronal injury in wild-type mice (WT, Homer1a^+/+). Additionally, Homer1a overexpression in the cortex of Homer1a^−/− mice alleviated NMDA-induced neuronal injury. These findings suggest that Homer1a may be a key neuroprotective endogenous molecule that protects against NMDA-induced neuronal injury by disassembling NR2B-PSD95-nNOS complexes and reducing the membrane distribution of NMDARs.

Ion transporter NKCC1, modulator of neurogenesis in murine olfactory neurons

Olfaction is one of the most crucial senses for vertebrates regarding foraging and social behavior. Therefore, it is of particular interest to investigate the sense of smell, its function on a molecular level, the signaling proteins involved in the process and the mechanism of required ion transport. In recent years, the precise role of the ion transporter NKCC1 in olfactory sensory neuron (OSN) chloride accumulation has been a controversial subject. NKCC1 is expressed in OSNs and is involved in chloride accumulation of dissociated neurons, but it had not been shown to play a role in mouse odorant sensation. Here, we present electro-olfactogram recordings (EOG) demonstrating that NKCC1-deficient mice exhibit significant defects in perception of a complex odorant mixture (Henkel100) in both air-phase and submerged approaches. Using next generation sequencing (NGS) and RT-PCR experiments of NKCC1-deficient and wild type mouse transcriptomes, we confirmed the absence of a highly expressed ion transporter that could compensate for NKCC1. Additional histological investigations demonstrated a reduced number of cells in the olfactory epithelium (OE), resulting in a thinner neuronal layer. Therefore, we conclude that NKCC1 is an important transporter involved in chloride ion accumulation in the olfactory epithelium, but it is also involved in OSN neurogenesis.