The Leptomeninges Produce Prostaglandin D2 Involved in Sleep Regulation in Mice

Microglial activation and neuroinflammation in acute and chronic cognitive deficits in sepsis

Sepsis is characterised by dysregulated immune responses to infection, leading to multi-organ dysfunction and high rates of mortality. With increasing survival rates in recent years long-term neurological and psychiatric consequences have become more apparent in survivors. Many patients develop sepsis associated encephalopathy (SAE) which encompasses the profound but usually transient neuropsychiatric syndrome delirium but also new brain injury that emerges in the months and years post-sepsis. It now clear that systemic inflammatory signals reach the brain during sepsis and that very significant neuroinflammation ensues. The major brain resident immune cell population, the microglia, has been implicated in acute and chronic cognitive dysfunction in animal models of sepsis based on a growing number of studies using bacterial endotoxin and in polymicrobial sepsis models such as cecal ligation and puncture. The current review explores the effects of sepsis on the brain, focussing on how systemic insults translate to microglial activation and neuroinflammation and how this disrupts neuronal function and integrity. We examine what has been demonstrated specifically with respect to microglial activation, revealing robust evidence for a role for neuroinflammation in sepsis-induced brain sequelae but less clear information on the extent of the specific microglial contribution to this, arising from findings using global knockout mice, non-selective drugs and treatments that equally target peripheral and central compartments. There is, nonetheless, clear evidence that microglia do become activated and do contribute to brain consequences of sepsis thus arguing for improved understanding of these neuroinflammatory processes toward the prevention and treatment of sepsis-induced brain dysfunction.

Association between idiopathic hypersomnia and a genetic variant in the PER3 gene

We aim to identify genetic markers associated with idiopathic hypersomnia, a disabling orphan central nervous system disorder of hypersomnolence that is still poorly understood. In our study, DNA was extracted from 79 unrelated patients diagnosed with idiopathic hypersomnia with long sleep time at the National Reference Center for Narcolepsy-France according to very stringent diagnostic criteria. Whole exome sequencing on the first 30 patients with idiopathic hypersomnia (25 females and 5 males) allowed the single nucleotide variants to be compared with a control population of 574 healthy subjects from the French Exome project database. We focused on the identification of genetic variants among 182 genes related to the regulation of sleep and circadian rhythm. Candidate variants obtained by exome sequencing analysis were then validated in a second sample of 49 patients with idiopathic hypersomnia (37 females and 12 males). Our study characterised seven variants from six genes significantly associated with idiopathic hypersomnia compared with controls. A targeted sequencing analysis of these seven variants on 49 other patients with idiopathic hypersomnia confirmed the relative over-representation of the A➔C variant of rs2859390, located in a potential splicing-site of PER3 gene. Our findings support a genetic predisposition and identify pathways involved in the pathogeny of idiopathic hypersomnia. A variant of the PER3 gene may predispose to idiopathic hypersomnia with long sleep time.

Sedative and hypnotic effects of the saponins from a traditional edible plant Liriope spicata Lour. in PCPA-induced insomnia mice

ETHNOPHARMACOLOGICAL RELEVANCE

Liriope spicata Lour., a species listed in the catalogue of 'Medicinal and Edible Homologous Species', is traditionally used for the treatment of fatigue, restlessness, insomnia and constipation.

AIM OF THE STUDY

This study is aimed to evaluate the sedative and hypnotic effect of the saponins from a natural plant L. spicata Lour. in vivo.

MATERIALS AND METHODS

The total saponin (LSTS) and purified saponin (LSPS) were extracted from L. spicata, followed by a thorough analysis of their major components using the HPLC-MS. Subsequently, the therapeutic efficacy of LSTS and LSPS was evaluated by the improvement of anxiety and depression behaviors of the PCPA-induced mice.

RESULTS

LSTS and LSPS exhibited similar saponin compositions but differ in their composition ratios, with liriopesides-type saponins accounting for a larger proportion in LSTS. Studies demonstrated that both LSTS and LSPS can extend sleep duration and immobility time, while reducing sleep latency in PCPA-induced mice. However, there was no significant difference in weight change among the various mice groups. Elisa results indicated that the LSTS and LSPS could decrease levels of NE, DA, IL-6, and elevate the levels of 5-HT, NO, PGD2 and TNF-α in mice plasma. LSTS enhanced the expression of neurotransmitter receptors, while LSPS exhibited a more pronounced effect in regulating the expression of inflammatory factors. In conclusion, the saponins derived from L. spicata might hold promise as ingredients for developing health foods with sedative and hypnotic effects, potentially related to the modulation of serotonergic and GABAAergic neuron expression, as well as immunomodulatory process.

Lipocalin-type prostaglandin D synthase: a glymphopathy marker in idiopathic hydrocephalus

Idiopathic normal pressure hydrocephalus in elderly people is considered a form of glymphopathy caused by malfunction of the waste clearance pathway, called the glymphatic system. Tau is a representative waste material similar to amyloid-β. During neurodegeneration, lipocalin-type prostaglandin D synthase (L-PGDS), a major cerebrospinal fluid (CSF) protein, is reported to act as a chaperone that prevents the neurotoxic aggregation of amyloid-β. L-PGDS is also a CSF biomarker in idiopathic normal pressure hydrocephalus and significantly correlates with tau concentration, age, and age-related brain white matter changes detected by magnetic resonance imaging. To investigate this glymphopathy, we aimed to analyze white matter changes and contributing factors in vivo and their interactions ex vivo. Cerebrospinal tap tests were performed in 60 patients referred for symptomatic ventriculomegaly. Patients were evaluated using an idiopathic normal pressure hydrocephalus grading scale, mini-mental state examination, frontal assessment battery, and timed up-and-go test. The typical morphological features of high convexity tightness and ventriculomegaly were measured using the callosal angle and Evans index, and parenchymal white matter properties were evaluated with diffusion tensor imaging followed by tract-based spatial statistics. Levels of CSF biomarkers, including tau, amyloid-β, and L-PGDS, were determined by ELISA, and their interaction, and localization were determined using immunoprecipitation and immunohistochemical analyses. Tract-based spatial statistics for fractional anisotropy revealed clusters that positively correlated with mini-mental state examination, frontal assessment battery, and callosal angle, and clusters that negatively correlated with age, disease duration, idiopathic normal pressure hydrocephalus grading scale, Evans index, and L-PGDS. Other parameters also indicated clusters that correlated with symptoms, microstructural white matter changes, and L-PGDS. Tau co-precipitated with L-PGDS, and colocalization was confirmed in postmortem specimens of neurodegenerative disease obtained from the human Brain Bank. Our study supports the diagnostic value of L-PGDS as a surrogate marker for white matter integrity in idiopathic normal pressure hydrocephalus. These results increase our understanding of the molecular players in the glymphatic system. Moreover, this study indicates the potential utility of enhancing endogenous protective factors to maintain brain homeostasis.

Adenosine A2A receptors and sleep

Adenosine, a known endogenous somnogen, induces sleep via A1 and A2A receptors. In this chapter, we review the current knowledge regarding the role of the adenosine A2A receptor and its agonists, antagonists, and allosteric modulators in sleep-wake regulation. Although many adenosine A2A receptor agonists, antagonists, and allosteric modulators have been identified, only a few have been tested to see if they can promote sleep or wakefulness. In addition, the growing popularity of natural sleep aids has led to an investigation of natural compounds that may improve sleep by activating the adenosine A2A receptor. Finally, we discuss the potential therapeutic advantage of allosteric modulators of adenosine A2A receptors over classic agonists and antagonists for treating sleep and neurologic disorders.

Neurobiology of dream activity and effects of stimulants on dreams

The sleep-wake cycle is the result of the activity of a multiple neurobiological network interaction. Dreaming feature is one interesting sleep phenomena that represents sensorial components, mostly visual perceptions, accompanied with intense emotions. Further complexity has been added to the topic of the neurobiological mechanism of dreams generation by the current data that suggests the influence of drugs on dream generation. Here, we discuss the review on some of the neurobiological mechanism of the regulation of dream activity, with special emphasis on the effects of stimulants on dreaming.

Sleep Disturbance and Alzheimer's Disease: The Glial Connection

Poor quality and quantity of sleep are very common in elderly people throughout the world. Growing evidence has suggested that sleep disturbances could accelerate the process of neurodegeneration. Recent reports have shown a positive correlation between sleep deprivation and amyloid-β (Aβ)/tau aggregation in the brain of Alzheimer's patients. Glial cells have long been implicated in the progression of Alzheimer's disease (AD) and recent findings have also suggested their role in regulating sleep homeostasis. However, how glial cells control the sleep-wake balance and exactly how disturbed sleep may act as a trigger for Alzheimer's or other neurological disorders have recently gotten attention. In an attempt to connect the dots, the present review has highlighted the role of glia-derived sleep regulatory molecules in AD pathogenesis. Role of glia in sleep disturbance and Alzheimer's progression.

Biochemical and Structural Characteristics, Gene Regulation, Physiological, Pathological and Clinical Features of Lipocalin-Type Prostaglandin D2 Synthase as a Multifunctional Lipocalin

Lipocalin-type prostaglandin (PG) D₂ synthase (L-PGDS) catalyzes the isomerization of PGH₂, a common precursor of the two series of PGs, to produce PGD₂. PGD₂ stimulates three distinct types of G protein-coupled receptors: (1) D type of prostanoid (DP) receptors involved in the regulation of sleep, pain, food intake, and others; (2) chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) receptors, in myelination of peripheral nervous system, adipocyte differentiation, inhibition of hair follicle neogenesis, and others; and (3) F type of prostanoid (FP) receptors, in dexamethasone-induced cardioprotection. L-PGDS is the same protein as β-trace, a major protein in human cerebrospinal fluid (CSF). L-PGDS exists in the central nervous system and male genital organs of various mammals, and human heart; and is secreted into the CSF, seminal plasma, and plasma, respectively. L-PGDS binds retinoic acids and retinal with high affinities (Kd < 100 nM) and diverse small lipophilic substances, such as thyroids, gangliosides, bilirubin and biliverdin, heme, NAD(P)H, and PGD₂, acting as an extracellular carrier of these substances. L-PGDS also binds amyloid β peptides, prevents their fibril formation, and disaggregates amyloid β fibrils, acting as a major amyloid β chaperone in human CSF. Here, I summarize the recent progress of the research on PGD₂ and L-PGDS, in terms of its “molecular properties,” “cell culture studies,” “animal experiments,” and “clinical studies,” all of which should help to understand the pathophysiological role of L-PGDS and inspire the future research of this multifunctional lipocalin.

The metabolic roots of senescence: mechanisms and opportunities for intervention

Cellular senescence entails a permanent proliferative arrest, coupled to multiple phenotypic changes. Among these changes is the release of numerous biologically active molecules collectively known as the senescence-associated secretory phenotype, or SASP. A growing body of literature indicates that both senescence and the SASP are sensitive to cellular and organismal metabolic states, which in turn can drive phenotypes associated with metabolic dysfunction. Here, we review the current literature linking senescence and metabolism, with an eye toward findings at the cellular level, including both metabolic inducers of senescence and alterations in cellular metabolism associated with senescence. Additionally, we consider how interventions that target either metabolism or senescent cells might influence each other and mitigate some of the pro-aging effects of cellular senescence. We conclude that the most effective interventions will likely break a degenerative feedback cycle by which cellular senescence promotes metabolic diseases, which in turn promote senescence.

Inflammation-Induced Attenuation of Prostaglandin D2 Elimination across Rat Blood-Brain Barrier: Involvement of the Downregulation of Organic Anion Transporter 3 and Multidrug Resistance-Associated Protein 4

Prostaglandin (PG) D₂ is a lipid mediator, and in the brain, overproduction of PGD₂ is reportedly involved in the progression and exacerbation of neuroinflammation. The objective of this study was to elucidate PGD₂ efflux transport, under normal and inflammatory conditions, across the blood-brain barrier (BBB), which is formed by brain capillaries. Elimination of [³H]PGD₂ across the BBB of normal and lipopolysaccharide (LPS)-induced inflammatory rats was examined by the intracerebral microinjection technique. After intracerebral injection, the percentage of [³H]PGD₂ remaining in the ipsilateral cerebrum decreased with time, with a half-life of 13 min. This [³H]PGD₂ elimination across the BBB was significantly inhibited by the co-administration of unlabeled PGD₂, which suggests carrier-mediated PGD₂ efflux transport at the BBB. In isolated rat brain capillaries, mRNA expression of organic anion transporter (Oat) 3, organic anion-transporting polypeptide (Oatp) 1a4, and multidrug resistance-associated protein (Mrp) 4 was observed. In addition, co-administration of substrates/inhibitors for Oat3, Oatp1a4, and/or Mrp4, such as benzylpenicillin and cefmetazole, reduced [³H]PGD₂ elimination across the BBB. Data suggest that Oat3 and Mrp4, but not Oatp1a4 are involved in PGD₂ elimination across the BBB, as Oatp1a4-expressing Xenopus (X.) oocytes did not show the significant [³H]PGD₂ uptake compared with water-injected X. oocytes. In LPS-treated rats, [³H]PGD₂ elimination across the BBB and mRNA expression levels of Oat3 and Mrp4 were significantly decreased. Our data suggest that Oat3- and Mrp4-mediated PGD₂ elimination across the BBB is attenuated under inflammatory conditions.

Bioactive Lipid Mediators in the Initiation and Resolution of Inflammation after Spinal Cord Injury

Neuroinflammation is a prominent feature of the response to CNS trauma. It is also an important hallmark of various neurodegenerative diseases in which inflammation contributes to the progression of pathology. Inflammation in the CNS can contribute to secondary damage and is therefore an excellent therapeutic target for a range of neurological conditions. Inflammation in the nervous system is complex and varies in its fine details in different conditions. It involves a wide variety of secreted factors such as chemokines and cytokines, cell adhesion molecules, and different cell types that include resident cell of the CNS, as well as immune cells recruited from the peripheral circulation. Added to this complexity is the fact that some aspects of inflammation are beneficial, while other aspects can induce secondary damage in the acute, subacute and chronic phases. Understanding these aspects of the inflammatory profile is essential for developing effective therapies. Bioactive lipids constitute a large group of molecules that modulate the initiation and the resolution of inflammation. Dysregulation of these bioactive lipid pathways can lead to excessive acute inflammation, and failure to resolve this by specialized pro-resolution lipid mediators can lead to the development of chronic inflammation. The focus of this review is to discuss the effects of bioactive lipids in spinal cord trauma and their potential for therapies.

Levels of trace blood elements associated with severe sleep disturbance in maintenance hemodialysis patients

PURPOSE

Sleep disturbance is frequently observed in patients on maintenance hemodialysis (MHD), and this population usually presents imbalances in trace elements. We investigated the association between blood trace element levels and sleep quality in patients on MHD.

METHODS

This cross-sectional and single-center study was performed in September 2019. Patients regularly undergoing hemodialysis for > 3 months at our center were recruited, and demographic, clinical, and laboratory parameters were recorded. The Pittsburgh Sleep Quality Index (PSQI) was applied to define sleep disturbance. Blood trace element (zinc, manganese, copper, selenium, and lead) levels were measured using an inductively coupled plasma mass spectrometer.

RESULTS

In total, 121 patients on MHD (male/female = 68:53) were enrolled in the study (mean age 63.7 ± 13.9 years, median dialysis vintage 38.0 [20.0, 60.0] months). According to PSQI, 56 (46%) patients experienced severe sleep disturbance. These patients were characterized by older age, higher serum parathyroid hormone levels, and lower blood selenium levels (all P < 0.05). No significant differences in blood zinc, manganese, copper, and lead levels were observed between groups. Univariate binary logistic regression showed that lower blood selenium levels were associated with severe sleep disturbance (odds ratio = 0.976, 95% confidence interval: 0.954-0.999, P = 0.038). Multivariate analyses also confirmed the results after adjusting for confounding factors.

CONCLUSION

Our study indicated an association between lower blood selenium levels and the occurrence of severe sleep disturbances in patients on MHD. However, a prospective study with a larger sample size and assessing the importance of selenium supplementation are needed to confirm the results.

Endothelial prostaglandin D2 opposes angiotensin II contractions in mouse isolated perfused intracerebral microarterioles

Hypothesis:

A lack of contraction of cerebral microarterioles to Ang II (“resilience”) depends on cyclooxygenase (COX) and lipocalin type prostaglandin D sythase L-PGDS producing PGD₂ that activates prostaglandin D type 1 receptors (DP1Rs) and nitric oxide synthase (NOS).

Materials & Methods:

Contractions were assessed in isolated, perfused vessels and NO by fluorescence microscopy.

Results:

The mRNAs of penetrating intraparenchymal cerebral microarterioles versus renal afferent arterioles were >3000-fold greater for L-PGDS and DP1R and 5-fold for NOS III and COX 2. Larger cerebral arteries contracted with Ang II. However, cerebral microarterioles were entirely unresponsive but contracted with endothelin 1 and perfusion pressure. Ang II contractions were evoked in cerebral microarterioles from COX1 –/– mice or after blockade of COX2, L-PGDS or NOS and in deendothelialized vessels but effects of deendothelialization were lost during COX blockade. NO generation with Ang II depended on COX and also was increased by DP1R activation.

Conclusion:

The resilience of cerebral arterioles to Ang II contractions is specific for intraparenchymal microarterioles and depends on endothelial COX1 and two products that are metabolized by L-PGDS to generate PGD₂ that signals via DP1Rs and NO.

Role of the L-PGDS-PGD2-DP1 receptor axis in sleep regulation and neurologic outcomes

To meet the new challenges of modern lifestyles, we often compromise a good night's sleep. In preclinical models as well as in humans, a chronic lack of sleep is reported to be among the leading causes of various physiologic, psychologic, and neurocognitive deficits. Thus far, various endogenous mediators have been implicated in inter-regulatory networks that collectively influence the sleep-wake cycle. One such mediator is the lipocalin-type prostaglandin D2 synthase (L-PGDS)-Prostaglandin D2 (PGD2)-DP1 receptor (L-PGDS-PGD2-DP1R) axis. Findings in preclinical models confirm that DP1R are predominantly expressed in the sleep-regulating centers. This finding led to the discovery that the L-PGDS-PGD2-DP1R axis is involved in sleep regulation. Furthermore, we showed that the L-PGDS-PGD2-DP1R axis is beneficial in protecting the brain from ischemic stroke. Protein sequence homology was also performed, and it was found that L-PGDS and DP1R share a high degree of homology between humans and rodents. Based on the preclinical and clinical data thus far pertaining to the role of the L-PGDS-PGD2-DP1R axis in sleep regulation and neurologic conditions, there is optimism that this axis may have a high translational potential in human therapeutics. Therefore, here the focus is to review the regulation of the homeostatic component of the sleep process with a special focus on the L-PGDS-PGD2-DP1R axis and the consequences of sleep deprivation on health outcomes. Furthermore, we discuss whether the pharmacological regulation of this axis could represent a tool to prevent sleep disturbances and potentially improve outcomes, especially in patients with acute brain injuries.

Social defeat stress induces phosphorylation of extracellular signal-regulated kinase in the leptomeninges in mice

Aims

Animal studies using various stress models have shown that excessive environmental stress induces depression? and anxiety?like behaviors through inflammatory responses in the brain and periphery. Although the leptomeningeal cells have multiple functions related to inflammatory responses in the brain, whether environmental stress influences the leptomeninges remains unknown. In this study, we aimed to examine phosphorylation of the extracellular signal‐regulated kinase (ERK) in the leptomeninges.

Methods

We subjected C57BL/6 male mice to a single episode of social defeat stress and analyzed the expression of phosphorylated ERK in the leptomeninges by immunohistochemistry.

Results

Social defeat stress in mice induced phosphorylation of ERK in the leptomeninges, adjacent to vascular endothelial cells and the glia limitans. This ERK phosphorylation was maintained for at least one hour after the stress.

Conclusions

This study shows the effect of environmental stress on the leptomeninges for the first time and paves the way for elucidating its functional role in stress‐induced changes in neural functions.

This study shows for the first time that social defeat stress induces phosphorylation of extracellular signal‐regulated kinase in the leptomeninges in mice. This finding paves the way for elucidating a potential role of the leptomeninges in mediating stress‐induced inflammatory signals from the periphery to the brain.

The year in review: progress in brain barriers and brain fluid research in 2018

This editorial focuses on the progress made in brain barrier and brain fluid research in 2018. It highlights some recent advances in knowledge and techniques, as well as prevalent themes and controversies. Areas covered include: modeling, the brain endothelium, the neurovascular unit, the blood–CSF barrier and CSF, drug delivery, fluid movement within the brain, the impact of disease states, and heterogeneity.