General anesthesia alters CNS and astrocyte expression of activity-dependent and activity-independent genes.

General anesthesia represents a common clinical intervention and yet can result in long-term adverse CNS effects particularly in the elderly or dementia patients. Suppression of cortical activity is a key feature of the anesthetic-induced unconscious state, with activity being a well-described regulator of pathways important for brain health. However, the extent to which the effects of anesthesia go beyond simple suppression of neuronal activity is incompletely understood. We found that general anesthesia lowered cortical expression of genes induced by physiological activity in vivo, and recapitulated additional patterns of gene regulation induced by total blockade of firing activity in vitro, including repression of neuroprotective genes and induction of pro-apoptotic genes. However, the influence of anesthesia extended beyond that which could be accounted for by activity modulation, including the induction of non activity-regulated genes associated with inflammation and cell death. We next focused on astrocytes, important integrators of both neuronal activity and inflammatory signaling. General anesthesia triggered gene expression changes consistent with astrocytes being in a low-activity environment, but additionally caused induction of a reactive profile, with transcriptional changes enriched in those triggered by stroke, neuroinflammation, and Aß/tau pathology. Thus, while the effects of general anesthesia on cortical gene expression are consistent with the strong repression of brain activity, further deleterious effects are apparent including a reactive astrocyte profile.

The consequences of neurodegenerative disease on neuron-astrocyte metabolic and redox interactions.

Brain metabolic pathways relating to bioenergetic and redox homeostasis are closely linked, and deficits in these pathways are thought to occur in many neurodegenerative diseases. Astrocytes play important roles in both processes, and growing evidence suggests that neuron-astrocyte intercellular signalling ensures brain bioenergetic and redox homeostasis in health. Moreover, alterations to this crosstalk have been observed in the context of neurodegenerative pathology. In this review, we summarise the current understanding of how neuron-astrocyte interactions influence brain metabolism and antioxidant functions in health as well as during neurodegeneration. It is apparent that deleterious and adaptive protective responses alter brain metabolism in disease, and that knowledge of both may illuminate targets for future therapeutic interventions.

Astrocyte-oligodendrocyte interaction regulates central nervous system regeneration.

Failed regeneration of myelin around neuronal axons following central nervous system damage contributes to nerve dysfunction and clinical decline in various neurological conditions, for which there is an unmet therapeutic demand. Here, we show that interaction between glial cells - astrocytes and mature myelin-forming oligodendrocytes - is a determinant of remyelination. Using in vivo/ ex vivo/ in vitro rodent models, unbiased RNA sequencing, functional manipulation, and human brain lesion analyses, we discover that astrocytes support the survival of regenerating oligodendrocytes, via downregulation of the Nrf2 pathway associated with increased astrocytic cholesterol biosynthesis pathway activation. Remyelination fails following sustained astrocytic Nrf2 activation in focally-lesioned male mice yet is restored by either cholesterol biosynthesis/efflux stimulation, or Nrf2 inhibition using the existing therapeutic Luteolin. We identify that astrocyte-oligodendrocyte interaction regulates remyelination, and reveal a drug strategy for central nervous system regeneration centred on targeting this interaction.

Good, bad, and neglectful: Astrocyte changes in neurodegenerative disease.

Astrocytes play key roles in CNS development as well as well as neuro-supportive roles in the mature brain including ionic, bioenergetic and redox homeostasis. Astrocytes undergo rapid changes following acute CNS insults such as stroke or traumatic brain injury, but are also profoundly altered in chronic neurodegenerative conditions such as Alzheimer's disease. While disease-altered astrocytes are often referred to as reactive, this does not represent a single cellular state or group of states, but a shift in astrocyte properties that is determined by the type of insult as well as spatio-temporal factors. Such changes can accelerate disease progression due to astrocytes neglecting their normal homeostatic neuro-supportive roles, as well as by gaining active neuro-toxic properties. However, other aspects of astrocytic responses to chronic disease can include the induction of adaptive-protective pathways. This is particularly the case when considering antioxidant defences, which can be up-regulated in many cell types, including astrocytes, in response to stresses, sometimes in concert with the activation of detoxification and proteostasis pathways. Protective responses, whilst potentially serving to mitigate neuronal dysfunction, may ultimately fail due to being insufficiently strong, or be offset by other deleterious changes to astrocytes occurring in parallel. Nevertheless, a greater understanding of early adaptive-protective responses of astrocytes to neurodegenerative disease pathology may point to ways in which these responses may be harnessed for therapeutic effect.

Reactive astrocytes acquire neuroprotective as well as deleterious signatures in response to Tau and Aß pathology.

Alzheimer's disease (AD) alters astrocytes, but the effect of Aß and Tau pathology is poorly understood. TRAP-seq translatome analysis of astrocytes in APP/PS1 ß-amyloidopathy and MAPTP301S tauopathy mice revealed that only Aß influenced expression of AD risk genes, but both pathologies precociously induced age-dependent changes, and had distinct but overlapping signatures found in human post-mortem AD astrocytes. Both Aß and Tau pathology induced an astrocyte signature involving repression of bioenergetic and translation machinery, and induction of inflammation pathways plus protein degradation/proteostasis genes, the latter enriched in targets of inflammatory mediator Spi1 and stress-activated cytoprotective Nrf2. Astrocyte-specific Nrf2 expression induced a reactive phenotype which recapitulated elements of this proteostasis signature, reduced Aß deposition and phospho-tau accumulation in their respective models, and rescued brain-wide transcriptional deregulation, cellular pathology, neurodegeneration and behavioural/cognitive deficits. Thus, Aß and Tau induce overlapping astrocyte profiles associated with both deleterious and adaptive-protective signals, the latter of which can slow patho-progression.

Author Correction: Neurons and neuronal activity control gene expression in astrocytes to regulate their development and metabolism.

This corrects the article DOI: 10.1038/ncomms15132.

Neurons and neuronal activity control gene expression in astrocytes to regulate their development and metabolism.

The influence that neurons exert on astrocytic function is poorly understood. To investigate this, we first developed a system combining cortical neurons and astrocytes from closely related species, followed by RNA-seq and in silico species separation. This approach uncovers a wide programme of neuron-induced astrocytic gene expression, involving Notch signalling, which drives and maintains astrocytic maturity and neurotransmitter uptake function, is conserved in human development, and is disrupted by neurodegeneration. Separately, hundreds of astrocytic genes are acutely regulated by synaptic activity via mechanisms involving cAMP/PKA-dependent CREB activation. This includes the coordinated activity-dependent upregulation of major astrocytic components of the astrocyte-neuron lactate shuttle, leading to a CREB-dependent increase in astrocytic glucose metabolism and elevated lactate export. Moreover, the groups of astrocytic genes induced by neurons or neuronal activity both show age-dependent decline in humans. Thus, neurons and neuronal activity regulate the astrocytic transcriptome with the potential to shape astrocyte-neuron metabolic cooperation.

Leukoreduced blood transfusion does not increase circulating soluble markers of inflammation: a randomized controlled trial.

BACKGROUND: Transfused blood may have immunomodulatory and proinflammatory effects. We report the first randomized study exploring whether leukoreduced red blood cell (RBC) transfusion increases circulating proinflammatory mediators, markers of neutrophil activation, and the acute-phase response in critically ill adults. STUDY DESIGN AND METHODS: Eighty-four patients were recruited from six general intensive care units in the United Kingdom as part of a laboratory study nested within a parallel-group randomized trial comparing restrictive and liberal leukoreduced RBC transfusion strategies in critically ill patients aged more than 55 years with measured hemoglobin concentrations of not more than 90 g/L (ClinicalTrials.gov NCT00944112). Forty-one patients received transfusion and 43 did not receive transfusion. Plasma was sampled at baseline, 6 hours, and 24 hours after randomization or transfusion, and concentrations of interleukin (IL)-1ß, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12-p70, interferon-γ, tumor necrosis factor-α, human neutrophil elastase, soluble L-selectin, and C-reactive protein were measured using cytokine bead array analysis and an enzyme-linked immunosorbent assay. RESULTS: Patients who received transfusion did not have significantly different inflammatory biomarker plasma concentrations at the time points compared to those who did not receive transfusion, with the exception of IL-8 concentrations at 24 hours, which were reduced in the transfused group (p = 0.02). After adjustment for baseline inflammatory biomarker concentrations, there were no significant differences between patients who received transfusion and those who did not. CONCLUSION: Concentrations of measured biomarkers were not significantly increased during the first 24 hours after leukoreduced RBC transfusion. These data do not support the contention that leukoreduced RBC transfusion is associated with a proinflammatory response in the general adult critically ill population.

Emergency department management of early sepsis: a national survey of emergency medicine and intensive care consultants.

OBJECTIVES: Early goal-directed therapy (EGDT) is recommended for sepsis management in current guidelines, but the underpinning evidence is controversial. Clinician beliefs and the capacity to implement all recommended elements of EGDT in emergency departments (EDs) are uncertain. Our study aimed to explore self-reported management of early sepsis by Scottish emergency medicine (EM) and intensive care medicine (ICM) consultants, delineate important differences and determine the guideline recommendations rated most important and deliverable within the ED. METHODS: A postal survey using a hypothetical patient with septic shock was sent to all EM and ICM consultants practising in Scotland. RESULTS: 67% (76/114) EM and 61% (96/157) ICM consultants responded. Normal saline was preferred by EM respondents ('always/often used': EM 86%, ICM 23%, p<0.0001), whereas ICM respondents preferred Hartmann's solution (EM 42%, ICM 72%, p=0.0164), gelofusin (EM 10%, ICM 63%, p<0.0001) and starch (EM 0%, ICM 24%, p<0.0001). More ICM respondents indicated they used central venous pressure and invasive arterial pressure monitoring in the ED, and initiated vasopressors (EM 57%, ICM 90%, p<0.0001). More ICM consultants used specific haemoglobin transfusion triggers (48% EM, 77% ICM, p=0.0002), but marked variation in haemoglobin triggers and targets was reported. Lactate was rated the most important single resuscitation parameter by both specialties; no ED and only two ICM consultants rated ScVO2 most important. CONCLUSIONS: Differences in early fluid and vasopressor management of sepsis exist between Scottish ICM and EM consultants. Transfusion practice is highly variable, suggesting clinical uncertainty. Lactate is considered more important than ScVO2 measurement.

Advanced Cardiac Resuscitation Evaluation (ACRE): a randomised single-blind controlled trial of peer-led vs. expert-led advanced resuscitation training.

BACKGROUND: Advanced resuscitation skills training is an important and enjoyable part of medical training, but requires small group instruction to ensure active participation of all students. Increases in student numbers have made this increasingly difficult to achieve. METHODS: A single-blind randomised controlled trial of peer-led vs. expert-led resuscitation training was performed using a group of sixth-year medical students as peer instructors. The expert instructors were a senior and a middle grade doctor, and a nurse who is an Advanced Life Support (ALS) Instructor.A power calculation showed that the trial would have a greater than 90% chance of rejecting the null hypothesis (that expert-led groups performed 20% better than peer-led groups) if that were the true situation. Secondary outcome measures were the proportion of High Pass grades in each groups and safety incidents.The peer instructors designed and delivered their own course material. To ensure safety, the peer-led groups used modified defibrillators that could deliver only low-energy shocks.Blinded assessment was conducted using an Objective Structured Clinical Examination (OSCE). The checklist items were based on International Liaison Committee on Resuscitation (ILCOR) guidelines using Ebel standard-setting methods that emphasised patient and staff safety and clinical effectiveness.The results were analysed using Exact methods, chi-squared and t-test. RESULTS: A total of 132 students were randomised: 58 into the expert-led group, 74 into the peer-led group. 57/58 (98%) of students from the expert-led group achieved a Pass compared to 72/74 (97%) from the peer-led group: Exact statistics confirmed that it was very unlikely (p = 0.0001) that the expert-led group was 20% better than the peer-led group.There were no safety incidents, and High Pass grades were achieved by 64 (49%) of students: 33/58 (57%) from the expert-led group, 31/74 (42%) from the peer-led group. Exact statistics showed that the difference of 15% meant that it was possible that the expert-led teaching was 20% better at generating students with High Passes. CONCLUSIONS: The key elements of advanced cardiac resuscitation can be safely and effectively taught to medical students in small groups by peer-instructors who have undergone basic medical education training.

Hearing impairment in Tanzanians with albinism.

Community-based studies have suggested that those affected with albinism, an important condition in East Africa, may be at a greater risk of developing hearing problems. This study shows that the prevalence of hearing loss is increased in Tanzanians with albinism and that hearing loss is associated with fewer years in education. 64 participants with albinism and 90 controls without were recruited from clinics held in the Western Kilimanjaro area. Hearing was evaluated using pure-tone audiometry at frequencies between 250 Hz to 8000 Hz and patients completed a questionnaire to evaluate their educational history. Of the participants with albinism, 33 (51.6% [95% CI: 39.3-63.8%]) had hearing impairment. This was significantly greater than the control group, where 20 (22.2% [95% CI: 13.6-30.8%]) had a similar hearing impairment (P < 0.001). Within the albinism group those with hearing impairment spent a mean of 6.9 years in education compared with those with normal hearing who spent a mean of 8.3 years in education (P = 0.046). Further studies are now required to determine the cause of these differences. Healthcare providers should be aware of hearing impairments when managing those with albinism and make the appropriate specialist referrals if further evaluation and treatment is required.