William M. Vanderheyden

Fatty-acid binding proteins modulate sleep and enhance long-term memory consolidation in Drosophila.

Sleep is thought to be important for memory consolidation, since sleep deprivation has been shown to interfere with memory processing. However, the effects of augmenting sleep on memory formation are not well known, and testing the role of sleep in memory enhancement has been limited to pharmacological and behavioral approaches. Here we test the effect of overexpressing the brain-type fatty acid binding protein (Fabp7) on sleep and long-term memory (LTM) formation in Drosophila melanogaster. Transgenic flies carrying the murine Fabp7 or the Drosophila homologue dFabp had reduced baseline sleep but normal LTM, while Fabp induction produced increases in both net sleep and LTM. We also define a post-training consolidation “window” that is sufficient for the observed Fabp-mediated memory enhancement. Since Fabp overexpression increases consolidated daytime sleep bouts, these data support a role for longer naps in improving memory and provide a novel role for lipid-binding proteins in regulating memory consolidation concurrently with changes in behavioral state.

Time of Day Regulates Subcellular Trafficking, Tripartite Synaptic Localization, and Polyadenylation of the Astrocytic Fabp7 mRNA

The astrocyte brain fatty acid binding protein (Fabp7) has previously been shown to have a coordinated diurnal regulation of mRNA and protein throughout mouse brain, and an age-dependent decline in protein expression within synaptoneurosomal fractions. Mechanisms that control time-of-day changes in expression and trafficking Fabp7 to the perisynaptic process are not known. In this study, we confirmed an enrichment of Fabp7 mRNA and protein in the astrocytic perisynaptic compartment, and observed a diurnal change in the intracellular distribution of Fabp7 mRNA in molecular layers of hippocampus. Northern blotting revealed a coordinated time-of-day-dependent oscillation for the Fabp7 mRNA poly(A) tail throughout murine brain. Cytoplasmic polyadenylation element-binding protein 1 (CPEB1) regulates subcellular trafficking and translation of synaptic plasticity-related mRNAs. Here we show that Fabp7 mRNA coimmunoprecipitated with CPEB1 from primary mouse astrocyte extracts, and its 3′UTR contains phylogenetically conserved cytoplasmic polyadenylation elements (CPEs) capable of regulating translation of reporter mRNAs during Xenopus oocyte maturation. Given that Fabp7 expression is confined to astrocytes and neural progenitors in adult mouse brain, the synchronized cycling pattern of Fabp7 mRNA is a novel discovery among known CPE-regulated transcripts. These results implicate circadian, sleep, and/or metabolic control of CPEB-mediated subcellular trafficking and localized translation of Fabp7 mRNA in the tripartite synapse of mammalian brain.

ERK Phosphorylation Regulates Sleep and Plasticity in Drosophila

Given the relationship between sleep and plasticity, we examined the role of Extracellular signal-regulated kinase (ERK) in regulating baseline sleep, and modulating the response to waking experience. Both sleep deprivation and social enrichment increase ERK phosphorylation in wild-type flies. The effects of both sleep deprivation and social enrichment on structural plasticity in the LNvs can be recapitulated by expressing an active version of ERK (UAS-ERK SEM) pan-neuronally in the adult fly using GeneSwitch (Gsw) Gsw-elav-GAL4. Conversely, disrupting ERK reduces sleep and prevents both the behavioral and structural plasticity normally induced by social enrichment. Finally, using transgenic flies carrying a cAMP response Element (CRE)-luciferase reporter we show that activating ERK enhances CRE-Luc activity while disrupting ERK reduces it. These data suggest that ERK phosphorylation is an important mediator in transducing waking experience into sleep.

Trauma exposure and sleep: using a rodent model to understand sleep function in PTSD

Post-traumatic stress disorder (PTSD) is characterized by intrusive memories of a traumatic event, avoidance behavior related to cues of the trauma, emotional numbing, and hyper-arousal. Sleep abnormalities and nightmares are core symptoms of this disorder. In this review, we propose a model which implicates abnormal activity in the locus coeruleus (LC), an important modifier of sleep–wake regulation, as the source of sleep abnormalities and memory abnormalities seen in PTSD. Abnormal LC activity may be playing a key role in symptom formation in PTSD via sleep dysregulation and suppression of hippocampal bidirectional plasticity.

Amyloid-β induces sleep fragmentation that is rescued by fatty acid binding proteins in Drosophila.

Disruption of sleep/wake activity in Alzheimers disease (AD) patients significantly affects their quality of life and that of their caretakers and is a major contributing factor for institutionalization. Levels of amyloid‐β (Aβ) have been shown to be regulated by neuronal activity and to correlate with the sleep/wake cycle. Whether consolidated sleep can be disrupted by Aβ alone is not well understood. We hypothesize that Aβ42 can increase wakefulness and disrupt consolidated sleep. Here we report that flies expressing the human Aβ42 transgene in neurons have significantly reduced consolidated sleep compared with control flies. Fatty acid binding proteins (Fabp) are small hydrophobic ligand carriers that have been clinically implicated in AD. Aβ42 flies that carry a transgene of either the Drosophila Fabp or the mammalian brain‐type Fabp show a significant increase in nighttime sleep and long consolidated sleep bouts, rescuing the Aβ42‐induced sleep disruption. These studies suggest that alterations in Fabp levels and/or activity may be associated with sleep disturbances in AD. Future work to determine the molecular mechanisms that contribute to Fabp‐mediated rescue of Aβ42‐induced sleep loss will be important for the development of therapeutics in the treatment of AD.

Cytoplasmic to nuclear localization of fatty-acid binding protein correlates with specific forms of long-term memory in Drosophila

We recently reported evidence implicating fatty-acid binding protein (Fabp) in the control of sleep and memory formation. We used Drosophila melanogaster to examine the relationship between sleep and memory through transgenic overexpression of mouse brain-Fabp, Fabp7, or the Drosophila Fabp homologue, (dFabp). The key findings are that, (1) a genetically induced increase in daytime consolidated sleep (naps) correlates with an increase in cognitive performance, and (2) a late “window” of memory consolidation occurs days after the traditionally understood “synaptic” consolidation. Exactly how Fabp-signaling may be involved in converting normal to enhanced long-term memory (LTM) is not known. Here we describe additional data which support relative subcellular compartmental localization of Fabp in regulating stage associations of different forms of memory in Drosophila. Anesthesia resistant memory (ARM) is a longer lasting memory that is produced by massed training, but unlike LTM produced by spaced training, it is insensitive to protein synthesis inhibitors and does not persist as long. We observed that the ratio of ARM to LTM performance index of Fabp7-transgenic flies is proportional to the relative cytoplasmic to nuclear Fabp7 expression level. These data suggest a common lipid-signaling cascade exists between phases of memory formation previously thought to be molecularly distinct.

Stress-free automatic sleep deprivation using air puffs

BACKGROUND Sleep deprivation via gentle handling is time-consuming and personnel-intensive. NEW METHOD We present here an automated sleep deprivation system via air puffs. Implanted EMG and EEG electrodes were used to assess sleep/waking states in six male Sprague-Dawley rats. Blood samples were collected from an implanted intravenous catheter every 4h during the 12-h light cycle on baseline, 8h of sleep deprivation via air puffs, and 8h of sleep deprivation by gentle handling days. RESULTS The automated system was capable of scoring sleep and waking states as accurately as our offline version (∼90% for sleep) and with sufficient speed to trigger a feedback response within an acceptable amount of time (1.76s). Manual state scoring confirmed normal sleep on the baseline day and sleep deprivation on the two manipulation days (68% decrease in non-REM, 63% decrease in REM, and 74% increase in waking). No significant differences in levels of ACTH and corticosterone (stress hormones indicative of HPA axis activity) were found at any time point between baseline sleep and sleep deprivation via air puffs. COMPARISON WITH EXISTING METHOD There were no significant differences in ACTH or corticosterone concentrations between sleep deprivation by air puffs and gentle handling over the 8-h period. CONCLUSIONS Our system accurately detects sleep and delivers air puffs to acutely deprive rats of sleep with sufficient temporal resolution during the critical 4-5h post learning sleep-dependent memory consolidation period. The system is stress-free and a viable alternative to existing sleep deprivation techniques.

Alzheimer’s disease and sleep–wake disturbances: Amyloid, astrocytes, and animal models

Sleep–wake abnormalities are common in patients with Alzheimers disease, and can be a major reason for institutionalization. However, an emerging concept is that these sleep–wake disturbances are part of the causal pathway accelerating the neurodegenerative process. Recently, new findings have provided intriguing evidence for a positive feedback loop between sleep–wake dysfunction and β-amyloid (Aβ) aggregation. Studies in both humans and animal models have shown that extended periods of wakefulness increase Aβ levels and aggregation, and accumulation of Aβ causes fragmentation of sleep. This perspective is aimed at presenting evidence supporting causal links between sleep–wake dysfunction and aggregation of Aβ peptide in Alzheimers disease, and explores the role of astrocytes, a specialized type of glial cell, in this context underlying Alzheimers disease pathology. The utility of current animal models and the unexplored potential of alternative animal models for testing mechanisms involved in the reciprocal relationship between sleep disruption and Aβ are also discussed. Dual Perspectives Companion Paper: Microglia-Mediated Synapse Loss in Alzheimers Disease by Lawrence Rajendran and Rosa Paolicelli