Faculty Bibliography

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. There is no specific treatment for FXS due to the lack of therapeutic targets. We report here that Elongation Factor 1α (EF1α) forms a complex with two other proteins: Tripartite motif-containing protein 3 (TRIM3) and Murine double minute (Mdm2). Both EF1α-Mdm2 and EF1α-TRIM3 protein complexes are increased in the brain of Fmr1 knockout mice as a result of FMRP deficiency, which releases the normal translational suppression of EF1α mRNA and increases EF1α protein levels. Increased EF1α-Mdm2 complex decreases PSD-95 ubiquitination (Ub-PSD-95) and Ub-PSD-95-C1q interaction. The elevated level of TRIM3-EF1α complex is associated with decreased TRIM3-Complement Component 3 (C3) complex that inhibits the activation of C3. Both protein complexes thereby contribute to a reduction in microglia-mediated phagocytosis and dendritic spine pruning. Finally, we created a peptide that disrupts both protein complexes and restores dendritic spine plasticity and behavioural deficits in Fmr1 knockout mice. The EF1α-Mdm2 and EF1α-TRIM3 complexes could thus be new therapeutic targets for FXS.

INTRODUCTION/BACKGROUND:Anesthesia often exacerbates memory recall difficulties in individuals with Alzheimer's disease (AD), but the underlying mechanisms remain unclear. METHODS:imaging, viral-based circuit tracing, and chemogenetic approaches to investigate anesthesia-induced remote memory impairment in mouse models of presymptomatic AD. RESULTS:Our study identified pyramidal neuron hyperactivity in the anterior cingulate cortex (ACC) as a significant contributor to anesthesia-induced remote memory impairment. This ACC hyperactivation arises from the disinhibition of local inhibitory circuits and increased excitatory inputs from the hippocampal CA1 region. Inhibiting hyperactivity in the CA1-ACC circuit improved memory recall after anesthesia. Moreover, anesthesia led to increased tau phosphorylation in the hippocampus, and inhibiting this hyperphosphorylation prevented ACC hyperactivity and subsequent memory impairment. DISCUSSION/CONCLUSIONS:Hippocampal-cortical hyperactivity plays a role in anesthesia-induced remote memory impairment. Targeting tau hyperphosphorylation shows promise as a therapeutic strategy to mitigate anesthesia-induced neural network dysfunction and retrograde amnesia in AD.

Poor sleep is associated with the risk of developing chronic pain, but how sleep contributes to pain chronicity remains unclear. Here we show that following peripheral nerve injury, cholinergic neurons in the anterior nucleus basalis (aNB) of the basal forebrain are increasingly active during nonrapid eye movement (NREM) sleep in a mouse model of neuropathic pain. These neurons directly activate vasoactive intestinal polypeptide-expressing interneurons in the primary somatosensory cortex (S1), causing disinhibition of pyramidal neurons and allodynia. The hyperactivity of aNB neurons is caused by the increased inputs from the parabrachial nucleus (PB) driven by the injured peripheral afferents. Inhibition of this pathway during NREM sleep, but not wakefulness, corrects neuronal hyperactivation and alleviates pain. Our results reveal that the PB-aNB-S1 pathway during sleep is critical for the generation and maintenance of chronic pain. Inhibiting this pathway during the sleep phase could be important for treating neuropathic pain.

Increased low frequency cortical oscillations are observed in people with neuropathic pain, but the cause of such elevated cortical oscillations and their impact on pain development remain unclear. By imaging neuronal activity in a spared nerve injury (SNI) mouse model of neuropathic pain, we show that neurons in dorsal root ganglia (DRG) and somatosensory cortex (S1) exhibit synchronized activity after peripheral nerve injury. Notably, synchronized activity of DRG neurons occurs within hours after injury and 1-2 days before increased cortical oscillations. This DRG synchrony is initiated by axotomized neurons and mediated by local purinergic signaling at the site of nerve injury. We further show that synchronized DRG activity after SNI is responsible for increasing low frequency cortical oscillations and synaptic remodeling in S1, as well as for inducing animals' pain-like behaviors. In naive mice, enhancing the synchrony, not the level, of DRG neuronal activity causes synaptic changes in S1 and pain-like behaviors similar to SNI mice. Taken together, these results reveal the critical role of synchronized DRG neuronal activity in increasing cortical plasticity and oscillations in a neuropathic pain model. These findings also suggest the potential importance of detection and suppression of elevated cortical oscillations in neuropathic pain states.

Perfluoroalkyl sulfonates (PFSAs), perfluoroalkyl carboxylates (PFCAs), and emerging alternatives and precursors of these compounds were determined in tissues of finless porpoise (Neophocaena asiaeorientalis sunameri) collected from East China Sea in 2009-2010 and 2018-2019. The median hepatic concentrations of emerging poly- and perfluoroalkyl substances (PFASs), including 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), 8:2 chlorinated polyfluorinated ether sulfonate (8:2 Cl-PFESA), 2,3,3,3-tetrafluoro-2-propanoate (HFPO-DA), and 4,8-dioxa-3H-perfluorononanoate (ADONA) were 16.2, 2.16, < LOQ (limit of quantification) and < LOQ ng/g ww (wet weight), respectively. The concentrations of legacy substances, perfluorooctanesulfonate (PFOS), and perfluorooctanoate (PFOA), were 86.9 and 1.95 ng/g ww, respectively. The liver concentrations of 6:2 Cl-PFESA, HFPO-DA, and perfluorohexanesulfonate (PFHxS) increased with time between 2009-2010 and 2018-2019. Further, concentrations of PFOA showed a declining trend in finless porpoise, whereas PFOS and its precursor (i.e., perfluorooctane sulfonamide [FOSA]) showed an increasing trend with time between 2009-2010 and 2018-2019. Analysis of PFASs in nine different tissues/organs of finless porpoise (i.e., liver, heart, intestine, spleen, kidney, stomach, lung, muscle, and skin) revealed a similar distribution pattern between 6:2 Cl-PFESA and PFOS; however, the tissue distribution patterns differed between HFPO-DA and PFOA. The concentrations of PFAS alternatives in kidney were similar or lower than the prototype compounds PFOS and PFOA (i.e., 8:2 Cl-PFESA < 6:2 Cl-PFESA ≈ PFOS; HFPO-DA < PFOA), implying slow renal excretion of PFAS alternatives as that of legacy PFASs. The estimates of body burdens of PFASs in porpoises suggested comparable accumulation of PFAS alternatives and legacy PFSAs and PFCAs. This study provides novel information on temporal trends and tissue distribution of emerging PFASs in marine mammals in China.

Changes in synaptic connections are believed to underlie long-term memory storage. Previous studies have suggested that sleep is important for synapse formation after learning, but how sleep is involved in the process of synapse formation remains unclear. To address this question, we used transcranial two-photon microscopy to investigate the effect of postlearning sleep on the location of newly formed dendritic filopodia and spines of layer 5 pyramidal neurons in the primary motor cortex of adolescent mice. We found that newly formed filopodia and spines were partially clustered with existing spines along individual dendritic segments 24 h after motor training. Notably, posttraining sleep was critical for promoting the formation of dendritic filopodia and spines clustered with existing spines within 8 h. A fraction of these filopodia was converted into new spines and contributed to clustered spine formation 24 h after motor training. This sleep-dependent spine formation via filopodia was different from retraining-induced new spine formation, which emerged from dendritic shafts without prior presence of filopodia. Furthermore, sleep-dependent new filopodia and spines tended to be formed away from existing spines that were active at the time of motor training. Taken together, these findings reveal a role of postlearning sleep in regulating the number and location of new synapses via promoting filopodial formation.

Peripheral nerve injury-induced mechanical allodynia is often accompanied by abnormalities in the higher cortical regions, yet the mechanisms underlying such maladaptive cortical plasticity remain unclear. Here, we show that in male mice, structural and functional changes in the primary somatosensory cortex (S1) caused by peripheral nerve injury require neuron-microglial signaling within the local circuit. Following peripheral nerve injury, microglia in the S1 maintain ramified morphology and normal density but up-regulate the mRNA expression of brain-derived neurotrophic factor (BDNF). Using in vivo two-photon imaging and Cx3cr1CreER;Bdnfflox mice, we show that conditional knockout of BDNF from microglia prevents nerve injury-induced synaptic remodeling and pyramidal neuron hyperactivity in the S1, as well as pain hypersensitivity in mice. Importantly, S1-targeted removal of microglial BDNF largely recapitulates the beneficial effects of systemic BDNF depletion on cortical plasticity and allodynia. Together, these findings reveal a pivotal role of cerebral microglial BDNF in somatosensory cortical plasticity and pain hypersensitivity.

Cognitive impairment is often observed in multiple sclerosis and its animal models, experimental autoimmune encephalomyelitis (EAE). Using mice with immunization-induced EAE, we have previously shown that the stability of cortical synapses is markedly decreased before the clinical onset of EAE. In this study, we examined learning-dependent structural synaptic plasticity in a spontaneous EAE model. Transgenic mice expressing myelin basic protein-specific T cell receptor genes develop EAE spontaneously at around 8 weeks of age. Using in vivo two-photon microscopy, we found that the elimination and formation rates of postsynaptic dendritic spines in somatosensory and motor cortices increased weeks before detectable signs of EAE and remained to be high during the disease onset. Despite the elevated basal spine turnover, motor learning-induced spine formation was reduced in presymptomatic EAE mice, in line with their impaired ability to retain learned motor skills. Additionally, we found a substantial elevation of IFN-γ mRNA in the brain of 4-week-old presymptomatic mice, and treatment of anti-IFN-γ antibody reduced dendritic spine elimination in the cortex. Together, these findings reveal synaptic instability and failure to form new synapses after learning as early brain pathology of EAE, which may contribute to cognitive and behavioral deficits seen in autoimmune diseases.

Accumulation and spread of tau in Alzheimer's disease and other tauopathies occur in a prion-like manner. However, the mechanisms and downstream consequences of tau trafficking remain largely unknown. We hypothesized that tau traffics from neurons to microglia via extracellular vesicles (EVs), leading to IL-6 generation and cognitive impairment. We assessed mice and neurons treated with anesthetics sevoflurane and desflurane, and applied nanobeam-sensor technology, an ultrasensitive method, to measure tau/p-tau amounts. Sevoflurane, but not desflurane, increased tau or p-tau amounts in blood, neuron culture medium, or EVs. Sevoflurane increased p-tau amounts in brain interstitial fluid. Microglia from tau knockout mice took up tau and p-tau when treated with sevoflurane-conditioned neuron culture medium, leading to IL-6 generation. Tau phosphorylation inhibitor lithium and EVs generation inhibitor GW4869 attenuated tau trafficking. GW4869 mitigated sevoflurane-induced cognitive impairment in mice. Thus, tau trafficking could occur from neurons to microglia to generate IL-6, leading to cognitive impairment.

In many parts of the nervous system, experience-dependent refinement of neuronal circuits predominantly involves synapse elimination. The role of sleep in this process remains unknown. We investigated the role of sleep in experience-dependent dendritic spine elimination of layer 5 pyramidal neurons in the visual (V1) and frontal association cortex (FrA) of 1-month-old mice. We found that monocular deprivation (MD) or auditory-cued fear conditioning (FC) caused rapid spine elimination in V1 or FrA, respectively. MD- or FC-induced spine elimination was significantly reduced after total sleep or REM sleep deprivation. Total sleep or REM sleep deprivation also prevented MD- and FC-induced reduction of neuronal activity in response to visual or conditioned auditory stimuli. Furthermore, dendritic calcium spikes increased substantially during REM sleep, and the blockade of these calcium spikes prevented MD- and FC-induced spine elimination. These findings reveal an important role of REM sleep in experience-dependent synapse elimination and neuronal activity reduction.