We demonstrate editing of post-mitotic neurons in the adult mouse brain following injection of Cas9 ribonucleoprotein (RNP) complexes in the hippocampus, striatum and cortex. Engineered variants of Cas9 with multiple SV40 nuclear localization sequences enabled a tenfold increase in the efficiency of neuronal editing in vivo. These advances indicate the potential of genome editing in the brain to correct or inactivate the underlying genetic causes of neurological diseases.
Inflammation is an immune activity designed to protect the host from pathogens and noxious agents. In its low-intensity form, presence of an inflammatory process must be inferred from appropriate biomarkers. Occult neuroinflammation is not just secondary to Alzheimer's disease (AD) but may contribute to its pathogenesis and promote its progression. A leaky blood-brain barrier (BBB) has been observed in early AD and may play a role in its initiation and development. Studies of the temporal evolution of AD's biomarkers have shown that, in AD, the brain's amyloid burden correlates poorly with cognitive decline. In contrast, cognitive deficits in AD correlate well with synapse loss. Oligomeric forms of amyloid-beta (oAβs) can be synaptotoxic and evidence of their deposition inside synaptic terminals of cognition-associated neurons explains early memory loss in AD better than formation of extracellular Aβ plaques. Among innate immune cells that reside in the brain, microglia sense danger signals represented by proteins like oAβ and become activated by neuronal damage such as that caused by bacterial endotoxins. The resulting reactive microgliosis has been implicated in generating the chronic form of microglial activation believed to promote AD's development. Genome-wide association studies (GWASs) have yielded data from patients with sporadic AD indicating that its causes include genetic variation in the innate immune system. Recent preclinical studies have reported that β-hydroxybutyrate (βOHB) may protect the brain from the adverse effects of both the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome and the deacetylation of histone. Consequently, there is an urgent need for clinical investigations designed to test whether an orally administered βOHB preparation, such as a ketone ester, can have a similar beneficial effect in human subjects.
The blood-brain barrier (BBB) is a continuous endothelial membrane within brain microvessels that has sealed cell-to-cell contacts and is sheathed by mural vascular cells and perivascular astrocyte end-feet. The BBB protects neurons from factors present in the systemic circulation and maintains the highly regulated CNS internal milieu, which is required for proper synaptic and neuronal functioning. BBB disruption allows influx into the brain of neurotoxic blood-derived debris, cells and microbial pathogens and is associated with inflammatory and immune responses, which can initiate multiple pathways of neurodegeneration. This Review discusses neuroimaging studies in the living human brain and post-mortem tissue as well as biomarker studies demonstrating BBB breakdown in Alzheimer disease, Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, multiple sclerosis, HIV-1-associated dementia and chronic traumatic encephalopathy. The pathogenic mechanisms by which BBB breakdown leads to neuronal injury, synaptic dysfunction, loss of neuronal connectivity and neurodegeneration are described. The importance of a healthy BBB for therapeutic drug delivery and the adverse effects of disease-initiated, pathological BBB breakdown in relation to brain delivery of neuropharmaceuticals are briefly discussed. Finally, future directions, gaps in the field and opportunities to control the course of neurological diseases by targeting the BBB are presented.
Innate immune memory is a vital mechanism of myeloid cell plasticity that occurs in response to environmental stimuli and alters subsequent immune responses. Two types of immunological imprinting can be distinguished-training and tolerance. These are epigenetically mediated and enhance or suppress subsequent inflammation, respectively. Whether immune memory occurs in tissue-resident macrophages in vivo and how it may affect pathology remains largely unknown. Here we demonstrate that peripherally applied inflammatory stimuli induce acute immune training and tolerance in the brain and lead to differential epigenetic reprogramming of brain-resident macrophages (microglia) that persists for at least six months. Strikingly, in a mouse model of Alzheimer's pathology, immune training exacerbates cerebral β-amyloidosis and immune tolerance alleviates it; similarly, peripheral immune stimulation modifies pathological features after stroke. Our results identify immune memory in the brain as an important modifier of neuropathology.
The brain is a genomic mosaic owing to somatic mutations that arise throughout development. Mobile genetic elements, including retrotransposons, are one source of somatic mosaicism in the brain. Retrotransposition may represent a form of plasticity in response to experience. Here, we use droplet digital polymerase chain reaction to show that natural variations in maternal care mediate the mobilization of long interspersed nuclear element-1 (LINE-1 or L1) retrotransposons in the hippocampus of the mouse brain. Increasing the amount of maternal care blocks the accumulation of L1. Maternal care also alters DNA methylation at YY1 binding sites implicated in L1 activation and affects expression of the de novo methyltransferase DNMT3a. Our observations indicate that early life experience drives somatic variation in the genome via L1 retrotransposons.
Perception can be described as a process of inference, integrating bottom-up sensory inputs and top-down expectations. However, it is unclear how this process is neurally implemented. It has been proposed that expectations lead to prestimulus baseline increases in sensory neurons tuned to the expected stimulus, which in turn, affect the processing of subsequent stimuli. Recent fMRI studies have revealed stimulus-specific patterns of activation in sensory cortex as a result of expectation, but this method lacks the temporal resolution necessary to distinguish pre- from poststimulus processes. Here, we combined human magnetoencephalography (MEG) with multivariate decoding techniques to probe the representational content of neural signals in a time-resolved manner. We observed a representation of expected stimuli in the neural signal shortly before they were presented, showing that expectations indeed induce a preactivation of stimulus templates. The strength of these prestimulus expectation templates correlated with participants' behavioral improvement when the expected feature was task-relevant. These results suggest a mechanism for how predictive perception can be neurally implemented.
This Editorial highlights an article in the current issue by Tapia-Rojas and Inestrosa suggesting that attenuation of Wnt signalling may be a triggering factor for the pathogenesis of Alzheimer disease (AD) in the J20 mouse model of AD. Their study utilises Wnt signalling inhibitors that operate at different points in the signalling pathway. The molecular changes of several key Wnt signaling components are examined, along with a thorough analysis of both the amyloid and tau based pathologies in the mouse brain. Studies focusing on inhibition of Wnt signalling in AD mice have the potential to provide much needed information regarding the pathological mechanisms by which attenuated Wnt signalling impacts on AD.
BACKGROUND:Numerous physical, psychological, and emotional benefits have been attributed to marijuana since its first reported use in 2,600 BC in a Chinese pharmacopoeia. The phytocannabinoids, cannabidiol (CBD), and delta-9-tetrahydrocannabinol (Δ9-THC) are the most studied extracts from cannabis sativa subspecies hemp and marijuana. CBD and Δ9-THC interact uniquely with the endocannabinoid system (ECS). Through direct and indirect actions, intrinsic endocannabinoids and plant-based phytocannabinoids modulate and influence a variety of physiological systems influenced by the ECS.METHODS:In 1980, Cunha et al. reported anticonvulsant benefits in 7/8 subjects with medically uncontrolled epilepsy using marijuana extracts in a phase I clinical trial. Since then neurological applications have been the major focus of renewed research using medical marijuana and phytocannabinoid extracts.RESULTS:Recent neurological uses include adjunctive treatment for malignant brain tumors, Parkinson's disease, Alzheimer's disease, multiple sclerosis, neuropathic pain, and the childhood seizure disorders Lennox-Gastaut and Dravet syndromes. In addition, psychiatric and mood disorders, such as schizophrenia, anxiety, depression, addiction, postconcussion syndrome, and posttraumatic stress disorders are being studied using phytocannabinoids.CONCLUSIONS:In this review we will provide animal and human research data on the current clinical neurological uses for CBD individually and in combination with Δ9-THC. We will emphasize the neuroprotective, antiinflammatory, and immunomodulatory benefits of phytocannabinoids and their applications in various clinical syndromes.
The increased number of elderly people worldwide poses a major medical and socio-economic challenge: the search of strategies to combat the consequences of the aging process. Oxidative stress and inflammation have been pointed out as the leading causes of brain aging, which in turn alters the functionality of brain. In this context, decline in adult neurogenesis (AN), due to modifications in the neural progenitor stem cells (NSCs) and their microenvironment, is among the aging alterations contributing to cognitive decline. Therefore, the consumption or administration of antioxidant and anti-inflammatory molecules, such as dietary polyphenols, is under study as a potential beneficial strategy for preventing brain aging alterations including AN decline. Polyphenols, through their antioxidant and anti-inflammatory properties, modulate several cascades and effectors involved in the regulation of AN (e.g., SIRT1, Wnt, NF-κB and Nrf2, among others). This work summarizes the latest discoveries regarding the mechanisms whereby polyphenols preserve AN and counteract the cognitive decline present in aging.
The decline of cognitive function occurs with aging, but the mechanisms responsible are unknown. Astrocytes instruct the formation, maturation, and elimination of synapses, and impairment of these functions has been implicated in many diseases. These findings raise the question of whether astrocyte dysfunction could contribute to cognitive decline in aging. We used the Bac-Trap method to perform RNA sequencing of astrocytes from different brain regions across the lifespan of the mouse. We found that astrocytes have region-specific transcriptional identities that change with age in a region-dependent manner. We validated our findings using fluorescence in situ hybridization and quantitative PCR. Detailed analysis of the differentially expressed genes in aging revealed that aged astrocytes take on a reactive phenotype of neuroinflammatory A1-like reactive astrocytes. Hippocampal and striatal astrocytes up-regulated a greater number of reactive astrocyte genes compared with cortical astrocytes. Moreover, aged brains formed many more A1 reactive astrocytes in response to the neuroinflammation inducer lipopolysaccharide. We found that the aging-induced up-regulation of reactive astrocyte genes was significantly reduced in mice lacking the microglial-secreted cytokines (IL-1α, TNF, and C1q) known to induce A1 reactive astrocyte formation, indicating that microglia promote astrocyte activation in aging. Since A1 reactive astrocytes lose the ability to carry out their normal functions, produce complement components, and release a toxic factor which kills neurons and oligodendrocytes, the aging-induced up-regulation of reactive genes by astrocytes could contribute to the cognitive decline in vulnerable brain regions in normal aging and contribute to the greater vulnerability of the aged brain to injury.
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive accumulation of β-amyloid fibrils and abnormal tau proteins in and outside of neurons. Representing a common form of dementia, aggravation of AD with age increases the morbidity rate among the elderly. Although, mutations in the ApoE4 act as potent risk factors for sporadic AD, familial AD arises through malfunctioning of APP, PSEN-1, and-2 genes. AD progresses through accumulation of amyloid plaques (Aβ) and neurofibrillary tangles (NFTs) in brain, which interfere with neuronal communication. Cellular stress that arises through mitochondrial dysfunction, endoplasmic reticulum malfunction, and autophagy contributes significantly to the pathogenesis of AD. With high accuracy in disease diagnostics, Aβ deposition and phosphorylated tau (p-tau) are useful core biomarkers in the cerebrospinal fluid (CSF) of AD patients. Although five drugs are approved for treatment in AD, their failures in achieving complete disease cure has shifted studies toward a series of molecules capable of acting against Aβ and p-tau. Failure of biologics or compounds to cross the blood-brain barrier (BBB) in most cases advocates development of an efficient drug delivery system. Though liposomes and polymeric nanoparticles are widely adopted for drug delivery modules, their use in delivering drugs across the BBB has been overtaken by exosomes, owing to their promising results in reducing disease progression.
Serotonergic psychedelics act as agonists at cortical 5-HT2A receptors and seem to induce personality changes. We conducted a systematic review of studies assessing the effects of these drugs on personality. Papers published from 1985-2016 were included from PubMed, LILACS, and SciELO databases. Three hundred and sixty-nine studies were identified, and 18 were included. Specific personality traits, such as Absorption and Self-Transcendence, seem to influence the effects of psychedelics, and psychedelic drug users and nonusers appear to differ in some personality traits. Psychedelics administered in controlled settings may induce personality changes, such as increased Openness and Self-Transcendence. Increases in global brain entropy induced by acute psychedelic administration predicted changes in Openness, and Self-Transcendence was negatively correlated with cortical thinning of the posterior cingulate cortex in long-term religious ayahuasca users. Acute and long-term use of psychedelics is associated with personality changes that appear to be modulated by 5-HT2A receptors. These changes seem to induce therapeutic effects that should be further explored in randomized controlled studies.
There has been an explosion of new findings recently giving us insights into the involvement of microglia in central nervous system (CNS) disorders. A host of new molecular tools and mouse models of disease are increasingly implicating this enigmatic type of nervous system cell as a key player in conditions ranging from neurodevelopmental disorders such as autism to neurodegenerative disorders such as Alzheimer's disease and chronic pain. Contemporaneously, diverse roles are emerging for microglia in the healthy brain, from sculpting developing neuronal circuits to guiding learning-associated plasticity. Understanding the physiological functions of these cells is crucial to determining their roles in disease. Here we focus on recent developments in our rapidly expanding understanding of the function, as well as the dysfunction, of microglia in disorders of the CNS.
Fasting may be exploited as a possible strategy for prevention and treatment of several diseases such as diabetes, obesity, and aging. On the other hand, high-fat diet (HFD) represents a risk factor for several diseases and increased mortality. The aim of the present study was to evaluate the impact of fasting on mouse brain aging transcriptome and how HFD regulates such pathways. We used the NCBI Gene Expression Omnibus (GEO) database, in order to identify suitable microarray datasets comparing mouse brain transcriptome under fasting or HFD vs aged mouse brain transcriptome. Three microarray datasets were selected for this study, GSE24504, GSE6285, and GSE8150, and the principal molecular mechanisms involved in this process were evaluated. This analysis showed that, regardless of fasting duration, mouse brain significantly expressed 21 and 30 upregulated and downregulated genes, respectively. The involved biological processes were related to cell cycle arrest, cell death inhibition, and regulation of cellular metabolism. Comparing mouse brain transcriptome under fasting and aged conditions, we found out that the number of genes in common increased with the duration of fasting (222 genes), peaking at 72 h. In addition, mouse brain transcriptome under HFD resembles for the 30% the one of the aged mice. Furthermore, several molecular processes were found to be shared between HFD and aging. In conclusion, we suggest that fasting and HFD play an opposite role in brain transcriptome of aged mice. Therefore, an intermittent diet could represent a possible clinical strategy to counteract aging, loss of memory, and neuroinflammation. Furthermore, low-fat diet leads to the inactivation of brain degenerative processes triggered by aging.
Recent data suggest that repairing the cerebral vasculature after traumatic brain injury (TBI) may help to improve functional recovery. The Wnt/β-catenin signaling pathway promotes blood vessel formation during vascular development, but its role in vascular repair after TBI remains elusive. In this study, we examined how the cerebral vasculature responds to TBI and the role of Wnt/β-catenin signaling in vascular repair. We induced a moderate controlled cortical impact in adult mice and performed vessel painting to visualize the vascular alterations in the brain. Brain tissue around the injury site was assessed for β-catenin and vascular markers. A Wnt transgenic mouse line was utilized to evaluate Wnt gene expression. We report that TBI results in vascular loss followed by increases in vascular structure at seven days post injury (dpi). Immature, non-perfusing vessels were evident in the tissue around the injury site. β-catenin protein expression was significantly reduced in the injury site at 7 dpi. However, there was an increase in β-catenin expression in perilesional vessels at 1 and 7 dpi. Similarly, we found increased number of Wnt-GFP-positive vessels after TBI. Our findings suggest that Wnt/β-catenin expression contributes to the vascular repair process after TBI.
New neurons continue to be generated in the subgranular zone of the dentate gyrus of the adult mammalian hippocampus. This process has been linked to learning and memory, stress and exercise, and is thought to be altered in neurological disease. In humans, some studies have suggested that hundreds of new neurons are added to the adult dentate gyrus every day, whereas other studies find many fewer putative new neurons. Despite these discrepancies, it is generally believed that the adult human hippocampus continues to generate new neurons. Here we show that a defined population of progenitor cells does not coalesce in the subgranular zone during human fetal or postnatal development. We also find that the number of proliferating progenitors and young neurons in the dentate gyrus declines sharply during the first year of life and only a few isolated young neurons are observed by 7 and 13 years of age. In adult patients with epilepsy and healthy adults (18-77 years; n = 17 post-mortem samples from controls; n = 12 surgical resection samples from patients with epilepsy), young neurons were not detected in the dentate gyrus. In the monkey (Macaca mulatta) hippocampus, proliferation of neurons in the subgranular zone was found in early postnatal life, but this diminished during juvenile development as neurogenesis decreased. We conclude that recruitment of young neurons to the primate hippocampus decreases rapidly during the first years of life, and that neurogenesis in the dentate gyrus does not continue, or is extremely rare, in adult humans. The early decline in hippocampal neurogenesis raises questions about how the function of the dentate gyrus differs between humans and other species in which adult hippocampal neurogenesis is preserved.
Beta-catenin is a protein with dual functions in the cell, playing a role in both adhesion between cells as well as gene transcription via the canonical Wnt signalling pathway. In the canonical Wnt signalling pathway, beta-catenin again plays multiple roles. In the embryonic stage, the regulation of beta-catenin levels activates genes that govern cell proliferation and differentiation. In an adult organism, beta-catenin continues to regulate the cell cycle - as a result over-expression of beta-catenin may lead to cancer. In the brain, dysfunctions in Wnt signalling related to beta-catenin levels may also cause various pathological conditions like Alzheimer's disease, Parkinson's disease, and depression. Beta-catenin can be influenced by stressful conditions and increases in glucocorticoid levels. In addition, beta-catenin can be regulated by neurotransmitters such as serotonin and dopamine. Fluctuations in beta-catenin in brain regions under duress have been associated with depressive-like behaviours. It is theorized that the change in behaviour can be attributed to the regulation of Dicer by beta-catenin. Dicer, a protein that produces micro-RNAs in the cell, is a target gene for beta-catenin. Amongst the micro-RNA that it produces are those involved in stress resilience. In this way, beta-catenin has taken its place in the well-studied biochemistry of stress and depression, and future research into this interesting protein may yet yield fruitful results in that field.
Radiation from galactic cosmic rays (GCR) poses a significant health risk for deep-space flight crews. GCR are unique in their extremely high-energy particles. With current spacecraft shielding technology, some of the predominant particles astronauts would be exposed to are 1H + 16O. Radiation has been shown to cause cognitive deficits in mice. The hippocampus plays a key role in memory and cognitive tasks; it receives information from the cortex, undergoes dendritic-dependent processing and then relays information back to the cortex. In this study, we investigated the effects of combined 1H + 16O irradiation on cognition and dendritic structures in the hippocampus of adult male mice three months postirradiation. Six-month-old male C57BL/6 mice were irradiated first with 1H (0.5 Gy, 150 MeV/n) and 1 h later with 16O (0.1 Gy, 600 MeV/n) at the NASA Space Radiation Laboratory (Upton, NY). Three months after irradiation, animals were tested for hippocampus-dependent cognitive performance using the Y-maze. Upon sacrifice, molecular and morphological assessments were performed on hippocampal tissues. During Y-maze testing, the irradiated mice failed to distinguish the novel arm, spending approximately the same amount of time in all three arms during the retention trial relative to sham-treated controls. Irradiated animals also showed changes in expression of glutamate receptor subunits and synaptic density-associated proteins. 1H + 16O radiation compromised dendritic morphology in the cornu ammonis 1 and dentate gyrus within the hippocampus. These data indicate cognitive injuries due to 1H + 16O at three months postirradiation.
Microglia are embryonically seeded macrophages that contribute to brain development, homeostasis, and pathologies. It is thus essential to decipher how microglial properties are temporally regulated by intrinsic and extrinsic factors, such as sexual identity and the microbiome. Here, we found that microglia undergo differentiation phases, discernable by transcriptomic signatures and chromatin accessibility landscapes, which can diverge in adult males and females. Remarkably, the absence of microbiome in germ-free mice had a time and sexually dimorphic impact both prenatally and postnatally: microglia were more profoundly perturbed in male embryos and female adults. Antibiotic treatment of adult mice triggered sexually biased microglial responses revealing both acute and long-term effects of microbiota depletion. Finally, human fetal microglia exhibited significant overlap with the murine transcriptomic signature. Our study shows that microglia respond to environmental challenges in a sex- and time-dependent manner from prenatal stages, with major implications for our understanding of microglial contributions to health and disease.
