Engrampigenetics: Epigenetics of engram memory cells

Epigenetic Peripheral Biomarkers for Early Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and represents the leading cause of cognitive impairment and dementia in older individuals throughout the world. The main hallmarks of AD include brain atrophy, extracellular deposition of insoluble amyloid-β (Aβ) plaques, and the intracellular aggregation of protein tau in neurofibrillary tangles. These pathological modifications start many years prior to clinical manifestations of disease and the spectrum of AD progresses along a continuum from preclinical to clinical phases. Therefore, identifying specific biomarkers for detecting AD at early stages greatly improves clinical management. However, stable and non-invasive biomarkers are not currently available for the early detection of the disease. In the search for more reliable biomarkers, epigenetic mechanisms, able to mediate the interaction between the genome and the environment, are emerging as important players in AD pathogenesis. Herein, we discuss altered epigenetic signatures in blood as potential peripheral biomarkers for the early detection of AD in order to help diagnosis and improve therapy.

Transcriptome and epigenome analysis of engram cells: Next-generation sequencing technologies in memory research

Transcription and epigenetic changes are integral components of the neuronal response to stimulation and have been postulated to be drivers or substrates for enduring changes in animal behavior, including learning and memory. Memories are thought to be deposited in neuronal assemblies called engrams, i.e., groups of cells that undergo persistent physical or chemical changes during learning and are selectively reactivated to retrieve the memory. Despite the research progress made in recent years, the identity of specific epigenetic changes, if any, that occur in these cells and subsequently contribute to the persistence of memory traces remains unknown. The analysis of these changes is challenging due to the difficulty of exploring molecular alterations that only occur in a relatively small percentage of cells embedded in a complex tissue. In this review, we discuss the recent advances in this field and the promise of next-generation sequencing (NGS) and epigenome editing methods for overcoming these challenges and address long-standing questions concerning the role of epigenetic mechanisms in memory encoding, maintenance and expression.

Neuronal ensemble-specific DNA methylation strengthens engram stability

Memories are encoded by memory traces or engrams, represented within subsets of neurons that are synchronously activated during learning. However, the molecular mechanisms that drive engram stabilization during consolidation and consequently ensure its reactivation by memory recall are not fully understood. In this study we manipulate, during memory consolidation, the levels of the de novo DNA methyltransferase 3a2 (Dnmt3a2) selectively within dentate gyrus neurons activated by fear conditioning. We found that Dnmt3a2 upregulation enhances memory performance in mice and improves the fidelity of reconstitution of the original neuronal ensemble upon memory retrieval. Moreover, similar manipulation in a sparse, non-engram subset of neurons does not bias engram allocation or modulate memory strength. We further show that neuronal Dnmt3a2 overexpression changes the DNA methylation profile of synaptic plasticity-related genes. Our data implicates DNA methylation selectively within neuronal ensembles as a mechanism of stabilizing engrams during consolidation that supports successful memory retrieval.

How the epigenome integrates information and reshapes the synapse

In the past few decades, the field of neuroepigenetics has investigated how the brain encodes information to form long-lasting memories that lead to stable changes in behaviour. Activity-dependent molecular mechanisms, including, but not limited to, histone modification, DNA methylation and nucleosome remodelling, dynamically regulate the gene expression required for memory formation. Recently, the field has begun to examine how a learning experience is integrated at the level of both chromatin structure and synaptic physiology. Here, we provide an overview of key established epigenetic mechanisms that are important for memory formation. We explore how epigenetic mechanisms give rise to stable alterations in neuronal function by modifying synaptic structure and function, and highlight studies that demonstrate how manipulating epigenetic mechanisms may push the boundaries of memory.

Neuroimaging Epigenetics: Challenges and Recommendations for Best Practices

Neuroimaging epigenetics is an interdisciplinary application of epigenetics to cognitive neuroscience that seeks to identify molecular and neural predictors of human behavior. This approach can be sensitive to the dynamic interaction between biological predisposition and environmental influences, and is potentially more informative than an approach using static genetic code. Recent work in this field has generated considerable enthusiasm, yet caution is warranted since any novel cross-disciplinary approach lacks a set of established conventions or standards. In this paper we review existing research in the field of imaging epigenetics, outline important caveats and considerations, and suggest a set of guidelines for researchers conducting this work.

The development of attachment: Integrating genes, brain, behavior, and environment

In humans, as in other animal species, early caregiver-infant interactions influence physiological and psychological processes by modulating brain sensitivity. Furthermore, early social interaction between caregiver and infant influences infants' cognitive and socioemotional development, and subsequently the development of social, familial, and romantic relationships later in life. Here, we have collected longitudinal and cross-sectional empirical studies as well as review and perspective articles that focus on human or non-human mammals with the aim to investigate how genetic, hormonal, behavioural, and environmental factors, as well as cultural contexts, regulate early interactional experiences, and how these experiences translate into social and non-social competences later in life (see Graphical Abstract).