Precise, dynamic control of metabolic fuel usage in response to environmental challenges such as altered food availability or temperature change is essential for animal survival. In mammals, metabolic flexibility—the capacity to shift cellular metabolism between carbohydrate and fatty acid oxidation—is understood to be largely regulated by circulating hormones such as insulin and glucagon. However, the role of the central nervous system in coordinating fuel selection and tissue metabolic tuning remains underexplored. Here, we investigated the mechanisms that mediate metabolic reprogramming following the acute activation of torpor-associated glutamatergic Adcyap1+ torpor-regulating neurons in the anteroventral preoptic area (avPOA Vglut2/PACAP ). The activation of these neurons rapidly shifts whole-body fuel use from glucose to fatty acids, irrespective of fuel/food availability. This shift is associated with reduced glucose utilization stemming from the transient induction of selective insulin resistance in skeletal muscle. We find that this reduction in skeletal muscle glucose metabolism does not require direct muscle innervation but is rather mediated in part via corticosterone. In contrast to their activation, avPOA Vglut2/PACAP neuronal silencing results in improved glucose tolerance, demonstrating powerful bidirectional control of tissue-specific glucose metabolism, whole-body glucose levels, and fuel usage. Together, our findings uncover a novel POA -skeletal muscle pathway that dynamically controls glucose utilization and metabolic flexibility.

Homeothermy, the physiologic capacity to maintain a constant core body temperature, provided a critical survival advantage for mammalian and avian phyla, enabling the colonization of diverse habitats. However, the higher metabolic demands associated with homeothermy necessitate greater food intake. When challenged by food deprivation or harsh environmental conditions, many mammalian and avian species initiate adaptive energy-conserving survival strategies-including hibernation and daily torpor-during which their body temperature decreases far below its homeostatic range. Despite their biological significance and potential biomedical applications, the neural circuit mechanisms regulating entry into these hypometabolic states and their relationship to characterized thermoregulatory pathways remain to be fully elucidated. Here we review known thermoregulatory mechanisms and recent findings concerning the neural control of torpor and hibernation to identify points of convergence as well as important next steps in pursuit of an understanding of these regulatory pathways.

Sensory experience refines neural circuits during critical periods of postnatal development1-3. Although neuronal activity is known to orchestrate the circuit wiring that underlies this process4,5, the environmental cues that restrain developmental plasticity as animals mature are less clear. Here we examine the experience-dependent maturation of the mouse primary visual cortex across postnatal development using paired single-cell transcriptomic and chromatin accessibility sequencing. In addition to identifying the activity-dependent gene programs that emerge within each cortical cell type, we find that light exposure drives astrocyte maturation through cell-type-specific recruitment of the glucocorticoid receptor (encoded by Nr3c1) to chromatin. Astrocyte glucocorticoid receptor signalling activates an extensive gene regulatory program that is partially conserved in human brain development and promotes maturation processes that may regulate critical period closure. Collectively, these findings reveal that astrocyte glucocorticoid receptor signalling restricts neuronal plasticity. Glucocorticoid regulation of astrocyte maturation may also contribute to the effects of early-life stress across the brain, and the disruption of this process may increase susceptibility to neuropsychiatric disease.

Neuronal activity shapes brain development and refines synaptic connectivity in part through dynamic changes in gene expression. While activity-regulated transcriptional programs have been extensively characterized, the holistic effects of neuronal activity on the full RNA life cycle remain relatively unexplored. Here, we show that neuronal activity influences multiple stages of RNA metabolism in vitro and in vivo . Among these, RNA stability emerges as a previously underappreciated regulator of gene expression, exerting a stronger influence than transcription on total RNA levels for ∼15% of activity-dependent genes. We go on to profile 3'UTR mRNA motifs that are sufficient to modulate activity-dependent mRNA stability and employ machine learning to identify the neuronal-specific RNA-binding protein HuD as a key regulator of activity-dependent mRNA stabilization. We demonstrate that HuD shapes activity-dependent mRNA abundance of hundreds of transcripts in both soma and distal neuronal processes and that neuronal activity drives the reorganization of HuD-interacting proteins, thereby stabilizing HuD-bound mRNAs and directing them into translationally active granules. Finally, we find that many variants associated with autism spectrum disorder (ASD) and other neurodevelopmental disorders disrupt or promote aberrant activity-dependent changes in mRNA stability. These findings reveal mRNA stability as a widespread mechanism of stimulus-responsive gene regulation in neurons with direct implications for the understanding of neurodevelopmental disorders.

Exposure to novel environments (NE) induces structural and functional changes in multiple brain areas, including the hippocampus, driven in part by changes in gene expression. However, the cell-type-specific transcriptional and chromatin responses to NE remain poorly understood. We employed single-nucleus multiomics and bulk RNA-seq of the hippocampal DG, CA3, and CA1 regions of male mice to profile gene expression and chromatin accessibility following NE exposure. We observed region-specific responses in excitatory neurons and diverse transcriptional changes in inhibitory and non-neuronal cells. NE-regulated genes were enriched for secreted factors, and their cell-type-specific receptor expression highlighted candidate signaling pathways involved in learning and memory. We identified thousands of cell-type-specific chromatin accessibility changes, with coordinated expression and accessibility patterns implicating FOS/AP-1 as a key regulator. These data provide a rich resource of chromatin accessibility and gene expression profiles across hippocampal cell types in response to NE, a physiological stimulus affecting learning and memory.

Mutations in the GJB2 gene cause DFNB1, the most common hereditary hearing loss. GJB2 is expressed by cochlear epithelial cells and fibrocytes, but not by sensory hair cells or neurons. Attempts to treat DFNB1 mouse models with gene therapy have not substantially restored function, as inappropriate expression in hair cells and neurons might compromise their electrical activity. Here, we use ATAC-seq to identify candidate gene regulatory elements (GREs) that can drive cell-type-specific expression of GJB2. HA-tagged GJB2, delivered to a conditional knockout mouse with AAV vectors carrying GREs, is expressed by the appropriate cells, prevents degeneration, and rescues hearing by only 10–20 dB. In a Gjb2 partial knockdown model, a vector lacking HA prevents degeneration and completely restores hearing. In cynomolgus monkey cochleas, human GJB2.HA delivered with similar vectors is located in the appropriate cell types and causes little or no compromise of hearing sensitivity. Together, these findings suggest that GRE-mediated expression of GJB2 can prevent hearing loss in DFNB1 patients. Mutations in GJB2 cause DFNB1, the most common hereditary deafness. ATAC-seq identification of gene regulatory elements enables targeted GJB2 delivery to cochlear cells, preventing hearing loss in mouse models.

Abstract Evolution of seasonal hibernation has enabled mammals to survive harsh conditions by entering a state of prolonged hypometabolism and hypothermia with body temperatures as low as 0-4°C 1–6 . Despite decades of physiological studies, the genetic tools to study hibernation have remained limited and the mechanisms that induce hibernation entry are still unknown. Focusing on the brain, we map state-dependent neuronal activity across the hibernation cycle in Syrian hamsters and identify the hypothalamic anterior preoptic area (aPOA) as a key regulator of hibernation entry. Single-nucleus RNA and chromatin profiling provided a map of neuronal populations present in the hamster POA and enabled the discovery and design of an enhancer AAV that selectively targets hibernation-associated aPOA subpopulations. Using this genetic approach, we show that Samd3 -positive aPOA glutamatergic neurons are necessary for entry into hibernation and that their activation is sufficient to induce a prolonged hypothermic state with associated nesting behavior. Together, we identify the first neuronal population that controls entry into hibernation, opening new avenues for investigating and manipulating the metabolic and physiological mechanisms underlying this extreme state of “suspended animation” and its potential applications in aging and disease.

Torpor and hibernation are extreme physiological adaptations of homeotherms associated with pro-longevity effects. Yet the underlying mechanisms of how torpor affects aging, and whether hypothermic and hypometabolic states can be induced to slow aging and increase healthspan, remain unknown. Here we demonstrate that the activity of a spatially defined neuronal population in the preoptic area, which has previously been identified as a torpor-regulating brain region, is sufficient to induce a torpor-like state (TLS) in mice. Prolonged induction of TLS slows epigenetic aging across multiple tissues and improves healthspan. We isolate the effects of decreased metabolic rate, long-term caloric restriction, and decreased core body temperature (Tb) on blood epigenetic aging and find that the decelerating effect of TLSs on aging is mediated by decreased Tb. Taken together, our findings provide novel mechanistic insight into the decelerating effects of torpor and hibernation on aging and support the growing body of evidence that Tb is an important mediator of the aging processes. Dissecting the effects of hypothermic and hypometabolic states on aging processes, the authors show that activation of neurons in the preoptic area induces a torpor-like state in mice that slows epigenetic aging and improves healthspan. These pro-longevity effects are mediated by reduced Tb, reinforcing evidence that Tb is a key mediator of aging processes.

Seasonal hibernation allows species to survive harsh environments by entering a profound hypometabolic and hypothermic state called deep torpor (DT). However, the neural mechanisms controlling entry into this state remain poorly understood. Here, we map neuronal activity across hibernation stages in the Syrian hamster and identify DT-associated activity in the hypothalamic anterior preoptic area (aPOA) as essential for hibernation entry. Single-nucleus multiomic profiling enabled the design of a novel enhancer adeno-associated virus selectively targeting candidate glutamatergic neuronal subpopulations. Using this tool, we demonstrate that activity of a subpopulation of Samd3-positive glutamatergic neurons in the hamster aPOA is both necessary and sufficient for DT induction. Together, our findings identify a neuronal population regulating hibernation entry and provide the first genetic access to manipulate this complex behavior. ### Competing Interest Statement The authors have declared no competing interest. G. Harold & Leila Y. Mathers Foundation, https://ror.org/02a7hjv13 Searle Scholars Program Pew Charitable Trusts, https://ror.org/02xhk2825 Longevity Impetus Grant from Norn Group, Hevolution Foundation and Rosenkranz Foundation MIT Research Support Committee Grant Howard Hughes Medical Institute, https://ror.org/006w34k90

Mutations in the chromatin reader and tumor suppressor ZMYND11 are the cause of ZMYND11-related syndromic intellectual disability (ZRSID), a disorder characterized by symptoms such as language and motor delay, behavioral disruptions, and seizures. We find that neuronal deletion of ZMYND11 in mice causes aberrant upregulation of non-neuronal gene programs, leading to reduced dendritic branching and spine density, as well as hyperactivity and abnormal motor behavior. We investigated the mechanism by which ZMYND11 regulates gene expression and discovered that ZMYND11 interacts with and inhibits the histone methyltransferase KMT2A (MLL1), a transcriptional co-activator which contributes to oncogenic and developmental gene programs. We find that a ZRSID-associated ZMYND11 point mutation abrogates ZMYND11 interaction with KMT2A, suggesting that this interaction is critical for the function of ZMYND11 in regulating brain development. Using a degron-tagged ZMYND11 mouse model to enable the rapid degradation of ZMYND11 in primary cortical neurons, we show that gene expression changes induced by ZMYND11 loss are attenuated by treatment with the KMT2A inhibitor revumenib, a drug which has recently been approved for the treatment of KMT2A-rearranged leukemia. Our findings shed light on the convergence of chromatin mechanisms regulating neuronal gene expression and raise the possibility that modulation of KMT2A activity may be a useful therapeutic avenue for ZRSID.

Cells must adapt to environmental changes to maintain homeostasis. One of the most striking environmental adaptations is entry into hibernation during which core body temperature can decrease from 37°C to as low at 4°C. How mammalian cells, which evolved to optimally function within a narrow range of temperatures, adapt to this profound decrease in temperature remains poorly understood. In this study, we conducted the first genome-scale CRISPR-Cas9 screen in cells derived from Syrian hamster, a facultative hibernator, as well as human cells to investigate the genetic basis of cold tolerance in a hibernator and a non-hibernator in an unbiased manner. Both screens independently revealed glutathione peroxidase 4 (GPX4), a selenium-containing enzyme, and associated proteins as critical for cold tolerance. We utilized genetic and pharmacological approaches to demonstrate that GPX4 is active in the cold and its catalytic activity is required for cold tolerance. Furthermore, we show that the role of GPX4 as a suppressor of cold-induced cell death extends across hibernating species, including 13-lined ground squirrels and greater horseshoe bats, highlighting the evolutionary conservation of this mechanism of cold tolerance. This study identifies GPX4 as a central modulator of mammalian cold tolerance and advances our understanding of the evolved mechanisms by which cells mitigate cold-associated damage—one of the most common challenges faced by cells and organisms in nature.

Neuronal activity-regulated gene expression plays a crucial role in sculpting neural circuits that underpin adaptive brain function. Transcriptional enhancers are now recognized as key components of gene regulation that orchestrate spatiotemporally precise patterns of gene transcription. We propose that the dynamics of enhancer activation uniquely position these genomic elements to finely tune activity-dependent cellular plasticity. Enhancer specificity and modularity can be exploited to gain selective genetic access to specific cell states, and the precise modulation of target gene expression within restricted cellular contexts enabled by targeted enhancer manipulation allows for fine-grained evaluation of gene function. Mounting evidence also suggests that enduring stimulus-induced changes in enhancer states can modify target gene activation upon restimulation, thereby contributing to a form of cell-wide metaplasticity. We advocate for focused exploration of activity-dependent enhancer function to gain new insight into the mechanisms underlying brain plasticity and cognitive dysfunction.

Spinal motor neuron (MN) dysfunction is the cause of a number of clinically significant movement disorders. Despite the recent approval of gene therapeutics targeting these MN-related disorders, there are no viral delivery mechanisms that achieve MN-restricted transgene expression. In this study, chromatin accessibility profiling of genetically defined mouse MNs was used to identify candidate cis-regulatory elements (CREs) capable of driving MN-selective gene expression. Subsequent testing of these candidates identified two CREs that confer MN-selective gene expression in the spinal cord as well as reduced off-target expression in dorsal root ganglia. Within one of these candidate elements, we identified a compact core transcription factor (TF)-binding region that drives MN-selective gene expression. Finally, we demonstrated that selective spinal cord expression driven by this mouse CRE is preserved in non-human primates. These findings suggest that cell-type-selective viral reagents in which cell-type-selective CREs drive restricted gene expression will be valuable research tools in mice and other mammalian species, with potentially significant therapeutic value in humans.

Mutations in MECP2 give rise to Rett syndrome (RTT), an X-linked neurodevelopmental disorder that results in broad cognitive impairments in females. While the exact etiology of RTT symptoms remains unknown, one possible explanation for its clinical presentation is that loss of MECP2 causes miswiring of neural circuits due to defects in the brain’s capacity to respond to changes in neuronal activity and sensory experience. Here, we show that MeCP2 is phosphorylated at four residues in the mouse brain (S86, S274, T308, and S421) in response to neuronal activity, and we generate a quadruple knock-in (QKI) mouse line in which all four activity-dependent sites are mutated to alanines to prevent phosphorylation. QKI mice do not display overt RTT phenotypes or detectable gene expression changes in two brain regions. However, electrophysiological recordings from the retinogeniculate synapse of QKI mice reveal that while synapse elimination is initially normal at P14, it is significantly compromised at P20. Notably, this phenotype is distinct from the synapse refinement defect previously reported for Mecp2 null mice, where synapses initially refine but then regress after the third postnatal week. We thus propose a model in which activity-induced phosphorylation of MeCP2 is critical for the proper timing of retinogeniculate synapse maturation specifically during the early postnatal period.

Neuronal activity is crucial for adaptive circuit remodelling but poses an inherent risk to the stability of the genome across the long lifespan of postmitotic neurons 1–5 . Whether neurons have acquired specialized genome protection mechanisms that enable them to withstand decades of potentially damaging stimuli during periods of heightened activity is unknown. Here we identify an activity-dependent DNA repair mechanism in which a new form of the NuA4–TIP60 chromatin modifier assembles in activated neurons around the inducible, neuronal-specific transcription factor NPAS4. We purify this complex from the brain and demonstrate its functions in eliciting activity-dependent changes to neuronal transcriptomes and circuitry. By characterizing the landscape of activity-induced DNA double-strand breaks in the brain, we show that NPAS4–NuA4 binds to recurrently damaged regulatory elements and recruits additional DNA repair machinery to stimulate their repair. Gene regulatory elements bound by NPAS4–NuA4 are partially protected against age-dependent accumulation of somatic mutations. Impaired NPAS4–NuA4 signalling leads to a cascade of cellular defects, including dysregulated activity-dependent transcriptional responses, loss of control over neuronal inhibition and genome instability, which all culminate to reduce organismal lifespan. In addition, mutations in several components of the NuA4 complex are reported to lead to neurodevelopmental and autism spectrum disorders. Together, these findings identify a neuronal-specific complex that couples neuronal activity directly to genome preservation, the disruption of which may contribute to developmental disorders, neurodegeneration and ageing.

The precise regulation of gene expression is fundamental to neurodevelopment, plasticity and cognitive function. Although several studies have profiled transcription in the developing human brain, there is a gap in understanding of accompanying translational regulation. In this study, we performed ribosome profiling on 73 human prenatal and adult cortex samples. We characterized the translational regulation of annotated open reading frames (ORFs) and identified thousands of previously unknown translation events, including small ORFs that give rise to human-specific and/or brain-specific microproteins, many of which we independently verified using proteomics. Ribosome profiling in stem-cell-derived human neuronal cultures corroborated these findings and revealed that several neuronal activity-induced non-coding RNAs encode previously undescribed microproteins. Physicochemical analysis of brain microproteins identified a class of proteins that contain arginine-glycine-glycine (RGG) repeats and, thus, may be regulators of RNA metabolism. This resource expands the known translational landscape of the human brain and illuminates previously unknown brain-specific protein products.

Neuronal activity-dependent gene expression is essential for brain development. Although transcriptional and epigenetic effects of neuronal activity have been explored in mice, such an investigation is lacking in humans. Because alterations in GABAergic neuronal circuits are implicated in neurological disorders, we conducted a comprehensive activity-dependent transcriptional and epigenetic profiling of human induced pluripotent stem cell-derived GABAergic neurons similar to those of the early developing striatum. We identified genes whose expression is inducible after membrane depolarization, some of which have specifically evolved in primates and/or are associated with neurological diseases, including schizophrenia and autism spectrum disorder (ASD). We define the genome-wide profile of human neuronal activity-dependent enhancers, promoters and the transcription factors CREB and CRTC1. We found significant heritability enrichment for ASD in the inducible promoters. Our results suggest that sequence variation within activity-inducible promoters of developing human forebrain GABAergic neurons contributes to ASD risk.

The advent of endothermy, which is achieved through the continuous homeostatic regulation of body temperature and metabolism1,2, is a defining feature of mammalian and avian evolution. However, when challenged by food deprivation or harsh environmental conditions, many mammalian species initiate adaptive energy-conserving survival strategies—including torpor and hibernation—during which their body temperature decreases far below its homeostatic set-point3–5. How homeothermic mammals initiate and regulate these hypothermic states remains largely unknown. Here we show that entry into mouse torpor, a fasting-induced state with a greatly decreased metabolic rate and a body temperature as low as 20 °C6, is regulated by neurons in the medial and lateral preoptic area of the hypothalamus. We show that restimulation of neurons that were activated during a previous bout of torpor is sufficient to initiate the key features of torpor, even in mice that are not calorically restricted. Among these neurons we identify a population of glutamatergic Adcyap1-positive cells, the activity of which accurately determines when mice naturally initiate and exit torpor, and the inhibition of which disrupts the natural process of torpor entry, maintenance and arousal. Taken together, our results reveal a specific neuronal population in the mouse hypothalamus that serves as a core regulator of torpor. This work forms a basis for the future exploration of mechanisms and circuitry that regulate extreme hypothermic and hypometabolic states, and enables genetic access to monitor, initiate, manipulate and study these ancient adaptations of homeotherm biology. A specific neuronal population in the medial and lateral preoptic area of the hypothalamus regulates entry into torpor in mice.

Maternal infection and inflammation during pregnancy are associated with neurodevelopmental disorders in offspring, but little is understood about the molecular mechanisms underlying this epidemiologic phenomenon. Here, we leveraged single-cell RNA sequencing to profile transcriptional changes in the mouse fetal brain in response to maternal immune activation (MIA) and identified perturbations in cellular pathways associated with mRNA translation, ribosome biogenesis and stress signaling. We found that MIA activates the integrated stress response (ISR) in male, but not female, MIA offspring in an interleukin-17a-dependent manner, which reduced global mRNA translation and altered nascent proteome synthesis. Moreover, blockade of ISR activation prevented the behavioral abnormalities as well as increased cortical neural activity in MIA male offspring. Our data suggest that sex-specific activation of the ISR leads to maternal inflammation-associated neurodevelopmental disorders.