A maternal brain hormone that builds bone.

In lactating mothers, the high calcium (Ca2+) demand for milk production triggers significant bone loss1. Although oestrogen normally counteracts excessive bone resorption by promoting bone formation, this sex steroid drops precipitously during this postpartum period. Here we report that brain-derived cellular communication network factor 3 (CCN3) secreted from KISS1 neurons of the arcuate nucleus (ARCKISS1) fills this void and functions as a potent osteoanabolic factor to build bone in lactating females. We began by showing that our previously reported female-specific, dense bone phenotype2 originates from a humoral factor that promotes bone mass and acts on skeletal stem cells to increase their frequency and osteochondrogenic potential. This circulatory factor was then identified as CCN3, a brain-derived hormone from ARCKISS1 neurons that is able to stimulate mouse and human skeletal stem cell activity, increase bone remodelling and accelerate fracture repair in young and old mice of both sexes. The role of CCN3 in normal female physiology was revealed after detecting a burst of CCN3 expression in ARCKISS1 neurons coincident with lactation. After reducing CCN3 in ARCKISS1 neurons, lactating mothers lost bone and failed to sustain their progeny when challenged with a low-calcium diet. Our findings establish CCN3 as a potentially new therapeutic osteoanabolic hormone for both sexes and define a new maternal brain hormone for ensuring species survival in mammals.

Spatial Coding Dysfunction and Network Instability in the Aging Medial Entorhinal Cortex.

Across species, spatial memory declines with age, possibly reflecting altered hippocampal and medial entorhinal cortex (MEC) function. However, the integrity of cellular and network-level spatial coding in aged MEC is unknown. Here, we leveraged in vivo electrophysiology to assess MEC function in young, middle-aged, and aged mice navigating virtual environments. In aged grid cells, we observed impaired stabilization of context-specific spatial firing, correlated with spatial memory deficits. Additionally, aged grid networks shifted firing patterns often but with poor alignment to context changes. Aged spatial firing was also unstable in an unchanging environment. In these same mice, we identified 458 genes differentially expressed with age in MEC, 61 of which had expression correlated with spatial firing stability. These genes were enriched among interneurons and related to synaptic transmission. Together, these findings identify coordinated transcriptomic, cellular, and network changes in MEC implicated in impaired spatial memory in aging.

MICROGLIA AGING IN THE HIPPOCAMPUS ADVANCES THROUGH INTERMEDIATE STATES THAT DRIVE INFLAMMATORY ACTIVATION AND COGNITIVE DECLINE.

During aging, microglia - the resident macrophages of the brain - exhibit dystrophic phenotypes and contribute to age-related neuroinflammation. While numerous hallmarks of age-related microglia dystrophy have been elucidated, the progression from homeostasis to dysfunction during the aging process remains unresolved. To bridge this gap in knowledge, we undertook complementary cellular and molecular analyses of microglia in the mouse hippocampus across the adult lifespan and in the experimental aging model of heterochronic parabiosis. Single-cell RNA-Seq and pseudotime analysis revealed age-related transcriptional heterogeneity in hippocampal microglia and identified intermediate states of microglial aging that also emerge following heterochronic parabiosis. We tested the functionality of intermediate stress response states via TGFß1 and translational states using pharmacological approaches in vitro to reveal their modulation of the progression to an inflammatory state. Furthermore, we utilized single-cell RNA-Seq in conjunction with an in vivo adult microglia-specific Tgfb1 conditional genetic knockout mouse model, to demonstrate that microglia advancement through intermediate aging states drives inflammatory activation and associated hippocampal-dependent cognitive decline.

Prenatal delivery of a therapeutic antisense oligonucleotide achieves broad biodistribution in the brain and ameliorates Angelman syndrome phenotype in mice.

Angelman syndrome (AS), an early-onset neurodevelopmental disorder characterized by abnormal gait, intellectual disabilities, and seizures, occurs when the maternal allele of the UBE3A gene is disrupted, since the paternal allele is silenced in neurons by the UBE3A antisense (UBE3A-AS) transcript. Given the importance of early treatment, we hypothesized that prenatal delivery of an antisense oligonucleotide (ASO) would downregulate the murine Ube3a-AS, resulting in increased UBE3A protein and functional rescue. Using a mouse model with a Ube3a-YFP allele that reports on-target ASO activity, we found that in utero, intracranial (IC) injection of the ASO resulted in dose-dependent activation of paternal Ube3a, with broad biodistribution. Accordingly, in utero injection of the ASO in a mouse model of AS also resulted in successful restoration of UBE3A and phenotypic improvements in treated mice on the accelerating rotarod and fear conditioning. Strikingly, even intra-amniotic (IA) injection resulted in systemic biodistribution and high levels of UBE3A reactivation throughout the brain. These findings offer a novel strategy for early treatment of AS using an ASO, with two potential routes of administration in the prenatal window. Beyond AS, successful delivery of a therapeutic ASO into neurons has implications for a clinically feasible prenatal treatment for numerous neurodevelopmental disorders.

Pain and Itch Processing in Aged Mice.

Most reports agree that aging negatively impacts pain processing and that the prevalence of chronic pain increases significantly with age. To improve current therapies, it is critical that aged animals be included in preclinical studies. Here we compared sensitivities to pain and itch-provoking stimuli in naïve and injured young and aged mice. Surprisingly, we found that in the absence of injury, aged male and female mice are significantly less responsive to mechanical stimuli and, in females, also to noxious thermal (heat) stimuli. In both older male and female mice, compared to younger (6-month-old mice), we also recorded reduced pruritogen-evoked scratching. On the other hand, after nerve injury, aged mice nevertheless developed significant mechanical hypersensitivity. Interestingly, however, and in contrast to young mice, aged mice developed both ipsilateral and contralateral postinjury mechanical allodynia. In a parallel immunohistochemical analysis of microglial and astrocyte markers, we found that the ipsilateral to the contralateral ratio of nerve injury-induced expression decreased with age. That observation is consistent with our finding of contralateral hypersensitivity after nerve injury in the aged but not the young mice. We conclude that aging has opposite effects on baseline versus postinjury pain and itch processing. PERSPECTIVE: Aged male and female mice (22-24 months) are less sensitive to mechanical, thermal (heat), and itch-provoking stimuli than are younger mice (6 months).

Neuronal activation of Gαq EGL-30/GNAQ late in life rejuvenates cognition across species.

Loss of cognitive function with age is devastating. EGL-30/GNAQ and Gαq signaling pathways are highly conserved between C. elegans and mammals, and murine Gnaq is enriched in hippocampal neurons and declines with age. We found that activation of EGL-30 in aged worms triples memory span, and GNAQ gain of function significantly improved memory in aged mice: GNAQ(gf) in hippocampal neurons of 24-month-old mice (equivalent to 70- to 80-year-old humans) rescued age-related impairments in well-being and memory. Single-nucleus RNA sequencing revealed increased expression of genes regulating synaptic function, axon guidance, and memory in GNAQ-treated mice, and worm orthologs of these genes were required for long-term memory extension in worms. These experiments demonstrate that C. elegans is a powerful model to identify mammalian regulators of memory, leading to the identification of a pathway that improves memory in extremely old mice. To our knowledge, this is the oldest age at which an intervention has improved age-related cognitive decline.

Brain-Derived CCN3 Is An Osteoanabolic Hormone That Sustains Bone in Lactating Females.

In lactating mothers, the high calcium (Ca 2+ ) demand for milk production triggers significant bone resorption. While estrogen would normally counteract excessive bone loss and maintain sufficient bone formation during this postpartum period, this sex steroid drops precipitously after giving birth. Here, we report that brain-derived CCN3 (Cellular Communication Network factor 3) secreted from KISS1 neurons of the arcuate nucleus (ARC KISS1 ) fills this void and functions as a potent osteoanabolic factor to promote bone mass in lactating females. Using parabiosis and bone transplant methods, we first established that a humoral factor accounts for the female-specific, high bone mass previously observed by our group after deleting estrogen receptor alpha (ER α ) from ARC KISS1 neurons 1 . This exceptional bone phenotype in mutant females can be traced back to skeletal stem cells (SSCs), as reflected by their increased frequency and osteochondrogenic potential. Based on multiple assays, CCN3 emerged as the most promising secreted pro-osteogenic factor from ARC KISS1 neurons, acting on mouse and human SSCs at low subnanomolar concentrations independent of age or sex. That brain-derived CCN3 promotes bone formation was further confirmed by in vivo gain- and loss-of-function studies. Notably, a transient rise in CCN3 appears in ARC KISS1 neurons in estrogen-depleted lactating females coincident with increased bone remodeling and high calcium demand. Our findings establish CCN3 as a potentially new therapeutic osteoanabolic hormone that defines a novel female-specific brain-bone axis for ensuring mammalian species survival.

Platelet-derived exerkine CXCL4/platelet factor 4 rejuvenates hippocampal neurogenesis and restores cognitive function in aged mice.

The beneficial effects of physical activity on brain ageing are well recognised, with exerkines, factors that are secreted into the circulation in response to exercise, emerging as likely mediators of this response. However, the source and identity of these exerkines remain unclear. Here we provide evidence that an anti-geronic exerkine is secreted by platelets. We show that platelets are activated by exercise and are required for the exercise-induced increase in hippocampal precursor cell proliferation in aged mice. We also demonstrate that increasing the systemic levels of the platelet-derived exerkine CXCL4/platelet factor 4 (PF4) ameliorates age-related regenerative and cognitive impairments in a hippocampal neurogenesis-dependent manner. Together these findings highlight the role of platelets in mediating the rejuvenating effects of exercise during physiological brain ageing.

Platelet factors are induced by longevity factor klotho and enhance cognition in young and aging mice.

Platelet factors regulate wound healing and can signal from the blood to the brain1,2. However, whether platelet factors modulate cognition, a highly valued and central manifestation of brain function, is unknown. Here we show that systemic platelet factor 4 (PF4) permeates the brain and enhances cognition. We found that, in mice, peripheral administration of klotho, a longevity and cognition-enhancing protein3-7, increased the levels of multiple platelet factors in plasma, including PF4. A pharmacologic intervention that inhibits platelet activation blocked klotho-mediated cognitive enhancement, indicating that klotho may require platelets to enhance cognition. To directly test the effects of platelet factors on the brain, we treated mice with vehicle or systemic PF4. In young mice, PF4 enhanced synaptic plasticity and cognition. In old mice, PF4 decreased cognitive deficits and restored aging-induced increases of select factors associated with cognitive performance in the hippocampus. The effects of klotho on cognition were still present in mice lacking PF4, suggesting this platelet factor is sufficient to enhance cognition but not necessary for the effects of klotho-and that other unidentified factors probably contribute. Augmenting platelet factors, possible messengers of klotho, may enhance cognition in the young brain and decrease cognitive deficits in the aging brain.

Platelet factors attenuate inflammation and rescue cognition in ageing.

Identifying therapeutics to delay, and potentially reverse, age-related cognitive decline is critical in light of the increased incidence of dementia-related disorders forecasted in the growing older population1. Here we show that platelet factors transfer the benefits of young blood to the ageing brain. Systemic exposure of aged male mice to a fraction of blood plasma from young mice containing platelets decreased neuroinflammation in the hippocampus at the transcriptional and cellular level and ameliorated hippocampal-dependent cognitive impairments. Circulating levels of the platelet-derived chemokine platelet factor 4 (PF4) (also known as CXCL4) were elevated in blood plasma preparations of young mice and humans relative to older individuals. Systemic administration of exogenous PF4 attenuated age-related hippocampal neuroinflammation, elicited synaptic-plasticity-related molecular changes and improved cognition in aged mice. We implicate decreased levels of circulating pro-ageing immune factors and restoration of the ageing peripheral immune system in the beneficial effects of systemic PF4 on the aged brain. Mechanistically, we identified CXCR3 as a chemokine receptor that, in part, mediates the cellular, molecular and cognitive benefits of systemic PF4 on the aged brain. Together, our data identify platelet-derived factors as potential therapeutic targets to abate inflammation and rescue cognition in old age.

The platelet transcriptome and proteome in Alzheimer's disease and aging: an exploratory cross-sectional study.

Introduction: Alzheimer's disease (AD) and aging are associated with platelet hyperactivity. However, the mechanisms underlying abnormal platelet function in AD and aging are yet poorly understood. Methods: To explore the molecular profile of AD and aged platelets, we investigated platelet activation (i.e., CD62P expression), proteome and transcriptome in AD patients, non-demented elderly, and young individuals as controls. Results: AD, aged and young individuals showed similar levels of platelet activation based on CD62P expression. However, AD and aged individuals had a proteomic signature suggestive of increased platelet activation compared with young controls. Transcriptomic profiling suggested the dysregulation of proteolytic machinery involved in regulating platelet function, particularly the ubiquitin-proteasome system in AD and autophagy in aging. The functional implication of these transcriptomic alterations remains unclear and requires further investigation. Discussion: Our data strengthen the evidence of enhanced platelet activation in aging and provide a first glimpse of the platelet transcriptomic changes occurring in AD.

Blood-to-brain communication in aging and rejuvenation.

Aging induces molecular, cellular and functional changes in the adult brain that drive cognitive decline and increase vulnerability to dementia-related neurodegenerative diseases. Leveraging systemic and lifestyle interventions, such as heterochronic parabiosis, administration of 'young blood', exercise and caloric restriction, has challenged prevalent views of brain aging as a rigid process and has demonstrated that aging-associated cognitive and cellular impairments can be restored to more youthful levels. Technological advances in proteomic and transcriptomic analyses have further facilitated investigations into the functional impact of intertissue communication on brain aging and have led to the identification of a growing number of pro-aging and pro-youthful factors in blood. In this review, we discuss blood-to-brain communication from a systems physiology perspective with an emphasis on blood-derived signals as potent drivers of both age-related brain dysfunction and brain rejuvenation.

Loss of neuronal Tet2 enhances hippocampal-dependent cognitive function.

DNA methylation has emerged as a critical modulator of neuronal plasticity and cognitive function. Notwithstanding, the role of enzymes that demethylate DNA remain to be fully explored. Here, we report that loss of ten-eleven translocation methylcytosine dioxygenase 2 (Tet2), which catalyzes oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), in adult neurons enhances cognitive function. In the adult mouse hippocampus, we detected an enrichment of Tet2 in neurons. Viral-mediated neuronal overexpression and RNA interference of Tet2 altered dendritic complexity and synaptic-plasticity-related gene expression in vitro. Overexpression of neuronal Tet2 in adult hippocampus, and loss of Tet2 in adult glutamatergic neurons, resulted in differential hydroxymethylation associated with genes involved in synaptic transmission. Functionally, overexpression of neuronal Tet2 impaired hippocampal-dependent memory, while loss of neuronal Tet2 enhanced memory. Ultimately, these data identify neuronal Tet2 as a molecular target to boost cognitive function.

Corrigendum: Long-Term Cognitive Impairments and Pathological Alterations in a Mouse Model of Repetitive Mild Traumatic Brain Injury.

[This corrects the article DOI: 10.3389/fneur.2014.00012.].

Microglial GPR56 is the molecular target of maternal immune activation-induced parvalbumin-positive interneuron deficits.

Parvalbumin-positive (PV+) interneurons play a critical role in maintaining circuit rhythm in the brain, and their reduction is implicated in autism spectrum disorders. Animal studies demonstrate that maternal immune activation (MIA) leads to reduced PV+ interneurons in the somatosensory cortex and autism-like behaviors. However, the underlying molecular mechanisms remain largely unknown. Here, we show that MIA down-regulates microglial Gpr56 expression in fetal brains in an interleukin-17a-dependent manner and that conditional deletion of microglial Gpr56 [Gpr56 conditional knockout (cKO)] mimics MIA-induced PV+ interneuron defects and autism-like behaviors in offspring. We further demonstrate that elevated microglial tumor necrosis factor-α expression is the underlying mechanism by which MIA and Gpr56 cKO impair interneuron generation. Genetically restoring Gpr56 expression in microglia ameliorates PV+ interneuron deficits and autism-like behaviors in MIA offspring. Together, our study demonstrates that microglial GPR56 plays an important role in PV+ interneuron development and serves as a salient target of MIA-induced neurodevelopmental disorders.

Exerkines in health, resilience and disease.

The health benefits of exercise are well-recognized and are observed across multiple organ systems. These beneficial effects enhance overall resilience, healthspan and longevity. The molecular mechanisms that underlie the beneficial effects of exercise, however, remain poorly understood. Since the discovery in 2000 that muscle contraction releases IL-6, the number of exercise-associated signalling molecules that have been identified has multiplied. Exerkines are defined as signalling moieties released in response to acute and/or chronic exercise, which exert their effects through endocrine, paracrine and/or autocrine pathways. A multitude of organs, cells and tissues release these factors, including skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (baptokines) and neurons (neurokines). Exerkines have potential roles in improving cardiovascular, metabolic, immune and neurological health. As such, exerkines have potential for the treatment of cardiovascular disease, type 2 diabetes mellitus and obesity, and possibly in the facilitation of healthy ageing. This Review summarizes the importance and current state of exerkine research, prevailing challenges and future directions.

MHC class I H2-Kb negatively regulates neural progenitor cell proliferation by inhibiting FGFR signaling.

Proteins of the major histocompatibility complex class I (MHC I), predominantly known for antigen presentation in the immune system, have recently been shown to be necessary for developmental neural refinement and adult synaptic plasticity. However, their roles in nonneuronal cell populations in the brain remain largely unexplored. Here, we identify classical MHC I molecule H2-Kb as a negative regulator of proliferation in neural stem and progenitor cells (NSPCs). Using genetic knockout mouse models and in vivo viral-mediated RNA interference (RNAi) and overexpression, we delineate a role for H2-Kb in negatively regulating NSPC proliferation and adult hippocampal neurogenesis. Transcriptomic analysis of H2-Kb knockout NSPCs, in combination with in vitro RNAi, overexpression, and pharmacological approaches, further revealed that H2-Kb inhibits cell proliferation by dampening signaling pathways downstream of fibroblast growth factor receptor 1 (Fgfr1). These findings identify H2-Kb as a critical regulator of cell proliferation through the modulation of growth factor signaling.