Grandfathers-to-Grandsons Transgenerational Transmission of Exercise Positive Effects on Cognitive Performance.

Physical exercise is a robust lifestyle intervention known for its enhancement of cognitive abilities. Nevertheless, the extent to which these benefits can be transmitted across generations (intergenerational inheritance to F1, and transgenerational to F2 and beyond) remains a topic of limited comprehension. We have already shown that cognitive improvements resulting from physical exercise can be inherited from parents to their offspring, proving intergenerational effects. So, we set out to explore whether these enhancements might extend transgenerationally, impacting the F2 generation. In this study, we initially examined the behavioral traits of second generation (F2) male mice, whose grandfathers (F0) had an exercise intervention. Our findings revealed that F2 mice with physically active grandpaternal F0 progenitors displayed significantly improved memory recall, encompassing both spatial and non-spatial information when compared to their counterparts from sedentary F0 progenitors, and proving for the first time the transgenerational inheritance of physical exercise induced cognitive enhancement. Surprisingly, while F2 memory improved (as was the case with F1), adult hippocampal neurogenesis remained unchanged between experimental and control groups (unlike in F1). Additionally, our analysis of small RNA sequences in the hippocampus identified 35 differentially expressed miRNAs linked to important brain function categories. Notably, two of these miRNAs, miRNA-144 and miRNA-298, displayed a robust negative correlation with cognitive performance. These findings highlight the enduring transgenerational transmission of cognitive benefits associated with exercise, even after two generations, suggesting that moderate exercise training can have lasting positive effects, possibly orchestrated by a specific set of miRNAs that exert their influence across multiple generations.

Dlk1 dosage regulates hippocampal neurogenesis and cognition.

Neurogenesis in the adult brain gives rise to functional neurons, which integrate into neuronal circuits and modulate neural plasticity. Sustained neurogenesis throughout life occurs in the subgranular zone (SGZ) of the dentate gyrus in the hippocampus and is hypothesized to be involved in behavioral/cognitive processes such as memory and in diseases. Genomic imprinting is of critical importance to brain development and normal behavior, and exemplifies how epigenetic states regulate genome function and gene dosage. While most genes are expressed from both alleles, imprinted genes are usually expressed from either the maternally or the paternally inherited chromosome. Here, we show that in contrast to its canonical imprinting in nonneurogenic regions, Delta-like homolog 1 (Dlk1) is expressed biallelically in the SGZ, and both parental alleles are required for stem cell behavior and normal adult neurogenesis in the hippocampus. To evaluate the effects of maternally, paternally, and biallelically inherited mutations within the Dlk1 gene in specific behavioral domains, we subjected Dlk1-mutant mice to a battery of tests that dissociate and evaluate the effects of Dlk1 dosage on spatial learning ability and on anxiety traits. Importantly, reduction in Dlk1 levels triggers specific cognitive abnormalities that affect aspects of discriminating differences in environmental stimuli, emphasizing the importance of selective absence of imprinting in this neurogenic niche.

The Role of Smad2 in Adult Neuroplasticity as Seen through Hippocampal-Dependent Spatial Learning/Memory and Neurogenesis.

Adult neural plasticity is an important and intriguing phenomenon in the brain, and adult hippocampal neurogenesis is directly involved in modulating neural plasticity by mechanisms that are only partially understood. We have performed gain-of-function and loss-of-function experiments to study Smad2, a transcription factor selected from genes that are demethylated after exercise through the analysis of an array of physical activity-induced factors, and their corresponding gene expression, and an efficient inducer of plasticity. In these studies, changes in cell number and morphology were analyzed in the hippocampal dentate gyrus (cell proliferation and survival, including regional distribution, and structural maturation/differentiation, including arborization, dendritic spines, and neurotransmitter-specific vesicles) of sedentary male mice, after evaluation in a battery of behavioral tests. As a result, we reveal a role for Smad2 in the balance of proliferation versus maturation of differentiating immature cells (Smad2 silencing increases both the proliferation and survival of cycling cells in the dentate granule cell layer), and in the plasticity of both newborn and mature neurons in mice (by decreasing dendritic arborization and dendritic spine number). Moreover, Smad2 silencing specifically compromises spatial learning in mice (through impairments of spatial tasks acquisition both in long-term learning and working memory). These data suggest that Smad2 participates in adult neural plasticity by influencing the proliferation and maturation of dentate gyrus neurons.SIGNIFICANCE STATEMENT Smad2 is one of the main components of the transforming growth factor-ß (TGF-ß) pathway. The commitment of cell fate in the nervous system is tightly coordinated by SMAD2 signaling, as are further differentiation steps (e.g., dendrite and axon growth, myelination, and synapse formation). However, there are no studies that have directly evaluated the role of Smad2 gene in hippocampus of adult animals. Modulation of these parameters in the adult hippocampus can affect hippocampal-dependent behaviors, which may shed light on the mechanisms that regulate adult neurogenesis and behavior. We demonstrate here a role for Smad2 in the maturation of differentiating immature cells and in the plasticity of mature neurons. Moreover, Smad2 silencing specifically compromises the spatial learning abilities of adult male mice.

Intergenerational transmission of the positive effects of physical exercise on brain and cognition.

Physical exercise has positive effects on cognition, but very little is known about the inheritance of these effects to sedentary offspring and the mechanisms involved. Here, we use a patrilineal design in mice to test the transmission of effects from the same father (before or after training) and from different fathers to compare sedentary- and runner-father progenies. Behavioral, stereological, and whole-genome sequence analyses reveal that paternal cognition improvement is inherited by the offspring, along with increased adult neurogenesis, greater mitochondrial citrate synthase activity, and modulation of the adult hippocampal gene expression profile. These results demonstrate the inheritance of exercise-induced cognition enhancement through the germline, pointing to paternal physical activity as a direct factor driving offspring's brain physiology and cognitive behavior.

Noggin rescues age-related stem cell loss in the brain of senescent mice with neurodegenerative pathology.

Increasing age is the greatest known risk factor for the sporadic late-onset forms of neurodegenerative disorders such as Alzheimer's disease (AD). One of the brain regions most severely affected in AD is the hippocampus, a privileged structure that contains adult neural stem cells (NSCs) with neurogenic capacity. Hippocampal neurogenesis decreases during aging and the decrease is exacerbated in AD, but the mechanistic causes underlying this progressive decline remain largely unexplored. We here investigated the effect of age on NSCs and neurogenesis by analyzing the senescence accelerated mouse prone 8 (SAMP8) strain, a nontransgenic short-lived strain that spontaneously develops a pathological profile similar to that of AD and that has been employed as a model system to study the transition from healthy aging to neurodegeneration. We show that SAMP8 mice display an accelerated loss of the NSC pool that coincides with an aberrant rise in BMP6 protein, enhanced canonical BMP signaling, and increased astroglial differentiation. In vitro assays demonstrate that BMP6 severely impairs NSC expansion and promotes NSC differentiation into postmitotic astrocytes. Blocking the dysregulation of the BMP pathway and its progliogenic effect in vivo by intracranial delivery of the antagonist Noggin restores hippocampal NSC numbers, neurogenesis, and behavior in SAMP8 mice. Thus, manipulating the local microenvironment of the NSC pool counteracts hippocampal dysfunction in pathological aging. Our results shed light on interventions that may allow taking advantage of the brain's natural plastic capacity to enhance cognitive function in late adulthood and in chronic neurodegenerative diseases such as AD.

Social dominance differentially alters gene expression in the medial prefrontal cortex without affecting adult hippocampal neurogenesis or stress and anxiety-like behavior.

Social hierarchies are crucial for a group's survival and can influence the way an individual behaves and relates to a given social context. The study of social rank has been classically based on ethological and observational paradigms, but it recently has taken advantage of the use of other approaches, such as the tube test that measures territorial dominance without the display of in situ aggression and is executable in group-living animals. However, little is known about how previous basal individual differences affect the development of dominance hierarchy measured in the tube test. We have analyzed in male mice body weight, locomotion, anxiety, and serum corticosterone both before and after the tube test, as well as adult hippocampal neurogenesis and transcriptome in the prefrontal cortex after the hierarchy had been established. We found differential gene expression between dominants and subordinates but no association between the other parameters and social status, neither pre- nor posttest. Our findings reveal that social rank in mice is stable along time and is not related to basal differences in stress, mood, or physical features. Lastly, real-time quantitative PCR analysis confirmed differential expression of vomeronasal and olfactory receptors in the cerebral cortex between dominant and subordinate individuals, suggesting that differential brain gene expression in the medial prefrontal cortex could potentially be used as a biomarker of social dominance.-Pallé, A., Zorzo, C., Luskey, V. E., McGreevy, K. R., Fernández, S., Trejo, J. L. Social dominance differentially alters gene expression in the medial prefrontal cortex without affecting adult hippocampal neurogenesis or stress and anxiety-like behavior.

The relationship between behavior acquisition and persistence abilities: Involvement of adult hippocampal neurogenesis.

The influence of the learning process on the persistence of the newly acquired behavior is relevant both for our knowledge of the learning/memory mechanisms and for the educational policy. However, it is unclear whether during an operant conditioning process with a continuous reinforcement paradigm, individual differences in acquisition are also associated to differences in persistence of the acquired behavior. In parallel, adult neurogenesis has been implicated in spatial learning and memory, but the specific role of the immature neurons born in the adult brain is not well known for this process. We have addressed both questions by analyzing the relationship between water maze task acquisition scores, the persistence of the acquired behavior, and the size of the different subpopulations of immature neurons in the adult murine hippocampus. We have found that task acquisition and persistence rates were negatively correlated: the faster the animals find the water maze platform at the end of acquisition stage, the less they persist in searching for it at the learned position in a subsequent non-reinforced trial; accordingly, the correlation in the number of some new neurons' subpopulations and the acquisition rate is negative while with persistence in acquired behavior is positive. These findings reveal an unexpected relationship between the efficiency to learn a task and the persistence of the new behavior after a non-reinforcement paradigm, and suggest that the immature neurons might be involved in different roles in acquisition and persistence/extinction of a learning task. © 2016 Wiley Periodicals, Inc.

Reducing GABAA α5 receptor-mediated inhibition rescues functional and neuromorphological deficits in a mouse model of down syndrome.

Down syndrome (DS) is associated with neurological complications, including cognitive deficits that lead to impairment in intellectual functioning. Increased GABA-mediated inhibition has been proposed as a mechanism underlying deficient cognition in the Ts65Dn (TS) mouse model of DS. We show that chronic treatment of these mice with RO4938581 (3-bromo-10-(difluoromethyl)-9H-benzo[f]imidazo[1,5-a][1,2,4]triazolo[1,5-d][1,4]diazepine), a selective GABA(A) α5 negative allosteric modulator (NAM), rescued their deficits in spatial learning and memory, hippocampal synaptic plasticity, and adult neurogenesis. We also show that RO4938581 normalized the high density of GABAergic synapse markers in the molecular layer of the hippocampus of TS mice. In addition, RO4938581 treatment suppressed the hyperactivity observed in TS mice without inducing anxiety or altering their motor abilities. These data demonstrate that reducing GABAergic inhibition with RO4938581 can reverse functional and neuromorphological deficits of TS mice by facilitating brain plasticity and support the potential therapeutic use of selective GABA(A) α5 NAMs to treat cognitive dysfunction in DS.

The meninges host a unique compartment of regulatory T cells that bulwarks adult hippocampal neurogenesis.

Our knowledge about the meningeal immune system has recently burgeoned, particularly our understanding of how innate and adaptive effector cells are mobilized to meet brain challenges. However, information on how meningeal immunocytes guard brain homeostasis in healthy individuals remains sparse. This study highlights the heterogeneous and polyfunctional regulatory-T (Treg) cell compartment in the meninges. A Treg subtype specialized in controlling Th1-cell responses and another known to control responses in B-cell follicles were substantial components of this compartment, foretelling that punctual Treg-cell ablation rapidly unleashed interferon-gamma production by meningeal lymphocytes, unlocked their access to the brain parenchyma, and altered meningeal B-cell profiles. Distally, the hippocampus assumed a reactive state, with morphological and transcriptional changes in multiple glial-cell types; within the dentate gyrus, neural stem cells showed exacerbated death and desisted from further differentiation, associated with inhibition of spatial-reference memory. Thus, meningeal Treg cells are a multifaceted bulwark to brain homeostasis at steady-state. One sentence summary: A distinct population of regulatory T cells in the murine meninges safeguards homeostasis by keeping local interferon-γ-producing lymphocytes in check, thereby preventing their invasion of the parenchyma, activation of hippocampal glial cells, death of neural stem cells, and memory decay.

IRS-2 Deficiency impairs NMDA receptor-dependent long-term potentiation.

The beneficial effects of insulin and insulin-like growth factor I on cognition have been documented in humans and animal models. Conversely, obesity, hyperinsulinemia, and diabetes increase the risk for neurodegenerative disorders including Alzheimer's disease (AD). However, the mechanisms by which insulin regulates synaptic plasticity are not well understood. Here, we report that complete disruption of insulin receptor substrate 2 (Irs2) in mice impairs long-term potentiation (LTP) of synaptic transmission in the hippocampus. Basal synaptic transmission and paired-pulse facilitation were similar between the 2 groups of mice. Induction of LTP by high-frequency conditioning tetanus did not activate postsynaptic N-methyl-D-aspartate (NMDA) receptors in hippocampus slices from Irs2(-/-) mice, although the expression of NR2A, NR2B, and PSD95 was equivalent to wild-type controls. Activation of Fyn, AKT, and MAPK in response to tetanus stimulation was defective in Irs2(-/-) mice. Interestingly, IRS2 was phosphorylated during induction of LTP in control mice, revealing a potential new component of the signaling machinery which modulates synaptic plasticity. Given that IRS2 expression is diminished in Type 2 diabetics as well as in AD patients, these data may reveal an explanation for the prevalence of cognitive decline in humans with metabolic disorders by providing a mechanistic link between insulin resistance and impaired synaptic transmission.

The elusive transcriptional memory trace.

Memory is the brain faculty to store and remember information. It is a sequential process in which four different phases can be distinguished: encoding or learning, consolidation, storage and reactivation. Since the discovery of the first Drosophila gene essential for memory formation in 1976, our knowledge of its mechanisms has progressed greatly. The current view considers the existence of engrams, ensembles of neuronal populations whose activity is temporally coordinated and represents the minimal correlate of experience in brain circuits. In order to form and maintain the engram, protein synthesis and, probably, specific transcriptional program(s) is required. The immediate early gene response during learning process has been extensively studied. However, a detailed description of the transcriptional response for later memory phases was technically challenging. Recent advances in transcriptomics have allowed us to tackle this biological problem. This review summarizes recent findings in this field, and discusses whether or not it is possible to identify a transcriptional trace for memory.

Stratification of radiosensitive brain metastases based on an actionable S100A9/RAGE resistance mechanism.

Whole-brain radiotherapy (WBRT) is the treatment backbone for many patients with brain metastasis; however, its efficacy in preventing disease progression and the associated toxicity have questioned the clinical impact of this approach and emphasized the need for alternative treatments. Given the limited therapeutic options available for these patients and the poor understanding of the molecular mechanisms underlying the resistance of metastatic lesions to WBRT, we sought to uncover actionable targets and biomarkers that could help to refine patient selection. Through an unbiased analysis of experimental in vivo models of brain metastasis resistant to WBRT, we identified activation of the S100A9-RAGE-NF-κB-JunB pathway in brain metastases as a potential mediator of resistance in this organ. Targeting this pathway genetically or pharmacologically was sufficient to revert the WBRT resistance and increase therapeutic benefits in vivo at lower doses of radiation. In patients with primary melanoma, lung or breast adenocarcinoma developing brain metastasis, endogenous S100A9 levels in brain lesions correlated with clinical response to WBRT and underscored the potential of S100A9 levels in the blood as a noninvasive biomarker. Collectively, we provide a molecular framework to personalize WBRT and improve its efficacy through combination with a radiosensitizer that balances therapeutic benefit and toxicity.

Exercise modulates insulin-like growth factor 1-dependent and -independent effects on adult hippocampal neurogenesis and behaviour.

While physical exercise clearly has beneficial effects on the brain, fomenting neuroprotection as well as promoting neural plasticity and behavioural modifications, the cellular and molecular mechanisms mediating these effects are not yet fully understood. We have analyzed sedentary and exercised animals to examine the effects of activity on behaviour (spatial memory and anxiety--as measured by a fear/exploration conflict test), as well as on adult hippocampal neurogenesis (a well-known form of neural plasticity). We have found that the difference in activity between sedentary and exercised animals induced a decrease in the fear/exploration conflict scores (a measure usually accepted as an anxiolytic effect), while no changes are evident in terms of spatial memory learning. The short-term anxiolytic-like effect of exercise was IGF1-dependent and indeed, the recall of hippocampus-dependent spatial memory is impaired by blocking serum IGF1 (as observed by measuring serum IGF levels in the same animals used to analyze the behaviour), irrespective of the activity undertaken by the animals. On the other hand, activity affected neurogenesis as reflected by counting the numbers of several cell populations, while the dependence of this effect on IGF1 varied according to the differentiation state of the new neurons. Hence, while proliferating precursors and postmitotic immature neurons (measured by means of doublecortin and calretinin) are influenced by serum IGF1 levels in both sedentary and exercised animals, premitotic immature neurons (an intermediate stage) respond to exercise independently of serum IGF1. Therefore, we conclude that physical exercise has both serum IGF1-independent and -dependent effects on neural plasticity. Furthermore, several effects mediated by serum IGF1 are induced by physical activity while others are not (both in terms of behaviour and neural plasticity). These findings help to delimit the role of serum IGF1 as a mediator of the effects of exercise, as well as to extend the role of serum IGF1 in the brain in basal conditions. Moreover, these data reveal the complexity of the interaction between neurogenesis, behaviour, and IGF1 under different levels of physical activity.

Gαi2+ vomeronasal neurons govern the initial outcome of an acute social competition.

Pheromone detection by the vomeronasal organ (VNO) mediates important social behaviors across different species, including aggression and sexual behavior. However, the relationship between vomeronasal function and social hierarchy has not been analyzed reliably. We evaluated the role of pheromone detection by receptors expressed in the apical layer of the VNO such as vomeronasal type 1 receptors (V1R) in dominance behavior by using a conditional knockout mouse for G protein subunit Gαi2, which is essential for V1R signaling. We used the tube test as a model to analyze the within-a-cage hierarchy in male mice, but also as a paradigm of novel territorial competition in animals from different cages. In absence of prior social experience, Gαi2 deletion promotes winning a novel social competition with an unfamiliar control mouse but had no effect on an established hierarchy in cages with mixed genotypes, both Gαi2-/- and controls. To further dissect social behavior of Gαi2-/- mice, we performed a 3-chamber sociability assay and found that mutants had a slightly altered social investigation. Finally, gene expression analysis in the medial prefrontal cortex (mPFC) for a subset of genes previously linked to social status revealed no differences between group-housed Gαi2-/- and controls. Our results reveal a direct influence of pheromone detection on territorial dominance, indicating that olfactory communication involving apical VNO receptors like V1R is important for the outcome of an initial social competition between two unfamiliar male mice, whereas final social status acquired within a cage remains unaffected. These results support the idea that previous social context is relevant for the development of social hierarchy of a group. Overall, our data identify two context-dependent forms of dominance, acute and chronic, and that pheromone signaling through V1R receptors is involved in the first stages of a social competition but in the long term is not predictive for high social ranks on a hierarchy.

Mechanisms mediating brain plasticity: IGF1 and adult hippocampal neurogenesis.

This review addresses the role of serum insulin-like growth factor 1 (IGF1) as one mechanism of adult neural plasticity, specifically, its regulation of hippocampal neurogenesis among other plasticity-related processes. It is suggested that IGF has been reused advantageously both for the control of energy expenditure as a function of the organism's activity and to protect, repair, and plastically modulate the brain. Moreover, because as the main source of IGF1 in the adult organism is outside the brain and its presence in this organ is a function of the activity, IGF1 becomes an ideal factor to induce plastic/neuroprotective functions as a function of the organism's activity. The link for this point of view comes from the original function of IGF1 during ontogeny/phylogeny, the promotion of cell survival and control of neural cell numbers, whereas one of the IGF1 functions in the adult brain is the control of hippocampal neurogenesis. The investigation of the IGF1 role as mediator of exercise effects suggests that many but not all the effects of physical activity are mediated by IGF1. These investigations have contributed to delimit the role of IGF1 as mediator of exercise actions, but at the same time are unveiling new roles for serum IGF1 inside the brain.

Treatment of male rats with finasteride, an inhibitor of 5alpha-reductase enzyme, induces long-lasting effects on depressive-like behavior, hippocampal neurogenesis, neuroinflammation and gut microbiota composition.

Persistent alteration of plasma neuroactive steroid levels associated with major depression has been recently reported in men after the suspension of the treatment for androgenetic alopecia with finasteride, an inhibitor of the enzyme 5alpha-reductase. Observations in male rats confirmed persistent alterations in neuroactive steroid levels also in the brain. In the present study, we have ascertained possible effects on depressive-like behavior, neurogenesis, gliosis, neuroinflammation and gut microbiota in male rats after subchronic treatment for 20 days with finasteride and after one month of its withdrawal. At the end of treatment there was an increase in the number of pH3 immunoreactive cells in the subgranular zone of the dentate gyrus together with an increase in the mRNA levels of TNF-α in the hippocampus. By one month after the end of finasteride treatment, rats showed depressive-like behavior coupled with a decrease in the number of pH3 immunoreactive cells in the subgranular zone of the dentate gyrus, a decrease in granule cell density in the granule cell layer and an increase in the number of GFAP immunoreactive astrocytes in the dentate gyrus. Finally, alteration of gut microbiota (i.e., an increase in Bacteroidetes phylum and in Prevotellaceae family at the end of the treatment and a decrease in Ruminococcaceae family, Oscillospira and Lachnospira genus at the end of the withdrawal period) was detected. In conclusion, finasteride treatment in male rats has long term effects on depressive-like behavior, hippocampal neurogenesis and neuroinflammation and gut microbiota composition.

Insulin and insulin-like growth factor I signalling in neurons.

Insulin-like peptides are an ancient acquisition in phylogeny, suggesting a crucial biological role for these family of peptides. Indeed, a key function of these hormones in cell metabolism and growth has been firmly established. However, their significance in neuronal physiology is less characterized, although progress in recent years on the neuroactive properties of insulin and insulin-like growth factor I (IGF-I) supports an important role for these hormones in brain function. During development, appropriate IGF-I input is critical in brain growth while the role of insulin at this stage, although not well defined yet, may be related to the control of neuronal survival. In the adult, IGF-I is a pleiotropic signal involved in numerous processes to maintain adequate brain cell functions, while the role of insulin is better known in relation to the control of food consumption and glucose metabolism. The potential involvement of IGF-I in brain diseases associated with neuronal death is strongly supported by its neuroprotective role. Further, the unexplained high incidence of glucose metabolism dysregulation in brain diseases makes also insulin a strong candidate in neuro-pathological research. Because mounting evidence suggests a complementary role of insulin and IGF-I in the brain, unveiling the cellular and molecular pathways involved in brain insulin/IGF-I actions is helping to establish potentially new therapeutic targets and its exploitation may lead to new treatments for a wide array of brain diseases.

The GSK-3-inhibitor VP2.51 produces antidepressant effects associated with adult hippocampal neurogenesis.

Glycogen synthase kinase 3 (GSK-3) is a constitutively active kinase that has been implicated in the mechanism of action of mood stabilizers. According to the neurogenic hypothesis of depression, newborn neurons in the adult dentate gyrus are required for the antidepressant effects of certain agents. We demonstrate that administration of the GSK-3 inhibitor VP2.51 (2.5 mg/kg ip, for 3.5 weeks) increases cell proliferation (pH3+ cells), as well as the short- and long-term survival of newborn neurons (assessed by the 24 h survival of BrdU+ and DCX+ neurons), while significantly increasing the commitment of cells to the granule neuron lineage (Prox1 immunoreactivity). In parallel, VP2.51 induces a net antidepressant effect, as judged by the decrease in the immobility time in the forced swim test of naïve mice (non-stressed mice), as well as a therapeutic effect on previously stressed mice (Porsolt-induced stress). Interestingly, the morphological changes were found prominently in the ventral region of the hippocampus. We found that these effects are neurogenesis dependent by combining the antimitotic temozolomide (50 mg/kg ip) with the drug. Importantly VP2.51 did not provoke changes in weight or in a battery of behavioral tests (learning/memory and activity tests). As the effects of VP2.51 were concomitant with the increase in ß-catenin expression and a shift towards the inactive form of GSK-3, we suggest that VP2.51 has therapeutic benefits following stress, and it may be a preventive treatment in situations where a potential depressive state and/or loss of memory is associated with diminished neurogenesis, through selective GSK3-beta inhibition.