Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound

The Role of Hyperbaric Oxygen Therapy in Neuroregeneration and Neuroprotection: A Review

Neurogenesis is a high energy-demanding process, which is why blood vessels are an active part of the neurogenic niche since they allow the much-needed oxygenation of progenitor cells. In this regard, although neglected for a long time, the "oxygen niche" should be considered an important intervenient in adult neurogenesis. One possible hypothesis for the failure of numerous neuroprotective trials is that they relied on compounds that target a highly specific neuroprotective pathway. This approach may be too limited, given the complexity of the processes that lead to cell death. Therefore, research should adopt a more multifactorial approach. Among the limited range of agents with multimodal neuromodulatory capabilities, hyperbaric oxygen therapy has demonstrated effectiveness in reducing secondary brain damage in various brain injury models. This therapy functions not only as a neuroprotective mechanism but also as a powerful neuroregenerative mechanism.

Tau and Alzheimer's disease: Past, present and future

My journey with tau started when in 1974 for the first time I isolated neurofibrillary tangles of paired helical filaments (PHFs) from autopsied Alzheimer's disease (AD) brains and discovered that they were made up of a ~50-70 KDa protein on SDS-polyacrylamide gels. Subsequently my team discovered that this PHF protein and the microtubule-associated factor called tau were one and the same protein. However, we found that tau in neurofibrillary tangles/PHFs in AD brain was abnormally hyperphosphorylated, and unlike normal tau, which promoted the assembly of tubulin into microtubules, the AD-hyperphosphorylated tau inhibited microtubule assembly. These discoveries of tau pathology in AD opened a new and a major area of research on tau and on the molecular pathology of this major cause of dementia in middle- and old-age individuals. Tau pathology, which without fail is made up of the aggregated hyperphosphorylated state of the protein, is also the hallmark lesion of a family of around 20 related neurodegenerative diseases, called tauopathies. Currently, tau pathology is a major drug target for the treatment of AD and related tauopathies. Both active and passive tau immunization human clinical trials at various stages are underway. Initial results range from negative to partially promising. Future studies will reveal whether tau therapy alone or in combination with drugs targeting Aβ and/or neurodegeneration will be required to achieve the most effective treatment for AD and related disorders.

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope. Neuroplasticity, in broad terms the ability of the brain to modify its structure in response to external stimulation or damage, has received growing attention as a possible therapeutic target, since the disruption of plastic mechanisms in the brain appear to correlate with various forms of cognitive impairment present in AD patients. Several pre-clinical and clinical studies have attempted to enhance neuroplasticity via different mechanisms, for example, regulating glucose or lipid metabolism, targeting the activity of neurotransmitter systems, or addressing neuroinflammation. In this review, we first describe several structural and functional aspects of neuroplasticity. We then focus on the current status of pharmacological approaches to AD stemming from clinical trials targeting neuroplastic mechanisms in AD patients. This is followed by an analysis of analogous pharmacological interventions in animal models, according to their mechanisms of action.

Age-related changes in mice behavior and the contribution of lipocalin-2

Aging causes considerable changes in the nervous system, inducing progressive and long-lasting loss of physiological integrity and synaptic plasticity, leading to impaired brain functioning. These age-related changes quite often culminate in behavioral dysfunctions, such as impaired cognition, which can ultimately result in various forms of neurodegenerative disorders. Still, little is known regarding the effects of aging on behavior. Moreover, the identification of factors involved in regenerative plasticity, in both the young and aged brain, is scarce but crucial from a regenerative point of view and for our understanding on the mechanisms that control the process of normal aging. Recently, we have identified the iron-trafficking protein lipocalin-2 (LCN2) as novel regulator of animal behavior and neuronal plasticity in the young adult brain. On the other hand, others have proposed LCN2 as a biological marker for disease progression in neurodegenerative disorders such as Alzheimer's disease and multiple sclerosis. Still, and even though LCN2 is well accepted as a regulator of neural processes in the healthy and diseased brain, its contribution in the process of normal aging is not known. Here, we performed a broad analysis on the effects of aging in mice behavior, from young adulthood to middle and late ages (2-, 12-, and 18-months of age), and in the absence of LCN2. Significant behavioral differences between aging groups were observed in all the dimensions analyzed and, in mice deficient in LCN2, aging mainly reduced anxiety, while sustained depressive-like behavior observed at younger ages. These behavioral changes imposed by age were further accompanied by a significant decrease in cell survival and neuronal differentiation at the hippocampus. Our results provide insights into the role of LCN2 in the neurobiological processes underlying brain function and behavior attributed to age-related changes.

Alzheimer's Disease: Challenges and a Therapeutic Opportunity to Treat It with a Neurotrophic Compound

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with an insidious onset and multifactorial nature. A deficit in neurogenesis and synaptic plasticity are considered the early pathological features associated with neurofibrillary tau and amyloid β pathologies and neuroinflammation. The imbalance of neurotrophic factors with an increase in FGF-2 level and a decrease in brain derived neurotrophic factor (BDNF) and neurotrophin 4 (NT-4) in the hippocampus, frontal cortex and parietal cortex and disruption of the brain micro-environment are other characteristics of AD. Neurotrophic factors are crucial in neuronal differentiation, maturation, and survival. Several attempts to use neurotrophic factors to treat AD were made, but these trials were halted due to their blood-brain barrier (BBB) impermeability, short-half-life, and severe side effects. In the present review we mainly focus on the major etiopathology features of AD and the use of a small neurotrophic and neurogenic peptide mimetic compound; P021 that was discovered in our laboratory and was found to overcome the difficulties faced in the administration of the whole neurotrophic factor proteins. We describe pre-clinical studies on P021 and its potential as a therapeutic drug for AD and related neurodegenerative disorders. Our study is limited because it focuses only on P021 and the relevant literature; a more thorough investigation is required to review studies on various therapeutic approaches and potential drugs that are emerging in the AD field.

A Potential Strategy for Treatment of Neurodegenerative Disorders by Regulation of Adult Hippocampal Neurogenesis in Human Brain

Abstract:

Adult hippocampal neurogenesis is a multistage mechanism that continues throughout the lifespan of human and non-human mammals. These adult-born neurons in the central nervous system (CNS) play a significant role in various hippocampus-dependent processes, including learning, mood regulation, pattern recognition, etc. Reduction of adult hippocampal neurogenesis, caused by multiple factors such as neurological disorders and aging, would impair neuronal proliferation and differentiation and result in memory loss. Accumulating studies have indicated that functional neuron impairment could be restored by promoting adult hippocampal neurogenesis. In this review, we summarized the small molecules that could efficiently promote the process of adult neurogenesis, particularly the agents that have the capacity of crossing the blood-brain barrier (BBB), and showed in vivo efficacy in mammalian brains. This may pave the way for the rational design of drugs to treat humnan neurodegenerative disorders in the future.

Peptides Derived from Growth Factors to Treat Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by progressive neuron losses in memory-related brain structures. The classical features of AD are a dysregulation of the cholinergic system, the accumulation of amyloid plaques, and neurofibrillary tangles. Unfortunately, current treatments are unable to cure or even delay the progression of the disease. Therefore, new therapeutic strategies have emerged, such as the exogenous administration of neurotrophic factors (e.g., NGF and BDNF) that are deficient or dysregulated in AD. However, their low capacity to cross the blood-brain barrier and their exorbitant cost currently limit their use. To overcome these limitations, short peptides mimicking the binding receptor sites of these growth factors have been developed. Such peptides can target selective signaling pathways involved in neuron survival, differentiation, and/or maintenance. This review focuses on growth factors and their derived peptides as potential treatment for AD. It describes (1) the physiological functions of growth factors in the brain, their neuronal signaling pathways, and alteration in AD; (2) the strategies to develop peptides derived from growth factor and their capacity to mimic the role of native proteins; and (3) new advancements and potential in using these molecules as therapeutic treatments for AD, as well as their limitations.

Molecular mechanisms of altered adult hippocampal neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia globally. AD is a progressive neurodegenerative disorder, eventually manifesting as severe cognitive impairment. Adult hippocampal neurogenesis (AHN) occurs throughout adulthood and plays an important role in hippocampus-dependent learning and memory. The stages of AHN, predominantly comprising the proliferation, differentiation, survival, and maturation of newborn neurons, are affected to varying degrees in AD. However, the exact molecular mechanisms remain to be elucidated. Recent evidence suggests that the molecules involved in AD pathology contribute to the compromised AHN in AD. Notably, various interventions may have common signaling pathways that, once identified, could be harnessed to enhance adult neurogenesis. This in turn could putatively rescue cognitive deficits associated with impaired neurogenesis as observed in animal models of AD. In this manuscript, we review the current knowledge concerning AHN under normal physiological and AD pathological conditions and highlight the possible role of specific molecules in AHN alteration in AD. In addition, we summarize in vivo experiments with emphasis on the effect of the activation of certain key signalings on AHN in AD rodent models. We propose that these signaling targets and corresponding interventions should be considered when developing novel therapies for AD.

Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by impairments in synaptic plasticity and cognitive performance. Cognitive dysfunction and loss of neuronal plasticity are known to begin decades before the clinical diagnosis of the disease. The important influence of congenital genetic mutations on the early development of AD provides a novel opportunity to initiate treatment during early development to prevent the Alzheimer-like behavior and synaptic dysfunction.

OBJECTIVE

To explore strategies for early intervention to prevent Alzheimer's disease.

METHODS

In the present study, we investigated the effect of treatment during early development with a ciliary neurotrophic factor (CNTF) derived peptidergic compound, P021 (Ac-DGGLAG-NH2) on cognitive function and synaptic plasticity in 3xTg-AD transgenic mouse model of AD. 3xTg-AD and genetic background-matched wild type female mice were treated from birth to postnatal day 120 with P021 in diet or as a control with vehicle diet, and cognitive function and molecular markers of neuroplasticity were evaluated.

RESULTS

P021 treatment during early development prevented cognitive impairment and increased expressions of pCREB and BDNF that activated downstream various signaling cascades such as PLC/PKC, MEK/ERK and PI3K/Akt, and ameliorated synaptic protein deficit in 4-month-old 3xTg-AD mice.

CONCLUSION

These findings indicate that treatment with the neurotrophic peptide mimetic such as P021 during early development can be an effective therapeutic strategy to rescue synaptic deficit and cognitive impairment in familial AD and related tauopathies.

Exercise reverses learning deficits induced by hippocampal injury by promoting neurogenesis

Hippocampal atrophy and cognitive decline are common sequelae of many neurodegenerative disorders, including stroke. To determine whether cognitive decline can be ameliorated by exercise-induced neurogenesis, C57BL/6 mice in which a unilateral hippocampal injury had been induced by injecting the vasoconstrictor endothelin-1 into their right hippocampus, were run voluntarily for 21 days on a running-wheel. We found the severe deficits in spatial learning, as detected by active place-avoidance task, following injury were almost completely restored in animals that ran whereas those that did not run showed no improvement. We show the increase in neurogenesis found in both the injured and contralateral hippocampi following running was responsible for the restoration of learning since bilateral ablation of newborn doublecortin (DCX)-positive neurons abrogated the cognitive improvement, whereas unilateral ablations of DCX-positive neurons did not prevent recovery, demonstrating that elevated neurogenesis in either the damaged or intact hippocampus is sufficient to reverse hippocampal injury-induced deficits.

Prenatal to early postnatal neurotrophic treatment prevents Alzheimer-like behavior and pathology in mice

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of middle-aged to old individuals. The pathophysiological process of AD is believed to begin many years before the emergence of clinical symptoms. The important influence of congenital genetic aberrations on the development of AD provides a novel opportunity to initiate prenatal to early postnatal pharmacological treatment to address the role of this critical period of brain development in the disease.

METHODS

We investigated for the first time the effect of oral treatment during prenatal to early postnatal development with a neurotrophic compound, P021 (Ac-DGGL^AG-NH2), on neurobehavior and AD-like pathology in 3xTg-AD, a transgenic mouse model of AD. The transgenic and control wild-type female mice were treated from prenatal day 8 to postnatal day 21 with a custom-made diet containing P021 or a vehicle diet, followed by a standard diet. AD-type cognitive function and pathological features were studied during adulthood and old age.

RESULTS

The P021 treatment rescued cognitive deficits at 4 months, reduced abnormal hyperphosphorylation and accumulation of tau at known major AD neurofibrillary pathology-associated sites, and decreased Aβ plaque load at 22 months in 3xTg-AD mice. Prenatal to early postnatal treatment with P021 also ameliorated certain markers of postsynaptic deficits, including PSD-95 levels and CREB activity, and decreased one measure of neuroinflammation, GFAP level in the brain at 4 and 22 months in 3xTg mice.

CONCLUSIONS

These findings suggest that neurotrophic impairment during early development can be one of the etiopathogenic factors of AD and that the neurotrophic peptide mimetic is a potential early prevention strategy for this disease.

Born to Protect: Leveraging BDNF Against Cognitive Deficit in Alzheimer's Disease

Alzheimer's disease is a chronic neurodegenerative devastating disorder affecting a high percentage of the population over 65 years of age and causing a relevant emotional, social, and economic burden. Clinically, it is characterized by a prominent cognitive deficit associated with language and behavioral impairments. The molecular pathogenesis of Alzheimer's disease is multifaceted and involves changes in neurotransmitter levels together with alterations of inflammatory, oxidative, hormonal, and synaptic pathways, which may represent a drug target for both prevention and treatment; however, an effective treatment for Alzheimer's disease still represents an unmet goal. As neurotrophic factors participate in the modulation of the above-mentioned pathways, they have been highlighted as critical contributors of Alzheimer's disease etiology, whose modulation might be beneficial for Alzheimer's disease. We focused on the neurotrophin brain-derived neurotrophic factor, providing several lines of evidence pointing to brain-derived neurotrophic factor as a plausible endophenotype of cognitive deficits in Alzheimer's disease, illustrating some of the most recent possibilities to modulate the expression of this neurotrophin in the brain in an attempt to ameliorate cognition and delay the progression of Alzheimer's disease. This review shows that otherwise disparate pharmacologic or non-pharmacologic approaches converge on brain-derived neurotrophic factor, providing a means whereby apparently unrelated medical approaches may nevertheless produce similar synaptic and cognitive outcomes in Alzheimer's disease pathogenesis, suggesting that brain-derived neurotrophic factor-based synaptic repair may represent a modifying strategy to ameliorate cognition in Alzheimer's disease.

Inhibition of AMD-Like Pathology With a Neurotrophic Compound in Aged Rats and 3xTg-AD Mice

Age-associated macular degeneration (AMD), which leads to loss of vision at its end stage, is one of the most common neurodegenerative diseases among the elderly. However, to date, no effective drug therapy is available for the prevention of AMD. Here, we report the occurrence of AMD pathology and its prevention by chronic treatment with the neurotrophic peptidergic compound P021, in aged rats and 3xTg-AD mice. We found photoreceptor degeneration, lipofuscin granules, vacuoles, and atrophy in retinal pigment epithelium (RPE) as well as Bruch’s membrane (BM) thickening; in aged rats, we even found rosette-like structure formation. Microgliosis and astrogliosis were observed in different retinal layers. In addition, we also found that total tau, phosphorylated tau, Aβ/APP, and VEGF were widely distributed in the sub-retina of aged rats and 3xTg mice. Importantly, chronic treatment with P021 for 3 months in rats and for 18 months in 3xTg mice ameliorated the pathological changes above. These findings indicate the therapeutic potential of P021 for prevention and treatment of AMD and retinal changes associated with aging and Alzheimer’s disease.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Targeting the Synapse in Alzheimer's Disease

Dynamic gain and loss of synapses is fundamental to healthy brain function. While Alzheimer's Disease (AD) treatment strategies have largely focussed on beta-amyloid and tau protein pathologies, the synapse itself may also be a critical endpoint to consider regarding disease modification. Disruption of mechanisms of neuronal plasticity, eventually resulting in a net loss of synapses, is implicated as an early pathological event in AD. Synaptic dysfunction therefore may be a final common biological mechanism linking protein pathologies to disease symptoms. This review summarizes evidence supporting the idea of early neuroplastic deficits being prevalent in AD. Changes in synaptic density can occur before overt neurodegeneration and should not be considered to uniformly decrease over the course of the disease. Instead, synaptic levels are influenced by an interplay between processes of degeneration and atrophy, and those of maintenance and compensation at regional and network levels. How these neuroplastic changes are driven by amyloid and tau pathology are varied. A mixture of direct effects of amyloid and tau on synaptic integrity, as well as indirect effects on processes such as inflammation and neuronal energetics are likely to be at play here. Focussing on the synapse and mechanisms of neuroplasticity as therapeutic opportunities in AD raises some important conceptual and strategic issues regarding translational research, and how preclinical research can inform clinical studies. Nevertheless, substrates of neuroplasticity represent an emerging complementary class of drug target that would aim to normalize synapse dynamics and restore cognitive function in the AD brain and in other neurodegenerative diseases.

A Novel Therapeutic Approach to Treat Alzheimer's Disease by Neurotrophic Support During the Period of Synaptic Compensation

Alzheimer’s disease (AD), at present, is considered an incurable disease and a major dilemma with no drug to stop or slow down its progression. Drugs that are currently available in the market are able to only transiently improve the clinical symptoms. The repeated failures in developing an effective drug has led to the suggestion that the medical intervention was probably too late to be effective since the pathology starts many years before the appearance of the clinical symptoms. Probably, at the time of the appearance of clinical symptoms the brain has undergone major neuronal and synaptic loss. Because of the uncertainty on when to use a prevention therapy, especially targeting amyloid-β (Aβ) and tau pathologies, interventions that rely on the regenerative capacity of the brain such as the modulation of the inherent neurogenesis and neuronal plasticity represent a promising therapeutic strategy. Such an approach can act both at early as well as late stages of the disease and remove the barrier of the time of intervention. In this article, we review studies mainly from our laboratory that show the merit of early intervention during the synaptic and neuronal compensation period where the brain still has the capacity to self-repair by offering neurotrophic support in reversing cognitive impairment, neuronal and synaptic deficits, Aβ, and tau pathologies and decreasing mortality in a transgenic mouse model of AD.

Innovative Therapy for Alzheimer's Disease-With Focus on Biodelivery of NGF

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with abnormal protein modification, inflammation and memory impairment. Aggregated amyloid beta (Aβ) and phosphorylated tau proteins are medical diagnostic features. Loss of memory in AD has been associated with central cholinergic dysfunction in basal forebrain, from where the cholinergic circuitry projects to cerebral cortex and hippocampus. Various reports link AD progression with declining activity of cholinergic neurons in basal forebrain. The neurotrophic molecule, nerve growth factor (NGF), plays a major role in the maintenance of cholinergic neurons integrity and function, both during development and adulthood. Numerous studies have also shown that NGF contributes to the survival and regeneration of neurons during aging and in age-related diseases such as AD. Changes in neurotrophic signaling pathways are involved in the aging process and contribute to cholinergic and cognitive decline as observed in AD. Further, gradual dysregulation of neurotrophic factors like NGF and brain derived neurotrophic factor (BDNF) have been reported during AD development thus intensifying further research in targeting these factors as disease modifying therapies against AD. Today, there is no cure available for AD and the effects of the symptomatic treatment like cholinesterase inhibitors (ChEIs) and memantine are transient and moderate. Although many AD treatment studies are being carried out, there has not been any breakthrough and new therapies are thus highly needed. Long-term effective therapy for alleviating cognitive impairment is a major unmet need. Discussion and summarizing the new advancements of using NGF as a potential therapeutic implication in AD are important. In summary, the intent of this review is describing available experimental and clinical data related to AD therapy, priming to gain additional facts associated with the importance of NGF for AD treatment, and encapsulated cell biodelivery (ECB) as an efficient tool for NGF delivery.

Short-Term Effects of Overnight Orthokeratology on Corneal Sensitivity in Chinese Children and Adolescents

Purpose

To assess the effects of the 3-month period of orthokeratology (OK) treatment on corneal sensitivity in Chinese children and adolescents.

Methods

Thirty subjects wore overnight OK lenses in both eyes for 3 months and were assessed at baseline, 1 day, 1 week, 1 month, and 3 months after the treatment. Changes in corneal sensitivity were measured by the Cochet–Bonnet (COBO) esthesiometer at the corneal apex and approximately 2 mm from the temporal limbus. Changes in refraction and corneal topography were also measured.

Results

Central corneal sensitivity suffered a significant reduction within the first month of the OK treatment period but returned to the baseline level at three months (F = 3.009, P=0.039), while no statistically significant difference occurred in temporal sensitivity (F = 2.462, P=0.074). The baseline of central corneal sensitivity correlated with age (r = −0.369, P=0.045). A marked change in refraction (uncorrected visual acuity, P < 0.001; spherical equivalent, P < 0.001) and corneal topographical condition (mean keratometry reading, P < 0.001; eccentricity value, P < 0.001; Surface Regularity Index, P < 0.001) occurred, but none of these measurements were correlated with corneal sensitivity.

Conclusions

A 3-month period OK treatment causes a reduction in central corneal sensitivity in Chinese children and adolescents but with a final recovery to the baseline level, which might be because neuronal adaptation occurred earlier in children and adolescents than in adults.

Ergothioneine-induced neuronal differentiation is mediated through activation of S6K1 and neurotrophin 4/5-TrkB signaling in murine neural stem cells

The promotion of neurogenesis is considered to be an effective therapeutic strategy for neuropsychiatric disorders because impairment of neurogenesis is associated with the onset and progression of these disorders. We have previously demonstrated that orally ingested ergothioneine (ERGO), a naturally occurring antioxidant and hydrophilic amino acid, promotes neurogenesis in the hippocampal dentate gyrus (DG) with its abundant neural stem cells (NSCs) and exerts antidepressant-like effects in mice. Independent of its antioxidant activities, ERGO induces in cultured NSCs this differentiation through induction of the basic helix-loop-helix transcription factor Math1. However, the upstream signaling of Math1 in the mechanisms underlying ERGO-induced neuronal differentiation remains unclear. The purpose of the present study was to elucidate the upstream signaling with the aim of discovering novel targets for the treatment of neuropsychiatric disorders. We focused on neurotrophic factor signaling, as it is important for the promotion of neurogenesis and the induction of antidepressant effects. We also focused on the signaling of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a known amino acid sensor, and the members of this signaling pathway, mTOR and p70 ribosomal protein S6 kinase 1 (S6K1). Exposure of cultured NSCs to ERGO significantly increased the expression of phosphorylated S6K1 (p-S6K1) at Thr389 in only 1 h, of phosphorylated mTOR (p-mTOR) in 6 h, and of the gene product of neurotrophin 4/5 (NT5) which activates tropomyosin receptor kinase B (TrkB) in 24 h. ERGO increased the population of βIII-tubulin-positive neurons, and this effect was suppressed by the inhibitors of S6K1 (PF4708671), mTORC1 (rapamycin), and TrkB (GNF5837). Oral administration of ERGO to mice significantly increased in the DG the expression of p-S6K1 at Thr389, the gene product of NT5, and phosphorylated TrkB but not that of p-mTOR. Thus, neuronal differentiation of NSCs induced by ERGO is mediated, at least in part, through phosphorylation of S6K1 at Thr389 and subsequent activation of TrkB signaling through the induction of NT5. Thus, S6K1 and NT5 might be promising target molecules for the treatment of neuropsychiatric disorders.

Intra-hippocampal D-cycloserine rescues decreased social memory, spatial learning reversal, and synaptophysin levels in aged rats

RATIONALE

Aging is characterized by a decrease in N-methyl-D-aspartate receptors (NMDARs) in the hippocampus, which might be one of the factors involved in the age-dependent cognitive decline. D-Cycloserine (DCS), a partial agonist of the NMDAR glycine recognition site, could improve memory deficits associated to neurodegenerative disorders and cognitive deficits observed in normal aging.

OBJECTIVES AND METHODS

The aim of the present study was to explore whether DCS would reverse age-dependent memory deficits and decreases in NMDA receptor subunits (GluN1, GluN2A, and GluN2B) and the presynaptic protein synaptophysin in Wistar rats. We investigated the effects of pre-training infusions of DCS (10 μg/hemisphere) in the ventral hippocampus on two hippocampal-dependent learning tasks, the social transmission of food preference (STFP), and the Morris water maze (MWM).

RESULTS

The results revealed that infusions of DCS administered before the acquisition sessions rescued deficits in the STFP retention and MWM reversal learning in old rats. DCS also significantly increased the hippocampal levels of synaptophysin in old rats, which correlated with STFP and MWM performance in all tests. Moreover, although the levels of the GluN1 subunit correlated with the MWM acquisition and reversal, DCS did not enhance the expression of such synaptic protein.

CONCLUSIONS

The present behavioral results support the role of DCS as a cognitive enhancer and suggest that enhancing the function of NMDARs and synaptic plasticity in the hippocampus may be related to improvement in social memory and spatial learning reversal in aged animals.

Prevention of Amyloid-β and Tau Pathologies, Associated Neurodegeneration, and Cognitive Deficit by Early Treatment with a Neurotrophic Compound

To date, neither any effective treatment nor prevention of Alzheimer's disease (AD), a major dementia causing disorder, are available. Herein, we investigated the secondary prevention of neurodegeneration, amyloid-β (Aβ) and tau pathologies with a neurotrophic compound P021 in 3xTg-AD mice. Previous work found that P021 can rescue at mild to moderate stages Aβ and tau pathologies in 3xTg-AD mice. To determine its potential clinical application, we sought to test the preventive effect of P021 on Aβ and tau pathologies by starting the treatment during the period of synaptic compensation several months before the appearance of any overt pathology in 3xTg-AD mice. We started a continuous treatment with P021 in 3-month-old female animals and followed its effect at 9-, 15- and 18-months post-treatment. Neurodegeneration at the above time points was studied using Fluorojade C staining, and tau and Aβ pathologies both immunohistochemically and by Western blots. Cognitive performance was studied by assessing episodic memory with Novel Object Recognition task at 16-17-months post-treatment. We found that P021 treatment initiated during the synaptic compensation period can prevent neurodegeneration, Aβ and tau pathologies, rescue episodic memory impairment, and markedly reduce mortality rate. These findings for the first time show effective prevention of AD changes with a neurotrophic compound that targets neurogenesis and synaptic plasticity, suggesting that improving the health of the neuronal network can prevent AD.

Factors that influence adult neurogenesis as potential therapy

Adult neurogenesis involves persistent proliferative neuroprogenitor populations that reside within distinct regions of the brain. This phenomenon was first described over 50 years ago and it is now firmly established that new neurons are continually generated in distinct regions of the adult brain. The potential of enhancing the neurogenic process lies in improved brain cognition and neuronal plasticity particularly in the context of neuronal injury and neurodegenerative disorders. In addition, adult neurogenesis might also play a role in mood and affective disorders. The factors that regulate adult neurogenesis have been broadly studied. However, the underlying molecular mechanisms of regulating neurogenesis are still not fully defined. In this review, we will provide critical analysis of our current understanding of the factors and molecular mechanisms that determine neurogenesis. We will further discuss pre-clinical and clinical studies that have investigated the potential of modulating neurogenesis as therapeutic intervention in neurodegeneration.

Prevention of dendritic and synaptic deficits and cognitive impairment with a neurotrophic compound

Background

The use of neurotrophic factors to treat Alzheimer’s disease (AD) is hindered by their blood–brain barrier impermeability, short half-life, and severe side effects. Peptide 021 (P021) is a neurotrophic/neurogenic tetra-peptide that was derived from the most active region of the ciliary neurotrophic factor (CNTF) by epitope mapping. Admantylated glycine was added to its C-terminal to increase its blood–brain barrier permeability and decrease its degradation by exopeptidases to make it druggable. Here, we report on the preventive effect of P021 in 3 × Tg-AD, a transgenic mouse model of AD.

Methods

P021 was administered in the diet at 3 months, i.e., 6–9 months before any overt amyloid beta (Aβ) or tau pathology, and during the period of synaptic compensation, and was continued until 21 months in 3 × Tg-AD mice. The 3 × Tg-AD mice and wild-type (WT) mice were treated identically but with a vehicle-only diet serving as controls. The effects of P021 on neurogenesis, dendritic and synaptic markers, and cognitive performance were investigated.

Results

We found that P021 treatment was able to rescue dendritic and synaptic deficits, boost neurogenesis, and reverse cognitive impairment in 3 × Tg-AD mice.

Conclusions

Availability of appropriate neurotrophic support during the period of synaptic compensation can prevent synaptic deficit and cognitive impairment, and P021 is a promising neurotrophic compound for this purpose.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0273-7) contains supplementary material, which is available to authorized users.

Early neurotrophic pharmacotherapy rescues developmental delay and Alzheimer's-like memory deficits in the Ts65Dn mouse model of Down syndrome

Down syndrome (DS), caused by trisomy 21, is the most common genetic cause of intellectual disability and is associated with a greatly increased risk of early-onset Alzheimer’s disease (AD). The Ts65Dn mouse model of DS exhibits several key features of the disease including developmental delay and AD-like cognitive impairment. Accumulating evidence suggests that impairments in early brain development caused by trisomy 21 contribute significantly to memory deficits in adult life in DS. Prenatal genetic testing to diagnose DS in utero, provides the novel opportunity to initiate early pharmacological treatment to target this critical period of brain development. Here, we report that prenatal to early postnatal treatment with a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic, Peptide 021 (P021), rescued developmental delay in pups and AD-like hippocampus-dependent memory impairments in adult life in Ts65Dn mice. Furthermore, this treatment prevented pre-synaptic protein deficit, decreased glycogen synthase kinase-3beta (GSK3β) activity, and increased levels of synaptic plasticity markers including brain derived neurotrophic factor (BNDF) and phosphorylated CREB, both in young (3-week-old) and adult (~ 7-month-old) Ts65Dn mice. These findings provide novel evidence that providing neurotrophic support during early brain development can prevent developmental delay and AD-like memory impairments in a DS mouse model.

Maintenance of membrane organization in the aging mouse brain as the determining factor for preventing receptor dysfunction and for improving response to anti-Alzheimer treatments

Although a major risk factor for Alzheimer's disease (AD), the "aging" parameter is not systematically considered in preclinical validation of anti-AD drugs. To explore how aging affects neuronal reactivity to anti-AD agents, the ciliary neurotrophic factor (CNTF)-associated pathway was chosen as a model. Comparison of the neuroprotective properties of CNTF in 6- and 18-month old mice revealed that CNTF resistance in the older animals is associated with the exclusion of the CNTF-receptor subunits from rafts and their subsequent dispersion to non-raft cortical membrane domains. This age-dependent membrane remodeling prevented both the formation of active CNTF-receptor complexes and the activation of prosurvival STAT3 and ERK1/2 pathways, demonstrating that age-altered membranes impaired the reactivity of potential therapeutic targets. CNTF-receptor distribution and CNTF signaling responses were improved in older mice receiving dietary docosahexaenoic acid, with CNTF-receptor functionality being similar to those of younger mice, pointing toward dietary intervention as a promising adjuvant strategy to maintain functional neuronal membranes, thus allowing the associated receptors to respond appropriately to anti-AD agents.

Neurotrophic factor small-molecule mimetics mediated neuroregeneration and synaptic repair: emerging therapeutic modality for Alzheimer's disease

Alzheimer's disease (AD) is an incurable and debilitating chronic progressive neurodegenerative disorder which is the leading cause of dementia worldwide. AD is a heterogeneous and multifactorial disorder, histopathologically characterized by the presence of amyloid β (Aβ) plaques and neurofibrillary tangles composed of Aβ peptides and abnormally hyperphosphorylated tau protein, respectively. Independent of the various etiopathogenic mechanisms, neurodegeneration is a final common outcome of AD neuropathology. Synaptic loss is a better correlate of cognitive impairment in AD than Aβ or tau pathologies. Thus a highly promising therapeutic strategy for AD is to shift the balance from neurodegeneration to neuroregeneration and synaptic repair. Neurotrophic factors, by virtue of their neurogenic and neurotrophic activities, have potential for the treatment of AD. However, the clinical therapeutic usage of recombinant neurotrophic factors is limited because of the insurmountable hurdles of unfavorable pharmacokinetic properties, poor blood-brain barrier (BBB) permeability, and severe adverse effects. Neurotrophic factor small-molecule mimetics, in this context, represent a potential strategy to overcome these short comings, and have shown promise in preclinical studies. Neurotrophic factor small-molecule mimetics have been the focus of intense research in recent years for AD drug development. Here, we review the relevant literature regarding the therapeutic beneficial effect of neurotrophic factors in AD, and then discuss the recent status of research regarding the neurotrophic factor small-molecule mimetics as therapeutic candidates for AD. Lastly, we summarize the preclinical studies with a ciliary neurotrophic factor (CNTF) small-molecule peptide mimetic, Peptide 021 (P021). P021 is a neurogenic and neurotrophic compound which enhances dentate gyrus neurogenesis and memory processes via inhibiting leukemia inhibitory factor (LIF) signaling pathway and increasing brain-derived neurotrophic factor (BDNF) expression. It robustly inhibits tau abnormal hyperphosphorylation via increased BDNF mediated decrease in glycogen synthase kinase-3β (GSK-3β, major tau kinase) activity. P021 is a small molecular weight, BBB permeable compound with suitable pharmacokinetics for oral administration, and without adverse effects associated with native CNTF or BDNF molecule. P021 has shown beneficial therapeutic effect in several preclinical studies and has emerged as a highly promising compound for AD drug development.

Elevated Tau Level in Aged Rat Cerebrospinal Fluid Reduced by Treatment with a Neurotrophic Compound

Alzheimer's disease (AD) is the single major cause of dementia in middle- to old-age individuals, and, as of yet, no disease-modifying therapeutic drug is available for its treatment. A major obstacle in the successful development of disease-modifying therapeutic drugs has been the lack of suitable animal models of the sporadic form of AD as well as a biomarker that can be used both for therapeutic preclinical studies and for human clinical trials. Previously we showed neurogenesis and neuronal plasticity deficits and cognitive impairment and their rescue with a neurotrophic peptidergic compound, DGGLAG named P021, in aged Fisher rats. Here we show that P021 is blood-brain-barrier-permeable, and chronic oral treatment with this compound can reduce the brain level of total tau in the aged rats. Furthermore, cerebrospinal fluid (CSF) levels of both tau and Aβ/AβPP are elevated in the aged animals, and chronic treatment with P021 can reduce tau but not Aβ/AβPP to that of the levels found in young adult rats. Importantly, P021 does not induce any detectable immune reaction in rats. Collectively, these studies show the therapeutic potential of P021 as a disease-modifying compound and the suitability of the aged Fisher rats as a model of cerebral aging in which the therapeutic efficacy of a tau-reducing compound can be monitored in the CSF.

Selective Brain-Targeted Antagonism of p38 MAPKα Reduces Hippocampal IL-1β Levels and Improves Morris Water Maze Performance in Aged Rats

Background: P38 mitogen activated protein kinase (MAPK) α modulates microglia-mediated inflammatory responses and a number of neuronal physiological processes.

Objective: To evaluate pre-clinically the pharmacological effects in the brain of p38 MAPKα inhibition with a brain-penetrant specific chemical antagonist.

Methods: VX-745, a blood-brain barrier penetrant, highly selective p38 MAPKα inhibitor, and clinical stage investigational drug, was utilized. Initially, a pilot study in 26-month-old Tg2576 mice was conducted. Subsequently, a definitive dose-response study was conducted in aged (20–22 months) rats with identified cognitive deficits; n = 15 per group: vehicle, 0.5, 1.5, and 4.5 mg/kg VX-745 by oral gavage twice daily for 3 weeks. Assessments in aged rats included IL-1β, PSD-95, TNFα protein levels in hippocampus; and Morris water maze (MWM) test for cognitive performance.

Results: Drug effect could not be assessed in Tg2576 mice, as little inflammation was evident. In cognitively-impaired aged rats, VX-745 led to significantly improved performance in the MWM and significant reduction in hippocampal IL-1β protein levels, though the effects were dissociated as the MWM effect was evident at a lower dose level than that required to lower IL-1β. Drug concentration-effect relationships and predicted human doses were determined.

Conclusions: Selective inhibition of p38 MAPKα with VX-745 in aged rats reduces hippocampal IL-1β levels and improves performance in the MWM. As the two effects occur at different dose levels, the behavioral effect appears to be via a mechanism that is independent of reducing cytokine production. The predicted human doses should minimize risks of systemic toxicity.

Exercise as a pro-cognitive, pro-neurogenic and anti-inflammatory intervention in transgenic mouse models of Alzheimer's disease

It is now well established, at least in animal models, that exercise elicits potent pro-cognitive and pro-neurogenic effects. Alzheimer's disease (AD) is one of the leading causes of dementia and represents one of the greatest burdens on healthcare systems worldwide, with no effective treatment for the disease to date. Exercise presents a promising non-pharmacological option to potentially delay the onset of or slow down the progression of AD. Exercise interventions in mouse models of AD have been explored and have been found to reduce amyloid pathology and improve cognitive function. More recent studies have expanded the research question by investigating potential pro-neurogenic and anti-inflammatory effects of exercise. In this review we summarise studies that have examined exercise-mediated effects on AD pathology, cognitive function, hippocampal neurogenesis and neuroinflammation in transgenic mouse models of AD. Furthermore, we attempt to identify the optimum exercise conditions required to elicit the greatest benefits, taking into account age and pathology of the model, as well as type and duration of exercise.

Insights into the Biology and Therapeutic Applications of Neural Stem Cells

The cerebral cortex is essential for our higher cognitive functions and emotional reasoning. Arguably, this brain structure is the distinguishing feature of our species, and yet our remarkable cognitive capacity has seemingly come at a cost to the regenerative capacity of the human brain. Indeed, the capacity for regeneration and neurogenesis of the brains of vertebrates has declined over the course of evolution, from fish to rodents to primates. Nevertheless, recent evidence supporting the existence of neural stem cells (NSCs) in the adult human brain raises new questions about the biological significance of adult neurogenesis in relation to ageing and the possibility that such endogenous sources of NSCs might provide therapeutic options for the treatment of brain injury and disease. Here, we highlight recent insights and perspectives on NSCs within both the developing and adult cerebral cortex. Our review of NSCs during development focuses upon the diversity and therapeutic potential of these cells for use in cellular transplantation and in the modeling of neurodevelopmental disorders. Finally, we describe the cellular and molecular characteristics of NSCs within the adult brain and strategies to harness the therapeutic potential of these cell populations in the treatment of brain injury and disease.

Aging affects new cell production in the adult hippocampus: A quantitative anatomic review

In the last century, cognitive impairment in elderly people was considered as the consequence of neuronal death. However, later analyses indicated that age-related reduction in neuron number was limited to specific regions of the central nervous system, and was irrelevant to brain dysfunction in both humans and non-human animals. Recent studies have indicated that progressive diminution of neural plasticity across an individual's life span may underlie age-related brain dysfunction. To date, various factors have been shown to contribute to neural plasticity. In particular, substantial data supports the importance of production of new cells in the adult brain: the rate of hippocampal neurogenesis wanes radically during aging; similarly, white matter homeostasis via oligodendrogenesis is also affected by aging. This review briefly summarizes quantitative studies on adult hippocampal neurogenesis and oligodendrogenesis. Although the hippocampus is traditionally recognized as the memory center of the brain, it has started to emerge as an integrator of cognition and emotion. One of the current research highlights is that diverse functions of the hippocampus are topographically embedded along its longitudinal and transverse axes. Here we discuss alterations in adult neurogenesis and oligodendrogenesis during aging from a topographic view point. The quantitative anatomic approach to age-related alterations in production of new cells in the hippocampus may give a novel insight into how brain functions suffer from aging.

Tau and neurodegenerative disease: the story so far

In 1975, tau protein was isolated as a microtubule-associated factor from the porcine brain. In the previous year, a paired helical filament (PHF) protein had been identified in neurofibrillary tangles in the brains of individuals with Alzheimer disease (AD), but it was not until 1986 that the PHF protein and tau were discovered to be one and the same. In the AD brain, tau was found to be abnormally hyperphosphorylated, and it inhibited rather than promoted in vitro microtubule assembly. Almost 80 disease-causing exonic missense and intronic silent mutations in the tau gene have been found in familial cases of frontotemporal dementia but, to date, no such mutation has been found in AD. The first phase I clinical trial of an active tau immunization vaccine in patients with AD was recently completed. Assays for tau levels in cerebrospinal fluid and plasma are now available, and tau radiotracers for PET are under development. In this article, we provide an overview of the pivotal discoveries in the tau research field over the past 40 years. We also review the current status of the field, including disease mechanisms and therapeutic approaches.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Taurine increases hippocampal neurogenesis in aging mice

Aging is associated with increased inflammation and reduced hippocampal neurogenesis, which may in turn contribute to cognitive impairment. Taurine is a free amino acid found in numerous diets, with anti-inflammatory properties. Although abundant in the young brain, the decrease in taurine concentration with age may underlie reduced neurogenesis. Here, we assessed the effect of taurine on hippocampal neurogenesis in middle-aged mice. We found that taurine increased cell proliferation in the dentate gyrus through the activation of quiescent stem cells, resulting in increased number of stem cells and intermediate neural progenitors. Taurine had a direct effect on stem/progenitor cells proliferation, as observed in vitro, and also reduced activated microglia. Furthermore, taurine increased the survival of newborn neurons, resulting in a net increase in adult neurogenesis. Together, these results show that taurine increases several steps of adult neurogenesis and support a beneficial role of taurine on hippocampal neurogenesis in the context of brain aging.

Role of adult hippocampal neurogenesis in cognition in physiology and disease: pharmacological targets and biomarkers

Adult hippocampal neurogenesis is a remarkable form of brain structural plasticity by which new functional neurons are generated from adult neural stem cells/precursors. Although the precise role of this process remains elusive, adult hippocampal neurogenesis is important for learning and memory and it is affected in disease conditions associated with cognitive impairment, depression, and anxiety. Immature neurons in the adult brain exhibit an enhanced structural and synaptic plasticity during their maturation representing a unique population of neurons to mediate specific hippocampal function. Compelling preclinical evidence suggests that hippocampal neurogenesis is modulated by a broad range of physiological stimuli which are relevant in cognitive and emotional states. Moreover, multiple pharmacological interventions targeting cognition modulate adult hippocampal neurogenesis. In addition, recent genetic approaches have shown that promoting neurogenesis can positively modulate cognition associated with both physiology and disease. Thus the discovery of signaling pathways that enhance adult neurogenesis may lead to therapeutic strategies for improving memory loss due to aging or disease. This chapter endeavors to review the literature in the field, with particular focus on (1) the role of hippocampal neurogenesis in cognition in physiology and disease; (2) extrinsic and intrinsic signals that modulate hippocampal neurogenesis with a focus on pharmacological targets; and (3) efforts toward novel strategies pharmacologically targeting neurogenesis and identification of biomarkers of human neurogenesis.

Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease

Besides the presence of amyloid beta (Aβ) plaques and neurofibrillary tangles, neurogenesis and synaptic plasticity are markedly impaired in Alzheimer's disease (AD) possibly contributing to cognitive impairment. In this context, neurotrophic factors serve as a promising therapeutic approach via utilization of regenerative capacity of brain to shift the balance from neurodegeneration to neural regeneration. However, besides more conventional "bystander" effect, to what extent can neurotrophic compounds affect underlying AD pathology remains questionable. Here we investigated the effect of chronic oral treatment with a ciliary neurotrophic factor (CNTF) derived peptidergic compound, P021 (Ac-DGGL(A)G-NH2), on disease pathology both at moderate and severe stages in a transgenic mouse model of AD. 3xTg-AD and wild type female mice were treated for 12months with P021 or vehicle diet starting at 9-10months of age. A significant reduction in abnormal hyperphosphorylation and accumulation of tau at known major AD neurofibrillary pathology associated sites was observed. The effect of P021 on Aβ pathology was limited to a significant decrease in soluble Aβ levels and a trend towards reduction in Aβ plaque load in CA1 region of hippocampus, consistent with reduction in Aβ generation and not clearance. This disease modifying effect was probably via increased brain derived neurotrophic factor (BDNF) expression mediated decrease in glycogen synthase kinase-3-β (GSK3β) activity we found in P021 treated 3xTg-AD mice. P021 treatment also rescued deficits in cognition, neurogenesis, and synaptic plasticity in 3xTg-AD mice. These findings demonstrate the potential of the neurotrophic peptide mimetic as a disease modifying therapy for AD.