BMP9 ameliorates amyloidosis and the cholinergic defect in a mouse model of Alzheimer's disease. Proc Natl Acad Sci U S A. 2013;110:19567-19572. [PMID: 24218590 DOI: 10.1073/pnas.1319297110]

The brain-bone axis: unraveling the complex interplay between the central nervous system and skeletal metabolism

The brain-bone axis has emerged as a captivating field of research, unveiling the intricate bidirectional communication between the central nervous system (CNS) and skeletal metabolism. This comprehensive review delves into the current state of knowledge surrounding the brain-bone axis, exploring the complex mechanisms, key players, and potential clinical implications of this fascinating area of study. The review discusses the neural regulation of bone metabolism, highlighting the roles of the sympathetic nervous system, hypothalamic neuropeptides, and neurotransmitters in modulating bone remodeling. In addition, it examines the influence of bone-derived factors, such as osteocalcin and fibroblast growth factor 23, on brain function and behavior. The therapeutic potential of targeting the brain-bone axis in the context of skeletal and neurological disorders is also explored. By unraveling the complex interplay between the CNS and skeletal metabolism, this review aims to provide a comprehensive resource for researchers, clinicians, and students interested in the brain-bone axis and its implications for human health and disease.

Cholinergic Reinforcement Signaling Is Impaired by Amyloidosis Prior to Its Synaptic Loss

Alzheimer's disease (AD) is associated with amyloidosis and dysfunction of the cholinergic system, which is crucial for learning and memory. However, the nature of acetylcholine signaling within regions of cholinergic-dependent plasticity and how it changes with experience is poorly understood, much less the impact of amyloidosis on this signaling. Therefore, we optically measure the release profile of acetylcholine to unexpected, predicted, and predictive events in visual cortex (VC)-a site of known cholinergic-dependent plasticity-in a preclinical mouse model of AD that develops amyloidosis. We find that acetylcholine exhibits reinforcement signaling qualities, reporting behaviorally relevant outcomes and displaying release profiles to predictive and predicted events that change as a consequence of experience. We identify three stages of amyloidosis occurring before the degeneration of cholinergic synapses within VC and observe that cholinergic responses in amyloid-bearing mice become impaired over these stages, diverging progressively from age- and sex-matched littermate controls. In particular, amyloidosis degrades the signaling of unexpected rewards and punishments, and attenuates the experience-dependent (1) increase of cholinergic responses to outcome predictive visual cues, and (2) decrease of cholinergic responses to predicted outcomes. Hyperactive spontaneous acetylcholine release occurring transiently at the onset of impaired cholinergic signaling is also observed, further implicating disrupted cholinergic activity as an early functional biomarker in AD. Our findings suggest that acetylcholine acts as a reinforcement signal that is impaired by amyloidosis before pathologic degeneration of the cholinergic system, providing a deeper understanding of the effects of amyloidosis on acetylcholine signaling and informing future interventions for AD.SIGNIFICANCE STATEMENT The cholinergic system is especially vulnerable to the neurotoxic effects of amyloidosis, a hallmark of Alzheimer's disease (AD). Though amyloid-induced cholinergic synaptic loss is thought in part to account for learning and memory impairments in AD, little is known regarding how amyloid impacts signaling of the cholinergic system before its anatomic degeneration. Optical measurement of acetylcholine (ACh) release in a mouse model of AD that develops amyloidosis reveals that ACh signals reinforcement and outcome prediction that is disrupted by amyloidosis before cholinergic degeneration. These observations have important scientific and clinical implications: they implicate ACh signaling as an early functional biomarker, provide a deeper understanding of the action of acetylcholine, and inform on when and how intervention may best ameliorate cognitive decline in AD.

β-Amyloid targeting nanodrug for neuron-specific delivery of nucleic acids in Alzheimer's disease mouse models

Delivery of therapeutic substances into the brain poses a significant challenge in the treatment of neurological disorders. This is primarily due to the blood-brain barrier (BBB), which restricts access, alongside the limited stability and distribution of these agents within the brain tissue. Here we demonstrate an efficient delivery of microRNA (miRNA) and antisense RNA preferentially to neurons compared to astroglia in the brain of healthy and Alzheimer's disease mice, via disulfide-linked conjugation with poly(ß-L-malic acid-trileucine)-copolymer a biodegradable, amphiphilic, and multivalent platform. By conjugating a D-configured (D3)-peptide (vector) for specific targeting, highly efficient delivery across the BBB is achieved through the Low-Density Lipoprotein Receptor-Related Protein-1 (LRP-1) transcytosis pathway, amyloid beta (Aβ) peptides. Nanodrug distribution was determined by fluorescent labeling and analyzed by microscopy in neurons, astroglia, and in extracellular amyloid plaques typical for Alzheimer's disease. Whereas D-configured BBB-vectors can efficiently target neurons, L-configured (e.g., AP2-peptide) guided vector can only cross BBB but not seem to bind neurons. An analysis of post-injection fluorescence distribution, and RNA-seq followed by real-time PCR validation, confirmed a successful in vivo delivery of morpholino-miRNA-186 nanoconjugates into mouse brain. The size and fluorescence intensity of the intracellular nanodrug particulates were analyzed and verified by a competition with non-fluorescent conjugates. Differentially expressed genes (DEGs) from RNA-seq were identified in the nanodrug injected mice, and the changes of selected DEGs related to Alzheimer's disease were further validated by western blot and real-time PCR. Collectively, these results demonstrated that D3-peptide-conjugated nanopolymer drug is able to achieve neuron-selective delivery of miRNA and can serve as an efficient brain delivery vehicle in Alzheimer's disease (AD) mouse models.

American Ginseng for the Treatment of Alzheimer's Disease: A Review

Alzheimer's disease (AD) is a prevalent degenerative condition that is increasingly affecting populations globally. American ginseng (AG) has anti-AD bioactivity, and ginsenosides, as the main active components of AG, have shown strong anti-AD effects in both in vitro and in vivo studies. It has been reported that ginsenosides can inhibit amyloid β-protein (Aβ) production and deposition, tau phosphorylation, apoptosis and cytotoxicity, as well as possess anti-oxidant and anti-inflammatory properties, thus suppressing the progression of AD. In this review, we aim to provide a comprehensive overview of the pathogenesis of AD, the potential anti-AD effects of ginsenosides found in AG, and the underlying molecular mechanisms associated with these effects. Additionally, we will discuss the potential use of AG in the treatment of AD, and how ginsenosides in AG may exert more potent anti-AD effects in vivo may be a direction for further research.

Direct Enhancement Effect of Hippocampal Cholinergic Neurostimulating Peptide on Cholinergic Activity in the Hippocampus

The cholinergic efferent network from the medial septal nucleus to the hippocampus is crucial for learning and memory. This study aimed to clarify whether hippocampal cholinergic neurostimulating peptide (HCNP) has a rescue function in the cholinergic dysfunction of HCNP precursor protein (HCNP-pp) conditional knockout (cKO). Chemically synthesized HCNP or a vehicle were continuously administered into the cerebral ventricle of HCNP-pp cKO mice and littermate floxed (control) mice for two weeks via osmotic pumps. We immunohistochemically measured the cholinergic axon volume in the stratum oriens and functionally evaluated the local field potential in the CA1. Furthermore, choline acetyltransferase (ChAT) and nerve growth factor (NGF) receptor (TrkA and p75NTR) abundances were quantified in wild-type (WT) mice administered HCNP or the vehicle. As a result, HCNP administration morphologically increased the cholinergic axonal volume and electrophysiological theta power in HCNP-pp cKO and control mice. Following the administration of HCNP to WT mice, TrkA and p75NTR levels also decreased significantly. These data suggest that extrinsic HCNP may compensate for the reduced cholinergic axonal volume and theta power in HCNP-pp cKO mice. HCNP may function complementarily to NGF in the cholinergic network in vivo. HCNP may represent a therapeutic candidate for neurological diseases with cholinergic dysfunction, e.g., Alzheimer's disease and Lewy body dementia.

Insulin‐like growth factor‐2 is a promising candidate for the treatment and prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Current AD treatments slow the rate of cognitive decline, but do not restore lost function. One reason for the low efficacy of current treatments is that they fail to target neurotrophic processes, which are thought to be essential for functional recovery. Bolstering neurotrophic processes may also be a viable strategy for preventative treatment, since structural losses are thought to underlie cognitive decline in AD. The challenge of identifying presymptomatic patients who might benefit from preventative treatment means that any such treatment must meet a high standard of safety and tolerability. The neurotrophic peptide insulin-like growth factor-2 (IGF2) is a promising candidate for both treating and preventing AD-induced cognitive decline. Brain IGF2 expression declines in AD patients. In rodent models of AD, exogenous IGF2 modulates multiple aspects of AD pathology, resulting in (1) improved cognitive function; (2) stimulation of neurogenesis and synaptogenesis; and, (3) neuroprotection against cholinergic dysfunction and beta amyloid-induced neurotoxicity. Preclinical evidence suggests that IGF2 is likely to be safe and tolerable at therapeutic doses. In the preventative treatment context, the intranasal route of administration is likely to be the preferred method for achieving the therapeutic effect without risking adverse side effects. For patients already experiencing AD dementia, routes of administration that deliver IGF2 directly access the CNS may be necessary. Finally, we discuss several strategies for improving the translational validity of animal models used to study the therapeutic potential of IGF2.

Newer modalities in the management of Alzheimer's dementia along with the role of aducanumab and lecanemab in the treatment of its refractory cases

Alzheimer's disease (AD) is a common neurological condition characterized by a gradual and progressive decline in memory, language, emotion, and cognition. It mainly affects elderly people. Due to the effects of AD, pharmaceutical medications and anticholinesterases have been vigorously promoted and approved by the FDA as a form of AD therapy. However, it was progressively found that these drugs did not address the underlying causes of AD pathogenesis; rather, they focused on the symptoms in order to enhance patients' cognitive outcomes. Consequently, a hunt for superior disease-modifying options is launched. Designing new therapeutic agents requires a thorough understanding of the neuroprotective processes and varied functions carried out by certain genes, and antibodies. In this comprehensive review article, we give an overview of the history of Alzheimer's disease, the significance of the blood-brain barrier in determining the scope of treatment options, as well as the advantages and disadvantages of the current therapeutic treatment options for stem cell therapy, immunotherapy, regenerative therapy, and improved Alzheimer's disease care and diagnosis. We have also included a discussion on the potential role of aducanumab and Lecanemab as a cutting-edge therapy in refractory Alzheimer's disease patients. Lecanemab has been recently approved by the FDA for the treatment of Alzheimer's disease.

Pyruvate dehydrogenase kinase 4 promotes osteoblastic potential of BMP9 by boosting Wnt/β-catenin signaling in mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9) is an effective osteogenic factor and a promising candidate for bone tissue engineering. The osteoblastic potential of BMP9 needs to be further increased to overcome its shortcomings. However, the details of how BMP9 triggers osteogenic differentiation in mesenchymal stem cells (MSCs) are unclear. In this study, we used real-time PCR, western blot, histochemical staining, mouse ectopic bone formation model, immunofluorescence, immunoprecipitation, and chromatin immunoprecipitation to investigate the role of pyruvate dehydrogenase kinase 4 (PDK4) in BMP9-induced osteogenic differentiation of C3H10T1/2 cells, as well as the underlying mechanism. We found that PDK4 was upregulated by BMP9 in C3H10T1/2 cells. BMP9-induced osteogenic markers and bone mass were increased by PDK4 overexpression, but decreased by PDK4 silencing. β-catenin protein level was increased by BMP9, which was enhanced by PDK overexpression and decreased by PDK4 silencing. BMP9-induced osteogenic markers were reduced by PDK4 silencing, which was almost reversed by β-catenin overexpression. PDK4 increased the BMP9-induced osteogenic markers, which was almost eliminated by β-catenin silencing. Sclerostin was mildly decreased by BMP9 or PDK4, and significantly decreased by combined BMP9 and PDK4. In contrast, sclerostin increased significantly when BMP9 was combined with PDK4 silencing. BMP9-induced p-SMAD1/5/9 was increased by PDK4 overexpression, but was reduced by PDK4 silencing. PDK4 interacts with p-SMAD1/5/9 and regulates the sclerostin promoter. These findings suggest that PDK4 can increase the osteogenic potential of BMP9 by enhancing Wnt/β-catenin signaling via the downregulation of sclerostin. PDK4 may be an effective target to strengthen BMP9-induced osteogenesis.

TAZ promotes osteogenic differentiation of mesenchymal stem cells line C3H10T1/2, murine multi-lineage cells lines C2C12, and MEFs induced by BMP9

Bone morphogenetic protein 9 (BMP9), also named as growth differentiation factor 2 (GDF-2), is the strongest cytokine that promotes osteogenic differentiation in the BMP family, and has broad clinical application value. Nevertheless, the mechanism of BMP9 promotes osteogenic differentiation remain unclear. TAZ, a transcriptional co-activator, has great effects on cell proliferation, differentiation, and stem cell self-renewal. In this research, we investigated the effects of TAZ in BMP9-induced osteogenic differentiation of mesenchymal stem cell line C3H10T1/2 (MSCs) and murine multi-lineage cell lines C2C12 and MEFs (MMCs) and explored its possible mechanisms. This study has found that BMP9 induces the expression of TAZ and promotes its nuclear translocation. Meanwhile, our study found that Ad-TAZ and TM-25659, a TAZ agonist, can enhance the osteogenic differentiation of MSCs and MMCs induced by BMP9. Conversely, Ad-si-TAZ and verteporfin, an inhibitor of TAZ, have the contradictory effect. Likewise, the promotion of TAZ to the BMP9-induced ectopic bone formation in vivo was confirmed by the subcutaneous transplantation of MSCs in nude mice. Furthermore, we have detected that TAZ might increase the levels of the phosphorylation of Smad1/5/8, p38, ERK1/2, and JNK induced by BMP9. Additionally, we also found that TAZ increased the total protein level of β-catenin induced by BMP9. In summary, our results strongly indicated that TAZ will promote the osteogenic differentiation in MSCs and MMCs induced by BMP9 through multiple signal pathways.

The potential regulatory role of BMP9 in inflammatory responses

Inflammation is a protective response of the body to pathogens and injury. Hence, it is particularly important to explore the pathogenesis and key regulatory factors of inflammation. BMP9 is a unique member of the BMP family, which is widely known for its strong osteogenic potential and insensitivity to the inhibition of BMP3. Recently, several studies have reported an underlying pivotal link between BMP9 and inflammation. What is clear, though not well understood, is that BMP9 plays a role in inflammation in a carefully choreographed manner in different contexts. In this review, we have summarized current studies focusing on BMP9 and inflammation in various tissues and the latest advances in BMP9 expression, signal transduction, and crystal structure to better understand the relationship between BMP9 and inflammation. In addition, we also briefly summarized the inflammatory characteristics of some TGF-β superfamily members to provide better insights and ideas for the study of BMP9 and inflammation.

The unsolved mystery of hippocampal cholinergic neurostimulating peptide: A potent cholinergic regulator

Cholinergic efferent networks located from the medial septal nucleus to the hippocampus play a pivotal role in learning and memory outcomes by generating regular theta rhythms that enhance information retention. Hippocampal cholinergic neurostimulating peptide (HCNP), derived from the N-terminus of HCNP precursor protein (HCNP-pp), promotes the synthesis of acetylcholine in the medial septal nuclei. HCNP-pp deletion significantly reduced theta power in CA1 possibly due to lower levels of choline acetyltransferase-positive axons in CA1 stratum oriens, suggesting cholinergic disruptions in the septo-hippocampal system. This review also explores HCNP as a potent cholinergic regulator in the septo-hippocampal network while also examining the limitations of our understanding of the neurostimulating peptide.

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.

Transcriptional signature in microglia associated with Aβ plaque phagocytosis

The role of microglia cells in Alzheimer’s disease (AD) is well recognized, however their molecular and functional diversity remain unclear. Here, we isolated amyloid plaque-containing (using labelling with methoxy-XO4, XO4⁺) and non-containing (XO4⁻) microglia from an AD mouse model. Transcriptomics analysis identified different transcriptional trajectories in ageing and AD mice. XO4⁺ microglial transcriptomes demonstrated dysregulated expression of genes associated with late onset AD. We further showed that the transcriptional program associated with XO4⁺ microglia from mice is present in a subset of human microglia isolated from brains of individuals with AD. XO4⁻ microglia displayed transcriptional signatures associated with accelerated ageing and contained more intracellular post-synaptic material than XO4⁺ microglia, despite reduced active synaptosome phagocytosis. We identified HIF1α as potentially regulating synaptosome phagocytosis in vitro using primary human microglia, and BV2 mouse microglial cells. Together, these findings provide insight into molecular mechanisms underpinning the functional diversity of microglia in AD.

Microglia associated with Aβ plaques may have a distinct transcriptional signature compared to those in plaque-free areas of the brain in Alzheimer’s disease (AD) models. Here the authors show that amyloid plaque phagocytosis is associated with a specific microglia transcriptional signature in a mouse model of AD.

The Expression of Activin Receptor-Like Kinase 1 (ACVRL1/ALK1) in Hippocampal Arterioles Declines During Progression of Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) in Alzheimer’s disease (AD)—deposition of beta amyloid (Aβ) within the walls of cerebral blood vessels—typically accompanies Aβ buildup in brain parenchyma and causes abnormalities in vessel structure and function. We recently demonstrated that the immunoreactivity of activin receptor-like kinase 1 (ALK1), the type I receptor for circulating BMP9/BMP10 (bone morphogenetic protein) signaling proteins, is reduced in advanced, but not early stages of AD in CA3 pyramidal neurons. Here we characterize vascular expression of ALK1 in the context of progressive AD pathology accompanied by amyloid angiopathy in postmortem hippocampi using immunohistochemical methods. Hippocampal arteriolar wall ALK1 signal intensity was 35% lower in AD patients (Braak and Braak Stages IV and V [BBIV-V]; clinical dementia rating [CDR1-2]) as compared with subjects with early AD pathologic changes but either cognitively intact or with minimal cognitive impairment (BBIII; CDR0-0.5). The intensity of Aβ signal in arteriolar walls was similar in all analyzed cases. These data suggest that, as demonstrated previously for specific neuronal populations, ALK1 expression in blood vessels is also vulnerable to the AD pathophysiologic process, perhaps related to CAA. However, cortical arterioles may remain responsive to the ALK1 ligands, such as BMP9 and BMP10 in early and moderate AD.

GABAergic Inhibitory Interneuron Deficits in Alzheimer's Disease: Implications for Treatment

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized clinically by severe cognitive deficits and pathologically by amyloid plaques, neuronal loss, and neurofibrillary tangles. Abnormal amyloid β-protein (Aβ) deposition in the brain is often thought of as a major initiating factor in AD neuropathology. However, gamma-aminobutyric acid (GABA) inhibitory interneurons are resistant to Aβ deposition, and Aβ decreases synaptic glutamatergic transmission to decrease neural network activity. Furthermore, there is now evidence suggesting that neural network activity is aberrantly increased in AD patients and animal models due to functional deficits in and decreased activity of GABA inhibitory interneurons, contributing to cognitive deficits. Here we describe the roles played by excitatory neurons and GABA inhibitory interneurons in Aβ-induced cognitive deficits and how altered GABA interneurons regulate AD neuropathology. We also comprehensively review recent studies on how GABA interneurons and GABA receptors can be exploited for therapeutic benefit. GABA interneurons are an emerging therapeutic target in AD, with further clinical trials urgently warranted.

Neurotherapeutic applications of nanomedicine for treating Alzheimer's disease

Alzheimer's disease (AD) is a progressive, irreversible, fatal brain disease which disturbs cognitive functions. It affects 35 million people worldwide and the number of people suffering may increase to 100 million by 2050 if no effective treatments are available. The present treatment improves cognitive functions and provide temporary symptomatic relief, but do not stop or delay the disease progression. Moreover, they are mainly available as conventional oral dosage forms and these conventional oral medications lack brain specificity and also produce side effects which leads to poor patient compliance. Brain drug targeting by nanomedicines is a promising approach to improve brain targeting specificity, brain bioavailability and patient compliance. The present review discuses about the currently available pharmacotherapy for AD and the neurotherapeutic applications as well as the advancements of nanomedicine for treating AD. It also highlights the recent advancements of various nanomedicines containing phytopharmaceuticals for treating AD. It is believed that nanomedicines containing approved drugs can be transformed into the clinics hence improve the life style of AD patients.

A systems biology approach for studying neurodegenerative diseases

Neurodegenerative diseases (NDDs), such as Alzheimer's (AD) and Parkinson's (PD), are among the leading causes of lost years of healthy life and exert a great strain on public healthcare systems. Despite being first described more than a century ago, no effective cure exists for AD or PD. Although extensively characterised at the molecular level, traditional neurodegeneration research remains marred by narrow-sense approaches surrounding amyloid β (Aβ), tau, and α-synuclein (α-syn). A systems biology approach enables the integration of multi-omics data and informs discovery of biomarkers, drug targets, and treatment strategies. Here, we present a comprehensive timeline of high-throughput data collection, and associated biotechnological advancements and computational analysis related to AD and PD. We hereby propose that a philosophical change in the definitions of AD and PD is now needed.

Reduced Cholinergic Activity in the Hippocampus of Hippocampal Cholinergic Neurostimulating Peptide Precursor Protein Knockout Mice

The cholinergic efferent network from the medial septal nucleus to the hippocampus has an important role in learning and memory processes. This cholinergic projection can generate theta oscillations in the hippocampus to efficiently encode novel information. Hippocampal cholinergic neurostimulating peptide (HCNP) induces acetylcholine synthesis in medial septal nuclei. HCNP is processed from the N-terminal region of a 186 amino acid, 21 kD HCNP precursor protein called HCNP-pp (also known as Raf kinase inhibitory protein (RKIP) and phosphatidylethanolamine-binding protein 1 (PEBP1)). In this study, we generated HCNP-pp knockout (KO) mice and assessed their cholinergic septo-hippocampal projection, local field potentials in CA1, and behavioral phenotypes. No significant behavioral phenotype was observed in HCNP-pp KO mice. However, theta power in the CA1 of HCNP-pp KO mice was significantly reduced because of fewer cholineacetyltransferase-positive axons in the CA1 stratum oriens. These observations indicated disruption of cholinergic activity in the septo-hippocampal network. Our study demonstrates that HCNP may be a cholinergic regulator in the septo-hippocampal network.

Comparative Effectiveness of Agmatine and Choline Treatment in Rats with Cognitive Impairment Induced by AlCl3 and Forced Swim Stress

AIM

Endogenous agmatine has a significant role in learning and memory processes as a neurotransmitter. Various studies described the physiological role of endogenous agmatine in learning and memory of multiple cognitive tasks suggesting elevated levels of agmatine during the learning process in the rat brain. Dietary intake of choline showed correlation with cognitive functions in human subjects and treatment with choline supplements validated the ability to diminish learning and cognitive impairment dementias.

METHODS

36 Albino rats were equally divided into three groups previously: a) control-water, b) Test I - AlCl3 (100 mg/Kg body weight), and c) Test II - Forced swim stress (FSS) for 14 days. On the next day of AlCl3 and FSS last administration, animals were allocated into further three groups and received the following treatments: a. water was given orally to the control group, b. Agmatine (100 mg/Kg Body Weight) group, and c. Choline (100 mg/Kg Body Weight) group for the next 14 days. Behaviors were assessed in Light/Dark Box, Open Field, Novel Object Recognition Test (NOR), T Maze Test, and Morris Water Maze Test.

RESULTS

Animals administered with agmatine demonstrated increased time spent in bright areas of light/dark box and square crossed while improved spatial memory in Morris water maze and T maze test and enhanced discrimination of novel object in NOR were observed in learning and memory paradigms along with choline.

CONCLUSION

The present study determines that agmatine at the dose of (100 mg/kg body weight) attenuates memory and cognitive impairment in comparison with choline supplements.

Dual dose-dependent effects of fingolimod in a mouse model of Alzheimer's disease

Lipid metabolism is abnormal in Alzheimer’s disease (AD) brain leading to ceramide and sphingosine accumulation and reduced levels of brain sphingosine-1-phosphate (S1P). We hypothesize that changes in S1P signaling are central to the inflammatory and immune-pathogenesis of AD and the therapeutic benefits of fingolimod, a structural analog of sphingosine that is FDA approved for the treatment of multiple sclerosis. We recently reported that the neuroprotective effects of fingolimod in 5xFAD transgenic AD mice treated from 1–3 months of age were greater at 1 mg/kg/day than at 5 mg/kg/day. Here we performed a dose-response study using fingolimod from 0.03 to 1 mg/kg/day in 5xFAD mice treated from 1–8 months of age. At 1 mg/kg/day, fingolimod decreased both peripheral blood lymphocyte counts and brain Aβ levels, but at the lowest dose tested (0.03 mg/kg/day), we detected improved memory, decreased activation of brain microglia and astrocytes, and restored hippocampal levels of GABA and glycerophosphocholine with no effect on circulating lymphocyte counts. These findings suggests that, unlike the case in multiple sclerosis, fingolimod may potentially have therapeutic benefits in AD at low doses that do not affect peripheral lymphocyte function.

New treatment modalities in Alzheimer's disease

Alzheimer’s disease (AD) is still a major public health challenge without an effective treatment to prevent or stop it. Routinely used acetylcholinesterase inhibitors and memantine seem to slow disease progression only to a limited extend. Therefore, many investigations on new drugs and other treatment modalities are ongoing in close association with increasing knowledge of the pathophysiology of the disease. Here, we review the studies about the new treatment modalities in AD with a classification based on their main targets, specifically pathologic structures of the disease, amyloid and tau, neural network dysfunction with special interest to the regulation of gamma oscillations, and attempts for the restoration of neural tissue via regenerative medicine. Additionally, we describe the evolving modalities related to gut microbiota, modulation, microglial function, and glucose metabolism.

Whole-Brain Mapping of Monosynaptic Afferent Inputs to Cortical CRH Neurons

Corticotropin-releasing hormone (CRH) is a critical neuropeptide modulating the mammalian stress response. It is involved in many functional activities within various brain regions, among which there is a subset of CRH neurons occupying a considerable proportion of the cortical GABAergic interneurons. Here, we utilized rabies virus-based monosynaptic retrograde tracing system to map the whole-brain afferent presynaptic partners of the CRH neurons in the anterior cingulate cortex (ACC). We find that the ACC CRH neurons integrate information from the cortex, thalamus, hippocampal formation, amygdala, and also several other midbrain and hindbrain nuclei. Furthermore, our results reveal that ACC CRH neurons receive direct inputs from two neuromodulatory systems, the basal forebrain cholinergic neurons and raphe serotoninergic neurons. These findings together expand our knowledge about the connectivity of the cortical GABAergic neurons and also provide a basis for further investigation of the circuit function of cortical CRH neurons.

Stem cell therapy in Alzheimer's disease: possible benefits and limiting drawbacks

Alzheimer's disease (AD) is the sixth leading cause of death globally and the main reason for dementia in elderly people. AD is a long-term and progressive neurodegenerative disorder that steadily worsens memory and communicating skills eventually leads to a disabled person of performing simple daily tasks. Unfortunately, numerous clinical trials exploring new therapeutic drugs have encountered disappointing outcomes in terms of improved cognitive performance since they are not capable of halting or stimulating the regeneration of already-damaged neural cells, and merely provide symptomatic relief. Therefore, a deeper understanding of the mechanism of action of stem cell may contribute to the development of novel and effective therapies. The revolutionary discovery of stem cells has cast a new hope for the development of disease-modifying treatments for AD, in terms of their potency in the replenishment of lost cells via differentiating towards specific lineages, stimulating in situ neurogenesis, and delivering the therapeutic agents to the brain. Herein, firstly, we explore the pathophysiology of AD. Next, we summarize the most recent preclinical stem cell reports designed for AD treatment, their benefits and outcomes according to cell type. We briefly review relevant clinical trials and their potential clinical applications in order to find a unique solution to effectively relieve the patients' pain.

Therapy of Dredging the Bowels Enhanced the Neuroprotective Effect of Nourishing Kidney Herbs on Hippocampal Cholinergic System in Alzheimer's Disease Model Rat Induced by Aβ 1-42

BACKGROUND

Therapy of nourishing kidney has been used for treating memory deficits of Alzheimer's disease (AD) for thousands of years based on traditional Chinese medicine. However, we found the therapy of dredging the bowels could alleviate both memory deficits and mental symptoms of AD in clinic.

OBJECTIVE

To determine whether the therapy of dredging the bowels could enhance the neuroprotective effect of nourishing kidney herbs for treating AD rats, and to explore the underlying mechanism of the combination of nourishing kidney and dredging the bowels (NKDB) herbs.

METHODS

60 rats were randomly divided into sham-operated group (SOG), model group (MG), nourishing kidney group (NKG), dredging the bowels group (DBG), nourishing kidney and dredging the bowels group (NKDBG), and donepezil hydrochloride group (DHG). The model establishment was performed by injecting Aβ 1-42 into the hippocampal CA1 region. Animals received aqueous solution of Chinese herbal medicine or western medicine while SOG received only distilled water. Ability of learning and memory were assessed by Morris water maze. Acetylcholinesterase(AChE) and choline acetyltransferase (ChAT) activity and positive cells in the hippocampus were detected by the biochemical and immunofluorescent assay.

RESULTS

All rats were in the same baseline. While after model establishment, ability of learning and memory of MG, NKG, DBG, NKDBG, and DHG were significantly impaired compared with SOG. Whereas after treatment, ability of learning and memory of NKG, DBG, NKDBG, and DHG were significantly improved compared with MG. Additionally, AChE activity of NKG, DBG, and NKDBG was significantly decreased, meanwhile ChAT activity showed an increased tendency. The number of AChE-positive cells and ChAT-positive cells of both NKDBG and DHG were significantly decreased and increased respectively, superior to those when compared with NKG and DBG. What's more, there was no significant difference between NKDBG and DHG.

CONCLUSION

Therapy of dredging the bowels could enhance the neuroprotective effect of nourishing kidney herbs by reversing morphological damage of hippocampal cholinergic system. Furthermore, treatment with NKDB herbs could be effectively against AD, providing a practical therapeutic strategy in clinic.

Genetically-Predicted Adult Height and Alzheimer's Disease

BACKGROUND

Observational studies have linked increased adult height with better cognitive performance and reduced risk of Alzheimer's disease (AD). It is unclear whether the associations are due to shared biological processes that influence height and AD or due to confounding by early life exposures or environmental factors.

OBJECTIVE

To use a genetic approach to investigate the association between adult height and AD.

METHODS

We selected 682 single nucleotide polymorphisms (SNPs) associated with height at genome-wide significance (p < 5×10-8) in the Genetic Investigation of ANthropometric Traits (GIANT) consortium. Summary statistics for each of these SNPs on AD were obtained from the International Genomics of Alzheimer's Project (IGAP) of 17,008 individuals with AD and 37,154 controls. The estimate of the association between genetically predicted height and AD was calculated using the inverse-variance weighted method.

RESULTS

The odds ratio of AD was 0.91 (95% confidence interval, 0.86-0.95; p = 9.8×10-5) per one standard deviation increase (about 6.5 cm) in genetically predicted height based on 682 SNPs, which were clustered in 419 loci. In an analysis restricted to one SNP from each height-associated locus (n = 419 SNPs), the corresponding OR was 0.92 (95% confidence interval, 0.86-0.97; p = 4.8×10-3).

CONCLUSIONS

This finding suggests that biological processes that influence adult height may have a role in the etiology of AD.

A small peptide derived from BMP-9 can increase the effect of bFGF and NGF on SH-SY5Y cells differentiation

The current aging of the world population will increase the number of people suffering from brain degenerative diseases such as Alzheimer's disease (AD). There are evidence showing that the use of growth factors such as BMP-9 could restored cognitive function as it acts on many AD hallmarks at the same time. However, BMP-9 is a big protein expensive to produce that can hardly access the central nervous system. We have therefore developed a small peptide, SpBMP-9, derived from the knuckle epitope of BMP-9 and showed its therapeutic potential in a previous study. Since it is known that the native protein, BMP-9, can act in synergy with other growth factors in the context of AD, here we study the potential synergistic effect of various combinations of SpBMP-9 with bFGF, EGF, IGF-2 or NGF on the cholinergic differentiation of human neuroblastoma cells SH-SY5Y. We found that, in opposition to IGF-2 or EGF, the combination of SpBMP-9 with bFGF or NGF can stimulate to a greater extent the neurite outgrowth and neuronal differentiation toward the cholinergic phenotype as shown by expression and localization of the neuronal markers NSE and VAchT and the staining of intracellular calcium. Those results strongly suggest that SpBMP-9 plus NGF or bFGF are promising therapeutic combinations against AD that required further attention.

Immunohistochemical Analysis of Activin Receptor-Like Kinase 1 (ACVRL1/ALK1) Expression in the Rat and Human Hippocampus: Decline in CA3 During Progression of Alzheimer's Disease

The pathophysiology of Alzheimer's disease (AD) includes signaling defects mediated by the transforming growth factor β-bone morphogenetic protein-growth and differentiation factor (TGFβ-BMP-GDF) family of proteins. In animal models of AD, administration of BMP9/GDF2 improves memory and reduces amyloidosis. The best characterized type I receptor of BMP9 is ALK1. We characterized ALK1 expression in the hippocampus using immunohistochemistry. In the rat, ALK1 immunoreactivity was found in CA pyramidal neurons, most frequently and robustly in the CA2 and CA3 fields. In addition, there were sporadic ALK1-immunoreactive cells in the stratum oriens, mainly in CA1. The ALK1 expression pattern in human hippocampus was similar to that of rat. Pyramidal neurons within the CA2, CA3, and CA4 were strongly ALK1-immunoreactive in hippocampi of cognitively intact subjects with no neurofibrillary tangles. ALK1 signal was found in the axons of alveus and fimbria, and in the neuropil across CA fields. Relatively strongest ALK1 neuropil signal was observed in CA1 where pyramidal neurons were occasionally ALK1-immunoractive. As in the rat, horizontally oriented neurons in the stratum oriens of CA1 were both ALK1- and GAD67-immunoreactive. Analysis of ALK1 immunoreactivity across stages of AD pathology revealed that disease progression was characterized by overall reduction of the ALK1 signal in CA3 in advanced, but not early, stages of AD. These data suggest that the CA3 pyramidal neurons may remain responsive to the ALK1 ligands, e.g., BMP9, during initial stages of AD and that ALK1 may constitute a therapeutic target in early and moderate AD.

Anxiety, neuroinflammation, cholinergic and GABAergic abnormalities are early markers of Gulf War illness in a mouse model of the disease

Gulf War Illness (GWI) is a chronic disease that affects the 1991 Gulf War (GW) veterans for which treatment is lacking. It has been hypothesized that drugs used to protect military personnel from chemical attacks and insects during the war: pyridostigmine bromide (PB),N, N-diethyl-m-toluamide (DEET), and permethrin (PER) together with stress may have contributed collectively and synergistically to generate GWI. There is a need to find markers of pathology to be used in pre-clinical trials. For this purpose we employed a previously validated mouse model of GWI evoked by daily exposure to PB (1.3 mg/kg), DEET (40 mg/kg), PER (0.13 mg/kg), and 5 min of restraint stress for 28 days to analyze behavior, brain pathology and neurochemical outcomes three months later. GWI-model mice were characterized by increased anxiety, decreased hippocampal levels of N-acetyl aspartate, GABA, the GABA-producing enzyme GAD-67 and microglial activation. We also observed that GWI model was sexually dimorphic on some measures: males had increased while females had decreased protein levels of the acetylcholine-synthesizing enzyme, choline acetyltransferase, in the septum and hippocampus and decreased levels of the receptor for brain-derived neurotrophic factor, TrkB140, in the hippocampus. Increased hippocampal levels of nerve growth factor were detected in males only. Together the data show behavioral and neuropathological abnormalities detected at 3 months post-exposure and that some of them are sexually dimorphic. Future preclinical studies for GWI may take advantage of this short latency model and should include both males and females as their response to treatment may differ.

Neuroprotective Actions of Dietary Choline

Choline is an essential nutrient for humans. It is a precursor of membrane phospholipids (e.g., phosphatidylcholine (PC)), the neurotransmitter acetylcholine, and via betaine, the methyl group donor S-adenosylmethionine. High choline intake during gestation and early postnatal development in rat and mouse models improves cognitive function in adulthood, prevents age-related memory decline, and protects the brain from the neuropathological changes associated with Alzheimer’s disease (AD), and neurological damage associated with epilepsy, fetal alcohol syndrome, and inherited conditions such as Down and Rett syndromes. These effects of choline are correlated with modifications in histone and DNA methylation in brain, and with alterations in the expression of genes that encode proteins important for learning and memory processing, suggesting a possible epigenomic mechanism of action. Dietary choline intake in the adult may also influence cognitive function via an effect on PC containing eicosapentaenoic and docosahexaenoic acids; polyunsaturated species of PC whose levels are reduced in brains from AD patients, and is associated with higher memory performance, and resistance to cognitive decline.

Peptides derived from the knuckle epitope of BMP-9 induce the cholinergic differentiation and inactivate GSk3beta in human SH-SY5Y neuroblastoma cells

The incidence of brain degenerative disorders like Alzheimer's disease (AD) will increase as the world population ages. While there is presently no known cure for AD and current treatments having only a transient effect, an increasing number of publications indicate that growth factors (GF) may be used to treat AD. GFs like the bone morphogenetic proteins (BMPs), especially BMP-9, affect many aspects of AD. However, BMP-9 is a big protein that cannot readily cross the blood-brain barrier. We have therefore studied the effects of two small peptides derived from BMP-9 (pBMP-9 and SpBMP-9). We investigated their capacity to differentiate SH-SY5Y human neuroblastoma cells into neurons with or without retinoic acid (RA). Both peptides induced Smad 1/5 phosphorylation and their nuclear translocation. They increased the number and length of neurites and the expression of neuronal markers MAP-2, NeuN and NSE better than did BMP-9. They also promoted differentiation to the cholinergic phenotype more actively than BMP-9, SpBMP-9 being the most effective as shown by increases in intracellular acetylcholine, ChAT and VAchT. Finally, both peptides activated the PI3K/Akt pathway and inhibited GSK3beta, a current AD therapeutic target. BMP-9-derived peptides, especially SpBMP-9, with or without RA, are promising molecules that warrant further investigation.

The behavioral deficits and cognitive impairment are correlated with decreased IGF-II and ERK in depressed mice induced by chronic unpredictable stress

AIM

To investigate the behavioral deficits, cognitive impairment and possible mechanisms induced by chronic unpredictable stress (CUS) in mice of different ages.

METHODS

The behaviors and cognition were tested using the open field test, tail suspension test and the Morris water maze. The changes in the insulin-like growth factor II (IGF-II) and the extracellular signal-regulated kinase (ERK) and phosphorylation (p-ERK) in the hippocampus (HP) and prefrontal cortex (PFC) were evaluated by immunohistochemistry.

RESULTS

The 15-month-old mice revealed a significant decline in spontaneous behavior and the learning-memory function and showed a decrease in IGF-II and p-ERK expression levels in HP and PFC. Four weeks of CUS exposure induced significant anxiety- and depression-like behavior and learning-memory function impairment in 3- to 15-month-old mice, and reduced IGF-II and p-ERK expression levels in HP and PFC, compared with control group mice, respectively.

CONCLUSIONS

The behavioral deficits and cognitive impairment induced by CUS and aging in mice could be associated with the down-regulated expression of IGF-II and p-ERK in HP and PFC. This role seems to be dependent on the intracellular ERK pathway.

Intranasal BMP9 Ameliorates Alzheimer Disease-Like Pathology and Cognitive Deficits in APP/PS1 Transgenic Mice

Alzheimer’s disease (AD) is the most common type of dementia and has no effective therapies. Previous studies showed that bone morphogenetic protein 9 (BMP9), an important factor in the differentiation and phenotype maintenance of cholinergic neurons, ameliorated the cholinergic defects resulting from amyloid deposition. These findings suggest that BMP9 has potential as a therapeutic agent for AD. However, the effects of BMP9 on cognitive function in AD and its underlying mechanisms remain elusive. In the present study, BMP9 was delivered intranasally to 7-month-old APP/PS1 mice for 4 weeks. Our data showed that intranasal BMP9 administration significantly improved the spatial and associative learning and memory of APP/PS1 mice. We also found that intranasal BMP9 administration significantly reduced the amyloid β (Aβ) plaques overall, inhibited tau hyperphosphorylation, and suppressed neuroinflammation in the transgenic mouse brain. Furthermore, intranasal BMP9 administration significantly promoted the expression of low-density lipoprotein receptor-related protein 1 (LRP1), an important membrane receptor involved in the clearance of amyloid β via the blood-brain barrier (BBB), and elevated the phosphorylation levels of glycogen synthase kinase-3β (Ser9), which is considered the main kinase involved in tau hyperphosphorylation. Our results suggest that BMP9 may be a promising candidate for treating AD by targeting multiple key pathways in the disease pathogenesis.

Perinatal Choline Supplementation Reduces Amyloidosis and Increases Choline Acetyltransferase Expression in the Hippocampus of the APPswePS1dE9 Alzheimer's Disease Model Mice

Prevention of Alzheimer's disease (AD) is a major goal of biomedical sciences. In previous studies we showed that high intake of the essential nutrient, choline, during gestation prevented age-related memory decline in a rat model. In this study we investigated the effects of a similar treatment on AD-related phenotypes in a mouse model of AD. We crossed wild type (WT) female mice with hemizygous APPswe/PS1dE9 (APP.PS1) AD model male mice and maintained the pregnant and lactating dams on a control AIN76A diet containing 1.1 g/kg of choline or a choline-supplemented (5 g/kg) diet. After weaning all offspring consumed the control diet. As compared to APP.PS1 mice reared on the control diet, the hippocampus of the perinatally choline-supplemented APP.PS1 mice exhibited: 1) altered levels of amyloid precursor protein (APP) metabolites-specifically elevated amounts of β-C-terminal fragment (β-CTF) and reduced levels of solubilized amyloid Aβ40 and Aβ42 peptides; 2) reduced number and total area of amyloid plaques; 3) preserved levels of choline acetyltransferase protein (CHAT) and insulin-like growth factor II (IGF2) and 4) absence of astrogliosis. The data suggest that dietary supplementation of choline during fetal development and early postnatal life may constitute a preventive strategy for AD.

Geniposide ameliorates cognitive deficits by attenuating the cholinergic defect and amyloidosis in middle-aged Alzheimer model mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory deficits and cognitive decline. Amyloid-β (Aβ) deposition and cholinergic defect are widely thought to be the underlying mechanism of learning and memory impairment. Geniposide, which is the main active component of the traditional Chinese herbal Gardenia jasminoides Ellis, elicits neuroprotective effects by alleviating inflammation responses and oxidative damages. In this study, we investigated the protective effect of geniposide on levels of cholinergic markers, RAGE, RAGE-dependent signalling pathways and amyloid accumulation in the APPswe/PS1dE9 AD model mouse. Geniposide suppressed MAPK signaling over-activation mediated by Aβ-RAGE interaction, resulting in reduced Aβ accumulation and amelioration of cholinergic deficits in the cerebral hippocampus. Furthermore, geniposide inhibited the toxic effect of oligomeric Aβ_1-42 induced cholinergic deficit by increasing ChAT levels and activity but decreasing AChE activity in cultured primary hippocampal neurons. These results indicated that geniposide enhanced cholinergic neurotransmission, which likely contributes to its memory enhancing effect.

Developmental specification of forebrain cholinergic neurons

Striatal cholinergic interneurons and basal forebrain cholinergic projection neurons, which together comprise the forebrain cholinergic system, regulate attention, memory, reward pathways, and motor activity through the neuromodulation of multiple brain circuits. The importance of these neurons in the etiology of neurocognitive disorders has been well documented, but our understanding of their specification during embryogenesis is still incomplete. All forebrain cholinergic projection neurons and interneurons appear to share a common developmental origin in the embryonic ventral telencephalon, a region that also gives rise to GABAergic projection neurons and interneurons. Significant progress has been made in identifying the key intrinsic and extrinsic factors that promote a cholinergic fate in this precursor population. However, how cholinergic interneurons and projection neurons differentiate from one another during development, as well as how distinct developmental programs contribute to heterogeneity within those two classes, is not yet well understood. In this review we summarize the transcription factors and signaling molecules known to play a role in the specification and early development of striatal and basal forebrain cholinergic neurons. We also discuss the heterogeneity of these populations and its possible developmental origins.

Whole-Brain Monosynaptic Afferent Inputs to Basal Forebrain Cholinergic System

The basal forebrain cholinergic system (BFCS) robustly modulates many important behaviors, such as arousal, attention, learning and memory, through heavy projections to cortex and hippocampus. However, the presynaptic partners governing BFCS activity still remain poorly understood. Here, we utilized a recently developed rabies virus-based cell-type-specific retrograde tracing system to map the whole-brain afferent inputs of the BFCS. We found that the BFCS receives inputs from multiple cortical areas, such as orbital frontal cortex, motor cortex, and insular cortex, and that the BFCS also receives dense inputs from several subcortical nuclei related to motivation and stress, including lateral septum, central amygdala, paraventricular nucleus of hypothalamus, dorsal raphe, and parabrachial nucleus. Interestingly, we found that the BFCS receives inputs from the olfactory areas and the entorhinal–hippocampal system. These results greatly expand our knowledge about the connectivity of the mouse BFCS and provided important preliminary indications for future exploration of circuit function.

Erinacine A-enriched Hericium erinaceus mycelium ameliorates Alzheimer's disease-related pathologies in APPswe/PS1dE9 transgenic mice

Background

The fruiting body of Hericium erinaceus has been demonstrated to possess anti-dementia activity in mouse model of Alzheimer’s disease and people with mild cognitive impairment. However, the therapeutic potential of Hericium erinaceus mycelia on Alzheimer’s disease remains unclear. In this study, the effects of erinacine A-enriched Hericium erinaceus mycelia (HE-My) on the pathological changes in APPswe/PS1dE9 transgenic mouse model of Alzheimer’s disease are studied.

Results

After a 30 day oral administration to 5 month-old female APPswe/PS1dE9 transgenic mice, we found that HE-My and its ethanol extracts (HE-Et) attenuated cerebral Aβ plaque burden. It’s worth noting that the attenuated portion of a plaque is the non-compact structure. The level of insulin-degrading enzyme was elevated by both HE-My and HE-Et in cerebral cortex. On the other hand, the number of plaque-activated microglia and astrocytes in cerebral cortex and hippocampus were diminished, the ratio of nerve growth factor (NGF) to NGF precursor (proNGF) was increased and hippocampal neurogenesis was promoted after these administrations. All the mentioned benefits of these administrations may therefore improve the declined activity of daily living skill in APPswe/PS1dE9 transgenic mice.

Conclusions

These results highlight the therapeutic potential of HE-My and HE-Et on Alzheimer’s disease. Therefore, the effective components of HE-My and HE-Et are worth to be developed to become a therapeutic drug for Alzheimer’s disease.

Network-driven plasma proteomics expose molecular changes in the Alzheimer's brain

Background

Biological pathways that significantly contribute to sporadic Alzheimer’s disease are largely unknown and cannot be observed directly. Cognitive symptoms appear only decades after the molecular disease onset, further complicating analyses. As a consequence, molecular research is often restricted to late-stage post-mortem studies of brain tissue. However, the disease process is expected to trigger numerous cellular signaling pathways and modulate the local and systemic environment, and resulting changes in secreted signaling molecules carry information about otherwise inaccessible pathological processes.

Results

To access this information we probed relative levels of close to 600 secreted signaling proteins from patients’ blood samples using antibody microarrays and mapped disease-specific molecular networks. Using these networks as seeds we then employed independent genome and transcriptome data sets to corroborate potential pathogenic pathways.

Conclusions

We identified Growth-Differentiation Factor (GDF) signaling as a novel Alzheimer’s disease-relevant pathway supported by in vivo and in vitro follow-up experiments, demonstrating the existence of a highly informative link between cellular pathology and changes in circulatory signaling proteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0095-2) contains supplementary material, which is available to authorized users.

Neural stem/progenitor cells in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and a worldwide health challenge. Different therapeutic approaches are being developed to reverse or slow the loss of affected neurons. Another plausible therapeutic way that may complement the studies is to increase the survival of existing neurons by mobilizing the existing neural stem/progenitor cells (NSPCs) - i.e. "induce their plasticity" - to regenerate lost neurons despite the existing pathology and unfavorable environment. However, there is controversy about how NSPCs are affected by the unfavorable toxic environment during AD. In this review, we will discuss the use of stem cells in neurodegenerative diseases and in particular how NSPCs affect the AD pathology and how neurodegeneration affects NSPCs. In the end of this review, we will discuss how zebrafish as a useful model organism with extensive regenerative ability in the brain might help to address the molecular programs needed for NSPCs to respond to neurodegeneration by enhanced neurogenesis.

Intrinsic Cholinergic Neurons in the Hippocampus: Fact or Artifact?

It is generally agreed that hippocampal acetylcholine (ACh) is synthesized and released exclusively from the terminals of the long-axon afferents whose cell bodies reside in the medial septum and diagonal band. The search for intrinsic cholinergic neurons in the hippocampus has a long history; however evidence for the existence of these neurons has been inconsistent, with most investigators failing to detect them using in situ hybridization or immunohistochemical staining of the cholinergic markers, choline acetyltransferase (ChAT) or vesicular acetylcholine transporter (VAChT). Advances in the use of bacterial artificial chromosome (BAC) transgenic mice expressing a reporter protein under the control of the genomic elements of the Chat gene (Chat-BAC mice) have facilitated studies of cholinergic neurons. Such mice show robust and faithful expression of the reporter proteins in all known cholinergic cell populations. The availability of the Chat-BAC mice re-ignited interest in hippocampal cholinergic interneurons, because a small number of such reporter-expressing cells is frequently observed in the hippocampus of these mice. However, to date, attempts to confirm that these neurons co-express the endogenous cholinergic marker ChAT, or release ACh, have been unsuccessful. Without such confirmatory evidence it is best to conclude that there are no cholinergic neurons in the hippocampus. Similar considerations apply to other BAC transgenic lines, whose utility as a discovery tool for cell populations heretofore not known to express the genes of interest encoded by the BACs, must be validated by methods that detect expression of the endogenous genes.

Rapid Activation of Bone Morphogenic Protein 9 by Receptor-mediated Displacement of Pro-domains

By non-covalent association after proteolytic cleavage, the pro-domains modulate the activities of the mature growth factor domains across the transforming growth factor-β family. In the case of bone morphogenic protein 9 (BMP9), however, the pro-domains do not inhibit the bioactivity of the growth factor, and the BMP9·pro-domain complexes have equivalent biological activities as the BMP9 mature ligand dimers. By using real-time surface plasmon resonance, we could demonstrate that either binding of pro-domain-complexed BMP9 to type I receptor activin receptor-like kinase 1 (ALK1), type II receptors, co-receptor endoglin, or to mature BMP9 domain targeting antibodies leads to immediate and complete displacement of the pro-domains from the complex. Vice versa, pro-domain binding by an anti-pro-domain antibody results in release of the mature BMP9 growth factor. Based on these findings, we adjusted ELISA assays to measure the protein levels of different BMP9 variants. Although mature BMP9 and inactive precursor BMP9 protein were directly detectable by ELISA, BMP9·pro-domain complex could only be measured indirectly as dissociated fragments due to displacement of mature growth factor and pro-domains after antibody binding. Our studies provide a model in which BMP9 can be readily activated upon getting into contact with its receptors. This increases the understanding of the underlying biology of BMP9 activation and also provides guidance for ELISA development for the detection of circulating BMP9 variants.

Intraneuronal APP and extracellular Aβ independently cause dendritic spine pathology in transgenic mouse models of Alzheimer's disease

Alzheimer’s disease (AD) is thought to be caused by accumulation of amyloid-β protein (Aβ), which is a cleavage product of amyloid precursor protein (APP). Transgenic mice overexpressing APP have been used to recapitulate amyloid-β pathology. Among them, APP23 and APPswe/PS1deltaE9 (deltaE9) mice are extensively studied. APP23 mice express APP with Swedish mutation and develop amyloid plaques late in their life, while cognitive deficits are observed in young age. In contrast, deltaE9 mice with mutant APP and mutant presenilin-1 develop amyloid plaques early but show typical cognitive deficits in old age. To unveil the reasons for different progressions of cognitive decline in these commonly used mouse models, we analyzed the number and turnover of dendritic spines as important structural correlates for learning and memory. Chronic in vivo two-photon imaging in apical tufts of layer V pyramidal neurons revealed a decreased spine density in 4–5-month-old APP23 mice. In age-matched deltaE9 mice, in contrast, spine loss was only observed on cortical dendrites that were in close proximity to amyloid plaques. In both cases, the reduced spine density was caused by decreased spine formation. Interestingly, the patterns of alterations in spine morphology differed between these two transgenic mouse models. Moreover, in APP23 mice, APP was found to accumulate intracellularly and its content was inversely correlated with the absolute spine density and the relative number of mushroom spines. Collectively, our results suggest that different pathological mechanisms, namely an intracellular accumulation of APP or extracellular amyloid plaques, may lead to spine abnormalities in young adult APP23 and deltaE9 mice, respectively. These distinct features, which may represent very different mechanisms of synaptic failure in AD, have to be taken into consideration when translating results from animal studies to the human disease.

Growth factor treatment to overcome Alzheimer's dysfunctional signaling

The number of people suffering from Alzheimer's disease (AD) will increase as the world population ages, creating a huge socio-economic burden. The three pathophysiological hallmarks of AD are the cholinergic system dysfunction, the β-amyloid peptide deposition and the Tau protein hyperphosphorylation. Current treatments have only transient effects and each tends to concentrate on a single pathophysiological aspect of AD. This review first provides an overall view of AD in terms of its pathophysiological symptoms and signaling dysfunction. We then examine the therapeutic potential of growth factors (GFs) by showing how they can overcome the dysfunctional cell signaling that occurs in AD. Finally, we discuss new alternatives to GFs that help overcome the problem of brain uptake, such as small peptides, with evidence from some of our unpublished data on human neuronal cell line.

Regulation of bone morphogenetic protein 9 (BMP9) by redox-dependent proteolysis

BMP9, a member of the TGFβ superfamily, is a homodimer that forms a signaling complex with two type I and two type II receptors. Signaling through high-affinity activin receptor-like kinase 1 (ALK1) in endothelial cells, circulating BMP9 acts as a vascular quiescence factor, maintaining endothelial homeostasis. BMP9 is also the most potent BMP for inducing osteogenic signaling in mesenchymal stem cells in vitro and promoting bone formation in vivo. This activity requires ALK1, the lower affinity type I receptor ALK2, and higher concentrations of BMP9. In adults, BMP9 is constitutively expressed in hepatocytes and secreted into the circulation. Optimum concentrations of BMP9 are essential to maintain the highly specific endothelial-protective function. Factors regulating BMP9 stability and activity remain unknown. Here, we showed by chromatography and a 1.9 Å crystal structure that stable BMP9 dimers could form either with (D-form) or without (M-form) an intermolecular disulfide bond. Although both forms of BMP9 were capable of binding to the prodomain and ALK1, the M-form demonstrated less sustained induction of Smad1/5/8 phosphorylation. The two forms could be converted into each other by changing the redox potential, and this redox switch caused a major alteration in BMP9 stability. The M-form displayed greater susceptibility to redox-dependent cleavage by proteases present in serum. This study provides a mechanism for the regulation of circulating BMP9 concentrations and may provide new rationales for approaches to modify BMP9 levels for therapeutic purposes.

IGF2 ameliorates amyloidosis, increases cholinergic marker expression and raises BMP9 and neurotrophin levels in the hippocampus of the APPswePS1dE9 Alzheimer's disease model mice

The development of an effective therapy for Alzheimer's disease (AD) is a major challenge to biomedical sciences. Because much of early AD pathophysiology includes hippocampal abnormalities, a viable treatment strategy might be to use trophic factors that support hippocampal integrity and function. IGF2 is an attractive candidate as it acts in the hippocampus to enhance memory consolidation, stimulate adult neurogenesis and upregulate cholinergic marker expression and acetylcholine (ACh) release. We performed a seven-day intracerebroventricular infusion of IGF2 in transgenic APPswe.PS1dE9 AD model mice that express green fluorescent protein in cholinergic neurons (APP.PS1/CHGFP) and in wild type WT/CHGFP littermates at 6 months of age representing early AD-like disease. IGF2 reduced the number of hippocampal Aβ40- and Aβ42-positive amyloid plaques in APP.PS1/CHGFP mice. Moreover, IGF2 increased hippocampal protein levels of the ACh-synthesizing enzyme, choline acetyltransferase in both WT/CHGFP and APP.PS1/CHGFP mice. The latter effect was likely mediated by increased protein expression of the cholinergic differentiating factor, BMP9, observed in IGF2-treated mice as compared to controls. IGF2 also increased the protein levels of hippocampal NGF, BDNF, NT3 and IGF1 and of doublecortin, a marker of neurogenesis. These data show that IGF2 administration is effective in reversing and preventing several pathophysiologic processes associated with AD and suggest that IGF2 may constitute a therapeutic target for AD.