Expression of Ki67, PCNA and the chromosome replication licensing protein Mcm2 in glial cells of the ageing human hippocampus increases with the burden of Alzheimer-type pathology

Microglial activation as a hallmark of neuroinflammation in Alzheimer's disease

Microglial activation has emerged as a hallmark of neuroinflammation in Alzheimer's disease (AD). Central to this process is the formation and accumulation of amyloid beta (Aβ) peptide and neurofibrillary tangles, both of which contribute to synaptic dysfunction and neuronal cell death. Aβ oligomers trigger microglial activation, leading to the release of pro-inflammatory cytokines, which further exacerbates neuroinflammation and neuronal damage. Importantly, the presence of activated microglia surrounding amyloid plaques is correlated with heightened production of cytokines such as interleukin (IL)-1β and tumor necrosis factor-alpha (TNF-α), creating a vicious cycle of inflammation. While microglia play a protective role by clearing Aβ plaques during the early stages of AD, their chronic activation can lead to detrimental outcomes, including enhanced tau pathology and neuronal apoptosis. Recent studies have highlighted the dualistic nature of microglial activation, showcasing both inflammatory (M1) and anti-inflammatory (M2) phenotypes that fluctuate based on the surrounding microenvironment. Disruption in microglial function and regulation can lead to neurovascular dysfunction, further contributing to the cognitive decline seen in AD. Moreover, emerging biomarkers and imaging techniques are unveiling the complexity of microglial responses in AD, providing avenues for targeted therapeutics aimed at modulating these cells. Understanding the intricate interplay between microglia, Aβ, and tau pathology is vital for developing potential interventions to mitigate neuroinflammation and its impact on cognitive decline in AD. This review synthesizes current findings regarding microglial activation and its implications for AD pathogenesis, offering insights into future therapeutic strategies.

Lycopene alleviates cognitive dysfunctions in an Alzheimer's disease rat model via suppressing the oxidative and neuroinflammatory signaling

Oxidative stress and neuroinflammation are key contributors to the development of neurodegenerative disorders, including Alzheimer's disease (AD). Lycopene (LYC) has demonstrated effectiveness in inhibiting inflammatory and oxidative stress markers and appears to exert a modulatory impact on several physiological pathways, behavioral manifestations, and cognitive symptoms associated with AD in animal models. In the present study, an AD model was established in male Wistar albino rats through daily oral administration of hydrated aluminum chloride (AlCl₃·6H₂O) at a dose of 75 mg/kg for six weeks. A Morris water maze (MWM) behavioral test was conducted to confirm memory impairment and cognitive deterioration in the treated rats. Animals exhibiting cognitive dysfunction were subsequently treated with LYC (5 mg/kg orally) for an additional six weeks, followed by a second MWM test before sacrifice. The findings revealed that LYC significantly enhanced performance and cognitive function in the AD model rats and markedly (p < 0.001) reduced the accumulation of amyloid β1-42, proinflammatory mediators [interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α)], malondialdehyde (MDA), and nitrite levels. Furthermore, LYC significantly (p < 0.001) decreased the acetylcholine (ACh) concentration, monoamine oxidase (MAO), creatine kinase (CK), and lactate dehydrogenase (LDH) activites. Additionally, LYC significantly (p < 0.001) increased the acetylcholinesterase (AChE) activity, nuclear factor erythroid-2-related factor 2 (Nrf2), serotonin, anti-inflammatory mediators [transforming growth factor beta-1 (TGF-β1) and interleukin-10 (IL-10)] levels, superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. The therapeutic efficacy of LYC was further supported by improvements in the histopathological appearance of brain tissues, significant (p < 0.001) enhancement of synaptophysin immunohistochemical expression, and suppression of the immunohistochemical expression of cell cycle-related proteins (Ki67 and proliferating cell nuclear antigen [PCNA]). In conclusion, LYC may represent a promising therapeutic agent for AD by targeting multiple pathogenic mechanisms.

Hippocampal neurogenesis in adult primates: a systematic review

It had long been considered that no new neurons are generated in the primate brain beyond birth, but recent studies have indicated that neurogenesis persists in various locations throughout the lifespan. The dentate gyrus of the hippocampus is of particular interest due to the postulated role played by neurogenesis in memory. However, studies investigating the presence of adult hippocampal neurogenesis (AHN) have reported contradictory findings, and no systematic review of the evidence has been conducted to date. We searched MEDLINE, Embase and PsycINFO on 27th June 2023 for studies on hippocampal neurogenesis in adult primates, excluding review papers. Screening, quality assessment and data extraction was done by independent co-raters. We synthesised evidence from 112 relevant papers. We found robust evidence, primarily supported by immunohistochemical examination of tissue samples and neuroimaging, for newly generated neurons, first detected in the subgranular zone of the dentate gyrus, that mature over time and migrate to the granule cell layer, where they become functionally integrated with surrounding neuronal networks. AHN has been repeatedly observed in both humans and other primates and gradually diminishes with age. Transient increases in AHN are observed following acute insults such as stroke and epileptic seizures, and following electroconvulsive therapy, and AHN is diminished in neurodegenerative conditions. Markers of AHN correlate positively with measures of learning and short-term memory, but associations with antidepressant use and mood states are weaker. Heterogeneous outcome measures limited quantitative syntheses. Further research should better characterise the neuropsychological function of neurogenesis in healthy subjects.

Early oxidative stress and DNA damage in Aβ-burdened hippocampal neurons in an Alzheimer's-like transgenic rat model

Oxidative stress is a key contributor to AD pathology. However, the earliest role of pre-plaque neuronal oxidative stress, remains elusive. Using laser microdissected hippocampal neurons extracted from McGill-R-Thy1-APP transgenic rats we found that intraneuronal amyloid beta (iAβ)-burdened neurons had increased expression of genes related to oxidative stress and DNA damage responses including Ercc2, Fancc, Sod2, Gsr, and Idh1. DNA damage was further evidenced by increased neuronal levels of XPD (Ercc2) and γH2AX foci, indicative of DNA double stranded breaks (DSBs), and by increased expression of Ercc6, Rad51, and Fen1, and decreased Sirt6 in hippocampal homogenates. We also found increased expression of synaptic plasticity genes (Grin2b (NR2B), CamkIIα, Bdnf, c-fos, and Homer1A) and increased protein levels of TOP2β. Our findings indicate that early accumulation of iAβ, prior to Aβ plaques, is accompanied by incipient oxidative stress and DSBs that may arise directly from oxidative stress or from maladaptive synaptic plasticity.

Exendin-4 Prevents Memory Loss and Neuronal Death in Rats with Sporadic Alzheimer-Like Disease

This study investigated the neuroprotective effects of exendin-4 (EXE-4), an analog of the glucagon-like peptide 1 receptor (GLP-1R) on memory and on the neuronal populations that constitute the hippocampus of rats submitted to a sporadic dementia of Alzheimer's type (SDAT). Male Wistar rats received streptozotocin (STZ icv, 3 mg/kg diluted in aCFS, 5 µl/ventricle) and were treated for 21 days with EXE-4 (10 µg/kg, ip; saline as the vehicle). Four groups were formed: vehicle, EXE-4, STZ, and STZ + EXE-4. The groups were submitted to Y-Maze (YM), object recognition (ORT), and object displacement tasks (ODT) to assess learning and memory. The brains were used for immunohistochemical and immunofluorescent techniques with antibodies to NeuN, cleaved caspase-3 (CC3), PCNA, doublecortin (DCX), synaptophysin (SYP), and insulin receptor (IR). STZ worsened spatial memory in the YMT, as well as short-term (STM) and long-term (LTM) memories in the ORT and ODT, respectively. EXE-4 protected against memory impairment in STZ animals. STZ reduced mature neuron density (NeuN) and increased cell apoptosis (CC3) in the DG, CA1, and CA3. EXE-4 protected against neuronal death in all regions. EXE-4 increased PCNA+ cells in all regions of the hippocampus, and STZ attenuated this effect. STZ reduced neurogenesis in DG per se as well as synaptogenesis induced by EXE-4. EXE-4 increased immunoreactivity to IR in the CA1. From these findings, EXE-4 showed a beneficial effect on hippocampal pyramidal and granular neurons in the SDAT showing anti-apoptotic properties and promoting cell proliferation. In parallel, EXE-4 preserved the memory of SDAT rats. EXE-4 appears to enhance synapses at CA3 and DG. In conclusion, these data indicate that agonists to GLP-1R have a beneficial effect on hippocampal neurons in AD.

Melatonin as a Harmonizing Factor of Circadian Rhythms, Neuronal Cell Cycle and Neurogenesis: Additional Arguments for Its Therapeutic Use in Alzheimer's Disease

The synthesis and release of melatonin in the brain harmonize various physiological functions. The apparent decline in melatonin levels with advanced aging is an aperture to the neurodegenerative processes. It has been indicated that down regulation of melatonin leads to alterations of circadian rhythm components, which further causes a desynchronization of several genes and results in an increased susceptibility to develop neurodegenerative diseases. Additionally, as circadian rhythms and memory are intertwined, such rhythmic disturbances influence memory formation and recall. Besides, cell cycle events exhibit a remarkable oscillatory system, which is downstream of the circadian phenomena. The linkage between the molecular machinery of the cell cycle and complex fundamental regulatory proteins emphasizes the conjectural regulatory role of cell cycle components in neurodegenerative disorders such as Alzheimer's disease. Among the mechanisms intervening long before the signs of the disease appear, the disturbances of the circadian cycle, as well as the alteration of the machinery of the cell cycle and impaired neurogenesis, must hold our interest. Therefore, in the present review, we propose to discuss the underlying mechanisms of action of melatonin in regulating the circadian rhythm, cell cycle components and adult neurogenesis in the context of AD pathogenesis with the view that it might further assist to identify new therapeutic targets.

LncRNA RP11-59J16.2 aggravates apoptosis and increases tau phosphorylation by targeting MCM2 in AD

Alzheimer’s disease (AD) is a degenerative disease of central nervous system with unclear pathogenesis, accounting for 60%–70% of dementia cases. Long noncoding RNAs (LncRNAs) play an important function in the development of AD. This study aims to explore the role of differentially expressed lncRNAs in AD patients’ serum in the pathogenesis of AD. Microarray analysis was performed in the serum of AD patients and healthy controls to establish lncRNAs and mRNAs expression profiles. GO analysis and KEGG pathway analysis revealed that G₁/S transition of mitotic cell cycle might be involved in the development of AD. The result showed that RP11-59J16.2 was up-regulated and MCM2 was down-regulated in serum of AD patients. SH-SY5Y cells were treated with Aβ 1–42 to establish AD cell model. Dual luciferase reporter gene analysis verified that RP11-59J16.2 could directly interact with 3′UTR of MCM2 and further regulate the expression of MCM2. Inhibition of RP11-59J16.2 or overexpression of MCM2, CCK-8 assay and Annexin V FITC/PI apoptosis assay kit results showed that RP11-59J16.2 could reduce cell viability, aggravate apoptosis and increase Tau phosphorylation in AD cell model by inhibiting MCM2. In short, our study revealed a novel lncRNA RP11-59J16.2 that could promote neuronal apoptosis and increase Tau phosphorylation by regulating MCM2 in AD model, and indicated that lncRNA RP11-59J16.2 might be a potential target molecule for AD development.

Neurogenesis in aging and age-related neurodegenerative diseases

Adult neurogenesis, the process by which neurons are generated in certain areas of the adult brain, declines in an age-dependent manner and is one potential target for extending cognitive healthspan. Aging is a major risk factor for neurodegenerative diseases and, as lifespans are increasing, these health challenges are becoming more prevalent. An age-associated loss in neural stem cell number and/or activity could cause this decline in brain function, so interventions that reverse aging in stem cells might increase the human cognitive healthspan. In this review, we describe the involvement of adult neurogenesis in neurodegenerative diseases and address the molecular mechanistic aspects of neurogenesis that involve some of the key aggregation-prone proteins in the brain (i.e., tau, Aβ, α-synuclein, …). We summarize the research pertaining to interventions that increase neurogenesis and regulate known targets in aging research, such as mTOR and sirtuins. Lastly, we share our outlook on restoring the levels of neurogenesis to physiological levels in elderly individuals and those with neurodegeneration. We suggest that modulating neurogenesis represents a potential target for interventions that could help in the fight against neurodegeneration and cognitive decline.

Neuroinflammation PET imaging of the translocator protein (TSPO) in Alzheimer's disease: an update

Neuroinflammation is a significant contributor to Alzheimer's disease (AD). Until now, PET imaging of the translocator protein (TSPO) has been widely used to depict the neuroimmune endophenotype of AD. The aim of this review was to provide an update to the results from 2018 and to advance the characterization of the biological basis of TSPO imaging in AD by re-examining TSPO function and expression and the methodological aspects of interest. Although the biological basis of the TSPO PET signal is obviously related to microglia and astrocytes in AD, the observed process remains uncertain and might not be directly related to neuroinflammation. Further studies are required to re-examine the cellular significance underlying a variation in the PET signal in AD and how it can be impacted by a disease-modifying treatment.

Reviving through human hippocampal newborn neurons

Recent contradictory data has renewed discussion regarding the existence of adult hippocampal neurogenesis (AHN) in humans, i.e., the continued production of new neurons in the brain after birth. The present review revisits the debate of AHN in humans from a historical point of view in the face of contradictory evidence, analyzing the methods employed to investigate this phenomenon. Thus, to date, of the 57 studies performed in humans that we reviewed, 84% (48) concluded in favor of the presence of newborn neurons in the human adult hippocampus. Besides quality of the tissue (such as postmortem intervals below 26hours as well as tissue conservation and fixation), considerations for assessing and quantify AHN in the human brain require the use of stereology and toxicological analyses of clinical data of the patient.

Adult Hippocampal Neurogenesis in Major Depressive Disorder and Alzheimer's Disease

Depression and dementia are major public health problems. Major depressive disorder (MDD) and Alzheimer's disease (AD) reciprocally elevate the risk for one another. No effective drug is available to treat AD and about one-third of depressive patients show treatment resistance. The biological connection between MDD and AD is still unclear. Uncovering this link might open novel ways of treatment and prevention to improve patient healthcare. Here, we discuss recent studies specifically on the role of human adult hippocampal neurogenesis (AHN) in MDD and AD. We compare diverse approaches to analyse the effect of MDD and AD on human AHN and analyse different studies implicating the role of human AHN as a potential converging mechanism in MDD and AD.

Expression of neurogenic markers in Alzheimer's disease: a systematic review and metatranscriptional analysis

Alzheimer's disease (AD) is the most common form of dementia characterized by substantial neuronal loss and progressive brain atrophy. Animal studies have suggested that the process of adult neurogenesis might be altered at the earliest phases of disease onset. The relationship between AD progression and adult neurogenesis in the human brain is, however, not well understood. Here, we present a systematic review of the postmortem studies that investigated changes in human adult neurogenesis in the AD brain. We present findings from 11 postmortem studies that were identified by a systematic search within the literature, focusing on what markers of neurogenesis were used, which stages of AD were investigated, and whether the studies had any confounding information that could potentially hinder clear interpretation of the presented data. In addition, we also review studies that examined transcriptomic changes in human AD postmortem brains and reveal upregulated expression of neural progenitor and proliferation markers and downregulated expression of later neurogenic markers in AD. Taken together, the existing literature seems to suggest that the overall level of human adult neurogenesis is reduced during the later stages of AD, potentially due to failed maturation and integration of new-born neurons. Further investigations using complementary methods such as in vitro disease modeling will be helpful to understand the exact molecular mechanisms underlying such pattern of change and to determine whether neurogenesis can be an effective therapeutic target for early intervention.

Deciphering the Astrocyte Reaction in Alzheimer's Disease

Reactive astrocytes were identified as a component of senile amyloid plaques in the cortex of Alzheimer's disease (AD) patients several decades ago. However, their role in AD pathophysiology has remained elusive ever since, in part owing to the extrapolation of the literature from primary astrocyte cultures and acute brain injury models to a chronic neurodegenerative scenario. Recent accumulating evidence supports the idea that reactive astrocytes in AD acquire neurotoxic properties, likely due to both a gain of toxic function and a loss of their neurotrophic effects. However, the diversity and complexity of this glial cell is only beginning to be unveiled, anticipating that astrocyte reaction might be heterogeneous as well. Herein we review the evidence from mouse models of AD and human neuropathological studies and attempt to decipher the main conundrums that astrocytes pose to our understanding of AD development and progression. We discuss the morphological features that characterize astrocyte reaction in the AD brain, the consequences of astrocyte reaction for both astrocyte biology and AD pathological hallmarks, and the molecular pathways that have been implicated in this reaction.

Quercetin ameliorates Aβ toxicity in Drosophila AD model by modulating cell cycle-related protein expression

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by β amyloid (Aβ) deposition and neurofibril tangles. It has been reported that a bioflavonoid, quercetin, could ameliorate AD phenotypes in C. elegans and mice. However, the mechanism underlying the ameliorative effect of quercetin is not fully understood yet. Drosophila models could recapitulate AD-like phenotypes, such as shortened lifespan, impaired locomotive ability as well as defects in learning and memory. So in this study, we investigated the effects of quercetin on AD in Drosophila model and explored the underlying mechanisms. We found quercetin could effectively intervene in AD pathogenesis in vivo. Mechanism study showed quercetin could restore the expression of genes perturbed by Aβ accumulation, such as those involved in cell cycle and DNA replication. Cyclin B, an important cell cycle protein, was chosen to test whether it participated in the AD ameliorative effects of quercetin. We found that cyclin B RNAi in the brain could alleviate AD phenotypes. Taken together, the current study suggested that the neuroprotective effects of quercetin were mediated at least partially by targeting cell cycle-related proteins.

Protective effects of 1α,25-Dihydroxyvitamin D3 on cultured neural cells exposed to catalytic iron

Recent studies have postulated a role for vitamin D and its receptor on cerebral function, and anti‐inflammatory, immunomodulatory and neuroprotective effects have been described; vitamin D can inhibit proinflammatory cytokines and nitric oxide synthesis during various neurodegenerative insults, and may be considered as a potential drug for the treatment of these disorders. In addition, iron is crucial for neuronal development and neurotransmitter production in the brain, but its accumulation as catalytic form (Fe³⁺) impairs brain function and causes the dysregulation of iron metabolism leading to tissue damage due to the formation of toxic free radicals (ROS). This research was planned to study the role of vitamin D to prevent iron damage in neuroblastoma BE(2)M17 cells. Mechanisms involved in neurodegeneration, including cell viability, ROS production, and the most common intracellular pathways were studied. Pretreatment with calcitriol (the active form of vitamin D) reduced cellular injury induced by exposure to catalytic iron.

Alterations of neuronal precursor cells in stages of human adult neurogenesis in heroin addicts

BACKGROUND

Adult neurogenesis has been shown to occur throughout life and different brain pathologies were demonstrated to be associated with altered neurogenesis. Here, an impact of heroin addiction on neurogenesis in humans is hypothesised.

METHODS

Post mortem hippocampal specimens of drug addicts with known heroin abuse and a group of non-addictive control subjects were analysed, using antibodies indicating different stages of neurogenesis. The subgranular zone of the dentate gyrus was examined qualitatively and quantitatively.

RESULTS

The data indicate (i) a decreased number of neural precursor cells, (ii) accompanied by low rates of proliferation and (iii) a marked loss of dendritic trees in targeting cells in heroin fatalities. (iv) The age-dependent increase of differentiating cells in the healthy controls was not observed in the addicts. Additionally, double immunofluorescence labelling indicated the precursor nature of Musashi-1 positive cells in the human subgranular zone of the dentate gyrus.

CONCLUSIONS

Present data firstly demonstrate the influence of drug addiction with known heroin abuse on different developmental stages of progenitors in the dentate gyrus. The patterns of antibody staining suggest a distinct inhibition of neurogenesis at the stage of neural precursor cells and revealed morphological changes in targeting cells in cases of heroin addicts as compared to healthy controls. These alterations could be considerable for memory and cognitive deficits as well as addictive behaviour in chronic drug abusers and may give rise to specific pro-neurogenic therapies.

Proliferation in the Alzheimer hippocampus is due to microglia, not astroglia, and occurs at sites of amyloid deposition

Microglia and astrocytes contribute to Alzheimer's disease (AD) etiology and may mediate early neuroinflammatory responses. Despite their possible role in disease progression and despite the fact that they can respond to amyloid deposition in model systems, little is known about whether astro- or microglia can undergo proliferation in AD and whether this is related to the clinical symptoms or to local neuropathological changes. Previously, proliferation was found to be increased in glia-rich regions of the presenile hippocampus. Since their phenotype was unknown, we here used two novel triple-immunohistochemical protocols to study proliferation in astro- or microglia in relation to amyloid pathology. We selected different age-matched cohorts to study whether proliferative changes relate to clinical severity or to neuropathological changes. Proliferating cells were found across the hippocampus but never in mature neurons or astrocytes. Almost all proliferating cells were colabeled with Iba1+, indicating that particularly microglia contribute to proliferation in AD. Proliferating Iba1+ cells was specifically seen within the borders of amyloid plaques, indicative of an active involvement in, or response to, plaque accumulation. Thus, consistent with animal studies, proliferation in the AD hippocampus is due to microglia, occurs in close proximity of plaque pathology, and may contribute to the neuroinflammation common in AD.

Electroacupuncture promotes neural cell proliferation in vivo through activation of the ERK1/2 signaling pathway

The aim of this study was to investigate the effect of electroacupuncture (EA) on cell proliferation and its molecular mechanisms. Sixty rats were randomly divided into 5 groups: sham operation control (SC), ischemia control (IC), EA, EA and DMSO injection (ED), EA and U0126 injection (EU). All the groups, with the exception of SC, underwent middle cerebral artery occlusion (MCAO), and DMSO or U0126 was injected into the rat in the ED or EU group 30 min prior to MCAO. Cell proliferation was evaluated by proliferating cell nuclear antigen (PCNA) immunostaining. The changes of cell cycle proteins (cyclin D1, CDK4, cyclin E, CDK2, p21 and p27) and the ERK1/2 pathway activation were examined by RT-PCR and western blot analysis. The results showed that the positive cell numbers of PCNA immunostaining in the EA and ED groups were more than those in the IC group (P<0.05). The mRNA and protein levels of p21 or p27 were obviously increased, however, the mRNA and protein levels of cyclin D1, CDK4, cyclin E and CDK2 were reduced in the IC and EU groups. The findings suggested that EA activates the ERK1/2 signaling pathway to protect brain injury during cerebral ischemia. However, this positive effect of EA can be blocked by U0126.

The effects of chronic alcoholism on cell proliferation in the human brain

Neurogenesis continues in the human subventricular zone and to a lesser extent in the hippocampal subgranular zone throughout life. Subventricular zone-derived neuroblasts migrate to the olfactory bulb where survivors become integrated as interneurons and are postulated to contribute to odor discrimination. Adult neurogenesis is dysregulated in many neurological, neurovascular and neurodegenerative diseases. Alcohol abuse can result in a neurodegenerative condition called alcohol-related brain damage. Alcohol-related brain damage manifests clinically as cognitive dysfunction and the loss of smell sensation (hyposmia) and pathologically as generalized white matter atrophy and focal neuronal loss. The exact mechanism linking chronic alcohol intoxication with alcohol-related brain damage remains largely unknown but rodent models suggest that decreased neurogenesis is an important component. We investigated this idea by comparing proliferative events in the subventricular zone and olfactory bulb of a well-characterized cohort of 15 chronic alcoholics and 16 age-matched controls. In contrast to the findings in animal models there was no difference in the number of proliferative cell nuclear antigen-positive cells in the subventricular zone of alcoholics (mean±SD=28.7±20.0) and controls (27.6±18.9, p=1.0). There were also no differences in either the total (p=0.89) or proliferative cells (p=0.98) in the granular cell layer of the olfactory bulb. Our findings show that chronic alcohol consumption does not affect cell proliferation in the human SVZ or olfactory bulb. In fact only microglial proliferation could be demonstrated in the latter. Therefore neurogenic deficits are unlikely to contribute to hyposmia in chronic alcoholics.

A phenotypic change but not proliferation underlies glial responses in Alzheimer disease

Classical immunohistochemical studies in the Alzheimer disease (AD) brain reveal prominent glial reactions, but whether this pathological feature is due primarily to cell proliferation or to a phenotypic change of existing resting cells remains controversial. We performed double-fluorescence immunohistochemical studies of astrocytes and microglia, followed by unbiased stereology-based quantitation in temporal cortex of 40 AD patients and 32 age-matched nondemented subjects. Glial fibrillary acidic protein (GFAP) and major histocompatibility complex II (MHC2) were used as markers of astrocytic and microglial activation, respectively. Aldehyde dehydrogenase 1 L1 and glutamine synthetase were used as constitutive astrocytic markers, and ionized calcium-binding adaptor molecule 1 (IBA1) as a constitutive microglial marker. As expected, AD patients had higher numbers of GFAP(+) astrocytes and MHC2(+) microglia than the nondemented subjects. However, both groups had similar numbers of total astrocytes and microglia and, in the AD group, these total numbers remained essentially constant over the clinical course of the disease. The GFAP immunoreactivity of astrocytes, but not the MHC2 immunoreactivity of microglia, increased in parallel with the duration of the clinical illness in the AD group. Cortical atrophy contributed to the perception of increased glia density. We conclude that a phenotypic change of existing glial cells, rather than a marked proliferation of glial precursors, accounts for the majority of the glial responses observed in the AD brain.

Ranking candidate disease genes from gene expression and protein interaction: a Katz-centrality based approach

Many diseases have complex genetic causes, where a set of alleles can affect the propensity of getting the disease. The identification of such disease genes is important to understand the mechanistic and evolutionary aspects of pathogenesis, improve diagnosis and treatment of the disease, and aid in drug discovery. Current genetic studies typically identify chromosomal regions associated specific diseases. But picking out an unknown disease gene from hundreds of candidates located on the same genomic interval is still challenging. In this study, we propose an approach to prioritize candidate genes by integrating data of gene expression level, protein-protein interaction strength and known disease genes. Our method is based only on two, simple, biologically motivated assumptions—that a gene is a good disease-gene candidate if it is differentially expressed in cases and controls, or that it is close to other disease-gene candidates in its protein interaction network. We tested our method on 40 diseases in 58 gene expression datasets of the NCBI Gene Expression Omnibus database. On these datasets our method is able to predict unknown disease genes as well as identifying pleiotropic genes involved in the physiological cellular processes of many diseases. Our study not only provides an effective algorithm for prioritizing candidate disease genes but is also a way to discover phenotypic interdependency, cooccurrence and shared pathophysiology between different disorders.

Neurogenesis in Alzheimer´s disease: a realistic alternative to neuronal degeneration?

Neural stem cells (NSC) are cells that have the capacity to generate multiple types of differentiated brain cells. In conditions in which there is a loss of key functional cell groups, such as neurons, inducing or introducing neural stem cells to replace the function of those cells that were lost during the disease has the greatest potential therapeutic applications. Indeed, the achievement of one of the main objectives of various investigations is already on the horizon for some conditions, such as Alzheimer's disease. It is not known whether impaired neurogenesis contributes to neuronal depletion and cognitive dysfunction in Alzheimer's disease (AD). The results of the different investigations are controversial; some studies have found that neurogenesis is increased in AD brains, but others have not.

Differential roles of phospholipases A2 in neuronal death and neurogenesis: implications for Alzheimer disease

The involvement of phospholipase A(2) (PLA(2)) in Alzheimer disease (AD) was first investigated nearly 15 years ago. Over the years, several PLA(2) isoforms have been detected in brain tissue: calcium-dependent secreted PLA(2) or sPLA(2) (IIA, IIC, IIE, V, X, and XII), calcium-dependent cytosolic PLA(2) or cPLA(2) (IVA, IVB, and IVC), and calcium-independent PLA(2) or iPLA(2) (VIA and VIB). Additionally, numerous in vivo and in vitro studies have suggested the role of different brain PLA(2) in both physiological and pathological events. This review aimed to summarize the findings in the literature relating the different brain PLA(2) isoforms with alterations found in AD, such as neuronal cell death and impaired neurogenesis process. The review showed that sPLA(2)-IIA, sPLA(2)-V and cPLA(2)-IVA are involved in neuronal death, whereas sPLA(2)-III and sPLA(2)-X are related to the process of neurogenesis, and that the cPLA(2) and iPLA(2) groups can be involved in both neuronal death and neurogenesis. In AD, there are reports of reduced activity of the cPLA(2) and iPLA(2) groups and increased expression of sPLA(2)-IIA and cPLA(2)-IVA. The findings suggest that the inhibition of cPLA(2) and iPLA(2) isoforms (yet to be determined) might contribute to impaired neurogenesis, whereas stimulation of sPLA(2)-IIA and cPLA(2)-IVA might contribute to neurodegeneration in AD.

Strategies to promote differentiation of newborn neurons into mature functional cells in Alzheimer brain

Adult neurogenesis occurs in the subgranular zone (SGZ) and subventricular zone (SVZ). New SGZ neurons migrate into the granule cell layer of the dentate gyrus (DG). New SVZ neurons seem to enter the association neocortex and entorhinal cortex besides the olfactory bulb. Alzheimer disease (AD) is characterized by neuron loss in the hippocampus (DG and CA1 field), entorhinal cortex, and association neocortex, which underlies the learning and memory deficits. We hypothesized that, if the AD brain can support neurogenesis, strategies to stimulate the neurogenesis process could have therapeutic value in AD. We reviewed the literature on: (a) the functional significance of adult-born neurons; (b) the occurrence of endogenous neurogenesis in AD; and (c) strategies to stimulate the adult neurogenesis process. We found that: (a) new neurons in the adult DG contribute to memory function; (b) new neurons are generated in the SGZ and SVZ of AD brains, but they fail to differentiate into mature neurons in the target regions; and (c) numerous strategies (Lithium, Glatiramer Acetate, nerve growth factor, environmental enrichment) can enhance adult neurogenesis and promote maturation of newly generated neurons. Such strategies might help to compensate for the loss of neurons and improve the memory function in AD.

Phospholipase A2 activation as a therapeutic approach for cognitive enhancement in early-stage Alzheimer disease

RATIONALE

Alzheimer disease (AD) is the leading cause of dementia in the elderly and has no known cure. Evidence suggests that reduced activity of specific subtypes of intracellular phospholipases A2 (cPLA2 and iPLA2) is an early event in AD and may contribute to memory impairment and neuropathology in the disease.

OBJECTIVE

The objective of this study was to review the literature focusing on the therapeutic role of PLA2 stimulation by cognitive training and positive modulators, or of supplementation with arachidonic acid (PLA2 product) in facilitating memory function and synaptic transmission and plasticity in either research animals or human subjects.

METHODS

MEDLINE database was searched (no date restrictions) for published articles using the keywords Alzheimer disease (mild, moderate, severe), mild cognitive impairment, healthy elderly, rats, mice, phospholipase A(2), phospholipid metabolism, phosphatidylcholine, arachidonic acid, cognitive training, learning, memory, long-term potentiation, protein kinases, dietary lipid compounds, cell proliferation, neurogenesis, and neuritogenesis. Reference lists of the identified articles were checked to select additional studies of interest.

RESULTS

Overall, the data suggest that PLA2 activation is induced in the healthy brain during learning and memory. Furthermore, learning seems to regulate endogenous neurogenesis, which has been observed in AD brains. Finally, PLA2 appears to be implicated in homeostatic processes related to neurite outgrowth and differentiation in both neurodevelopmental processes and response to neuronal injury.

CONCLUSION

The use of positive modulators of PLA2 (especially of cPLA2 and iPLA2) or supplementation with dietary lipid compounds (e.g., arachidonic acid) in combination with cognitive training could be a valuable therapeutic strategy for cognitive enhancement in early-stage AD.

Multifunctional drug treatment in neurotrauma

Although the concepts of secondary injury and neuroprotection after neurotrauma are experimentally well supported, clinical trials of neuroprotective agents in traumatic brain injury or spinal cord injury have been disappointing. Most strategies to date have used drugs directed toward a single pathophysiological mechanism that contributes to early necrotic cell death. Given these failures, recent research has increasingly focused on multifunctional (i.e., multipotential, pluripotential) agents that target multiple injury mechanisms, particularly those that occur later after the insult. Here we review two such approaches that show particular promise in experimental neurotrauma: cell cycle inhibitors and small cyclized peptides. Both show extended therapeutic windows for treatment and appear to share at least one important target.

Analysis of the extracellular matrix protein SC1 during reactive gliosis in the rat lithium-pilocarpine seizure model

When the nervous system is subjected to stressful stimuli, reactive gliosis often ensues. This phenomenon consists of the hypertrophy of astrocyte processes as well as the proliferation of these cells. In this study, the lithium-pilocarpine model of temporal lobe epilepsy was employed to study the effects of status epilepticus (SE) on the localization of SC1 protein in reactive astrocytes. SC1 is an anti-adhesive extracellular matrix protein strongly expressed in the mammalian brain. At 1 day following SE, SC1 transiently localized to hypertrophied astrocyte processes that were closely associated with neurons and blood vessels. SC1 was also detected at 7 days post-SE in proliferating astrocytes labeled with the cell division marker PCNA. These findings indicate that the anti-adhesive protein SC1 is ideally localized to create an environment conducive to process extension and cellular proliferation in reactive astrocytes.

Determination of key aspects of precursor cell proliferation, cell cycle length and kinetics in the adult mouse subgranular zone

Neurogenesis studies on the adult mouse hippocampal subgranular zone (SGZ) typically report increases or decreases in proliferation. However, key information is lacking about these proliferating SGZ precursors, from the fundamental--what dose of bromodeoxyuridine (BrdU) is appropriate for labeling all S phase cells?--to the detailed--what are the kinetics of BrdU-labeled cells and their progeny? To address these questions, adult C57BL/6J mice were injected with BrdU and BrdU-immunoreactive (IR) cells were quantified. Initial experiments with a range of BrdU doses (25-500 mg/kg) suggested that 150 mg/kg labels all actively dividing precursors in the mouse SGZ. Experiments using a saturating dose of BrdU suggested BrdU bioavailability is less than 15 min, notably shorter than in the developing mouse brain. We next explored precursor division and maturation by tracking the number of BrdU-IR cells and colabeling of BrdU with other cell cycle proteins from 15 min to 30 days after BrdU. We found that BrdU and the Gap2 and mitosis (G2/M) phase protein pHisH3 maximally colocalized 8 h after BrdU, indicating that the mouse SGZ precursor cell cycle length is 14 h. In addition, triple labeling with BrdU and proliferating cell nuclear antigen (PCNA) and Ki-67 showed that BrdU-IR precursors and/or their progeny express these endogenous cell cycle proteins up to 4 days after BrdU injection. However, the proportion of BrdU/Ki-67-IR cells declined at a greater rate than the proportion of BrdU/PCNA-IR cells. This suggests that PCNA protein is detectable long after cell cycle exit, and that reliance on PCNA may overestimate the length of time a cell remains in the cell cycle. These findings will be critical for future studies examining the regulation of SGZ precursor kinetics in adult mice, and hopefully will encourage the field to move beyond counting BrdU-IR cells to a more mechanistic analysis of adult neurogenesis.

Altered neurogenesis in Alzheimer's disease

BACKGROUND

Exciting preliminary work indicates an increase in progenitor activity in the subgranular zone of the dentate gyrus of people with Alzheimer's disease (AD) compared to that of controls. We examine progenitor activity in the other main progenitor niche, the subventricular zone (SVZ), as well as potential associations with key pathological and neurochemical substrates.

METHOD

Immunocytochemistry techniques utilizing nestin and Musashi1 antibodies were used to examine progenitor activity in the SVZ and to enable comparisons between seven patients with AD and seven controls, based upon the quantification of the percentage area covered, using the Image Pro Plus v.4.1 image analysis system. AD pathology was staged using the Consortium to Establish a Registry for Alzheimer's Disease and Braak criteria. Choline acetyl transferase (ChAT) was measured in the temporal cortex as an indication of the severity of cortical cholinergic deficits. Glial fibrillary acidic protein (GFAP) was used to label astrocytes.

RESULTS

There was a significant ninefold decrease (Z = 2.2, P = .046) of Musashi1 immunoreactivity in the SVZ of patients with AD in comparison with that of controls, but there was a significant increase in nestin immunoreactivity in the same region (Z = 2.2, P = .028) without any significant change in GFAP immunoreactivity. Reduced ChAT enzymatic activity was the main association of Musashi immunoreactivity (R = -.90, P = .03).

DISCUSSION

The current results indicate a significant reduction of progenitor cells (as labeled by Musashi1) in the SVZ of patients with AD, but an increase in GFAP-negative astrocyte-like cells with progenitor characteristics. Cortical cholinergic loss was strongly associated with the reduction of progenitors, with potential implications of important treatment targets.