TGF-β1 is increased in a transgenic mouse model of familial Alzheimer's disease and causes neuronal apoptosis

Overexpression of TGFBR3 Aggravates Cognitive Impairment and Neuroinflammation by Promoting Microglia M1 Polarization in the APP/PS1 Mouse Model of Alzheimer's Disease

Transforming growth factor beta receptor 3 (TGFBR3), also known as betaglycan, is a member of the TGF-β receptor family. In our previous study, bioinformatics analysis revealed that TGFBR3 levels are elevated in patients with Alzheimer's disease (AD) and identified TGFBR3 as a potential risk factor for the disease. However, the precise role of TGFBR3 in the pathogenesis of AD remains largely unclear. In this study, we first validated the elevated levels of TGFBR3 in postmortem brain tissues from AD patients using immunohistochemical staining. Subsequently, gain-of-function experiments and behavioral tests were conducted to explore the functional role of TGFBR3 in the APP/PS1 mouse model. Our findings confirmed that TGFBR3 levels were significantly increased in AD patients compared to normal controls. Overexpression of TGFBR3 in APP/PS1 mice impaired spatial learning and memory abilities and promoted amyloid-β (Aβ) accumulation. Additionally, TGFBR3 overexpression exacerbated neuronal apoptosis and synaptic loss. We also observed that overexpression of TGFBR3 triggered an inflammatory response by promoting microglial polarization to the M1 phenotype, although it had no effect on astrocyte activation. In conclusion, our study demonstrates that increased TGFBR3 levels worsen cognitive impairment and accelerate pathological progression in APP/PS1 mice, suggesting that TGFBR3 could serve as a potential therapeutic target for AD treatment.

Inhibition of the Transforming Growth Factor-β Signaling Pathway Confers Neuroprotective Effects on Beta-Amyloid-Induced Direct Neurotoxicity and Microglia-Mediated Neuroinflammation

Background: Abnormal elevation of transforming growth factor-beta (TGF-β) has been observed among Alzheimer's disease (AD) patients. This may be due to microglia-mediated release of proinflammatory cytokines, which promote neuroinflammation and neuronal apoptosis. Silencing of TGFBR1, a gene encoding TGF-β receptor type I (TGF-βR1), has resulted in neuronal survival from amyloid-beta (Aβ)-induced neurotoxicity. Therefore, the present study investigated the neuroprotective effect of TGF-βR1 inhibitors (RepSox, Galunisertib, and Vactosertib) against Aβ-induced direct neurotoxicity and microglia-mediated neuroinflammation. Methods: The neuroprotective effect of TGF-βR1 inhibitors against Aβ-induced direct neurotoxicity and microglia-mediated neuroinflammation were investigated using the RealTime-Glo™ MT Cell Viability Assay. The inhibitory effect of TGF-βR1 inhibitors on Aβ-induced microglia-mediated production of proinflammatory cytokines (TNF-α and IL-1β) was determined using enzyme-linked immunosorbent assay (ELISA). Results: TGF-βR1 inhibitors (RepSox, Galunisertib, and Vactosertib) at the tested concentrations (6.25-150 nM) showed no significant cytotoxicity effects on SH-SY5Y and BV-2 cells. Moreover, treatments with these inhibitors exhibited neuroprotection on SH-SY5Y cells against Aβ-induced direct neurotoxicity. The trend of cell viability after 24 h treatment also supports the microscopic images of the cells' morphology. Furthermore, pretreatment with these inhibitors conferred indirect neuroprotective effect against Aβ-induced microglia-mediated neuroinflammation by attenuating the production of proinflammatory cytokines (TNF-α and IL-1β). Conclusion: The inhibition of the TGF-β signaling pathway in neuronal and microglia cells by TGF-βR1 inhibitors resulted in neuroprotection against Aβ-induced direct neurotoxicity and microglia-mediated neuroinflammation. Hence, targeting the TGF-β signaling pathway in both neuronal and microglia cells could provide a promising therapeutic strategy in AD.

Viral hepatitis moderates the impact of TGFB1 on neurocognitive impairment

Recent studies have identified a correlation between chronic viral hepatitis and cognitive impairment, yet the underlying mechanisms remain unclear. This study investigated the influence of TGFB1 genetic polymorphisms on cognitive function in individuals with and without hepatitis infections, hypothesizing that these polymorphisms and the viral hepatitis-induced inflammatory environment interact to affect cognitive abilities. Participants (173 with viral hepatitis and 258 healthy controls) were recruited. Genotyping of TGFB1 SNPs was performed using the C2-58 Axiom Genome-Wide TWB 2.0 Array Plate. Cognitive function was assessed using the MMSE and MoCA tests. Our results showed that healthy individuals carrying the C allele of rs2241715 displayed better performance in sentence writing (p = 0.020) and language tasks (p = 0.022). Notably, viral hepatitis was found to moderate the impact of the rs2241715 genotype on language function (p = 0.002). Similarly, those carrying the T allele of rs10417924 demonstrated superior orientation to time (p = 0.002), with viral hepatitis modifying the influence of the SNP on this particular cognitive function (p = 0.010). Our findings underscore the significant role of TGFβ1 in cognitive function and the moderating impact of viral hepatitis on TGFB1 SNP effects. These findings illuminate the potential of TGFB1 as a therapeutic target for cognitive impairment induced by viral hepatitis, thus broadening our understanding of TGFβ1 functionality in the pathogenesis of neurodegeneration.

Human-Soybean Allergies: Elucidation of the Seed Proteome and Comprehensive Protein-Protein Interaction Prediction

The soybean crop, Glycine max (L.) Merr., is consumed by humans, Homo sapiens, worldwide. While the respective bodies of literature and -omics data for each of these organisms are extensive, comparatively few studies investigate the molecular biological processes occurring between the two. We are interested in elucidating the network of protein-protein interactions (PPIs) involved in human-soybean allergies. To this end, we leverage state-of-the-art sequence-based PPI predictors amenable to predicting the enormous comprehensive interactome between human and soybean. A network-based analytical approach is proposed, leveraging similar interaction profiles to identify candidate allergens and proteins involved in the allergy response. Interestingly, the predicted interactome can be explored from two complementary perspectives: which soybean proteins are predicted to interact with specific human proteins and which human proteins are predicted to interact with specific soybean proteins. A total of eight proteins (six specific to the human proteome and two to the soy proteome) have been identified and supported by the literature to be involved in human health, specifically related to immunological and neurological pathways. This study, beyond generating the most comprehensive human-soybean interactome to date, elucidated a soybean seed interactome and identified several proteins putatively consequential to human health.

Tissue-specific features of microglial innate immune responses

As tissue-resident macrophages of the brain, microglia are increasingly considered as cellular targets for therapeutical intervention. Innate immune responses in particular have been implicated in central nervous system (CNS) infections, neuro-oncology, neuroinflammatory and neurodegenerative diseases. We here review the impact of 'nature and nurture' on microglial innate immune responses and summarize documented tissue-specific adaptations. Overall, such adaptations are associated with regulatory processes rather than with overt differences in the expressed repertoire of activating receptors of different tissue-resident macrophages. Microglial responses are characterized by slower kinetics, by a more persistent nature and by a differential usage of downstream enzymes and accessory receptors. We further consider factors like aging, previous exposure to inflammatory stimuli, and differences in the microenvironment that can modulate innate immune responses. The long-life span of microglia in the metabolically active CNS renders them susceptible to the phenomenon of 'inflammaging', and major challenges lie in the unraveling of the factors that underlie age-related alterations in microglial behavior.

The glial-specific hypermethylated 3' untranslated region of histone deacetylase 1 may modulates several signal pathways in Alzheimer's disease

AIMS

Epigenetic regulation plays an important role in the progression of Alzheimer's disease (AD). Here, we identified differential methylation probes (DMP) and investigated their potential mechanistic roles in AD.

MAIN METHODS

DMPs were identified via bioinformatic analysis of GSE66351, which was made up with 106 AD samples and 84 control samples derived from three separate brain regions. Differentially expressed genes (DEGs) were analyzed based on GSE5281 comprising 45 control samples and 58 AD samples. Gene ontology (GO), gene set enrichment analysis (GSEA), and protein-protein interaction (PPI) were used to identify pathways and hub genes.

KEY FINDINGS

We found 9007 DMPs in Occipital Cortex glia, 1527 in OC neurons, 100 in Temporal Cortex, and 194 in Frontal Cortex. 74 DEGs were identified in Primary Visual Cortex, 67 of which were downregulated while seven upregulated. 482 were upregulated and 697 downregulated in medial temporal gyrus. In superior frontal gyrus, 687 were upregulated and 85 downregulated. GO and PPI revealed that pathways involving epithelial-cell differentiation, cellular responses to lipids, transcription corepressor activities, apoptotic and organ growth were modulated by histone deacetylase 1 (HDAC1) and associated with AD. Additionally, GSEA illustrated that the transforming growth factor beta signaling pathway was significantly enriched in some brain regions and HDAC1 played an important role in this pathway.

SIGNIFICANCE

We found the glial-specific 3'UTR of HDAC1 was hypermethylated and HDAC1 was overexpressed in AD patients. Moreover, we also speculate that HDAC1 triggered signaling pathways linked to many different biological processes and functions via the regulation of histone deacetylation.

Identification of the Potential Key Long Non-coding RNAs in Aged Mice With Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a significant complication of surgery, particularly in elderly patients. Emerging researches showed that long non-coding RNA (lncRNA) may play a vital role in the pathogenesis of POCD. Here we aimed to identify potential key lncRNAs involved in the development of POCD. LncRNA and mRNA expression profiles in hippocampal tissues from POCD and control mice were analyzed by microarray assay. Gene ontology (GO) and KEGG pathway enrichment analyses were conducted to probe the functions of dysregulated genes. Then, important factors of the mainly affected biological processes were measured in the hippocampus. Correlated coding–non-coding co-expression (CNC) networks were constructed. Finally, the potential key pairs of lncRNA and target mRNA implicated in POCD were probed. Our data showed that 868 differentially expressed lncRNAs and 690 differentially expressed mRNAs were identified in total. GO and KEGG analyses indicated that the differentially expressed genes were mainly associated with inflammatory and apoptotic signaling pathways. Surgery-induced inflammatory cytokines and apoptosis were significantly increased in hippocampal tissues of aged mice. In CNC network analysis, we found that LncRNA uc009qbj.1 was positively correlated with apoptosis-associated gene Vrk2 level. LncRNA ENSMUST00000174338 correlated positively with expression of the inflammation and apoptosis-associated gene Smad7. LncRNA NONMMUT00000123687 mediated gene expression by binding the inflammation-regulated transcription factor Meis2. Our results suggested that these potential key lncRNAs and mRNAs may play a crucial role in the development of POCD through mediating neuronal inflammation or apoptosis.

Identification of the Potential Key Long Non-coding RNAs in Aged Mice With Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a significant complication of surgery, particularly in elderly patients. Emerging researches showed that long non-coding RNA (lncRNA) may play a vital role in the pathogenesis of POCD. Here we aimed to identify potential key lncRNAs involved in the development of POCD. LncRNA and mRNA expression profiles in hippocampal tissues from POCD and control mice were analyzed by microarray assay. Gene ontology (GO) and KEGG pathway enrichment analyses were conducted to probe the functions of dysregulated genes. Then, important factors of the mainly affected biological processes were measured in the hippocampus. Correlated coding-non-coding co-expression (CNC) networks were constructed. Finally, the potential key pairs of lncRNA and target mRNA implicated in POCD were probed. Our data showed that 868 differentially expressed lncRNAs and 690 differentially expressed mRNAs were identified in total. GO and KEGG analyses indicated that the differentially expressed genes were mainly associated with inflammatory and apoptotic signaling pathways. Surgery-induced inflammatory cytokines and apoptosis were significantly increased in hippocampal tissues of aged mice. In CNC network analysis, we found that LncRNA uc009qbj.1 was positively correlated with apoptosis-associated gene Vrk2 level. LncRNA ENSMUST00000174338 correlated positively with expression of the inflammation and apoptosis-associated gene Smad7. LncRNA NONMMUT00000123687 mediated gene expression by binding the inflammation-regulated transcription factor Meis2. Our results suggested that these potential key lncRNAs and mRNAs may play a crucial role in the development of POCD through mediating neuronal inflammation or apoptosis.

The role of TGF-β superfamily signaling in neurological disorders

The TGF-β superfamily signaling is involved in a variety of biological processes during embryogenesis and in adult tissue homeostasis. Faulty regulation of the signaling pathway that transduces the TGF-β superfamily signals accordingly leads to a number of ailments, such as cancer and cardiovascular, metabolic, urinary, intestinal, skeletal, and immune diseases. In recent years, a number of studies have elucidated the essential roles of TGF-βs and BMPs during neuronal development in the maintenance of appropriate innervation and neuronal activity. The new advancement implicates significant roles of the aberrant TGF-β superfamily signaling in the pathogenesis of neurological disorders. In this review, we compile a number of reports implicating the deregulation of TGF-β/BMP signaling pathways in the pathogenesis of cognitive and neurodegenerative disorders in animal models and patients. We apologize in advance that the review falls short of providing details of the role of TGF-β/BMP signaling or mechanisms underlying the pathogenesis of neurological disorders. The goal of this article is to reveal a gap in our knowledge regarding the association between TGF-β/BMP signaling pathways and neuronal tissue homeostasis and development and facilitate the research with a potential to develop new therapies for neurological ailments by modulating the pathways.

Let's make microglia great again in neurodegenerative disorders

All of the common neurodegenerative disorders-Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and prion diseases-are characterized by accumulation of misfolded proteins that trigger activation of microglia; brain-resident mononuclear phagocytes. This chronic form of neuroinflammation is earmarked by increased release of myriad cytokines and chemokines in patient brains and biofluids. Microglial phagocytosis is compromised early in the disease process, obfuscating clearance of abnormal proteins. This review identifies immune pathologies shared by the major neurodegenerative disorders. The overarching concept is that aberrant innate immune pathways can be targeted for return to homeostasis in hopes of coaxing microglia into clearing neurotoxic misfolded proteins.

Single-Base Resolution Mapping of 5-Hydroxymethylcytosine Modifications in Hippocampus of Alzheimer's Disease Subjects

Epigenetic modifications to cytosine have been shown to regulate transcription in cancer, embryonic development, and recently neurodegeneration. While cytosine methylation studies are now common in neurodegenerative research, hydroxymethylation studies are rare, particularly genome-wide mapping studies. As an initial study to analyze 5-hydroxymethylcytosine (5-hmC) in the Alzheimer's disease (AD) genome, reduced representation hydroxymethylation profiling (RRHP) was used to analyze more than 2 million sites of possible modification in hippocampal DNA of sporadic AD and normal control subjects. Genes with differentially hydroxymethylated regions were filtered based on previously published microarray data for altered gene expression in hippocampal DNA of AD subjects. Our data show significant pathways for altered levels of 5-hmC in the hippocampus of AD subjects compared to age-matched normal controls involved in signaling, energy metabolism, cell function, gene expression, protein degradation, and cell structure and stabilization. Overall, our data suggest a possible role for the dysregulation of epigenetic modifications to cytosine in late stage AD.

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCTION

Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease.

DEVELOPMENT

Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF.

CONCLUSIONS

iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

Dynamic self-guiding analysis of Alzheimer's disease

We applied a self-guiding evolutionary algorithm to initiate the synthesis of the Alzheimer's disease-related data and literature. A protein interaction network associated with amyloid-beta precursor protein (APP) and a seed model that treats Alzheimer's disease as progressive dysregulation of APP-associated signaling were used as dynamic “guides” and structural “filters” in the recursive search, analysis, and assimilation of data to drive the evolution of the seed model in size, detail, and complexity. Analysis of data and literature across sub-disciplines and system-scale discovery platforms suggests a key role of dynamic cytoskeletal connectivity in the stability, plasticity, and performance of multicellular networks and architectures. Chronic impairment and/or dysregulation of cell adhesions/synapses, cytoskeletal networks, and/or reversible epithelial-to-mesenchymal-like transitions, which enable and mediate the stable and coherent yet dynamic and reconfigurable multicellular architectures, may lead to the emergence and persistence of the disordered, wound-like pockets/microenvironments of chronically disconnected cells. Such wound-like microenvironments support and are supported by pro-inflammatory, pro-secretion, de-differentiated cellular phenotypes with altered metabolism and signaling. The co-evolution of wound-like microenvironments and their inhabitants may lead to the selection and stabilization of degenerated cellular phenotypes, via acquisition of epigenetic modifications and mutations, which eventually result in degenerative disorders such as cancer and Alzheimer's disease.

Signaling pathways regulating neuron-glia interaction and their implications in Alzheimer's disease

Astrocytes are the most abundant cells in the central nervous system. They play critical roles in neuronal homeostasis through their physical properties and neuron-glia signaling pathways. Astrocytes become reactive in response to neuronal injury and this process, referred to as reactive astrogliosis, is a common feature accompanying neurodegenerative conditions, particularly Alzheimer's disease. Reactive astrogliosis represents a continuum of pathobiological processes and is associated with morphological, functional, and gene expression changes of varying degrees. There has been a substantial growth of knowledge regarding the signaling pathways regulating glial biology and pathophysiology in recent years. Here, we attempt to provide an unbiased review of some of the well-known players, namely calcium, proteoglycan, transforming growth factor β, NFκB, and complement, in mediating neuron-glia interaction under physiological conditions as well as in Alzheimer's disease. This review discusses the role of astrocytic NFκB and calcium as well as astroglial secreted factors, including proteoglycans, TGFβ, and complement in mediating neuronal function and AD pathogenesis through direct interaction with neurons and through cooperation with microglia.

Trafficking protein particle complex 6A delta (TRAPPC6AΔ) is an extracellular plaque-forming protein in the brain

Tumor suppressor WWOX is involved in the progression of cancer and neurodegeneration. Here, we examined whether protein aggregation occurs in the brain of nondemented, middle-aged humans and whether this is associated with WWOX downregulation. We isolated an N-terminal internal deletion isoform, TPC6AΔ, derived from alternative splicing of the TRAPPC6A (TPC6A) gene transcript. TPC6AΔ proteins are present as aggregates or plaques in the extracellular matrix of the brain such as in the cortex. Filter retardation assays revealed that aggregate formation of TPC6AΔ occurs preceding Aβ generation in the hippocampi of middle-aged postmortem normal humans. In a Wwox gene knockout mouse model, we showed the plaques of pT181-Tau and TPC6AΔ in the cortex and hippocampus in 3-week-old mice, suggesting a role of WWOX in limiting TPC6AΔ aggregation. To support this hypothesis, in vitro analysis revealed that TGF-β1 induces dissociation of the ectopic complex of TPC6AΔ and WWOX in cells, and then TPC6AΔ undergoes Ser35 phosphorylation-dependent polymerization and induces caspase 3 activation and Aβ production. Similarly, knockdown of WWOX by siRNA resulted in dramatic aggregation of TPC6AΔ. Together, when WWOX is downregulated, TPC6AΔ is phosphorylated at Ser35 and becomes aggregated for causing caspase activation that leads to Tau aggregation and Aβ formation.

Effects of piceatannol and pterostilbene against β-amyloid-induced apoptosis on the PI3K/Akt/Bad signaling pathway in PC12 cells

Piceatannol and pterostilbene both showed protective effect against Aβ-induced apoptosis in PC12 cells, however, with different PI3K/Akt signaling pathways.

WWOX dysfunction induces sequential aggregation of TRAPPC6AΔ, TIAF1, tau and amyloid β, and causes apoptosis

Aggregated vesicle-trafficking protein isoform TRAPPC6AΔ (TPC6AΔ) has a critical role in causing caspase activation, tau aggregation and Aβ generation in the brains of nondemented middle-aged humans, patients with Alzheimer's disease (AD) and 3-week-old Wwox gene knockout mice. WWOX blocks neurodegeneration via interactions with tau and tau-phosphorylating enzymes. WWOX deficiency leads to epilepsy, mental retardation and early death. Here, we demonstrated that TGF-β1 induces shuttling of endogenous wild-type TPC6A and TPC6AΔ in between nucleoli and mitochondria (~40-60 min per round trip), and WWOX reduces the shuttling time by 50%. TGF-β1 initially maximizes the binding of TPC6AΔ to the C-terminal tail of WWOX, followed by dissociation. TPC6AΔ then undergoes aggregation, together with TIAF1 (TGF-β1-induced antiapoptotic factor), in the mitochondria to induce apoptosis. An additional rescue scenario is that TGF-β1 induces Tyr33 phosphorylation and unfolding of WWOX and its the N-terminal WW domain slowly binds TPC6AΔ to block aggregation and apoptosis. Similarly, loss of WWOX induces TPC6AΔ polymerization first, then aggregation of TIAF1, amyloid β and tau, and subsequent cell death, suggesting that a cascade of protein aggregation leads to neurodegeneration.

Distinctive RNA expression profiles in blood associated with Alzheimer disease after accounting for white matter hyperintensities

BACKGROUND

Defining the RNA transcriptome in Alzheimer Disease (AD) will help understand the disease mechanisms and provide biomarkers. Though the AD blood transcriptome has been studied, effects of white matter hyperintensities (WMH) were not considered. This study investigated the AD blood transcriptome and accounted for WMH.

METHODS

RNA from whole blood was processed on whole-genome microarrays.

RESULTS

A total of 293 probe sets were differentially expressed in AD versus controls, 5 of which were significant for WMH status. The 288 AD-specific probe sets classified subjects with 87.5% sensitivity and 90.5% specificity. They represented 188 genes of which 29 have been reported in prior AD blood and 89 in AD brain studies. Regulated blood genes included MMP9, MME (Neprilysin), TGFβ1, CA4, OCLN, ATM, TGM3, IGFR2, NOV, RNF213, BMX, LRRN1, CAMK2G, INSR, CTSD, SORCS1, SORL1, and TANC2.

CONCLUSIONS

RNA expression is altered in AD blood irrespective of WMH status. Some genes are shared with AD brain.

TGF-β1 protection against Aβ1-42-induced neuroinflammation and neurodegeneration in rats

Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, is a key regulator of the brain's responses to injury and inflammation. Alzheimer's disease (AD), the most common neurodegenerative disorder, involves inflammatory processes in the brain in addition to the hallmarks, amyloid-β (Aβ) plaques and neurofibrillary tangles. Recently, we have shown that T-helper (Th) 17 cells, a subpopulation of CD4+ T-cells with high proinflammation, also participate in the brain inflammatory process of AD. However, it is poorly known whether TGF-β1 ameliorates the lymphocyte-mediated neuroinflammation and, thereby, alleviates neurodegeneration in AD. Herein, we administered TGF-β1 via the intracerebroventricle (ICV) in AD model rats, by Aβ1-42 injection in both sides of the hippocampus, to show the neuroprotection of TGF-β1. The TGF-β1 administration after the Aβ1-42 injection ameliorated cognitive deficit and neuronal loss and apoptosis, reduced amyloid precursor protein (APP) expression, elevated protein phosphatase (PP)2A expression, attenuated glial activation and alleviated the imbalance of the pro-inflammatory/anti-inflammatory responses of T-lymphocytes, compared to the Aβ1-42 injection alone. These findings demonstrate that TGF-β1 provides protection against AD neurodegeneration and suggest that the TGF-β1 neuroprotection is implemented by the alleviation of glial and T-cell-mediated neuroinflammation.

The role of the immune system in neurodegenerative disorders: Adaptive or maladaptive?

Neurodegenerative diseases share common features, including catastrophic neuronal loss that leads to cognitive or motor dysfunction. Neuronal injury occurs in an inflammatory milieu that is populated by resident and sometimes, infiltrating, immune cells - all of which participate in a complex interplay between secreted inflammatory modulators and activated immune cell surface receptors. The importance of these immunomodulators is highlighted by the number of immune factors that have been associated with increased risk of neurodegeneration in recent genome-wide association studies. One of the more difficult tasks for designing therapeutic strategies for immune modulation against neurodegenerative diseases is teasing apart beneficial from harmful signals. In this regard, learning more about the immune components of these diseases has yielded common themes. These unifying concepts should eventually enable immune-based therapeutics for treatment of Alzheimer׳s and Parkinson׳s diseases and amyotrophic lateral sclerosis. Targeted immune modulation should be possible to temper maladaptive factors, enabling beneficial immune responses in the context of neurodegenerative diseases. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Innate immunity in Alzheimer's disease: a complex affair

Alzheimer's disease (AD) is characterized by three major histopathological hallmarks: β-amyloid deposits, neurofibrillary tangles and gliosis. While neglected for decades, the neuroinflammatory processes coordinated by microglia are now accepted as etiologic events in AD evolution. Microglial cells are found in close vicinity to amyloid plaques and display various activation phenotypes determined by the expression of a wide range of cytokines, chemokines, and innate immune surface receptors. During the development of AD pathology, microglia fail to restrict amyloid plaques and may contribute to neurotoxicity and cognitive deficit. Nevertheless, under specific activation states, microglia can participate in cerebral amyloid clearance. This review focuses on the complex relationship between microglia and Aβ pathology, and highlights both deleterious and beneficial roles of microglial activation states in the context of AD. A deeper understanding of microglial biology will hopefully pave the way for next-generation AD therapeutic approaches aimed at harnessing these enigmatic innate immune cells of the central nervous system.

Serrapeptase and nattokinase intervention for relieving Alzheimer's disease pathophysiology in rat model

Serrapeptase (SP) and nattokinase (NK) are proteolytic enzymes belonging to serine proteases. In this study, we hypothesized that SP and NK could modulate certain factors that are associated with Alzheimer's disease (AD) pathophysiology in the experimental model. Oral administration of aluminium chloride (AlCl3) in a dose of 17 mg/kg body weight (bw) daily for 45 days induced AD-like pathology in male rats with a significant increase in brain acetylcholinesterase (AchE) activity, transforming growth factor β (TGF-β), Fas and interleukin-6 (IL-6) levels. Meanwhile, AlCl3 supplementation produced significant decrease in brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1) when compared with control values. Also, AlCl3 administration caused significant decline in the expression levels of disintegrin and metalloproteinase domain 9 (ADAM9) and a disintegrin and metalloproteinase domain 10 (ADAM10) genes in the brain. Histological investigation of brain tissue of rat model of AD showed neuronal degeneration in the hippocampus and focal hyalinosis with cellular as well as a cellular amyloid plaques formation. Oral administration of SP or NK in a rat model of AD daily for 45 days resulted in a significant decrease in brain AchE activity, TGF-β, Fas and IL-6 levels. Also, the treatment with these enzymes produced significant increase in BDNF and IGF-1 levels when compared with the untreated AD-induced rats. Moreover, both SP and NK could markedly increase the expression levels of ADAM9 and ADAM10 genes in the brain tissue of the treated rats. These findings were well confirmed by the histological examination of the brain tissue of the treated rats. The present results support our hypothesis that the oral administration of proteolytitc enzymes, SP and/or NK, would have an effective role in modulating certain factors characterizing AD. Thus, these enzymes may have a therapeutic application in the treatment of AD.

Neurotrophins role in depression neurobiology: a review of basic and clinical evidence

Depression is a neuropsychiatric disorder affecting a huge percentage of the active population especially in developed countries. Research has devoted much of its attention to this problematic and many drugs have been developed and are currently prescribed to treat this pathology. Yet, many patients are refractory to the available therapeutic drugs, which mainly act by increasing the levels of the monoamines serotonin and noradrenaline in the synaptic cleft. Even in the cases antidepressants are effective, it is usually observed a delay of a few weeks between the onset of treatment and remission of the clinical symptoms. Additionally, many of these patients who show remission with antidepressant therapy present a relapse of depression upon treatment cessation. Thus research has focused on other possible molecular targets, besides monoamines, underlying depression. Both basic and clinical evidence indicates that depression is associated with several structural and neurochemical changes where the levels of neurotrophins, particularly of brain-derived neurotrophic factor (BDNF), are altered. Antidepressants, as well as other therapeutic strategies, seem to restore these levels. Neuronal atrophy, mostly detected in limbic structures that regulate mood and cognition, like the hippocampus, is observed in depressed patients and in animal behavioural paradigms for depression. Moreover, chronic antidepressant treatment enhances adult hippocampal neurogenesis, supporting the notion that this event underlies antidepressants effects. Here we review some of the preclinical and clinical studies, aimed at disclosing the role of neurotrophins in the pathophysiological mechanisms of depression and the mode of action of antidepressants, which favour the neurotrophic/neurogenic hypothesis.

Clearance of amyloid-β peptides by microglia and macrophages: the issue of what, when and where

Accumulation of senile plaques consisting of amyloid-β peptide (Aβ) aggregates is a prominent pathological feature in Alzheimer's disease. Effective clearance of Aβ from the brain parenchyma is thought to regulate the development and progression of the disease. Macrophages in the brain play an important role in Aβ clearance by a variety of phagocytic and digestive mechanisms. Subpopulations of macrophages are heterogeneous such that resident microglia in the parenchyma, blood macrophages infiltrating from the periphery, and perivascular macrophages residing along cerebral vessels make functionally distinct contributions to Aβ clearance. Despite phenotypic similarities between the different macrophage subsets, a series of in vivo models have been derived to differentiate their relative impacts on Aβ dynamics as well as the molecular mechanisms underlying their activities. This review discusses the key findings from these models and recent research efforts to selectively enhance macrophage clearance of Aβ.

The effects of apolipoproteins E3 and E4 on the transforming growth factor-β system in targeted replacement mice

BACKGROUND

This study examined the possibility that apolipoprotein E4 (apoE4), the most prevalent genetic risk factor of Alzheimer's disease, interacts isoform specifically with the transforming growth factor (TGF)-β system.

METHODS

This was pursued by measurements of the effects of apoE3 and apoE4 on the levels of TGF-β ligands and on activation of the Smad system in brains of human apoE targeted replacement mice, utilizing Western blot.

RESULTS

The study revealed that apoE4 reduces, isoform specifically, the levels of TGF-β(1), TGF-β(2) and TGF-β(3) in the septum and of TGF-β(3) in the hippocampus. In contrast, the levels and extent of phosphorylation of Smad1, 5 and 8 as well as of Smad2 and Smad3 in these brain areas were not affected by apoE4, suggesting that the apoE4-driven effects on the TGF-β system may be mediated via the Smad-independent non-canonical pathway.

CONCLUSION

The possible role of the TGF-β system in mediating the pathological effects of apoE4 is discussed.

Neurovascular function in Alzheimer's disease patients and experimental models

The ability of the brain to locally augment glucose delivery and blood flow during neuronal activation, termed neurometabolic and neurovascular coupling, respectively, is compromised in Alzheimer's disease (AD). Since perfusion deficits may hasten clinical deterioration and have been correlated with negative treatment outcome, strategies to improve the cerebral circulation should form an integral element of AD therapeutic efforts. These efforts have yielded several experimental models, some of which constitute AD models proper, others which specifically recapture the AD cerebrovascular pathology, characterized by anatomical alterations in brain vessel structure, as well as molecular changes within vascular smooth muscle cells and endothelial cells forming the blood-brain barrier. The following paper will present the elements of AD neurovascular dysfunction and review the in vitro and in vivo model systems that have served to deepen our understanding of it. It will also critically evaluate selected groups of compounds, the FDA-approved cholinesterase inhibitors and thiazolidinediones, for their ability to correct neurovascular dysfunction in AD patients and models. These and several others are emerging as compounds with pleiotropic actions that may positively impact dysfunctional cerebrovascular, glial, and neuronal networks in AD.

Smad7: not only a regulator, but also a cross-talk mediator of TGF-β signalling

TGF-β (transforming growth factor-β) is a pleiotropic cytokine regulating diverse cellular processes. It signals through membrane-bound receptors, downstream Smad proteins and/or other signalling mediators. Smad7 has been well established to be a key negative regulator of TGF-β signalling. It antagonizes TGF-β signalling through multiple mechanisms in the cytoplasm and in the nucleus. Smad7 can be transcriptionally induced by TGF-β and other growth factors and serves as an important cross-talk mediator of the TGF-β signalling pathway with other signalling pathways. Accordingly, it plays pivotal roles in embryonic development and adult homoeostasis, and altered expression of Smad7 is often associated with human diseases, such as cancer, tissue fibrosis and inflammatory diseases.

Intact memory in TGF-β1 transgenic mice featuring chronic cerebrovascular deficit: recovery with pioglitazone

The roles of chronic brain hypoperfusion and transforming growth factor-beta 1 (TGF-β1) in Alzheimer's disease (AD) are unresolved. We investigated the interplay between TGF-β1, cerebrovascular function, and cognition using transgenic TGF mice featuring astrocytic TGF-β1 overexpression. We further assessed the impact of short, late therapy in elderly animals with the antioxidant N-acetyl-L-cysteine (NAC) or the peroxisome proliferator-activated receptor-γ agonist pioglitazone. The latter was also administered to pups as a prophylactic 1-year treatment. Elderly TGF mice featured cerebrovascular dysfunction that was not remedied with NAC. In contrast, pioglitazone prevented or reversed this deficit, and rescued the impaired neurovascular coupling response to whisker stimulation, although it failed to normalize the vascular structure. In aged TGF mice, neuronal and cognitive indices--the stimulus-evoked neurometabolic response, cortical cholinergic innervation, and spatial memory in the Morris water maze--were intact. Our findings show that impaired brain hemodynamics and cerebrovascular function are not accompanied by memory impairment in this model. Conceivably in AD, they constitute aggravating factors against a background of aging and underlying pathology. Our data further highlight the ability of pioglitazone to protect the cerebrovasculature marked by TGF-β1 increase, aging, fibrosis, and antioxidant resistance, thus of high relevance for AD patients.

TGF-β induces TIAF1 self-aggregation via type II receptor-independent signaling that leads to generation of amyloid β plaques in Alzheimer's disease

The role of a small transforming growth factor beta (TGF-β)-induced TIAF1 (TGF-β1-induced antiapoptotic factor) in the pathogenesis of Alzheimer's disease (AD) was investigated. TIAF1 physically interacts with mothers against DPP homolog 4 (Smad4), and blocks SMAD-dependent promoter activation when overexpressed. Accordingly, knockdown of TIAF1 by small interfering RNA resulted in spontaneous accumulation of Smad proteins in the nucleus and activation of the promoter governed by the SMAD complex. TGF-β1 and environmental stress (e.g., alterations in pericellular environment) may induce TIAF1 self-aggregation in a type II TGF-β receptor-independent manner in cells, and Smad4 interrupts the aggregation. Aggregated TIAF1 induces apoptosis in a caspase-dependent manner. By filter retardation assay, TIAF1 aggregates were found in the hippocampi of nondemented humans and AD patients. Total TIAF1-positive samples containing amyloid β (Aβ) aggregates are 17 and 48%, respectively, in the nondemented and AD groups, suggesting that TIAF1 aggregation occurs preceding formation of Aβ. To test this hypothesis, in vitro analysis showed that TGF-β-regulated TIAF1 aggregation leads to dephosphorylation of amyloid precursor protein (APP) at Thr668, followed by degradation and generation of APP intracellular domain (AICD), Aβ and amyloid fibrils. Polymerized TIAF1 physically interacts with amyloid fibrils, which would favorably support plaque formation in vivo.

Transgenic mice overexpressing APP and transforming growth factor-beta1 feature cognitive and vascular hallmarks of Alzheimer's disease

High brain levels of amyloid-β (Aβ) and transforming growth factor-β1 (TGF-β1) have been implicated in the cognitive and cerebrovascular alterations of Alzheimer's disease (AD). We sought to investigate the impact of combined increases in Aβ and TGF-β1 on cerebrovascular, neuronal, and mnemonic function using transgenic mice overproducing these peptides (A/T mice). In particular, we measured cerebrovascular reactivity, evoked cerebral blood flow and glucose uptake during brain activation, cholinergic status, and spatial memory, along with cerebrovascular fibrosis, amyloidosis, and astrogliosis, and their evolution with age. An assessment of perfusion and metabolic responses was considered timely, given ongoing efforts for their validation as AD biomarkers. Relative to wild-type littermates, A/T mice displayed an early progressive decline in cerebrovascular dilatory ability, preserved contractility, and reduction in constitutive nitric oxide synthesis that establishes resting vessel tone. Altered levels of vasodilator-synthesizing enzymes and fibrotic proteins, resistance to antioxidant treatment, and unchanged levels of the antioxidant enzyme, superoxide dismutase-2, accompanied these impairments. A/T mice featured deficient neurovascular and neurometabolic coupling to whisker stimulation, cholinergic denervation, cerebral and cerebrovascular Aβ deposition, astrocyte activation, and impaired Morris water maze performance, which gained severity with age. The combined Aβ- and TGF-β1-driven pathology recapitulates salient cerebrovascular, neuronal, and cognitive AD landmarks and yields a versatile model toward highly anticipated diagnostic and therapeutic tools for patients featuring Aβ and TGF-β1 increments.

Concerted changes in transcripts in the prefrontal cortex precede neuropathology in Alzheimer's disease

Using the Braak staging for neurofibrillary changes as an objective indicator of the progression of Alzheimer's disease, we have performed a systematic search for global gene expression changes in the prefrontal cortex during the course of Alzheimer's disease. In the prefrontal cortex, senile plaques and neurofibrillary changes start to appear around Braak stage III, allowing for the detection of changes in gene expression before, during and after the onset of Alzheimer's disease neuropathology. Two distinct patterns of tightly co-regulated groups of genes were observed: (i) an increase in expression in early Braak stages, followed by a decline in expression in later stages (the UPDOWN clusters; containing 865 genes) and (ii) a decrease in expression in early Braak stages, followed by an increase in expression in later stages (the DOWNUP clusters; containing 983 genes). The most profound changes in gene expression were detected between Braak stages II and III, just before or at the onset of plaque pathology and neurofibrillary changes in the prefrontal cortex. We also observed an increase in intracellular beta amyloid staining from Braak stages I to III and a clear decrease in Braak stages IV to VI. These data suggest a link between specific gene expression clusters and Alzheimer's disease-associated neuropathology in the prefrontal cortex. Gene ontology over-representation and functional gene network analyses indicate an increase in synaptic activity and changes in plasticity during the very early pre-symptomatic stage of the disease. In later Braak stages, the decreased expression of these genes suggests a reduction in synaptic activity that coincides with the appearance of plaque pathology and neurofibrillary changes and the clinical diagnosis of mild cognitive impairment. The interaction of the ApoE genotype with the expression levels of the genes in the UPDOWN and DOWNUP clusters demonstrates that the accelerating role of ApoE-ε4 in the progression of Alzheimer's disease is reflected in the temporal changes in gene expression presented here. Since the UPDOWN cluster contains several genes involved in amyloid precursor protein processing and beta amyloid clearance that increase in expression in parallel with increased intracellular beta amyloid load, just before the onset of plaque pathology in the prefrontal cortex, we hypothesize that the temporally orchestrated increase in genes involved in synaptic activity represents a coping mechanism against increased soluble beta amyloid levels. As these gene expression changes occur before the appearance of Alzheimer's disease-associated neuropathology, they provide an excellent starting point for the identification of new targets for the development of therapeutic strategies aimed at the prevention of Alzheimer's disease.

miR-106b aberrantly expressed in a double transgenic mouse model for Alzheimer's disease targets TGF-β type II receptor

MicroRNAs (miRNAs) are abundantly expressed in the brain and play an important role in disorders of the brain, including Alzheimer's diseases (AD). Growing body of evidence suggests that the TGF-β signaling pathway plays a key role in the pathogenesis of AD. However, it is unclear whether miRNAs involved in AD pathogenesis by regulating TGF-β signaling. Here we found that miR-106b and TGF-β type II receptor (TβR II) were aberrantly expressed in APPswe/PS∆E9 mice (a double transgenic mouse model for AD). Sequence analysis revealed two putative binding sites for miR-106b in the 3' UTR of the TβR II mRNA. Our results showed that the expression of miR-106b was inversely correlated with TβR II protein levels and miR-106b can directly inhibit the TβR II translation in vitro. After induced neurodifferentiation with all-trans retinoic acid, we observed significant neurodegeneration in SH-SY5Y cells stably transfected with miR-106b. Western blot analysis revealed unchanged total Smad2/3 protein levels, but reduced phospho-Smad2/3 (p-Smad2/3) and increased Smad6/7 protein levels in the miR-106b stably transfected cell line. Exposure of SH-SY5Y cells to Aβ42 oligomers led to the expression of miR-106b was first increased and then decreased and TβR II levels reduced. Our in vitro results suggested that Aβ42 oligomer-induced miR-106b leads to impairment in TGF-β signaling through TβR II, concomitant with retinoic acid-induced neurodegeneration in SH-SY5Y cells. These results show that TβR II is a functional target of miR-106b and that miR-106b may influence TGF-β signaling, thereby contributing to the pathogenesis of AD.

Phospholipase A2 and arachidonic acid in Alzheimer's disease

Essential fatty acids (EFA) play a critical role in the brain and regulate many of the processes altered in Alzheimer's disease (AD). Technical advances are allowing for the dissection of complex lipid pathways in normal and diseased states. Arachidonic acid (AA) and specific isoforms of phospholipase A(2) (PLA(2)) appear to be critical mediators in amyloid-beta (Abeta)-induced pathogenesis, leading to learning, memory, and behavioral impairments in mouse models of AD. These findings and ongoing research into lipid biology in AD and related disorders promise to reveal new pharmacological targets that may lead to better treatments for these devastating conditions.

Genetic predisposition to inflammation: a new risk factor of Alzheimer's disease

Inflammation has been shown to play an important role in the progression of Alzheimer's disease (AD). Recent epidemical study indicates that the incidence of AD in some populations is substantially influenced by the gene polymorphisms of the inflammation mediators. Meanwhile, an ensured risk factor, the ApoE epsilon4 allele is also reported to directly promote inflammation. Accordingly, it appears that an individual genetic background has partly determined his predisposition for AD by the extent of the inflammation response to the chronic stimulus by beta-amyloid peptide (Abeta) deposits and other antigen stressor in the elderly. Hence we present a hypothesis that the inflammation genotypes may contribute to AD susceptibility. This may provide a new orientation both for future identification of individuals at risk and for personalized medication.