TGF-beta 1 protects against Abeta-neurotoxicity via the phosphatidylinositol-3-kinase pathway

MicroRNA-455-3P as a peripheral biomarker and therapeutic target for mild cognitive impairment and Alzheimer's disease

MicroRNAs are small non-coding RNAs evolutionary conserved molecules. They regulate cellular processes, including RNA silencing, post-translational gene expression and neurodegeneration. MicroRNAs are involved with human diseases such as cancer, Alzheimer's disease (AD) and others. Interestingly, cerebrospinal fluids (CSF) and the blood of AD patients have altered expressions of many RNAs, which may serve as potential peripheral biomarkers. The intensive investigation from our lab revealed that microRNA-455-3 P (miR-455-3p) is a strong candidate as a potential biomarker and therapeutic target for AD. Several genes implicated in the pathogenesis of AD are directly targeted by miR-455-3p. Several years of our lab research revealed that miR-455-3p regulates important physiological processes associated with AD, such as the processing of the amyloid precursor protein (APP), TGF-β signaling, the regulation of oxidative stress, mitochondrial biogenesis, and synaptic damages. The expression of miR-455-3p in mild cognitive impaired subjects and AD patients pointed out its involvement in AD progression. Recently, our lab generated both transgenic and knockout mice for miR-455-3p. Interestingly miR-455-3p transgenic mice showed superior cognitive learning, improved memory and extended lifespan compared to age matched wild-type mice, whereas miR-455-3-p knockout mice showed cognitive decline and reduced lifespan. Information derived from mouse models further demonstrated the advantageous impact of miR-455-3p on dendritic growth, synaptogenesis, and mitochondrial biogenesis in preventing the onset and progression of AD. The identification of miR-455-3p as a biomarker was suggested by its presence in postmortem AD brains, B-lymphocytes, and fibroblasts. Our hypothesis that miR-455-3p could be a peripheral biomarker and therapeutic target for AD.

Specific exercise patterns generate an epigenetic molecular memory window that drives long-term memory formation and identifies ACVR1C as a bidirectional regulator of memory in mice

Exercise has beneficial effects on cognition throughout the lifespan. Here, we demonstrate that specific exercise patterns transform insufficient, subthreshold training into long-term memory in mice. Our findings reveal a potential molecular memory window such that subthreshold training within this window enables long-term memory formation. We performed RNA-seq on dorsal hippocampus and identify genes whose expression correlate with conditions in which exercise enables long-term memory formation. Among these genes we found Acvr1c, a member of the TGF ß family. We find that exercise, in any amount, alleviates epigenetic repression at the Acvr1c promoter during consolidation. Additionally, we find that ACVR1C can bidirectionally regulate synaptic plasticity and long-term memory in mice. Furthermore, Acvr1c expression is impaired in the aging human and mouse brain, as well as in the 5xFAD mouse model, and over-expression of Acvr1c enables learning and facilitates plasticity in mice. These data suggest that promoting ACVR1C may protect against cognitive impairment.

Low TGF-β1 plasma levels are associated with cognitive decline in Down syndrome

Almost all individuals with Down's syndrome (DS) show the characteristic neuropathological features of Alzheimer's disease (AD) by the age of 40, yet not every individual with DS experiences symptoms of AD later in life. Similar to neurotypical developing subjects, AD in people with DS lasts for a long preclinical phase in which biomarkers follow a predictable order of changes. Hence, a prolonged asymptomatic period precedes the onset of dementia, underscoring the importance of identifying new biomarkers for the early detection and monitoring of cognitive decline in individuals with DS. Blood-based biomarkers may offer an alternative non-invasive strategy for the detection of peripheral biological alterations paralleling nervous system pathology in an early phase of the AD continuum. In the last few years, a strong neurobiological link has been demonstrated between the deficit of transforming growth factor-β1 (TGF-β1) levels, an anti-inflammatory cytokine endowed with neuroprotective activity, and early pro-inflammatory processes in the AD brain. In this clinical prospective observational study, we found significant lower plasma TGF-β1 concentrations at the first neuropsychological evaluation (baseline = T0) both in young adult DS individuals (19-35 years) and older DS subjects without AD (35-60 years) compared to age- and sex-matched healthy controls. Interestingly, we found that the lower TGF-β1 plasma concentrations at T0 were strongly correlated with the following cognitive decline at 12 months. In addition, in young individuals with DS, we found, for the first time, a negative correlation between low TGF-β1 concentrations and high TNF-α plasma concentrations, a pro-inflammatory cytokine that is known to be associated with cognitive impairment in DS individuals with AD. Finally, adopting an ex vivo approach, we found that TGF-β1 concentrations were reduced in parallel both in the plasma and in the peripheral blood mononuclear cells (PBMCs) of DS subjects, and interestingly, therapeutic concentrations of fluoxetine (FLX) applied to cultured PBMCs (1 µM for 24 h) were able to rescue TGF-β1 concentrations in the culture media from DS PBMCs, suggesting that FLX, a selective serotonin reuptake inhibitor (SSRI) endowed with neuroprotective activity, might rescue TGF-β1 concentrations in DS subjects at higher risk to develop cognitive decline.

The role of transforming growth factor β1 /Smad pathway in Alzheimer's disease inflammation pathology

Alzheimer's disease (AD), a progressive disorder, has become a global health problem and is now the main cause of dementia. The aetiology of AD is complex and remains elusive making effective AD treatment difficult. Current drugs for AD only improve symptoms but do not interfere with pathogenic mechanisms. Three main hypotheses have been brought forward regarding AD aetiology, one of them being the 'inflammation hypothesis'. A number of studies have demonstrated that inflammation plays a critical role in AD. Self-limiting neuroinflammation is considered beneficial to AD, whereas chronic inflammation aggravates brain injury and neuronal death. Transforming growth factor β 1(TGF-β1) is an anti-inflammatory cytokine with neuroprotective properties. Smad proteins are downstream molecules of TGF-β signalling. They are cytoplasmic transcription factors that can regulate targeted gene expression. In AD, impairments of TGF-β1/Smad pathways have been observed. Moreover, microglia, astrocytes, inflammasomes, and insulin resistance also have been implicated in AD pathogenesis. Elucidating the molecular mechanisms underlying AD pathogenesis is a fundamental step toward designing new treatment options. In this review, we detail the changes in TGF-β1/Smad pathways in AD and hope this will facilitate further research on AD treatment.

Microglia in the Neuroinflammatory Pathogenesis of Alzheimer's Disease and Related Therapeutic Targets

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide, characterized by progressive neuron degeneration or loss due to excessive accumulation of β-amyloid (Aβ) peptides, formation of neurofibrillary tangles (NFTs), and hyperphosphorylated tau. The treatment of AD has been only partially successful as the majority of the pharmacotherapies on the market may alleviate some of the symptoms. In the occurrence of AD, increasing attention has been paid to neurodegeneration, while the resident glial cells, like microglia are also observed. Microglia, a kind of crucial glial cells associated with the innate immune response, functions as double-edge sword role in CNS. They exert a beneficial or detrimental influence on the adjacent neurons through secretion of both pro-inflammatory cytokines as well as neurotrophic factors. In addition, their endocytosis of debris and toxic protein like Aβ and tau ensures homeostasis of the neuronal microenvironment. In this review, we will systematically summarize recent research regarding the roles of microglia in AD pathology and latest microglia-associated therapeutic targets mainly including pro-inflammatory genes, anti-inflammatory genes and phagocytosis at length, some of which are contradictory and controversial and warrant to further be investigated.

Fighting fire with fire: the immune system might be key in our fight against Alzheimer's disease

The ultimate cause of Alzheimer's disease (AD) is still unknown and no disease-modifying treatment exists. Emerging evidence supports the concept that the immune system has a key role in AD pathogenesis. This awareness leads to the idea that specific parts of the immune system must be engaged to ward off the disease. Immunotherapy has dramatically improved the management of several previously untreatable cancers and could hold similar promise as a novel therapy for treating AD. However, before potent immunotherapies can be rationally designed as treatment against AD, we need to fully understand the dynamic interplay between AD and the different parts of our immune system. Accordingly, here we review the most important aspects of both the innate and adaptive immune system in relation to AD pathology. Teaser: Emerging results support the concept that Alzheimer's disease is affected by the inability of the immune system to contain the pathology of the brain. Here, we discuss how we can engage our immune system to fight this devastating disease.

Human iPSC-Derived Neurons as A Platform for Deciphering the Mechanisms behind Brain Aging

With an increased life expectancy among humans, aging has recently emerged as a major focus in biomedical research. The lack of in vitro aging models-especially for neurological disorders, where access to human brain tissues is limited-has hampered the progress in studies on human brain aging and various age-associated neurodegenerative diseases at the cellular and molecular level. In this review, we provide an overview of age-related changes in the transcriptome, in signaling pathways, and in relation to epigenetic factors that occur in senescent neurons. Moreover, we explore the current cell models used to study neuronal aging in vitro, including immortalized cell lines, primary neuronal culture, neurons directly converted from fibroblasts (Fib-iNs), and iPSC-derived neurons (iPSC-iNs); we also discuss the advantages and limitations of these models. In addition, the key phenotypes associated with cellular senescence that have been observed by these models are compared. Finally, we focus on the potential of combining human iPSC-iNs with genome editing technology in order to further our understanding of brain aging and neurodegenerative diseases, and discuss the future directions and challenges in the field.

Improving Cognition with Nutraceuticals Targeting TGF-β1 Signaling

Rescue of cognitive function represents an unmet need in the treatment of neurodegenerative disorders such as Alzheimer's disease (AD). Nutraceuticals deliver a concentrated form of a presumed bioactive(s) agent(s) that can improve cognitive function alone or in combination with current approved drugs for the treatment of cognitive disorders. Nutraceuticals include different natural compounds such as flavonoids and their subclasses (flavan-3-ols, catechins, anthocyanins, and flavonols), omega-3, and carnosine that can improve synaptic plasticity and rescue cognitive deficits through multiple molecular mechanisms. A deficit of transforming growth factor-β1 (TGF-β1) pathway is an early event in the pathophysiology of cognitive impairment in different neuropsychiatric disorders, from depression to AD. In the present review, we provide evidence that different nutraceuticals, such as Hypericum perforatum (hypericin and hyperforin), flavonoids such as hesperidin, omega-3, and carnosine, can target TGF-β1 signaling and increase TGF-β1 production in the central nervous system as well as cognitive function. The bioavailability of these nutraceuticals, in particular carnosine, can be significantly improved with novel formulations (nanoparticulate systems, nanoliposomes) that increase the efficacy and stability of this peptide. Overall, these studies suggest that the synergism between nutraceuticals targeting the TGF-β1 pathway and current approved drugs might represent a novel pharmacological approach for reverting cognitive deficits in AD patients.

Gene Expression Profile in Different Age Groups and Its Association with Cognitive Function in Healthy Malay Adults in Malaysia

The mechanism of cognitive aging at the molecular level is complex and not well understood. Growing evidence suggests that cognitive differences might also be caused by ethnicity. Thus, this study aims to determine the gene expression changes associated with age-related cognitive decline among Malay adults in Malaysia. A cross-sectional study was conducted on 160 healthy Malay subjects, aged between 28 and 79, and recruited around Selangor and Klang Valley, Malaysia. Gene expression analysis was performed using a HumanHT-12v4.0 Expression BeadChip microarray kit. The top 20 differentially expressed genes at p < 0.05 and fold change (FC) = 1.2 showed that PAFAH1B3, HIST1H1E, KCNA3, TM7SF2, RGS1, and TGFBRAP1 were regulated with increased age. The gene set analysis suggests that the Malay adult's susceptibility to developing age-related cognitive decline might be due to the changes in gene expression patterns associated with inflammation, signal transduction, and metabolic pathway in the genetic network. It may, perhaps, have important implications for finding a biomarker for cognitive decline and offer molecular targets to achieve successful aging, mainly in the Malay population in Malaysia.

Therapeutic B-cell depletion reverses progression of Alzheimer's disease

The function of B cells in Alzheimer's disease (AD) is not fully understood. While immunoglobulins that target amyloid beta (Aβ) may interfere with plaque formation and hence progression of the disease, B cells may contribute beyond merely producing immunoglobulins. Here we show that AD is associated with accumulation of activated B cells in circulation, and with infiltration of B cells into the brain parenchyma, resulting in immunoglobulin deposits around Aβ plaques. Using three different murine transgenic models, we provide counterintuitive evidence that the AD progression requires B cells. Despite expression of the AD-fostering transgenes, the loss of B cells alone is sufficient to reduce Aβ plaque burden and disease-associated microglia. It reverses behavioral and memory deficits and restores TGFβ+ microglia, respectively. Moreover, therapeutic depletion of B cells at the onset of the disease retards AD progression in mice, suggesting that targeting B cells may also benefit AD patients.

TGFB3 downregulation causing chordomagenesis and its tumor suppression role maintained by Smad7

Chordoma is a rare bone tumor arising from notochordal remnants, but the underlying mechanism remains elusive. By integrated mRNA and microRNA analyses, we found significant downregulation of TGFB3 along with upregulation of its inhibitor, miR-29 family in chordoma comparing with notochord. Somatic copy number gains of miR-29 loci in chordoma highlighted a mechanism of inactivation of TGFB3 signaling in tumor formation. In zebrafish, knockout and knockdown homologous tgfb3 resulted in a chordoma-like neoplasm. On the other hand, Smad7 negative feedback regulation of transforming growth factor-β (TGF-β) signaling is retentive in chordoma cell UM-Chor1 despite its disruption in most cancer cells (e.g. A549). Therefore, contrary to other cancers, exogenous TGF-β activated Smad7 by downregulating miR-182 and inhibited cell migration and invasion in UM-Chor1. Meanwhile, TGF-β decreased chordoma characteristic protein Brachyury. Altogether, downregulation of TGFB3 causes chordomagenesis, showing a feasible target for therapies. The retention of Smad7 negative regulation may maintain the suppressor role of TGF-β in chordoma.

Reduced Dpp expression accelerates inflammation-mediated neurodegeneration through activated glial cells during altered innate immune response in Drosophila

The progression of neurodegenerative disease is very complex biological process and the molecular crosstalk of inflammatory cytokines during neurodegeneration is associated with multiple cascade signalling. Few evidences suggest that environmental toxin, Paraquat (PQ) administration activates the microglia and intensify the release of proinflamatory cytokines during progression of Parkinson''s disease (PD) but the proper aetiology remained unknown. However, the fundamental role of anti-inflammatory molecule Decapentaplegic (Dpp), homologue of the secreted mammalian Transforming growth factor-β (TGF-β) signalling molecule during neurodegeneration of invertebrate fly model is yet to establish. To elucidate the molecular processes during early stage of Parkinson's disease, we observed neuro-toxin plays a determining role in the increased vulnerability to a particular PQ exposure that is attended by decreased lifespan, severe locomotor deficits, and more loss of dopaminergic (DA) neuron in PQ-treated Dpp deficient fly than wild type (WT). Simultaneously, activated microglia induced the inflammatory response with the release of pro-inflammatory and anti-inflammatory cytokine in Drosophila during neurodegeneration. Moreover, neuro-toxin exposure altered the expression of innate immune genes in both WT and mutant fly compared to the respective PQ-treated flies. Interestingly, PQ exposure reduced the expression of innate immune genes in mutant fly compared to WT. It may indicate that PQ exposure had broken down the immune defence response in mutant fly than WT whereas, without PQ exposure the innate immune tolerance level was higher in fly with reduced Dpp expression than WT. Thus, we observed the conserve anti-inflammatory factor TGF-β may exhibit a crucial defensive role during inflammation mediated neurodegeneration in invertebrate Drosophila melanogaster.

Cell cycle re-entry of neurons and reactive neuroblastosis in Huntington's disease: Possibilities for neural-glial transition in the brain

Huntington's disease (HD) is an autosomal dominant pathogenic condition that causes progressive degeneration of GABAergic neurons in the brain. The abnormal expansion of the CAG repeats in the exon 1 of the Huntingtin gene (HTT gene) has been associated with the onset and progression of movement disorders, psychiatric disturbance and cognitive decline in HD. Microglial activation and reactive astrogliosis have been recognized as the key pathogenic cellular events in the brains of HD subjects. Besides, HD has been characterized by induced quiescence of neural stem cells (NSCs), reactive neuroblastosis and reduced survival of newborn neurons in the brain. Strikingly, the expression of the mutant HTT gene has been reported to induce the cell cycle re-entry of neurons in HD brains. However, the underlying basis for the induction of cell cycle in neurons and the fate of dedifferentiating neurons in the pathological brain remain largely unknown. Thus, this review article revisits the reports on the regulation of key signaling pathways responsible for altered cell cycle events in diseased brains, with special reference to HD and postulates the occurrence of reactive neuroblastosis as a consequential cellular event of dedifferentiation of neurons. Meanwhile, a substantial number of studies indicate that many neuropathogenic events are associated with the expression of potential glial cell markers by neuroblasts. Taken together, this article represents a hypothesis that transdifferentiation of neurons into glial cells might be highly possible through the transient generation of reactive neuroblasts in the brain upon certain pathological conditions.

Selective Neuronal Vulnerability in Alzheimer's Disease: A Network-Based Analysis

A major obstacle to treating Alzheimer's disease (AD) is our lack of understanding of the molecular mechanisms underlying selective neuronal vulnerability, a key characteristic of the disease. Here, we present a framework integrating high-quality neuron-type-specific molecular profiles across the lifetime of the healthy mouse, which we generated using bacTRAP, with postmortem human functional genomics and quantitative genetics data. We demonstrate human-mouse conservation of cellular taxonomy at the molecular level for neurons vulnerable and resistant in AD, identify specific genes and pathways associated with AD neuropathology, and pinpoint a specific functional gene module underlying selective vulnerability, enriched in processes associated with axonal remodeling, and affected by amyloid accumulation and aging. We have made all cell-type-specific profiles and functional networks available at http://alz.princeton.edu. Overall, our study provides a molecular framework for understanding the complex interplay between Aβ, aging, and neurodegeneration within the most vulnerable neurons in AD.

Amelioration of BPSD-Like Phenotype and Cognitive Decline in SAMP8 Mice Model Accompanied by Molecular Changes after Treatment with I2-Imidazoline Receptor Ligand MCR5

Behavioural and psychological symptoms of dementia (BPSD), including fear-anxiety- and depressive-like behaviour, are present in Alzheimer's disease (AD), together with memory decline. I₂-imidazoline receptors (I₂-IRs) have been associated with neuropsychiatric and neurodegenerative disorders, further, I₂-IR ligands have demonstrated a neuroprotective role in the central nervous system (CNS). In this study, we assessed the effect of the I₂-IR ligand MCR5 on both cognitive and non-cognitive symptoms in the Senescence accelerated mice prone 8 (SAMP8) mouse model. Oral administration of I₂-IR ligand MCR5 (5 mg/kg/day for four weeks) in 10-month SAMP8 mice ameliorated both BPSD-like phenotype and cognitive decline by attenuating depressive-like behaviour, reducing fear-anxiety-like behaviour and improving cognitive performance using different tasks. Interaction of I₂-IR ligand MCR5 with serotoninergic system did not account for behavioural or cognitive improvement, although changes in molecular pathways underlying depression and anxiety phenotype were observed. MCR5 increased levels of p-AKT, phosphorylated glycogen synthase kinase 3 β (GSK3β) at Ser9 and phosphorylated mammalian target of rapamycin complex 1 (mTORC1) levels in SAMP8 treated mice compared to SAMP8 control. Moreover, MCR5 treatment altered N-methyl-d-aspartate receptor (NMDA) 2B phosphorylation, and decreased the protein levels of phosphorylated cyclin-dependent kinase 5 (p-CDK5) and dopamine- and cyclic adenosine monophosphate (cAMP)-regulated phosphoprotein of Mr 32 kDa phosphorylated at Thr75 (p-DARPP32), with a parallel increase in protein kinase A (PKA) and p-cAMP response element-binding (pCREB) levels. Consistent with these changes MCR5 attenuated neuroinflammation by decreasing expression of pro-inflammatory markers such as Tumor necrosis factor-alpha (Tnf-α), Interleukin 1β (Il-1β), Interleukin 6 (Il-6), and promoted synaptic plasticity by increasing levels of postsynaptic density protein 95 (PSD95) as well as ameliorating tropomyosin-related kinase B (TrkB) and nerve growth factor receptor (NGFR) signalling. Collectively, these results increase the potential of highly selective I₂-IR ligands as therapeutic agents in age-related BPSD and cognitive alterations.

Senescence as an Amyloid Cascade: The Amyloid Senescence Hypothesis

Due to their postmitotic status, the potential for neurons to undergo senescence has historically received little attention. This lack of attention has extended to some non-postmitotic cells as well. Recently, the study of senescence within the central nervous system (CNS) has begun to emerge as a new etiological framework for neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The presence of senescent cells is known to be deleterious to non-senescent neighboring cells via development of a senescence-associated secretory phenotype (SASP) which includes the release of inflammatory, oxidative, mitogenic, and matrix-degrading factors. Senescence and the SASP have recently been hailed as an alternative to the amyloid cascade hypothesis and the selective killing of senescence cells by senolytic drugs as a substitute for amyloid beta (Aß) targeting antibodies. Here we call for caution in rejecting the amyloid cascade hypothesis and to the dismissal of Aß antibody intervention at least in early disease stages, as Aß oligomers (AßO), and cellular senescence may be inextricably linked. We will review literature that portrays AßO as a stressor capable of inducing senescence. We will discuss research on the potential role of secondary senescence, a process by which senescent cells induce senescence in neighboring cells, in disease progression. Once this seed of senescent cells is present, the elimination of senescence-inducing stressors like Aß would likely be ineffective in abrogating the spread of senescence. This has potential implications for when and why AßO clearance may or may not be effective as a therapeutic for AD. The selective killing of senescent cells by the immune system via immune surveillance naturally curtails the SASP and secondary senescence outside the CNS. Immune privilege restricts the access of peripheral immune cells to the brain parenchyma, making the brain a safe harbor for the spread of senescence and the SASP. However, an increasingly leaky blood brain barrier (BBB) compromises immune privilege in aging AD patients, potentially enabling immune infiltration that could have detrimental consequences in later AD stages. Rather than an alternative etiology, senescence itself may constitute an essential component of the cascade in the amyloid cascade hypothesis.

Fluoxetine and Vortioxetine Reverse Depressive-Like Phenotype and Memory Deficits Induced by Aβ1-42 Oligomers in Mice: A Key Role of Transforming Growth Factor-β1

Depression is a risk factor for the development of Alzheimer’s disease (AD), and the presence of depressive symptoms significantly increases the conversion of mild cognitive impairment (MCI) into AD. A long-term treatment with antidepressants reduces the risk to develop AD, and different second-generation antidepressants such as selective serotonin reuptake inhibitors (SSRIs) are currently being studied for their neuroprotective properties in AD. In the present work, the SSRI fluoxetine and the new multimodal antidepressant vortioxetine were tested for their ability to prevent memory deficits and depressive-like phenotype induced by intracerebroventricular injection of amyloid-β (1-42) (Aβ_1-42) oligomers in 2-month-old C57BL/6 mice. Starting from 7 days before Aβ injection, fluoxetine (10 mg/kg) and vortioxetine (5 and 10 mg/kg) were intraperitoneally injected daily for 24 days. Chronic treatment with fluoxetine and vortioxetine (both at the dose of 10 mg/kg) was able to rescue the loss of memory assessed 14 days after Aβ injection by the passive avoidance task and the object recognition test. Both antidepressants reversed the increase in immobility time detected 19 days after Aβ injection by forced swim test. Vortioxetine exerted significant antidepressant effects also at the dose of 5 mg/kg. A significant deficit of transforming growth factor-β1 (TGF-β1), paralleling memory deficits and depressive-like phenotype, was found in the hippocampus of Aβ-injected mice in combination with a significant reduction of the synaptic proteins synaptophysin and PSD-95. Fluoxetine and vortioxetine completely rescued hippocampal TGF-β1 levels in Aβ-injected mice as well as synaptophysin and PSD-95 levels. This is the first evidence that a chronic treatment with fluoxetine or vortioxetine can prevent both cognitive deficits and depressive-like phenotype in a non-transgenic animal model of AD with a key contribution of TGF-β1.

Immune Signaling in Neurodegeneration

Neurodegenerative diseases of the central nervous system progressively rob patients of their memory, motor function, and ability to perform daily tasks. Advances in genetics and animal models are beginning to unearth an unexpected role of the immune system in disease onset and pathogenesis; however, the role of cytokines, growth factors, and other immune signaling pathways in disease pathogenesis is still being examined. Here we review recent genetic risk and genome-wide association studies and emerging mechanisms for three key immune pathways implicated in disease, the growth factor TGF-β, the complement cascade, and the extracellular receptor TREM2. These immune signaling pathways are important under both healthy and neurodegenerative conditions, and recent work has highlighted new functional aspects of their signaling. Finally, we assess future directions for immune-related research in neurodegeneration and potential avenues for immune-related therapies.

MicroRNA in Alzheimer's disease revisited: implications for major neuropathological mechanisms

Pathology of Alzheimer's disease (AD) goes far beyond neurotoxicity resulting from extracellular deposition of amyloid β (Aβ) plaques. Aberrant cleavage of amyloid precursor protein and accumulation of Aβ in the form of the plaque or neurofibrillary tangles are the known primary culprits of AD pathogenesis and target for various regulatory mechanisms. Hyper-phosphorylation of tau, a major component of neurofibrillary tangles, precipitates its aggregation and prevents its clearance. Lipid particles, apolipoproteins and lipoprotein receptors can act in favor or against Aβ and tau accumulation by altering neural membrane characteristics or dynamics of transport across the blood-brain barrier. Lipids also alter the oxidative/anti-oxidative milieu of the central nervous system (CNS). Irregular cell cycle regulation, mitochondrial stress and apoptosis, which follow both, are also implicated in AD-related neuronal loss. Dysfunction in synaptic transmission and loss of neural plasticity contribute to AD. Neuroinflammation is a final trail for many of the pathologic mechanisms while playing an active role in initiation of AD pathology. Alterations in the expression of microRNAs (miRNAs) in AD and their relevance to AD pathology have long been a focus of interest. Herein we focused on the precise pathomechanisms of AD in which miRNAs were implicated. We performed literature search through PubMed and Scopus using the search term: ('Alzheimer Disease') OR ('Alzheimer's Disease') AND ('microRNAs' OR 'miRNA' OR 'MiR') to reach for relevant articles. We show how a limited number of common dysregulated pathways and abnormal mechanisms are affected by various types of miRNAs in AD brain.

Topical Ocular Delivery of TGF-β1 to the Back of the Eye: Implications in Age-Related Neurodegenerative Diseases

Dysregulation of the transforming growth factor-β1 (TGF-β1)/selected small mother against decapentaplegic (SMAD) pathway can be implicated in development of age-related macular degeneration (AMD), and the delivery of TGF-β1 could be beneficial for AMD. We developed a new ophthalmic formulation of TGF-β1 assessing the ocular pharmacokinetic profile of TGF-β1 in the rabbit eye. Small unilamellar vesicles (SUV) loaded with TGF-β1 were complemented with Annexin V and Ca²⁺, and the vitreous bioavailability of TGF-β1 was assessed after topical ocular administration by a commercial ELISA kit. We detected high levels of TGF-β1 (C_max 114.7 ± 12.40 pg/mL) in the vitreous after 60 min (T_max) from the topical application of the liposomal suspension. Ocular tolerability was also assessed by a modified Draize’s test. The new formulation was well tolerated. In conclusion, we demonstrated that the novel formulation was able to deliver remarkable levels of TGF-β1 into the back of the eye after topical administration. Indeed, this TGF-β1 delivery system may be useful in clinical practice to manage ophthalmic conditions such as age-related macular degeneration, skipping invasive intraocular injections.

Icariin Attenuates Synaptic and Cognitive Deficits in an Aβ1-42-Induced Rat Model of Alzheimer's Disease

Icariin (ICA), a prenylated flavanol glycoside present in abundant quantities in Epimedium sagittatum, has shown promise in the treatment and prevention of Alzheimer's disease. Damage to synaptic plasticity induced by amyloid-beta-mediated neurotoxicity is considered a main pathological mechanism driving the learning and memory deficits present in patients with Alzheimer's disease. This study investigated the neuroprotective effects of icariin in an Aβ_1–42-induced rat model of Alzheimer's disease. Our results showed that Aβ_1–42 injection induced loss of learning and memory behaviour in the Morris water maze, which could be reversed with intragastric administration of ICA. Furthermore, ICA reversed decreases in PSD-95, BDNF, pTrkB, pAkt, and pCREB expressions and prevented deterioration of synaptic interface structure. These findings indicate that ICA may improve synaptic plasticity through the BDNF/TrkB/Akt pathway and provide further evidence for its clinical application to improve learning and memory in patients with Alzheimer's disease.

Losartan improves cerebrovascular function in a mouse model of Alzheimer's disease with combined overproduction of amyloid-β and transforming growth factor-β1

Alterations of the renin-angiotensin system have been implicated in the pathogenesis of Alzheimer's disease. We tested the efficacy of losartan (10 mg/kg/day for three months), a selective angiotensin II type 1 receptor antagonist, in alleviating cerebrovascular and cognitive deficits in double-transgenic mice (six months at endpoint) that overexpress a mutated form of the human amyloid precursor protein (APP_Swe,Ind) and a constitutively active form of the transforming growth factor-β1, thereafter named A/T mice. Losartan rescued cerebrovascular reactivity, particularly the dilatory responses, but failed to attenuate astroglial activation and to normalize the neurovascular uncoupling response to sensory stimulation. The cognitive deficits of A/T mice were not restored by losartan nor were the increased brain levels of soluble and insoluble Aβ_1-40 and Aβ_1-42 peptides normalized. Our results are the first to demonstrate the capacity of losartan to improve cerebrovascular reactivity in an Alzheimer's disease mouse model of combined Aβ-induced vascular oxidative stress and transforming growth factor-β1-mediated vascular fibrosis. These data suggest that losartan may be promising for restoring cerebrovascular function in patients with vascular diseases at risk for vascular dementia or Alzheimer's disease. However, a combined therapy may be warranted for rescuing both vascular and cognitive deficits in a multifaceted pathology like Alzheimer's disease.

Retinal and Circulating miRNAs in Age-Related Macular Degeneration: An In vivo Animal and Human Study

Age related macular degeneration (AMD) is the leading cause of blindness among people aged 50 and over. Retinal deposition of amyloid-β (Aβ) aggregates in AMD patients has suggested a potential link between AMD and Alzheimer's disease (AD). We have evaluated the differential retinal expression profile of miRNAs in a rat model of AMD elicited by Aβ. A serum profile of miRNAs in AMD patients has been also assessed using single TaqMan assay. Analysis of retina from rats intravitreally injected with Aβ revealed that miR-27a, miR-146a, and miR-155 were up-regulated in comparison to control rats. Seven miRNA (miR-9, miR-23a, miR-27a, miR-34a, miR-126, miR-146a, and miR-155) have been found to be dysregulated in serum of AMD patients in comparison to control group. Analysis of pathways has revealed that dysregulated miRNAs, both in the AMD animal model and in AMD patients, can target genes regulating pathways linked to neurodegeneration and inflammation, reinforcing the hypothesis that AMD is a protein misfolding disease similar to AD. In fact, miR-9, miR-23a, miR-27a, miR-34a, miR-146a, miR-155 have been found to be dysregulated both in AMD and AD. In conclusion, we suggest that miR-9, miR-23a, miR-27a, miR-34a, miR-146a, miR-155 represent potential biomarkers and new pharmacological targets for AMD.

Effect of the PI3K/AKT signaling pathway on hypoxia-induced proliferation and differentiation of bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cell (BM-MSC) transplantation has been demonstrated to be an effective way of augmenting angiogenesis of ischemic tissue. The low oxygen conditions in ischemic tissue directly affect the biological behavior of engrafted cells. However, to date, the mechanism through which hypoxia regulates self-renewal, differentiation and paracrine function of BM-MSCs remains unclear. Clarification of this mechanism would be beneficial to the use of stem cell-based therapy. The PI3K/AKT pathway has been extensively investigated for its role in cell proliferation, cell transformation, paracrine function and angiogenesis. The present study aimed to analyze the role of PI3K/AKT pathway in hypoxia-induced proliferation of BM-MSCs and their differentiation into endothelial cells in vitro by the application of LY294002, a PI3K/AKT pathway inhibitor, with cells cultured in normoxia serving as a control. The results showed that rat BM-MSCs at passage 3 and 4 displayed only few phenotypical differences in the expression of surface antigens as detected by flow cytometry. When compared with the cells treated in normoxia, the proliferation of BM-MSCs in hypoxia was promoted, a greater number of cells expressed CD31 and a higher expression of vascular endothelial growth factor was observed after culture in hypoxic conditions. However, by inhibiting with LY294002, these changes induced by hypoxia were partly inhibited. In conclusion, the present study showed that the PI3K/AKT pathway served an important role in hypoxia-enhanced in vitro proliferation of BM-MSCs and their differentiation into endothelial cells and paracrine vascular endothelial growth factor.

Fluoxetine Prevents Aβ1-42-Induced Toxicity via a Paracrine Signaling Mediated by Transforming-Growth-Factor-β1

Selective reuptake inhibitors (SSRIs), such as fluoxetine and sertraline, increase circulating Transforming-Growth-Factor-β1 (TGF-β1) levels in depressed patients, and are currently studied for their neuroprotective properties in Alzheimer’s disease. TGF-β1 is an anti-inflammatory cytokine that exerts neuroprotective effects against β-amyloid (Aβ)-induced neurodegeneration. In the present work, the SSRI, fluoxetine, was tested for the ability to protect cortical neurons against 1 μM oligomeric Aβ_1-42-induced toxicity. At therapeutic concentrations (100 nM–1 μM), fluoxetine significantly prevented Aβ-induced toxicity in mixed glia-neuronal cultures, but not in pure neuronal cultures. Though to a lesser extent, also sertraline was neuroprotective in mixed cultures, whereas serotonin (10 nM–10 μM) did not mimick fluoxetine effects. Glia-conditioned medium collected from astrocytes challenged with fluoxetine protected pure cortical neurons against Aβ toxicity. The effect was lost in the presence of a neutralizing antibody against TGF-β1 in the conditioned medium, or when the specific inhibitor of type-1 TGF-β1 receptor, SB431542, was added to pure neuronal cultures. Accordingly, a 24 h treatment of cortical astrocytes with fluoxetine promoted the release of active TGF-β1 in the culture media through the conversion of latent TGF-β1 to mature TGF-β1. Unlike fluoxetine, both serotonin and sertraline did not stimulate the astrocyte release of active TGF-β1. We conclude that fluoxetine is neuroprotective against Aβ toxicity via a paracrine signaling mediated by TGF-β1, which does not result from a simplistic SERT blockade.

TGFβ Contributes to the Anti-inflammatory Effects of Tauroursodeoxycholic Acid on an Animal Model of Acute Neuroinflammation

The bile acid conjugate tauroursodeoxycholic acid (TUDCA) is a neuroprotective agent in various animal models of neuropathologies. We have previously shown the anti-inflammatory properties of TUDCA in an animal model of acute neuroinflammation. Here, we present a new anti-inflammatory mechanism of TUDCA through the regulation of transforming growth factor β (TGFβ) pathway. The bacterial lipopolysaccharide (LPS) was injected intravenously (iv) on TGFβ reporter mice (Smad-binding element (SBE)/Tk-Luc) to study in their brains the real-time activation profile of the TGFβ pathway in a non-invasive way. The activation of the TGFβ pathway in the brain of SBE/Tk-Luc mice increased 24 h after LPS injection, compared to control animals. This activation peak increased further in mice treated with both LPS and TUDCA than in mice treated with LPS only. The enhanced TGFβ activation in mice treated with LPS and TUDCA correlated with both an increase in TGFβ3 transcript in mouse brain and an increase in TGFβ3 immunoreactivity in microglia/macrophages, endothelial cells, and neurons. Inhibition of the TGFβ receptor with SB431542 drug reverted the effect of TUDCA on microglia/macrophages activation and on TGFβ3 immunoreactivity. Under inflammatory conditions, treatment with TUDCA enhanced further the activation of TGFβ pathway in mouse brain and increased the expression of TGFβ3. Therefore, the induction of TGFβ3 by TUDCA might act as a positive feedback, increasing the initial activation of the TGFβ pathway by the inflammatory stimulus. Our findings provide proof-of-concept that TGFβ contributes to the anti-inflammatory effect of TUDCA under neuroinflammatory conditions.

Inflammatory Cytokines and Alzheimer's Disease: A Review from the Perspective of Genetic Polymorphisms

Neuroinflammatory processes are a central feature of Alzheimer's disease (AD) in which microglia are over-activated, resulting in the increased production of pro-inflammatory cytokines. Moreover, deficiencies in the anti-inflammatory system may also contribute to neuroinflammation. Recently, advanced methods for the analysis of genetic polymorphisms have further supported the relationship between neuroinflammatory factors and AD risk because a series of polymorphisms in inflammation-related genes have been shown to be associated with AD. In this review, we summarize the polymorphisms of both pro- and anti-inflammatory cytokines related to AD, primarily interleukin-1 (IL-1), IL-6, tumor necrosis factor alpha, IL-4, IL-10, and transforming growth factor beta, as well as their functional activity in AD pathology. Exploration of the relationship between inflammatory cytokine polymorphisms and AD risk may facilitate our understanding of AD pathogenesis and contribute to improved treatment strategies.

The dual roles of cytokines in Alzheimer's disease: update on interleukins, TNF-α, TGF-β and IFN-γ

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders in the elderly. Although the mechanisms underlying AD neurodegeneration are not fully understood, it is well recognized that inflammation plays a crucial role in the initiation and/or deterioration of AD neurodegeneration. Increasing evidence suggests that different cytokines, including interleukins, TNF-α, TGF-β and IFN-γ, are actively participated in AD pathogenesis and may serve as diagnostic or therapeutic targets for AD neurodegeneration. Here, we review the progress in understanding the important role that these cytokines or neuroinflammation has played in AD etiology and pathogenesis.

TGF-β1 prevents rat retinal insult induced by amyloid-β (1-42) oligomers

To set up a retinal degenerative model in rat that mimics pathologic conditions such as age-related macular degeneration (AMD) using amyloid-β (Aβ) oligomers, and assess the effect of TGF-β1. Sprague-Dawley male rats were used. Human Aβ1-42 oligomers were intravitreally (ITV) injected (10µM) in the presence or in the absence of recombinant human TGF-β1 (1ng/μl ITV injected). After 48h, the animals were sacrificed and the eyes removed and dissected. The apoptotic markers Bax and Bcl-2 were assessed by western blot analysis in retina lysates. Gene-pathway network analysis was carried out in order to identify pathways involved in AMD. Treatment with Aβ oligomers induced a strong increase in Bax protein level (about 4-fold; p<0.01) and a significant reduction in Bcl-2 protein level (about 2-fold; p<0.05). Co-injection of TGF-β1 triggered a significant reduction of Bax protein induced by Aβ oligomers. Bioinformatic analysis revealed that Bcl-2 and PI3K-Akt are the most connected nodes, for genes and pathways respectively, in the enriched gene-pathway network common to AMD and Alzheimer disease (AD). Overall, these data indicate that ITV injection of Aβ1-42 oligomers in rat induces molecular changes associated with apoptosis in rat retina, highlighting a potential pathogenetic role of Aβ oligomers in AMD. Bioinformatics analysis confirms that apoptosis pathways can take part in AMD. Furthermore, these findings suggest that human recombinant TGF-β1 can prevent retinal damage elicited by Aβ oligomers.

Anti-Inflammatory Effects of Ginsenoside-Rh2 Inhibits LPS-Induced Activation of Microglia and Overproduction of Inflammatory Mediators Via Modulation of TGF-β1/Smad Pathway

Microglia activation plays an important role in neuroinflammation and contributes to several neurological disorders. Hence, inhibition of both microglia activation and pro-inflammatory cytokines may lead to the effective treatment of neurodegenerative diseases. In this study, we found that GRh2 inhibited the inflammatory response to lipopolysaccharide (LPS) and prevented the LPS-induced neurotoxicity in microglia cells. GRh2 significantly decreased the generation of nitric oxide production, and tumor necrosis factor-α, interleukin (IL)-6, IL-1β, cyclooxygenase-2 and inducible nitric oxide synthase in LPS-induced activated microglia cells. Furthermore, GRh2 (20 and 50 μM) significantly increased TGF-β1 expression and reduced the expression of Smad. These results suggest that GRh2 effectively inhibits microglia activation and production of pro-inflammatory cytokines via modulating the TGF-β1/Smad pathway.

Beclin 1 regulates neuronal transforming growth factor-β signaling by mediating recycling of the type I receptor ALK5

Background

Beclin 1 is a key regulator of multiple trafficking pathways, including autophagy and receptor recycling in yeast and microglia. Decreased beclin 1 levels in the CNS result in neurodegeneration, an effect attributed to impaired autophagy. However, neurons also rely heavily on trophic factors, and signaling through these pathways requires the proper trafficking of trophic factor receptors.

Results

We discovered that beclin 1 regulates signaling through the neuroprotective TGF-β pathway. Beclin 1 is required for recycling of the type I TGF-β receptor ALK5. We show that beclin 1 recruits the retromer to ALK5 and facilitates its localization to Rab11⁺ endosomes. Decreased levels of beclin 1, or its binding partners VPS34 and UVRAG, impair TGF-β signaling.

Conclusions

These findings identify beclin 1 as a positive regulator of a trophic signaling pathway via receptor recycling, and suggest that neuronal death induced by decreased beclin 1 levels may also be due to impaired trophic factor signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0065-0) contains supplementary material, which is available to authorized users.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

Effect of Regulatory T Cells on Promoting Apoptosis of T Lymphocyte and Its Regulatory Mechanism in Sepsis

With both in vivo and in vitro experiments, the present study was conducted to investigate the effect of regulatory T cell (Treg) on promoting T-lymphocyte apoptosis and its regulatory mechanism through transforming growth factor-beta (TGF-β1) signaling in mice. A murine model of polymicrobial sepsis was reproduced by cecal ligation and puncture (CLP); PC61 and anti-TGF-β antibodies were used to decrease counts of CD4(+)CD25(+) Tregs and inhibit TGF-β activity, respectively. Splenic CD4(+)CD25(+) Tregs and CD4(+)CD25(-) T cells were isolated. Phenotypes, including cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), forkhead/winged helix transcription factor p3 (Foxp3), and TGFβ1(m+), as well as the apoptotic rate of CD4(+)CD25(-) T cell, were analyzed by flow cytometry. Real-time reverse transcription-polymerase chain reaction was performed to determine mRNA expression of TGF-β1, and the expressions of Smad2/Smad3, Bcl-2 superfamily members of Bcl-2/Bim, cytochrome C, the mitochondrial membrane potential, and caspases in CD4(+)CD25(-) T cells were simultaneously determined. After treatment with PC61 or anti-TGF-β antibody, CTLA-4, Foxp3, and TGFβ1(m+) expressions of CD4(+)CD25(+) Tregs were markedly decreased in comparison to that of the CLP group and the apoptosis rate of CD4(+)CD25(-) T cells was significantly positively correlated with the expression of TGF-β1. Meanwhile, levels of P-Smad2/P-Smad3, proapoptotic protein Bim, cytochrome C, and activity of caspase-3, -8, -9 were downregulated, whereas the mitochondrial membrane potential and antiapoptotic protein Bcl-2 expression were restored. Taken together, our data indicated that the TGF-β1 signal could be partly involved in the apoptosis of CD4(+)CD25(-) T cells promoted by CD4(+)CD25(+) Tregs, therefore inhibition of TGF-β1 expression may provide a novel strategy for the improvement of host immunosuppression following sepsis.

A key role for TGF-β1 in hippocampal synaptic plasticity and memory

Transforming Growth Factor β1 (TGF-β1) is a well-known neuroprotective and neurotrophic factor demonstrated to play a role in synaptic transmission. However, its involvement in physiological mechanisms underlying synaptic plasticity and memory at hippocampal level has not been thoroughly investigated. Here, we examine the role of TGF-β1 in hippocampal long-term potentiation (LTP) and memory in adult wild type mice. Our data provide evidence that administration of exogenous TGF-β1 is able to convert early-phase-LTP into late-phase-LTP. Furthermore, we show that the block of the endogenous TGF-β1 signaling pathway by the specific TGF-β1 inhibitor SB431542, impairs LTP and object recognition memory. The latter impairment was rescued by administration of exogenous TGF-β1, suggesting that endogenously produced TGF-β1 plays a role in physiological mechanisms underlying LTP and memory. Finally, TGF-β1 functional effect correlates with an increased expression of the phosphorylated transcription factor cAMP-Responsive Element Binding protein.

Study of the association of the T869C polymorphism of the transforming growth factor-β1 gene with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common multifactorial disorder characterized by hyperandrogenism, insulin resistance and chronic oligoanovulation. In addition, a number of females with PCOS have ovaries with multiple cysts, an irregular or no menstrual cycle and an imbalance of female hormones compared with normal controls. The transforming growth factor β1 (TGF‑β1) gene is one of the genes associated with obesity and type 2 diabetes, which are characteristic symptoms of PCOS. The present study, therefore, investigated the association between the T869C polymorphism of the TGF‑β1 gene, a single nucleotide polymorphism (SNP) of TGF‑β1 and PCOS. The genomic DNA from 285 patients with PCOS and 129 healthy control individuals was used in the present study. P<0.05 was considered to indicate a statistically significant difference between the groups. The present study findings suggested that the frequency of genotypes provided no significant association between the T869C polymorphism in the TGF‑β1 gene and patients with PCOS. Although the present study concluded that the T869C polymorphism in the TGF‑β1 gene is not associated with the pathogenesis of PCOS, further studies regarding the correlation between other SNPs of the TGF‑β1 gene and PCOS are required.

Growth factor treatment to overcome Alzheimer's dysfunctional signaling

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

Protection of TGF-β1 against neuroinflammation and neurodegeneration in Aβ1-42-induced Alzheimer's disease model rats

Neuroinflammation has been reported to be associated with Alzheimer’s disease (AD) pathogenesis. Neuroinflammation is generally considered as an outcome of glial activation; however, we recently demonstrated that T helper (Th)17 cells, a subpopulation of proinflammatory CD4+ T cells, are also involved in AD pathogenesis. Transforming growth factor (TGF)-β1, a cytokine that can be expressed in the brain, can be immunosuppressive, but its effects on lymphocyte-mediated neuroinflammation in AD pathogenesis have not been well addressed. In the current study we administered TGF-β1 via intracerebroventricle (ICV) and intranasal (IN) routes in AD model rats to investigate its antiinflammatory and neuroprotective effects. The AD rat model was prepared by bilateral hippocampal injection of amyloid-β (Aβ)_1–42. TGF-β1 was administered via ICV one hour prior to Aβ_1–42 injection or via both nares seven days after Aβ_1–42 injection. ICV administration of TGF-β1 before Aβ_1–42 injection remarkably ameliorated Aβ_1–42-induced neurodegeneration and prevented Aβ_1–42-induced increases in glia-derived proinflammatory mediators (TNF-α, IL-1β and iNOS), as well as T cell-derived proinflammatory cytokines (IFN-γ, IL-2, IL-17 and IL-22), in the hypothalamus, serum or cerebrospinal fluid (CSF) in a concentration-dependent manner. TGF-β1 pretreatment also prevented Aβ_1–42-induced decreases in the neurotrophic factors, IGF-1, GDNF and BDNF, and in the antiinflammatory cytokine, IL-10. Similarly, IN administration of TGF-β1 after Aβ_1–42 injection reduced neurodegeneration, elevation of proinflammatory mediators and cytokines, and reduction of neurotrophic and antiinflammatory factors, in the hypothalamus, serum or CSF. These findings suggest that TGF-β1 suppresses glial and T cell-mediated neuroinflammation and thereby alleviates AD-related neurodegeneration. The effectiveness of IN administered TGF-β1 in reducing Aβ_1–42 neurotoxicity suggests a possible therapeutic approach in patients with AD.

Dab2 attenuates brain injury in APP/PS1 mice via targeting transforming growth factor-beta/SMAD signaling

Transforming growth factor-beta (TGF-β) type II receptor (TβRII) levels are extremely low in the brain tissue of patients with Alzheimer's disease. This receptor inhibits TGF-β1/SMAD signaling and thereby aggravates amyolid-beta deposition and neuronal injury. Dab2, a specific adapter protein, protects TβRII from degradation and ensures the effective conduction of TGF-β1/SMAD signaling. In this study, we used an adenoviral vector to overexpress the Dab2 gene in the mouse hippocampus and investigated the regulatory effect of Dab2 protein on TGF-β1/SMAD signaling in a mouse model of Alzheimer's disease, and the potential neuroprotective effect. The results showed that the TβRII level was lower in APP/PS1 mouse hippocampus than in normal mouse hippocampus. After Dab2 expression, hippocampal TβRII and p-SMAD2/3 levels were significantly increased, while amyloid-beta deposition, microglia activation, tumor necrosis factor-α and interleulin-6 levels and neuronal loss were significantly attenuated in APP/PS1 mouse brain tissue. These results suggest that Dab2 can exhibit neuroprotective effects in Alzheimer's disease by regulating TGF-β1/SMAD signaling.

Flexibilide obtained from cultured soft coral has anti-neuroinflammatory and analgesic effects through the upregulation of spinal transforming growth factor-β1 in neuropathic rats

Chronic neuroinflammation plays an important role in the development and maintenance of neuropathic pain. The compound flexibilide, which can be obtained from cultured soft coral, possesses anti-inflammatory and analgesic effects in the rat carrageenan peripheral inflammation model. In the present study, we investigated the antinociceptive properties of flexibilide in the rat chronic constriction injury (CCI) model of neuropathic pain. First, we found that a single intrathecal (i.t.) administration of flexibilide significantly attenuated CCI-induced thermal hyperalgesia at 14 days after surgery. Second, i.t. administration of 10-μg flexibilide twice daily was able to prevent the development of thermal hyperalgesia and weight-bearing deficits in CCI rats. Third, i.t. flexibilide significantly inhibited CCI-induced activation of microglia and astrocytes, as well as the upregulated proinflammatory enzyme, inducible nitric oxide synthase, in the ipsilateral spinal dorsal horn. Furthermore, flexibilide attenuated the CCI-induced downregulation of spinal transforming growth factor-β1 (TGF-β1) at 14 days after surgery. Finally, i.t. SB431542, a selective inhibitor of TGF-β type I receptor, blocked the analgesic effects of flexibilide in CCI rats. Our results suggest that flexibilide may serve as a therapeutic agent for neuropathic pain. In addition, spinal TGF-β1 may be involved in the anti-neuroinflammatory and analgesic effects of flexibilide.

TGFβ produced by IL-10 redirected astrocytes attenuates microglial activation

While there clearly is an intimate relationship between astrocytes and microglia, few studies have examined these potentially dynamic interactions. In this study, cytokine-mediated communication between microglia and astrocytes under inflammatory conditions was investigated. We have previously shown that activated microglia produce Interleukin (IL)-10, a regulatory cytokine that plays an important role in resolving neuroinflammation. Nonetheless, the mechanism by which IL-10 attenuates pro-inflammatory cytokine expression in the brain is unclear. Here, we show that IL-10 redirected astrocytes regulate the activation of microglia in a transforming growth factor (TGF)-β dependent manner. In support of this concept, astrocytes in the brain maintained higher IL-10 receptor (IL-10R1) expression and primary astrocytes in culture were markedly more sensitive to the anti-inflammatory effects of IL-10 compared with microglia. Moreover, studies using primary cultures and an astrocyte-microglia coculture system revealed that astrocytes mediated the anti-inflammatory effects of IL-10 on microglia through the production of TGFβ. For instance, only when astrocytes were present did IL-10 stimulation reduce the expression of IL-1β and increase expression of anti-inflammatory mediators fractalkine receptor (CX3 CR1) and interleukin 4 receptor-α (IL-4Rα) in microglia. Importantly, these IL-10-astrocyte dependent effects on microglia were blocked by a TGFβ inhibitor. Furthermore, inhibition of TGFβ signaling in the brain resulted in prolonged sickness behavior and amplified pro-inflammatory cytokine expression in mice challenged with lipopolysaccharide. Taken together, IL-10 stimulated the production of TGFβ by astrocytes, which in turn, attenuated microglial activation. Overall, these findings provide novel insight into the mechanisms by which astrocytes modulate microglia under inflammatory conditions.

Serum TGF-β1 and SMAD3 levels are closely associated with coronary artery disease

Background

Coronary artery disease (CAD) is one of the most common diseases leading to mortality and morbidity worldwide. There is considerable debate on whether serum transforming growth factor β1 (TGF-β1) levels are associated with long-term major adverse cardiovascular events in patients with CAD, and to date, no study has specifically addressed levels in patients with different degrees of CAD severity.

Methods

Serum TGF-β1 and mothers against decapentaplegic homolog 3 (SMAD3) concentrations were evaluated in 279 patients with CAD and 268 controls without CAD. The clinical and biochemical characteristics of all subjects were also determined and analyzed.

Results

TGF-β1 and SMAD3 concentrations in CAD patients were significantly higher than those in the controls. The serum TGF-β1 level in acute myocardial infarction (AMI) was significantly higher than that in both stable angina pectoris (SAP) and unstable angina pectoris (UAP) (p < 0.05), while there was no marked difference between levels in SAP and UAP (p > 0.05). SMAD3 levels showed no obvious difference among AMI, SAP, and UAP. TGF-β1 and SMAD3 are potential biomarkers for CAD, and may be more accurate than Lpa, ApoA1, uric acid, BUN, or triglycerides (TG).

Conclusions

Serum TGF-β1 and SMAD3 levels are closely associated with CAD, and may become useful biomarkers for diagnosis and risk stratification.

HIV-1 stimulates nuclear entry of amyloid beta via dynamin dependent EEA1 and TGF-β/Smad signaling

Clinical evidence indicates increased amyloid deposition in HIV-1-infected brains, which contributes to neurocognitive dysfunction in infected patients. Here we show that HIV-1 exposure stimulates amyloid beta (Aβ) nuclear entry in human brain endothelial cells (HBMEC), the main component of the blood-brain barrier (BBB). Treatment with HIV-1 and/or Aβ resulted in concurrent increase in early endosomal antigen-1 (EEA1), Smad, and phosphorylated Smad (pSmad) in nuclear fraction of HBMEC. A series of inhibition and silencing studies indicated that Smad and EEA1 closely interact by influencing their own nuclear entry; the effect that was attenuated by dynasore, a blocker of GTP-ase activity of dynamin. Importantly, inhibition of dynamin, EEA1, or TGF-β/Smad effectively attenuated HIV-1-induced Aβ accumulation in the nuclei of HBMEC. The present study indicates that nuclear uptake of Aβ involves the dynamin-dependent EEA1 and TGF-β/Smad signaling pathways. These results identify potential novel targets to protect against HIV-1-associated dysregulation of amyloid processes at the BBB level.

Role of the Transforming-Growth-Factor-β1 Gene in Late-Onset Alzheimer's Disease: Implications for the Treatment

Late-onset Alzheimer's disease (LOAD) is the most common form of dementia in the elderly. LOAD has a complex and largely unknown etiology with strong genetic determinants. Genetics of LOAD is known to involve several genetic risk factors among which the Apolipoprotein E (APOE) gene seems to be the major recognized genetic determinant. Recent efforts have been made to identify other genetic factors involved in the pathophysiology of LOAD such as genes associated with a deficit of neurotrophic factors in the AD brain. Genetic variations of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), and transforming-growth-factor-β1 (TGF-β1) are known to increase the risk to develop LOAD and have also been related to depression susceptibility in LOAD. Transforming-Growth-Factor-β1 (TGF-β1) is a neurotrophic factor that exerts neuroprotective effects against ß-amyloid-induced neurodegeneration. Recent evidence suggests that a specific impairment in the signaling of TGF-β is an early event in the pathogenesis of AD. TGF-β1 protein levels are predominantly under genetic control, and the TGF-β1 gene, located on chromosome 19q13.1–3, con-tains several single nucleotide polymorphisms (SNPs) upstream and in the transcript region, such as the SNP at codon +10 (T/C) and +25 (G/C), which is known to influence the level of expression of TGF-β1. In the present review, we summarize the current literature on genetic risk factors for LOAD, focusing on the role of the TGF-β1 gene, finally discussing the possible implications of these genetic studies for the selection of patients eligible for neuroprotective strategies in AD.

TGFβ signaling induces expression of Gadd45b in retinal ganglion cells

PURPOSE

Growth arrest and DNA damage protein 45b (Gadd45b) functions as an intrinsic neuroprotective molecule protecting retinal ganglion cells (RGCs) from injury. This study was performed to elucidate further the induction pathway of Gadd45b expression in RGCs.

METHODS

The induction of Gadd45b expression in response to TGFβNFκB signaling was investigated in RGC5 cultures in vitro and murine retina in vivo. Gadd45b mRNA and protein expression were detected by quantitative real-time RT-PCR, immunoblot assay, immunohistochemistry, and immunocytochemistry. Activation of NFκB and TGFβ/Gadd45b signaling were assessed by measuring phosphorylation of NFκB and using specific inhibitors. Gadd45b siRNA was transfected into RGC5 to silence Gadd45b mRNA expression.

RESULTS

Expression of TGFβ receptors I and II was detected in RGC5 in vitro and RGCs in vivo. TGFβ induced abundant Gadd45b mRNA and protein expression, exhibiting a dose-dependent response in vitro. Exogenous TGFβ1 induced upregulation of Gadd45b expression in RGCs in murine retina in vivo. TGFβ stimulated phosphorylation of NFκB, and inhibition of NFκB phosphorylation blocked induction of Gadd45b by TGFβ in RGC5 cells. Induction of Gadd45b by TGFβ increased the resistance of RGC5 cells against TNFα cytotoxicity and paraquat oxidative stress.

CONCLUSIONS

TGFβ signaling induced Gadd45b expression in RGCs. Modulation of the TGFβ/NFκB/Gadd45b signaling pathway may provide a means to enhance the neuroprotective effect of Gadd45b in RGCs.

Sinularin from indigenous soft coral attenuates nociceptive responses and spinal neuroinflammation in carrageenan-induced inflammatory rat model

Three decades ago, the marine-derived compound sinularin was shown to have anti-edematous effects on paw edema induced by carrageenan or adjuvant. To the best of our knowledge, no new studies were conducted to explore the bioactivity of sinularin until we reported the analgesic properties of sinularin based on in vivo experiments. In the present study, we found that sinularin significantly inhibits the upregulation of proinflammatory proteins, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) and upregulates the production of transforming growth factor-β (TGF-β) in lipopolysaccharide (LPS)-stimulated murine macrophage RAW 264.7 cells according to western blot analysis. We found that subcutaneous (s.c.) administration of sinularin (80 mg/kg) 1 h before carrageenan injection significantly inhibited carrageenan-induced nociceptive behaviors, including thermal hyperalgesia, mechanical allodynia, cold allodynia, and hindpaw weight-bearing deficits. Further, s.c. sinularin (80 mg/kg) significantly inhibited carrageenan-induced microglial and astrocyte activation as well as upregulation of iNOS in the dorsal horn of the lumbar spinal cord. Moreover, s.c. sinularin (80 mg/kg) inhibited carrageenan-induced tissue inflammatory responses, redness and edema of the paw, and leukocyte infiltration. The results of immunohistochemical studies indicate that s.c. sinularin (80 mg/kg) could upregulate production of TGF-β1 in carrageenan-induced inflamed paw tissue. The present results demonstrate that systemic sinularin exerts analgesic effects at the behavioral and spinal levels, which are associated with both inhibition of leukocyte infiltration and upregulation of TGF-β1.