The transcriptional landscape of Alzheimer's disease and its association with Wnt signaling pathway.

Alzheimer's disease (AD) is a neurological disorder primarily affecting the elderly. The disease manifests as progressive deterioration in cognitive functions, leading to a loss of autonomy. The identification of transcriptional changes in susceptible signaling pathways has provided clues to the origin and progression of AD and has pinpointed synapse loss as the prominent event in early stages of the disease. Synapse failure represents a key pathological correlate of cognitive decline in patients. Genetics and transcriptomics studies have also identified novel genes, processes, and pathways associated with AD. This evidence suggests that a deficiency in Wnt signaling pathway contributes to AD pathogenesis by inducing synaptic dysfunction and neuronal degeneration. In the adult nervous system, Wnt signaling plays a crucial role in synaptic physiology, modulating the synaptic vesicle cycle, trafficking neurotransmitter receptors, and modulating the expression of different genes associated with these processes. In this review, we describe the general transcriptional landscape associated with AD, specifically transcriptional changes associated with the Wnt signaling pathway and their effects in the context of disease.

Andrographolide restores glucose uptake in rat hippocampal neurons.

Cerebral glucose hypometabolism is a common pathophysiological characteristic of many neurodegenerative diseases. This metabolic dysfunction includes alterations in glucose transport from the blood into the neurons by the facilitative glucose transporters (GLUTs). Several studies suggest that metabolic disturbances precede clinical symptoms and correlate with disease progression. Some groups have started to explore the use of therapeutic strategies that target decreased cerebral glucose metabolism to promote its availability. We selected Andrographolide (Andro), a natural product obtained from Andrographis paniculate that has both anti-hyperglycemic and anti-diabetic effects. Although it was shown to promote glucose uptake in vivo, the underlying mechanisms remain unclear. Here, we evaluated the acute effects of Andro on glucose transport and metabolism using primary rat hippocampal neuronal cultures. Our results showed that Andro enhances neuronal glucose uptake and stimulates glucose metabolism by inducing GLUT3 and 4 expression in neurons, as well as by promoting glycolysis. We also observed that Andro-mediated effects depend on the activity of AMP-activated protein kinase (AMPK), one of the central regulators of glucose metabolism. Our studies open the possibility to use Andro as a drug to restore glucose levels in neurodegenerative diseases.

Canonical Wnt Signaling Modulates the Expression of Pre- and Postsynaptic Components in Different Temporal Patterns.

Wnt ligands play critical roles in neuronal development, synapse formation, synaptic activity, and plasticity. Synaptic plasticity requires molecular remodeling of synapses, implying the expression of key synaptic components. Some studies have linked Wnt signaling activity to changes in synaptic protein levels. However, the presynaptic and postsynaptic gene expression profiles of hippocampal neurons exposed to Wnt proteins have not been studied. Hence, we treated rat cultured hippocampal neurons with recombinant Wnt3a, lithium, and the Wnt inhibitor Dkk-1 for different treatment durations and measured the mRNA and protein levels of pre- and postsynaptic components. The ligand Wnt3a promoted the differential temporal expression of genes encoding presynaptic and postsynaptic proteins. Gene expression of the presynaptic proteins Rim1, piccolo (Pclo), Erc2, Ctbp1 and Rimbp2 increased in a specific temporal pattern. Simultaneously, the mRNA and protein levels of postsynaptic components showed a different temporal expression pattern, e.g., the mRNAs for postsynaptic scaffolding components such as postsynaptic density protein-95 (PSD-95/Dlg4), Homer1 and Shank1 were temporally regulated by both Wnt3a and lithium. On the other hand, the mRNA levels of the gene encoding the protein calcium/calmodulin-dependent protein kinase IV (Camk4), canonically upregulated by Wnt, were increased. Our results suggest that Wnt signaling orchestrates expressional changes in genes encoding presynaptic and postsynaptic components, probably as part of a synaptic plasticity mechanism in neurons.

Cognitive impairment in heart failure is associated with altered Wnt signaling in the hippocampus.

Age represents the highest risk factor for death due to cardiovascular disease. Heart failure (HF) is the most common cardiovascular disease in elder population and it is associated with cognitive impairment (CI), diminishing learning and memory process affecting life quality and mortality in these patients. In HF, CI has been associated with inadequate O2 supply to the brain; however, an important subset of HF patients displays CI with almost no alteration in cerebral blood flow. Importantly, nothing is known about the pathophysiological mechanisms underpinning CI in HF with no change in brain tissue perfusion. Here, we aimed to study memory performance and learning function in a rodent model of HF that shows no change in blood flow going to the brain. We found that HF rats presented learning impairments and memory loss. In addition, HF rats displayed a decreased level of Wnt/ß-catenin signaling downstream elements in the hippocampus, one pathway implicated largely in aging diseases. Taken together, our results suggest that in HF rats CI is associated with dysfunction of the Wnt/ß-catenin signaling pathway. The mechanisms involved in the alterations of Wnt/ß-catenin signaling in HF and its contribution to the development/maintenance of CI deserves future investigations.

Wnt Signaling Upregulates Teneurin-3 Expression via Canonical and Non-canonical Wnt Pathway Crosstalk.

Teneurins (Tens) are a highly conserved family of proteins necessary for cell-cell adhesion. Tens can be cleaved, and some of their proteolytic products, such as the teneurin c-terminal associated-peptide (TCAP) and the intracellular domain (ICD), have been demonstrated to be biologically active. Although Tens are considered critical for central nervous system development, they have also been demonstrated to play important roles in adult tissues, suggesting a potential link between their deregulation and various pathological processes, including neurodegeneration and cancer. However, knowledge regarding how Ten expression is modulated is almost absent. Relevantly, the functions of Tens resemble several of the effects of canonical and non-canonical Wnt pathway activation, including the effects of the Wnt pathways on neuronal development and function as well as their pivotal roles during carcinogenesis. Accordingly, in this initial study, we decided to evaluate whether Wnt signaling can modulate the expression of Tens. Remarkably, in the present work, we used a specific inhibitor of porcupine, the key enzyme for Wnt ligand secretion, to not only demonstrate the involvement of Wnt signaling in regulating Ten-3 expression for the first time but also reveal that Wnt3a, a canonical Wnt ligand, increases the expression of Ten-3 through a mechanism dependent on the secretion and activity of the non-canonical ligand Wnt5a. Although our work raises several new questions, our findings seem to demonstrate the upregulation of Ten-3 by Wnt signaling and also suggest that Ten-3 modulation is possible because of crosstalk between the canonical and non-canonical Wnt pathways.

Modulation of Glucose Metabolism in Hippocampal Neurons by Adiponectin and Resistin.

Obese individuals exhibit altered circulating levels of adipokines, the proteins secreted by adipose tissue to mediate tissue cross-talk and regulate appetite and energy expenditure. The effect of adipokines on neuronal glucose metabolism, however, remains largely unknown. Two adipokines produced in adipose tissue, adiponectin and resistin, can gain access to the central nervous system (CNS), and their levels in the cerebrospinal fluid (CSF) are altered in obesity. We hypothesized that dysregulated adipokines in the CNS may underlie the reported link between obesity and higher risk of neurological disorders like Alzheimer's disease (AD), by affecting glucose metabolism in hippocampal neurons. Using cultured primary rat hippocampal neurons and mouse hippocampus slices, we show that recombinant adiponectin and resistin, at a concentration found in the CSF, have opposing effects on glucose metabolism. Adiponectin enhanced glucose uptake, glycolytic rate, and ATP production through an AMP-activated protein kinase (AMPK)-dependent mechanism; inhibiting AMPK abrogated the effects of adiponectin on glucose uptake and utilization. In contrast, resistin reduced glucose uptake, glycolytic rate, and ATP production, in part, by inhibiting hexokinase (HK) activity in hippocampal neurons. These data suggest that altered CNS levels of adipokines in the context of obesity may impact glucose metabolism in hippocampal neurons, brain region involved in learning and memory functions.

Wnt-induced activation of glucose metabolism mediates the in vivo neuroprotective roles of Wnt signaling in Alzheimer disease.

Dysregulated Wnt signaling is linked to major neurodegenerative diseases, including Alzheimer disease (AD). In mouse models of AD, activation of the canonical Wnt signaling pathway improves learning/memory, but the mechanism for this remains unclear. The decline in brain function in AD patients correlates with reduced glucose utilization by neurons. Here, we test whether improvements in glucose metabolism mediate the neuroprotective effects of Wnt in AD mouse model. APPswe/PS1dE9 transgenic mice were used to model AD, Andrographolide or Lithium was used to activate Wnt signaling, and cytochalasin B was used to block glucose uptake. Cognitive function was assessed by novel object recognition and memory flexibility tests. Glucose uptake and the glycolytic rate were determined using radiotracer glucose. The activities of key enzymes of glycolysis such as hexokinase and phosphofructokinase, Adenosine triphosphate (ATP)/Adenosine diphosphate (ADP) levels and the pentose phosphate pathway and activity of glucose-6 phosphate dehydrogenase were measured. Wnt activators significantly improved brain glucose utilization and cognitive performance in transgenic mice. Wnt signaling enhanced glucose metabolism by increasing the expression and/or activity of hexokinase, phosphofructokinase and AMP-activated protein kinase. Inhibiting glucose uptake partially abolished the beneficial effects of Wnt signaling on learning/memory. Wnt activation also enhanced glucose metabolism in cortical and hippocampal neurons, as well as brain slices derived from APPswe/PS1E9 transgenic mice. Combined, these data provide evidence that the neuroprotective effects of Wnt signaling in AD mouse models result, at least in part, from Wnt-mediated improvements in neuronal glucose metabolism.

Hypothyroidism and Cognitive Disorders during Development and Adulthood: Implications in the Central Nervous System.

Thyroid hormones (THs) play a critical function in fundamental signaling of the body regulating process such as metabolism of glucose and lipids, cell maturation and proliferation, and neurogenesis, to name just a few. THs trigger biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). For years, a close relationship between the THs hormones and the central nervous system (CNS) has been described, not only for neuronal cells but also for glial development and differentiation. A deficit in thyroid hormones triiodothyronine (T3) and thyroxine (T4) is observed in the hypothyroid condition, generated by a iodine deficiency or an autoimmune response of the body. In the hypothyroid condition, several cellular deregulation and alterations have been described in dendrite spine morphology, cell migration and proliferation, and impaired synaptic transmission in the hippocampus, among others. The aim of this review is to describe the role of the thyroid hormones with focus in brain function and neurodegenerative disorders.

Transcriptional Auto-Regulation of RUNX1 P1 Promoter.

RUNX1 a member of the family of runt related transcription factors (RUNX), is essential for hematopoiesis. The expression of RUNX1 gene is controlled by two promoters; the distal P1 promoter and the proximal P2 promoter. Several isoforms of RUNX1 mRNA are generated through the use of both promoters and alternative splicing. These isoforms not only differs in their temporal expression pattern but also exhibit differences in tissue specificity. The RUNX1 isoforms derived from P2 are expressed in a variety of tissues, but expression of P1-derived isoform is restricted to cells of hematopoietic lineage. However, the control of hematopoietic-cell specific expression is poorly understood. Here we report regulation of P1-derived RUNX1 mRNA by RUNX1 protein. In silico analysis of P1 promoter revealed presence of two evolutionary conserved RUNX motifs, 0.6kb upstream of the transcription start site, and three RUNX motifs within 170bp of the 5'UTR. Transcriptional contribution of these RUNX motifs was studied in myeloid and T-cells. RUNX1 genomic fragment containing all sites show very low basal activity in both cell types. Mutation or deletion of RUNX motifs in the UTR enhances basal activity of the RUNX1 promoter. Chromatin immunoprecipitation revealed that RUNX1 protein is recruited to these sites. Overexpression of RUNX1 in non-hematopoietic cells results in a dose dependent activation of the RUNX1 P1 promoter. We also demonstrate that RUNX1 protein regulates transcription of endogenous RUNX1 mRNA in T-cell. Finally we show that SCL transcription factor is recruited to regions containing RUNX motifs in the promoter and the UTR and regulates activity of the RUNX1 P1 promoter in vitro. Thus, multiple lines of evidence show that RUNX1 protein regulates its own gene transcription.

SVCT2 Overexpression in Neuroblastoma Cells Induces Cellular Branching that is Associated with ERK Signaling.

Expression of the sodium and ascorbic acid (AA) cotransporter SVCT2 is induced during the period of cellular arborization and synaptic maturation of early postnatal (P1-P5) rat cerebral neurons. The physiological importance of the transporter for neurons is evidenced by the lethality and delayed neuronal differentiation detected in mice with ablation of SVCT2. The mechanism(s) involved in these defects and the role of SVCT2 in neuronal branching have not been determined yet. To address this, we used lentiviral expression vectors to increase the levels of SVCT2 in N2a cells and analyzed the effects on neurite formation. Expression of a fusion protein containing the human SVCT2wt and EYFP induced an increase in the number of MAP2+ neurites and filopodia in N2a cells. Overexpression of SVCT2 and treatment with AA promoted ERK1/2 phosphorylation. Our data suggest that enhanced expression of the high affinity AA transporter SVCT2, which tightly regulates intracellular AA concentrations, induces neuronal branching that then activates key signaling pathways that are involved in the differentiation and maturation of cortical neurons during postnatal development.

TRINITY heart valve prosthesis: a novel repositionable and retrievable transapical transcatheter aortic valve system.

AIMS: Transcatheter aortic valve implantation (TAVI) has become a viable option for selected high-risk patients with severe and symptomatic aortic stenosis. First- and second-generation TAVI devices are either self- or balloon-expandable, and are often not repositionable or not fully retrievable, leading to suboptimal positioning in some cases. This may result in paravalvular regurgitation, AV conduction delay, or compromise of coronary perfusion. A broader application of TAVI requires advances in both valve and delivery systems. Therefore, in order to facilitate accurate positioning, to minimise paravalvular leakage, possibly to reduce the risk of AV conduction delay, and possibly to be able to abort the procedure, a "next-generation" TAVI system has been developed which is repositionable and retrievable, the TRINITY heart valve system. METHODS AND RESULTS: The TRINITY heart valve system was implanted in a first-in-human study using the transapical approach to demonstrate feasibility and procedural success. All endpoints were adjudicated according to VARC definitions at seven and 30 days. The TRINITY heart valve system was implanted in a 74-year-old patient with severe symptomatic aortic valve stenosis. In this case, repositioning of the TRINITY resulted in optimal position without paravalvular leakage and with perfect function. CONCLUSIONS: The TRINITY heart valve is a repositionable and retrievable TAVI system. Both the implantation result and short-term clinical and haemodynamic outcome were excellent.

Altered chromatin modifications in AML1/RUNX1 breakpoint regions involved in (8;21) translocation.

The RUNX1/AML1 gene is the most frequent target for chromosomal translocation, and often identified as a site for reciprocal rearrangement of chromosomes 8 and 21 in patients with acute myelogenous leukemia. Virtually all chromosome translocations in leukemia show no consistent homologous sequences at the breakpoint regions. However, specific chromatin elements (DNase I and topoisomerase II cleavage) have been found at the breakpoints of some genes suggesting that structural motifs are determinant for the double strand DNA-breaks. We analyzed the chromatin organization at intron 5 of the RUNX1 gene where all the sequenced breakpoints involved in t(8;21) have been mapped. Using chromatin immunoprecipitation assays we show that chromatin organization at intron 5 of the RUNX1 gene is different in HL-60 and HeLa cells. Two distinct features mark the intron 5 in cells expressing RUNX1: a complete lack or significantly reduced levels of Histone H1 and enrichment of hyperacetylated histone H3. Strikingly, induction of DNA damage resulted in formation of t(8;21) in HL-60 but not in HeLa cells. Taken together, our results suggest that H1 depletion and/or histone H3 hyperacetylation may have a linkage with an increase susceptibility of specific chromosomal regions to undergo translocations.