1,721,033 research outputs found
Dicer expression and localization in post-mitotic neurons
No full textRNA-mediated gene silencing is recently emerged as a fundamental mechanism of regulation of gene expression in many organisms and tissues, with special emphasis with respect to the nervous system. With the aim to study the components of RNA silencing machinery, we have investigated the expression profile and localization of dicer protein RNase III endonuclease in cultures of post-mitotic neurons. Dicer catalyzes the processing of double-stranded RNAs (dsRNAs) into ≈21–25 nucleotide-long small interfering (si)RNAs and micro (mi)RNAs, and it represents an essential step in the biogenesis of these small noncoding RNA molecules. We show that in rat primary neurons dicer is localized in the somatodendritic compartment, at the Golgi-reticulum area network level. This peculiar distribution was altered by brefeldin A treatment. Moreover the Golgi-reticulum dicer signal was observed also in primary astroglial cells. In addiction dicer was observed to be regulated during the embryogenesis and development in several tissues. In fact its expression is developmentally regulated in cultured cerebellar granule neurons. This is the first study in which dicer is shown preferentially distributed in the Golgi-reticulum area in post-mitotic terminally differentiated neuronal and glial cells and that its profile is modulated during maturation and development of in vitro cultured cerebellar granule neurons
NGF and BDNF signaling control amyloidogenic route and Aβ production in hippocampal neurons
No full textSignaling pathways acticated by chemokine receptor CXCR2 and AMPA-type glutamate receptors and involvement in granule cells survival
No full textWe show that treatment of cerebellar granules with interleukin-8 (IL-8), growth-related gene product beta (GRObeta) or AMPA induced activation of PI3-K/Akt and of ERK pathways, the latter being independent of PI3-K and dependent on PTX-sensitive G proteins. We also show that AMPA-mediated neuron survival was abolished both by ERK kinase inhibitor PD98059 and AMPA-Rs blocker CNQX, and that chemokine-mediated survival was blocked by the PI3-K inhibitors LY294002 and wortmannin. We conclude that the neurotrophic effects of AMPA need the contemporary activation of ERKs and stimulation of AMPA-Rs, and that PI3-K/Akt activation is a determinant pathway for the lL-8/GRObeta anti-apoptotic activity
MicroRNA-101 regulates amyloid precursor protein expression in hippocampal neurons.
No full textThe amyloid precursor protein (APP) and its proteolytic
product amyloid beta (A) are associated with both familial and
sporadic forms of Alzheimer disease (AD). Aberrant expression
and function of microRNAs has been observed in AD. Here, we
show that in rat hippocampal neurons cultured in vitro, the
down-regulation of Argonaute-2, a key component of the
RNA-induced silencing complex, produced an increase in
APP levels. Using site-directed mutagenesis, a microRNA
responsive element (RE) for miR-101 was identified in the
3-untranslated region (UTR) of APP. The inhibition of
endogenous miR-101 increased APP levels, whereas lentiviral-
mediated miR-101 overexpression significantly reduced
APPandA load in hippocampal neurons. In addition, miR-101
contributed to the regulation of APP in response to the proinflammatory
cytokine interleukin-1 (IL-l). Thus, miR-101 is a
negative regulator of APP expression and affects the accumulation
of A, suggesting a possible role for miR-101 in neuropathological
condition
Substance P activates ADAM9 mRNA expression and induces α-secretase-mediated amyloid precursor protein cleavage
No full textAltered levels of Substance P (SP), a neuropeptide endowed with neuroprotective and anti-apoptotic properties, were found in brain areas and spinal fluid of Alzheimer's disease (AD) patients. One of the hallmarks of AD is the abnormal extracellular deposition of neurotoxic beta amyloid (Aβ) peptides, derived from the proteolytic processing of amyloid precursor protein (APP). In the present study, we confirmed, the neurotrophic action of SP in cultured rat cerebellar granule cells (CGCs) and investigated its effects on APP metabolism. Incubation with low (5 mM) potassium induced apoptotic cell death of CGCs and amyloidogenic processing of APP, whereas treatment with SP (200 nM) reverted these effects via NK1 receptors. The non-amyloidogenic effect of SP consisted of reduction of Aβ(1-42), increase of sAPPα and enhanced α-secretase activity, without a significant change in steady-state levels of cellular APP. The intracellular mechanisms whereby SP alters APP metabolism were further investigated by measuring mRNA and/or steady-state protein levels of key enzymes involved with α-, β- and γ-secretase activity. Among them, Adam9, both at the mRNA and protein level, was the only enzyme to be significantly down-regulated following the induction of apoptosis (K5) and up-regulated after SP treatment. In addition to its neuroprotective properties, this study shows that SP is able to stimulate non-amyloidogenic APP processing, thereby reducing the possibility of generation of toxic Aβ peptides in brain
Neuronal specific processing of VGF protein and regulated secretion of peptides derived from its carboxy-terminal
No full textTau cleavage and dephosphorylation in cerebellar granule neurons undergoing apoptosis
No full textCerebellar granule cells undergo apoptosis in culture after deprivation of potassium and serum. During this process we found that tau, a neuronal microtubule-associated protein that plays a key role in the maintenance of neuronal architecture, and the pathology of which correlates with intellectual decline in Alzheimer's disease, is cleaved. The final product of this cleavage is a soluble dephosphorylated tau fragment of 17 kDa that is unable to associate with microtubules and accumulates in the perikarya of dying cells. The appearance of this 17 kDa fragment is inhibited by both caspase and calpain inhibitors, suggesting that tau is an in vivo substrate for both of these proteases during apoptosis. Tau cleavage is correlated with disruption of the microtubule network, and experiments with colchicine and taxol show that this is likely to be a cause and not a consequence of tau cleavage. These data indicate that tau cleavage and change in phosphorylation are important early factors in the failure of the microtubule network that occurs during neuronal apoptosis. Furthermore, this study introduces new insights into the mechanism(s) that generate the truncated forms of tau present in Alzheimer's disease
Tyrosine kinase nerve growth factor receptor switches from prosurvival to proapoptotic activity via Abeta-mediated phosphorylation
No full textEndogenous Aβ causes cell death via early tau hyperphosphorylation
No full textAlzheimer's disease (AD) is characterized by A beta overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M. T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 A beta antibodies or by specific beta and/or gamma-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12 h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3 beta-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial traffickin
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