2,118 research outputs found
Membrane protein remodeling in microglia exposed to amyloid peptides
Infection, neurodegeneration, and other conditions associated with loss of brain
homeostasis, induce changes in microglial morphology, gene expression and function,
generally referred to as “activation”. Alzheimer’s disease (AD) is the most common
dementia and is characterized by neuroinfammatory changes, including alterations
in the morphology and distribution of microglia and astrocytes, and deposition of
complement and other infammatory mediators. Our previous observations show that
microglial cells challenged in vitro with amyloid peptides clustered and rounded up,
dramatically changing their morphology. Besides, in these cells we observed the early
acetylation and then the phosphorylation of STAT3 which is required for the expression
of the epsilon isoform of 14-3-3, a marker of Abeta-activated microglia (1, 2). We
applied afnity partitioning approach combined with high throughput mass spectrometric
analysis in order to identify variation of proteins on plasma membrane of BV2
immortalized microglia upon treatment with amyloid peptides. By this method several
proteins up- or down-regulated by amyloid treatment were identifed in microglial
plasma membrane. Among them annexins (5 and 7), IFITM3 and MARK3. These data
have been confrmed in primary microglial cultures.
In microglia, plasma membrane plays a relevant role in the cross-talking with the external neuronal
environment and in the resulting trophic or infammatory response of these sentinel cells. As such,
knowledge of the microglia responsiveness to beta amyloids in term of changes in its plasma
membrane proteome is imperative for unveiling the molecular landscape in which AD occurs
Impairment of the autophagic flux in astrocytes intoxicated by trimethyltin
Autophagy is a lysosomal catabolic route for protein aggregates and damaged organelles which in different stress conditions, such as starvation, generally improves cell survival. An impairment of this degradation pathway has been reported to occur in many neurodegenerative processes. Trimethyltin (TMT) is a potent neurotoxin present as an environmental contaminant causing tremors, seizures and learning impairment in intoxicated subjects. The present data show that in rat primary astrocytes autophagic vesicles (AVs) appeared after few hours of TMT treatment. The analysis of the autophagic flux in TMT-treated astrocytes was consistent with a block of the late stages of autophagy and was accompanied by a progressive accumulation of the microtubule associated protein light chain 3 (LC3) and of p62/SQSTM1. Interestingly, an increased immunoreactivity for p62/SQSTM1 was also observed in hippocampal astrocytes detected in brain slices of TMT-intoxicated rats. The time-lapse recordings of AVs in EGFP-mCherry-LC3B transfected astrocytes demonstrated a reduced mobility of autophagosomes after TMT exposure respect to control cells. The observed block of the autophagic flux cannot be overcome by known autophagy inducers such as rapamycin or 0.5mM lithium. Although ineffective when used at 0.5mM, lithium at higher concentrations (2mM) was able to protect astrocyte cultures from TMT toxicity. This effect correlated well with its ability to determine the phosphorylation/inactivation of glycogen kinase synthase-3β (GSK-3β)
Lithium limits trimethyltin-induced cytotoxicity and proinflammatory response in microglia without affecting the concurrent autophagy impairment
Trimethyltin (TMT) is a highly toxic molecule present as an environmental contaminant causing neurodegeneration particularly of the limbic system both in humans and in rodents. We recently described the occurrence of impairment in the late stages of autophagy in TMT-intoxicated astrocytes. Here we show that similarly to astrocytes also in microglia, TMT induces the precocious block of autophagy indicated by the accumulation of the autophagosome marker, microtubule associated protein light chain 3. Consistent with autophagy impairment we observe in TMT-treated microglia the accumulation of p62/SQSTM1, a protein specifically degraded through this pathway. Lithium has been proved effective in limiting neurodegenerations and, in particular, in ameliorating symptoms of TMT intoxication in rodents. In our in vitro model, lithium displays a pro-survival and anti-inflammatory action reducing both cell death and the proinflammatory response of TMT-treated microglia. In particular, lithium exerts these activities without reducing TMT-induced accumulation of light chain 3 protein. In fact, the autophagic block imposed by TMT is unaffected by lithium administration. These results are of interest as defects in the execution of autophagy are frequently observed in neurodegenerative diseases and lithium is considered a promising therapeutic agent for these pathologies. Thus, it is relevant that this cation can still maintain its pro-survival and anti-inflammatory role in conditions of autophagy bloc
Thrombin regulates the ability of Schwann cells to support neuritogenesis and to maintain the integrity of the nodes of Ranvier
Schwann cells (SC) are characterized by a remarkable plasticity that enables them to promptly respond to nerve injury promoting axonal regeneration. In peripheral nerves after damage SC convert to a repair-promoting phenotype activating a sequence of supportive functions that drive myelin clearance, prevent neuronal death, and help axon growth and guidance. Regeneration of peripheral nerves after damage correlates inversely with thrombin levels. Thrombin is not only the key regulator of the coagulation cascade but also a protease with hormone-like activities that affects various cells of the central and peripheral nervous system mainly through the protease-activated receptor 1 (PAR1). Aim of the present study was to investigate if and how thrombin could affect the axon supportive functions of SC. In particular, our results show that the activation of PAR1 in rat SC cultures with low levels of thrombin or PAR1 agonist peptides induces the release of molecules, which favor neuronal survival and neurite elongation. Conversely, the stimulation of SC with high levels of thrombin or PAR1 agonist peptides drives an opposite effect inducing SC to release factors that inhibit the extension of neurites. Moreover, high levels of thrombin administered to sciatic nerve ex vivo explants induce a dramatic change in SC morphology causing disappearance of the Cajal bands, enlargement of the Schmidt-Lanterman incisures and calcium-mediated demyelination of the paranodes. Our results indicate thrombin as a novel modulator of SC plasticity potentially able to favor or inhibit SC pro-regenerative properties according to its level at the site of lesion
Measuring source properties and quasi-normal-mode frequencies of heavy massive black-hole binaries with LISA
The laser-interferometer space antenna (LISA) will be launched in the mid
2030s. It promises to observe the coalescence of massive black-hole (BH)
binaries with signal-to-noise ratios (SNRs) reaching thousands. Crucially, it
will detect some of these binaries with high SNR both in the inspiral and the
merger-ringdown stages. Such signals are ideal for tests of General Relativity
(GR) using information from the whole waveform. Here, we consider
astrophysically motivated binary systems at the high-mass end of the population
observable by LISA, and simulate their LISA signals using the newly developed
parametrised, multipolar, aligned-spin effective-one-body model: pSEOBNRv5HM.
The merger-ringdown signal in this model depends on the binary properties
(masses and spins), and also on parameters that describe fractional deviations
from the GR quasi-normal-mode frequencies of the remnant BH. Performing full
Bayesian analyses, we assess to which accuracy LISA will be able to constrain
deviations from GR in the ringdown signal when using information from the whole
signal. We find that these deviations can typically be constrained to within
and in the best cases to within . We also show that we can measure
the binary masses and spins with great accuracy even for very massive BH
systems with low SNR in the inspiral: individual source-frame masses can
typically be constrained to within and as precisely as , and
individual spins can typically be constrained to within and as precisely
as . Finally, we probe the accuracy of the SEOBNRv5HM waveform family by
performing synthetic injections of GR numerical-relativity waveforms. For the
source parameters considered, we measure erroneous deviations from GR due to
systematics in the waveform model. These results confirm the need for improving
waveform models to perform tests of GR with binary BHs at high SNR with LISA.Comment: 15 pages, 18 with appendices, 19 figure
Autophagy is differently regulated in astrocytes and microglia exposed to environmental toxic molecules
Autophagy is generally considered a degradation pathway involved in many neurodegenerative processes. It can be observed in different stress conditions such as starvation generally improving cell survival. Our previous results described the occurrence of autophagy in neuronal cultures exposed to the toxic compound trimethyltin (TMT) (1). TMT belongs to a family of organotin compounds with wide industrial and agricultural applications, especially as heat stabilizers in PVC production and as biocides. In the nervous system TMT determines the selective destruction of neurons in specific brain regions such as the olfactory bulb and the hippocampus. When this toxic molecule was administered to glial cells we observed in astrocytes a rapid block of the autophagic flux and a consequent increased expression of LC3 and p62 which can be observed both in cultured astrocytes and in the brain of intoxicated animals. Conversely, in microglia autophagy was not impaired in the same conditions and p62 accumulation was not observed neither in vitro primary cultures, nor in brain sections of TMT-treated rats. The protein p62 (also known as SQTM1) is known to be selectively degraded through autophagy and its accumulation activates the transcription factor Nrf2 by sequestering Keap1 (2). To note the block of autophagy has been reported to exert an immunosopressive effect in macrophages (3). Thus, the impairment of autophagy in astrocytes could be related to their limited production of pro-inflammatory cytokines and nitric oxide respect to microglia observed after TMT treatment.
This work was supported by grant from Ricerca Scientifica 2013 to L.F
Thrombin receptor PAR-1 is a glial cell receptor involved in the regeneration of peripheral nerves
Thrombin, a multifunctional serine protease, is a key enzyme in the coagulation cascade. Most of its actions are mediated by a G protein-coupled protease activated receptor (PAR-1) which is highly expressed in glial cells especially after injury (Pompili et al., 2006; Pompili et al., 2011) . In the peripheral nerves thrombin and PAR-1 specific agonist peptides produce changes in nerve conduction compatible with a conduction block. Aim of the present study is to determine if the activation of this receptor affects the neurotrophic properties of Schwann cells. In peripheral nerves PAR-1 was predominantly observed by immunofluorescence on non-compacted Schwann cell microvilli at the node of Ranvier. Moreover, PAR- 1 was highly expressed in Schwann cell cultures obtained from both neonatal and adult rat sciatic nerves. When PAR-1 specific peptides were added to these cultures an increased proliferation rate was observed. The synthesis and secretion of several growth factors by Schwann cells treated with PAR-1 agonist peptides were studied by RT-PCR, western blot and proteomics analyses
Theoretical groundwork supporting the precessing-spin two-body dynamics of the effective-one-body waveform models SEOBNRv5
Waveform models are essential for gravitational-wave (GW) detection and
parameter estimation of coalescing compact-object binaries. More accurate
models are required for the increasing sensitivity of current and future GW
detectors. The effective-one-body (EOB) formalism combines the post-Newtonian
(PN) and small mass-ratio approximations with numerical-relativity results, and
produces highly accurate inspiral-merger-ringdown waveforms. In this paper, we
derive the analytical precessing-spin two-body dynamics for the
\texttt{SEOBNRv5} waveform model, which has been developed for the upcoming
LIGO-Virgo-KAGRA observing run. We obtain an EOB Hamiltonian that reduces to
the exact Kerr Hamiltonian in the test-mass limit. It includes the full 4PN
precessing-spin information, and is valid for generic compact objects (i.e.,
for black holes or neutron stars). We also build an efficient and accurate EOB
Hamiltonian that includes partial precessional effects, notably orbit-averaged
in-plane spin effects for circular orbits, and derive 4PN-expanded
precessing-spin equations of motion, consistent with such an EOB Hamiltonian.
The results were used to build the computationally-efficient precessing-spin
multipolar \texttt{SEOBNRv5PHM} waveform model.Comment: 35 page
pySEOBNR: a software package for the next generation of effective-one-body multipolar waveform models
We present pySEOBNR, a Python package for gravitational-wave (GW) modeling
developed within the effective-one-body (EOB) formalism. The package contains
an extensive framework to generate state-of-the-art inspiral-merger-ringdown
waveform models for compact-object binaries composed of black holes and neutron
stars. We document and demonstrate how to use the built-in quasi-circular
precessing-spin model SEOBNRv5PHM, whose aligned-spin limit (SEOBNRv5HM) has
been calibrated to numerical-relativity simulations and the nonspinning sector
to gravitational self-force data using pySEOBNR. Furthermore, pySEOBNR contains
the infrastructure necessary to construct, calibrate, test, and profile new
waveform models in the EOB approach. The efficiency and flexibility of pySEOBNR
will be crucial to overcome the data-analysis challenges posed by upcoming and
next-generation GW detectors on the ground and in space, which will afford the
possibility to observe all compact-object binaries in our Universe.Comment: 21 pages, 4 figure
Protease-activated receptor-1 in Schwann cells and its possible role in the regeneration of peripheral nerves
Protease-activated receptor-1 (PAR-1) is the prototypic member of a family of four
G-protein-coupled receptors that signal in response to extracellular proteases. In the
peripheral nervous system, the expression and/or the role of PARs are still poorly
investigated. High PAR-1 mRNA expression was found in the rat dorsal root ganglia
and the signal intensity of PAR-1 mRNA increased in response to sciatic nerve transection,
both in the proximal and in the distal part of the lesioned nerve (1). Other
authors revealed that functional PAR-1 receptor exists specifically in the non-compacted
Schwann cell myelin microvilli at the nodes of Ranvier in the sciatic nerve
(2). Schwann cells are the principal population of glial cells of the peripheral nervous
system which myelinate axons playing an important role during axonal regeneration
and remyelination (3). The present study was aimed to determine if the activation of
PAR-1 affects the neurotrophic properties of Schwann cells. We observed a specific
staining for PAR-1 in Schwann cells of rat sciatic nerve and also in primary Schwann
cell cultures. To study the role of PAR-1 in Schwann cell cultures, we activated this
receptor with a specific activating peptide (PAR-1 AP). Conditioned medium from
PAR-1 AP-treated Schwann cells reduced the LDH release of PC12 cells respect to the
medium of the untreated cells, suggesting that the stimulation of PAR-1 induces the
production of pro-survival molecules. Also an increased neurite outgrowth on PC12
cells was observed using the conditioned medium from Schwann cells treated with
PAR-1 AP respect to the control obtained from untreated cells. The synthesis and
secretion of several factors produced by Schwann cells treated with PAR-1 AP were
investigated by proteomics, western blot and RT-PCR analyses. By these experiments
we identified as putative neurotrophic candidates some molecules, such as Macrophage
migration inhibitory factor, Syndecan 4 and Annexin A2
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