Glucocorticoid receptor in astrocytes regulates midbrain dopamine neurodegeneration through connexin hemichannel activity

The precise contribution of astrocytes in neuroinflammatory process occurring in Parkinson's disease (PD) is not well characterized. In this study, using GR(Cx30CreERT2) mice that are conditionally inactivated for glucocorticoid receptor (GR) in astrocytes, we have examined the actions of astrocytic GR during dopamine neuron (DN) degeneration triggered by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The results show significantly augmented DN loss in GR(Cx30CreERT2) mutant mice in substantia nigra (SN) compared to controls. Hypertrophy of microglia but not of astrocytes was greatly enhanced in SN of these astrocytic GR mutants intoxicated with MPTP, indicating heightened microglial reactivity compared to similarly-treated control mice. In the SN of GR astrocyte mutants, specific inflammation-associated transcripts ICAM-1, TNF-alpha and Il-1 beta as well as TNF-alpha protein levels were significantly elevated after MPTP neurotoxicity compared to controls. Interestingly, this paralleled increased connexin hemichannel activity and elevated intracellular calcium levels in astrocytes examined in acute midbrain slices from control and mutant mice treated with MPP+. The increased connexin-43 hemichannel activity was found in vivo in MPTP-intoxicated mice. Importantly, treatment of MPTP-injected GR(Cx30CreERT2) mutant mice with TAT-Gap19 peptide, a specific connexin-43 hemichannel blocker, reverted both DN loss and microglial activation; in wild-type mice there was partial but significant survival effect. In the SN of postmortem PD patients, a significant decrease in the number of astrocytes expressing nuclear GR was observed, suggesting the participation of astrocytic GR deregulation of inflammatory process in PD. Overall, these data provide mechanistic insights into GR-modulated processes in vivo, specifically in astrocytes, that contribute to a pro-inflammatory state and dopamine neurodegeneration in PD pathology

Süße Geschmacksrezeptoren in normalen und pathologischen Rattengehirnen

The mammalian sweet taste receptors (T1Rs) are G protein-coupled receptor complexes, which have recently been proposed to be associated with the brain glucose sensor. Here, we investigated the expression of sweet taste receptors T1R1 and T1R3 in normal and pathological rat brain, including tissue libraries of C6 rat glioma and rat brain of middle cerebral artery occlusion (MCAO), by immunohistological methods. The results demonstrated that neurons located in different brain regions, including the cortex, hippocampus, hypothalamus and habenula, showed immunohistological signals of T1R1 and T1R3. Additionally, significant T1R1 and T1R3 immunoreactivities were also observed in the intra-ventricular epithelial cells of the choroid plexus and ependyma. Furthermore, immunohistological signals of T1R1 and T1R3 were evidently observed in C6 tumor cells. In addition, we have compared the expression levels of T1R1 and T1R3 in the ischemic core and penumbra areas with non-ischemic areas of the MCAO model. The data showed that the signal intensity of T1R1 and T1R3 was significantly increased in the ischemic areas at day 1, 3 and 7 after MCAO compared with their controls, respectively. Particularly, T1R1 reached the peak level at day 7 (all p < 0.05). To our knowledge, this is the first demonstration of the expression of the sweet taste receptors, T1R1 and T1R3, in C6 rat glioma and rat MCAO ischemia. The present results indicated that ischemic injury might affect the expression of G-protein-coupled sweet taste receptors in rat brain, suggesting sweet taste receptors might play important roles in the physiological and pathological processes in the mammalian nervous system.Die T1R-Proteine sind G-Protein-gekoppelte Rezeptoren, die die Geschmacksqualität „süß“, vermitteln. Vor kurzem wurden die T1Rs in Verbindung mit dem Glukose-Sensor des Säugergehirns gebracht. Wir untersuchten die Expression von T1R1 und T1R3 in normalen und pathologischen Rattengehirnen mittels immunohistologischer Methoden. In unseren Experimenten wurde sowohl gesundes, als auch Gewebe von Hirntumor (Gliom, C6) und MCAO-Läsionen verwendet. Unsere Ergebnisse deuten auf ein unterschiedliches Expressionsnievau von T1R1 und T1R3 in verschiedenen Gehirnregionen hin, insbesondere in der Hirnrinde, im Hippocampus, Hypothalamus und der Habenula. Außerdem konnte die erhöhte Expression von T1R1 und T1R3 auch in den intraventrikulären Epithelzellen des Plexus choroideus und im Ependym nachgewiesen werden. Darüber hinaus haben wir auch die erhöhte Expression von T1R1 und T1R3 in C6 Tumorzellen beobachtet. Im MCAO-Modell ließ sich nachweisen, daß die Expression von T1R1 und T1R3 deutlich in den ischämischen Bereichen an den Tagen 1, 3 und 7 nach Reperfusion erhöht war, wobei die höchste Expression von T1R1 am 7 Tag nach der Reperfusion festgestellt werden konnte (p <0,05). Unsere Experimente liefern den ersten Nachweis einer Veränderung in der Expression von T1R1 und T1R3 in C6 Ratten Gliomen und im MCAO Modell. Die vorliegenden Ergebnisse zeigen, dass in Folge der ischämischen Schädigung die Expression von G-Protein-gekoppelte Rezeptoren verändert werden kannt. Unsere Ergebnisse deuten darauf hin, dass T1R eine Rolle in den physiologischen und pathologischen Prozesse im ZNS der Säugetiere haben

Remediation of diesel contaminated soils using persulfate under alkaline condition

A laboratory study was conducted to assess the feasibility of remediating diesel-contaminated soils using sodium persulfate (SPS) oxidation under an alkaline pH. Lime (CaO) and sodium hydroxide (NaOH) were used as the alkaline sources, and various factors, including temperature, reaction time and concentration level, were investigated. Moreover, the combined usage of hydrogen peroxide (HP) and SPS in the presence or absence of NaOH was also studied. It was found that lime hydration resulted in rapid increases in pH (>12) and temperature (75 �C maximum) at a CaO/H2 O mass ratio of 3/20. In the NaOH or CaO/SPS system, the maximum diesel degradation achieved was approximately 30 %. It was observed that using a larger amount of alkaline increased SPS decomposition and had almost no effect on diesel degradation. Limited solubilization of contaminants may have inhibited the effectiveness of alkalineactivated persulfate oxidation during the aqueous phase and hence resulted in incomplete diesel degradation. The highest rate of diesel degradation (i.e., 56 % in 7 days) was achieved using the dual oxidation system, in which a HP/SPS molar ratio of 3.3/0.5 was used. An aggressive oxidation process, coupled with HP, may enhance desorption of diesel from soils and allow oxidation to occur during the aqueous phase

Pathological potential of oligodendrocyte precursor cells: terra incognita

Adult oligodendrocyte precursor cells (aOPCs), transformed from fetal OPCs, are idiosyncratic neuroglia of the central nervous system (CNS) that are distinct in many ways from other glial cells. OPCs have been classically studied in the context of their remyelinating capacity. Recent studies, however, revealed that aOPCs not only contribute to post-lesional remyelination but also play diverse crucial roles in multiple neurological diseases. In this review we briefly present the physiology of aOPCs and summarize current knowledge of the beneficial and detrimental roles of aOPCs in different CNS diseases. We discuss unique features of aOPC death, reactivity, and changes during senescence, as well as aOPC interactions with other glial cells and pathological remodeling during disease. Finally, we outline future perspectives for the study of aOPCs in brain pathologies which may instigate the development of aOPC-targeting therapeutic strategies

A laboratory treatability study for pilot-scale soil washing of Cr, Cu, Ni and Zn contaminated soils

As part of this study, laboratory- and pilot-scale washing of soils contaminated with Cr, Cu, Ni, and Zn were performed. The soil washing agents used included strong acids (hydrochloric acid (HCl) and sulfuric acid (H2SO4)) and chelating agents (ethylenediaminetetraacetic acid calcium disodium salt (EDTA) and citric acid (CA)). A positive correlation was observed between the removal efficiency of the washing process and the concentration of the washing solution. Moreover, the effect of H2SO4 on metal removal with respect to concentration variations was more pronounced in the batch studies due mainly to acid dissolution of the heavy metals. Using H2SO4 concentrations of between 300 and 1000 mM, the removal efficiencies achieved when targeting Cr, Cu, Ni, Zn and the total metal content were 41–42, 38–68, 23–25, 47–53, and 42–55%. The removal efficiencies recorded during the engineering pilot scale washing of the field soils using H2SO4 are comparable to those obtained in the batch study

Monitoring gap junctional communication in astrocytes from acute adult mouse brain slices using the gap-FRAP technique

International audienceIntercellular communication through gap junction channels plays a key role in cellular homeostasis and in synchronizing physiological functions, a feature that is modified in number of pathological situations. In the brain, astrocytes are the cell population that expresses the highest amount of gap junction proteins, named connexins. Several techniques have been used to assess the level of gap junctional communication in astrocytes, but so far they remain very difficult to apply in adult brain tissue. Here, using specific loading of astrocytes with sulforhodamine 101, we adapted the gap-FRAP (Fluorescence Recovery After Photobleaching) to acute hippocampal slices from 9 month-old adult mice. We show that gap junctional communication monitored in astrocytes with this technique was inhibited either by pharmacological treatment with a gap junctional blocker or in mice lacking the two main astroglial connexins, while a partial inhibition was measured when only one connexin was knocked-out. We validate this approach using a mathematical model of sulforhodamine 101 diffusion in an elementary astroglial network and a quantitative analysis of the exponential fits to the fluorescence recovery curves. Consequently, we consider that the adaptation of the gap-FRAP technique to acute brain slices from adult mice provides an easy going and valuable approach that allows overpassing this age-dependent obstacle and will facilitate the investigation of gap junctional communication in adult healthy or pathological brain

Inactive variants of death receptor p75(NTR) reduce Alzheimer's neuropathology by interfering with APP internalization

10.15252/embj.2020104450EMBO JOURNAL40

Contribution of Astroglial Cx43 Hemichannels to the Modulation of Glutamatergic Currents by D-Serine in the Mouse Prefrontal Cortex

International audienceAstrocytes interact dynamically with neurons by modifying synaptic activity and plasticity. This interplay occurs through a process named gliotransmission, meaning that neuroactive molecules are released by astrocytes. Acting as a gliotransmitter, D-serine, a co-agonist of the NMDA receptor at the glycine-binding site, can be released by astrocytes in a calcium [Ca2+]i-dependent manner. A typical feature of astrocytes is their high expression level of connexin43 (Cx43), a protein forming gap junction channels and hemichannels associated with dynamic neuroglial interactions. Pharmacological and genetic inhibition of Cx43 hemichannel activity reduced the amplitude of NMDA EPSCs in mouse layer 5 prefrontal cortex pyramidal neurons without affecting AMPA EPSC currents. This reduction of NMDA EPSCs was rescued by addition of D-serine in the extracellular medium. LTP of NMDA and AMPA EPSCs after high-frequency stimulation was reduced by prior inhibition of Cx43 hemichannel activity. Inactivation of D-serine synthesis within the astroglial network resulted in the reduction of NMDA EPSCs, which was rescued by adding extracellular D-serine. We showed that the activity of Cx43 hemichannels recorded in cultured astrocytes was [Ca2+]I dependent. Accordingly, in acute cortical slices, clamping [Ca2+]i at a low level in astroglial network resulted in an inhibition of NMDA EPSC potentiation that was rescued by adding extracellular D-serine. This work demonstrates that astroglial Cx43 hemichannel activity is associated with D-serine release. This process, occurring by direct permeation of D-serine through hemichannels or indirectly by Ca2+ entry and activation of other [Ca2+]i-dependent mechanisms results in the modulation of synaptic activity and plasticity.SIGNIFICANCE STATEMENT We recorded neuronal glutamatergic (NMDA and AMPA) responses in prefrontal cortex (PFC) neurons and used pharmacological and genetic interventions to block connexin-mediated hemichannel activity specifically in a glial cell population. For the first time in astrocytes, we demonstrated that hemichannel activity depends on the intracellular calcium concentration and is associated with D-serine release. Blocking hemichannel activity reduced the LTP of these excitatory synaptic currents triggered by high-frequency stimulation. These observations may be particularly relevant in the PFC, where D-serine and its converting enzyme are highly expressed