TrkB receptor interacts with mGlu2 receptor and mediates antipsychotic-like effects of mGlu2 receptor activation in the mouse.

Metabotropic glutamate receptor 2 (mGlu2) attracts particular attention as a possible target for a new class of antipsychotics. However, the signaling pathways transducing the effects of mGlu2 in the brain remain poorly characterized. Here, we addressed this issue by identifying native mGlu2 interactome in mouse prefrontal cortex. Nanobody-based affinity purification and mass spectrometry identified 149 candidate mGlu2 partners, including the neurotrophin receptor TrkB. The later interaction was confirmed both in cultured cells and prefrontal cortex. mGlu2 activation triggers phosphorylation of TrkB on Tyr816 in primary cortical neurons and prefrontal cortex. Reciprocally, TrkB stimulation enhances mGlu2-operated Gi/o protein activation. Furthermore, TrkB inhibition prevents the rescue of behavioral deficits by glutamatergic antipsychotics in phencyclidine-treated mice. Collectively, these results reveal a cross-talk between TrkB and mGlu2, which is key to the behavioral response to glutamatergic antipsychotics.

Targeting the Brain with Single-Domain Antibodies: Greater Potential Than Stated So Far?

Treatments for central nervous system diseases with therapeutic antibodies have been increasingly investigated over the last decades, leading to some approved monoclonal antibodies for brain disease therapies. The detection of biomarkers for diagnosis purposes with non-invasive antibody-based imaging approaches has also been explored in brain cancers. However, antibodies generally display a low capability of reaching the brain, as they do not efficiently cross the blood-brain barrier. As an alternative, recent studies have focused on single-domain antibodies (sdAbs) that correspond to the antigen-binding fragment. While some reports indicate that the brain uptake of these small antibodies is still low, the number of studies reporting brain-penetrating sdAbs is increasing. In this review, we provide an overview of methods used to assess or evaluate brain penetration of sdAbs and discuss the pros and cons that could affect the identification of brain-penetrating sdAbs of therapeutic or diagnostic interest.

Nanobody-based sensors reveal a high proportion of mGlu heterodimers in the brain.

Membrane proteins, including ion channels, receptors and transporters, are often composed of multiple subunits and can form large complexes. Their specific composition in native tissues is difficult to determine and remains largely unknown. In this study, we developed a method for determining the subunit composition of endogenous cell surface protein complexes from isolated native tissues. Our method relies on nanobody-based sensors, which enable proximity detection between subunits in time-resolved Förster resonance energy transfer (FRET) measurements. Additionally, given conformation-specific nanobodies, the activation of these complexes can be recorded in native brain tissue. Applied to the metabotropic glutamate receptors in different brain regions, this approach revealed the clear existence of functional metabotropic glutamate (mGlu)2-mGlu4 heterodimers in addition to mGlu2 and mGlu4 homodimers. Strikingly, the mGlu4 subunits appear to be mainly heterodimers in the brain. Overall, these versatile biosensors can determine the presence and activity of endogenous membrane proteins in native tissues with high fidelity and convenience.

Developmental exposure to the A6-pesticide causes changes in tyrosine hydroxylase gene expression, neurochemistry, and locomotors behavior in larval zebrafish.

Purpose: In recent years, the increase in the biopesticides synthesis for alternative agricultural uses has required their impacts study. Among these compounds, several of them are known to exert endocrinedisrupting (EDs) effects causing deregulation of physiological functions affecting cell signaling pathways involved in neural cell differentiation leading to developmental neurotoxicity. The objective of our study was to determine the impact of the biopesticide A6 structurally related to estrogenic EDs on zebrafish larvae, to define its toxicity, the mechanisms responsible, and to monitor the locomotors activity at nanomolar concentrations (0. 0.5, 5 and 50 nM).Materials and methods: Using imaging analysis tools, immunohistochemistry, quantitative PCR, and an automated behavior recording system (Zebrabox) we were able to assess these effects.Results: We have shown through its blue fluorescence properties that it accumulates in different parts of the body such as the intestine, adipose tissue, muscles, yolk sac and head. A6 also disrupted swimming behavior by affecting the expression of tyrosine hydroxylase (TH) in dopaminergic neurons.Conclusions: In conclusion, our study provided a mechanistic understanding of the A6 neurotoxic effect which could be the result of its binding to the estrogen receptor.

Prenatal exposure to low doses of fungicides corrupts neurogenesis in neonates.

Neurogenesis plays a crucial role during neurodevelopment and its dysfunction can lead to neurodevelopmental disorders. A recent hypothesis stipulates that exogenous factors could corrupt this process and predispose to neurodegenerative disorders later in life. The presence of pesticide residues in the diet represents a threat of which we have recently become aware of. Indeed, they could corrupt neurogenesis, especially during gestation, potentially leading to impaired neuronal and synaptic functions. Since the effects of this low-noise contamination have not yet been evaluated on the neurodevelopment, we investigated the impact of fungicide residues on WT mice exposed throughout gestation. Thus, mice were exposed to fungicides, cyprodinil, mepanipyrim and pyrimethanil, alone at 0.1 µg/L during gestation until P3. Besides, another group was exposed to a cocktail of these three fungicides (0.1 µg/L each) for the same time. Exposure was performed through drinking water at the regulatory limit dose of the European countries (0.1 µg/L). No general toxicity was observed in neonates on body and brain weight upon fungicide exposure. However, results showed that gestational exposure to fungicide residues substantially promoted an increase of neural precursor cells at P3. This corrupted neurogenesis was linked to increased levels of ß-catenin, likely through the crosstalk of the PI3K/Akt and Wnt/ß-catenin pathways, both involved in cell proliferation. Fungicide exposure also altered protein expression of PSD95 and NMDA receptors in P3 neonates, two targets of the ß-catenin signaling pathway. Adult neural stem cell extractions from mice treated with the fungicide cocktail, showed an increase proliferation and differentiation combined with a reduction of their migration properties. In addition, in vitro studies on hippocampal primary cell cultures treated with various concentrations of fungicides showed neurotoxic effects. To conclude, corruption of neurogenesis by this chemical assault could be a fertile ground for the development of neurological diseases later in life.

Ethinylestradiol (EE2) residues from birth control pills impair nervous system development and swimming behavior of zebrafish larvae.

The ubiquitous use of ethinylestradiol (EE2), an active constituent of birth control preparations, results in continuous release of this synthetic estrogen to surface waters. Many studies document the untoward effects of EE2 on the endocrine system of aquatic organisms. Effects of environmental EE2 on the nervous system are still poorly documented. We studied effects of pico- to nanomolar concentrations of EE2 on early nervous system development of zebrafish larvae. EE2 disrupted axonal nerve regeneration and hair cell regeneration up to 50%. Gene expression in larval brain tissues showed significantly upregulated expression of target genes, such as estrogen and progesterone receptors, and aromatase B. In contrast, downregulation of the tyrosine hydroxylase, involved in the synthesis of neurotransmitters, occurred concomitant with diminution of proliferating cells. Overall, the size of exposed fish larvae decreased by 25% and their swimming behavior was modified compared to non-treated larvae. EE2 interferes with nervous system development, both centrally and peripherally, with negative effects on regeneration and swimming behavior. Survival of fish and other aquatic species may be at risk in chronically EE2-contaminated environments.

Fungicide Residues Exposure and ß-amyloid Aggregation in a Mouse Model of Alzheimer's Disease.

BACKGROUND: Pesticide residues have contaminated our environment and nutrition over the last century. Although these compounds are present at very low concentrations, their long-term effects on human health is of concern. The link between pesticide residues and Alzheimer's disease is not clear and difficult to establish. To date, no in vivo experiments have yet modeled the impact of this chronic contamination on neurodegenerative disorders. OBJECTIVES: We investigated the impact of fungicide residues on the pathological markers of Alzheimer's disease in a transgenic mouse model. METHODS: Transgenic (J20, hAPPSw/Ind) mice were chronically exposed to a cocktail of residues of cyprodinil, mepanipyrim, and pyrimethanil at 0.1µg/L in their drinking water for 9 months. We assessed the effects of fungicide residues on the pathological markers of the disease including Aß aggregates, neuroinflammation, and neuronal loss. Then, we studied the dynamics of Aß aggregation in vivo via a longitudinal study using two-photon microscopy. Finally, we investigated the molecular mechanisms involved in the production and clearance of Aß peptides. RESULTS: We found that a chronic exposure to three fungicide residues exacerbated aggregation, microgliosis, and neuronal loss. These fungicides also increased vascular amyloid aggregates reminiscent of cerebral amyloid angiopathy between 6 and 9 months of treatment. The mechanism of action revealed that fungicides promoted Aß peptide fibril formation in vitro and involved an in vivo overexpression of the levels of the ß-secretase-cleaving enzyme (BACE1) combined with impairment of Aß clearance through neprylisin (NEP). CONCLUSIONS: Chronic exposure of the J20 mouse model of Alzheimer's disease to a cocktail of fungicides, at the regulatory concentration allowed in tap water (0.1µg/L), strengthened the preexisting pathological markers: neuroinflammation, Aß aggregation, and APP ß-processing. We hypothesize prevention strategies toward pesticide long-term exposure may be an alternative to counterbalance the lack of treatment and to slow down the worldwide Alzheimer's epidemic. https://doi.org/10.1289/EHP5550.

Low doses of bioherbicide favour prion aggregation and propagation in vivo.

Public concerns over the use of synthetic pesticides are growing since many studies have shown their impact on human health. A new environmental movement in occidental countries promoting an organic agriculture favours the rebirth of botanical pesticides. These products confer an effective alternative to chemical pesticides such as glyphosate. Among the biopesticides, the α-terthienyls found in the roots of Tagetes species, are powerful broad-spectrum pesticides. We found that an α-terthienyl analogue with herbicidal properties, called A6, triggers resistant SDS oligomers of the pathogenic prion protein PrPSc (rSDS-PrPSc) in cells. Our main question is to determine if we can induce those rSDS-PrPSc oligomers in vitro and in vivo, and their impact on prion aggregation and propagation. Using wild-type mice challenged with prions, we showed that A6 accelerates or slows down prion disease depending on the concentration used. At 5 mg/kg, A6 is worsening the pathology with a faster accumulation of PrPSc, reminiscent to soluble toxic rSDS-PrPSc oligomers. In contrast, at 10 and 20 mg/kg of A6, prion disease occurred later, with less PrPSc deposits and with rSDS-PrPSc oligomers in the brain reminiscent to non-toxic aggregates. Our results are bringing new openings regarding the impact of biopesticides in prion and prion-like diseases.

Plasma cholesterol level determines in vivo prion propagation.

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases with an urgent need for therapeutic and prophylactic strategies. At the time when the blood-mediated transmission of prions was demonstrated, in vitro studies indicated a high binding affinity of the scrapie prion protein (PrPSc) with apoB-containing lipoproteins, i.e., the main carriers of cholesterol in human blood. The aim of the present study was to explore the relationship between circulating cholesterol-containing lipoproteins and the pathogenicity of prions in vivo. We showed that, in mice with a genetically engineered deficiency for the plasma lipid transporter, phospholipid transfer protein (PLTP), abnormally low circulating cholesterol concentrations were associated with a significant prolongation of survival time after intraperitoneal inoculation of the 22L prion strain. Moreover, when circulating cholesterol levels rose after feeding PLTP-deficient mice a lipid-enriched diet, a significant reduction in survival time of mice together with a marked increase in the accumulation rate of PrPSc deposits in their brain were observed. Our results suggest that the circulating cholesterol level is a determinant of prion propagation in vivo and that cholesterol-lowering strategies might be a successful therapeutic approach for patients suffering from prion diseases.

Zeb family members and boundary cap cells underlie developmental plasticity of sensory nociceptive neurons.

Dorsal root ganglia (DRG) sensory neurons arise from heterogeneous precursors that differentiate in two neurogenic waves, respectively controlled by Neurog2 and Neurog1. We show here that transgenic mice expressing a Zeb1/2 dominant-negative form (DBZEB) exhibit reduced numbers of nociceptors and altered pain sensitivity. This reflects an early impairment of Neurog1-dependent neurogenesis due to the depletion of specific sensory precursor pools, which is slightly later partially compensated by the contribution of boundary cap cells (BCCs). Indeed, combined DBZEB expression and genetic BCCs ablation entirely deplete second wave precursors and, in turn, nociceptors, thus recapitulating the Neurog1(-/-) neuronal phenotype. Altogether, our results uncover roles for Zeb family members in the developing DRGs; they show that the Neurog1-dependent sensory neurogenesis can be functionally partitioned in two successive phases; and finally, they illustrate plasticity in the developing peripheral somatosensory system supported by the BCCs, thereby providing a rationale for sensory precursor diversity.