Biology subjects

Pare, J.-F.

Publications and source records attributed to Pare, J.-F..

5 recordsLinked to original sources

bioRxiv2023

Structural Plasticity of GABAergic Pallidothalamic Terminals in MPTP-treated Parkinsonian Monkeys: A 3D Electron Microscopic Analysis

The globus pallidus pars interna (GPi) is a major source of GABAergic inhibition upon the motor thalamus. GPi neurons are endowed with properties that allow them to fire at a high rate and maintain a tonic inhibitory influence upon thalamocortical neurons. In parkinsonism, the firing rate of GPi neurons is further increased and their firing pattern switches from a tonic to a bursty mode, two pathophysiological changes associated with increased GABAergic pallidothalamic activity. At the thalamic level, GPi terminals display ultrastructural features (large diameter, multiple synapses, large number of mitochondria) that allow them to maintain tonic synaptic inhibition at high firing rate upon thalamocortical neurons in the parvocellular ventral anterior nucleus (VApc) and the centromedian nucleus (CM), the two main GPi-recipient motor thalamic nuclei in nonhuman primates. To determine if changes of GPi neurons activity are associated with neuroplastic reorganization of GPi terminals and their synapses, we used a Single Block Facing/Scanning Electron Microscopy (SBF/SEM), high resolution 3D electron microscopic approach to compare the morphometry of GPi terminals between 2 control and 2 MPTP-treated parkinsonian monkeys. Our findings demonstrate that pallidothalamic terminals in VApc and CM undergo major ultrastructural changes in parkinsonian monkeys: (1) increased terminal volume in both nuclei, (2) increased surface area of synapses in both nuclei, (3) increased number of synapses/GPi terminals in the CM, but not VApc, (4) increased total volume of mitochondria/terminals in both nuclei but not in the number of mitochondria. In contrast, the ultrastructure of putative GABAergic terminals from the reticular thalamic nucleus was not affected in both the VApc and CM of parkinsonian monkeys. Our findings also show striking morphological differences in terminal volume, number/area of synapses and volume/number of mitochondria between GPi terminals in VApc and CM of control monkeys. In conclusion, results of this study demonstrate that GABAergic pallidothalamic terminals are endowed with a high level of structural plasticity that may contribute to the development and maintenance of the abnormal increase in pallidal GABAergic outflow to the thalamus in the parkinsonian state. Furthermore, the evidence for ultrastructural differences between GPi terminals in VApc and CM suggests that Morphologically distinct pallidothalamic terminals underlie specific physiological properties of pallidal inputs to VApc and CM in normal and diseased states.

neuroscience↗

bioRxiv2023

Tyrosinase-induced neuromelanin accumulation triggers rapid dysregulation and degeneration of the mouse locus coeruleus

The locus coeruleus (LC), the major source of norepinephrine (NE) in the brain, is among the first sites of pathology in both Alzheimers disease (AD) and Parkinsons disease (PD), and it undergoes catastrophic degeneration later in both disorders. Dysregulation of the LC is thought to contribute to early behavioral symptoms of AD and PD such as anxiety and sleep disturbances, while frank LC loss promotes cognitive decline. However, the mechanisms responsible for this selective vulnerability are unknown. It has been suggested that neuromelanin (NM) pigment contributes to LC susceptibility, but a causal relationship has been difficult to test because rodents do not naturally produce NM. Here, we report that viral-mediated expression of human tyrosinase-induced pigmentation in male and female mouse LC neurons recapitulated key macroscopic and ultrastructural features of natural primate NM. One week of NM accumulation resulted in LC neuron hyperactivity, reduced tissue NE levels, transcriptional changes, and anxiety-like behavior. By 6 weeks, NM accumulation was associated with severe cell-autonomous LC neuron degeneration, neuroinflammation, and microglial engulfment of the pigment granules, while the anxiety-like behavior abated. These phenotypes are reminiscent of LC dysfunction and cell death in AD and PD, validating this model for studying the consequences of NM accumulation in the LC as it relates to neurodegenerative diseases. Significance StatementAlzheimers disease (AD) and Parkinsons disease (PD) are the most common neurodegenerative diseases worldwide. Because therapies that cure or prevent their progression are lacking, research is focused on the identifying the earliest signs of disease as targets for diagnosis and treatment. The locus coeruleus (LC), the main source of norepinephrine (NE) in the brain, is one of the first brain regions affected in both AD and PD. Early on, LC dysregulation promotes behavioral symptoms of AD and PD, while its subsequent degeneration accelerates disease progression. Here we identify neuromelanin (NM) pigment as an LC vulnerability factor that induces neuronal hyperactivity followed by cell death. Approaches that mitigate NM accumulation and toxicity may target the earliest phases of neurodegenerative disease.

neuroscience↗

bioRxiv2023

RGS14 is neuroprotective against seizure-induced mitochondrial oxidative stress and pathology in hippocampus

RGS14 is a complex multifunctional scaffolding protein that is highly enriched within pyramidal cells (PCs) of hippocampal area CA2. There, RGS14 suppresses glutamate-induced calcium influx and related G protein and ERK signaling in dendritic spines to restrain postsynaptic signaling and plasticity. Previous findings show that, unlike PCs of hippocampal areas CA1 and CA3, CA2 PCs are resistant to a number of neurological insults, including degeneration caused by temporal lobe epilepsy (TLE). While RGS14 is protective against peripheral injury, similar roles for RGS14 during pathological injury in hippocampus remain unexplored. Recent studies show that area CA2 modulates hippocampal excitability, generates epileptiform activity and promotes hippocampal pathology in animal models and patients with TLE. Because RGS14 suppresses CA2 excitability and signaling, we hypothesized that RGS14 would moderate seizure behavior and early hippocampal pathology following seizure activity. Using kainic acid (KA) to induce status epilepticus (KA-SE) in mice, we show loss of RGS14 (RGS14 KO) accelerated onset of limbic motor seizures and mortality compared to wild type (WT) mice, and that KA-SE upregulated RGS14 protein expression in CA2 and CA1 PCs of WT. Utilizing proteomics, we saw loss of RGS14 impacted the expression of a number of proteins at baseline and after KA-SE, many of which associated unexpectedly with mitochondrial function and oxidative stress. RGS14 was shown to localize to the mitochondria in CA2 PCs of mice and reduce mitochondrial respiration in vitro. As a readout of oxidative stress, we found RGS14 KO dramatically increased 3-nitrotyrosine levels in CA2 PCs, which was greatly exacerbated following KA-SE and correlated with a lack of superoxide dismutase 2 (SOD2) induction. Assessing for hallmarks of seizure pathology in RGS14 KO, we observed worse neuronal injury in area CA3 (but none in CA2 or CA1), and a lack of microgliosis in CA1 and CA2 compared to WT. Together, our data demonstrates a newly appreciated neuroprotective role for RGS14 against intense seizure activity in hippocampus. Our findings are consistent with a model where, after seizure, RGS14 is upregulated to support mitochondrial function and prevent oxidative stress in CA2 PCs, limit seizure onset and hippocampal neuronal injury, and promote microglial activation in hippocampus.

neuroscience↗

bioRxiv2023

Autophagy mediates cancer cell resistance to doxorubicin induced by the Programmed Death 1/Programmed Death Ligand 1 immune checkpoint axis

BackgroundWhile the Programmed Death 1/Programmed Death Ligand 1 (PD-1/PD-L1) immune checkpoint is an important mechanism of immune evasion in cancer, recent studies have shown that it can also lead to resistance to chemotherapy in cancer cells via reverse signaling. Here we describe a novel mechanism by which autophagy mediates cancer cell drug resistance induced by PD-1/PD-L1 signaling. MethodsHuman and mouse breast cancer cells were treated with recombinant PD-1 (rPD-1) to stimulate PD-1/PD-L1 signaling. Activation of autophagy was assessed by immunoblot analysis of microtubule-associated protein 1A/1B-light chain 3 (LC3)-II and Beclin 1 protein levels, two important markers of autophagy. Moreover, autophagosome formation was assessed in human breast cancer cells using green fluorescence protein (GFP)-tagged LC3. Cells were either treated with Beclin 1 or Atg7 shRNA to assess the role of autophagy on resistance to doxorubicin mediated by PD-1/PD-L1 signalling. We then investigated signaling mechanisms upstream of PD-1/PD-L1 induced autophagy by assessing phosphorylation of extracellular signal-related kinase (ERK). ResultsTreatment of cells with rPD-1 resulted in a time-dependent increase in LC3-II as well as Beclin 1, and an increase in autophagosome formation. Knockdown of Beclin 1 or Atg7 prevented drug resistance induced by PD-1/PD-L1 signaling. Exposure of breast cancer cells to rPD-1 resulted in increased ERK phosphorylation and inhibition of ERK activation abolished autophagy induced by PD-1/PD-L1 signaling. ConclusionsThese studies provide a rationale for the use of PD-1/PD-L1 immune checkpoint blockers and autophagy inhibitors as potential chemosensitizers in cancer therapy.

cancer biology↗

bioRxiv2021

Enhancers of host immune tolerance to bacterial infection discovered using linked computational and experimental approaches

Current therapeutic strategies against bacterial infections focus on reduction of pathogen load through antibiotics; however, stimulation of host tolerance to infection might offer an alternative approach. Here we used computational transcriptomics and a Xenopus embryo infection model to rapidly discover infection response pathways, identify potential tolerance inducer drugs, and validate their ability to induce broad tolerance. Xenopus embryos exhibit natural tolerance to A. baumanii, K. pneumoniae, S. aureus, and S. pneumoniae bacteria, whereas A. hydrophila and P. aeruginosa produce infection that leads to death. Transcriptional profiling led to definition of a 20-gene signature that allows for discrimination between tolerant and susceptible states, as well as identification of active and passive tolerance responses based on the degree of engagement of gene transcription modulation. Upregulation of metal ion transport and hypoxia pathways reminiscent of responses observed in primate and mouse infection models were identified as tolerance mediators, and drug screening in the susceptible A. hydrophila infection model confirmed that a metal chelator (deferoxamine) and HIF-1 agonist (1,4-DPCA) increase embryo survival despite high pathogen load. These data demonstrate the value of combining the Xenopus embryo infection model with multi-omics analyses for mechanistic discovery and drug repurposing to induce host tolerance to bacterial infection.

immunology↗