Matching Items (4)

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Toxic Oligomeric Alpha-Synuclein Variants Present in Human Parkinson’s Disease Brains Are Differentially Generated in Mammalian Cell Models

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Misfolding and aggregation of α-synuclein into toxic soluble oligomeric α-synuclein aggregates has been strongly correlated with the pathogenesis of Parkinson’s disease (PD). Here, we show that two different morphologically distinct

Misfolding and aggregation of α-synuclein into toxic soluble oligomeric α-synuclein aggregates has been strongly correlated with the pathogenesis of Parkinson’s disease (PD). Here, we show that two different morphologically distinct oligomeric α-synuclein aggregates are present in human post-mortem PD brain tissue and are responsible for the bulk of α-synuclein induced toxicity in brain homogenates from PD samples. Two antibody fragments that selectively bind the different oligomeric α-synuclein variants block this α-synuclein induced toxicity and are useful tools to probe how various cell models replicate the α-synuclein aggregation pattern of human PD brain. Using these reagents, we show that mammalian cell type strongly influences α-synuclein aggregation, where neuronal cells best replicate the PD brain α-synuclein aggregation profile. Overexpression of α-synuclein in the different cell lines increased protein aggregation but did not alter the morphology of the oligomeric aggregates generated. Differentiation of the neuronal cells into a cholinergic-like or dopaminergic-like phenotype increased the levels of oligomeric α-synuclein where the aggregates were localized in cell neurites and cell bodies.

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Date Created
  • 2015-07-22

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Human α4β2 Nicotinic Acetylcholine Receptor as a Novel Target of Oligomeric α-Synuclein

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Cigarette smoking is associated with a decreased incidence of Parkinson disease (PD) through unknown mechanisms. Interestingly, a decrease in the numbers of α4β2 nicotinic acetylcholine receptors (α4β2-nAChRs) in PD patients

Cigarette smoking is associated with a decreased incidence of Parkinson disease (PD) through unknown mechanisms. Interestingly, a decrease in the numbers of α4β2 nicotinic acetylcholine receptors (α4β2-nAChRs) in PD patients suggests an α4β2-nAChR-mediated cholinergic deficit in PD. Although oligomeric forms of α-synuclein have been recognized to be toxic and involved in the pathogenesis of PD, their direct effects on nAChR-mediated cholinergic signaling remains undefined. Here, we report for the first time that oligomeric α-synuclein selectively inhibits human α4β2-nAChR-mediated currents in a dose-dependent, non-competitive and use-independent manner. We show that pre-loading cells with guanyl-5′-yl thiophosphate fails to prevent this inhibition, suggesting that the α-synuclein-induced inhibition of α4β2-nAChR function is not mediated by nAChR internalization. By using a pharmacological approach and cultures expressing transfected human nAChRs, we have shown a clear effect of oligomeric α-synuclein on α4β2-nAChRs, but not on α4β4- or α7-nAChRs, suggesting nAChR subunit selectivity of oligomeric α-synuclein-induced inhibition. In addition, by combining the size exclusion chromatography and atomic force microscopy (AFM) analyses, we find that only large (>4 nm) oligomeric α-synuclein aggregates (but not monomeric, small oligomeric or fibrillar α-synuclein aggregates) exhibit the inhibitory effect on human α4β2-nAChRs. Collectively, we have provided direct evidence that α4β2-nAChR is a sensitive target to mediate oligomeric α-synuclein-induced modulation of cholinergic signaling, and our data imply that therapeutic strategies targeted toward α4β2-nAChRs may have potential for developing new treatments for PD.

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Created

Date Created
  • 2013-02-10

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Focal and Systemic Immune Responses Following Intracerebral Hemorrhage

Description

Intracerebral hemorrhage (ICH) is a devastating type of acute brain injury with high mortality and disability. Acute brain injury swiftly alters the immune reactivity within and outside the brain; however,

Intracerebral hemorrhage (ICH) is a devastating type of acute brain injury with high mortality and disability. Acute brain injury swiftly alters the immune reactivity within and outside the brain; however, the mechanisms and influence on neurological outcome remains largely unknown. My dissertation investigated how ICH triggers focal and systemic immune responses and their impact hemorrhagic brain injury. At the focal level, a significant upregulation of interleukin (IL)-15 was identified in astrocytes of brain sections from ICH patients. A transgenic mouse line where the astrocytic IL-15 expression is controlled by a glial fibrillary acidic protein promoter (GFAP-IL-15tg) was generated to investigate its role in ICH. Astrocyte-targeted expression of IL-15 exacerbated brain edema and neurological deficits following ICH. Aggravated ICH injury was accompanied by an accumulation of pro-inflammatory microglia proximal to astrocytes in perihematomal tissues, microglial depletion attenuated the augmented ICH injury in GFAP-IL-15tg mice. These findings suggest that IL-15 mediates the crosstalk between astrocytes and microglia, which worsens ICH injury.Systemic immune response was investigated by leveraging the novel method of obtaining and analyzing bone marrow cells from the cranial bone flaps of ICH patients. A swift increase of hematopoietic stem cell (HSCs) population in the bone marrow was identified, along with a shift towards the myeloid cell lineage. Human findings were mirrored in an ICH mouse model. Fate mapping these HSCs revealed increased genesis of Ly6Clow monocytes in the bone marrow, which transmigrate into the hemorrhagic brain and give rise to alternative activation marker bearing macrophage. Blockade of the β3-adrenergic receptor or inhibition of Cdc42 abolished ICH-induced myeloid bias of HSCs. Importantly, mirabegron, a Food and Drug Administration-approved β3 adrenergic receptor agonist, and a Cdc42 activator, IL-3, enhanced bone marrow generation of Ly6Clow monocytes and improved recovery. These results suggest that brain injury modulates HSC lineage destination to curb distal brain inflammation, implicating the bone marrow as a unique niche for self-protective neuroimmune interactions. Together, these results demonstrate how acute brain injury exerts a profound yet distinct effect on immune responses within and outside the brain and sheds new light on neuroimmune interactions with potential clinical implications.

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Created

Date Created
  • 2020

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A novel mechanism underlies pathological, beta-amyloid-induced neuronal hyperexcitation

Description

Patients with Alzheimer's disease (AD) exhibit a significantly higher incidence of unprovoked seizures compared to age-matched non-AD controls, and animal models of AD (i.e., transgenic human amyloid precursor protein, hAPP

Patients with Alzheimer's disease (AD) exhibit a significantly higher incidence of unprovoked seizures compared to age-matched non-AD controls, and animal models of AD (i.e., transgenic human amyloid precursor protein, hAPP mice) display neural hyper-excitation and epileptic seizures. Hyperexcitation is particularly important because it contributes to the high incidence of epilepsy in AD patients as well as AD-related synaptic deficits and neurodegeneration. Given that there is significant amyloid-β (Aβ) accumulation and deposition in AD brain, Aβ exposure ultimately may be responsible for neural hyper-excitation in both AD patients and animal models. Emerging evidence indicates that α7 nicotinic acetylcholine receptors (α7-nAChR) are involved in AD pathology, because synaptic impairment and learning and memory deficits in a hAPPα7-/- mouse model are decreased by nAChR α7 subunit gene deletion. Given that Aβ potently modulates α7-nAChR function, that α7-nAChR expression is significantly enhanced in both AD patients and animal models, and that α7-nAChR play an important role in regulating neuronal excitability, it is reasonable that α7-nAChRs may contribute to Aβ-induced neural hyperexcitation. We hypothesize that increased α7-nAChR expression and function as a consequence of Aβ exposure is important in Aβ-induced neural hyperexcitation. In this project, we found that exposure of Aβ aggregates at a nanomolar range induces neuronal hyperexcitation and toxicity via an upregulation of α7-nAChR in cultured hippocampus pyramidal neurons. Aβ up-regulates α7-nAChRs function and expression through a post translational mechanism. α7-nAChR up-regulation occurs prior to Aβ-induced neuronal hyperexcitation and toxicity. Moreover, inhibition of α7-nAChR or deletion of α7-nAChR prevented Aβ induced neuronal hyperexcitation and toxicity, which suggests that α7-nAChRs are required for Aβ induced neuronal hyperexcitation and toxicity. These results reveal a profound role for α7-nAChR in mediating Aβ-induced neuronal hyperexcitation and toxicity and predict that Aβ-induced up-regulation of α7-nAChR could be an early and critical event in AD etiopathogenesis. Drugs targeting α7-nAChR or seizure activity could be viable therapies for AD treatment.

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Created

Date Created
  • 2011