[Show abstract][Hide abstract] ABSTRACT: Background:
Parkinson disease (PD) is a progressive neurodegenerative disorder characterized by loss of dopamine neurons in the substantia nigra pars compacta (SNpc) and widespread aggregates of the protein alpha-synuclein (α-syn). Increasing evidence points to inflammation as a chief mediator; however, the role of α-syn in triggering and sustaining inflammation remains unclear. In models of Alzheimer's disease (AD), multiple sclerosis (MS) and neurotoxin models of PD, the chemokine CX3CL1 (fractalkine) and its receptor (CX3CR1) have important roles in modulating neuroinflammation.
To examine the role of fractalkine signaling in α-syn-induced-neuroinflammation and neurodegeneration, we used an in vivo mouse model in which human α-syn is overexpressed by an adeno associated viral vector serotype 2 (AAV2) and in vitro phagocytosis and protein internalization assays with primary microglia treated with aggregated α-syn.
We observed that loss of CX3CR1 expression led to a reduced inflammatory response, with reduced IgG deposition and expression of MHCII 4 weeks post-transduction. Six months post transduction, AAV2 mediated overexpression of α-syn leads to loss of dopaminergic neurons, and this loss was not exacerbated in animals with deletion of CX3CR1. To determine the mechanism by which CX3CR1affects inflammatory responses in α-syn-induced inflammation, phagocytosis was assessed using a fluorescent microsphere assay as well as by microglial uptake of aggregated α-syn. CX3CR1-/- microglia showed reduced uptake of fluorescent beads and aggregated α-syn.
Our results suggest that one mechanism by which CX3CR1-/- attenuates inflammation is at the level of phagocytosis of aggregated α-syn by microglia. These data implicate fractalkine signaling as a potential therapeutic target for regulating inflammatory response in α-syn models PD.
[Show abstract][Hide abstract] ABSTRACT: Gene-based therapies for neurological diseases continue to develop briskly. As disease mechanisms are elucidated, flexible gene delivery platforms incorporating transcriptional regulatory elements, therapeutic genes and targeted delivery are required for the safety and efficacy of these approaches. Adenovirus serotype 5 (Ad5)-based vectors can carry large genetic payloads to provide this flexibility, but do not transduce neuronal cells efficiently. To address this, we have developed a tropism-modified Ad5 vector with neuron-selective targeting properties for evaluation in models of Parkinson disease therapy. A panel of tropism-modified Ad5 vectors was screened for enhanced gene delivery in a neuroblastoma cell line model system. We used these observations to design and construct an unbiased Ad vector platform, consisting of an unmodified Ad5 and a tropism-modified Ad5 vector containing the fiber knob domain from canine Ad serotype 2 (Ad5-CGW-CK2). Delivery to the substantia nigra or striatum showed that this vector produced a neuronally-restricted pattern of gene expression. Many of the transduced neurons were from regions with afferent projections to the injection site, implicating that OPEN ACCESS Viruses 2014, 6 3294 the vector binds the presynaptic terminal resulting in presynaptic transduction. We show that Ad5-CGW-CK2 can selectively transduce neurons in the brain and hypothesize that this modular platform is potentially adaptable to clinical use.
[Show abstract][Hide abstract] ABSTRACT: To shorten the time between brain harvesting and microglia isolation, and characterization, we utilized the MACS(®) neural dissociation kit followed by OctoMACS(®) CD11b magnetic bead isolation technique to positively select for brain microglia expressing the pan-microglial marker CD11b, a key subunit of the membrane attack complex (MAC). This protocol yields a viable and highly pure (>95%) microglial population of approximately 500,000 cells per pup that is amenable for in vitro characterization within hours or days after being harvested from brain tissue. Primary microglia from C57Bl/6 mice were plated for next-day analyses of morphology and cellular markers by immunocytochemistry or for analysis of gene expression under resting or LPS-stimulated conditions. The ease of isolation enables investigators to perform molecular and cellular analyses without having to wait 1-2 weeks to isolate microglia by conventional methods involving mechanical agitation to dislodge these from astrocyte beds.
No preview · Article · Jul 2013 · Methods in molecular biology (Clifton, N.J.)
[Show abstract][Hide abstract] ABSTRACT: Accumulation of α-synuclein (α-syn) in the brain is a core feature of Parkinson disease (PD) and leads to microglial activation, production of inflammatory cytokines and chemokines, T-cell infiltration, and neurodegeneration. Here, we have used both an in vivo mouse model induced by viral overexpression of α-syn as well as in vitro systems to study the role of the MHCII complex in α-syn-induced neuroinflammation and neurodegeneration. We find that in vivo, expression of full-length human α-syn causes striking induction of MHCII expression by microglia, while knock-out of MHCII prevents α-syn-induced microglial activation, antigen presentation, IgG deposition, and the degeneration of dopaminergic neurons. In vitro, treatment of microglia with aggregated α-syn leads to activation of antigen processing and presentation of antigen sufficient to drive CD4 T-cell proliferation and to trigger cytokine release. These results indicate a central role for microglial MHCII in the activation of both the innate and adaptive immune responses to α-syn in PD and suggest that the MHCII signaling complex may be a target of neuroprotective therapies for the disease.
Full-text · Article · Jun 2013 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Background
The protein alpha-synuclein (α-SYN), which is found in the Lewy bodies of dopamine-producing (DA) neurons in the substantia nigra (SN), has an important role in the pathogenesis of Parkinson’s disease (PD). Previous studies have shown that neuroinflammation plays a key role in PD pathogenesis. In an AAV-synuclein mouse model of PD, we have found that over-abundance of α-SYN triggers the expression of NF-κB p65, and leads to microglial activation and DA neurodegeneration. We also have observed that Fcγ receptors (FcγR), proteins present on the surface of microglia that bind immunoglobulin G (IgG) and other ligands, are key modulators of α-SYN-induced neurodegeneration.
In order to study the role of FcγRs in the interactions of α-SYN and microglia, we treated the primary microglial cultures from wild-type (WT) and FcγR−/− mice with aggregated human α-SYN in vitro.
Using immunocytochemistry, we found that α-SYN was taken up by both WT and FcγR−/− microglia, however, their patterns of internalization were different, with aggregation in autophagosomes in WT cells and more diffuse localization in FcγR−/− microglia. In WT microglia, α-SYN induced the nuclear accumulation of NF-κB p65 protein and downstream chemokine expression while in FcγR−/− mouse microglia, α-SYN failed to trigger the enhancement of nuclear NF-κB p65, and the pro-inflammatory signaling was reduced.
Our results suggest that α-SYN can interact directly with microglia and can be internalized and trafficked to autophagosomes. FcγRs mediate this interaction, and in the absence of the gamma chain, there is altered intracellular trafficking and attenuation of pro-inflammatory NF-κB signaling. Therefore, blocking either FcγR signaling or downstream NF-κB activation may be viable therapeutic strategies in PD.
Full-text · Article · Nov 2012 · Journal of Neuroinflammation
[Show abstract][Hide abstract] ABSTRACT: The exact biological role of the cytokine tumor necrosis factor (TNF) in the central nervous system (CNS) is not well understood; but overproduction of TNF by activated microglia has been implicated in neuronal death, suggesting that TNF inhibition in the CNS may be a viable neuroprotective strategy. We investigated the role of TNF signaling in regulation of microglia effector functions using molecular, cellular, and functional analyses of postnatal and adult microglia populations in the CNS. No differences were found by flow cytometric analyses in the basal activation state between TNF-null and wild-type mice. Although TNF-null microglia displayed an atypical morphology with cytoplasmic vacuoles in response to stimulation with lipopolysaccharide (LPS), the phagocytic response of TNF-null microglia to Escherichia coli particles in vitro was normal and there were no signs of enhanced caspase 3 activation or apoptosis. Functionally, conditioned media from LPS-stimulated TNF-null microglia was found to have significantly reduced levels of IL-10, IL-6, IL-1β, IL-12, and CXCL1 relative to wild-type microglia and exerted no cytotoxic effects on neurally differentiated dopaminergic (DA) MN9D cells. In contrast, incubation of wild-type microglia with TNF inhibitors selectively depleted the levels of soluble TNF and its cytotoxicity on MN9D cells. To distinguish whether reduced cytotoxicity by LPS-activated TNF-null microglia could be attributed to deficient autocrine TNF signaling, we employed primary microglia deficient in one or both TNF receptors (TNFR1 and TNFR2) in co-culture with MN9D cells and found that neither receptor is required to elicit LPS-evoked TNF production and cytotoxicity on DA cells.
[Show abstract][Hide abstract] ABSTRACT: Parkinson's disease (PD) is a progressive neurodegenerative disorder typified by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Recent evidence indicates that neuroinflammation may play a critical role in the pathogenesis of PD, particularly tumor necrosis factor (TNF). We have previously shown that soluble TNF (solTNF) is required to mediate robust degeneration induced by 6-hydroxydopamine (6-OHDA) or lipopolysaccharide. What remains unknown is whether TNF inhibition can attenuate the delayed and progressive phase of neurodegeneration. To test this, rats were injected in the SNpc with lentivirus encoding dominant-negative TNF (lenti-DN-TNF) 2 weeks after receiving a 6-OHDA lesion. Remarkably, when examined 5 weeks after the initial 6-OHDA lesion, no further loss of nigral DA neurons was observed. Lenti-DN-TNF also attenuated microglial activation. Together, these data suggest that TNF is likely a critical mediator of nigral DA neuron death during the delayed and progressive phase of neurodegeneration, and that microglia may be the principal cell type involved. These promising findings provide compelling reasons to perform DN-TNF gene transfer studies in nonhuman primates with the long-term goal of using it in the clinic to prevent the delayed and progressive degeneration of DA neurons that gives rise to motor symptoms in PD.
Full-text · Article · Oct 2010 · Molecular Therapy
[Show abstract][Hide abstract] ABSTRACT: Microglial activation and overproduction of inflammatory mediators in the central nervous system (CNS) have been implicated in Alzheimer's disease (AD). Elevated levels of the pro-inflammatory cytokine tumor necrosis factor (TNF) have been reported in serum and post-mortem brains of patients with AD, but its role in progression of AD is unclear. Using novel engineered dominant negative TNF inhibitors (DN-TNFs) selective for soluble TNF (solTNF), we investigated whether blocking TNF signaling with chronic infusion of the recombinant DN-TNF XENP345 or a single injection of a lentivirus encoding DN-TNF prevented the acceleration of AD-like pathology induced by chronic systemic inflammation in 3xTgAD mice. We found that chronic inhibition of solTNF signaling with either approach decreased the LPS-induced accumulation of 6E10-immunoreactive protein in hippocampus, cortex, and amygdala. Immunohistological and biochemical approaches using a C-terminal APP antibody indicated that a major fraction of the accumulated protein was likely to be C-terminal APP fragments (beta-CTF) while a minor fraction consisted of Av40 and 42. Genetic inactivation of TNFR1-mediated TNF signaling in 3xTgAD mice yielded similar results. Taken together, our studies indicate that soluble TNF is a critical mediator of the effects of neuroinflammation on early (pre-plaque) pathology in 3xTgAD mice. Targeted inhibition of solTNF in the CNS may slow the appearance of amyloid-associated pathology, cognitive deficits, and potentially the progressive loss of neurons in AD.
Full-text · Article · May 2009 · Neurobiology of Disease
[Show abstract][Hide abstract] ABSTRACT: Epidemiological studies suggest that chronic use of nonsteroidal anti-inflammatory drugs lowers the incidence of Parkinson's disease (PD) in humans and implicate neuroinflammatory processes in the death of dopamine (DA) neurons. Here, we demonstrate that regulator of G-protein signaling 10 (RGS10), a microglia-enriched GAP (GTPase accelerating protein) for Galpha subunits, is an important regulator of microglia activation. Flow-cytometric and immunohistochemical analyses indicated that RGS10-deficient mice displayed increased microglial burden in the CNS, and exposure to chronic systemic inflammation induced nigral DA neuron loss measured by unbiased stereology. Primary microglia isolated from brains of RGS10-deficient mice displayed dysregulated inflammation-related gene expression profiles under basal and stimulated conditions in vitro compared with that of primary microglia isolated from wild-type littermates. Similarly, knockdown of RGS10 in the BV2 microglia cell line resulted in dysregulated inflammation-related gene expression, overproduction of tumor necrosis factor (TNF), and enhanced neurotoxic effects of BV2 microglia on the MN9D dopaminergic cell line that could be blocked by addition of the TNF decoy receptor etanercept. Importantly, ablation of RGS10 in MN9D dopaminergic cells further enhanced their vulnerability to microglial-derived death-inducing inflammatory mediators, suggesting a role for RGS10 in modulating the sensitivity of dopaminergic neurons against inflammation-mediated cell death. Together, our findings indicate that RGS10 limits microglial-derived TNF secretion and regulates the functional outcome of inflammatory stimuli in the ventral midbrain. RGS10 emerges as a novel drug target for prevention of nigrostriatal pathway degeneration, the neuropathological hallmark of PD.
Full-text · Article · Sep 2008 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience