Melissa K. McCoy

TNF signaling inhibition in the CNS: implications for normal brain function and neurodegenerative disease

The role of tumor necrosis factor (TNF) as an immune mediator has long been appreciated but its function in the brain is still unclear. TNF receptor 1 (TNFR1) is expressed in most cell types, and can be activated by binding of either soluble TNF (solTNF) or transmembrane TNF (tmTNF), with a preference for solTNF; whereas TNFR2 is expressed primarily by microglia and endothelial cells and is preferentially activated by tmTNF. Elevation of solTNF is a hallmark of acute and chronic neuroinflammation as well as a number of neurodegenerative conditions including ischemic stroke, Alzheimers (AD), Parkinsons (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). The presence of this potent inflammatory factor at sites of injury implicates it as a mediator of neuronal damage and disease pathogenesis, making TNF an attractive target for therapeutic development to treat acute and chronic neurodegenerative conditions. However, new and old observations from animal models and clinical trials reviewed here suggest solTNF and tmTNF exert different functions under normal and pathological conditions in the CNS. A potential role for TNF in synaptic scaling and hippocampal neurogenesis demonstrated by recent studies suggest additional in-depth mechanistic studies are warranted to delineate the distinct functions of the two TNF ligands in different parts of the brain prior to large-scale development of anti-TNF therapies in the CNS. If inactivation of TNF-dependent inflammation in the brain is warranted by additional pre-clinical studies, selective targeting of TNFR1-mediated signaling while sparing TNFR2 activation may lessen adverse effects of anti-TNF therapies in the CNS.

Blocking Soluble Tumor Necrosis Factor Signaling with Dominant-Negative Tumor Necrosis Factor Inhibitor Attenuates Loss of Dopaminergic Neurons in Models of Parkinson's Disease

The mechanisms that trigger or contribute to loss of dopaminergic (DA) neurons in Parkinsons disease (PD) remain unclear and controversial. Elevated levels of tumor necrosis factor (TNF) in CSF and postmortem brains of PD patients and animal models of PD implicate this proinflammatory cytokine in the pathophysiology of the disease; but a role for TNF in mediating loss of DA neurons in PD has not been clearly demonstrated. Here, we report that neutralization of soluble TNF (solTNF) in vivo with the engineered dominant-negative TNF compound XENP345 (a PEGylated version of the TNF variant A145R/I97T) reduced by 50% the retrograde nigral degeneration induced by a striatal injection of the oxidative neurotoxin 6-hydroxydopamine (6-OHDA). XENP345 was neuroprotective only when infused into the nigra, not the striatum. XENP345/6-OHDA rats displayed attenuated amphetamine-induced rotational behavior, indicating preservation of striatal dopamine levels. Similar protective effects were observed with chronic in vivo coinfusion of XENP345 with bacterial lipopolysaccharide (LPS) into the substantia nigra, confirming a role for solTNF-dependent neuroinflammation in nigral degeneration. In embryonic rat midbrain neuron/glia cell cultures exposed to LPS, even delayed administration of XENP345 prevented selective degeneration of DA neurons despite sustained microglia activation and secretion of solTNF. XENP345 also attenuated 6-OHDA-induced DA neuron toxicity in vitro. Collectively, our data demonstrate a role for TNF in vitro and in vivo in two models of PD, and raise the possibility that delaying the progressive degeneration of the nigrostriatal pathway in humans is therapeutically feasible with agents capable of blocking solTNF in early stages of PD.

Intranigral lentiviral delivery of dominant negative TNF attenuates neurodegeneration and behavioral deficits in hemiparkinsonian rats

Neuroinflammatory processes have been implicated in the progressive loss of ventral midbrain dopaminergic (DA) neurons that give rise to Parkinsons disease (PD), a late-onset movement disorder that affects 2% of the population over the age of 70 years. We have shown earlier, in two rat models of PD, that inhibition of the proinflammatory cytokine tumor necrosis factor (TNF) through nigral infusion of dominant-negative (DN-TNF) protein (XENP345) attenuates DA neuron loss. The objectives of this study were to develop a constitutive lentiviral vector encoding dominate-negative TNF, and to determine whether a gene therapy approach to deliver DN-TNF directly into the rodent substantia nigra could prevent or attenuate neurotoxin-induced DA neuron loss and associated behavioral deficits. Here we demonstrate that a single injection of lentivirus-expressing DN-TNF into rat substantia nigra, administered concomitant with a striatal 6-hydroxydopamine lesion, results in sufficiently high expression of inhibitor in vivo to attenuate both DA neuron loss and behavioral deficits resulting from striatal dopamine depletion. Our findings demonstrate the feasibility and efficacy of dominant-negative TNF gene transfer as a novel neuroprotective strategy to prevent or delay nigrostriatal pathway degeneration. This strategy holds the potential for therapeutic application in the treatment of PD.

The synthetic triterpenoid CDDO-methyl ester modulates microglial activities, inhibits TNF production, and provides dopaminergic neuroprotection

BackgroundRecent animal and human studies implicate chronic activation of microglia in the progressive loss of CNS neurons. The inflammatory mechanisms that have neurotoxic effects and contribute to neurodegeneration need to be elucidated and specifically targeted without interfering with the neuroprotective effects of glial activities. Synthetic triterpenoid analogs of oleanolic acid, such as methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oate (CDDO-Me, RTA 402) have potent anti-proliferative and differentiating effects on tumor cells, and anti-inflammatory activities on activated macrophages. We hypothesized that CDDO-Me may be able to suppress neurotoxic microglial activities while enhancing those that promote neuronal survival. Therefore, the aims of our study were to identify specific microglial activities modulated by CDDO-Me in vitro, and to determine the extent to which this modulation affords neuroprotection against inflammatory stimuli.MethodsWe tested the synthetic triterpenoid methyl-2-cyano-3,12-dioxooleana-1,9-dien-28-oate (CDDO-Me, RTA 402) in various in vitro assays using the murine BV2 microglia cell line, mouse primary microglia, or mouse primary peritoneal macrophages to investigate its effects on proliferation, inflammatory gene expression, cytokine secretion, and phagocytosis. The antioxidant and neuroprotective effects of CDDO-Me were also investigated in primary neuron/glia cultures from rat basal forebrain or ventral midbrain.ResultsWe found that at low nanomolar concentrations, treatment of rat primary mesencephalon neuron/glia cultures with CDDO-Me resulted in attenuated LPS-, TNF- or fibrillar amyloid beta 1–42 (Aβ1–42) peptide-induced increases in reactive microglia and inflammatory gene expression without an overall effect on cell viability. In functional assays CDDO-Me blocked death in the dopaminergic neuron-like cell line MN9D induced by conditioned media (CM) of LPS-stimulated BV2 microglia, but did not block cell death induced by addition of TNF to MN9D cells, suggesting that dopaminergic neuroprotection by CDDO-Me involved inhibition of microglial-derived cytokine production and not direct inhibition of TNF-dependent pro-apoptotic pathways. Multiplexed immunoassays of CM from LPS-stimulated microglia confirmed that CDDO-Me-treated BV2 cells produced decreased levels of specific subsets of cytokines, in particular TNF. Lastly, CDDO-Me enhanced phagocytic activity of BV2 cells in a stimulus-specific manner but inhibited generation of reactive oxygen species (ROS) in mixed neuron/glia basal forebrain cultures and dopaminergic cells.ConclusionThe neuroimmune modulatory properties of CDDO-Me indicate that this potent antioxidant and anti-inflammatory compound may have therapeutic potential to modify the course of neurodegenerative diseases characterized by chronic neuroinflammation and amyloid deposition. The extent to which synthetic triterpenoids afford therapeutic benefit in animal models of Parkinsons and Alzheimers disease deserves further investigation.

Autologous transplants of Adipose-Derived Adult Stromal (ADAS) cells afford dopaminergic neuroprotection in a model of Parkinson's disease

Adult adipose contains stromal progenitor cells with neurogenic potential. However, the stability of neuronal phenotypes adopted by Adipose-Derived Adult Stromal (ADAS) cells and whether terminal neuronal differentiation is required for their consideration as alternatives in cell replacement strategies to treat neurological disorders is largely unknown. We investigated whether in vitro neural induction of ADAS cells determined their ability to neuroprotect or restore function in a lesioned dopaminergic pathway. In vitro-expanded naïve or differentiated ADAS cells were autologously transplanted into substantia nigra 1 week after an intrastriatal 6-hydroxydopamine injection. Neurochemical and behavioral measures demonstrated neuroprotective effects of both ADAS grafts against 6-hydroxydopamine-induced dopaminergic neuron death, suggesting that pre-transplantation differentiation of the cells does not determine their ability to survive or neuroprotect in vivo. Therefore, we investigated whether equivalent protection by naïve and neurally-induced ADAS grafts resulted from robust in situ differentiation of both graft types into dopaminergic fates. Immunohistological analyses revealed that ADAS cells did not adopt dopaminergic cell fates in situ, consistent with the limited ability of these cells to undergo terminal differentiation into electrically active neurons in vitro. Moreover, re-exposure of neurally-differentiated ADAS cells to serum-containing medium in vitro confirmed ADAS cell phenotypic instability (plasticity). Lastly, given that gene expression analyses of in vitro-expanded ADAS cells revealed that both naïve and differentiated ADAS cells express potent dopaminergic survival factors, ADAS transplants may have exerted neuroprotective effects by production of trophic factors at the lesion site. ADAS cells may be ideal for ex vivo gene transfer therapies in Parkinsons disease treatment.

Regulator of G-Protein Signaling 10 Promotes Dopaminergic Neuron Survival via Regulation of the Microglial Inflammatory Response

Epidemiological studies suggest that chronic use of nonsteroidal anti-inflammatory drugs lowers the incidence of Parkinsons 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 Gα 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.

TNF: a key neuroinflammatory mediator of neurotoxicity and neurodegeneration in models of Parkinson's disease.

Microglia activation and overproduction of inflammatory mediators in the CNS have been implicated in Parkinson’s disease (PD) [1]. Epidemiological studies suggest that chronic use of non-steroidal anti-inflammatory drugs (NSAIDs) at lower doses is associated with lower incidence of idiopathic PD compared to non-NSAID users [2, 3, 4]. However, key molecular mediators of neurotoxicity that directly contribute to neurodegeneration have not been identified. A role for the pro-inflammatory cytokine tumor necrosis factor (TNF) has been implicated in PD (reviewed in [5]). Nigral midbrain dopaminergic (DA) neurons are extremely sensitive to TNF [6], and the CSF and post-mortem brains of patients with both diseases display elevated levels of TNF [7, 8]. Lastly, although no robust genetic association between TNF and development of PD has been demonstrated, a single nucleotide polymorphism (SNP) in the TNF promoter gene has been associated with a rare form of early-onset idiopathic PD [9]. Using engineered dominant-negative TNF variants (DN-TNFs) [10] and the decoy TNF receptor etanercept, we investigated the extent to which TNF-dependent mechanisms are required for loss of DA neurons in vitro and in vivo in two different models of parkinsonism.

P3-265: In vivo and in vitro validation of TNF as a key neuroinflammatory mediator of neurotoxicity and neurodegeneration in models of PD and AD

Background: Microglia activation and overproduction of inflammatory mediators in the CNS have been implicated in both Parkinson’s (PD) and Alzheimer’s disease (AD). However, key molecular mediators of neurotoxicity that directly contribute to neurodegeneration have not been identified. A role for the pro-inflammatory cytokine tumor necrosis factor (TNF) has been implicated in both PD and AD. Nigral midbrain dopaminergic (DA) neurons and certain populations of cholinergic neurons are extremely sensitive to TNF; and the CSF and post-mortem brains of patients with both diseases display elevated levels of TNF. Methods: Using our engineered dominant negative TNF variants (DN-TNFs) and the decoy receptor etanercept, we found that TNF-dependent mechanisms are required for progressive in vitro and in vivo degeneration of the nigrostriatal pathway. Results: Specifically, inhibition of TNF signaling in vitro with anti-TNF biologics attenuated DA neuron loss even after delayed administration. In vivo, unilateral intrastriatal injections of 6-OHDA or intranigral chronic low dose LPS infusion resulted in a 65-70 % loss of ipsilateral nigral DA neurons; while co-administration of DN-TNFs on the lesion side reduced neuronal loss by half and attenuated ipsiversive circling behavior in 6-OHDA lesioned rats. Experiments are underway to identify targets and signaling pathways that transduce the neurotoxic effects of TNF. Using both primary microglia and the BV2 microglia cell line we are identifying signaling cascades activated by TNF receptors (R1 and R2) that regulate microglial activities and microglial-derived oxidant stress. Results from these studies are providing new clues about the role of TNF in early (pre-plaque) versus late stages (aggressive plaque) of amyloid beta/p-tauassociated neurotoxicity and its contribution to cholinergic neurodegeneration. We hypothesize that TNF contributes to the reported increase in microglial burden and exacerbated hippocampal and entorhinal cortex neuropathology in 3xTgAD following chronic systemic LPS exposure. Therefore, we expect that blocking TNF signaling in vivo in these mice with anti-TNF biologics and lentiviral-derived DN-TNFs will severely blunt the LPS effect. Conclusions: Timely inhibition of the TNF pathway may slow the progressive loss of neurons in both PD and AD. [Funding by MJ Fox Foundation, American Health Assistance Foundation, and UTSW Alzheimer’s Disease Center; NIH, NIA P30AG12300.]