Alpha-synuclein inclusion responsive microglia are resistant to CSF1R inhibition.

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by the presence of proteinaceous alpha-synuclein (α-syn) inclusions (Lewy bodies), markers of neuroinflammation and the progressive loss of nigrostriatal dopamine (DA) neurons. These pathological features can be recapitulated in vivo using the α-syn preformed fibril (PFF) model of synucleinopathy. We have previously determined that microglia proximal to PFF-induced nigral α-syn inclusions increase in soma size, upregulate major-histocompatibility complex-II (MHC-II) expression, and increase expression of a suite of inflammation-associated transcripts. This microglial response is observed months prior to degeneration, suggesting that microglia reacting to α-syn inclusion may contribute to neurodegeneration and could represent a potential target for novel therapeutics. The goal of this study was to determine whether colony stimulating factor-1 receptor (CSF1R)-mediated microglial depletion impacts the magnitude of α-syn aggregation, nigrostriatal degeneration, or the response of microglial in the context of the α-syn PFF model. Male Fischer 344 rats were injected intrastriatally with either α-syn PFFs or saline. Rats were continuously administered Pexidartinib (PLX3397B, 600 mg/kg), a CSF1R inhibitor, to deplete microglia for a period of either 2 or 6 months. CSF1R inhibition resulted in significant depletion (~ 43%) of ionized calcium-binding adapter molecule 1 immunoreactive (Iba-1ir) microglia within the SNpc. However, CSF1R inhibition did not impact the increase in microglial number, soma size, number of MHC-II immunoreactive microglia or microglial expression of Cd74, Cxcl10, Rt-1a2, Grn, Csf1r, Tyrobp, and Fcer1g associated with phosphorylated α-syn (pSyn) nigral inclusions. Further, accumulation of pSyn and degeneration of nigral neurons was not impacted by CSF1R inhibition. Paradoxically, long term CSF1R inhibition resulted in increased soma size of remaining Iba-1ir microglia in both control and PFF rats, as well as expression of MHC-II in extranigral regions. Collectively, our results suggest that CSF1R inhibition does not impact the microglial response to nigral pSyn inclusions and that CSF1R inhibition is not a viable disease-modifying strategy for PD.

Stoll AC ，Kemp CJ ，Patterson JR ，Kubik M ，Kuhn N ，Benskey M ，Duffy MF ，Luk KC ，Sortwell CE ... -  《Journal of Neuroinflammation》

Microglial depletion does not impact alpha-synuclein aggregation or nigrostriatal degeneration in the rat preformed fibril model.

Stoll AC ，Kemp CJ ，Patterson JR ，Kubik M ，Kuhn N ，Benskey M ，Duffy MF ，Luk K ，Sortwell CE ... -  《-》

Lewy body-like alpha-synuclein inclusions trigger reactive microgliosis prior to nigral degeneration.

Duffy MF ，Collier TJ ，Patterson JR ，Kemp CJ ，Luk KC ，Tansey MG ，Paumier KL ，Kanaan NM ，Fischer DL ，Polinski NK ，Barth OL ，Howe JW ，Vaikath NN ，Majbour NK ，El-Agnaf OMA ，Sortwell CE ... -  《Journal of Neuroinflammation》

Neuroinflammatory gene expression profiles of reactive glia in the substantia nigra suggest a multidimensional immune response to alpha synuclein inclusions.

Stoll AC ，Kemp CJ ，Patterson JR ，Howe JW ，Steece-Collier K ，Luk KC ，Sortwell CE ，Benskey MJ ... -  《-》

Time course and magnitude of alpha-synuclein inclusion formation and nigrostriatal degeneration in the rat model of synucleinopathy triggered by intrastriatal α-synuclein preformed fibrils.

Animal models that accurately recapitulate the accumulation of alpha-synuclein (α-syn) inclusions, progressive neurodegeneration of the nigrostriatal system and motor deficits can be useful tools for Parkinson's disease (PD) research. The preformed fibril (PFF) synucleinopathy model in rodents generally displays these PD-relevant features, however, the magnitude and predictability of these events is far from established. We therefore sought to optimize the magnitude of α-syn accumulation and nigrostriatal degeneration, and to understand the time course of both. Rats were injected unilaterally with different quantities of α-syn PFFs (8 or 16 μg of total protein) into striatal sites selected to concentrate α-syn inclusion formation in the substantia nigra pars compacta (SNpc). Rats displayed an α-syn PFF quantity-dependent increase in the magnitude of ipsilateral SNpc inclusion formation at 2 months and bilateral loss of nigral dopamine neurons at 6 months. Unilateral 16 μg PFF injection also resulted in modest sensorimotor deficits in forelimb adjusting steps associated with degeneration at 6 months. Bilateral injection of 16 μg α-syn PFFs resulted in symmetric bilateral degeneration equivalent to the ipsilateral nigral degeneration observed following unilateral 16 μg PFF injection (~50% loss). Bilateral PFF injections additionally resulted in alterations in several gait analysis parameters. These α-syn PFF parameters can be applied to generate a reproducible synucleinopathy model in rats with which to study pathogenic mechanisms and vet potential disease-modifying therapies.

Patterson JR ，Duffy MF ，Kemp CJ ，Howe JW ，Collier TJ ，Stoll AC ，Miller KM ，Patel P ，Levine N ，Moore DJ ，Luk KC ，Fleming SM ，Kanaan NM ，Paumier KL ，El-Agnaf OMA ，Sortwell CE ... -  《-》