Intrastriatal injection of preformed alpha-synuclein fibrils alters central and peripheral immune cell profiles in non-transgenic mice

Abstract

Parkinson’s disease (PD) is characterized by the accumulation of alpha-synuclein (α-syn) inclusions, the major component of Lewy bodies. Extracellular α-syn aggregates act as a damage-associated molecular pattern (DAMP) and the presence of autoantibodies against α-syn species in the cerebrospinal fluid and the serum of PD patients implicate the involvement of innate and adaptive immune responses. In non-transgenic (Tg) mice, intrastriatal injection of preformed fibril (PFF) α-syn results in widespread pathologic α-syn inclusions in the CNS. While the PFF model has been broadly utilized to study the mechanistic relationship between α-syn transmission and other neuropathological phenotypes, the immune phenotypes in this model are not clearly demonstrated. This study aimed to characterize the immune phenotypes during pathologic α-syn propagation by utilizing PFF α-syn–injected non-tg mice. Here, we showed that pathologic α-syn inclusions are prevalent in various brain regions and the gut at 5 months post injection (p.i.), preceding the degeneration of dopaminergic neurons in substantia nigra (SN). We discovered a distinct inflammatory response involving both activation of microglia and astrocytes and infiltration of B, CD4+ T, CD8+ T, and natural killer cells in the brain at 5 months p.i. Moreover, PFF α-syn–injected mice display significant alterations in the frequency and number of leukocyte subsets in the spleen and lymph nodes with minimum alterations in the blood. Our data provide primary evidence that intracerebral-initiated synucleinopathies in non-tg mice alter immune cell profiles both in the CNS and peripheral lymphoid organs. Furthermore, our data provides support for utilizing this mouse model to assess the mechanistic connection between immune responses and synuclein pathology.

Neuroinflammation is associated with infiltration of T cells in Lewy body disease and α-synuclein transgenic models

“…This finding was supported by the increased number of CD3+ T cell co-expressing IFNγ and moderately elevated IFNγ mRNA levels in α-syn tg brains, as both CD4+ helper T cells, particularly Th1, and NKT cells are among the most predominant producers of IFNγ. This is in agreement with a recent study showing increase numbers of NK cells in a prion-like model of PD, were T cell infiltration with NK profile was observed after injection of α-syn pff in the striatum of wildtype mice [74]. However, additional studies will be needed to confirm the possibility that NKT cells participate in the neuro-immune response in the α-syn tg model of DLB, including intracellular flow cytometry staining of cytokines such as IFNγ and IL4 in CD1d-tet+ TCR-β+ cells.…”

Modeling Parkinson’s Disease With the Alpha-Synuclein Protein

“…In addition, these studies demonstrated that the vagus nerve and endogenous a-Syn are required for the gut-to-brain transmission of pathologic a-Syn because truncal vagotomy was performed prior to inoculation of PFFs (Uemura et al, 2018;Kim et al, 2019) and the PFFs injection in the Snca null mice (Kim et al, 2019) prevents the spread of pathologic a-Syn to the brain. Similarly, another recent study has shown that intrastriatal injection of a-Syn PFFs induces the Lewy body-like pathology within the enteric nervous system of wild type mice (Earls et al, 2019). Likewise, other studies have shown that nigral overexpression of rAAV-a-Syn in rats produces concomitant alterations on the enteric nervous system-accumulation of a-Syn deposits (Ulusoy et al, 2017) and a loss of enteric neurons and changes in the gut microbiome (O'Donovan et al, 2020), which reflects that a-Syn pathology in the brain may impact on the gastrointestinal system and that the gut-to-brain communication via the vagus nerve may underlie the path of pathology progression.…”

“…It is noteworthy that in the PFFs models, microglial activation might appear as resulting from an immune reaction due to the inoculation of foreign a-Syn fibrils. Indeed, it has been shown that striatal injection of a-Syn PFFs but not monomers in WT mice can trigger neuroinflammation by increasing peripheral immune cells infiltration in the CNS (Earls et al, 2019). Apparently, this immune reaction would precede the dopaminergic neurodegeneration (Harms et al, 2017) but, it cannot be excluded that the magnitude and the efficacy of the immune reaction can also modulate the spread of the pathology observed as it was recently suggested by (Earls et al, 2020).…”

T cell infiltration and upregulation of MHCII in microglia leads to accelerated neuronal loss in an α-synuclein rat model of Parkinson’s disease

“…Gene triplication has also been shown to cause PD, indicating that aggregation of α-syn protein is associated with dopaminergic neuron loss [8][9][10]. Intracellular inclusions of oligomeric α-syn (Lewy body) are accompanied by surveying microglia that shift into a pro-inflammatory and phagocytic state resulting in the release of proinflammatory cytokines such as IL-1, IL-6, TNF-α, and CD40 ligand [11][12][13][14]. Neuronal loss in SNpc is caused, in part, from persistent inflammation in the brain resulting from pro-inflammatory microglia and dendritic cells.…”