Parkinson’s disease (PD) is characterized by the build-up of α-synuclein (α-syn) in the brain, where it drives neurodegeneration. Importantly, aggregated α-syn also accumulates in the cerebrospinal fluid (CSF) of PD patients, and while increasingly used for diagnosis, its pathological role remains poorly understood. Here, we demonstrate that α-syn accumulation in central nervous system (CNS) border tissues promotes CNS clearance deficits, as observed in PD patients. We find that aggregated α-syn accumulates not only in the CSF but also in the dura mater of individuals with PD, and, using acute and chronic mouse models, show that α-syn deposition in these sites induces immune alterations in CNS borders and disrupts CNS clearance. Mechanistically, we reveal that α-syn at CNS borders elevates CSF TNF and demonstrate that both TNF and α-syn aggregates themselves impair lymphatic endothelial cell function. These findings demonstrate a pathological role for α-syn in the CNS border tissues and position meningeal immunity as a contributor to CNS clearance deficits in PD pathogenesis.

Background/Objectives: Brain cancers offer poor prognoses to patients accompanied by symptoms that drastically impact the patient and their family. Brain tumours recruit local non-transformed cells to provide trophic support and immunosuppression within the tumour microenvironment, supporting tumour progression. Given the localisation and supportive role of pericytes at the brain vasculature, we explored the potential for brain pericytes to contribute to the brain cancer microenvironment. Methods: To investigate this, primary brain pericytes were treated with factors commonly upregulated in brain cancers. Immunofluorescent labelling identified changes to brain pericyte cell signalling, cytometric bead array measured inflammatory secretion, and flow cytometry investigated brain pericyte phagocytosis. Results: The TGFβ superfamily cytokines TGFβ and GDF-15 activated SMAD2/3 and inhibited C/EBP-δ, revealing a potential mechanism behind the pleiotropic action of TGFβ on brain pericytes. IL-17 induced secretion of IL-6 without activating NFκB, STAT1, SMAD2/3, or C/EBP-δ signalling pathways. IL-27 and IFNγ induced STAT1 signalling and significantly reduced brain pericyte phagocytosis. The remaining brain cancer-derived factors did not induce a measured response, indicating that these factors may act on other cell types or require co-stimulation with other factors to produce significant effects. Conclusions: We identify several brain cancer-secreted factors which alter relevant brain pericyte functions. This reveals mechanisms through which brain tumours may regulate brain pericyte activity and these data start to uncover the supportive role these cells may play in brain cancers.

Brain cancers offer poor prognoses to patients accompanied by symptoms that drastically impact the patient and their family. Brain tumours recruit local non-transformed cells to provide trophic support and immunosuppression within the tumour microenvironment, supporting tumour progression. Given the localization and supportive role of pericytes at the brain vasculature, we explored the potential for brain pericytes to contribute to the brain cancer microenvironment. To investigate this, primary brain pericytes were treated with factors commonly upregulated in brain cancers. Changes to brain pericyte cell signalling, inflammatory secretion, and phagocytosis were investigated. The TGFβ superfamily cytokines TGFβ and GDF-15 activated SMAD2/3 and inhibited C/EBP-δ, revealing a potential mechanism behind the pleiotropic action of TGFβ on brain pericytes. IL-17 induced secretion of IL-6 without activating NFκB, STAT1, SMAD2/3, or C/EBP-δ signalling pathways. IL-27 and IFNγ induced STAT1 signalling and significantly reduced pericyte phagocytosis. The remaining brain cancer-derived factors did not induce a measured response, indicating that these factors may act on other cell types or require co-stimulation with other factors to produce significant effects. Together, these findings show potential mechanisms by which brain pericytes contribute to aspects of inflammation and starts to uncover the supportive role brain pericytes may play in brain cancers.

Background: iPSC-derived cells are increasingly used to model complex diseases in vitro because they can be patient derived and can differentiate into any cell in the adult human body. Recent studies have demonstrated the generation of brain pericytes using a neural crest-based differentiation protocol. However, the inflammatory response of these iPSC-derived brain pericytes has not been investigated. We aimed to investigate the response of iPSC-derived brain pericytes to common inflammatory stimuli, thereby assessing the suitability of these cells to study inflammatory disease. Methods: Brain pericytes were differentiated from iPSCs for 42 days. The expression of brain pericyte markers was assessed by RT-qPCR and immunofluorescent staining at days 0, 15, 21, and 42 of differentiation to validate the brain pericyte-like phenotype. Nuclear localisation of NFκB and STAT1 was assessed by immunofluorescence following IL-1β- and TNF-treatment in day 21 and day 42 iPSC-derived pericytes, and primary human pericytes. Cytometric bead array assessed the concentration of secreted inflammatory factors in the cell medium and phagocytosis was investigated using fluorescent carboxylated beads and flow cytometry. Results: At day 42 of differentiation, but not at day 21, cells expressed brain pericyte markers. Generally, iPSC-derived pericytes lacked consistent responses to inflammatory treatment compared to primary human pericytes. Day 21 and 42 iPSC-derived pericytes exhibited a NFκB response to IL-1β treatment comparable to primary human pericytes. Day 21 iPSC-derived pericytes exhibited a STAT1 response with IL-1β treatment which was absent in day 42 cells, but present in a subset of primary human pericytes. TNF treatment presented similar NFκB responses between day 21 and 42 iPSC-derived and primary human pericytes, but a STAT1 response was again present in a subset of primary human pericytes which was absent in both day 21 and day 42 iPSC-derived pericytes. Numerous differences were observed in the secretion of cytokines and chemokines following treatment of iPSC-derived and primary human pericytes with IL-1β and TNF. iPSC-derived pericytes exhibited greater rates of phagocytosis than primary human pericytes. Conclusions: With the increase in iPSC-derived cells in research, labs should undertake validation of lineage specificity when adapting an iPSC-derived differentiation protocol. In our hands, the inflammatory response of iPSC-derived pericytes was different to that of primary human pericytes, raising concern regarding the use of iPSC-derived pericytes to study neuroinflammatory disease. Graphical Brain pericytes can be generated from iPSCs. The work presented here shows the generation of phenotypically distinct pericytes from the original protocol, demonstrating the significant variability present within some iPSC differentiation protocols. Furthermore, functional differences are demonstrated between iPSC-derived brain pericytes and primary brain pericytes, revealing limitations in the use of iPSC-derived brain pericytes to model brain pericyte biology. Key Points: What is already known about this topic?: Brain pericyte-like cells can be generated from induced pluripotent stem cells, however their responses to inflammatory stimuli has not been assessed. What does this study add?: iPSC-derived brain pericytes exhibit different inflammatory responses compared to primary brain pericytes, showing that some iPSC-derived cell models are not appropriate for modelling all aspects of a cell’s biology. Furthermore, the iPSC-derived pericytes generated here were markedly different to those generated from the original article. It is therefore important for each lab to optimise the generation of iPSC-derived cell in their own hands to account for potential inter-lab variability.