iPSC-Derived Microglia as a Model to Study Inflammation in Idiopathic Parkinson’s Disease

Abstract

Parkinson’s disease (PD) is a neurodegenerative disease with unknown cause in the majority of patients, who are therefore considered “idiopathic” (IPD). PD predominantly affects dopaminergic neurons in the substantia nigra pars compacta (SNpc), yet the pathology is not limited to this cell type. Advancing age is considered the main risk factor for the development of IPD and greatly influences the function of microglia, the immune cells of the brain. With increasing age, microglia become dysfunctional and release pro-inflammatory factors into the extracellular space, which promote neuronal cell death. Accordingly, neuroinflammation has also been described as a feature of PD. So far, studies exploring inflammatory pathways in IPD patient samples have primarily focused on blood-derived immune cells or brain sections, but rarely investigated patient microglia in vitro. Accordingly, we decided to explore the contribution of microglia to IPD in a comparative manner using, both, iPSC-derived cultures and postmortem tissue. Our meta-analysis of published RNAseq datasets indicated an upregulation of IL10 and IL1B in nigral tissue from IPD patients. We observed increased expression levels of these cytokines in microglia compared to neurons using our single-cell midbrain atlas. Moreover, IL10 and IL1B were upregulated in IPD compared to control microglia. Next, to validate these findings in vitro, we generated IPD patient microglia from iPSCs using an established differentiation protocol. IPD microglia were more readily primed as indicated by elevated IL1B and IL10 gene expression and higher mRNA and protein levels of NLRP3 after LPS treatment. In addition, IPD microglia had higher phagocytic capacity under basal conditions—a phenotype that was further exacerbated upon stimulation with LPS, suggesting an aberrant microglial function. Our results demonstrate the significance of microglia as the key player in the neuroinflammation process in IPD. While our study highlights the importance of microglia-mediated inflammatory signaling in IPD, further investigations will be needed to explore particular disease mechanisms in these cells.

Targeting α-Synuclein in Parkinson's Disease by Induced Pluripotent Stem Cell Models

“…iPSCs can be employed for addressing several pathophysiological mechanisms and life-style parameters that are implicated in the disorder. For example, there are studies deciphering the implication of inflammation in PD, employing iPSC-derived macrophages ( 198 ) and microglial cells ( 199 ). The influence of metabolism and diet were addressed in metabolomic studies ( 200 – 202 ) and studies that control the nutrient composition of the culture medium ( 203 ).…”

Single-Cell Transcriptomics Uncovers Cellular Heterogeneity, Mechanisms, and Therapeutic Targets for Parkinson’s Disease

“…Herein, we employed scRNA-seq data of the midbrain specimens from PD patients and healthy individuals. In the previous research, 12 cell types were identified including astrocytes, CADPS2 high , DaNs, endothelial cells, ependymal cells, excitatory cells, GABA, inhibitory cells, microglial cells, OPCs, oligodendrocytes, and pericytes ( Badanjak et al, 2021 ). Different from previous research, five cell clusters were identified in this study, composed of oligodendrocytes, astrocytes, neurons, microglial cells, and endothelial cells.…”

“…scRNA-seq data of midbrain specimens from five idiopathic PD patients and six healthy individuals were downloaded from the Gene Expression Omnibus (GEO) database ( https://www.ncbi.nlm.nih.gov/gds/ ; accession: GSE157783) ( Badanjak et al, 2021 ). Single-nucleus suspension was prepared by scraping off the tissues from the glass slides and utilizing the modified version of the standard 10x Genomics nuclei isolation protocol.…”

Does the Expression and Epigenetics of Genes Involved in Monogenic Forms of Parkinson’s Disease Influence Sporadic Forms?

“…LRRK2 is also expressed in primary microglia from adult mice and it is upregulated upon IFN-y stimulation or lipopolysaccharide (LPS) treatment [ 102 ]. An iPSC study revealed that basal LRRK2 mRNA expression was lower in sporadic PD microglia, and after treatment of the cells with LPS, sporadic PD microglia had a significantly lower amount of LRRK2 protein than control microglia [ 103 ]. However, the mechanisms linking LRRK2 downregulation to microglia dysfunction in PD remains to be elucidated.…”