Park7/DJ-1 Deficiency Impairs Microglial Activation in Response to LPS-Induced Inflammation

Neurology Biochemistry Life Sciences Immunology Medicine Cell Biology
Park7/DJ-1 lipopolysaccharide microglia neuroinflammation Parkinson's disease microglia morphology

Important Research Interpretation from “Journal of Neuroinflammation” 2024: The Impact of Park7/DJ-1 Deficiency on Microglial Activation

Academic Background

Parkinson’s Disease (PD) is the second most common neurodegenerative disease, characterized by the accumulation of α-synuclein and progressive loss of dopaminergic neurons. Aging is the primary risk factor for PD, but environmental factors such as pesticide exposure and infections are also thought to promote PD onset and progression. Recent studies have shown that microglia are activated in the early stages of PD and in pathological anatomy (such as the substantia nigra). However, the specific role of microglia in PD is not fully elucidated.

To better understand the role of microglia in PD, this study used a Park7/DJ-1 gene deletion model. The Park7 gene encodes the multifunctional protein DJ-1, known to play a role in transcriptional regulation and antioxidant stress. DJ-1 deficiency caused by Park7 gene mutations is a genetic cause of early-onset PD. This study aimed to investigate the transcriptional programs and morphological adaptations of microglia in response to lipopolysaccharide (LPS)-induced inflammation under Park7/DJ-1 deficiency conditions, validating the multiple-hit hypothesis, which posits that PD etiology is determined by a combination of genetic and environmental risk factors.

Research Source

This study was authored by Frida Lind-Holm Mogensen, Carole Sousa, et al., from institutions including the Luxembourg Institute of Health, University of Luxembourg, and TU Dortmund University. The paper was published in the “Journal of Neuroinflammation” in 2024.

Research Process and Methods

Experimental Design

The study used Park7/DJ-1 knockout (KO) and wild-type mice, as well as human Park7/DJ-1 mutant induced pluripotent stem cell (iPSC)-derived microglia and mouse bone marrow-derived macrophages (BMDMs). After LPS-induced inflammatory stimulation, comprehensive phenotypic characterization was performed using single-cell RNA sequencing (scRNA-seq), bulk RNA sequencing, flow cytometry, and immunofluorescence analysis.

Experimental Steps

  1. Animal Model and Genotyping

    • Used 3-4 month old Park7/DJ-1 KO mice and wild-type littermates.
    • Confirmed Park7/DJ-1 deletion by PCR genotyping.

  2. Cell Isolation and Flow Cytometry Sorting

    • Mice were injected with LPS or PBS (control), and CD11b+CD45int microglia were isolated by flow cytometry staining.

  3. RNA Sequencing and Data Analysis

    • Performed single-cell RNA sequencing (Drop-seq) on isolated microglia.
    • Conducted principal component analysis (PCA) and differential gene expression analysis.

  4. Cell Morphology Analysis

    • Analyzed microglial morphological features using immunofluorescence staining and 3D microscopy imaging.
    • Classified microglial morphology using the in-house developed Microglia and Immune Cell Morphology Analysis and Clustering (MIC-MAC 2) tool.

  5. Bone Marrow-Derived Macrophage Differentiation and Treatment

    • Isolated bone marrow cells from Park7/DJ-1 KO and wild-type mice and induced differentiation into macrophages.
    • Treated bone marrow-derived macrophages with LPS, analyzing gene expression and cell morphology changes.

  6. Induced Pluripotent Stem Cell-Derived Microglia Analysis

    • Used iPSCs carrying Park7 mutations to induce microglia, analyzing gene expression and morphology.

Main Research Findings

Gene Expression Analysis

  1. Differential Gene Expression

    • Microglia from Park7/DJ-1 KO mice showed different gene expression profiles after LPS treatment compared to wild-type, particularly downregulation of genes related to type II interferon and DNA damage response.
    • Similar gene expression downregulation was observed in iPSC-derived microglia with Park7/DJ-1 deficiency after LPS treatment.

  2. Gene Enrichment Analysis

    • GO (Gene Ontology) analysis showed upregulation of DNA damage response genes in Park7/DJ-1 KO mouse microglia after LPS treatment, reflecting involvement of repair and tolerance mechanisms.
    • In human iPSC-derived microglia, reduced expression of immune response and interferon signaling-related genes was observed after LPS treatment.

Cell Morphology Analysis

  1. Baseline Morphology

    • Park7/DJ-1 KO mouse microglia were more compact at baseline, showing fewer branches and processes, indicating a more compact morphological structure compared to wild-type.

  2. Morphological Adaptation After LPS Treatment

    • After LPS treatment, Park7/DJ-1 KO mouse microglia showed reduced morphological adaptability, displaying fewer amoeboid cell morphologies and maintaining more compact forms compared to wild-type.

ROS (Reactive Oxygen Species) Level Analysis

  • Assessed ROS levels in Park7/DJ-1 KO mouse microglia and macrophages through in vivo imaging.
    • Results showed increased ROS content in cytoplasm and mitochondria, and decreased mitochondrial membrane potential in Park7/DJ-1 KO cells at baseline and after LPS treatment, reflecting cellular stress response and insufficient compensatory mechanisms.

Research Conclusions

This study demonstrates that Park7/DJ-1 gene deficiency significantly affects the response capacity of microglia under inflammatory conditions. Specifically: - Gene Expression Downregulation: Particularly reduced expression of genes related to type II interferon signaling pathways. - Reduced Morphological Adaptation: Under LPS-induced systemic inflammation, microglia with long-term Park7/DJ-1 KO showed fewer amoeboid morphologies, maintaining compact structures. - Increased ROS Levels: Park7/DJ-1 deficient cells showed elevated ROS levels at baseline and after LPS treatment, reflecting oxidative stress and impaired repair mechanisms.

Significance and Value of the Research

The findings of this study have important implications for understanding PD pathology and developing potential therapeutic strategies. By revealing the effects of Park7/DJ-1 deficiency on microglial response and morphological adaptation, it contributes to further understanding the pathogenesis of PD, especially its role in neuroinflammation. This provides new ideas for developing targeted therapies, such as enhancing antioxidant defenses or regulating inflammatory responses in microglia to delay or prevent PD progression. Additionally, the successful application of iPSC technology will aid future research in further exploring PD pathology and treatment in human cell models.

Through detailed multi-level analysis, this study reveals the key role of Park7/DJ-1 in regulating microglial function and morphology, while providing new potential directions for early diagnosis and intervention in PD.