Introduction Parkinson’s disease (PD) is increasingly recognized as a neurological disorder characterized not only by neurodegeneration but also by chronic immune dysregulation across the lifespan. Although the initiating events underlying PD remain unclear, accumulating evidence suggests that inflammatory processes may contribute to disease susceptibility and progression. Mutations in leucine-rich repeat kinase 2 (LRRK2), particularly the gain-of-function G2019S variant, represent the common genetic cause of familial PD and have been implicated in immune regulation and infection susceptibility. To date, most research has focused on the effect of LRRK2 mutation in neurons and the contributions of G2019S-mediated kinase activity to neuronal toxicity, leaving the role of G2019S-mediated kinase activity in immune cell homeostasis and its contribution to PD pathogenesis largely unresolved. Methods Here, we used murine overexpression models of wildtype and G2019S variant of mouse Lrrk2 to examine how Lrrk2 G2019S shapes host defense across viral and bacterial infection models. We tested systemic sepsis and Escherichia coli infection to examine bacterial clearance. We followed up by testing macrophage responses to intracellular (Listeria monocytogenes) or primarily extracellular (Pseudomonas aeruginosa) bacteria. Finally, tested antibody-mediated immunity using influenza and cytotoxic T cell-mediated immunity using lymphocytic choriomeningitis virus (LCMV) infection. Results We found that Lrrk2 G2019S overexpression enhanced survival and bacterial clearance during P. aeruginosa lung infection, whereas the same genotype worsened outcomes in polymicrobial sepsis, with increased mortality, pulmonary myeloid infiltration and a hematopoietic cell-intrinsic phenotype. During L. monocytogenes infection, Lrrk2 G2019S selectively reduced non-classical monocytes without altering disease progression. In influenza and LCMV infection, G2019S altered antigen-specific CD8+ T cell distribution without major changes in cell memory responses clinical severity. Discussion Together, these data show that Lrrk2 G2019S selectively reprograms innate and adaptive immunity in a pathogen- and tissue-dependent manner, uncoupling inflammatory magnitude from effective host defense. These results and previous work support a model in which the G2019S LRRK2 variant contributes to maladaptive inflammatory responses to specific infection challenges, providing insight into how lifetime immune perturbations may intersect with genetic susceptibility to influence lifetime infection risk.
Background Neurodegenerative diseases including Parkinson’s disease (PD) are increasingly associated with dysfunction in both central and peripheral immune systems. Pathogenic mutations in leucine-rich repeat kinase 2 (LRRK2) represent a major cause of familial PD, while common polymorphisms are associated with inflammatory diseases. Methods Here, using immunophenotyping flow cytometry and quantitative PCR (qPCR), we compared immune cell populations and function across both the central and peripheral immune systems in C57BL/6J wild type (WT), Lrrk2 p.G2019S knock-in (GKI) and Lrrk2 knock-out (LKO) models in basal and ex vivo immune-stimulated conditions. Results With a focus on T cell biology, compared to their WT counterparts at baseline, GKI mice exhibit higher populations of Cd8+ and TH17 T cell subsets in the brain, whereas LKO mice exhibited unique central memory (TCM), follicular helper (TFH), and TH2 lineages. In the periphery, GKI mice demonstrated higher TH1, TH2, and TH17 subset expansions, whereas peripheral alterations in LKO are largely restricted to TH17 subsets. Within mutant genotypes, a striking discrepancy was observed between baseline gene expression and the translated proteins encoded, that reveals a fundamental loss of basal immune homeostasis. This phenomenon was further exposed following an acute (6-hour) ex vivo lipopolysaccharide (LPS) immune challenge. Following stimulation, GKI immune cells had reduced transcription, alongside stalled translation, for almost all effector molecules examined, while LKO immune cells had fewer transcriptional changes compared to wild type. Overall, both mutant lines had stalled or flatline effector molecule production after immune stimulation, suggesting a profound loss of functional responsiveness. This hypothesis was supported by a significant increase in surface protein of the inhibitory receptor Pd-1 on regulatory T cells (TREG) and TH1/TH2 Cd4+ T cell subsets in GKI mice. LKO immune landscapes trended toward similar exhaustion patterns, albeit less evident. Conclusions These data suggest that bidirectional disruptions to normal Lrrk2 function break immune homeostasis. Immune cell function should be carefully considered when targeting LRRK2 kinase activity in patients with PD.
Robert C. Sharp, Shannon C. Wall, Jordan C. Follet et al.· bioRxiv· 0 citations
Environmental exposures across the lifespan shape the immune landscape and can influence responses to later challenges. Both innate and adaptive immunity affect the trajectory of neurodegenerative diseases. We have recently shown in mice that microglia slow tauopathy progression by limiting tau spread within the CNS and into the periphery, and that a granzyme K-expressing CD8+ T cell subset engages microglia to reduce microglial distress, restrict tau dissemination, and delay neurological decline in a PD-1/TIGIT-dependent manner. Similar microglia-T cell interactions were observed in human brains with tau-rich lesions associated with age, Alzheimer’s disease, or chronic traumatic encephalopathy. Here, we investigated how systemic viral infection influences disease course in mice expressing mutant human tau.
Single cell TCR sequencing, flow cytometry, immunofluorescence, and behavioral assessments were used to define immune changes and disease progression in P301S (Thy1a promoter) mice following systemic infection.
We found that dual PD-1/TIGIT blockade accelerates neurological dysfunction. In contrast, intravenous LCMV Armstrong infection elicited robust peripheral immune activation yet did not alter the overall rate of decline in P301S mice; instead, it produced a marked increase in variability among individual disease trajectories. We further identified a tauopathy-specific surface marker signature that delineates a subset of Trm-like granzyme K+ CD8+ T cells in the CNS and draining lymph nodes that appears to slow disease progression. The heightened heterogeneity observed after viral infection suggests that systemic immune challenges may perturb this population in unpredictable ways.
These data demonstrate that tauopathy progression is highly sensitive to systemic immune perturbations, including non-neurotropic viral infections. They underscore the complexity of neurodegenerative disease and highlight how lifelong immunological challenges shape CNS pathology.
Intramural program at the National Institute of Neurological Disorders & Stroke and the National Institute of Allergy & Infectious Diseases, NIH Defense Health Agency (310286-1.00-65642 and 311661-5.00-66323)
Neuroimmunology (NEUR)
Yvonne L. Latour, Dorian B. McGavern· Journal of Immunology· 0 citations
Feedback mechanisms regulate immune activation and prevent excessive tissue damage. TNFAIP3, also known as A20, serves as a crucial brake on inflammation, and mutations or haploinsufficiency of this gene are linked to diseases characterized by inappropriate inflammation. In this study, we document highly conserved patterns of cell type-specific gene expression, regulation, and induction of TNFAIP3, and employ transgenic and gnotobiotic mouse models to investigate how adaptive immunity and the gut microbiome contribute to pathology arising from impaired A20 function. Contrary to our expectations, systemic inflammation resulting from Tnfaip3 deficiency in CD11c (Itgax)-expressing cells developed independently of autoreactive antibodies, B cells, and T cells. The microbiome also proved dispensable for disease manifestations in these models. These findings suggest that in diseases caused by insufficient TNFAIP3/A20 activity, autoantibodies may reflect a downstream consequence of disease rather than a causative driver, suggesting autoinflammatory rather than autoimmune pathology. These insights carry therapeutic implications for the treatment of TNFAIP3-associated diseases.
Karel F. A. Van Damme, Pieter Hertens, D. Sichien et al.· Frontiers in Immunology· 0 citations
RNA dysregulation is a recognized contributor to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), the most common motor neuron (MN) disease. However, the molecular mechanisms linking defects in RNA metabolism to selective neuronal vulnerability remain poorly understood. Alterations in the cellular levels of R-loops –structures forming by reannealing of the nascent RNA with the template DNA during transcription- have been observed in neurodegeneration, but it is unclear how perturbations in R-loop homeostasis contribute to neuronal dysfunction. Here we investigate the molecular basis of a juvenile form of ALS dubbed ALS4 that is caused by mutations in the helicase SETX, which plays important roles in the resolution of R-loops and transcription termination. Using isogenic human induced pluripotent stem cell-derived MNs, we show that ALS4-associated SETX mutations induce progressive axonal defects and widespread transcriptomic alterations, including reduced expression or altered splicing of transcripts critical for neuronal function. ALS4 MNs exhibit a transcriptional signature marked by cellular stress, aberrant cell cycle re-entry, and compromised neuronal identity that is partially shared by other forms of ALS. Mechanistically, these defects are partly driven by downstream aberrant activation of the TGF-β signaling pathway, whose pharmacological inhibition ameliorates axonal defects. Finally, our analyses support a link between mutant SETX ectopic activity at R-loops and the observed alterations in RNA expression and splicing, providing new insights into how RNA dysregulation can drive neuronal dysfunction Altogether, our work reveals how perturbations at the interface of transcription and R-loop metabolism can reshape neuronal identity and drive disease. Teaser Deregulation of TGF-β signaling drives axonal defects and compromised motor neuron identity in senataxin-mediated ALS
Marta Giannini, Thierry Gostan, Amal Zine El Aabidine et al.· bioRxiv· 0 citations
All animals age. However, aging is a heterogeneous process, and individual organisms age differently. Moreover, within the same organism, cells or organs do not age at the same speed. For instance, neurodegeneration, a hallmark of aging, generally manifests later than other peripheral aging signs. The genetic determinants of aging are not completely understood. Gain-of-function (GoF) mutations in leucine-rich repeat kinase 2 (LRRK2GoF) are major genetic risk factors for Parkinson's disease (PD). By analyzing PD patients and LRRK2GoF mice, we show that PD represents an accelerated aging disorder driven by STING-dependent inflammation. This inflammation begins peripherally, disrupts the blood-brain barrier, and causes dopaminergic neurodegeneration. Mechanistically, aging or LRRK2GoF causes endolysosomal decline, resulting in cytosolic self-DNA accumulation and the release of DNA-containing extracellular vesicles (EVs) that activate the cGAS-STING pathway within and between cells. Our findings identify LRRK2GoF as a key driver of accelerated aging and systemic inflammaging through DNA-containing EVs, highlighting potential therapeutic targets to counteract inflammaging and neurodegeneration.
M. Öberg, Caitlyn Myers, Najmeh Saffarzadeh et al.· Cell Reports· 1 citation
Inflammasomes are crucial for innate immune defense to many microbial infections but are also subjected to stringent cellular regulation to avoid persistent, aberrant activation that could lead to lethal sepsis and autoinflammatory conditions. Ubiquitination is one of the most important posttranslational modifications involved in many immune signaling pathways, including the nucleotide-binding and oligomerization domain (NOD)-like receptor 3 (NLRP3) inflammasome. However, its role in the non-canonical caspase-4 inflammasomes is poorly understood.
To address this significant gap, we constructed 375 individual ubiquitin E3 ligase knockout lines by CRISPR-Cas9 and performed an unbiased screening. This library represents almost all the currently known definite E3 ligases (total ∼377).
Our screen identified 15 positive regulators of the caspase-4 inflammasome; one of the top hits was Muscle Excess 3B (MEX3B), an RNA-binding protein with a ubiquitin ligase domain. We found that deletion of MEX3B inhibited caspase-4 and gasdermin D (GSDMD) activation, pyroptosis, and secretion of inflammasome-dependent inflammatory cytokines in human cell lines and murine primary macrophages upon priming with interferon gamma (IFN-γ) and transfection with lipopolysaccharide (LPS). Notably, MEX3B was also crucial for canonical inflammasome signaling such as NLRP3 and NLRC4. Mechanistically, MEX3B was required for caspase-1 activation but not NLRP3 oligomerization. The role of MEX3B in inflammasome signaling was reliant on its RNA-binding, but not E3 ligase activity. However, the expression of caspase-4 and GSDMD, IFN-γ and Toll-like receptor (TLR4) signaling, and apoptosis remained intact in MEX3B-/- cells.
Our results suggest that MEX3B is a pan-inflammasome regulator targeting inflammatory caspases. Ongoing work is to investigate both the NLRP3 and caspase-4 inflammasome signaling in Mex3b-/- mice and elucidate the molecular mechanism of action of MEX3B.
National Institute of Allergy and Infectious Diseases, USA
Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)
Penghua Wang, Jason G. Cahoon, Duomeng Yang et al.· Journal of Immunology· 0 citations