It is suggested that bidirectional disruptions to normal LRRK2 function break immune homeostasis and immune cell function should be carefully considered when targeting LRRK2 kinase activity in patients with PD.
Abstract
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.
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.
Andrea R. Merchak, Mary K. Herrick, M. Houser et al.· Frontiers in Cellular Neuros...· 0 citations
Systemic complement protects the vascular compartment, while cell-intrinsic complement components shape tissue immunity by regulating normal cell physiology and metabolism. In human CD4 T helper cells, intracellular C5a generation engages the intracellular receptor C5aR1, promoting Th1 differentiation. Here, we identify a counter-regulatory role for the alternative C5a receptor, C5aR2, in restraining T cell effector responses by studying the first reported family with a heterozygous C5aR2 mutation. The affected individuals present with an autoinflammatory syndrome, and disease penetrance tracks with the mutation: the affected mother and child carry the variant, whereas the unaffected father and siblings do not.
To define the impact of the C5aR2 mutation, we performed single-cell RNA sequencing, in vitro stimulation assays, and flow cytometric profiling of patient and control PBMCs. CPM inhibition or deletion, C5aR2 agonism, and transcriptional profiling of Cpm- or C5ar2-deficient mouse CD4 T cells, along with a T cell transfer colitis model, were used to define mechanistic consequences.
Patient samples exhibited a profound loss of naïve and central memory CD4 and CD8 T cells, accompanied by expansion of IFN-γ—producing effector memory populations. The C5aR2 mutation abolishes C5aR2 β-arrestin signaling. Additionally, we identified carboxypeptidase M (CPM) as a T cell—intrinsic enzyme generating C5a-desArg, a potent ligand for C5aR2. Loss or inhibition of CPM heightened inflammatory T cell responses, which were normalized by C5aR2 agonism. Mouse Cpm- or C5ar2-deficient CD4 T cells displayed overlapping transcriptional perturbations, and Cpm-knockout CD4 T cells induced more severe colitis.
Collectively, our data uncover a previously unrecognized CPM-dependent mechanism that balances C5aR1 and C5aR2 signaling to limit pathological T cell activation, revealing an intrinsic complement-driven checkpoint that constrains effector T cell immunity.
NHLBI/NIH intramural program
Immune Mechanisms of Human Disease (HUM)
Erin E. West, Nicolas S. Merle, Ayden Case et al.· Journal of Immunology· 0 citations
Aging is the primary risk factor for a wide spectrum of chronic diseases, ranging from infectious diseases and cancer to autoimmunity and neurodegeneration. One of the key drivers of this increased susceptibility is the progressive decline in immune function-immunosenescence that reshapes the host's inflammatory landscape. Emerging evidence points to an age-associated expansion of cytotoxic CD4+ T cells (CD4 CTLs), which can play context-dependent protective or pathogenic roles in host homeostasis and disease, reflecting their unique integration of helper and cytotoxic programs as well as their preferential expansion during aging. On the protective side, CD4 CTLs contribute to immune surveillance and host defense against viral infections and malignancies. Conversely, in selected settings, they can function as pathogenic effectors in autoimmune and neurodegenerative disorders. In this review, we synthesize the emerging biology of CD4 CTLs, highlighting their differentiation and dual roles in protection and pathology. Beyond a descriptive overview, we propose a conceptual framework that places age-associated CD4 CTL expansion at the intersection of aging and age-associated disease. Rather than viewing late-life pathologies as fully independent events, we suggest that at least a subset may be partially interconnected by recurrent CD4 CTL programs, while emphasizing that the strength of evidence and the degree of causality differ substantially by disease context. This framework provides a basis for asking when CD4 CTLs should be enhanced, restrained, or more precisely redirected to promote healthy longevity.
Tatsuya Hasegawa, Kosei Nishitani, K. Kabashima· International Immunology· 0 citations
Sporadic Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disorder characterized by numerous pathological processes occurring both in the brain and in the periphery, including chronic local or systemic inflammation, cerebrovascular impairment, oxidative stress, mitochondrial dysfunction, amyloidosis, synaptic and neuronal network dysfunction, metabolic syndrome, and disrupted cell signaling pathways. Although these mechanisms have been extensively studied, the contribution of the peripheral immune system to the etiology and progression of AD remains poorly understood. Emerging evidence suggests that pathological events in the brain, such as amyloid and phosphorylated tau accumulation, neurodegeneration, and neuroinflammation, may trigger systemic immune responses that alter the distribution and function of peripheral immune cells. However, available findings remain inconsistent. In the present study, we examined age-dependent alterations in peripheral blood immune cell populations in Tg-SwDI mice, a transgenic model of AD. We documented for the first time that transgenic mice exhibited increased proportions of neutrophils and an elevated neutrophil-to-lymphocyte ratio (NLR), along with reduced percentages of T lymphocytes compared with wild-type controls. Furthermore, significant differences in T-cell subpopulations were observed between Tg-SwDI and wild-type animals. Our findings are partially consistent with reported clinical observations in patients with AD. Because no single transgenic mouse model fully recapitulates the complex pathology of AD, and many therapeutic approaches successful in preclinical models have failed in clinical trials, a detailed characterization of disease-related alterations in each model is essential for selecting the most appropriate model to investigate specific mechanisms or therapeutic approaches.
Adrian Rodriguez-Lopez, Gonzalo Acero, Georgina Díaz et al.· Journal of Neuroimmunology· 0 citations
Investigation of how systemic viral infection influences disease course in mice expressing mutant human tau finds that dual PD-1/TIGIT blockade accelerates neurological dysfunction and identifies 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.
Yvonne L. Latour, Dorian B. McGavern· Journal of Immunology· 0 citations
Type 1 diabetes (T1D) is an autoimmune disorder caused by T cell-mediated destruction of pancreatic β cells. There is a critical need to develop novel therapies for this disease, which requires further understanding of T1D pathogenesis. One pathway that is implicated is signaling through the immune receptor NKG2D. However, NKG2D’s role has remained unclear due to conflicting reports in the literature.
We generated multiple novel mouse strains on the non-obese diabetic (NOD) background to better define the role of NKG2D in autoimmune diabetes. We compared diabetes incidence, insulitis, including digital spatial profiling, and islet-specific CD8+ CTL generation between mice genetically deficient in NKG2D (NKG2D KO) and wild-type (WT) mice housed in both specific-pathogen-free (SPF) and germ-free (GF) conditions.
NKG2D KO mice had delayed diabetes, insulitis, and CD8+ T cell pancreatic infiltration, with the most significant effect in GF and male mice. Further, we found that NKG2D signaling did not occur in the pancreas, that NKG2D ligands were expressed in the pancreatic lymph node, that deletion of NKG2D in CD8+ T cells was required to delay diabetes, that there was reduced differentiation of CTL from islet-specific naive NKG2D KO CD8+ T cells, and that the transcriptome of NKG2D KO CTL was altered. Additionally, we found that blocking NKG2D signaling similarly reduced human CTL differentiation.
The results of our studies definitively demonstrate that NKG2D in CD8+ T cells plays a critical role in autoimmune diabetes. We show this role is to enhance CTL generation rather than the CTL effector response in islets as previously proposed. Further, our data explain the conflicting reports surrounding NKG2D’s role, as we reveal the existence of redundant, compensatory signaling that is influenced by the microbiome and sex. This inherent redundancy strongly suggests that signaling through NKG2D or its compensatory pathway is critical for islet-specific CTL generation.
Breakthrough T1D (3-SRA-2023-1412-S-B and 1-INO-2022-1118-A-N), NIH P20GM104936
Basic Autoimmunity (BA)
M. Markiewicz, Zoe K Bedrosian, Allison Manning et al.· Journal of Immunology· 0 citations