Autoimmunity and Inflammation Due to a Gain-of-Function Mutation in Phospholipase Cγ2 that Specifically Increases External Ca2+ Entry

Single-cell profiling uncovers the intricate pathological niche diversity in brain, lymph node, bone, and adrenal metastases of lung cancer

PURPOSE

The aim of this study is to explore the pathological niche of cancer metastasis and the site-specific interactions between tumor cells and the microenvironment, understand the mechanisms driving metastasis progression and identify potential therapeutic targets.

METHODS

Data from four lung cancer metastasis datasets (GSE123902, GSE131907, GSE148071, and GSE186344) were downloaded and subjected to stringent quality control and filtering. Cell types were identified using canonical markers, and pseudotime trajectory analysis was performed to evaluate cell differentiation. Functional and pathway enrichment analyses, including ssGSEA and GO/KEGG, were conducted. CellphoneDB was used to analyze intercellular communication, ranking receptor-ligand interactions based on communication strength.

RESULTS

Eleven cell types were identified after quality control, revealing significant heterogeneity and site-specific functionality in lung cancer metastases. CTLs showed notable activity in antigen presentation and T-cell differentiation pathways, with DNAJB1⁺ CTLs playing a dominant role in cytotoxicity and immune regulation. B cells, myeloid cells, and CAFs were involved in immune modulation, defense, and matrix remodeling through specific signaling pathways. Tumor cell subclusters drove proliferation, migration, and immune evasion via immune-regulatory, Hippo, and TGF-beta pathways. No overlapping pathways were observed across metastatic sites. Cell communication analysis identified PPIA-BSG and APP-CD74 as key axes in brain and lymph node metastases, while FN1-Integrin and CTLA4-CD86 dominated in bone and adrenal metastases, respectively.

CONCLUSIONS

In summary, this study highlights the functional heterogeneity and site-specific interactions of cells in lung cancer metastases, providing insights into the mechanisms shaping metastatic niches and potential therapeutic strategies.

Pharmacogenetics of therapies in rheumatoid arthritis: An update

Rheumatoid arthritis (RA) is a systemic autoimmune inflammatory arthritis. Despite many treatment advances, achieving remission or low-disease activity in RA remains challenging, often requiring trial and error approaches with numerous medications. Precision medicine, particularly pharmacogenomics, explores how genetic factors influence drug response in individual patients, and incorporates such factors to develop personalized treatments for individual patients. Genetic variations in drug-metabolizing enzymes, transporters, and targets may contribute to inter-individual differences in drug efficacy and toxicity. Advancements in molecular sequencing have allowed rapid identification of such variants, including single nucleotide polymorphisms (SNPs). This review highlights recent major findings in the pharmacogenetics of therapies in RA, focusing on key genes and SNPs to provide insights into current trends and developments in this field.

The crystal and cryo-EM structures of PLCγ2 reveal dynamic interdomain recognitions in autoinhibition

Phospholipase C gamma 2 (PLCγ2) plays important roles in cell signaling downstream of various membrane receptors. PLCγ2 contains a multidomain inhibitory region critical for its regulation, while it has remained unclear how these domains contribute to PLCγ2 activity modulation. Here we determined three structures of human PLCγ2 in autoinhibited states, which reveal dynamic interactions at the autoinhibition interface, involving the conformational flexibility of the Src homology 3 (SH3) domain in the inhibitory region, and its previously unknown interaction with a carboxyl-terminal helical domain in the core region. We also determined a structure of PLCγ2 bound to the kinase domain of fibroblast growth factor receptor 1 (FGFR1), which demonstrates the recognition of FGFR1 by the nSH2 domain in the inhibitory region of PLCγ2. Our results provide structural insights into PLCγ2 regulation that will facilitate future mechanistic studies to understand the entire activation process.

Characterization of a Novel Pathogenic PLCG2 Variant Leading to APLAID Syndrome Responsive to a TNF Inhibitor

OBJECTIVE

Autoinflammation and phospholipase C (PLC) γ2-associated antibody deficiency and immune dysregulation (APLAID) syndrome is an autoinflammatory disease caused by gain-of-function variants in PLCG2. This study investigates the pathogenic mechanism of a novel variant of PLCG2 in a patient with APLAID syndrome.

METHODS

Whole-exome sequencing and Sanger sequencing were used to identify the pathogenic variant in the patient. Single-cell RNA sequencing, immunoblotting, luciferase assay, inositol monophosphate enzyme-linked immunosorbent assay, calcium flux assay, quantitative PCR, and immunoprecipitation were used to define inflammatory signatures and evaluate the effects of the PLCG2 variant on protein functionality and immune signaling.

RESULTS

We identified a novel de novo variant, PLCG2 p.D993Y, in a patient with colitis, pansinusitis, skin rash, edema, recurrent respiratory infections, B-cell deficiencies, and hypogammaglobulinemia. The single-cell transcriptome revealed exacerbated inflammatory responses in the patient's peripheral blood mononuclear cells. Expression of the D993Y variant in HEK293T, COS-7, and PLCG2 knock-out THP-1 cell lines showed heightened PLCγ2 phosphorylation; elevated inositol-1,4,5-trisphosphate production and intracellular Ca2+ release; and activation of the MAPK, NF-κB, and NFAT signaling pathways compared with control-transfected cells. In vitro experiments indicated that the D993Y variant altered amino acid properties, disrupting the interaction between the catalytic and autoinhibitory domains of PLCγ2, resulting in PLCγ2 autoactivation.

CONCLUSION

Our findings demonstrated that the PLCG2 D993Y variant is a gain-of-function mutation via impairing its autoinhibition, activating multiple inflammatory signaling pathways, thus leading to APLAID syndrome. This study further broadens the molecular underpinnings and phenotypic spectrum of PLCγ2-related disorders.

A longitudinal single-cell atlas of anti-tumour necrosis factor treatment in inflammatory bowel disease

Precision medicine in immune-mediated inflammatory diseases (IMIDs) requires a cellular understanding of treatment response. We describe a therapeutic atlas for Crohn's disease (CD) and ulcerative colitis (UC) following adalimumab, an anti-tumour necrosis factor (anti-TNF) treatment. We generated ~1 million single-cell transcriptomes, organised into 109 cell states, from 216 gut biopsies (41 subjects), revealing disease-specific differences. A systems biology-spatial analysis identified granuloma signatures in CD and interferon (IFN)-response signatures localising to T cell aggregates and epithelial damage in CD and UC. Pretreatment differences in epithelial and myeloid compartments were associated with remission outcomes in both diseases. Longitudinal comparisons demonstrated disease progression in nonremission: myeloid and T cell perturbations in CD and increased multi-cellular IFN signalling in UC. IFN signalling was also observed in rheumatoid arthritis (RA) synovium with a lymphoid pathotype. Our therapeutic atlas represents the largest cellular census of perturbation with the most common biologic treatment, anti-TNF, across multiple inflammatory diseases.

Single-cell peripheral immunoprofiling of lewy body and Parkinson's disease in a multi-site cohort

BACKGROUND

Multiple lines of evidence support peripheral organs in the initiation or progression of Lewy body disease (LBD), a spectrum of neurodegenerative diagnoses that include Parkinson's Disease (PD) without or with dementia (PDD) and dementia with Lewy bodies (DLB). However, the potential contribution of the peripheral immune response to LBD remains unclear. This study aims to characterize peripheral immune responses unique to participants with LBD at single-cell resolution to highlight potential biomarkers and increase mechanistic understanding of LBD pathogenesis in humans.

METHODS

In a case-control study, peripheral mononuclear cell (PBMC) samples from research participants were randomly sampled from multiple sites across the United States. The diagnosis groups comprise healthy controls (HC, n = 159), LBD (n = 110), Alzheimer's disease dementia (ADD, n = 97), other neurodegenerative disease controls (NDC, n = 19), and immune disease controls (IDC, n = 14). PBMCs were activated with three stimulants (LPS, IL-6, and IFNa) or remained at basal state, stained by 13 surface markers and 7 intracellular signal markers, and analyzed by flow cytometry, which generated 1,184 immune features after gating.

RESULTS

The model classified LBD from HC with an AUROC of 0.87 ± 0.06 and AUPRC of 0.80 ± 0.06. Without retraining, the same model was able to distinguish LBD from ADD, NDC, and IDC. Model predictions were driven by pPLCγ2, p38, and pSTAT5 signals from specific cell populations under specific activation. The immune responses characteristic for LBD were not associated with other common medical conditions related to the risk of LBD or dementia, such as sleep disorders, hypertension, or diabetes.

CONCLUSIONS AND RELEVANCE

Quantification of PBMC immune response from multisite research participants yielded a unique pattern for LBD compared to HC, multiple related neurodegenerative diseases, and autoimmune diseases thereby highlighting potential biomarkers and mechanisms of disease.

Human and Murine Toll-like Receptor-Driven Disease in Systemic Lupus Erythematosus

The pathogenesis of systemic lupus erythematosus (SLE) is linked to the differential roles of toll-like receptors (TLRs), particularly TLR7, TLR8, and TLR9. TLR7 overexpression or gene duplication, as seen with the Y-linked autoimmune accelerator (Yaa) locus or TLR7 agonist imiquimod, correlates with increased SLE severity, and specific TLR7 polymorphisms and gain-of-function variants are associated with enhanced SLE susceptibility and severity. In addition, the X-chromosome location of TLR7 and its escape from X-chromosome inactivation provide a genetic basis for female predominance in SLE. The absence of TLR8 and TLR9 have been shown to exacerbate the detrimental effects of TLR7, leading to upregulated TLR7 activity and increased disease severity in mouse models of SLE. The regulatory functions of TLR8 and TLR9 have been proposed to involve competition for the endosomal trafficking chaperone UNC93B1. However, recent evidence implies more direct, regulatory functions of TLR9 on TLR7 activity. The association between age-associated B cells (ABCs) and autoantibody production positions these cells as potential targets for treatment in SLE, but the lack of specific markers necessitates further research for precise therapeutic intervention. Therapeutically, targeting TLRs is a promising strategy for SLE treatment, with drugs like hydroxychloroquine already in clinical use.

De novo variants in PLCG1 are associated with hearing impairment, ocular pathology, and cardiac defects

Phospholipase C isozymes (PLCs) hydrolyze phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and diacylglycerol, important signaling molecules involved in many cellular processes. PLCG1 encodes the PLCγ1 isozyme that is broadly expressed. Hyperactive somatic mutations of PLCG1 are observed in multiple cancers, but only one germline variant has been reported. Here we describe three unrelated individuals with de novo heterozygous missense variants in PLCG1 (p.Asp1019Gly, p.His380Arg, and p.Asp1165Gly) who exhibit variable phenotypes including hearing loss, ocular pathology and cardiac septal defects. To model these variants in vivo, we generated the analogous variants in the Drosophila ortholog, small wing (sl). We created a null allele slT2A and assessed the expression pattern. sl is broadly expressed, including in wing discs, eye discs, and a subset of neurons and glia. Loss of sl causes wing size reductions, ectopic wing veins and supernumerary photoreceptors. We document that mutant flies exhibit a reduced lifespan and age-dependent locomotor defects. Expressing wild-type sl in slT2A mutant rescues the loss-of-function phenotypes whereas expressing the variants causes lethality. Ubiquitous overexpression of the variants also reduces viability, suggesting that the variants are toxic. Ectopic expression of an established hyperactive PLCG1 variant (p.Asp1165His) in the wing pouch causes severe wing phenotypes, resembling those observed with overexpression of the p.Asp1019Gly or p.Asp1165Gly variants, further arguing that these two are gain-of-function variants. However, the wing phenotypes associated with p.His380Arg overexpression are mild. Our data suggest that the PLCG1 de novo heterozygous missense variants are pathogenic and contribute to the features observed in the probands.

PLCG2 and IFNAR1: The Potential Biomarkers Mediated by Immune Infiltration and Osteoclast Differentiation of Ankylosing Spondylitis in the Peripheral Blood

Objectives

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease characterized by chronic spinal inflammation, arthritis, gut inflammation, and enthesitis. We aimed to identify the key biomarkers related to immune infiltration and osteoclast differentiation in the pathological process of AS by bioinformatic methods.

Methods

GSE25101 from the Gene Expression Omnibus was used to obtain AS-associated microarray datasets. We performed bioinformatics analysis using R software to validate different expression levels. The purpose of the GO and KEGG enrichment analyses of DEGs was to exclude key genes. Using weighted correlation network analysis (WGCNA), we examined all expression profile data and identified differentially expressed genes. The objective was to investigate the interaction between genetic and clinical features and to identify the essential relationships underlying coexpression modules. The CIBERSORT method was used to make a comparison of the immune infiltration in whole blood between the AS group and the control group. The WGCNA R program from Bioconductor was used to identify hub genes. RNA extraction reverse transcription and quantitative polymerase chain reaction were conducted in the peripheral blood collected from six AS patients and six health volunteers matched by age and sex.

Results

125 DEGs were identified, consisting of 36 upregulated and 89 downregulated genes that are involved in the cell cycle and replication processes. In the WGCNA, modules of MCODE with different algorithms were used to find 33 key genes that were related to each other in a strong way. Immune infiltration analysis found that naive CD4+ T cells and monocytes may be involved in the process of AS. PLCG2 and IFNAR1 genes were obtained by screening genes meeting the conditions of immune cell infiltration and osteoclast differentiation in AS patients among IGF2R, GRN, SH2D1A, LILRB3, IFNAR1, PLCG2, and TNFRSF1B. The results demonstrated that the levels of PLCG2 mRNA expression in AS were considerably higher than those in healthy individuals (P=0.003). IFNAR1 mRNA expression levels were considerably lower in AS than in healthy individuals (P < 0.0001).

Conclusions

Dysregulation of PLCG2 and IFNAR1 are key factors in disease occurrence and development of AS through regulating immune infiltration and osteoclast differentiation. Explaining the differences in immune infiltration and osteoclast differentiation between AS and normal samples will contribute to understanding the development of spondyloarthritis.

Phospholipase C-γ as a Potential Therapeutic Target for Graves' Orbitopathy

BACKGRUOUND

Phospholipase C-γ (PLC-γ) plays a crucial role in immune responses and is related to the pathogenesis of various inflammatory disorders. In this study, we investigated the role of PLC-γ and the therapeutic effect of the PLC-specific inhibitor U73122 using orbital fibroblasts from patients with Graves' orbitopathy (GO).

METHODS

The expression of phospholipase C gamma 1 (PLCG1) and phospholipase C gamma 2 (PLCG2) was evaluated using polymerase chain reaction in GO and normal orbital tissues/fibroblasts. The primary cultures of orbital fibroblasts were treated with non-toxic concentrations of U73122 with or without interleukin (IL)-1β to determine its therapeutic efficacy. The proinflammatory cytokine levels and activation of downstream signaling molecules were determined using Western blotting.

RESULTS

PLCG1 and PLCG2 mRNA expression was significantly higher in GO orbital tissues than in controls (P<0.05). PLCG1 and PLCG2 mRNA expression was significantly increased (P<0.05) in IL-1β, tumor necrosis factor-α, and a cluster of differentiation 40 ligand-stimulated GO fibroblasts. U73122 significantly inhibited the IL-1β-induced expression of proinflammatory molecules, including IL-6, IL-8, monocyte chemoattractant protein-1, cyclooxygenase-2, and intercellular adhesion molecule-1 (ICAM-1), and phosphorylated protein kinase B (p-Akt) and p38 (p-p38) kinase in GO fibroblasts, whereas it inhibited IL-6, IL-8, and ICAM-1, and p-Akt and c-Jun N-terminal kinase (p-JNK) in normal fibroblasts (P<0.05).

CONCLUSION

PLC-γ-inhibiting U73122 suppressed the production of proinflammatory cytokines and the phosphorylation of Akt and p38 kinase in GO fibroblasts. This study indicates the implications of PLC-γ in GO pathogenesis and its potential as a therapeutic target for GO.

Plaque attack by microglial PLCγ2

PLCγ2 is genetically linked to Alzheimer's disease (AD), but it is unclear how PLCγ2 contributes to pathology. Tsai et al. demonstrate that AD-associated PLCG2 variants bidirectionally orchestrate microglial responses to plaques and impact neural function in an AD mouse model. This positions PLCγ2 as a key microglial signaling node and shows that targeting PLCγ2 could have therapeutic benefits in AD.

Mercury intoxication disrupts tonic signaling in B cells, and may promote autoimmunity due to abnormal phosphorylation of STIM-1 and other autoimmunity risk associated phosphoproteins involved in BCR signaling

Epidemiological studies link exposure to mercury with autoimmune disease. Unfortunately, in spite of considerable effort, no generally accepted mechanistic understanding of how mercury functions with respect to the etiology of autoimmune disease is currently available. Nevertheless, autoimmune disease often arises because of defective B cell signaling. Because B cell signaling is dependent on phosphorylation cascades, in this report, we have focused on how mercury intoxication alters phosphorylation of B cell proteins in antigen-non stimulated (tonic) mouse (BALB/c) splenic B cells. Specifically, we utilized mass spectrometric techniques to conduct a comprehensive unbiased global analysis of the effect of inorganic mercury (Hg2+) on the entire B cell phosphoproteome. We found that the effects were pleotropic in the sense that large numbers of pathways were impacted. However, confirming our earlier work, we found that the B cell signaling pathway stood out from the rest, in that phosphoproteins which had sites which were affected by Hg2+, exhibited a much higher degree of connectivity, than components of other pathways. Further analysis showed that many of these BCR pathway proteins had been previously linked to autoimmune disease. Finally, dose response analysis of these BCR pathway proteins showed STIM1_S575, and NFAT2_S259 are the two most Hg2+ sensitive of these sites. Because STIM1_S575 controls the ability of STIM1 to regulate internal Ca2+, we speculate that STIM1 may be the initial point of disruption, where Hg2+ interferes with B cell signaling leading to systemic autoimmunity, with the molecular effects pleiotropically propagated throughout the cell by virtue of Ca2+ dysregulation.

Myeloid Src-family kinases are critical for neutrophil-mediated autoinflammation in gout and motheaten models

Autoinflammatory diseases include a number of monogenic systemic inflammatory diseases, as well as acquired autoinflammatory diseases such as gout. Here, we show that the myeloid Src-family kinases Hck, Fgr, and Lyn are critical for experimental models of gout, as well as for genetically determined systemic inflammation in the Ptpn6me-v/me-v (motheaten viable) mouse model. The Hck-/-Fgr-/-Lyn-/- mutation abrogated various monosodium urate (MSU) crystal-induced pro-inflammatory responses of neutrophils, and protected mice from the development of gouty arthritis. The Src-family inhibitor dasatinib abrogated MSU crystal-induced responses of human neutrophils and reduced experimental gouty arthritis in mice. The Hck-/-Fgr-/-Lyn-/- mutation also abrogated spontaneous inflammation and prolonged the survival of the Ptpn6me-v/me-v mice. Spontaneous adhesion and superoxide release of Ptpn6me-v/me-v neutrophils were also abolished by the Hck-/-Fgr-/-Lyn-/- mutation. Excessive activation of tyrosine phosphorylation pathways in myeloid cells may characterize a subset of autoinflammatory diseases.

Inborn Errors of Immunity and Autoimmune Disease

Autoimmunity may be a manifestation of inborn errors of immunity, specifically as part of the subgroup of primary immunodeficiency known as primary immune regulatory disorders. However, although making a single gene diagnosis can have important implications for prognosis and management, picking patients to screen can be difficult, against a background of a high prevalence of autoimmune disease in the population. This review compares the genetics of common polygenic and rare monogenic autoimmunity, and explores the molecular mechanisms, phenotypes, and inheritance of autoimmunity associated with primary immune regulatory disorders, highlighting the emerging importance of gain-of-function and non-germline somatic mutations. A novel framework for identifying rare monogenic cases of common diseases in children is presented, highlighting important clinical and immunologic features that favor single gene disease and guides clinicians in selecting appropriate patients for genomic screening. In addition, there will be a review of autoimmunity in non-genetically defined primary immunodeficiency such as common variable immunodeficiency, and of instances where primary autoimmunity can result in clinical phenocopies of inborn errors of immunity.

Activation Mechanisms and Diverse Functions of Mammalian Phospholipase C

Phospholipase C (PLC) plays pivotal roles in regulating various cellular functions by metabolizing phosphatidylinositol 4,5-bisphosphate in the plasma membrane. This process generates two second messengers, inositol 1,4,5-trisphosphate and diacylglycerol, which respectively regulate the intracellular Ca²⁺ levels and protein kinase C activation. In mammals, six classes of typical PLC have been identified and classified based on their structure and activation mechanisms. They all share X and Y domains, which are responsible for enzymatic activity, as well as subtype-specific domains. Furthermore, in addition to typical PLC, atypical PLC with unique structures solely harboring an X domain has been recently discovered. Collectively, seven classes and 16 isozymes of mammalian PLC are known to date. Dysregulation of PLC activity has been implicated in several pathophysiological conditions, including cancer, cardiovascular diseases, and neurological disorders. Therefore, identification of new drug targets that can selectively modulate PLC activity is important. The present review focuses on the structures, activation mechanisms, and physiological functions of mammalian PLC.

Identification of immune cell infiltration and effective biomarkers of polycystic ovary syndrome by bioinformatics analysis

BACKGROUND

Patients with polycystic ovary syndrome (PCOS) exhibit a chronic inflammatory state, which is often accompanied by immune, endocrine, and metabolic disorders. Clarification of the pathogenesis of PCOS and exploration of specific biomarkers from the perspective of immunology by evaluating the local infiltration of immune cells in the follicular microenvironment may provide critical insights into disease pathogenesis.

METHODS

In this study, we evaluated immune cell subsets and gene expression in patients with PCOS using data from the Gene Expression Omnibus database and single-sample gene set enrichment analysis.

RESULTS

In total, 325 differentially expressed genes were identified, among which TMEM54 and PLCG2 (area under the curve = 0.922) were identified as PCOS biomarkers. Immune cell infiltration analysis showed that central memory CD4⁺ T cells, central memory CD8⁺ T cells, effector memory CD4⁺ T cells, γδ T cells, and type 17 T helper cells may affect the occurrence of PCOS. In addition, PLCG2 was highly correlated with γδ T cells and central memory CD4⁺ T cells.

CONCLUSIONS

Overall, TMEM54 and PLCG2 were identified as potential PCOS biomarkers by bioinformatics analysis. These findings established a basis for further exploration of the immunological mechanisms of PCOS and the identification of therapeutic targets.

G-CSF drives autoinflammation in APLAID

Missense mutations in PLCG2 can cause autoinflammation with phospholipase C gamma 2-associated antibody deficiency and immune dysregulation (APLAID). Here, we generated a mouse model carrying an APLAID mutation (p.Ser707Tyr) and found that inflammatory infiltrates in the skin and lungs were only partially ameliorated by removing inflammasome function via the deletion of caspase-1. Also, deleting interleukin-6 or tumor necrosis factor did not fully prevent APLAID mutant mice from autoinflammation. Overall, these findings are in accordance with the poor response individuals with APLAID have to treatments that block interleukin-1, JAK1/2 or tumor necrosis factor. Cytokine analysis revealed increased granulocyte colony-stimulating factor (G-CSF) levels as the most distinct feature in mice and individuals with APLAID. Remarkably, treatment with a G-CSF antibody completely reversed established disease in APLAID mice. Furthermore, excessive myelopoiesis was normalized and lymphocyte numbers rebounded. APLAID mice were also fully rescued by bone marrow transplantation from healthy donors, associated with reduced G-CSF production, predominantly from non-hematopoietic cells. In summary, we identify APLAID as a G-CSF-driven autoinflammatory disease, for which targeted therapy is feasible.

Autoimmunity and Frontotemporal Lobar Degeneration: From Laboratory Study to Clinical Practice

Frontotemporal lobar degeneration (FTLD) is a group of neurodegenerative diseases with heterogenous clinical, genetic, and pathological characteristics that show similar impairment of areas in the frontal and/or temporal lobes. Prime doctors' lack of awareness of this complex disease makes early identification and accurate intervention difficult. Autoimmune diseases and autoantibodies are manifestations of different levels of autoimmune reactions. This review presents research findings examining the relationship between autoimmunity and FTLD in terms of autoimmune diseases and autoantibodies with a focus on identifying potential diagnosis and treatment approaches. The findings indicate that the same or similar pathophysiological mechanisms may exist from clinical, genetic, and pathological perspectives. However, the existing evidence is not sufficient to extract substantial conclusions. On the basis of the current situation, we propose future research patterns using prospective studies on large populations and combined clinical and experimental research. Autoimmune reactions or, more generally, inflammatory reactions should receive increased attention from doctors and scientists of all disciplines.

Molecular Classification of Extrapulmonary Neuroendocrine Carcinomas With Emphasis on POU2F3-positive Tuft Cell Carcinoma

Extrapulmonary neuroendocrine carcinomas (EP-NECs) are associated with a poor clinical outcome, and limited information is available on the biology and treatment of EP-NECs. We studied EP-NECs by applying the recent novel findings from studies of pulmonary neuroendocrine carcinomas, including POU2F3, the master regulator of tuft cell variant of small cell lung carcinomas. A cohort of 190 patients with surgically resected EP-NECs or poorly differentiated carcinomas (PDCs) were established. Immunohistochemistry (IHC) for POU2F3 along with ASCL1, NEUROD1, YAP1, and conventional neuroendocrine markers was performed on tissue microarrays. Selected cases with or without POU2F3 expression were subjected to targeted gene expression profiling using nCounter PanCancer Pathway panel. POU2F3-positive tuft cell carcinomas were present in 12.6% of EP-NEC/PDCs, with variable proportions according to organ systems. POU2F3 expression was negatively correlated with the expression levels of ASCL1, NEUROD1, and conventional neuroendocrine markers ( P <0.001), enabling IHC-based molecular classification into ASCL1-dominant, NEUROD1-dominant, POU2F3-dominant, YAP1-dominant, and not otherwise specified subtypes. Compared wih POU2F3-negative cases, POU2F3-positive tuft cell carcinomas showed markedly higher expression levels of PLCG2 and BCL2 , which was also validated in the entire cohort by IHC. In addition to POU2F3, YAP1-positive tumors were a distinct subtype among EP-NEC/PDCs, characterized by unique T-cell inflamed microenvironment. We found rare extrapulmonary POU2F3-positive tumors arising from previously unappreciated cells of origin. Our data show novel molecular pathologic features of EP-NEC/PDCs including potential therapeutic vulnerabilities, thereby emphasizing the need for focusing on unique features of EP-NEC/PDCs.

Aberrant B Cell Signaling in Autoimmune Diseases

Aberrant B cell signaling plays a critical in role in various systemic and organ-specific autoimmune diseases. This is supported by genetic evidence by many functional studies in B cells from patients or specific animal models and by the observed efficacy of small-molecule inhibitors. In this review, we first discuss key signal transduction pathways downstream of the B cell receptor (BCR) that ensure that autoreactive B cells are removed from the repertoire or functionally silenced. We provide an overview of aberrant BCR signaling that is associated with inappropriate B cell repertoire selection and activation or survival of peripheral B cell populations and plasma cells, finally leading to autoantibody formation. Next to BCR signaling, abnormalities in other signal transduction pathways have been implicated in autoimmune disease. These include reduced activity of several phosphates that are downstream of co-inhibitory receptors on B cells and increased levels of BAFF and APRIL, which support survival of B cells and plasma cells. Importantly, pathogenic synergy of the BCR and Toll-like receptors (TLR), which can be activated by endogenous ligands, such as self-nucleic acids, has been shown to enhance autoimmunity. Finally, we will briefly discuss therapeutic strategies for autoimmune disease based on interfering with signal transduction in B cells.

The P522R protective variant of PLCG2 promotes the expression of antigen presentation genes by human microglia in an Alzheimer's disease mouse model

The P522R variant of PLCG2, expressed by microglia, is associated with reduced risk of Alzheimer's disease (AD). Yet, the impact of this protective mutation on microglial responses to AD pathology remains unknown. Chimeric AD and wild-type mice were generated by transplanting PLCG2-P522R or isogenic wild-type human induced pluripotent stem cell microglia. At 7 months of age, single-cell and bulk RNA sequencing, and histological analyses were performed. The PLCG2-P522R variant induced a significant increase in microglial human leukocyte antigen (HLA) expression and the induction of antigen presentation, chemokine signaling, and T cell proliferation pathways. Examination of immune-intact AD mice further demonstrated that the PLCG2-P522R variant promotes the recruitment of CD8+ T cells to the brain. These data provide the first evidence that the PLCG2-P522R variant increases the capacity of microglia to recruit T cells and present antigens, promoting a microglial transcriptional state that has recently been shown to be reduced in AD patient brains.

Genome-wide association study of liver enzyme elevation in an extended cohort of rheumatoid arthritis patients starting low-dose methotrexate

Aim: A follow-up genome-wide association study (GWAS) in an extended cohort of rheumatoid arthritis (RA) patients starting low-dose methotrexate (MTX) treatment was performed to identify further genetic variants associated with alanine aminotransferase (ALT) elevation. Patients & methods: A GWAS was performed on 346 RA patients. Two outcomes within the first 6 months of MTX treatment were assessed: ALT >1.5-times the upper level of normal (ULN) and maximum level of ALT. Results: SPATA9 (rs72783407) was significantly associated with maximum level of ALT (p = 2.58 × 10^-8) and PLCG2 (rs60427389) was tentatively associated with ALT >1.5 × ULN. Conclusion: Associations with SNPs in genes related to male fertility (SPATA9) and inflammatory processes (PLCG2) were identified.

PLCγ2 impacts microglia-related effectors revealing variants and pathways important in Alzheimer’s disease

Alzheimer’s disease (AD) is an irreversible neurodegenerative disease mainly characterized by memory loss and cognitive decline. The etiology of AD is complex and remains incompletely understood. In recent years, genome-wide association studies (GWAS) have increasingly highlighted the central role of microglia in AD pathology. As a trans-membrane receptor specifically present on the microglia in the central nervous system, phosphatidylinositol-specific phospholipase C gamma 2 (PLCγ2) plays an important role in neuroinflammation. GWAS data and corresponding pathological research have explored the effects of PLCG2 variants on amyloid burden and tau pathologies that underline AD. The link between PLCγ2 and other AD-related effectors in human and mouse microglia has also been established, placing PLCγ2 downstream of the triggering receptor expressed on myeloid cells 2 (TREM2), toll-like receptor 4 (TLR4), Bruton’s tyrosine kinase (BTK), and colony-stimulating factor 1 receptor (CSF1R). Because the research on PLCγ2’s role in AD is still in its early stages, few articles have been published, therefore in this paper, we integrate the relevant research published to date, review the structural features, expression patterns, and related pathways of PLCγ2, and summarize the recent studies on important PLCG2 variants related to AD. Furthermore, the possibility and challenge of using PLCγ2 to develop therapeutic drugs for AD are also discussed.

Identification of variants in genes associated with autoinflammatory disorders in a cohort of patients with psoriatic arthritis

Objectives

Besides adaptive immunity genes, genetic risk factors for psoriatic arthritis (PsA) include innate immunity loci, which suggests an autoinflammatory disease mechanism, at least in a subset of patients. Here, we aimed at investigating the autoinflammatory genetic background of PsA.

Methods

A total of 120 patients with PsA visiting the outpatient clinics of the Hannover University hospital underwent targeted next-generation sequencing, searching for variations in genes linked with inborn errors of immunity classified as autoinflammatory disorders (AIDs). Deleteriousness of rare variants was evaluated through in silico analysis.

Results

We found 45 rare predicted deleterious variants in 37 out of 120 (30.8%) patients with PsA. Relatively common were variants in AP1S3, PLCG2, NOD2 and NLRP12. All 45 variants were monoallelic and 25 of them, identified in 20 out of 120 (16.7%) patients, were localised in genes associated with autosomal dominant (AD) disorders. Detection of those variants is associated with pustular psoriasis or a coexisting inflammatory bowel disease (IBD).

Conclusions

Approximately 30% of patients with PsA harboured at least one variant in a gene associated with an AID, suggesting an autoinflammatory disease mechanism. Detection of variants in genes linked to AD-AIDs may explain extra-articular manifestations of PsA, such as pustular psoriasis and IBD.

Atopy as Immune Dysregulation: Offender Genes and Targets

Allergic diseases are a heterogeneous group of disorders resulting from exaggerated type 2 inflammation. Although typically viewed as polygenic multifactorial disorders caused by the interaction of several genes with the environment, we have come to appreciate that allergic diseases can also be caused by monogenic variants affecting the immune system and the skin epithelial barrier. Through a myriad of genetic association studies and high-throughput sequencing tools, many monogenic and polygenic culprits of allergic diseases have been described. Identifying the genetic causes of atopy has shaped our understanding of how these conditions occur and how they may be treated and even prevented. Precision diagnostic tools and therapies that address the specific molecular pathways implicated in allergic inflammation provide exciting opportunities to improve our care for patients across the field of allergy and immunology. Here, we highlight offender genes implicated in polygenic and monogenic allergic diseases and list targeted therapeutic approaches that address these disrupted pathways.

Identification of Molecular Subtypes and a Prognostic Signature Based on Inflammation-Related Genes in Colon Adenocarcinoma

Both tumour-infiltrating immune cells and inflammation-related genes that can mediate immune infiltration contribute to the initiation and prognosis of patients with colon cancer. In this study, we developed a method to predict the survival outcomes among colon cancer patients and direct immunotherapy and chemotherapy. We obtained patient data from The Cancer Genome Atlas (TCGA) and captured inflammation-related genes from the GeneCards database. The package “ConsensusClusterPlus” was used to generate molecular subtypes based on inflammation-related genes obtained by differential expression analysis and univariate Cox analysis. A prognostic signature including four genes (PLCG2, TIMP1, BDNF and IL13) was also constructed and was an independent prognostic factor. Cluster 2 and higher risk scores meant worse overall survival and higher expression of human leukocyte antigen and immune checkpoints. Immune cell infiltration calculated by the estimate, CIBERSORT, TIMER, ssGSEA algorithms, tumour immune dysfunction and exclusion (TIDE), and tumour stemness indices (TSIs) were also compared on the basis of inflammation-related molecular subtypes and the risk signature. In addition, analyses of stratification, somatic mutation, nomogram construction, chemotherapeutic response prediction and small-molecule drug prediction were performed based on the risk signature. We finally used qRT–PCR to detect the expression levels of four genes in colon cancer cell lines and obtained results consistent with the prediction. Our findings demonstrated a four-gene prognostic signature that could be useful for prognostication in colon cancer patients and designing personalized treatments, which could provide new versions of personalized management for these patients.

Uveal melanoma-associated mutations in PLCβ4 are constitutively activating and promote melanocyte proliferation and tumorigenesis

[Figure: see text].

Bruton's Tyrosine Kinase (BTK) Inhibitors and Autoimmune Diseases: Making Sense of BTK Inhibitor Specificity Profiles and Recent Clinical Trial Successes and Failures

Clinical development of BTK kinase inhibitors for treating autoimmune diseases has lagged behind development of these drugs for treating cancers, due in part from concerns over the lack of selectivity and associated toxicity profiles of first generation drug candidates when used in the long term treatment of immune mediated diseases. Second generation BTK inhibitors have made great strides in limiting off-target activities for distantly related kinases, though they have had variable success at limiting cross-reactivity within the more closely related TEC family of kinases. We investigated the BTK specificity and toxicity profiles, drug properties, disease associated signaling pathways, clinical indications, and trial successes and failures for the 13 BTK inhibitor drug candidates tested in phase 2 or higher clinical trials representing 7 autoimmune and 2 inflammatory immune-mediated diseases. We focused on rheumatoid arthritis (RA), multiple sclerosis (MS), and systemic lupus erythematosus (SLE) where the majority of BTK nonclinical and clinical studies have been reported, with additional information for pemphigus vulgaris (PV), Sjogren’s disease (SJ), chronic spontaneous urticaria (CSU), graft versus host disease (GVHD), and asthma included where available. While improved BTK selectivity versus kinases outside the TEC family improved clinical toxicity profiles, less profile distinction was evident within the TEC family. Analysis of genetic associations of RA, MS, and SLE biomarkers with TEC family members revealed that BTK and TEC family members may not be drivers of disease. They are, however, mediators of signaling pathways associated with the pathophysiology of autoimmune diseases. BTK in particular may be associated with B cell and myeloid differentiation as well as autoantibody development implicated in immune mediated diseases. Successes in the clinic for treating RA, MS, PV, ITP, and GVHD, but not for SLE and SJ support the concept that BTK plays an important role in mediating pathogenic processes amenable to therapeutic intervention, depending on the disease. Based on the data collected in this study, we propose that current compound characteristics of BTK inhibitor drug candidates for the treatment of autoimmune diseases have achieved the selectivity, safety, and coverage requirements necessary to deliver therapeutic benefit.

CRAC Channel Controls the Differentiation of Pathogenic B Cells in Lupus Nephritis

Store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel is the main Ca²⁺ influx pathway in lymphocytes and is essential for immune response. Lupus nephritis (LN) is an autoimmune disease characterized by the production of autoantibodies due to widespread loss of immune tolerance. In this study, RNA-seq analysis revealed that calcium transmembrane transport and calcium channel activity were enhanced in naive B cells from patients with LN. The increased expression of ORAI1, ORAI2, and STIM2 in naive B cells from patients with LN was confirmed by flow cytometry and Western blot, implying a role of CRAC channel in B-cell dysregulation in LN. For in vitro study, CRAC channel inhibition by YM-58483 or downregulation by ORAI1-specific small-interfering RNA (siRNA) decreased the phosphorylation of Ca²⁺/calmodulin-dependent protein kinase2 (CaMK2) and suppressed Blimp-1 expression in primary human B cells, resulting in decreased B-cell differentiation and immunoglobulin G (IgG) production. B cells treated with CaMK2-specific siRNA showed defects in plasma cell differentiation and IgG production. For in vivo study, YM-58483 not only ameliorated the progression of LN but also prevented the development of LN. MRL/lpr lupus mice treated with YM-58483 showed lower percentage of plasma cells in the spleen and reduced concentration of anti-double-stranded DNA antibodies in the sera significantly. Importantly, mice treated with YM-58483 showed decreased immune deposition in the glomeruli and alleviated kidney damage, which was further confirmed in NZM2328 lupus mice. Collectively, CRAC channel controlled the differentiation of pathogenic B cells and promoted the progression of LN. This study provides insights into the pathogenic mechanisms of LN and that CRAC channel could serve as a potential therapeutic target for LN.

Phospholipase Cγ2 is Essential for Experimental Models of Epidermolysis Bullosa Acquisita

Phospholipase Cγ2 (PLCγ2) mediates tyrosine kinase‒coupled receptor signaling in various hematopoietic lineages. Although PLCγ2 has been implicated in certain human and mouse inflammatory disorders, its contribution to autoimmune and inflammatory skin diseases is poorly understood. In this study, we tested the role of PLCγ2 in a mouse model of epidermolysis bullosa acquisita triggered by antibodies against type VII collagen (C7), a component of the dermo-epidermal junction. PLCγ2-deficient (Plcg2^-/-) mice and bone marrow chimeras with a Plcg2^-/- hematopoietic system were completely protected from signs of anti-C7-induced skin disease, including skin erosions, dermal‒epidermal separation, and inflammation, despite normal circulating levels and skin deposition of anti-C7 antibodies. PLCγ2 was required for the tissue infiltration of neutrophils, eosinophils, and monocytes/macrophages as well as for the accumulation of proinflammatory mediators (including IL-1β, MIP-2, and LTB₄) and reactive oxygen species. Mechanistic experiments revealed a role for PLCγ2 in the release of proinflammatory mediators and reactive oxygen species but not in the intrinsic migratory capacity of leukocytes. The phospholipase C inhibitor U73122 inhibited dermal-epidermal separation of human skin sections incubated with human neutrophils in the presence of anti-C7 antibodies. Taken together, our results suggest a critical role for PLCγ2 in the pathogenesis of the inflammatory form of epidermolysis bullosa acquisita.

PLCγ2 regulates TREM2 signalling and integrin-mediated adhesion and migration of human iPSC-derived macrophages

Human genetic studies have linked rare coding variants in microglial genes, such as TREM2, and more recently PLCG2 to Alzheimer's disease (AD) pathology. The P522R variant in PLCG2 has been shown to confer protection for AD and to result in a subtle increase in enzymatic activity. PLCγ2 is a key component of intracellular signal transduction networks and induces Ca²⁺ signals downstream of many myeloid cell surface receptors, including TREM2. To explore the relationship between PLCγ2 and TREM2 and the role of PLCγ2 in regulating immune cell function, we generated human induced pluripotent stem cell (iPSC)- derived macrophages from isogenic lines with homozygous PLCG2 knockout (Ko). Stimulating TREM2 signalling using a polyclonal antibody revealed a complete lack of calcium flux and IP1 accumulation in PLCγ2 Ko cells, demonstrating a non-redundant role of PLCγ2 in calcium release downstream of TREM2. Loss of PLCγ2 led to broad changes in expression of several macrophage surface markers and phenotype, including reduced phagocytic activity and survival, while LPS-induced secretion of the inflammatory cytokines TNFα and IL-6 was unaffected. We identified additional deficits in PLCγ2- deficient cells that compromised cellular adhesion and migration. Thus, PLCγ2 is key in enabling divergent cellular functions and might be a promising target to increase beneficial microglial functions.

PIP2 depletion and altered endocytosis caused by expression of Alzheimer's disease-protective variant PLCγ2 R522

Variants identified in genome-wide association studies have implicated immune pathways in the development of Alzheimer's disease (AD). Here, we investigated the mechanistic basis for protection from AD associated with PLCγ2 R522, a rare coding variant of the PLCG2 gene. We studied the variant's role in macrophages and microglia of newly generated PLCG2-R522-expressing human induced pluripotent cell lines (hiPSC) and knockin mice, which exhibit normal endogenous PLCG2 expression. In all models, cells expressing the R522 mutation show a consistent non-redundant hyperfunctionality in the context of normal expression of other PLC isoforms. This manifests as enhanced release of cellular calcium ion stores in response to physiologically relevant stimuli like Fc-receptor ligation or exposure to Aβ oligomers. Expression of the PLCγ2-R522 variant resulted in increased stimulus-dependent PIP₂ depletion and reduced basal PIP₂ levels in vivo. Furthermore, it was associated with impaired phagocytosis and enhanced endocytosis. PLCγ2 acts downstream of other AD-related factors, such as TREM2 and CSF1R, and alterations in its activity directly impact cell function. The inherent druggability of enzymes such as PLCγ2 raises the prospect of PLCγ2 manipulation as a future therapeutic approach in AD.

The role of PLCγ2 in immunological disorders, cancer, and neurodegeneration

Phosphatidylinositol-specific phospholipase Cγ2 (PLCγ2) is a critical signaling molecule activated downstream from a variety of cell surface receptors that contain an intracellular immunoreceptor tyrosine-based activation motif. These receptors recruit kinases such as Syk, BTK, and BLNK to phosphorylate and activate PLCγ2, which then generates 1D-myo-inositol 1,4,5-trisphosphate and diacylglycerol. These well-known second messengers are required for diverse membrane functionality including cellular proliferation, endocytosis, and calcium flux. As a result, PLCγ2 dysfunction is associated with a variety of diseases including cancer, neurodegeneration, and immune disorders. The diverse pathologies associated with PLCγ2 are exemplified by distinct genetic variants. Inherited mutations at this locus cause PLCγ2-associated antibody deficiency and immune dysregulation, in some cases with autoinflammation. Acquired mutations at this locus, which often arise as a result of BTK inhibition to treat chronic lymphocytic leukemia, result in constitutive downstream signaling and lymphocyte proliferation. Finally, a third group of PLCγ2 variants actually has a protective effect in a variety of neurodegenerative disorders, presumably by increased uptake and degradation of deleterious neurological aggregates. Therefore, manipulating PLCγ2 activity either up or down could have therapeutic benefit; however, we require a better understanding of the signaling pathways propagated by these variants before such clinical utility can be realized. Here, we review the signaling roles of PLCγ2 in hematopoietic cells to help understand the effect of mutations driving immune disorders and cancer and extrapolate from this to roles which may relate to protection against neurodegeneration.

Untangling the genetic link between type 1 and type 2 diabetes using functional genomics

There is evidence pointing towards shared etiological features between type 1 diabetes (T1D) and type 2 diabetes (T2D) despite both phenotypes being considered genetically distinct. However, the existence of shared genetic features for T1D and T2D remains complex and poorly defined. To better understand the link between T1D and T2D, we employed an integrated functional genomics approach involving extensive chromatin interaction data (Hi-C) and expression quantitative trait loci (eQTL) data to characterize the tissue-specific impacts of single nucleotide polymorphisms associated with T1D and T2D. We identified 195 pleiotropic genes that are modulated by tissue-specific spatial eQTLs associated with both T1D and T2D. The pleiotropic genes are enriched in inflammatory and metabolic pathways that include mitogen-activated protein kinase activity, pertussis toxin signaling, and the Parkinson's disease pathway. We identified 8 regulatory elements within the TCF7L2 locus that modulate transcript levels of genes involved in immune regulation as well as genes important in the etiology of T2D. Despite the observed gene and pathway overlaps, there was no significant genetic correlation between variant effects on T1D and T2D risk using European ancestral summary data. Collectively, our findings support the hypothesis that T1D and T2D specific genetic variants act through genetic regulatory mechanisms to alter the regulation of common genes, and genes that co-locate in biological pathways, to mediate pleiotropic effects on disease development. Crucially, a high risk genetic profile for T1D alters biological pathways that increase the risk of developing both T1D and T2D. The same is not true for genetic profiles that increase the risk of developing T2D. The conversion of information on genetic susceptibility to the protein pathways that are altered provides an important resource for repurposing or designing novel therapies for the management of diabetes.

Resistance Mutations to BTK Inhibitors Originate From the NF-κB but Not From the PI3K-RAS-MAPK Arm of the B Cell Receptor Signaling Pathway

Since the first clinical report in 2013, inhibitors of the intracellular kinase BTK (BTKi) have profoundly altered the treatment paradigm of B cell malignancies, replacing chemotherapy with targeted agents in patients with chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), and Waldenström's macroglobulinemia. There are over 20 BTKi, both irreversible and reversible, in clinical development. While loss-of-function (LoF) mutations in the BTK gene cause the immunodeficiency X-linked agammaglobulinemia, neither inherited, nor somatic BTK driver mutations are known. Instead, BTKi-sensitive malignancies are addicted to BTK. BTK is activated by upstream surface receptors, especially the B cell receptor (BCR) but also by chemokine receptors, and adhesion molecules regulating B cell homing. Consequently, BTKi therapy abrogates BCR-driven proliferation and the tissue homing capacity of the malignant cells, which are being redistributed into peripheral blood. BTKi resistance can develop over time, especially in MCL and high-risk CLL patients. Frequently, resistance mutations affect the BTKi binding-site, cysteine 481, thereby reducing drug binding. Less common are gain-of-function (GoF) mutations in downstream signaling components, including phospholipase Cγ2 (PLCγ2). In a subset of patients, mechanisms outside of the BCR pathway, related e.g. to resistance to apoptosis were described. BCR signaling depends on many proteins including SYK, BTK, PI3K; still based on the resistance pattern, BTKi therapy only selects GoF alterations in the NF-κB arm, whereas an inhibitor of the p110δ subunit of PI3K instead selects resistance mutations in the RAS-MAP kinase pathway. BTK and PLCγ2 resistance mutations highlight BTK's non-redundant role in BCR-mediated NF-κB activation. Of note, mutations affecting BTK tend to generate clone sizes larger than alterations in PLCγ2. This infers that BTK signaling may go beyond the PLCγ2-regulated NF-κB and NFAT arms. Collectively, when comparing the primary and acquired mutation spectrum in BTKi-sensitive malignancies with the phenotype of the corresponding germline alterations, we find that certain observations do not readily fit with the existing models of BCR signaling.

Protective genes and pathways in Alzheimer's disease: moving towards precision interventions

Alzheimer's disease (AD) is a progressive, neurodegenerative disorder that is characterized by neurodegeneration, cognitive impairment, and an eventual inability to perform daily tasks. The etiology of Alzheimer's is complex, with numerous environmental and genetic factors contributing to the disease. Late-onset AD is highly heritable (60 to 80%), and over 40 risk loci for AD have been identified via large genome-wide association studies, most of which are common variants with small effect sizes. Although these discoveries have provided novel insight on biological contributors to AD, disease-modifying treatments remain elusive. Recently, the concepts of resistance to pathology and resilience against the downstream consequences of pathology have been of particular interest in the Alzheimer's field as studies continue to identify individuals who evade the pathology of the disease even into late life and individuals who have all of the neuropathological features of AD but evade downstream neurodegeneration and cognitive impairment. It has been hypothesized that a shift in focus from Alzheimer's risk to resilience presents an opportunity to uncover novel biological mechanisms of AD and to identify promising therapeutic targets for the disease. This review will highlight a selection of genes and variants that have been reported to confer protection from AD within the literature and will also discuss evidence for the biological underpinnings behind their protective effect with a focus on genes involved in lipid metabolism, cellular trafficking, endosomal and lysosomal function, synaptic function, and inflammation. Finally, we offer some recommendations in areas where the field can rapidly advance towards precision interventions that leverage the ideas of protection and resilience for the development of novel therapeutic strategies.

TREM2/PLCγ2 signalling in immune cells: function, structural insight, and potential therapeutic modulation

The central role of the resident innate immune cells of the brain (microglia) in neurodegeneration has become clear over the past few years largely through genome-wide association studies (GWAS), and has rapidly become an active area of research. However, a mechanistic understanding (gene to function) has lagged behind. That is now beginning to change, as exemplified by a number of recent exciting and important reports that provide insight into the function of two key gene products – TREM2 (Triggering Receptor Expressed On Myeloid Cells 2) and PLCγ2 (Phospholipase C gamma2) – in microglia, and their role in neurodegenerative disorders. In this review we explore and discuss these recent advances and the opportunities that they may provide for the development of new therapies.

Four diseases, PLAID, APLAID, FCAS3 and CVID and one gene (PHOSPHOLIPASE C, GAMMA-2; PLCG2): Striking clinical phenotypic overlap and difference

We suggest PLAID, APLAID, and FCAS3 have to be considered as different aspects of the same underlying condition, because of our long-term clinical and genetical experiences. Some CVID patients have the same disease-causing mutations in PLCG2 gene, so it may be better to define all of them as "PLCG2deficiency."

PLCG2 rs72824905 Variant Reduces the Risk of Alzheimer's Disease and Multiple Sclerosis

We aimed to evaluate the association of PLCG2 rs72824905 variant with Alzheimer's disease (AD) and multiple sclerosis (MS) using large-scale genetic association study datasets. We selected 50,024 AD cases and 467,330 controls, and 32,367 MS cases and 36,012 controls. We found moderate heterogeneity of rs72824905 in different studies. We found significant association between rs72824905 G allele and reduced AD risk (OR = 0.66, 95% CI 0.59-0.74, p = 5.91E-14). Importantly, rs72824905 G allele could also significantly reduce the risk of MS with OR = 0.94, p = 3.63E-05. Hence, the effects of rs72824905 on AD and MS are consistent.

Neutrophil Phospholipase Cγ2 Drives Autoantibody-Induced Arthritis Through the Generation of the Inflammatory Microenvironment

OBJECTIVE

Gain-of-function mutations and genome-wide association studies have linked phospholipase Cγ2 (PLCγ2) to various inflammatory diseases, including arthritis in humans and mice. PLCγ2-deficient (Plcg2^-/- ) mice are also protected against experimental arthritis. This study was undertaken to test how PLCγ2 triggers autoantibody-induced arthritis in mice.

METHODS

PLCγ2 was deleted from various mouse cellular lineages. Deletion efficacy and specificity were tested by immunoblotting and intracellular flow cytometry. Autoantibody-induced arthritis was triggered by K/BxN serum transfer. The role of neutrophil PLCγ2 was further investigated by analysis of the inflammatory exudate, competitive in vivo migration assays, and in vitro functional studies.

RESULTS

PLCγ2 deficiency in the entire hematopoietic compartment completely blocked autoantibody-induced arthritis. Arthritis development was abrogated by deletion of PLCγ2 from myeloid cells or neutrophils but not from mast cells or platelets. Neutrophil infiltration was reduced in neutrophil-specific PLCγ2-deficient (Plcg2^{Δ PMN} ) mice. However, this was not due to an intrinsic migration defect since Plcg2^{Δ PMN} neutrophils accumulated normally when wild-type cells were also present in mixed bone marrow chimeras. Instead, the Plcg2^{Δ PMN} mutation blocked the accumulation of interleukin-1β, macrophage inflammatory protein 2 (MIP-2), and leukotriene B₄ (LTB₄ ) in synovial tissues and reduced the secondary infiltration of macrophages. These findings were supported by in vitro studies showing normal chemotactic migration but defective immune complex-induced respiratory burst and MIP-2 or LTB₄ release in PLCγ2-deficient neutrophils.

CONCLUSION

Neutrophil PLCγ2 is critical for arthritis development, supposedly through the generation of the inflammatory microenvironment. PLCγ2-expressing neutrophils exert complex indirect effects on other inflammatory cells. PLCγ2-targeted therapies may provide particular benefit in inflammatory diseases with a major neutrophil component.

Phospholipase C families: Common themes and versatility in physiology and pathology

Phosphoinositide-specific phospholipase Cs (PLCs) are expressed in all mammalian cells and play critical roles in signal transduction. To obtain a comprehensive understanding of these enzymes in physiology and pathology, a detailed structural, biochemical, cell biological and genetic information is required. In this review, we cover all these aspects to summarize current knowledge of the entire superfamily. The families of PLCs have expanded from 13 enzymes to 16 with the identification of the atypical PLCs in the human genome. Recent structural insights highlight the common themes that cover not only the substrate catalysis but also the mechanisms of activation. This involves the release of autoinhibitory interactions that, in the absence of stimulation, maintain classical PLC enzymes in their inactive forms. Studies of individual PLCs provide a rich repertoire of PLC function in different physiologies. Furthermore, the genetic studies discovered numerous mutated and rare variants of PLC enzymes and their link to human disease development, greatly expanding our understanding of their roles in diverse pathologies. Notably, substantial evidence now supports involvement of different PLC isoforms in the development of specific cancer types, immune disorders and neurodegeneration. These advances will stimulate the generation of new drugs that target PLC enzymes, and will therefore open new possibilities for treatment of a number of diseases where current therapies remain ineffective.

Severe Autoinflammatory Manifestations and Antibody Deficiency Due to Novel Hypermorphic PLCG2 Mutations

Autoinflammatory diseases (AIDs) were first described as clinical disorders characterized by recurrent episodes of seemingly unprovoked sterile inflammation. In the past few years, the identification of novel AIDs expanded their phenotypes toward more complex clinical pictures associating vasculopathy, autoimmunity, or immunodeficiency. Herein, we describe two unrelated patients suffering since the neonatal period from a complex disease mainly characterized by severe sterile inflammation, recurrent bacterial infections, and marked humoral immunodeficiency. Whole-exome sequencing detected a novel, de novo heterozygous PLCG2 variant in each patient (p.Ala708Pro and p.Leu845_Leu848del). A clear enhanced PLCγ2 activity for both variants was demonstrated by both ex vivo calcium responses of the patient's B cells to IgM stimulation and in vitro assessment of PLC activity. These data supported the autoinflammation and PLCγ2-associated antibody deficiency and immune dysregulation (APLAID) diagnosis in both patients. Immunological evaluation revealed a severe decrease of immunoglobulins and B cells, especially class-switched memory B cells, with normal T and NK cell counts. Analysis of bone marrow of one patient revealed a reduced immature B cell fraction compared with controls. Additional investigations showed that both PLCG2 variants activate the NLRP3-inflammasome through the alternative pathway instead of the canonical pathway. Collectively, the evidences here shown expand APLAID diversity toward more severe phenotypes than previously reported including dominantly inherited agammaglobulinemia, add novel data about its genetic basis, and implicate the alternative NLRP3-inflammasome activation pathway in the basis of sterile inflammation.

The Alzheimer's disease-associated protective Plcγ2-P522R variant promotes immune functions

Background

Microglia-specific genetic variants are enriched in several neurodegenerative diseases, including Alzheimer’s disease (AD), implicating a central role for alterations of the innate immune system in the disease etiology. A rare coding variant in the PLCG2 gene (rs72824905, p.P522R) expressed in myeloid lineage cells was recently identified and shown to reduce the risk for AD.

Methods

To assess the role of the protective variant in the context of immune cell functions, we generated a Plcγ2-P522R knock-in (KI) mouse model using CRISPR/Cas9 gene editing.

Results

Functional analyses of macrophages derived from homozygous KI mice and wild type (WT) littermates revealed that the P522R variant potentiates the primary function of Plcγ2 as a Pip2-metabolizing enzyme. This was associated with improved survival and increased acute inflammatory response of the KI macrophages. Enhanced phagocytosis was observed in mouse BV2 microglia-like cells overexpressing human PLCγ2-P522R, but not in PLCγ2-WT expressing cells. Immunohistochemical analyses did not reveal changes in the number or morphology of microglia in the cortex of Plcγ2-P522R KI mice. However, the brain mRNA signature together with microglia-related PET imaging suggested enhanced microglial functions in Plcγ2-P522R KI mice.

Conclusion

The AD-associated protective Plcγ2-P522R variant promotes protective functions associated with TREM2 signaling. Our findings provide further support for the idea that pharmacological modulation of microglia via TREM2-PLCγ2 pathway-dependent stimulation may be a novel therapeutic option for the treatment of AD.

Using Genetics in Periodontal Disease to Justify Implant Failure in Down Syndrome Patients

Peri-implant bone loss leading to dental implant failure does not develop in the same way across subjects who apparently present the same condition—specifically, in the case of Down syndrome patients with the same genetic disorder—given that they do not necessarily develop immune–inflammatory disorders to the same extent. Methods: This retrospective case-control study was aimed at identifying the possible genes involved in implant failure in Down syndrome patients by matching the periodontal disease variable by means of a retrospective case-control study. This process involved using the functional analysis of gene expression software Transcriptome Analysis Console (TAC, Affymetrix, Thermo Fisher Scientific, Waltham, MA, USA) and a search for the possible candidate genes involved. Focus was placed on the 92 genes related to the inflammation identified from the TaqMan™ Array Plate Human Inflammation Kit (Thermo Fisher Scientific, Waltham, MA, USA). Results: Six genes showed statistically significant results (p < 0.05) in our comparison. Three of them—PLCG2 (p = 0.0333), ALOX5 (p = 0.03) and LTAH4 (p = 0.0081)—were overexpressed in the implant reject group, and the following three were down-regulated: VCAM1 (p = 0.0182), PLA2G2A (p = 0.0034) and PLA2G10 (p = 0.047). Conclusion: Statistically significant differences exist in the gene expression involved in osteoclastogenesis, inflammatory response and host defensive response.

Functionally heterogeneous human satellite cells identified by single cell RNA sequencing

Although heterogeneity is recognized within the murine satellite cell pool, a comprehensive understanding of distinct subpopulations and their functional relevance in human satellite cells is lacking. We used a combination of single cell RNA sequencing and flow cytometry to identify, distinguish, and physically separate novel subpopulations of human PAX7+ satellite cells (Hu-MuSCs) from normal muscles. We found that, although relatively homogeneous compared to activated satellite cells and committed progenitors, the Hu-MuSC pool contains clusters of transcriptionally distinct cells with consistency across human individuals. New surface marker combinations were enriched in transcriptional subclusters, including a subpopulation of Hu-MuSCs marked by CXCR4/CD29/CD56/CAV1 (CAV1+). In vitro, CAV1+ Hu-MuSCs are morphologically distinct, and characterized by resistance to activation compared to CAV1- Hu-MuSCs. In vivo, CAV1+ Hu-MuSCs demonstrated increased engraftment after transplantation. Our findings provide a comprehensive transcriptional view of normal Hu-MuSCs and describe new heterogeneity, enabling separation of functionally distinct human satellite cell subpopulations.

The Role of Calcium-Calcineurin-NFAT Signaling Pathway in Health and Autoimmune Diseases

Calcium (Ca²⁺) is an essential signaling molecule that controls a wide range of biological functions. In the immune system, calcium signals play a central role in a variety of cellular functions such as proliferation, differentiation, apoptosis, and numerous gene transcriptions. During an immune response, the engagement of T-cell and B-cell antigen receptors induces a decrease in the intracellular Ca²⁺ store and then activates store-operated Ca²⁺ entry (SOCE) to raise the intracellular Ca²⁺ concentration, which is mediated by the Ca²⁺ release-activated Ca²⁺ (CRAC) channels. Recently, identification of the two critical regulators of the CRAC channel, stromal interaction molecule (STIM) and Orai1, has broadened our understanding of the regulatory mechanisms of Ca²⁺ signaling in lymphocytes. Repetitive or prolonged increase in intracellular Ca²⁺ is required for the calcineurin-mediated dephosphorylation of the nuclear factor of an activated T cell (NFAT). Recent data indicate that Ca²⁺-calcineurin-NFAT1 to 4 pathways are dysregulated in autoimmune diseases. Therefore, calcineurin inhibitors, cyclosporine and tacrolimus, have been used for the treatment of such autoimmune diseases as systemic lupus erythematosus and rheumatoid arthritis. Here, we review the role of the Ca²⁺-calcineurin–NFAT signaling pathway in health and diseases, focusing on the STIM and Orai1, and discuss the deregulated calcium-mediated calcineurin-NFAT pathway in autoimmune diseases.