Wiskott-Aldrich syndrome protein restricts cGAS/STING activation by dsDNA immune complexes

Cell shape sensing licenses dendritic cells for homeostatic migration to lymph nodes

Immune cells experience large cell shape changes during environmental patrolling because of the physical constraints that they encounter while migrating through tissues. These cells can adapt to such deformation events using dedicated shape-sensing pathways. However, how shape sensing affects immune cell function is mostly unknown. Here, we identify a shape-sensing mechanism that increases the expression of the chemokine receptor CCR7 and guides dendritic cell migration from peripheral tissues to lymph nodes at steady state. This mechanism relies on the lipid metabolism enzyme cPLA2, requires nuclear envelope tensioning and is finely tuned by the ARP2/3 actin nucleation complex. We also show that this shape-sensing axis reprograms dendritic cell transcription by activating an IKKβ-NF-κB-dependent pathway known to control their tolerogenic potential. These results indicate that cell shape changes experienced by immune cells can define their migratory behavior and immunoregulatory properties and reveal a contribution of the physical properties of tissues to adaptive immunity.

The role of the cGAS-STING signaling pathway in viral infections, inflammatory and autoimmune diseases

Pattern recognition receptors are an essential part of the immune system, which detect pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) and help shape both innate and adaptive immune responses. When dsDNA is present, cyclic GMP-AMP Synthase (cGAS) produces a second messenger called cyclic GMP-AMP (cGAMP), which then triggers an adaptor protein called STING, and eventually activates the expression of type I interferon (IFN) and pro-inflammatory cytokines in immune cells. The cGAS-STING signaling pathway has been receiving a lot of attention lately as a key immune-surveillance mediator. In this review, we summarize the present circumstances of the cGAS-STING signaling pathway in viral infections and inflammatory diseases, as well as autoimmune diseases. Modulation of the cGAS-STING signaling pathway provides potential strategies for treating viral infections, inflammatory diseases, and autoimmune diseases.

Mechanotransduction in response to ECM stiffening impairs cGAS immune signaling in tumor cells

The tumor microenvironment (TME) plays decisive roles in disabling T cell-mediated antitumor immunity, but the immunoregulatory functions of its biophysical properties remain elusive. Extracellular matrix (ECM) stiffening is a hallmark of solid tumors. Here, we report that the stiffened ECM contributes to the immunosuppression in TME via activating the Rho-associated coiled-coil-containing protein kinase (ROCK)-myosin IIA-filamentous actin (F-actin) mechanosignaling pathway in tumor cells to promote the generation of TRIM14-scavenging nonmuscle myosin heavy chain IIA (NMHC-IIA)-F-actin stress fibers, thus accelerating the autophagic degradation of cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS) to deprive tumor cyclic GMP-AMP (cGAMP) and further attenuating tumor immunogenicity. Pharmacological inhibition of myosin IIA effector molecules with blebbistatin (BLEB) or the RhoA upstream regulator of this pathway with simvastatin (SIM) restored tumor-intrinsic cGAS-mediated cGAMP production and enhanced antitumor immunity. Our work identifies that ECM stiffness is an important biophysical cue to regulate tumor immunogenicity via the ROCK-myosin IIA-F-actin axis and that inhibiting this mechanosignaling pathway could boost immunotherapeutic efficacy for effective solid tumor treatment.

Understanding immunoactinopathies: A decade of research on WAS gene defects

Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a dysregulated actin cytoskeleton and affect hematopoietic cells especially because of their unique capacity to survey the body for invading pathogens and altered self, such as cancer cells. These cell motility and cell-to-cell interaction properties depend on the dynamic nature of the actin cytoskeleton. Wiskott-Aldrich syndrome (WAS) is the archetypical immunoactinopathy and the first described. WAS is caused by loss-of-function and gain-of-function mutations in the actin regulator WASp, uniquely expressed in hematopoietic cells. Mutations in WAS cause a profound disturbance of actin cytoskeleton regulation of hematopoietic cells. Studies during the last 10 years have shed light on the specific effects on different hematopoietic cells, revealing that they are not affected equally by mutations in the WAS gene. Moreover, the mechanistic understanding of how WASp controls nuclear and cytoplasmatic activities may help to find therapeutic alternatives according to the site of the mutation and clinical phenotypes. In this review, we summarize recent findings that have added to the complexity and increased our understanding of WAS-related diseases and immunoactinopathies.

Genome editing for primary immunodeficiencies: A therapeutic perspective on Wiskott-Aldrich syndrome

Primary immunodeficiency diseases (PIDs) are a group of rare inherited disorders affecting the immune system that can be conventionally treated with allogeneic hematopoietic stem cell transplantation and with experimental autologous gene therapy. With both approaches still facing important challenges, gene editing has recently emerged as a potential valuable alternative for the treatment of genetic disorders and within a relatively short period from its initial development, has already entered some landmark clinical trials aimed at tackling several life-threatening diseases. In this review, we discuss the progress made towards the development of gene editing-based therapeutic strategies for PIDs with a special focus on Wiskott - Aldrich syndrome and outline their main challenges as well as future directions with respect to already established treatments.

The Actin Cytoskeleton Responds to Inflammatory Cues and Alters Macrophage Activation

Much remains to be learned about the molecular mechanisms underlying a class of human disorders called actinopathies. These genetic disorders are characterized by loss-of-function mutations in actin-associated proteins that affect immune cells, leading to human immunopathology. However, much remains to be learned about how cytoskeletal dysregulation promotes immunological dysfunction. The current study reveals that the macrophage actin cytoskeleton responds to LPS/IFNγ stimulation in a biphasic manner that involves cellular contraction followed by cellular spreading. Myosin II inhibition by blebbistatin blocks the initial contraction phase and lowers iNOS protein levels and nitric oxide secretion. Conversely, conditional deletion of Arp2/3 complex in macrophages attenuates spreading and increases nitric oxide secretion. However, iNOS transcription is not altered by loss of myosin II or Arp2/3 function, suggesting post-transcriptional regulation of iNOS by the cytoskeleton. Consistent with this idea, proteasome inhibition reverses the effects of blebbistatin and rescues iNOS protein levels. Arp2/3-deficient macrophages demonstrate two additional phenotypes: defective MHCII surface localization, and depressed secretion of the T cell chemokine CCL22. These data suggest that interplay between myosin II and Arp2/3 influences macrophage activity, and potentially impacts adaptive-innate immune coordination. Disrupting this balance could have detrimental impacts, particularly in the context of Arp2/3-associated actinopathies.

Diagnosis and clinical management of Wiskott-Aldrich syndrome: current and emerging techniques

INTRODUCTION

Wiskott-Aldrich syndrome (WAS) serves as the prototype of how variants in a gene which encodes a protein central to actin cytoskeletal homeostasis can manifest clinically in a variety of ways including infection, atopy, autoimmunity, inflammation, bleeding, neutropenia, non-malignant lymphoproliferation, and malignancy. Despite the discovery of the WAS gene almost 30 years ago, our understanding of the pathophysiological mechanisms underlying WAS continues to unfold.

AREAS COVERED

This review will provide an overview of the approach to the diagnosis of WAS as well as the management of its associated complications. Advances in the use of allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy as well as the associated challenges unique to WAS will be discussed.

EXPERT OPINION

Basic research, combined with clinical research focusing on longitudinal analysis of WAS patients, will help clarify determinants that influence WAS pathogenesis as well as clinical complications and outcomes. Advances in curative approaches including the use of alternative donor HSCT for WAS continue to evolve. Gene therapy employing safer and more effective protocols ensuring full correction of WAS will provide life-saving benefit to WAS patients that are unable to undergo HSCT.

Macrophage SCAP Contributes to Metaflammation and Lean NAFLD by Activating STING-NF-κB Signaling Pathway

BACKGROUND & AIMS

Sterol regulatory element binding protein cleavage-activating protein (SCAP) is a cholesterol sensor that confers a broad range of functional effects in metabolic diseases. Lean nonalcoholic fatty liver disease (NAFLD) is characterized by a decrease in subcutaneous fat and ectopic fat deposition in the liver. SCAP may mediate the development of lean NAFLD, but the mechanism of action remains unclear.

METHODS

C57BL/6J wild-type and macrophage SCAP-specific knockout mice (SCAP^ΔMϕ) were subjected to Paigen diet (PD) feeding induced lean NAFLD. Inflammation and lipid metabolism of adipose and liver were evaluated. The STING-NF-κB signaling pathway was examined in vivo and in vitro to explore the underlying mechanism of macrophage SCAP on metaflammation.

RESULTS

The data showed heterogeneity of lipid metabolic processes in liver and epididymal white adipose tissue due to inflammation mediated by macrophage infiltration. Meanwhile, we found that the macrophage SCAP was abnormally increased in the adipose and liver tissues of PD-fed mice. Intriguingly, the SCAP^ΔMϕ mice attenuated PD-induced metaflammation and ectopic lipid deposition by reducing hepatic stimulator of interferon gene (STING)-nuclear factor kappa B (NF-κB) pathway activation. In-depth molecular analysis revealed that SCAP specifically recruits the STING and tank-binding kinase 1 onto the Golgi to activate the NF-κB in macrophages, thereby promoting the release of inflammatory factors. This process ultimately led to an increased lipolysis in adipocytes and lipid uptake and synthesis in hepatocytes.

CONCLUSIONS

Our findings suggest that SCAP acts as a novel regulator of the macrophage inflammatory response and the pathogenesis of lean NAFLD by activating the STING-NF-κB signaling pathway. Inhibition of macrophage SCAP may represent a new therapeutic strategy for the treatment of lean NAFLD.

Molecular Tuning of Actin Dynamics in Leukocyte Migration as Revealed by Immune-Related Actinopathies

Motility is a crucial activity of immune cells allowing them to patrol tissues as they differentiate, sample or exchange information, and execute their effector functions. Although all immune cells are highly migratory, each subset is endowed with very distinct motility patterns in accordance with functional specification. Furthermore individual immune cell subsets adapt their motility behaviour to the surrounding tissue environment. This review focuses on how the generation and adaptation of diversified motility patterns in immune cells is sustained by actin cytoskeleton dynamics. In particular, we review the knowledge gained through the study of inborn errors of immunity (IEI) related to actin defects. Such pathologies are unique models that help us to uncover the contribution of individual actin regulators to the migration of immune cells in the context of their development and function.

Self-DNA Sensing by cGAS-STING and TLR9 in Autoimmunity: Is the Cytoskeleton in Control?

Modified or misplaced DNA can be recognized as a danger signal by mammalian cells. Activation of cellular responses to DNA has evolved as a defense mechanism to microbial infections, cellular stress, and tissue damage, yet failure to control this mechanism can lead to autoimmune diseases. Several monogenic and multifactorial autoimmune diseases have been associated with type-I interferons and interferon-stimulated genes (ISGs) induced by deregulated recognition of self-DNA. Hence, understanding how cellular mechanism controls the pathogenic responses to self-nucleic acid has important clinical implications. Fine-tuned membrane trafficking and cellular compartmentalization are two major factors that balance activation of DNA sensors and availability of self-DNA ligands. Intracellular transport and organelle architecture are in turn regulated by cytoskeletal dynamics, yet the precise impact of actin remodeling on DNA sensing remains elusive. This review proposes a critical analysis of the established and hypothetical connections between self-DNA recognition and actin dynamics. As a paradigm of this concept, we discuss recent evidence of deregulated self-DNA sensing in the prototypical actin-related primary immune deficiency (Wiskott-Aldrich syndrome). We anticipate a broader impact of actin-dependent processes on tolerance to self-DNA in autoimmune disorders.

Cytosolic DNA-STING-NLRP3 axis is involved in murine acute lung injury induced by lipopolysaccharide

The role of NOD-like receptor protein 3 (NLRP3)-mediated pyroptosis in acute lung injury (ALI) has been well identified previously. Stimulator of interferon genes (STING) is an indispensable adaptor protein, which could regulate inflammation and pyroptosis during infection; however, its role in lipopolysaccharide (LPS)-induced ALI remains obscure. This study aimed to explore whether STING participated in the development of LPS-induced ALI as well as the underlying mechanism. We confirmed that LPS significantly enhanced the expression and phosphorylation of STING in lung tissue and primary macrophages from mice. STING deficiency relieved inflammation and oxidative stress in LPS-treated murine lungs and macrophages. Meanwhile, STING deficiency also abolished the activation of NLRP3 inflammasome and pyroptosis; however, NLRP3 overexpression by adenovirus offset the beneficial effects of STING deficiency in macrophages treated with LPS. Additionally, the level of mitochondrial DNA (mt-DNA) significantly increased in macrophages after LPS treatment. Intriguingly, although exogenous mt-DNA stimulation did not influence the level of STING, it could still trigger the phosphorylation of STING as well as pyroptosis, inflammation, and oxidative stress of macrophages. And the adverse effects induced by mt-DNA could be offset after STING was knocked out. Furthermore, the inhibition of the sensory receptor of cytosolic DNA (cyclic GMP-AMP synthase, cGAS) also blocked the activation of STING and NLRP3 inflammasome, meanwhile, it alleviated ALI without affecting the expression of STING after LPS challenge. Furthermore, cGAS inhibition also blocked the production of cGAMP induced by LPS, indicating that mt-DNA and cGAS could activate STING-NLRP3-mediated pyroptosis independent of the expression of STING. Finally, we found that LPS upregulated the expression of transcription factor c-Myc, which subsequently enhanced the activity of STING promoter and promoted its expression without affecting its phosphorylation. Collectively, our study disclosed that LPS could activate STING in a cytosolic DNA-dependent manner and upregulate the expression of STING in a c-Myc-dependent manner, which cooperatively contribute to ALI.