Wiskott Aldrich syndrome protein regulates non-selective autophagy and mitochondrial homeostasis in human myeloid cells

Bioinformatics Approach to Investigating the Immuno-Inflammatory Mechanisms of Periodontitis in the Progression of Atherosclerosis

Unstable atherosclerotic plaques are a major cause of acute cardiovascular events and ischemic stroke. Clinical studies have suggested a link between periodontitis and atherosclerotic plaque progression, but the underlying mechanisms remain unclear. To investigate this, transcriptomic datasets related to periodontitis and atherosclerosis were downloaded from Gene Expression Omnibus. A weighted gene co-expression network analysis was used to identify gene modules associated with periodontitis, and the Limma R package identified differentially expressed genes (DEGs) between unstable and stable plaques. Overlapping genes were defined as periodontitis-related DEGs, followed by functional enrichment analysis and protein-protein interaction network construction. Machine learning methods were used to identify biomarkers for unstable plaques related to periodontitis, which were validated using external datasets. Immune infiltration and single-cell analyses were performed to explore the relationship between biomarkers and immune cells. A total of 161 periodontitis-related DEGs were identified, with the pathway analysis showing associations with immune regulation and collagen matrix degradation. HCK, NCKAP1L, and WAS were identified as biomarkers for unstable plaques, demonstrating a high diagnostic value (AUC: 0.9884, 95% CI: 0.9641-1). Immune infiltration analysis revealed an increase in macrophages within unstable plaques. Single-cell analysis showed HCK expression in macrophages and dendritic cells, while NCKAP1L and WAS were expressed in macrophages, dendritic cells, NK cells, and T cells. Consensus clustering identified three expression patterns within unstable plaques. Our findings were validated in atherosclerotic mouse models with periodontitis. This study provides insights into how periodontitis contributes to plaque instability, supporting diagnosis and intervention in patients with periodontitis.

Actin-nucleation promoting factor N-WASP influences alpha-synuclein condensates and pathology

Abnormal intraneuronal accumulation of soluble and insoluble α-synuclein (α-Syn) is one of the main pathological hallmarks of synucleinopathies, such as Parkinson's disease (PD). It has been well documented that the reversible liquid-liquid phase separation of α-Syn can modulate synaptic vesicle condensates at the presynaptic terminals. However, α-Syn can also form liquid-like droplets that may convert into amyloid-enriched hydrogels or fibrillar polymorphs under stressful conditions. To advance our understanding on the mechanisms underlying α-Syn phase transition, we employed a series of unbiased proteomic analyses and found that actin and actin regulators are part of the α-Syn interactome. We focused on Neural Wiskott-Aldrich syndrome protein (N-WASP) because of its association with a rare early-onset familial form of PD. In cultured cells, we demonstrate that N-WASP undergoes phase separation and can be recruited to synapsin 1 liquid-like droplets, whereas it is excluded from α-Syn/synapsin 1 condensates. Consistently, we provide evidence that wsp-1/WASL loss of function alters the number and dynamics of α-Syn inclusions in the nematode Caenorhabditis elegans. Together, our findings indicate that N-WASP expression may create permissive conditions that promote α-Syn condensates and their potentially deleterious conversion into toxic species.

NPFs-mediated actin cytoskeleton: a new viewpoint on autophagy regulation

Macroautophagy/autophagy is a lysosome-dependent catabolic process induced by various cellular stress conditions, maintaining the homeostasis of cells, tissues and organs. Autophagy is a series of membrane-related events involving multiple autophagy-related (ATG) proteins. Most studies to date have focused on various signaling pathways affecting ATG proteins to control autophagy. However, mounting evidence reveals that the actin cytoskeleton acts on autophagy-associated membranes to regulate different events of autophagy. The actin cytoskeleton assists in vesicle formation and provides the mechanical forces for cellular activities that involve membrane deformation. Although the interaction between the actin cytoskeleton and membrane makes the role of actin in autophagy recognized, how the actin cytoskeleton is recruited and assembles on membranes during autophagy needs to be detailed. Nucleation-promoting factors (NPFs) activate the Arp2/3 complex to produce actin cytoskeleton. In this review, we summarize the important roles of the actin cytoskeleton in autophagy regulation and focus on the effect of NPFs on actin cytoskeleton assembly during autophagy, providing new insights into the occurrence and regulatory mechanisms of autophagy. Video Abstract.

ARP2/3 complex associates with peroxisomes to participate in pexophagy in plants

Actin-related protein (ARP2/3) complex is a heteroheptameric protein complex, evolutionary conserved in all eukaryotic organisms. Its conserved role is based on the induction of actin polymerization at the interface between membranes and the cytoplasm. Plant ARP2/3 has been reported to participate in actin reorganization at the plasma membrane during polarized growth of trichomes and at the plasma membrane-endoplasmic reticulum contact sites. Here we demonstrate that individual plant subunits of ARP2/3 fused to fluorescent proteins form motile spot-like structures in the cytoplasm that are associated with peroxisomes in Arabidopsis and tobacco. ARP2/3 is found at the peroxisome periphery and contains the assembled ARP2/3 complex and the WAVE/SCAR complex subunit NAP1. This ARP2/3-positive peroxisomal domain colocalizes with the autophagosome and, under conditions that affect the autophagy, colocalization between ARP2/3 and the autophagosome increases. ARP2/3 subunits co-immunoprecipitate with ATG8f and peroxisome-associated ARP2/3 interact in vivo with the ATG8f marker. Since mutants lacking functional ARP2/3 complex have more peroxisomes than wild type, we suggest that ARP2/3 has a novel role in the process of peroxisome degradation by autophagy, called pexophagy.

The multiple links between actin and mitochondria

Actin plays many well-known roles in cells, and understanding any specific role is often confounded by the overlap of multiple actin-based structures in space and time. Here, we review our rapidly expanding understanding of actin in mitochondrial biology, where actin plays multiple distinct roles, exemplifying the versatility of actin and its functions in cell biology. One well-studied role of actin in mitochondrial biology is its role in mitochondrial fission, where actin polymerization from the endoplasmic reticulum through the formin INF2 has been shown to stimulate two distinct steps. However, roles for actin during other types of mitochondrial fission, dependent on the Arp2/3 complex, have also been described. In addition, actin performs functions independent of mitochondrial fission. During mitochondrial dysfunction, two distinct phases of Arp2/3 complex-mediated actin polymerization can be triggered. First, within 5 min of dysfunction, rapid actin assembly around mitochondria serves to suppress mitochondrial shape changes and to stimulate glycolysis. At a later time point, at more than 1 h post-dysfunction, a second round of actin polymerization prepares mitochondria for mitophagy. Finally, actin can both stimulate and inhibit mitochondrial motility depending on the context. These motility effects can either be through the polymerization of actin itself or through myosin-based processes, with myosin 19 being an important mitochondrially attached myosin. Overall, distinct actin structures assemble in response to diverse stimuli to affect specific changes to mitochondria.

Not too little, not too much: the impact of mutation types in Wiskott-Aldrich syndrome and RAC2 patients

Primary immune deficiencies (PIDs) are genetic disorders impacting the appropriate development or functioning of any portion of the immune system. The broad adoption of high-throughput sequencing has driven discovery of new genes as well as expanded phenotypes associated with known genes. Beginning with the identification of WAS mutations in patients with severe Wiskott-Aldrich Syndrome, recognition of WAS mutations in additional patients has revealed phenotypes including isolated thrombocytopenia and X-linked neutropenia. Likewise RAC2 patients present with vastly different phenotypes depending on the mutation-ranging from reticular dysgenesis or severe neutrophil dysfunction with neonatal presentation to later onset common variable immune deficiency. This review examines genotype-phenotype correlations in patients with WAS (Wiskott-Aldrich Syndrome) and RAC2 mutations, highlighting functional protein domains, how mutations alter protein interactions, and how specific mutations can affect isolated functions of the protein leading to disparate phenotypes.

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.

CLDN6 inhibits breast cancer metastasis through WIP-dependent actin cytoskeleton-mediated autophagy

BACKGROUND

As a breast cancer suppressor gene, CLDN6 overexpression was found to inhibit breast cancer metastasis in our previous studies, but the specific mechanism remains unclear. This study aimed to clarify the role and mechanism of CLDN6 in inhibiting breast cancer metastasis.

METHODS

Western blot, immunofluorescence and transmission electron microscopy were performed to detect autophagy. Wound healing, transwell assays and lung metastasis mouse models were used to examine breast cancer metastasis. Phalloidin staining and immunofluorescent staining were used to observe actin cytoskeleton. mRNA seq, RT-PCR, western blot, chromatin immunoprecipitation, dual luciferase reporter assay, co-immunoprecipitation and immunofluorescence were performed to define the molecular mechanism. The expression levels and clinical implication of CLDN6, WIP and LC3 in breast cancer tissues were evaluated using immunohistochemistry.

RESULTS

We demonstrated that CLDN6 inhibited breast cancer metastasis through autophagy in vitro and vivo. We unraveled a novel mechanism that CLDN6 regulated autophagy via WIP-dependent actin cytoskeleton assembly. Through its PDZ-binding motif, overexpressed CLDN6 interacted with JNK and upregulated JNK/c-Jun pathway. C-Jun promoted WIP expression at the transcriptional level. Notably, we observed c-Jun transcriptionally upregulated CLDN6 expression, and there was a positive feedback loop between CLDN6 and JNK/c-Jun. Finally, we found that CLDN6, WIP and LC3 expression correlated with each other, and WIP expression was significantly associated with lymph node metastasis of breast cancer patients.

CONCLUSIONS

The data provide a new insight into the inhibitory effects of CLDN6-mediated autophagy on breast cancer metastasis, and revealed the new mechanism of CLDN6 regulating autophagy through WIP-dependent actin cytoskeleton. Our findings enrich the theoretical basis for CLDN6 as a potential biomarker for breast cancer diagnosis and therapy.

Branching out in different directions: Emerging cellular functions for the Arp2/3 complex and WASP-family actin nucleation factors

The actin cytoskeleton impacts practically every function of a eukaryotic cell. Historically, the best-characterized cytoskeletal activities are in cell morphogenesis, motility, and division. The structural and dynamic properties of the actin cytoskeleton are also crucial for establishing, maintaining, and changing the organization of membrane-bound organelles and other intracellular structures. Such activities are important in nearly all animal cells and tissues, although distinct anatomical regions and physiological systems rely on different regulatory factors. Recent work indicates that the Arp2/3 complex, a broadly expressed actin nucleator, drives actin assembly during several intracellular stress response pathways. These newly described Arp2/3-mediated cytoskeletal rearrangements are coordinated by members of the Wiskott-Aldrich Syndrome Protein (WASP) family of actin nucleation-promoting factors. Thus, the Arp2/3 complex and WASP-family proteins are emerging as crucial players in cytoplasmic and nuclear activities including autophagy, apoptosis, chromatin dynamics, and DNA repair. Characterizations of the functions of the actin assembly machinery in such stress response mechanisms are advancing our understanding of both normal and pathogenic processes, and hold great promise for providing insights into organismal development and interventions for disease.

Deciphering actin remodelling in immune cells through the prism of actin-related inborn errors of immunity

Actin cytoskeleton remodelling drives cell motility, cell to cell contacts, as well as membrane and organelle dynamics. Those cellular activities operate at a particularly high pace in immune cells since these cells migrate through various tissues, interact with multiple cellular partners, ingest microorganisms and secrete effector molecules. The central and multifaceted role of actin cytoskeleton remodelling in sustaining immune cell tasks in humans is highlighted by rare inborn errors of immunity due to mutations in genes encoding proximal and distal actin regulators. In line with the specificity of some of the actin-based processes at work in immune cells, the expression of some of the affected genes, such as WAS, ARPC1B and HEM1 is restricted to the hematopoietic compartment. Exploration of these natural deficiencies highlights the fact that the molecular control of actin remodelling is tuned distinctly in the various subsets of myeloid and lymphoid immune cells and sustains different networks associated with a vast array of specialized tasks. Furthermore, defects in individual actin remodelling proteins are usually associated with partial cellular impairments highlighting the plasticity of actin cytoskeleton remodelling. This review covers the roles of disease-associated actin regulators in promoting the actin-based processes of immune cells. It focuses on the specific molecular function of those regulators across various immune cell subsets and in response to different stimuli. Given the fact that numerous immune-related actin defects have only been characterized recently, we further discuss the challenges lying ahead to decipher the underlying patho-mechanisms.

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.

Mitochondria-actin cytoskeleton crosstalk in cell migration

Mitochondria perform diverse functions in the cell and their roles during processes such as cell survival, differentiation, and migration are increasingly being appreciated. Mitochondrial and actin cytoskeletal networks not only interact with each other, but this multifaceted interaction shapes their functional dynamics. The interrelation between mitochondria and the actin cytoskeleton extends far beyond the requirement of mitochondrial ATP generation to power actin dynamics, and impinges upon several major aspects of cellular physiology. Being situated at the hub of cell signaling pathways, mitochondrial function can alter the activity of actin regulatory proteins and therefore modulate the processes downstream of actin dynamics such as cellular migration. As we will discuss, this regulation is highly nuanced and operates at multiple levels allowing mitochondria to occupy a strategic position in the regulation of migration, as well as pathological events that rely on aberrant cell motility such as cancer metastasis. In this review, we summarize the crosstalk that exists between mitochondria and actin regulatory proteins, and further emphasize on how this interaction holds importance in cell migration in normal as well as dysregulated scenarios as in cancer.

The Actin Regulators Involved in the Function and Related Diseases of Lymphocytes

Actin is an important cytoskeletal protein involved in signal transduction, cell structure and motility. Actin regulators include actin-monomer-binding proteins, Wiskott-Aldrich syndrome (WAS) family of proteins, nucleation proteins, actin filament polymerases and severing proteins. This group of proteins regulate the dynamic changes in actin assembly/disassembly, thus playing an important role in cell motility, intracellular transport, cell division and other basic cellular activities. Lymphocytes are important components of the human immune system, consisting of T-lymphocytes (T cells), B-lymphocytes (B cells) and natural killer cells (NK cells). Lymphocytes are indispensable for both innate and adaptive immunity and cannot function normally without various actin regulators. In this review, we first briefly introduce the structure and fundamental functions of a variety of well-known and newly discovered actin regulators, then we highlight the role of actin regulators in T cell, B cell and NK cell, and finally provide a landscape of various diseases associated with them. This review provides new directions in exploring actin regulators and promotes more precise and effective treatments for related diseases.

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.

HMGB1 could restrict 1,3-β-glucan induced mice lung inflammation by affecting Beclin1 and Bcl2 interaction and promoting the autophagy of epithelial cells

Fungi were microorganisms that are ubiquitous in a variety of environments. Inhalation of fungi-contaminated organic dust led to hypersensitivity pneumonitis and might eventually cause irreversible pulmonary fibrosis. Studies showed that maintaining the homeostasis of epithelial cells was vital for defending the exogenous fungi invasion. HMGB1-dependent autophagy played a critical role in maintaining cell homeostasis in multiple inflammatory diseases. However, the actual role of HMGB1-dependent autophagy in hypersensitivity pneumonitis was unclear. In our study, mice were exposed to 0.3 mg/50 μL 1,3-β-glucan solution by intratracheal instillation to set up the lung inflammation model. To investigate the role of HMGB1-dependent autophagy in 1,3-β-glucan induced lung inflammation, AAV-sh-HMGB1 was intratracheally injected to silence HMGB1 in the lung. Our finding suggested that silencing HMGB1 could aggravate the 1,3-β-glucan induced lung inflammation by inhibiting the autophagy of epithelial cells. And ubiquitination of Beclin1 contributed to decreasing the interaction of Beclin1 and Bcl2, which might be a key regulatory mechanism of HMGB1 on 1,3-β-glucan induced autophagy.

Infection and autoinflammation in inborn errors of immunity: brothers in arms

The binary view of inborn errors of immunity classified as either autoinflammatory conditions or primary immunodeficiency in the strict sense, that is, increased susceptibility to infection is challenged by the description of recent inborn errors of immunity (IEI) triggers leading to activation and disruption of cell death pathways, play a major part in the pathophysiology of infection and autoinflammation. In addition, molecules with a double role in the extracellular versus intracellular milieu add to the complexity. In all, in-depth study of human inborn errors of immunity will continue to instruct us on fundamental immunology and lead to novel therapeutic targets and approaches that can be used in other monogenic and polygenic/complex immune disorders.

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.

Regulation of diurnal energy balance by mitokines

The mammalian system of energy balance regulation is intrinsically rhythmic with diurnal oscillations of behavioral and metabolic traits according to the 24 h day/night cycle, driven by cellular circadian clocks and synchronized by environmental or internal cues such as metabolites and hormones associated with feeding rhythms. Mitochondria are crucial organelles for cellular energy generation and their biology is largely under the control of the circadian system. Whether mitochondrial status might also feed-back on the circadian system, possibly via mitokines that are induced by mitochondrial stress as endocrine-acting molecules, remains poorly understood. Here, we describe our current understanding of the diurnal regulation of systemic energy balance, with focus on fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), two well-known endocrine-acting metabolic mediators. FGF21 shows a diurnal oscillation and directly affects the output of the brain master clock. Moreover, recent data demonstrated that mitochondrial stress-induced GDF15 promotes a day-time restricted anorexia and systemic metabolic remodeling as shown in UCP1-transgenic mice, where both FGF21 and GDF15 are induced as myomitokines. In this mouse model of slightly uncoupled skeletal muscle mitochondria GDF15 proved responsible for an increased metabolic flexibility and a number of beneficial metabolic adaptations. However, the molecular mechanisms underlying energy balance regulation by mitokines are just starting to emerge, and more data on diurnal patterns in mouse and man are required. This will open new perspectives into the diurnal nature of mitokines and action both in health and disease.