MST1/2 Balance Immune Activation and Tolerance by Orchestrating Adhesion, Transcription, and Organelle Dynamics in Lymphocytes

The immunometabolic function of VGLL3 and female-biased autoimmunity

Autoimmune diseases exhibit a pronounced yet unexplained prevalence among women. Vestigial-like family member 3 (VGLL3), a female-biased factor that promotes autoimmunity, has recently been discovered to assist cells in sensing and adapting to nutritional stress. This role of VGLL3 may confer a selective advantage during the evolution of placental mammals. However, the excessive activation of the VGLL3-mediated energy-sensing pathway can trigger inflammatory cell death and the exposure of self-antigens, leading to the onset of autoimmunity. These observations have raised the intriguing perspective that nutrient sensing serves as a double-edged sword in immune regulation. Mechanistically, VGLL3 intersects with Hippo signaling and activates multiple downstream, immune-associated genes that play roles in metabolic regulation. Understanding the multifaceted roles of VGLL3 in nutrient sensing and immune modulation provides insight into the fundamental question of sexual dimorphism in immunometabolism and sheds light on potential therapeutic targets for autoimmune diseases.

Molecules in the hippo pathway that regulate Th17 differentiation reveal the severity of ankylosing spondylitis

AIM

Ankylosing spondylitis (AS) is a chronic, progressive, and inflammatory autoimmune disease of unknown origin that affects the axial skeleton and sacroiliac joints, resulting in pain and loss of function. AS is characterized by the overdifferentiation of T helper 17 (Th17) cells, which contribute to the development of the disease. The Hippo signaling pathway is an important regulator of Th17 differentiation, but its role in patients with AS is unclear. We aimed to investigate the role of key molecules of the Hippo signaling pathway in inflammatory Th17 differentiation in patients with AS and to examine their correlation with disease stages.

METHODS

We examined the activity of the Hippo pathway in patients with AS and the regulation of Th17 differentiation during AS-mediated inflammation. Blood samples were collected from 60 patients with AS at various stages and 30 healthy controls. Peripheral blood mononuclear cells (PBMCs) were isolated from peripheral blood by density gradient centrifugation. The Serum Interleukin-17 (IL-17) levels in patients with AS and healthy controls were quantified by ELISA. The key molecules of Hippo pathway were assessed by real-time PCR for their mRNA expression, and protein levels were determined by Western blot analysis.

RESULTS

Elevated serum interleukin-17 (IL-17) levels were observed in patients with AS compared with healthy controls. The protein and mRNA levels of retinoic acid receptor-related orphan receptor γt (RORγt), transcriptional coactivator with a PDZ-binding motif (TAZ), and key upstream transcription factors in the Hippo signaling pathway were measured. The expression of RORγt and TAZ was increased in the blood of patients with AS, whereas the expression of other Hippo pathway proteins, such as MST1/2 and NDR1/2, was significantly decreased. Increased levels of IL-17 and TAZ were significantly associated with disease activity. In addition, MST1, MST2, and NDR1 levels were negatively correlated with TAZ, RORγt, and IL-17 levels.

CONCLUSION

Our findings suggest that the Hippo pathway plays a significant role in the regulation of Th17 differentiation and disease activity in patients with AS. The upregulation of TAZ and downregulation of key Hippo pathway proteins, such as MST1/2 and NDR1/2, may contribute to AS pathogenesis. These proteins may serve as biomarkers and may lead to the development of novel therapeutic strategies for AS.

MST1/2 in inflammation and immunity

The mammalian Sterile 20-like kinase 1/2 (MST1/2) belongs to the serine/threonine (GC) protein kinase superfamily. Collective studies confirm the vital role MST1/2 in inflammation and immunity. MST1/2 is closely related to the progress of inflammation. Generally, MST1/2 aggravates the inflammatory injury through MST1-JNK, MST1-mROS, MST1-Foxo3, and NF-κB pathways, as well as several regulatory factors such as tumor necrosis factor-α (TNF-α), mitochondrial extension factor 1 (MIEF1), and lipopolysaccharide (LPS). Moreover, MST1/2 is also involved in the regulation of immunity to balance immune activation and tolerance by regulating MST1/2-Rac, MST1-Akt1/c-myc, MST1-Foxos, MST1-STAT, Btk pathways, and lymphocyte function-related antigen 1 (LFA-1), which subsequently prevents immunodeficiency syndrome and autoimmune diseases. This article reviews the effects of MST1/2 on inflammation and immunity.

The role of non-canonical Hippo pathway in regulating immune homeostasis

The Hippo pathway is a crucial signaling pathway that is highly conserved throughout evolution for the regulation of organ size and maintenance of tissue homeostasis. Initial studies have primarily focused on the canonical Hippo pathway, which governs organ development, tissue regeneration, and tumorigenesis. In recent years, extensive research has revealed that the non-canonical Hippo pathway, centered around Mst1/2 as its core molecule, plays a pivotal role in immune response and function by synergistically interacting with other signal transduction pathways. Consequently, the non-canonical Hippo pathway assumes significant importance in maintaining immune system homeostasis. This review concentrates on the research progress of the non-canonical Hippo pathway in regulating innate immune cell anti-infection responses, maintaining redox homeostasis, responding to microenvironmental stiffness, and T-cell differentiation.

Radix Scrophulariae Extracts Exert Effect on Hyperthyroidism via MST1/Hippo Signaling Pathway

OBJECTIVE

To explore the mechanism of Radix Scrophulariae (RS) extracts in the treatment of hyperthyroidism rats by regulating proliferation, apoptosis, and autophagy of thyroid cell through the mammalian sterile 20-like kinase 1 (MST1)/Hippo pathway.

METHODS

Twenty-four rats were randomly divided into 4 groups according to a random number table: control, model group, RS, and RS+Hippo inhibitor (XMU-MP-1) groups (n=6 per group). Rats were gavaged with levothyroxine sodium tablet suspension (LST, 8 μ g/kg) for 21 days except for the control group. Afterwards, rats in the RS group were gavaged with RS extracts at the dose of 1,350 mg/kg, and rats in the RS+XMU-MP-1 group were gavaged with 1,350 mg/kg RS extracts and 1 mg/kg XMU-MP-1. After 15 days of administration, thyroid gland was taken for gross observation, and histopathological changes were observed by hematoxylin-eosin staining. The structure of Golgi secretory vesicles in thyroid tissues was observed by transmission electron microscopy. The expression of thyrotropin receptor (TSH-R) was observed by immunohistochemistry. Terminal-deoxynucleoitidyl transferase mediated nick end labeling assay was used to detect cell apoptosis in thyroid tissues. Real-time quantity primer chain reaction and Western blot were used to detect the expressions of MST1, p-large tumor suppressor gene 1 (LATS1), p-Yes1 associated transcriptional regulator (YAP), proliferating cell nuclear antigen (PCNA), G1/S-specific cyclin-D1 (Cyclin D1), B-cell lymphoma-2 (Bcl-2), Caspase-3, microtubule-associated proeins light chain 3 II/I (LC3-II/I), and recombinant human autophagy related 5 (ATG5). Thyroxine (T4) level was detected by enzyme-linked immunosorbent assay.

RESULTS

The thyroid volume of rats in the model group was significantly increased compared to the normal control group (P<0.01), and pathological changes such as uneven size of follicular epithelial cells, disorderly arrangement, and irregular morphology occurred. The secretion of small vesicles by Golgi apparatus was reduced, and the expressions of receptor protein TSH-R and T4 were significantly increased (P<0.01), while the expressions of MST1, p-LATS1, p-YAP, Caspase-3, LC3-II/I, and ATG5 were significantly decreased (P<0.01). The expressions of Bcl-2, PCNA, and cyclin D1 were significantly increased (P<0.01). Compared with the model group, RS extracts reduced the volume of thyroid gland, improved pathological condition of the thyroid gland, promoted secretion of the secretory vesicles with double-layer membrane structure in thyroid Golgi, significantly inhibited the expression of TSH-R and T4 levels (P<0.01), upregulated MST1, p-LATS1, p-YAP, Caspase-3, LC3-II/I, and ATG5 expressions (P<0.01), and downregulated Bcl-2, PCNA, and Cyclin D1 expressions (P<0.01). XMU-MP-1 inhibited the intervention effects of RS extracts (P<0.01).

CONCLUSION

RS extracts could inhibit proliferation and promote apoptosis and autophagy in thyroid tissues through MST1/Hippo pathway for treating hyperthyroidism.

The hippo kinases MST1/2 in cardiovascular and metabolic diseases: A promising therapeutic target option for pharmacotherapy

Cardiovascular diseases (CVDs) and metabolic disorders are major components of noncommunicable diseases, causing an enormous health and economic burden worldwide. There are common risk factors and developmental mechanisms among them, indicating the far-reaching significance in exploring the corresponding therapeutic targets. MST1/2 kinases are well-established proapoptotic effectors that also bidirectionally regulate autophagic activity. Recent studies have demonstrated that MST1/2 influence the outcome of cardiovascular and metabolic diseases by regulating immune inflammation. In addition, drug development against them is in full swing. In this review, we mainly describe the roles and mechanisms of MST1/2 in apoptosis and autophagy in cardiovascular and metabolic events as well as emphasis on the existing evidence for their involvement in immune inflammation. Moreover, we summarize the latest progress of pharmacotherapy targeting MST1/2 and propose a new mode of drug combination therapy, which may be beneficial to seek more effective strategies to prevent and treat CVDs and metabolic disorders.

MST1: A future novel target for cardiac diseases

Major heart diseases pose a serious threat to human health. Finding early diagnostic markers and key therapeutic targets is an urgent scientific problem in this field. Mammalian sterile 20-like kinase 1 (MST1) is a protein kinase, and the occurrence of many heart diseases is related to the continuous activation of the MST1 gene. With the deepening of the research, the potential role of MST1 in promoting the development of heart disease has become more apparent. Therefore, to better understand the role of MST1 in the pathogenesis of heart disease, this work systematically summarizes the role of MST1 in the pathogenesis of heart disease, gives a comprehensive overview of its possible strategies in the diagnosis and treatment of heart disease, and analyzes its potential significance as a marker for the diagnosis and treatment of heart disease.

MST1 controls murine neutrophil homeostasis via the G-CSFR/STAT3 axis

The release of neutrophils from the bone marrow into the blood circulation is essential for neutrophil homeostasis and the protection of the organism from invading microorganisms. Granulocyte colony-stimulating factor (G-CSF) plays a pivotal role in this process and guides granulopoiesis as well as the release of bone marrow neutrophils into the blood stream both during homeostasis and in case of infection through activation of the G-CSF receptor/signal transduction and activation of transcription 3 (STAT3) signaling pathway. Here, we investigated the role of the mammalian sterile 20-like kinase 1 (MST1) for neutrophil homeostasis and neutrophil mobilization. We found increased plasma levels of G-CSF in Mst1 ^-/- mice compared to wild type mice both under homeostatic conditions as well as after stimulation with the proinflammatory cytokine TNF-α. In addition, G-CSF-induced mobilization of neutrophils from the bone marrow into the blood circulation in vivo was markedly reduced in the absence of MST1. Interestingly, this was not accompanied by differences in the number of blood neutrophils. Addressing the underlying molecular mechanism of MST1-regulated neutrophil mobilization, we found reduced STAT3 phosphorylation and impaired upregulation of CXCR2 in Mst1 ^-/- bone marrow neutrophils compared to wild type cells, while JAK2 phosphorylation was not altered. Taken together, we identify MST1 as a critical modulator of neutrophil homeostasis and neutrophil mobilization from the bone marrow, which adds another important aspect to the complex role of MST1 in regulating innate immunity.

cfDNA Methylation Profiles and T-Cell Differentiation in Women with Endometrial Polyps

DNA methylation is a part of the regulatory mechanisms of gene expression, including chromatin remodeling and the activity of microRNAs, which are involved in the regulation of T-cell differentiation and function. However, the role of cfDNA methylation in T-cell differentiation is entirely unknown. In patients with endometrial polyps (EPs), we have found an imbalance of T-cell differentiation and an aberrant cfDNA methylation profile, respectively. In this study, we investigated the relationship between cfDNA methylation profiles and T-cell differentiation in 14 people with EPs and 27 healthy controls. We found that several differentially methylated genes (DMGs) were associated with T-cell differentiation in people with EPs (ITGA2-Naïve CD4, r = -0.560, p = 0.037; CST9-EMRA CD4, r = -0.626, p = 0.017; and ZIM2-CM CD8, r = 0.576, p = 0.031), but not in healthy controls (all p > 0.05). When we combined the patients' characteristics, we found a significant association between ITGA2 methylation and polyp diameter (r = 0.562, p = 0.036), but this effect was lost when adjusting the level of Naïve CD4 T-cells (r = 0.038, p = 0.903). Moreover, the circulating sex hormone levels were associated with T-cell differentiation (estradiol-Naïve CD4, r = -0.589, p = 0.027), and the cfDNA methylation profile (testosterone-ZIM2, r = -0.656, p = 0.011). In conclusion, this study has established a link between cfDNA methylation profiles and T-cell differentiation among people with EPs, which may contribute to the etiology of EPs. Further functional studies are warranted.

cGAS/STING signaling in the regulation of rheumatoid synovial aggression

Background

Fibroblast-like synoviocytes (FLSs) play a critical role in promoting synovial aggression and joint destruction in rheumatoid arthritis (RA). Cyclic GMP-AMP synthase (cGAS)/stimulator of interferon gene (STING) signaling plays an important role in controlling a series of cellular biological processes. However, it is still unclear whether cGAS/STING signaling regulates rheumatoid synovial aggression.

Methods

Cell migration and invasion were detected using a Transwell chamber. Gene expression was measured using quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and protein expression was detected by western blotting. Reactive oxygen species (ROS) levels were measured by 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) probe. F-actin staining and immunofluorescence assays were used to investigate lamellipodia formation and nuclear translocation, respectively. A severe combined immunodeficiency (SCID) mouse model was established to observe the migration and invasion of RA FLSs in vivo.

Results

Our results showed that cytosolic double-stranded DNA (dsDNA)-induced cGAS/STING activation promoted the in vitro migration and invasion of RA FLSs. Moreover, RA FLSs treated with cGAS or STING short hairpin RNA (shRNA) exhibited reduced invasion into cartilage in the SCID model. Mechanistically, we determined that cGAS/STING activation leads to increased mitochondrial ROS levels, and thereby increases phosphorylation of mammalian sterile 20-like kinase 1 (MST1), a core component of the Hippo pathway, subsequently promoting activation of forkhead box1 (FOXO1). MST1 and FOXO1 knockdown also diminished the migration and invasion of RA FLSs.

Conclusions

Our findings suggest that cGAS/STING signaling has an important role in regulating rheumatoid synovial aggression and that targeting cGAS/STING may represent a novel potential therapy for RA.

YAP/Hippo Pathway and Cancer Immunity: It Takes Two to Tango

Hippo pathway with its main molecule YAP is a crucial pathway for development, tissue homeostasis, wound healing, tissue regeneration, and cancer. In this review, we discuss the multiple effects of the YAP/Hippo pathway in the immune system and cancer. We analyzed a series of effects: extracellular vesicles enhanced immunity through inhibition of LATS1/2, ways of modulation of the tumor microenvironment, YAP- and TAZ-mediated upregulation of PDL1, high expression of YAP and PDL1 in EGFR-TKI-resistant cells, enhanced YAP activity in inflammation, and the effect of the Hippo pathway on T cells, B cells, Tregs, macrophages, and myeloid-derived suppressor cells (MDSCs). These pleiotropic effects render the YAP and Hippo pathway a key pathway for exploitation in the future, in order to enhance our immunotherapy treatment strategies in oncology.

Extracellular vesicles derived from astrocytes facilitated neurite elongation by activating the Hippo pathway

Spinal cord injury (SCI) often causes severe neurological dysfunction, and facilitating neurite elongation is particularly important in its treatment. Astrocytes (AS) play an important role in the central nervous system (CNS), and their high plasticity and versatility provide a feasible entry point for relevant research. Our purpose was to explore whether extracellular vesicles (EVs) from astrocytes (AS-EVs) and lipopolysaccharide (LPS)-preactivated astrocytes (LPAS-EVs) facilitate neurite elongation, to explore the underlying mechanism, and to verify whether these EVs promote locomotor recovery in rats. We used LPS to preactivate astrocytes and cocultured them with PC12 cells to observe neurite changes, then extracted and identified AS-EVs and LPAS-EVs and the role and mechanism of these EVs in facilitating neurite elongation was examined in vivo and vitro. We demonstrated that AS-EVs and LPAS-EVs facilitated the elongation of neurites and the recovery of rats with SCI. LPAS-EVs had a stronger effect than AS-EVs, by activating the Hippo pathway, promoting monopole spindle binding protein 1 (MOB1) expression, and reducing Yes-associated protein (YAP) levels. The data also suggest a feedback regulation between MOB1 and p-YAP/YAP. In sum, AS-EVs and LPAS-EVs can play an active role in facilitating neurite elongation by activating the Hippo pathway. These findings provide a new strategy for treating SCI and other CNS-related injuries.

A Novel STK4 Mutation Impairs T Cell Immunity Through Dysregulation of Cytokine-Induced Adhesion and Chemotaxis Genes

Purpose

Human serine/threonine kinase 4 (STK4) deficiency is a rare, autosomal recessive genetic disorder leading to combined immunodeficiency; however, the extent to which immune signaling and host defense are impaired is unclear. We assessed the functional consequences of a novel, homozygous nonsense STK4 mutation (NM_006282.2:c.871C > T, p.Arg291*) identified in a pediatric patient by comparing his innate and adaptive cell-mediated and humoral immune responses with those of three heterozygous relatives and unrelated controls.

Methods

The genetic etiology was verified by whole genome and Sanger sequencing. STK4 gene and protein expression was measured by quantitative RT-PCR and immunoblotting, respectively. Cellular abnormalities were assessed by high-throughput RT-RCR, RNA-Seq, ELISA, and flow cytometry. Antibody responses were assessed by ELISA and phage immunoprecipitation-sequencing.

Results

The patient exhibited partial loss of STK4 expression and complete loss of STK4 function combined with recurrent viral and bacterial infections, notably persistent Epstein–Barr virus viremia and pulmonary tuberculosis. Cellular and molecular analyses revealed abnormal fractions of T cell subsets, plasmacytoid dendritic cells, and NK cells. The transcriptional responses of the patient’s whole blood and PBMC samples indicated dysregulated interferon signaling, impaired T cell immunity, and increased T cell apoptosis as well as impaired regulation of cytokine-induced adhesion and leukocyte chemotaxis genes. Nonetheless, the patient had detectable vaccine-specific antibodies and IgG responses to various pathogens, consistent with a normal CD19 + B cell fraction, albeit with a distinctive antibody repertoire, largely driven by herpes virus antigens.

Conclusion

Patients with STK4 deficiency can exhibit broad impairment of immune function extending beyond lymphoid cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01115-2.

Hippo Signal Transduction Mechanisms in T Cell Immunity

Hippo signaling pathways are evolutionarily conserved signal transduction mechanisms mainly involved in organ size control, tissue regeneration, and tumor suppression. However, in mammals, the primary role of Hippo signaling seems to be regulation of immunity. As such, humans with null mutations in STK4 (mammalian homologue of Drosophila Hippo; also known as MST1) suffer from recurrent infections and autoimmune symptoms. Although dysregulated T cell homeostasis and functions have been identified in MST1-deficient human patients and mouse models, detailed cellular and molecular bases of the immune dysfunction remain to be elucidated. Although the canonical Hippo signaling pathway involves transcriptional co-activator Yes-associated protein (YAP) or transcriptional coactivator with PDZ motif (TAZ), the major Hippo downstream signaling pathways in T cells are YAP/TAZ-independent and they widely differ between T cell subsets. Here we will review Hippo signaling mechanisms in T cell immunity and describe their implications for immune defects found in MST1-deficient patients and animals. Further, we propose that mutual inhibition of Mst and Akt kinases and their opposing roles on the stability and function of forkhead box O and β-catenin may explain various immune defects discovered in mutant mice lacking Hippo signaling components. Understanding these diverse Hippo signaling pathways and their interplay with other evolutionarily-conserved signaling components in T cells may uncover molecular targets relevant to vaccination, autoimmune diseases, and cancer immunotherapies.