Glycogen synthase kinase 3 activity during development of bone marrow-derived dendritic cells (DCs) essential for the DC function to induce T helper 2 polarization

Glycogen synthase kinase-3: A potential immunotherapeutic target in tumor microenvironment

Glycogen synthase kinase-3(GSK-3) is a protein kinase that can phosphorylate over a hundred substrates and regulate cell differentiation, proliferation, and death. Researchers have acknowledged the pivotal role of abnormal activation of GSK-3 in the progression of various diseases over the past few decades. Recent studies have mostly concentrated on investigating the function of GSK-3 in the tumor microenvironment, specifically examining the interaction between TAM, NK cells, B cells, and T cells. Furthermore, GSK-3 exhibits a strong association with immunological checkpoints, such as programmed cell death protein 1. Novel GSK-3 inhibitors have potential in tumor immunotherapy, exerting beneficial effects on hematologic diseases and solid tumors. Nevertheless, there is a lack of reviews about the correlation between tumor-associated immune cells and GSK-3. This study intends to analyze the function and mechanism of GSK-3 comprehensively and systematically in the tumor microenvironment, with a special focus on its influence on various immune cells. The objective is to present novel perspectives for GSK-3 immunotherapy.

GSK3α/β Restrain IFN-γ-Inducible Costimulatory Molecule Expression in Alveolar Macrophages, Limiting CD4+ T Cell Activation

Macrophages play a crucial role in eliminating respiratory pathogens. Both pulmonary resident alveolar macrophages (AMs) and recruited macrophages contribute to detecting, responding to, and resolving infections in the lungs. Despite their distinct functions, it remains unclear how these macrophage subsets regulate their responses to infection, including how activation by the cytokine IFN-γ is regulated. This shortcoming prevents the development of therapeutics that effectively target distinct lung macrophage populations without exacerbating inflammation. We aimed to better understand the transcriptional regulation of resting and IFN-γ-activated cells using a new ex vivo model of AMs from mice, fetal liver-derived alveolar-like macrophages (FLAMs), and immortalized bone marrow-derived macrophages. Our findings reveal that IFN-γ robustly activates both macrophage types; however, the profile of activated IFN-γ-stimulated genes varies greatly between these cell types. Notably, FLAMs show limited expression of costimulatory markers essential for T cell activation upon stimulation with only IFN-γ. To understand cell type-specific differences, we examined how the inhibition of the regulatory kinases GSK3α/β alters the IFN-γ response. GSK3α/β controlled distinct IFN-γ responses, and in AM-like cells, we found that GSK3α/β restrained the induction of type I IFN and TNF, thus preventing the robust expression of costimulatory molecules and limiting CD4+ T cell activation. Together, these data suggest that the capacity of AMs to respond to IFN-γ is restricted in a GSK3α/β-dependent manner and that IFN-γ responses differ across distinct macrophage populations. These findings lay the groundwork to identify new therapeutic targets that activate protective pulmonary responses without driving deleterious inflammation.

GSK3α/β restrains IFNγ-inducible costimulatory molecule expression in alveolar macrophages, limiting CD4+ T cell activation

Macrophages play a crucial role in eliminating respiratory pathogens. Both pulmonary resident alveolar macrophages (AMs) and recruited macrophages contribute to detecting, responding to, and resolving infections in the lungs. Despite their distinct functions, it remains unclear how these macrophage subsets regulate their responses to infection, including how activation by the cytokine IFNγ is regulated. This shortcoming prevents the development of therapeutics that effectively target distinct lung macrophage populations without exacerbating inflammation. We aimed to better understand the transcriptional regulation of resting and IFNγ-activated cells using a new ex vivo model of AMs from mice, fetal liver-derived alveolar-like macrophages (FLAMs), and immortalized bone marrow-derived macrophages (iBMDMs). Our findings reveal that IFNγ robustly activates both macrophage types; however, the profile of activated IFNγ-stimulated genes varies greatly between these cell types. Notably, FLAMs show limited expression of costimulatory markers essential for T cell activation upon stimulation with only IFNγ. To understand cell type-specific differences, we examined how the inhibition of the regulatory kinases GSK3α/β alters the IFNγ response. GSK3α/β controlled distinct IFNγ responses, and in AM-like cells, we found GSK3α/β restrained the induction of type I IFN and TNF, thus preventing the robust expression of costimulatory molecules and limiting CD4+ T cell activation. Together, these data suggest that the capacity of AMs to respond to IFNγ is restricted in a GSK3α/β-dependent manner and that IFNγ responses differ across distinct macrophage populations. These findings lay the groundwork to identify new therapeutic targets that activate protective pulmonary responses without driving deleterious inflammation.

Regulatory Dendritic Cells Induced by K313 Display Anti-Inflammatory Properties and Ameliorate Experimental Autoimmune Encephalitis in Mice

As a GSK-3β inhibitor reported by our group, K313 is a novel benzoxazole derivative and displays anti-inflammatory properties in RAW264.7 macrophages without cytotoxicity. The activity of GSK-3β affects the differentiation and maturation of bone marrow-derived dendritic cells (DCs). This study aims to investigate whether K313 can be used to induce regulatory/tolerogenic dendritic cells (DCregs), and the therapeutic effects of DCregs induced by K313 in the autoimmune model of experimental autoimmune encephalitis (EAE). The results show that compared with LPS stimulated mature DCs, K313-treated bone marrow-derived DCs display obvious tolerogenic characteristics with decreased expression of co-stimulatory molecules, downregulated secretions of pro-inflammatory cytokines and unregulated secretion of anti-inflammatory cytokine IL-10. The above characteristics conform to the typical phenotypes of DCregs. Moreover, K313-modified DCregs inhibit antigen-specific T cell responses in vitro. Furthermore, by adoptive transfer, K313 modified DCregs to the EAE mice, and the development of disease was ameliorated to some extent. In addition, treatment with K313-modified DCregs also significantly reduced the percentages of splenetic Th1 and Th17 cells and increased the percentage of regulatory T cells in EAE mice. In conclusion, K313-modified DCregs show anti-inflammatory properties in vitro and have a significant positive effect on the EAE disease in vivo. Our data indicate that K313-induced DCregs pulsed with auto-antigen might have potential use as a therapeutic approach for autoimmune inflammation of the central nervous system.

Wnt5a signaling increases IL-12 secretion by human dendritic cells and enhances IFN-γ production by CD4+ T cells

Wnt5a is a secreted pleiotropic glycoprotein produced in an inflammatory state by a wide spectrum of ubiquitous cell populations. Recently, we demonstrated that Wnt5a skews the differentiation of human monocyte derived dendritic cells (moDCs) to a tolerogenic functional state. In this study we focus our interest on the role of this Wnt ligand after DC differentiation, during their maturation and function. We show that the expression of Wnt receptors is tightly regulated during the life cycle of DCs suggesting a differential responsiveness to Wnt signaling conditioned by their differentiation stage and the maturational stimuli. Furthermore, we confirm that Wnt5a is the main non-canonical Wnt protein expressed by DCs and its production increases upon specific stimuli. Exogenous Wnt5a improved the endocytic capacity of immature DCs but it is not a stimulatory signal on its own, slightly affecting the maturation and function of DCs. However, knocking down Wnt5a gene expression in maturing DCs demonstrates that DC-derived Wnt5a is necessary for normal IL-12 secretion and plays a positive role during the development of Th1 responses. Wnt5a acts both in autocrine and paracrine ways. Thus, human naive CD4(+) T cells express Wnt receptors and, the addition of Wnt5a during CD3/CD28 stimulation enhances IL-2 and IFN-γ production. Taken together these results suggest a time-dependent role for Wnt5a during inflammatory responses conditioned by the differentiation stage of cellular targets.

Decreased store operated Ca2+ entry in dendritic cells isolated from mice expressing PKB/SGK-resistant GSK3

Dendritic cells (DCs), key players of immunity, are regulated by glycogen synthase kinase GSK3. GSK3 activity is suppressed by PKB/Akt and SGK isoforms, which are in turn stimulated by the PI3K pathway. Exposure to bacterial lipopolysaccharides increases cytosolic Ca²⁺-concentration ([Ca²⁺]_i), an effect augmented in DCs isolated from mutant mice expressing PKB/SGK-resistant GSK3α,β (gsk3^KI). Factors affecting [Ca²⁺]_i include Ca²⁺-release from intracellular stores (CRIS), store-operated Ca²⁺-entry (SOCE) through STIM1/STIM2-regulated Orai1, K⁺-dependent Na⁺/Ca²⁺-exchangers (NCKX), K⁺-independent Na⁺/Ca²⁺-exchangers (NCX) and calbindin-D28k. The present study explored whether PKB/SGK-dependent GSK3α, β-activity impacts on CRIS, SOCE, NCKX, NCX or calbindin. DCs were isolated from gsk3^KI mice and respective wild-type mice (gsk3^WT), [Ca²⁺]_i estimated from Fura2 fluorescence, Orai1, STIM1, STIM2 as well as calbindin-D28k protein abundance determined by Western blotting and mRNA levels quantified by real time PCR. As a result, thapsigargin-induced CRIS and SOCE were significantly blunted by GSK3-inhibitors SB216763 (1–10 µM, 30 min) or GSK-XIII (10 µM, 30 min) but were significantly lower in gsk3^WT than in gsk3^KIDCs. Orai1, STIM1 and STIM2 protein abundance was significantly lower and calbindin-D28k abundance significantly higher in gsk3^KI than in gsk3^WTDCs. Activity of NCKX and NCX was significantly higher in gsk3^KI than in gsk3^WTDCs and was significantly increased by SB216763 (1 µM, 30 min) or GSK-XIII (10 µM, 30 min). Treatment of gsk3^WT DCs with SB216763 (1 µM, 4–24 h) or GSK-XIII (10 µM, 4–24 h) did not significantly modify the protein abundance of Orai1, STIM1 and STIM2. The present observations point to a dual role of GSK3 in the regulation of Ca²⁺ in DCs. Acute inhibition of GSK3 blunted the increase of [Ca²⁺]_i following CRIS and SOCE and stimulated NCKX/NCX activity. However, expression of PKB/SGK-resistant GSK3α, β downregulated the increase of [Ca²⁺]_i following CRIS and SOCE, an effect at least partially due to downregulation of Orai1, STIM1 and STIM2 expression as well as upregulation of Na⁺/Ca²⁺-exchanger activity and calbindin D28k expression.

PKB/SGK-dependent GSK3-phosphorylation in the regulation of LPS-induced Ca2+ increase in mouse dendritic cells

The function of dendritic cells (DCs) is modified by glycogen synthase kinase GSK3 and GSK3 inhibitors have been shown to protect against inflammatory disease. Regulators of GSK3 include the phosphoinositide 3 kinase (PI3K) pathway leading to activation of protein kinase B (PKB/Akt) and serum and glucocorticoid inducible kinase (SGK) isoforms, which in turn phosphorylate and thus inhibit GSK3. The present study explored, whether PKB/SGK-dependent inhibition of GSK3 contributes to the regulation of cytosolic Ca(2+) concentration following stimulation with bacterial lipopolysaccharides (LPS). To this end DCs from mutant mice, in which PKB/SGK-dependent GSK3α,β regulation was disrupted by replacement of the serine residues in the respective SGK/PKB-phosphorylation consensus sequence by alanine (gsk3(KI)), were compared to DCs from respective wild type mice (gsk3(WT)). According to Western blotting, GSK3 phosphorylation was indeed absent in gsk3(KI) DCs. According to flow cytometry, expression of antigen-presenting molecule major histocompatibility complex II (MHCII) and costimulatory molecule CD86, was similar in unstimulated and LPS (1μg/ml, 24h)-stimulated gsk3(WT) and gsk3(KI) DCs. Moreover, production of cytokines IL-6, IL-10, IL-12 and TNFα was not significantly different in gsk3(KI) and gsk3(WT) DCs. In gsk3(WT) DCs, stimulation with LPS (1μg/ml) within 10min led to transient phosphorylation of GSK3. According to Fura2 fluorescence, LPS (1μg/ml) increased cytosolic Ca(2+) concentration, an effect significantly more pronounced in gsk3(KI) DCs than in gsk3(WT) DCs. Conversely, GSK3 inhibitor SB216763 (3-[2,4-Dichlorophenyl]-4-[1-methyl-1H-indol-3-yl]-1H-pyrrole-2,5-dione, 10μM, 30min) significantly blunted the increase of cytosolic Ca(2+) concentration following LPS exposure. In conclusion, PKB/SGK-dependent GSK3α,β activity participates in the regulation of Ca(2+) signaling in dendritic cells.

AKT/SGK-sensitive phosphorylation of GSK3 in the regulation of L-selectin and perforin expression as well as activation induced cell death of T-lymphocytes

Survival and function of T-lymphocytes critically depends on phosphoinositide (PI) 3 kinase. PI3 kinase signaling includes the PKB/Akt and SGK dependent phosphorylation and thus inhibition of glycogen synthase kinase GSK3α,β. Lithium, a known unspecific GSK3 inhibitor protects against experimental autoimmune encephalomyelitis. The present study explored, whether Akt/SGK-dependent regulation of GSK3 activity is a determinant of T cell survival and function. Experiments were performed in mutant mice in which Akt/SGK-dependent GSK3α,β inhibition was disrupted by replacement of the serine residue in the respective SGK/Akt-phosphorylation consensus sequence by alanine (gsk3(KI)). T cells from gsk3(KI) mice were compared to T cells from corresponding wild type mice (gsk3(WT)). As a result, in gsk3(KI) CD4(+) cells surface CD62L (L-selectin) was significantly less abundant than in gsk3(WT) CD4(+) cells. Upon activation in vitro T cells from gsk3(KI) mice reacted with enhanced perforin production and reduced activation induced cell death. Cytokine production was rather reduced in gsk3(KI) T cells, suggesting that GSK3 induces effector function in CD8(+) T cells. In conclusion, PKB/Akt and SGK sensitive phosphorylation of GSK3α,β is a potent regulator of perforin expression and activation induced cell death in T lymphocytes.

Regulation of dendritic cell development by GM-CSF: molecular control and implications for immune homeostasis and therapy

Dendritic cells (DCs) represent a small and heterogeneous fraction of the hematopoietic system, specialized in antigen capture, processing, and presentation. The different DC subsets act as sentinels throughout the body and perform a key role in the induction of immunogenic as well as tolerogenic immune responses. Because of their limited lifespan, continuous replenishment of DC is required. Whereas the importance of GM-CSF in regulating DC homeostasis has long been underestimated, this cytokine is currently considered a critical factor for DC development under both steady-state and inflammatory conditions. Regulation of cellular actions by GM-CSF depends on the activation of intracellular signaling modules, including JAK/STAT, MAPK, PI3K, and canonical NF-κB. By directing the activity of transcription factors and other cellular effector proteins, these pathways influence differentiation, survival and/or proliferation of uncommitted hematopoietic progenitors, and DC subset–specific precursors, thereby contributing to specific aspects of DC subset development. The specific intracellular events resulting from GM-CSF–induced signaling provide a molecular explanation for GM-CSF–dependent subset distribution as well as clues to the specific characteristics and functions of GM-CSF–differentiated DCs compared with DCs generated by fms-related tyrosine kinase 3 ligand. This knowledge can be used to identify therapeutic targets to improve GM-CSF–dependent DC-based strategies to regulate immunity.

Regulation by glycogen synthase kinase-3 of inflammation and T cells in CNS diseases

Elevated markers of neuroinflammation have been found to be associated with many psychiatric and neurodegenerative diseases, such as mood disorders, Alzheimer's disease, and multiple sclerosis (MS). Since neuroinflammation is thought to contribute to the pathophysiology of these diseases and to impair responses to therapeutic interventions and recovery, it is important to identify mechanisms that regulate neuroinflammation and potential targets for controlling neuroinflammation. Recent findings have demonstrated that glycogen synthase kinase-3 (GSK3) is an important regulator of both the innate and adaptive immune systems' contributions to inflammation. Studies of the innate immune system have shown that inhibitors of GSK3 profoundly alter the repertoire of cytokines that are produced both by peripheral and central cells, reducing pro-inflammatory cytokines, and increasing anti-inflammatory cytokines. Furthermore, inhibitors of GSK3 promote tolerance to inflammatory stimuli, reducing inflammatory cytokine production upon repeated exposure. Studies of the adaptive immune system have shown that GSK3 regulates the production of cytokines by T cells and the differentiation of T cells to subtypes, particularly Th17 cells. Regulation of transcription factors by GSK3 appears to play a prominent role in its regulation of immune responses, including of NF-κB, cyclic AMP response element binding protein, and signal transducer and activator of transcription-3. Invivo studies have shown that GSK3 inhibitors ameliorate clinical symptoms of both peripheral and central inflammatory diseases, particularly experimental autoimmune encephalomyelitis, the animal model of MS. Therefore, the development and application of GSK3 inhibitors may provide a new therapeutic strategy to reduce neuroinflammation associated with many central nervous system diseases.

Glycogen synthase kinase-3β: a mediator of inflammation in Alzheimer's disease?

Proliferation and activation of microglial cells is a neuropathological characteristic of brain injury and neurodegeneration, including Alzheimer's disease. Microglia act as the first and main form of immune defense in the nervous system. While the primary function of microglia is to survey and maintain the cellular environment optimal for neurons in the brain parenchyma by actively scavenging the brain for damaged brain cells and foreign proteins or particles, sustained activation of microglia may result in high production of proinflammatory mediators that disturb normal brain functions and even cause neuronal injury. Glycogen synthase kinase-3β has been recently identified as a major regulator of immune system and mediates inflammatory responses in microglia. Glycogen synthase kinase-3β has been extensively investigated in connection to tau and amyloid β toxicity, whereas reports on the role of this enzyme in neuroinflammation in Alzheimer's disease are negligible. Here we review and discuss the role of glycogen synthase-3β in immune cells in the context of Alzheimer's disease pathology.

Dendritic cell maturation occurs through the inhibition of GSK-3β

Dendritic cell (DC) maturation results in changes in antigen processing and presentation, governing the fate of adaptive immunity. Understanding the intracellular signaling pathways governing DC maturation is therefore critical. In this study, we observed that the kinase, GSK-3β, is present in its active form in resting immature DCs isolated from the spleen and bone marrow of mice. Induction of DC maturation using GM-CSF, IL-4 and TNF-α resulted in GSK-3β inhibition, as reflected by increased phosphorylation of Serine 9 on the kinase, and concomitant stabilization of its substrate, β-catenin. Treatment of immature DCs with a GSK-3β inhibitor increased cell surface expression of CD80, CD86 and CD40 on DCs, enhancing their ability to present antigen and activating IL-2 secretion by T cells. GSK-3β inhibition also parallels dendritic cell maturation in vivo. Our results show that GSK-3β signaling controls DC maturation and suggest that this kinase could be manipulated to modulate adaptive immunity.

Glycogen synthase kinase 3: a point of convergence for the host inflammatory response

The phosphatidylinositol 3-kinase (PI3K) pathway has been shown to play a central role in regulating the host inflammatory response. Recent studies characterizing the downstream effector molecules within the PI3K pathway have identified that the serine/threonine kinase, glycogen synthase kinase 3 (GSK3), plays a pivotal role in regulating the production of pro- and anti-inflammatory cytokines. In innate immune cells, GSK3 inactivation augments anti-inflammatory cytokine production while concurrently suppressing the production of pro-inflammatory cytokines. The role of GSK3 in T cell biology has also been studied in detail and is involved in regulating multiple downstream signaling processes mediated by the T cell receptor (TCR), the co-stimulatory molecule CD28, and the IL-17 receptor. In vivo studies assessing the therapeutic properties of GSK3 inhibitors have shown that the inactivation of GSK3 can protect the host from immune-mediated pathology and death. This review will highlight the immunological importance GSK3 plays within different signal transduction pathways of the immune system, the cellular mechanisms regulating the activity of GSK3, the role of GSK3 in innate and adaptive immune responses, and the in vivo use of GSK3 inhibitors to treat inflammatory mediated diseases in animals.

Role of glycogen synthase kinase 3 (GSK-3) in innate immune response of human immature dendritic cells to Aspergillus fumigatus

Dysregulation of the Th1/Th2 cytokine balance and a switch to a Th2 immune response contribute to the development of and the unfavorable outcome from invasive aspergillosis (IA). We explore in this paper the role of glycogen synthase kinase 3 (GSK-3) in human immature dendritic cells (iDCs) relative to infection caused by A. fumigatus by the use of GSK-3 inhibitors (LiCl, SB415286) and RNA interference technology. In iDCs exposed to A. fumigatus germ tubes, inhibition of GSK-3 with LiCl or SB415286, as well as transfection with small interfering RNA, led to markedly elevated expression of the anti-inflammatory cytokine IL-10. In contrast, pro-inflammatory cytokine response was only partially regulated by GSK-3. Screening of patients after allogeneic stem cell transplantation (with or without IA) for the presence of genetic markers (rs334558, rs6438552) in the GSK-3 gene revealed no significant association with an increased risk for IA. In conclusion, GSK-3 might be involved in the regulation of the anti-inflammatory response of iDCs in the context of infections due to A. fumigatus, albeit the exact mechanisms have to be clarified in future experiments.