Transglutaminase 2 is involved in amyloid-beta1–42-induced pro-inflammatory activation via AP1/JNK signalling pathways in THP-1 monocytes

Study of tissue transglutaminase spliced variants expressed in THP-1 derived macrophages exhibiting distinct functional phenotypes

Tissue transglutaminase (TG2) expressed in monocytes and macrophage is known to participate in processes during either early and resolution stages of inflammation. The alternative splicing of tissue transglutaminase gene is a mechanism that increases its functional diversity. Four spliced variants are known with truncated C-terminal domains (TGM2_v2, TGM2_v3, TGM2_v4a, TGM2_v4b) but scarce information is available about its expression in human monocyte and macrophages. We studied the expression of canonical TG2 (TGM2_v1) and its short spliced variants by RT-PCR during differentiation of TPH-1 derived macrophages (dTHP-1) using two protocols (condition I and II) that differ in Phorbol-12-myristate-13-acetate dose and time schedule. The production of TNF-α and IL-1β in supernatant of dTHP-1, measured by ELISA in supernatants showed higher proinflammatory milieu in condition I. We found that the expression of all mRNA TG2 spliced variants were up-regulated during macrophage differentiation and after IFN-γ treatment of dTHP-1 cells in both conditions. Nevertheless, the relative fold increase or TGM2_v3 in relation with TGM2_v1 was higher only with the condition I. M1/M2-like THP-1 macrophages obtained with IFN-γ/IL-4 treatments showed that the up-regulation of TGM2_v1 induced by IL-4 was higher in relation with any short spliced variants. The qualitative profile of relative contribution of spliced variants in M1/M2-like THP-1 cells showed a trend to higher expression of TGM2_v3 in the inflammatory functional phenotype. Our results contribute to the knowledge about TG2 spliced variants in the biology of monocyte/macrophage cells and show how the differentiation conditions can alter their expression and cell function.

Rotenone-induced oxidative stress in THP-1 cells: biphasic effects of baicalin

BACKGROUND

Several results demonstrated that microglia and peripheral monocytes/macrophages infiltrating the central nervous system (CNS) are involved in cell response against toxic compounds. It has been shown that rotenone induces neurodegeneration in various in vitro experimental models. Baicalin, a natural compound, is able to attenuate cell damage through anti-oxidant, anti-microbial, anti-inflammatory, and immunomodulatory action. Using THP-1 monocytes, we investigated rotenone effects on mitochondrial dysfunction and apoptosis, as well as baicalin ability to counteract rotenone toxicity.

METHODS AND RESULTS

THP-1 cells were exposed to rotenone (250 nM), in the presence/absence of baicalin (10-500 μM) for 2-24 h. Reactive Oxygen Species production (ROS), mitochondrial activity and transmembrane potential (Δψm), DNA damage, and caspase-3 activity were assessed. Moreover, gene expression of mitochondrial transcription factor a (mtTFA), interleukin-1β (IL-1β), B-cell lymphoma 2 (Bcl2) and BCL2-associated X protein (Bax), together with apoptotic morphological changes, were evaluated. After 2 h of rotenone incubation, increased ROS production and altered Δψm were observed, hours later resulting in DNA oxidative damage and apoptosis. Baicalin treatment at 50 µM counteracted rotenone toxicity by modulating the expression levels of some proteins involved in mitochondrial biogenesis and apoptosis. Interestingly, at higher baicalin concentrations, rotenone-induced alterations persisted.

CONCLUSIONS

These results give evidence that exposure to rotenone may promote the activation of THP-1 monocytes contributing to enhanced neurodegeneration. In this context, baicalin at low concentration exerts beneficial effects on mitochondrial function, and thus may prevent the onset of neurotoxic processes.

Molecular regulation after mucosal injury and regeneration in ulcerative colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammatory disease with a complex etiology. Intestinal mucosal injury is an important pathological change in individuals with UC. Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5+) intestinal stem cells (ISCs) exhibit self-renewal and high differentiation potential and play important roles in the repair of intestinal mucosal injury. Moreover, LGR5+ ISCs are intricately regulated by both the Wnt/β-catenin and Notch signaling pathways, which jointly maintain the function of LGR5+ ISCs. Combination therapy targeting multiple signaling pathways and transplantation of LGR5+ ISCs may lead to the development of new clinical therapies for UC.

The Outside-In Journey of Tissue Transglutaminase in Cancer

Tissue transglutaminase (TG2) is a member of the transglutaminase family that catalyzes Ca²⁺-dependent protein crosslinks and hydrolyzes guanosine 5′-triphosphate (GTP). The conformation and functions of TG2 are regulated by Ca²⁺ and GTP levels; the TG2 enzymatically active open conformation is modulated by high Ca²⁺ concentrations, while high intracellular GTP promotes the closed conformation, with inhibition of the TG-ase activity. TG2’s unique characteristics and its ubiquitous distribution in the intracellular compartment, coupled with its secretion in the extracellular matrix, contribute to modulate the functions of the protein. Its aberrant expression has been observed in several cancer types where it was linked to metastatic progression, resistance to chemotherapy, stemness, and worse clinical outcomes. The N-terminal domain of TG2 binds to the 42 kDa gelatin-binding domain of fibronectin with high affinity, facilitating the formation of a complex with β-integrins, essential for cellular adhesion to the matrix. This mechanism allows TG2 to interact with key matrix proteins and to regulate epithelial to mesenchymal transition and stemness. Here, we highlight the current knowledge on TG2 involvement in cancer, focusing on its roles translating extracellular cues into activation of oncogenic programs. Improved understanding of these mechanisms could lead to new therapeutic strategies targeting this multi-functional protein.

Transglutaminase 2 mediates UVB-induced matrix metalloproteinase-1 expression by inhibiting nuclear p65 degradation in dermal fibroblasts

Matrix metalloproteinases (MMPs) play a key role in tissue remodelling by cleaving extracellular matrix (ECM) components. In the skin, UV irradiation increases expression of MMPs that causes dysregulation of ECM homeostasis in dermis, leading to acceleration of skin aging. However, the mediator(s) that links UV irradiation to the upregulation of MMPs have not been fully defined. Previously, we showed that UVB irradiation activated transglutaminase 2 (TG2) in keratinocytes, eliciting an inflammatory response by activating NF-κB signalling. In this study, we reported the role of TG2 in mediating the UVB-induced expression of MMP-1. In human dermal fibroblasts, UVB irradiation enhanced the expression and activity of TG2, which in turn promotes the expression of MMP-1. Analyses of MMP-1 promoter showed that activation of the NF-κB signalling pathway, rather than AP-1, was responsible for the TG2-mediated upregulation of MMP-1. Moreover, Western blot analysis revealed that TG2 increased the activity of NF-κB by inhibiting degradation of p65 in the nucleus. Furthermore, ex vivo skin from TG2-knockout mice exhibited significantly reduced levels of MMP-1 compared to that from wild-type mice. These results indicate that TG2 functions as a mediator for the UVB-induced expression of MMP-1 in dermal fibroblasts, providing a new target for preventing skin photodamage.

Naringin derivatives as glucosamine-6-phosphate synthase inhibitors based preservatives and their biological evaluation

Glucosamine-6-Phosphate synthase enzyme has been targeted for development of better and safe preservative due to its role in microbial cell wall synthesis. In recent year's demand of preservatives for the food, cosmetics and pharmaceuticals have increased. Although, the available synthetic preservatives have associated unwanted adverse effects, soa chain of naringin derivatives were schemed synthesized and judged for antioxidant, antimicrobial, preservative efficacy, stability study and topical evaluation. Molecular docking resulted with excellent dock score and binding energy for compound 7, compound 6 and compound 1 as compared to standard drugs. Resultant data of antimicrobial activity revealed compound 7as most potent antimicrobial compound for P. mirabilis, P. aeruginosa, S. aureus, E. coli, C. albicans, and A. niger, respectively, as compared to the standard drugs. The preservative efficacy test of compound 7 in White Lotion USP showed the log cfu/mL value within prescribed limit of USP standard. Compound 7 stabilize the White lotion USP from microbial growth for a period of six months under accelerated storage condition. Compound 7 was further evaluated for toxicity by using the Draize test in rabbits and showed no sign of eye and skin irritation. The outcome demonstrated that synthesized naringin compounds showed glorious antioxidant, antimicrobial, preservative efficacy, stable and safe as compared to standards.

Elucidation of The Anti-Inflammatory Effect of Vanillin In Lps-Activated THP-1 Cells

Vanillin, a kind of phenolic compound, is naturally found in food and beverage and widely used as a flavoring agent. In view of the safety and universality of vanillin, exploring the functions of vanillin on human is of great value. Thus, lipopolysaccharide (LPS)-activated THP-1 cells were selected as the cell model to evaluate the anti-inflammatory effect of vanillin in this study. On the basis of the results, vanillin markedly suppressed the expression of inflammatory cytokines (that is, TNF-α, IL-1β, IL-6, and IL-8), mediators (NO, iNOS, PGE2, and COX-2), and NLRP3 inflammasome (that is, NLRP3, ASC, and caspase-1), blocked the LPS-induced activation of the NF-κB/IκBα/AP-1 signaling pathway, and activated the gene expression of the Nrf2/HO-1 signaling pathway. In addition, it was confirmed that vanillin was unable to react with LPS due to the results of quantification by HS-SPME-GC-MS. Hence, vanillin could effectively attenuate LPS-induced inflammatory response by regulating the expression of intracellular signaling pathways in THP-1 cells. It is a potent anti-inflammatory component found in food and beverage. These findings might contribute to the overall understanding of the potential health benefits of vanillin for food application. PRACTICAL APPLICATION: In this study, the anti-inflammatory effect of vanillin (VA) was evaluated by ELISA, real-time PCR, and western blot in LPS-induced THP-1 cells. The hypothesis that VA could react with LPS was excluded due to the results of quantification by HS-SPME-GC-MS. On the basis of the result, vanillin could effectively attenuate LPS-induced inflammatory response in THP-1 cells and was a potent anti-inflammatory component natural in food and beverage. These findings might contribute to the overall understanding of the potential health benefits of vanillin for food application.

IL-18 induced IL-23/IL-17 expression impairs Aβ clearance in cultured THP-1 and BV2 cells

Recent studies have provided overwhelming evidence of the involvement of microglia-related molecular networks in the pathogenesis of Alzheimer's diseases (AD). The potential involvement of pro-inflammatory cytokines interleukin (IL)-18, IL-23 and IL-17 on amyloid (Aβ) clearance is still unclear. In this study, we addressed that there might be a net relationship among IL-18, IL-23, and IL-17 and they can affect Aβ clearance in cultured macrophage/microglia cells. In human macrophage cell line THP-1, Aβ42 incubation could increase the expression of IL-18, IL-23 and IL-17 in a concentration dependent manner. THP-1 cell could clear Aβ42 in the culture medium time-dependently, but its capacity of Aβ clearance was impaired by IL-18, IL-23 or IL-17 treatment. Similarly, the capacity of the microglia cell line BV2 to clear Aβ42 was impaired by IL-18, IL-23 or IL-17 treatment. In co-cultures of BV2 with APP/PS1 neuron, Aβ was efficiently cleared by BV2 cell, but Aβ clearance was impaired by IL-18, IL-23 or IL-17 treatment. The effects of IL-18, IL-23 and IL-17 could be blocked by their corresponding neutralizing antibodies. In addition, the inhibitory effects of IL-18 were blocked by IL-23 or IL-17 neutralizing antibodies while the inhibitory effects of IL-23 were blocked by IL-17 neutralizing antibodies. Our study provides evidences showing that amyloid induced IL-18/IL-23/IL-17 axis could impair macrophage and microglia-mediated Aβ clearance. Thus, IL-18/IL-23/IL-17 axis might be a therapeutic target in AD.

Anti-inflammatory Mechanism Involved in 4-Ethylguaiacol-Mediated Inhibition of LPS-Induced Inflammation in THP-1 Cells

4-Ethylguaiacol, a common aroma compound of baijiu (a traditional Chinese alcoholic beverage), was assessed for its potential anti-inflammatory effects in an LPS-induced THP-1 cell model. To characterize the effect of 4-ethylguaiacol on the LPS-induced inflammatory response, the mRNA and protein expression of the TLR4-MAPKs-NF-κB-IκBα-AP-1, Nrf2-HO-1, and AMPK-SIRT1 pathways were monitored by ELISA, real-time PCR, and Western blotting. On the basis of the result, 4-ethylguaiacol exerted anti-inflammatory effects at doses of 10, 100, and 500 μM (the concentration of 4-ethylguaiacol in gujinggong baijiu is in the range of 1044 ± 44 to 1661 ± 63 μg/L) and significantly mitigated LPS-induced inflammation via activation of the Nrf2-HO-1 and AMPK-SIRT1 pathways and inhibition of NF-κB and AP-1 activation, thereby markedly inhibiting the activation of inflammasomes and down-regulating the production of inflammatory cytokines. These results indicated that 4-ethylguaiacol could reverse LPS-induced inflammatory responses and is a natural, potent anti-inflammatory component in baijiu.

Transglutaminases in Monocytes and Macrophages

Macrophages are key players in various inflammatory disorders and pathological conditions via phagocytosis and orchestrating immune responses. They are highly heterogeneous in terms of their phenotypes and functions by adaptation to different organs and tissue environments. Upon damage or infection, monocytes are rapidly recruited to tissues and differentiate into macrophages. Transglutaminases (TGs) are a family of structurally and functionally related enzymes with Ca²⁺-dependent transamidation and deamidation activity. Numerous studies have shown that TGs, particularly TG2 and Factor XIII-A, are extensively involved in monocyte- and macrophage-mediated physiological and pathological processes. In the present review, we outline the current knowledge of the role of TGs in the adhesion and extravasation of monocytes, the expression of TGs during macrophage differentiation, and the regulation of TG2 expression by various pro- and anti-inflammatory mediators in macrophages. Furthermore, we summarize the role of TGs in macrophage phagocytosis and the understanding of the mechanisms involved. Finally, we review the roles of TGs in tissue-specific macrophages, including monocytes/macrophages in vasculature, alveolar and interstitial macrophages in lung, microglia and infiltrated monocytes/macrophages in central nervous system, and osteoclasts in bone. Based on the studies in this review, we conclude that monocyte- and macrophage-derived TGs are involved in inflammatory processes in these organs. However, more in vivo studies and clinical studies during different stages of these processes are required to determine the accurate roles of TGs, their substrates, and the mechanisms-of-action.