Activated toll-like receptor 4 is involved in oridonin-induced phagocytosis via promotion of migration and autophagy-lysosome pathway in RAW264.7 macrophages

Natural Compounds Oridonin and Shikonin Exhibit Potentially Beneficial Regulatory Effects on Select Functions of Microglia

Accumulating evidence indicates that the adverse neuroimmune activation of microglia, brain immunocytes that support neurons, contributes to a range of neuroinflammatory disorders, including Alzheimer's disease. Correcting the abnormal functions of microglia is a potential therapeutic strategy for these diseases. Nucleotide-binding domain leucine-rich repeat and pyrin domain-containing receptor (NLRP) 3 inflammasomes are implicated in adverse microglial activation and their inhibitors, such as the natural compounds oridonin and shikonin, reduce microglial immune responses. We hypothesized that some of the beneficial effects of oridonin and shikonin on microglia are independent of their suppression of NLRP3 inflammasomes. Murine and human microglia-like cells were stimulated with bacterial lipopolysaccharide (LPS) only, which did not induce NLRP3 inflammasome activation or the resulting secretion of interleukin (IL)-1β, allowing for the identification of other anti-inflammatory effects. Under these experimental conditions, both oridonin and shikonin reduced nitric oxide (NO) secretion and the cytotoxicity of BV-2 murine microglia towards HT-22 murine neuronal cells, but upregulated BV-2 cell phagocytic activity. Only oridonin inhibited the secretion of tumor necrosis factor (TNF) by stimulated BV-2 microglia, while only shikonin suppressed the respiratory burst response of human HL-60 microglia-like cells. This observed discrepancy indicates that these natural compounds may have different molecular targets in microglia. Overall, our results suggest that oridonin and shikonin should be further investigated as pharmacological agents capable of correcting dysfunctional microglia, supporting their potential use in neuroinflammatory disorders.

Microglial autophagy in cerebrovascular diseases

Microglia are considered core regulators for monitoring homeostasis in the brain and primary responders to central nervous system (CNS) injuries. Autophagy affects the innate immune functions of microglia. Recently some evidence suggests that microglial autophagy is closely associated with brain function in both ischemic stroke and hemorrhagic stroke. Herein, we will discuss the interaction between autophagy and other biological processes in microglia under physiological and pathological conditions and highlight the interaction between microglial metabolism and autophagy. In the end, we focus on the effect of microglial autophagy in cerebrovascular diseases.

Cordyceps militaris Immunomodulatory Protein Promotes the Phagocytic Ability of Macrophages through the TLR4-NF-κB Pathway

Enhancing the phagocytosis of immune cells with medicines provides benefits to the physiological balance by removing foreign pathogens and apoptotic cells. The fungal immunomodulatory protein (FIP) possessing various immunopotentiation functions may be a good candidate for such drugs. However, the effect and mechanism of FIP on the phagocytic activity is limitedly investigated. Therefore, the present study determined effects of Cordyceps militaris immunomodulatory protein (CMIMP), a novel FIP reported to induce cytokines secretion, on the phagocytosis using three different types of models, including microsphere, Escherichia Coli and Candida albicans. CMIMP not only significantly improved the phagocytic ability (p < 0.05), but also enhanced the bactericidal activity (p < 0.05). Meanwhile, the cell size, especially the cytoplasm size, was markedly increased by CMIMP (p < 0.01), accompanied by an increase in the F-actin expression (p < 0.001). Further experiments displayed that CMIMP-induced phagocytosis, cell size and F-actin expression were alleviated by the specific inhibitor of TLR4 (p < 0.05). Similar results were observed in the treatment with the inhibitor of the NF-κB pathway (p < 0.05). In conclusion, it could be speculated that CMIMP promoted the phagocytic ability of macrophages through increasing F-actin expression and cell size in a TLR4-NF-κB pathway dependent way.

Immunomodulatory activity of puerarin in RAW264.7 macrophages and cyclophosphamide-induced immunosuppression mice

CONTEXT

Puerarin, a natural isoflavone extracted from Radix puerariae, is famous for treating various cardiovascular and cerebrovascular diseases. However, little is known about its direct immunomodulatory activity.

OBJECTIVE

This study was designed to investigate the in vitro and in vivo immunomodulatory effects of Radix puerariae by using the murine monocyte-macrophage cell line RAW264.7 and immunosuppressed cyclophosphamide-induced mice.

METHODS

MTT and neutral red phagocytosis assays were conducted to evaluate the in vitro immunomodulatory activities of puerarin on cell viability and phagocytosis by measuring the proliferation, phagocytic, nitric oxide (NO) ability, and TNF-α production ability of stimulated and lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Immunosuppressed cyclophosphamide-induced mice were used to evaluate the in vivo immunomodulatory activities of puerarin by measuring IL-4 and IFN-γ, the serum half hemolysis value, spleen and thymus index, and proliferation assay for splenic lymphocytes.

RESULTS AND DISCUSSION

Results showed that puerarin improves immunomodulatory activity by increasing cell proliferation, cell phagocytosis, and NO secretion in RAW264.7 macrophages and reduces the abnormal immunologic activity by decreasing cell phagocytosis and NO secretion in LPS-stimulated RAW264.7 macrophages. In addition, puerarin enhanced the immunologic activity of cyclophosphamide-induced immunosuppression mice by increasing the secretion of NO, IFN-γ, and IL-4, the serum half hemolysis value (HC₅₀), the spleen and thymus index, and proliferation for splenic lymphocytes.

CONCLUSION

Puerarin exhibited an upregulated immunomodulatory effect on RAW264.7 macrophages and immunosuppression mice. In addition, puerarin had a downregulated immunomodulatory effect on RAW264.7 macrophages. The results suggest that puerarin could be a promising immunomodulator to assist in the treatment of tumors.

Treponema pallidum Dysregulates Monocytes and Promotes the Expression of IL-1β and Migration in Monocytes Through the mTOR Signaling Pathway

Monocytes are widely involved in the body's defense response, and abnormally regulated monocyte subsets are closely related to the pathogenesis of various diseases. It is unclear whether Treponema pallidum (Tp) dysregulates monocyte subsets and impacts the functions of monocytes. This study aims to analyze the distribution of monocyte subsets in syphilis patients and the effect of Tp on monocyte functions to explore the pathogenesis of syphilis. Flow cytometry was employed to detect monocyte subsets. With or without pre-treatment with rapamycin, THP-1 cell migration stimulated by Tp was investigated by a Transwell migration assay, and THP-1 cell phagocytosis was studied using fluorescent microspheres. IL-1β and TNF-α expression was quantified by PCR and flow cytometry, while LC3 and mTOR were investigated in Tp-exposed THP-1 cells using western blotting. Tp infection led to an increase in the proportion of CD14⁺⁺CD16⁺ monocytes and a decrease in the proportion of CD14⁺⁺CD16^- monocytes. In addition, Tp promoted monocyte (THP-1) CD14 and CD16 expression in vitro, induced the expression of IL-1β and TNF-α in a dose-dependent manner and promoted the migration and autophagy of monocytes. Furthermore, mTOR phosphorylation on monocytes was stimulated by Tp, and the levels peaked at 30 min. Pre-treatment with rapamycin (mTOR inhibitor) attenuated the expression of IL-1β and migration in Tp-exposed THP-1 cells. Tp abnormally regulates monocyte subsets and promotes migration, autophagy, and the expression of IL-1β and TNF-α in THP-1 cells. Meanwhile, the mTOR affected the expression of IL-1β and migration in Tp-exposed THP-1 cells. This study is important as it sheds light on the mechanism by which monocytes interact with Tp during infection.

Paeonol promotes the phagocytic ability of macrophages through confining HMGB1 to the nucleus

Phagocytosis is a basic immune response to the pathogens invading. Immunosuppression may occur in diseases like sepsis and cancer, and cause a low phagocytic ability of phagocytes. High mobility group protein B1 (HMGB1) is a DNA chaperone which is closely related to the phagocytosis. Nonetheless, its influence on phagocytosis is still controversial. We found that paeonol could inhibit the translocation of HMGB1 from the nucleus to the cytoplasm, it may have an impact on phagocytosis. In the present study, we performed in vivo and in vitro experiments to investigate the influence of paeonol on phagocytosis. Zymosan was used to test the phagocytic function of macrophages. Our results showed that paeonol promotes the phagocytosis of macrophages through confining HMGB1 to the nucleus. Through interacting with P53, the nuclear HMGB1 keep it in the nucleus and decrease the negative influence of P53 on the phosphorylation of Focal Adhesion Kinase (FAK). The increasing of phosphorylated FAK promotes the formation of pseudopod and enhances the phagocytic ability of macrophages.

Xenophagy in innate immunity: A battle between host and pathogen

Autophagy is a fundamental bulk intracellular degradation and recycling process that directly eliminates intracellular microorganisms through "xenophagy" in various types of cells, especially in macrophages. Meanwhile, bacteria have evolved strategies and cellular self-defense mechanisms to prevent autophagosomal degradation and even attack the immune system of host. The lack of knowledge about the roles of autophagy in innate immunity severely limits our understanding of host defensive system and the development of farmed industry consisting of aquaculture. Increasing evidence in recent decades has shown the importance of autophagy. This review focuses on the triggering of xenophagy, targeting of invading pathogens to autophagosomes and elimination in the autophagolysosomes during pathogen infection. How the pathogen can escape from the xenophagy pathway was also discussed. Overall, we aim to reduce diseases and improve industrial production in aquaculture by providing theoretical and technical guidance on xenophagy.

Modulation of neuropathology and cognitive deficits by lipopolysaccharide preconditioning in a mouse pilocarpine model of status epilepticus

Recent studies indicate that microglia may play a critical role in epileptogenesis during the early post-status epilepticus (SE) period. In this study, we aimed to elucidate the effects of preconditioning of microglia with lipopolysaccharide (LPS) on neuropathology and cognitive deficits in a mouse pilocarpine model of SE. Mice were treated with an intraperitoneal injection of LPS 24 h before SE induction. The open field test at 13 days after SE showed that LPS preconditioning suppressed SE-induced hyperactivity. The Y-maze test at 14 days after SE showed that LPS preconditioning ameliorated SE-induced working memory impairment. The extent of neuronal damage was decreased by LPS preconditioning in the hippocampus of mice euthanized at 15 days after SE. Gene profile analysis of hippocampal microglia at 15 days after SE showed that the expression level of interleukin-1β was increased by SE induction but decreased by LPS preconditioning. By contrast, SE induction increased the expression levels of phagocytosis-related genes, and LPS preconditioning further enhanced their expression. Interestingly, LPS preconditioning increased the numerical density of hippocampal microglia expressing the 5D4 keratan sulfate epitope, a population of cells known to be involved in phagocytosis. The voxel density of glutamatergic synapses was increased by SE induction but decreased by LPS preconditioning, while GABAergic synapses were not affected by these procedures. Our findings indicate that LPS preconditioning may in part alleviate SE-related abnormal synaptogenesis and cognitive deficits, and also suggest that modulation of microglial activation during the early post-SE period may be a novel strategy for epilepsy treatment.

Oridonin Alleviates IRI-Induced Kidney Injury by Inhibiting Inflammatory Response of Macrophages via AKT-Related Pathways

BACKGROUND Acute kidney injury (AKI) is one of the most common complications in clinic, but there is still no effective treatment. Oridonin, extracted from Rabdosia rubescens, has been identified to promote inhibitory effects on tumor, inflammatory and fibrosis by previous study. This study aimed to assess the kidney-protective role of Oridonin in AKI and the underlying mechanism by which Oridonin improves AKI in vivo and inhibits inflammation in LPS-induced bone marrow-derived macrophages (BMDM) in vitro. MATERIAL AND METHODS SPF C57BL/6J male mice (8 - 10 weeks old, body weight 20 - 25 g) were divided into 3 groups - sham group, AKI group, and Oridonin-treated AKI group - with 6 mice in each group. In the in vitro study, LPS-induced inflammatory BMDM cells were treated with Oridonin and agonist of AKT. The expression and secretion levels of inflammation-related indicators and AKT-related signaling molecules were detected by real-time PCR, ELISA, Western blot, and immunofluorescence. Also, various methods are used to assess renal function and pathological changes. RESULTS The results showed that Oridonin treatment significantly improved the serum creatinine and BUN levels in AKI mice. Interestingly, treatment with Oridonin also resulted in decreased the infiltration of macrophages in renal tissues of AKI mice, which was associated with decreased expression and activation of AKT and its related signaling pathways, such as NF-kappaB and STAT3, suggesting that Oridonin attenuates AKI kidney injury via a mechanism associated with reducing the inflammatory response of macrophages in the AKI kidney. This was investigated in vitro in macrophages, and the results showed that Oridonin reduced the LPS-stimulated inflammatory response in macrophages. Mechanistically, the addition of Oridonin reversed LPS-induced downregulation of AKT, NF-kappaB, and STAT3 expression and inflammatory response in macrophages, suggesting that Oridonin has a protective role, via the AKT-related signaling pathways, in reducing the inflammatory response of macrophages in AKI mice. This was further confirmed by adding agonist of AKT of IGF-1 to block the inhibitory effect of Oridonin on inflammatory response in vitro. CONCLUSIONS Oridonin ameliorates AKI kidney injuries by suppressing AKT-mediated inflammatory response of macrophages.