A critical role of toll-like receptor 2 (TLR2) and its' in vivo ligands in radio-resistance

A comprehensive review of sensors of radiation-induced damage, radiation-induced proximal events, and cell death

Radiation, a universal component of Earth's environment, is categorized into non-ionizing and ionizing forms. While non-ionizing radiation is relatively harmless, ionizing radiation possesses sufficient energy to ionize atoms and disrupt DNA, leading to cell damage, mutation, cancer, and cell death. The extensive use of radionuclides and ionizing radiation in nuclear technology and medical applications has sparked global concern for their capacity to cause acute and chronic illnesses. Ionizing radiation induces DNA damage either directly through strand breaks and base change or indirectly by generating reactive oxygen species (ROS) and reactive nitrogen species (RNS) via radiolysis of water. This damage triggers a complex cellular response involving recognition of DNA damage, cell cycle arrest, DNA repair mechanisms, release of pro-inflammatory cytokines, and cell death. This review focuses on the mechanisms of radiation-induced cellular damage, recognition of DNA damage and subsequent activation of repair processes, and the critical role of the innate immune response in resolution of the injury. Emphasis is placed on pattern recognition receptors (PRRs) and related receptors that detect damage-associated molecular patterns (DAMPs) and initiate downstream signaling pathways. Radiation-induced cell death pathways are discussed in detail. Understanding these processes is crucial for developing strategies to mitigate the harmful effects of radiation and improve therapeutic outcomes.

The TLR2/TLR6 ligand FSL-1 mitigates radiation-induced hematopoietic injury in mice and nonhuman primates

Thrombocytopenia, hemorrhage, anemia, and infection are life-threatening issues following accidental or intentional radiation exposure. Since few therapeutics are available, safe and efficacious small molecules to mitigate radiation-induced injury need to be developed. Our previous study showed the synthetic TLR2/TLR6 ligand fibroblast stimulating lipopeptide (FSL-1) prolonged survival and provided MyD88-dependent mitigation of hematopoietic acute radiation syndrome (H-ARS) in mice. Although mice and humans differ in TLR number, expression, and function, nonhuman primate (NHP) TLRs are like those of humans; therefore, studying both animal models is critical for drug development. The objectives of this study were to determine the efficacy of FSL-1 on hematopoietic recovery in small and large animal models subjected to sublethal total body irradiation and investigate its mechanism of action. In mice, we demonstrate a lack of adverse effects, an easy route of delivery (subcutaneous) and efficacy in promoting hematopoietic progenitor cell proliferation by FSL-1. NHP given radiation, followed a day later with a single subcutaneous administration of FSL-1, displayed no adversity but showed elevated hematopoietic cells. Our analyses revealed that FSL-1 promoted red blood cell development and induced soluble effectors following radiation exposure. Cytologic analysis of bone marrow aspirates revealed a striking enhancement of mononuclear progenitor cells in FSL-1-treated NHP. Combining the efficacy of FSL-1 in promoting hematopoietic cell recovery with the lack of adverse effects induced by a single administration supports the application of FSL-1 as a viable countermeasure against H-ARS.

Cordyceps sinensis aqueous extract regulates the adaptive immunity of mice subjected to 60 Co γ irradiation

Cordyceps sinensis (CS) is a traditional Chinese medicine that is known for treating various diseases, and particularly for exerting therapeutic effects in immune disorders. The adaptive immunoregulatory effects of CS aqueous extract (CSAE) on γ-irradiated mice have not been reported previously. The study aimed to evaluate the therapeutic effects of CSAE in mice immunosuppressed by irradiation. We observed that CSAE administration significantly increased body weight and spleen index, as well as the number of white blood cells, lymphocytes, and platelets in peripheral blood, T and B lymphocytes in spleen tissue, and total serum immunoglobulins in irradiated mice, whereas total serum pro-inflammatory cytokine levels were decreased. Collectively, CSAE maintained the structural integrity of spleen tissue and repaired its damage in irradiated mice as shown by hematoxylin and eosin staining, and decreased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive splenocytes. Mechanistically, CSAE upregulated Bcl-2, and downregulated Bax and cleaved caspase-3 in spleen of irradiated mice. However, there were no significant differences in red blood cells and neutrophils in different groups. The results revealed that CSAE had protective effects against irradiation-induced immunosuppression, which was likely associated with an antiapoptotic effect and the regulation of adaptive immunity.

Ionizing radiation and toll like receptors: A systematic review article

Ionizing radiation, including X and gamma rays, are used for various purposes such as; medicine, nuclear power, research, manufacturing, food preservation and construction. Furthermore, people are also exposed to ionizing radiation from their workplace or the environment. Apart from DNA fragmentation resulting in apoptosis, several additional mechanisms have been proposed to describe how radiation can alter human cell functions. Ionizing radiation may alter immune responses, which are the main cause of human disorders. Toll like receptors (TLRs) are important human innate immunity receptors which participate in several immune and non-immune cell functions including, induction of appropriate immune responses and immune related disorders. Based on the role played by ionizing radiation on human cell systems, it has been hypothesized that radiation may affect immune responses. Therefore, the main aim of this review article is to discuss recent information regarding the effects of ionizing radiation on TLRs and their related disorders.

Tumor suppressor role of miR-876-5p in gastric cancer

Gastric cancer (GC) is the second most common cancer cause of cancer-related mortality worldwide. Recent studies have demonstrated the function of microRNAs (miRNAs) in the pathogenesis of GC. miR-876-5p demonstrated an antitumor role in hepatocellular carcinoma and lung cancer; however, the function of miR-876-5p has not yet been fully identified in GC. Thus, the present study aimed to investigate the role of miR-876-5p in GC. The results of the present study demonstrated low expression levels of miR-876-5p in GC tumor tissues. Furthermore, overexpression of miR-876-5p inhibited GC cell proliferation and promoted apoptosis, whilst miR-876-5p knockdown promoted GC cell proliferation and decreased cisplatin sensitivity of GC cells. Transforming growth factor β-receptor 1 was demonstrated to be a potential target gene of miR-876-5p. Overall, the results of the present study suggest that miR-876-5p plays an antitumor role in GC.

The mechanism for the radioprotective effects of zymosan-A in mice

It proved that Zymosan-A protected the haematopoietic system from radiation-induced damage via Toll-Like Receptor2 in our previous study. In this study, we investigated the potential mechanism for the radioprotective effects of Zymosan-A. The mice were treated with Zymosan-A (50 mg/kg, dissolved in NS) via peritoneal injection 24 and 2 hours before ionizing radiation. Apoptosis of bone marrow cells and the levels of IL-6, IL-12, G-CSF and GM-CSF were evaluated by flow cytometry assay. DNA damage was determined by γ-H2AX foci assay. In addition, RNA sequencing was performed to identify differentially expressed genes (DEGs). Zymosan-A protected bone marrow cells from radiation-induced apoptosis, up-regulated IL-6, IL-12, G-CSF and GM-CSF in bone marrow cells. Zymosan-A also protected cells from radiation-induced DNA damage. Moreover, RNA sequencing analysis revealed that Zymosan-A induced 131 DEGs involved in the regulation of immune system process and inflammatory response. The DEGs were mainly clustered in 18 KEGG pathways which were also associated with immune system processes. Zymosan-A protected bone marrow cells from radiation-induced apoptosis and up-regulated IL-6, IL-12, G-CSF and GM-CSF. Moreover, Zymosan-A might also exhibit radioprotective effects through regulating immune system process and inflammatory response. These results provided new knowledge regarding the radioprotective effect of Zymosan-A.

Toll-like receptor 2 and 4 have opposing roles in the pathogenesis of cigarette smoke-induced chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is the third leading cause of morbidity and death and imposes major socioeconomic burdens globally. It is a progressive and disabling condition that severely impairs breathing and lung function. There is a lack of effective treatments for COPD, which is a direct consequence of the poor understanding of the underlying mechanisms involved in driving the pathogenesis of the disease. Toll-like receptor (TLR)2 and TLR4 are implicated in chronic respiratory diseases, including COPD, asthma and pulmonary fibrosis. However, their roles in the pathogenesis of COPD are controversial and conflicting evidence exists. In the current study, we investigated the role of TLR2 and TLR4 using a model of cigarette smoke (CS)-induced experimental COPD that recapitulates the hallmark features of human disease. TLR2, TLR4, and associated coreceptor mRNA expression was increased in the airways in both experimental and human COPD. Compared with wild-type (WT) mice, CS-induced pulmonary inflammation was unaltered in TLR2-deficient ( Tlr2-/-) and TLR4-deficient ( Tlr4-/-) mice. CS-induced airway fibrosis, characterized by increased collagen deposition around small airways, was not altered in Tlr2-/- mice but was attenuated in Tlr4-/- mice compared with CS-exposed WT controls. However, Tlr2-/- mice had increased CS-induced emphysema-like alveolar enlargement, apoptosis, and impaired lung function, while these features were reduced in Tlr4-/- mice compared with CS-exposed WT controls. Taken together, these data highlight the complex roles of TLRs in the pathogenesis of COPD and suggest that activation of TLR2 and/or inhibition of TLR4 may be novel therapeutic strategies for the treatment of COPD.

The Toll-Like Receptor 2/6 Agonist, FSL-1 Lipopeptide, Therapeutically Mitigates Acute Radiation Syndrome

Risks of radiation exposure from nuclear incidents and cancer radiotherapy are undeniable realities. These dangers urgently compel the development of agents for ameliorating radiation–induced injuries. Biologic pathways mediated by myeloid differentiation primary response gene 88 (MyD88), the common adaptor for toll–like receptor (TLR) and Interleukin–1 receptor signaling, are critical for radioprotection. Treating with agonists prior to radiation enhances survival by activating TLR signaling, whereas radiomitigating TLR–activating therapeutics given after exposure are less defined. We examine the radiomitigation capability of TLR agonists and identify one that is superior for its efficacy and reduced toxic consequences compared to other tested agonists. We demonstrate that the synthetic TLR2/6 ligand Fibroblast–stimulating lipopeptide (FSL–1) substantially prolongs survival in both male and female mice when administered 24 hours after radiation and shows MyD88–dependent function. FSL–1 treatment results in accelerated hematopoiesis in bone marrow, spleen and periphery, and augments systemic levels of hematopoiesis–stimulating factors. The ability of FSL–1 to stimulate hematopoiesis is critical, as hematopoietic dysfunction results from a range of ionizing radiation doses. The efficacy of a single FSL–1 dose for alleviating radiation injury while protecting against adverse effects reveals a viable radiation countermeasures agent.

Involvement of reactive oxygen species in ionizing radiation-induced upregulation of cell surface Toll-like receptor 2 and 4 expression in human monocytic cells

Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen-associated molecular patterns and are indispensable for antibacterial and antiviral immunity. Our previous report showed that ionizing radiation increases the cell surface expressions of TLR2 and TLR4 and enhances their responses to agonists in human monocytic THP1 cells. The present study investigated how ionizing radiation increases the cell surface expressions of TLR2 and TLR4 in THP1 cells. The THP1 cells treated or not treated with pharmaceutical agents such as cycloheximide and N-acetyl-L-cysteine (NAC) were exposed to X-ray irradiation, following which the expressions of TLRs and mitogen-activated protein kinase were analyzed. X-ray irradiation increased the mRNA expressions of TLR2 and TLR4, and treatment with a protein synthesis inhibitor cycloheximide abolished the radiation-induced upregulation of their cell surface expressions. These results indicate that radiation increased those receptors through de novo protein synthesis. Furthermore, treatment with an antioxidant NAC suppressed not only the radiation-induced upregulation of cell surface expressions of TLR2 and TLR4, but also the radiation-induced activation of the c-Jun N-terminal kinase (JNK) pathway. Since it has been shown that the inhibitor for JNK can suppress the radiation-induced upregulation of TLR expression, the present results suggest that ionizing radiation increased the cell surface expressions of TLR2 and TLR4 through reactive oxygen species-mediated JNK activation.

Differences in sustained alterations in protein expression between livers of mice exposed to high-dose-rate and low-dose-rate radiation

Molecular mechanisms of radiation dose-rate effects are not well understood. Among many possibilities, long-lasting sustained alterations in protein levels would provide critical information. To evaluate sustained effects after acute and chronic radiation exposure, we analyzed alterations in protein expression in the livers of mice. Acute exposure consisted of a lethal dose of 8 Gy and a sublethal dose of 4 Gy, with analysis conducted 6 days and 3 months after irradiation, respectively. Chronic irradiation consisted of a total dose of 8 Gy delivered over 400 days (20 mGy/day). Analyses following chronic irradiation were done immediately and at 3 months after the end of the exposure. Based on antibody arrays of protein expression following both acute lethal and sublethal dose exposures, common alterations in the expression of two proteins were detected. In the sublethal dose exposure, the expression of additional proteins was altered 3 months after irradiation. Immunohistochemical analysis showed that the increase in one of the two commonly altered proteins, MyD88, was observed around blood vessels in the liver. The alterations in protein expression after chronic radiation exposure were different from those caused by acute radiation exposures. Alterations in the expression of proteins related to inflammation and apoptosis, such as caspase 12, were observed even at 3 months after the end of the chronic radiation exposure. The alterations in protein expression depended on the dose, the dose rate, and the passage of time after irradiation. These changes could be involved in long-term effects of radiation in the liver.

Heat-killed salmonella typhimurium (HKST) protects mice against radiation in TLR4-dependent manner

It is urgently required to develop novel safe and effective radioprotectors to alleviate radiation damages. Recently, several toll like receptors (TLRs), including TLR2, TLR4, TLR5, TLR9, have been proved to exert protective effects against ionizing radiation. Due to different tissue-distribution and distinct functions of TLRs, we hypothesized that co-activation of multiple TLRs simultaneously may produce extensive and stronger radioprotective effects. In this study, we found the co-agonist of TLR2, TLR4 and TLR5, heat-killed salmonella typhimurium (HKST) significantly inhibited radiation-induced cell apoptosis, increased cell survival and alleviated DNA damage. HKST also prolonged animal survival and protected radiosensitive tissues against radiation damages, such as bone marrow, spleen and testis. Decrease of CD4+ and CD8+ cells were also reversed by HKST treatment. By using TLR2 and TLR4 knockout mice, we found that most of radioprotective effects of HKST were abrogated in TLR4 knock out mice. And HKST failed to inhibited cell apoptosis in TLR5 knock down cells. In conclusion, we demonstrated that HKST effectively protected cells and radiosensitive tissues against radiation injury in a TLR4 biased mechanism, suggesting HKST as a potential radioprotector with low toxicity.