Toll-Like recepctors (TLRs) and retinoic acid inducible gene – I (RIG-I) activation by viral analogs in bovine endometrial cells

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Toll-like receptor 9 activation: a novel mechanism linking placenta-derived mitochondrial DNA and vascular dysfunction in pre-eclampsia

Emerging evidence suggests that in addition to being the 'power houses' of our cells, mitochondria facilitate effector responses of the immune system. Cell death and injury result in the release of mtDNA (mitochondrial DNA) that acts via TLR9 (Toll-like receptor 9), a pattern recognition receptor of the immune system which detects bacterial and viral DNA but not vertebrate DNA. The ability of mtDNA to activate TLR9 in a similar fashion to bacterial DNA stems from evolutionarily conserved similarities between bacteria and mitochondria. mtDNA may be the trigger of systemic inflammation in pathologies associated with abnormal cell death. PE (pre-eclampsia) is a hypertensive disorder of pregnancy with devastating maternal and fetal consequences. The aetiology of PE is unknown and removal of the placenta is the only effective cure. Placentas from women with PE show exaggerated necrosis of trophoblast cells, and circulating levels of mtDNA are higher in pregnancies with PE. Accordingly, we propose the hypothesis that exaggerated necrosis of trophoblast cells results in the release of mtDNA, which stimulates TLR9 to mount an immune response and to produce systemic maternal inflammation and vascular dysfunction that lead to hypertension and IUGR (intra-uterine growth restriction). The proposed hypothesis implicates mtDNA in the development of PE via activation of the immune system and may have important preventative and therapeutic implications, because circulating mtDNA may be potential markers of early detection of PE, and anti-TLR9 treatments may be promising in the management of the disease.

Toll-like receptors 2, 3 and 4 and thymic stromal lymphopoietin expression in fatal asthma

Background Airway inflammation in asthma involves innate immune responses. Toll-like receptors (TLRs) and thymic stromal lymphopoietin (TSLP) are thought to be involved in airway inflammation, but their expression in asthmatics both large and small airways has not been investigated. Objective To analyse the expression of TLR2, TLR3, TLR4 and TSLP in large and small airways of asthmatics and compare their expression in smoking and non-smoking asthmatics; to investigate whether TLR expression is associated with eosinophilic or neutrophilic airway inflammation and with Mycoplasma pneumoniae and Chlamydophila pneumoniae infection. Methods Using immunohistochemistry and image analysis, we investigated TLR2, TLR3, TLR4 and TSLP expression in large and small airways of 24 victims of fatal asthma, FA, (13 non-smokers, 11 smokers) and nine deceased control subjects (DCtrl). TLRs were also measured in 18 mild asthmatics (MA) and 12 healthy controls (HCtrl). M. pneumoniae and C. pneumoniae in autopsy lung tissue were analysed using real-time polymerase chain reaction. Airway eosinophils and neutrophils were measured in all subjects. Results Fatal asthma patients had higher TLR2 in the epithelial and outer layers of large and small airways compared with DCtrls. Smoking asthmatics had lower TLR2 levels in the inner and outer layers of the small airways than non-smoking asthmatics. TSLP was increased in the epithelial and outer layers of the large airways of FA. FA patients had greater TLR3 expression in the outer layer of large airways and greater TLR4 expression in the outer layer of small airways. Eosinophilic airway inflammation was associated with TLR expression in the epithelium of FA. No bacterial DNA was detected in FA or DCtrls. MA and HCtrls had only a small difference in TLR3 expression. Conclusions and Clinical Relevance Increased expression of TLR 2, 3 and 4 and TSLP in fatal asthma may contribute to the acute inflammation surrounding asthma deaths.

Toll-like receptor 3: implications for proinflammatory microenvironment in human breast cancer

Under many circumstances, the host constituents that are found in the tumor microenvironment support a malignancy network and provide the cancer cells with advantages in proliferation, invasiveness and metastasis establishment at remote organs. It is known that Toll like receptors (TLRs) are expressed not only on immune cells but also on cancer cells and it has suggested a deleterious role for TLR3 in inflammatory disease. Hypothesizing that altered IFN gamma signaling may be a key mechanism of immune dysfunction common to cancer as well CXCR4 is overexpressed among breast cancer patients, the mRNA expression of TLR3, CXCR4 and IFN gamma in breast cancer tumor tissues was investigated. No statistically significant differences in the expression of CXCR4 mRNA, IFN gamma and TLR3 between healthy and tumor tissues was observed, however, it was verified a positive correlation between mRNA relative expression of TLR3 and CXCR4 (p < 0.001), and mRNA relative expression of TLR3 was significantly increased in breast cancer tumor tissue when compared to healthy mammary gland tissue among patients expressing high IFN gamma (p = 0.001). Since the tumor microenvironment plays important roles in cancer initiation, growth, progression, invasion and metastasis, it is possible to propose that an overexpression of IFN gamma mRNA due to the pro-inflammatory microenvironment can lead to an up-regulation of CXCR4 mRNA and consequently to an increased TLR3 mRNA expression even among nodal negative patients. In the future, a comprehensive study of TLR3, CXCR4 and IFN gamma axis in primary breast tumors and corresponding healthy tissues will be crucial to further understanding of the cancer network.

Toll-like receptor-3-induced mitochondrial dysfunction in cultured human hepatocytes

Several studies have shown the presence of liver mitochondrial dysfunction during sepsis. TLR3 recognizes viral double-stranded RNA and host endogenous cellular mRNA released from damaged cells. TLR3 ligand amplifies the systemic hyperinflammatory response observed during sepsis and in sepsis RNA escaping from damaged tissues/cells may serve as an endogenous ligand for TLR3 thereby modulating immune responses. This study addressed the hypothesis that TLR3 might regulate mitochondrial function in cultured human hepatocytes. HepG2 cells were exposed to TLR-3 ligand (dsRNA--polyinosine-polycytidylic acid; Poly I:C) and mitochondrial respiration was measured. Poly I:C induced a reduction in maximal mitochondrial respiration of human hepatocytes which was prevented partially by preincubation with cyclosporine A (a mitochondrial permeability transition pore-opening inhibitor). Poly-I:C induced activation of NF-κB, and the mitochondrial dysfunction was accompanied by caspase-8 but not caspase-3 activation and by no major alterations in cellular or mitochondrial ultrastructure.

Protein level expression of Toll-like receptors 2, 4 and 9 in renal disease

Toll-like receptors (TLR) recognize a variety of ligands, including pathogen-associated molecular patterns and link innate and adaptive immunity. Individual receptors can be up-regulated during infection and inflammation. We examined the expression of selected TLRs at the protein level in various types of renal disease.

Role of Toll interleukin-1 receptor (IL-1R) 8, a negative regulator of IL-1R/Toll-like receptor signaling, in resistance to acute Pseudomonas aeruginosa lung infection

Toll interleukin-1 receptor (IL-1R) 8 (TIR8), also known as single Ig IL-1 receptor (IL-R)-related molecule, or SIGIRR, is a member of the IL-1R-like family, primarily expressed by epithelial cells. Current evidence suggests that TIR8 plays a nonredundant role as a negative regulator in vivo under different inflammatory conditions that are dependent on IL-R and Toll-like receptor (TLR) activation. In the present study, we examined the role of TIR8 in innate resistance to acute lung infections caused by Pseudomonas aeruginosa, a Gram-negative pathogen responsible for life-threatening infections in immunocompromised individuals and cystic fibrosis patients. We show that Tir8 deficiency in mice was associated with increased susceptibility to acute P. aeruginosa infection, in terms of mortality and bacterial load, and to exacerbated local and systemic production of proinflammatory cytokines (gamma interferon [IFN-γ], tumor necrosis factor alpha [TNF-α], IL-1β, and IL-6) and chemokines (CXCL1, CXCL2, and CCL2). It has been reported that host defense against P. aeruginosa acute lung infection can be improved by blocking IL-1 since exaggerated IL-1β production may be harmful for the host in this infection. In agreement with these data, IL-1RI deficiency rescues the phenotype observed in Tir8-deficient mice: in Tir8-/- IL-1RI-/- double knockout mice we observed higher survival rates, enhanced bacterial clearance, and reduced levels of local and systemic cytokine and chemokine levels than in Tir8-deficient mice. These results suggest that TIR8 has a nonredundant effect in modulating the inflammation caused by P. aeruginosa, in particular, by negatively regulating IL-1RI signaling, which plays a major role in the pathogenesis of this infectious disease.

Therapeutic role of toll-like receptor modification in cardiovascular dysfunction

http://www.ncbi.nlm.nih.gov/pubmed/23070056

Hepatic and renal cytochrome p450 gene regulation during citrobacter rodentium infection in wild-type and toll-like receptor 4 mutant mice.

Citrobacter rodentium is the rodent equivalent of human enteropathogenic Escherichia coli infection. This study investigated regulation of hepatic and renal cytochrome P450 (P450) mRNAs, hepatic P450 proteins, cytokines, and acute phase proteins during C. rodentium infection. Female C3H/HeOuJ (HeOu) and C3H/HeJ (HeJ) mice [which lack functional toll-like receptor 4 (TLR4)] were infected with C. rodentium by oral gavage and sacrificed 6 days later. Hepatic CYP4A10 and 4A14 mRNAs were decreased in HeOu mice (<4% of control). CYP3A11, 2C29, 4F14, and 4F15 mRNAs were reduced to 16 to 55% of control levels, whereas CYP2A5, 4F16, and 4F18 mRNAs were induced (180, 190, and 600% of control, respectively). The pattern of P450 regulation in HeJ mice was similar to that in HeOu mice for most P450s, with the exception of the TLR4 dependence of CYP4F15. Hepatic CYP2C, 3A, and 4A proteins in both groups were decreased, whereas CYP2E protein was not. Renal CYP4A10 and 4A14 mRNAs were significantly down-regulated in HeOu mice, whereas other P450s were unaffected. Most renal P450 mRNAs in infected HeJ mice were increased, notably CYP4A10, 4A14, 4F18, 2A5, and 3A13. Hepatic levels of interleukin (IL)-1beta, IL-6, and tumor necrosis factor alpha (TNFalpha) mRNAs were significantly increased in infected HeOu mice, whereas only TNFalpha mRNA was significantly increased in HeJ mice. Hepatic alpha1-acid glycoprotein was induced in both groups, whereas alpha-fibrinogen and angiotensinogen were unchanged. These data indicate that hepatic inflammation induced by C. rodentium infection is mainly TLR4-independent and suggest that hepatic P450 down-regulation in this model may be cytokine-mediated.