Elevated TLR4 Research Articles

A Critical Role for TLR4 Induction of Autophagy in the Regulation of Enterocyte Migration and the Pathogenesis of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) develops in response to elevated TLR4 signaling in the newborn intestinal epithelium and is characterized by TLR4-mediated inhibition of enterocyte migration and reduced mucosal healing. The downstream processes by which TLR4 impairs mucosal healing remain incompletely understood. In other systems, TLR4 induces autophagy, an adaptive response to cellular stress. We now hypothesize that TLR4 induces autophagy in enterocytes and that TLR4-induced autophagy plays a critical role in NEC development. Using mice selectively lacking TLR4 in enterocytes (TLR4(ΔIEC)) and in TLR4-deficient cultured enterocytes, we now show that TLR4 activation induces autophagy in enterocytes. Immature mouse and human intestine showed increased expression of autophagy genes compared with full-term controls, and NEC development in both mouse and human was associated with increased enterocyte autophagy. Importantly, using mice in which we selectively deleted the autophagy gene ATG7 from the intestinal epithelium (ATG7(ΔIEC)), the induction of autophagy was determined to be required for and not merely a consequence of NEC, because ATG7(ΔIEC) mice were protected from NEC development. In defining the mechanisms involved, TLR4-induced autophagy led to impaired enterocyte migration both in vitro and in vivo, which in cultured enterocytes required the induction of RhoA-mediated stress fibers. These findings depart from current dogma in the field by identifying a unique effect of TLR4-induced autophagy within the intestinal epithelium in the pathogenesis of NEC and identify that the negative consequences of autophagy on enterocyte migration play an essential role in its development.

Hepatitis C virus load and expression of a unique subset of cellular genes in circulating lymphoid cells differentiate non‐responders from responders to pegylated interferon alpha–ribavirin treatment

Based on investigations of liver biopsy material, certain cellular genes have been implicated as correlates of success or failure to interferon alpha-ribavirin (IFN/RBV) therapy against hepatitis C. The current study aimed at determining whether expression of host genes thought to be relevant to HCV replication in the liver would be correlated with HCV infection status in peripheral blood mononuclear cells (PBMCs) and also with patient responsiveness to IFN/RBV treatment. Therefore, PBMCs from patients with chronic hepatitis C responding (n = 35) or not (n = 49) to IFN/RBV and from healthy controls (n = 15) were evaluated for HCV RNA load and cellular gene expression. Non-responders had 3- to 10-fold higher basal levels of interleukin (IL)-8, IFN-stimulated gene 15 (ISG15), 2',5'-oligoadenylate synthetase (OAS), and Toll-like receptors (TLR)-4, -5, and -7 compared to responders. Non-responders with similar post-treatment follow-ups as responders persistently expressed 6- to 20-fold greater levels of IL-8, ISG15, and OAS after therapy. Higher expression of IFN-α, IFN-γ, and IFN-λ was found in PBMCs of individuals achieving sustained virological response, either before or after therapy. Pre-treatment HCV RNA loads in PBMCs of non-responders were significantly higher (P = 0.016) than those of responders. In conclusion, the data indicate that immune cells of responders and non-responders to IFN/RBV therapy exhibited significantly different virological and host gene expression profiles. Elevated baseline HCV loads and TLR-4, -5, and -7 levels, and persistently high levels of IL-8, ISG15, and OAS were correlated with IFN non-responsiveness. The results warrant further investigations on the utilization of PBMCs for predicting success or failure to IFN-based therapies.

The expression of genes involved in NF-κB activation in peripheral blood mononuclear cells of patients with gestational diabetes

In patients with obesity and type 2 diabetes, the changes in insulin resistance are associated with the changes in expression of genes involved in nuclear factor-κB (NF-κB) activation in peripheral blood mononuclear cells (PBMCs). As such studies have never been carried out in patients with gestational diabetes (GDM), in this study, we evaluated the expression of genes involved in NF-κB activation and related to glucose metabolism in PBMCs obtained from pregnant women with GDM and normal glucose tolerance (NGT). RT-PCR was performed in 60 pregnant women divided into three groups: GDM at the 1st visit, i.e. in the 24th-28th weeks of gestation (GDM1), NGT at the first visit and GDM in the 29th-32nd weeks (GDM2), and NGT at both visits. The tests were repeated 3 months postpartum. The GDM1 group had significantly higher TLR2 (P=0.024), TLR4 (P=0.037), STAT1 (P=0.027), and CX3CL1 (P=0.017) mRNA expression, whereas the GDM2 group showed markedly lower TNFRSF1A (P=0.042), PPARG (P=0.018), STAT3 (P=0.013), and CX3CL1 (P=0.038) mRNA expression in comparison with the NGT group. The women with NGT at the 1st visit who later developed GDM had significantly higher fasting glucose (P=0.01), HOMA-IR (P=0.004), and TLR2 mRNA expression (P=0.04), as well as lower ISSI2 (P=0.01) and disposition indices, DI₃₀ (P=0.03) and DI₁₂₀ (P=0.01), than had the women who remained normoglycemic. Our results suggest that elevated TLR2 expression, as well as higher fasting glucose and lower compensation for increased insulin resistance, may represent early metabolic disturbances in the development of GDM.

PP127. CMV infection and TLR2 expression in HELLP syndrome

The HELLP syndrome is a serious complication in pregnancy characterized by haemolysis, elevated liver enzymes and low platelet count occurring in 10-20% of cases with severe preeclampsia and associated with metabolic disorders symptoms later in life. Emerging evidence indicated that cytomegalovirus (CMV) infection and TLR signaling activation are associated with severe preeclampsia and metabolic disorder conditions. The aim of this study was to examine CMV sero-prevalence and its associated TLR signaling activation in patients with HELLPs. A case-control study was performed. Subjects included women with HELLP syndrome (n=6) and normal pregnancy controls (n=20), who matched with cases for maternal age, gestational age and parity. Maternal serum CMV serology and cytokines response were measured by ELISA. TLR2 and TLR4 expression on peripheral Neutrophils were detected by real-time PCR. CMV IgG seropositivity was more prevalent among HELLP syndrome patients than normal pregnancy controls (85% versus 40%, p<0.01). Patients with HELLP syndrome also had elevated TLR2 (p<0.01) and IL-1β mRNA expressions (p<0.05) and increased TNF-α: IL-10 (p<0.05) and IL-6: IL-10 (p<0.05) ratio compared with matched normal pregnancy controls. It is important to consider pregnancy CMV infection through TLR2 signaling in modulation of innate immune response in maternal HELLP syndrome, and may be linked with increased metabolic disorders later in life.

LPS hypersensitivity of gp130 mutant mice is independent of elevated haemopoietic TLR4 signaling

Correction to: Immunology and Cell Biology (2012) 90, 559–563; doi:10.1038/icb.2011.56; published online 14 June 2011 Since the publication of this article, the authors have noticed an error. One of the co-authors, Andrew Jarnicki, was inadvertently omitted from the paper. This error has now been rectified, and the corrected article appears in this issue. The html and online pdf versions have also been rectified and now show the correct authorship. The authors would like to apologize for this error.

Short‐term bed rest increases inflammation as evidenced by elevated TLR4, NFκB1 and IL6 expression in skeletal muscle of older adults

Aging is characterized by increased systemic and tissue inflammation. However, it is currently unknown if a period of inactivity exacerbates muscle inflammation in older adults. We hypothesized that short‐term bed rest would increase muscle levels of TLR4 and NFκB expression and circulating cytokine levels in older adults. Six healthy, older adults participated in a strict bed rest model for 7 consecutive days. Serum samples and muscle biopsies were taken before and day 7 of bed rest. Serum samples were analyzed for cytokine expression. Muscle samples were analyzed using western blotting and qPCR for TLR4, HSP60, Iκβα protein expression and IL6, NFκB1, IL1β, TNFα, TNFRSA1, SOCS3, IL10, and IL15 mRNA expression. Participants lost ~4% leg lean mass due to bed rest. Additionally, the cytokine, interferon gamma was significant elevated in serum samples after bed rest (P&lt;0.05). In the muscle, TLR4 protein expression and IL6, NFκB1, IL10 and IL15 mRNA expression were increased after bed rest (P&lt;0.05). We conclude that short‐term bed rest increases IL6 expression perhaps through a TLR4/NFκB mechanism, and may contribute to muscle loss observed following a period of bed rest. An increase in the anti‐inflammatory cytokines, IL10 and IL15 may represent a compensatory response to reduce inflammation. Funding: K01AG038556, R01AG018311, R01AR049877, 1UL1RR029876, P30AG024832

Involvement of TNFα-induced TLR4–NF-κB and TLR4–HIF-1α feed-forward loops in the regulation of inflammatory responses in glioma

The precise role of different toll-like receptor (TLR) superfamily members is just beginning to get elucidated in glioblastoma multiforme (GBM). In this study, we observed heightened TLR4 levels in GBM tumor samples as compared to adjacent normal tissue. Since the pro-inflammatory cytokine tumor necrosis factor (TNF)α induces NF-κB activation in GBM, and as several common signaling mediators are involved in TNFα and TLR4-mediated NF-κB activation, we investigated the role of TLR4 in the regulation of NF-κB activation and inflammatory responses in TNFα-treated glioma cells. TNFα elevated TLR4 expression and inhibition of TLR4 signaling by either signaling inhibitor, neutralizing antibody, or small interfering RNA (siRNA)-attenuated TNFα-induced NF-κB activation. TLR4-mediated NF-κB activation was independent of canonical myeloid differentiation factor 88 signaling but involved toll/IL-1R homology domain-containing adaptor protein-inducing interferon-β. Inhibition of TLR4 signaling abrogated TNFα-induced increase in (1) transcription factors interferon (IFN) regulatory factor 3 and STAT-1 and (2) IFNβ and inflammatory cytokines/chemokines expression. Furthermore, TNFα-induced TLR4-dependent increase in AKT activation and HIF-1α transcriptional activation suggested the existence of TLR4-AKT-HIF-1α axis. Importantly, TNFα-induced TLR4 was abrogated in cells transfected with dominant negative IκB and HIF-1α siRNA. Our studies indicate that TNFα triggered TLR4-HIF-1α and NF-κB-TLR4 feed-forward loops act in tandem to sustain inflammatory response in glioma.

TLR4 Protein Contributes to Cigarette Smoke-induced Matrix Metalloproteinase-1 (MMP-1) Expression in Chronic Obstructive Pulmonary Disease

Cigarette smoke is the major risk factor associated with the development of chronic obstructive pulmonary disease and alters expression of proteolytic enzymes that contribute to disease pathology. Previously, we reported that smoke exposure leads to the induction of matrix metalloproteinase-1 (MMP-1) through the activation of ERK1/2, which is critical to the development of emphysema. To date, the upstream signaling pathway by which cigarette smoke induces MMP-1 expression has been undefined. This study demonstrates that cigarette smoke mediates MMP-1 expression via activation of the TLR4 signaling cascade. In vitro cell culture studies demonstrated that cigarette smoke-induced MMP-1 was regulated by TLR4 via MyD88/IRAK1. Blockade of TLR4 or inhibition of IRAK1 prevented cigarette smoke induction of MMP-1. Mice exposed to acute levels of cigarette smoke exhibited increased TLR4 expression. To further confirm the in vivo relevance of this signaling pathway, rabbits exposed to acute cigarette smoke were found to have elevated TLR4 signaling and subsequent MMP-1 expression. Additionally, lungs from smokers exhibited elevated TLR4 and MMP-1 levels. Therefore, our data indicate that TLR4 signaling, through MyD88 and IRAK1, plays a predominant role in MMP-1 induction by cigarette smoke. The identification of the TLR4 pathway as a regulator of smoke-induced protease production presents a series of novel targets for future therapy in chronic obstructive pulmonary disease.

LPS hypersensitivity of gp130 mutant mice is independent of elevated haemopoietic TLR4 signaling

Among the many inflammatory mediators induced by the prototypical inflammatory stimulus lipopolysaccharide (LPS), which signals via Toll-like receptor (TLR)-4, interleukin (IL)-6 has recently been shown to feedback and augment TLR4 signaling when overproduced in LPS hypersensitive gp130(F/F) mice. This regulation by IL-6 in gp130(F/F) mice requires hyperactivation of the latent transcription factor signal transducer and activator of transcription (STAT) 3 via the IL-6 signaling receptor subunit gp130. However, the identity of LPS/TLR4-responsive inflammatory signaling pathways and gene networks, which are modulated by IL-6 (via gp130/STAT3), and the extent to which the tissue and cellular context of this regulation contributes to LPS-induced endotoxic shock in gp130(F/F) mice, are unknown. We report here that in LPS-treated macrophages from gp130(F/F) mice, gp130 hyperactivation upregulated the LPS-induced expression of inflammatory mediators downstream of Janus kinase (JAK)/STAT, nuclear factor κ-light-chain-enhancer of activated B cells, interferon regulatory factor and c-Jun N-terminal kinase/p38 mitogen-activated protein kinase pathways. Notably, however, LPS administration to bone marrow chimeras indicated that heightened LPS/TLR4 signaling in haemopoietic-derived gp130(F/F) immune cells is dispensable for the hypersensitivity of gp130(F/F) mice to LPS-induced endotoxemia. To understand the molecular consequences of gp130 hyperactivity in non-haemopoietic tissue on LPS-induced systemic inflammation, global gene expression profiling of livers from LPS-treated gp130(F/F) mice was performed and identified 264 hepatic LPS-responsive genes, which are differentially regulated by hyperactive gp130 signaling. Collectively, the substantial transcriptional reprogramming of LPS-responsive genes in gp130(F/F) mice emphasizes non-haemopoietic gp130 signaling as a key regulator of systemic inflammatory responses during LPS-induced endotoxemia.

Spontaneous preterm labor is associated with an increase in the proinflammatory signal transducer TLR4 receptor on maternal blood monocytes

BackgroundLocalized inflammation and increased expression of TLR4 receptors within the uterus has been implicated in the pathogenesis of preterm labor. It remains unclear whether intrauterine inflammatory responses activate the maternal peripheral circulatory system. Therefore we determined whether increased TLR4 expression is present in the peripheral maternal white blood cells of women with spontaneous preterm labor.MethodsThis is a cross-sectional study of 41 preterm labor cases and 41 non-preterm controls. For each case and control sample, RNA was purified from white blood cells and TLR4 mRNA pool size was evaluated by quantitative PCR. Protein expression levels were determined by flow cytometry. Statistical evaluation using multiple linear regressions was used to determine any significant differences between the cases and controls. The purpose was to determine association prevalence of TLR4 levels and preterm labor.ResultsAdjusted mean TLR4 mRNA levels of 0.788 ± 0.037 (standard error) for preterm labor and 0.348 ± 0.038 for the corresponding pregnant control women were statistically significantly different (P = 0.002). Using the lower 95% confidence interval of the mean expression level in PTL subjects (0.7) as a cutoff value for elevated TLR4 mRNA levels, 25/41 (60.9%) of PTL patients expressed elevated TLR4 mRNA as compared to 0/41 (0%) in control subjects. The TLR4 receptor levels in the granulocyte fraction of white blood cells from preterm labor and pregnant controls were similar. However, TLR4+/CD14+monocytes were 2.3 times more frequent (70% vs. 30%) and TLR4 also had a 2.6-fold higher density (750 vs. 280 molecules per cell) in preterm labor women compared with pregnant controls. There was no difference in the levels of TLR4 in patients at term.ConclusionsPatients with preterm labor exhibited elevated levels of CD14+ maternal blood monocytes each bearing enhanced expression of TLR4, indicating that the peripheral circulatory system is activated in patients with preterm labor. Elevated leukocyte TLR4 levels may be a useful biomarker associated with preterm labor.

Elevated Toll-Like Receptor 4 Expression and Signaling in Muscle From Insulin-Resistant Subjects

OBJECTIVE— Tall-like receptor (TLR)4 has been implicated in the pathogenesis of free fatty acid (FFA)-induced insulin resistance by activating inflammatory pathways, including inhibitor of κB (IκB)/nuclear factor κB (NFκB). However, it is not known whether insulin-resistant subjects have abnormal TLR4 signaling. We examined whether insulin-resistant subjects have abnormal TLR4 expression and TLR4-driven (IκB/NFκB) signaling in skeletal muscle.RESEARCH DESIGN AND METHODS— TLR4 gene expression and protein content were measured in muscle biopsies in 7 lean, 8 obese, and 14 type 2 diabetic subjects. A primary human myotube culture system was used to examine whether FFAs stimulate IκB/NFκB via TLR4 and whether FFAs increase TLR4 expression/content in muscle.RESULTS— Obese and type 2 diabetic subjects had significantly elevated TLR4 gene expression and protein content in muscle. TLR4 muscle protein content correlated with the severity of insulin resistance. Obese and type 2 diabetic subjects also had lower IκBα content, an indication of elevated IκB/NFκB signaling. The increase in TLR4 and NFκB signaling was accompanied by elevated expression of the NFκB-regulated genes interleukin (IL)-6 and superoxide dismutase (SOD)2. In primary human myotubes, acute palmitate treatment stimulated IκB/NFκB, and blockade of TLR4 prevented the ability of palmitate to stimulate the IκB/NFκB pathway. Increased TLR4 content and gene expression observed in muscle from insulin-resistant subjects were reproduced by treating myotubes from lean, normal-glucose-tolerant subjects with palmitate. Palmitate also increased IL-6 and SOD2 gene expression, and this effect was prevented by inhibiting NFκB.CONCLUSIONS— Abnormal TLR4 expression and signaling, possibly caused by elevated plasma FFA levels, may contribute to the pathogenesis of insulin resistance in humans.

Elevated amount of Toll-like receptor 4 mRNA in bronchial epithelial cells is associated with airway inflammation in horses with recurrent airway obstruction

Recurrent airway obstruction (RAO) is characterized by neutrophilic airway inflammation and obstruction, and stabling of susceptible horses triggers acute disease exacerbations. Stable dust is rich in endotoxin, which is recognized by Toll-like receptor (TLR) 4. In human bronchial epithelium, TLR4 stimulation leads to elevation of interleukin (IL)-8 mRNA expression. The zinc finger protein A20 negatively regulates this pathway. We hypothesized that TLR4 and IL-8 mRNA and neutrophil numbers are elevated and that A20 mRNA is not increased in RAOs during stabling compared with controls and with RAOs on pasture. We measured the maximal change in pleural pressure (DeltaPpl(max)), determined inflammatory cell counts in bronchoalveolar lavage fluid (BAL), and quantified TLR4, IL-8, and A20 mRNA in bronchial epithelium by quantitative RT-PCR. We studied six horse pairs, each pair consisting of one RAO and one control horse. Each pair was studied when the RAO-affected horse had airway obstruction induced by stabling and after 7, 14, and 28 days on pasture. Stabling increased BAL neutrophils, DeltaPpl(max), and TLR4 (4.14-fold change) significantly in RAOs compared with controls and with RAOs on pasture. TLR4 correlated with IL-8 (R2 = 0.75). Whereas stabling increased IL-8 in all horses, A20 was unaffected. IL-8 was positively correlated with BAL neutrophils (R2 = 0.43) and negatively with A20 (R2 = 0.44) only in RAO-affected horses. Elevated TLR4 expression and lack of A20 upregulation in bronchial epithelial cells from RAO-affected horses may contribute to elevated IL-8 production, leading to exaggerated neutrophilic airway inflammation in response to inhalation of stable dust.