Toll-Like Receptor 4 Signaling Pathway Mediates Inhalant Organic Dust-Induced Bone Loss
نویسندگان
چکیده
Agriculture workers have increased rates of airway and skeletal disease. Inhalant exposure to agricultural organic dust extract (ODE) induces bone deterioration in mice; yet, mechanisms underlying lung-bone crosstalk remain unclear. Because Toll-like receptor 2 (TLR2) and TLR4 are important in mediating the airway consequences of ODE, this study investigated their role in regulating bone responses. First, swine facility ODE stimulated wild-type (WT) bone marrow macrophages to form osteoclasts, and this finding was inhibited in TLR4 knock-out (KO), but not TLR2 KO cells. Next, using an established intranasal inhalation exposure model, WT, TLR2 KO and TLR4 KO mice were treated daily with ODE or saline for 3 weeks. ODE-induced airway neutrophil influx and cytokine/chemokine release were similarly reduced in TLR2 and TLR4 KO animals as compared to WT mice. Utilizing micro-computed tomography (CT), analysis of tibia showed loss of bone mineral density, volume and deterioration of bone micro-architecture and mechanical strength induced by ODE in WT mice were significantly reduced in TLR4 but not TLR2 KO animals. Bone marrow osteoclast precursor cell populations were analyzed by flow cytometry from exposed animals. In WT animals, exposure to inhalant ODE increased osteoclast precursor cell populations as compared to saline, an effect that was reduced in TLR4 but not TLR2 KO mice. These results show that TLR2 and TLR4 pathways mediate ODE-induced airway inflammation, but bone deterioration consequences following inhalant ODE treatment is strongly dependent upon TLR4. Thus, the TLR4 signaling pathway appears critical in regulating the lung-bone inflammatory axis to microbial component-enriched organic dust exposures.
منابع مشابه
Immunological and inflammatory responses to organic dust in agriculture.
PURPOSE OF REVIEW Agriculture represents a major industry worldwide, and despite protection against the development of IgE-mediated diseases, chronic exposure to agriculture-related organic dusts is associated with an increased risk of developing respiratory disease. This article will review the literature regarding new knowledge of important etiologic agents in the dusts and focus on the immun...
متن کاملPhospholipase Cγ-2 and intracellular calcium are required for lipopolysaccharide-induced Toll-like receptor 4 (TLR4) endocytosis and interferon regulatory factor 3 (IRF3) activation.
Toll-like receptor 4 (TLR4) is unique among the TLRs in its use of multiple adaptor proteins leading to activation of both the interferon regulatory factor 3 (IRF3) and nuclear factor κB (NF-κB) pathways. Previous work has demonstrated that TLR4 initiates NF-κB activation from the plasma membrane, but that subsequent TLR4 translocation to the endosomes is required for IRF3 activation. Here we h...
متن کاملIntracellular Bacterial Infection-Induced IFN- Is Critically but Not Solely Dependent on Toll-Like Receptor 4-Myeloid Differentiation Factor 88-IFN- -STAT1 Signaling
Infection of murine bone marrow-derived macrophages (BMM ) with Chlamydia pneumoniae induces IFN-dependent IFNsecretion that leads to control of the intracellular bacterial growth. Enhanced growth of C. pneumoniae in Toll-like receptor (TLR) 4 / and myeloid differentiation factor (MyD) 88 / (but not TLR2 / , TLR6 / , or TLR9 / ) BMM is shown in this study. Reduced accumulation of IFNand IFNmRNA...
متن کاملThe Implication of Androgens in the Presence of Protein Kinase C to Repair Alzheimer’s Disease-Induced Cognitive Dysfunction
Aging, as a major risk factor of memory deficiency, affects neural signaling pathways in hippocampus. In particular, age-dependent androgens deficiency causes cognitive impairments. Several enzymes like protein kinase C (PKC) are involved in memory deficiency. Indeed, PKC regulatory process mediates α-secretase activation to cleave APP in β-amyloid cascade and tau proteins phosphorylation mecha...
متن کامل