title: Toll-Like Receptor 4 Signaling Pathway Mediates Inhalant Organic Dust-Induced Bone Loss.
abstract: 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.
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Staab
authors.affiliation: Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.|Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Geoffrey M
authors.initials: GM
authors.lastname: Thiele
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Dillon
authors.initials: D
authors.lastname: Clarey
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.|Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.|Department of Environmental, Agricultural, and Occupational Health, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Wyatt
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.|Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.
authors.forename: Debra J
authors.initials: DJ
authors.lastname: Romberger
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Adam D
authors.initials: AD
authors.lastname: Wells
authors.affiliation: Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Anand
authors.initials: A
authors.lastname: Dusad
authors.affiliation: Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.affiliation: Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.|Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Lynell W
authors.initials: LW
authors.lastname: Klassen
authors.affiliation: Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.|Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Ted R
authors.initials: TR
authors.lastname: Mikuls
authors.affiliation: Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, United States of America.|Rheumatology Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Duryee
authors.affiliation: Pulmonary, Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, NE, United States of America.
authors.forename: Jill A
authors.initials: JA
authors.lastname: Poole
mesh_terms: D000393:Air Pollutants / Q000737:chemistry / Q000633:toxicity*; D000818:Animals; D001851:Bone Diseases, Metabolic / Q000000981:diagnostic imaging / Q000209:etiology* / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D018925:Chemokines / Q000032:analysis; D016207:Cytokines / Q000032:analysis; D004195:Disease Models, Animal; D004391:Dust / Q000032:analysis*; D019570:Inhalation Exposure; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009504:Neutrophils / Q000166:cytology / Q000276:immunology; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D011014:Pneumonia / Q000209:etiology / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D000071681:Tartrate-Resistant Acid Phosphatase / Q000097:blood; D013977:Tibia / Q000000981:diagnostic imaging; D051195:Toll-Like Receptor 2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D000393:Air Pollutants; D018925:Chemokines; D016207:Cytokines; D004391:Dust; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D000071681:Tartrate-Resistant Acid Phosphatase