title: Non-essential role for TLR2 and its signaling adaptor Mal/TIRAP in preserving normal lung architecture in mice.
abstract: Myeloid differentiation factor 88 (MyD88) and MyD88-adaptor like (Mal)/Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) play a critical role in transducing signals downstream of the Toll-like receptor (TLR) family. While genetic ablation of the TLR4/MyD88 signaling axis in mice leads to pulmonary cell death and oxidative stress culminating in emphysema, the involvement of Mal, as well as TLR2 which like TLR4 also signals via MyD88 and Mal, in the pathogenesis of emphysema has not been studied. By employing an in vivo genetic approach, we reveal here that unlike the spontaneous pulmonary emphysema which developed in Tlr4(-/-) mice by 6 months of age, the lungs of Tlr2(-/-) mice showed no physiological or morphological signs of emphysema. A more detailed comparative analysis of the lungs from these mice confirmed that elevated oxidative protein carbonylation levels and increased numbers of alveolar cell apoptosis were only detected in Tlr4(-/-) mice, along with up-regulation of NADPH oxidase 3 (Nox3) mRNA expression. With respect to Mal, the architecture of the lungs of Mal(-/-) mice was normal. However, despite normal oxidative protein carbonylation levels in the lungs of emphysema-free Mal(-/-) mice, these mice displayed increased levels of apoptosis comparable to those observed in emphysematous Tlr4(-/-) mice. In conclusion, our data provide in vivo evidence for the non-essential role for TLR2, unlike the related TLR4, in maintaining the normal architecture of the lung. In addition, we reveal that Mal differentially facilitates the anti-apoptotic, but not oxidant suppressive, activities of TLR4 in the lung, both of which appear to be essential for TLR4 to prevent the onset of emphysema.
authors.affiliation: Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, Victoria, Australia.
authors.forename: Saleela M
authors.initials: SM
authors.lastname: Ruwanpura
authors.forename: Louise
authors.initials: L
authors.lastname: McLeod
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Lilja
authors.forename: Gavin
authors.initials: G
authors.lastname: Brooks
authors.forename: Lovisa F
authors.initials: LF
authors.lastname: Dousha
authors.forename: Huei J
authors.initials: HJ
authors.lastname: Seow
authors.forename: Steven
authors.initials: S
authors.lastname: Bozinovski
authors.forename: Ross
authors.initials: R
authors.lastname: Vlahos
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Hertzog
authors.forename: Gary P
authors.initials: GP
authors.lastname: Anderson
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Jenkins
mesh_terms: D000368:Aged; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D004646:Emphysema / Q000378:metabolism; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008168:Lung / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008875:Middle Aged; D018384:Oxidative Stress / Q000235:genetics / Q000502:physiology; D017472:Receptors, Interleukin-1 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism
chemical_list: D008562:Membrane Glycoproteins; D017472:Receptors, Interleukin-1; C499045:TIRAP protein, mouse; C493487:Tlr4 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4