No abstract

Tetraspanins facilitate the formation of multiple molecular complexes at specialized membrane microdomains and regulate cell activation and motility. In the present study, the role of tetraspanin CD9 in LPS-induced macrophage activation and lung inflammation was investigated in vitro and in vivo. When CD9 function was ablated with mAb treatment, small interfering RNA transfection, or gene knockout in RAW264.7 cells or bone marrow-derived macrophages, these macrophages produced larger amounts of TNF-α, matrix metalloproteinase-2, and -9 upon stimulation with LPS in vitro, when compared with control cells. Sucrose gradient analysis revealed that CD9 partly colocalized with the LPS-induced signaling mediator, CD14, at low-density light membrane fractions. In CD9 knockout macrophages, CD14 expression, CD14 and TLR4 localization into the lipid raft, and their complex formation were increased whereas IκBα expression was decreased when compared with wild-type cells, suggesting that CD9 prevents the formation of LPS receptor complex. Finally, deletion of CD9 in mice enhanced macrophage infiltration and TNF-α production in the lung after intranasal administration of LPS in vivo, when compared with wild-type mice. These results suggest that macrophage CD9 negatively regulates LPS response at lipid-enriched membrane microdomains.

CD9 and CD81 are closely related tetraspanins that regulate cell motility and signaling by facilitating the organization of multimolecular membrane complexes, including integrins. We show that CD9 and CD81 are down-regulated in smoking-related inflammatory response of a macrophage line, RAW264.7. When functions of CD9 and CD81 were ablated with monoclonal antibody treatment, small interfering RNA transfection, or gene knock-out, macrophages were less motile and produced larger amounts of matrix metalloproteinase (MMP)-2 and MMP-9 than control cells in vitro. In line with this, CD9/CD81 double-knock-out mice spontaneously developed pulmonary emphysema, a major pathological component of chronic obstructive pulmonary disease (COPD). The mutant lung contained an increased number of alveolar macrophages with elevated activities of MMP-2 and MMP-9 and progressively displayed enlarged airspace and disruption of elastic fibers in the alveoli. Secretory cell metaplasia, a finding similar to goblet cell metaplasia in cigarette smokers, was also observed in the epithelium of terminal bronchioles. With aging, the double-knockout mice showed extrapulmonary phenotypes, including weight loss, kyphosis, and osteopenia. These results suggest that the tetraspanins CD9 and CD81 regulate cell motility and protease production of macrophages and that their dysfunction may underlie the progression of COPD.Chronic obstructive pulmonary disease (COPD), 5 a disease defined by incompletely reversible airflow limitation, results from abnormal inflammatory response to chronic cigarette smoking. Pulmonary emphysema is a major component of COPD, and a dominant hypothesis in its pathophysiology is that persistent infiltration of inflammatory cells and production of proteases, including matrix metalloproteinases (MMPs) in the lung, lead to tissue destruction and airspace enlargement (1, 2). In patients with emphysema, there was an increase in bronchoalveolar lavage fluid (BALF) concentrations and macrophage expression of MMP-9 (3). Studies of human samples have shown increases of MMP-2 and MMP-9 in smoking-related emphysema (4). Alveolar macrophages secrete elastolytic enzymes, including MMP-2, MMP-9, and MMP-12, and play a pivotal role in the pathophysiology of COPD. There was a marked increase in the numbers of macrophages in airways, lung parenchyma, BALF, and sputum in patients with emphysema (2). Macrophages are activated by cigarette smoke to release inflammatory mediators such as TNF-␣, chemokines, and reactive oxygen species as well as MMPs, providing a cellular mechanism that links smoking with inflammation in COPD (2). It was recently proposed that lowered activity of histone deacetylases (HDACs), which are suppressors of inflammatory genes, accounts for the persistent activation of macrophages in COPD patients (5).The tetraspanin proteins include at least 33 members, including CD9, CD63, CD81, CD82, and CD151 in mammals. They are characterized by the structure that spans the plasma membrane four times and have a propensity to form co...

Adiponectin-knockout mice develop progressive chronic obstructive pulmonary disease-like phenotype with systemic inflammation and extrapulmonary phenotypes. Hypoadiponectinemia could thus play a critical role in the progression of chronic obstructive pulmonary disease and concomitant comorbidities through endothelial dysfunction. Together, adiponectin could be a novel target for chronic obstructive pulmonary disease therapy.

Background: The molecular mechanisms regulating lymphangiogenesis remain unclear. Results: Tetraspanin CD9 modulates molecular organization of integrins in LEC, thereby supporting several functions required for lymphangiogenesis. Conclusion: Deletion of CD9 diminished lymphangiogenesis in mice and humans. Significance: Given that CD9 mediates inflammation and tumor progression, CD9 might be a key component not only in tumor metastasis, but also in inflammation.