GSE106987
SAGE analysis of alveolar macrophages from metastatic lung and untreated lung
Macrophages in lungs can be classified into two subpopulations, alveolar macrophages (AMs) and interstitial macrophages (IMs), which reside in the alveolar and interstitial spaces, respectively. Accumulating evidence indicates the involvement of IMs in lung metastasis but the roles of AMs in lung metastasis still remain elusive. An intravenous injection of a mouse hepatocellular carcinoma (HCC) cell line, BNL, caused lung metastasis foci with infiltration of AMs and IMs. Comprehensive determination of arachidonic acid (AA) metabolite levels revealed increases in leukotrienes (LTs) and prostaglandins in lungs in this metastasis model. A 5-lipoxygenase (LOX) inhibitor but not a cyclooxygenase inhibitor reduced the numbers of metastatic foci, particularly those with larger sizes. A major 5-LOX metabolite, LTB4, augmented in vitro cell proliferation of human HCC cell lines as well as BNL cells. Moreover, in this lung metastasis course, AMs exhibited higher expression levels of the 5-LOX and LTB4 than IMs. Consistently, 5-LOX-expressing AMs increased in the lungs of human HCC patients with lung metastasis, compared with those without lung metastasis. Furthermore, intratracheal clodronate liposome injection selectively depleted AMs but not IMs, together with reduced LTB4 content and metastatic foci numbers in this lung metastasis process. Finally, IMs in mouse metastatic foci produced CCL2, thereby recruiting blood-borne, CCR2-expressing AMs into lungs. Thus, AMs can be recruited under the guidance of IM-derived CCL2 into metastatic lungs and can eventually contribute to the progression of lung metastasis by providing a potent AA-derived tumor growth promoting mediator, LTB4. Overall design: Total RNA was extracted from AMs of untreated mice and mice injected intravenously with BNL cells. The resultant total RNAs were subjected to SAGE