LncRNA FGD5-AS1 promotes M2 polarization of tumor-associated macrophages to facilitate the malignant phenotype of non-small cell lung cancer cells

Background: Tumor-associated macrophages (TAMs) take up a high proportion among immune cells in the tumor microenvironment (TME), and their M2- polarized phenotype has been implicated in promoting non-small cell lung cancer (NSCLC) development. Long non-coding RNA FGD5-AS1 (FGD5-AS1) is up-regulated within multiple tumor types, which has been shown to modulate both TAMs polarization and metabolic reprogramming. However, its exact mechanisms in NSCLC are largely unclear. This study aims to investigate whether FGD5-AS1 regulates M2 polarization of TAMs and thereby influences the malignant progression of NSCLC, as well as to explore the underlying molecular mechanisms.

Methods: Human monocytic leukemia THP-1 cells were induced to differentiate into M0 macrophages in vitro and subsequently co-cultured with NSCLC cell lines (A549 and NCI-H1299) to mimic the TME and generate TAMs. The impacts of FGD5-AS1 silencing on M2 polarization of TAMs were assessed using flow cytometry and quantitative real-time polymerase chain reaction (qRT-PCR). To investigate the molecular mechanism underlying FGD5-AS1-mediated regulation of M2 polarization, Wnt5a was overexpressed via lentiviral transduction in FGD5-AS1-silenced M0 macrophages, followed by evaluation of Wnt5a expression and M2 polarization status using flow cytometry, qRT-PCR, and Western blot analysis. Finally, FGD5-AS1-silenced M0 macrophages were subjected to co-culture using A549 as well as NCI-H1299 cells, and functional consequences of FGD5-AS1- regulated M2-polarized TAMs on NSCLC cell growth, invasion, migration, alongside epithelial-mesenchymal transition (EMT) were evaluated using cell counting kit-8 (CCK-8), scratch, Transwell, and Western blotting assays.

Results: FGD5-AS1 showed remarkable up-regulation inside M2-polarized TAMs. FGD5-AS1 knockdown inhibited the M2 polarization of TAMs, as evidenced by down-regulated M2 macrophage marker levels including CD206, IL-10, TGF-β, and CCL22, along with decreased Wnt5a protein levels. Mechanistically, overexpression of Wnt5a reversed the inhibitory effects of FGD5-AS1 silencing on M2 polarization, indicating that Wnt5a acts downstream of FGD5-AS1 in this regulatory axis. Notably, silencing FGD5-AS1 in M0 macrophages attenuated the proliferation, migration, invasion, and EMT of A549 and NCI-H1299 cells in the co-culture system, suggesting a functional role of FGD5-AS1-modulated TAMs in promoting malignant phenotypes of NSCLC cells.

Conclusions: FGD5-AS1 may promote M2 polarization of TAMs through upregulation of Wnt5a, thereby contributing to the enhancement of malignant phenotypes in NSCLC cancer cells.