Abstract Rationale Colony stimulating factor-1 (CSF-1) is well known to promote pulmonary fibrosis (PF) and lung cancer progression by inducing macrophage M2-like polarization. However, the mechanism by which CSF-1 drives M2 polarization remains unclear. Our previous studies demonstrated that chitinase-3-like-1 (CHI3L1) induces macrophage M2 polarization and contributes to the progression of pulmonary fibrosis and tumors. Based on these findings, we hypothesized that CSF-1-induced M2 polarization might be mediated through CHI3L1 and sought to test this hypothesis. Methods Human monocytes were differentiated into pre-M2 macrophages and stimulated with CSF-1. M2 polarization was assessed by qRT-PCR and Western blot analysis of representative M2 markers, CD163 and CD206. To determine the signaling hierarchy among the pathways, we used specific inhibitors and neutralizing antibodies targeting each axis, including CHI3L1, NAMPT, and SPP1. Results 1. CSF-1 robustly induced macrophage M2 polarization, which was dependent on CHI3L1 expression. 2. Upon CSF-1 stimulation, NAMPT and SPP1 were temporally upregulated and acted upstream to increase CHI3L1 expression. 3. CHI3L1 in turn enhanced the expression of NAMPT and SPP1 in a positive feedback loop, amplifying CSF-1-mediated M2 polarization signaling. These findings were validated using CHI3L1 neutralizing antibody treatment, which significantly attenuated CSF-1-induced M2 marker expression, confirming the functional role of CHI3L1 in this signaling axis. Conclusions We identified a novel mechanism by which CSF-1 drives macrophage M2 polarization through the CSF-1-NAMPT-osteopontin (SPP1)-CHI3L1 axis, herein termed the CNOC pathway. CHI3L1 functions as a central amplifier that augments CSF-1 signaling via positive-feedback regulation of NAMPT and SPP1. These findings underscore the pivotal role of CHI3L1 in pulmonary fibrosis and cancer and provide a mechanistic rationale for overcoming CSF-1R-inhibitor resistance observed in various diseases by combining the anti-CHI3L1 monoclonal antibody (FRG) with CSF-1R blockade. Further studies are ongoing to evaluate this therapeutic strategy. Collectively, these data highlight CHI3L1 as a promising therapeutic target to modulate pro-fibrotic and pro-tumoral macrophage differentiation within the pathogenic lung microenvironment. This abstract is funded by: P01 HL114501
Jeong et al. (Fri,) studied this question.