Evaluating the Role of SDF-1/CXCR7/CXCR4 Axis in LPS-Stimulated Bone Marrow-Derived Macrophages

CXCR7, also known as ACKR3, is an atypical chemokine receptor that is believed to be inducible for CXCR4 and has a ten-fold greater binding capacity for stromal cell-derived factor (SDF-1) than CXCR4. While the SDF-1/CXCR4/CXCR7 axis is well-documented for its regulatory role in macrophage phenotype and function, its specific involvement in the polarization of bone marrow-derived macrophages (BMDMs) remains underexplored. This study aimed to elucidate the dynamic expression patterns of CXCR7, CXCR4, and SDF-1 during BMDM polarization and to dissect the contribution of the SDF-1/CXCR7/CXCR4 axis in this context. To achieve this, we employed recombinant SDF-1, the CXCR7 antagonist CCX771, and small interfering RNA (siRNA) to interrogate the axis's role in BMDM polarization. Our findings revealed a marked upregulation of CXCR7 and concurrent downregulation of CXCR4 and SDF-1 during BMDM polarization. Both recombinant SDF-1 and CCX771 were observed to inhibit M1 polarization, as evidenced by reduced expression of TNF-alpha, iNOS, and CD80. Interestingly, silencing CXCR7 did not affect M1 polarization directly but amplified SDF-1's inhibitory effect on M1 polarization. Moreover, TC14012, which functions as a CXCR7 agonist and CXCR4 antagonist, was found to potentiate LPS-induced M1 polarization in BMDMs. These results suggest that the SDF-1/CXCR7/CXCR4 axis plays a pivotal role in modulating macrophage polarization, with LPS promoting M1 polarization through the upregulation of CXCR7, thereby disrupting the SDF-1/CXCR4 axis and its downstream signaling pathways in BMDMs.