ABSTRACT
Objective: To investigate the effects of colony-stimulating factor 1 receptor (CSF-1R) inhibitor pexidartinib (PLX3397) on the senescence of bone marrow-derived macrophages (BMDM) stimulated by lipopolysaccharide (LPS). Methods: BMDM were isolated and cultured from femurs and tibiae of 10 male C57BL/6 mice aged 6-8 weeks (obtained from Laboratory Animal Center of Guizhou Medical University). They were divided into blank control group, LPS group (treated with 1 μg/ml LPS for 24 h) as well as low, medium and high concentration PLX3397 pretreatment groups (treated with 100, 500 and 1 000 nmol/L PLX3397 for 4 h respectively followed by 1 μg/ml LPS for 24 h). The corresponding markers of macrophages were detected by flow cytometry. Cell viability was detected by cell counting kit-8 and cellular senescence was detected by senescence-associated-β-galactosidase (SA-β-gal) staining. Meanwhile, protein expressions of cycle-dependent kinase inhibitor p16, p21 and CSF-1R were detected by Western blotting, and the expressions of p16 and p21 were detected by intracellular immunofluorescence. Real-time fluorescence quantitative PCR (RT-qPCR) was used to investigate the mRNA levels of senescence-associated secretory phenotype (SASP) genes including interleukin (IL), IL-1β, chemokine-1/10 (CXCL-1/10), matrix metalloproteinase-8 (MMP-8), and transforming growth factor-β (TGF-β). Results: The rate of SA-β-gal positive staining in medium and high concentration PLX3397 pretreatment groups [(39.33±4.93)% and (36.33±3.06)% respectively] were significantly downregulated compared with LPS group [(52.00±3.00)%] (P=0.020, P=0.005). The expression of CSF-1R protein in low, medium and high concentration PLX3397 pretreatment groups were (0.74±0.18, 0.61±0.07, 0.54±0.06), all of which were significantly lower than that in LPS group (1.16±0.08) (P=0.013, P=0.002, P<0.001). The expression levels of CSF-1R mRNA in low, medium and high concentration PLX3397 pretreatment groups (1.04±0.06, 0.90±0.05, 1.18±0.08) showed similar trend (2.90±0.25) (P<0.001). The average fluorescence intensity of p16 in all PLX3397 pretreatment groups were 49.76±3.65, 48.21±1.72, 47.99±1.26 respectively, which were significantly lower than that in LPS group (66.88±5.85) (P=0.001, P<0.001, P<0.001). The average fluorescence intensity of p21 in medium and high concentration PLX3397 pretreatment groups were (34.43±3.62, 30.13±0.86), significantly lower than that in LPS group (46.82±5.33) (P=0.043, P=0.007). The expression of p16 protein in low, medium and high concentration PLX3397 pretreatment groups (0.56±0.04, 0.55±0.04, 0.35±0.19) were significantly lower than that in LPS group (0.98±0.10) (P=0.003, P=0.002, P<0.001), as well the expression of p21 protein (0.69±0.20, 0.42±0.08, 0.26±0.14) (P=0.032, P=0.002, P<0.001). According to the results of RT-qPCR, the expressions of IL-6, IL-1β, CXCL-1, CXCL-10 and MMP-8 in PLX3397 pretreatment groups were significantly lower than those in LPS group (P<0.001), while the expression of TGF-β increased (P<0.001). Conclusions: LPS could induce the cell senescence, increase the secretion of SASP and aggravate local inflammation by activating the CSF-1R on the cell surface of bone marrow-derived macrophages. CSF-1R inhibitor PLX3397 might attenuate CSF-1R activation associated with LPS and inhibit the senescence of bone marrow-derived macrophages induced by LPS.