Fig. 4

Inducible MMP-9 expression reduces LPS-induced IL-6 secretion in Hepa1-6 cells without affecting Il6 mRNA levels. Hepa1-6 cells were transduced with a doxycycline (Dox)-inducible MMP-9 expression construct (pLVX-Tet-On-mMMP-9). (A) MMP-9 enzymatic activity in the conditioned medium was assessed by zymography following Dox treatment (1 µg/mL, 24 h). (B) Intracellular MMP-9 protein levels were evaluated by immunoblotting. (C–F) Cells were co-treated with 24-hour Dox (1 µg/mL) and 8-hour LPS (100 ng/mL). The mRNA levels of Mmp9, Il6, and Tnf were measured by qPCR. Rpl19 was used as a housekeeping gene. (D) Secreted IL-6 levels in the conditioned medium were measured by ELISA following 24-hour co-treatment with Dox and LPS stimulation. Data are presented as mean ± SEM (n = 3–6 per group). Statistical comparisons were performed using unpaired t-tests. *P < 0.05, **P < 0.01 vs. control; ns: not significant. m: marker.