CXCL6 Is a Novel Biliary Marker and a Downstream Target of MMP7 in Biliary Atresia.

Objective: MMP7 has been identified as a potential biomarker for biliary atresia (BA) diagnosis. However, the mechanism of MMP7 and its downstream signaling pathway remain unknown in the pathogenesis of BA. Herein, this study was performed to figure out MMP7's downstream target.

Methods: Single-cell RNA sequencing (scRNA-seq) was performed to screen out MMP7's downstream molecule CXCL6. QRT-PCR, immunohistochemistry, western blot, and ELISA were used to determine the expressions of MMP7 and CXCL6 in the liver and serum of BA and controls. Immunofluorescence was conducted to validate the hepatic cellular expressions of MMP7 and CXCL6. In vitro, overexpression and knockdown of MMP7 in biliary epithelial cells (BECs) were established to verify the MMP7's regulation on CXCL6.

Results: ScRNA-seq demonstrated that MMP7 and CXCL6 were exclusively expressed on cholangiocytes and up-regulated in BA when compared with normal controls (NC). QRT-PCR, immunohistochemistry, western blot and ELISA validated the higher expressions of MMP7 and CXCL6 in the liver and serum of BA when compared with non-BA cholestasis (CS) and NC. Immunofluorescence further verified the biliary localization of MMP7 and CXCL6 in BA. Hepatic and serum CXCL6 expressions were positively correlated with MMP7 expressions, and both expressions were correlated with the stages of fibrosis in BA. Overexpression of MMP7 promoted CXCL6 expression, while knocking down MMP7 inhibited CXCL6 expression in BECs.

Conclusions: CXCL6 is a downstream target of MMP7, and is identified as a novel biliary marker in BA. The production of CXCL6 by MMP7 may exert pathological roles in the liver fibrogenesis of BA.