Mechanisms and targeted prevention of abnormal ductular reaction caused by a low concentration of Benzo(a)pyrene.

The impact of long-term exposure to low concentrations of environmental pollutants on hepatobiliary diseases is a major public health issue. Benzo(a)pyrene (B[a]P) is a common environmental toxin classified by the International Agency for Research on Cancer as a Group I carcinogen. Abnormal ductular reaction (DR) is a major pathological feature of hepatobiliary diseases; however, the underlying molecular mechanisms of B[a]P-induced abnormal DR remain unclear. This study revealed that chronic exposure to a low concentration of B[a]P increased the expression of a glucose-regulated protein (GRP75) in cholangiocytes. As GRP75 is a bridge protein for the endoplasmic reticulum (ER)-mitochondrial junction, the overexpression of GRP75 abnormalizes ER-mitochondria coupling. These biological processes facilitated Ca²⁺ release from the ER into the mitochondria and caused mitochondrial Ca²⁺ overload, leading to the overproduction of reactive oxygen species (ROS). The increased ROS activates epithelial-mesenchymal transition (EMT) and ultimately induces a profibrotic phenotype in bile duct cells (BECs). These cells secreted collagen and activated hepatic stellate cells through paracrine activity, which synergistically promoted the development and progression of fibrosis. Finally, via drug screening and functional analysis, we innovatively revealed a traditional Chinese medicine monomer, luteolin, which could prevent B[a]P-induced abnormal DR and hepatic fibrosis by targeting GRP75. Our study offers new insights into environmental toxin-induced hepatobiliary diseases and suggests a potential key interventional target or approach for the prevention of abnormal DR.