Benzo[a]pyrene induces epithelial tight junction disruption and apoptosis via inhibiting the initiation of autophagy in intestinal porcine epithelial cells

Abstract

Ingestion of food contaminated with benzo[a]pyrene (B[a]P) poses health risks to animals and humans. However, the toxicity of B[a]P exposure on the intestinal barrier function and underlying mechanisms remain obscure. In the present study, intestinal porcine epithelial cells (IPEC-1) were challenged with different doses of B[a]P and its deleterious effects were determined. We found that B[a]P exposure led to impaired intestinal tight junction function as evidenced by reduced transepithelial electric resistance, increased permeability, and downregulated intestinal tight junction protein levels. Further study demonstrated that B[a]P treatment induced cell cycle arrest, and resulted in oxidative damage-related apoptosis in IPEC-1 cells. Intriguingly, we observed an inhibition of autophagy and an activation of unfolded protein response (UPR) in B[a]P-challenged cells, when compared with controls. To investigate the role of autophagy on B[a]P-induced epithelial tight junction disruption and apoptosis, cells were cotreated with B[a]P and rapamycin, and rapamycin dramatically improved intestinal tight junction and reduced apoptosis, indicating a protective effect of autophagy for the cells in response to B[a]P treatment. We also explored the role of UPR in B[a]P-induced cellular damage by using 4-phenylbutyric acid, an antagonist of UPR. Interestingly, B[a]P-induced apoptosis and dysfunction of the intestinal tight junction were exacerbated by 4-phenylbutyric acid, and the 4-phenylbutyric acid didn't ameliorate the inhibitory effects of B[a]P on microtubule-associated protein 1 light chain 3 (LC3-II) and lysosomal-associated membrane protein 2 (LAMP2) in IPEC-1 cells. These novel findings provided herein indicated that B[a]P induces intestinal epithelial tight junction disruption and apoptotic cell death via inhibiting autophagy in IPEC-1 cells.