Doxycycline Induces Mitophagy and Suppresses Production of Interferon-ß in IPEC-J2 Cells

Xing, Yang; Liqi, Zhu; Jian, Lin; Qinghua, Yu; Qian, Yang

Previous studies have reported that DOX inhibits the proliferation of various cell lines (Lokeshwar et al., 2002; Wu et al., 2006; Ahler et al., 2013) . In our study, DOX treated 24 h would not inhibit cell viability by the MTT assay. We observed a high dose of DOX enhanced cell viability, it might be due to that mitochondrial mass could affect the result of MTT assay (Gerlier and Thomasset, 1986) . DOX inhibits oxidative phosphorylation, increases the level of ROS, and reduces ATP synthesis through its mitochondrial actions (Kalghatgi et al., 2013) . Our results show that DOX increased the level of ROS or mitoROS in a dose dependent manner and induced oxidative stress in IPEC-J2 cells. The mitochondrial membrane potential of IPEC-J2 cells was not affected by DOX (Figure 2) , albeit three studies have reported that DOX decreases mitochondrial membrane potential (Sourdeval et al., 2006) . DOX provides a balance between mitochondrial fission and the accumulation of fragmented mitochondria (Moullan et al., 2015) . The number of dysfunctional mitochondria increased significantly in IPEC-J2 cells after DOX incubation (Figure 2) . We can observe that the number of dysfunctional mitochondria for both 1 and 100 ug/ml of DOX is similar. It might be due to the fact that 100 ug/ml DOX can induce significantly mitophagy to maintain relative mitochondrial dynamics by removing damaged mitochondria. A review reported that six of seven studies support the apoptotic action of DOX, whereas one study showed an anti-apoptotic effect (Sagar et al., 2010) . Unexpectedly, we found that DOX increased the number of dysfunctional mitochondria without apoptosis.