Hypoxia-induced HIF-1α promotes invasion into tilapia.

is a nuclear transcription factor, and its activity is tightly regulated by the level of available oxygen in cells. Here, we investigated the roles of in the invasion of into tilapia under hypoxic environments. We found that the expression levels of in examined tissues of hypoxic tilapia were significantly upregulated, indicating that the tissue cells have been in hypoxic conditions. After 24-h infection with , we found that bacterial burden counts increased significantly in all examined tissues of hypoxic fish. To explore why the bacterial count increased significantly in the tissues of hypoxic fish, we modulated expression through RNAi technology. The results indicated that expression levels were positively related to expression. Since c-Met is the receptor of InlB that plays critical roles in the adhesion and invasion of , the ∆ strain was used to further explore the reason for the significant increase in bacterial counts in hypoxic fish. As expected, the decrease in the adhesion ability of ∆ suggested that InlB mediates infection in tilapia. After being infected with ∆ strain, we found that the bacterial counts in hypoxic fish were not affected by hypoxic conditions or expression levels. These findings indicate that may promote the internalization of InlB by upregulating expression and therefore contributes to the invasion of into hypoxic tilapia. IMPORTANCE is a zoonotic food-borne bacterial pathogen with a solid pathogenicity for humans. After ingestion of highly contaminated food, is able to cross the intestine invading phagocytic and nonphagocytic cells and causes listeriosis. China is the world's largest supplier of tilapia. The contamination rate of to tilapia products was as high as 2.81%, causing a severe threat to public health. This study revealed the underlying regulatory mechanisms of in the invasion of into tilapia under hypoxic environments. This study will be helpful for better understanding the molecular mechanisms of hypoxic environments in infection to tilapia. More importantly, our data will provide novel insights into the prevention and control of this pathogen in aquaculture.