Estradiol inhibits autophagy of Mycobacterium tuberculosis-infected 16HBE cells and controls the proliferation of intracellular Mycobacterium tuberculosis

Tracheobronchial tuberculosis (TBTB) is most common in young, middle-aged females. Despite adequate anti-tuberculosis therapy, >90% of patients develop tracheobronchial stenosis, which has a high rate of resulting in disability. The present study aimed to explore the effect of estradiol on the development of TBTB. Estrogen receptor (ER) expression in granulomatous tissue was assessed via immunofluorescence. In order to determine whether estrogen affected the proliferation of intracellular Mycobacterium tuberculosis (Mtb), 16HBE cells were infected with Mtb in vitro, followed by estradiol treatment. Intracellular Mtb was quantified via colony counting. The effect of estradiol on autophagy of infected 16HBE cells was determined via western blotting and transmission electron microscopy. Necrosis assays of infected 16HBE cells were analyzed using propidium iodide staining and assessing lactate dehydrogenase (LDH) release. To determine how estradiol affects autophagy, infected 16HBE cells were treated with ER-specific and non-specific modulators. Reactive oxygen species (ROS) levels were analyzed via flow cytometry. Additionally, the protein expression levels of autophagy-associated proteins were determined via western blotting. Mtb could enter human lobar bronchial goblet cells and ciliated cells in patients with TBTB. The results also demonstrated that ER alpha was expressed in granulomatous tissue from patients with TBTB. Administration of 10(-6) M estradiol reduced the number of intracellular Mtb colony-forming units in vitro in the 16HBE human bronchial epithelial cell line at day 3 after infection. Furthermore, cells treated with estradiol and infected with Mtb released less LDH at 72 h and exhibited reduced necrosis levels at 24 h compared with the untreated cells. In addition, autophagy of infected 16HBE cells was inhibited by estradiol. Estradiol and the specific ER alpha agonist had similar effects on autophagy in infected 16HBE cells. Additionally, treatment with the ER alpha antagonist abolished the inhibition of autophagy by estradiol in infected 16BHE cells. Compared with the untreated infected 16HBE cells, the ROS levels in the infected 16HBE cells treated with estradiol and the ER alpha agonist significantly decreased. The levels of phosphorylated (p)-mTOR and p-AKT notably increased in estradiol- and ER alpha agonist-treated infected 16HBE cells. In summary, estradiol may serve a key role in the development of TBTB through binding to ER alpha.

Automated summary

Tracheobronchial tuberculosis (TBTB) is most common in young, middle-aged females. Despite adequate anti-tuberculosis therapy, tracheobronchial stenosis still occurs in most patients, leading to a high disability rate. This study investigated the role of estradiol in the development of TBTB and found that estradiol may play a key role through binding to ER alpha.