Carvacrol alleviates endoplasmic reticulum stress and inflammation induced by lipopolysaccharide by enhancing endoplasmic reticulum autophagy in dairy mammary epithelial cells

Mastitis is a common disease in dairy cows and has various causes. Because of its enormous negative impact on cow health, welfare, and productivity, it results in huge economic losses and threatens sustainability of the dairy industry. In dairy cows with mastitis, excessive inflammation caused by LPS is an important factor leading to mammary tissue damage. It has been reported that there is a coupling effect between endoplasmic reticulum (ER) stress (ER-stress) and inflammatory response. When ER-stress occurs, misfolded and unfolded proteins accumulate in the ER lumen and lead to ER expansion, which can be degraded by the ER autophagy (ER-phagy) pathway to maintain cell homeostasis and ER morphology and activity. Therefore, the search for effective activators that enhance ER-phagy of bovine mammary epithelial cells may be the focus of relieving ER-stress and inflammation in dairy cows with mastitis. Using in vivo experiments, we investigated ER-phagy, ER-stress, and the nuclear factor kappa-B (NF-κB) inflammatory pathway in mammary tissue of healthy cows and cows with clinical mastitis. We found that ER-stress pathways and NF-κB inflammatory pathways were activated while the ER-phagy was blocked in mammary tissue of cows with clinical mastitis compared with healthy cows. In in vitro experiments, we used LPS to stimulate the immortalized bovine mammary epithelial cell line (MAC-T cells) to produce in vitro bovine mastitis models and the effects of carvacrol (CAV) on ER-stress and inflammation were investigated. In accordance with our research, CAV was found to alleviate LPS-induced inflammation and ER-stress in MAC-T cells. In addition, by knocking down ER-phagy protein FAM134B, we demonstrated that the effect of CAV on ER-stress and inflammation disappeared after knocking down FAM134B. These outcomes suggest that CAV can relieve LPS-induced inflammation and ER-stress by enhancing ER-phagy in MAC-T cells. Therefore the application of CAV deserves further study as a potential nonresistant treatment for dairy cows with clinical mastitis and a good alternative for antibiotics.