l-Glutamic Acid Alleviates Mastitis in Dairy Cows by Targeting the Sirt5/Nrf2/Prdx1 Signaling Axis and Mitochondrial Function.

Mastitis in dairy cows is an inflammatory disease that severely affects the health and lactation functions of dairy cows. Mitochondrial damage is closely related to the inflammatory response. How to effectively alleviate mitochondrial damage is the key to preventing and treating mastitis in dairy cows. In this study, we found elevated levels of inflammatory response and mitochondrial damage accompanied by reduced expression of Sirt5 (Sirtuin5) in cows with mastitis compared with healthy cows. This suggests that Sirt5 plays an important role in mastitis in dairy cows. Subsequently, we further analyzed mammary gland tissue from healthy and mastitis cows by untargeted metabolomics (LC-MS/MS) and screened for the differential metabolite l-glutamic acid (l-Glu). To further validate the effect of l-Glu on mastitis in dairy cows, we conducted a study using MAC-T cells. The results showed that l-Glu was able to ameliorate LPS-induced mitochondrial damage by activating Sirt5 and promoting mitochondrial fusion and the upregulation of mitochondrial membrane potential (MMP) levels. In contrast, l-Glu was unable to protect mitochondrial function after knocking down Sirt5. Furthermore, we found that l-Glu was able to upregulate the expression of nuclear factor E2-related factor (Nrf2) and peroxiredoxin 1 (Prdx1) in LPS-induced MAC-T cells, and promoted the entry of Nrf2 into the nucleus, which was reversed by knocking down Sirt5. Next, we further explored whether l-Glu alleviates mitochondrial damage through the Nrf2/Prdx1 signaling axis by using the Nrf2 inhibitor RA. The results showed that the use of RA promoted LPS-induced mitochondrial damage and blocked the protective effect of l-Glu on mitochondrial function. In conclusion, l-Glu ameliorates mitochondrial damage by targeting Sirt5 to activate the Nrf2/Prdx1 signaling axis and alleviate mastitis in dairy cows. This study provides a new target and theoretical basis for the clinical control of mastitis. l-Glu could be added as a dietary supplement to the diets of dairy cows and maintain mammary gland homeostasis, thereby protecting the health and economic value of dairy cows.