Conjugated Linoleic Acid Ameliorates Staphylococcus aureus-Induced Inflammation, Oxidative Stress, and Mitophagy via the PPARG-UCP2 Pathway in Hu Sheep Mastitis

Staphylococcus aureus (S. aureus)-induced mastitis poses a significant threat to animal husbandry. This condition triggers sustained mammary inflammation, oxidative stress, and disrupts mitochondrial homeostasis, ultimately impairing mammary gland function and milk yield. Conjugated linoleic acid (CLA) is a long-chain fatty acid found in meat and dairy products derived from ruminants. It exhibits multiple biological activities, including anti-cancer, anti-inflammatory, and antioxidative stress-alleviating effects. Thus, this study sought to determine whether CLA alleviates S. aureus-induced mastitis in Hu sheep through the PPARG-UCP2 axis. Fifteen lactating Hu sheep were randomly allocated into three groups (n = 5): control group, model group, and CLA group. The CLA group received 1 mg/mammary gland of CLA via intramammary infusion for seven days, followed by S. aureus challenge (5 × 107 cells/mL, 2 mL/mammary gland) in the model and CLA groups, while the control group received saline. Venous blood and mammary tissue samples were collected at two days post-infection. The results demonstrated that S. aureus infection significantly upregulated the expression of inflammatory factors (IL-1β, IL-6, and NF-κB) in the mammary tissue of Hu sheep, p < 0.01. Relative to the control, the model group showed increased ROS and MDA levels, a diminished NAD+/NADH ratio, and downregulated expression of the antioxidant factors SOD, Nrf2, HO-1, and SIRT3, p < 0.01. Furthermore, the expression of p-AMPK and mitophagy-related factors (PARKIN, PINK1, and LC3b) showed a statistically significant increase in the model group than in the control group, p < 0.01. S. aureus infection also suppressed the expression of PPARG and UCP2, p < 0.01. In contrast, the CLA group showed lower levels of inflammatory factors (IL-1β, IL-6, and NF-κB), ROS and MDA, while the NAD+/NADH ratio and the expression of antioxidant factors (SOD, p-Nrf2, HO-1, and SIRT3) were elevated compared with the model group, p < 0.01. Moreover, the expression of p-AMPK and mitophagy-related factors (PARKIN, PINK1, and LC3b) was reduced in the CLA group relative to the model group, p < 0.05. Concurrently, the expression of PPARG and UCP2 was higher in the CLA group than in the model group, p < 0.001. These findings demonstrated that S. aureus infection induced mastitis in Hu sheep mammary tissue, whereas CLA alleviated the infection by upregulating the PPARG-UCP2 pathway, thereby reducing inflammation, oxidative stress, and mitophagy levels. This study offers a novel perspective on mammary tissue repair during mastitis and expands the understanding of UCP2’s biological role.