<i>Klebsiella pneumoniae</i> Induces Ferroptosis and Lactation Dysfunction in Bovine Mastitis via NCOA4-Mediated Ferritinophagy

<i>Klebsiella pneumoniae</i>, a major bovine mastitis pathogen, disrupts mammary gland function through poorly understood mechanisms. This study demonstrates that <i>K. pneumoniae</i> infection triggers ferroptosis in bovine mammary epithelial cells (BMECs) via nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy, leading to lactation impairment. RNA sequencing revealed enrichment in ferroptosis, autophagy, and iron metabolism pathways. Infection time-dependently suppressed glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) expression, causing mitochondrial membrane potential collapse and lipid peroxidation. Crucially, <i>K. pneumoniae</i> activated NCOA4-dependent ferritin degradation, elevating intracellular Fe²⁺. NCOA4 knockdown alleviated ferroptosis, restored GPX4/SLC7A11 expression, reduced the bacterial load, and partially rescued lactation markers (fatty acid synthase, acetyl-CoA carboxylase 1, and β-casein). In vivo, infected mammary glands showed iron overload, 4-hydroxynonenal accumulation, lactation protein suppression, and pathological damage, correlating with NCOA4/ferritin heavy chain 1 upregulation. These findings establish NCOA4-mediated ferritinophagy as a key driver of <i>K. pneumoniae</i>-induced ferroptosis and lactation dysfunction, suggesting novel therapeutic targets for mastitis.