M6A-regulated LncRNA7825 maintains epithelial barrier integrity to restrict bacterial infection.

The blood-milk barrier is essential for maintaining the homeostasis of the mammary microenvironment and safeguarding milk quality. Bacterial infection-induced mastitis is a major disease burden in the dairy industry. During bacterial mastitis, the blood-milk barrier is highly susceptible to disruption, and breakdown of structure integrity is among the earliest pathological events. However, the molecular regulatory mechanisms underlying this process remain poorly understood. In this study, we identify LncRNA7825 as a critical regulatory molecule, a host-protective long non-coding RNA that preserves epithelial tight junction integrity under bacterial challenge and plays a pivotal role in maintaining mammary epithelial homeostasis. By integrating MeRIP-seq and RNA-seq data from our previous studies, we found that LncRNA7825 is significantly downregulated at the transcriptional level following bacterial infection and is dynamically regulated by N6-methyladenosine (m6A) modification. Notably, elevated cellular m6A levels achieved via ALKBH5 knockdown result in reduced transcription of LncRNA7825. Functional studies showed that overexpression of LncRNA7825 restores mitochondrial potential, limits ROS accumulation, and attenuates epithelial apoptosis induced by multiple mastitis-associated pathogens. Importantly, LncRNA7825 preserves tight junction organization and effectively restricts bacterial adhesion to and invasion of mammary epithelial cells. Furthermore, LncRNA7825 is divergently transcribed with its neighboring gene DIP2A from a shared bidirectional promoter, forming a coordinated transcriptional unit that participates in regulating the pathological process of bacterial infection. Collectively, our findings demonstrate that LncRNA7825 acts as a multi-layered regulatory factor that integrates epitranscriptomic regulation, mitochondrial homeostasis, and coordinated genomic transcription to protect mammary epithelial barrier integrity during bacterial infection.