Mycoplasma bovis Infection Induces Apoptosis Through Gadd45/XIAP in Bovine Macrophages

Mycoplasma bovis (M. bovis) adheres to host cells and persists intracellularly, causing chronic inflammation and significant economic losses in the cattle industry. The role of host cell apoptosis in this host-pathogen interaction remains unclear. This study isolated and identified the M. bovis Xinjiang strain XJ01 from diseased cattle in China. XJ01 exhibited typical "fried egg" colony morphology, distinct biochemical characteristics, and a 1.02 Mb genome (29.33% GC content) encoding 939 genes, including 93 unique genes. Functional analysis under optimal infection conditions (MOI = 1000, 24 h) revealed that XJ01 induced significant apoptosis and reduced viability in bovine macrophages (BoMac). This was accompanied by mitochondrial homeostasis disruption, characterized by increased Bax expression and suppressed Bcl-2 levels. Transcriptome analysis identified 9926 differentially expressed genes. KEGG pathway enrichment indicated significant activation of apoptosis and P53 signaling pathways, with Gadd45 and XIAP identified as key regulators. Mechanistic validation demonstrated that Gadd45 overexpression or XIAP knockdown enhanced Bax expression, inhibited Bcl-2, increased apoptosis rates, and consequently significantly reduced intracellular bacterial load at 24 h post-infection. Conversely, suppressing Gadd45 or overexpressing XIAP promoted pathogen survival. Collectively, this study reveals that M. bovis XJ01 activates host stress signaling to upregulate Gadd45 and suppress XIAP, thereby triggering mitochondrial apoptosis as a mechanism to eliminate intracellular bacteria-illustrating a self-limiting antibacterial mechanism.