m6A-modified exosome-derived circHIF1α binding to KH domain of IGF2BP3 mediates DNA damage and arrests G1/S transition phase to resists bacterial infection in bacteremia

BackgroundAnimal and human health are seriously threatened by bacterial infections, which can lead to bacteremia and extremely high rates of morbidity and mortality. Recently, there have been reports indicating the involvement of exosomal circular RNAs (circRNAs) in a range of human disorders and tumor types. However, the role of exosomal circRNAs in bacterial infection remains elusive.MethodsWe extracted and identified exosomes from the culture medium of PIEC cells infected with or without Glaesserella parasuis. RNA sequencing analysis was performed on the exosomes to screen and identify circRNAs (circHIF1 alpha) associated with Glaesserella parasuis infection. PIEC cells were infected with Staphylococcus aureus or Streptococcus suis 2 to further determine whether exosome-derived circHIF1 alpha was the crucial circHIF1 alpha associated with bacterial infections. The transmission process of exosomes and their circHIF1 alpha between cells was clarified via exosome tracing and co-culture assay. Moreover, the mechanism of circHIF1 alpha being packaged into exosomes was explored, and the effects of exosomes and their circHIF1 alpha on cell proliferation, DNA damage and cell cycle were analyzed. In addition, the binding mode and site of interacting proteins with circHIF1 alpha were further determined. In vivo and in vitro, the role of exosomes and their circHIF1 alpha in host resistance to bacterial infection was confirmed.ResultsWe first discovered a new circHIF1 alpha that was very stable and detectable, encapsulated into exosomes by hnRNPA2B1, and whose expression in exosomes of bacterially infected PIEC cells significantly decreased. Additionally, exosomal circHIF1 alpha reduced bacterial infection both in vitro and in vivo and suppressed the growth of reception cells. Mechanistically, the circHIF1 alpha interacted with the KH domain of IGF2BP3 in an m6A-modified manner, which mediated DNA damage to arrest the cells at the G1/S phase through the interaction between the regulator of Chromosome Condensation 2 (RCC2) and gamma-H2AX protein. Exosomal circHIF1 alpha is a unique therapeutic target for bacterial infection since this work highlights its critical function in fighting bacterial infection.