Mycoplasma hyopneumoniae Mhp597 is a cytotoxicity, inflammation and immunosuppression associated nuclease

Nucleases are ubiquitously recognized as essential proteins in mycoplasmas because these organisms lack most capacities for de novo synthesis of nucleotides. Some of these proteins were proved to be important pathogenic factors during the Infection of mycoplasms. In this study, the protein Mhp597 from M. hyopneumoniae was expressed and purified in Escherichia coli. Analysis of Nuclease activity showed that recombinant Mhp597 (rMhp597) was a CA₂₊ or Mg₂₊ dependent thermostable Nuclease with very high activity and neutrophil extracellular traps (NETs) induced by M. hyopneumoniae were completely degraded by this Nuclease. In addition, when PK15 cells were incubated with different concentrations of rMhp597, their viability was reduced and cell Apoptosis was observed in a dose-dependent manner. To further investigate the host immune system response, we report that rMhp597 up-regulated the exression of inflammatory genes showing that TLR4/MyD88/NF-κB signal pathway was involved. On the other hand, rMhp597 down-regulated the expression of type I IFN (IFN-α/β) and promoted the multiplication of porcine reproductive and respiratory syndrome virus (PRRSV). Recombinant rMhp597δ^315-377 lacking C-terminal 63 Amino acids exhibited all biological functions mentioned above except for Nuclease activity. In summary, Mhp597 is a dynamic secreted Nuclease involved in cytotoxicity, inflammation and immunosuppression.