Incomplete autophagy promotes the replication of Mycoplasma hyopneumoniae.

Autophagy is an important cellular homeostatic mechanism for recycling of degradative proteins and damaged organelles. Autophagy has been shown to play an important role in cellular responses to bacteria and bacterial replication. However, the role of autophagy in Mycoplasma hyopneumoniae infection and the pathogenic mechanism is not well characterized. In this study, we showed that M. hyopneumoniae infection significantly increases the number of autophagic vacuoles in host cells. Further, we found significantly enhanced expressions of autophagy marker proteins (LC3-II, ATG5, and Beclin 1) in M. hyopneumoniae-infected cells. Moreover, immunofluorescence analysis showed colocalization of P97 protein with LC3 during M. hyopneumoniae infection. Interestingly, autophagic flux marker, p62, accumulated with the induction of infection. Conversely, the levels of p62 and LC3-II were decreased after treatment with 3-MA, inhibiting the formation of autophagosomes, during infection. In addition, accumulation of autophagosomes promoted the expression of P97 protein and the survival of M. hyopneumoniae in PK-15 cells, as the replication of M. hyopneumoniae was down-regulated by adding 3-MA. Collectively, these findings provide strong evidence that M. hyopneumoniae induces incomplete autophagy, which in turn enhances its reproduction in host cells. These findings provide novel insights into the interaction of M. hyopneumoniae and host.