Glaesserella parasuis serotype 5 disrupts the swine respiratory epithelial barrier via NBR1-mediated selective autophagic degradation of Claudin-1.

Abstract

Glaesserella parasuis (G. parasuis) colonizes the upper respiratory tract of pigs and can cause systemic infection through disruption of the epithelial barrier of the respiratory tract, resulting in substantial economic losses to the swine industry worldwide. A previous study revealed that infection with the G. parasuis serotype 5 strain HPS5-SQ breaks through the swine respiratory epithelial barrier by inducing autophagic degradation of the tight junction protein Claudin-1. However, the underlying mechanism remains incompletely understood. In this study, co-immunoprecipitation (Co-IP) results revealed that Claudin-1 interacted with the selective autophagy receptor NBR1 during HPS5-SQ infection and that HPS5-SQ promoted the interaction between NBR1 and Claudin-1. Moreover, colocalization of Claudin-1, NBR1 and the autophagic marker protein LC3 was observed in HPS5-SQ-infected cells. These results suggested that NBR1 is involved in the degradation of Claudin-1 in HPS5-SQ-infected swine tracheal epithelial cells (STECs). In addition, knockout of NBR1 suppressed the reduction in Claudin-1 expression in HPS5-SQ-infected STECs, significantly restored the integrity of Claudin-1 and inhibited the increase in swine respiratory epithelial barrier permeability, resulting in decreased HPS5-SQ translocation. In general, the above results indicated that autophagic degradation of Claudin-1 induced by G.parasuis serotype 5 was dependent on the NBR1 receptor. Consequently, the epithelial barrier was disrupted. This study further revealed the mechanism by which G. parasuis serotype 5 breaks through the swine respiratory barrier, which is conducive to clarifying the pathogenic mechanism of G. parasuis infection.