Lipopolysaccharide (LPS)-induced autophagy is involved in the restriction of Escherichia coli in peritoneal mesothelial cells
Department of Nephrology, The First Affiliated Hospital, Sun Yat-sen University, 58th, Zhongshan Road II, Guangzhou 510080, China
BMC Microbiology 2013, 13:255 doi:10.1186/1471-2180-13-255Published: 13 November 2013
Host cell autophagy is implicated in the control of intracellular pathogen. Escherichia coli (E.coli) is the most common organism caused single-germ enterobacterial peritonitis during peritoneal dialysis. In this study, we investigated autophagy of peritoneal mesothelial cells and its role in defense against E.coli.
Autophagy in human peritoneal mesothelial cell line (HMrSV5) was induced by lipopolysaccharide (LPS) in a dose-dependent and time-dependent way, which was demonstrated by increased expression of Beclin-1 and light chain 3 (LC3)-II, the accumulation of punctate green fluorescent protein-LC3, and a higher number of monodansylcadaverine-labeled autophagic vacuoles. After incubation of HMrSV5 cells with E.coli following LPS stimulation, both the intracellular bactericidal activity and the co-localization of E.coli (K12-strain) with autophagosomes were enhanced. Conversely, blockade of autophagy with 3-methyladenine, wortmannin or Beclin-1 small-interfering RNA (siRNA) led to a significant reduction in autophagy-associated protein expression, attenuation of intracellular bactericidal activity, and reduced co-localization of E.coli with monodansylcadaverine-labeled autophagosomes. In addition, treatment of HMrSV5 cells with LPS caused a dose-dependent and time-dependent increase in Toll-like receptor 4 (TLR4) expression. Both knockdown of TLR4 with siRNA and pharmacological inhibition of TLR4 with Polymyxin B significantly decreased LPS-induced autophagy. Furthermore, TLR4 siRNA attenuated remarkably LPS-induced intracellular bactericidal activity.
Our findings demonstrated for the first time that LPS-induced autophagy in peritoneal mesothelial cells could enhance the intracellular bactericidal activity and the co-localization of E.coli with autophagosomes. The activation of TLR4 signaling was involved in this process. These results indicate that LPS-induced autophagy may be a cell-autonomous defense mechanism triggered in peritoneal mesothelial cells in response to E.coli infection.