Title : Alpha-1-antitripsin, a key target to understand Shigella pathogenesis in humans
Abstract:
Shigella spp. are highly adapted pathogens that cause bacillary dysentery in human and non-human primates. An unusual feature of Shigella pathogenesis is that this organism invades and subsequently colonizes the colonic epithelia from the basolateral pole. Therefore, Shigella has evolved the ability to disrupt the intestinal epithelial barrier to reach the submucosa and invade epithelial cells. Our lab has previously described that the secreted Serine Protease A (SepA), which belongs to the family of Serine Protease Autotransporters of Enterobacteriaceae, is responsible for the initial destabilization of the intestinal epithelial barrier that facilitates Shigella invasion. However, the mechanisms used by SepA to regulate this process remain unknown. Therefore, to investigate the protein targets cleaved by SepA in the gut, we incubated a sample of homogenized human colon with purified SepA or with a catalytically inactive mutant of this protease. The results revealed that SepA targets an array of 18 different proteins, including α-1-antitrypsin (AAT), a major circulating serine proteinase inhibitor in humans. In contrast to other serine proteases, SepA cleaved AAT without forming an inhibitory complex. Instead, SepA’s enzymatic activity significantly increased in the presence of high concentrations of AAT (1:5 and 1:10 in a molar ratio). We determined that SepA hydrolyzes the Met-358-Ser-359 bond of AAT, which results in the release of a 4.2 kDa peptide previously described to behave as a neutrophil chemoattractant. Furthermore, we demonstrated that the products of the AAT-SepA reaction induce a mild but significant increase in neutrophil transepithelial migration in vitro. Moreover, the presence of AAT during Shigella infection stimulated an increase in neutrophil transmigration and dramatically enhanced the number of bacteria invading enterocytes in a SepA-dependent manner. We conclude that by cleaving AAT, SepA releases a chemoattractant that promotes neutrophil migration, which in turn disrupts the intestinal epithelial barrier to enable Shigella invasion. We posit that the activation of SepA by an excess of AAT could be physiologically relevant during the earlier stages of Shigella infection when the amount of synthesized SepA would be very low compared to the concentration of AAT in the intestinal lumen. Altogether, our results could be critical to explain the high infectivity of Shigella in vivo despite the requirement of first reaching the basolateral side to invade and colonize the colonic epithelium.
What will audience learn from your presentation?
- The audience will learn how Shigella, a human enteric pathogen, has evolved to hijack the immune system to facilitate the colonization of the colon. This knowledge will be relevant for the design of new in vivo models to study Shigella infection, which ultimately could be used for the development of new vaccines or therapies to treat this disease.
