The differential roles of Giardia duodenalis-secreted tenascins in inducing intestinal epithelial cell apoptosis and the attributed EGFR-STAT3 axis regulation.

Giardia duodenalis is an important extracellular protozoan parasite of the gut responsible for waterborne diarrhea in human and nonhuman animals worldwide. Giardia trophozoites express and secrete excretory-secretory proteins (ESPs) affecting structural, cellular, and soluble components of the host small intestinal milieu, of which tenascins are present in high abundance. Giardia-induced intestinal epithelial cell (IEC) apoptosis is known as an important aspect of pathogenesis of giardiasis, while the underlying molecular mechanisms remain largely unclear. Here we used in vitro models of IECs to explore the regulatory mechanism of Giardia-induced apoptosis. We initially confirmed the occurrence of apoptosis and the activation of epidermal growth factor receptor (EGFR) when IECs were exposed to Giardia trophozoites, and EGFR activation involved Giardia-induced IEC apoptosis. The recombinant Tenascin15, Tenascin30, and Tenascin33 were then studied for their potential to activate EGFR/signal transducer and activator of transcription 3 (STAT3)-dependent IEC apoptosis. All the three recombinant proteins were demonstrated to be effective in triggering IEC apoptosis and EGFR/STAT3 activation. Strikingly, IEC apoptosis induced by rTenascin15 and rTenascin30 were found to be dependent on the activation and nuclear translocation of EGFR and STAT3, while this is not the case for rTenascin33. Collectively, our study identified tenascins as potential virulence factors related to Giardia-induced IEC apoptosis, and demonstrated that EGFR-STAT3 axis played a critical regulatory role in the process, advancing our understanding of the pathogenesis of Giardia infection.