Early host-parasite interaction models reveal a key role for fibrinolysis in Fasciola hepatica intestinal migration

Fasciola hepatica is the most common etiologic agent of fasciolosis, a parasitic disease that affects millions of ruminants worldwide and a zoonotic human infection of public health concern. Upon ingestion of infective metacercariae, F. hepatica newly excysted juveniles (FhNEJ) emerge in the duodenum and cross the intestinal wall to initiate a migration route that culminates with their establishment within the hepatic bile ducts. The ability of FhNEJ to exploit the broad-spectrum activities of host plasmin, the central protease of the fibrinolytic system, has been proposed as a strategy employed by these parasites to migrate across the intestinal wall while minimising energy expenditure.

Mouse intestinal epithelial cells (mPSIEC) were stimulated with FhNEJ and plasminogen (PLG), the zymogen of plasmin, to understand whether FhNEJ-stimulated plasmin generation modulates processes relevant to parasite migration through the intestinal wall, including extracellular matrix (ECM) degradation and the secretion of ECM-degrading enzymes. Plasmin-mediated cellular responses were further examined by proteomic analysis of mPSIEC whole-cell lysates. In parallel, the contribution of the fibrinolytic system in FhNEJ migration was studied in vivo by infecting mice with F. hepatica metacercariae following pharmacological inhibition of fibrinolysis.

Co-stimulation of mPSIEC with FhNEJ and PLG led to increased plasmin generation in the intestinal pericellular space, which was associated with enhanced collagen degradation and secretion of the urokinase-type plasminogen activator. In addition, using independent cell culture replicates and a stringent statistical pipeline, we identified a robust set of differentially expressed proteins in mPSIEC following stimulation with FhNEJ and PLG. These proteins were involved in cell adhesion, migration, ECM remodelling, immune evasion and fibrinolysis. Despite inter-experimental variability, FhNEJ migration in mice was reduced upon pharmacological inhibition of fibrinolysis, supporting the contribution of host fibrinolysis to parasite invasion in vivo.

Altogether, this work provides unprecedented insights into the role of the host fibrinolytic system to FhNEJ migration across mammalian host tissues, thereby advancing our understanding of host-parasite relationships during early stage fasciolosis and highlighting interesting directions for future research in this area.