Investigation of a Selective Transglutaminase 2 Antagonist as a Novel Therapeutic Agent for Cystic Fibrosis

Abstract

Cystic fibrosis (CF) is a genetic disorder, characterised by the presence of a dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR) protein. Currently approved therapeutic compounds all act by targeting CFTR directly. Yet, emerging evidence suggests that the proteostasis network within CF airway epithelial cells is severely disrupted, leading to fibrotic alterations of the extracellular matrix (ECM). TG2 is reported to be a key regulator of these pathogenic changes. With the advent of potent and selective inhibitors of TG2, a novel therapeutic avenue may now exist in CF. In this study, both immortalised and primary CF human bronchial epithelial cells (HBECs) were used to investigate the role of TG2, as regards the development of fibrosis in CF airway epithelia. It was shown that the deposition of TG2 and fibronectin is elevated in the ECM of both IB3 cells and CF primary HBECs. Notably, IB3 cells were found to undergo epithelial-mesenchymal transition (EMT)-derived myofibroblast transdifferentiation, with CF primary HBECs also exhibiting varying levels of EMT progression. Proof of concept experiments using CF primary HBECs revealed that the use of a CFTR corrector (VX-809) and TG2 specific inhibitor (1-155) in combination, could have a potentially additive therapeutic effect. A more in-depth investigation with IB3 cells, served to further validate these findings. It was demonstrated that the treatment of IB3 cells with VX-809 and 1-155, could completely reverse EMT-derived myofibroblast transdifferentiation and fully restore the barrier function of CF airway epithelium. Furthermore, the development of these pathogenic processes, was shown to be dependent on the interrelationship between extracellular TG2 and TGFβ1 signal transduction. The mechanism of cellular TG2 export in CF was also examined. Extracellular vesicles released by IB3 cells were determined to have increased TG2 expression and activity. IB3 cells were shown to secrete elevated levels of exosomes, which were found to be reduced after combination treatment with VX-809 and 1-155. The findings within this study confirm the importance of extracellular TG2 in the pathogenesis of CF and suggest that pharmacological inhibition of its aberrant activity, represents a viable therapeutic approach.