Trypsin-Like Proteases and Their Role in Muco-Obstructive Lung Diseases.

John C. Lockhart,Gary J. Litherland,Emma L. Carroll,Lorcan P. McGarvey,Anne Crilly,Fionnuala T. Lundy,Mariarca Bailo,S. Lorraine Martin,James A. Reihill,Mark A. Hollywood

doi:10.3390/ijms22115817

Abstract

Trypsin-like proteases (TLPs) belong to a family of serine enzymes with primary substrate specificities for the basic residues, lysine and arginine, in the P1 position. Whilst initially perceived as soluble enzymes that are extracellularly secreted, a number of novel TLPs that are anchored in the cell membrane have since been discovered. Muco-obstructive lung diseases (MucOLDs) are characterised by the accumulation of hyper-concentrated mucus in the small airways, leading to persistent inflammation, infection and dysregulated protease activity. Although neutrophilic serine proteases, particularly neutrophil elastase, have been implicated in the propagation of inflammation and local tissue destruction, it is likely that the serine TLPs also contribute to various disease-relevant processes given the roles that a number of these enzymes play in the activation of both the epithelial sodium channel (ENaC) and protease-activated receptor 2 (PAR2). More recently, significant attention has focused on the activation of viruses such as SARS-CoV-2 by host TLPs. The purpose of this review was to highlight key TLPs linked to the activation of ENaC and PAR2 and their association with airway dehydration and inflammatory signalling pathways, respectively. The role of TLPs in viral infectivity will also be discussed in the context of the inhibition of TLP activities and the potential of these proteases as therapeutic targets.

Highlights

At the turn of the 21st century, the field of degradomics emerged as a discipline that employs genomic and proteomic approaches to elucidate protease and protease-substrate repertoires, or “degradomes”, on an organism-wide scale [1]
The dysregulation of proteolytic activity is apparent in a broad range of chronic muco-obstructive lung diseases (MucOLDs) which include cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), non-CF bronchiectasis, asthma and primary ciliary dyskinesia [4,5]
This review provides an overview of serine Trypsin-like proteases (TLPs) before focusing on their role in the activation of ENaC, protease-activated receptor 2 (PAR2) and viruses

Summary

Introduction

At the turn of the 21st century, the field of degradomics emerged as a discipline that employs genomic and proteomic approaches to elucidate protease and protease-substrate repertoires, or “degradomes”, on an organism-wide scale [1]. This review provides an overview of serine TLPs before focusing on their role in the activation of ENaC, PAR2 and viruses Their inhibition and potential as therapeutic targets are discussed. Serine proteases employ a classical catalytic triad mechanism which relies on the coordination of an Asp, His and Ser residue within the active site Together, they execute a charge-relay that results in the covalent catalysis of the substrate; the nucleophilic Ser, responsible for initiating catalysis, is generated as a result of deprotonation by His which acts as a general acid–base, orientated by the proton-withdrawing Asp [14]. TLPs are members of the S1A subfamily that possess primary substrate specificities for the basic residues lysine and arginine in the P1 position [14] These enzymes play key roles in numerous biological systems such as digestion, blood coagulation, wound healing and immunity. TMPRSS2 may play a specialised but nonvital role that is evident only in the context of systemic distress and disease [32]

Matriptase

Structure and Function of ENaC

TLPs Contribute to the Proteolytic Activation of ENaC

Regulation of PAR2 by TLPs

Role of PAR2 in Inflammation

Proteolytic Regulation of Virus Cell Entry

Activation of Influenza by TLPs

Activation of Coronavirus by TLPs

Endogenous Kunitz-Type Inhibitors

Exogenous Large- and Small-Molecule Inhibitors of TLPs

Conclusions

Findings