Protean proteases: at the cutting edge of lung diseases

Proteases were traditionally viewed as mere protein-degrading enzymes with a very restricted spectrum of substrates. A major expansion in protease research has uncovered a variety of novel substrates, and it is now evident that proteases are critical pleiotropic actors orchestrating pathophysiological processes. Recent findings evidenced that the net proteolytic activity also relies upon interconnections between different protease and protease inhibitor families in the protease web. In this review, we provide an overview of these novel concepts with a particular focus on pulmonary pathophysiology. We describe the emerging roles of several protease families including cysteine and serine proteases. The complexity of the protease web is exemplified in the light of multidimensional regulation of serine protease activity by matrix metalloproteases through cognate serine protease inhibitor processing. Finally, we will highlight how deregulated protease activity during pulmonary pathogenesis may be exploited for diagnosis/prognosis purposes, and utilised as a therapeutic tool using nanotechnologies. Considering proteases as part of an integrative biology perspective may pave the way for the development of new therapeutic targets to treat pulmonary diseases related to intrinsic protease deregulation.