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Protease-mediated degradation of proteins is critical in a plethora of physiological processes. Neutrophils secrete serine proteases including cathepsin G (CatG), neutrophile elastase (NE), and proteinase 3 (PR3) together with lactoferrin (LF) as a first cellular immune response against pathogens. Here, we demonstrate that LF increases the catalytic activity of CatG at physiological concentration, with its highest enhancing capacity under acidic (pH 5.0) conditions, and broadens the substrate selectivity of CatG. On a functional level, the enzymatic activity of CatG was increased in the presence of LF in granulocyte-derived supernatant. Furthermore, LF enhanced CatG-induced activation of platelets as determined by cell surface expression of CD62P. Consequently, LF-mediated enhancement of CatG activity might promote innate immunity during acute inflammation. [ABSTRACT FROM AUTHOR]

Neutrophil serine proteases, including elastase, proteinase 3, and cathepsin G, are closely related enzymes stored in similar amounts in azurophil granules and released at the same time from triggered neutrophils at inflammatory sites. We have synthesized new fluorescence resonance energy transfer (FRET) substrates with different fluorescence donor-acceptor pairs that allow all three proteases to be quantified at the same time and in the same reaction mixture. This was made possible because the fluorescence emission spectra of the fluorescence donors do not overlap and because the values of the specificity constants were in the same range. Thus, similar activities of proteases can be measured with the same sensitivity. In addition, these substrates contain an N-terminal 2-(2-(2-aminoethoxy)ethoxy)acetic acid (PEG) moiety that makes them cell permeable. Using the mixture of these selected substrates, we were able to detect the neutrophil serine protease (NSP) activity on the activated neutrophil membrane and in the neutrophil lysate in a single measurement. Also, using the substrate mixture, we were in a position to efficiently determine NSP activity in human serum of healthy individuals and patients with diagnosed Wegener disease or microscopic polyangiitis. [ABSTRACT FROM AUTHOR]

Dysregulation of the proteolytic balance is often associated with diseases. Serine proteases and matrix metalloproteases are involved in a multitude of biological processes and notably in the inflammatory response. Within the framework of digestive inflammation, several studies have stressed the role of serine proteases and matrix metalloproteases (MMPs) as key actors in its pathogenesis and pointed to the unbalance between these proteases and their respective inhibitors. Substantial efforts have been made in developing new inhibitors, some of which have reached clinical trial phases, notwithstanding that unwanted side effects remain a major issue. However, studies on the proteolytic imbalance and inhibitors conception are directed toward host serine/MMPs proteases revealing a hitherto overlooked factor, the potential contribution of their bacterial counterpart. In this review, we highlight the role of proteolytic imbalance in human digestive inflammation focusing on serine proteases and MMPs and their respective inhibitors considering both host and bacterial origin. [ABSTRACT FROM AUTHOR]