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Granulomatosis with polyangiitis (GPA) is a rare but serious necrotizing auto-immune vasculitis. GPA is mostly associated with the presence of Anti-Neutrophil Cytoplasmic Antibody (ANCA) targeting proteinase 3 (PR3-ANCA), a serine protease contained in neutrophil granules but also exposed at the membrane. PR3-ANCAs have a proven fundamental role in GPA: they bind neutrophils allowing their auto-immune activation responsible for vasculitis lesions. PR3-ANCAs bind neutrophil surface on the one hand by their Fab binding PR3 and on the other by their Fc binding Fc gamma receptors. Despite current therapies, GPA is still a serious disease with an important mortality and a high risk of relapse. Furthermore, although PR3-ANCAs are a consistent biomarker for GPA diagnosis, relapse management currently based on their level is inconsistent. Indeed, PR3-ANCA level is not correlated with disease activity in 25% of patients suggesting that not all PR3-ANCAs are pathogenic. Therefore, the development of new biomarkers to evaluate disease activity and predict relapse and new therapies is necessary. Understanding factors influencing PR3-ANCA pathogenicity, i.e. their potential to induce auto-immune activation of neutrophils, offers interesting perspectives in order to improve GPA management. Most relevant factors influencing PR3-ANCA pathogenicity are involved in their interaction with neutrophils: level of PR3 autoantigen at neutrophil surface, epitope of PR3 recognized by PR3-ANCA, isotype and glycosylation of PR3-ANCA. We detailed in this review the advances in understanding these factors influencing PR3-ANCA pathogenicity in order to use them as biomarkers and develop new therapies in GPA as part of a personalized approach. [ABSTRACT FROM AUTHOR]

Polymorphonuclear neutrophils contain at least four serine endopeptidases, namely neutrophil elastase (NE), proteinase 3 (PR3), cathepsin G (CatG), and NSP4, which contribute to the regulation of infection and of inflammatory processes. In physiological conditions, endogenous inhibitors including α2‐macroglobulin (α2‐M), serpins [α1‐proteinase inhibitor (α1‐PI)], monocyte neutrophil elastase inhibitor (MNEI), α1‐antichymotrypsin, and locally produced chelonianins (elafin, SLPI) control excessive proteolytic activity of neutrophilic serine proteinases. In contrast to human NE (hNE), hPR3 is weakly inhibited by α1‐PI and MNEI but not by SLPI. α2‐M is a large spectrum inhibitor that traps a variety of proteinases in response to cleavage(s) in its bait region. We report here that α2‐M was more rapidly processed by hNE than hPR3 or hCatG. This was confirmed by the observation that the association between α2‐M and hPR3 is governed by a kass in the ≤ 105 m−1·s−1 range. Since α2‐M‐trapped proteinases retain peptidase activity, we first predicted the putative cleavage sites within the α2‐M bait region (residues 690–728) using kinetic and molecular modeling approaches. We then identified by mass spectrum analysis the cleavage sites of hPR3 in a synthetic peptide spanning the 39‐residue bait region of α2‐M (39pep‐α2‐M). Since the 39pep‐α2‐M peptide and the corresponding bait area in the whole protein do not contain sequences with a high probability of specific cleavage by hPR3 and were indeed only slowly cleaved by hPR3, it can be concluded that α2‐M is a poor inhibitor of hPR3. The resistance of hPR3 to inhibition by endogenous inhibitors explains at least in part its role in tissue injury during chronic inflammatory diseases and its well‐recognized function of major target autoantigen in granulomatosis with polyangiitis. [ABSTRACT FROM AUTHOR]

Abstract Cathepsin C (CatC) is a highly conserved tetrameric lysosomal cysteine dipeptidyl aminopeptidase. The best characterized physiological function of CatC is the activation of pro-inflammatory granule-associated serine proteases. These proteases are synthesized as inactive zymogens containing an N-terminal pro-dipeptide, which maintains the zymogen in its inactive conformation and prevents premature activation, which is potentially toxic to the cell. The activation of serine protease zymogens occurs through cleavage of the N-terminal dipeptide by CatC during cell maturation in the bone marrow. In vivo data suggest that pharmacological inhibition of pro-inflammatory serine proteases would suppress or attenuate deleterious effects mediated by these proteases in inflammatory/auto-immune disorders. The pathological deficiency in CatC is associated with Papillon-Lefèvre syndrome (PLS). The patients however do not present marked immunodeficiency despite the absence of active serine proteases in immune defense cells. Hence, the transitory pharmacological blockade of CatC activity in the precursor cells of the bone marrow may represent an attractive therapeutic strategy to regulate activity of serine proteases in inflammatory and immunologic conditions. A variety of CatC inhibitors have been developed both by pharmaceutical companies and academic investigators, some of which are currently being employed and evaluated in preclinical/clinical trials. [ABSTRACT FROM AUTHOR]

Cathepsin C (CatC, syn. Dipeptidyl peptidase I) is a lysosomal cysteine proteinase expressed in several tissues including inflammatory cells. This enzyme is important for maintaining multiple cellular functions and for processing immune cell-derived proteases. While mutations in the CatC gene were reported in Papillon-Lefèvre syndrome, a rare autosomal recessive disorder featuring hyperkeratosis and periodontitis, evidence from clinical and preclinical studies points toward pro-inflammatory effects of CatC in various disease processes that are mainly mediated by the activation of neutrophil serine proteinases. Moreover, tumor-promoting effects were ascribed to CatC. The aim of this review is to highlight current knowledge of the CatC as a potential therapeutic target in inflammatory disorders. [Display omitted] • Cathepsin C activates granule serine proteinases involved in inflammation. • Cathepsin C contributes to the pathogenesis of different acute and chronic diseases. • Potential of cathepsin C inhibition to ameliorate inflammation in preclinical models. • Need for studies evaluating CatC inhibitors repurposing in chronic inflammatory diseases. [ABSTRACT FROM AUTHOR]

Neutrophils are one of the most important military services of the armed forces of the immune system, a crucial line of defense against bacterial or fungal onslaughts. One of their mechanisms of action relies on the production of serine proteases. One of these enzymes is proteinase 3 (PR3), which is engaged in the processing of pro-inflammatory cytokines, receptors, heat shock proteins and in the generation of antibacterial peptides. Despite its protective function, uncontrolled activity of PR3 has been associated with the progression of inflammation and tissue injury. Although PR3 was characterized at the beginning of 90's of the last century for the first time, the research on the development of its inhibitors is barely noticeable. Here we present the recent findings on the design, synthesis and the activity of phosphonic PR3 inhibitors together with the historical perspective. Image 1 • Proteinase 3 is considered an interesting drug target since its activity has been associated with different pathophysiological disorders. • Several classes of PR3 inhibitors such as isocoumarins, N -hydroxysuccinimides, thiatriazolidine and phosphonates have been developed. • Diaryl esters of phosphonic analogues of amino acids represent an interesting class of irreversible inhibitors of proteinase 3. • Phosphonic inhibitors can be easily turned into the activity-based probes useful for protease visualization either in vitro or in cell assays. [ABSTRACT FROM AUTHOR]

Background Vascular damage and primary graft dysfunction increase with prolonged preservation times of transplanted donor lungs. Hence, storage and conservation of donated lungs in protein-free, dextran-containing electrolyte solutions, like Perfadex, is limited to about 6 hours. We hypothesized that transplanted lungs are protected against neutrophil-mediated proteolytic damage by adding α 1 -anti-trypsin (AAT), a highly abundant human plasma proteinase inhibitor, to Perfadex. Methods A realistic clinically oriented murine model of lung transplantation was used to simulate the ischemia–reperfusion process. Lung grafts were stored at 4°C in Perfadex solution supplemented with AAT or an AAT mutant devoid of elastase-inhibiting activity for 18 hours. We examined wild-type and proteinase 3/neutrophil elastase (PR3/NE) double-deficient mice as graft recipients. Gas exchange function and infiltrating neutrophils of the transplanted lung, as well as protein content and neutrophil numbers in the bronchoalveolar lavage fluid, were determined. Results AAT as a supplement to Perfadex reduced the extent of primary graft dysfunction and early neutrophil responses after extended storage for 18 hours at 4°C and 4-hour reperfusion in the recipients. Double-knockout recipients that lack elastase-like activities in neutrophils were also protected from early reperfusion injury, but not lung grafts that were perfused with a reactive center mutant of AAT devoid of elastase-inhibiting activity. Conclusions PR3 and NE, the principal targets of AAT, are major triggers of post-ischemic reperfusion damage. Their effective inhibition in the graft and recipient is a promising strategy for organ usage after storage for >6 hours. [ABSTRACT FROM AUTHOR]