Characterization of peroxidasin and DUOX1 in pulmonary fibrosis

Abstract

Peroxidasin (PXDN) is a heme peroxidase enzyme expressed in the extracellular matrix in several tissues. This enzyme catalyzes the formation of hypobromous acid (HOBr) from H2O2 and bromide. HOBr oxidizes amino acid residues to form covalent sulfilimine bonds in collagen IV in the basement membrane, a unique post-translational modification in biological systems. However, it is still unclear whether the peroxidase activity of PXDN is restricted to sulfilimine-bond formation or whether it also has other roles than collagen IV crosslinking. Emerging studies have shown aberrant PXDN expression associated with various cardiovascular disorders, cancer and kidney fibrosis, but mechanisms are unclear. However, the role of PXDN on fibrosis seems to be unrelated of collagen IV crosslink. In this regard, we got some exciting unpublished results about the possible contribution of PXDN in fibrosis. Through proteomic evaluation we identified which extracellular matrix proteins are modified (brominated) by the action of HOBr. Laminin was the protein with the greatest intensity of modifications. Interestingly, it has recently been shown that PXDN binds to laminin in the basement membrane, but the reason for this binding has not yet been investigated. Moreover, laminin can be a genetic modifier of TGF-beta1 effector responses that significantly affect the development of pulmonary fibrosis. The role of PXDN in lung diseases such as pulmonary fibrosis is complete not known, as well as, the cellular origin of PXDN in any fibrotic condition. Similarly, the exact source of H2O2 used by PXDN in the collagen IV crosslink reaction, or in other functions of PXDN, remains an enigma. Nox/Duox family NADPH oxidases are transmembrane enzymes specialized in producing reactive oxygen species and have a well-known intertwined relationship with heme peroxidases in several biological contexts. Also, NADPH oxidases appear to contribute to pulmonary fibrosis. Indeed, exciting new preliminary studies by the Professor van der Vliet research group, using mice with global DUOX1-deficiency, suggest that DUOX1 contributes to experimentally-induced lung fibrosis, especially in aging mice. They also observed an increase of DUOX1 protein in non-epithelial cell types during pulmonary fibrosis, which implies previously unrecognized functions of DUOX1 in lung biology distinct from its known epithelial functions. Some recent studies also suggest a contributing role for DUOX1 in fibroblast activation, but cell-specific role of DUOX1 during fibrosis, and its potential interaction with PXDN, is not known. Since DUOX1 may be an extracellular H2O2 source for PXDN, and both DUOX1 and PXDN enzymes may be implicated in fibrotic remodeling, we raised two main questions: 1. Does PXDN contribute to pulmonary fibrosis and are fibroblasts be the major cellular source of PXDN in pulmonary fibrosis? 2. Is DUOX1 enhanced in fibroblasts during pulmonary fibrosis and does it contribute to PXDN expression or activity? Given the central role played by fibroblasts in the development of fibrosis, combined with the expertise and recent preliminary results by Professor van der Vliet with respect to NADPH oxidases in airway biology and pulmonary fibrosis, we believe that this partnership will significantly contribute to advancing our knowledge of PXDN and its biological and/or pathological mechanisms within redox biochemistry. (AU)