Development of a Rabbit Model for Myeloperoxidase Deficiency - ABSTRACT Myeloperoxidase (MPO) is a unique peroxidase, predominantly expressed in neutrophils and stored in their azurophilic granules, and accounts for ~5% of the total cell protein. Among all the discovered peroxidases, MPO is the only one that catalyzes two-electron oxidation of chloride anion to produce hypochlorous acid (HOCl) in the presence of H2O2 derived from the NADPH oxidase. Clinical validation of the importance of the oxidant-dependent system for optimal host defense rests in part on the severe and often fatal infections seen in patients with chronic granulomatous disease (CGD), an inherited disorder with non-functional phagocyte NADPH oxidase. Intriguingly, individuals with inherited MPO deficiency develop a narrow set of infections, largely by fungi. The molecular basis for such a phenotype of MPO deficiency is not clearly known, but likely reflects actions by uncharacterized antimicrobial activities that may lie in reserve but are recruited under severe stress. Clinical data further suggest that MPO contributes to tissue damage and inflammation, and is involved in the pathogenesis of many inflammatory diseases including cardiovascular diseases, kidney diseases, pulmonary inflammation, rheumatoid arthritis, skin inflammation, and neuronal diseases. In spite of the long-observed clinical association between MPO and inflammation, the exact role of MPO in the onset and progression of inflammatory diseases remains largely elusive. One of the major obstacles impeding progress in understanding the contribution of MPO to host defense and to inflammation biology is the lack of a faithful animal model. Widely used in the field, MPO-knockout (MPO-KO) mice fail in many settings to recapitulate MPO-associated human diseases, as data obtained often contradict those seen in humans. To meet the urgent need for an accurate faithful animal model, we have produced an MPO-KO rabbit model using CRIPSR/Cas9 gene editing technology. Due to many similarities between the rabbit and human immune systems, we expect this novel model to be of great value in studying clinical MPO deficiency. Our overarching hypothesis is that rabbit MPO deficiency replicates human MPO deficiency in both infection and inflammation diseases, providing a valuable tool for novel basic discovery and therapeutic development. There are two specific aims in this R21 proposal: 1) to determine if rabbit MPO deficiency reproduces human MPO deficiency in infection; 2) to discover if rabbit MPO deficiency recapitulates human MPO deficiency in inflammation. Completion of this research will establish a larger animal model for human MPO deficiency for basic research and therapeutic development, which is expected to greatly advance our understanding of the biology of MPO and the MPO- related diseases, and to facilitate the search for effective interventions for these conditions.
