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Secreted circulating protein factors mediate key aspects of inter-organ communication in the kidney, urological, and hematological systems; however, our ability to monitor secreted protein trafficking within the body and identify their cellular and tissue targets remains extremely limited. Existing methods, such as the use of radiolabeled ligands, are laborious and not easily scalable. The goal of the proposed studies is to deploy a novel highly scalable method for the multiplex in vivo tracking of secreted factors to identify “zipcode” domains which home through blood to the kidney. We are developing barcoded-secreted protein complexes that are smaller than most vascular fenestrations and are stable over moderate timeframes in vivo. To this end, a pooled protein library of recombinant secreted protein subdomains will be administered to mice. Subsequent harvesting of blood, liver, and kidney to recover local barcodes will provide a measure of the ability of the corresponding protein domains to selectively traffic to kidney. This approach promises unprecedented insight into the targeting of circulating factors, with correspondingly important implications for the targeted delivery of future protein- and vector-based therapeutics. Indeed, while chronic kidney diseases affect >10% of the world’s population, these disorders are currently only managed with immunosuppressive agents, antihypertensives, and diuretics, with partial but limited success. Protein- and gene-based therapeutic strategies have been restricted by glomerular filtration barrier- mediated exclusion of virtually all proteins above 50 kDa. Progress in overcoming these obstacles would thus have immense therapeutic benefits, and the identification of natural kidney zipcode domains within secreted proteins would directly inform efforts to engineer targeted biologics. Our novel approach to identify zipcode domains will be tested in the mouse kidney to demonstrate the power and broad applicability of this transformative technology.
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