Our laboratory has pioneered proteomic methods for disease discovery that evolved from our basic research on lysosomal enzyme targeting. Lysosomes are membrane-bound, acidic organelles that are found in all eukaryotic cells. They contain a variety of different proteases, glycosidases, lipases, phosphatases, nucleases and other hydrolytic enzymes, most of which are delivered to the lysosome by the mannose 6-phosphate targeting system. In this pathway, lysosomal enzymes are recognized as different from other glycoproteins and are selectively phosphorylated on mannose residues. The mannose 6-phosphate serves as a recognition marker that allows the enzymes to bind mannose 6-phosphate receptors which ferry the lysosomal enzymes to the lysosome. In the lysosome, the enzymes function in concert to break down complex biological macromolecules into simple components. The importance of these enzymes is underscored by over forty different lysosomal storage disorders (e.g., Tay Sach's disease) where loss of a single lysosomal enzyme leads to severe health problems including neurodegeneration, progressive mental retardation and early death.
We have two basic approaches for disease discovery. In a “disease to protein” approach, we use proteomic methods to compare to complement of lysosomal proteins in control and disease specimens. If the disease specimen lacks a given lysosomal protein, this provides a clue for further genetic studies to determine if there are underlying mutations in the corresponding gene. In a “protein to disease” approach, we identify new lysosomal proteins and use their known or predicted properties to associate them with diseases of unknown etiology. Using such approaches we have identified the gene defect in several lysosomal storage disorders, most notably late infantile neuronal ceroid lipofuscinosis (LINCL) and Niemann Pick Type C2 disease.
We and our collaborators extend this discovery research in several directions. For newly solved disease, we develop biochemical and genetic tests for diagnosis and carrier screening. We also generate mouse models to investigate disease pathophysiology and to aid in the development of potential therapeutics. Another focus is to investigate the structural, biochemical, and functional properties of lysosomal proteins of interest, and to use this information to develop protein-based therapeutics. This multi-faceted approach continues to provide new insights and advances in lysosome biology and medicine.